François Boux de Casson

Background: Computer-assisted navigation (CAN) offers dynamic intraoperative guidance in total ankle arthroplasty (TAA). Although laboratory data suggest superior precision, in vivo evidence is lacking. This study used weightbearing computed tomography (WBCT) to evaluate CAN accuracy of postoperative TAA implant position relative to the plan. We hypothesized that absolute discrepancies would be <3 mm or <3°. Methods: Thirteen consecutive patients (November 2024–November 2025) underwent TAA using CAN. Preoperative computed tomography–based 3D models were used for templating. Postoperative WBCT scans were used to measure final implant seating, and computerized measurements were used to identify implant placement discrepancy. We analyzed absolute discrepancies between planned vs final postoperative positions. Results: Tibial absolute discrepancies were within desired limits for varus/valgus (1.65° ± 1.43°), slope (1.87° ± 1.34°), and cut height (0.68 ± 0.62 mm) but not for axial rotation (3.97 ± 2.64). For the talus, varus/valgus (2.93° ± 1.86°) and cut height (0.66 ± 0.71 mm) absolute discrepancies were within desired limits. The increased talar slope deviation (3.90 ± 2.89) in the final position may be due to non-navigated implant impaction. Conclusion: Although discrepancies persisted in tibial rotational alignment and talar positioning, the low variability across measurements suggests that CAN may support accurate implant positioning. These short-term positioning accuracy findings support the utility of CAN as a potential tool for enhancing implant positioning reproducibility in TAA. Level of Evidence: Level IV, case series.

The adoption of guidance technologies in total joint arthroplasty has expanded greatly in recent decades. This study aims to retrospectively evaluate the intra-operative performance of computer-assisted navigation (CAN) total shoulder arthroplasty (TSA) over years, analyzing temporal performance evolution and influencing factors. Over 40,000 cases utilizing a single CAN system (Exactech GPS) across an 8-year span were analyzed. We investigated the registration and navigation phases for anatomic (aTSA) and reverse (rTSA) procedures, focusing on factors influencing performance and temporal evolution. Data were stratified by surgeon volume, native anatomy, implant type, and procedural workflow. Key findings include: (1) Navigation times were longer for rTSA (mean 15:42 min) compared to aTSA (mean 10:01 min). (2) Glenoid retroversion > 20° and inferior inclination increased both registration and navigation durations for aTSA and rTSA. (3) Augmented implants extended navigation time for aTSA but not rTSA. (4) Surgeon experience significantly influenced performance; high-volume surgeons demonstrated markedly faster times, with a mean navigation time reduction of up to 7:16 min (aTSA) and 13:52 min (rTSA) compared to low-volume counterparts. (5) Registration time decreased over the years for all surgeon profiles, indicating system learning curves and increasing user familiarity. Additionally, repeated registration prolonged both registration and navigation phases, suggesting an impact on operator confidence or tracker visibility issues. Navigation performance trends over the years showed initial increases for aTSA due to added navigation steps but subsequent reductions for high- and medium-volume surgeons, underscoring the evolving efficiency of system use. The study highlights key factors influencing CAN efficiency and supports its potential to improve surgical accuracy and reduce variability, even among low-volume surgeons. This large-scale analysis underscores the utility of CAN in optimizing TSA workflows while identifying areas for potential improvement, particularly for complex anatomical cases.

Purpose Variability in the resting arm position may influence impingement-free range of motion (ROM) after reverse total shoulder arthroplasty (rTSA). The relationship between the neck-shaft angle (NSA) and arm position remains unclear. This study evaluated the humerothoracic angle (HTA) as a proxy for the resting arm position in the coronal plane, its variability and change after rTSA, and its associations with NSA. Methods This multicenter prospective study included 172 patients who underwent rTSA by nine surgeons. Standard radiographs were obtained preoperatively and at two years. Radiographic measurements of HTA and true NSA were blinded. Intraclass correlation coefficients (ICC) were calculated for HTA. Paired t-tests and ANOVA assessed group differences. Regression analyses evaluated predictors of postoperative HTA and HTA changes. Results Preoperative HTA (9.5° ± 8.6°) increased significantly to 13.2° ± 10.2° postoperatively (p < .001). NSA > 145° resulted in higher postoperative HTA than NSA < 135° (p < .0001). Multiple regression showed that NSA (β = 0.4; p < .0001) and preoperative HTA (β = 0.3; p = .0003) were strong predictors of postoperative HTA. Measurement reliability of HTA was excellent (intra-observer ICC = 0.92; inter-observer ICC = 0.89). Conclusion The resting arm position in the coronal plane, as quantified by HTA, exhibits significant variability pre- and post-rTSA, with a postoperative shift towards greater abduction. NSA strongly influenced the arm position, with larger NSAs being associated with more abducted arm positions. Consideration of how implant alignment and design affect the resting arm position may help refine preoperative planning and optimize impingement-free ROM after rTSA.

