P. H. L. RAMZAN and S. E. POWELL † Rossdale and Partners, Beaufort Cottage Stables, High Street, Newmarket, Suffolk CB8 8JS; and †Rossdales Equine Diagnostic Centre, Cotton End Road, Exning, Suffolk CB8 7NN, UK. Equine Veterinary Journal 2010 42 2 164 - 169 Sagittal fracture of the proximal phalanx (P1) is an important musculoskeletal injury of the performance horse. Although widely considered to be monotonic in nature, there is emerging evidence that some P1 fractures may have stress-injury aetiology. Three cases are described in which imaging features found were suggestive of prodromal bone injury. All cases returned to full performance use after a period of rest. The authors conclude that it is possible that some P1 fractures in the Thoroughbred racehorse may develop through stress/fatigue injury pathways. It is proposed that intervention prior to overt fracture may be possible in some cases.