Patellar tendinopathy

INTRODUCTION — Patellar tendinopathy is a common condition that can develop in active individuals, notably athletes involved in jumping and running sports.

The presentation, diagnosis, and management of patellar tendinopathy are reviewed here. Other injuries and conditions involving the quadriceps muscles and tendons, and the knee generally, are discussed separately. (See "Quadriceps muscle and tendon injuries" and "Approach to the adult with knee pain likely of musculoskeletal origin" and "Approach to the adult with unspecified knee pain".)

ANATOMY AND BIOMECHANICS — The anatomy and biomechanics of the quadriceps muscles and tendons, including the patellar tendon, are reviewed separately. Details pertaining specifically to patellar tendinopathy are discussed below. (See "Quadriceps muscle and tendon injuries", section on 'Anatomy and biomechanics'.)

The distal tendon of the quadriceps muscle group begins proximal to the knee joint, envelops the patella, and inserts on the tibial tuberosity (figure 1 and picture 1). The portion of the tendon distal to the patella is called the patellar tendon (some texts refer to it as the patellar ligament). In addition to its role in knee extension, the tendon provides joint stability during landing and deceleration from running, and it acts as a passive stabilizer of the patella.

The patellar tendon is composed of densely packed collagen fiber bundles aligned in parallel to the longitudinal axes of the tendon and the tibia. It is surrounded by a tendon sheath, which consists of extracellular matrix. Its fascicles usually originate from the distal two thirds of the anterior surface of the patella, although anatomic variants have been described, including a doubled patellar tendon and another in which tendon fibers originate from the deep surface of the patella apex [1-3].

The patellar tendon origin usually has a crescent shape with the medial and lateral fascicles attached to the patella more proximally than the central fascicles. At its insertion on the proximal tibia, the tendon fans out, mingling distally with the fascia of the iliotibial tract [4]. The varied shape of the proximal attachment may account for the varied appearance of the tendon on ultrasound and magnetic resonance imaging (MRI). During passive knee flexion, when the tendon translates distally, movement of the superficial tendon may be restricted by passive resistance of the quadriceps muscle. This restricted movement may contribute to injury risk [5].

Systematic reviews of the relationship between jumping mechanics and patellar tendinopathy describe several patterns associated with an increased risk for developing the condition [6-8]. These include:

●Jumping with horizontal displacement of the torso (ie, poor control of torso)

●Stiff movement patterns involving too little hip and knee flexion during landing from a vertical jump (may be associated with too short a rebound time [ie, time between landing and jumping])

●Quadriceps-dominant rather than gluteal muscle-dominant hip flexion-extension pattern when landing from of a vertical jump

A landing pattern with increased hip and knee flexion, minimal dynamic knee valgus, and a soft touchdown may reduce the risk for patellar tendinopathy.

EPIDEMIOLOGY — Patellar tendinopathy is common, especially in jumping sports (eg, basketball, volleyball) and sports characterized by rapid acceleration, deceleration, and change of direction. Patellar tendinopathy is twice as common in male athletes. In contrast to other tendinopathies, patellar tendinopathy can present during adolescence, but prevalence is highest in athletes 20 to 30 years old. While a systematic review did not identify any specific occupational risk factors [9], a survey study with 1505 respondees reported an association with physically demanding labor [10].

Prevalence may be as high as 50 percent among elite volleyball and basketball players [11-13]. Among recreational athletes participating in a range of sports (basketball, volleyball, handball, football [soccer], field hockey, and track and field), the overall prevalence is approximately 8.5 percent, but rates vary widely among sports with different loading characteristics. Prevalence is highest among volleyball players (14.4 percent) and lowest among football (soccer) players (2.5 percent). The condition is common in ballet dancers [14] and represents about 10 percent of the reported injuries among Olympic-style weightlifters [15]. A survey of 3053 undergraduate students in Hong Kong found statistically significant associations between anterior knee symptoms and total hours spent participating in combat sports, football, yoga, and basketball or engaging in any sport at a highly competitive level but found no association with cycling, cross-training, badminton, running, or hiking [16]. Nevertheless, in the authors' clinical experience, mountaineering, hiking, and downhill walking may occasionally provoke symptoms of patellar tendinopathy, particularly in untrained individuals.

