Quadriceps muscle and tendon injuries

INTRODUCTION — Injuries of the quadriceps muscles and tendons are common among athletes and active adults. Most can be diagnosed by a careful history and physical examination, and conservative management is successful for the large majority.

The presentation, diagnosis, and management of quadriceps injuries are reviewed here. Patellar tendinopathy and other lower extremity injuries are discussed separately, including the following topics. (See "Patellar tendinopathy" and "Hamstring muscle and tendon injuries" and "Approach to the adult with knee pain likely of musculoskeletal origin" and "Running injuries of the lower extremities: Risk factors and prevention" and "Patellofemoral pain" and "Iliotibial band syndrome".)

ANATOMY AND BIOMECHANICS — The quadriceps muscles are composed of the rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius (picture 1 and figure 1 and figure 2 and figure 3 and figure 4). The rectus femoris lies centrally at the anterior thigh and has two origins (figure 5). More superficial fibers begin as a tendon at the anterior inferior iliac spine (AIIS), while deeper fibers arise from the acetabular rim. These two muscle sections fuse with a myofascial layer, sometimes called the central tendon, that extends two-thirds the length of the rectus femoris. The vastus lateralis muscle originates at the proximal, lateral border of the femur and the area of the greater trochanter (figure 6 and figure 7). The vastus lateralis (figure 8) has the largest volume of all of the quadriceps. It contributes to knee extension but also pulls the patella laterally. The vastus medialis is the smallest of the quadriceps and originates at the medial femur near the intertrochanteric line. The vastus medialis (figure 9) counteracts the vastus lateralis by pulling the patella medially. As a shorter muscle with less mass, the vastus medialis must maintain adequate strength to counteract the vastus lateralis. The vastus intermedius (figure 10) originates from the proximal portion of the femur at the superior intertrochanteric line (figure 11). The vastus intermedius helps to stabilize midline tracking of the patella during knee extension.

The combined action of the quadriceps can generate powerful knee extension. The muscles insert onto the patella as the common quadriceps tendon. This tendon then envelops the patella and inserts onto the tibial tuberosity. The portion of the tendon that extends inferior to the patella is generally referred to as the patella tendon.

Innervation of the quadriceps muscles is from the femoral nerve (figure 12), which arises from nerve roots at the second to fourth lumbar vertebrae (L2 to L4). The vastus lateralis and vastus medialis receive a greater portion of their innervation from the L3 nerve root.

The basic action of the quadriceps muscles is to extend the knee. Coordinated action of the individual quadriceps muscles helps direct the force vertically between the hip and knee joints [1]. However, the quadriceps perform other important functions for movement and stabilization. The rectus femoris plays important roles in hip flexion and stabilization of the pelvis during the early swing phase of gait [2,3]. Most quadriceps activation in normal walking occurs during the early phase of the gait cycle unless the individual is walking uphill or climbing steps [4]. The quadriceps group plays an important role in controlling deceleration and providing stability when landing from a jump, sprinting, changing direction at high speed (ie, cutting), or running downhill [5-7].

As the only quadriceps muscle that crosses both the knee and hip joints, the rectus femoris is involved in hip flexion and knee extension and is active during a wider range of athletic movements than the other quadriceps [8]. Another important role of the rectus femoris is to stabilize anterior translation of the pelvis during running and jumping, which results from a functional reversal of the origin and insertion of the muscle. In other words, when an athlete lands from a jump or when the lead leg strikes the ground during running, the distal insertion of the knee extensors works via the patellar and quadriceps tendons to stabilize the knee, rather than extend it. In this scenario, the origin of the rectus femoris at the pelvis functions like an extensor by performing a controlled eccentric contraction to stabilize and rotate the pelvis forward as the individual transitions from the early stance phase through the toe off and early swing phases of the gait cycle.

To function effectively, the quadriceps and hamstrings must work synergistically to stabilize knee extension and flexion [9-11]. Lack of coordination due to discrepancies in strength or flexibility, or to dysfunction of either muscle, can place abnormal loads on the knee and increase the risk of injury, including ACL tears and other knee injuries [12-14]. For several reasons, the rectus femoris is at greater risk of injury compared to the other quadriceps. In addition to its role in a wider range of movements, the rectus femoris can generate greater force when it contracts due to its greater length and relatively high percentage (approximately 65 percent) of type II (fast twitch) muscle fibers [8]. In addition to generating greater force, type II fibers fatigue more quickly, another risk factor for injury. (See "Anterior cruciate ligament injury".)

EPIDEMIOLOGY AND RISK FACTORS

Activities and mechanisms associated with injury — Injuries to the quadriceps muscles and tendons range from mild muscle contusions to complete tendon rupture. High quality evidence describing the epidemiology and risk factors for these injuries is limited, but some clinically relevant information is provided here.

Quadriceps muscle contusions and strains are common sports injuries [15,16]. Quadriceps muscle contusions are more likely to be sustained in high-impact contact sports, such as American football or rugby or ice hockey. A prospective study of 117 quadriceps contusions performed at the United States Military Academy reported that 4.7 percent were sustained from rugby, 2.3 percent from karate and judo, and 1.6 percent from American football [17]. However, this study of military cadets may not be representative of the general population, and the overall incidence may be much higher [18].

Quadriceps muscle strains occur more often in sports such as soccer that involve eccentric contraction of the muscle during sprinting, jumping, or kicking [8,19,20]. In a prospective observational study of professional English soccer clubs, the incidence of injuries was reported as follows: muscle strains 41 percent, tendon sprains 20 percent, and muscle contusions 20 percent [21]. A large prospective study of elite European football (soccer) athletes demonstrated that most quadriceps injuries were mild to moderate tissue tears [22]. Fatigue plays a significant role in these injuries as the majority occurs later in athletic contests [23].

Slow running on a level surface involves minimal eccentric contraction of the quadriceps and thus, little risk of quadriceps injury. However, downhill running places greater stress on the quadriceps muscles and tendons leading to a correspondingly greater risk of injury. In addition, during the later stages of an endurance event (eg, 10 km run, marathon), the quadriceps muscles, which play an important role controlling deceleration and providing stability during landing, fatigue and greater stress is placed on the tendons, which are thereby placed at higher risk of tearing.

Most quadriceps muscle injuries occur in sports involving sprinting or explosive movement (eg, jumping, cutting) where the quadriceps is needed to generate power and elevation, as during the airborne phase of the running stride. Examples include basketball, volleyball, and long or high jumping in which the power necessary for explosive jumps puts the athlete at risk for such injuries.

