Approach to acute knee pain and injury in children and skeletally immature adolescents

INTRODUCTION — The evaluation of acute knee injury in the child or skeletally immature adolescent athlete will be presented here.

The evaluation of children with joint pain and swelling, the evaluation of chronic knee pain in children and skeletally immature adolescents, and the approach to knee pain in the athlete or active adult, including skeletally mature adolescents, are discussed separately:

●(See "Evaluation of the child with joint pain and/or swelling".)

●(See "Approach to chronic knee pain or injury in children or skeletally immature adolescents".)

●(See "Approach to the adult with knee pain likely of musculoskeletal origin".)

ANATOMIC CONSIDERATIONS — The anatomy of the knee with an emphasis on biomechanics is discussed in detail separately. (See "Physical examination of the knee", section on 'Anatomy'.)

The growth plate or physis represents a major anatomical difference between adult and pediatric bone. Growing long bones in children and younger adolescents are composed of the following segments: diaphysis (shaft), metaphysis (where the bone flares), physis (growth plate), and epiphysis (secondary ossification center) (figure 1).

Growth plates mark a weak point in pediatric bone and are susceptible to fracture. Because the tensile strength of pediatric bone is less than that of the ligaments, the same injury mechanism that causes a ligamentous injury in adults (ligamentous sprain, strain, or tear) is more likely to cause a bone injury in children: The physis will separate from the epiphysis, creating a physeal fracture before disruption or "spraining" of an adjacent strong and flexible ligament. After closure of the physis, the tensile strength of bone exceeds that of the ligaments and ligamentous injury without bone injury occurs more commonly. (See "General principles of fracture management: Fracture patterns and description in children", section on 'Physeal (growth plate)' and "General principles of fracture management: Fracture patterns and description in children", section on 'Physeal fracture description'.)

In general, physeal closure around the knee occurs in late adolescence. However, the timing of physeal closure varies in individual patients and by bone and patient sex. The typical age of physeal closure of the distal femur, proximal tibia, proximal fibula, and tibial tuberosity are provided in the figure (figure 2).

DEFINITIONS

Acute injury — For this topic, acute injury refers to sudden trauma (eg, a collision between players, a fall while riding a bicycle, or a motor vehicle collision). Of note, some chronic conditions may become apparent during evaluation for a traumatic injury, such as a slipped capital femoral epiphysis (SCFE) or a septic arthritis. (See 'Referred pain' below and 'Systemic disease' below.)

Acute pain — Acute pain is distinguished by duration. For most musculoskeletal conditions, pain for less than six weeks is usually described as acute or subacute, while pain lasting longer than six weeks is typically characterized as chronic. While the six-week threshold is arbitrary, it can be useful because many self-limited injuries heal by the end of six weeks with appropriate rest. Acute pain typically has no progressive pattern. In response to a particular trauma, acute pain flares, lasts a predictable period, and then subsides as healing occurs.

Chronic knee pain in children and skeletally immature adolescents is discussed separately. (See "Approach to chronic knee pain or injury in children or skeletally immature adolescents".)

EPIDEMIOLOGY — Acute knee injuries occur frequently in children and skeletally immature adolescents. Based upon emergency department visits, the incidence in children and adolescents ranges from 3 to 12 knee injuries per 1000 persons [1,2]. Sports, recreation (eg, bicycle riding and trampoline use), and falls from stairs or furniture are the most frequent activities that result in injury [1,2]. In the United States, American football, basketball, and soccer account for the largest proportion of sports-related knee injuries [1]. Outside of the United States, soccer and basketball pose the greatest risk [3].

Among children 5 to 14 years of age, the most common knee injuries are cutaneous contusions, lacerations, ligamentous sprains or strains, fractures, or patellar dislocations [1,2]. Although fractures occur more frequently in children and skeletally immature adolescents than in skeletally mature adolescents and adults, ligamentous sprains or strains are still the most common injury in these patients, and anterior cruciate ligament (ACL) tears are the most common condition [4]. About 2 percent of knee injuries result in hospitalization [1] and up to 17 percent of knee injuries warrant surgical repair [3]. Multiple studies in high school athletes have found that adolescent girls have a significantly higher risk of a major knee injury from sports compared to boys [1,5-7].

SPECIFIC CONDITIONS

Limb-threatening injuries — These injuries are associated with a significant risk of neurovascular compromise or infection and require rapid recognition and treatment (algorithm 1).

Displaced proximal tibial fracture — Displaced proximal tibial physeal fractures are most common in young adolescents who sustain high energy hyperextension forces. Ligamentous injury and internal knee derangement are additional associated injuries.

Specific fractures include (see "Proximal tibial fractures in children", section on 'Mechanism of injury' and "Acute compartment syndrome of the extremities", section on 'Clinical features'):

●Tibial tubercle fractures – Tibial tubercle fractures are most frequently seen in young male athletes while jumping (eg, planting the foot to dunk a basketball) (figure 3).

●Proximal tibial physeal fractures – Proximal physeal fractures can be associated with posterior displacement of the metaphyseal fragment with laceration of the popliteal artery (figure 4).

●Tibial tubercle apophyseal fractures – Tibial tubercle apophyseal fractures are at significant risk for developing an acute compartment syndrome. Acute tibial tubercle apophyseal fractures are distinct from tibial tubercle apophysitis (Osgood-Schlatter disease) which has a gradual onset.

Physical findings of these injuries include a large hemarthrosis, pain, and deformity. Anterior-posterior (AP) and lateral plain radiographic views of the lower leg, including the knee and ankle, should be obtained. (See "Proximal tibial fractures in children", section on 'Physical findings' and "Proximal tibial fractures in children", section on 'Radiographic findings'.)

The management of proximal tibial physeal or apophyseal fractures is discussed separately. (See "Proximal tibial fractures in children", section on 'Initial management' and "Proximal tibial fractures in children", section on 'Physeal fractures' and "Proximal tibial fractures in children", section on 'Tibial tubercle avulsion'.)

Displaced femoral physeal fracture — A hyperextension injury of the distal femur can result in the anterior displacement of the epiphysis. In this situation, the proximal fracture fragment can be driven posterior into the popliteal fossa where it can damage popliteal vessels and the common peroneal or posterior tibial nerves. Alternatively, when a valgus-type force is applied directly to the lateral side of the distal femur as with American football injuries, it generally results in a Salter-Harris type II or III fracture (figure 5). These fractures frequently have an associated anterior cruciate ligament (ACL) tear with knee instability. Less commonly, they may be open fractures. (See "Distal femoral fractures in children", section on 'Mechanism of injury'.)

