INTRODUCTION — The approach to children and skeletally immature adolescents with chronic knee pain will be reviewed here. The approach to acute knee pain in these patients and the evaluation of children with joint pain or swelling are discussed separately. (See "Approach to acute knee pain and injury in children and skeletally immature adolescents" and "Evaluation of the child with joint pain and/or swelling".)
Chronic injury — In children and skeletally immature adolescents, chronic injury can arise from any of the following situations:
●An acute injury that does not heal properly (eg, an anterior cruciate ligament tear that is not fully rehabilitated or in which surgical repair fails)
●Insidious onset of pain without specific injury related to excessive activity that is beyond the body's ability to accommodate (eg, iliotibial band syndrome in a soccer player or runner)
Chronic pain — Pain lasting longer than six weeks is typically characterized as chronic. While the six-week threshold is arbitrary, it can be useful since many self-limited acute injuries (contusions) heal by the end of six weeks with appropriate rest. Among active children and skeletally immature adolescents, chronic pain often has a progressive pattern. As an example, a child with Osgood-Schlatter disease may initially only have pain over the tibial tuberosity at the end of a basketball practice but may progress over weeks to the point where pain develops after five minutes of playing or even at rest.
Chronic pain should also alert the clinician to the possibility of a systemic disease (eg, reactive arthritis, toxic synovitis, osteomyelitis, septic arthritis, arthritis as part of a rheumatologic disease, or malignancy) that is presenting as bone or joint pain (table 1).
HISTORY — In the evaluation of a child or skeletally immature adolescent with knee pain or injury, it is important to characterize the pain, identify other musculoskeletal symptoms, identify the underlying etiology, determine if systemic symptoms are present, and assess for prior knee injury or surgery [1,2].
Pain description — A detailed description of the pain is essential at making the correct diagnosis. The following questions help to characterize the pain:
●How long have you had knee pain? – Chronic pain is defined by a duration of six weeks or longer. The evaluation of acute complaints is discussed separately. (See 'Definitions' above and "Approach to acute knee pain and injury in children and skeletally immature adolescents".)
●Was there a clear onset of pain? – A clear onset of pain suggests an acute injury that is persisting while progressively worsening pain with insidious onset is more typical of an overuse injury or joint pain as a manifestation of systemic illness.
However, in the history of the progressively worsening pain it is useful to ask if there was a specific change in training, such as the intensity, duration or frequency of training, or equipment, such as a new pair of shoe or running on a new surface or the addition of running stairs. This can be considered a clear onset of symptoms. (See "Evaluation of the child with joint pain and/or swelling", section on 'Differential diagnosis'.)
●Where is the pain located? – The location of the pain often correlates with the specific knee structures that are damaged and helps to narrow the differential diagnosis. Chronic knee injuries often involve only one knee while systemic disease frequently presents with bilateral knee and pain in other joints. (See 'Diagnostic approach' below and "Evaluation of the child with joint pain and/or swelling", section on 'History'.)
●How severe is the pain? – Patients should be asked to rate their pain using any one of the age-appropriate validated pain scores. Pain out of proportion to what would be expected for the injury may indicate significant systemic illness or a chronic pain syndrome. (See "Pain in children: Approach to pain assessment and overview of management principles", section on 'Severity assessment'.)
●Is the pain associated with swelling in the knee? – Constant, intermittent, or activity-related swelling may be helpful in assessing for structural versus systemic etiologies. Intermittent or activity-related swelling suggests structural conditions (eg, osteochondritis dissecans), while persistent swelling is more characteristic of underlying systemic diseases (eg, juvenile idiopathic arthritis).
●Do you have any hip pain or mechanical sensations? – An abnormal gait to avoid hip internal rotation can be the source of knee pain.
●Do you have back pain? Is there any associated numbness, tingling, or weakness in your leg? – The dermatomes of L3-S2 include the knee (L3-medial, L4- anterior, L5-lateral, S1-2- posterior). Rarely, in children and adolescents, knee pain may arise from lesions affecting these nerve roots.
●Do you have any other lower extremity injuries with pain on the same or opposite side? – Knee pain may arise from alterations in gait due to injuries in other joints.
●Does the pain only occur with specific activities? – Specific activities that trigger pain can be helpful in diagnosing knee pathology. As an example, pain with prolonged sitting or when climbing or descending stairs is a classic part of the history of patellofemoral pain.
●How much does this pain limit activities? – This can sometimes be a more objective measure of the severity of pain in pediatric patients.
●Does the pain occur at night? – Unilateral pain that awakens the patient from sleep can suggest a significant pathologic process, such as bone tumors or leukemia; conditions like tendinitis or patellofemoral pain rarely cause night pain. (See "Evaluation of the child with joint pain and/or swelling", section on 'Severity'.)
By contrast, bilateral nocturnal pain that is paroxysmal, localized deep in the calf or thigh, described as crampy, and resolves by the morning in school-age and younger children is consistent with growing pains. (See "Growing pains", section on 'Clinical features'.)
●What interventions have you tried for pain? Have they helped? – Pain that is improved with icing and rest, for example, is not likely to be due to a systemic process such as arthritis, infection or malignancy. Furthermore, response or lack of improvement to specific measures, such as a brace or rehabilitation exercises, can provide clues to the diagnosis.
●What makes the pain worse? – Specific movements or activities that exacerbate the pain can also help narrow the possible diagnoses and suggest activities to be avoided, such as what is meant by relative rest in prescribing a treatment plan.
Other musculoskeletal symptoms — In patients who recall a specific event that was followed by pain, the clinician should determine the following:
●Mechanism of injury – For example, was it triggered by a specific event, or did it arise after repetitive activity? If a specific event was involved, are there videotapes of it or eyewitnesses who can describe what happened? Alternatively, the clinician can ask the patient to act out the injury to the extent that they can, in the office. For example, "Show me exactly what position you were in when it happened." If repetitive activity was involved, what was the activity? What are the training demands of the activity? Was the patient using the appropriate equipment and sports technique?
●Mechanical symptoms (eg, locking, popping, or catching) – Locking of the knee suggests a mechanical block, as might occur with osteochondritis dissecans, a meniscal tear, or loose piece of cartilage. Note that it is important to differentiate a true mechanical block from the feeling that the knee is stuck or might pop if moved. Patients with a mechanical block often say they can unlock the knee by massaging or moving it in a certain manner.
If the patient describes hearing an audible pop at the initial injury, anterior cruciate ligament (ACL) or other ligament tear is a concern. Teenagers and young adults who sustain an acute meniscal tear may also experience an audible pop at the time of injury.
