Total Hip Replacement with a Fully Hydroxyapatite-Coated Shortened Stem: Five- to Thirteen-Year Follow-Up Results.

Background: Shortened femoral stems aim to mimic the biomechanical performance of traditional stems while preserving more bone and minimizing soft tissue damage. Our objective is to assess the outcomes of patients treated with a shortened stem (Furlong Evolution, JRI Orthopaedics, Sheffield, UK) to analyze the implant's efficacy and survivorship. Methods: This retrospective observational study included all patients aged 18 to 70 undergoing uncemented shortened stem total hip replacement at Hospital del Mar between 2010 and 2018. Hip function and pain were assessed with the Merle d'Aubigné-Postel scale and visual analog scale, respectively. A radiographic analysis measured stem and cup orientation, leg length discrepancy, stem subsidence, and radiolucencies around the cup. Perioperative complications, prosthetic failures, and reoperations were documented. Results: A total of 109 patients (74 male, 35 female) of a mean age of 51.8 ± 8.8 years were included. The average follow-up was 91 ± 17.4 months. Radiographically, 71 (65.1%) of the stems had been inserted at the appropriate angulation (±3°), and 102 (93.6%) of the cups had been placed in the Lewinnek safety zone. Leg length discrepancy was observed in 19 (17.4%) cases. The mean Merle d'Aubigné-Postel score improved from 13.1 ± 1.39 preoperatively to 17.8 ± 0.49 at 6 months postoperatively (p < 0.001). Merle d'Aubigné-Postel subscales also reflected a statistically significant improvement (p < 0.001). The mean pain score 12 months postoperatively was 0.52 ± 1.22, with 95.4% of patients declaring themselves satisfied or highly satisfied. The expected 13-year survival according to a Kaplan-Meier analysis was 100% in the absence of infection and 91.3% if revision for any cause is taken as a survival endpoint. Conclusions: The shortened stem under analysis provides excellent functional results and long-term survival rates.

Orthopedic Surgeons' Accuracy When Orienting an Acetabular Cup. A Comparison with Untrained Individuals.

Background and Objectives: Previous studies demonstrated a huge variability among surgeons when it comes to reproducing the position of an acetabular cup in total hip arthroplasty. Our main objective is to determine if orthopedic surgeons can replicate a given orientation on a pelvic model better than untrained individuals. Our secondary objective is to determine if experience has any influence on their ability for this task. Materials and Methods: A group of specialist orthopedic hip surgeons and a group of volunteers with no medical training were asked to reproduce three given (randomly generated) acetabular cup orientations (inclination and anteversion) on a pelvic model. Error was measured by means of a hip navigation system and comparisons between groups were made using the appropriate statistical methods. Results: The study included 107 individuals, 36 orthopedic surgeons and 71 untrained volunteers. The mean error among surgeons was slightly greater as regards both inclination (7.84 ± 5.53 vs. 6.70 ± 4.03) and anteversion (5.85 ± 4.52 vs. 5.48 ± 3.44), although statistical significance was not reached (p = 0.226 and p = 0.639, respectively). Similarly, although surgeons with more than 100 procedures a year obtained better results than those with less surgical experience (8.01 vs. 7.67 degrees of error in inclination and 5.83 vs. 5.87 in anteversion), this difference was not statistically significant, either (p = 0.852 and p = 0.981). Conclusions: No differences were found in the average error made by orthopedic surgeons and untrained individuals. Furthermore, the surgeons' cup orientation accuracy was not seen to improve significantly with experience.

Biomechanical Behavior of an Hydroxyapatite-Coated Traditional Hip Stem and a Short One of Similar Design: Comparative Study Using Finite Element Analysis.

BACKGROUND: The objective is to compare, by the means of finite elements analysis, the biomechanical behavior of a conventional stem of proven performance with a short stem based on the same fixation principles. METHODS: A 3D femur was modeled from CT scan data, and real bone density measures were incorporated into it. Load stresses were applied to that bone in 3 different scenarios: without prosthesis, with the conventional stem, and with the short stem. Different bone loading patterns were compared by Gruen's zones both visually and statistically using Welch's test. RESULTS: The implantation of a stem generates a certain degree of stress shielding in the surrounding bone, but the pattern of the change is very similar in the compared stem models. Although there is statistical significance (P < 0.01) in the mean stress variation in most of the Gruen's zones, the magnitude of the difference is always under 2 MPa (range: 0.01 - 1.74 MPa). CONCLUSIONS: The bone loading patterns of the traditional stem and the short stem are very similar. Although there is no evidence of a link between biomechanics and clinical outcomes, our results may suggest that theoretical advantages of short stems can be exploited without the fear of altering bone loading patterns.