The presence of a distal femur fracture will usually be suspected based upon the history of a high-energy mechanism with physical examination findings of pain and swelling around the distal femur and knee (picture 1). Patients with distal femur fractures will often be in severe pain and unable to bear weight. Associated hamstring muscle spasms will cause the knee to be flexed with resultant obvious knee deformity. A careful neurovascular examination is imperative. Due to the risk of vascular compromise associated with distal femoral fractures, the soft tissues around the knee must also be examined for compartment syndrome at the initial presentation and subsequently. (See "Acute compartment syndrome of the extremities", section on 'Clinical features'.)

Initial evaluation of a suspected distal femur fracture should include standard anterior posterior (AP) and lateral radiographs of the knee and entire femur, including the hip, to determine fracture line, degree of displacement and to rule-out an associated knee dislocation. The management of distal femoral physeal fractures is discussed separately. (See "Distal femoral fractures in children", section on 'Plain radiographs' and "Distal femoral fractures in children", section on 'Initial treatment' and "Distal femoral fractures in children", section on 'Definitive care'.)

Knee dislocation (tibiofemoral) dislocation — Knee (tibiofemoral) dislocations are much less common than physeal fractures in skeletally immature children and adolescents. Suspected dislocations warrant emergency imaging with plain radiographs and reduction followed by careful neurovascular assessment, including arterial imaging (eg, Doppler flow study, Computed tomographic angiogram, or arteriography of the popliteal artery). If emergency imaging is not available, then reduction should be attempted and transfer to a facility with vascular surgery, vascular radiology, and orthopedic surgery expertise should be performed. (See "Knee (tibiofemoral) dislocation and reduction", section on 'Procedure' and "Knee (tibiofemoral) dislocation and reduction", section on 'Postreduction management'.)

Knee dislocations are most common after high-velocity trauma (eg, motor vehicle accident or fall from height) but can occur with low-velocity trauma in contact sports. Mechanisms of injury include hyperextension, valgus rotary stress, and varus rotary stress. Knee dislocations result from the rupture of at least two, but usually three, of the four major ligaments, resulting in multidirectional instability. The ACL and posterior cruciate ligament (PCL) usually are involved, although this is not always the case. Most knee dislocations are anterior or posterior, with the direction of dislocation indicating the movement of the tibia relative to the femur. (See "Knee (tibiofemoral) dislocation and reduction", section on 'Clinical presentation and mechanism of injury'.)

Knee dislocations usually are obvious when there is gross deformity of the knee. Although in children and adolescents with an obvious deformity, displaced fractures may look like a knee dislocation. Knee dislocations that have reduced spontaneously may be more subtle. Thus, whenever it is clear from the initial evaluation that two ligaments have ruptured (the ACL/medial collateral ligament [MCL] combination is most common), the possibility of a spontaneously reduced knee dislocation must be considered and the neurovascular status of the lower extremity carefully monitored. It is important to inquire about the mechanism and the position of the leg immediately following the injury, and whether it changed subsequently. Complications of knee dislocation include popliteal artery and peroneal nerve injury, which occur primarily after anterior-posterior and lateral dislocations, respectively (figure 6). In one observational study of 2267 children 19 years of age or younger with tibiofemoral (knee) dislocations, vascular injury occurred in 2.4 percent of patients [8]. (See "Knee (tibiofemoral) dislocation and reduction", section on 'Clinical presentation and mechanism of injury' and "Knee (tibiofemoral) dislocation and reduction", section on 'Postreduction management' and "Knee (tibiofemoral) dislocation and reduction", section on 'Complications'.)

Penetrating joint wound — Lacerations that extend into the knee capsule may have associated ligamentous or tendon laceration and pose a significant risk of joint infection. These wounds can be identified as follows:

●Direct visualization of joint capsule disruption when examining the wound

●Air or a radiopaque foreign body seen within the joint on plain radiographs

●In patients in whom suspicion for laceration into the knee joint (traumatic arthrotomy) is high but not confirmed by examination or radiographs, arthrocentesis with injection of a large volume of normal saline into the joint space (also called the saline load test) and observation of the saline coming out of the wound site (see "Severe lower extremity injury in the adult patient", section on 'Soft tissue and bone assessment')

Such injuries warrant prompt orthopedic consultation for debridement and repair.

Common injuries — The most common knee injuries in children and skeletally immature adolescents consist of cutaneous injuries, ligamentous tears, fractures, and patellar dislocations. Anterior cruciate ligament (ACL) tears are the most common ligamentous injury. (See 'Epidemiology' above.)

Cutaneous injury — Abrasions, lacerations, and ecchymoses commonly accompany knee injuries in children and skeletally immature adolescents [1,2]. Patients without internal derangement (eg, fractures, chondral lesions, and injuries to the ligaments or menisci) will have a normal examination of the knee, will be able to bear weight, and will have a normal or near-normal gait. Oral analgesia with acetaminophen or ibuprofen and local measures (eg, cleaning and covering an abrasion or laceration and providing cold therapy for contusions) can ease apprehension and facilitate cooperation with the knee examination. Lacerations and puncture wounds near the knee joint should be assessed for disruption of the joint capsule. (See 'Penetrating joint wound' above.)

Wounds that enter the joint warrant prompt consultation with an orthopedic surgeon. Superficial abrasions and lacerations should undergo irrigation and debridement. Lacerations through the dermis warrant closure. Wounds should be dressed with an antibiotic ointment and absorbent dressing. Tetanus prophylaxis should be provided as needed (table 1). (See "Minor wound evaluation and preparation for closure", section on 'Irrigation' and "Skin laceration repair with sutures", section on 'Indications' and "Skin laceration repair with sutures", section on 'Suturing techniques' and "Minor wound evaluation and preparation for closure", section on 'Debridement'.)

Ligamentous injury — Examination of the ligaments includes palpation for tenderness and assessment of laxity with various maneuvers. These maneuvers, described below, can be performed gently to yield a preliminary diagnosis without causing great discomfort. Guarding frequently limits the sensitivity of the physical examination in patients with acute injuries.

