Comparison of the Tibial Posterior Slope Angle Between the Tibial Mechanical Axis and Various Diaphyseal Tibial Axes After Total Knee Arthroplasty

Yoshinori Ishii; Hideo Noguchi; Junko Sato; Ikuko Takahashi; Hana Ishii; Ryo Ishii; Kei Ishii; Shin-Ichi Toyabe

doi:10.1016/j.artd.2022.06.015

Comparison of the Tibial Posterior Slope Angle Between the Tibial Mechanical Axis and Various Diaphyseal Tibial Axes After Total Knee Arthroplasty

Arthroplast Today. 2022 Sep 19:17:137-141. doi: 10.1016/j.artd.2022.06.015. eCollection 2022 Oct.

Authors

Yoshinori Ishii¹, Hideo Noguchi¹, Junko Sato¹, Ikuko Takahashi¹, Hana Ishii², Ryo Ishii³, Kei Ishii⁴, Shin-Ichi Toyabe⁵

Affiliations

¹ Ishii Orthopaedic & Rehabilitation Clinic, Gyoda, Saitama, Japan.
² Kanazawa Medical University, School of Plastic Surgery, Ishikawa, Japan.
³ Shinshu University Hospital, Nagano, Japan.
⁴ Iwate Prefectural Ninohe Hospital, Ninohe, Iwate, Japan.
⁵ Niigata University Crisis Management Office, Niigata University Hospital, Niigata University Graduate School of Medical and Dental Sciences, Niigata, Japan.

Abstract

Background: The posterior tibial slope angle (PTS) is crucial for sagittal alignment after total knee arthroplasty (TKA). This study aimed to determine which PTS based on the lateral view of standard knee radiographs (LSKRs; 36 × 43 cm) reflects the PTS based on a full-length lateral tibial radiograph (FLTR).

Methods: A total of 290 patients (355 knees) who underwent primary TKA were retrospectively recruited. Cross-sectional views from the 3-dimensional digital model of the tibial prosthesis and bone complex in the sagittal plane were used as FLTRs and LSKRs. Considering the region 21.5 cm proximal to the site of FLTR as the spot for LSKR to determine the 5 tibial diaphyseal axes, the axis that simulates the PTS as determined by the tibial mechanical axis between the center of the tibial component and the ankle plafond in LSKR was determined and compared.

Results: PTS (α₅) defined by the line connecting the midpoints of tibial width between the region 10-cm distal to the knee joint and the distal end of the tibia based on LSKR revealed the least mean difference (0.13° ± 1.00°) and the strongest correlation (P < .001, r = 0.948) with PTS based on FLTR (α₀). The number of knees in α₅, indicating a difference of <2° from α₀, was 333 of 355 (93.8%). The equivalence test results indicated that α₀ and α₅ were statistically equivalent within a difference of 2° (P < .001).

Conclusions: PTS (α₅) can be used as a clinically reliable substitution of the true PTS on an FLTR for evaluating sagittal alignment after TKA.

Keywords: Posterior tibial slope; Total knee arthroplasty; diaphyseal axis; full-length lateral tibial radiograph; lateral view of standard knee radiograph; mechanical axis.