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Key Features

Essentials of Diagnosis

  • Pain experienced with bending activities (kneeling, squatting, climbing stairs)

  • Lateral deviation or tilting of the patella in relation to the femoral groove

General Considerations

  • Also known as anterior knee pain, chondromalacia, or "runner's knee," describes any pain involving the patellofemoral joint

  • Pain affects any or all of the anterior knee structures, including the medial and lateral aspects of the patella as well as the quadriceps and patellar tendon insertions

  • Patellofemoral pain is also associated with muscle strength and flexibility imbalances as well as altered hip and ankle biomechanics

  • Abnormal patellar tracking during flexion can lead to abnormal articular cartilage wear and pain

  • When the patient has ligamentous hyperlaxity, the patella can sublux out of the groove, usually laterally

  • There are two common presentations

    • Patients whose ligaments and patella are too loose (hypermobility)

    • Patients who have soft tissues that are too tight leading to excessive pressure on the joint

Clinical Findings

Symptoms and Signs

  • Pain

    • Usually occurs in the anterior knee with bending movements and less commonly in full extension

    • May sometimes be referred to the posterior knee or over the medial or lateral inferior patella

  • Symptoms may begin after a trauma or after repetitive physical activity, such as running and jumping

  • When maltracking, palpable and sometimes audible crepitus can occur

  • Intra-articular swelling usually does not occur unless there are articular cartilage defects or unless osteoarthritis develops

  • On physical examination, it is important to palpate the articular surfaces of the patella

  • Patellar mobility can be assessed by medially and laterally deviating the patella

    • Deviation by one-quarter of the diameter of the kneecap is consider normal

    • Deviation by greater than one-half of the diameter suggests excessive mobility

Diagnosis

Imaging

  • Radiographs may show lateral deviation or tilting of the patella in relation to the femoral groove

  • MRI may show thinning of the articular cartilage but is not clinically necessary, except prior to surgery or to exclude other pathology

Diagnostic Studies

  • Apprehension sign

    • Suggests instability of the patellofemoral joint

    • Positive when the patient becomes apprehensive when the patella is deviated laterally (Table 41–7)

  • Patellar grind test

    • Performed by grasping the knee superior to the patella and pushing it downward with the patient supine and the knee extended, pushing the patella inferiorly

    • The patient is asked to contract the quadriceps muscle to oppose this downward translation, with reproduction of pain or grinding being considered a positive sign for chondromalacia of the patella

Table 41–7.Knee examination.

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