Osseous spinal pathology and epaxial muscle ultrasonography in Thoroughbred racehorses

Osseous pathologic changes in the thoracic region of the equine vertebral column: A descriptive post-mortem study in three breeds

BACKGROUND

Data on equine thoracic pathology hardly exist in breeds other than Thoroughbreds.

OBJECTIVES

To describe pathological changes of the osseous thoracic vertebral column in Warmblood horses, Shetland ponies and Konik horses, and to compare prevalence and severity.

STUDY DESIGN

Descriptive post-mortem study.

METHODS

Computed tomography was used to examine the thoracic vertebral column of 34 Warmblood horses, 28 Shetland ponies, and 18 Konik horses. Osteoarthritis (OA), periarticular osteolysis, osseous cyst-like lesions and fragments of articular processes (APJs), costovertebral and costotransverse joints, soft tissue mineralisation surrounding these joints, intervertebral disc (IVD) mineralisation, impingement of spinous processes (SPs) and spondylosis were scored.

RESULTS

APJ aplasia (98%; 58/59) occurred in 14 Shetland ponies. OA predominated in Warmblood horses across all joints (45% vs. 29 and 32%, p < 0.001). OA and periarticular osteolysis were found in particular in the costotransverse joints (p < 0.001) across all breeds. Warmblood and Konik horses had more and severe soft tissue mineralisation than Shetland ponies (2.3%, score 1.5 and 3.2%, score 1.3, respectively, vs. 0.3%, score 0.9, p < 0.01). Mid location was most often affected with highest severity score (4.2%, 1.5, p < 0.001). Konik horses displayed the highest IVD mineralisation (20%, p < 0.001), which notably increased with age (p < 0.001) compared with Warmblood horses (4.5%) and Shetland ponies (1.1%). SPs impingement was absent in Shetland ponies, and most prevalent in Warmblood horses (11.2%, p < 0.001) compared with Konik horses (2.2%). Osseous cyst-like lesions, fragments and spondylosis were minimal in all breeds and nearly absent in Shetland ponies.

MAIN LIMITATIONS

Clinical histories and macroscopic and histologic examinations were unavailable.

CONCLUSIONS

Distinct breed differences exist in prevalence and severity of thoracic vertebral column osseous pathologies. Costotransverse joint pathology is more common than APJ pathology in all breeds. Warmblood horses are prone to OA, spondylosis and SPs impingement; Konik horses exhibit significant IVD mineralisation, and Shetland ponies demonstrate a high prevalence of APJ aplasia. Periarticular osteolysis, osseous cyst-like lesions, fragments and soft tissue mineralisation are notably low in Shetland ponies.

Computed tomography of the equine caudal spine and pelvis: Technique, image quality and anatomical variation in 56 clinical cases (2018-2023)

BACKGROUND

Cross-sectional imaging improves the diagnostic accuracy of complex anatomical regions. Computed tomography (CT) of the pelvis and caudal spine in a large group of live horses and ponies has not been previously reported.

OBJECTIVE

To describe the procedure for acquiring CT images of horses' caudal spine/pelvis under general anaesthesia (GA) and to detail the image quality, artefacts and anatomical variations in this region.

STUDY DESIGN

Retrospective case series.

METHODS

Horses with CT of the caudal spine/pelvis were included. Horses under 6 months and CT examination performed post-mortem were excluded. Protocols, image quality, region of interest, anatomical features and morbidities were analysed.

RESULTS

Fifty-six horses (8 months to 20 years, 85-680 kg) met the inclusion criteria. GA ranged from 10 to 60 min (mean: 30, median: 32). There were no adverse events recorded in any of the horses associated with the procedure. Images of all horses were considered of diagnostic quality. Anatomical variations were common and included the location of diverging (widest) interspinous space, the presence of spina bifida in the lumbar and sacral spine, the shape of the last lumbar vertebra and the location of intertransverse joints in terms of where they were present and the degree of fusion/modelling.

MAIN LIMITATIONS

Not all horses underwent CT examination of the same regions, the upper size limit of horses is unknown and will vary depending on bore size and table infrastructure. Image noise, particularly in large horses and beam hardening artefacts from hardware and pelvis degraded image quality. Images were of insufficient quality in large horses for soft tissue interpretation.

CONCLUSION

CT of the caudal spine and pelvis in live horses with wide-bore CT machines and modified patient infrastructure was safe and produced diagnostic images.

Comparison of ultrasonographic and computed tomographic imaging of equine thoracolumbar articular process joints

BACKGROUND

Osteoarthritis of the equine thoracolumbar articular process joints (APJs) has been linked to back pain. Changes are commonly diagnosed through nuclear scintigraphy, radiography and ultrasonography (US).

