Maximizing The Effectiveness Of The Evans Calcaneal Osteotomy

Author(s): 
Michelle Butterworth, DPM, FACFAS

The Evans calcaneal osteotomy, first described in 1975, is a lateral column lengthening procedure that preserves the calcaneocuboid joint.1 This laterally based opening wedge osteotomy is historically known to provide transverse plane correction for pes planovalgus deformities.

   In reality, the Evans calcaneal osteotomy provides multi-planal correction and foot and ankle surgeons routinely utilize it to correct both pediatric and adult pes planovalgus deformities.2-7 In addition to lengthening the lateral column and reducing forefoot abduction, the Evans calcaneal osteotomy realigns the midtarsal joint and reduces calcaneal eversion. This procedure also places tension on the long plantar ligaments and provides significant arch elevation and stabilization. It is because of this powerful, tri-planal correction that the Evans calcaneal osteotomy has become the cornerstone of flexible flatfoot correction for me.

   Although this osteotomy provides great correction, surgeons typically perform adjunctive procedures in the medial column and a posterior lengthening to gain full reduction of the pes planovalgus deformity. There is a small learning curve but few complications result when one technically performs the Evans calcaneal osteotomy correctly. Accordingly, I would like to offer some surgical pearls to ensure predictable, successful results.

What You Should Know About Incision Placement And Dissection

The surgeon usually performs the Evans calcaneal osteotomy with the patient under general anesthesia in a supine position. Bump the leg over in a lateral position using an inflatable beanbag. Then one can deflate the beanbag at the completion of the procedure to access other areas of the foot and lower extremity for additional procedures. A thigh tourniquet ensures good visualization and provides access for a gastrocnemius recession or Achilles tendon lengthening, which surgeons routinely perform concomitantly with the Evans osteotomy.

   Place an oblique incision over the anterior lateral calcaneus. Start the incision just dorsal to the most superior aspect of the anterior process of the calcaneus and continue proximally and plantarly in line with the relaxed skin tension lines. The midline of the incision is usually about 1 to 1.5 cm proximal to the calcaneocuboid joint where one will make the osteotomy. The incision should end just plantar to the inferior edge of the calcaneus. This landmark is typically more superior than expected and it is common to continue the incision too far plantarly. I recommend drawing anatomic landmarks and drawing the incision itself for accuracy.

   This incision is advantageous because it is within the relaxed skin tension lines, minimizing scar formation. This incision also provides good visualization of the surgical site but one should be aware of the surrounding vital structures. Surgeons will sometimes encounter the intermediate dorsal cutaneous nerve in the superior aspect of the incision and the peroneal tendons and sural nerve are in the inferior aspect. Also, the surgeon may occasionally encounter a communicating branch from the intermediate dorsal cutaneous nerve.

   One can also utilize a longitudinal lateral incision. Although it parallels the peroneal tendons and sural nerve, and there is less risk for injury to these structures, this incision is against the relaxed skin tension lines. With the lengthening of the lateral column, thick scarring can result.

   Perform blunt dissection through the subcutaneous tissues until you encounter the extensor digitorum brevis muscle belly. Identify the peroneal tendons just inferior to the muscle belly and retract the tendons plantarly. Make an incision along the inferior edge of the extensor digitorum brevis muscle belly and its overlying deep fascia. Take care not to violate the peroneal tendons or their tendon sheath. Then make a vertical incision along the proximal edge of the muscle belly at about the level of the sinus tarsi. Tag the extensor digitorum brevis muscle belly and its overlying deep fascia with sutures, reflect them off the underlying bone and retract them distally to expose the anterior calcaneus.

   Identify the calcaneocuboid joint but avoid aggressive dissection. The ligaments must remain intact so the joint is not destabilized. Identify the calcaneocuboid joint with a Freer elevator and then place an 18 gauge needle into the joint as a reference point. Using a key elevator, proceed to reflect the remaining soft tissues, exposing the anterior lateral calcaneus for osteotomy placement.

