Difference in trochanteric thickness between well-aligned and malaligned polished collarless stem.

Background: Surgical techniques and instruments are continuously evolving to improve placement of components in ideal position. We investigated if there is difference in greater trochanter thickness between the stems in satisfactory position and stems in malposition and to assess the ideal thickness of trochanter for femoral stem placement in neutral position as under reaming of trochanter can result in stem malposition.

Methods: Measurement of greater trochanteric thickness in 95 hip replacements (posterior approach) was performed by a junior doctor and two hip fellows using the trauma CAD/PACS software. The stem was considered neutral if the central axis of femur passes through the distal tip of stem in AP and in varus if the tip of stem was lateral to the femoral shaft axis.

Results: 79 patients had stem in satisfactory position and 16 patients in varus malposition. Mean trochanteric thickness was 12.6 mm (+/-0.56 mm 95%CI, Median 12.5 mm, SD 2.5 mm) in neutral stems while mean thickness in the varus stem was 18.4 mm (+/-1.01 mm 95%CI, Median 17.8 mm, SD 2 mm). There was statistical significant difference between both groups with p< 0.0001 with intra-observer correlation at 99% between the senior personal while correlation was at 80% between the senior personnel and junior doctor. No statistically significant difference was noted in measurements between the senior personal.

Conclusions: The study confirms the significant difference in greater trochanteric thickness between the well aligned and misaligned femoral components. The study raises the possibility that trochanteric thickness can be used as an accessory surgical aid to check if sufficient broaching has been done laterally to allow the stem to be seated in neutral position with an ideal remnant thickness of 12.5 mm. A surgical instrument can be developed to measure the intraoperative thickness of the trochanter which can be a useful tool for young hip surgeons for better placement of components.