●Instability (eg, "giving way") or functional limitation – It is important to distinguish true mechanical instability from pain-mediated instability. True instability occurs when the knee subluxes or "gives way" during a routine activity (eg, climbing stairs, walking) without pain preceding the episode. Such instability occurs with ligament tears and patellar instability and is more likely to be accompanied by immediate pain, disability, falling to the ground, and swelling. Pain-mediated instability occurs when knee or other lower extremity pain inhibits motor nerves controlling the quadriceps muscles causing the knee to buckle. Typically, these patients do not fall to the ground, do not have subsequent swelling, and can ambulate afterward. This can occur with any number of painful conditions.
Systemic symptoms — Patients with musculoskeletal pain should be asked whether constitutional symptoms, such as fevers, chills, weight loss, poor growth, fatigue, or rash, accompany the pain. The presence of such symptoms suggests a systemic illness, and further investigation for infectious, rheumatologic, or neoplastic causes may be necessary. Knee pain that awakens the patient at night raises the concern for an infiltrative process (eg, a bone tumor or leukemia).
The clinician should also determine whether there is a history of tick bite or annular rash in regions endemic for Lyme disease and ask about morning stiffness as a possible manifestation of pauciarticular juvenile idiopathic arthritis. (See "Evaluation of the child with joint pain and/or swelling", section on 'History'.)
Prior knee injury or surgery — The most predictive risk factor for future knee injury is a history of prior injury. Patients should be queried regarding the timeline and treatment of any past lower extremity injuries and whether they were adequately rehabilitated. For example, ask the patient if they returned to 100 percent of function. Often, "new" injuries turn out to be complications of old injuries or incompletely rehabilitated injuries (eg, patellofemoral pain from changes in running gait caused by plantar fasciitis).
Surgery is another important risk factor for evaluating knee pain. Surgical repairs can fail, leading to symptoms from recurrent injury. In addition, children and adolescents who undergo surgery that successfully restores function inevitably experience some degree of deconditioning that predisposes to new overuse injuries. This risk is greatest in those patients who undergo suboptimal rehabilitation or attempt to return to activities too quickly. In our opinion, these patients should be reevaluated first by the surgeon who did the procedure.
Activity level — In order to assess the patient's stress to their knee, a careful history of their sports and physical activity is extremely important as follows:
●In which sports or activities are they participating?
●What position do they play?
●How frequently are they participating in their sport (in school and outside of school)?
●How many practices per week are they participating in?
●How many games do they have per week?
●Are they playing tournaments on the weekend?
●Is there a change in the level of activity associated with the onset of the knee pain?
PHYSICAL EXAMINATION — The physical examination should determine the presence of any findings of systemic disease as follows (see "Evaluation of the child with joint pain and/or swelling", section on 'Physical examination'):
●Weight loss or change in the growth curve
●Erythema and/or warmth over the knee
●Tenderness or swelling in other joints or over other regions of the body
Further evaluation of pediatric patients with joint pain and swelling and findings of systemic disease are discussed separately. (See "Evaluation of the child with joint pain and/or swelling", section on 'Diagnostic studies'.)
In addition, all children and skeletally immature adolescents with chronic knee pain warrant evaluation of the hip for findings of slipped capital femoral epiphysis (SCFE) or avascular necrosis (Legg-Calvé-Perthes disease), such as pain and limited range of motion at the hip. (See "Evaluation and management of slipped capital femoral epiphysis (SCFE)", section on 'Clinical manifestations' and "Approach to hip pain in childhood", section on 'Legg-Calvé-Perthes and secondary avascular necrosis'.)
In pediatric patients without signs of systemic disease or hip pathology, a careful knee examination guided by history with attention to lower extremity malalignment, the site of greatest tenderness, patellar tracking, evidence of muscle inflexibility, inadequate strength, poor proprioception, and close evaluation of gait can frequently identify the underlying cause. 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 the location of pain. (See "Physical examination of the knee".)
The physical examination techniques used to diagnose ligamentous and meniscal injuries in patients with chronic knee pain are the same as those for acute injuries (see "Physical examination of the knee", section on 'Assessing joint stability' and "Physical examination of the knee", section on 'Tests for meniscal tear'):
●McMurray, modified McMurray, and bounce home test to evaluate the menisci (picture 1)
●Valgus stress test to evaluate the medial collateral ligament (MCL) (picture 2)
●Varus stress test to evaluate the lateral collateral ligament (LCL) (picture 2)
●Posterior drawer and posterior sag test to evaluate the posterior cruciate ligament (PCL) (figure 2)
Guidance about which examination techniques are most useful for diagnosing specific chronic conditions is provided in the text below and a topic devoted to the knee examination. (See 'Diagnostic approach' below and "Physical examination of the knee".)
Pain from overuse or trauma — For the purposes of this topic, chronic knee pain is pain occurring during or after specific activities that has persisted for approximately six weeks or longer. In many pediatric patients, the diagnosis of chronic knee pain from overuse or trauma can be determined by a skillful history and physical examination. (See 'History' above and "Physical examination of the knee".)
Plain radiographs are recommended when there are mechanical symptoms of locking or catching, when an effusion is present, when the examiner is unable to reproduce the patient's chief knee complaints, and in patients who meet any one of the Ottawa knee rules criteria. (See 'Diagnostic imaging' below.)
Chronic knee pain associated with overuse or trauma is typically progressive, becoming more painful with increasingly less intense activity over time. In patients whose history fits this description, examination of the following structures is essential (see "Physical examination of the knee"):
●Patella and patellar ligament (tendon) and quadriceps tendon (picture 5)
●Inferior pole of the patella and tibial tubercle (picture 5)
●Iliotibial band (picture 6)
●Lateral and medial meniscus
●Knee joint (figure 3)
●Pes anserine tendon and bursa (picture 7)
The location of pain and tenderness provides a useful means of narrowing the possible causes and determining which provocative diagnostic maneuvers should be performed. The differential diagnosis for chronic knee pain in children and skeletally immature adolescents by location of pain is provided in the table (table 2).
In addition, assessment of the tightness of the hamstring, quadriceps, gastrocnemius, soleus, and hip flexor muscles and lower extremity alignment can be helpful as follows:
●Muscle inflexibility – Tight musculature is not a primary diagnosis and alone does not explain a patient's knee pain. However, restricted hamstring or iliopsoas or gastrocnemius-soleus flexibility is a common secondary finding in patients with patellofemoral pain and pes anserine pain, while quadriceps or hip flexor tightness serves as secondary findings in patients suffering from patellofemoral pain, patellar tendinitis, traction apophysitis (Sinding-Larsen-Johansson disease or Osgood Schlatter syndrome), and other types of chronic knee pain. Thus, the secondary finding of decreased muscle flexibility can support the primary diagnosis and identify contributing kinetic chain abnormalities that will need to be rehabilitated.
