November 2025 Newsletter
AN INTRODUCTION TO STRESS FRACTURES
What is a stress fracture?
A stress fracture refers to a fracture occurring in normal bone of the healthy patient caused by repetitive stresses.
The specific and repeatable sites of stress fractures within the racehorse are mirrored in human athletes and manual labourers. For example, the “march fracture” is a stress fracture usually affecting the second metatarsal bone (in the foot) and frequently seen in military recruits.
Another risk factor would be “deconditioning” and demineralisation of the bone without a satisfactory period of rehabilitation to allow bone strengthening. As an example, stress fractures of the humerus (shoulder) in racehorses have been recorded following a period of inactivity for another lesion (tendon injury, surgery…). In these cases, the modifications in training have taken place over too short a period of time for sufficient bone adaptation to take place.
The assumption that the training regime and surfaces are strongly associated with the development of fractures is supported by a frequent clinical observation of “clusters” of bone injury observed within groups of horses trained within the same regime.
How to diagnose a stress fracture?
Stress fracture can go from early microfailure to complete disruption. Radiographs and ultrasound scans are the usual imaging techniques used to establish a diagnosis. However, there are some limitations.
Early-stage fractures
Detecting it at an early “stress reaction” stage can be challenging. This can be explained by bone metabolism.
Some cells play a significant part in the healing process. They are called osteoblasts, derived from the Greek osteo=bone and blast=immature cells. We could say that their role is to “build” some new bone material.
However, when a fracture occurs, some cells will “clean” the debris and destroys the parts that are no longer viable, they are called osteoclasts. This name has a Greek etymology too, with osteo=bone and clast=break. In the context of a fracture, they would get rid of the damaged pieces of the bone. On average, it would take these cells 10 to 14 days to complete the task, but sometimes up to 3 weeks. This is the reason why a fracture line is not always obviously visible on the radiographs or ultrasound scans in the early stages.
Bone scan (scintigraphy) is a different technique which is very useful in these specific circumstances.
A small amount of radioactive material (considered as a tracer) is injected intravenously, travels through the blood vessels and collects in the bones. This tracer will collect more in the areas of abnormal activity such as fractures.
By focusing not only on the appearance of the bone but also on the turnover of the bone cells, it enables a quicker way to detect stress fractures not visible on radiographs or ultrasound scans.
Most frequent locations
The most common sites are the tibia, the ilium (pelvis), the fetlock (condyles and frontal fractures of the first phalanx), the 3rd carpal bone in knees, the radius (forearm) and the humerus (shoulder). A few examples are presented below.
Fatigue fracture of the metacarpal condyle (arrows). Equine Sports Medicine and Surgery 2004
Third carpal bone fracture in the knee (black arrows). P.H.L Ramzan Equine veterinary journal 2018
Fracture of the ilium (white arrow showing a disruption of the bone surface). Puccetti et al.Equine vet Journal 2021
Tibial fracture (black arrow). Manual of Equine Lameness (Baxter)
What kind of rehabilitation after a stress fracture?
Recommendations are influenced by severity and location of the injury. Stress fractures at anatomical sites that are considered high risk for either catastrophic deterioration or recurrence of injury must be treated more conservatively than injuries at “low-risk” sites. Some stress fractures (for example humeral fracture in the shoulder) may propagate at low levels of exercise and the relative proportion of time spent on box rest/walking should be determined following clinical examination.
For mild to moderate stress fractures, a period of box rest (2 to 4 weeks) followed by walking exercise (2 to 6 weeks depending on the injury) would be appropriate. Soundness should be monitored at each “step up” and the rehabilitation program amended accordingly.
For severe fractures or at risk of catastrophic propagation, surgery can be considered (fetlocks) or tying up for initial period of stable confinement (displaced fracture of the pelvis for example).
Conclusion
Identifying the specific risks factors leading to their development and early warning signs of their potential occurrence is a priority to manage these conditions.
It appears to be important to educate bones very early in the training programme. This can be achieved by short burst of faster-paced exercise than is the average for this particular level of training. This has the effect to stimulate bone metabolism/activity to model the skeleton in readiness to faster paces.
I hope you enjoyed reading this newsletter.
Best regards,
Cyrielle
References
M.C.Shepherd. Stress fractures.Equine vet Educ.2010
P.H.L Ramzan. The racehorse, a veterinary manual. 2014
Jane H. Wilson. Stress fractures in athletes: diagnosis and management. Equine vet Educ. 1994
M.C.Mackinnon et al.Analysis of stress fractures associated with lameness in Thoroughbred flat racehorses training on different track surfaces undergoing nuclear scintigraphic examination. Equine vet.J. 2014