OBJECTIVES

(1) To assess the agreement of APJ grades between US and computed tomography (CT) images; (2) to assess the effect of location on the agreement of APJ grades between US and CT images. It was hypothesised that: (1) Periarticular modelling and modification of the joint space would have the highest and lowest agreement between US and CT images, respectively; (2) Caudal thoracolumbar APJ grades would have higher agreement between US and CT images than mid thoracic APJs.

STUDY DESIGN

Comparative diagnostic imaging study using cadaveric specimens.

METHODS

Disarticulated thoracolumbar spines of six equids euthanised for reasons unrelated to back pain, underwent US and CT examination of the APJs. Images were assessed for periarticular modelling, modification of the joint space and enlargement of the APJ. Intra-observer, inter-modality and inter-observer agreement using multilevel weighted kappa statistics to evaluate the effects of location, US/CT characteristic and their interaction.

RESULTS

Intra-observer agreement of US and CT grades ranged from moderate to perfect. Between T15 and L1, inter-modality agreement (CT vs. US) for periarticular modelling was moderate, and fair for enlargement and modification of the joint space. Inter-observer agreement (US vs. US) of periarticular modelling was substantial between T15 and L1, moderate between L1 and L5 and fair between T10 and T15. Wide confidence intervals (CIs) seen for most grades apart from inter-observer grades of periarticular modelling at T15-L5, introducing a degree of uncertainty into the results.

MAIN LIMITATIONS

Large prevalence index influenced kappa values, small sample size.

CONCLUSIONS

Good inter-observer (US vs. US) and inter-modality (CT vs. US) agreement of caudal thoracolumbar APJ periarticular modelling. This US characteristic provides a measure of bone change, therefore supporting the use of diagnostic ultrasound. Inter-modality CIs were wide, highlighting the study and imaging modality limitations.

Osseous pathologic changes in the lumbar region of the equine vertebral column: A descriptive post-mortem study in three breeds

BACKGROUND

Data on equine lumbar pathology hardly exist in breeds other than Thoroughbreds.

OBJECTIVES

To describe pathological changes of the osseous lumbar vertebral column in Warmblood horses, Shetland ponies and Konik horses.

STUDY DESIGN

Descriptive post-mortem study.

METHODS

The lumbar vertebral columns of 34 Warmblood horses, 28 Shetland ponies, and 18 Konik horses were examined by computed tomography (CT). Osteoarthritis (OA) of articular processes (APJs), OA of intertransverse joints (ITJs), intervertebral disc (IVD) mineralisation, impingement of spinous (SPs) and transverse (TPs) processes and spondylosis were scored. Breed differences in prevalence and severity of pathologies were analysed by linear regression analysis and by calculating Spearman's rank correlation coefficients (rs).

RESULTS

In Warmblood horses, the prevalence of OA of APJs, impingement of SPs and TPs was respectively 90%, 36%, and 35%, significantly higher than in the other breeds (p < 0.001). In Konik horses, IVD mineralisation (40%) and spondylosis (10%) were more frequent than in Warmbloods and Shetland ponies (p = 0.03). Severity score for OA of ITJs was highest in Shetland ponies (p < 0.001). For impingement of SPs, severity score was highest in Warmbloods (p = 0.03), and of TPs lowest in Shetland ponies (p = 0.003). For all parameters, except for spondylosis in Shetland ponies, there was a positive correlation between percentage of vertebrae affected and age, with IVD mineralisation scores increasing faster in Konik horses (p < 0.001). In all breeds, there was also a positive relation between scores of severity and age for OA of APJs and ITJs and for IVD mineralisation, with severity scores increasing faster in Shetland ponies (p = 0.04). Strong left/right correlations of the severity scores were seen for OA of the APJ, ITJ, impingement of TPs, and paramedian spondylosis (rs = 0.74-0.86, all p < 0.001).

MAIN LIMITATIONS

Clinical histories were not available.

CONCLUSIONS

There are distinct breed differences between prevalence and severity of osseous pathologies of the lumbar spine. Warmblood horses have higher scores for most pathologies with IVD mineralisation being more important in Konik horses and OA of ITJs in Shetland ponies.