●Lower extremity malalignment – The gait and kinetic chain of the lower extremity should be observed. It is important to note variations in alignment, such as genu valgum (knock knees), genu varum (bow legs), pes cavus (high-arched feet), pes planus or pronation (flat feet), and hallux valgus (lateral deviation of the great toe). To the extent that any of these kinetic chain variations interfere with load distribution throughout the lower extremity, they can contribute to overuse injuries of the lower extremities and pelvis. These injuries will recur unless the kinetic chain abnormalities are corrected. (See "Approach to the child with knock-knees", section on 'Management' and "Approach to the child with bow-legs", section on 'Management'.)
The clinician should also observe the athlete standing on one foot at a time, and then as the patient slowly flexes the knee of the supporting leg. Weakness in the external rotators of the hip (eg, the piriformis) manifests as excessive internal rotation of the femur, a "corkscrew" configuration (ie, the knee of the involved leg moves excessively inward in a valgus motion), and instability or unsteadiness during a single-leg squat. (See "Physical examination of the knee", section on 'Functional strength tests'.)
Weakness of the hip abductors can also manifest as a Trendelenburg motion, in which the patient flexes the lumbar spine (ie, leans over the planted foot), often describing it as "losing their balance."
A patient who is quadriceps dominant, compared with the hamstrings and gluteus muscles, will bend forward when doing the single-leg squat. This relative imbalance of quadriceps strength to hamstring and gluteus strength affects the movement of the patellofemoral joint and the weight-bearing capability of the lower leg; it has implications for the long-term rehabilitation of all patients with chronic knee pain.
Pain with systemic symptoms — Chronic or acute knee pain in an child or adolescent without inciting trauma or a history of overuse is a "red flag" that a more extensive evaluation is required, particularly if the pain is associated with constitutional symptoms, such as fever, night sweats, chills, malaise, weight loss, or fatigue or if the pain is severe enough to awaken the patient from sleep. In patients with knee pain unrelated to trauma or overuse but associated with systemic symptoms, a thorough physical examination should be performed, in addition to careful assessment of the knee. Depending upon the history and examination findings, additional testing including synovial fluid analysis, diagnostic imaging, and appropriate laboratory studies may be necessary. (See "Evaluation of the child with joint pain and/or swelling", section on 'Diagnostic studies' and 'Diagnostic imaging' below.)
The evaluation of chronic joint pain or swelling not caused by overuse or trauma is discussed separately. Important diagnoses that may present primarily with unilateral knee pain (eg, referred pain from hip pathology and tumors both malignant and benign) are discussed below. (See "Evaluation of the child with joint pain and/or swelling" and 'Referred hip pain' below and 'Tumors (malignant and benign)' below.)
Diagnostic imaging — Plain radiographs and magnetic resonance imaging (MRI) are the studies performed most often in the evaluation of chronic knee pain in children and adolescents when the diagnosis cannot be made based on the history and physical examination alone.
Suggested indications for each imaging modality include the following:
●Plain radiographs – Plain radiographs are recommended in patients with mechanical symptoms (eg, locking or catching), an effusion, findings of systemic disease (eg, fever or pain awakening from sleep), inability of the examiner to reproduce the patient's knee pain complaint, and any one of the following Ottawa knee rules criteria (see "Approach to acute knee pain and injury in children and skeletally immature adolescents", section on 'Plain radiographs'):
•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)
Plain radiographs are useful in evaluating for degenerative disease, loose bodies, osteochondritis dissecans, infection, bone tumors, and destructive lesions.
Special views may be necessary, depending upon the diagnostic consideration:
•The lesion of osteochondritis dissecans (on the lateral surface of the medial femoral condyle tunnel) is best demonstrated by the tunnel view. (See "Osteochondritis dissecans (OCD): Clinical manifestations, evaluation, and diagnosis", section on 'Imaging'.)
•The position of the patella is best evaluated with the sunrise view. (See "Patella fractures", section on 'Diagnostic imaging'.)
Plain radiographs of other regions (eg, hip, lumbar spine) should be obtained when clinical findings suggest referred hip or back pain or when additional joints may be affected by systemic disease.
●MRI – MRI is better able to demonstrate ligamentous and meniscal lesions [3,4]. However, its use should be limited to patients in whom the diagnosis is in question. For example, if a teenage swimmer complains of medial knee pain that, on exam, is most consistent with pes anserine tendinitis or patellofemoral pain and responds to appropriate rehabilitation, an MRI is not necessary.
However, if the patient is adherent with rehabilitation that addresses the proper etiologies but is not improving, MRI may be indicated to assess for possible medial meniscus injury or chronic medial collateral ligament (MCL) insufficiency if the plan is to undergo diagnostic arthroscopy only if the MRI is abnormal. This approach recognizes that the positive predictive value for MRI-diagnosed meniscal injuries is less than 50 percent compared with arthroscopy, whereas the negative predictive value of MRI is greater than 95 percent but the same as clinical examination [5-7].
MRI is approximately 90 percent accurate in identifying surgically confirmed anterior cruciate ligament (ACL) and meniscal injuries [3,4,8]. However, it is no more accurate than the physical examination by an experienced clinician [8-10]. For this reason, providers who are unskilled in the knee examination should refer patients with knee complaints to a sports medicine clinician or orthopedic surgeon with training in sports medicine before ordering an MRI.
CONDITIONS BY LOCATION OF PAIN — Causes and distinguishing features for chronic knee pain in children and skeletally immature adolescents are provided in the table (table 2).
Anterior pain — The patellofemoral pain is the most common cause of chronic anterior knee pain among adolescents evaluated by sports medicine specialists . Other common conditions in children and skeletally immature adolescents include Sinding-Larsen-Johansson (SLJ) syndrome, patellar tendinitis, Osgood-Schlatter disease, plica syndrome, and patellar subluxation (table 3). (See "Patellofemoral pain", section on 'Epidemiology' and "Recognition and initial management of patellar dislocations", section on 'Epidemiology' and "Osgood-Schlatter disease (tibial tuberosity avulsion)", section on 'Epidemiology'.)
Undiagnosed and unrehabilitated anterior cruciate ligament tears and lateral discoid meniscus tears are important traumatic causes of chronic knee pain. (See "Anterior cruciate ligament injury", section on 'Mechanism and presentation' and "Meniscal injury of the knee", section on 'Mechanism and presentation'.)
Fat pad impingement, osteochondritis dissecans, referred pain from hip and back pathology, bipartite patella, patella stress fractures, benign and malignant tumors, and prepatellar bursitis are less common causes of chronic anterior knee pain.
When possible, localization of the pain to specific structures supports the clinical diagnosis.
Poorly localized pain
Patellofemoral pain — Patellofemoral pain (PFP) is the most common condition causing chronic knee pain among patients referred to sports medicine specialists. Patients with PFP often complain of pain when ascending or descending stairs, running, or squatting, and pain and stiffness when rising from the seated position (the "theater" or "movie-goer" sign). The onset of PFP symptoms often follows a change in training, such as increased running mileage or pace, jumping activities, adding steps to the workout, squats, longer workouts, or new training techniques. (See "Patellofemoral pain", section on 'History'.)