Quadriceps tendon rupture is uncommon and occurs less often than patellar tendon rupture. It occurs more often in adults older than 50 years but can occur in younger athletes, often during a landing from a jump or while executing a sudden change in direction (cutting) at high speed. (See "Overview of the musculoskeletal complications of diabetes mellitus" and "Use of androgens and other hormones by athletes", section on 'Side effects and complications' and "Fluoroquinolones", section on 'Tendinopathy'.)

Risk factors for quadriceps injury — Data providing insight into the risk factors for quadriceps injury are limited. Numerous studies suggest that game competition is associated with a higher risk of lower extremity injury compared to practice, with some studies reporting rates up to 25 times greater for game competition [24-30]. However, data specific to quadriceps injuries are not available.

Leg dominance is a known risk factor for quadriceps injuries, with injuries approximately two times more likely in the dominant leg [30-32]. One small, prospective observational study of young adult soccer players reported an association between strength and flexibility asymmetry and quadriceps injury [33]. Although these findings are not consistent among studies [34], nevertheless, many experts believe that significant asymmetries in strength and flexibility between legs, as well as significant strength asymmetries between the quadriceps and hamstring muscle groups (which must work in coordinated fashion during virtually all functional movement) in the same lower extremity, predispose to injury.

Prior quadriceps or recent hamstring injury appears to increase the risk for subsequent quadriceps injury [30,31]. Some researchers theorize that gait alterations due to hamstring injury predispose the athlete to the subsequent quadriceps injury. A few observational studies have reported a trend towards increased quadriceps injury risk among shorter, heavier soccer players [31,33], but others have found no association between injury risk and increased weight [34].

While increased age is associated with increased risk for patellar and quadriceps tendon rupture, it does not appear to be a risk factor for quadriceps muscle injuries, according to three large prospective studies [31-33]. A number of comorbidities and drugs may increase the risk for patellar or quadriceps tendon rupture at any age, including diabetes mellitus, obesity, metabolic bone disease (hyperparathyroidism), chronic renal failure (usually associated with secondary hyperparathyroidism) [35,36], polyneuropathy [37], anabolic steroid abuse, glucocorticoids (systemic or local injection), and fluoroquinolones [38-41].

CLINICAL PRESENTATION AND EXAMINATION — The quadriceps muscles and tendons can sustain several types of injury. The clinical presentation, including the mechanism of injury, for the most common types are discussed below.

Quadriceps strain — A quadriceps strain is a tear in one or more of the quadriceps muscles. Quadriceps strains occur most frequently during maneuvers that involve sudden, forceful eccentric contraction. Examples include landing from a high jump, suddenly changing direction while running fast (ie, cutting), and landing (ie, stabilization after footstrike) while running downhill. Eccentric contraction occurs as the muscles lengthen, knee flexes, and hip extends. This creates great tension across the muscle-tendon unit, which is essentially stretching under a load. Therefore, sports that involve repeated eccentric contraction and place high loads on the quadriceps pose the greatest risk of quadriceps injury. These include sports requiring frequent jumping (eg, basketball, volleyball), sprinting, or kicking (soccer/football). A less common mechanism of injury involves excessive passive stretching of an already maximally or near maximally stretched quadriceps muscle, as might occur with dance, gymnastics, yoga, or stretching itself.

Quadriceps muscle strains cause pain and dysfunction, which may appear immediately or up to several days later. Depending upon the extent of the tear, symptoms range from mild discomfort to severe pain. Pain often increases with passive or active knee flexion or passive or active hip extension. Severe strains may result in both swelling and ecchymosis. In some instances, patients may describe feeling a “pop” or sudden tightness in the involved area at the time of injury. Typically, the patient experiences anterior thigh pain with weightbearing and ambulation.

Three regions of the quadriceps are most likely to sustain a muscle strain: the musculotendinous junction just above the knee (proximal quadriceps tendon); the proximal rectus femoris tendon at its origin on the anterior inferior iliac spine (AIIS); and, the myotendinous intersection (or central tendon) that lies between the superficial and deeper portions of the muscle at the proximal two-thirds of the rectus femoris. The rectus femoris is the quadriceps muscle most susceptible to strain because it is longest and generates the greatest force. In soccer and other kicking sports, the most common location of injury is along the central tendon, but in running and walking activities, injury at either the distal or proximal musculotendinous junction is more typical [8]. (See 'Anatomy and biomechanics' above.)

During the examination, the strength of both knee and hip extension should be assessed, as this helps to determine the severity of the strain. Grade one muscle strains involve minimal tearing of muscle fibers with no loss in strength. Grade two involves a more severe tear that causes significant pain, some loss of strength, and possibly a palpable muscle defect. Grade three injuries involve a complete muscle tear and substantial loss of strength.

With larger tears, thigh asymmetry may be noted, along with a nontender or mildly tender muscle mass. Defects can occur at any part of the muscle but most commonly occur proximal to the “central tendon” (the fascial interface between the deep and superficial bundles of the proximal two-thirds of the rectus femoris). Smaller defects may be noted in both the vastus medialis oblique and vastus lateralis should they be injured, and are typically found in the distal muscle at the musculotendinous junction of the quadriceps tendon.

Quadriceps contusion — Quadriceps contusions are caused by direct trauma to the muscle, such as being hit by a ball, helmet, or some other hard object [42]. The risk of quadriceps contusion is increased in the mid quadriceps (ie, central portion of the rectus femoris) due to the frequency of trauma to that location and the increased vascularity in that portion of the muscle but decreased near the rectus femoris origin at the AIIS. The impact damages blood vessels and muscle tissue, which can result in a hematoma. Any comorbidities or medications that increase the risk of bleeding can increase the size of the hematoma. Large contusions left untreated (and rarely minor contusions also) may result in myositis ossificans, a calcification of the hematoma. (See 'Myositis ossificans' below.)

The patient typically gives a history of trauma to the anterior thigh and describes a palpable mass in that location and pain that increases with knee flexion. The thigh is focally tender at the site of the contusion. Palpation along the injured muscle can help localize the site of greatest muscle damage. Measuring the circumference of both thighs provides a basis for determining the degree of swelling, and can be used to gauge recovery. Strength testing of the quadriceps by resisting knee extension and hip flexion in both the injured and uninjured extremities helps to determine the severity of injury.

Knee flexion has been used to assess the severity and prognosis of quadriceps contusions [16,42]. Patients with quadriceps contusions classified as mild have a normal gait, localized tenderness, and active knee flexion greater than 90 degrees. Patients with moderate contusions have an antalgic gait, a swollen tender mass in the quadriceps, and 45 to 90 degrees of active knee flexion. Severe contusions are characterized by a severely antalgic gait, a noticeably swollen tender mass, and less than 45 degrees of active knee flexion. Particularly with severe injuries and more pronounced physical findings, the history and mechanism of injury provide the most useful means for distinguishing between quadriceps strain and quadriceps contusion.

