Proximal Sesamoid Bone Fracture Research Articles

Metacarpophalangeal Joint Pathology and Bone Mineral Density Increase with Exercise but Not with Incidence of Proximal Sesamoid Bone Fracture in Thoroughbred Racehorses

Proximal sesamoid bone (PSB) fracture is the leading cause of fatal musculoskeletal injury in Thoroughbred racehorses in Hong Kong and the US. Efforts are underway to investigate diagnostic modalities that could help identify racehorses at increased risk of fracture; however, features associated with PSB fracture risk are still poorly understood. The objectives of this study were to (1) investigate third metacarpal (MC3) and PSB density and mineral content using dual-energy X-ray absorptiometry (DXA), computed tomography (CT), Raman spectroscopy, and ash fraction measurements, and (2) investigate PSB quality and metacarpophalangeal joint (MCPJ) pathology using Raman spectroscopy and CT. Forelimbs were collected from 29 Thoroughbred racehorse cadavers (n = 14 PSB fracture, n = 15 control) for DXA and CT imaging, and PSBs were sectioned for Raman spectroscopy and ash fraction measurements. Bone mineral density (BMD) was greater in MC3 condyles and PSBs of horses with more high-speed furlongs. MCPJ pathology, including palmar osteochondral disease (POD), MC3 condylar sclerosis, and MC3 subchondral lysis were greater in horses with more high-speed furlongs. There were no differences in BMD or Raman parameters between fracture and control groups; however, Raman spectroscopy and ash fraction measurements revealed regional differences in PSB BMD and tissue composition. Many parameters, including MC3 and PSB bone mineral density, were strongly correlated with total high-speed furlongs.

Radiomics Modeling of Catastrophic Proximal Sesamoid Bone Fractures in Thoroughbred Racehorses Using μCT.

Proximal sesamoid bone (PSB) fractures are the most common musculoskeletal injury in race-horses. X-ray CT imaging can detect expressed radiological features in horses that experienced catastrophic fractures. Our objective was to assess whether expressed radiomic features in the PSBs of 50 horses can be used to develop machine learning models for predicting PSB fractures. The μCTs of intact contralateral PSBs from 50 horses, 30 of which suffered catastrophic fractures, and 20 controls were studied. From the 129 intact μCT images of PSBs, 102 radiomic features were computed using a variety of voxel resampling dimensions. Decision Trees and Wrapper methods were used to identify the 20 top expressed features, and six machine learning algorithms were developed to model the risk of fracture. The accuracy of all machine learning models ranged from 0.643 to 0.903 with an average of 0.754. On average, Support Vector Machine, Random Forest (RUS Boost), and Log-regression models had higher performance than K-means Nearest Neighbor, Neural Network, and Random Forest (Bagged Trees) models. Model accuracy peaked at 0.5 mm and decreased substantially when the resampling resolution was greater than or equal to 1 mm. We find that, for this in vitro dataset, it is possible to differentiate between unfractured PSBs from case and control horses using μCT images. It may be possible to extend these findings to the assessment of fracture risk in standing horses.

Proximal sesamoid bone microdamage is localized to articular subchondral regions in Thoroughbred racehorses, with similar fracture toughness between fracture and controls.

To determine whether proximal sesamoid bone (PSB) microdamage and fracture toughness differ between Thoroughbred racehorses sustaining PSB fracture and controls. Cadaveric case-control. Twenty-four Thoroughbred racehorses (n=12 PSB fracture, n=12 control). Proximal sesamoid bones were dissected, and gross pathological changes and morphological measurements were documented. High-speed exercise history data were evaluated. Microdamage was assessed in fracture, fracture-contralateral limb (FXCL) and control PSBs using whole bone lead uranyl acetate (LUA) staining with micro-CT imaging or basic fuchsin histological analysis. Fracture toughness mechanical testing was carried out in 3-point-bending of microbeams created from PSB flexor cortices. Data were analyzed using ordinal logistic and linear regression models. Microdamage was detected most commonly in the articular subchondral region of PSBs via LUA micro-CT and basic fuchsin histology. There were no differences in microdamage between FXCL and control PSBs. Fracture toughness values were similar for FXCL (1.31 MPa√m) and control (1.35 MPa√m) PSBs. Exercise histories were similar except that horses sustaining fracture spent a greater percentage of their careers in rest weeks. Microdamage was detected in the articular region of PSBs but was not greater in horses sustaining catastrophic PSB fracture. Fracture toughness of PSB flexor cortices did not differ between FXCL and control PSBs. Although uncommon, microdamage is localized to the articular region of Thoroughbred racehorse PSBs. Catastrophic PSB failure is not associated with lower PSB flexor cortex fracture toughness.

