Sometimes when reading an article, you come across something that is extremely profound, an idea that you know will change a practice paradigm. The discussion on equinus at first glance may seem to have reached its pinnacle but I propose that the discussion on equinus has barely scratched the surface.
Foot and Ankle Clinics of North America supports me in this opinion with its December 2014 edition titled “The Gastrocnemius.” The entire issue consists of 13 articles, all related to equinus. Our orthopedic foot and ankle colleagues believe that equinus is a topic requiring significantly more discussion.
James Amis, MD, authored what I consider a landmark article titled “The Gastrocnemius: A New Paradigm for the Human Foot and Ankle.”1 In this chapter, Dr. Amis discuss the origins of equinus and that is what I would like to focus on in this blog. He describes four general categories that lead to gastrocnemius contracture: activity changes, physiologic changes in muscles and tendons, genetics, and reverse evolution.
Amis further divides the activity changes category into three subcategories. Generalized decreased activities with aging result in the muscle-tendon unit not stretching to its maximum distance. As we age and become more sedentary, the gastrocsoleus complex shortens according to the Law of Davis (over time our soft tissue contracts to the shortest position possible).2 We are no longer our younger selves running, jumping and playing, which maximally stretches out the gastrocsoleus complex. This isolated gastrocnemius contracture is slow and develops over years. Activity-related equinus explains why equinus is so common in the adult population and is typically limited in the pediatric population to pathologic situations.
Recent changes in activity such as bed rest from a surgery or injury also lead to contracture of the gastrocsoleus complex.1 Due to the Law of Davis, this sudden reduction in activity results in gastrocsoleus complex contracture.1 This type of contracture occurs quickly.
The final type of contracture due to change in activity occurs in athletes. Athletic contracture is particularly an issue for running-related activities as the knee never fully extends while dorsiflexing the foot. The running gait cycle leads to shortening of the gastrocsoleus complex with adaptation over time.1
Physiologic changes to muscle and tendon occur with aging, leading to internal changes.1 Several factors occur with aging that are inescapable. These factors include cross-linking of collagen fibers, connective tissues becoming less compliant, and a decreasing amount of elastin in soft tissue. All of this causes contracture of the muscle-tendon unit.1
Genetics also plays a role in muscle-tendon tightness, explaining why some people have tighter muscles than other people with this tendency occurring along family lines.1
The final category is an interesting topic called reverse evolution. Approximately 2.2 to 3 million years ago, humans transformed from quadrupeds to bipeds.3,4 For this to occur, certain muscles had to lengthen (hip flexors, hamstrings, gastrocsoleus complex) and others had to shorten (quadriceps, tibialis anterior).1 The ankle could then dorsiflex approximately 70 degrees and the knee and hip extend as well for bipedal gait. As Dr. Amis states, “Because these muscle groups adapted later in the evolutionary process, they are the first to move backward and tighten as a person ages, reverting to their former positions. This is called a predilection pattern, leading to many problems with the calves and the hamstrings.”1
Dr. Amis makes a very strong statement: “I believe that there is a simple, singular, silent, and remote cause of the many foot and ankle problems, which are mechanically created, leading to incremental damage to the foot and ankle through leveraged forces: the human calf that becomes too tight with age. In short, the isolated gastrocnemius contracture is the common denominator that leads to many of the human non-traumatic foot and ankle problems.”1
The contracting nature of our gastrocsoleus complex with age produces a pathological event that over time results in secondary pathologies. Should we not consider intervention once the patient has a primary pathological event before secondary changes occur?
1. Amis J. The gastrocnemius. Foot Ankle Clin. 2014;19(4):637-647.
2. Nutt J. Diseases and Deformities of the Foot. E.B. Treat & Company, New York, 1913.
3. Morton D. Evolution of the longitudinal arch of the human foot. J Bone Joint Surg Am. 1924;6(1):56-90.
4. Schmitt D. Insights into the evolution of human bipedalism from experimental studies of humans and other primates. J Experimental Biol. 2003;206(9):1437-1448.
Editor's note: Dr. DeHeer is the inventor of the EQ/IQ brace.