Mistakes and complications in the surgical treatment of ambulatory equino planovalgus foot deformities in patients with cerebral palsy using extra-articular subtalar arthrodesis

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Abstract


Aim.

To evaluate the results of a modified technique for extra-articular arthrodesis of the subtalar joint for patients with cerebral palsy with an ambulatory form of equine-planovalgus deformity of the foot. The mistakes and complications that occurred during treatment with this technique are discussed.

Materials and methods.

Between 2005 and 2015, this surgical method for performing arthrodesis of the subtalar joint, was performed on 544 patients (989 feet) between 4 and 15 years old. Correction of equinus contracture was performed using Achilles tendon plasty or dissection of the tendon of the gastrocnemius muscle. Abnormal muscle tone was reduced either by administering Dysport® in the calf muscle or by selective neurotomy of the tibial nerve.

Results.

Good results were achieved for 72% of cases, satisfactory for 23% of cases, and unsatisfactory for 5% of cases. Unsatisfactory results of treatment were associated with overvaluation of the degree of mobility of the deformity and with a number of technical and tactical mistakes.

Conclusion.

This analysis of mistakes and complications of extra-articular arthrodesis of the subtalar joint will allow surgeons to avoid these issues in the future and improve the quality of treatment for similar patients.


Introduction

The surgical treatment of equino-planovalgus foot deformities in patients with cerebral palsy (CP) is of great interest to professionals involved in this area of orthopedics. This is largely due to the fact that among all deformities of the lower limbs, the equino-planovalgus deformity has always occupied a leading position. According to existing literature [1], this abnormality occurs in 25% of children or adolescent patients with cerebral palsy, which undoubtedly shows its considerable importance.

Considering the surgical correction of equino-planovalgus deformity of the feet in patients with CP, we have always been interested primarily in the mobile form. From our point of view, surgical correction of the mobile form remains the most promising approach to take, in contrast to that for the rigid form. While a wide range of surgical operations exist for mobile forms, the most predominantly used are foot-preserving techniques. Even if surgery is performed at the age of 2.5 years, the technique does not affect growth and development of the foot and does not interfere significantly with shock absorption via intra-articular arthrodesis. For a number of years, we have used our own modification [2], extra-articular arthrodesis of the subtalar joint, as an effective surgical alternative.

Aim

The goal of this study is to examine data regarding the treatment of patients with CP and a mobile form of equino-planovalgus deformity of the foot using our own modification of a technique involving extra-articular arthrodesis of the subtalar joint. We also analyze the most frequently encountered technical and tactical errors discovered during the treatment of patients using this method to correct deformities.

Materials and methods

Between 2005 and 2015, 544 patients (4-15 years of age) underwent our modified surgical procedure to correct a mobile equino-planovalgus foot deformity (989 feet in total). All patients, or their parents or guardians, signed a voluntary informed consent form to participate in the study and for performance of the surgery.

Extra-articular arthrodesis of the subtalar joint was first described by Grice [3]. On the basis of this initial surgical concept, we developed an original surgical method, which we describe in detail below. The main anatomical cause of this particular deformity is instability of the subtalar joint, and initially, impaired interposition of the talus and calcaneus. Indication for surgery is the presence of a mobile form of equino-planovalgus deformity of the foot, lack of a longitudinal arch, and a valgus position of the heel greater than 10° in a patient with cerebral palsy between the ages of 4 and 15 years. Surgery is performed in two steps. The first step is to harvest an autotransplant from the fibula, by resecting a fragment through an incision on the outer surface of the lower leg, between its middle and lower thirds. The second step is correction of the foot deformity by fixation of the talus and calcaneus bones into their correct position.

To carry out arthrodesis, an incision is made through the skin and subcutaneous adipose tissue such that the peroneal muscle tendons can be mobilized in the projection of the tarsal sinus. Adipose tissue is then removed from the sinus. Next, we use an awl to make a canal that ends blindly in the neck of the talus. The direction of the canal needs to be from the bottom up and from the outside inwards. Following that, a groove is made on the superolateral surface of the anterolateral segment of the calcaneus bone. The width of the groove should be slightly larger than the diameter of the autotransplant. This is important because it allows optimal adjustment of the autotransplant to the positioning of the bones. One end of the graft has to be shaped as a ledge. Then, the transplant is inserted into the canal in the talar neck and into the groove in the calcaneus. During this procedure, the position of the proximal end of the autotransplant should be with the ledge outside, and the ledge should rest on the cortex of the talar neck in order to provide support for the talus and calcaneus in their correct positions. When pressure is applied to the transplant’s distal end, it should about the upper part of the cortex of the calcaneus bone (pivot point). This transforms the transplant into a lever which moves the talus and calcaneus bones into a position that is close to normal anatomy. Once the corrected position has been optimized, the autotransplant is fixed with one or two transosteal Kirschner wires, and the wound is sutured in layers.

