Axial orientation of the femoral trochlea is superior to femoral anteversion for predicting patellar instability

Abstract

PurposeThe femoral anteversion angle is considered to be the same as femoral torsion; however, the femoral anteversion angle is strongly inluenced by the femoral posterior condylar morphology. It remains unclear whether the femoral anteversion angle and axial orientation of the femoral trochlea can predict patellar instability. This study aimed to redeine the femoral inherent torsion, verify whether the femoral anteversion angle relects the femoral inherent torsion, and compare the validity and calculate the cut-of values of the femoral anteversion angle and femoral trochlear axial orientation for predicting patellar instability. Methods Seventy-three patients with patellar instability and 73 matched controls underwent computed tomography to measure the femoral anteversion angle, femoral inherent torsion, and femoral trochlear axial orientation. Pearson's product moment correlation coeicients and linear regression were calculated to determine correlations between measurements. Receiver operating characteristic curves and nomograms were plotted to evaluate the predictive validity of the femoral anteversion angle and femoral trochlear axial orientation for patellar instability. Results All measurements showed excellent intra-and inter-observer reliability. Compared with the control group, the patellar instability group had a signiicantly larger femoral anteversion angle (25.4 ± 6.4° vs. 20.2 ± 4.5°) and femoral inherent torsion (18.3 ± 6.7° vs. 15.8 ± 3.4°), and signiicantly smaller femoral trochlear axial orientation (58.1 ± 7.3° vs. 66.9 ± 5.1°). The femoral anteversion angle and femoral trochlear axial orientation had area under the receiver operating characteristic curve values of 79 and 84%, respectively, and cut-of values of 24.5° and 62.7°, respectively. The calibration curve and decision curve analysis showed that the femoral trochlear axial orientation performed better than the femoral anteversion angle in predicting patellar instability. There was a strong correlation between the femoral anteversion angle and femoral inherent torsion (r > 0.8). Linear regression analysis of the femoral inherent torsion with the femoral anteversion angle as the prediction variate showed moderate goodness-of-it (adjusted R 2 = 0.69). ConclusionThe femoral anteversion angle moderately relects the femoral inherent torsion. The femoral trochlear axial orientation is better than the femoral anteversion in predicting patellar instability in terms of predictive eiciency, consistency with reality, and net clinical beneit. These indings warn orthopaedists against overstating the role of the femoral anteversion angle in patellar instability, and suggest that the femoral trochlear axial orientation could aid in identifying at-risk patients and developing surgical strategies for patellar instability. Level of evidence III. KeywordsPatellar instability • Femoral anteversion • Femoral inherent torsion • Axial orientation of the femoral trochlea * Fei Wang

Decreased femoral trochlea axial orientation corrected by derotational distal femur osteotomy in patients with patellar dislocation yields satisfactory outcomes

“…Our findings resembled Chen et al's [4] previously established study that the TAO was better for predicting patellar dislocation than the FAA, and the cut-off value was 62.7°, demonstrating that the pathological threshold is reproducible and reliable. Moreover, in our study, a TAO value of 62.7°exhibited substantial sensitivity (0.531) and specificity (0.891).…”

“…The TAO is defined as the angle between the femoral neck axis and the angular bisector line of the femoral trochlear groove. The method of measuring the TAO was described by Chen et al [4]. The axis of the femoral neck is the line drawn through the center of the femoral head and the middle of the femoral neck at the level where the femoral head center, femoral neck and most cephalic junction of the greater trochanter could be connected.…”

“…Therefore, the ability to predict patellar dislocation using the FAA is affected by the variation of the femoral posterior condyle [2]. Chen et al [4] proposed a new measurement named the axial orientation of the femoral trochlea (TAO), which is superior to FAA in predictions of patellar dislocation. The TAO is unaffected by variation of the posterior condyle of the femur and truly indicates the internal torsion of the femoral trochlear groove.…”