Does every athlete have equinus? How can physicians accurately measure ankle joint dorsiflexion? How effective is therapeutic stretching? This author reviews the literature to answer these questions and examines the relationship between equinus, Achilles tendinopathy and plantar fasciitis.
Equinus in the athlete is a controversial topic. Some have opined that since almost every athlete has equinus but a smaller percentage of athletes actually suffer from a pathology, equinus may not actually be pathologic.1,2
This thinking follows the old adage of “not seeing the forest for the trees.” Just because a physician sees an athlete at a specific point in time with equinus deformity but without symptomatology, that does not mean the equinus deformity is not a pathological entity that will eventually result in pathology. Although many authors have previously answered this question, Johnson and Christensen provided prophetic insight on equinus by stating “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 . …”3
Amis described the consequence of equinus by saying, “Thus, the mere concept that equinus has anything to do with foot pathology is generally unknown or disregarded. The split second effect, described here, defines exactly how the silent equinus contracture creates incremental and significant damage and injury to the human foot and ankle resulting in a wide variety of pathological conditions.”4
Much of the misconception about equinus and preventative conservative treatment in athletes is based on a confusion regarding stretching terminology. Surgical treatment of equinus in the asymptomatic athlete is not part of this discussion and has little to no evidence-based support. The other component of the confusion on this topic is a fundamental lack of awareness of evidence-based research on the role of equinus as the primary risk factor for the three most common running-related injuries.
Accordingly, let us take a closer look at the evidence-based research to clarify this topic and hopefully provide insight on how simple therapeutic stretching for equinus leads to improved athletic performance while reducing the risk of potentially career-threatening injuries.
Defining Equinus: What The Emerging Literature Reveals
Substantial evidence-based research on evaluating and defining equinus has surfaced over the past several months.5,6 The literature describes 23 different methods to measure ankle joint dorsiflexion.5 The ankle joint dorsiflexion angle can differ between 8.5 and 10 degrees depending on placement of the foot in a pronated position versus a supinated position. This variation in measurement contributes to the lack of consensus for a definition of equinus.5,7
The method of equinus evaluation described by Root and colleagues (subtalar neutral with locking of the midtarsal joint while dorsiflexing the ankle) has poor inter-rater and intra-rater reliability, according to a 2017 investigation by Gatt and coworkers.5 Conversely, supinating the foot reduces the midtarsal joint to 2.5 degrees of motion (considered clinically insignificant), producing a reproducible method to evaluate equinus deformity.5
Dayton and colleagues confirmed the findings by Gatt and coworkers.6 In their study, Dayton and coauthors compared ankle joint dorsiflexion clinically and radiographically (ankle maximally dorsiflexed with a lateral view measuring the tibiotalar angle) with the foot supinated, pronated and in neutral position.6 The radiographic findings showed little difference between foot position but clinical examination demonstrated a mean difference of 14 degrees between pronated and supinated foot positions. The researchers also found a significant difference of 9.08 degrees between neutral and supinated positions. The authors recommended a supinated foot position as being more reliable to measure the ankle joint range of motion.6
Gatt and colleagues sought a definition for equinus based on the relationship between static diagnosis and dynamic function of foot and ankle dorsiflexion in late midstance.5 It is well established that 10 degrees of ankle dorsiflexion is required in late midstance to allow the body to move over the foot without compensation.4,5 Using a validated gait analysis system, the researchers evaluated two groups based on clinical examination (-5 degrees or less of ankle dorsiflexion and -5 degrees to 0 degrees of ankle dorsiflexion) for the amount of ankle-foot dorsiflexion in late midstance.5 The authors demonstrated a significant difference between the groups with the -5 degrees group averaging 4.4 degrees of dorsiflexion and the -5 degrees to 0 degrees group averaging 13.9 degrees. Based on these findings, the authors recommended a definition for equinus of -5 degrees or less of ankle joint dorsiflexion with the knee extended.