RISK FACTORS — Numerous potential risk factors for patellar tendinopathy have been described, but the quality of evidence is limited [17]. Potential risk factors include higher training volumes (eg, increased jump training, more volleyball sets played per week), following a lower workload for several weeks or longer [18], decreased ankle dorsiflexion, decreased hamstring and quadriceps flexibility, higher countermovement jump height, and higher body weight. There is limited evidence that a lower foot arch may increase risk [19].

Survey data from self-reports by an international cohort of athletes participating in numerous sports found statistically significant associations between patellar tendinopathy and each of the following factors: male sex, more than 20 hours of training per week, previous knee injury, and hamstring inflexibility [20]. Of these, the association with training more than 20 hours per week was notably strong (odds ratio [OR] 8.94, 95% CI 4.68-17.08).

Abnormal knee extension mechanics may increase risk. A laboratory study involving isokinetic testing of knee extension in 170 professional basketball players reported that characteristic changes in knee extensor torque (a so-called "Camel's Back curve") at 60 degrees per second had a sensitivity and specificity of 81 and 100 percent, respectively, for identifying players with a history of jumper's knee [21]. This phenomenon may reflect a protective inhibitory mechanism and may alter jumping mechanics. Prospective studies are required to determine if such isokinetic testing of the leg extensors can help to identify jumping sport athletes at risk for patellar tendinopathy.

Although uncommon in young athletes, medication-related tendon pathology may develop. Fluoroquinolones can contribute to tendinopathy, including that of the patellar tendon, and even tendon rupture [22,23]. Other medications purported to have adverse effects on tendons include glucocorticoids, aromatase inhibitors, and HMG-CoA-reductase inhibitors (statins) although evidence is limited and no cases of resulting patellar tendinopathy have been reported [24]. (See "Fluoroquinolones", section on 'Musculoskeletal' and "Managing the side effects of tamoxifen and aromatase inhibitors", section on 'Aromatase inhibitors'.)

While debate continues about the role of central obesity, hyperlipidemia, and type 2 diabetes mellitus in Achilles tendinopathy [25-27], no such association has been reported for patellar tendinopathy [28-30]. A magnetic resonance imaging (MRI)-based study found an association between obesity and patellar tendon abnormalities, but no information on clinical characteristics was provided. Tendinopathy and enthesopathy are uncommon extra-articular manifestations of gout more likely to affect the popliteus and quadriceps tendons when they do occur [31]. While the patellar tendon has been mentioned as a possible site for the involvement of calcium pyrophosphate deposition disease, to our knowledge, only four case reports exist [32-35].

CLINICAL PRESENTATION — The most characteristic clinical features of patellar tendinopathy are:

●Pain localized to the inferior pole of the patella (patients often point to this spot)

●Load-related pain that increases with the demand on the knee extensors, especially in activities that store and release energy in the patellar tendon (eg, jumping, hopping)

Pain is usually of gradual onset, and symptoms often start after a spike in training load or changes in the playing surface or shoe wear. Over weeks to months, pain worsens from repetitive overuse without adequate time for recovery. The process ultimately results in inadequate healing, tendon degeneration, and chronic pain. (See "Overview of overuse (persistent) tendinopathy".)

Pain typically occurs immediately when the tendon is loaded and resolves when loading ceases (ie, at rest). Pain is often worse when landing from a jump and is dose dependent, with higher loads causing greater pain. Due to both pain and dysfunction, jumping athletes often report a decrease in athletic performance, such as reduced jump height or diminished ability to change direction rapidly. Although rarely experienced at rest, pain can develop with prolonged sitting (especially in a car).

A misleading feature common among athletes is the so-called "warm-up" phenomenon, in which patellar tendon pain may decrease during training. Athletes often misinterpret the importance of the initial pain and continue training. Players often experience increased pain or stiffness after the training or match and the following day.

In contrast to pain due to overuse patellar tendinopathy caused by jumping sports, that caused by walking and running tends to localize to the midportion of the tendon and sometimes toward the insertion on the tibial tubercle.

