Cam impingement of the posterior femoral condyle in unicompartmental knee arthroplasty.

ABSTRACT

PURPOSE: There has been much emphasis on the importance of cam impingement, which is a cause of pain and knee hyperflexion restriction in unicompartmental knee arthroplasty (UKA). This study aimed to correlate cam impingement in the posterior femoral condyle with an α-angle showing the severity of the impingement. METHODS: The study groups consisted of 87 knees of 74 patients operated on with phase 3 medial Oxford UKA. Postoperatively, Group A (68 knees, 78.2 %) had no remnant of cam lesion; Group B (19 knees, 21.8 %) had cam lesion remnants. In Group C (18 knees, 20.7 %), which is a subgroup of Group A, cam lesions seen preoperatively were cleaned and not seen postoperatively. RESULTS: The mean increase in active flexion was 20.4° (± 7.3°) in Group A, 9.7° (± 6.1°) in Group B and 20.8° (± 7.3°) in Group C. The difference between Group A and Group B and between Group B and Group C was statistically significant (p < 0.001, p < 0.001). The mean decrease of α-angle was 11.2° (± 4.1°) in Group B, and 31.1° (± 3.4°) in Group C. The difference was statistically significant (p < 0.001). Mean Oxford Knee Scores were 24 preoperatively, 41 postoperatively in Group A; 22 preoperatively, 38 postoperatively in Group B; and 24 preoperatively, 40 postoperatively in Group C. The differences were not significant. CONCLUSIONS: Posterior condylar cam lesion is an impingement which limits hyperflexion and may be an early clinical finding prior to bearing dislocation and wear. The α-angle is a marker showing the severity of this cam lesion. This problem can be overcome using intraoperative fluoroscan views during cam excison and replacing the femoral component in 105° knee flexion.