To identify sensory nerve endings in the human hip joint capsule and in the pseudocapsule after total hip replacement.

Ten hip joint capsules from patients undergoing bipolar hip replacement for acute femoral neck fracture, and six pseudocapsules from patients undergoing revision hip surgery for failed total hip replacement were harvested and stained in bulk using a modified gold-chloride method. Sensory nerve endings were identified using the criteria described by Freeman and Wyke.

Three morphologically distinct types of nerve endings were identified in the normal human hip joint capsules; type I Ruffini corpuscles, type II Pacinian corpuscles and type IV free nerve endings. In contrast, no proprioceptive nerve endings (type I and II receptors) were observed in pseudocapsular tissues. A small number of type IV receptors were noted in the pseudocapsule, but these were significantly fewer in number than in normal hip capsular tissue.

The pseudocapsule that forms after hip replacement surgery may protect joint stability through a mechanical check-rein effect rather than through a proprioceptive feedback mechanism.