Does Stem Design Affect Primary Stability of Splined Tapered Fluted Stems? A Biomechanical Cadaver Study

Tapered fluted stems are an excellent solution for revision hip arthroplasty following periprosthetic fractures. However, existing implant designs differ in terms of the number of splines, taper angle, and cross-sectional design, and there is a lack of knowledge on the biomechanical effect of these design variations. Therefore, the objective of this study was to compare the primary stability of two representative stem designs and the extent and distribution of stem-bone contact in a periprosthetic fracture model. It was hypothesized that a greater number of splines would lead to greater stability.

There were six pairs of cadaver femora included and underwent computed tomography imaging for templating. An extended trochanteric osteotomy was created and then reduced using three cerclage cables. Subsequently, one femur in each pair was implanted with 1 of 2 commercial designs of tapered fluted stems. During specimen preparation, the position and orientation of the reamer and the stems were measured by laser scanning, allowing measurement of stem-bone contact. Subsequently, each specimen was subjected to 1,000 cycles of biomechanical loading tests, and stem-bone motion was measured using a motion capture system.

The average subsidence of the two stems after loading was 313 ± 138 and 181 ± 113 μm (P > 0.05). The largest micromotion during each loading-unloading cycle was observed in the first cycle for both stems, and it remained constant in the subsequent cycles. There was more anterior stem-bone contact than posterior region in both stems, and the average contact area was comparable (1,546 ± 533 and 1,525 ± 587 mm², P > 0.05).

Different geometric designs did not lead to significant changes in the extent and distribution of stem-bone contact, and both stems demonstrated similar primary stability under the loads tested in this study.