Given the various ways people compensate for equinus as well as the many conditions associated with equinus, the author provides an anatomical primer, addresses biomechanical influences and offers pearls on surgical treatment Equinus is defined as the inability to dorsiflex the ankle sufficiently enough to allow the heel to contact the supporting surface without some form of compensation in the mechanics of the lower limb and foot. During the stance phase of gait, the greatest degree of dorsiflexion required is just before heel lift when the knee is maximally extended and the ankle must dorsiflex past perpendicular for smooth ambulation. There is a great deal of controversy in the literature as to the amount of dorsiflexion truly necessary for this to occur. It is therefore better to consider a normative range of values necessary for normal gait rather than a definitive number. The accepted range of normal ankle joint dorsiflexion is 3 to 15 degrees past perpendicular with the knee extended. When evaluating the destructive influence of equinus on the limb, the method of compensation that a patient may exhibit is of equal or more importance than the numerical value found on physical examination. There have been numerous articles and texts published on the methods by which a patient may compensate for an equinus deformity and to what degree he or she may compensate. The method by which patients compensate will often determine what symptoms and pathological conditions may coexist and can affect a multitude of systems. Common methods of compensation include triplanar rearfoot motion resulting in pronation, early heel off, abducted gait, midfoot collapse, hip flexion, lumbar lordosis and genu recurvatum or persistent knee flexion. Therefore, patients can present with a variety of conditions such as low back pain, chondromalacia of the knee, Achilles tendinopathy, posterior tibial tendinopathy, painful flatfoot condition, plantar fasciitis, calcaneal apophysitis, Lisfranc joint arthrosis, Charcot arthropathy, hallux valgus or rigidus, plantar ulceration, forefoot calluses, metatarsalgia and hammertoe contractures associated with the equinus deformity. A fully compensated equinus deformity will often result in a severely hypermobile flatfoot with the rearfoot maximally everted and the forefoot inverted to the rearfoot due to the excessive pronation of the subtalar joint resulting in unlocking and instability of the midtarsal joint.
Key Anatomical Considerations With Equinus
To appreciate the causal effect of equinus deformity on the lower limb, a physician must fully comprehend the anatomy of the posterior compartment of the lower leg. The posterior compartment is divided into superficial and deep muscle groups separated by the deep transverse fascia. The superficial compartment of the posterior leg is responsible for the equinus deformity and is made up of the plantaris muscle as well as the gastrocnemius and soleus muscles, which combine to form the tendo-Achilles. The gastrocnemius muscle originates from two heads (medial and lateral) connected to the femoral condyles that then descend into the lower leg as two separate muscles. The medial head is typically larger and extends more distally than the lateral head and then the muscle bellies attach to a broad aponeurosis on the anterior surface of the muscle. The medial head of the gastrocnemius attains a maximum force of 500 Newtons (a Newton is the metric equivalent of a pound; 1 N = 0.224 lbs) while the lateral head attains a force of 700 N. The soleus can attain a maximum force of 900 N. The soleus does not cross the knee joint and takes origin from the posterior aspect of the proximal tibia and its surrounding fibrous tissue. As these two muscles descend in the leg, the gastrocnemius aponeurosis and the soleus tendon merge to form the tendo-Achilles and insert on the posterior aspect of the calcaneus. With some varying frequency, the tendo-Achilles does spiral from medial to lateral so the gastrocnemius fibers insert more on the lateral calcaneus and the soleus fibers insert more on the medial aspect. The final muscle in the posterior superficial compartment is the plantaris muscle. The plantaris is a very small muscle arising from the distal lateral femur and posterior knee capsule, and runs inferomedially between the gastrocnemius and soleus muscles. The tendon lies along the medial Achilles tendon and inserts on the posteromedial aspect of the calcaneus adjacent to the tendo-Achilles. Due to its origin and insertion, the plantaris functions to flex the knee and plantarflex the ankle but it is much smaller, and therefore much weaker, than the gastrocnemius. Another structure in the posterior compartment of the leg that may be affected by surgical treatment of equinus is the sural nerve. The formation of the sural nerve is from the medial sural branch off the tibial nerve and the peroneal communicating nerve from the common peroneal nerve. The medial sural nerve arises from the tibial nerve in the popliteal space and courses between the two heads of the gastrocnemius muscle. It pierces the aponeurosis in the middle of the leg and receives the peroneal communicating nerve to form the sural nerve. The peroneal communicating nerve descends superficial to the deep fascia overlying the gastrocnemius while the medial sural nerve is deep to the deep fascia until it pierces through it. The most common location for this to occur is 10 to 20 cm from the tip of the lateral malleolus and then the sural nerve descends along the lateral border of the Achilles tendon and passes 1 to 1.5 cm behind the lateral malleolus. As certain procedures have recently gained increased use, so has the interest in the surgical anatomy of the sural nerve. Injury to the sural nerve has increased in frequency due to the recent popularity for the higher gastrocnemius recessions such as Strayer and Baumann in which surgeons perform the recessions in areas where the medial sural branch has not yet pierced through the aponeurosis or is running between the gastrocnemius heads.1,2 Tashjian describes the width of the gastrocnemius soleal junction as 58 cm with the average distance of the sural nerve from the lateral border as 12 mm.3 This junction was at approximately 50 percent of the length from the tip of the lateral malleolus to the fibular head. Pinney, et. al., further examined this and the location of the sural nerve was highly variable, which has added to the difficulty in avoiding injury to this nerve.4 They noted that the sural nerve was superficial to the deep fascia in 42.5 percent of the cases and deep to the fascia in 57.5 percent of the cases. In 12.5 percent of the cases, the nerve was directly against the gastrocnemius tendon and had to be dissected off the tendon. Injury may be unavoidable, especially since surgeons perform the majority of the high gastrocnemius recession procedures with the patient in a supine position and place the incision medially or posteromedially, making visualization difficult along the lateral aspect of the aponeurosis where the nerve is located.
