Working Diagnosis:
The working diagnosis at this time was chronic nonunion of bilateral femoral neck fractures complicated by vitamin D deficiency, secondary hyperparathyroidism, and suspected X-Linked Hypophosphatemia (XLH).

Treatment:
Treatment prior to presentation in clinic consisted of conservative pain management, protected weight bearing with a walker, and a methylprednisolone taper. Recommendations for vitamin D, calcium, and physical therapy were given.

After sports medicine evaluation, crutches were provided to minimize weight bearing on the right lower extremity with continued conservative pain management. The importance of vitamin D and calcium supplementation were emphasized.

Further laboratory evaluation demonstrated severe vitamin D deficiency with secondary hyperparathyroidism. He was started on ergocalciferol 50,000 IU weekly. He was evaluated by endocrine who later increased this to twice weekly. Calcium carbonate 500 mg daily and calcitriol 0.25 mcg were added daily. Four months later, potassium sodium phosphate 280-160-250 mg twice daily was prescribed due to persistent hypophosphatemia.

Without significant response to treatment and concern for XLH, his endocrinology team changed ergocalciferol to cholecalciferol 2,000 IU daily while continuing calcitriol, phosphate supplementation, and calcium carbonate.

Burosumab 70 mg every four weeks was recommended for suspected XLH and was recently initiated, though delayed due to social barriers.

Additional referrals for physical therapy, aqua therapy, endocrinology, and DEXA scans were provided throughout his care course and unfortunately weren’t utilized.

Outcome:
The patient has remained ambulatory and independent in activities of daily living, though ambulatory precautions were likely not followed. He presented to clinic without assistive devices. His pain moderately improved, although repeat radiographs demonstrated persistent nonunion without significant interval healing.

He has continued to follow with sports medicine and endocrinology for laboratory and radiographic monitoring. Recent goals of care have included utilizing referrals for aqua therapy, physical therapy, and DEXA scans to improve strength and assess bone density.

He has been receiving burosumab for targeted therapy. However, social barriers have continued to impede the patient’s treatment course.

Author's Comments:
This case demonstrated that chronic bilateral hip pain in young adults may represent longstanding fracture nonunion and underlying metabolic bone disease. Despite the fractures being identified 10 years earlier, the patient failed to receive appropriate management for his condition. The delayed recognition of low vitamin D, persistent low phosphate, history of rickets, and absence of follow-up contributed to a prolonged treatment course.

The causes of this patient’s constellation of symptoms were multifactorial. This included smoking, daily proton pump inhibitor use, but most importantly coxa vara and XLH. A prior case report described a unilateral femoral neck stress fracture in a 47-year-old patient with XLH and coxa vara who was treated with cephalomedullary nailing with improvement [1]. Another case described a 26-year-old female with bilateral coxa vara, low vitamin D, high parathyroid hormone, and no previous trauma, who presented with bilateral groin pain and a unilateral femoral neck stress fracture. The etiology was thus attributed to osteomalacia and coxa vara. She underwent osteotomy and medical treatment with improvement [2]. In these patients, focal stress experienced at the femoral neck due to coxa vara deformities resulted in imbalanced muscle fatigue and thus increased the risk of stress fractures [3].

XLH is an inherited disease where increased fibroblast growth hormone 23 (FGF23) causes renal phosphate wasting, decreased 1-alpha-hydroxylase activity, and decreased 1,25(OH)2 vitamin D absorption. Parathyroid hormone is released in response to low vitamin D levels. This increases 1-alpha-hydroxylase in the kidneys which converts inactive 25-OH to active 1,25-OH vitamin D. Calcium and vitamin D supplementation are not effective in correcting vitamin D levels in XLH. Burosumab is the treatment of choice through FGF23 inhibition [4]. It is thus key to evaluate for metabolic bone disease in younger patients with atypical or bilateral stress fractures.

