Tibial tubercle–trochlear groove distance and angle are higher in children with patellar instability

Abstract

Abstract Purpose The purpose of this study was to assess the variations in tibial tubercle–trochlear groove distance and angle as a function of age and gender in a population of children without patellar instability (PI) compared with those with PI. Methods A retrospective review of 869 children’s knee MRIs, ages 5 to 15 years, were evaluated using a control group (792 children) without evidence of PI and a group with PI (77 children). Tibial tubercle–trochlear groove distance (TT–TGd) and angle (TT–TGa) were measured twice by two readers to assess intra‐ and inter‐observer reliability and compared between PI and control groups. In both groups, functions of age and gender on TT–TGd and TT–TGa values were evaluated. Results Both TT–TGd and TT–TGa measurements showed excellent intra‐ and inter‐observer reliability. The mean TT–TGd for the PI group was 17.2 mm (SD 6.6) and significantly higher than the mean TT–TGd for the control group (10.4 SD 3.8 mm, P = 0.001). The mean TT–TGa for the PI was 20.8° (SD 8.3°), which was also significantly higher than the mean TT–TGa for the control group (12.5° SD 4.6°, P < 0.001). Control group revealed a positive correlation between age and TT–TGd measurements ( r = 0.243, P < 0.001). The mean TT–TGa for girls (13.3° SD 4.7°) was higher than the mean TT–TGa for boys (11.9° SD 4.4°) in the control group ( P < 0.001). Conclusion TT–TGa and TT–TGd are reliable and can be used for the evaluation of the extansor mechanism alignment in children with and without PI. However, it must be considered that TT–TGd is increasing in growing patients. Soft‐tissue procedures may be prone to failure, since bony procedures for patellar alignment cannot be done until skeletal maturity. Level of evidence III.