What You Should Know About Biomechanical Influences
The biomechanical influences and the phasic activity of each muscle are different and therefore result in a different effect on the extremity during gait. Phasic activity of the triceps surae occurs shortly after heel contact until just before toe off. The soleus exhibits continuous activity in symmetrical standing whereas the gastrocnemius is active only intermittently. The soleus is also stronger than the gastrocnemius and exerts greater maximum force as described above. It fires at about 15 to 20 percent of stance phase, just slightly ahead of the gastrocnemius. The soleus functions to slow the forward progression of the tibia, thus allowing the femur to rotate over it and extend the knee joint. The soleus also stabilizes the lateral aspect of the foot as the foot begins resupination and the opposite side comes forward. Once the lateral side of the foot is stable, the peroneus longus can use the cuboid as a fulcrum to stabilize the first ray. This would explain why the development of a severe hypermobile flatfoot is often seen with an equinus deformity. Johnson and Christensen showed the function of the peroneus longus to be significantly dampened by the equinus, leading to insufficiency in stabilizing the first ray and the medial column.5 The phasic activity and function of the gastrocnemius muscle reaches its peak at 50 to 60 percent of midstance of gait when the gastrocnemius muscle simultaneously flexes the knee and plantarflexes the ankle. This is the moment when the maximum effect of an equinus deformity is noted. However, when a tight posterior muscle group is present, the foot and/or leg must compensate to maintain the foot securely on the ground. If the foot is able to compensate, the rearfoot will severely pronate through the subtalar joint, allowing for unlocking of the midtarsal joint and increased dorsiflexion through the oblique axis of the midtarsal joint. As discussed above, the lower limb may also compensate with hip flexion, lumbar lordosis, genu recurvatum or persistent knee flexion to maintain the foot on the ground or lift the heel off the ground early in the gait cycle. In all cases, the function of the foot is compromised and the patient will develop symptoms depending on his or her own method of compensation.
