Unisex knee prosthesis and patient specific knee prosthesis has the same anterior knee pain and patellar tracking

Background:The anterior knee pain (AKP) is one of major problem of TKA. The incidence of anterior knee after TKA was 4% to 49%. The cause of AKP after TKA from surgical technique errors including joint line elevation, instability, malalignment of prosthesis, and maltracking of patella. However, AKP still has presented even high volume surgeon that prosthesis had good alignment and good stability, one of the risk factor is female. Due to female has higher Q-angle, greater anteroposterior (AP)/mediolateral(ML) ratio, smaller anterior condyle, and trochlea has higher degree of valgus angle than male. Therefore, female should has AKP even surgery with good surgical technique. The gender specific knee prosthesis was design for female to restore Q-angle, reduce anteroposterior (AP)/mediolateral(ML) ratio for reducing overhang of femoral component, increase valgus angle of trochlea groove, and reduce thickness of anterior part of prosthesis for prevention overstuff with patella. For these reasons, the gender specific knee prosthesis should reduce AKP and improve patellar tracking in female. And there is no study to compare AKP and patellar tracking between Unisex knee prosthesis and gender specific knee prosthesis following minimally invasive surgery (MIS) TKA.

Investigators asked whether AKP and patellar tracking differ between unisex knee prosthesis and gender specific knee prosthesis following MIS TKA with patellar resurfacing.

Methods:The participants were randomized into 2 groups (Gp) with computer program to make a list of random numbers of participant. Gp1 was gender specific knee prosthesis; consisted of 40 participants (40 knees) and Gp2 was unisex knee prosthesis; consisted of 40 participants (40 knees). The sample size was calculate base on anterior knee pain after TKA with a risk difference of 27% (3% versus 20%) (1,3). The 40 participants from each group would have 90% power at the 5% significant level.

Patrticipants were follow up at 2 wks, 6 wks, 3 mo, 6mo, 1 year and 2 years. At each follow up, the % anterior knee pain, VAS for anterior knee pain were record. The knee society score also was recorded and compared between two group.

All participants were operated with same surgeon and same instrumentation.

Inclusion Criteria:

Aymptomatic knee OA with

• varus deformity < 30 degrees
• range of motion > 90 degrees
• flexion contracture < 20 degrees
• recurvatum < 20 degrees

Exclusion Criteria:

• gout
• postraumatic arthritis
• osteonecrosis of knee
• inflammatory joint disease