Displaced patellar stress fracture revealing primary hyperparathyroidism: a case report.

Background: Stress fractures are fatigue-induced injuries that typically affect weight-bearing bones of the lower limb. While often associated with mechanical overuse, atypical sites of fracture-such as the patella-should raise suspicion for underlying systemic pathology. Primary hyperparathyroidism (PHPT), characterised by autonomous parathyroid hormone overproduction, can lead to cortical bone resorption and fragility, predisposing patients to such fractures. Case Description: A 45-year-old physically active woman presented to her general practitioner with non-specific right knee pain and no history of trauma. Clinical examination was unremarkable, and initial management was conservative. Four weeks later, she developed acute pain and functional impairment. Urgent radiography revealed a displaced transverse patellar stress fracture, which was surgically managed with open reduction and internal fixation using tension band wiring. Routine follow-up in primary care prompted biochemical investigations that revealed elevated serum calcium (2.9 mmol/L) and parathyroid hormone (122 pmol/L), confirming a diagnosis of PHPT. Imaging identified a solitary parathyroid adenoma, and she underwent successful parathyroidectomy. Eight months later, she experienced hardware-related skin complications requiring surgical removal of the tension band. She made a full recovery, with resolution of hypercalcaemia and no recurrence of symptoms. Conclusions: This case highlights the importance of considering endocrine causes in patients presenting with stress fractures at uncommon sites. The diagnostic journey from a seemingly benign musculoskeletal complaint to the discovery of PHPT underscores the pivotal role of multidisciplinary coordination across primary care, orthopaedics, and endocrinology.