Surveying The Literature To Find An Absolute Definition Of Equinus

“Equinus deformity is the most profound causal agent in foot pathomechanics and is frequently linked to common foot pathology,” is a quote from an article by Johnson and Christensen.1 This statement about equinus is something that is vastly underappreciated. It is profound but in my opinion, we as practitioners are not paying enough attention to it. I believe that is because there is no absolute definition of equinus.

I propose to provide an absolute definition of equinus based on three very profound articles. I have sifted through almost everything written on equinus and have come to the conclusion that there is an absolute definition. In the literature, the definition of equinus ranges between -10 degrees and +22 degrees of ankle joint dorsiflexion for normal ambulation. The consensus of 13 different studies was 10 degrees.1-4 Arriving at a definite definition should make communication between specialties and communication among podiatrists much easier when discussing equinus.

For example, I am the team podiatrist for the Indiana Pacers and Indiana Fever, and I think every player has equinus. The trainers do not think any of the players have equinus. It is a matter of definition and evaluation.

What The Research Reveals

The first article I would like to discuss helps establish a definition of equinus but also shows how frequently it is associated with the pathologies we see every day in our practices.

In 1995, Hill evaluated 206 new patients over a six week period of time from the Kaiser Permanente clinics.2 Twenty-six patients were excluded from the study because they did not meet criteria as they had conditions like ingrown toenails, onychomycosis, verrucae plantaris, etc. Six patients of the 174 remaining had normal ankle joint dorsiflexion. Of the 168 patients left, three has gastrocnemius equinus and 165 had gastrocsoleus equinus.

Hill used a definition of 3 degrees of ankle joint dorsiflexion with the knee extended.2 In the study, 96.5 percent of the patients with foot, ankle or leg symptoms had equinus. While I think equinus is very common, I think his definition was a little insufficient and will use the remaining two articles to further discern a definite definition.

In 1991, Grady and Saxena did a non-blinded examination of ankle joint dorsiflexion with various times of stretching exercises of 30 seconds, two minutes or five minutes once a day for six months.3 The study found the average pre-stretching measurements of the 25 participants to be 2.86 +/- 2.99 degrees of dorsiflexion with the knee extended and 9.02 +/- 2.35 degrees of dorsiflexion with the knee flexed. Their study showed no statistical significance to the improved ankle joint dorsiflexion to recommend manual stretching.

The key point for this discussion is the pre-treatment numbers. The patients underwent measuring with a goniometer in subtalar neutral with the midtarsal joint locked.3 This number is similar to Hill’s definition of 3 degrees but again, I think it is slightly off.

DiGiovanni and colleagues’ study examined the frequency of equinus in a symptomatic patient group and control group, and the reliability of clinical evaluation of equinus in comparison to an equinometer (think of a computer measurement of ankle joint dorsiflexion).4 They used two definitions of equinus: 5 degrees and 10 degrees ankle joint dorsiflexion with the knee extended. In the symptomatic group, the average ankle joint dorsiflexion with the knee extended was 4.5 degrees. In the control group, it was 13.1 degrees.

The 5-degree group consisted of 65 percent of the symptomatic patients and 24 percent of the control group.4 The 10-degree group consisted of 88 percent of the symptomatic group and 44 percent of the control group. The reliability of clinical exam in comparison to the equinometer for the 5-degree group was 76 percent for the symptomatic group and 94 percent for the control group. For the 10-degree group, the reliability was 88 percent for the symptomatic group and 79 percent for the control group.

The following quote from their article summarizes their findings: “We have selected < 5º of maximal ankle dorsiflexion with the knee in full extension as our definition because it allowed us to diagnose the problem in those who were at risk (symptomatic patients) with fairly good reproducibility (76%) and, more importantly, we were able to reliably avoid (in 94% of the cases) unnecessary treatment of those who were not at risk (asymptomatic people).”4

Final Notes

When examining this literature, it is clear to me that the standard definition of equinus should be 5 degrees of ankle-foot dorsiflexion with the knee extended. The first two studies’ numbers are very close to this and the third study recommended using this value.1-3 It is important to have the subtalar joint in neutral position and the midtarsal joint locked.

In my next blog, I will discuss why I think night splints are ineffective and the solution I have come up with to solve the most profound condition we as foot and ankle specialists treat. Best wishes. Stay diligent.

References

1. Johnson CH, Christensen JC. Biomechanics of the first ray part V: the effect of equinus deformity. J Foot Ankle Surg. 2005; 44(2):114-120.

2. Hill RS. Ankle equinus: prevalence and linkage to common
foot pathology. JAPMA. 1995; 85(6):295-300.

3. Grady JF, Saxena A. Effects of stretching the gastrocnemius muscle. J Foot Surg. 1991; 30(5):465-9.

4. DiGiovanni CW, Kuo R, Tejwani N, et al. Isolated gastrocnemius tightness. J Bone Joint Surg Am. 2002; 84-A(6):962-70.