Stress fracture of the palmar, distal cortex of the third metacarpal bone: A diagnostic challenge with a good prognosis

Abstract

Background: Transverse stress fracture of the palmar cortex of the distal aspect of the third metacarpal bone (TSF PCD McIII) is poorly documented. Objectives: To describe the typical signalment of this injury, the common clinical and radiological signs and prognosis. Study design: A retrospective hospital-based case series with follow-up of racing records. Methods: All cases of TSF PCD McIII diagnosed among racehorses in training at the Hong Kong Jockey Club between 2011 and 2019 were identified. Clinical records were reviewed and documented signs were recorded for each case. Findings from a predefined list of radiological features were listed. Descriptive statistics were used to describe the age and training profile of horses, the clinical and radiological findings and time to return to ridden exercise. Results: Twenty-three cases (n = 23) were identified. The majority (57%) had recently started or returned to training from a break and 35% (n = 8) of cases had not yet undertaken timed gallops at the time of injury. Most cases (20/23; 87%) were lame; in nine (39%), lameness was severe. Localised swelling of superficial soft tissues was reported in 15/23 (65%) cases. Pain on palpation of the distal McIII was present in 15/23 (65%) cases and in response to fetlock flexion in 12/23 (52%). Diffuse, localised increase in radiopacity, disruption to the outline of the bone periosteal surface and outward displacement of the button of the splint bone were common radiological features in early cases (70%, 67% and 67% of all cases). Sixty-one per cent of cases (14/23) were initially misdiagnosed. Most horses (n = 18/23) resumed training and racing after a median of 83 and 246 days. Main limitations: Clinical notes were not consistent between cases. Radiographs were taken at different times. Conclusions: Horses commencing training are at risk of TSF PCD McIII, which presents with confusing clinical signs and subtle radiological findings. The long-term outlook is favourable.

Intracortical remodelling increases in highly loaded bone after exercise cessation

“…It was not possible to cut 100 μm sections from the entire cross‐section of the distal metaphysis of the third metacarpal bone, and so our analysis was restricted to the lateral half of the bone in this location. The palmar/palmarolateral cortex of the third metacarpal bone is the most common location for stress fractures in the distal metaphyseal region of this bone (Shan et al., 2022 ), and, therefore, we believe that the results from this location are likely to reflect relevant findings. The anatomical location from which specimens from the tibia were sampled was chosen because this is a common location for stress fractures to occur in our population of horses based on diagnosis by nuclear scintigraphy.…”

Intracortical remodelling increases in highly-loaded bone after exercise cessation

“…Further, our results may have been confounded by the effects of insertion of the deltoid muscle on local bone mechanics in this region. The palmarolateral cortex of the third metacarpal bone is the most common location for stress fractures in the distal metaphyseal region of this bone [82] and, therefore, we believe that the results from this location are more likely to reflect relevant findings. The anatomical location from which specimens from the tibia were sampled was chosen because this is a common location for stress fractures to occur in our population of horses based on diagnosis by nuclear scintigraphy.…”

Fractures in Thoroughbred racing and the potential for pre‐race identification of horses at risk

“…These foci which are the result of fatigue damage of the bone matrix, act as stress risers that can compromise the mechanical integrity of the whole bone. 67,68 A strong body of evidence indicates that such lesions are part of the pathophysiological pathway to most common fractures that occur in racehorses, including sagittal fractures of the proximal phalanx, 69,70 parasagittal fractures of the distal condyles of the third metacarpal and metatarsal bones, 71 transverse fractures of the distal metaphysis of the third metacarpal bone, 72 complete diaphyseal fractures of the third metacarpal bone, 73 transverse fractures of the proximal sesamoid bones, [74][75][76] slab fractures of the third carpal bone, 77 and stress fractures of the humerus, 67,68 scapula, 78,79 tibia, 80 ilium and lumbar vertebrae. 81…”