Abstract:

BACKGROUND: The rate of complications of patellofemoral joint following total knee arthroplasty (TKA) is about 39%. There are many causes for these complications, and patellar baja, one of important causes for patellofemoral joint problem has been frequently ignored.
OBJECTIVE: To investigate the mechanism of patella baja following primary TKA.
METHODS: Clinical data of 78 cases (85 knees) undergoing primary TKA knees in Department of Orthopedics, Third Hospital of Hebei Medical University between July 2003 and January 2009, were retrospectively analyzed. According to HSS scores, they were assigned to high scores and low scores groups. X-ray of two groups before and after TKA was compared. Insall-salvati index was used to measure the height of patella and Hofmann’s procedure was used to measure the variation of the joint line. Logistic regression was performed to analyze the correlation of patellar baja with the insall-salvati index and the proximally transferring joint line.
RESULTS AND CONCLUSION: The 59 knees in high scores group did not suffered patellar baja; 23 of 26 knees in low scores group occurred patellar baja, and the insall-salvati index was 1.1±0.1 in 6 knees and joint line elevated (7±2.3) mm in 17 knees. Patella baja were correlated with insall-salvati index and elevation of joint line through the logistic regression. The patella baja was caused by the tibial polyethylene thicker than the tibial resecting bone, i.e. elevated proximally transferring joint line and contracted patellar ligament. Therefore, we should maintain the original joint line maximally during TKA and enhance knee rehabilitation as soon as possible to restrain patellar ligament contracture.