Equinus Deformity: Too Many Questions, Not Enough Answers

Forty-six years ago, Root and colleagues defined “ankle equinus” as being a structural limitation of ankle joint dorsiflexion of less than 10 degrees of dorsiflexion.¹ Throughout my education in podiatry school, I learned that “equinus deformity” was one of the worst deforming forces that could be present within the human foot. I learned that if a patient had less than 10 degrees of ankle joint dorsiflexion, the potential for serious dysfunction and deformity of the foot over time due to this “equinus deformity” was significantly increased.

Now, after over 32 years of clinical practice and teaching, I have a very different perspective on the measurement and clinical significance of what DPMs call “equinus deformity.” During that time, it became very clear that “equinus deformity” is not always associated with pathology. “Equinus deformity” may be present in many otherwise normally functioning individuals who are asymptomatic.

For example, I have examined thousands of asymptomatic running athletes over the past three decades and have found that most of them have “equinus deformity,” even though they are performing at high levels of athletic competition on a regular basis. Why do these high-performance athletes and other asymptomatic individuals seem to function and perform perfectly fine with less than 10 degrees of ankle joint dorsiflexion if “equinus deformity” is so bad? Is there a competitive advantage for runners and other running athletes who have an “equinus deformity”? Could “equinus deformity” not be so evil after all?

I certainly have seen many patients in whom a limitation of ankle joint dorsiflexion or “equinus deformity” was likely the main biomechanical cause of their pathologies. However, I am also not so certain that the “equinus deformity” I measured in the patient would also be considered an “equinus deformity” by another podiatrist. Why? Well, the Root and colleagues method of measuring ankle joint dorsiflexion in a non-weightbearing setting with the subtalar joint in neutral, like many of the other biomechanical measurements we learned to obtain in podiatry school, does not have good reliability.

The measurement of ankle joint dorsiflexion advocated by Root and coworkers, using a goniometer in a non-weightbearing setting with the subtalar joint in neutral, demonstrates only a moderate intra-rater reliability and poor inter-rater reliability.^2,3 In other words, if one DPM measures ankle joint dorsiflexion and finds 10 degrees of ankle joint dorsiflexion in an individual, another podiatrist may find only 3 degrees of ankle dorsiflexion in that same individual. Unfortunately, this clinical scenario probably happens more than we all want to believe.

Interestingly, for many years, other health professionals have been using the lunge test, an ankle joint dorsiflexion test that research has shown to have good reliability.^4,5 The lunge test is a weightbearing test in which one places the foot on the ground and the ankle is dorsiflexed by flexing the knee forward toward a wall. However, the weightbearing lunge test, since patients do not do it in subtalar joint neutral but do it weightbearing with the knee flexed, demonstrates a much greater range of dorsiflexion than the ankle dorsiflexion test used by most DPMs. In a study of cavus, normal arched and planus feet, Burns and Crosbie found the lunge test had 26 degree, 32 degree and 43 degree dorsiflexion angles respectively.⁶ In other words, the lunge test demonstrates about 20 degrees more ankle joint dorsiflexion than the non-weightbearing ankle joint dorsiflexion test.

So what does “ankle equinus” mean and what is the best method to measure it? The answer to this question is far too complicated for this column. However, I do know that before the podiatric surgeon starts to consider exactly how much “equinus deformity” the patient has and starts making surgical decisions about lengthening the gastrocnemius muscle or Achilles tendon based on that one measurement parameter, he or she may want to stop and consider something very important. The surgeon may want to consider that his or her measurement of ankle dorsiflexion for this patient may not be what another skilled podiatrist would measure for ankle dorsiflexion in the same patient. The best podiatrists aren’t afraid to question their own knowledge and judgment for the benefit of their patients.

Dr. Kirby 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 in private practice in Sacramento, Calif.

References

1.    Root ML, Orien WP, Weed JH, RJ Hughes. Biomechanical Examination of the Foot, Volume 1. Clinical Biomechanics Corporation, Los Angeles, 1971, pp. 90-97.
2.    Kim PJ, Peace R, Mieras J, Thomas T, Freemen D, Page J. Interrater and intrarater reliability in the measurement of ankle joint dorsiflexion is independent of examiner experience and technique used. J Am Podiatr Med Assoc. 2011;101(5): 407-414.
3.    Elveru RA, Rothstein JM, Lamb RL. Goniometric reliability in a clinical setting: subtalar and ankle joint measurements. Physical Therapy. 1988;68(5):672-677.
4.    Bennell K, Talbot R, Wajswelner H, Techovanich W, Kelly D, Hall AJ. Intra-rater and inter-rater reliability of a weight-bearing lunge measure of ankle dorsiflexion. Australian J Physiother. 1998;44(3):175-180.
5.    Powden CJ, Hock JM, Hock MC. Reliability and minimal detectable change of the weight-bearing lunge test: a systematic review. Manual Therapy. 2015;20(4):524-532.
6.    Burns J, Crosbie J. Weight bearing ankle dorsiflexion range of motion in idiopathic pes cavus compared to normal and pes planus feet. Foot. 2005;15(2):91-94.