Tibial tuberosity-tibial intercondylar midpoint distance measured on computed tomography scanner is not biased during knee rotation and could be clinically more relevant than current measurement systems.

PURPOSE

The purpose of this retrospective cross-sectional case-control study was to evaluate an alternative imaging test for lateralization of the tibial tuberosity, unbiased towards knee rotation.

METHODS

On axial CT images of 129 knees, classified as cases (two or more patellar luxations) and controls (no patellar luxations), two raters gauged the standard tibial tuberosity-trochlear groove (TT-TG) distance, tibial tuberosity-femoral intercondylar midpoint (TT-FIM) distance, and new tibial tuberosity-tibial intercondylar midpoint (TT-TIM) distance singly, and knee longitudinal rotation angles (LRAs), and the presence of femoral trochlear dysplasia (FTD) jointly.

RESULTS

All imaging tests intercorrelated and discriminated between stability groups. TT-TIM had the lowest values with the highest precision. Though poorly, TT-TG and TT-FIM negatively correlated with age and LRAs regarding femur, but positively with presence of FTD, whereas TT-TIM was unbiased. The accuracy of TT-TG (> 20 mm), TT-FIM (> 20 mm), and TT-TIM (> 13 mm) was good with almost perfect reproducibility. Only TT-TIM was sex-biased (p = 0.009), with > 12 mm cut-off in females and (presumably) > 14 mm in males.

CONCLUSION

TT-TIM is an alternative imaging test for lateralization of the tibial tuberosity, unbiased towards knee rotation.