Table 1 Summarizing the differential diagnosis for the common causes of the AKP and their clinical presentations

Articular cartilage injury

The patient may describe a history of trauma, and the mechanical symptoms may occur if a loose body is present.

May have effusion or have a tenderness of the involved structure (e.g., femoral condyles, patella).

Chondromalacia patellae

The patient may have a retro-patellar pain, a history of trauma, or an effusion on the examination.

Hoffa’s disease

The patient may have a pain and tenderness localized to infrapatellar fat pad.

Osgood–Schlatter disease

The patient may have tenderness and/or swelling at the insertion of the patellar tendon at the tibial tubercle in an adolescent.

Patellar instability/subluxation

The patient may have an intermittent pain with a sensation of instability or movement of the patella.

May have a swelling or a locking can occur with loose bodies. May have tenderness over the medial retinaculum.

Patellar tendinopathy

The patient may have tenderness over the tendon.

The tendon may be thickened if the condition is chronic.

Pes anserine bursitis

The pain is usually described as medial rather than anterior in location with tenderness over the pes anserine bursa.

Prepatellar bursitis

May be medial or lateral to the patella; if symptomatic, tenderness can be demonstrated on examination.

Plica synovialis

The patient may have a characteristic swelling anterior to the patella following trauma.

Quadriceps tendinopathy

The patient may have tenderness over the tendon.

Sinding–Larsen–Johansson syndrome

The patient may have tenderness at the patellar tendon insertion in the inferior pole of the patella in an adolescent.

Symptomatic bipartite patella

The patient may have tenderness directly over the patella with characteristic radiographic findings.