Restoration of Hip Biomechanics after a Hemiarthroplasty for a Femoral Neck Fracture—Who Does It Better?

Introduction: The restoration of the preoperative biomechanics of the hip, in particular leg length and femoral offset, are critical in restoring normal function and diminishing the risk of dislocation following hip arthroplasty. This study compares the consistency of arthroplasty and non-arthroplasty orthopedic surgeons in restoring the normal biomechanics of the hip when performing a hemiarthroplasty for the treatment of a femoral neck fracture. Methods: We retrospectively reviewed the preoperative and postoperative digital radiographs of 175 hips that had a modular hemiarthroplasty for the treatment of a displaced femoral neck fracture at a Level 1 academic hospital. Fifty-two hips were treated by one of the three fellowship-trained arthroplasty surgeons (Group A), and 123 were treated by one of the nine non-arthroplasty fellowship-trained orthopedic surgeons (Group B). Results: Patients in Group A were more likely to have their femoral offset restored to normal than patients in Group B, both with respect to under correcting the offset (p = 0.031) and overcorrecting the offset (p = 0.010). Overall, there was no difference in restoration of leg lengths between the two groups (p = 0.869). Conclusions: Following a hemiarthroplasty for a displaced femoral neck fracture, the normal biomechanics of the hip are more likely to be restored by an arthroplasty-trained surgeon than by a non-arthroplasty-trained surgeon. Identifying the inconsistency of non-arthroplasty surgeons and, to a lesser degree, arthroplasty surgeons in restoring hip biomechanics is important for sensitizing surgeons to rectify this in the future with appropriate templating and femoral implant selection.

Hip implants can restore anatomical and medialized rotation centres in most cases

Aims Hip arthroplasty does not always restore normal anatomy. This is due to inaccurate surgery or lack of stem sizes. We evaluated the aptitude of four total hip arthroplasty systems to restore an anatomical and medialized hip rotation centre. Methods Using 3D templating software in 49 CT scans of non-deformed femora, we virtually implanted: 1) small uncemented calcar-guided stems with two offset options (Optimys, Mathys), 2) uncemented straight stems with two offset options (Summit, DePuy Synthes), 3) cemented undersized stems (Exeter philosophy) with three offset options (CPT, ZimmerBiomet), and 4) cemented line-to-line stems (Kerboul philosophy) with proportional offsets (Centris, Mathys). We measured the distance between the templated and the anatomical and 5 mm medialized hip rotation centre. Results Both rotation centres could be restored within 5 mm in 94% and 92% of cases, respectively. The cemented undersized stem performed best, combining freedom of stem positioning and a large offset range. The uncemented straight stem performed well because of its large and well-chosen offset range, and despite the need for cortical bone contact limiting stem positioning. The cemented line-to-line stem performed less well due to a small range of sizes and offsets. The uncemented calcar-guided stem performed worst, despite 24 sizes and a large and well-chosen offset range. This was attributed to the calcar curvature restricting the stem insertion depth along the femoral axis. Conclusion In the majority of non-deformed femora, leg length, offset, and anteversion can be restored accurately with non-modular stems during 3D templating. Failure to restore hip biomechanics is mostly due to surgical inaccuracy. Small calcar guided stems offer no advantage to restore hip biomechanics compared to more traditional designs. Cite this article: Bone Jt Open 2021;2(7):476–485.