Anatomy of the extensor mechanism in reference to quadriceps-sparing TKA

The introduction of minimally invasive surgical techniques in total joint arthroplasty has ushered in a range of new terminology that often is unclear. One such term is quadriceps-sparing total knee arthroplasty (TKA). We examined 100 knees intraoperatively in 100 patients at the time of TKA, dissected 45 entire cadaveric leg specimens, and did high-resolution 3-Tesla magnetic resonance imaging scans on five normal knees to specifically determine: (1) the distal most insertion point of the vastus medialis obliquus; (2) the angle of insertion of the vastus medialis obliquus; and (3) the length of the vastus medialis obliquus tendon. The medial anatomy of the extensor mechanism was consistent. The inferior edge of the VMO inserted at or near the midpole of the patella in each case. The tendon inserted at 50° (range, 46°- 52°). One hundred of the 150 patients (66%) had a tendon that measured 1.2 ± 0.1 cm, whereas 50 of 150 patients (33%) had a substantially longer tendon (2.2 ± 0.2 cm). Any medial arthrotomy that extends more proximal than the midpole of the patella detaches a portion of the quadriceps tendon. The term "quadriceps sparing" should not be applied to any surgical approach with a capsular incision that extends more proximal than the midpole of the patella.