Sensory Innervation in Human Hip Joint Capsule and Pseudocapsule After Total Hip Replacement: A Morphological Investigation

Abstract

Purpose : To identify sensory nerve endings in the human hip joint capsule and in the pseudocapsule after total hip replacement. Materials and Methods : Ten hip joint capsules from patients undergoing bipolar hip replacement for acute femoral neck frac-ture, 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. Results : 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. Conclusion : 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.