Midvastus approach in total knee arthroplasty - A description and a cadaveric study determining the distance of the popliteal artery from the patellar margin of the incision

Total knee arthroplasty (TRA), one of the most efficacious procedures in or thopedics, requires complete exposure of the knee joint for precise instrum entation. Although most orthopedic surgeons agree that TKA is easily perfor med using a medial parapatellar approach, a large segment of the patellar b lood flow is disrupted by this exposure. The southern or subvastus approach addresses these concerns; however, the procedure has the disadvantage of i nadequate exposure in certain patients. A compromise between these two appr oaches, a midvastus approach, has been described. To decrease potential neu rovascular injury, this cadaveric study of the midvastus approach determine s the proximity of the incision to the popliteal vascular bundle and addres ses the innervation pattern of the vastus medialis oblique. A midvastus art hrotomy was performed on 19 female and 15 male adult cadaveric knees. The m idpoint of the superior pole of the patella and the superomedial patellar p rominence were marked. After determining the midpoint between the 2 previou sly mentioned landmarks, an incision was made from that point paralleling t he fibers of the vastus medialis oblique medially to the popliteal vascular bundle. The length of the incision was measured three times using calipers ; measurements were averaged for each individual specimen, then by gender, and, finally, overall. Ninety-five percent confidence intervals were determ ined. Differences were assessed by an independent t-test with an or level o f significance at .05. In addition, the terminal branches of the femoral ne rve innervating the vastus medialis oblique were dissected in 5 cadavers. T he femoral nerve branched extensively to innervate the vastus medialis obli que. The average distance between the patella and the popliteal vessels was 8.8 +/- 1.4 cm. The average distance in males, 9.5 +/- 1.4 cm, was signifi cantly greater than the distance in females, 8.3 +/- 1.2 cm (P < .02). The distance appeared proportionate to the size of the extremity. The midvastus approach is a viable alternative for primary TKA in selected patients who are not obese and who have not had previous arthrotomy or osteotomy. The av erage distance (8.8 cm) and corresponding range (6.5 an minimum to 12.3 cm aximum) are sufficient to suggest a maximal safe distance for sharp dissect ion of 4.5 cm from the patellar margin in an adult. For additional exposure , the muscle can be safely split further with blunt dissection.