We retrospectively reviewed the records of the 59 patients who underwent surgery between April 1984 and 2004. There is no funding source for this study. Human Ethics and Consent to Participate declarations are not applicable. The diagnosis of childhood osteonecrosis was determined through historical, clinical, and radiographic findings. The average age at the onset of osteonecrosis was 8.4 years (ranging from 6 to 10 years), and the average age at the time of THA was 28.6 years (ranging from 19 to 41 years).

Patients in this study were selected based on the following criteria: hip osteonecrosis before age ten, radiographic evidence of femoral deformities during childhood that could complicate the THA procedure and minimum five-year follow-up. No antecedent of infection was noted, and no bacteria was obtained from specimens obtained during surgery. The evaluation considered patients’ conditions [6], leg length, limp, and pain patterns. Surgeries on the opposite limb, such as epiphysiodesis, were recorded. Leg lengths were measured using a tape measure and blocks under the shorter limb to determine exact discrepancies and identify the length that best balanced the pelvis. A preoperative assessment of femoral and sciatic nerve function was conducted.

The patient cohort consisted of 27 men and 32 women, with an average body mass index (BMI) of 23.6 kg/m² (ranging from 16.1 to 33.8 kg/m²). Most patients were homozygous for the sickle cell gene (haemoglobin SS), with three patients having hemoglobin S/hemoglobin C, and two having hemoglobin S associated with beta-thalassemia. The medical record review included transfusion documentation, chelation history, and recent laboratory values. Chronic transfusion was defined as receiving eight or more transfusions per year or at least one transfusion every seven weeks.

Risk factors for low bone mass [7,8,9] were observed during chilhood. We observed delayed growth and pubertal development, milk avoidance, lactose intolerance, deficiencies in bone-forming nutrients (Calcium, Vitamin D, Zinc), and low serum 25-OH vitamin D levels. Additionally, transfusion therapy can lead to iron overload and endocrine abnormalities. Growth failure [9–10] was characterized by a height Z-score lower than − 2.5 and/or the use of growth hormone therapy.

The need for ongoing thyroid hormone replacement therapy identified hypothyroidism. In females, hypogonadism was defined as being over 13 years old and not yet at Tanner B2, over 14 years old requiring estrogen replacement therapy, or over 15 years old with primary amenorrhea. In males, it was defined as being over 14 years old and not yet at Tanner G2, or over 17 years old and not yet at Tanner G4. Endocrinopathy was considered as dysfunction in at least one of three axes studied: growth failure, hypogonadism, or hypothyroidism.

Patients underwent a preoperative evaluation, as previously described, including a haematologic consultation. Blood products were matched for ABO Rhesus (Cc D Ee) and Kell antigens to prevent alloimmunization. Antibiotics were administered during surgery and for three days afterward. Implants were secured with antibiotic-loaded cement, and intraoperative cultures were obtained, all of which were negative.

Preoperative radiographic assessments classified patients into four categories based on the severity of hip dysplasia. The minimum radiographic evaluations included anteroposterior pelvis and Lauenstein lateral radiographs. CT scans were used to determine hip versions accurately. Arteriography was used to visualize arteries and plan incisions to avoid vascular injury in complex THA procedures, especially in patients with altered vascular anatomy due to previous surgeries.

Patients were positioned laterally, and a curvilinear lateral incision was used for posterolateral exposure. The hip was dislocated posteriorly unless it was already severely subluxed or dislocated. The true acetabulum was exposed, and the acetabular cartilage was removed using a small reamer.

The decision to perform a subtrochanteric osteotomy with bone resection and derotation was based on preoperative planning and intraoperative evaluation of soft tissue tension during attempts to reduce the femoral head into the acetabulum. The procedure was evaluated by pulling the leg with the knee flexed to about 90° while maintaining consistent distal traction. While the trial stem was inserted into the proximal femur fragment, the trial femoral head was reduced into the cup. Traction was applied to the distal femur while the knee flexed at approximately 90°. The bony overlap length at the osteotomy site was excised from the distal femur (Fig. 2). On average, the excised femoral segment measured 38.4 mm, with a range of 33 to 45 mm. The osteotomy was made at an optimal level below the lesser trochanter, with the average osteotomy site being 21.1 mm (range: 15 to 30 mm) below the trochanter.

Abnormal anatomy of the proximal femur in a patient with SCD and hip osteonecrosis when 6 year old

Measurement of the shortening during the surgery

Following this, the hip was prepared for the stem. Stems were cemented implants. The contact cuts were planarized both for the proximal and distal femur. Clamps and a transitory plate held both fragments in place to insert the cement and stem. Before cement was used, a rubber blade was temporarily wrapped around the femur to prevent cement from leaking through the osteotomy cut. The femoral component was inserted with the implant anteverted at 10–15°. During reconstruction, the anteversion of both femoral and acetabular components was assessed to maintain stability, aiming for a combined anteversion between 30° and 45°. Intraoperative assessment using the Ranawat Sign helped avoid stability issues.

Statistical analysis employed chi-square tests, Student’s t-tests, and analysis of variance.