The John Insall Award: Both morphotype and gender influence the shape of the knee in patients undergoing TKA

Abstract

There is an ongoing debate whether gender differences in the dimensions of the knee should influence the design of TKA components. We hypothesized that not only gender but also the patient's morphotype determined the shape of the distal femur and proximal tibia and that this factor should be taken into account when designing gender-specific TKA implants. We reviewed all 1000 European white patients undergoing TKA between April 2003 and June 2007 and stratified each into one of three groups based on their anatomic constitution: endomorph, ectomorph, or mesomorph. Of the 250 smallest knees, 98% were female, whereas 81% of the 250 largest knees were male. In the group with intermediate-sized knees, female knees were narrower than male knees. Patients with smaller knees (predominantly female) demonstrated large variability between narrow and wide mediolateral dimensions irrespective of gender. The same was true for larger knees (predominantly male). This variability within gender could partially be explained by morphotypic variation. Patients with short and wide morphotype (endomorph) had, irrespective of gender, wider knees, whereas patients with long and narrow morphotype (ectomorph) had narrower knees. The shape of the knee is therefore not only dependent on gender, but also on the morphotype of the patient.

Level of evidence: Level I, diagnostic study. See Guidelines for Authors for a complete description of levels of evidence.

Fig. 1

This diagram depicts the three different morphotypes: endomorph (left), mesomorph (middle), and ectomorph (right).

Fig. 2

On this computed tomographic scan, the measurements of the distal femoral geometry are shown.

Fig. 3

On this picture, the measurements on the calibrated full leg radiographs are shown to determine the pelvis width/total leg length ratio.

Fig. 4

This picture shows how the morphotype characterization was based on the pelvis width/total leg length ratio as endomorph (left), mesomorph (middle), or ectomorph (right).

Fig. 5

On this computed tomographic scan, the measurements of the tibial geometry are shown.

Fig. 6

This graph demonstrates the femoral aspect ratio in function of the femoral size (CE) and gender of the patient.

Fig. 7

This graph demonstrates the tibial aspect ratio in function of the tibial size (AB) and gender of the patient.