Cam impingement of the posterior femoral condyle in unicompartmental knee arthroplasty

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.

Level of evidence

II.