03 June 2008
THE FOOT IN PRADER-WILLI SYNDROME: A CASE REPORT
The Prader-Willi syndrome (PWS) is a rare, congenital, non-hereditary disorder causing neuroendocrine disturbances.1 Patients present infantile hypotonia, a low to moderate degree of mental retardation, short stature and obesity. Their obesity is due to altered hypothalamic function. They lack the sensation of satiety, so that from two years old they have a compulsive attitude to food with an insatiable appetite.2 The incidence varies between 1/8000 and 1/25 000 live births, and appears in both sexes and all races.3 In most cases, the ætiology is the inactivation of several paternal genes located on chromosome 15q11-q13, either by deletion or disruption.4 PWS can be diagnosed by the Holm criteria.5 Patients affected with PWS may present alterations of the feet and the lower limbs deriving from the skeleto-muscular characteristics of the syndrome (obesity in particular).
A 14-year-old patient with PWS (low severity) presented at our podiatric department with pain at the first metatarsophalangeal joint (1st MTPJ) of both feet. Body mass index was 27, corresponding to overweight. The standing examination showed collapse of the medial longitudinal arch and bilateral valgus of the hindfoot, due to overweight and ligamentous hyperlaxity (Fig. 1A). Under load, the extension of the 1st MTPJ was limited, indicating the presence of functional hallux limitus (FHL). The dynamic examination showed excess of pronation during the entire support phase of the walking cycle. The diagnosis was FHL due to pronated feet. Molds were made with plaster bandages under no-load conditions, neutralizing the subtalar joint and extending the hallux to tighten the plantar fascia and to raise the medial arch. A custom-designed plantar orthotic treatment was implemented (Fig. 1B), with no added modifications. The primary aim was to control the late pronation at the midstance and propulsive period of gait. At the six-month follow-up, the pain in the 1st MTPJ had disappeared.
Obesity together with possible residual sequelae of the hypotonia are risk factors that can produce structural and functional deformities in the foot.6 During gait, the ligamentous laxity added to the excess weight will originate greater elongation of the plantar ligaments, allowing the displacement of the astragalus in plantar flexion and adduction, and the evertion of the calcaneus, giving rise to pronate or flat feet.7
During the propulsive period of gait cycle, pronation leads to articular instability. At the 1st MTPJ, the proximal phalanx is unable to completely extend on the first metatarsal head. Thus the extent of articular movement is limited, and FHL and pain appears. If this situation is prolonged without treatment and the patient's weight is not controlled, irreversible morphological changes will occur that may cause painful symptoms in adulthood. The primary aim of the orthotics was to control the pronation. This reduces the valgus hindfoot (Fig. 1B) and provides a more physiological medial longitudinal arch (Fig. 1C). As a result, less tension is applied to the foot's ligaments, muscles, and tendons. The orthotics also allows the 1st MTPJ to maintain a normal amplitude of movement, avoiding the appearance of pain and eventual anchylosis (Fig. 1D).
We propose the use of 3-mm thick polypropylene for the orthotics. This material permits good pronation control, is flexible, light, and has elastic memory. In this way, the foot is kept in its neutral position without atrophying the soft tissue.
The authors’ recommend an orthopædic examination of the feet in patients with PWS or other rare syndromes. Since in these patients walking begins at approximately two years, the orthotic treatment should be started once gait is totally eslablished, beyond the three years of life. Early treatment with orthotics and a multi-disciplinary approach to the care of children with rare syndromes could avoid short- and long-term problems deriving from an inadequate function of the foot, and improve the quality of life of these patients.8