Prader-Willi syndrome (PWS) is an uncommon disorder of genetic etiology. Loss of function of genes in the paternal copy of Chr 15q11.2-q13 results in PWS ^[1]. The underlying mechanisms of this genetic syndrome are numerous such as deletion, maternal uniparental disomy, imprinting defect, and translocation ^[1]. There are several associated musculoskeletal manifestations, and hip dysplasia (HD) is one of the common clinical findings with a prevalence between 10% and 30% [2-4]. Although the clinical features and diagnosis of PWS are well described in the literature, the challenges in the management protocol still exist [2, 3]. Here, we present the case of a female child who was diagnosed with PWS. She had an associated developmental dysplasia of the hip (DDH) and was managed like other patients of DDH from a surgical viewpoint.

A 4-year-old female child was brought by her parents to our hospital with complaints of shortening in the left lower limb. She had severe obesity, hypotonia of all four limbs, feeding difficulty, and an inability to stand unsupported. Her obesity had been present since birth. She was diagnosed with PWS according to the diagnostic criteria of Holm et al. ^[5]. We considered Simpson-Golabi-Behmel syndrome type 1 and Tatton-Brown-Rahman syndrome as the differential diagnoses. However, based on the clinical features PWS is considered the most probable diagnosis and was later confirmed by genetic evaluation. Child had some behavioral issues related to anger control. She had not received any growth hormone therapy in the past and had never suffered any fracture. During her physical examination, we noted asymmetrical skin folds with increased skin folds on her left thigh and associated femoral shortening. She could walk with support but limped while doing so. She had a wide-based, externally rotated stance position, the range of motion of all joints of the upper and lower limbs was recorded. Generalized ligamentous laxity was observed in the patient. Lower limb length was measured, and a limb length discrepancy of 2 cm was noted. Observation of standing spinal sagittal and coronal alignment was unremarkable (Fig. 1).

Management

Evaluation of radiographs of the pelvis, spine as well as hip was done. Radiographs revealed a dislocated femoral head on the left side with the femoral head significantly smaller in size than the opposite side (acetabular index [AI] -35, center-edge angle of Wiberg -15) (Fig. 2). The parents were counseled about the condition and were informed about the need for timely surgical intervention to relocate the femoral head in the acetabulum. After consultation with the pediatrics and the anesthesia teams, a plan was made to treat the dislocation surgically. The patient was positioned supine, general anesthesia was administered, and intravenous antibiotic for surgical prophylaxis was administered. The endotracheal intubation by the standard technique was unsuccessful; consequently, fiberoptic intubation was performed. The anesthesia team also had difficulty securing intravenous access. After assessment of the degree of anteversion, we performed an adductor longus tenotomy. The Sommerville approach was used. However, after the skin incision, we encountered a thick layer of subcutaneous fat. This made the process of exposure difficult, and we had to use Langenbeck retractors normally used for spine surgery in adult patients. The difficulty in retraction necessitated the help of another surgical assistant. Further, the muscular structures were noted to be of reduced bulk than expected. The iliopsoas tendon was identified at the level of pelvic brim and after properly isolating it, it was released. Following “T” shaped capsulotomy, the femoral head was visualized and found to be malformed and appeared as if it had shrunk. The ligamentum teres was elongated but was thin and was excised after tracing it to the depths of the acetabular cavity. We excised the transverse acetabular ligament and fatty tissue from the floor of the acetabular fossa. Following a provisional reduction of the femoral head a plan for femoral shortening and de-rotation was made. The femur was shortened by 2 cm and fixed with a dynamic compression plate. The reduction and its stability were reassessed, and it was decided to add on a Dega osteotomy to improve the anterolateral acetabular coverage. The excised piece of femur was used to hold the osteotomy open. Capsulorrhaphy was performed using non-absorbable suture (Fig. 3). Although the hip was found to be stable after the procedure, the thick fat layer around the thigh and the buttock prompted us to add on a Kirschner wire (K-wire) for added stability and peace of mind while applying the hip spica (Fig. 4). After applying a snugly fitting one and half hip spica, the patient was shifted out.