Background The aim of this study was to define the variability of the scapulohumeral position during preoperative Computed Tomography (CT) acquisition and to evaluate its influence on angular lateralization and distalization measurements. We hypothesized that the preoperative resting arm position, in terms of humeral abduction, flexion and internal rotation, would vary significantly between patients and that this variability would influence the lateralization (LSA) and distalization shoulder angle (DSA). Methods We analyzed a prospectively collected database of preoperative de-identified CT scans from a single Total Shoulder Arthroplasty (TSA) planning system (Equinoxe, Exactech GPS, Blue-Ortho), including all cases with scapular and humeral segmentation. Validated three-dimensional (3D) bone models were used to compute and automatically position scapular and humeral landmarks. These included: the superior glenoid tubercle; the most lateral border of the acromion and the most lateral border of the greater tuberosity. The position of the humerus relative to the scapula was automatically calculated, allowing the angles of abduction, flexion and internal rotation of the scapulohumeral joint to be assessed. Additionally, the potential relationship between the body mass index (BMI) and the resting arm position was assessed. Finally, LSA and DSA were calculated. A multiple linear regression analysis was performed to assess the relationship between the humeral position and the LSA and DSA. Results A total of 21,863 patients were included. Preoperative humeral positioning relative to the scapula showed a mean abduction of 10.3°±12.4 (-14.0°; 36.6°), mean flexion of 3.9°±8.9 (-16.0°; 26.1°) and mean internal rotation of 6.5°±18.9 (-41.4°; 48.9°). The preoperative median of LSA and DSA were 87.4°±14.3° and 43°±12.4, respectively. Among the independent variables, abduction showed the strongest negative correlation with LSA (β = -0.2998, p < 0.0001), followed by flexion (β = -0.04342, p < 0.0001). Internal rotation was positively correlated with LSA (β = 0.1229, p < 0.0001). For DSA, abduction had a weak positive influence (β = 0.04321, p < 0.0001), while flexion (β = −0.04302, p < 0.0001) and internal rotation (β = −0.04654, p < 0.0001) were negatively associated. Notably, a 10° variation in abduction, flexion or internal rotation led to a -3°, -0.4° and + 1.2° change in LSA, respectively, whereas DSA was minimally affected, with variations limited to + 0.4°, -0.4° and − 0.5°, respectively. Conclusion The resting arm position during preoperative CT scans varies significantly, potentially affecting the preoperative planning of TSA. The main findings of this study suggest that there exists a weak correlation between the initial scapulohumeral position and the LSA/DSA measurements. Level of evidence Level IV. Case series with no comparison group.

Purpose: Gap‐balanced total knee arthroplasty (TKA) technique relies on initial ligament evaluation, particularly in patient‐specific implantation using computer‐assisted technologies. This cadaveric study aimed to compare the reproducibility and reliability of medial and lateral gap measurements between manual stress testing and dynamic ligament balancer.Methods: Initial gap acquisitions were assessed from eight cadaveric knees (four specimens) during the same navigated TKA procedure by five differently skilled surgeons (three seniors and two juniors). Medial and lateral gaps were sequentially acquired from extension to maximum knee flexion, applying manual stress prior to any bone cuts (conventional technique), and using intra‐articular tensioning device placed between the tibial cut and the native femur (instrumented technique). Reproducibility was assessed using intraclass correlation coefficient (ICC), stratified by the measurement technique, the type of gaps and the operator experience. Differences in gaps (mm) between techniques were assessed using the Bland and Altmann method.Results: The instrumented technique showed higher ICCs than the conventional technique for medial and lateral gaps (0.87 vs. 0.60, P = 0.002, and 0.92 vs. 0.25, p < 0.0001, respectively), and showed no difference in ICCs between medial and lateral gap acquisitions (0.87 vs. 0.92, p = 0.8). Senior surgeons achieved higher ICCs than juniors, while non‐significant with both techniques. Differences in gaps between techniques increased with knee flexion angle (0.8, 2.8 and 3.5 mm at 10°, 45° and 90° of flexion angle, respectively) and decreased with the operator experience (p = 0.003).Conclusion: The instrumented balancing technique offered better reproducibility than using manual valgus and varus stress, when measuring medial and lateral gaps. Tensioning devices may play a significant role in enhancing initial gap acquisition, disregarding the flexion angle and the operator experience.Level of Evidence: Level IV (observational study involving cadaveric specimens).