Physiological Achilles Tendon Length and Its Relation to Tibia Length

Abstract

The optimal intraoperative Achilles tendon length (ATL) adjustment is crucial for the physiological functioning of the musculotendinous unit. To date, the resting ATL and its relation to tibia length (TL) have never been defined in healthy subjects. We thus performed metric measurements of the ATL and TL. Case series. Clinical and radiological measurements. Fifty-two subjects placed in a 3-T magnetic resonance imaging with the ankle in neutral position. Unilateral ATL measured from the calcaneal insertion to the beginning of the medial gastrocnemius muscle, TL measured from the intercondylar eminence to the center of the ankle, and qualitative tendon parameters in T2 sequences and human parameters were noted; results were correlated with age, gender, body height, weight, body mass index (BMI), and side of the AT and TL. The mean ATL was 180.6 ± 25.0 mm and the mean TL was 371.9 ± 25.4 mm with an ATL:TL ratio of 49 ± 5%. Achilles tendon length correlated significantly with body height (R = 38%, P < 0.0001) and with TL (R = 41%, P < 0.0001) but did not correlate with age, BMI, and side of the AT. Tibia length correlated with body height (R = 83%, P < 0.0001) and in multivariate linear regression, TL was the only independent predictor of ATL following the algorithm, ATL (mm) = 0.6 × TL (mm) - 53 (R = 41%). We defined a new way to measure the ATL in a consistent way in healthy subjects and showed correlations between ATL, TL and body height and defined an algorithm of ATL based on TL. The ATL and the ATL-algorithm might be important in patients with impaired tendons such as AT ruptures.