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Sex-specific versus standard posterior cruciate-substituting total knee prosthesis

Background The introduction of sex-specific (SS) knee prosthesis designs was an approach to offer more sizing options and is based on the anatomic sex differences. These SS components were though to provide better fitting to female femora and consequently improve the clinical outcome. Materials and methods In the period between February 2011 and March 2013, a prospective superiority randomized controlled clinical trial was conducted to compare the clinical outcome of SS versus the standard posterior stabilized (PS) knee prosthesis in women. The primary outcome measure was the postoperative range of knee flexion, and the secondary outcome measure was the knee function as reflected on the performance of daily activities. The OXFORD Knee Score, Knee Society Score, and Knee Society Score for function were recorded preoperatively and then at 3, 12 months, and annually thereafter. Female patients with degenerative or inflammatory arthritis who were 50 years or older and their knee deformities were totally articular were included. A total of 64 patients with 80 knees were enrolled in this trial, and 40 knees were allocated to each group. Knees in the SS group had total knee arthroplasty using SS knee prosthesis, with SS femoral component (the experimental group), whereas knees in the PS group had standard PS knee design with standard femoral component (the control group). Equal randomization (1 : 1 ratio) was undertaken according to a computer-generated randomization table. Results The mean preoperative knee flexion range of motion (ROM) was 110 and 108° in the SS and PS groups, respectively. At the latest follow-up, the mean postoperative knee flexion ROM was 115 and 113° the SS and PS groups, respectively. The mean improvement in the knee flexion ROM in both groups was 5° (range: 0–25), with no statistically significant difference between the two groups. All knees except one had full extension. No statistically significant difference was observed between the two groups when the OXFORD Knee Score, the Knee Society Score, and the Knee Society Score for function were compared. Conclusion No clinical advantage was observed in the ROM or function between knees that received SS knee prosthesis when compared with those who received PS knee implants. The SS total knee arthroplasty though designed to provide better fitting to the female distal femur does not provide any clinical advantage over the standard PS knee prosthesis. A logic question is whether a separate implant is required for women or modifications to the knee prostheses geometry and more sizes are required to accommodate all patients? Level of evidence Level II.