●Anterior cruciate ligament (ACL) – ACL tears are the most common ligamentous knee injury in children and skeletally immature adolescents. They are typically sustained through a non-contact injury but may also occur with a direct blow to the knee that results in hyperextension or valgus deformation. These tears are suspected on the basis of a suggestive history (sudden change of direction or landing during sport causing the knee to "pop" or give out) and clinical findings (acute knee effusion with positive Lachman (picture 2), pivot shift (figure 7), and/or anterior drawer tests (figure 8)). Contact injuries that cause ACL tears are often associated with fractures (eg, tibial eminence fracture) or medial meniscus tears. The performance and interpretation of provocative maneuvers to identify ACL injuries are discussed in greater detail separately. (See "Anterior cruciate ligament injury", section on 'Physical examination'.)

A definitive diagnosis of an ACL tear is made by magnetic resonance imaging (MRI) or knee arthroscopy. In many instances, the clinical presentation can establish the diagnosis of an ACL tear; yet, the MRI is necessary to rule in or out other intraarticular injuries that will influence the decision to have surgery. (See "Anterior cruciate ligament injury", section on 'Diagnosis'.)

The treatment of ACL injuries, including pediatric considerations, is discussed separately. (See "Anterior cruciate ligament injury", section on 'Treatment'.)

●Medial collateral ligament (MCL) – The MCL may be injured via a direct valgus stress from a blow to the lateral aspect of the knee or via an indirect stress through abduction or rotation of the lower leg. Direct blows typically cause more severe injury. (See "Medial (tibial) collateral ligament injury of the knee", section on 'Mechanism of injury and healing'.)

Clinical findings of MCL tears consist of tenderness over the ligament and ligamentous laxity (see "Medial (tibial) collateral ligament injury of the knee", section on 'Physical examination'). Laxity of the MCL is evaluated with the valgus stress test (picture 3 and movie 1). Laxity with the knee flexed to 30 degrees suggests an isolated MCL sprain. Laxity with valgus stress at 0 degrees of flexion (full extension) may indicate:

•Fracture (eg, of the distal femoral epiphysis or physis)

•Posteromedial compartment involvement with a tear of the capsular component of the MCL

•Grade 3 ACL sprain in addition to grade 3 MCL sprain (because the ACL provides some medial stability in full extension). If it is clear from the examination that both the ACL and MCL are torn, the possibility of knee dislocation must be evaluated. (See 'Knee dislocation (tibiofemoral) dislocation' above.)

Radiographs should be obtained if the patient is unable to bear weight or if focal bony tenderness, gross deformity, or an effusion is present. (See 'Plain radiographs' below.)

The diagnosis of a MCL injury is made clinically based upon the history, clinical presentation, and examination findings and is generally straightforward. MRI may be used to establish a definitive diagnosis but is not mandatory unless another ligamentous or meniscal injury that would require surgery is suspected or the patient has sustained severe trauma. (See "Medial (tibial) collateral ligament injury of the knee", section on 'Diagnosis'.)

The treatment of MCL injuries is discussed separately. (See "Medial (tibial) collateral ligament injury of the knee", section on 'Initial treatment' and "Medial (tibial) collateral ligament injury of the knee", section on 'Follow-up and rehabilitation'.)

●Lateral collateral ligament (LCL) – Isolated injuries of the LCL are relatively uncommon. Most occur in association with injuries to the posterolateral corner (PLC), posterior cruciate ligament (PCL), lateral meniscus, and/or ACL. (See "Lateral collateral ligament injury and related posterolateral corner injuries of the knee", section on 'Mechanism of injury'.)

Patients who have sustained a LCL injury typically present following a blow to the medial or anteromedial aspect of their knee while it was fully extended, and report lateral or posterolateral knee pain. Alternatively, patients can sustain a noncontact LCL injury from a sudden varus moment (knee bending laterally) while the knee is hyperextending. (See "Lateral collateral ligament injury and related posterolateral corner injuries of the knee", section on 'Common presentations'.)

The most common examination finding in patients with an LCL injury is tenderness along the lateral knee (picture 4). Localized soft tissue swelling may also be appreciated at the site of injury. Laxity of the LCL is evaluated with the varus stress test (picture 3) as follows (see "Lateral collateral ligament injury and related posterolateral corner injuries of the knee", section on 'Examination findings'):

•Laxity with varus testing at 30 degrees of flexion indicates an isolated LCL sprain.

•Gross instability on varus testing with the knee fully extended suggests disruption of the capsular component of the LCL, the midportion of the PCL, and posterolateral corner instability, including the arcuate popliteal complex.

Another finding of grade 3 LCL sprains is that the normally taut LCL is absent when the patient sits with the involved knee in a figure-of-four position.

A preliminary diagnosis of LCL tear is made based upon clinical findings. Plain radiographs and MRI are frequently also indicated in patients with instability noted with the knee fully extended to identify associated injuries to other structures. (See 'Imaging' below.)

The management of LCL tears is discussed separately. (See "Lateral collateral ligament injury and related posterolateral corner injuries of the knee", section on 'Initial treatment' and "Lateral collateral ligament injury and related posterolateral corner injuries of the knee", section on 'Follow-up and definitive care'.)

●Posterior cruciate ligament (PCL) – Acute PCL injuries are rare in children and skeletally immature adolescents but, when present, are often associated with significant knee instability and increased risk for neurovascular compromise due to injury to multiple structures. It can present with symptoms similar to those associated with LCL tears.

The posterior cruciate ligament is evaluated with the posterior sag test and the posterior drawer test. In the posterior sag test, the patient is supine, with hips flexed to 45 degrees, knees flexed to 90 degrees, and the feet flat on the table. In a positive test, the involved leg sags backward relative to the uninvolved leg (picture 5). A positive posterior drawer test (figure 9) also suggests PCL injury. (See "Physical examination of the knee", section on 'Tests for PCL injury and posterior stability'.)

Associated injury to the posterolateral corner is suggested by positive external rotation recurvatum, posterolateral drawer, reverse shift, and dial (picture 6) tests which are discussed in detail separately. (See "Lateral collateral ligament injury and related posterolateral corner injuries of the knee", section on 'Examination findings'.)

Knee injuries involving the PCL and posterolateral corner are typically severe and plain radiographs to identify associated fractures and MRI is necessary. Patients with these injuries warrant prompt consultation with an orthopedic surgeon with pediatric sports medicine expertise. (See "Posterior cruciate ligament injury".)

