Lateral Tibial Slope Should Be Considered When Planning Medial Unicompartmental Knee Arthroplasty

The purpose of this study was to evaluate the effects of medial tibial slope (MPTS) and lateral tibial slope (LPTS) on clinical scores and range of motion (ROM) after unicompartmental knee arthroplasty (UKA).

A total of one hundred eighty-two patients with medial compartment osteoarthritis, treated by UKA between January 2011 and May 2017, were retrospectively evaluated. Postoperative MPTS and LPTS were measured using computed tomography (CT). Patients were categorized into four groups based on MPTS and LPTS values: Group 1 had MPTS and LPTS>5°; Group 2 had MPTS>5°, LPTS<5°; Group 3 had MPTS<5°, LPTS>5°; and Group 4 had MPTS and LPTS<5°. Preoperative and postoperative Knee Society Score (KSS) and ROM were compared.

The mean age of the patients was 64.3±5.2 years (range: 52-78) and the mean body mass index (BMI) was 26±1.6 kg/m² (range: 22-29.6). There were no significant differences between the groups regarding age, BMI, follow-up period, and gender (p=0.402, p=0.076, p=0.712 and p=0.787, respectively). The postoperative KSS scores and postoperative maximum flexion in patients with both MPTS and LPTS>5° were significantly higher compared to the other groups (p<0.001 for both).

Sagittal alignment should not be overlooked in UKA. Unlike previous studies that evaluated only MPTS using a lateral radiograph and ignored LPTS, this study demonstrated that LPTS affects postoperative ROM and clinical scores. Therefore, defining MPTS along with LPTS is recommended.