Skewfoot: a rare deformity, not to be confused with metatarsus adductus

C.M. Donders1

W.H. Nijhuis2 R.J.B. Sakkers2 C.J.A. van Bergen3 1Department of Orthopaedic Surgery, Meander Hospital, Amersfoort, The Netherlands 2Department of Orthopaedic Surgery, Wilhelmina Children's Hospital, UMC Utrecht, The Netherlands

3Department of Orthopaedic Surgery, Amphia Hospital, Breda, The Netherlands

Corresponding author: C.M. Donders, lilian.donders@gmail.com


Skewfoot is a rare deformity that is characterized by combined forefoot varus/adduction and hindfoot valgus. It may mimic the more common metatarsus adductus and clubfoot.

Patient: a four-year-old boy with a bilateral foot deformity had been treated with serial plaster casting, anti-varus shoes and ortheses for two years, based on the diagnosis of metatarsus adductus. The position of the forefoot had only slightly improved. New physical examination and weight-bearing X-rays revealed the diagnosis of skewfoot. Intervention and outcome: a ‘wait-and-see’ approach was advised. In case of development of complaints in the future, the possibility of surgical correction was explained.

Comparison/literature: skewfoot, serpentine foot or Z-shaped foot is a rare deformity. It is characterized by combined forefoot varus/adduction and hindfoot valgus, which implies a lateral shift of the forefoot. The literature is scarce with low numbers of patients and various treatment techniques. There is still debate about the optimal treatment of skewfoot. Surgical correction can be indicated when prolonged non-operative treatment fails to relieve pain, including intolerance to orthoses, rapid destruction of shoes and callus or ulceration under the head of the talus, which are often seen in rigid or severe skewfoot deformities.

Recommendation: the general belief is that most children with idiopathic skewfeet have no complaints in the long term. We only recommend surgical correction of the hindfoot and forefoot in a persistent symptomatic skewfoot of an adolescent child despite prolonged nonoperative treatment.

Introduction Skewfoot is a rare deformity that is characterized by combined forefoot varus/adduction and hindfoot valgus. A skewfoot deformity may mimic the more common metatarsus adductus or a clubfoot. This report is about a case of bilateral skewfeet that had been diagnosed and treated as metatarsus adductus for two years. The background and treatment options of skewfoot are discussed in the light of the available literature.

Patient A 4-year-old boy presented with a bilateral foot deformity. He had been treated with serial plaster casting, followed by anti-varus shoes in daytime and orthoses at night for two years, based on the diagnosis of metatarsus adductus. His mother explained that the position of the forefoot had only slightly improved in comparison to the start of the treatment. The boy had no complaints. The physical examination showed no leg length discrepancy and a slight valgus leg axis, with an intermalleolar distance of 3 cm. A combination of hindfoot valgus and forefoot varus/adduction was seen (more pronounced on the right side) (figure 1). The talocrural and subtalar joints had a normal range of motion. The Lichtblau test demonstrates contracture of the abductor hallucis muscle. The test is performed as follows. The heel of the foot is grasped with one hand and the index finger bracing the base of the fifth metatarsal. The thumb of the opposite hand pushes against the medial aspect of the head of the first metatarsal creating an abduction stress at the tarso-metatarsal joints. A tight abductor hallucis tendon can be seen or palpated with the index finger.1 This test was positive on the right foot and negative on the left foot. The forefoot varus/adduction was barely redressable in the right foot and partly redressable in the left. On the anteroposterior weight-bearing X-ray the talo-navicular joint was in valgus/abduction and the tarso-metatarsal joint in varus/adduction. This combination indicated a lateral shift in the midfoot (figure 2).

Figure 1. Digital pictures of the skewfeet in standing position. Note the forefoot varus/adduction and the hindfoot valgus (lack of ‘too-many-toes’ sign when assessed from posterior), most notable on the right side.

image

Figure 2.a

Figure 2a and 2b. Weight-bearing X-ray of the right foot. The talo-navicular joint is in valgus/abduction and the tarso-metatarsal joint in varus/adduction.

image

Figure 2.b

Intervention The parents were counselled on the diagnosis of skewfoot. A ‘wait-and-see’ approach was advised because there were no complaints. In case of development of complaints in the future, such as pain and trouble wearing shoes, the possibility of a surgical alignment correction was explained. There will be a follow-up on the patient until the end of growth.

Comparison Skewfoot is also known as serpentine foot and Z-shaped foot. In French it is called ‘Le pied en Z’. In 1863, Henke was the first to describe the combination of forefoot varus/adduction and hindfoot valgus. McCormick and Blount introduced the term skewfoot in 1949.2 This combined deformity is rare, but incidence may be underestimated due to similarities with metatarsus adductus and clubfoot. The diagnosis is based on clinical and radiologic confirmation of forefoot varus/adduction and hindfoot valgus.3

Conservative treatment Different studies provide insight into the natural history and outcomes of non-operative treatment of skewfoot. In a prospective study, Berg reported 23 skewfeet that were treated with cast immobilization or a Denis Browne bar and 8 that received no treatment.4 All the patients with a complex skewfoot deformity (i.e., adduction of the forefoot combined with both a laterally translated midfoot and a valgus hindfoot) had a flatfoot deformity at follow-up. In the simple skewfeet (adduction of the forefoot combined with a valgus hindfoot, but with a normally positioned midfoot), only 31% had a flatfoot deformity at follow-up. At the two-year follow-up evaluation only one patient (with an untreated complex skewfoot deformity) had an uncorrected varus/adduction of the forefoot. Jawish et al. retrospectively reviewed fifteen skewfeet in children, aged three months to two years, who had received conservative treatment by means of a plaster cast for three to six months followed by correcting shoes.5 The researchers defined a good result as a clinically normal looking foot and a radiologically minimal residual distortion or very modest growth disorder. This good result was achieved in twelve of the fifteen patients.

