Correlations between intra and extraarticular factors measured by computed tomography in patients with recurrent patellar dislocation

Introduction: Lateral patellar dislocation (LPD) is a common injury of the knee, most frequent in young patients. It has a multifactorial etiology with several underlying risk factors. In most cases, patellar dislocation occurs on the lateral side, with the rupture of the medial patellofemoral ligament (MPFL), appearing in more than 80% of the cases. The tibial tuberosity-trochlear groove (TT-TG) distance of 20 mm or more in patients with lateral patellar dislocation is a gold standard for the surgical indication of tibial tubercle osteotomy (TTO).

Hypothesis: Our investigation aimed to establish whether there is a correlation between the TT-TG distance and other bony landmarks, like trochlear groove medialization, tibial tuberosity lateralization, and knee rotation angle, in the surgical algorithm for the patient with patellar dislocation.

Methods: We conducted a prospective study, analyzing and comparing data from two groups, 33 patients with a diagnosis of patellar dislocation, and a control group of 30 patients, with meniscal injury, but healthy contralateral limb. Using computed tomography, we measured the TT-TG distance, femoral anteversion, tibial torsion, knee rotation angle, tuberosity lateralization, and trochlear groove medialization of all the patients in our study. The measurements were conducted by two independent orthopedic surgeons in a randomized manner. Using an unpaired t test, we compared and analyzed each parameters value from the study and the control group.

Results: Comparing the two groups, we observed a significant difference for TT-TG distance, knee rotation angle and tibial tuberosity lateralization with higher values in the study group compared to the control group (CI 95% 6.44-9.72, CI 95% 8.64-10.39, CI 95% 3.77-5.46, respectively), with a p value < 0.0001 in all cases. Also, the TT-TG distance positively correlated with knee rotation angle (r=.97, p=0.01) and tibial tuberosity lateralization (r=.86, p=0.0001) in the study group.

Conclusions: The TT-TG distance measurement usually defines the lateralization of the tibial tuberosity; yet, in some cases, it can be caused by the trochlear groove medialization, or high rotation between the femur and tibia. Our study revealed that knee rotation and tuberosity lateralization were factors implicated in patellar dislocation and they should be taken into account when making the decision of tibial tubercle osteotomy.