Association between tibiofemoral rotation and patellofemoral alignment before and after surgical realignment for lateral patellar instability
Sebastian Schmidt, Abd El Nasser Oudeh, Emmanouil Liodakis, Felix Zimmermann, Peter BalcarekAbstract
Purpose
To evaluate the relationship between tibiofemoral rotation (TFR) and patellofemoral alignment parameters before and after surgical stabilisation for patellar instability and to determine whether correction of extensor mechanism (apparatus) alignment is associated with a reduction in TFR.
Methods
A total of 141 patients (99 females; mean age 24.5 ± 8.2 years) treated for recurrent patellar instability were included. Medial patellofemoral ligament reconstruction and thin‐flap trochleoplasty were performed, with tibial tubercle osteotomy (TTO) added when indicated. Pre and postoperative parameters, including trochlear bump, patellar tendon–trochlear groove angle (PT‐TGA), sagittal tibial tubercle–trochlear groove distance (sTTTG), tibial tubercle–trochlear groove distance (TT‐TG), lateral trochlear inclination (LTI), bisect offset and Caton‐Deschamps index (CDI), were assessed alongside TFR. Associations were analysed using Pearson/Spearman coefficients and multivariable linear regression models. Intra and interobserver reliability were assessed using intraclass correlation coefficients (ICC).
Results
Significant postoperative improvements were observed across all alignment parameters ( p < 0.001). The largest reductions were recorded for trochlear bump (−3.74 mm), PT‐TGA (−10.02°) and sTTTG (−4.57 mm). TFR also decreased significantly (−1.55°, 95% CI: 0.86–2.23°, p < 0.001). Preoperatively, TFR was most strongly correlated with PT‐TGA ( r = 0.52) and bisect offset ( r = 0.445), while no associations with trochlear bump or CDI were found. Postoperatively, TFR remained associated with PT‐TGA ( r = 0.305), sTTTG ( r = 0.258) and bisect offset ( r = 0.237). Changes in TFR (Δ TFR) were primarily correlated with PT‐TGA (Δ PT‐TGA) and bisect offset (Δ bisect offset). In multivariable models, PT‐TGA was identified as the sole independent predictor of preoperative TFR ( β = 0.33) and Δ TFR ( β = 0.376). Postoperatively, TFR was independently predicted by PT‐TGA ( β = 0.289), sTTTG ( β = 0.247) and CDI ( β = −0.225). Intraobserver reliability was excellent (ICC: 0.947–0.992) and interobserver reliability was good to excellent (ICC: 0.877–0.956).
Conclusion
TFR was significantly associated with axial patellofemoral alignment, most consistently with PT‐TGA and decreased significantly following surgical realignment of the extensor mechanism, although rotation was not addressed directly. The parallel changes in TFR and PT‐TGA indicate that rotational alignment is related to extensor mechanism alignment and should be interpreted in conjunction with it rather than as an isolated, fixed parameter.
Level of Evidence
Level IV.