Patellar tendinopathy — The clinical presentation and examination findings associated with patellar tendinopathy (a more common condition than quadriceps tendinopathy) are discussed separately. (See "Patellar tendinopathy".)

Quadriceps tendinopathy — Quadriceps tendinopathy is less common than patellar tendinopathy but also develops over weeks to months from repetitive overuse without adequate time for the tendon to recover. This results in inadequate healing, tendon degeneration (usually at the myotendinous junction), and chronic pain. (See "Overview of overuse (persistent) tendinopathy".)

In addition to the characteristic degenerative tendon changes, calcific tendinopathy or partial or complete tendon tear can result from untreated tendinopathy. Repetitive distance running has been associated with pathologic changes at the patellar insertion of the quadriceps tendon (enthesopathy) as well as calcific tendinopathy in that area.

In moderate to severe quadriceps (or patellar) tendinopathy, the patient’s gait is usually antalgic, knee motion is limited, and the patient is unable to bear full weight on the affected extremity [43]. Symptoms often include pain with knee flexion during ambulation and diminished ability to extend the knee. With mild tendopathy, patients usually have a normal gait and experience pain only with jumping or strenuous activity involving the affected tendon. Pain can be elicited during resisted knee extension. Location helps to determine which tendon is involved. Tenderness at the superior pole of the patella where the quadriceps tendon inserts, or just proximal, suggests quadriceps tendinopathy. Pain elicited with hip flexion may indicate tendinopathy of the proximal rectus femoris tendon. Tenderness on deep palpation of the anterior inferior iliac spine region suggests proximal rectus femoris tendinopathy or avulsion.

Quadriceps and patellar tendon tears — Tendon tears and complete ruptures occur more often in the patellar tendon (distal to the patella) than the quadriceps tendon (proximal to the patella) [44]. Tendon injuries involving either tendon are usually acute and in athletes occur following a sudden, strong contraction of the quadriceps muscles, as happens when landing from a high jump or making a sudden change in direction at high speed. The movement is followed immediately by sharp pain at the knee, which can be disabling with large or complete tears.

With non-athletes, tendon tears may occur when a person falls backward while their foot or feet are caught or fixed to the ground and unable to move. In such cases, the falling body weight exerts a large eccentric force at the distal quadriceps tendon. Multiple case reports describe this phenomenon [41,44,45]. Case reports also describe bilateral quadriceps tendon ruptures in older patients and a few in younger athletes that occur with awkward backwards falls or when the upper trunk is forcefully driven backwards while the patient is kneeling with their full weight on maximally flexed knees, as can occur in American football or other contact sports.

With complete tendon tears, the patient may experience a sudden “pop” or tearing sensation at the patella, followed immediately by swelling and difficulty bearing weight. An acute hemarthrosis may develop. Focal tenderness along the anterior knee is present just above the patella or at the superior border for quadriceps ruptures and at the distal pole or anywhere along the course of the patellar tendon for a patellar tendon tear. The site of complete tendon tears is commonly about 2 cm distal to the patellar tendon insertion or 2 cm proximal to the quadriceps tendon insertion. With a quadriceps tendon rupture, there may be a palpable defect just proximal to the superior pole of the patella. Typically, knee extension is limited with partial tears and absent with complete tears. The patient with a complete tear cannot maintain a straight leg and cannot raise the leg against gravity while supine.

Partial tears of the patellar or quadriceps tendon often involve avulsions of a portion of the tendon at its insertion into the patella. Therefore, with any suspected extensor tendon tear, clinicians should look for a patellar fracture, which is more common than isolated tendon rupture but may present in a similar manner [46]. (See "Patella fractures".)

In patients with an acute tendon rupture, consider secondary causes such as anabolic steroid abuse, renal disease, metabolic bone disease (hyperparathyroidism), and medications associated with tendon rupture (eg, quinolones). (See 'Epidemiology and risk factors' above.)

IMAGING STUDIES — With the exception of bedside ultrasound, diagnostic imaging is not indicated for most quadriceps muscle or tendon injuries, as the diagnosis is made clinically based on the history and examination findings.

Clinicians trained in musculoskeletal ultrasound (US) often perform a bedside evaluation to confirm their initial diagnosis, as US provides excellent imaging of the quadriceps muscles and tendons, and can be done serially to monitor healing [47-49]. US imaging can be performed for the proximal tendon origin (image 1 and image 2), muscle belly (image 3), and distal tendon insertion (image 4). Though US appears to be an accurate tool for assessing quadriceps injuries (image 5), its sensitivity and specificity in this setting are not well studied. US is used for the following purposes:

●Determine the presence and size of muscle and tendon tears. Dynamic assessment can help to reveal such injuries.

●Assess muscle and tendon function dynamically to see if the tendon or muscle tear gaps open with motion or mild resistance.

●Determine the presence and size of any hematoma.

●Determine the presence of calcifications related to hematomas or myositis ossificans and early signs of calcification show up more quickly on US than other imaging.

●Identify neovascularization, which may be associated with tendinopathy.

●Determine if chronic tendinopathy likely existed leading to the tendon tear.

Plain radiographs of acute muscle strains are typically unremarkable but may be helpful in differentiating between soft tissue and bony abnormalities (eg, femoral stress fractures, bone tumor, myositis ossificans). Radiographs should be obtained in patients with suspicious or peculiar symptoms, such as night pain and symptoms that do not improve with appropriate conservative treatment. In such cases, the radiographs obtained generally include anteroposterior (AP) and lateral views of the femur and possibly dedicated views of the knee or hip joint for distal or proximal injuries respectively that seem to affect these joints.

A complete quadriceps or patellar tendon tear is often associated with a patellar avulsion fracture. If such an injury is suspected, AP, lateral, and sunrise views of the knee should be obtained. A low-riding patella (ie, patella baja) on these views suggests a quadriceps tendon rupture (image 6); a high-riding patella suggests a patellar tendon rupture (image 7). Small avulsions are typically detected accurately with ultrasound, but when the patella is displaced superiorly or inferiorly, additional radiographs are helpful to assess the overall patellar position. (See "Patella fractures".)

Magnetic resonance imaging (MRI) studies are generally obtained only when the presentation is unusual or concerning (eg, presence of constitutional signs raises concern for a tumor), the diagnosis becomes uncertain after a patient does not improve with conservative management, or a definitive diagnosis must be made rapidly. We consider MRI the diagnostic study of choice when experienced musculoskeletal ultrasonographers are not available. However, it can be difficult to distinguish between muscle contusion and muscle strain with MRI and a careful history is needed to delineate these injuries. When ultrasound image quality is poor (as can occur with obese patients) and a more definitive diagnosis is needed, MRI is a useful alternative. In addition, when surgery is indicated, MRI may be valuable preoperatively (it is best to let the surgeon make this determination), unless the history and the examination and ultrasound findings all indicate a complete tendon tear, in which case MRI is generally not necessary [50,51]. (See 'Clinical presentation and examination' above.)