Pain may occur in one or both knees. If an athlete is participating in a sport that has a side preference (eg, basketball players often jump off one leg when shooting a layup or fencers will have more problems on the leg that they lunge onto), it would be logical to have unilateral pain. If they are in sports such as running or cycling, that stress the knee symmetrically, then unilateral symptoms should prompt a more detailed exam of the entire kinetic chain to identify any contributing asymmetries.
Pain is often poorly localized "under" or "around" the patella, and is usually described as "achy" but may be "sharp." Some patients may describe the affected knee as "giving way" or "buckling." In PFP, this perceived instability may be due to pain inhibiting proper contraction of the quadriceps, but it must be distinguished from instability arising from a patellar dislocation or subluxation, or from ligamentous injury of the knee. Although some patients may describe a "catching" sensation under the patella, true locking of the knee or effusion are signs of intraarticular pathology NOT explained by the diagnosis of PFP. Such findings require further evaluation. (See "Patellofemoral pain", section on 'History' and "Approach to acute knee pain and injury in children and skeletally immature adolescents".)
On physical examination, PFP is suggested by the following physical findings (see "Patellofemoral pain", section on 'Clinical presentation and examination'):
●Observation – Vastus medialis atrophy, angular and rotational deformities of the lower extremity
●Palpation – Quadriceps or patellar tendon tenderness; tenderness in the peripatellar areas, especially on the cartilaginous surfaces (patellar facets), especially in the lateral superior region, in our experience; and rarely, an effusion
●Strength – Limited quadriceps strength, hip abductor weakness (may cause increased quadriceps strength), and external rotator weakness
●Range of motion of the knee (crepitus with range of motion is a nonspecific finding)
●Quadriceps, iliopsoas, gastrocnemius-soleus, and hamstring tightness
●Excessive foot pronation
In addition, special testing of patellofemoral function within the context of the history and physical examination can help establish the diagnosis. (See "Patellofemoral pain", section on 'Special tests'.)
PFP is a clinical diagnosis with no pathognomonic sign or symptom. In the child or skeletally immature adolescent it must be distinguished from other causes of anterior knee pain (table 3). (See "Patellofemoral pain", section on 'Diagnosis and differential diagnosis'.)
The management of PFP is discussed in detail separately. (See "Patellofemoral pain", section on 'Initial treatment' and "Patellofemoral pain", section on 'Diagnosis and differential diagnosis'.)
Patellar subluxation — Patellar subluxation refers to excessive lateral movement of the patella and may occur as a result of trauma or in patients with laxity. These patients often complain of anterior and/or medial knee pain; popping or clicking with movement; and occasionally knee swelling, stiffness, or catching. Physical examination findings include a positive patellar apprehension test (apprehension and quadriceps contraction when the patella is pushed laterally by the examiner). The patella may also be high-riding and demonstrate abnormal tracking. In addition, patients may have tenderness of the underside of the patella (patellar facets) and tenderness over the medial femoral condyle. (See "Recognition and initial management of patellar dislocations", section on 'Patellar subluxation'.)
Patients with clinical findings suggesting patellar subluxation warrant plain radiographs including a sunrise view to evaluate for avulsion fractures of the patella or femoral condyle and patellar/femoral trochlear dysplasia. Treatment of patellar subluxation is provided separately. (See "Recognition and initial management of patellar dislocations", section on 'Patellar subluxation'.)
Osteochondritis dissecans — Osteochondritis dissecans (OCD) is defined as osteonecrosis of subchondral bone. Specifically, OCD is a localized lesion in which a segment of subchondral bone and articular cartilage separates from the underlying bone, leaving either a stable or unstable fragment. (See "Osteochondritis dissecans (OCD): Clinical manifestations, evaluation, and diagnosis", section on 'Definition'.)
OCD of the knee typically presents with pain that may begin with a specific injury or can develop over several months in highly active patients. The pain is worsened by exercise. Early or small OCD lesions found in the knee typically will present with nonspecific, poorly localized knee pain with activity. As the process progresses, the patient may report gradual onset of stiffness, and intermittent swelling during or after activity. When advanced or larger lesions are present, the patient may experience catching or locking, especially if a loose foreign body is present. Loss of range of motion, however, is uncommon. (See "Osteochondritis dissecans (OCD): Clinical manifestations, evaluation, and diagnosis", section on 'Clinical presentation'.)
The patient often has tenderness over the medial femoral condyle in the flexed knee. Wilson sign (pain with extension of the knee with the tibia medially rotated which resolves when the tibia is rotated laterally) is helpful if positive although it is negative in many patients with OCD.
Patients with suspected OCD should initially undergo plain radiographs of the affected joint to make the diagnosis. Most OCD lesions are found on the medial femoral condyle and consist of a subchondral bony fragment surrounded by a crescent-shaped radiolucency (image 1). Tunnel views of the knee often provide the best visualization of the lesions in this location (image 2). (See "Osteochondritis dissecans (OCD): Clinical manifestations, evaluation, and diagnosis", section on 'Imaging'.)
The management of OCD is discussed separately. (See "Management of osteochondritis dissecans (OCD)".)
Anterior cruciate ligament injury — The signs of chronic anterior cruciate ligament (ACL) insufficiency include poorly localized pain, shifting, giving way, swelling, and anterior pain and do not differ from acute ACL injury. Up to 90 percent of patients with chronic ACL insufficiency will develop meniscal injuries. The physical examination techniques used to diagnose chronic ACL injuries are the same as those for acute injuries (ligamentous laxity on testing with anterior drawer (picture 3), Lachman (picture 4), and pivot shift test (figure 1)). (See "Anterior cruciate ligament injury", section on 'Physical examination'.)
The management of ACL injuries is discussed separately. (See "Anterior cruciate ligament injury", section on 'Treatment'.)
Referred hip pain — Chronic anterior knee pain can indicate referred pain from primary pathology in the hip, such as a slipped capital femoral epiphysis or Legg-Calvé-Perthes disease (avascular necrosis of the femoral head).
Adolescents with slipped capital femoral epiphysis (SCFE) can present with knee or thigh pain. Examination of the knee is normal, but range of motion of the hips, particularly internal rotation, is often limited. Urgent referral is necessary since a delay in diagnosis can be catastrophic. (See "Evaluation and management of slipped capital femoral epiphysis (SCFE)", section on 'Clinical manifestations'.)
Legg-Calvé-Perthes disease is the name for idiopathic avascular necrosis of the secondary ossification center of the femoral head, which generally presents between 3 and 12 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'.)