Predicting return to racing after repair of fractures of the metacarpal/metatarsal condyles in Thoroughbred racehorses.

To identify prognostic factors for return to racing after lag screw repair of condylar fractures and develop a predictive model for return to racing. Retrospective cohort study. A total of 356 horses referred to a single referral hospital in the UK with a third metacarpal/metatarsal condylar fracture between January 1999 and December 2018. Age, sex, fracture site, fracture characteristics, surgery related variables and complications were retrieved from case records. Data were divided into two sets for model training and model validation. Univariable analyses were performed, and predictors were selected in a stepwise fashion for inclusion in the multivariable logistic regression model. Sensitivity and specificity were evaluated using the second dataset. Older horses, fillies, fractures of forelimbs, complex, complete, displaced or propagating fractures and concurrent proximal sesamoid bone fracture were negatively associated with return to racing. Colts and geldings were 3 and 4 times more likely to race than fillies, respectively. Horses with hindlimb, incomplete or nonpropagating fractures were 4, 5 and 4 times more likely to race than those with a forelimb, complete or propagating fracture, respectively. Using a predicted probability cut-off threshold of 0.5, a predictive model was created within one dataset (sensitivity=84%, specificity=50.5%) and applied to another (sensitivity=83.1%, specificity=24.0%). Negative prognostic factors were identified and led to a predictive model with acceptable sensitivity and specificity in the tested population. The results provide proof of concept for the model in the reported population and justify further validation in different populations of horses.

In vitro motions of the medial and lateral proximal sesamoid bones under mid-stance load conditions are consistent with racehorse fracture configurations

Proximal sesamoid bone (PSB) fractures in racehorses are likely fatigue fractures that occur due to repetitive loads and stress remodeling. The loading circumstances that may induce damage in the PSBs are not well understood. The goal of this study was to determine in three-dimensions, PSB motions relative to the opposing metacarpal condyle during simulated mid-stance loads. Seven equine cadaveric forelimbs were axially loaded in a material testing system to simulate standing and mid-stance walk, trot, and gallop load conditions (1.8–10.5 kN). Joint angles were determined by tracking the positions of bone-fixed kinematic markers. Internal-external rotation, abduction–adduction, and flexion–extension of each PSB relative to the third metacarpal condyle were compared between loads and between PSBs using an ANOVA with Tukey-Kramer post hoc tests for pairwise comparisons. The medial PSB rotated externally and the lateral PSB apex abducted during limb loading. Medial PSB external rotation was significantly greater at the gallop load condition than at the walk or trot load conditions. The medial and lateral PSB motions observed in this study are consistent with location of fatigue damage and fracture configurations frequently seen in medial and lateral PSBs from Thoroughbred racehorses. Specifically, medial PSB external rotation is consistent with the development of an abaxial subchondral medial PSB lesion that is reported in association with medial PSB transverse fracture and lateral PSB abduction is consistent with axial longitudinal fracture of the lateral PSB.

Determination of correlation of proximal sesamoid bone osteoarthritis with high-speed furlong exercise and catastrophic sesamoid bone fracture in Thoroughbred racehorses.

To examine whether proximal sesamoid bone (PSB) articular cartilage and bone osteoarthritic changes or palmar osteochondral disease (POD) scores were associated with exercise history and catastrophic PSB fracture in Thoroughbred racehorses. PSBs from 16 Thoroughbred racehorses (8 with and 8 without PSB fracture). Exercise history was collected, and total career high-speed furlongs was used as the measure of total exercise per horse. At necropsy, medial and lateral condyles of the third metacarpus from each forelimb were assigned a POD score, followed by imaging with micro-CT for evaluation of osteophyte size. Three investigators that were blinded to the type of PSB (fracture or no fracture) used the Osteoarthritis Research Society International (OARSI) scoring system to evaluate acellularity, chondrocyte necrosis, cartilage fibrillation, chondrone formation, safranin O stain uptake, and tidemark advancement of 1 central sagittal tissue section/PSB (4 PSBs/horse). Cartilage thickness and bone necrosis were scored on the basis of histologic examination. POD score, osteophyte size score, percentage of bone necrosis, tidemark advancement, chondrone formation, and total OARSI score were greater in horses with more accrued total career high-speed furlongs. Scores for POD, osteophyte size, fibrillation, acellularity, chondrone formation, and total OARSI were greater for horses with PSB fracture. OARSI scoring revealed that more advanced osteoarthritic changes strongly correlated with total career high-speed furlongs and PSB fracture. However, the effect of exercise was dominant, suggesting that exercise history will be important to include in future models that aim to assess risk factors for catastrophic PSB fracture.