The Detection of Thoracolumbar Spine Injuries in Horses with Chronic Laminitis Using a Novel Clinical-Assessment Protocol and Ultrasonographic Examination

Postural adaptation is a prominent feature in horses affected by laminitis. Laminitis induces intense pain, especially in the forelimbs, prompting affected horses to assume a caudally displaced trunk posture, resulting in the hyperflexion of the thoracolumbar spine. This study assessed the nature and prevalence of thoracolumbar injuries in horses with chronic laminitis compared to horses without it. Sixty horses were used (thirty laminitic and thirty non-laminitic) of different athletic purposes and ages (2-20 years). The experimental protocol entailed a single assessment of horses' thoracolumbar spines, utilizing physical examination by MACCTORE, a scoring system developed specifically for this study. Additional evaluations included the Grimace Equine Pain Scale (HGS) and ultrasound exams. Statistical tests were used to compare values (Mann-Whitney or t-test) and lesions prevalences (Fisher) between groups (p < 0.05). The results showed a higher pain manifestation (HGS and heart rate, p < 0.0001) and thoracolumbar-spine-injury levels in chronic laminitis horses, both in MACCTORE clinical examinations (11.7 ± 4.8 vs. 4.2 ± 3.3, p < 0.0001) and general ultrasonographic indices (39.6 ± 12.0 vs. 20.7 ± 7.1, p < 0.0001), including specific examination approaches for various spinal elements. Horses with laminitis presented with a 14-fold higher prevalence of ultrasound-relevant lesions in the thoracolumbar spine (CI: 4.4 to 50.6, p < 0.0001) compared to controls. These findings constitute new evidence of an association between chronic laminitis and the presence of thoracolumbar spine injuries in horses, which may be confirmed by more sophisticated study designs.

Advances in the Clinical Diagnostics to Equine Back Pain: A Review of Imaging and Functional Modalities

Back pain is common in ridden horses. Back diseases in horses include Impinging Dorsal Spinous Processes, Ventral Spondylosis, Osteoarthritis of Articular Process, Intervertebral Discs Disease, Vertebral Fractures, Conformational Abnormalities, Desmopathy of the Supraspinous Ligament, Desmopathy of the Intraspinous Ligament, and Longissimus Muscle Strain. Back pain may also develop as a result of lameness (particularly hindlimb lameness). A poorly fitting saddle and an unbalanced rider are also considered important factors influencing the development of back pain in horses. The conventional diagnosis of equine back pain includes a clinical examination and diagnostic imaging examination using ultrasound, radiography, and thermography. Advanced diagnostic modalities of equine back pain involve the objectification of standard procedures through the use of algometers, a lameness locator, biometric mats, and the geometric morphometrics method. In addition to modern diagnostic methods, such as computed tomography and scintigraphy, advances in the diagnosis of equine back pain include the use of electromyography and functional electrical stimulation. The aim of this review article is to familiarize clinicians with the usefulness and capabilities of conventional diagnostic protocols and advanced diagnostic modalities. Although orthopedic examination and traditional diagnostic methods will remain the foundation of the diagnosis of back diseases, modern methods meet the growing expectations towards high-performance horses and allow for deeper diagnostics and objective monitoring of rehabilitation and training progress.

Investigation of Potential Serum Biomarkers for the Diagnosis of Chronic Back Pain in Horses

Back pain is one of the most common triggers of performance failure in athletic and riding horses. Diagnosis of equine back pain has been very challenging for equine practitioners, particularly in chronic cases. Therefore, the identification of blood biomarkers would facilitate the clinical differentiation of chronic back pain. This study aimed to investigate serum biomarkers of glial cell activation, axonal damage, and inflammation for the diagnosis of equine chronic back pain. Serum samples from forty horses comprising chronic back pain (CBP), back pain concurrent with lameness (BPL), lameness (LN), and healthy control (HC) (n=10 per group) were screened for ionized calcium-binding adaptor molecule 1 (Iba-1), glial fibrillary acidic protein (GFAP), phosphorylated neurofilament-H (pNF-H) by ELISA, and proinflammatory cytokines (IL-1β, IL-6, and TNF-α) by multiplex assay. Serum concentrations of GFAP (3.81±1.72 ng/mL) and pNF-H (0.76±0.18 ng/mL) were significantly (p<0.05) higher in horses with CBP when compared with other groups. Iba-1 was not significantly higher in CBP horses. There was no significant difference between the pro-inflammatory cytokines among the groups. The levels of IL-1β, IL-6, and TNF-α were also increased in the CBP than the HC control horses but lower in relation to BPL and LN horses. In addition, serum Iba-1, GFAP, and pNF-H showed a high discriminatory capacity for horses with CBP with high sensitivity (50-100%) and specificity (70-100%). This study provides evidence that serum levels of the GFAP and pNF-H may be useful in the clinical differentiation of horses with chronic back pain.

