PATELLOFEMORAL DEGENERATION PATTERNS

Abstract

During knee arthroplasty operations, it appeared that different patterns of patellar degeneration occur. To confirm this, 123 patellae were evaluated in a prospective study. The patellae of patients who had undergone patellar surgery or osteotomy were excluded.

The femur was divided into three condyles and nine areas, and the patella into three facets and nine areas. Areas of grade-III or more degeneration on the patella and femoral condyle were recorded. In 74 knees (60%), the patellar degeneration was less than grade III. In 49 (40 %), the 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 femoral and patellar degeneration. Further analysis was undertaken to determine whether there was any pattern of degeneration between the patellar and femoral lesions.

The medial femoral condyle, central and central-medial patella had the highest incidence of degeneration. These probably represent areas of greatest load-bearing in the knee. The areas with least degeneration were in the lateral femur and the superior patella, probably the lowest load-bearing areas. It was noted that any pattern of patellar degeneration could occur with any pattern of femoral degeneration. Lateral and central patellar facet degeneration is a well-recognised clinical and radiological condition. Medial patellar facet degeneration was a common finding. The medial facet is especially loaded in the flexed knee. A fixed flexion contractor, common in medial compartment osteoarthritis, may partially explain the high incidence of medial facet degeneration in these patients. Medial patellar facet degeneration is not a well-recognised condition and in the literature is generally considered secondary to lateral release. In this series, patients with lateral releases were excluded.

Standard patellar skyline views show only the unloaded medial facet. Medial patellar facet degeneration is probably more common than is clinically recognised, and may account for unexplained anterior knee pain, especially in the flexed knee. In this situation, pain will be aggravated by a lateral retinacular release.