32 Maturation of proximal sesamoid bones in Thoroughbred horses

Proximal sesamoid bone (PSB) injuries account for approximately 50% of fatal catastrophic musculoskeletal injuries in Thoroughbred racehorses. In addition, PSB fractures are not uncommon in Thoroughbred foals and yearlings as a result of energetic or intense free exercise. The ability to interpret some PSB pathology assessments, however, is more difficult given the limited information published on the normal development and maturation of these paired sesamoid bones. Further, information on the level of normal variation in PSB morphological and structural parameters within the Thoroughbred population as a function of age, body size, gender, and inter-animal differences generally are not well documented. This project aims to address these knowledge gaps through analyses of PSB anatomy from 18 Thoroughbreds obtained on postmortem examination representing an age range from birth to skeletal maturity using micro–CT Bone Morphometry Evaluation (μCT BME, n = 8 horses) and clinical CT evaluation (n = 10 horses). The μCT BME was performed on the left front medial PSB in 8 horses ranging from 4 d to 5 years of age. When graphed, the following were observed: 2nd order polynomic relationships with a positive trend between age and bone volume fraction (R 2 = 0.8125), trabecular thickness (R 2 = 0.8084), and degree of anisotropy (R 2 = 0.914); a 2nd order polynomic relationship with a negative trend between age and trabecular number (R 2 = 0.9242); a negative logarithmic relationship between age and connectivity density (R 2 = 0.9439); and a positive exponential relationship between age and trabecular spacing (R 2 = 0.7818). Clinical CT evaluations were performed on medial and lateral PSBs from the respective right and left forelimbs in 10 horses ranging in age from 2 to 5 years of age utilizing Mindways CT Bone Investigational Toolkit for bone mineral density (BMD) analysis. A one-way ANOVA indicates no significant differences ( P = 0.755) in BMD between the 20 PSB in the left forelimb and the contralateral 20 PSB in the right forelimb. However, significant differences, measured though one-way ANOVA, existed between the 20 lateral PSB (10 from the left forelimb and 10 from the right forelimb) and the 20 medial PSB ( P = 0.006). These findings provide a first of its type reference on the development and maturation timeline of equine PSBs, as well as confirming structural differences between lateral and medial PSBs. The data also document rapid PSB changes between birth and 18 mo of age. The long-term objective of this project is to define normal structural and morphological characteristics of Thoroughbred PSBs as a basis for comparison to PSB pathologies.

Microstructural properties of the proximal sesamoid bones of Thoroughbred racehorses in training.

