The Anterior-posterior Distance Between the Tibial Tuberosity and Trochlear Groove

OBJECTIVES: Tibial tuberosity osteotomy is often performed to correct excessive lateralization of the tuberosity in patients with patellar instability. An anteriorizing component has been recommended in the setting of chondral pathology, yet the ideal anterior-posterior relationship of the tibial tuberosity to the trochlear groove is unknown. METHODS: Patients with symptomatic patellar instability underwent static CT imaging, and were compared to age- and gender-matched controls. All knees were imaged in full extension. Tibial-tuberosity-trochlear-groove (TTTG) distance was measured to quantify lateralization of the tuberosity, as well as the anterior-posterior distance between these two points (APTTTG distance). Lateral trochlear inclination (LTI), sulcus angle (SA) and trochlear depth (TD) were measured as indicators of trochlear dysplasia. Measurements were compared between the symptomatic and control groups using paired t-tests. Correlations between APTTTG with LTI, SA and TD were assessed using linear regression analyses. RESULTS: 22 knees in 18 patients with symptomatic patellar instability were included in the study group, with 22 control knees. TTTG and APTTTG distances were 19.9 mm and 8.3 mm in the symptomatic group, versus 16.8 mm and -0.5 mm in the control group, with a difference of 3.1 mm (p=0.002) and 8.8 mm (p<0.0001) respectively. The symptomatic group displayed greater trochlear dysplasia with lower LTI (13.0° vs 21.9°, p<0.0001), higher SA (152.7° vs 137.7°, p<0.0001) and lower TD (1.3mm vs 6.0mm, p<0.0001). There was strong correlation between APTTTG and TD (r=0.62, R2=0.39, p<0.0001). CONCLUSION: Our findings demonstrate that the trochlear groove is almost 9mm more anterior to the tibial tuberosity in patients with symptomatic instability, and this distance correlates with measurements of trochlear dysplasia. While further studies are needed to determine the relationship between APTTTG distance and patellar instability, these findings suggest that the anterior-posterior relationship between the trochlea and tuberosity may be a factor to consider when planning for tibial tuberosity osteotomy in patients with trochlear dysplasia.