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 (TKA), one of the most efficacious procedures in orthopedics, requires complete exposure of the knee joint for precise instrumentation. Although most orthopedic surgeons agree that TKA is easily performed using a medial parapatellar approach, a large segment of the patellar blood flow is disrupted by this exposure. The southern or subvastus approach addresses these concerns; however, the procedure has the disadvantage of inadequate exposure in certain patients. A compromise between these two approaches, a midvastus approach, has been described. To decrease potential neurovascular injury, this cadaveric study of the midvastus approach determines the proximity of the incision to the popliteal vascular bundle and addresses the innervation pattern of the vastus medialis oblique. A midvastus arthrotomy was performed on 19 female and 15 male adult cadaveric knees. The midpoint of the superior pole of the patella and the superomedial patellar prominence were marked. After determining the midpoint between the 2 previously mentioned landmarks, an incision was made from that point paralleling the 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 determined. Differences were assessed by an independent t-test with an alpha level of significance at .05. In addition, the terminal branches of the femoral nerve innervating the vastus medialis oblique were dissected in 5 cadavers. The femoral nerve branched extensively to innervate the vastus medialis oblique. 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 significantly 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 average distance (8.8 cm) and corresponding range (6.5 cm minimum to 12.3 cm maximum) are sufficient to suggest a maximal safe distance for sharp dissection of 4.5 cm from the patellar margin in an adult. For additional exposure, the muscle can be safely split further with blunt dissection.