Investigating The Link Between Equinus And Injuries In Athletes
In a 2012 systematic review, Lopes and colleagues examined running-related musculoskeletal injuries.8 After evaluating 2,924 potential studies, the authors found eight studies (involving a total of 3,500 runners) that matched their study criteria of discussing the incidence or prevalence of running-related musculoskeletal injuries. The review found 28 running-related musculoskeletal injuries with the three most common general running-related musculoskeletal injuries being medial tibial stress syndrome (prevalence of 9.5 percent), Achilles tendinopathy (prevalence between 6.2 and 9.5 percent) and plantar fasciitis (prevalence from 5.2 to 17.5 percent).8
The relationship between equinus and plantar fasciitis is no longer debatable. Patel and DiGiovanni found that 83 percent of patients with plantar fasciitis (either acute or chronic) have an underlying equinus deformity.9 A more recent study by Nakale and colleagues also examined the association between equinus and plantar fasciitis.10 With remarkably similar results to the Patel and DiGiovanni study, Nakale and coworkers showed 80 percent of the plantar fasciitis group had an equinus deformity. The study found a “very strong association” between isolated gastrocnemius tightness and plantar fasciitis as well as a strong association between isolated gastrocnemius tightness and other foot and ankle pathology. The authors also noted women and middle-aged people are at higher risk for plantar fasciitis. The study authors suggest treating isolated gastrocnemius tightness early when managing plantar fasciitis and other lower extremity pathology.
A study by McNamee and colleagues examined the risk factors for developing plantar fasciitis in runners.11 The study found “strong evidence” linking limited ankle dorsiflexion and plantar fasciitis in physically active patients. For the loss of every 1 degree of ankle range of motion (ROM), the risk factor for plantar fasciitis increased by 14.6 percent. Longitudinal arch angle and body mass index (BMI) did not significantly affect plantar fasciitis risk. These later findings are in direct contrast to the commonly held assumption of a pronated foot structure and increased BMI being risk factors for plantar fasciitis.
Riddle and coworkers evaluated risk factors for plantar fasciitis in a patient population that included active people.12 Ankle joint dorsiflexion of ≤0 degrees had an odds ratio of 23.3 for plantar fasciitis in comparison to ankle joint dorsiflexion ≥ 10 degrees. A BMI of ≥ 30 kg/m2 resulted in an increased odds ratio of 5.6 for plantar fasciitis in comparison to BMI ≤ 25 kg/m2. Likewise, an increased activity level resulted in an increased odds ratio of 3.6 in comparison to those with a more sedentary lifestyle. Equinus was a significantly higher risk factor for developing plantar fasciitis in comparison to the other factors although the researchers found all three factors to be statistically significant. Sullivan and colleagues also found that abnormal BMI and decreased ankle joint dorsiflexion along with reduction in foot and ankle strength increased the risk of plantar fasciitis in the general population.13
Key Insights On Achilles Tendinopathy In Athletes With Equinus
Becker and coworkers examined the biomechanics of runners with Achilles tendinopathies or medial tibial stress syndrome in comparison to matched, uninjured control patients.14 There was a statistically significant difference in ankle joint dorsiflexion between the injured groups and the control groups with the injured groups showing less dorsiflexion. A difference in standing tibial varus was statistically significant between the injured group and control group while the nine other remaining biomechanical findings showed no difference between groups. The authors noted reduced static dorsiflexion in injured patients correlates with previous studies that reported a lack of static ankle dorsiflexion to predict the development of both medial tibial stress syndrome and Achilles tendinopathies.
The relationship between equinus and Achilles tendinopathy is rooted in the evolutionary transformation from quadrupedal gait to bipedal gait that occurred over 2 to 3 million years.15-19 For bipedal gait to occur, the calcaneus dropped 70 degrees to sit flat on the ground.15 The gastrocnemius soleus, hamstrings and hip flexors lengthened for this structural change to occur. Since this occurred later in the evolutionary process, these muscles are the first to tighten with aging. The result is “shortening of the muscles and non-uniform tendon force would theoretically result in intratendinous shear strain, and therefore cause sliding between the planes of tissue layers parallel to the acting forces … subsequently this shear stress could cause inflammation of the peritenon.”19
Although all three pathologies described by Lopes and coworkers can result in significant loss of playing time for an athlete, Achilles tendinopathies progressing to Achilles tendon rupture are potentially career-ending.8 Trofa and colleagues found that out of 62 patients who played in the National Basketball League, National Football League or Major League Baseball, 30 percent did not return to competition after an Achilles tendon rupture.20 In the first year following a rupture, professional athletes who did return to play performed at substantially lower levels in comparison to their pre-injury performance metrics, taking two years to return to pre-injury performance levels.