PHYSICAL EXAMINATION — Physical examination of the knee is reviewed in detail separately; elements of the examination that are of special relevance to patellar tendinopathy are discussed below. (See "Physical examination of the knee".)

Generally, no obvious knee swelling is present. Palpation of the knee reveals focal tenderness at the inferior pole of the patella, where the patellar tendon originates, or just distal in the body of the tendon (picture 2 and picture 1). While it is characteristic of patellar tendinopathy, focal tenderness at this location may also be caused by conditions such as patellofemoral pain [36]. (See 'Differential diagnosis' below.)

Focal pain is elicited with patellar tendon loading maneuvers like hopping or deceleration. The single-leg decline squat (picture 3) typically causes a lot of localized pain early in knee flexion. This movement may be used to aid diagnosis and define the degree of tendon irritability.

An examination of the entire kinetic chain is necessary to identify relevant deficits at the hip, knee, and ankle-foot region. Weakness of the gluteal, quadriceps, and calf muscles is common among these patients. Inflexibility of the quadriceps or hamstring muscles can exacerbate patellar tendinopathy. In addition, it is important to assess asymmetries in foot and ankle mechanics. The foot and ankle need adequate motion to function as effective shock absorbers and thus prevent excessive loading of the knee (and other structures). A high-arched (cavus-type) or hyperpronated ("flat" or planus-type) foot can be functionally stiff, limiting shock absorption, as can reduced ankle dorsiflexion (eg, from a previous ankle sprain) [37].

Although there are no established thresholds, we define acceptable ankle dorsiflexion as 15 to 25 degrees and acceptable ankle movement from supination to pronation as roughly 25 degrees. A reduction in ankle dorsiflexion of more than 10 degrees (or >3 cm reduced knee-to-wall distance with weightbearing lunge test [38]) compared with the contralateral ankle is often clinically important, and such patients may benefit from physiotherapy or manual therapy designed to increase ankle mobility [39]. (See 'Adjunct treatments' below.)

DIAGNOSTIC IMAGING

Approach to imaging — With the exception of bedside ultrasound, diagnostic imaging is generally not indicated for patellar tendinopathy, as the diagnosis can be made based on the history and examination findings alone in most cases. Imaging should be used to rule out other, possibly coexisting, pathology (see below) and assist with clinical reasoning, including working through the differential diagnosis as indicated. Clinicians trained in musculoskeletal ultrasound often perform a bedside evaluation to confirm their initial diagnosis, as ultrasound provides excellent imaging of the patellar tendon [40-42].

Although ultrasound and magnetic resonance imaging (MRI) can show abnormalities of the patellar tendon, they should not be considered a gold standard for diagnosis. The prevalence of imaging abnormalities in sporting populations is high [43,44], and ultrasound and MRI abnormalities do not always correlate with pain and diminished function [45]. The role of serial imaging to monitor healing remains a topic for debate, as symptoms and function often improve without complete resolution of the pathologic changes seen on standard medical imaging (eg, grayscale ultrasound, MRI) [46].

Standard radiographs of the knee add little to the diagnosis of patellar tendinopathy although they may confirm a suspected calcifying tendinitis, tendon avulsion injury, or a bipartite patella. Therefore, we generally do not recommend standard radiographs of the knee in athletes with subacute onset of anterior knee pain suggestive of patellar tendinopathy. (See "Approach to the adult with knee pain likely of musculoskeletal origin".)

Ultrasound — Ultrasound examination with power or color Doppler can be used to visualize pathologic changes in the patellar tendon, including tendon tears. Characteristic findings of patellar tendinopathy include hypoechoic regions, tendon thickening and neovascularization, and sometimes calcification in the proximal dorsal portion of the tendon (image 1 and image 2 and image 3). The role of serial ultrasound imaging to monitor healing is debated, as symptoms and function often improve without complete resolution of the pathologic changes seen on ultrasound. (See "Musculoskeletal ultrasound of the knee".)

