The safe distance for the superior gluteal nerve in direct lateral approach to the hip and its relation with the femoral length: a cadaver study

Abstract

The most inferior branch (MIB) of the superior gluteal nerve (SGN) is vulnerable during direct lateral approach to the hip. A safe distance proximal to the tip of the greater trochanter varying from 3 to 5 cm has been reported in different studies. Anatomical studies defining safe zones and clinical studies reporting the results use various reference points, and the oblique course of the MIB contributes to the confusion. Numerous efforts have been made to standardize the safe zone using patient characteristics such as body height; however, contradictory results have been reported. The purpose of this study was to measure the safe distance in line to the gluteal split and also to determine the relationship of the safe distance with femoral length, as a stable component of body height. Fifteen lower extremities of 12 formalin-fixed cadavers (M/F: 7/5) were dissected. The most prominent lateral palpable part of the trochanter major (TM) was determined and the dissection in the gluteus medius muscle (GMM) was performed starting from this point upwards in line of the muscle fibers. The distances between the MIB in the plane of dissection in the GMM to the TM and also to the trochanteric apex (TA) were measured. Femoral lengths were measured between the TM point and the lateral epicondyle. Spearman's correlation and Mann-Whitney U tests were used for statistical analysis. The SGN in 13 hips had spray pattern and neural trunk pattern in two. The plane of dissection was within the anterior third of the GMM in all hips. The average femoral length was 37.5 cm. Average distance between TM and MIB was 44 mm; in three hips, the distance was <30 mm. The average distance between TA and TM was 21 mm. There was no statistically significant correlation between femoral length and TM-MIB distance. The distance from the TM to the MIB is highly variable and independent from body height or femoral length. The so called "safe zone" in which damage of significant nerve damage is excluded can have a rather small dimension in some patients. Short patients are not at increased risk and tall patients are not risk free. Modern techniques in total hip replacement which try to minimize proximal interruption of the GMM are therefore justified.