A Closer Look At The Benefits Of Stretching
If the three main running-related pathologies all have equinus as their one singular risk factor, why is therapeutic stretching of the athlete to reduce injury risk not commonplace?
The misunderstanding centers around confusion about stretching terminology. The goal of stretching a muscle and tendon is to increase range of motion, flexibility and muscle control. Static stretching is “a stretch ... held in a challenging but comfortable position for a period of time” while dynamic stretching is “stretch ... performed by moving through a challenging but comfortable range of motion.”21 Stretching can also be passive (using body weight, gravity, another person or a device) or active (contraction of the muscle in opposition to the muscle you are stretching). Athletes do warm-up stretching just prior to athletic participation while therapeutic stretching mainly aids individuals in regaining the function affected by a loss in ROM and occasionally to alleviate pain.22 In regard to elite basketball players, the impression among health care providers is that stretching reduces athletic explosiveness. This is only partially correct.
Research on the acute effects of stretching on strength performance shows stretching exercises before a main strength activity significantly worsened the performance of 4.5 to 28 percent of athletes in most studies due to a reduction in strength.23 However, the chronic effects of static stretching on strength performance produce significant gains in flexibility (important in cases involving equinus) while increasing eccentric, concentric and isometric peak torque.23 Authors attribute this to hypertrophy of the stretched muscles.
In their systematic review of acute and chronic stretching on athletic performance, Stone and colleagues found consistently reduced performance with acute (warm-up static) stretching.24 Seven of the articles they reviewed on chronic (therapeutic static) stretching showed improved athletic performance and two articles showed no effect (negative or positive). In regard to chronic therapeutic static stretching, the authors concluded that studies generally indicated enhanced performance with stretching, especially maximum strength and explosive strength performances. As a whole, the studies in the review noted a small degree of enhanced performance, about 3 to 4 percent. The authors emphasized that “in high-level sports, a small percentage of improvement can actually be a lot.”24
Athletes sometimes use ballistic stretching (static or dynamic stretching in a bouncing motion) as warm-up stretching but a study by Medeiros and Martini notes ballistic stretching did not increase dorsiflexion range of motion.25 The authors argued that regular stretching, particularly with a static component, can effectively improve ankle mobility in healthy patients.25
Stretching is an effective, safe and simple method of treatment for equinus. Equinus is the primary risk factor for the top three running-related injuries for athletes: plantar fasciitis, Achilles tendinopathy and medial tibial stress syndrome. Chronic therapeutic stretching to treat equinus reduces the risk for these three injuries while improving lower extremity biomechanics. An additional benefit is improvement in athletic performance.
Why isn’t regular therapeutic stretching the norm for athletes? The reasons are multifactorial but evidence-based research dictates a paradigm shift. Health care providers and athletes both need to increase their awareness of equinus deformity and implement simple, effective chronic therapeutic stretching to treat equinus.
Dr. DeHeer is a Fellow of the American College of Foot and Ankle Surgeons, and a Diplomate of the American Board of Podiatric Surgery. He is also a team podiatrist for the Indiana Pacers and the Indiana Fever. Dr. DeHeer is in private practice with various offices in Indianapolis and is the founder of Step by Step Haiti.
Dr. DeHeer has disclosed that he is the Principal of IQ Medical, the manufacturer of the Equinus Brace.
1. Kirby K. Equinus deformity: too many questions, not enough answers. Pod Today. 2017; 30(12):58.
2. Jarvis HL, 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.
3. 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.
4. Amis J. The split second effect: the mechanism of how equinus can damage the human foot and ankle. Frontiers Surg. 2016; 3:38.
