Abstract
Pes planus is a common problem, and although the condition is predominantly idiopathic, in children it may be associated with neuromuscular disease and other disorders including tarsal coalition and the accessory navicular syndrome. The discussion in this chapter is limited to the flexible flatfoot, with or without the presence of an accessory navicular. By and large, similar principles of correction apply to treatment of flexible flatfoot in the child and to management of flatfoot in the adult, with the exception that a rupture of the posterior tibial tendon is not encountered in children, in whom rigid deformities are less common as well. The discussion of the rigid flatfoot in the child is presented in the chapter on tarsal coalition.
Key Words
Pes planus, pediatric, flexible flatfoot, accessory navicular
Pes planus is a common problem, and although the condition is predominantly idiopathic, in children it may be associated with neuromuscular disease and other disorders including tarsal coalition and the accessory navicular syndrome. The discussion in this chapter is limited to the flexible flatfoot, with or without the presence of an accessory navicular. By and large, similar principles of correction apply to treatment of flexible flatfoot in the child and to management of flatfoot in the adult, with the exception that a rupture of the posterior tibial tendon is not encountered in children, in whom rigid deformities are less common as well. The discussion of the rigid flatfoot in the child is presented in Chapter 24 (Tarsal Coalition).
The difficulty in management of the flatfoot deformity in childhood is to know for whom and when treatment is required. Children who have severe flexible flatfeet, and who are symptomatic but have not responded well to management with orthoses, will require surgery. With those children who have severe flatfoot deformity but are asymptomatic, whether to persevere with nonoperative treatment or to proceed to surgical correction becomes a difficult decision. The adolescent with severe flatfoot who has a sibling or a parent with similar deformity that was not helped by orthoses may also benefit from earlier surgery. We find it helpful to examine the child every 6 months, to get a “feel” for the severity of the deformity and to look for any progression of the deformity or symptoms. There are of course children with asymptomatic flatfeet, whose parents are anxious about the shape of the feet, but who clearly do not require any treatment at all. With the passage of time, flexible feet in pediatric patients will become more rigid; this may happen in early adolescence or young adulthood. Adaptive changes inevitably take place in the hindfoot that alter its relationship with the forefoot. To keep the foot plantigrade, as the hindfoot everts and the calcaneus moves into valgus, the forefoot has to supinate. The Achilles tendon moves laterally with the calcaneus, and the axis of force on the subtalar joint changes, increasing the likelihood of a contracture of the gastrocnemius-soleus. As these structural changes take place, rigidity increases, and of course, the surgical treatment alternatives become bewilderingly complex. Unfortunately, there remains a feel for the management of the flexible flatfoot in the child. Many of our colleagues will not treat this condition, and yet it is quite evident in follow-up that the deformity is progressing. The younger the child, the easier the corrective surgery. The use of arthroereisis in the young child is frequently quite sufficient for treatment, without the addition of a hindfoot and or forefoot osteotomy ( Fig. 13.1 ). Why then do we wait? Certainly, there is a potential morbidity from surgical correction in the child, and failure does indeed occur, but failure does not imply an irreversible condition, since one can simply use a more integrated treatment including osteotomies and a gastrocnemius recession.
In the young child with a symptomatic flexible flatfoot, we hope to reduce the hindfoot into neutral with a subtalar arthroereisis, with or without a lengthening of the gastrocnemius. If the forefoot is supinated with reduction of the hindfoot deformity, then it is very useful to add an opening wedge plantar flexion osteotomy of the medial cuneiform to maintain the forefoot in a plantigrade position. The many variations of this basic deformity must be appreciated; in some children, for example, the heel is in far more valgus, for which a subtalar arthroereisis does not provide sufficient correction, so a medial translational osteotomy of the calcaneus is required either as an isolated procedure or in addition to the arthroereisis. As the adaptive changes take place, gradually increasing abduction of the forefoot relative to the hindfoot occurs, and the navicular moves off the head of the talus (uncovering of the talus). In these feet, a medial translational osteotomy of the calcaneus is not sufficient for correction, and a lengthening of the lateral column of the foot is required. Perhaps the most obvious difference in management of flatfoot between children and adults is that in the former, arthroereisis and osteotomy are emphasized, and arthrodesis should be avoided. Unfortunately, arthrodesis still has to be part of the treatment algorithm in children, because some adolescents will have a rigid flatfoot, not associated with a tarsal coalition. Each of these procedures is discussed next.
Arthroereisis
Indications and Rationale
The goal of arthroereisis in the child is to properly orient the talus over the calcaneus; the joint is then allowed to remodel. This remodeling is expected to help prevent further problems later in life, such as degeneration or rigidity of the hindfoot. An arthroereisis implant can be considered to function as an internal orthotic device. This procedure has many advantages; most important, however, are the maintenance of motion it affords and the minimal associated morbidity. The indications for arthroereisis in the child are broad. Treatment results for children undergoing arthroereisis have been excellent, provided that the talonavicular joint is not significantly uncovered and the midfoot abducted off the head of the talus. The procedure seems to work very well in younger children who have predominantly heel valgus, presumably because they have more capacity for remodeling and adaptation of the forefoot. We think that a foot with less than 35% uncovering of the talonavicular joint can be treated with arthroereisis. More than that, one should consider a lateral column-lengthening procedure ( Fig. 13.2 ). Once the talonavicular joint sags, particularly as seen on the lateral radiographic view, these feet can still be treated with arthroereisis, but seem to require more correction of the pronation deformity and a medial displacement calcaneal osteotomy may be required ( Fig. 13.3 ). If there is abduction deformity greater than 35%, with uncovering of the talonavicular joint, then neither the arthroereisis nor the medial displacement osteotomy is likely to be successful. More of the talocalcaneal deformity is corrected with arthroereisis than abduction of the transverse tarsal joint. Most important, children are able to bear weight in a boot within days after the arthroereisis surgery.