Fracture — Children and skeletally immature adolescents are at risk for the following fractures after acute knee trauma (see 'Anatomic considerations' above):

●Physeal fractures – Fractures of the physes (growth plates) of the distal femur and proximal tibia are important causes of knee pain in the young athlete. Patients with these fractures typically have pain, swelling, and/or deformity at the site of injury and are unable to walk. Patients with displaced physeal fractures are at risk for neurovascular compromise or an acute compartment syndrome, depending upon the type of fracture. The diagnosis is made by plain radiography. (See 'Displaced proximal tibial fracture' above and 'Displaced femoral physeal fracture' above and 'Plain radiographs' below.)

Management of these injuries is discussed separately. (See "Proximal tibial fractures in children", section on 'Initial management' and "Proximal tibial fractures in children", section on 'Physeal fractures' and "Distal femoral fractures in children", section on 'Initial treatment' and "Distal femoral fractures in children", section on 'Definitive care'.)

●Tibial spine (intercondylar eminence) avulsion fractures – The tibial spine is an important bony prominence that anchors the attachment of the ACL. Tibial spine avulsion fractures result from hyperextension of the knee with concurrent rotation of the femur on the tibia. It is the same mechanism as an ACL injury in skeletally mature patients. Patients with tibial spine fractures have a hemarthrosis, knee joint tenderness, and a markedly decreased range of motion. The diagnosis is confirmed by plain radiographs. (See "Proximal tibial fractures in children", section on 'Mechanism of injury' and "Proximal tibial fractures in children", section on 'Physical findings'.)

Management of tibial spine fractures is discussed separately. (See "Proximal tibial fractures in children", section on 'Tibial spine avulsion'.)

●Patellar sleeve fractures – Patellar sleeve fractures are caused by an indirect force applied to the patella through sudden, forceful contraction of the quadriceps. This might occur when someone lands on their feet after jumping from a moderate height or comes to a sudden stop from a full sprint. (See "Patella fractures", section on 'Mechanism of injury and fracture pattern'.)

Examination of the patient with a patella fracture typically reveals a knee joint effusion or hemarthrosis and focal tenderness of the patella. The patient may not be able to extend the knee against gravity, and a gap in the extensor mechanism may be palpable. (See "Patella fractures", section on 'Clinical presentation and examination'.)

Diagnosis of a patellar sleeve fracture is based upon clinical findings and imaging. Radiographic findings include a high-riding patella or a distal fracture fragment. However, an unremarkable plain radiograph does not rule out a fracture because bone fragments can be difficult to see. Other imaging (eg, ultrasound, computed tomography [CT], or MRI) may be necessary to confirm the diagnosis when clinical suspicion is high. The management of avulsion fractures is similar to that for quadriceps or patellar tendon injuries; surgery is typically required. (See "Patella fractures", section on 'Pediatric considerations'.)

●Osteochondral fractures – Osteochondral fractures to the intraarticular portions of the femoral condyles or tibial plateau frequently accompany patellar dislocation, ligamentous tears, or meniscal injuries in children and skeletally immature adolescents [9,10]. Osteochondral fragments may arise from these fractures with resulting mechanical symptoms (eg, catching or locking) [11]. If untreated, these fractures may develop into osteochondral defects and, ultimately, may cause osteoarthritis. These patients will typically complain of continued pain, swelling and mechanical complaints. These fractures may be detected by MRI [12]. Patients with these injuries warrant referral to an orthopedic surgeon with pediatric expertise.

Patellar dislocation — Patellar dislocation typically occurs when the lower leg is externally rotated and the quadriceps muscle forcefully contract to extend the knee. Patellar dislocation also can follow collision with another person, particularly if the knee sustains valgus (inward) force (eg, football injuries). Patients with first-time dislocations often report hearing a loud sound and feeling a sensation of tearing and dislocation. (See "Recognition and initial management of patellar dislocations", section on 'Mechanisms of injury'.)

An unreduced acute dislocation usually demonstrates obvious lateral patellar displacement on inspection of the knee (picture 7). Displacement in any other direction is rare in children and skeletally immature adolescents. In a patient with normal elasticity who dislocates the patella for the first time, lateral dislocation tears the medial patellar stabilizers, including the medial retinaculum, which causes a rapidly enlarging medial hematoma. By contrast, patients who have chronic subluxation of the patella, or in whom the patellofemoral joint is hypermobile, the bleeding and swelling after an episode may be minimal. Acute patellar dislocation can be complicated by bone and chondral fracture. Treatment consists of reduction of the lateral dislocation (figure 10). Dislocations in any other direction warrant emergency imaging and prompt consultation with an orthopedic surgeon with pediatric expertise. (See "Recognition and initial management of patellar dislocations", section on 'Clinical features and diagnosis' and "Recognition and initial management of patellar dislocations", section on 'Reduction of lateral dislocations'.)

Patients with a spontaneously reduced patellar dislocation and, to a lesser extent, with patellar subluxation, have pain in the medial patellar retinacular area and are apprehensive when the examiner tries to push the patella laterally (apprehension test (figure 11)). Medial joint line tenderness (picture 8) and pain with valgus testing (picture 3) can cause confusion between the diagnoses of medial collateral ligament (MCL) sprain and patellar subluxation or dislocation. The apprehension test should be negative in patients with MCL sprain. (See "Medial (tibial) collateral ligament injury of the knee", section on 'Diagnosis'.)

Muscle strain or tear — Injuries to the muscles (eg, tears and strains) surrounding the knee may present acutely, or as an acute exacerbation of a chronic problem. Acute injuries typically involve sudden, forceful eccentric contraction of the involved muscle. The muscle groups most commonly injured include the hamstring, quadriceps, and gastrocnemius. The symptoms of muscle injury include local pain which can be severe and limit range of motion. Significant swelling, tenderness to palpation, and ecchymosis may be present. The diagnosis of a muscle strain or tear is based upon clinical findings. Diagnostic imaging (eg, ultrasound or magnetic resonance imaging) is only employed if there is diagnostic uncertainty. Clinical features and management of muscle strains and tears, by muscle group are provided separately. (See "Quadriceps muscle and tendon injuries" and "Calf injuries not involving the Achilles tendon" and "Hamstring muscle and tendon injuries".)

