Revision hip arthroplasty following recurrence of a phosphaturic mesenchymal tumor
In March 2003, a 47-year-old man was referred from the endocrine clinic to the outpatient center of our department with diffuse hip pain on the right side. In 1997, he had severe osteomalacia and was treated symptomatically with phosphate and calcitriol. There was no family history of any disease inducing osteomalacia, such as inborn errors of metabolism or chronic renal disease.\nAt the time of our investigation, laboratory tests revealed hypophosphatemia with 0.44 mmol/l of phosphate (normal range: 0.81–1.6 mmol/l), normal serum calcium (under substitution with calcitriol) with 2.6 mmol/l (normal range: 2.0–2.6 mmol/l), and low urinary inorganic phosphorus excretion with 15 mmol/24 h (normal range: 21–85 mmol/24 h).\nMagnetic resonance imaging (MRI) and computed tomography (CT) scanning showed a destructive lesion, 5 cm in diameter, in the right os ilium and obturator internus muscle (Fig. ). FGF-23 levels were significantly high and an octreotide scan was positive for radionuclide uptake in the right acetabulum. CT-observed biopsy of the right acetabulum was performed, and histological analysis revealed a benign phosphaturic tumor (PHT) of mixed connective tissue type.\nAfter tumor resection through an ilioinguinal approach, serum phosphate levels normalized. To address persistent hip pain, a total hip arthroplasty was performed, and complete remission of clinical symptoms accomplished.\nEight years later, the patient presented with hip pain on the same side over a longer period. CT scan and MRI revealed tumor recurrence (Fig. ) on the dorsomedial circumference of the acetabulum with a bone defect 2 cm in diameter. Signs of loosening of the cup of the hip arthroplasty were considered secondary. Biochemical evaluation revealed hypophosphatemia with 0.69 mmol/l of phosphate, normal serum calcium of 2.42 mmol/l and a secondary hyperparathyroidism with parathyroid hormone of 85.7 ng/l (normal range: 15–65 ng/l). An octreotide scan of the right hip showed massive enhancement of the acetabulum. Assessment of FGF-23 was inconclusive.\nIn revision surgery, the stem was fixed but the socket was easily removed and the center of the acetabulum exhibited massive destruction. There was no clear demarcation between the tumor mass, consisting of soft tissue, and its surroundings. After wide resection of the tumor, the bone defect was filled with homologous bone and a 52-mm roof reinforcement ring (Mathys), with a cemented 50-mm low-profile cup (Mathys), was implanted (Fig. ).\nHistological analysis of the removed tissue showed the same benign PHT as previously excised in 2003. Re-evaluation 1 year after revision arthroplasty revealed normal phosphate levels, and the patient reported no symptoms or complaints.