Ultrasound examination may offer additional benefits. Abnormalities seen on ultrasound may help to identify asymptomatic athletes at risk for developing patellar tendinopathy [47,48] or aggravating an asymptomatic but high-grade intrasubstance tear of the tendon. Prevention strategies and a more cautious approach to rehabilitation are appropriate for such athletes. (See 'Prevention' below.)

Preliminary studies suggest that advanced ultrasound techniques such as ultrasonic tissue characterization (UTC) [49] and shear wave elastography (SWE) may help to detect early degenerative changes that may be present in an asymptomatic, contralateral tendon. SWE may be more useful for detecting reduced tendon stiffness and monitoring treatment effects [50-52].

Magnetic resonance imaging — The most characteristic finding of patellar tendinopathy on MRI is a focal, hyperintense signal within the proximal tendon imaged with a T2-weighted, turbo spin echo (TSE) technique (image 4). Pathologic findings typically involve the central third of the tendon but may also be seen in the medial tendon. An indistinct posterior tendon border may be seen and edema may be present within the adjacent infrapatellar (Hoffa's) fat pad. Clinicians should be aware that increased signal intensity in the patellar tendon using three-dimensional, T1-weighted MRI pulse sequences with fat suppression is considered a normal finding as it is caused by the so-called "magic angle effect," an MRI artifact [53].

In rare instances when the diagnosis is uncertain and it is important to investigate or exclude other possible causes of knee pain, MRI may be obtained. Given the associated costs, we suggest using conventional MRI to exclude an osteochondral defect, synchondrosis in a radiograph-confirmed bipartite patella, and fat pad swelling or intrasubstance tear of the patellar tendon in a high-performance (jumping) athlete, as this information provides guidance for rehabilitation and return to sport. (See "Approach to the adult with unspecified knee pain" and "Approach to the adult with knee pain likely of musculoskeletal origin".)

Novel, advanced, three-dimensional ultrashort echo time (UTE) MRI techniques, such as T2* relaxation time, show biochemical changes and increased unbound water content in the damaged patellar tendon [54]. Furthermore, changes in T2* relaxation time appear to correlate with clinical improvement during a well-structured exercise intervention [55]. Although UTE MRI appears to be a promising technology to assist with management of tendinopathies, further research is required to understand its limitations and clinical usefulness for predicting the development of patellar tendinopathy and monitoring healing. It should be noted that UTE MRI techniques are time consuming and only available in specialized research hospitals.

DIAGNOSIS — Patellar tendinopathy is a common condition that develops in active individuals, such as long-distance hikers, and especially athletes participating in sports that involve extensive jumping or running and jumping. In most cases, the diagnosis is made clinically based on a history of such activity, gradual development of load-dependent pain just below the patella, and focal tenderness at the inferior pole of the patella or just distal to that location. Musculoskeletal ultrasound or magnetic resonance imaging (MRI) can be used to rule out other conditions and improve the likeliness of the diagnosis.

DIFFERENTIAL DIAGNOSIS — Anterior knee pain is a common presenting complaint for both athletes and non-athletes and may present a significant clinical challenge, as a number of pain-producing structures may be involved. The approach to the patient with knee pain is reviewed in detail separately; diagnoses that may be confused with patellar tendinopathy are described briefly below. (See "Approach to the adult with unspecified knee pain" and "Approach to the adult with knee pain likely of musculoskeletal origin".)

●Patellofemoral pain – The patellofemoral joint is a common source of anterior knee pain in athletes. Patellofemoral pain is primarily a diagnosis of exclusion, as there are no clear criteria or tests to establish the diagnosis. In contrast to the discrete, focal pain of patellar tendinopathy, patellofemoral pain is felt diffusely in the area of the patella or just inferior. Athletes with patellofemoral pain often report aggravation of symptoms with activities that produce low tendon loads, such as prolonged sitting, walking, or cycling. Assessments of hopping and the decline squat can help distinguish between the two conditions. Patients with patellofemoral pain often demonstrate pelvic instability, greater knee flexion, and dynamic knee valgus (knee caves inward) when hopping on one leg [56]. They also have less pain with deeper squats than patients with patellar tendinopathy. (See "Patellofemoral pain".)

