Palpation is repeated whilst the proximal hand displaces the patella laterally with a constant force: any patellar instability or apprehension should be detected with this test, which is often performed with greater diagnostic value under general anaesthesia.

Factors contributing to patellofemoral instability include anteverted hips, shallow femoral grooves, flattened lateral femoral condyles, and high-riding or flat patellae. In addition, instability may be due to generalised ligament laxity, recurvatum, external tibial torsion, a lax medial retinaculum, weak, tight or dysplastic quadriceps, a tight iliotibial band and valgus knees.

All of these factors must be examined when assessing patellofemoral instability, a condition more common in women. Patellar subluxation often remains undiagnosed, as the clinical signs are rather subtle.

Next, the patella is displaced medially. This tests the degree of tightness of the lateral retinaculum, which will be relevant in patellar instability, especially if a lateral release is contemplated.

The medial structures are palpated. The medial collateral ligament arises proximally above the medial femoral condyle, crosses the joint line and enters below the pes anserinus.

In the acute first and second degree tears, tenderness is usually proximal to the medial femoral condyle. With chronic tenderness a Pellegrini-Stieda lesion should be suspected: this is a heterotopic ossification in the disrupted attachment of the medial collateral ligament, apparent on radiographic examination.

Ligament tenderness will be consistent with the site of the tear.

The joint line is now palpated anteriorly to posteriorly marked tenderness suggests a meniscal tear or capsular strain.

It is also associated with osteochondral fracture, which is often very difficult to distinguish clinically from a meniscal tear, and degenerative joint disease.

Anterior tenderness is most common in the knee locked by a bucket handle tear of the medial meniscus; posterior tenderness is most common in a cleavage tear of the posterior horn.

A complex tear of the meniscus.