though may be considered as part of the aetiology.
Where does the pain come from in PFPS? Pain in PFPS may arise from the following structures in the knee extensor mechanism: ● subchondral bone ● synovium ● retinaculum ● muscle ● nerve.
It was once thought that chondromalacia patellae was the cause of the pain. This condition is characterised by macroscopic softening, fissuring and fragmentation of the patella cartilage, which is associated with retropatellar pain and crepitation during activities that load the patellofemoral joint. This was thought to be the cause of PFPS pain. Articular carti- lage is however aneural and clearly cannot be the cause of pain. This is further illustrated by some investigators who have found no relationship between the extent of macroscopic cartilaginous lesions and the severity of symptoms and these changes can be seen in individuals who have never suffered with knee pain.
It is the view of several authors that malalignment of the patella in the femoral trochlear, induced by one or more of the risk factors mentioned in tables 2 and 3, can lead to overload of the retinaculum and subchondral bone (5). Investigators have looked at neural markers in the excised lat- eral retinaculum of patients with isolated symptomatic patellofemoral malalignment. They observed increased neural growth factor production, which induces prolifera- tion of nociceptive axons.
a neuroanatomic basis of patients with isolated symptomatic patellofemoral malalignment and supported the sugges- tion that the lateral retinaculum may have a key role in the origin of pain.
Others have measured intraosseous patel- lar pressure in patients with PFPS. They found an abnormal increase in pressure. In a further study by the same group they showed that this intraosseous hyperten- sion was associated with an increased uptake on bone scintigraphy scanning (the scanning of radioactivity in an area). This was more apparent in individuals
Table 3: Risk factors for the development of PFPS from prospective studies (7)
PFPS patients are more likely to have a history of overuse or particularly overload exercise than clinical features of biomechanical malalignment. The evidence suggests the intrinsic factors worth assessing are: tight quadriceps, decreased quadriceps strength, leg length discrepancy and patellar mobility.
with associated patellar cartilage and subchondral changes. A more recent theory suggests that PFPS due to a supra-
physiological mechanical loading can cause a chemical irritation of nerve end- ings leading to peripatellar synovitis. This