Meniscal tear — Meniscal injuries are caused when the patient twists the leg while bearing weight (eg, when landing from a jump). Meniscal injuries are sometimes described as "torn cartilage" or a "locked knee." The mechanisms for meniscal injuries are similar to those of ACL injuries, and these injuries often occur together in children and skeletally immature adolescents [13,14]. Weightbearing is usually limited by pain, and swelling typically develops within 24 hours. Mechanical symptoms may be more common than pain because only the periphery of the menisci contains nerve fibers. Mechanical symptoms include locking, popping, and catching. Other symptoms include swelling, pain with rotation or flexion (particularly at the extremes of those motions), pain along the joint line, weakness or giving way, and a generalized aching. (See "Meniscal injury of the knee", section on 'Mechanism and presentation'.)

Signs of meniscal injuries, which are similar to those in children with chondral fractures or injuries to the articular cartilage [15] include effusion, joint line tenderness (picture 8), positive McMurray or modified McMurray test (picture 9), positive bounce-home test (figure 12), and restricted joint motion. These tests are discussed in detail separately. (See "Physical examination of the knee", section on 'Special tests for specific conditions'.)

A working diagnosis is based upon clinical findings. The positive predictive value of the clinical examination for medial and lateral meniscal injuries in children and adolescents is 15 and 34 percent, respectively, compared with arthroscopic examination; the negative predictive value for each is over 95 percent [16]. MRI is frequently employed to assist in making the diagnosis; however, like the clinical examination, the positive predictive value is low compared with arthroscopy (see "Meniscal injury of the knee", section on 'Diagnosis'). Thus, after clinical examination, if the experienced clinician thinks there is no meniscal tear, they are justified in not getting an MRI; if they think one is present, then an MRI is a reasonable next step, although both clinical examination and MRI have a low positive predictive value compared with arthroscopy [17].

The treatment of meniscal injuries is discussed separately. (See "Meniscal injury of the knee", section on 'Treatment'.)

Other — Less commonly, acute knee pain in children and skeletally immature adolescents arises from tendon injury, pain referred from hip pathology, or as a local manifestation of systemic disease in a patient with incidental knee trauma.

Quadriceps and patellar tendon injury — Quadriceps and patellar tendon injuries occur uncommonly in children and skeletally immature adolescents. Patients with these injuries may have a secondary cause of tendon weakness such as anabolic steroid abuse, renal disease, metabolic bone disease, or medications associated with tendon rupture (eg, quinolone antibiotics). Tendon tears and complete rupture 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. (See "Quadriceps muscle and tendon injuries", section on 'Quadriceps and patellar tendon tears'.)

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. Typically, knee extension is limited with partial tears and absent with complete tears. Patellar fractures frequently accompany tendon tears. (See "Quadriceps muscle and tendon injuries", section on 'Quadriceps and patellar tendon tears'.)

Diagnosis is made based upon clinical findings and may be confirmed with bedside ultrasound. Plain radiographs are indicated to evaluate for an associated patellar fracture. Management of quadriceps and patellar tendon injuries is discussed separately. (See "Quadriceps muscle and tendon injuries", section on 'Quadriceps and patellar tendon tears' and "Quadriceps muscle and tendon injuries", section on 'Quadriceps and patellar tendon tears'.)

Popliteus tendinitis — Patients with popliteus tendinitis have pain that is localized to the posterior lateral knee. The pain is of relatively acute onset; it may occur during prolonged descents during hiking or running, and is exacerbated by excessive forefoot pronation. This is because the popliteus muscle is a secondary restraint to anterior femoral translation in descent, and may be required to be more active as the quadriceps, hamstrings, and iliotibial band (ITB) muscles are exhausted with prolonged exercise. Chronic popliteus tendinitis may be confused with iliotibial band syndrome. (See "Calf injuries not involving the Achilles tendon", section on 'Popliteus tendinopathy'.)

Referred pain — Acute knee pain can be referred pain from primary pathology in the hip, such as septic arthritis, osteomyelitis, slipped capital femoral epiphysis (SCFE), and Legg-Calvé-Perthes disease. Typically, the pain is anterior, dull, nonradiating, and does not localize to bone or soft tissues of the knee. In such patients, the knee examination is usually normal and the hip examination demonstrates a limited range of motion and/or pain. Patients with septic arthritis have significant pain on any movement of the hip. The clinician should urgently involve an orthopedic surgeon for joint drainage in patients with a septic hip. (See "Bacterial arthritis: Treatment and outcome in infants and children" and "Approach to hip pain in childhood", section on 'Examination'.)

Adolescents with SCFE can present with knee or thigh pain. Range of motion of the hips, particularly internal rotation, is often limited. Urgent referral is necessary because a delay in diagnosis can lead to worsening of the condition and an increased risk of complications (eg, osteonecrosis of the femoral head or narrowing of the joint space) which can be crippling. (See "Evaluation and management of slipped capital femoral epiphysis (SCFE)", section on 'Clinical manifestations'.)

Legg-Calvé-Perthes disease or idiopathic avascular necrosis of the femoral head generally presents between 3 and 12 years of age with a peak incidence at 5 to 7 years of age. Patients complain of acute or chronic knee pain with activity. (See "Approach to hip pain in childhood", section on 'Legg-Calvé-Perthes and secondary avascular necrosis'.)

Systemic disease — In some pediatric patients, serious systemic illness may present with a history of incidental trauma. Fever, local findings of inflammation, rash, a history of chronic knee pain, or a past medical history that identifies an underlying bleeding disorder can help identify these patients. Systemic disease that may cause unilateral knee pain and/or swelling includes septic arthritis, juvenile idiopathic arthritis, osteomyelitis, Lyme disease (endemic areas), hemoglobinopathy, bleeding disorder, benign bone tumors, or malignancy (eg, leukemia, osteosarcoma, or Ewing sarcoma) (table 2). (See "Evaluation of the child with joint pain and/or swelling", section on 'Initial evaluation'.)

EVALUATION — The acute evaluation of young child and adolescent athletes with acute knee injury requires identification and rapid management of limb-threatening injuries with gross deformity or neurovascular compromise (algorithm 1).

In patients without limb-threatening injuries, a careful history and physical examination can establish a working diagnosis. In children and skeletally immature adolescents, radiographic evaluation is frequently necessary to identify fractures, hip conditions with referred knee pain, and to fully characterize internal knee abnormalities. (See 'Imaging' below and 'Specific conditions' above.)