Correction of an equinus contracture is performed at the same time as arthrodesis surgery. This is performed by release of the gastrocnemius muscle tendon (the Strayer procedure) or by extension of the Achilles tendon. Equinus contracture (dorsiflexion of the foot less than 70°) was present in 96.5% of our present cases. The Strayer operation was performed on 823 feet while Achilles tendon extension was performed on 131 feet. Abnormal muscle tone of the triceps tibialis was reduced by intramuscular injections of Dysport (give name of company here, and city/country if journal requires) into the muscle or by selective neurotomy of the tibial nerve. Indication for this procedure was increased tonus of triceps tibialis which was no less than 3 points on the Ashworth scale. Dysport was used in 14 cases while selective neurotomy was performed in 21 cases.

Results

On average, preliminary muscle tone reduction measures resulted in a decline in tonus to 1.5 points. Treatment outcomes were evaluated 6 months and more after patients began to walk. The duration of follow-up observation varied from 6 months to 9.5 years.

Evaluation criteria included: (1) the degree of heel valgus correction; (2) the degree of longitudinal arch correction; (3) the absence/presence of complications; (4) the degree of longitudinal arch angle correction; (5) the degree of talocalcaneal divergence angle correction. Outcomes were considered as being ‘good’ if the heel valgus angle was 0-6°, the longitudinal arch was normal or reduced by no more than 20%, the longitudinal arch angle was increased by no more than 5°, and the talocalcaneal divergence angle had increased by no more than 5°, and also on the basis that there were no complications.

Outcomes were considered as being ‘satisfactory’ if the heel valgus angle was 6-10°, the longitudinal arch had been reduced by no more than 50%, the longitudinal arch angle had increased by no more than 15°, the talocalcaneal divergence angle had increased by no more than 10°, and that there were no complications.

Outcomes were considered ‘unsatisfactory’ if the heel valgus angle was more than 15°, the longitudinal arch had been reduced by more than 50%, the longitudinal arch angle had increased by more than 15°, the talocalcaneal divergence angle had increased by more than 10°, or if there were complications during treatment which were independent of other clinical results.

Analysis showed that ‘good’ outcomes were achieved in 72% of cases (712 feet), ‘satisfactory’ outcomes in 23% (223 feet), and ‘unsatisfactory’ outcomes in 5% (54 feet) of cases. Below we provide a detailed description of a clinical case with a good outcome.

Patient D was an 8-year-old male with a diagnosis of CP, spastic diplegia, contractures of the limb joints, and equino-planovalgus deformity of the feet. Gurgical intervention involved extra-articular arthrodesis of the subtalar joint and gastrocnemius muscle release (Figures 1 and 2).

We believe that unsatisfactory outcomes following treatment were associated with diagnostic shortcomings such as an overestimated degree of mobility in patients over 10 years old, the presence of significant changes in bone and joint structure, and tactical and technical errors during the surgical correction of foot deformities. We identified two types of tactical error: firstly, the incomplete correction of equinus contracture (18 cases) and secondly, harvesting of the autotransplant from a site which was too low (the middle part of the lower third of the fibula), thus resulting in elevation of the lateral ankle and ankle joint instability (one case). We also identified four types of technical error: [1] using an inadequate autotransplant size resulting in residual deformity (five cases) and overcorrection (four cases); [2] neuropathy of the n. cutaneus dorsalis lateralis (two cases); [3] incorrect positioning of the autotransplant in the talus canal and in the calcaneus groove resulting in ankle area pain syndrome (two cases); and [4] fracture of the talar neck (two cases).

Discussion

It should be noted that correction of concomitant equinus contracture provides guaranteed evidence of the effectiveness of the surgical intervention developed herein. In order to determine which surgical method of correction to apply, we routinely use the Silfverskiöld test. If the test is positive, we perform gastrocnemius release. However, if the test result is negative, we perform elongation of the Achilles tendon, during which parts of the tendon are joined in a position when the foot axis and lower leg angle is 90°. If results from the Silfverskiöld test are unclear, we perform extension of the Achilles tendon. The first reason for this is that the incomplete correction of equinus contracture predetermines the incomplete surgical correction of foot deformity. The second reason is that stabilization of the subtalar joint always leads to restriction of dorsiflexion in the foot, which exacerbates the degree of residual equinus contracture. Restricted dorsiflexion is associated with rigid horizontal positioning of the talus and fixation of the trochlea tali in the talocrural joint. In case the equinus contracture is purely tonic, it is necessary to lower the tonus of the triceps surae muscle by an injection of botulinum toxin (Dysport or Botox) or by performing selective neurotomy of the tibial nerve.

