Given the common nature of pes planus and the frequent use of the Evans calcaneal osteotomy, these authors review keys to patient assessment and procedure selection as well as the evolution of the landmark procedure.
Pes planus is the most common foot deformity among the general population in the United States.1 Studies suggest approximately 45 percent of children between the ages of 3 and 6 years old have pes planus.1 The prevalence of pes planus decreases with age and approximately 20 percent of adults have flat feet. The majority of adult-acquired flatfoot is flexible and not painful.2 Pes planus can lead to painful inefficient gait and the etiology can be congenital or acquired.
The classic patient with congenital pes planus presents as an adolescent complaining of awkward or unsteady gait, and often “rolls the ankle” inward. The patient’s parent may describe the child as being clumsy or having difficulty keeping up with his or her peers. Acquired pes planus often presents in adulthood and is most common in obese females over the age of 40.3 Clinically, these patients often complain of medial ankle pain due to soft tissue attenuation or tearing, and new onset of a medial ankle “bump” due to talar head uncovering.3 It is not uncommon for these patients to complain of lateral ankle pain as well due to calcaneofibular impingement.
In general, pes planus can be classified as either flexible or rigid. Johnson and Strom classified three stages of flatfoot with a fourth later added by Myerson. Stage 2 is the most common clinical presentation as it is still flexible with no intra-articular involvement but has become significantly painful.4 Stage 2 is often characterized as the initial presentation of posterior tibial tendon dysfunction (PTTD) as one rarely sees patients with stage 1 flatfoot in a clinical setting due to a lack of pain. If a Stage 2 patient is indeed flexible, he or she may have a normal appearing foot when non-weightbearing, and it is manually reducible.
PTTD is in fact a very complex deformity involving both osseous and soft tissue pathology. While PTTD is a controversial topic, two things are present regardless of order: a deficiency of the medial soft tissue structures and a shortened lateral column. Pes planus is a triplanar deformity. As the rearfoot assumes a valgus position, there is abduction of the forefoot and the sagittal plane sags as the midtarsal joint is unlocked. This creates a hypermobile, compensated forefoot varus. There is more often than not a component of equinus that is the driving force of the deformity and one must address this surgically as well. During the gait cycle, early heel rise will be present with abductory twist of the forefoot and the “too many toes” sign.
Pertinent Principles On Radiographic Evaluation
Radiographs are critical in determining intra-articular involvement and planal dominance. As we stated above, it is important to note that stage 2 flatfoot may appear normal when the patient is non-weightbearing so weightbearing X-rays are key.
One can assess transverse planal dominance on a dorsoplantar view. A crucial angle to assess radiographically is the talocalcaneal angle, also known as Kite’s angle. As a pes planus deformity worsens, this angle will increase. There is direct correlation between an increase in Kite’s angle and the percentage of talar head uncovering. Clinicians may also assess talar head uncovering on a dorsoplantar view and this is denoted by medial exposure of the talar head in relation to the talonavicular joint. One will see peritalar subluxation when the transverse plane is the dominant plane of deformity.
Utilize a lateral weightbearing view to evaluate for sagittal planal dominance. The first angle to identify is the talo-first metatarsal angle or Meary’s angle. This is the relationship between the bisection of the first metatarsal and talus. This angle should be no greater than four degrees in either direction. The calcaneal inclination angle is the angle created between the plantar surface of the calcaneus and the supporting surface.5 This angle normally ranges from 18 to 24 degrees and decreases with worsening pes planus deformity.
Lastly, you evaluate the talar declination angle on the lateral view, which is the relationship between the longitudinal axis of the talus and the supporting surface. Similar to the calcaneal inclination angle, normal values are between 18-24 degrees but are inversely proportional. An increase in this number represents a worsening pes planus deformity in the sagittal plane.
When it comes to frontal plane dominance, one can only truly evaluate this with either a long leg calcaneal axial or a Saltzman view. Both of these views provide information on calcaneal position in relation to the tibia. A valgus position of the rearfoot in relation to the tibia correlates to frontal plane deformity. Regardless of dominance, a triplanar deformity often exists.5 It is important to note that the Evans osteotomy offers triplanar correction but the procedure is most effective in addressing a transverse dominant pes planus deformity.
A Quick Primer On The History And Evolution Of The Evans Calcaneal Osteotomy
For surgical reconstruction of pes planus deformity in stage 1 and 2, one would employ extra-articular approaches whereas stages 3 and 4 often require arthrodesis. One of the most utilized extra-articular osteotomies for pes planus correction is the Evans osteotomy. Evans introduced his osteotomy in a paper, which was published in 1975 following his passing in 1974.6 He stumbled upon the idea after overcorrecting a few cases of clubfoot with a shortening arthrodesis of the lateral column.
