Occurrence and distribution of free nerve endings in the distal iliotibial tract system of the knee.

Free nerve endings (FNE) are nociceptive sensory elements transmitting information on pain and inflammation from the connective tissues to the brain. They form an important part of the proprioceptive sensory system of the knee. We present a qualitative and quantitative analysis of FNEs in the distal iliotibial tract (ITT), documenting their occurrence in this structure as well as their specific distribution pattern. FNEs were found in all elements of the distal ITT, with their maximum density in the fixation sites of the distal ITT to the femur and the tibia. This finding correlates well with anatomical and biomechanical studies and stresses the importance of the deep ITT fibre system for lateral knee stability. The relative number of FNEs in the distal ITT ranges from 5 to 10 per 50 mm2 and is comparable to the frequency found in the synovial sheath of the cruciate ligaments. These findings have clinical implications for surgical procedures on the lateral side of the knee. The distinct anatomy of the distal ITT should be respected in all procedures, since extensive operations in this area may cause pain and loss of range-of-motion due to alterations of proprioceptive function.