Proximal sesamoid bone fractures are common catastrophic injuries in racehorses. Understanding the response of proximal sesamoid bones to race training can inform fracture prevention strategies. To describe proximal sesamoid bone microstructure of racehorses and to investigate the associations between microstructure and racing histories. Cross-sectional. Proximal sesamoid bones from 63 Thoroughbred racehorses were imaged using micro-computed tomography. Bone volume fraction (BVTV) and bone material density (BMD) of the whole bone and four regions (apical, midbody dorsal, midbody palmar and basilar) were determined. Generalised linear regression models were used to identify the associations between bone parameters and race histories of the horses. The mean sesamoid BVTV was 0.79±0.08 and BMD was 806.02±24.66mg HA/ccm. BVTV was greater in medial sesamoids compared with lateral sesamoids (0.80±0.07 vs 0.79±0.08; P<.001) predominantly due to differences in the apical region (medial-0.76±0.08 vs lateral-0.72±0.07; P<.001). BVTV in the midbody dorsal region (0.86±0.06) was greater than other regions (midbody palmar-0.79±0.07, basilar-0.78±0.06 and apical-0.74±0.08; P<.001). BVTV was greater in sesamoids with more microcracks on their articular surface (Coef. 0.005; 95% CI 0.001, 0.009; P=.01), greater extent of bone resorption on their abaxial surface (Grade 2-0.82±0.05 vs Grade 1-0.80±0.05 or Grade 0-0.79±0.06; P=.006), in horses with a low (0.82±0.07) or mid handicap rating (0.78±0.08) compared with high rating (0.76±0.07; P<.001), in 2- to 5-year-old horses (0.81±0.07) compared with younger (0.68±0.08) or older horses (0.77±0.08; P<.001) and in horses that commenced their racing career at less than 4years of age (0.79±0.08 vs 0.77±0.77; P<.001). BMD was greater in the midbody dorsal (828.6±19.6mg HA/ccm) compared with other regions (apical-805.8±21.8, midbody palmar-804.7±18.4 and basilar-785.0±17.1; P<.001), in horses with a handicap rating (low-812.1±20.0, mid-821.8±21.3 and high-814.6±19.4) compared with those with no rating (791.08±24.4, P<.001), in females (806.7±22.0) and geldings (812.2±22.4) compared with entires (792.7±26.2; P=.02) and in older horses (<2-year-old-763.7±24.8 vs 2- to 5-year-old-802.7±23.4, and 6- to 12-year-old-817.8±20.0; P=.002). Data were cross-sectional. Densification of the proximal sesamoid bones is associated with the commencement of racing in younger horses and the presence of bone fatigue-related pathology. Lower sesamoid BVTV was associated with longevity and better performance.

Appraising the Welfare of Thoroughbred Racehorses in Training in Queensland, Australia: The Incidence and Type of Musculoskeletal Injuries Vary between Two-Year-Old and Older Thoroughbred Racehorses

Simple SummaryMusculoskeletal injuries (MSI) remain a concerning cause of racehorse morbidity and mortality with serious ethical and welfare consequences. Previous research examining risk factors for injuries report inconsistent findings. Age is thought to affect the risk of injury, but, to date, there have been no prospective studies specifically comparing injuries between two-year-old versus older horses. We aimed to: (1) determine the incidence of injuries for two-year-old and older horses, and whether this was affected by training track, season, or rainfall, and (2) determine the types of injuries affecting two-year-old and older horses, and whether horses trialled or raced after injury. Data were collected through personal structured weekly interviews with participating trainers over a 13-month period. Data were analysed using Poisson regression. The incidence of MSI in the current study was low (0.6%). The incidence of MSI in two-year-old horses was higher than older horses. Types of MSI varied between two-year-old and older horses and affected whether horses subsequently trialled or raced from 11 to 23 months after injury. A larger proportion of two-year-old horses had dorsal metacarpal disease and traumatic lacerations. A smaller proportion of two-year-old horses had suspensory desmitis, superficial digital flexor tendonitis, proximal sesamoid bone fractures, and fetlock joint injuries than older horses. Training track and rainfall did not affect the incidence of injuries. The season affected the incidence of injuries in two-year-old horses but not in older horses.Musculoskeletal injuries (MSI) remain a concerning cause of racehorse morbidity and mortality with important ethical and welfare consequences. Previous research examining risk factors for MSI report inconsistent findings. Age is thought to affect MSI risk, but, to date, there have been no prospective studies comparing MSI in two-year-old versus older horses. This study aimed to: (1) determine the incidence of MSI for two-year-old and older horses, and whether this was affected by training track, season, or rainfall, and (2) determine the types of MSI affecting two-year-old and older horses, and whether horses trialled or raced after injury. A prospective survey was conducted with data collected through personal structured weekly interviews with participating trainers over a 13-month period. Data were analysed using Poisson regression. The incidence of MSI in the current study was low (0.6%). The incidence of MSI in two-year-old horses was higher than older horses (p < 0.001). Types of MSI varied between two-year-old and older horses (p < 0.001) and affected whether horses subsequently trailed or raced from 11 to 23 months after injury (p < 0.001). A larger proportion of two-year-old horses had dorsal metacarpal disease and traumatic lacerations. A smaller proportion of two-year-old horses had suspensory ligament desmitis, superficial digital flexor tendonitis, proximal sesamoid bone fractures, and fetlock joint injuries than older horses. Training track and rainfall did not affect MSI. The season affected MSI in two-year-old horses (p < 0.001) but not older horses. The major limitation was that trainers in this study were metropolitan (city) and our findings may not be generalisable to racehorses in regional (country) areas. Another significant limitation was the assumption that MSI was the reason for failure to trial or race after injury. In conclusion, the incidence of MSI was low in the current study and the types and the risk factors for MSI are different for two-year-old and older horses.