Referred back pain — Anterior knee pain caused by L2/L3/L4 radiculopathy is rare in children and adolescents. These patients also complain of back pain. Pain radiates to the anterior aspect of the leg down into the knee and occasionally down the medial aspect of the lower leg as far as the arch of the foot. On examination, there may be weakness of hip flexion, knee extension, and hip adduction. Higher lesions may result in greater weakness of the hip flexors. Sensation may be reduced over the anterior thigh down to the medial aspect of the lower leg. A reduced knee reflex may also be present. (See "Acute lumbosacral radiculopathy: Etiology, clinical features, and diagnosis", section on 'L2/L3/L4 radiculopathy'.)
Because radiculopathy is rare in children and adolescents, plain radiographs and additional imaging, typically magnetic resonance imaging (MRI) are indicated to identify the cause. Depending upon the findings, consultation with a pediatric neurologist or neurosurgeon is warranted.
Urgent neuroimaging and consultation with a pediatric neurosurgeon should be performed in patients with any one of the following findings:
●Acute radiculopathy with progressive neurologic deficits
●Radiculopathy with urinary retention, saddle anesthesia, or bilateral neurologic symptoms or signs
●Suspected epidural abscess
Patellar stress fracture — Patella stress fractures are rare in children and skeletally immature adolescents but may present with an insidious onset of knee pain in patients who regularly engage in strenuous activity. Patients will have tenderness over the patella. Plain radiographs are normal within two to three weeks of the onset of pain and may not show abnormalities for months. MRI provides the most sensitive and specific means to establish the diagnosis. Patella stress fractures are at a high risk for nonunion and warrant prompt referral to a sports medicine clinician or pediatric orthopedic surgeon for management. (See "Overview of stress fractures", section on 'Diagnosis' and "Overview of stress fractures", section on 'High-risk sites'.)
Tumors (malignant and benign) — Chronic anterior knee pain may rarely arise from tumors of the bone or bone marrow (eg, primary malignant, metastatic, or benign bone tumors and leukemias). Osteosarcomas, Ewing sarcoma, and many benign bone tumors have a predilection for the distal femur and proximal tibia. (See "Overview of common presenting signs and symptoms of childhood cancer", section on 'Bone and joint pain' and "Osteosarcoma: Epidemiology, pathology, clinical presentation, and diagnosis", section on 'Clinical presentation' and "Clinical presentation, staging, and prognostic factors of Ewing sarcoma", section on 'Clinical presentation'.)
Trauma, often minor, may be the initiating event that calls attention to a benign or malignant bone tumor. However, benign bone tumors are most often asymptomatic and discovered incidentally on physical examination or radiographs when being evaluated for acute trauma. By contrast, the pain associated with malignant tumors, which may be mild at first, can be aggravated by exercise, and is often worse at night. A distinct soft tissue mass can sometimes be appreciated. When present, it is usually firmly attached to the bone and moderately to markedly tender to palpation. Fever may be present at diagnosis in patients with Ewing sarcoma or leukemia. (See "Nonmalignant bone lesions in children and adolescents" and "Osteosarcoma: Epidemiology, pathology, clinical presentation, and diagnosis" and "Clinical presentation, staging, and prognostic factors of Ewing sarcoma".)
Radiographs should be obtained in a timely manner for any child who complains of persistent bone or joint pain, especially if the pain is abrupt in onset, nocturnal, or associated with swelling; a palpable mass; or limited range of motion. Laboratory evaluation including a complete blood count with differential erythrocyte sedimentation rate (ESR) or C-reactive protein (CRP), alkaline phosphatase, and lactate dehydrogenase (LDH) also should be obtained. Further evaluation of children with suspected cancer or primary or metastatic malignant bone tumor is discussed in more detail separately. (See "Bone tumors: Diagnosis and biopsy techniques" and "Overview of common presenting signs and symptoms of childhood cancer", section on 'Bone and joint pain'.)
The clinical features, common locations, and plain radiographic features of benign bone tumors are summarized in the table and discussed separately (table 4). (See "Nonmalignant bone lesions in children and adolescents".)
Traction apophysitis — In children and skeletally immature adults, apophysitis can result from chronic microtrauma at the insertion of the patellar tendon at the tibial tubercle (Osgood-Schlatter disease) and the inferior pole of the patella (Sinding-Larsen-Johansson disease).
Osgood-Schlatter disease (tibial tubercle apophysitis) — Osgood-Schlatter disease is an overuse injury caused by repetitive strain and chronic traction on the secondary ossification center (apophysis) of the tibial tubercle. It occurs in active adolescents who recently have undergone a rapid growth spurt. The anterior knee pain increases gradually over time, and may be exacerbated by direct trauma, running, jumping, or kneeling. The characteristic physical finding is exquisite tenderness over the tibial tubercle, focal swelling and warmth directly over the apophysis, and an otherwise completely normal knee examination. (See "Osgood-Schlatter disease (tibial tuberosity avulsion)", section on 'Clinical presentation'.)
The diagnosis of Osgood-Schlatter disease is made by clinical examination. Radiographs are not necessary unless the patient has atypical complaints (pain at night, pain that is unrelated to activity, acute onset of pain, associated systemic complaints), pain that is not directly over the tibial tubercle, or clinical concern for tibial tubercle avulsion. Patients with avulsion will not be able to take four steps and will have marked pain with quadriceps contraction. (See "Osgood-Schlatter disease (tibial tuberosity avulsion)", section on 'Diagnostic evaluation'.)
The management of tibial tuberosity apophysitis (Osgood-Schlatter disease) is discussed separately. (See "Osgood-Schlatter disease (tibial tuberosity avulsion)", section on 'Management'.)
Sinding-Larsen-Johansson disease (patellar apophysitis) — Sinding-Larsen-Johansson (SLJ) disease results from excessive activities that involve jumping with repetitive traction exerted by the patellar tendon on the patella and avulsion of the secondary ossification center (apophysis) of the inferior pole of the patella . SLJ disease is sometimes incorrectly called "jumper's knee", a term that is used in adults to describe patellar and quadriceps tendinitis. SLJ disease typically affects children between 10 and 13 years of age. Physical examination demonstrates pain and swelling at the lower pole of the patella. Patellar tendon thickening and infrapatellar bursitis may also be present . Otherwise, the patient should have no knee effusion or ligamentous laxity.
Clinical findings establish the diagnosis of SLJ disease. Imaging is usually not necessary unless the patient has atypical complaints (pain at night, pain that is unrelated to activity, acute onset of pain, associated systemic complaints), pain that is not over the inferior pole of the patella, or clinical concern for a patellar sleeve fracture. Patients with sleeve fractures will not be able to take four steps and will have significant pain with quadriceps contraction.
If obtained, plain radiographs findings of SLJ disease consist of fragmentation and irregular calcification if the ossification centers . However, this finding is also seen in asymptomatic children and adolescents. Bedside ultrasound by an experienced provider can also demonstrate fragmentation of the lower pole of the patella, patellar tendon thickening at this insertion site, and infrapatellar bursitis .
