The influence of knee position on ankle dorsiflexion - a biometric study (BMC Musculoskeletal Disorders)

Background: Musculus gastrocnemius tightness (MGT) can be diagnosed by comparing ankle dorsiflexion (ADF) with the knee extended and flexed. Although various measurement techniques exist, the degree of knee flexion needed to eliminate the effect of the gastrocnemius on ADF is still unknown. The aim of this study was to identify the minimal degree of knee flexion required to eliminate the restricting effect of the musculus gastrocnemius on ADF. Methods: Bilateral ADF of 20 asymptomatic volunteers aged 18-40 years (50% female) was assessed prospectively at six different degrees of knee flexion (0[degree sign], 20[degree sign], 30[degree sign], 45[degree sign], 60[degree sign], 75[degree sign], Lunge). Tests were performed following a standardized protocol, non weightbearing and weightbearing, by two observers. Statistics comprised of descriptive statistics, t-tests, repeated measurement ANOVA and ICC. Results: 20 individuals with a mean age of 27 +/- 4 years were tested. No significant side to side differences were observed. The average ADF [95% confidence interval] for non weightbearing was 4[degree sign] [1[degree sign]-8[degree sign]] with the knee extended and 20[degree sign] [16[degree sign]-24[degree sign]] for the knee 75[degree sign] flexed. Mean weightbearing ADF was 25[degree sign] [22[degree sign]-28[degree sign]] for the knee extended and 39[degree sign] [36[degree sign]-42[degree sign]] for the knee 75[degree sign] flexed. The mean differences between 20[degree sign] knee flexion and full extension were 15[degree sign] [12[degree sign]-18[degree sign]] non weightbearing and 13[degree sign] [11[degree sign]-16[degree sign]] weightbearing. Significant differences of ADF were only found between full extension and 20[degree sign] of knee flexion. Further knee flexion did not increase ADF. Conclusion: Knee flexion of 20[degree sign] fully eliminates the ADF restraining effect of the gastrocnemius. This knowledge is essential to design a standardized clinical examination assessing MGT.