A case of patellar fractures in monozygotic twin gymnasts

We present a case of near identical patellar fractures in adolescent monozygotic twins who are both high-level competitive gymnasts. These patients presented 14 months apart with almost identical history and clinical findings. Both had an intense training regime involving over 30 hours per week of load-bearing exercise. Clinical and radiological examinations suggested avulsion or sleeve fracture of the inferior pole of the patella with minimal displacement. Diagnoses of patellar stress fracture with avulsion of the distal pole and symptomatic bipartite patella could not be reliably excluded. Both fractures were treated conservatively with immobilisation of the knee in extension. An excellent functional result was observed in both patients with return to full activity at 8 weeks. This is the first published case of identical injury to the patella in monozygotic twins. A significant genetic influence on bone mineral density (BMD) has been reported and low BMD is associated with increased susceptibility to fracture. These injuries corroborate a genetic influence on susceptibility to fracture. There is a requirement for further work to investigate genetic factors influencing susceptibility to fracture.