The evaluation of chronic knee or joint complaints is discussed separately. (See "Approach to chronic knee pain or injury in children or skeletally immature adolescents" and "Evaluation of the child with joint pain and/or swelling".)

Limb-threatening injury — When assessing an acute knee injury in the child or skeletally immature adolescent, the clinician should identify those injuries or conditions that require immediate treatment by an orthopedic surgeon. Key findings include any one of the following (algorithm 1) [18]:

●Gross deformity

●Neurovascular compromise

●Inability to bear weight

●Large knee effusion

●Penetrating injury into the joint space

●Findings of popliteal artery injury (eg, active hemorrhage, expanding or pulsatile hematoma located in the popliteal fossa, absent distal pulses, or extremity ischemia) (see "Severe lower extremity injury in the adult patient", section on 'Vascular assessment')

Many but not all of these injuries can be identified upon gross inspection and a careful physical examination with close attention to the neurovascular status. Knee (tibiofemoral) dislocations should undergo emergency plain radiography followed by immediate reduction by a knowledgeable clinician. Patients with displaced fractures should have the knee immobilized or splinted in a position of comfort without worsening neurovascular status as soon as possible, and, undergo emergency management based upon the specific condition. (See 'Limb-threatening injuries' above.)

History — The following questions are helpful in the evaluation of a child or skeletally immature adolescent with acute knee pain or injury [19]:

●Is there a single event with a definable mechanism of injury? If so, are there videotapes or eyewitnesses who can describe what happened?

●Where is the pain?

●Are there mechanical symptoms (eg, locking, popping, or catching)?

●Can you bend and straighten the knee all the way?

●If there is swelling, when did it begin after the injury?

●Is there a sense of instability (ie, "giving way") or functional limitation (eg, is the athlete able to bear weight without pain)?

●Is there a history of previous knee injury? If so, how was it evaluated and treated?

●Is there history of any chronic pain or illness prior to the acute injury?

●Was there any fever or limp prior to the injury that suggests an underlying chronic condition not related to knee trauma?

Knowing the mechanism of injury can also help to narrow the differential diagnosis (table 3). However, the precise mechanism of injury can sometimes be difficult to ascertain and many mechanisms can cause more than one injury. Thus, the mechanism of injury should be correlated with the rest of the history and physical findings.

It is also important to consider causes of knee pain that are unrelated to sports activity. In some pediatric patients, serious systemic illness may present with a history of incidental trauma. Past medical history, family history, and review of systems should focus on symptoms or signs of other causes of unilateral knee pain and/or swelling (eg, septic arthritis, juvenile idiopathic arthritis, osteomyelitis, Lyme disease [endemic areas], hemoglobinopathy, bleeding disorder, malignancy [eg, leukemia, osteosarcoma, or Ewing sarcoma], slipped capital femoral epiphysis [SCFE], or Legg-Calve-Perthes disease) (table 2). (See "Evaluation of the child with joint pain and/or swelling", section on 'Initial evaluation'.)

Physical examination — The physical examination of any joint is classically divided into inspection, palpation, range of motion, strength and neurovascular testing. For the lower extremities and only if fracture and/or joint instability are excluded, gait should also be evaluated. Special tests are selected based upon the most likely diagnostic category, which is based in turn upon the history, including the mechanism of any injury and physical findings. Guidance about which examination techniques are most useful for diagnosing specific knee injuries in children and skeletally immature athletes is provided in the text above and a topic devoted to the knee examination. (See 'Specific conditions' above and "Physical examination of the knee".)

Because of the greater likelihood of fractures in children and young adolescents, the clinician should first evaluate for the need for plain radiographs suggested by a gross deformity, neurovascular deficit, large knee effusion, bony tenderness, penetrating injury into the joint, or signs of referred pain from the hip. If indicated, radiographs should be obtained prior to performing provocative maneuvers or having the patient bear weight or walk (algorithm 1). (See 'Anatomic considerations' above and 'Imaging' below.)

●Inspection – The legs should be fully exposed. The overall position of the leg and presence of gross deformities should be noted; comparison with the opposite knee may be helpful [19]. Gross deformity should alert the clinician to a potentially limb-threatening injury. (See 'Limb-threatening injury' above.)

The skin and soft tissues should be inspected for erythema, swelling, abrasions, laceration, puncture wound, bruising, and foreign body. Swelling within 24 hours of an acute knee injury suggests internal derangement [20].

●Neurovascular – The neurovascular status should be evaluated in all patients with acute knee injury and is of utmost importance in patients with gross deformities. Emergency involvement of an orthopedic surgeon with pediatric expertise and, whenever possible, a vascular surgeon is warranted for all patients in whom popliteal artery compromise is suspected.

The neurovascular examination includes:

•Palpation of the dorsalis pedis and posterior tibial pulses and comparison to the unaffected leg to evaluate vascular integrity

•Examination of the popliteal fossa for an expanding hematoma

•Assessment of sensation in the web space between the first and second toes, and ability to actively extend the great toe to evaluate deep peroneal nerve function

•Assessment of sensation of the plantar surface of the foot and ability to actively plantarflex the ankle to evaluate posterior tibial nerve function

•Ability to evert the ankle to evaluate superficial peroneal nerve function

Neurovascular injury occurs most commonly in knee dislocations and displaced fractures. It is uncommon after ligamentous injury, even if two ligaments are injured. However, the varus stress caused by simultaneous injury to the LCL and one of the cruciate ligaments can be sufficient to injure the superficial peroneal nerve. (See 'Limb-threatening injury' above.)

●Palpation – For patients who have no gross deformity and whose neurovascular integrity is intact, the physical examination should proceed by asking the patient to indicate, with one finger, the most painful spot. The distal femur, femoral condyles, proximal tibia, and entire patella should be palpated for possible fracture. Patients who have bony point tenderness or tenderness proximal to the joint lines (suggesting fracture) should have the extremity immobilized and undergo plain radiography. (See 'Imaging' below.)

●Range of motion – Once a fracture has been excluded based upon physical findings and/or plain radiographs, range of motion of the knee should be evaluated by asking the patient to flex and extend the knee. Patients without full active range of motion should undergo passive assessment of flexion (picture 10) and full passive extension). (See "Physical examination of the knee", section on 'Range of motion and muscle flexibility'.)

