Case reveal » Veterinary Diagnostic Imaging » College of Veterinary Medicine

A well-defined, sharply marginated, and longitudinal radiolucent fracture (green arrows) is seen extending from the proximodorsal articular surface of the right proximal phalanx, along the cranial cortex.
Along the dorsal and dorsomedial aspect of the proximal phalanx, mild irregular periostal proliferation is identified (pink arrowheads).

Along the proximal margin of the proximal sesamoid bones, mild enthesophyte formation is seen.
Surrounding the metatarsophalangeal joint, the soft tissues are moderately thickened, and there is a moderate increase in soft tissue opacity in the region of the digital sheath.

Conclusions:

Right proximal phalanx incomplete dorsal articular fracture with associated mild periosteal proliferation with moderate joint effusion/synovial proliferation.
Moderate digital sheath effusion.

The medial suspensory ligament branch is mildly to moderately enlarged with focal mild fiber abnormalities that are identified when the limb is imaged non-weight bearing. There is mild enthesopathy of the medial and lateral suspensory ligament branches at the attachment on the sesamoid bones.

Arthroscopic-assisted reduction and fixation of the proximal phalangeal fracture of the right hind fetlock was performed using a 3.5 mm cortical bone screw placed in lag fashion.

Short frontal plane fractures of the proximal phalanx (P1) are a distinct subset of equine orthopedic injuries, primarily affecting racehorses, particularly Thoroughbreds, and are more commonly observed in the hindlimbs. These fractures typically involve the dorsoproximal articular surface of P1 and are characterized by their uniplanar orientation, extending from the subchondral bone proximally to the dorsal cortex distally, often medial to the sagittal groove.

Radiographic evaluation is central to diagnosis, with the lateral projection being key to identifying these fractures. In the 2017 study by Wright and Minshall, all 22 fractures were visible on lateromedial radiographs, which revealed sharply or poorly marginated fracture lines. The fractures were best visualized using dorsal 70–80° lateral-palmar/plantar medial oblique (D70–80°L-Pa/PLMO) projections, especially when centered medial to the sagittal groove.

Computed tomography (CT) provided enhanced visualization, confirming the curved, mediolaterally symmetric fracture plane and aiding in surgical planning. CT consistently showed fractures originating just lateral to the sagittal groove and exiting dorsomedially, with a mean dorsopalmar depth of 9.4 mm. Periosteal new bone formation was often present, especially in cases with delayed presentation, indicating a possible prodromal phase of bone failure.

These fractures are typically non-displaced and occur during training or racing, suggesting a fatigue-related etiology. The consistent morphology across cases supports a common pathophysiology, likely involving repetitive stress between the dorsoproximal P1 and the distal metatarsal condyle during maximal joint extension. This mechanism is exacerbated by soft tissue fatigue, reducing the limb’s ability to resist overload.

The preferred treatment is minimally invasive surgical repair using a single lag screw, guided by arthroscopy and radiography. Wright et al. reported successful outcomes in 21 Thoroughbred racehorses, with 16 returning to racingand performance metrics comparable to pre-injury levels. The lag screw technique allows for effective interfragmentary compression, minimizing articular incongruity and reducing the risk of degenerative joint disease.
In contrast, conservative management has been associated with slower healing and variable outcomes, as noted in earlier studies (Markel et al., 1985). Horses treated surgically demonstrated faster radiographic healing, with fracture lines disappearing between 8 and 16 weeks postoperatively. No significant degenerative changes were observed during follow-up.

While short frontal plane fractures are confined to the dorsoproximal epiphysis and metaphysis, long frontal plane fractures extend into the diaphysis and may involve both the metacarpophalangeal and proximal interphalangeal joints. The 2025 study by Findley et al. described successful standing surgical repair of long frontal fractures in 13 cases, all in hindlimbs. Despite their complexity, 73% of horses returned to racing, with outcomes comparable to sagittal fracture repairs.

Wright, I. M., and G. J. Minshall. “Short frontal plane fractures involving the dorsoproximal articular surface of the proximal phalanx: description of the injury and a technique for repair.” Equine Veterinary Journal 50.1 (2018): 54-59.
Richardson, Dean W. “Fractures of the proximal phalanx.” Equine fracture repair (2019): 295-319.
Markel, Mark D., and Dean W. Richardson. “Noncomminuted fractures of the proximal phalanx in 69 horses.” Journal of the American Veterinary Medical Association 186.6 (1985): 573-579.
Findley, Judith A., Bruce M. Bladon, and Henry D. O’Neill. “Standing repair of long frontal plane fractures of the proximal phalanx in UK Thoroughbred racehorses: A retrospective analysis of 13 fractures.” Equine Veterinary Journal (2025).