Study Guide

Patellofemoral Knee Pain

Key Points:

Description:

Osteochondroses


Osteochondroses of the knee are a frequent cause of anterior knee pain in children and adolescents.  They are postulated to be the result of fatigue failure in response to traction stresses on apophyses about the patellofemoral joint in growing children.  Two common osteochondroses about the knee are Osgood-Schlatter disease and Sinding-Larsen-Johansson disease.  Osgood-Schlatter disease is the result of repetitive traction of the patellar tendon on the tibial tubercle apophysis; whereas Sinding-Larsen-Johansson is the result of repetitive traction on the inferior pole of the patella. (Yen, 2014) In 30%-50% of cases, Osgood-Schlatter disease is found bilaterally. (Yen, 2014; Samim, 2014)   Sinding-Larsen-Johansson has been considered the pediatric form of patellar tendinopathy. (Samim, 2014) Both conditions typically present in children and adolescents 10-14 years of age, though these pathologies can be seen in younger children as well. (Yen, 214; Samim, 2014; Wilson, 2014) Often Sinding-Larsen-Johansson may occur at younger ages within this group, while the typical patient with Osgood-Schlatter syndrome may be in the slightly older range.
    

Patellar Tendinopathy (Jumper’s Knee)

    
Patellar tendinopathy is one of the most common tendinopathies in athletes, particularly those active in jumping sports like basketball or volleyball. (Samim, 2014) It can be difficult to distinguish patellar tendinopathy from osteochondroses, as some patients will have both conditions. (Wilson, 2014)  Tenderness of the patellar tendon, particularly when the knee is in full extension and the tendon fibers are relaxed, is a common and reliable exam finding. (Wilson, 2014)

Bipartite Patella


Bipartite patella is the result of failure of fusion of a secondary ossification center of the patella.  Normally, the patella forms from a single ossification center though there are occasionally two or more centers of ossification. (Wilson, 2014) The most common secondary ossification center location is the superolateral patella. (Samim, 2014)  Up to 25% of cases are bilateral. (Wilson, 2014) Bipartite patella is rarely symptomatic, but when painful, patients present with pain with kneeling or squatting and tenderness over the secondary ossification center. (Samim, 2014)

Plica Syndrome


Plica syndrome is a less common cause of anterior knee pain and is the result of a thickened band of synovium that impinges on the femoral condyle during knee range of motion.  The medial peri-patellar plica is a diagnosis of exclusion, particularly in children. (Wilson, 2014)   When symptomatic, patients complain of anteromedial peripatellar pain with activity and a snapping or catching sensation in the knee. (Wilson, 2014)  Patients are tender over the medial peripatellar soft tissues and a thickening of the synovium medial to the patella is often palpable. 

Idiopathic Anterior Knee Pain


Patients with anterior knee pain may have no anatomic abnormality, no history of trauma and no abnormal findings of exam.  The term “idiopathic anterior knee pain” has been suggested as a diagnosis of exclusion for these cases. (Wilson, 2014)  Therefore, a thorough physical and radiographic evaluation, including evaluation of the hip, is required prior to giving this diagnosis. (Wilson, 2014)  This condition is seen in both active individuals and those who are more sedentary. (Wilson, 2014)  The etiology of idiopathic anterior knee pain is thought to be at least in part due to muscle imbalances or abnormalities in muscle activation. (Wilson, 2014)  Weakness in hip abduction and hip external rotation, as well as decreased activation of the vastus medialis obliques (VMO) and gluteus medius, have been associated with anterior knee pain. (Wilson, 2014)

Epidemiology:

Anterior knee pain is common in pediatric and adolescent patients.  In fact, patellofemoral pain is the most common overuse condition in adolescent athletes participating in running and/or jumping sports like track and field or basketball. (Paterno, 2013)  

Clinical Findings:

Evaluation of anterior knee pain in children and adolescents requires a thorough history in addition to physical exam.  The onset of pain is important to consider when evaluating anterior knee pain.  Many cases of anterior knee pain in children and adolescents are chronic in nature or have an insidious onset.  Also termed “runner’s knee,” patellofemoral pain is anterior knee pain that increases with running, jumping, stair climbing, squatting or sitting with the knees flexed for a prolonged period of time. (Paterno, 2013) Patients with Osgood-Schlatter or Sinding-Larsen-Johansson disease often have pain with kneeling as well. (Yen, 2014)

Physical exam of a child with anterior knee pain should include a complete ligamentous exam and should assess the flexibility of the hip flexors, quadriceps and hamstrings.  Patients with Osgood-Schlatter disease will often have an enlargement of the tibial tubercle and tenderness over the tibial tubercle.  Those with Sinding-Larsen-Johansson will present with tenderness over the inferior pole of the patella.  The torsional profile should be determined with the child in the prone position to assess hip inward and outward rotation range of motion. The thigh-foot axis determines the amount of tibial torsion.  Significant inward femoral and outward tibial torsion (torsional malaignment) is a common correlated finding in patients with anterior knee pain.

Focal patellar pain that is the result of trauma warrants radiographic examination to rule out fracture, specifically patellar sleeve fractures or osteochondral injuries. 

Imaging Studies:

Radiographic evaluation of anterior knee pain begins with plain radiographs including standing AP, lateral in 30° of flexion and Merchant views of the involved knee.  Radiographs can show anatomic variations in patellofemoral alignment such as patella alta or patella baja.  The tibial tubercle apophysis should be evaluated.  An abnormal appearance of the tibial tubercle apophysis or fragmentation of the tibial tubercle suggests Osgood-Schlatter disease. (Yen, 2014; Samim, 2014) Fragmentation of the inferior pole of the patella or calcification at the junction of the patella and the patellar tendon suggests Sinding-Larsen-Johansson disease. (Yen, 2014) In the case of bipartite patella, a well-corticated, non-united fragment will be seen, usually at the superolateral patella. (Samim, 2014) Magnetic resonance imaging (MRI) can be used to evaluate anterior knee pain in cases that fail non-operative treatment, have unusual history or symptoms which may indicate cartilage injury, osteochondritis dissecans, or symptomatic bipartite patella.  Symptomatic bipartite patella is associated with marrow edema seen on the MRI within and adjacent to the secondary ossification center fragment. (Samim, 2014)

Treatment:

Patellofemoral pain conditions are primarily managed nonoperatively.  The mainstays of treatment are activity modification, anti-inflammatories and physical therapy. (Wilson, 2014) Therapy protocols should emphasize core and hip strengthening to improve patellofemoral kinematics. (Earl, 2011) For patients with excessive or mistimed pronation, proper shoe wear, the use of foot orthoses, or gait training may be helpful.  Osteochondroses of the knee are self-limiting in most patients, resolving once patients reach skeletal maturity.  In cases of bipartite patella, immobilization with a cast or knee immobilizer can be utilized if activity modification does not lead to symptom resolution. This may be more useful in younger patients.(Wilson, 2014)     

Operative management is rarely indicated.  In some cases of Osgood-Schlatter disease or Sinding-Larsen-Johansson disease, refractory to all nonoperative interventions, ossicle excision can be performed. (Milewski, 2012)   Recalcitrant pain associated with patellar tendinopathy can be treated with debridement of the diseased portion of the tendon with or without excision of the inferior pole or the patella. (Wilson, 2014) In cases of chronic and persistent pain associated with a bipartite patella, the fragment may be excised either arthroscopically or open. (Wilson, 2014)

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References:

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