Limited evidence suggests that MRI demonstrates high sensitivity and specificity for identifying most quadriceps muscle and tendon injuries, including complete and partial tendon tears, tendinopathy, and hematomas [50,52,53]. The false positive rate for complete ruptures of the quadriceps and patellar tendons ranges from 4 to 5 percent with MRI, and is somewhat higher in ultrasound; although, these numbers are from small, limited studies. In one such study that compared MRI and US for the diagnosis of patellar tendinopathy, both showed good sensitivity but US better specificity [54]. In a retrospective study of quadriceps tendon ruptures, both US and MRI were reported to have sensitivity, but the specificity of US was more limited [50].

DIAGNOSIS — Quadriceps injuries can generally be diagnosed on the basis of a suggestive history and examination findings. These are described in detail above for each major condition. (See 'Clinical presentation and examination' above.)

The most common quadriceps injury is a muscle strain, which typically occurs during maneuvers that involve sudden, forceful eccentric contraction, such as landing from a high jump, suddenly changing direction while running fast (ie, cutting), and landing (ie, stabilization after footstrike) during a sprint, particularly when running downhill. Injury most often occurs during sports that require repeated performance of such maneuvers, such as basketball, volleyball, and soccer. Depending upon the extent of the tear, symptoms range from mild discomfort to severe pain. Pain often increases with passive or active knee flexion or passive or active hip extension, and focal tenderness is present at the site of the tear. In contrast, quadriceps muscle contusion results from direct trauma, usually to the mid-anterior thigh, causing immediate pain and significant, palpable swelling and tenderness.

Imaging studies are usually obtained only when the diagnosis is unclear or the presentation is unusual or concerning (eg, presence of constitutional signs, no improvement in symptoms with rest, poor response to appropriate therapy). However, clinicians experienced with musculoskeletal ultrasound often perform an examination to confirm the diagnosis and extent of injury (image 5). (See 'Imaging studies' above.)

DIFFERENTIAL DIAGNOSIS — In many cases, the mechanism of injury, symptom location, and examination findings make diagnosis of quadriceps muscle and tendon injuries straightforward. However, diagnosis may be difficult if the history or the timing of the injury is unclear, or there is a delay before the patient presents for medical care. Sometimes confusion or a delay in diagnosis occurs when an acute injury complicates a chronic condition and the mechanism does not seem consistent with the degree of tissue damage. Listed below are other specific causes of anterior thigh pain that may mimic a quadriceps muscle or tendon injury:

●Femoral shaft stress fracture – A stress fracture of the femoral shaft is an overuse injury that some patients may initially misinterpret as a less severe muscle strain. Patients typically do not recall a specific injury. Pain may begin after activity, prompting the patient to think they “pulled something.” However, unlike minor muscle strains, a femoral shaft stress fracture does not respond well to a brief respite from activities and is more likely to cause night pain. Examination typically reveals a poorly localized, deep ache around the site of the fracture, while tenderness from a quadriceps strain is more focal and exacerbated by direct palpation or muscle contraction. A fulcrum maneuver to the femoral shaft will elicit pain if stress fracture is present. Imaging is necessary for a definitive diagnosis. (See "Overview of stress fractures".)

●Patellar stress fracture – Though rare, a patellar stress fracture can mimic a quadriceps tendon problem, particularly if the fracture site lies at the proximal pole of the patella. A patellar stress fracture typically has a gradual onset, similar to that of a quadriceps tendon problem. However, pain and tenderness are located in the patella, rather than the tendon. Imaging studies (radiograph, US, MRI) differentiate between these injuries. (See "Overview of stress fractures".)

●Referred lumbar spine pain – Neuropathic pain from the lumbar spine can be referred causing discomfort in the anterior thigh, which may mimic quadriceps injury. Typically, there is no history of injury and symptoms include low back pain. Neural sensitivity may be elicited with a modified Thomas test (picture 2) or passive knee flexion and extension. (See "Acute lumbosacral radiculopathy: Etiology, clinical features, and diagnosis", section on 'L2/L3/L4 radiculopathy'.)

●Bone or soft tissue tumor – The initial symptoms and signs of a soft tissue or bone tumor can be mistaken for a quadriceps contusion. Often a history of acute injury immediately prior to the onset of symptoms distinguishes a quadriceps injury, but patients may mistakenly attribute their symptoms to unrelated minor trauma making diagnosis difficult. Typically, findings associated with a soft tissue or bone tumor develop gradually. Imaging studies can help to distinguish among these entities and are recommended when the clinical picture is unclear. (See "Bone tumors: Diagnosis and biopsy techniques" and "Nonmalignant bone lesions in children and adolescents".)

●Acute compartment syndrome of the anterior thigh – A thigh injury associated with significant internal bleeding or swelling can raise pressures within the anterior thigh compartment possibly leading to an acute compartment syndrome, manifested by a tense anterior thigh and severe pain. Acute compartment syndrome is a true emergency requiring immediate surgical evaluation. (See "Acute compartment syndrome of the extremities".)

●Meralgia paresthetica ‒ Meralgia paresthetica is a nerve entrapment of the lateral femoral cutaneous nerve. Symptoms are typical for a nerve entrapment and include numbness or burning, rather than a muscle ache, and are located more lateral than is typically seen with quadriceps muscle and tendon injuries. In addition, burning or numbness often radiate, which does not occur with muscle injuries. (See "Meralgia paresthetica (lateral femoral cutaneous nerve entrapment)".)

●Femoral nerve injury ‒ Femoral nerve injury is thought to occur secondary to psoas muscle strain or a psoas bursitis, in which a hematoma or fluid collection compresses the nerve. Patients experience sharp, burning pain in the groin and thigh, which is often accompanied by muscle weakness or numbness [55,56]. The radiating nature of the pain and the presence of muscle weakness help to differentiate this injury from quadriceps strain, which tends to be well-localized. (See "Overview of lower extremity peripheral nerve syndromes", section on 'Femoral nerve'.)

INDICATIONS FOR ORTHOPEDIC CONSULT OR REFERRAL — Surgical treatment is indicated for complete quadriceps and patellar tendon ruptures and for high grade partial ruptures. These patients should be referred for orthopedic management. In addition, injuries that lead to massive bleeding and concern for acute compartment syndrome require immediate surgical evaluation. Otherwise, quadriceps muscle and tendon injuries are generally treated conservatively. (See "Acute compartment syndrome of the extremities".)

