Evaluation of Two Clinical Stem-Fit Philosophies Within the Femoral Canal Using a Preoperative Planning Tool: Could a Hybrid Approach Be Best?

Background: Total hip arthroplasty (THA) has transformed patient lives, yet evolving expectations and the number of postoperative foot angle changes have underscored the need for precise component positioning. The objective of this study was to use 3-dimensional (3D) preoperative planning to evaluate stem alignment and orientation for three THA systems using two different stem-fit algorithms. It was hypothesized that the different stem alignments would yield similar changes in stem orientation and placement within the canal for all 3 systems.

Methods: This study introduced a novel 3D preoperative planning tool, comparing two different surgical stem-fit philosophies within the canal: "canal fit" (CF) and "anatomical fit" (AF). We virtually implanted 10 subjects with three different THA implant systems using both philosophies, evaluating 60 total fits within the canals. The CF philosophy aimed to minimize cortical bone removal. In contrast, the AF philosophy prioritized aligning the implanted head with the anatomical head center.

Results: Detailed analyses revealed that AF led to fixation occurring mainly on the medial aspect of the stem, while CF exhibited a more even distribution between medial and lateral sides. The AF philosophy achieved significantly closer placement of the implanted head to the anatomical center (2.0 to 2.1 mm) compared to the CF philosophy (3.0 to 6.0 mm) (P < 0.01). The AF resulted in neutral stem orientation (0°) across all stems, whereas the CF exhibited greater malrotation (2.0 to 7.0°) (P < 0.02). The AF required more bone removal (0.13 to 0.46 cm³) than the CF (0.02 to 0.06 cm³) (P < 0.01).

Conclusions: The findings underscore the importance of 3D planning, emphasizing its potential to improve stem version alignment in THA. The results from this study may advocate 3D preoperative planning with robotic surgery to plan stem placement within the canal while maintaining anatomical femoral head restoration.