●Knee bursitis – The prepatellar bursa is affected most often and presents as a superficial swelling at the anterior knee, but infrapatellar bursitis near the tibial insertion of the patellar tendon can occur. The condition can develop after direct trauma or prolonged kneeling. Infective bursitis can occur if a wound exists and requires immediate medical management. The history of patients with bursitis typically does not involve intense sport, gradual onset, or increased pain with jumping. Pain is more variable in nature and location; tenderness is not focal at the inferior pole of the patella. Swelling is typically not a feature of patellar tendinopathy. (See "Knee bursitis" and "Septic bursitis".)

●Osgood-Schlatter disease (tibial tuberosity avulsion) – In younger athletes (10 to 15 years old), repetitive or excessive traction of the patellar tendon at the apophysis of the tibial tuberosity can cause an avulsion injury, commonly referred to as Osgood-Schlatter disease (picture 4). This injury typically occurs during the adolescent growth spurt and causes local swelling and pain. Focal tenderness is present at the tendon insertion rather than the inferior pole of the patella. Increased traction on the tendon during running or jumping aggravates symptoms. Patient age and examination findings are usually sufficient to distinguish the condition from patellar tendinopathy. (See "Osgood-Schlatter disease (tibial tuberosity avulsion)".)

●Sinding-Larsen-Johansson (SLJ) disease (inferior patella apophysis avulsion) – SLJ disease is caused by activities that involve abundant jumping. This causes repetitive traction by the patellar tendon on the patella, ultimately producing an avulsion of the secondary ossification center (apophysis) at the inferior pole of the patella. SLJ disease typically affects children between 10 and 13 years, whereas patellar tendinopathy primarily affects young, active adults. Physical examination demonstrates pain and swelling at the inferior pole of the patella. Patellar tendon thickening and infrapatellar bursitis may also be present, while knee effusion and ligamentous laxity are not present. Imaging is not usually necessary, but if obtained, plain radiographs reveal fragmentation and irregular calcification of the ossification centers (a finding seen in some asymptomatic children and adolescents), while ultrasound shows fragmentation of the lower pole of the patella, patellar tendon thickening at the origin, and infrapatellar bursitis.

●Fat pad syndrome – The infrapatellar (Hoffa) fat pad lies deep to the patellar tendon and extends from the inferior pole of the patella to the upper tibia (figure 2). Impingement of the fat pad causes a vague ache deep to the patella that can become abruptly sharper and more painful at a specific angle of knee flexion. Pain is load dependent and is typically felt during end-range extension or hyperextension of the knee. The condition is seen most often in dancers, gymnasts, and swimmers; whose activities require kicking or maximum knee extension. In contrast to patellar tendinopathy, swelling can develop, and pain is more diffuse and located inferior to the anterior knee. The fat pad itself is tender.

●Plica syndrome – The abnormal plica, an intra-articular band of thickened, fibrotic tissue, may cause pain in the region of the anteromedial knee, sometimes associated with a popping or catching sensation. Pain is often worse with activity. Sometimes, a tender, thickened band is palpable at the medial edge of the patellofemoral joint. The location of pain and the absence of focal tenderness at the patellar tendon help to distinguish this condition from patellar tendinopathy.

●Quadriceps tendinopathy – Tendinopathy of the extensor mechanism of the knee can develop at the quadriceps tendon as well as the patellar tendon, although it is less common. An important clinical feature to distinguish between the two is the location of pain and tenderness, which with quadriceps tendinopathy is found at the superior pole of the patella, usually at the central to lateral margin. Pain is aggravated by a deep squat, when the tendon is compressed against the femoral condyle. Quadriceps tendinopathy is more common among older athletes and appears to be related to activities requiring deep knee flexion, such as Olympic weightlifting. However, it can also occur in athletes in field and court sports who flex their knee deeply when changing direction and decelerating.

MANAGEMENT — The principles and evidence pertaining to the general treatment of tendinopathy is reviewed separately. (See "Overview of the management of overuse (persistent) tendinopathy".)

