Natural history and pathogenesis of the patella clunk syndrome.
The current study aims to test the importance of the design of total knee prostheses in the 'patella clunk syndrome', which is one of the possible patellofemoral complications that can occur after total knee replacement. Three patient cohorts consisting of 75 consecutive patients with 80 Insall-Burstein II (IB II) total knee replacements; 57 patients with 60 Anatomic Modular Knee (AMK) total knee replacements; and 103 patients with 106 Low Contact Stress Rotating Platform (LCS) total knee replacements were studied during the period from 1995 to 2001. This was an unselected series of elderly patients with knee arthritis of comparable demographics; we excluded only those patients receiving revision surgery. We recorded the preoperative and postoperative Knee Society scores, and the patient subgroups with postoperative patellofemoral complications were analysed in detail and were serially followed up. Radiological analysis followed the recommendation of the Knee Society, and the degree of pain was recorded on a visual analogue scale. Also, since the majority of patients with patella clunk syndrome had refused operation and were followed up for several years, an idea of the natural history of this condition was obtained. The relative frequency of occurrence of patella clunk syndrome among patients with the IB II, AMK, and LCS prostheses was 8.8%, 3.3%, and 0%, respectively. The calculated p value is strongly significant when comparing the IB II group with the LCS group (p<0.01); and of borderline significance when comparing the AMK with the LCS group (p=0.05); and not statistically significant between the IB II and AMK groups (p=0.19). Analysis of the results also showed that about half of the patients who underwent conservative treatment still had incapacitating symptoms after several years of follow-up, while the other half showed progressive improvement over time. Given a good surgical technique in component placement and debridement of the peripatella synovium, the design of a total knee prosthesis has a strong bearing on the incidence of the patella clunk syndrome. The natural history of the patella clunk syndrome reveals that for as yet uncertain reasons about 50% will improve with time even when given conservative treatment.