Limited ankle dorsiflexion (ADF) alters the gait kinematics and is held responsible for common foot pathologies including Achilles tendinopathy, stress fractures, metatarsalgia and plantar heel pain 1-5. The most common cause for limited ADF is isolated Musculus gastrocnemius tightness (MGT) 3,6.
The joint kinematics of the ankle are influenced by knee flexion as the M. gastrocnemius bridges both joints. The muscle is under tension when the knee is fully extended, as the origin of the muscle is then furthest proximal. The M. gastrocnemius then restrains ADF. Knee flexion approximates the muscle's origin, thereby reducing the tension of the M. gastrocnemius, and consequently increases ADF. Ankle dorsiflexion is then limited by other anatomical structures of the ankle joint. Figure 1 illustrates this principle. In the case of MGT, ADF is limited with the knee fully extended but substantially increases by flexion of the knee 4.
Clinical examination for MGT takes advantage of the above outlined principled and was first published in 1923 by Silfverskiöld, a Swedish orthopedic surgeon 7. Since then, numerous examination techniques have been described, all of which compare the ADF with the knee extended and flexed. Published clinical tests can be categorized into non-weightbearing 5,8, weightbearing 9,10, and instrumented 11,12. Today, non-weightbearing examination is most commonly conducted 13. The patient is placed supine on the examination couch and ADF is assessed with the knee fully extended and typically 90° flexed (Figure 2A). On the contrary, weightbearing ADF measurements are conducted with the subject upright in lunge stance. The rear knee is extended or bent and the subject is asked to lean forward just before heel liftoff (Figure 2B). For both tests MGT is diagnosed, if the ADF with the knee extended is impaired and knee flexion results in a significant increase of ADF.
Although non-weightbearing tests are frequently performed, weightbearing testing has several advantages. First, only one investigator is needed for weightbearing examination, whereas two examiners are required to achieve reliable non-weightbearing measurements. Second, the weightbearing examination more closely reflects the load during gait. Third, the force applied to the ankle is independent of the examiner. Fourth, weightbearing examination features a higher intra- and inter- rater reliability 9,10,13-15.
The major limitation of all tests for MGT is that the minimal degree of knee flexion needed to eliminate the restraining effect of the M. gastrocnemius on ADF is unknown 8,15. Whereas 90° of knee flexion are typically applied in non-weightbearing testing 5,8,16, this is not feasible for the weightbearing examination. The broad population is unable to perform a Lunge with 90° of knee flexion without lifting the heel off the ground. Consequently, most studies conducting weightbearing examinations did not control for knee flexion 8,15. In order to perform reliable weightbearing examinations it is essential to identify the minimal degree of knee flexion needed to eliminate the restraining effect of the M. gastrocnemius on ADF.
Overall, literature argues for weightbearing testing for the diagnosis of MGT. In order to provide a valid weightbearing examination procedure, the minimal degree of knee flexion required to eliminate the ADF restraining effect of the M. gastrocnemius must be known. The aim of this study was to investigate the influence of knee flexion on ADF in non-weightbearing and weightbearing testing and to provide a step-by-step guide to conduct non-weightbearing and weightbearing examination for MGT.