Abstract
Degenerate chondral surfaces can be assessed in many ways, but arthroscopy is often performed without proper categorisation, mapping, zoning or sizing of lesions. Progression of disease in un-resurfaced compartments is well-recognised to occur, but is only one of several failure mechanism in partial knee replacement.
A validated ‘Functional Zone’ mapping method was used to document articular surface damage in 250 sequential cases of knee arthroscopy in patients over the age of 40. Size, shape, location and severity of each chondral lesion were noted using the Outerbridge classification. Analysis determined rates of involvement of particular compartments and assessed potential for partial replacement or local treatment and also to consider the risk of future progression. Radiographs including antero-posterior standing, postero-anterior flexion views (Rosenberg), lateral and skyline views were graded (Kellgren and Lawrence) and compared with the arthroscopic findings.
Our results showed that out of the 210 knees with Grade 3 or greater damage 13.3% of knees showed ‘isolated’ medial disease of Outerbridge Grade 3 or worse. Isolated lateral disease was noted in 1.4%, patello-femoral disease in 24.3%, bi-compartmental (Medial/PFJ) disease in 30.9% with tibio-femoral and tri-compartmental disease seen in 15.2%. The combination of lateral and patello-femoral disease was seen in 14.8%. Provided that Grade 1 and 2 changes (which were found in other compartments in high percentages) were ignored and ACL status considered, this information seemed to indicate that at the time these procedures were performed, 13.3% of cases were suitable for a medial uni-compartmental device, with sub-analysis of lesion sizes indicating that 17 out of 28 cases (60.7%) were suitable for a localised resurfacing. Lateral uni-compartmental replacement seemed suitable for only 1.4%, patello-femoral replacement in 24.3%, bi-compartmental in 30.9% and total knee replacement in 30%. The mean age for partial resurfacing was 53years and 59 years for total joint replacements.
Radiological analysis found that the antero-posterior standing views had only 66% sensitivity and 73% specificity for the presence of Grade 3 changes or worse in the medial compartment in comparison with Rosenberg views having a sensitivity of 73% and a specificity of 83%. Skyline views had a sensitivity of 56% and 100% specificity.
This study indicates that a large proportion of cases may be suited to local and limited resurfacing. Cases suitable for Patello-femoral and Bi-compartmental replacements were very common, but with the patella-femoral joint's tendency to be more forgiving in terms of symptoms, meaning that indications for uni-compartmental replacement might well be much higher than the arthroscopic findings suggested. On the other hand, the presence of high levels of Grade 1 and 2 changes in other compartments seems to indicate a need for caution particularly in younger patients. This study also indicates a need for better methods of assessing local cartilage health such as enhanced MRI scanning or spectroscopy.