INITIAL TREATMENT — Initial treatment varies depending upon the specific type of quadriceps muscle or tendon injury. Below, treatment is described for common quadriceps muscle and tendon injuries: quadriceps muscle strain, quadriceps muscle contusion, quadriceps tendinopathy, and quadriceps and patellar tendon rupture.

Quadriceps strain — The initial treatment for the various grades of quadriceps strain is similar, but healing rates vary depending upon the severity of injury. Rest, Ice, Compression, and Elevation (RICE) therapy is standard, particularly during the first 24 to 48 hours of treatment, to limit the extent of localized bleeding, swelling, and pain [57,58]. Cryotherapy appears to be a safe and effective means of reducing pain and likely plays a role in lowering tissue metabolism and reducing secondary hypoxic injury. We apply ice to the affected area for approximately 15 minutes every one to two hours while the patient is awake. Ice is not applied directly to the skin to avoid cold-induced injury. The leg should be kept elevated above heart level. Crutches are used in patients with severe strains who are unable to bear weight.

We suggest initiating passive range of motion focused primarily on knee flexion and gentle stretching of the quadriceps (picture 3) to the point of mild discomfort as early as possible. Plausible benefits to this approach include pain reduction, improved mobility, and activation of neuromuscular pathways. However, high quality evidence supporting these interventions is lacking. We encourage patients to perform isometric muscle contraction, if tolerated, as part of the initial stages of treatment to prevent muscle atrophy.

Nonsteroidal antiinflammatory drugs (NSAIDs) may be given to treat pain and inflammation, but evidence of benefit for such treatment is lacking. Some have raised concerns that NSAID treatment may increase bleeding from injured muscle, delay healing, weaken tissue, and lead to impaired function, but there is no evidence suggesting that short-term treatment is harmful [59,60]. Our patients often take a short course (no longer than five to seven days) of NSAIDs. The effect of NSAIDs on tendon healing is discussed separately. Acetaminophen may also be used for analgesia. (See "Nonselective NSAIDs: Overview of adverse effects", section on 'Healing of musculoskeletal injury'.)

Quadriceps contusion — The initial treatment for quadriceps contusion is similar to that for quadriceps strain (RICE therapy as described immediately above). The goals of treatment include minimizing intramuscular bleeding and the extent of injury, and restoring full range of motion. The knee of the contused thigh should be immobilized immediately in 120 degrees of flexion with an elastic wrap (picture 4). This position of flexion should be maintained for the first 24 hours. Prospective observational studies suggest that maintaining this position as described reduces the time required for healing and return to play [17,61].

NSAIDs may be used during the first 72 hours for mild contusions [59]; a five to seven day course for moderate to severe contusions is reasonable [62]. Acetaminophen may also be used for analgesia. Appropriate early management, particularly for severe injuries, is critical for minimizing discomfort and hastening return to play.

Following removal of the flexion wrap after the first 24 to 48 hours, motion exercises for both leg extension and hip flexion should be performed several times daily within a range of movement that does not cause pain [17].

Quadriceps tendinopathy — Quadriceps tendinopathy is a rare condition encountered mostly in older athletes and those with chronic medical conditions such as diabetes, chronic renal failure, and hypothyroidism. In addition, the condition is associated with sports that require frequent jumping [63]. Little published evidence is available regarding optimal treatment, but many sports medicine physicians follow an approach similar to that used for patellar tendinopathy. (See "Patellar tendinopathy".)

The management of chronic overuse tendinopathy is reviewed separately. (See "Overview of the management of overuse (persistent) tendinopathy".)

Icing, supportive taping, and patellar tendon straps are adjunctive treatments that provide some relief of symptoms. A short course of oral or topical NSAIDs can be used for analgesia. There is no high quality evidence supporting treatment with glucocorticoid, prolotherapy, platelet-rich plasma [64], or other injections. (See "Biologic therapies for tendon and muscle injury".)

Calcific tendinopathy — Case reports of calcific tendinopathy of the distal quadriceps tendon exist [65]. These cases vary in presentation, and imaging study results range from flecks of calcium adjacent to the superior pole of the patella to calcific deposits mimicking quadriceps rupture. Some reported cases involve the proximal rectus femoris and present as upper thigh or anterior hip pain [66]. Little published evidence is available to guide management. Physical therapy focused on improved function and remodeling of tissue through various massage and deep tissue treatments is our initial approach.

Quadriceps and patellar tendon tears — Complete quadriceps tendon rupture is a rare injury more common among older athletes or those with chronic medical conditions. Early diagnosis is key, as prompt surgical intervention for repair improves outcomes [45]. Initial care consists of Rest, Ice, Compression, Elevation (RICE therapy); analgesics; non-weightbearing status with crutches; and, prompt orthopedic referral. (See 'Quadriceps and patellar tendon tears' above.)

Incomplete quadriceps tendon rupture is much more common, but there is little evidence to guide treatment. Initial care is the same as for complete ruptures, although smaller partial tears do not require the patient to be non-weightbearing. As symptoms allow following acute treatment, the patient begins a gradual program of quadriceps tendon rehabilitation. In most cases surgical referral is not necessary. Persistent or worsening pain, increasing weakness, an enlarging palpable defect or extension of the tear as visualized on ultrasound are among the reasons for orthopedic referral of a patient with a partial tear.

FOLLOW-UP CARE — Rehabilitation of quadriceps muscle and tendon injuries consists primarily of mobility and strengthening exercises. Evidence to inform the most effective treatment for these injuries is extremely limited [67]; no randomized trials comparing the relative effectiveness of rehabilitation protocols have been performed. Thus, the following guidelines are based upon observational data, clinical experience, and expert opinion.

Quadriceps strain — The treatment of quadriceps strains varies depending upon their severity. Rehabilitation of first-degree strains typically advances quickly. Therapy for more severe strains advances more gradually through the steps described immediately below. In addition to this description, a sample rehabilitation protocol involving specific goals, activities, and indications for progression is provided in the accompanying table (table 1). Many of the eccentric strength exercises used in the rehabilitation of quadriceps tendinopathy may also be used to treat quadriceps strains. (See 'Quadriceps tendinopathy' below.)

Stage one of rehabilitation consists of the basic interventions outlined above, including gentle passive range of motion focused primarily on knee flexion and gentle stretching of the quadriceps muscles. (See 'Quadriceps strain' above.)

Stage two of rehabilitation is focused on achieving pain free motion. Mobility and stretching exercises are performed, with the range of motion gradually increased as pain permits. The patient may progress from partial weightbearing to full weightbearing during this stage. If strength training is performed, only isometric contractions or isotonic exercises using light resistance are permitted (picture 5).

