The Normal Patella—Does it Exist? A Histologic Analysis

It is unclear if healthy-appearing patellae in patients having total knee arthroplasty (TKA) can be selectively retained. In the study reported here, we hypothesized that grossly normal-appearing patellae in TKA candidates would show significant evidence of microscopic degeneration and thinning of the articular cartilage.

Ninety-six consecutive patients (110 knees) with primary degenerative osteoarthritis were recruited from a single institution between November 2010 and June 2011. Thirteen patellae (11 patients) had grossly normal-appearing cartilage. A pathologist measured patellar cartilage thickness in each quadrant and evaluated for evidence of microscopic degenerative change.

Mean cartilage thickness was 2.35 mm (range, 1.0-3.0 mm) for superomedial quadrant, 2.31 mm (range, 1.5-3.0 mm) for superolateral quadrant, 2.31 mm (range, 1.0-4.0 mm) for inferomedial quadrant, and 2.62 mm (range, 1.5-3.5 mm) for inferolateral quadrant. Four-point mean (SD) was 2.39 (0.79) mm. Each patella demonstrated at least 2 of the predefined histologic markers of degeneration: fibrillation, fibrosis, chondrocyte proliferation, cyst formation, and fissuring and/or thinning.

Even healthy-appearing patellae on gross examination have clear histologic markers of early to moderate articular degeneration.

Further comparisons of cartilage thickness using area measurements are needed before the significance of the effect of this deterioration on the technique of selective patellar retention during TKA can be known.