Initial pain and load management — The first steps in management are to determine whether symptoms require that the patient refrain from specific loading activities and sport participation, and to reduce pain to an acceptable level. It is important to assess patellar tendon irritability, which involves determining the duration of symptoms following loading. "Stable" tendon pain subsides to manageable levels within 24 hours, whereas "irritable" tendon pain persists longer than 24 hours following loading. Studies suggest that up to 24 hours of pain after tendon-loading activities (eg, squatting, jumping) may be acceptable during rehabilitation.

Pain can be assessed using a standard 0 to 10 scale where 0 is no pain and 10 is the worst pain imaginable. During and after patellar tendon-loading activities, pain should not exceed 3 out of 10 and should subside within 24 hours. Icing and a short course of oral or topical nonsteroidal antiinflammatory drugs (NSAIDs) can be used to provide some relief of symptoms early in the course of tendinopathy. (See "Overview of the management of overuse (persistent) tendinopathy", section on 'Treatments'.)

Functional tests such as single-leg step-down, single-leg lunges, double- or single-leg hopping, or box jumps may reveal asymmetries in the loading pattern of the trunk, pelvis, knees, and ankles. Any deficits in the kinetic chain, such as pelvic drop, knee caving in (ie, valgus knee motion), decreased ankle dorsiflexion, or decreased flexibility of the hamstring or quadriceps, should be identified and appropriate interventions made. Other potential risk factors, such as excessive training volumes or sudden increases in training load (frequency, intensity, and duration of training sessions), should be addressed.

Rehabilitation: strength training and progressive tendon loading — The core of rehabilitation consists of a strength training program with progressive tendon-loading exercises that prepare the tendon to withstand the high loads sustained during sport or heavy labor.

Although there is no single way to rehabilitate an injury, the authors' preferred approach involves a four-stage program that includes the following:

●Isometric exercises (static; example is plank (picture 5))

●Isotonic exercises (dynamic; important example is leg press (picture 6))

●Energy-storage exercises (explosive; examples include jumping squat variations, agility sprints with direction change)

●Sport-specific exercises

All exercises are performed within the limits of acceptable pain. In a randomized trial of 76 young males with patellar tendinopathy, this approach produced greater improvements in symptoms and earlier return to sport than a program focused on eccentric strength exercises [57]. A summary of the program used in the trial is provided; greater detail from supplementary materials published with the trial can be found in the following references [58].

In older or high-performance athletes, we recommend a grayscale ultrasound of the patellar tendon to assess whether any significant underlying degenerative changes or intrasubstance tears are present. If so, a less aggressive approach to rehabilitation should be used, as tendon tissue may take longer to adapt to the increased loads.

Once base muscle strength is achieved (eg, as assessed by handheld dynamometer or manual muscle strength testing [59]), patients can begin performing functional strength and endurance exercises, such as stair climbing and walking lunges. When strength and endurance are adequate to perform such exercises for 10 to 15 repetitions in a functionally correct manner, the rate of loading is increased by introducing plyometric exercises such as hopping, skipping, and jumping. Sport-specific loading is then introduced using drills that mimic the movements of the sport [60]. In all stages, "stable" tendon pain (a maximum 3 of 10) is acceptable. The authors' preferred program is outlined in the following table (table 1). (See 'Initial pain and load management' above.)

While not the authors' preferred approach, rehabilitation programs emphasizing eccentric strength exercises are effective and continue to be used by some physical therapists. In such programs, the early stages of rehabilitation emphasize stretching and isometric strengthening exercises [61-64]. Once pain diminishes, controlled, progressive, heavy-load exercise including eccentric strengthening can be initiated [65-68]. Examples of eccentric quadriceps exercises used during rehabilitation include the leg extension (picture 7), eccentric squat variations (picture 8 and picture 3), step-down (picture 9), reverse Nordic lower (picture 10), overhead reverse lunge (picture 11), drop squat (picture 12), and drop jumps (picture 13). A sample rehabilitation protocol emphasizing eccentric strength exercises (not the authors' preferred approach) is outlined in the following table (table 2).

Adjunct treatments — Although many adjunct treatments for patellar tendinopathy are in use, evidence supporting their effectiveness is limited. Wraps and taping to support the tendon are two such interventions. In a randomised trial comparing these interventions with a placebo taping method, both reduced pain in the short term, but neither was more effective than placebo subsequently [69].