The child was discharged after a 2-day hospital stay. The parents were taught about the spica care. She was followed up every 2 weeks for the first 4 weeks, then after every 4 weeks until cast removal (Fig. 5 and 6). Cast removal was done after 12 weeks. After the cast removal, the patient was advised for hip range of motion exercises. Weight bearing was permitted as tolerated and initially with support and later without support. Regular follow-up was done every 1 month for the next 3 months, then every 4 months. At the 2-year follow-up, she showed significant clinical improvement. Lower limb length discrepancy was corrected. The walking pattern and the foot progression had improved. She was able to bear more weight comfortably on the affected limb as compared to her pre-operative status. The range of motion of the operated hip was significantly improved. Generalized ligamentous laxity was still noted. On radiographs, the femoral head still appeared to be small but well contained within the acetabulum.

PWS is an unusual and rare disease that results from the dysfunction of genes located in the paternal copy of Chr 15q11-q. With a prevalence of 30%, HD is one of the common clinical findings among the multiple musculoskeletal symptoms that are associated with it ^[2]. If HD is not identified in these patients, there may be a delay in diagnosis, a chronic subluxation of the hip joint, and eventually degenerative joint disease [2, 3]. For defining the features of PWS, Goldberg has proposed a “5H”: Hypotonia, Hypogonadism, Hyperphagia, Hands and feet small, and Hypo-mentation ^[6]. To emphasize the value of a timely diagnosis of “Hip dysplasia” in children with PWS, West and Ballock have proposed expanding to “6H” ^[3]. Many psychiatric disorders are commonly seen in PWS patients like impulse control disorder, organic personality disorder, oppositional defiant disorder, and dysthymic disorder; our patient had some behavioral issues related to her anger control. As stated earlier, on examination, she had a wide based externally rotated stance position, a similar finding has previously been described by Volpe et al. ^[7] range of motion of all joints was recorded, and generalized ligamentous laxity was observed in the patient. These patients are difficult to operate on. Anesthetic difficulties of PWS include morbid obesity, perioperative morbidity and mortality, the risk for difficulties with airway management, risk of aspiration, difficult monitoring, and difficult vascular access and risk for perioperative respiratory failure, abnormalities in the ventilation, and thermo-regulation. Other perioperative concerns are reduced pulmonary reserve, arrhythmias, cor-pulmonale, obstructive sleep apnea, and diabetes mellitus which are generally seen in obese patients. Because of these physiological changes, PWS presents a serious challenge to anesthesiologists. A thorough preoperative workup is thus necessary for the identification of co-morbidities and optimizing them in planning for perioperative management [8, 9].

