Causes / typical injury mechanism: Pathologic lateral knee soft-tissue restraints, most commonly consisting of a tight lateral retinaculum and vastus lateralis, lead to chronic overload and increased pressure on the lateral patellar facet, causing pain.

Classic history and presentation: Lateral patellar compression syndrome classically presents as lateral knee pain that worsens with stair climbing / descending or sitting for long periods of time. Additionally, deep squats with the knee past 90 degrees of flexion can result in pain. The pain is typically in the anterolateral aspect of the knee. Additionally, there may be medial peripatellar pain at the location of the medial patellotibial ligament, located at the inferiomedial aspect of the patella by the joint line. Patients may present with an extension block during the get-up phase of ambulation.

Prevalence:

• Age – Common among adolescents and adults younger than 60 years
• Sex / gender – Female predominance

Risk factors:

• Activities such as running, squatting, and climbing and descending stairs repetitively
• Female sex
• Foot abnormalities (rear foot eversion and pes pronatus)
• Overuse or sudden increase in physical activity level
• Quadriceps weakness / atrophy
• Increased femoral anteversion
• Genu valgum (knock-kneed)
• Excessive foot pronation or rear foot eversion
• External tibial torsion (increased Q-angle increasing patellofemoral malalignment)
• Weak gluteal musculature or core musculature

Pathophysiology: Aberrant and pathologic lateral restraint causes improper tracking of the patella within the trochlear groove during knee flexion, leading to increased contact pressure. This increased contact pressure leads to excessive patellar tilt, reduced patellar mobility, and increased osteoarthritis or chondromalacia within the patellofemoral joint.