A radiomics platform for computing imaging features from µCT images of Thoroughbred racehorse proximal sesamoid bones: Benchmark performance and evaluation.

Proximal sesamoid bone (PSB) fractures are the most common fatal musculoskeletal injury in North American racehorses. Computed tomography has the potential to detect morphological changes in bone structure but can be challenging to analyse reliably and quantitatively. To develop a radiomics platform that allows the comparison of features from micro-CTs (µCT) of PSBs in horses that sustained catastrophic fractures with horses that did not. To compare features calculated with a radiomics approach with features calculated from a previously published study that used quantitative µCT in the same specimens. Retrospective study of cadaver specimens of µCT images of PSBs using prospectively applied radiomics. Radiomics features were computed on standardised CT datasets to benchmark the software. Features from µCT images of PSBs from eight horses that sustained PSB fracture and eight controls were computed using the contralateral, intact forelimb from horses sustaining PSB fracture (cases, n=19) and all available forelimbs for controls (n=30). Two-hundred and fifteen radiomic features were calculated, and similar or comparable features were compared with those reported in a previous study that used the same specimens. Morphologic features computed with the radiomics approach, such as volume, minor axis dimensions and anisotropy were highly correlated with previously published data. A high number of imperceptible radiomic features, such as entropy, coarseness and histogram features were also found to be significantly different (P<.01). The extent of the differences in image features for the cases and controls PSBs depends on radiomic calculation settings. Only datasets obtained from cadaver specimens were included in the study. A radiomics approach for analysing µCT images of PSBs was able to identify and reproduce differences in image features in cases and controls. Furthermore, radiomics revealed many more imperceptible image features between cases and control PSBs.

Subchondral focal osteopenia associated with proximal sesamoid bone fracture in Thoroughbred racehorses.

Proximal sesamoid bone (PSB) fracture is the most common fatal injury in Thoroughbred (TB) racehorses in the United States. Epidemiological and pathological evidence indicates PSB fracture is likely the acute culmination of a chronic stress-related process. However, the aetiopathogenesis of PSB fracture is poorly understood. To characterise bone abnormalities that precede PSB fracture. Two retrospective case-control groups of PSBs from TB racehorses with, and without, unilateral biaxial PSB fracture. Proximal sesamoid bones were harvested post-mortem from TB racehorses subjected to euthanasia for unilateral biaxial PSB fracture (cases) or causes unrelated to PSB fracture (controls) while racing or training. The fractured medial PSB (FX-PSB) and contralateral intact medial PSB (CLI-PSB) from racehorses that sustained PSB fracture, and an intact medial PSB (CTRL-PSB) from racehorses that did not have a PSB fracture were collected as case and control specimens. Study 1 distributions of morphological features were compared among case and control groups using visual examination, photographs, radiographs and histology of whole PSBs and serial sagittal sections (10 FX-PSB, 10 CLI-PSB and 10 CTRL-PSB). Study 2 local bone volume fraction and mineral densities were compared among case and control PSBs using microcomputed tomography (9 FX-PSB, 9 CLI-PSB and 9 CTRL-PSB). A focal subchondral lesion characterised by colocalised focal discoloration, radiolucency, osteopenia, low tissue mineral density and a surrounding region of dense cancellous bone was identified in most case horses but not in controls. This subchondral lesion was found in a slightly abaxial mid-body location and was bilaterally present in most case horses. The post-mortem samples may not represent the spectrum of abnormalities that occur throughout the development of the subchondral lesion. Lateral PSBs were not examined, so their contribution to biaxial PSB fracture pathogenesis is unknown. Abaxial subchondral lesions are consistent with pre-existing injury and likely associated with PSB fracture.

Catastrophic musculoskeletal injuries in Thoroughbred racehorses on racetracks in Gauteng, South Africa.

