Although equinus is reportedly “the most profound causal agent in foot pathomechanics,” the phenomenon has yet to be addressed fully in the diabetic foot. Accordingly, these authors discuss the definition of equinus and offer insights on the efficacy of stretching, night splints, a new bracing option, tendo-Achilles lengthening and gastrocnemius recession.

There have been remarkable strides in diabetic foot care in the past two decades with marked improvement in amputation prevention. The collaboration between the vascular community and podiatric wound care community has made a profound impact as well. Another significant improvement for our patients with diabetes has been the increased attention on preventive foot care, consisting of routine diabetic foot care, diabetic shoes and orthoses, and periodic foot exams. These preventive measures have made a significant impact in keeping the diabetic foot out of harm’s way.

However, there is one final piece to the puzzle that has yet to be formally addressed and recognized with the respect it deserves. Evaluation and management of equinus is the final step we must take to provide a comprehensive preventive care program for the diabetic foot.

For good reason, researchers have described equinus as “the most profound causal agent in foot pathomechanics and frequently linked to common foot pathology,” and “the greatest symptom producer of the human foot.”1 The devastation that equinus imparts upon the foot and lower extremity in the non-diabetic patient is well documented in the literature, but it can literally be life-threatening in the patient with diabetes. The morbidity associated with a below the knee amputation is unfortunately well known. Often, the precipitating factor to the amputation is a diabetic foot ulcer.

When one reviews the literature, it is undeniable that equinus significantly increases the risk of a diabetic foot ulcer. Therefore, the treatment of equinus can reasonably be considered a life-saving preventative measure.

In order to understand the depth of involvement of equinus in diabetic foot pathology, an understanding of the biomechanical impact of equinus on the foot is crucial. Olipa and colleagues described the center of pressure in the foot to be approximately 6 cm anterior to the ankle joint.2 Without the counterbalance of the gastroc-soleus complex, this anterior displacement of the center of pressure would make us fall forward in normal standing.

With equinus, the center of pressure moves distally and laterally, moving it farther away from the axis of the subtalar joint laterally. This increased distance from the axis of the subtalar joint results in a pronatory moment within the foot. This movement cannot be overcome by the supinatory moment created by the medially located gastroc-soleus complex insertion into the posterior aspect of the calcaneus. Besides an increase of pronatory forces due to equinus, the other results are increased pressure on the forefoot and decreased pressure on the rearfoot.

Johnson and Christensen evaluated the effect of equinus biomechanically on the medial column of the foot by using cadaver weightbearing models in their landmark series on first ray pathomechanics.1 The authors applied sensors to each of the individual bones making up the medial column of the foot. They applied loading of the Achilles tendon and then recorded three-dimensional data for each segment of the medial column.

The results showed plantarflexion of the talus and navicular, and dorsiflexion of the medial cuneiform and first metatarsal occurring through the naviculocuneiform joint. This occurs due to the dampening of the effect of the peroneal longus tendon eversion of the medial cuneiform that leads to locking of the midtarsal joint. This lack of midtarsal joint locking leads to the aforementioned medial column instability. This study showed the effect of equinus is not a stretching of the plantar ligaments over a period of time that leads to first ray instability but is in fact a dampening of the peroneus longus function that leads to first ray hypermobility.

The tragedy that is the diabetic Charcot deformity crystalizes with this understanding of medial column pathomechanics. This is why early equinus intervention is recommended in the acute Charcot deformity as patients can avoid much of the resultant deformity with release of the contracted gastroc-soleus complex. However, the biomechanical considerations of equinus are only one part of the understanding of this deformity.

Arriving At A Precise Definition Of Equinus

It is important to arrive at a standard definition of equinus before undertaking an evaluation of the deformity. The definition of equinus ranges from -10 degrees to + 22 degrees in the literature with +10 degrees as a consensus of 13 different studies. In 1975, Sgarlato first described the definition as +10 degrees with the subtalar joint in neutral position and the midtarsal joint locked.3

In 2002, DiGiovanni and co-workers examined ankle joint dorsiflexion in symptomatic patients and a control group, and the reliability of testing.4 The ankle joint dorsiflexion with the knee extended averaged 4.5 degrees in the symptomatic group and 13.1 degrees in the control group. The percentage of symptomatic patients with less than 5 degrees dorsiflexion was 65 percent and was 24 percent in the control group. The percentage of symptomatic patients with less than 10 degrees dorsiflexion was 88 percent and 44 percent in the control group respectively.

In regard to patients with less than 5 degrees of dorsiflexion, the study authors confirmed the correct diagnosis with an equinometer in 76 percent of the symptomatic group and 94 percent of the control group. For those with less than 10 degrees of dorsiflexion, researchers confirmed the correct diagnosis with the equinometer in 88 percent of the symptomatic group and 79 percent of the control group respectively.