The bounce home test is another test of knee extension. It is performed with the patient supine. The knee is passively flexed to approximately 15 degrees and then permitted to fall into extension with gravity (figure 12). The test is positive if the knee does not fully extend (known as "true locking"). True locking can be caused by a displaced torn meniscal flap, a loose intraarticular body, articular surface damage, or a torn anterior cruciate ligament (ACL).

●Ligaments – Tenderness and/or laxity suggests a ligamentous injury (sprain), the severity of which is graded by the degree of laxity for the specific ligament. The grades of sprains are easiest to determine in the immediate post-injury period before the onset of swelling and secondary muscle spasm. (See "Physical examination of the knee", section on 'Assessing joint stability'.)

●Meniscus – Meniscal tear is suggested by joint line tenderness, joint effusion, loss of smooth passive motion, inability to fully extend the knee, inability to kneel or squat, palpable catching at the joint line as detected by the McMurray maneuver (picture 9) or pain elicited by provocative testing (eg, Thessaly test). (See "Meniscal injury of the knee", section on 'Provocative testing'.)

●Muscles – The muscles about the knee should be inspected for swelling and ecchymosis and palpated for signs of tenderness. The integrity of the quadriceps mechanism and quadriceps strength are assessed by asking the patient to extend the leg against resistance placed at the lower leg (picture 11). Within a few days of disuse, quadriceps tone becomes notably reduced. Limited muscle contraction may be caused by effusion, pain, or mechanical obstruction; internal derangement should be suspected. (See "Physical examination of the knee", section on 'Quadriceps strength'.)

●Gait – The gait of patients in whom the initial evaluation does not suggest fracture or dislocation should be observed to see if they are able to bear weight. Movement of the knee is painful and guarded in patients with internal derangement (ie, fracture, chondral lesion, injury to the cruciate or collateral ligaments, and/or menisci). Patients with these injuries usually have little spontaneous knee movement and are unable to bear weight, particularly if more than one structure is involved (eg, the medial meniscus and ACL).

Imaging

Plain radiographs — Plain radiographs are indicated for children and skeletally immature adolescents who have one or more of the following findings [19-22]:

●Gross deformity

●Large knee effusion

●Palpable tenderness over the femoral or tibial physis, fibular head, or patella

●Inability to bear weight or to walk four steps

●Concern for laceration or penetrating injury extending into the knee joint

Specific views should be ordered depending upon the site of injury. Standard views for the knee, distal femur, and patella are described in the table (table 4). Prior to radiographs, the patient should undergo careful evaluation of the hip and ankle. Those patients with abnormal findings should undergo hip and/or ankle radiographs. Hip pathology can frequently cause pain that is referred to the knee. (See 'Referred pain' above.)

Patients with complicated fractures of the patella, distal femur, or proximal tibia may require additional imaging (eg, computed tomography [CT] or magnetic resonance imaging [MRI]) to fully characterize the injury [20]. The choice of study varies according to the injury. Consultation with an orthopedic surgeon is advised. (See "Proximal tibial fractures in children", section on 'Radiographic findings' and "Distal femoral fractures in children", section on 'Other imaging'.)

In addition, although derived in adults, the Ottawa knee rules have undergone validation in a multicenter trial of 750 children aged 2 to 16 years who presented to the emergency department with a knee injury and had 100 percent sensitivity (95% CI 95-100 percent) for identifying fractures although 89 percent of patients underwent plain radiography. [23]. In a subsequent meta-analysis that included this study and two other prospective, observational studies (1130 children, most >5 years of age), the pooled sensitivity and specificity were 99 and 46 percent, respectively, with a pooled negative predictive value of 99.8 percent (fracture prevalence 8.7 percent) [24]. Based on these findings, application of the Ottawa knee rules in children older than five years of age could result in an estimated reduction in radiography as high as 40 percent, depending upon local practice. However, large validation and implementation studies of the Ottawa knee rules in children are lacking.

According to the rule, plain radiographs should be obtained in children with the following features after acute knee trauma (see "Approach to the adult with knee pain likely of musculoskeletal origin", section on 'Imaging in the evaluation of acute knee pain'):

●Isolated tenderness of patella (with no other bony tenderness of the knee)

●Tenderness at the head of the fibula

●Inability to flex the knee to 90 degrees

●Inability to bear weight both immediately and in the emergency department for four steps, regardless of limp (ie, unable to transfer weight onto each lower limb two times)

Magnetic resonance imaging — Magnetic resonance imaging (MRI) is the best technique for the diagnosis of soft tissue injuries including, tears of the ligaments, menisci, tendons, and muscles [19,20,25]. It can also identify evidence of patellar dislocation in patients with spontaneous reduction. MRI is not necessary in all children and skeletally immature adolescents with acute internal derangement but should be used if the diagnosis is in question, if they do not improve with conservative treatment, or if the plan is to undergo diagnostic arthroscopy only if the MRI is abnormal [26]. Examples of conditions for which MRI would be indicated include patellar dislocation with post-reduction locking that suggests an intraarticular foreign body or a clinical meniscal injury that does not improve with nonoperative management.

MRI without contrast has a sensitivity approaching 95 percent for surgically confirmed anterior cruciate ligament (ACL) and meniscal injuries in children [22,27]. However, it is no more accurate, and is sometimes less accurate, than the physical examination of an experienced clinician [16,28,29]. For this reason, clinicians who are unskilled in the knee examination should consult with a sports medicine physician or orthopedic surgeon with training in sports medicine before obtaining a MRI.

Imaging of the popliteal artery — In patients with concern for popliteal artery disruption (eg, knee [tibiofemoral] dislocation or displaced distal femoral physeal fractures), options for imaging include Doppler flow ultrasound, computed tomography angiography, arteriography, or magnetic resonance angiography. Selection of the imaging modality should be performed in consultation with an orthopedic or vascular surgeon. (See "Knee (tibiofemoral) dislocation and reduction", section on 'Imaging'.)

Arthroscopy — Based upon observational studies, the most common indications for arthroscopy in children with acute knee injuries include ACL tears, meniscal lesions, osteochondral fractures, and tibial intercondylar eminence fractures [30]. Arthroscopy is the most accurate method of diagnosing the cause of internal derangement in patient with a knee effusion. False-positive results are rare, and with the exception of posterior meniscus injuries, false-negative results are also rare. Arthroscopy is used selectively, as an adjunct to the history, physical examination, and MRI when there is a diagnostic dilemma. The only absolute indication for arthroscopy is mechanical disruption of normal knee function.