The incidence and types of catastrophic musculoskeletal injuries in Thoroughbreds that resulted in euthanasia on selected racetracks in South Africa between 1998 and 2012 were investigated by an observational retrospective investigation. Data from the National Horseracing Authority of Southern Africa for these racetracks were used to calculate incidence rates in Thoroughbreds (n = 114) that sustained catastrophic musculoskeletal injuries during racing that required immediate euthanasia, based on the diagnosis made by the on-site veterinarian as well as on fetlock radiographs and dissections of 53 cadaver limbs of horses that sustained a catastrophic musculoskeletal injury. The proximal sesamoid bones and the distal suspensory ligament were involved in 55.26% of horses; 73.58% of the cadaver limb radiographs were of the left forelimb, 64.15% were closed fractures, and 74.47% had biaxial proximal sesamoid bone fractures. Catastrophic musculoskeletal injuries occurred almost exclusively unilaterally and involved mostly the left front leg. The average incidence rate for a catastrophic musculoskeletal injury occurring in a year at any of the tracks was 0.6 of 1000 starts.

In vitro biomechanical comparison of headless compression versus cortex screws for fixation of simulated midbody proximal sesamoid bone fractures in horses

A midbody fracture of a proximal sesamoid bone (PSB) is a severe injury, especially in racehorses. Screw fixation may be the only option for horses to return to athletic activity. In a cadaveric biomechanical study, fixation of simulated transverse midbody PSB fractures with a 4.5 mm headless compression screw (HCS) was compared to the fixation using a 4.5 mm cortex screw (CS) inserted in lag fashion. The front limbs of 8 horses were prepared with a standardized midbody transverse osteotomy in each medial PSB. The left or the right limb of each pair was randomly assigned to the CS or HCS group. Fracture reduction and fixation was controlled by radiography. Markers were fixed proximal and distal to the osteotomy to document gap opening by an image correlation measurement. Cyclic compressive loading was applied with a hydraulic cylinder in an axial manner leading to tensile cyclic loading in the PSBs. After mechanical testing all limbs were radiographed to document the mode of failure. The mean cycles to total failure were 27,803 for the HCS group and 36,624 for the CS group, respectively. A mean of 14,444 cycles (HCS group) versus 27,464 cycles (CS group) was recorded at a fracture gap opening of 10 %. The mean value of initial stiffness was 300 N/mm (HCS group) versus 590 N/mm (CS group). On post-testing radiographs, failure by screw breakage was detected in 3/8 limbs of the HCS group and in 2/8 limbs of the CS group. Screw pullout and bone failure was noted in 5 limbs in each group. In one limb of the CS group, the medial suspensory branch was disrupted and the fracture fixation was intact. None of the differences between HCS and CS constructs reached statistical significance. However, the lower absolute numbers of cycles sustained before failure, at 10 % gap opening and lower initial stiffness of HCS constructs as well as limitations of the study warrant further investigation before clinical use of the HCS for this indication can be recommended.

Can quantitative computed tomography detect bone morphological changes associated with catastrophic proximal sesamoid bone fracture in Thoroughbred racehorses?

Fracture of the proximal sesamoid bones continues to be the most common fatal musculoskeletal injury in US racehorses. Identifying factors that influence fracture risk could lead to screening techniques to reduce catastrophic injury rates and improve animal welfare. To identify morphological differences between proximal sesamoid bones of the contralateral limb of fracture and control horses and assess the feasibility of computed tomography (CT) to detect traits associated with proximal sesamoid bone fracture. We hypothesised that horses with proximal sesamoid bone fracture would have greater bone density. Cross-sectional cadaver morphological study. Proximal sesamoid bone morphology was measured using high-resolution micro-CT images from 16 Thoroughbred racehorses (eight fracture, eight control) euthanised on New York racetracks. Nominal logistic regression models and receiver operating characteristic curves were created to assess the ability of CT-derived morphological traits to accurately classify fracture horses vs. controls. Bone volume fraction was greater in the fracture group (90.39 ± 1.76%) as compared to controls (87.20 ± 2.79%, P<0.0001). Bone volume fraction, bone width, trabecular thickness and degree of anisotropy were significantly different between fracture and control horses. Receiver operating characteristic curves showed that a combined model that incorporates bone volume fraction and width can identify fracture from control horses with an area under the curve of 0.938, indicating high accuracy at classifying fracture horses from controls. The number of horses per group is small, although the total number of sesamoids imaged is reasonable (n = 62). In vivo CT at the resolution performed in this study is currently unattainable; however, density and width could be measured with quantitative CT. Differences in proximal sesamoid bone morphology were identified between fracture and control horses. As improved technology becomes accessible, quantitative CT could potentially be used as a clinical imaging technique to estimate proximal sesamoid bone fracture risk in Thoroughbred racehorses.

