The aim of the study was to find out whether the frequency and intensity of patellar pain can be affected by individual rotational alignment of the femoral component in total knee arthroplasty, as compared with the standard 3 degrees of external femoral rotation in conventional procedures.
In randomly selected patients treated for knee osteoarthritis by total joint replacement between January 2007 and January 2011, the occurrence of patellar pain was assessed. The evaluated knees were allocated to two groups. Group 1 included 350 knee joints with conventional femoral rotational alignment, i.e., 3 degrees of external rotation. Group 2 comprised 380 knee joints with an individual rotational alignment of the femoral component based on the condylar twist angle. Post-operative anterior knee pain was assessed on the following scale: 1, no pain; 2, occasional mild pain; 3, moderate pain; 4, severe pain.
In group 1, 312 knee joints were free from pain, 15 occasionally experienced mild pain, 15 had moderate and eight had severe pain. A total of 23 revision operations were performed for patellar pain at the anterior knee and pain around the patella refractory to non-steroidal anti-rheumatic and rehabilitation therapy. In group 2, there were 331 pain-free knees, 48 with occasional mild pain, one with moderate pain and no knee with severe pain. No revision surgery was required. One patient with moderate patellar pain underwent surgery for spinal canal stenosis; after that knee pain was only mild. The groups were compared, as to pain assessment results, using the test of equality of relative frequencies, i.e., score categories 1+2 versus 3+4 of 350 (group 1) equalled 23 (6.57%) were compared with 1 (0.26%) of 380 (group 2); the difference was significant (p < 0.001). Using the same test for comparison of the frequency of repeat operations, i.e., 23 (0.57%) of 350 (group 1) versus 0 (0%) of 380 (group 2), also gave a significant result (p = 0.001).
Mild and occasional pain was recorded in both groups, suggesting that femoral component malrotation is not the only cause of patellar pain following total knee arthroplasty. A markedly lower incidence of moderate and severe pain and no need for revision surgery found in group 2 provides evidence that the use of individual rotational alignment of the femoral component is fully justified.
An individual rotational alignment of the femoral component can significantly reduce the incidence of moderate to severe patellar pain or even need for revision surgery.