In 1961, Evans published a series of overcorrected clubfeet that he addressed with a lateral lengthening osteotomy.6 At this point, he realized that in a normal foot, the medial and lateral columns are essentially equal. Evans then deduced that talipes equinovarus was a result of a long lateral column and calcaneovalgus from a short lateral column. He spent the next several years testing his theory and ultimately realized that the classically described osteotomy provided triplanar correction. Evans found that this procedure medialized the navicular over the talar head, reducing the convexity of the medial column, the midfoot slightly plantarflexed on the rearfoot and the calcaneus took on a more varus position. It wasn’t until 1993 that these findings were radiographically confirmed in a study published by Sangeorzan and colleagues.7 Originally, it was thought that the tension of the windless mechanism was responsible for restoration of the arch and plantarflexion of the forefoot on the rearfoot. This was disproved by Horton and colleagues in 1998.8
Keys To Appropriate Procedure Selection
With the advances of three-dimensional computed tomography (CT), the triplanar effects of the Evans osteotomy were better understood. In a 2005 study, Dumontier and colleagues very elegantly demonstrated the changes that occurred primarily in the transverse and sagittal planes, giving the appearance of a restored arch.9 This correction of the forefoot on the hindfoot helps drive the calcaneus into varus although there was no significant improvement in the calcaneal-tibial position. This concept is important to understand during the pre-op evaluation in order to select the appropriate procedure for the patient.
Additionally, it may be important to subclassify patients with stage 2 flatfoot in order to identify the appropriate treatment algorithm. Patients with stage 2a flatfoot have more medial symptoms, less severe abduction and are able to perform a symptomatic single heel raise. These patients benefit from posterior tibial tendon repair or flexor digitorum longus transfer along with a medial calcaneal slide osteotomy.
Patients with stage 2b flatfoot have lateral pain due to calcaneofibular impingement and a more severely abducted forefoot. For these patients, a lateral column lengthening with medial soft tissue repair or transfer would be ideal. In severe cases with large frontal plane deformities, a double calcaneal osteotomy may be warranted. Tarsal coalition and calcaneocuboid joint arthritis are relative contraindications for an Evans osteotomy. However, an immature calcaneus is the only absolute contraindication to this procedure.
A Closer Look At Technique Considerations And Modifications To The Original Procedure
There are many options for incision placement for the Evans osteotomy. Two of the most common are oblique and transverse. The surgeon centers the oblique incision over the sinus tarsi from the anterior beak of the calcaneus to the inferior border of the calcaneus proximally (See top photo on page 53). This approach poses more concern for transecting the sural nerve or peroneal tendons.
The transverse incision begins just anterior and distal to the fibula and extends distally to the base of the fourth metatarsal. (See bottom photo on page 53) The advantages of the transverse incision include more exposure for fixation, the ability to identify and repair peroneal pathology, and decreased risk of sural nerve injury.
No matter the incisional approach, the surgeon identifies and retracts the sural nerve first. Proceed to incise the peroneal tendon sheath and mobilize the peroneal tendon in order to retract it away from the calcaneus. Once at the level of the periosteum, identify the calcaneocuboid joint but do not violate the capsule. It is of the utmost importance to maintain dorsal and plantar ligament structure to ensure dorsal dislocation of the anterior fragment does not occur after the osteotomy.
Evans’ original surgical technique required an osteotomy 1.5 centimeters proximal to and parallel with the calcaneocuboid joint, which he packed with ipsilateral tibial cortical bone graft. With his original technique, Evans did not utilize fixation and kept patients non-weightbearing in a plaster cast for upwards of four months. Evans originally performed the technique as a lateral column lengthening, not an opening wedge osteotomy. While this technique has withstood the test of time, it has evolved over the years.
There is some controversy as to exactly where and what direction to place the osteotomy. In the mid-1990s, Mosca published a modified technique utilizing a trapezoidal, tricortical iliac crest wedge.10 He theorized that the center of rotation for correction was around the central aspect of the talus, not necessarily the medial cortex of the calcaneus. For this reason, he proposed the osteotomy should be somewhere between an opening wedge and a distracting osteotomy. Mosca also concluded that surgeons should orient the osteotomy from posterolateral to anteromedial in an oblique fashion to avoid violating the middle facet.
This was later confirmed by Mahan and Flanigan in 2001, and again by Hyer and colleagues in 2013, who reasoned the orientation of the osteotomy was more advantageous for preserving the sustentaculum tali.11,12 If one inadvertently violates the sustentaculum tali, it could lead to consequences such as fracture, flexor hallucis longus damage or severance, and tarsal tunnel syndrome due to hypertrophic bone formation. 11,13,14 In the largest study to date of the Evans osteotomy, the current recommendation for the starting point of the osteotomy is located between 1.1 to 1.5 centimeters with an average of 1.3 centimeters proximal to the calcaneaocuboid joint.15
In 1999, Hintermann and coauthors introduced a new technique for lateral column lengthening through the calcaneus.16 They discussed starting the incision 1.3 cm from the calcaneocuboid joint and angling the osteotomy anterolateral to posteromedial through the sustentaculum tali. Hintermann and colleagues performed the osteotomy obliquely in between the middle and posterior subtalar joint facets. The concept behind the direction of the osteotomy revolved around the talonavicular joint axis, where the center of rotation occurs.16,17 While this theoretically makes sense, it is our personal assertion that we do not recommend this technique due to the risks associated with violating the sustentaculum tali.