Histopathological study of the influence of platelet rich-plasma and low level laser therapy on healing of experimentally fractured proximal sesamoid bone in equine

The objective of this study was to evaluate the effects of platelet rich plasma and low level laser therapy (diode laser) on the healing of proximal sesamoid bone fracture. Eighteen healthy adult donkeys were divided into three equal groups: First group was used as control group, second group was treated by platelet rich plasma and the third group treated by diode laser. Also each group was divided to two equal subgroups according to period of postoperative macroscopical, histopathological examination: (one and three months post operation). All animals were exposed experimentally to transverse mid body fracture of lateral proximal sesamoid bone, in control group the bone fixed internally by screw and followed by external fixation with Plaster of Paris under general anesthesia, the second and third groups were exposed to similar surgical procedure except in second group injected of autologous platelet rich plasma in the fracture site, and the third group exposed to serial session of low level laser. All experimental animals were in a good health postoperatively, except hyper granulation tissue was observed in one animal belongs to the first group and another one belongs to the second group exhibited superficial exudates at the site of operation. Histopathological examination showed connective tissues and thin bone trabecular filling the fractured gap in first group at one month postoperatively, whereas, the bone trabecular was replaced by compact bone at three months postoperatively. Moreover lamellar bone and thick compact bone formation were seen at one month in third group, as well as to a lesser degree in the second group; however the fractured gap was filled with compacted bone mainly at three months postoperativelyin third group. In conclusions, both laser and platelet rich plasma were enhanced healing of the proximal sesamoid bones fracture but the superiority of better healing was occurred by laser treatment.

Diagnosis and management of proximal sesamoid bone fractures in the horse

SummaryFractures of the proximal sesamoid bones (PSBs) range in severity from simple to complex and comminuted and can be articular or nonarticular. The majority of PSB fractures are diagnosed in racehorses, but PSB fractures, especially simple ones, do occur in sport horses undertaking various disciplines. For simple apical, basilar and abaxial articular PSB fractures, surgical removal via arthroscopy carries the best prognosis for return to athletic performance. Removal of apical and abaxial PSB fractures generally result in a favourable prognosis for return to racing but are dependent on the amount of suspensory ligament injury. Removal of basilar PSB fracture fragments results in a less favourable or fair prognosis for return to racing. Mid‐body PSB fractures typically require (lag screw) surgical fixation preferably with arthroscopic guidance and carry a fair to guarded prognosis for return to racing.

Association of catastrophic biaxial fracture of the proximal sesamoid bones with bony changes of the metacarpophalangeal joint identified by standing magnetic resonance imaging in cadaveric forelimbs of Thoroughbred racehorses.

To compare bony changes in the metacarpophalangeal joint (MCPJ) of racehorses with (cases) and without (controls) biaxial proximal sesamoid bone (PSB) fracture as determined by 2 grading scales applied to images of cadaveric forelimbs obtained by means of standing MRI (sMRI). Case-control study. Forelimbs from 74 Thoroughbred racehorses (21 cases and 53 controls) that were euthanized at a Florida racetrack. Both forelimbs were harvested from cases and controls. Each forelimb underwent sMRI to obtain images of the MCPJ. Two grading scales were described and used for image evaluation; one assessed the density of the PSBs, and the other assessed the integrity of the subchondral bone (SCB) plate at the distopalmar aspect of the third metacarpal bone (MC3). Logistic regression was used to compare the grades between case and control limbs. Biaxial PSB fracture was associated with a total PSB grade (sum of lateral and medial PSB grades) ≥ 5 for the fractured limb, total MC3 SCB grade (sum of lateral and medial MC3 SCB grades) ≥ 5 for the contralateral limb, and the presence of orthopedic disease in the contralateral MC3. For cases with biaxial PSB fracture, the density of the PSBs in the affected limb was greater and the MC3 of the contralateral limb was more likely to have orthopedic disease, compared with those for controls. Further evaluation of sMRI as a screening tool for identification of racehorses at risk of biaxial PSB fracture is warranted.