Keys To Correct Osteotomy Placement

Correct osteotomy placement is crucial for success of this procedure and I will draw the osteotomy prior to execution to ensure accuracy. Perform the osteotomy 11 to 15 mm proximal to the calcaneocuboid joint. If the osteotomy is too distal or too close to the calcaneocuboid joint, the anterior fragment of the calcaneus will be too small and unstable, and can dislocate dorsally. A small anterior fragment could also become dysvascular, resulting in healing difficulties. Finally, if the osteotomy is too distal, it can violate the anterior facet of the subtalar joint. If it is too proximal, it can violate the middle facet of the subtalar joint and subsequent pain and arthritis could result.

   According to Hyer and colleagues, the majority of calcanei (56 percent) in a study had a conjoined anterior and middle talocalcaneal facet, 3 percent had an absent anterior facet, and 41 percent had separate facets.8 The mean distance from the anterior border of the calcaneus to the proximal edge of the anterior facet was 11.04 mm and the mean separation between the anterior and middle facets, when present, was 3.85 mm. Therefore, the ideal placement of this osteotomy is 11 to 15 mm proximal to the calcaneocuboid joint.

   One should make the osteotomy perpendicular to the lateral wall of the calcaneus and weightbearing surface, and parallel to the calcaneocuboid joint. Make the osteotomy from lateral to medial with a sagittal saw. Then utilize an osteotome to continue the cut through the medial cortex. Do this very carefully to avoid violation of the medial neurovascular bundle and tendons. Proceed to open the osteotomy. I utilize a lamina spreader without teeth but one may use a mini-distractor if desired. If the osteotomy is resistant to distraction, it is probably incomplete. The most common place of osseous continuance is the plantar medial aspect. One can use an osteotome to gingerly transect any points of osseous connection.

   Then open the osteotomy until you have achieved the desired correction. The ideal position of the rearfoot is with the heel in a rectus or slight valgus position.

Pertinent Insights On Utilizing Bone Grafts

One would then measure the gap at the osteotomy site and fashion a bone graft. The correction in most pediatric patients averages 10 mm and typically ranges from 8 to 12 mm. In an adult, the maximum graft size to utilize is 8 mm. I typically do not use grafts over these dimensions because it can cause increased pressure and secondary pain and arthritis at the calcaneocuboid joint. If further correction is needed and the graft has reached its maximum size, I will typically perform a posterior calcaneal displacement osteotomy in addition to the Evans osteotomy instead of utilizing a larger graft.

   I utilize allogeneic bone graft. Many authors have shown that due to the increased vascularity of the calcaneus, allogeneic bone graft incorporates very well and this procedure does not warrant an autogenous graft.9-11 Also, a combined corticocancellous graft is the most advantageous graft for this procedure. The cancellous bone allows increased vascularity and aids in graft incorporation and healing. The cortical bone adds strength to the graft to combat the compressive forces within the osteotomy. I prefer to use an allogeneic tricortical iliac crest bone graft, 15 to 18 mm in width. This width will typically allow enough bone graft for the Evans osteotomy and a Cotton osteotomy if this procedure is also needed for further correction of the medial arch.

   Then fashion the bone graft into a trapezoidal shape. The cortical bone is going to be on the dorsal, lateral and plantar aspects, and the cancellous bone will be on the distal and proximal aspects of the osteotomy. The most lateral aspect of the graft is the widest and it tapers down to about 3 to 4 mm as it goes medially.

   Precut allogeneic bone wedges are also available. I have utilized some of these grafts with success but these grafts are only bicortical. These grafts are also sometimes longer than desired, from lateral to medial, especially in pediatric patients, and one needs to cut and shorten the grafts to fit properly. If you are using precut grafts, I recommend minimal tamping and manipulation of these grafts to maintain their strength and integrity. I do not have experience utilizing other types of grafting/wedge material at the osteotomy site. My preferred choice, based on experience, success and reproducible outcomes, is allogeneic, tricortical iliac crest bone graft, cut and fashioned individually.

   After fashioning the graft, open the osteotomy site, insert the bone graft and tamp it into place so the lateral edge lines up evenly with the lateral wall of the calcaneus and there is no prominence. Place the bone graft in the central part of the osteotomy. The surgeon needs to ensure the graft is not too dorsal entering the subtalar joint. The bone graft usually does not fill the entire space of the osteotomy. However, the graft typically incorporates very well and these spaces are not cause for concern. One can add additional bone graft if desired but this is not standard for me.

