Background Postoperative changes in coronal plane alignment of the knee (CPAK) phenotype have been reported after total knee arthroplasty (TKA). This study investigated whether estimated CPAK phenotype transitions, including their magnitude and direction, were associated with patient-reported outcome measures (PROMs) after imageless ROSA-assisted TKA. We hypothesised that more extensive phenotype transitions would be associated with worse postoperative PROMs. Methods This retrospective single-surgeon study included 231 patients who underwent imageless ROSA-assisted TKA between January 2022 and May 2024. Estimated CPAK phenotypes were derived from short weight-bearing knee radiographs. Patients were classified by postoperative estimated CPAK transition status and further categorised into minor or major change groups by transition magnitude. Exploratory analyses evaluated row and column changes. Outcomes at final follow up (mean 15.7 months) included the Forgotten Joint Score (FJS), Western Ontario and McMaster Universities Osteoarthritis Index, and Visual Analogue Scale. Results Estimated CPAK phenotype transition occurred in 193/231 patients (83.5%); FJS was 76.8 ± 19.9 in patients with transition and 78.3 ± 16.9 without transition (mean difference −1.42 points, 95% confidence interval −7.19 to 4.61; P = 0.758). No significant PROM differences were detected according to transition magnitude or direction. In multivariable analysis, neither minor nor major change was independently associated with FJS. Conclusion Estimated CPAK phenotype transitions were frequent after imageless ROSA-assisted TKA, but their presence, magnitude and direction were not significantly associated with worse short-term PROMs. Preservation of the estimated preoperative CPAK phenotype may not be necessary for satisfactory short-term outcomes, although confirmation using direct full-length alignment measurements is required.
Background Medial stabilized (MS) inserts have been introduced to improve knee kinematics and mid-flexion stability in total knee arthroplasty (TKA). However, direct comparisons between MS and cruciate-retaining (CR) designs are often confounded by patient-related factors. Purpose To compare postoperative knee flexion between MS and CR designs using a prediction model-based counterfactual framework. Methods This retrospective two-phase study included patients who underwent primary TKA at a single institution. In Phase 1, a multivariable regression model was developed using 129 CR-TKA cases to predict 1-year postoperative knee flexion based on preoperative and intraoperative variables. Internal validation was performed using 10-fold cross-validation, and model performance and calibration were assessed using out-of-fold predictions. In Phase 2, the validated model was applied to MS-TKA cases to estimate the postoperative flexion expected under a hypothetical CR condition. Predicted CR flexion and observed MS flexion were compared using paired t-tests. Results In the CR cohort (n = 129), the mean difference between predicted and observed postoperative flexion was 0.07° (95% confidence interval (CI), −1.5 to 1.7°; P = 0.996). Ten-fold cross-validation demonstrated moderate predictive performance (R2 = 0.218, mean absolute error = 7.78°, root mean squared error = 9.84°). In the MS cohort (n = 24), observed postoperative flexion (120.0 ± 10.5°) did not differ significantly from the predicted CR flexion (122.5 ± 6.5°), with a mean paired difference of −2.43° (95% CI, −6.59 to 1.73°; P = 0.239). Conclusion The CR-based prediction model demonstrated moderate internal predictive performance within the study cohort. Within the limitations of this exploratory analysis, no statistically significant difference in postoperative knee flexion was detected between observed MS-TKA outcomes and the flexion predicted under hypothetical CR conditions. Larger externally validated studies with adequate statistical power are required before definitive conclusions regarding implant-specific differences can be drawn.
Background To evaluate the test–retest reliability and validity of My Jump Lab compared with a force platform for assessing vertical jump performance after anterior cruciate ligament reconstruction (ACLR). Methods A total of 102 individuals, 6–24 months post-ACLR and cleared for return-to-sport (RTS) testing, performed the single-leg vertical jump (SLVJ) and single-leg drop jump (SLDJ), assessed using My Jump Lab and a force platform. Jump height derived from flight time (FT) and take-off velocity (ToV), reactive strength index (RSI) and limb symmetry index (LSI) were analyzed. Test–retest reliability, inter-instrument reliability, agreement and association, diagnostic accuracy, and association with force-platform-derived kinetic (force at zero velocity, peak landing force, and concentric net impulse) variables were assessed. Results My Jump Lab demonstrated excellent test–retest reliability (intraclass correlation coefficient (ICC) = 0.992–0.997; standard error of measurement = 0.24–0.41 cm; minimal detectable change = 0.65–1.14 cm). Associations with the force platform were strong to very strong for jump height (r = 0.786–0.987), RSI (r = 0.975), and LSI (r = 0.760–0.983). Inter-instrument reliability was excellent for FT and RSI (ICC = 0.974–0.983) and fair for ToV (ICC = 0.750). Bland–Altman analyses showed mean biases ranging from −1.21 to −0.08 cm for jump height and −0.29 cm/s for RSI. Accuracy for LSI ≥ 90% ranged from 87.3% to 94.1%. SLVJ jump height showed moderate-to-good associations with force-platform-derived kinetic (r = 0.534–0.678). Conclusions My Jump Lab provides reliable and valid measures of vertical jump performance post-ACLR and may complement RTS assessment when force platforms are unavailable.
Background Heel strike transient (HST), an abrupt increase in vertical ground reaction force (vGRF) following heel strike (HS), has been reported in patients after total knee arthroplasty (TKA). However, the contribution of swing-to-stance tibiofemoral kinematics to HST remains unclear. This study examined the relationship between tibiofemoral kinematics during this transition and HST after TKA. Methods Seventeen patients who underwent TKA were analyzed using force plate measurements and validated 2D/3D registration. Tibiofemoral kinematics, including knee flexion angle, rotation, and anteroposterior (AP) translation, were calculated immediately before and after HS. HST was defined when post-HS vGRF did not rise gradually but showed a distinct transient peak with a peak-to-subsequent-minimum ratio of ≥1.2. Results Patients were classified into the HST group (n = 8) and non-HST group (n = 9) according to the presence of HST. Two-way analysis of variance revealed a significant interaction between group and gait phase for flexion angle (P < 0.01). Post-hoc analysis revealed a significant decrease in flexion angle after HS (P < 0.01) in the HST group. For lateral AP translation, a significant main effect of group was observed (P = 0.036). No significant group-related differences were found in internal/external rotation or medial AP translation. Conclusions Compared with the non-HST group, the HST group showed a greater extension-directed change in flexion angle and a more anterior position of the lateral contact point across the before- and after-HS. These findings suggest that HST is associated with a distinct tibiofemoral kinematic pattern during the terminal swing-to-early stance transition.