More recently, Demetracopoulos and colleagues introduced a modification to the Evans osteotomy with a z-shaped, step-cut lengthening calcaneal osteotomy (SLCO).18 One makes the step-cut lengthening calcaneal osteotomy with a dorsal vertical limb half the width of the calcaneus, beginning 1.3 cm from the calcaneocuboid joint. One would extend the osteotomy proximally through a transfer limb that is twice as long as the vertical limb and complete it with a vertical limb extending through the proximal plantar portion of calcaneus.
This osteotomy allows surgeons to insert grafts into each vertical limb to lengthen the lateral column (see left photo on page 54). The benefits of this osteotomy are that it does not permit dorsal dislocation of the distal fragment but does allow fixation to span the transverse calcaneal limb, providing added stability (see right photo on page 54). This fixation can prevent loss of correction that can occur during graft resorption. A study published in 2018 by Saunders and colleagues demonstrated that the step-cut osteotomy had similar outcome scores and correction of deformity as an Evans osteotomy.19 The study authors also reported statistically significant improvement in healing time and fewer non-unions in comparison to the Evans osteotomy.
Assessing The Fixation Options
As technology improves, graft and fixation options for these procedures continue to evolve. Graft options include autograft, allograft and titanium wedges. Fixation can span from screws or plates to staples. Understanding the advantages and disadvantages of each option can help you choose the appropriate combination with the least amount of complications. Some of the most common complications to avoid are recurrence (due to graft resorption or hardware failure); peroneal injury (due to hardware); dorsal dislocation of the distal fragment; and calcaneocuboid joint arthritis.
With the ease of access to allografts and titanium wedges, autografts are no longer favored for the Evans osteotomy. The advantages of an allograft include the availability of precut and premeasured wedges. The disadvantages are time to incorporation and possible loss of correction. A biomechanical study by Xia and colleagues of calcaneocuboid joint pressure after lateral column lengthening revealed that the ideal graft size is around 8 mm. 20 It is important to note that if one prefers allograft without fixation, there will be a few millimeters of resorption. Therefore, it may be advantageous to slightly oversize the allograft to compensate.
Titanium Evans osteotomy wedges are available with a large selection of sizes and shapes. The advantage of such wedges over the traditional technique is there is no loss of correction. The open architecture, coarseness of surface design and lattice structure enhance bone ingrowth (see top photo). When one packs autograft within the wedge, you have an ideal construct for maintaining correction and allowing for bony ingrowth (see bottom image). The disadvantage of theses wedges lies in the cost. Many of these newer wedge options are constructed through more expensive additive manufacturing.
In regard to fixation, the primary options surgeons utilize today are plates with or without built-in wedges or spacers, and staples. Historically, surgeons employed screws but they would often lead to calcaneocuboid impingement due to the angle of insertion. Screws also required a much longer incision. Plating is good option to span the graft site but can lead to peroneal irritation and subsequent removal. Results from a study in 2015 by Brigido and colleagues demonstrated that a locking plate maintains mid-calcaneal length versus tricortical allograft without fixation on six-month postoperative images.21 Thus, the best combination of fixation with an allograft would be a locking plate.
Staples are another viable option although they lack the stability of a locking plate. The prime benefit of staple fixation is their small footprint, which is less likely to cause peroneal irritation and require removal. Staples are a desirable option for the step-cut lengthening calcaneal osteotomy as one can place three points of fixation to prevent movement in all three planes.
Taking all of the aforementioned information into consideration, we present several personal recommendations for successful Evans-type osteotomy for pes planus.
• First, make sure to identify planal dominance in order to perform the most appropriate calcaneal osteotomy.
• When choosing fixation, maintaining mid-calcaneal length is the most important consideration.
• We recommend a transverse incision in case further exposure or procedures are warranted.
• Pair a locking plate with tricortical graft to avoid loss of correction during graft absorption.
• Employ your fixation of choice when utilizing a titanium graft.
• Lastly, we recommend pairing three staple fixation with a step-cut Z-osteotomy.
Dr. Constant is a Fellow in the Department of Foot and Ankle Surgery at Coordinated Health in Bethlehem, PA.
Dr. Brigido is the Section Chief of Foot and Ankle Reconstruction at Coordinated Health in Bethlehem, PA. He is board-certified in foot surgery and reconstructive rearfoot and ankle surgery by the American Board of Foot and Ankle Surgery. Dr. Brigido is also a Clinical Professor of Surgery at the Geisinger Commonwealth School of Medicine in Scranton, PA.
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