Key Considerations For Appropriate Treatment
Treatment of equinus can range from conservative attempts at stretching the posterior muscle group to more extensive treatment with surgical intervention. Some authors have shown that stretching of both the gastrocnemius and soleus has been beneficial.6 However, the results are not long lasting and relapse is a frequent occurrence. Surgical intervention in symptomatic patients, either with isolated equinus or equinus as a component of a more complex deformity, has become commonplace in many treatment regimens. Numerous gastrocnemius recession or tendo-Achilles lengthening techniques have been described to resolve an equinus deformity with varying complications seen depending on the procedure chosen. When deciding to perform a lengthening to resolve an equinus condition, consider the risks and benefits that one can achieve with such a procedure and the degree of deforming force present along with any spasticity. As with any lengthening or tendon transfer, there is some residual deficit in the function of the muscle. Sammarco and associates retrospectively evaluated patients with a unilateral gastrocnemius recession that were followed an average of over two years postoperatively. Patients were noted to have residual diminished fatigue resistance and strength compared to the contralateral limb.7 In most cases, this is not appreciable to the patient or problematic in his or her overall function. However, it is something to consider when evaluating a patient for a tendon lengthening. It is also important to evaluate what type of equinus is present as this will impact what surgical procedure one chooses to correct the condition. For example, in the patient with an underlying neurological condition, such as cerebral palsy that results in spastic equinus or equinus so excessive that the patient is in a true toe walking position, there is little controversy in procedure selection. The surgeon will consider either a tendo-Achilles lengthening or a Murphy tendo-Achilles advancement to reduce the affects of the overlying neurological component of the deformity. The greater controversy lies in treating a neurologically normal patient who suffers with an acquired equinus condition. The debate is over what one considers to be a pathological equinus condition and what treatment option one should choose. As stated earlier, the measured values of ankle joint dorsiflexion necessary for normal gait vary in the literature. Evaluating the range of dorsiflexion available with the knee straight and the knee flexed as described by Silverskiöld is considered the standard protocol to differentiate a gastrocnemius equinus from a triceps surae equinus.8 However, it is much more complex than this simplified technique. The overall foot type and the method of compensation are far more important than the actual numeric value one obtains on range of motion of the ankle. A cavus foot will exhibit an equinus condition as the talus is already in a dorsiflexed attitude within the ankle mortise. Accordingly, this limits the amount of dorsiflexion still available. A posterior lengthening in this patient population would be inappropriate and ineffective unless one opts for a full reconstruction of the cavus foot. One must also evaluate the patient via radiographic examination for a bony block of the anterior ankle resulting in equinus. In the hypermobile collapsing pes valgoplanus foot, the method of compensation is by far the most devastating on the function of the foot. The degree of midfoot collapse and dorsiflexion of the midfoot to achieve additional motion as the leg passes over the foot results in numerous complications as reviewed earlier. In evaluating the patient, the method by which the patient is compensating for the equinus as he or she ambulates and stands is far more important than merely measuring the degree of dorsiflexion available. If there is extensive midfoot break and abduction of the foot with calcaneal eversion, then the pathological effects of the equinus on the foot are more severe than in the foot that maintains the arch, and may compensate more proximally for the equinus. There are some numeric guidelines when it comes to measuring dorsiflexion of the ankle joint. One may consider these along with the evaluation of the method of compensation and its pathological effects on the function of the limb. According to Root and associates, the necessary amount of dorsiflexion just prior to heel off and knee flexion is 10 degrees past perpendicular.9 However, a more recent study by DiGiovanni and coworkers evaluated the degree of dorsiflexion in neurologically normal symptomatic patients in comparison to an asymptomatic control group.9 The authors of this study concluded that the patient population had less maximum ankle dorsiflexion with knee extension than the control group and when the knee was flexed, this difference between the two groups was no longer present. DiGiovanni and colleagues also noted numeric values for symptomatic equinus of less than 5 degrees past perpendicular with knee extension for gastrocnemius equinus and less than 10 degrees past perpendicular with the knee flexed for triceps surae equinus.10 When determining the proper procedure choice to correct an equinus deformity, one must consider the measured degree of dorsiflexion with the knee flexed and extended as well as the pathomechanical compensation of the foot and lower limb. Procedures may range from tendo-Achilles lengthening to isolated gastrocnemius recession. In the neurologically normal patient, the gastrocnemius equinus is a much more common occurrence than triceps surae equinus.
What You Should Know About Tendo-Achilles Lengthening
There are inherent risks to the lengthening of the entire tendo-Achilles complex that one should consider before performing the procedure. These risks include over-lengthening of a non-spastic muscle group and weakening of the soleus. As noted earlier, the soleus plays a major role in the stance phase of gait with slowing of the forward progression of the tibia, thereby allowing the femur to rotate over it and extend the knee joint. The surgical weakening of the soleus could lead to significant knee instability, especially in the athlete. However, in certain patients with limited function and mobility who are high-risk surgical candidates, the surgeon may opt to lengthen the tendo-Achilles via a percutaneous approach to reduce operating room time and potential delayed healing. One may employ Hoke’s triple hemisection with good success in the high-risk surgical candidate such as a diabetic patient with neurological or vascular compromise.10 The patient is usually supine with the leg in an elevated position in order to gain access to the posterior Achilles while the foot is under dorsiflexion stress. Insert a #11 surgical blade in the midsection of the tendon 2 cm proximal to the Achilles insertion and cautiously turn the blade to cut the medial half of the tendo-Achilles. Withdraw the blade and reinsert it approximately 2.5 cm proximally in the central Achilles, turning the blade to cut the lateral half of the tendo-Achilles. Make a final incision 2.5 cm further proximally with the medial half of the tendo-Achilles transected. At each stage of this procedure, one dorsiflexes the foot while the leg is elevated and the surgeon can feel the release of the Achilles at each sectioning of the tendon fibers. One must be cautious of aggressively dorsiflexing the foot or sectioning more than half of the Achilles fibers at each location as ruptures of the tendo-Achilles can occur. In order to correct greater degrees of equinus, the distance between each sectioning should be greater than 2.5 cm to avoid rupturing as the foot is dorsiflexed and the fibers lengthened. Damage to nearby structures can also occur as described by Salamon.11 The tibial nerve is only 8.3 mm from the proximal cut, the sural nerve is only 8 mm from the lateral midsection cut and the flexor hallucis longus tendon is only 9 mm from the midsection cut and 5.7 mm from the proximal cut. Therefore, controlled transection of the fibers is warranted throughout the procedure. One can also employ open tendo-Achilles lengthening (TAL) for a triceps surae equinus. This procedure provides a reduced risk of rupture than the percutaneous approach but increased risk of complication with delayed healing and hypertrophic scar formation. The surgeon usually performs the open TAL in the frontal plane, transecting the inferior fibers anteriorly and transecting the superior fibers posteriorly. Be cautious not to over-lengthen the tendon as this could result in profound weakness and dysfunction in the neurologically normal patient.
