Knee extensor mechanics after subtotal excision of the patella.

Two sets of six fresh frozen autopsy specimens were used to test the quadriceps force requirements for knee extension after sequential distal-to-proximal and proximal-to-distal excisions of the patella. The quadriceps force as a function of knee flexion angle was recorded for varying amounts of excision and compared with the results for total patellectomy. Excision of the proximal one half or less resulted in lower force requirements when compared with total patellectomy. The effects of removal of the proximal three-fourths length of patella were inconsistent and actually increased the force requirements in three knees. The effects of distal to proximal excisions indicate a biomechanical advantage to maintaining a fragment equal to at least three fourths the length of the proximal patella. Retaining a fragment of adequate size preserves at least some of the mechanical advantage provided by the intact patella.