5. Gatt A, De Giorgio S, Chockalingam N, Formoas 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.
6. Dayton P, Feilmeier M, Parker K, et al. Experimental comparison of the clinical measurement of ankle joint dorsiflexion and radiographic tibiotalar position. J Foot Ankle Surg. 2017; 56(5):1036-1040.
7. Charles J, Scutter SD, Buckley J. Static ankle joint equinus: toward a standard definition and diagnosis. J Am Podiatr Med Assoc. 2010; 100(3):195-203.
8. Lopes AD, Hespanhol Junior LC, Yeung SS, Costa LO, et al. What are the main running-related musculoskeletal injuries? Sports Med. 2012; 42(10):891-905.
9. Patel A, DiGiovanni B. Association between plantar fasciitis and isolated contracture of the gastrocnemius. Foot Ankle Int. 2011; 32(1):5-8.
10. Nakale NT, Strydom A, Saragas NP, Ferrao PNF. Association between plantar fasciitis and isolated gastrocnemius tightness. Foot Ankle Int. 2018; 39(3):271-277.
11. McNamee MJ. Analysis of plantar fasciitis risk factors among intercollegiate and recreational runners: a matched case-control study. Thesis submitted to the Graduate Council of Texas State University, May 2016.
12. Riddle DL, Pulisic M, Pidcoe P, Jonson RE. Risk factors for plantar fasciitis: a matched case-control study. J Bone Joint Surg. 2003; 85(5):872-877.
13. Sullivan J, Burns J, Adams R, et al. Musculoskeletal and activity-related factors associated with plantar heel pain. Foot Ankle Int. 2015; 36(1):37-45.
14. Becker J, James S, Wayner R, et al. Biomechanical factors associated with achilles tendinopathy and medial tibial stress syndrome in runners. Am J Sports Med. 2017; 45(11):2614-2621.
15. Amis J. The gastrocnemius: a new paradigm for the human foot and ankle. Foot Ankle Clin. 2014; 19(4):637-647.
16. Bojsen-Møller J, Magnusson SP, Rasmussen LR, et al. Muscle performance during maximal isometric and dynamic contractions is influenced by the stiffness of the tendinous structures. J Appl Physiol. 2005; 99(3):986-994.
17. Lintz F, Higgs A, Millett M, et al. The role of plantaris longus in Achilles tendinopathy: a biomechanical study. Foot Ankle Surg. 2011; 17(4):252-255.
18. Malvankar S, Khan WS. Evolution of the Achilles tendon: The athlete’s Achilles heel? Foot. 2011; 21(4):193-197.
19. Järvinen TA, Kannus P, Maffulli N, Khan KM. Achilles tendon disorders: etiology and epidemiology. Foot Ankle Clin. 2005; 10(2):255-266.
20. Trofa DP, Miller JC, Jang ES, et al. Professional athletes’ return to play and performance after operative repair of an Achilles tendon rupture. Am J Sports Med. 2017; 45(12):2864-2871.
21. Human Kinetics. Types of stretches. Available at http://www.humankinetics.com/excerpts/excerpts/types-of-stretches .
22. Lederman E. Introduction to therapeutic and functional stretching. In Lederman E (ed.): Therapeutic Stretching, chapter 1. Elsevier, Netherlands, 2013, pp.1–14.
23. Rubini EC, Costa ALL, Gomes PSC. The effects of stretching on strength performance. Sports Med. 2007; 37(3):213-224.
24. Stone M. Stretching: Acute and chronic? The potential consequences. Strength Cond J. 2006; 28(6):66.
25. Medeiros DM, Martini TF. Chronic effect of different types of stretching on ankle dorsiflexion range of motion: Systematic review and meta-analysis. Foot. 2018; 34:28–35.
For further reading, see the DPM Blog “Why Equinus Is The Root Of All Foot Evils” at https://tinyurl.com/yaxcgap2, “Understanding The Biomechanics Of Equinus” in the September 2014 issue of Podiatry Today or “Understanding And Managing Equinus Deformities” in the May 2011 issue.