Therefore, it becomes clear with the results of this study that equinus should be universally defined as less than 5 degrees of ankle joint dorsiflexion with the subtalar joint in neutral position and the midtarsal joint locked with the knee extended.4

Evaluating Equinus And Its Associated Pathologies

The clinical evaluation of equinus is one of the primary stumbling blocks between professions that inhibits effective communication. Clinicians can use the Silfverskiold test to determine the type of equinus. With this examination, one first places the subtalar joint in neutral position and locks the midtarsal joint by supinating the forefoot. Proceed to perform maximum dorsiflexion of the ankle with the knee in full extension. Then check this with the knee in flexion.

If the ankle joint dorsiflexes greater than 90 percent with both the knee extended and flexed, there is no equinus. If the ankle joint dorsiflexes greater than 90 percent with the knee flexed by less than 90 degrees with the knee extended, the result is gastrocnemius equinus. If the ankle dorsiflexion is less than 90 percent with both the knee flexed and extended, then it can either be gastroc-soleus equinus or osseous equinus.

One can determine this by the quality of the end range of motion and with a charger view or dorsiflexion stress lateral ankle X-ray. A soft end range of motion is more likely associated with a gasctroc-soleus equinus, especially if no anterior ankle impingement is present on the X-ray.

The pathologies associated with equinus are numerous and consist of proximal and distal pathologies. The proximal pathologies associated with equinus are numerous and easily overlooked due to the profound distal pathologies that often overshadow these proximal deformities. Lumbar lordosis, hip flexion, knee flexion, genu recurvatum and hamstring contractures have all been attributed to equinus. We will discuss the more obvious distal pathologies that directly result from or have a relationship to equinus with some of the well documented literature.

The study by Aronow and colleagues was one of the first to not only explore the changes on forefoot and rearfoot pressures associated with equinus, but also examined the midfoot changes as well.5 Researchers applied a load to the gastroc-soleus complex and then applied a load to just the gastrocnemius muscle. They subsequently measured the changes in pressures. In the gastroc-soleus group, the rearfoot pressures decreased by 18 percent and the midfoot and forefoot pressures increased by 38 and 59 percent respectively. In the gastrocnemius group, the rearfoot pressures decreased by 16 percent and the midfoot and forefoot pressures increased by 32 and 50 percent respectively.

These numbers were very consistent with other studies on the effect of equinus and forefoot pressure changes.6,7 When researchers removed the loads, the pressures on the forefoot decreased 32 percent and the rearfoot pressures increased 32 percent. These additional findings were similar to those of Mueller and co-workers, who measured the effect of a tendo-Achilles lengthening on pressure changes in the foot.8 In the study by Mueller and colleagues, the forefoot pressures decreased 31 percent and the rearfoot pressures increased by 34 percent.

In 1997, Grant and colleagues examined the effects of diabetes on the Achilles tendon.9 They took Achilles tendon samples from 12 patients with diabetes and five non-diabetic patients with foot pathology undergoing foot surgery. Researchers subsequently examined these specimens under an electron microscope.

The findings showed the patients with diabetes had increased packing density of collagen fibrils, decreases in fibrillar diameter and abnormal fibril morphology.9 The researchers theorized that the cause of these findings is non-enzymatic glycation over many years. In the non-diabetic patients, the fine structure of the Achilles tendon remained normal. These changes in the patients with diabetes lead to extreme shortening of the gastroc-soleal complex.

The effect that this extreme shortening of the Achilles tendon has on the diabetic foot is what Lavery, Armstrong and Boulton examined in their study in 2002.10 They reviewed 1,666 patients with diabetes over two years, placed patients in risk categories and treated them according to risk-based protocols. The authors defined equinus as ankle joint dorsiflexion of less than 0 degrees. Their findings showed the equinus group had peak plantar pressures in the forefoot that were three times higher in the forefoot in comparison to the non-equinus group.

In this study, the authors found a 10.3 percent rate of equinus in patients with diabetes. We think this is easily low because of the study authors’ definition of equinus. Remember, there is no standard definition of equinus. Patients with equinus also had a significantly longer duration of diabetes than those without equinus.

Assessing The Use Of Stretching And Night Splints

Clinicians can address equinus via either conservative care or surgical care. As with most pathological conditions, one should attempt conservative care initially. The two main forms of conservative care are manual stretching and bracing.

