Abstract
The aim of this study was to evaluate whether using a predetermined entry point and standard value for valgus cut could restore normal mechanical axis of the TKA.
The study included 125 consecutive patients, who underwent TKA under care of the senior author (NJD). Details of height, weight, BMI were noted. All the radiographs were taken with the patient standing, with the knees in maximum extension, with the patella facing forward. The long leg radiographs were evaluated and the mechanical axis and anatomical axis were marked. The entry point (EP) and the angle between the anatomical and the mechanical axis of the femur ware measured, which is valgus angle of distal femoral cut (VA). Statistical analysis was done using SPSS (Table 1). Proportion of the cases with VA less than 6 degrees or more than 7 degrees were identified. Similarly cases with EP distance less than 0 and more than 5mms were also identified. Cases with VA of 6–7 degrees and EP 0–5mms were identified as one group. Correlation was performed using nonparametric tests.
The results revealed the angle between the anatomical and the mechanical axis ranges from 4 to 9.5 degrees (mean 6.8 degree and standard deviation 1.11 degree). Only 53% had an angle of between 6 and 7 degrees, with 7% of knees having an angle of less than 5 degree or greater than 8 degrees.
The site of entry of the jig showed variation from 30mms medial to the centre to 18mms lateral to the centre with the mean entry point of 5.04mms medial to centre of the notch, with a standard deviation of 8.5mms.
Overall only 33% of the knees templated would have an optimal femoral jig placement and distal femoral angle cut with an entry point in the centre of the notch or up to 5mms medial to centre and a distal valgus cut of between 6 and 7 degrees. The author feel this study gives evidence that if the mechanical axis is to be restored then long leg pre-operative radiographs should be performed and used as a key component to the pre-operative plan.
Table 1. Spearman’s rho correlations, between the valgus angle and entry point to the height, weight and BMI of the patients.
Correspondence should be addressed to Mr Tim Wilton, BASK at the Royal College of Surgeons, 35–43 Lincoln’s Inn Fields, London WC2A 3PE.
