PMC7368196_01
Radiographs of lower extremity genu valgus. (a) At age 22, ten years prior to the current presentation, radiography displays genu valgum of the left knee measuring 17  with a hypoplastic lateral femoral condyle. (b) At current presentation, at age 32, redemonstration of genu valgum of the left knee measuring 23  with narrowing of the joint compartments at the knees and osteochondral irregularity of the talar dome on the right.
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During this clinic appointment, X-ray images showed a significant genu valgum deformity at a Q- angle of 17  (Figure 1). X-ray scans were performed that showed a Q-angle of 23 , worsened from her presentation 10 years prior (Figure 1).
Bone mineral density (BMD) scans (current presentation). (a) The BMD within the lumbar spine is 1.140 g/cm2 which corresponds to a Z-score of -0.4. (b) The BMD within the left total hip is 0.807 g/cm2 which corresponds a Z-score of -1.4. The BMD within the left femoral neck is 0.819 g/cm2 which corresponds to a Z-score of -1.3.
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Bone mineral density scans showed osteopenia of the left femoral head with normal lumbar spine density (Figure 2).
Renal ultrasound (current presentation). (a) Left kidney measuring 11.7 cm in length. (b) Right kidney measuring 11.5 cm in length. Both kidneys have homogenous cortical echoes. The renal pyramids are hyperechoic consistent with bilateral medullar nephrocalcinosis.
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A renal ultrasound showed bilateral medullary nephrocalcinosis, without calculi (Figure 3).
Iliac crest bone biopsy prior to phosphorus supplementation. Modified Masson-Goldner trichrome (a)-(e). High porosity of the cortical bone (a) and decreased cancellous bone volume (b). Low bone turnover and mild hypocellularity of bone marrow (c). Rare osteoid seam of normal thickness (d) and few osteoclasts (e). Fluorescent light microscopy: few tetracycline label (f) and evidence of a previous oxytetracycline label (g).
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Histopathological findings included high porosity of the cortical bone, decreased cancellous bone, and decreased osteoid surface (Figure 4). These results show previous weakly diffuse tetracycline deposition (Figures 4(e) and 4(f)), determined to be most likely due to her recent prescription of doxycycline for facial acne therapy which was stopped in advance of the biopsy.
Postoperative radiographs. Postoperative imaging following corrective left total knee arthroplasty: anterior-posterior (a) and lateral views (b).
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Six months after starting phosphorus supplementation, she underwent an uncomplicated left total knee arthroplasty (TKA) leading to gait correction (Figure 5).
Intraoperative surgical biopsy after phosphorus supplementation. Modified Masson-Goldner trichrome of a femur specimen obtained at the time of knee arthroplasty displayed thin cortical bone and high porosity (a). Thin trabecula and adipose bone marrow (b). No significant change in comparison with her prior biopsy.
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Biopsy at the time of surgery showed thin cortical bone and high porosity without evidence of osteomalacia, not significantly changed in comparison with her previous biopsy (Figure 6).