Summary

Quantifying and mapping osteoarthritic cartilage wear can enable improved accuracy in component placement during matched resection and lead to a better understanding of the biomechanical factors that influence the progression of OA.

Abstract

Introduction

Osteoarthritis (OA) is a degenerative disease characterised by cartilage wear. The gold-standard treatment for end-stage knee OA is total knee arthroplasty (TKA). Although preferential cartilage degradation in one compartment of the knee is well established, the discrepancy in wear between compartments and the pattern of wear within the degrading compartment are not well understood. This study aims to quantify average compartmental cartilage thicknesses & compare them with Howell’s assumptions for matched resection [1] as well as identifying trends in sub-compartmental cartilage degradation.

Method

Ethics approval to conduct this study was obtained from the NSW Government's Ethics Review Committee. Recruitment was conducted for every patient receiving a TKA from a single surgeon at the same hospital from the July 2017 to January 2018. 23 TKA recipients (2 bilaterals; 25 knees; all varus; 18 left & 7 right) with an average age of 68 were included in this study. Bone resections were collected following surgery and scanned using a 3D laser-scanner to generate a mesh of the cartilage surface. The cartilage was then dissolved using corrosive chemicals and a second scan was taken of the bony surface. The bony mesh was then digitally subtracted from the cartilage mesh to obtain a 3D representation of the patient’s cartilage thickness profile. Condylar apex & tibial well landmarks were used to divide medial & lateral compartments into anterior & posterior sub-regions. Welch two sample t-tests were performed to determine the significance of compartmental & sub-compartmental thickness variation.

Results

The average lateral and medial compartmental thicknesses were 1.93 mm (± 0.58) & 1.09 mm (± 0.56) for the tibia, 1.64 mm (± 0.45) & 0.64 mm (± 0.44) for the distal femur and 1.63 mm (± 0.51) & 1.61 mm (± 0.53) for the posterior femur. Lateral and medial cartilage thicknesses were significantly different for the tibia (p < 0.001) & distal femur (p < 0.001) but not the posterior femur.

Significantly greater wear was found in the anterior subregion of the medial tibial compartment (p = 0.033), the posterior subregion of the medial distal femoral condyle (p = 0.002) and the inferior subregion of the medial posterior femoral condyle (p < 0.001). There was no significant difference between subregional thickness in the lateral compartments of each resection.

Discussion

The average cartilage thicknesses identified in this study do not support Howell’s cartilage wear assumptions for matched resection. Where Howell proposed 1 & 2 mm cartilage discrepancies between compartments of the posterior & distal femoral condyles, respectively, this study indicates no difference between posterior condyles and only 1 mm difference between distal femoral condyles. When examining subregional cartilage variation it is evident that for a varus population cartilage wear is greatest in the anterior region of the tibia & the posterior region of the distal femur. These results could lead to improved accuracy in matched resection and a better understanding of how biomechanical factors influence the progression of cartilage degeneration in OA sufferers.

[1] S. Howell, M. Hull, and M. Mahfouz, “Kinematic alignment in total knee arthroplasty,” Insa. Scott Surg. Knee, pp. 1255–1268, 2012.