   After placing the graft, assess its stability. Since the bone graft is under significant compression, it is usually very stable within the osteotomy and fixation is not routine. If the anterior fragment of the calcaneus appears to be unstable or dorsally dislocated, one can obtain fixation with a percutaneous Kirschner wire or Steinman pin. The two main reasons for displacement of the anterior fragment are aggressive dissection of the calcaneocuboid ligaments creating instability or placement of too large of a graft. The surgeon may want to reassess the graft size if dorsal displacement of the anterior process is present.

A Few Considerations On Closure And Post-Op Protocol

Perform standard tissue and skin closure. Then assess the foot for remaining deformities. Typically, a forefoot supinatus is present, warranting additional procedures such as a Cotton medial cuneiform osteotomy. Also, one needs to address any equinus deformity and treat it to gain full correction.

   Postoperatively, the patient is non-weightbearing in a cast for about six weeks or until he or she achieves osseous consolidation radiographically. The patient then transitions to a controlled ankle motion (CAM) walker and begins weightbearing and range of motion exercises over the next three weeks. Continuation to full weightbearing and normal shoegear then ensues as pain and swelling permit. Obviously, one can modify this post-op course as needed depending on the other procedures performed.

In Conclusion

I have found the Evans calcaneal osteotomy to be a powerful procedure resulting in triplanal correction for flexible pes planovalgus deformities. I have found that this surgical technique is reliable and consistently renders successful results. It is the workhorse for this deformity but it cannot stand alone. Additional procedures such as a Cotton osteotomy and gastrocnemius recession or Achilles tendon lengthening are typically necessary to gain full correction.

   Dr. Butterworth is a Fellow and the Immediate Past President of the American College of Foot and Ankle Surgeons. She is in private practice in Kingstree, S.C.

References
1. Evans D. Calcaneo-valgus deformity. J Bone Joint Surg. 1975; 57(3):270-8.
2. Mahan KT, McGlamry ED. Evans calcaneal osteotomy for flexible pes valgus deformity. Clin Podiatr Med Surg. 1987; 4(1):137-51.
3. Roye DP, Raimondo RA. Surgical treatment of the child’s and adolescent’s flexible flatfoot. Clin Podiatr Med Surg. 2000; 17(3):515-30.
4. Mosier-LaClair S, Pomeroy G, Manoli A. Operative treatment of the difficult stage 2 adult acquired flatfoot deformity. Foot Ankle Int. 2001; 6(1):95-119.
5. Viegas GV. Reconstruction of the pediatric flexible planovalgus foot by using an Evans calcaneal osteotomy and augmentative medial split tibialis anterior tendon transfer. J Foot Ankle Surg. 2003; 42(4):199-207.
6. Zwipp H, Rammelt S. Modified Evans osteotomy for the operative treatment of acquired pes planovalgus. Oper Orthop Traumatol. 2006; 18(2):182-97.
7. Hix J, Kim C, Mendicino RW, Saltrick K, Catanzariti AR. Calcaneal osteotomies for the treatment of adult-acquired flatfoot. Clin Podiatr Med Surg. 2007; 24(4):699-719.
8. Hyer CF, Lee T, Block AJ et al. Evaluation of the anterior and middle talocalcaneal articular facets and the Evans osteotomy. J Foot Ankle Surg. 2002; 41(6):389-393.
9. Mahan KT, Hillstrom H. Bone grafting in foot and ankle surgery: A review of 300 cases. J Am Podiatr Med Assoc. 1998; 88(3):109-18.
10. John S, Child BJ, Hix J, et al. A retrospective analysis of anterior calcaneal osteotomy with allogeneic bone graft. J Foot Ankle Surg. 2010; 49(4):375-79.
11. Grier KM, Walling AK. The use of tricortical autograft versus allograft in lateral column lengthening for adult acquired flatfoot deformity: An analysis of union rates and complications. Foot Ankle Int. 2010; 31(9):760-69.

   For further reading, see “Essential Insights On The Evans Calcaneal Osteotomy” in the June 2009 issue of Podiatry Today.

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