SLJ disease spontaneously resolves, typically in 12 to 18 months which coincides with the typical duration of peak growth in adolescents. However, it should be treated as any other overuse injury of the knee extensor mechanism, including rest with activity as tolerated, rehabilitation, application of ice, and a short course of nonsteroidal antiinflammatory drugs (eg, ibuprofen) for patients with acute pain and swelling. Rarely, pain may necessitate knee immobilization. Once pain and swelling is controlled, reduction of activity and a patellar sleeve may permit a limited return to sports .
Patellar and quadriceps tendinitis — The patellar and quadriceps tendons are the major extensor tendons of the knee. Tendinitis of these extensor tendons results from overuse and is sometimes called "jumper's knee" [14,15]. Patients, particularly those involved in running and jumping sports, complain of chronic anterior knee pain that may be worse after going up or down stairs or prolonged sitting. Among children and skeletally immature adolescents, patellar tendinitis is more commonly seen than quadriceps tendinitis and may be seen in combination with Sinding-Larsen-Johansson disease (patellar apophysitis). (See "Patellar tendinopathy" and 'Sinding-Larsen-Johansson disease (patellar apophysitis)' above.)
The location of tenderness distinguishes between these disorders: the patellar tendon in patients with patellar tendinitis and the superior pole of the patella in those with quadriceps tendinitis. The diagnosis is made clinically. Treatment of patellar and quadriceps tendinitis is discussed separately. (See "Patellar tendinopathy" and "Quadriceps muscle and tendon injuries".)
Fat pad impingement (Hoffa disease) — In the knee, the infrapatellar fat pad is deep to the patellar tendon and extends from the inferior pole of the patella to the upper tibia (figure 4). Impingement of the fat pad causes vague achy pain deep to the patella that can be abrupt and sharp at a specific angle of flexion or extension . Primary fat pad impingement is characterized by pain at terminal extension of the knee and is seen most often in dancers, gymnasts, or swimmers whose activities require kicking or maximum knee extension . Fat pad impingement may also complicate patellar tendinitis, patellar sleeve fractures, or surgery to the cruciate ligaments or meniscus . Rarely, pain may arise from primary conditions of the fat pad including direct trauma and tumors (eg, pigmented villonodular synovitis, hemangiomas, and sarcomas) .
On physical examination, the patient has diffuse tenderness over the patellar tendon and infrapatellar fat pad and may have pain when performing knee extension against resistance . Pain symptoms should be reproduced by the Bounce home test (figure 5).
Infiltration of the fat pad with local anesthetic relieves the pain and can be used to differentiate fat pad impingement from other causes of anterior knee pain.
Management depends upon the cause of impingement. Primary fat pad impingement frequently responds well to physical therapy and a short course of nonsteroidal antiinflammatory drugs (eg, ibuprofen) [2,13,16]. Treatment of the underlying cause typically resolves impingement due to patellar tendinitis, sleeve fractures or other etiologies (eg, fat pad tumors).
If there is no anatomic lesion that is filling up the space making impingement easier, classic hyperextension injuries can result in the fat pad being pinched as well as potentially stretching the posterior capsule. In our experience, eccentric hamstring strength training will help these patients from repetitively impinging. (See "Hamstring muscle and tendon injuries", section on 'Follow-up care and rehabilitation'.)
Bipartite and tripartite patella — Bipartite and tripartite patella are rare causes of chronic knee pain in young adolescents . These abnormalities occur at the lateral or supero-lateral portion of the patella. Symptoms can mimic iliotibial band (ITB) syndrome (fibers from the ITB insert in this region) and patellar instability which also causes lateral peripatellar pain. Affected patients may complain of pain at the separated fragments with strenuous activity. Examination demonstrates tenderness over the lateral or supero-lateral portion of the patella. Bony prominence at the site of tenderness can also occur. Radiographs identify the developmental anomaly but must be correlated with clinical findings of tenderness to make the diagnosis. Patients with symptomatic bipartite or tripartite patellae warrant referral to a sports medicine specialist for further management.
Prepatellar bursitis — Direct repetitive trauma (as in wrestling or in a patient who spends a lot of time on his knees, such as those with conditions that affect ambulation) may cause inflammation of the prepatellar bursa, located between the patella and overlying skin. With chronic inflammation, the walls of the prepatellar bursa may thicken and become fibrotic. Patients typically have swelling and tenderness of the anterior knee (picture 8). The diagnosis can usually be made by simple inspection and palpation of the anterior patella. (See "Knee bursitis", section on 'Prepatellar and superficial infrapatellar bursitis'.)
Plica syndrome — Plica syndrome may present with isolated medial pain or medial pain in association with anterior pain. Plica syndrome is caused by a redundant synovial thickening called a plica, usually in the medial superior portion of the medial retinaculum coursing toward the medial quadriceps tendon (figure 4). Patients may complain of anterior or medial pain that is worse with activity, such as running, squatting, going up or down stairs, or kneeling, and after prolonged sitting (cinema sign). The pain is often accompanied by a popping sensation with knee flexion. Patients may also report clicking, catching, knee pseudo-locking (false locking), or giving way. In most patients, only one knee is involved. Physical examination is nonspecific and may include a thickened tender plicae palpated in the medial superior portion of the knee, swelling medial to the patellar border, vague tenderness over the medial femoral condyle or patellar facet, or rarely, a snapping sensation during active or passive knee extension. (See "Plica syndrome of the knee", section on 'Clinical manifestations'.)
The diagnosis of plica syndrome is primarily based upon clinical features and should only be made once other causes of knee pain have been excluded. Plain radiographs are frequently required to exclude other causes of knee pain. The type of imaging performed is determined by the leading alternative diagnoses. If magnetic resonance imaging (MRI) is performed, a plica will be found in most patients, and MRI does not help distinguish between a normal variant and plica syndrome. Arthroscopy provides a definitive diagnosis if a thickened, fibrotic plica is demonstrated but is only performed when other diagnoses are considered or when conservative treatment fails. The treatment of plica syndrome is discussed separately. (See "Plica syndrome of the knee", section on 'Diagnosis' and "Plica syndrome of the knee", section on 'Initial treatment'.)
Other causes — Other causes of chronic medial knee pain and important distinguishing characteristics include the following (table 2):
●Osteochondritis dissecans – Patients with advanced osteochondritis dissecans may have tenderness of the medial femoral epicondyle and, if an intraarticular foreign body is present, locking or catching during range of motion. (See "Osteochondritis dissecans (OCD): Clinical manifestations, evaluation, and diagnosis", section on 'Clinical presentation'.)
