A systematic review and meta-analysis of the hip capsule innervation and its clinical implications

Abstract

Detailed understanding of the innervation of the hip capsule (HC) helps inform surgeons' and anaesthetists' clinical practice. Post-interventional pain following radiofrequency nerve ablation (RFA) and dislocation following total hip arthroplasty (THA) remain poorly understood, highlighting the need for more knowledge on the topic. This systematic review and meta-analysis focuses on gross anatomical studies investigating HC innervation. The main outcomes were defined as the prevalence, course, density and distribution of the nerves innervating the HC and changes according to demographic variables. HC innervation is highly variable; its primary nerve supply seems to be from the nerve to quadratus femoris and obturator nerve. Many articular branches originated from muscular branches of the lumbosacral plexus. It remains unclear whether demographic or anthropometric variables may help predict potential differences in HC innervation. Consequently, primary targets for RFA should be the anterior inferomedial aspect of the HC. For THA performed on non-risk patients, the posterior approach with capsular repair appears to be most appropriate with the lowest risk of articular nerve damage. Care should also be taken to avoid damaging vessels and muscles of the hip joint. Further investigation is required to form a coherent map of HC innervation, utilizing combined gross and histological investigation.

Figure 1

PRISMA flow chart displaying the search results based on Moher et al.(2010). The dotted line represents the articles located from the search of the databases undergoing forwards and backwards chain sampling to located further articles.

Figure 2

Prevalence of the obturator nerve innervating the hip capsule. Results indicate the variation in prevalence across studies with 95% confidence intervals. There is high heterogeneity between studies as shown by the I² statistic of 85%.

Figure 3

Prevalence of the femoral nerve innervating the hip capsule. Results indicate the variation in prevalence across studies, as well as the high heterogeneity as shown by the I² statistic of 95%.

Figure 4

Sketch summarizing consensus findings on the distribution of innervation patterns of the accessory obturator, femoral, obturator, nerve to quadratus femoris, sciatic and superior gluteal nerves. Sketch adapted from Tomlinson et al (2020). The top row of sketches represents the anterior capsule and the bottom row shows the posterior capsule. Insufficient information was available on the distribution of innervation from other nerves of the lumbosacral plexus; therefore, they were not included in this diagram. The intensity of the shading relates to the percentage of studies that agree that a particular region of the hip capsule receives innervation from a certain nerve. Darker regions depict areas where the literature demonstrates more general consensus that the region is innervated by the nerve. Lighter areas are regions of less general consensus that the regions are supplied by a particular nerve. D distal, I inferior, L lateral, M medial, P proximal, S superior.