Why Can’t We Accurately Measure Pure Ankle Joint Range of Motion
In their landmark paper evaluating the connection between gastrocnemius contracture and foot pathologies, DiGiovanni and coworkers found that 88 percent of patients with metatarsalgia and midfoot symptoms had concomitant contracture of the gastrocnemius muscle.1
The study authors defined gastrocnemius contractureas less than 10 degrees of dorsiflexion of the ankle measured by a goniometer with the knee in an extended position. This method is identical to that taught by Root in which the examiner passively dorsiflexes the foot and aligns a goniometer at the lateral ankle. The clinician places one arm of the instrument along the posterior edge of the distal fibula with the other arm aligning with the lateral margin of the foot, extending to the head of the fifth metatarsal with the foot positioned in subtalar neutral.2 Root also previously defined equinus of the ankle as a condition in which dorsiflexion was limited to under 10 degrees with the knee extended, which appears to be predictive of pathology, according to the study by DiGiovanni and colleagues.1
However, the reliability of a non-weightbearing measure of ankle joint range of motion as described by Root has been challenged.3 Reliability refers to the reproducibility of the findings of a test when performed repeatedly by the same rater (intra-rater) and between multiple raters (inter-rater).4 Reliability does not reflect the clinical value of a test or verify whether the test is a true or accurate measure of joint range of motion. Given the questionable value of goniometric measure of ankle joint range of motion in a non-weightbearing position, researchers developed a weightbearing lunge test, which showed good intra- and inter-rater reliability.5,6 Since then, multiple researchers have reported variations of the lunge test employing different methods of measurement, including the use of a goniometer, an inclinometer and a tape measure.7-9
The lunge test has questionable clinical relevance as one has the patient perform the test in an upright standing position with the knee flexed. This fails to identify gastrocnemius contracture, which is most critical in contributing to ankle equinus and a myriad of reported foot and leg pathologies.10-14 Thus,Munteanu and coworkers developed and tested a modified lunge test with the knee extended and found very good intra- and inter-rater reliability.15
Aside from demonstrating reliability in providing accurate and reproducible measurement results, what do these lunge tests actually tell us? What are the normal and abnormal ranges of measures, and do these tests actually measure true ankle joint range of motion?
Researchers have used the modified weightbearing lunge test (as developed by Munteanu and colleagues) to measure static ankle joint dorsiflexion range of motion in several studies. This “normal” range of dorsiflexion is between 33 and 39 degrees.15,16 In a study that compared younger healthy adults to older patients with diabetes, Searle and coworkers determined that a threshold of 30 degrees of dorsiflexion would designate restricted or “hypomobile” ankle dorsiflexion from healthy individuals.17 This begs a question: if the gold standard for required ankle joint dorsiflexion during gait is 10 degrees, why would a modified lunge test of less than 29 degrees of dorsiflexion be identified as pathologic?
The answer to this question is twofold. Static tests of joint alignment and joint mobility do not accurately predict performance of the foot during gait.18-20 Despite the full weightbearing position of the measured limb in full knee extension, the modified lunge test places the patient in a posture which is never duplicated in the walking gait cycle.
Furthermore, when humans walk, sensorimotor mechanisms take over and these mechamisms are not employed during static examination. This is clearly demonstrated in a study of static measure of ankle joint dorsiflexion and kinematic measure of ankle and foot dorsiflexion during dynamic gait performed by Gatt and coworkers.21 Using the traditional Root method of measurement, the authors showed that study participants who had negative five degrees of ankle joint dorsiflexion with the leg extended actually achieved 14 degrees of dorsiflexion during gait, which was verified by 3-D motion capture with a multi-segment foot model. How could this be?
Gatt and team showed that with simple goniometer measurement of ankle joint dorsiflexion off-weightbearing and with full weightbearing during a lunge test, the measurement is really a total of both ankle and footsagittal plane motion. In fact, the motion across the midtarsal joint and tarsometatarsal joints in the sagittal plane during gait totals 50 percent greater than that of the ankle joint alone. This has been verified in other studies.22,23
The significant contribution of joints of the foot to overall “dorsiflexion” during gait is largely dependent upon position of the rearfoot. From a supinated to pronated position of the subtalar joint, overall foot and ankle dorsiflexion will be affected by up to 10 degrees.24-26 Whether off-weight bearing or full weightbearing, the ability of the examiner to accurately reproduce the position of the foot into subtalar “neutral” has proven to be very unreliable.27 Clearly, foot position will influence overall “foot dorsiflexion” in the lunge test and one could make an erroneous diagnosis of gastrocnemius equinus as this test is really measuring foot mobility rather than pure ankle joint mobility.
The bottom line is that we do not currently have an accurate method to measure true ankle joint dorsiflexion in patients in the clinical setting. Current techniques have numerous shortcomings. While the weightbearing lunge test has been shown to be reliable in terms of reproducibility of measurement, it has questionable clinical relevance. The weightbearing lunge test shows that over 30 degrees of dorsiflexion of the foot is required for healthy people yet only 10 degrees is actually required for normal gait. Therefore, this test by no means reproduces the posture and demands on the foot and ankle that occur during dynamic gait. The joints of the foot contribute more sagittal plane motion during gait than the ankle joint and we need to take this factor into account as we search for more reliable ways to evaluate our patients for true ankle equinus.
Dr. Richie is an Adjunct Associate Professor within the Department of Applied Biomechanics at the California School of Podiatric Medicine at Samuel Merritt University in Oakland, Calif. He is a Fellow and Past President of the American Academy of Podiatric Sports Medicine. Dr. Richie is a Fellow of the American College of Foot and Ankle Surgeons.
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