Measuring Parallelism to the Ground in Bipedal Stance Phase: Mechanical Versus Kinematic Alignment in Total Knee Arthroplasty

Malaak Hamzeh; Kaelyn Gwynne; Brian J Panish; Bradley Gelfand; Evan Argintar

doi:10.7759/cureus.55173

Measuring Parallelism to the Ground in Bipedal Stance Phase: Mechanical Versus Kinematic Alignment in Total Knee Arthroplasty

Cureus. 2024 Feb 28;16(2):e55173. doi: 10.7759/cureus.55173. eCollection 2024 Feb.

Authors

Malaak Hamzeh¹, Kaelyn Gwynne¹, Brian J Panish¹, Bradley Gelfand², Evan Argintar³

Affiliations

¹ Orthopaedic Surgery, Georgetown University School of Medicine, Washington, DC, USA.
² Orthopaedic Surgery, MedStar Georgetown University Hospital, Washington, DC, USA.
³ Orthopaedic Surgery, MedStar Washington Hospital Center, Washington, DC, USA.

Abstract

Introduction The goal of total knee arthroplasty is to replace diseased cartilage and bone with an artificial implant to improve the patient's quality of life. The knee has historically been reconstructed to the patient's mechanical axis (MA). However, kinematically aligned techniques have been increasingly used. Kinematic alignment requires less soft-tissue resection and aligns the knee with what is anatomically natural to the patient, while there is concern that kinematically aligned knees will lead to earlier failure due to potential unequal weight distribution on the implant. The purpose of this study is to compare the parallelism from the floor of the joint-line cuts using kinematic and mechanical alignment and understand if the MA is a proper estimation of the tibial-ankle axis (TA). Methods A retrospective study was conducted by recruiting all high tibial osteotomy and distal femoral osteotomy recipients operated on by two surgeons in two MedStar Health hospitals from 01/2013 to 07/2020 with full-length films in preparation for restorative procedures. Baseline osteoarthritis was graded using the Kellgren-Lawrence classification system with all patients presenting as Grade 0. The TA and the joint-line orientations of the MA and kinematic axis (KA) were measured on 66 legs. The average distance from parallelism to the ground was compared between the MA and the KA and between the MA and the TA using a paired t-test. Results KA joint-line orientation (1.705° deviation) was more parallel to the floor in the bipedal stance phase than the MA (2.316° deviation, p=0.0156). The MA (2.316° deviation) was not a proper estimation of the TA (4.278° deviation, p=0.0001). Conclusion By utilizing the KA technique, the restoration of the natural joint line, as well as a joint that is more parallel to the floor in the stance phase compared to the MA, is achieved. The parallelism to the ground of the KA during the bipedal stance phase suggests an even load distribution across the knee. In addition, due to its similarity to the KA and anatomical significance in weight-bearing distribution, further investigation into the hip-to-calcaneal axis as an approximation of the joint line is warranted.

Keywords: bipedal stance phase; joint line; kinematic alignment; kinematic axis; kinematically aligned total knee arthroplasty; knee arthroplasty; parallelism; tibial-ankle axis; total knee replacement (tkr); weight bearing.