The pediatric patient typically adapts to the arthroereisis very well, and the incidence of implant failure is low in this age group. By contrast, in our own experience with use of arthroereisis as an adjunctive procedure in a group of carefully selected adult patients, sinus tarsi pain warranted implant retrieval in more than half of the cases. In children, however, implant removal has been necessary in about 10% of the cases, probably because the foot adapts as it matures. One cause for failure of the implant regardless of the age of the patient is inadequate correction of the forefoot. When the hindfoot is restored to a neutral position with the implant, some supination of the forefoot occurs. If the forefoot is able to compensate by increased plantar flexion of the first metatarsal, then a plantigrade foot is maintained. If the supination exceeds this adaptive ability, however, then to maintain the forefoot in a plantigrade position, the hindfoot has to evert during the foot flat phase of gait. This increased eversion then compresses the subtalar implant, causing pain. For this reason, a gastrocnemius recession and an opening wedge osteotomy of the medial cuneiform is absolutely necessary if supination is excessive. Residual forefoot supination is easily assessed intraoperatively with the use of a rigid flat plate to determine the position of the first ray with simulated weight bearing. Given the low morbidity of the cuneiform osteotomy and gastrocnemius recession in contrast to implant failure, a low threshold for performing these adjunctive procedures should be maintained.
Surgical Technique
An incision is made in the sinus tarsi, approximately 1 cm in length. To locate the exact position for the incision, it is necessary to palpate the “soft spot” between the distal tip of the fibula and the anterior process of the calcaneus. The incision is placed inferior to the intermediate dorsal cutaneous branch of the superficial peroneal nerve and dorsal to the peroneal tendons. A guide pin that functions as a cannula for the arthroereisis dilators and sizers is inserted into the tarsal canal from lateral to medial, pushed through a puncture on the medial foot, and then clamped ( Fig. 13.4 ). The anatomy of the tarsal canal must be appreciated—the canal is shaped like an oblique cone and passes from anterolateral to posteromedial. The guide pin should therefore be inserted in the same plane as that of the tarsal canal and not directly medially. A slight resistance to the insertion of the pin can be felt as it traverses the interosseous ligament; then it is pushed through until it is protruding on the medial skin. The clamp on the guide pin prevents loss of position of the guide during repeated insertion of the sizers and trial implants.
Once the guide pin is secure, the first cannulated trial sizer is inserted to get a feel for the position, location, and size of the tarsal canal. The range of motion of the subtalar joint is carefully assessed with each incremental increase in the size of the dilator. The dorsiflexion of the foot now occurs more directly through the ankle joint, rather than in an oblique direction with a combined motion of dorsiflexion and eversion through the subtalar joint. If too large a prosthesis is inserted, motion of the subtalar joint will be limited. An important point here is that the goal of this operation is simply to limit excessive eversion of the hindfoot. If the prosthesis is too small, correction of hindfoot valgus will not be obtained, and dorsiflexion of the foot through the subtalar joint will persist. The appropriate sizer should limit abnormal subtalar joint slightly but allow for eversion.
The sizer is withdrawn, a trial implant is inserted, and the position of the implant is checked radiographically. The implant should rest between the middle and the posterior facets. On the anteroposterior view of the foot, the lateral edge of the prosthesis should be 4 mm medial to the lateral edge of the talar neck. If the position of the implant is incorrect, as noted on the anteroposterior radiograph of the hindfoot, then it is easy to adjust the final position by screwing clockwise or counterclockwise in the sinus tarsi.
The range of motion of the subtalar joint is assessed. The eversion with the foot in neutral dorsiflexion should be particularly noted. As stated, the primary goal of correction is to limit excessive subtalar joint eversion. The effect of the implant on the range of motion of the ankle and the position of the forefoot is not as important as the limitation of excessive subtalar eversion. In most young children treated for a flexible flatfoot deformity, insertion of the implant is sufficient to provide appropriate correction. The forefoot should be plantigrade, and no excessive supination of the forefoot should be present after hindfoot correction. If supination is present, an opening wedge osteotomy of the medial cuneiform is an excellent procedure to correct any residual forefoot supination after correction of the hindfoot. A gastrocnemius recession is also commonly performed as required by the presence of contracture.
Correction of the Accessory Navicular Syndrome
A painful accessory navicular bone is almost always associated with a flatfoot of variable degree. Although this condition is more prevalent among children, it can also be present in adults, with symptoms resulting from disruption of the synchondrosis between the body of the navicular and the os naviculare. As the synchondrosis is stressed, disruption of the attachment of the accessory navicular bone and thus of the posterior tibial tendon occurs, with consequent proximal migration of the accessory navicular bone. Elongation of the posterior tibial tendon and an acquired flatfoot then occur. In the child, however, the accessory navicular bone can be painful either as a result of stress on the synchondrosis or from pressure in the shoe secondary to an uncorrected pronated flatfoot ( Fig. 13.5 ).
