Trochlear Dysplasia Is Associated With Increased Sagittal Tibial Tubercle Trochlear-Groove Distance in Patients With Patellar Instability.

ABSTRACT

PURPOSE: To compare the sagittal position of the tibial tubercle in relation the trochlea groove in patients with and without trochlear dysplasia (TD). Patients with high-grade TD show a significantly increased sagittal position of the tibial tubercle in relation to the trochlear groove (sTTTG) compared with patients without TD. This may affect patellofemoral loading and contribute to the increased prevalence of cartilage lesions seen in the patellofemoral joint of patients with dysplasia of the trochlear groove. METHODS: All patients between January 2017 and December 2020 with high-grade TD (Dejour type B, C, and D) who underwent patellar-stabilizing surgery for patellar instability at a single institution were included in the current study. Patients without preoperative magnetic resonance imaging (MRI), any previous osteotomy on the affected lower extremity, or cruciate ligament insufficiency were excluded. Patients who underwent knee arthroscopy for meniscal repair/debridement without any signs of TD or any of the aforementioned criteria served as the control group. Preoperative MRI was retrospectively assessed to compare common patellofemoral anatomic parameters including patellar angle, patellar tilt, patella morphology according to Wiberg, Caton-Deschamps index, PF index, trochlear sulcus angle, sulcus depth, lateral inclination angle of the trochlea, tibiofemoral rotation, TTTG, and sTTTG distance between both groups. The sTTTG is measured as the distance between the nadir point of the cartilaginous trochlear groove and the most anterior point of the tibial tubercle on an axial MRI. Independent predictors for the sTTTG were assessed for patients with TD. RESULTS: Patients with high-grade TD (n = 82) showed an increased patellar tilt, Caton-Deschamps index, trochlear sulcus angle, lateral tibiofemoral rotation angle, TTTG, and sTTTG (9.16 ± 4.47 mm vs 2.66 ± 4.21 mm) compared with the control group (n = 83) (P < .001). Patellar angle, PF index, sulcus depth, and lateral inclination angle of the trochlear were significantly decreased in the TD group (P < .001). The sTTTG was similar in all TD groups (n.s.). Among patients with TD, both tibiofemoral rotation and patellar height were independent predictors of the sTTTG (P < .05). CONCLUSIONS: Patients with high-grade TD show not only abnormal values in common patellofemoral instability risk factors but also a significantly increased sTTTG compared with patients without TD. LEVEL OF EVIDENCE Level III, retrospective case comparative study.