APPROACH — The clinician should rapidly identify and manage knee injuries that are limb-threatening as follows (algorithm 1):

●Gross deformity – Patients with a gross deformity may have a tibiofemoral dislocation, displaced fracture, or a patellar dislocation. Patients with neurovascular compromise require emergency plain radiography to distinguish between a displaced fracture or tibiofemoral dislocation, emergency consultation with an orthopedic surgeon with pediatric expertise and vascular surgeon, and emergency imaging of the popliteal artery with the choice of modality determined by the consultants. Tibiofemoral dislocations should undergo emergency reduction by a knowledgeable clinician. (See 'Limb-threatening injuries' above and "Knee (tibiofemoral) dislocation and reduction", section on 'Procedure'.)

Patellar dislocations do not cause neurovascular compromise and can undergo reduction by a knowledgeable clinician prior to radiography. (See "Recognition and initial management of patellar dislocations", section on 'Reduction of lateral dislocations'.)

●Neurovascular compromise – Neurovascular compromise may occur with or without gross deformity and may be caused by fractures, knee (tibiofemoral) dislocation, or multiple ligamentous tears. Patients with neurovascular compromise warrant emergency plain radiographs, special imaging of the popliteal artery (eg, Doppler flow study) and consultation with an orthopedic surgeon with pediatric expertise and vascular surgeon. (See 'Knee dislocation (tibiofemoral) dislocation' above.)

●Penetrating joint wound – Open wounds that extend into the joint based upon direct inspection, radiographic features (eg, air in the joint on plain radiograph), or as determined by the saline load test (arthrocentesis with injection of a large volume of normal saline into the joint space and observation of the saline coming out of the wound site) warrant prompt care by an orthopedic surgeon with pediatric expertise. (See 'Penetrating joint wound' above.)

In patient without limb-threatening injuries, the clinician should obtain radiographs if any one of the following findings is present or alternatively, according to the Ottawa knee rule (see 'Plain radiographs' above):

●Gross deformity

●Large knee effusion

●Palpable tenderness over the femoral or tibial physis, fibular head, or patella

●Inability to bear weight or to walk four steps

●Concern for laceration or penetrating injury extending into the knee joint

Patients should also undergo careful evaluation of range of motion and palpation of the hip and ankle. Those patients with abnormal findings should undergo hip and/or ankle radiographs. Hip pathology can frequently cause pain that is referred to the knee. (See 'Referred pain' above.)

Patients with fractures should receive orthopedic treatment based upon the specific injury and further evaluation to identify associated soft tissue injuries (eg, anterior cruciate ligament [ACL] tear with meniscal injury) and/or an osteochondral fracture. (See 'Fracture' above.)

In patients in whom fractures are not present on plain radiographs but who have a knee effusion, the location of pain, along with key historical features and a careful physical examination can often identify the most likely cause (table 5A-B). (See 'Ligamentous injury' above and 'Meniscal tear' above and 'Quadriceps and patellar tendon injury' above.)

Patients with isolated cutaneous or muscle injury do not usually have a knee effusion. Pain is localized to the wound, cutaneous bruise, or affected muscle. (See 'Cutaneous injury' above and 'Muscle strain or tear' above and 'Popliteus tendinitis' above.)

Systemic disease with unilateral knee pain and/or swelling often has a more indolent and chronic history and is accompanied by findings of inflammation including fever, warmth, and erythema (table 2). (See 'Systemic disease' above.)

SUMMARY AND RECOMMENDATIONS

●The acute evaluation of children and skeletally immature adolescents with acute knee injury requires rapid identification and management of limb-threatening injuries identified by gross deformity, neurovascular compromise, or penetrating injury into the knee joint (algorithm 1). These patients warrant emergency plain radiographs of the knee and emergency consultation with an orthopedic surgeon.

●Knee (tibiofemoral) dislocations should undergo immediate reduction by a knowledgeable clinician. Patients with displaced fractures should have the knee immobilized or splinted in a position of comfort and without worsening neurovascular status pending definitive treatment. Patients with neurovascular compromise warrant specialized imaging as determined by orthopedic and vascular surgery consultants. (See 'Limb-threatening injury' above and 'Limb-threatening injuries' above and 'Approach' above.)

●After evaluation and management of any limb-threatening injury, a careful history and physical examination can provide a working diagnosis. The differential diagnosis can often be narrowed based upon the mechanism of injury (table 3). The clinician should obtain plain radiographs if any one of the following findings is present or alternatively, according to the Ottawa knee rule (see 'History' above and 'Physical examination' above and 'Plain radiographs' above):

•Gross deformity

•Large knee effusion

•Palpable tenderness over the femoral or tibial physis, fibular head, or patella

•Inability to bear weight or to walk four steps

•Concern for laceration or penetrating injury extending into the knee joint

Patients should also undergo careful evaluation of range of motion and palpation of the hip and ankle. Those patients with abnormal findings should undergo hip and/or ankle radiographs in addition to knee radiographs. Hip pathology can frequently cause pain that is referred to the knee. (See 'Referred pain' above.)

●In patients in whom fractures are not present on plain radiographs but who have a knee effusion, the location of pain, along with key historical features and a careful physical examination can often identify the most likely cause (table 5A-B). (See 'Ligamentous injury' above and 'Meniscal tear' above and 'Quadriceps and patellar tendon injury' above.)

●Patients with isolated cutaneous or muscle injury do not usually have a knee effusion. Pain is localized to the wound, cutaneous bruise, or affected muscle. (See 'Cutaneous injury' above and 'Muscle strain or tear' above and 'Popliteus tendinitis' above.)

●Magnetic resonance imaging (MRI) is the best technique for the diagnosis of soft tissue injuries including, tears of the ligaments, menisci, tendons, and muscles. It can also identify evidence of patellar dislocation in patients with spontaneous reduction. MRI is not necessary in all children and skeletally immature adolescents with clinical findings of these injuries but should be used if the diagnosis is in question. Clinicians who are unskilled in the knee examination should consult with a sports medicine physician or orthopedic surgeon with training in sports medicine before obtaining an MRI. (See 'Magnetic resonance imaging' above.)

●Physical findings for the diagnosis of specific acute knee conditions are also provided. (See 'Specific conditions' above.)