In a meta-analysis, Radford and co-workers showed that calf muscle stretching provided a small but statistically significant increase in ankle joint dorsiflexion.11 Their analysis showed that 15 to 30 minutes per day provided the greatest amount of ankle joint dorsiflexion (3.03 degrees) for each of the three groups. In their study, Grady and Saxena had patients stretch once per day for 30 seconds, two minutes or five minutes with the knee extended over a six-month period of time.4 The increase in ankle joint dorsiflexion for each group was 2.15, 2.3 and 2.7 degrees respectively. These totals were not statistically significant but when one takes into account the minimal amount of daily stretching, the results are actually encouraging.

In discussing the problems with manual stretching, Hill stated: “Active stretching requires detail in teaching the proper technique, and must be done at least four times a day at 5-minute to 8-minute sessions. The most serious mistakes patients make during their previous attempts at stretching are inadequate stretch time and abducted foot position during the stretch. It is critical that the foot be adducted 10 degrees during the stretching to lock the subtalar-midtarsal joints for maximum benefit at the calf.”13

Night splints have long been the only mode of bracing for equinus treatment but there are several flaws with them. First, they are designed for patients to use at night while sleeping and the most common sleeping position with these braces is on the side with knees bent.

This means that the gastrocnemius muscle is not stretching. Remember that as the gastrocnemius muscle crosses the knee and ankle both, it is most often the contracted structure. The adherence with night splints is also very poor based on my personal experience. These two factors lead to the mediocre results attributed to night splints as described in the Evans study, which showed only six of 20 patients achieving 10 degrees of dorsiflexion with the use of night splints.14

Can The EQ/IQ Brace Be A Viable Alternative To Night Splints?

The answer the lead author has developed to address ineffectual manual stretching and the failures of night splints is the EQ/IQ brace (IQ Med). Patients do not need to sleep in this brace. The lead author recommends using it 30 minutes in the morning and 30 minutes in the evening (15 minutes stretching the gastroc-soleus complex and 15 minutes stretching the soleus).

The EQ/IQ brace has an above-the-knee extension with a hinge at the knee. The extension allows the knee to lock into extension to stretch the gastrocnemius muscle. The hinge can release to allow for ease of application and isolated stretching of the soleus. There is also a hinge at the ankle joint that allows the treating physicians to set exactly the amount of dorsiflexion they desire based on the patient’s biomechanical exam. (The lead author suggests maybe 5 degrees the first month and then going up to 10 degrees the second month and, if needed, 15 degrees the third month.) The hinge goes from -30 degrees to +30 degrees, in 5-degree increments.

We as podiatrists measure everything from X-ray angles to forefoot varus position. Yet we slap on a night splint and tell our patients to pull as tight as they can. This makes no sense to us. We should have more control and precision over the treatment of this condition.

The lead author has made this brace ambulatory with a negative heel rocker sole, which allows ambulation with a fixed dorsiflexed position. The rocker soles are going to be removable and come in different soles to match the amount of ankle joint dorsiflexion (i.e. 5, 10 and 15 degrees). There is an adjustable wedge that goes under the hallux to engage the windlass mechanism. These wedges come in various degrees (i.e. 35, 50 and 65 degrees) and Velcro to the foot bed. The lead author has made varying degrees of wedges to allow for those with hallux limitus or rigidus. The femoral and tibial uprights are adjustable for leg and thigh length, and the physician should set the uprights. Finally, the standard foot beds will fit a small/medium size foot, but one can replace the foot bed with an extended version that will fit a large/extra-large size.

Most manual stretching is recommended to last about 30 minutes per day.11 However, the lead author believes an hour a day is reasonable from an adherence standpoint in comparison to six to eight hours at night while disturbing the patient’s sleep. The ambulatory component of the brace is also important. The lead author foresees patients getting dressed in the morning and then putting on the brace and stretching while performing their morning rituals. A similar scenario would play itself out for the evening stretching.

A final consideration is that this is not a brace patients will be able to buy at a drug store or on the Internet. The lead author has had patients complain about the expense of a night splint when they can find the same thing for about 20 percent of the price of the brace. This is a technical device that a physician must set, monitor and adjust. This brace will have a significant positive impact on the practice management component of your practice. Most importantly, it will provide you with a better way to treat the equinus deformity, the most significant producer of foot and ankle pathologies.

What You Should Know About Tendo-Achilles Lengthening And Gastrocnemius Recession

The surgical approach to equinus is well documented in the literature and mainly focuses on two different procedures, the tendo-Achilles lengthening (TAL) or gastrocnemius recession.

The TAL approach most surgeons commonly utilize is the Hoke triple hemisection. This procedure employs three stab incisions starting 1 cm proximal to the insertion of the gastroc-soleus complex with two medial incisions and one lateral incision between the two medial incisions. One would section the tendon through the central portion and incise in the respective direction of the stab incisions. The tendon then slides to a lengthened position. This procedure is not without potential complications such as under-lengthening or, much worse, over-lengthening.

