The gender-specific total knee arthroplasty (TKA) debate focuses on differences in distal femoral mediolateral to anteroposterior aspect ratio between males and females. However, randomized studies have been unable to demonstrate significant differences in outcomes utilizing gender-specific implants. No studies have examined the effect of intermediate femoral component sizes on outcome. We compared outcomes before and after intermediate sizing availability.
We identified 331 patients (413 knees) who underwent primary TKA between 2003 and 2004 with a single complete knee system. There were 121 males and 210 females. Three intermediate femoral sizes were added in March 2004 to the six initial options. Patients before March 2004 were assigned to group 1 (n=178), and after to group 2 (n=235).
Follow-up averaged 8.5 years. Preoperative demographics and clinical scores were similar between groups. Knee Society (KS) clinical and functional scores improved in females in both groups, but there was no significant difference. Male patients in group 2 had a significant improvement in KS clinical scores compared to male patients in group 1 (group 1: 33.9, group 2: 41.1; p=0.01). Females in group 2 had significantly less need for manipulation, 1.9%, versus females in group 1, 8.7% (p=0.01). MUA rates were similar for men between groups. Overall, there were 19 revisions (4.6%) with no differences between groups or by genders. Once intermediate sizes were available, they were used in 48% of females and 13% of males. The average femoral component size for females in group 1 was 65 mm and decreased in group 2 to 62.5 mm. The average size of femoral components in males was 70 mm in both groups.
Availability of intermediate size femoral component sizes was associated with a lower rate of manipulation in female patients. Greater KS clinical score improvement was observed in men after availability of additional femoral sizes.