Complex social circumstances, costly care, and low health literacy likely remains a barrier for many. A scoping review examined recovery after hip fractures and identified key factors, including social support, socioeconomic factors, and living arrangements correlating with physical functional recovery, mortality risk, and quality of life [5]. The patient upon presentation 10 years prior had not been followed in the outpatient setting. He frequented the ED, which is not equipped for long term management. With consistent education, diagnostic transparency, and support in navigating the healthcare system, this patient had improved follow-up and engagement with multidisciplinary care.

Editor's Comments:
XLH has an estimated incidence of 1 per 20,000 to 25,000 births, making it the most prevalent form of heritable hypophosphatemic rickets. It is an X-linked dominant disease, with females being less impacted due to possible X-inactivation. The disease is caused by a loss of function mutation in the phosphate-regulating endopeptidase homolog X-linked gene, also known as PHEX. This causes elevations of FGF23 which results in low phosphate and vitamin D levels. Children with XLH typically present with short stature, lower limb deformities, rickets, and craniosynostosis (premature closure of skull sutures). This progresses into osteomalacia, arthritis, fracture nonunion, pain, and decreased mobility in the adult population [6]. Historically, it had been treated with vitamin supplementation which has been ineffective in managing this disease. Burosumab, a human monoclonal antibody to FGF23, has been shown to improve stiffness and physical function in adults [7] as well as improvement in rickets and growth in pediatric patients when compared to standard treatment [8]. It is of critical importance to consider this in younger patients with abnormal fractures, pain, and stiffness. It is difficult to diagnose and requires a multidisciplinary team for appropriate management. Prompt diagnosis and treatment can make a significant impact on a patient’s quality of life. Equally important in the comprehensive care of patients similar to this one, is an assessment of social determinants of health (SDOH) given the complexity of the care needed that includes frequent follow up lab testing, multiple specialist consultations, frequent primary care follow up and the cost of disease modifying agents such as Burosumab. Without attention to these details, a patient may easily become lost in our medical system and receive incomplete or suboptimal care.

References:
1. Tirta M, Rahbek O, Kold S. Case Report of Femoral Neck Stress Fracture in X-linked Hypophosphatemic Rachitis Patient Treated with Mechanical Axis Correction and a Literature Review. J Orthop Case Rep. 2023;13(2):5-9.

2. Sariyilmaz K, Ozkunt O, Sungur M, Dikici F, Yazicioglu O. Osteomalacia and coxa vara. An unusual co-existence for femoral neck stress fracture. Int J Surg Case Rep. 2015;16:137-140.

3. Carpintero P, Leon F, Zafra M, Serrano-Trenas JA, Román M. Stress fractures of the femoral neck and coxa vara. Arch Orthop Trauma Surg. 2003;123(6):273-277.

4. Imel EA, Glorieux FH, Whyte MP, et al. Burosumab vs Phosphate/Active Vitamin D in Pediatric X-Linked Hypophosphatemia: A Subgroup Analysis by Dose Level. J Clin Endocrinol Metab. 2023;108(11):2990-2998.

5. Auais M, Al-Zoubi F, Matheson A, et al. Understanding the role of social factors in recovery after hip fractures: A structured scoping review. Health Soc Care Community. 2019;27(6):1375-1387.

6. Dahir K, Roberts MS, Krolczyk S, Simmons JH. X-Linked Hypophosphatemia: A New Era in Management. J Endocr Soc. 2020;4(12).

7. Shejil Kumar, Christian M Girgis, Brian Tran, Malu Alvarez, Roderick J Clifton-Bligh, Burosumab in adults with X-linked hypophosphatemia: real-world experience from a retrospective study in Sydney, JBMR Plus, Volume 9, Issue Supplement 5, December 2025, Pages v39�"v46.

8. Imel EA. Burosumab for Pediatric X-Linked Hypophosphatemia. Curr Osteoporos Rep. 2021 Jun;19(3):271-277.

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