The gastrocnemius recession is one of my favorite procedures and is well documented in the literature.15 I prefer the Baumann intramuscular approach to lengthening of the gastrocnemius aponeurosis. This provides controlled, sequential lengthening. Place the incision at the medial aspect of the calf midway between the posterior calf and anterior border of the tibia. The incision is typically 3 to 4 cm long and one deepens this to the level of the deep fascia. Incise the fascia revealing the gastrocnemius and soleus muscle bellies. Use a finger to identify the natural separation between the aponeurosis of the two muscles and insert a speculum to spread them apart.

With the patient’s foot dorsiflexed and the knee extended, use a long-handled #15 blade to cut the proximal portion of the gastrocnemius aponeurosis including the intramuscular septum. This is a complete release from lateral to medial. If one notes inadequate dorsiflexion, I recommend a second more distal release (1 cm distal to the initial release) over a soleus recession based on the study by Herzenberg and Lamm.15

In this study, the preoperative group had 1 degree of ankle joint dorsiflexion with the knee extended. After gastrocnemius recession, single and double dorsiflexion increased significantly (9 and 15 degrees respectively). Adding a soleus recession only increased dorsiflexion by 1 degree. Therefore, it is more effective to perform a double gastrocnemius recession.

In Conclusion

When it comes to preventative care that has been championed over the past two decades for the patient with diabetes, there has been significant progress in amputation prevention. The one missing piece to the puzzle that has been ignored is the treatment of equinus. With adequate treatment of those patients with diabetes who have equinus, we can further decrease their risk of ulceration and amputation.

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.

Dr. Borer is a first-year resident at Westview Hospital in Indianapolis.

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. Opila KA, Wagner SS, Schiowitz S, Chen J. Postural alignment in barefoot and high-heeled stance. Spine. 1998;13(5):542-547.

3. Sgarlato TE, Morgan J, Shane HS, Frenkenberg A. Tendo Achilles lengthening and its effect on foot disorders. J Am Podiatry Assoc. 1975; 65(9):849-871.

4. DiGiovanni CW, Kuo R, Tejwani N, Price R, Hansen Jr. ST, Cziernecki J, Sangeorzan BJ. Isolated gastrocnemius tightness. J Bone Joint Surg Am. 2002; 84-A(6):962-970.

5. Aronow MS, Diaz-Doran V, Sullivan RJ, Adams DJ. The effect of triceps surae contracture force on plantar foot pressure distribution. Foot Ankle Int. 2006; 27(1):43-52.

6. Jones RL. The human foot. An experimental study of its mechanics, and the role of its muscles and ligaments in the support of the arch. Am J Anat. 1941; 68:1-38.

7. Ward ED, Phillips RD, Patterson PE, Werkhoven GJ. The effects of extrinsic muscle forces on the forefoot-to-rearfoot loading relationship in vitro. J Am Podiatr Med Assoc. 1998;88(10):471-482.

8. Mueller MJ, Sinacore DR, Hastings MK, Strube MJ, Johnson JE. Effect of Achilles tendon lengthening on neuropathic plantar ulcers. A randomized clinical trial. J Bone Joint Surg. 2003;85-A(8):1436-1445.

9. Grant WP, Sullivan R, Sonenshine DE, Adam M, Slusser JH, Carson KA, Vinik AI. Electron microscopic investigation of the effects of diabetes mellitus on the Achilles tendon. J Foot Ankle Surg. 1997;36(4):272-278.

10. Lavery LA, Armstrong DG, Boulton AJ. Ankle equinus deformity and its relationship to high plantar pressure in a large population with diabetes mellitus. J Am Podiatr Med Assoc. 2002;92(9):479-482.

11. Radford JA, Burns J, Buchbinder R, Landorf KB, Cook C. Does stretching increase ankle dorsiflexion range of motion? A systematic review. Br J Sports Med. 2006; 40(10):870-875.

12. Grady JF, Saxena A. Effects of stretching the gastrocnemius muscle. J Foot Surg. 1991;30(5):465-469.

13. Hill RS. Ankle equinus. Prevalence and linkage to common foot pathology. J Am Podiatr Assoc. 1995;85(6):295-300.

14. Evans A. Podiatric medical applications of posterior night stretch splinting. J Am Podiatr Med Assoc. 2001;91(7):356-360.

15. Herzenberg JE, Lamm BM, Corwin C, Sekel J. Isolated recession of the gastrocnemius muscle: the Baumann procedure. Foot Ankle Int. 2007;28(11):1154-1159.

For further reading, see “Understanding And Managing Equinus Deformities” in the May 2011 issue of Podiatry Today or the DPM Blog “Why Do We Overlook Equinus In Patients With Diabetes?” at http://tinyurl.com/5t2ug69 .