Abstract
Correct sizing of knee arthroplasty implants avoids problems such as stiffness from too large an implant, or periprosthetic fractures from undersizing. Currently most implants are based on a generic unisex population. Femoral component sizing is therefore based solely on the AP measurement after the distal femoral cut. In order to investigate the differences between the New Zealand population and other populations with reported anthropometrics we studied the anthropometrics of the male and female distal femur.
The distal femur of 26 cadaveric knees was resected using standard cutting guides. Using a sizing guide the AP dimension was measured from the posterior condyle to the anterior cortex just proximal to the trochlea (posterior referencing). The ML dimension was measured at the cut surface in the coronal plane of the epicondylar axis.
Overall AP measurement had a mean(standard deviation) of 62(±6.7) mm, the ML measurements had a mean (sd.) of 72(±6.6)mm yielding an ML/AP(100) ratio of 117(±11). The male AP mean was 67(±4.5) mm and female AP 57 (±4.4)mm. The male ML was 77 (±4.7)mm and female ML 68 (±4.5)mm. The ML/AP ratio for male was 111(±12) and female was 120 (±10).
This pilot study has shown differences between genders in the NZ population even with this small sample size. As this data is important for designers of total knee implants, planning is currently underway to perform measurements intraoperatively from approximately 400 patients undergoing total knee replacement.
Correspondence should be addressed to: Associate Professor N. Susan Stott, Orthopaedic Department, Starship Children’s Hospital, Private Bag 92024, Auckland, New Zealand.
