Aims: Computer-assisted 3D preoperative planning software has the potential to improve postoperative stability in total hip arthroplasty (THA). Commonly, preoperative protocols simulate two functional positions (standing and relaxed sitting) but do not consider other common positions that may increase postoperative impingement and possible dislocation. This study investigates the feasibility of simulating commonly encountered positions, and positions with an increased risk of impingement, to lower postoperative impingement risk in a CT-based 3D model.Methods: A robotic arm-assisted arthroplasty planning platform was used to investigate 11 patient positions. Data from 43 primary THAs were used for simulation. Sacral slope was retrieved from patient preoperative imaging, while angles of hip flexion/extension, hip external/internal rotation, and hip abduction/adduction for tested positions were derived from literature or estimated with a biomechanical model. The hip was placed in the described positions, and if impingement was detected by the software, inspection of the impingement type was performed.Results: In flexion, an overall impingement rate of 2.3% was detected for flexed-seated, squatting, forward-bending, and criss-cross-sitting positions, and 4.7% for the ankle-over-knee position. In extension, most hips (60.5%) were found to impinge at or prior to 50° of external rotation (pivoting). Many of these impingement events were due to a prominent ischium. The mean maximum external rotation prior to impingement was 45.9° (15° to 80°) and 57.9° (20° to 90°) prior to prosthetic impingement. No impingement was found in standing, sitting, crossing ankles, seiza, and downward dog.Conclusion: This study demonstrated that positions of daily living tested in a CT-based 3D model show high rates of impingement. Simulating additional positions through 3D modelling is a low-cost method of potentially improving outcomes without compromising patient safety. By incorporating CT-based 3D modelling of positions of daily living into routine preoperative protocols for THA, there is the potential to lower the risk of postoperative impingement events.Cite this article: Bone Jt Open 2023;4(6):416–423.

Background: Lateral locked plating remains an important treatment strategy for distal femoral fractures but has been associated with nonunion rates ranging from 6% to 20%. The objective of this study was to identify factors associated with nonunion following lateral locked plating of distal femoral fractures with use of a Bayesian analysis. Methods: All consecutive patients ≥18 years of age who were treated with lateral locked plating for a distal femoral fracture at 2 Level-I trauma centers between 2006 and 2024 and who had ≥3 months of follow-up were included. Multivariable Bayesian logistic regression analysis was performed to identify factors associated with nonunion, which was defined as a reoperation to promote healing, and the results are reported as odds ratios (ORs) with 95% credible intervals (CrIs). Probabilities of >95% were considered very strong evidence of an association with nonunion, and probabilities of 90% to 95% were considered strong evidence. Results: A total of 560 patients (median age, 68 years; 29% male; 90% White; 97% non-Hispanic; 41% with distal periprosthetic fractures) were included. Fifty-four patients (9.6%) underwent reoperation to promote healing. There was very strong evidence that multifragmentary comminution of the metaphysis (versus simple fracture: OR, 2.60; 95% CrI, 0.91 to 8.06), medial cortical comminution of >0 to 25 mm (versus 0 mm: OR, 3.11; 95% CrI, 1.35 to 7.48), and varus (lateral distal femoral angle [LDFA] of ≥84°: OR, 3.04; 95% CrI, 1.46 to 6.51) or valgus (LDFA of ≤78°: OR, 2.42; 95% CrI, 0.96 to 5.99) malalignment increased the odds of nonunion. A screw density of ≤0.60 proximal to the working length reduced the odds of nonunion (versus ≥0.81: OR, 0.40; 95% CrI, 0.16 to 0.95), although the size and certainty of this effect varied in the sensitivity analysis that utilized alternative thresholds. There was strong evidence that obesity increased the odds of nonunion (OR, 1.64; 95% CrI, 0.86 to 3.13) and that intact wedge fractures reduced the odds of nonunion (versus simple fracture: OR, 0.35; 95% CrI, 0.05 to 1.74). Conclusions: One in 10 patients developed nonunion and underwent reoperation to promote healing. Surgeons should restore coronal plane alignment and may consider augmenting fixation in the presence of multifragmentary comminution. Constructs in which all screw holes proximal to the working length are filled should be avoided, although the optimal configuration remains unclear and depends on other construct characteristics influencing biomechanics. Overall, the small to moderate effect sizes highlight the multifactorial etiology of nonunion following lateral locked plating of distal femoral fractures. Level of Evidence: Prognostic Level III . See Instructions for Authors for a complete description of levels of evidence.

OBJECTIVES: To determine the rate of and risk factors for reoperation to promote fracture union of periprosthetic distal femur fractures treated with lateral locked plating. METHODS: Design: Retrospective cohort study. Setting: Two level 1 trauma centers. Patient Selection Criteria: Adult patients undergoing operative treatment for a periprosthetic distal femur fracture (AO/OTA 33A or 33C) between 2006 and 2023 with a minimum follow-up of 3 months. Outcome Measures and Comparisons: Reoperation to promote fracture union compared across patient, fracture, and treatment characteristics. RESULTS: Two hundred and eighteen patients [mean age 72 years (range: 52–84), 77% women] were included. There were 133 (61%) Su type 2 fractures, 10 (4.6%) open injuries, and 118 (54%) fractures with multifragmentary comminution of the metaphysis. Twenty (9.2%) patients required reoperation to promote fracture union, including 15 (6.9%) patients who presented with nonunion with implant failure. In multivariable logistic regression analysis, body mass index [5-point increase; OR: 1.37 (95% CI, 1.00–1.86), P = 0.047], multifragmentary metaphyseal comminution [OR: 5.17 (95% CI, 1.47–18.3), P = 0.011], and varus malalignment [OR: 5.88 (95% CI, 1.29–26.8), P = 0.023] were associated with increased odds of reoperation for nonunion, whereas the use of titanium plates was protective [OR: 0.21 (95% CI, 0.07–0.63), P = 0.005]. CONCLUSIONS: In this study of 218 patients undergoing lateral locked plating for a periprosthetic distal femur fracture, 9 out of 10 patients did not undergo reoperation to promote fracture union. Factors associated with reoperation included increased body mass index, the presence of multifragmentary metaphyseal comminution, and varus malalignment with a lateral distal femoral angle of ≥84 degrees. The use of titanium plates was associated with decreased odds of reoperation although this finding should be interpreted in the context of varying plate designs and configurations. These results may help delineate indications for the selection of specific fixation constructs when treating periprosthetic distal femur fractures. LEVEL OF EVIDENCE: Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.