Stage three of rehabilitation focuses on improving basic function and may begin when the patient is fully weightbearing and demonstrates full, pain-free motion of the knee and hip. Eccentric strengthening begins in earnest during this stage; exercise repetitions, speed, and resistance are gradually increased. Ice and compression are used as needed to manage post-exercise pain and swelling, which should be mild. Quadriceps dominant continuous activities like cycling or a stair-step machine may be started but only at low resistance initially. Over time, the duration and resistance may be increased gradually.

Patients may begin the fourth and final stage of rehabilitation when they can perform activities of daily living without pain and the function of the affected muscle and tendon is comparable to the unaffected side. The goal of this stage is to regain the ability to perform sport-specific movements. Thus, this stage of rehabilitation varies with the demands of the sport. Activities such as plyometrics (eg, box jumps, bounding) and multidirectional activities (eg, short sprints with rapid changes of direction) are common. This final stage is completed when the athlete can perform all functions necessary to participate in their sport with minimal or no symptoms.

Particularly during the latter stages of rehabilitation, clinicians must be on guard for the competitive athlete recovering from a significant strain who wants to increase the intensity and volume of their rehabilitation training too quickly. This phenomenon is common and understandable but increases the risk for delayed healing and recurrence.

Operative intervention is rarely necessary for quadriceps strains and generally reserved for patients with complete tears of the proximal rectus femoris or avulsion injuries when conservative treatment has been unsuccessful (ie, patient unable to return to their desired level of activity). Experimental treatments for acute muscle injuries, such as glucocorticoids and platelet rich plasma (PRP), are the subject of ongoing research and are discussed separately. (See "Hamstring muscle and tendon injuries", section on 'Glucocorticoid injection' and "Hamstring muscle and tendon injuries", section on 'PRP and other biologic injections'.)

Quadriceps contusion — Rehabilitation for moderate or severe quadriceps contusions is similar to that for quadriceps muscle strains. Ice and compressive therapy are continued, at least until there are noticeable improvements in range of motion and pain. We recommend avoiding deep massage and muscle manipulation, as such treatment may aggravate the injury. Unloading the muscle by using crutches to avoid weightbearing is continued until muscle swelling has subsided (ie, muscle size and firmness equals that of the uninjured quadriceps) and motion has been regained [61].

Once the patient achieves at least 120 degrees of pain-free knee flexion and can bear full weight, strengthening exercises are initiated in a manner similar to that for quadriceps muscle strains. A sample rehabilitation protocol involving flexion exercises and functional progressions is provided in the accompanying table (table 2). According to one uncontrolled prospective study, this type of protocol reduced recovery times for moderate to severe contusions from 8 to 10 weeks to 3 weeks or less [17].

For patients having difficulty regaining pain free motion or who have persistent pain and muscle firmness from a hematoma, aspiration may be performed. This can be done with relative ease in experienced hands using ultrasound guidance. No controlled studies are available to help determine the optimal timing or specific selection criteria. In the author and editors’ opinion, aspiration should be reserved for large hematomas that are clearly restricting the ability to achieve pain free motion. Aspiration is more likely to reduce the extent of muscle damage and weakness caused by the hematoma if performed within the first week of injury. Our clinical experience suggests that earlier intervention makes drainage easier, as the hematoma is mostly liquid initially but becomes more gelatinous and clotted with time.

Operative intervention is rarely indicated for quadriceps contusion. The primary indication is the need for hematoma evacuation and decompression [68]. Again, there is no evidence to support this intervention. The increased use and availability of ultrasound guided aspiration further limits the need for operative evacuation. Experimental treatments for acute muscle injuries, such as glucocorticoids and platelet rich plasma (PRP), are the subject of ongoing research and are discussed separately. (See "Hamstring muscle and tendon injuries", section on 'Glucocorticoid injection' and "Hamstring muscle and tendon injuries", section on 'PRP and other biologic injections'.)

Quadriceps tendinopathy — The general concepts of tendinopathy treatment, specifically those drawn from the treatment of patellar tendinopathy, provide a useful guide for treating quadriceps tendinopathy as well [69]. Early on, stretching and isometric strengthening exercises are emphasized [70-73]. Controlled, progressive, heavy load exercise, including eccentric strengthening, is the cornerstone of treatment and can be initiated when pain diminishes [74-77]. Examples of eccentric quadriceps exercises used during rehabilitation include the leg extension (picture 6), eccentric squat variations (picture 7 and picture 8), step down (picture 9), reverse Nordic lower (picture 10), overhead reverse lunge (picture 11), drop squat (picture 12), and drop jumps (picture 13). The treatment of tendinopathy is reviewed separately (see "Overview of the management of overuse (persistent) tendinopathy"). A sample rehabilitation protocol involving specific goals, activities, and indications for progression is provided in the accompanying table (table 3).

Cases of calcific quadriceps tendinopathy that are not responsive to initial conservative measures will likely require surgical referral and intervention. Aspiration and lavage of the calcified portion of tendon has been reported in the literature for calcific supraspinatus tendinopathy, but controlled studies of this procedure for the quadriceps and patellar tendons are lacking and we cannot recommend such a procedure at this time. (See "Calcific tendinopathy of the shoulder".)

Quadriceps and patellar tendon tears — Incomplete quadriceps and patellar tendon tears can be treated nonsurgically. For more significant partial tears, immobilization for three to six weeks is typically recommended, with weekly follow-up to monitor progress and gradually advance activity [45,78]. Once the patient can perform a straight leg raise (picture 5) without pain, they may begin flexing the knee but only to the point of initial discomfort [45]. Treatment then consists of three basic tasks: isometric contraction of the quadriceps, straight leg raises, and knee flexion mobility exercises but, again, only to the point of initial discomfort. Once the patient can flex their knee to at least 90 degrees with minimal discomfort, they may begin performing light resistance knee extension exercises beginning with a 30 degree arc (picture 14). Clinical healing is demonstrated when the patient experiences no pain with full knee flexion or resisted knee extension. Musculoskeletal ultrasound is a useful aid for assessing tendon healing. Once healing is demonstrated, the patient may begin a formal physical therapy program designed to gradually return them to sport.

Complete patellar or quadriceps tendon tears require surgical intervention. Operative repair within one week of injury greatly improves outcomes [45]. Postoperative care and rehabilitation is beyond the scope of this topic.