When You Should Consider A Gastrocnemius Recession
Foot and ankle surgeons see few non-neurological patients present with true or severe triceps surae equinus. Most of the symptomatic patients will have acquired gastrocnemius equinus. Therefore, a gastrocnemius recession is a much more appropriate procedure choice and holds fewer risks than the tendo-Achilles lengthening. The amount of dorsiflexion a surgeon obtains in an isolated gastrocnemius recession averages approximately 18 degrees, according to Pinney and DiDomenico.13,14 Most patients with an equinus deformity will not require more additional dorsiflexion than this. Therefore, performing a TAL, even on a mild to moderate triceps surae equinus, is usually not required. Researchers have described numerous gastrocnemius recession procedures and all of these have their own risks and benefits. One of the most common gastrocnemius recession techniques is the Baker or reverse Baker (or Fulp and McGlamry), in which one lengthens the gastrocnemius tendon in a tongue and groove fashion.15 Advantages of this technique include a very controlled lengthening with sliding of the tendon to the appropriate length. However, the disadvantage is that the patient must usually be prone on the operating room table. This increases surgical risk and necessitates turning the patient to a supine position if one has to perform other procedures. Another potential disadvantage is that one would usually perform this procedure slightly more inferior than the aponeurosis of the gastrocnemius. Therefore, the surgeon would be lengthening some of the soleus fibers as well as they become congruent with the descending fibers of the gastrocnemius. Recently, the Strayer procedure, described in 1950, has regained popularity.16 The Strayer procedure involves lengthening of the gastrocnemius aponeurosis. The advantage of the Strayer procedure is that one may perform it from a medial or posteromedial approach with the patient in the supine position. The surgeon can also ensure isolation to the gastrocnemius fibers with no soleus component. However, since the procedure’s rise in popularity, there has been an increase in the number of surgical or iatrogenic injuries to the sural nerve, which pierces through the fascia in this area with some variability and is difficult to visualize on the lateral side of the gastrocnemius through the medial incisional approach. The use of the endoscopic technique for this procedure may aid in the visualization of the nerve and lessen the risk of injury. Some surgeons have opted to progress even more proximally, as described by Baumann, and modify this procedure to lengthen just the aponeurosis at the level where the gastrocnemius muscle starts to invest into the posterior aspect of the aponeurosis. The aponeurosis is present only on the anterior side of the muscle bellies. Therefore, there is reduced risk of injury to the sural nerve. Exercise caution, however, as the medial sural nerve runs from the popliteal space between the gastrocnemius muscle bellies, and can still be damaged depending on its course.
According to many foot and ankle surgeons, the equinus condition imparts a major deforming force on the foot and is a causative factor in many foot and ankle pathological deformities. The degree of deformity depends on the foot type and the method of compensation with some foot types stable while others are highly unstable in face of the equinus. There are no absolute numbers by which to determine the appropriate course of treatment. However, rarely is the soleus muscle contracted in the neurologically normal patient. This allows for a gastrocnemius recession, as opposed to a tendo-Achilles lengthening, to correct the equinus deformity, which leads to less weakening of the posterior muscle group and fewer risks. Understanding the surgical anatomy and ensuring thorough patient evaluation and selection can help improve the overall outcome of the equinus release. Dr. Crawford is a Fellow and member of the Executive Board of Directors of the American College of Foot and Ankle Surgeons. She is board certified in foot and ankle surgery by the American Board of Podiatric Surgery. Dr. Crawford is also on the Board of Medical Advisors of the Northwest Podiatric Foundation for Education & Research, USA, and is in private practice at the Ankle and Foot Clinic of Everett in Everett, Wa. For related articles, see “Addressing Tendon Balancing Concerns In Diabetic Patients” in the March 2003 issue of Podiatry Today, “Roundtable Insights On Adult-Acquired Flatfoot” in the June 2005 issue or the June 2005 supplement “A Closer Look At Subtalar Implants.” Also be sure to visit the archives at www.podiatrytoday.com.