While multiple studies support the effectiveness of topical nitroglycerin for chronic tendinopathy generally, the only randomized trial involving patellar tendinopathy did not demonstrate benefit [70]. (See "Overview of the management of overuse (persistent) tendinopathy", section on 'Topical nitroglycerin (glyceryl trinitrate)'.)

Although evidence is limited, extracorporeal shock wave therapy (ESWT) may be used as an adjunct therapy for patellar tendinopathy. While a single randomized trial reported no benefit from ESWT when compared with placebo in the in-season management of jumping athletes with patellar tendinopathy [71], studies in other tendinopathies suggest it may provide some benefit [72]. Further study is needed to ascertain the effectiveness of ESWT for reducing pain and improving function and to determine optimal treatment parameters. The role of ESWT in the treatment of tendinopathy generally is discussed separately. (See "Overview of the management of overuse (persistent) tendinopathy", section on 'Shock wave therapy'.)

Although we are not aware of any high-quality studies that have systematically assessed the role of foot biomechanics or footwear in patellar tendinopathy, foot and shoe biomechanics may influence knee-loading patterns. In the authors' clinical experience, patients with patellar tendinopathy and hyperpronation of the hind- or forefoot may benefit from a stiff sports shoe with a straighter last shape that resists torsional stress. If these adjustments provide insufficient relief, referral to a (sports) podiatrist may be helpful. Video analysis of the lower limb kinematics may provide insight into mechanical flaws. If the functional malalignment cannot be managed with an appropriate sports shoe, the patient may benefit from custom-made orthotics.

Patients with stiff foot types (high arched/pes cavus or hyperpronated/pes planus) or with limited foot or ankle mobility may benefit from an exercise program to increase the mobility and strength of the foot and ankle. Referral to a physical therapist is appropriate in such cases.

No high-quality evidence supports the use of glucocorticoids, prolotherapy, platelet-rich plasma [22], or other injections [73]. (See "Overview of the management of overuse (persistent) tendinopathy", section on 'Treatments'.)

INDICATIONS FOR SURGICAL REFERRAL — Surgery is rarely required if training loads are limited and an appropriate rehabilitation program is implemented [74]. Sometimes, elite athletes with unresolving pain due to persistent excessive loading elect to have surgery [75,76]. The surgical methods employed allow for immediate tendon loading and return to full sport after 8 to 16 weeks of rehabilitation.

For others, if symptoms fail to improve by 12 months despite appropriate physical therapy and related conservative measures, surgical referral is a reasonable option, although evidence is largely limited to small, observational studies [74-77]. For patients and athletes whose primary activity is walking or running, surgery may enable a return to full activity.

COMPLICATIONS — In otherwise healthy individuals, complications of patellar tendinopathy are rare. Complete rupture of the patellar tendon occurs rarely, but the risk may be increased with intratendinous glucocorticoid injections [78].

RETURN TO PLAY AND WORK — In general, patients should not return to full sport or heavy labor until they demonstrate in a rehabilitation or training setting that they can sustain repeated sport- or labor-specific knee loads without an increase in symptoms or visual analogue score (VAS) for pain the following day.

At a minimum, the patient recovering from patellar tendinopathy should meet the following criteria before returning to sport or heavy labor:

●Full, pain-free motion of the knee

●Hip abduction, quadriceps, hamstring, and calf muscle strength approximately equal to that of the uninjured extremity

●Ability to perform all sports- or labor-specific tasks with a VAS ≤2 (scale of 0 to 10)

Rehabilitation generally requires at least three months, and often more than six months, from diagnosis to return to full activity. Fewer than 50 percent of patellar tendinopathy patients are able to return to their competitive sport at six months following a comprehensive rehabilitation program including appropriate tendon-loading exercise [57].

PREVENTION — Jumping and running sport athletes, military recruits, and patients with a previous history of anterior knee pain are at increased risk for developing patellar tendinopathy. Although evidence is scant, the following interventions may help to reduce risk in these populations:

●Ankle mobility screening – Screen athletes participating in high-risk sports for diminished ankle dorsiflexion and pronation-supination; implement ankle mobility exercises if such limitations are identified.

