Assessing the accuracy of presumptive distal femoral cuts in the conduct of conventional total knee replacement in Kenyan patients with end stage osteoarthritis of the knee

Abstract

Background: Total Knee Replacements in our setting are performed using conventional techniques. This involves use of an  intramedullary rod and jig to perform the Distal Femoral Cut (DFC). Ideally the magnitude of the Valgus Correction Angle (VCA) used to perform the DFC should equal the angle subtended by the femoral anatomical and mechanical axes at the knee. This relationship can be determined preoperatively using whole lower limb radiographs or presumed to be ideal and of a magnitude between 50 and 70 (60 being common). Assumption may be erroneous given the influence of Coronal Femoral Bowing (CFB) and the Neck Shaft Angle (NSA) on the relationship.
Objective: The purpose of this study was to determine the accuracy of presumptive cuts in our setting.
Methods: This was a cross sectional study in four orthopaedic centers in Kenya namely Kenyatta National Hospital (KNH), St Francis Community Hospital Kasarani, PCEA Kikuyu Hospital and the Aga Khan University Hospital Nairobi. Patients with end stage osteoarthritis of the knee scheduled for surgery were screened. Whole lower limb radiographs with limbs in 150 of internal rotation were taken and used to determine the VCA, CFB and NSA. The rate of error with use of presumptive cuts within prescribed limits was then determined.
Results: Eighty two limbs in 48 patients were studied. Fifty nine were in varus 21 in valgus and 2 in neutral alignment. The average VCA for all libs was 6.290(sd 1.800). Considering only limbs in varus alignment the VCA averaged 6.510(sd 1.950). Use of presumptive cuts of 60 in these limbs would potentially result in erroneous cuts in 9.8% of limbs in varus alignment. There was a strong positive correlation between CFB and the VCA.
Conclusions: Routine use of whole lower limb radiographs could improve the accuracy of DFC. In their absence use a VCA of greater magnitude within the prescribed limits in patients with significant clinical varus alignment.