The site used for autotransplant harvest and the size of the autotransplant are very important. Our preference is segmental resection of the fibula between its middle and lower thirds. This allows us to avoid undesirable complications such as elevation of the lateral ankle followed by destabilization of the ankle joint. Correction of ankle instability caused by this complication is very challenging and therefore surgeons must select the autotransplant harvest site very carefully indeed. In younger patients, we removed a bone segment which was 3 cm in size for autotransplantation while in adolescent patients, we selected a segment of 4 cm. However, if the autotransplant is too large and needs effort to be inserted, there is a possibility that this practice might result in varus deformity of the heel, and, correspondingly, foot supination. Furthermore, during wound suturing, it is necessary to make sure that the sensitive n. cutaneus dorsalis lateralis is not taken into the seam. If this nerve is positioned too close to the developing scar, it may result in pain along the lateral tibia that worsens when the patient is walking. In the two cases described above, conservative treatment-water-jet treatment with novocaine and Ringer’s solution-led to the cessation of symptoms arising from nerve irritation.

One of the most important elements of surgery is the precise positioning and depth of the canal in the talus. This must be executed strictly in the talar neck and point towards the area between the trochlea tali and the talus head. The ideal canal depth should be such that the part of the graft inserted into the talar neck is located directly under its upper cortex which supports the stability of correction. The presence of the massive bone tongue in the canal facilitates bone consolidation. In cases where the canal points towards the block or head of the talus and perforates the cartilage surface of one or the other, it is possible to position the transplant in the hollow of the ankle or talocalcaneal-navicular joint, thus causing development of deforming arthrosis and pain syndrome.

We pay significant attention to the position of the distal portion of the graft. The optimal position is when the transplant, being in the groove, rests upon the outer cortex of the calcaneus. If the transplant rests on the trabecular bone, a significant portion of its correction capability is lost. This is because the trabecular bone does not have the strength of compact bone osteons. Sometimes, there is excess of transplant tissue above the cortex. In such cases, the wearing of shoes can result in chronic soft tissue trauma and pain. This is particularly evident in the cases of older children, where the diameter of the fibula is already quite significant. If the body of calcaneus was anatomically very short, and the diameter of the transplant was large, we made a groove directly by the front facet of the subtalar joint. Positioning the groove in this location did not affect the degree of correction and did not result in the development of pain. In our view, the most serious complications of improper surgical technique during this operation are fractures of the talar neck with development of a false joint, or aseptic necrosis of the talar neck. Due to the possibilities of such complications occurring, particular attention should be paid to patients with severely reduced mobility, who almost always have pronounced osteoporosis. In these cases a surgeon should proceed by inserting the graft with the utmost care and accuracy, since these are patients with a dramatically increased risk of fracture.

Conclusion

In this paper, we describe a novel method for extra-articular arthrodesis of the subtalar joint for the treatment of patients with CP and the mobile form of equino-planovalgus deformity of the foot. By deploying this method, and by being aware of the complications involved and potential causes of error, it will be possible for surgeons to improve post-surgical outcome and minimize the incidence of errors and complications.

Funding information and conflict of interest

This work was supported by The Turner Scientific and Research Institute for Children’s Orthopedics, Saint Petersburg, Russian Federation. The authors declare no conflicts of interest associated with the publication of this paper.

Valery V Umnov

Author for correspondence.
umnovvv@gmail.com
The Turner Scientific and Research Institute for Children’s Orthopedics
Russian Federation

MD, PhD, professor, head of the department of infantile cerebral palsy. The Turner Scientific and Research Institute for Children’s Orthopedics.

Dmitry V Umnov

dmitry.umnov@gmail.com
The Turner Scientific and Research Institute for Children’s Orthopedics
Russian Federation

MD, PhD, research associate of the department of infantile cerebral palsy. The Turner Scientific and Research Institute for Children’s Orthopedics

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  • Патент РФ на изобретение № 2372041/10.11.09. Бюл. № 31. Умнов В.В., Умнов Д.В. Способ лечения плоско-вальгусной деформации стопы у детей. [Patent RUS 2372041/10.11.09. Byul. № 31, Umnov VV, Umnov DV. Sposob lecheniya plosco-valgusnoy deformatsii stopi u detei. (In Russ).]
  • Grice DS. An extra-articular arthrodesis ofthe subastragal joint for correction of paralytic flatfeet in children. J Bone J Surg Am. 1952;34:927-956.

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