Abstract
Purpose
We analyzed the frequency, causes and treatment of dislocation of polyethylene insertion among various causes of failure of unicompartmental knee arthroplasty.
Materials and Methods
We studied 69 knee joints of 65 patients who underwent medial unicompartmental knee arthroplasty using from June 2005 to December 2010. Average age was 61.8 and average follow-up period was 20 months. Radiologic results evaluated preoperative and postopertative mechanical axis deviation, tibio-fibular angle and postoperative implant position in total 69 knees(A group), failed 15 cases(B group) and 10 cases(C group) of bearing dislocation. We demonstrated treatment on failure group and analyzed preoperative and postoperative HSS and Lysolm score.
Results
Failures were observed in 15 cases(21.7%) on follow-up. dislocation of polyethylene insertion was observed in 10 cases at average 26.7 months (3–60). There were 2 cases of dislocation of insert without loosening of implant and 8 cases of dislocation of insert with loosening of implant. Tibio-femoral angle in A, B and C group were corrected form preoperative varus 8.1°, 7.3° and 6.3° to postoperative valgus 3.6°, 4.0° and 3.5°. Thickness of inserted polyethylene in A, B and C were 4.7 mm, 5.2 mm and 4.8 mm, but each groups didn't show statistical significance. HSS and Lysolm score improvement had statistical significance.
Conclusion
Dislocation of polyethylene insert (66.1%) in cases of the failure was most common. Coronal correction angle and thickness of inserted polyethylene showed no difference between dislocation gourp and non-dislocation group, so we consider that polyethylene dislocation after unicompartmental knee arthroplasty seems to be due to structural problem of the implant.
