A plain radiography may underestimate the steep posterior tibial slope of the medial condyle in elderly Japanese with varus knee osteoarthritis undergoing arthroplasties

Abstract

Purpose: Understanding the native posterior tibial slope (PTS) is important especially in cruciate ligament retaining total knee arthroplasty (TKA) and uni-compartmental knee arthroplasty (UKA). This study investigated the efficacy of PTS with lateral knee radiograph (radiographic PTS) by comparing it with PTS of medial and lateral tibial condyles (MPTS and LPTS) by computed tomography (CT). Methods: In patients who underwent TKA and UKA on varus knee osteoarthritis, radiographic PTS, MPTS, and LPTS were measured. Spearman's correlation was used to compare the radiographic PTS and PTS on CT. More than 3° delta PTS (CT PTS - radiographic PTS) were defined as positive outliers. Results: Three-hundred and twenty-six osteoarthritic knees (278 TKAs and 48 UKAs) were evaluated. The mean radiographic PTS, MPTS, LPTS was 8.0 ​± ​2.9°, 10.2 ​± ​4.2°, and 8.3 ​± ​3.3°, respectively. Plain radiograph tended to underestimate steep MPTS, and its correlations to LPTS (ρ ​= ​0.65, p ​< ​0.001) and MPTS (ρ ​= ​0.54, p ​< ​0.001) were moderate. The positive outliers were observed in 136/326 (42%) and 36/326 (12%) knees in medial and lateral condyles, respectively. Even in UKA, the positive outliers were observed in 13/48 (28%) knees in medial condyle. Conclusions: Radiographic PTS better reproduced LPTS, but did not accurately reproduce MPTS in varus knee osteoarthritis. Radiographic PTS may not detect steep medial PTS. Surgeons should be cautious because the actual PTS of the medial tibial condyle may be different from that preoperatively measured on plain radiographs.

Keywords

• Knee
• Osteoarthritis
• Radiography
• Computed tomography
• Posterior tibial slope
• Arthroplasty