THE RATIONALE FOR GENDER SPECIFIC FEMORAL STEMS FOR TOTAL HIP ARTHROPLASTY

Abstract

Differences in femoral anatomy have been partially ascribed to gender differences. Traditionally, femoral stems for THA have been designed across an entire population including both males and females. The purpose of this study was to compare the applicability of two femoral stem systems in male and female populations via preoperative templating.

Methods: All patients seen during a single month who presented complaining of knee pain had screening pelvis x-rays. These x-rays formed a consecutive cohort of hips for the templating study. During templating, the acetabular component was placed in a fully medialised position at 45o of abduction. The center of rotation was marked. The femoral neck osteotomy was set at 15 mm proximal to the lesser trochanter. Templates of equal magnification were utilized for both systems. System 1 had a double tapered wedge body design, a fixed 135o neck-shaft angle with two different offsets (6 mm difference) and two different neck lengths (4 mm difference). There were 7 head options with different lengths. System 2 had the same body design with a modular neck offering 20 different offsets/lengths and 7 different neck-shaft angles, with only one head option. Neck length and offset were independent of body size for both systems. Based upon templating, the categories were: No obvious advantage of either system, System 1 preferred, System 2 preferred, Neither system appropriate. Preference was determined based upon providing at least one additional length or offset option, and avoiding the extra extended offset option in System 2 based upon the theoretical risk of disassociation due to extremely high moments.

Results: There were 20 female patients contributing 40 hips and 27 males contributing 54 hips. Among the males, there was no obvious advantage in 20/54 hips (37%), System 1 was preferred in 11/54 hips (20.4%), System 2 was preferred in 15/54 hips (27.8%), and neither system was appropriate in 8/54 hips (14.8%). In addition, System 1 could have been used in 33/54 hips (61.1%), while System 2 could have been used in 42/54 hips (77.8%). Overall, 46/54 male hips (85.2 %) could be implanted with this stem. Among the females, there was no obvious advantage in 17/40 hips (42.5%), System 1 was preferred in 1/40 hip (2.5%), System 2 was preferred in 13/40 hips (32.5%), and neither system was appropriate in 9/40 hips (22.5%). In addition, System 1 could have been used in 22/40 hips (55%), while System 2 could have been used in 31/40 hips (77.5%). Overall, 31/40 female hips (77.5 %) could be implanted with this stem.

Discussion: Significantly, there are gender differences in applicability of femoral stems. Specifically, more neck length and offset options seem to be required for females. One criticism of this study would be that the neck osteotomy length was fixed. In practical application, surgeons frequently adjust the level of the neck osteotomy to successfully reconstruct the hip. Further study is necessary to determine the role of neck-shaft angle, bone quality and adjustment of neck osteotomy height.