COMPLICATIONS

Myositis ossificans — Myositis ossificans (MO) is a heterotopic ossification that develops within a muscle and is known to occur following quadriceps contusion and, less commonly, quadriceps muscle strain. It remains unclear why MO occurs, but it can develop at any site of muscle injury. It is estimated to occur in 9 to 14 percent of muscle contusions overall [79-81], but the more severe the contusion, the greater the risk. Incidence ranges from 4 percent with mild injuries to 18 percent with more severe contusions [16].

Obtaining greater than 120 degrees of knee flexion as soon as possible following injury may help prevent MO. NSAIDs, specifically indomethacin, used early in course are known to prevent heterotopic bone formation, but specific studies of NSAIDs for the prevention of MO are lacking [62,82].

MO may be palpable as early as four to five days after a quadriceps contusion but may take several weeks to develop [57,83]. Early symptoms include persistent pain and swelling that does not appear to be resolving. Later symptoms include a worsening of pain with activity or swelling, early morning or night pain, and decreasing range of motion after two to three weeks. If MO is suspected, plain radiographs or ultrasound should be obtained. Two to four weeks are typically needed for MO to become visible on plain radiographs (image 8 and image 9). Periosteal bone reaction at the periphery is the first finding. As the lesion matures over a period of 10 weeks to four to six months, the peripheral bone matures and an eggshell appearance develops [84].

Ultrasound findings may precede radiographic findings; however, the early appearance on ultrasound can be difficult to differentiate from sarcoma, and this scenario may be particularly difficult if there is no history of significant trauma [85]. The same can be true for early findings on MRI [86]. If the clinical picture is unclear based on the history and advanced imaging, referral to a specialist in musculoskeletal radiology or bone and soft tissue tumors is indicated.

Full development of a MO lesion usually takes 6 to 12 months. Most often the body resorbs the bone, which can be seen on plain radiographs [87]. Bone scan can also be used to determine whether a lesion is fully developed. While a mature MO lesion is positive only on the delayed phase of a triple phase bone scan (and negative on the pool and flow phases), developing bone is positive on all three phases [88,89]. Surgical excision of MO is rarely indicated. Criteria for possible surgical excision include complete maturation of the lesion, limited knee flexion, and predisposition to further injury [83]. (See "Surgical reconstruction of the lower extremity".)

Anterior thigh compartment syndrome — Anterior thigh compartment syndrome is a rare complication of quadriceps contusion but may occur with severe injury or in patients at increased risk of bleeding [60]. Compartment syndrome arises due to elevated pressures within a closed space bound by fascia, typically from bleeding. The elevated pressures prevent adequate blood flow to tissues within the compartment, and possibly to distal tissues as well, ultimately causing ischemia. The most common and important clinical symptom is pain out of proportion to the injury or examination, and a tense muscle compartment. With compartment syndrome of the anterior thigh, passive knee flexion exacerbates pain. Acute compartment syndrome is a surgical emergency and is discussed in detail separately. (See "Acute compartment syndrome of the extremities".)

Quadriceps weakness — Weakness of the quadriceps can develop following any quadriceps injury. The incidence of significant weakness following more common injuries such as quadriceps strain or contusion is not known but typically there is no or minimal residual weakness once healing is complete. Incomplete ruptures of the quadriceps tendon are more likely to cause weakness or quadriceps atrophy than common strains. However, appropriate rehabilitation minimizes the risks of developing this complication. Elite athletes in sports that place a large demand on the quadriceps tendon through jumping or sprinting may detect some relative weakness. Even with operative repair of complete quadriceps tendon ruptures, decreased strength and loss of complete knee flexion are expected. These complications are less likely with timely repair (ie, within one week of injury).

RETURN TO PLAY OR SPORT — Return to play or sport is guided by the general principles already discussed in the follow-up care and rehabilitation section. In general, symmetric pain free range of motion (ROM) is observed. The injured quadriceps should have no more than a 15 percent reduction in strength compared with the uninjured side. In addition, a functional progression of sport specific activities should be observed by the medical staff treating the athlete prior to full return to competitive activities. A thigh wrap may help initially for athletes returning following a muscle strain (picture 15).

Athletes who suffer a quadriceps contusion should be fitted with a thigh pad that covers an area greater than the size of the contusion, and such padding should be used for the remainder of the season [17,61].

PREVENTION — Quadriceps strains have a high recurrence rate and thus prevention takes on great importance [31]. Although high quality studies comparing prevention programs are lacking, most interventions focus on improving quadriceps muscle flexibility and strength, eliminating any significant asymmetries in strength or mobility between the lower extremities or between the quadriceps and hamstrings in the same leg, and improving core stability [8].

Flexibility — Improving quadriceps flexibility in patients with limited flexibility is a central part of most quadriceps injury prevention programs. Reduced flexibility means the muscle has limited capacity to withstand the stresses experienced during sudden contraction when the muscle is stretched (eccentric contraction). Many clinicians recommend that patients achieve approximately 130 degrees or more of knee flexion to help prevent injury recurrence [33,90].

In addition to knee flexion, many experts believe that the ability to achieve maximal hip extension is important for preventing quadriceps injuries, as limited extension places increased stress on the quadriceps. Full hip extension lengthens the quadriceps muscles producing a greater potential force moment when the muscles contract. The athlete with limited hip extension may have a flexion contracture from prior injuries to hip flexors. These individuals must compensate for the reduced length of the quadriceps by contracting them more forcefully, which increases the risk of muscular injury. Therefore, most programs include stretching exercises designed to lengthen the hip flexors (eg, iliopsoas, rectus femoris).

Greater iliopsoas muscle flexibility may also help to prevent quadriceps injury by reducing the risk of trauma to the femoral nerve, which travels adjacent to the iliopsoas before continuing on to the quadriceps. This concept applies to kicking sports in particular (eg, soccer, dance), which require repeated lumbar extension and hip extension of the plant leg, followed by forceful hip adduction and flexion of the swing leg, a combination of muscle actions that can predispose to femoral nerve injury in either leg if there is any weakness or limitation of iliopsoas motion [91]. Nerve injury can occur from traction, scar tissue or a tight muscle compressing the nerve, or swelling from inflammation of an injured muscle causing direct pressure on the nerve.

Strength — Quadriceps strains occur when the muscles contract powerfully and the force of the contraction exceeds the tensile strength of the muscle [8,92,93]. Increasing the length over which the muscle can contract to generate optimal force may protect the muscle from injury. Eccentric exercise training focuses on lengthening the muscle while it is working under a load. In contrast, concentric exercises involve a muscle that shortens while working under a load. As an example, when a person performs the first part of a pull-up and raises their body up to the bar their biceps are performing a concentric contraction; when they lower their body back down, their biceps are performing an eccentric contraction.