Surgically, the problems that can be anticipated include difficulty in retraction due to increased fat, difficulty in identification of the structures, and difficulty in using instruments. Passage of Gigli saw for a Salter procedure can be challenging due to the above points and a Dega or Pemberton osteotomy can be done instead to circumvent this problem. Dega osteotomy was done in this case. After reduction, the chances of re-dislocation become high as applying an appropriate hip spica can be difficult. This can be addressed by placing an additional K-wire from the femur to the ilium in a reduced position of the hip as was done in our patient. The orthopedic symptoms of PWS were initially reported by Pearson et al. ^[10] in a roentgenographic study involving five cases. Another study by Holm et al. ^[5] reported orthopedic findings and devised clinical criteria for the diagnosis of PWS. Kroonen et al. ^[1] concluded that scoliosis, an out-toeing gait pattern, genu valgum, and an idiopathic leg length disparity were the most consistently observed clinical orthopedic symptoms of PWS. The first reports of an elevated incidence of HD in the literature were documented by Butler et al. ^[11] and West and Ballock ^[3] Trizno et al. identified the prevalence of dysplastic hip in PWS patients to be as high as around 30% ^[2]. Torrado et al. concluded environmental factors appear to play an essential role in these children. Extreme prenatal and postnatal hypotonia, which is typically observed in neonates with PWS, may have a significant role in the development of this condition ^[12]. Kroonen et al., in their study, reported that 4 patients benefited from a shoe lift, who had a discrepancy of leg length more than 2 cm. Hip pathology in their series was identified radiographically in only 2 of 26 cases. No patient in their series required surgery for the hip. They concluded surgical decisions regarding the reconstruction of the hip to be individualized. AI and center edge angle are common radiographic parameters used to diagnose DDH [13, 14]. Shim et al. ^[4] and Trizno et al. ^[2] stated the use of the AI and center edge angle in their work. Shim et al. stated that PWS has a significant prevalence of lower limb malalignment. Radiographic studies revealed that just 1 patient had a leg length difference >2 cm. They reported HD was present in a total of 8 patients (22.2%). Three among them underwent hip surgery, 2 patients for varus derotational osteotomy of proximal femur and 1 case for shelf acetabuloplasty. Miao et al. ^[15] in 2024 published a retrospective study in 175 PW patients, and HD was found in 47 patients, an incidence of 38.2%, which was 2 times that of normal population. The median age of onset was found to be 1.8 years old, suggesting that in recent years, there has been an increase in awareness regarding hip development in PWS patients. They concluded that in the rhGH treatment group, the incidence of HD was lower, which may be due to the effects of rhGH therapy on weight-bearing capacity and muscle growth. The proportion of patients getting orthopedic treatment was 12.7%, which was lower than the previous studies suggesting early rehabilitation exercise for HD is being considered. They mentioned that PWS in patients who receive treatment for HD may be reversed after complete remission a few years later. The asymptomatic mild residual acetabular dysplasia may also worsen, and therefore, conducting a continuous radiological evaluation of the hip joint in PWS patients is necessary and evaluating the developmental level of the hip joint. Laumonerie et al. ^[16] conducted retrospective cohort study on 72 patients between January 2004 and December 2016 and performed and analyzed a total of 274 radiographic measurements including Center-edge angle of Wiberg, AI, and neck-shaft angle. Their study showed that the PWS population receiving growth hormone treatment at an early stage of development had a favorable evolution of hip radiographic measures and concluded to take into account observation alone in the HD treatment protocol for these patients. Trizno et al. screened twenty patients after birth with Ortolani’s test and Barlow’s tests for HD and two patients showed positive results. 8 out of 27 patients (30%) underwent hip treatment, 2 patients managed by Pavlik harness, 1 by Pavlik harness followed by closed reduction, 3 by closed reduction, 1 by open reduction, and 1 had unspecified surgery (at an outside hospital) for HD. HD improved in three of the eight individuals and recurred in two patients. One patient needed surgical reduction after the Pavlik harness because of a delayed diagnosis. Open reduction, capsulorrhaphy, Salter osteotomy, femoral shortening, iliopsoas lengthening, and derotational osteotomy were performed on the left side. Bernese periacetabular osteotomy and internal fixation were performed on the right hip. Early diagnosis and using the Pavlik harness produced better results. No correlation between females and the prevalence of HD are demonstrated by Trizno et al. because gonadal insufficiency is seen in PWS female embryo causing poor estrogen production. Their research stated that PWS is a risk factor for dysplastic hip and recommended screening for HD radiographically at regular intervals of 1, 2, 5, 10, and 15 years in PWS patients to allow for early intervention, satisfactory treatment outcomes, and to avoid degenerative changes in later stages. They concluded that for the patients who underwent successful treatment for HD, the mean age at diagnosis was 2 months ^[2]. HD must be diagnosed as soon as possible. When HD is discovered before the age of 6 months, conservative treatment options are ideal. This is crucial since obesity and behavioral abnormalities, such as picking of skin and self-mutilation, increase the likelihood of postoperative complications. Surgery is usually needed in cases who present late or those who have delay in diagnosis and neglected cases. In these patients, often chronic subluxation of the hip joint and degenerative joint disease is seen. To conclude, at 6 weeks of age, every baby should have a screening ultrasound of the hip joint. If the results are abnormal, treatment with a stiff brace or Pavlik harness should be started. Patients with dysplastic hip are monitored at regular follow-up. For PWS patients, screening for HD at regular intervals using radiographs, USG, or both is advised to facilitate early intervention, optimize treatment results, and avert further degenerative changes. Limitation of this study is it only involves single case study with short duration of follow-up. More prospective studies involving larger population of PWS children with neglected chronically dislocated hip managed surgically and including longer follow-up are required in the future.

PWS is associated with hip dysplasia (HD) with a prevalence between 10% and 30%. A failure to recognize HD in PWS can lead to a diagnostic delay and hip joint being chronically subluxated and subsequent degenerative joint disease. Growth hormone treatment at an early stage of development has shown favorable outcome in these patients. The present case demonstrates that a neglected, chronically dislocated hip in PWS can be managed like a case of DDH with the associated challenges.

Multiple musculoskeletal manifestations, including HD, are associated with PWS. There is a high prevalence of HD (10–30%) in PWS, and failure to recognize this can lead to a diagnostic delay, chronic subluxation/dislocation of the hip joint, and subsequent degeneration. Growth hormone treatment at an early stage of development has a favorable outcome in these patients. A neglected, chronically dislocated hip in PWS can be managed like a case of DDH, with the associated challenges.