What The Study By Jarvis And Colleagues Got Wrong About Equinus

Let’s play a game. You pick any set of numbers and I will guarantee those numbers will be chosen for the lottery sometime during your life. The only catch is you must predict the day those numbers will be picked.

My example is the same game Jarvis and colleagues are playing with their controversial article titled, “Challenging the foundations of the clinical model of foot function: further evidence that the Root model assessments fail appropriately to classify foot function.”¹ Doug Richie, DPM, in his recent DPM Blog, did an excellent job examining this article (https://www.podiatrytoday.com/blogged/defending-root-new-study-jarvis-and-colleagues-all-it-cracked-be ).

I am going to critically examine the methodology of the equinus portion of the Jarvis article. Then I am going to do what I do best: use the literature to disprove the absurd conclusion that equinus is not a pathological condition. The authors state, “The high number of cases in a symptom-free group is good evidence that the deformities are in fact not deformities nor abnormalities at all. Indeed, other literature has identified these ‘deformities’ in symptom-free populations.”¹

Jarvis and colleagues measure for equinus based on old techniques. Gatt and colleagues in their recent article discussed the assessment of equinus and I will use their research to refute the measurement techniques discussed by Jarvis and colleagues.² Jarvis referenced an earlier study, also led by Jarvis and coworkers, to describe their technique.³ The technique consisted of one arm of the goniometer placed along the fibula and the other arm parallel to the plantar surface of the foot. Researchers measured ankle joint dorsiflexion with the knee flexed and extended.

Gatt and colleagues note that 23 different methods of equinus measurement documented in the literature.² Jarvis and colleagues do not mention foot position in their descriptions of equinus evaluation and utilize a digital goniometer to measure.¹ This product lacks evidence-based validation as a reliable tool. Several recent articles stress the importance of supinating the foot while dorsiflexing the ankle.^2,4-6 The difference in measurement based on a supinated foot in comparison with a pronated foot can vary as much as 8.5 to 10 degrees.^7-9 Supination of the foot reduces midtarsal joint motion to a clinically insignificant amount of 2.5 degrees.⁹

Additionally, researchers did not place the hinge of the measuring device at the ankle joint axis. On this point, Gatt and coworkers stated, “It stands to reason that should one wish to measure foot dorsiflexion, the axis of the goniometer in line with the axis of the ankle which passes between the malleoli.”² 

The measurement of dynamic ankle joint dorsiflexion during gait in the Jarvis and colleagues study revealed no statistical difference between the group with < 10 degrees of static ankle joint dorsiflexion (considered the equinus group) and the group with > 10 degrees of static ankle joint dorsiflexion (non-equinus group), 5.6 and 6.6 degrees of dynamic ankle joint dorsiflexion during midstance of gait respectively.¹ Conversely, Gatt and coworkers, through the use of optoelectronic motion capture systems, demonstrated that ankle dorsiflexion exceeded 10 degrees during late midstance, which is consistent with the results of numerous authors and refutes the dynamic measurements recorded by Jarvis.² The discrepancy is another major red flag for the Jarvis study pertaining to the equinus findings. When < 10 degrees of ankle joint dorsiflexion occurs during late midstance to allow the body to move forward over a planted foot, compensatory changes occur proximally and distally to the ankle. Increasing load applied to the Achilles tendon is well known to inhibit the function of the peroneus longus tendon, resulting in a plantarflexion moment of the naviculocuneiform joint.^10,11 Thordarson and colleagues, as well as Amis, have clearly documented the arch deforming force due to the increasing load of the Achilles tendon.^12,13

The brilliance behind the study by Gatt and co-workers is the correlation between static ankle/foot dorsiflexion as it relates to dynamic function.² This pilot study showed a statistically difference between the group with -5 degrees of static ankle joint dorsiflexion (4.4 mean dynamic ankle joint dorsiflexion during midstance) and the group with 0 to -5 degrees (13.9 degrees). This is the first article to display the relationship between static and dynamic measurement, demonstrating the point when pathological forces occur. This is evidence-based research, unlike the speculative opinions spouted by Jarvis and coworkers.

The most absurd reach made by Jarvis and colleagues is that in their sample of 140 asymptomatic volunteers, a certain number of participants demonstrated < 10 degrees of dorsiflexion yet displayed no pathology.¹ They used this observation to claim that equinus must, therefore, be normal.