●Pes anserinus tendinitis – The pes anserinus is the site of insertion of the semitendinosus, gracilis, and sartorius tendons. Pes anserinus tendinitis is manifest as tenderness over the pes anserinus bursa, in the medial superior region of the tibia (picture 9). The pain is worsened by resisted contraction of the muscles that insert at the pes anserinus as follows (see "Knee bursitis", section on 'Diagnosis' and "Knee bursitis", section on 'Pes anserinus pain syndrome (formerly anserine bursitis)'):
•Resisted knee flexion (semitendinosus)
•Resisted forward flexion of the hip with the hip slightly externally rotated, the knee extended, and the patient supine (sartorius)
•Resisted hip adduction (gracilis)
The treatment of pes anserinus involves rehabilitation that focuses on hip strength and balance to address knee valgus and internal rotation. (See "Knee bursitis", section on 'Treatment'.)
●Medial meniscus injury – Patients with medial meniscus injury may report catching or locking of the knee. Physical examination demonstrates pain over the medial joint line (picture 10) and positive McMurray or modified McMurray tests (picture 1). Treatment is discussed separately. (See "Meniscal injury of the knee", section on 'Treatment'.)
●Medial collateral ligament injury – Patients with a chronic medial collateral ligament (MCL) injury have tenderness over the ligament and a positive valgus stress test (picture 2). Management is provided separately. (See "Medial (tibial) collateral ligament injury of the knee", section on 'Initial treatment'.)
●Medial superior tibial stress fracture – Stress fracture at the medial superior tibia can also be a source of medial knee pain. Initial plain radiographs frequently show no bony abnormality. MRI often confirms the diagnosis. Stress fractures are discussed in greater detail separately. (See "Overview of stress fractures".)
●Adductor magnus strain – Adductor magnus strain is manifest as pain proximal to the origin of the MCL (approximately 4 cm proximal to the medial joint line) with resisted hip adduction. Pain at the adductor tubercle may also result from patellar instability with resulting stretching of the insertion of the medial patellar ligament, a more common condition in children and adolescents. (See "Adductor muscle and tendon injury", section on 'Clinical presentation' and 'Patellar subluxation' above.)
●Referred hip pain – Referred hip pain can be also be medial. Knee examination is normal, but the hip examination is abnormal and reflects the underlying condition. (See 'Referred hip pain' above.)
●Bone tumors – Tumors of the bone or bone marrow (eg, primary malignant, metastatic, or benign bone tumors and leukemias) can rarely cause medial pain and swelling, depending upon the location and size of the tumor. (See 'Tumors (malignant and benign)' above.)
Discoid meniscus and lateral meniscus injury — Children and skeletally immature adolescents may have a lack of development of the normal crescent shape of the meniscus with persistence of meniscal tissue over the tibial plateau . Although a discoid meniscus may occur on either side, a lateral discoid meniscus is most common. Patients may report lateral pain associated with catching or popping during active knee extension. A discoid meniscus also tears more easily than a normal, crescent-shaped meniscus. Patients with a chronic lateral meniscal tear have a subjective history of the knee locking, swelling, and/or possibly giving way. On physical examination, they have lateral joint line tenderness (picture 10) and may have a positive McMurray or modified McMurray test (picture 1). Management is as for a meniscal injury, although a torn discoid meniscus frequently warrants arthroscopic surgery. (See "Meniscal injury of the knee", section on 'Treatment'.)
Chronic lateral meniscus tears in the absence of a discoid meniscus are uncommon in children and skeletally immature adolescents and usually are associated with injury to other structures (eg, lateral collateral ligament, posterolateral corner injury, or anterior cruciate ligament). Clinical findings are the same as described above for discoid meniscus tears.
Iliotibial band syndrome — The iliotibial band (ITB) is formed by fascia from the hip flexors, extensors, and abductors. Iliotibial band syndrome (ITBS) is an overuse injury of the lateral knee that occurs primarily in runners and cyclists. Patients typically describe the insidious onset of pain localized to where the ITB courses over the lateral femoral epicondyle (LFE). Initially pain occurs only during sport. It is typically sharp or burning and occurs just prior to or during foot-strike when running, or as the knee extends (down-pedal position) when cycling. Over time, the pain can become constant and deep, persisting throughout exercise. Less commonly, pain persists for hours or days after exercise. (See "Iliotibial band syndrome", section on 'Patient presentation'.)
Key examination findings associated with ITBS include focal tenderness at the distal ITB where it courses over the LFE (picture 11), and a positive Noble compression test, which a number of experts believe is the single best test to confirm ITBS. The Ober test (picture 12) is another maneuver used by some to assess for ITB inflexibility, which can contribute to ITBS. Performance of the Noble compression and Ober tests are described in detail separately. (See "Iliotibial band syndrome", section on 'Physical examination'.)
ITBS is a clinical diagnosis. Imaging is usually not necessary, but the clinician needs to differentiate ITBS from chronic popliteus tendinitis. The treatment of ITBS is provided separately. (See "Iliotibial band syndrome", section on 'Treatment'.)
Other causes — Less common causes of chronic lateral knee pain in children and adolescents and important clinical manifestations include the following (table 2):
●Lateral collateral ligament injury – Chronic lateral collateral ligament (LCL) insufficiency typically occurs in combination with other injuries (eg, posterolateral corner, anterior or posterior cruciate ligament injury, or lateral meniscus tears). Clinical findings for chronic or acute LCL injury are the same and consist of tenderness along the lateral knee (picture 6), localized soft tissue swelling, and laxity of the LCL on varus stress testing (picture 2). The dial test is also performed to detect an associated injury to the posterior lateral corner (picture 13). (See "Lateral collateral ligament injury and related posterolateral corner injuries of the knee", section on 'Examination findings'.)
The treatment of LCL injuries is discussed separately. (See "Lateral collateral ligament injury and related posterolateral corner injuries of the knee", section on 'Initial treatment'.)
●Biceps femoris tendinitis – Posterolateral knee pain can be caused by tendinitis of the biceps femoris muscles Patients with biceps femoris tendinitis have tenderness along the biceps tendon that increases with resisted knee flexion on the proximal fibula and may be accompanied by the sensation that the knee is popping, rubbing, or snapping mechanical sensations (eg, popping, rubbing, or snapping) if the fibula is mobilized by the examiner moving the fibula anteriorly or posteriorly.
Management of biceps femoris tendinitis is discussed separately. (See "Hamstring muscle and tendon injuries".)
●Referred hip pain – Referred hip pain can also manifest at the lateral knee. Knee examination is normal, but the hip examination is abnormal and reflects the underlying condition. (See 'Referred hip pain' above.)
●Referred back pain – Referred back pain from an L5 radiculopathy is a rare cause of lateral knee pain in children and adolescents. The pain localizes to the back and radiates down the lateral aspect of the leg to the knee and into the foot. On examination, strength can be reduced in foot dorsiflexion, toe extension, foot inversion, and foot eversion. Weakness of leg abduction may also be evident in severe cases due to involvement of gluteus minimus and medius. Atrophy may be present in the extensor digitorum brevis muscle of the foot and the tibialis anterior muscle of the lower leg. In severe cases, there may be "tibial ridging," a condition in which the normal convexity of the anterior compartment of the leg is lost because of atrophy, leaving a prominent sharp contour of the medial aspect of the tibial bone. (See "Acute lumbosacral radiculopathy: Etiology, clinical features, and diagnosis", section on 'L5 radiculopathy'.)