●Muscle tightness screening – Screen athletes participating in high-risk sports for hamstring, quadriceps, and calf muscle tightness; implement flexibility exercises if such limitations are identified.

A flexibility program for the hips, knees, and ankles can be found in the following reference [79].

●Gradual increases in training volume – Place reasonable limits on sudden increases in training volumes, particularly on training involving jumping and lower extremity plyometric exercises. Increase training loads and volumes gradually; avoid weekly increases of more than 10 percent in jumping load.

When an athlete returns to sport following any type of injury (including concussion) or illness and has not been able to maintain 80 percent of their normal weekly training load, the authors use the following rule of thumb for a safe return to sport: multiply the total of weeks off from training by two to estimate the total time required to resume pre-injury/pre-illness training load and volume. In any given week, do not exceed 10 percent increases in jumping load.

●Foot arch screening – Particularly for athletes whose feet are flat (pes planus) or with a low arch, the authors have found custom orthotics and supportive shoes that resist torsion to be useful.

In high-risk sports, we recommend daily monitoring of jump totals (eg, digital jump counter or smart watch) and avoiding any sudden increase in training load or volume [80].

Strength training may reduce risk. A systematic scoping review of studies of prevention and in-season management of patellar tendinopathy found that greater weekly resistance training volume was associated with a reduced risk of injury [81]. In-season resistance training using eccentric, heavy slow, or isometric exercises were all reported to be feasible and beneficial for reducing risk.

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)" and "Society guideline links: Knee pain".)

SUMMARY AND RECOMMENDATIONS

●Epidemiology and risk factors – Patellar tendinopathy is a common condition primarily affecting athletes who play sports involving a great deal of jumping (eg, volleyball) or rapid acceleration and deceleration (eg, basketball). High training volume, poor landing technique (eg, poor torso control, minimal hip and knee flexion), and mobility restrictions (eg, diminished ankle dorsiflexion, hamstring and quadriceps tightness) may contribute. (See 'Epidemiology' above and 'Risk factors' above and 'Anatomy and biomechanics' above.)

●Clinical presentation and physical examination – Characteristic features include pain and tenderness localized to the inferior pole of the patella and load-related pain that increases with the demands placed on the knee extensors, particularly during activities such as jumping and hopping. Symptom onset is gradual, often begins after a sudden increase in training load or change in playing surface, and increases over weeks to months. Pain typically occurs immediately when the patellar tendon is loaded and subsides with rest. The single-leg decline squat (picture 3) typically causes a lot of localized pain early in knee flexion.

●Diagnostic imaging and diagnosis – With the exception of bedside ultrasound, diagnostic imaging is generally not indicated, as the diagnosis can be made based on the history and examination findings alone in most cases.

●Differential diagnosis – The differential diagnosis includes patellofemoral pain, knee bursitis, tibial tuberosity avulsion (Osgood-Schlatter), inferior patella apophysis avulsion (Sinding-Larsen-Johansson), and other conditions. (See 'Differential diagnosis' above.)

●Management – Initial management includes providing analgesia and determining whether symptoms require the patient to refrain from specific loading activities and sport participation. For long-term management, we suggest a physical therapy program involving a progression of isometric and then dynamic strength exercises, rather than a program focused on eccentric or other exercises (Grade 2C). The authors' preferred program is summarized in the following table (table 1); details about the program, including descriptions of exercises and alternatives, are provided in the text. Surgical referral is rarely required. (See 'Initial pain and load management' above and 'Rehabilitation: strength training and progressive tendon loading' above.)

●Return to sport or heavy labor – Rehabilitation generally requires at least three months. The following criteria should be met before the patient returns to sport or heavy labor:

•Full, pain-free motion of the knee

•Hip abduction, quadriceps, hamstring, and calf muscle strength approximately equal to that of the uninjured extremity

•Ability to perform all sports- or work-specific tasks with a visual analogue score (VAS) ≤2 (scale of 0 to 10)