Use of Standing MRI and a New MRI Grading System of the Subchondral Bone of the Distal Third Metacarpal Bone to Identify Bone Changes in the Thoroughbred Racehorse When Comparing 21 Cases of Catastrophic Biaxial Proximal Sesamoid Bone Fracture with 53 Controls

Reasons for performing studyBiaxial fracture of the proximal sesamoid bones (PSB) is the leading cause of fetlock failure resulting in euthanasia in Thoroughbred racehorses in California, Kentucky and Hong Kong. Identifying alterable risk factors to reduce biaxial PSB fractures could have a significant impact on reducing the occurrence of catastrophic failure of the fetlock (CFF).ObjectivesWe hypothesised that standing MRI (sMRI) would identify a greater degree of bone change in Thoroughbred racehorses with CFF from biaxial PSB fracture when compared to controls.Study designRetrospective cohort study.MethodsBone changes from Florida Thoroughbred racehorses with CFF due to biaxial fracture of the PSB (n = 21) were compared to controls (n = 53) using the sMRI. Data for control limbs were Florida racehorses that were subjected to euthanasia for reasons other than CFF (enteritis, pneumonitis, etc.). All forelimb fetlocks underwent sMRI imaging within 72 h of euthanasia. Bone scores were assigned to the subchondral bone (SCB) on the distal palmar aspect of the lateral and medial condyle of the third metacarpal bone (McIII) and the lateral and medial PSB. All information for analysis from sMRI images for cases and controls for all Thoroughbred racehorses was reviewed and collected by the lead author. The association between the dichotomous outcomes of PSB fracture with independent variables was assessed using bivariable and multivariable logistic regression analysis with significance set at P&lt;0.05.ResultsThe proportion of cases with &gt;75% sclerosis of the ipsilateral lateral PSB (43%, 9/21) was significantly greater than that among controls (6%, 3/53). The proportion of cases with SCB lesion grade &gt;3 of the contralateral palmar lateral condyle (29%, 6/21) was significantly greater than that among controls (0%, 0/53).ConclusionsThe sMRI identified a significantly greater degree of bone change in racehorses with PSB fracture compared to control horses. These identified changes may be useful as a screening tool to identify horses at increased risk of fetlock fracture during racing.Ethical animal research: Explicit owner informed consent for participation in this study was not given but permission for post mortem examination was given by the Racing Authority. Sources of funding: None. Competing interests: No competing interests have been declared.

Biomechanical testing of a hybrid locking plate fixation of equine sesamoid osteotomies

To compare the biomechanical properties of a hybrid locking compression plate (LCP) construct with the compression screw technique as a treatment for transverse mid-body proximal sesamoid bone fractures. Ten paired forelimbs from abattoir horses were used. The medial proximal sesamoid bone of each limb was osteotomized transversely and randomly assigned, to either repair with a two-hole 3.5 mm LCP or a 4.5 mm cortical screw placed in lag fashion. Each limb was tested biomechanically by axial loading in single cycle until failure. The point of failure was evaluated from the load-displacement curves. Then a gross evaluation and radiographs were performed to identify the mode of failure. The loads to failure of limbs repaired with the hybrid LCP construct (4968 N ± 2167) and the limbs repaired with the screw technique (3009 N ± 1091) were significantly different (p <0.01). The most common mode of failure was through a comminuted fracture of the apical fragment of the proximal sesamoid bone. The LCP technique has potential to achieve a better fracture stability and healing when applied to mid-body fractures of the proximal sesamoid bone. Further testing, particularly fatigue resistance is required to corroborate its potential as a treatment option for mid-body fractures of the proximal sesamoid bone.

Morphologic Radiographic Study of the Proximal Sesamoid Bones of the Forelimb in Thoroughbred Racehorses in Training

The aim of this study was to identify differences in bone shape (height and width) of proximal sesamoid bones (PSB) in 2-year-old Thoroughbred racehorses in training. Dorsal 15° proximal-palmarodistal oblique images of each metacarpophalangeal joint were acquired before the horses started training and at 1year after the start of exercise and racing. There were no changes in height and width of PSBs induced by training. There was a significant difference of height and width between medial and lateral PSBs. In both forelimbs, the medial PSB was significantly wider and shorter than the lateral PSB. The medial PSB of the right forelimb was significantly wider than that of the left forelimb. These results might explain some limb predilection for fracture of PSBs. The difference in strain pattern between medial and lateral PSBs in different loading conditions needs to be investigated.