Abstract
To investigate whether there are different patterns of patellar degeneration, 123 consecutive knee arthroplasties were investigated. Knees on which previous patellar surgery or osteotomies had been done were excluded. Areas of grade-III or more degeneration of the patella and femoral condyle were recorded.
The femur was divided into three condyles and nine areas. The patella was divided into three facets and nine areas. In 74 (60%) of the knees, patellar degeneration was less than grade III. In 49 (40%) knees, patellar degeneration was grade III or more. In these 49 knees, there were 122 lesions in the nine areas of the femur and 77 lesions in the nine areas of the patella. These lesions were analysed to determine the most common areas of degeneration in the femur and patella and to establish whether there was any pattern of degeneration between the patella and femoral lesions.
The highest incidence of degeneration was found in the medial femoral condyle, central and central-medial patella, probably the areas of highest load in the knee. The areas of least degeneration were in the lateral femur and the superior patella, which are probably the lowest weight-bearing areas. Any pattern of patellar degeneration can occur with any pattern of femoral degeneration.
Lateral and central-patellar facet degeneration are well-recognised clinical and radiological entities. In this series, medial patellar facet degeneration was commonly found. Medial patellar facet degeneration is less well recognised and in the literature is referred to only as secondary to lateral release. In this series, patients with lateral releases were excluded.
The medial facet is especially loaded in the flexed knee. A fixed flexion contracture, as is common in medial compartment osteoarthritis, explains the high incidence of medial facet degeneration. Standard patellar skyline views show only the unloaded medial facet. Medial patellar facet degeneration is probably more common than is recognised and may be a cause of unexplained anterior knee pain, especially in the flexed knee.
The abstracts were prepared by Professor M.B.E. Sweet. Correspondence should be addressed to him at PO Box 47363, Parklands, Johannesburg 2121, South Africa.