Eccentric exercise training can increase the length and thus reduce the tension in the quadriceps during a contraction, as well as increasing the muscles’ mass, strength, and power more than isometric or concentric exercises [94]. Controlled studies are lacking, but in a small study of professional soccer players, those who performed a preseason program consisting of eccentric training demonstrated both an increase in the length of the quadriceps muscle and fewer injuries during the season compared to a control group [95]. Examples of eccentric quadriceps exercises include the reverse Nordic lower (picture 10), overhead reverse lunge (picture 11), eccentric squats (picture 7 and picture 8), and others (picture 12) [8].

Core stability — Activities such as kicking and sprinting that place heavy loads on the quadriceps muscles also require coordination among multiple other muscle groups. Groups of muscles that work together to perform movements are often referred to as a kinetic chain. Within such a chain, a deficiency in strength or mobility in one muscle group may lead to dysfunction in others, predisposing to injury. The muscles and connective tissues of the thoracic, lumbar, abdominal, and pelvic regions constitute an essential part of nearly all kinetic chains involved in performing athletic movements. They stabilize the torso and serve as the crucial connection between the upper and lower extremities, allowing forces generated by one extremity to be transmitted to other extremities.

As an example, the kicking motion requires multiple coordinated actions, including: thoracic extension that shifts the center of gravity posteriorly, lumbar and abdominal stabilization of the lower torso, hip extension and knee flexion of the kicking leg, and contralateral activation of the quadratus lumborum. Weakness in the core musculature may lead to abnormal activation of the quadriceps during kicking and predispose to injury. Dynamic core exercises that simulate the fundamental actions of kicking and strengthen the core musculature may help to prevent the development of dysfunctional movement patterns due to core muscle weakness (picture 16) [8].

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: General issues in muscle and tendon injury diagnosis and management" and "Society guideline links: Muscle and tendon injuries of the lower extremity (excluding Achilles)".)

SUMMARY AND RECOMMENDATIONS

●Anatomy and biomechanics – The quadriceps muscles are located in the anterior thigh and are composed of the rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius (picture 1 and figure 12 and figure 3). The rectus femoris is the only muscle to cross both the knee and hip joints, and is the most frequently injured muscle. The quadriceps play an important role in knee extension, hip flexion, pelvic stabilization, and the control of deceleration and landing. (See 'Anatomy and biomechanics' above.)

●Quadriceps strain – These injuries consist of a tear in one or more of the quadriceps muscles. Strains occur most frequently during maneuvers involving sudden, forceful eccentric contraction. Examples include landing from a high jump, suddenly changing direction while running fast, and landing while running downhill. Sports that involve repeated eccentric contraction (eg, basketball, volleyball, soccer [football]) pose the greatest risk. Strains cause pain and dysfunction, which may manifest immediately or up to several days later. Depending upon the extent of the tear, symptoms range from mild discomfort to severe pain. Pain typically occurs with weightbearing and often increases with passive or active knee flexion or passive or active hip extension. More severe tears can cause significant swelling and ecchymosis. (See 'Quadriceps strain' above and 'Initial treatment' above.)

●Quadriceps contusions – Quadriceps contusions are caused by direct trauma to the muscle, such as being hit by a ball or helmet, usually in the mid-anterior thigh. The trauma causes a palpable, tender mass and pain increases with knee flexion. Severe contusions cause significant pain, limit knee flexion, and patients typically walk with a limp. In addition to standard interventions (ie, rest, ice, compression, elevation), initial care includes immobilizing the knee in 120 degrees of flexion using an elastic wrap for 24 hours immediately following the injury. (See 'Quadriceps contusion' above and 'Initial treatment' above.)

●Patellar tendinopathy – This injury is more common than quadriceps tendinopathy and is discussed in detail separately. (See "Patellar tendinopathy".)

●Quadriceps tendinopathy – Tendinopathy develops over weeks to months from repetitive overuse without adequate time for recovery leading to tendon degeneration. In moderate to severe quadriceps tendinopathy, gait is usually antalgic, knee motion is limited, and the patient is unable to bear full weight on the affected extremity. Symptoms often include pain with knee flexion during ambulation and diminished ability to extend the knee. With mild tendopathy, pain occurs only with jumping or strenuous activity involving the affected tendon. Pain can be elicited by resisted knee extension. Tenderness at the superior pole of the patella where the quadriceps tendon inserts, or just proximal, suggests quadriceps tendinopathy. Treatment is with physical therapy. (See 'Quadriceps tendinopathy' above and "Overview of the management of overuse (persistent) tendinopathy".)

●Tendon tears – Quadriceps and patellar tendon tears and complete ruptures are relatively uncommon but occur more often in the patellar tendon (distal to the patella) than the quadriceps tendon (proximal to the patella). Tears in athletes occur following a sudden, strong contraction of the quadriceps muscles, as happens when landing from a high jump or making a sudden change in direction at high speed. The movement is followed immediately by sharp pain at the knee, which can be disabling with large or complete tears. Tears can also occur when a person falls backward while their foot or feet are caught or fixed to the ground and unable to move. Typically, knee extension is limited with partial tears and absent with complete tears. The patient with a complete tear cannot maintain a straight leg and cannot raise the leg against gravity while supine. (See 'Quadriceps and patellar tendon tears' above.)

●Diagnostic imaging – With the exception of bedside ultrasound, diagnostic imaging is not indicated for most quadriceps muscle or tendon injuries, as the diagnosis is made clinically based on the history and examination findings. Clinicians trained in musculoskeletal ultrasound often perform a bedside evaluation to confirm their initial diagnosis and to monitor healing during follow-up. (See 'Imaging studies' above.)

●Differential diagnosis – In most cases, the mechanism of injury, symptom location, and examination findings make diagnosis of quadriceps muscle and tendon injuries straightforward. However, diagnosis may be difficult if the history or the timing of the injury is unclear, or there is a delay before the patient presents for medical care. Descriptions of causes of anterior thigh pain that may mimic a quadriceps muscle or tendon injury are provided. (See 'Differential diagnosis' above.)

●Indications for surgical referral – Surgical referral is indicated for complete quadriceps and patellar tendon ruptures and for high grade partial tears. Injuries that lead to massive bleeding and concern for acute compartment syndrome require immediate surgical evaluation. (See 'Indications for orthopedic consult or referral' above.)

●Management – Most quadriceps muscle and tendon injuries are treated conservatively, including a progressive physical therapy regimen once initial healing has occurred. Rehabilitation programs are outlined in the text, as are management and strategies for prevention. (See 'Initial treatment' above and 'Follow-up care' above and 'Prevention' above.)

●Complications – Major complications from quadriceps muscle and tendon injuries are uncommon but may include myositis ossificans, anterior thigh compartment syndrome, and residual weakness. (See 'Complications' above.)