Tibial tubercle-Roman arch (TT-RA) distance is superior to tibial tubercle-trochlear groove (TT-TG) distance when evaluating coronal malalignment in patients with knee osteoarthritis

Abstract

Objectives: To verify tibial tubercle-Roman arch (TT-RA) distance is superior to tibial tubercle-trochlear groove (TT-TG) distance in preoperative assessment of patellofemoral joints in patients with knee osteoarthritis.

Methods: Patients with knee osteoarthritis from 2016 to 2020 were considered eligible for inclusion in this study. We divided the patients into valgus group and varus group and did 1:1 matching for the two groups. We measured the TT-TG distance, TT-RA distance, patellar height, patella tilt, hip-knee-ankle (HKA) angle, and Iwano's classification of patellofemoral osteoarthritis (PFOA) by computed tomography images or radiographs. The intraclass correlation coefficient (ICC) of each measurement, the correlations and differences among the parameters, and binary logistic regression analysis were conducted.

Results: Each group in this study included 75 knees. The inter-observer and intra-observer reliability of the TT-TG distance decreased with the increasing degree of PFOA (ICC < 0.75). The reliability of the TT-RA distance showed excellent agreement in different stages of Iwano's classification. The HKA angle was poorly correlated with the TT-TG distance (r = 0.34, p = 0.003) and the TT-RA distance (r = 0.39, p = 0.001) in valgus knees. As the HKA angle increased by 1 degree, the TT-TG and TT-RA distance increased by nearly 0.45 mm and 0.61 mm, respectively. Valgus malalignment and severe PFOA revealed significant ORs of 3.26 (95% CI [1.06-10.03], p = 0.036) and 3.10 (95% CI [1.01-9.54], p = 0.048) with regard to pathological TT-RA distance, respectively.

Conclusion: The TT-RA distance was more reliable than the TT-TG distance in patients with knee osteoarthritis. Valgus malalignment and severe PFOA were risk factors for pathological TT-RA distance.

Key points: • The TT-RA distance is a reliable and repeatable alternative to the TT-TG distance in evaluating coronal malalignment, especially in patients with severe PFOA. • We validated the significant relationships between TT-TG distance or TT-RA distance and HKA angle in valgus knees, while the correlations among such parameters were not significant in varus knees. • Pathological lateralization of the tibial tubercle was prone to be traced in patients with valgus malalignment or severe PFOA, which could contribute to the patellofemoral malalignment.

Keywords: Anthropometry; Knee; Osteoarthritis; Patellofemoral joint.