Surgical treatment A few studies investigated the surgical treatment of this challenging pathology. Jawish et al. retrospectively reviewed 29 skewfeet in children from three months to 12 years old who had been treated with an isolated release of the Lisfranc joint or in combination with various osteotomies.5 A poor outcome was found in ten out of fifteen cases with early surgical treatment. In contrast, only four out of fourteen cases had a poor outcome with late surgical treatment after failed conservative treatment. Growth disturbances of tarsal bones were seen in 18 out of 29 cases. The investigators recommended conservative treatment before the age of one, and surgical treatment only in the case of failure of conservative treatment in older children. Mosca proposed a surgical technique for skewfoot correction after non-operative treatment for a minimum of one year (pain on weight bearing and callus and/or ulceration).6 He described a calcaneal lengthening osteotomy, a medial cuneiform opening wedge osteotomy and lengthening of the Achilles tendon. Satisfactory results were reported in five out of six treated skewfeet after a follow-up of at least two years. Asirvatham and Stevens treated seventeen skewfeet and twelve metatarsus adductus by medial capsulotomy and adductor hallucis lengthening after failure of non-operative measures (in-toeing and shoe-wear problems, excessive tripping, and failure to achieve and maintain correction).7 One patient, aged seven, was treated with a medial cuneiform opening-wedge osteotomy for significant residual metatarsus adductus deformity. Two patients complained of intermittent pain on the dorsum of the ankle, and one patient had persistent difficulties with shoe fitting. All the feet had an improved talo–first metatarsal angle at a mean follow-up of 3.6 years. No subgroup analysis was performed.

Outcome Until now the patient had no complaints. There will be a follow-up on this patient until the end of growth.

Recommendation Skewfoot, serpentine foot or Z-shaped foot is a rare deformity. It is characterized by combined forefoot varus/adduction and hindfoot valgus. The diagnosis should be strongly considered in the case of resistance to treatment of metatarsus adductus. This case report is a good example of prolonged misdiagnosis. To date there are no long-term follow-up studies with a large cohort of untreated versus treated skewfeet that reveal the amount of spontaneous correction of the deformities. The literature is scarce, with small numbers of patients and various treatment techniques. The general belief is that the majority of idiopathic skewfeet cause few symptoms in the long term. A ‘wait-and-see’ approach is recommended in asymptomatic cases. Non-operative treatment (e.g. plaster cast, orthoses or correcting shoes) is the first choice in symptomatic feet.8,9 However, rigid or severe skewfoot deformities are often intolerant to orthoses and are associated with rapid destruction of shoes, callus or ulceration under the head of the talus, and persistent pain.6,7 We recommend combined surgical correction of the hindfoot and forefoot in a symptomatic skewfoot of the adolescent child who has failed prolonged non-operative treatment.2,6,10-12 Disclosure statement No conflicts of interest to disclose.

References 1. Lichtblau, S. Section of the Abductor Hallucis Tendon for Correction of Metatarsus Varus Deformity. Clinical Orthopaedics & Related Research. July/August 1975; 110:227-232. 2. McCormick D, Blount W. Metatarsus adductovarus “Skewfoot.” J Ann Med Assoc. 1949;141(7):449–53. 3. Peterson H. Skewfoot (forefoot adduction with heel valgus). J Pediat Orthop. 1986;6:24–30. 4. Berg E. A reappraisal of metatarsus adductus and skewfoot. Bone Jt Surg Am. 1986;68(8):1185–96. 5. Jawish R, Rigault P, Padovani J, Kalit. Pied « en Z » ou « serpentin » chez l’enfant et l’adolescent. Chir Pediatr. 1990;31(6):314–21. 6. Mosca VS. Calcaneal Lengthening for Valgus Deformity of the Hindfoot. J Bone Jt Surg Am. 1995;77:1937–45. 7. Asirvatham R, Stevens P. Idiopathic Forefoot-Adduction Deformity: Medial Capsulotomy and Abductor Hallucis Lengthening for Resistant and Severe Deformities. J Pediatr Orthop. 1997;17(4):496–500. 8. Farsetti P, Weinstein S, Ponseti I. The Untreated Long-Term Functional and Radiographic Treated Outcomes of and Non-Operatively Adductus *. J Bone Jt Surg. 1994;76(2):257–65. 9. Evans A, Rome K. A Cochrane review of the evidence for non-surgical interventions for flexible pediatric flat feet. Eur J Rehabil Med. 2011;47:69–89. 10. Hagmann S, Dreher T, Wenz W. Skewfoot. Foot Ankle Clin. 2009;14(3):409–34. 11. Wan S. Metatarsus Adductus and Skewfoot Deformity. Clin Podiatr Med Surg. 2006;23:23–40. 12. Siegel SJ. The Modified Lepird Procedure for Correction of Metatarsus Adductus. J Foot Ankle Surg. 2019 Sep;58(5):1045-1050.