Effect of intraarticular pressure on patellar position. Computed tomography study in cadaveric specimens

The purpose of the study was to evaluate the effect of articular fluid distention on patellar position at different degrees of knee angulation.

Patellar position in 10 cadaveric knee specimens was determined with 30, 100, and 200 mm Hg joint distention at 45, 20, and 5 degrees of knee flexion using computed tomography. Patellar tilting and lateromedial and anteroposterior displacement of the patellar position were analyzed.

Lateral tilting increased with greater articular distention and decreasing knee flexion. At 5 degrees of flexion and 200 mm Hg of distention, change in lateral tilting ranged from -7 to +5 degrees. At 45 degrees of flexion and increased distention, the patellar shift ranged from 6 mm medialization to 1 mm lateralization for 200 mm Hg, but the patellar position was more variable at 5 degrees of flexion with increasing intraarticular pressure (range 7 mm medialization to 8 mm lateralization). With increasing articular pressure the patellae were increasingly displaced anteriorly with the most pressure-dependent changes at 45 and 20 degrees of knee flexion.

Fluid distentions of the knee joint have unpredictable and varying effects on the patellar position and vary considerably among persons. When judging patellar position during arthroscopy and in patients with large joint effusions, the arthroscopist and radiologist should be aware of these effects.