[Nerve distribution and density in the canine hip joint capsule. Comparison of healthy and dysplastic hip joints]

The hip-joint capsule is exposed to increased tension forces during canine hip dysplasia, resulting in inflammation of the capsular tissue. It has been postulated that inflammation is associated with an increased nerve-distribution density. Therefore, it could be supposed that the nerve-distribution density in the hip-joint capsule is higher in dogs with dysplastic hip compared to healthy dogs.

In 16 Labrador Retriever dogs that had been euthanised due to unrelated reasons, the hip joints were classified as normoplastic (group 1, n = 18) or dysplastic (group 2, n = 14) based on radiography. Following staining of the capsular nerve fibres by the Sihler method, histological specimens of the hip-joint capsules were scanned. By subdividing each specimen into 10 quadrants numbered from dorsomedial (Q01) to craniodorsolateral (Q10), the ratio of black to white pixels was calculated digitally for each specimen and each quadrant by using a semiautomatic image analysis. Statistical analysis was performed using an independent t-test.

Comparison of the mean values of each quadrant showed a significantly higher (p < 0.03) nerve distribution density for the craniodorsolateral quadrant (Q10) in group 2 when compared to group 1. Mean nerve-distribution density for all quadrants combined was not significantly different between the two groups.

The increase in nerve-distribution density of the craniodorsal region of the hip-joint capsule in dogs with dysplastic hip could be the result of increased tension forces on this area following hip-joint dysplasia. The craniodorsal region of the hip-joint capsule is an important origin of pain and coxarthrosis in canine hip dysplasia.

The results provide the pathophysiological basis for the efficacy of hip-joint denervation. Denervation of the cranial region of the acetabular rim is essential to reduce capsular inflammation and joint-related pain in canine hip dysplasia.