Because radiculopathy is rare in children and adolescents, plain radiographs and additional imaging, typically magnetic resonance imaging are indicated to identify the cause. Depending upon the findings, consultation with a pediatric neurologist or neurosurgeon is warranted.
Urgent neuroimaging and consultation with a pediatric neurosurgeon should be performed in patients with any of the following findings:
•Acute radiculopathy with progressive neurologic deficits
•Radiculopathy with urinary retention, saddle anesthesia, or bilateral neurologic symptoms or signs
•Suspected epidural abscess
●Bone tumors – Tumors of the bone or bone marrow (eg, primary malignant, metastatic, or benign bone tumors and leukemias) can rarely cause lateral pain and swelling, depending upon the location and size of the tumor. (See 'Tumors (malignant and benign)' above.)
Posterior pain — Causes of chronic posterior knee pain include the following (table 2):
●Popliteal (Baker's) cyst – In children, popliteal (Baker's) cysts typically arise from the gastrocnemius-semimembranous bursa and do not extend from the knee joint. They cause asymptomatic swelling in the popliteal fossa on physical examination that appears as a medial popliteal mass that is most prominent with the patient standing and the knee fully extended. The swelling softens or disappears upon knee flexion to 45 degrees (defined as Foucher’s sign), as the tension on the cyst is relieved (picture 14). Most resolve spontaneously without treatment. Less commonly painful popliteal (Baker's) cysts can arise from injury to the knee joint or inflammatory joint changes. Popliteal (Baker's) cysts are discussed in greater detail separately. (See "Popliteal (Baker's) cyst", section on 'Children' and "Popliteal (Baker's) cyst", section on 'Diagnosis'.)
●Hamstring (semimembranous or biceps femoris) tendinitis – Semimembranous or biceps femoris distal tendinitis can cause posteromedial and posterolateral knee pain, respectively. Tenderness can be isolated to the body of the tendon or its insertion site. These structures are less commonly injured in children and adolescents. Evaluation and management of hamstring tendinopathy is discussed in detail separately. (See "Hamstring muscle and tendon injuries".)
●Popliteus tendinitis – Patients with popliteus tendinitis often report walking or running down steep hills. Tendinitis can usually be diagnosed clinically. Important findings include tenderness of the tendon and increased pain with resisted activity. Patients with popliteus tendinitis have tenderness to palpation in the region of the posterior inferior lateral femoral condyle that increases with resisted internal rotation of the tibia in the posterior lateral knee. (See "Calf injuries not involving the Achilles tendon", section on 'Popliteus tendinopathy'.)
●Referred hip pain – Referred hip pain can be also be posterior. Knee examination is normal, but the hip examination is abnormal and reflects the underlying condition. (See 'Referred hip pain' above.)
●Posterior cruciate ligament injury – Chronic posterior cruciate ligament (PCL) injury is rare in children. Symptoms include posterolateral pain and a feeling of instability when fully extending the knee. On physical examination, patients will display a positive posterior drawer test and/or posterior sag test. (See "Physical examination of the knee", section on 'Tests for PCL injury and posterior stability'.)
●Deep venous thrombosis – Deep venous thrombosis of the popliteal vein occurs rarely in normal healthy children. When present, the physical examination findings may include warmth, swelling, redness, a palpable cord, and tenderness on compression of the site. Laboratory studies, including a D-dimer and imaging (eg, ultrasound) are necessary to make the diagnosis. The pathophysiology, clinical manifestations, and treatment of deep vein thrombosis in children are discussed separately. (See "Venous thrombosis and thromboembolism (VTE) in children: Risk factors, clinical manifestations, and diagnosis" and "Venous thrombosis and thromboembolism (VTE) in children: Treatment, prevention, and outcome".)
●Referred back pain – S1 radiculopathy is a rare cause of posterior knee pain in children and adolescents. The pain radiates down the posterior aspect of the leg into the foot from the back. On examination, weakness of plantar flexion (gastrocnemius muscle) is specific. There may also be weakness of leg extension (gluteus maximus) and toe flexion. Sensation is generally reduced on the posterior aspect of the leg and the lateral edge of the foot. Ankle reflex loss is typical. (See "Acute lumbosacral radiculopathy: Etiology, clinical features, and diagnosis", section on 'S1 radiculopathy'.)
Because radiculopathy is rare in children and adolescents, plain radiographs and additional imaging, typically magnetic resonance imaging are indicated to identify the cause. Depending upon the findings consultation with a pediatric neurologist or neurosurgeon is warranted.
Urgent neuroimaging and consultation with a pediatric neurosurgeon should be performed in patients with any of the following findings:
•Acute radiculopathy with progressive neurologic deficits
•Radiculopathy with urinary retention, saddle anesthesia, or bilateral neurologic symptoms or signs
•Suspected epidural abscess
●Bone tumors – Tumors of the bone or bone marrow (eg, primary malignant, metastatic, or benign bone tumors and leukemias) can rarely cause posterior pain and swelling alone, depending upon the location and size of the tumor. (See 'Tumors (malignant and benign)' above.)
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SUMMARY AND RECOMMENDATIONS
●Definitions – For this topic, chronic knee pain is pain occurring during or after specific activities that has persisted for approximately six weeks or longer. In many patients, the diagnosis of chronic knee pain from overuse or trauma can be determined by the history and physical examination. (See 'History' above and 'Physical examination' above.)
●Differential diagnosis – The location of pain and tenderness provides a useful means of narrowing the possible causes and determining which provocative diagnostic maneuvers should be performed. The differential diagnosis organized by location of pain and by distinguishing features of conditions associated with diffuse or localized anterior knee pain are provided in the tables (table 2 and table 3). (See 'Pain from overuse or trauma' above and 'Conditions by location of pain' above.)
●Diagnostic imaging – Plain radiographs are recommended when there are mechanical symptoms of locking or catching, when an effusion is present, when the examiner is unable to reproduce the patient's chief knee complaints, and in patients who meet any of the Ottawa knee rules criteria. (See 'Diagnostic imaging' above.)
●Signs of possible dangerous causes – Chronic or acute knee pain in a child or skeletally immature adolescent without inciting trauma or a history of overuse is a "red flag" that a more extensive evaluation is required. This is especially so if the pain is associated with constitutional symptoms, such as fever, night sweats, chills, malaise, weight loss, or fatigue, or if the pain is severe enough to awaken the child from sleep. (See 'Pain with systemic symptoms' above.)
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