We studied the accuracy of using the tibialis anterior tendon (TAT) as a distal landmark for extramedullary alignment in total knee arthroplasty. Forty-five consecutive ankle magnetic resonance imaging scans were reviewed. On the computerized images, a digital ruler was used to measure the distance from the midpoint of the distal tibia (point M) to the TAT. Mean distance was 1.89 mm; range was 0 to 4.5 mm (95% confidence interval, 1.45-2.33). For 7 (15.6%) of the 45 scans, the distance was 0 mm. On 38 scans (84.4%), the TAT was within 2 mm of point M. The TAT is an easily palpable fixed anatomical structure that corresponds very closely to the midpoint of the distal tibia.