References 1. Strayer LM: Gastrocnemius recession: five-year report of cases. J Bone Joint Surg 40-A: 1019, 1958. 2. Baumann JU, Koch HG : Lengthening of the anterior aponeurosis of the gastrocnemius muscle [in German]. Operat Orthop Traumatol 1: 254, 1989. 3. Tashjian RZ, Appel AJ, Banerjee R, DiGiovanni CW: Anatomic study of the gastrocnemius-soleus junction and its relationship to the sural nerve. Foot Ankle Int 24(6): 473-476, 2003. 4. Pinney SJ, Sangeorzan BJ, Hansen ST: Surgical anatomy of the gastrocnemius recession (Strayer procedure). Foot Ankle Int 25(4): 247-250, 2004. 5. Johnson CH, Christensen JC: Biomechanics of the first ray part V: the effect of equinus deformity. J Foot Ankle Surg 44(1): 114-120, 2005. 6. Grady JF, Saxena A: Effects of stretching the gastrocnemius muscle. J Foot Surg 30(5): 465-469, 1991. 7. Sammarco GJ, Bagwe MR, Sammarco VJ, Magur EG: The effects of unilateral gastrocsoleus recession. Foot Ankle Int 27(7): 508-511, 2006. 8. Silverskiold N: Reduction of the uncrossed two-joint muscles of the leg to one-joint muscles in spastic conditions. Acta Chir Scand 56: 315, 1924. 9. Root ML, Orien WP, Weed JH: Normal and abnormal function of the foot, Clinical Biomechanics Corp, Los Angeles, 1977. 10. DiGiovanni CW, Kuo R, Tejwani N, Price R, Hansen ST, Cziernecki J, Sangeorzan BJ: Isolated gastrocnemius tightness. J Bone Joint Surg 84-A(6): 962-970, 2002. 11. Hoke M: An operation for the correction of extremely relaxed flat feet. J Bone Joint Surg 13: 773, 1931. 12. Salamon ML, Pinney SJ, Van Bergeyk A, Hazelwood S: Surgical anatomy and accuracy of percutaneous Achilles tendon lengthening. Foot Ankle Int 27(6): 411-413, 2006. 13. Pinney SJ, Hansen ST, Sangeorzan BJ: The effect of ankle dorsiflexion of gastrocnemius recession. Foot Ankle Int 23(1): 26-29, 2002. 14. DiDomenico LA, Adams HB, Garchar D: Endoscopic gastrocnemius recession for the treatment of gastrocnemius equinus. J Am Podiatr Assoc 95(4): 410-413, 2005. 15. Fulp MJ, McGlamry ED: Gastrocnemius tendon recession. Tongue in groove procedure to lengthen gastrocnemius tendon. J Am Podiatry Assoc. 64(3):163-71, 1974. 16. Strayer LM: Recession of the gastrocnemius: an operation to relieve spastic contracture of the calf muscles. J Bone Joint Surg 32-A: 671, 1950
Additional References 1. Feehery RV: Surgery of the Achilles tendon and posterior muscle group. Clin Podiatr Med Surg 8(3): 513-542, 1991. 2. Hill RS: Ankle equinus: prevalence and linkage to common foot pathology. J Am Podiatr Assoc 85(6): 295-300, 1995. 3. Lamm BM, Paley D, Herzenberg JE: Gastrocnemius Soleus Recession: a simpler, more limited approach. J Am Podiatr Med Assoc 95(1): 18-25, 2005. 4. Lee WC, Ko HS: Achilles tendon lengthening by triple hemisection in adult. Foot Ankle Int 26(12): 1017-1020, 2005. 5. Saraph V, Zwick EB, Uitz C, et al: The Baumann procedure for fixed contracture of the gastrocsoleus in cerebral palsy: evaluation of function of the ankle after multilevel surgery. J Bone Joint Surg 82-B: 535, 2000. 6. Saxena A, Kim W: Ankle dorsiflexion in adolescent athletes. J Am Podiatr Assoc 93(4): 312-314, 2003. 7. Silver RL, De la Garza J, Rang M: The myth of muscle balance. J Bone Joint Surg 67-B(3) : 432-437, 1985.