Many authors have shown the association between equinus and lower extremity pathologies. For example, consider the paradigm shift in recalcitrant plantar fasciitis being treated surgically via a gastrocnemius recession as opposed to a plantar fasciotomy.^14-17 Gastrocnemius recession is documented therapy to address other conditions such as metatarsalgia, midfoot pain, Achilles tendonitis, calf pain and pes plano valgus. Amis demonstrated the pathological force due to equinus occurred for only 1/10th of a second during late midstance, resulting in “occult, unrecognized, overuse of imbalance” occurring over thousands of daily steps over a period of years.¹³ Johnson and Christensen stated, “In clinical practice, the early destructive influence of equinus is often not appreciated. Instead, we are usually faced with the end result of equinus effects … .”¹¹ I have created a list of lower extremity pathologies associated with equinus in the literature.¹⁸ I updated the references, which now stand at 158 for more than 30 conditions.

I am astonished the Jarvis and colleagues article was published. I review articles for peer-reviewed journals. The methodology and conclusions are beyond flawed in this study. On the other hand, the Gatt article is valuable and useful information based on sound scientific methods. Some of my podiatric colleagues are spouting the ridiculous findings of Jarvis and colleagues as real evidence-based research, but it is “fake news.” Buyer beware.

References

1. Jarvis H, Nester CJ, Bowden PD, Jones RK. Challenging the foundations of the clinical model of foot function: further evidence that the root model assessments fail to appropriately classify foot function. J Foot Ankle Res. 2017; 10(1):7.
2. Gatt A, DeGiorgio S, Chockalingam N, Formosa C. A pilot investigation into the relationship between static diagnosis of ankle equinus and dynamic ankle and foot dorsiflexion during stance phase of gait: Time to revisit theory? Foot. 2017; 30:47-52.
3. Jarvis HL, Nester CJ, Jones RK, et al. Inter-assessor reliability of practice based biomechanical assessment of the foot and ankle. J Foot Ankle Res. 2012; 5(1):14.
4. Barouk P, Barouk LS. Clinical diagnosis of gastrocnemius tightness. Foot Ankle Clin. 2014; 19(4):659-667.
5. Morales-Muñoz P, De Los Santos Real R, Barrio Sanz P, et al. Proximal gastrocnemius release in the treatment of mechanical metatarsalgia. Foot Ankle Int. 2016; 37(7):782-789.
6. Liu RW, Xie KK. Association between Achilles tightness and lower extremity injury in children. HSS Journal. 2016; 12(3):245-249.
7. Tiberio D, Bohannon RW, Zito MA. Effect of subtalar joint position on the measurement of maximum ankle dorsiflexic. Clin Biomech. 1989; 4(3):189-191.
8. Woodburn J. Video joint angle position analysis of the subtalar joint position on maximum ankle joint dorsiflexion. J Br Podiatr Med. 1991; 46:19-22.
9. Gatt A, Chockalingam N, Larose Chevalier T. Sagittal plane kinematics of the foot during passive ankle dorsiflexion. Prosthet Orthotics J. 2011; 35(4):425-431.
10. Johnson CH, Christensen JC. Biomechanics of the first ray part I. The effects of peroneus longus function: A three-dimensional kinematic study on a cadaver model. J Foot Ankle Surg. 1999; 38(5):313-321.
11. Johnson CH, Christensen JC. Biomechanics of the first ray part V: The effect of equinus deformity: A 3-dimensional kinematic study on a cadaver model. J Foot Ankle Surg. 2005; 44(2):114-120.
12. Thordarson DB, Schmotzer H, Chon J, Peters J. Dynamic support of the human longitudinal arch: a biomechanical evaluation. Clin Orthop Rel Res. 1995; 316:165-172.
13. Amis J. The split second effect: the mechanism of how equinus can damage the human foot and ankle. Front Surg. 2016; 3:38.
14. Abbassian A, Kohls-Gatzoulis J, Solan MC. Proximal medial gastrocnemius release in the treatment of recalcitrant plantar fasciitis. Foot Ankle Int. 2012; 33(1):14-19.
15. Maskill JD, Bohay DR, Anderson JG. Gastrocnemius recession to treat isolated foot pain. Foot Ankle Int. 2010; 31(1):19-23.
16. Molund M, Paulsrud O, Ellingsen Husebye E, et al. Results after gastrocnemius recession in 73 patients. Foot Ankle Surg. 2014; 20(4):272-275.
17. Monteagudo M, Maceira E, Garcia-Virto V, Canosa R. Chronic plantar fasciitis: plantar fasciotomy versus gastrocnemius recession. Int Orthoped. 2013; 37(9):1845-1850.
18. DeHeer PA. Equinus and lengthening techniques. Clin Podiatr Med Surg. 2017; 34(2):207–27.