Cavus Foot Correction

History

Establishing the correct diagnosis through a detailed history with the patient and guardian and physical examination is the first step in avoiding complications. Elucidating if the deformity was present at birth or has been progressive, if it is painful or painless, birth history, presence of developmental delay, and gait disturbance must all be addressed. Patients may present for the deformity itself but also may present with a chief complaint indirectly related to the underlying problem, such as lateral plantar calluses or a history of recurrent ankle instability. It is the role of the surgeon to recognize that the chief complaint may be just a portion of the larger underlying pathology. A past medical history of a neurological condition involving either the central or peripheral nervous system may be the underlying etiology of the deformity. Specifically, Charcot-Marie-Tooth (CMT) disease has been found to be the most common overall and neurologic cause of cavus foot deformity (up to 66% of cases). However, other conditions such as cerebral palsy, Friedrich ataxia, scoliosis, spinal muscular atrophy, and spinal dysraphism must also be ruled out. If any of these conditions are suspected, referral to a pediatric neurologist is indicated for evaluation and possible genetic studies. If not secondary to an underlying neurological condition, then history of prior musculotendinous or nerve trauma, as well as compartment syndrome, must be ruled out. Determining if the cause of the deformity is progressive versus nonprogressive, which typically is post-traumatic and has a better prognosis, can help the surgeon avoid the possible complications of recurrence and undercorrection.

Physical Examination

Comprehensive physical examination is an important aspect of the preoperative assessment of a pediatric cavus foot patient. This should include examination of all extremities to evaluate for an associated neurologic condition, as well as examination of the spine for scoliosis or dysraphism. In regard to the lower extremity, hip examination, leg length, and alignment must also be taken into account as either playing a role in or compensating for the cavus deformity. Standing and sitting evaluation of the feet, as well as gait, are elementary to the foot and ankle exam. Gait analysis in a laboratory setting may be indicated in particularly severe cases.

Evaluation of the entire foot for structures involved in the deformity is critical. Underdiagnosis of aspects of the deformity may lead to inadequate treatment, which can lead to undercorrection or recurrent deformity complications. There are several different algorithmic approaches to evaluation of the foot and ankle to assess the deformity comprehensively. Tachdjian described 10 evaluation points, including: deformity apex, cavus versus calcaneocavus, hindfoot position, presence of claw-toe deformity, skin changes (specifically on the sole), abnormal shoe wear, deformity rigidity, muscle strength, stability of neurologic disease, and age/skeletal maturity. Japas described seven points of clinical evaluation, including: unilateral or bilateral deformity, cavus or calcaneovarus, hindfoot alignment and result of Coleman block test, apex of cavus deformity, toe position, rigidity/flexibility, muscle strength, and neurological changes. A surgeon who abides by these steps will adequately recognize the entirety of the deformity.

Strength assessment plays a particularly important role in preoperative planning. Surgical transfer of a tendon that is clinically weak may lead to failed transfer and eventual further muscle imbalance. Detailed neurologic assessment is imperative, as deficits can likewise cause complications. Decreased sensation in particular places the patient at risk of complications with Charcot arthropathy and wound issues from the casting that inevitably follows surgical procedures.

One of the major aspects of the physical examination that cannot be overlooked is the hindfoot and its rigidity or flexibility. A properly performed Coleman block test to assess for residual hindfoot varus in the presence of the block indicates to the surgeon the need for a calcaneal osteotomy or arthrodesis to address the hindfoot, rather than solely a dorsiflexion closing-wedge osteotomy of the first metatarsal for a forefoot-driven hindfoot varus ( Fig. 37.1A,B ). Likewise, the range of motion of each of the major joints, including ankle, subtalar, Chopart, and metatarsophalangeal joints, must be well documented.

Imaging

Anteroposterior, oblique, and lateral weight-bearing plain film foot and ankle radiographs should be performed for all patients who present with cavus deformity. Meary’s angle should be calculated not only to calculate the cavus of the foot but also to determine the exact location apex of the deformity (the intersection of the line longitudinal through the talus and that through the first metatarsal) in the foot, which can play a role in surgical decision-making. Consider a case where the apex is more distal than typical, such as at the tarsometatarsal (TMT) joint, which would call for a TMT arthrodesis rather than a first metatarsal closing-wedge osteotomy. Furthermore, evaluation of the physes with radiographs allows the surgeon to calculate the remaining skeletal growth, which plays a role in balancing soft tissues as well as deciding on performing osteotomies or arthrodesis. Bone quality and degenerative changes in the various articulations of the foot may also be evaluated with radiographs of the feet.

In addition to radiographic foot and ankle series, radiographs of the pelvis are indicated in certain neurologic cases, such as CMT, to evaluate for hip dysplasia. Additionally, radiographic scoliosis series for scoliosis or spinal dysraphism is indicated.