[The overstretched patellar tendon in patellar apex syndrome]

Pain syndromes of the patella in persons active in sports are extremely frequent. The most important subgroup (by incidence rate) is the apex patellae syndrome (jumper's knee). Since all attempts at ascribing objective diagnostic criteria with satisfactory reproducibility to this syndrome, have failed to date, we have tried to define this disease pattern by means of analysis of the patellar movement. 35 patients with primary apex patellae syndrome (56 painful knee joints) and 15 healthy subjects (30 knee joints) were examined. The movement of the patella while stretching the knee in the posterior-anterior ray path was recorded on x-ray film and on magnetic tape. Assessment of the vertical movements of the patellae--in relation to the angle of extension of the knee joints--yielded the following results: 1. Initial and final positions of the patella in the apex patellae syndrome were the same as those of the control group. 2. If the knee was stretched from a 30 degree angle, the path travelled by the patella was significantly longer in case of apex patellae syndrome. The mobile performance of the patella in the apex patellae syndrome is seen as an expression of an elongated patellar ligament. Enhanced long-term longitudinal stretch is considered to be the cause of such elongation. The principal sign of the syndrome, namely, pain at the apex patellae, can be explained by: 1. an elongation of the patellar tendon with formation of an angle between the patellar ligament and the patella on the sagittal plane during flexing and strain, 2. deterioration of the plastic ligament properties and impulse absorption capacities due to overstretching.(ABSTRACT TRUNCATED AT 250 WORDS)