Abstract
Introduction: The technique of quadriceps sparing knee arthroplasty involves a pure capsular incision, without violation of the extensor mechanism. This capsular incision should be placed distal to Vastus Medialis Obliquus (VMO). It is well known that the termination of VMO is variable and may make the quadriceps sparing approach difficult. We initiated this study based on the hypothesis that the quadriceps sparing approach is not possible in all patients undergoing total knee arthroplasty.
Methods: We examined the axial MRI images of the knee joint performed over a period of 12 months at our institute. A total of 198 MRI scans were analysed between two observers.
To calculate the patellar height the apex of the patella was considered as ‘Reference Slice 1’. The consecutive slices were followed distally to the last slice in which the patella was visible. From ‘Reference Slice 1’ VMO muscle was followed distally to the slice in which the muscle was last visible. We calculated the patella height and VMO muscle length as the product of the number of MRI slices and MRI slice thickness.
Results: Of the 134 patients aged less than 50 years, 68 patients (50.7%) had a VMO that terminated in the proximal half of the patella. Out of 64 patients aged 50 years or older, 51 patients (79.7%) had a VMO that terminated in the proximal half of the patella.
A statistically significant inverse relationship was noted between the level of insertion of VMO and the age of the patient.
Discussion: Our results will have an implication on the use of the quadriceps sparing approach, as they highlight another possible limitation of this approach. Patients need to be warned before the TKA that the quadriceps sparing approach may not be possible in all, especially if they are younger.
Correspondence should be addressed to: Tim Wilton, BASK, c/o BOA, The Royal College of Surgeons, 35–43 Lincoln’s Inn Fields, London WC2A 3PE.