Ultrasonography of the paralumbar muscles as a new aid during melarsomine treatment in canine heartworm disease. Description and illustration of the method - A preliminary study

Melarsomine is used intramuscularly to destroy adult heartworms when treating canine heartworm disease (HWD). This drug is highly irritative and can elicit local complications. Therefore, melarsomine should be injected into the paralumbar muscles by strictly adhering to the manufacturers' prescriptions. However, it is not known how to determine the optimal location of the needle during the injection process. Ultrasonography (US) of the epaxial (paralumbar) musculature was used as a new method to measure the cross-sectional diameter of the paralumbar musculature, to determine the required location of the injection needle, and to study the local side effects in two dogs with HWD. The macroscopic appearance of the melarsomine solution during injection was demonstrated by video imaging. Melarsomine was not fully gravitating, but its majority was spreading along the thickest fascia of the musculature. Three minutes thereafter, no ultrasound signs of the melarsomine solution were seen, suggesting a full absorption at least ultrasonographically. This procedure was simulated in vitro with methylene blue solution having the same appearance. Removing the injection needle only after 5 min post-injection could prevent undesirable leakage of the drug through the injection channel into the subcutaneous tissue. Ultrasonography can be a useful aid during the treatment of HWD with melarsomine according to this preliminary study.

Use and repeatability of 3D light scanning to measure transverse dorsal profile size and symmetry in the thoracic region in horses

Equine epaxial muscle size, thoracolumbar profile and symmetry in horses is of clinical interest due to relationships with pain and pathology. Flexible-curve rulers have previously been used to gather reliable, objective measures of thoracic profile, however, 3D light-scanning offers a potential non-contact alternative method to estimate cross sectional area (CSA) of the region. 3D light-scans of the thoracic epaxial region were taken from ten endurance horses (7 geldings, 3 mares; 8±2 years). Total CSA of the combined epaxial musculature, using computer software, was calculated at scapula and T18 levels (depth: 15 cm). Intra and inter-rater (n=3) reliability of CSA measurements was assessed using Friedman’s analyses and post-hoc Wilcoxon rank tests (three repeated measures). Intraclass correlation estimates (ICC ± 95% confidence intervals (CI)) were calculated (mean-rating, absolute-agreement, 2-way mixedeffects model). Paired t-tests assessed differences between right and left areas. No significant differences existed for transverse plane-cuts (scapula, T18 P>0.05) between light-scans. Right and left areas were significantly different at the withers (P=0.012) with the left side larger in 70% of scans, but no significant differences were found between sides at T18. No differences existed for different plane-cuts of the same horse (P=0.53; ICC: 0.76; CIs: 0.43-0.92). While reliability was reduced between all raters (P=0.02; ICC: 0.70; CIs: 0.56-0.82), no significant differences occurred between two different assessors experienced in using the software (P=0.88; ICC: 0.90; CIs: 0.82-0.95). Intra-rater reliability for assessing thoracic profile and inter-rater reliability ICC values with experienced analysts was interpreted as good/excellent. The results suggest 3D light-scanning is an objective, non-invasive method to record size and symmetry of the epaxial region in horses and warrants validity testing against current measurement methods such as the flexible-curve ruler.

Influence of Chronic Lameness on Thoracolumbar Musculus Multifidus Structure in the Horse

The clinical relationship between equine limb lameness and secondary back dysfunction is largely unknown. Proper function of the spine is critical to maintain the integrity of the kinetic chain and attenuate forces from the appendicular skeleton. The musculus multifidus (m. multifidus) is the primary muscle providing spinal intersegmental stabilization and a functional relationship between m. multifidus hypertrophy and equine postural stability has been established. The relationship between equine thoracolumbar m. multifidus cross-sectional area (CSA) and limb lameness is unknown. The objective was to evaluate ultrasonographic changes in thoracolumbar m. multifidus CSA in horses with chronic single limb lameness, compared with sound horses. We hypothesized that the CSA of m. multifidus, ipsilateral to the lame limb would be smaller than the contralateral side, and within the sound group there would be no difference between sides. Thirty-six horses were enrolled, with twelve horses per group: sound, forelimb lame, and hindlimb lame. M. multifidus CSA was measured ultrasonographically at multiple spinal levels and compared between groups, spinal levels, and sides. M. multifidus CSA at the spinal level T18 was significantly larger than at all other measured levels, regardless of group (P≤.05). CSA at all levels was significantly larger in sound horses than the forelimb lame group, regardless of side (P= 0.002). This is the first study to evaluate the impact of chronic lameness on the axial skeleton and showed a decrease in m. multifidus CSA with forelimb lameness. These results support that axial skeletal adaptation occurs in response to naturally occurring chronic lameness.

Electromyography of the Multifidus Muscle in Horses Trotting During Therapeutic Exercises

Thoracolumbar pain has been identified in both human and equine patients. Rehabilitation and conditioning programs have focused specifically on improving trunk and abdominal muscle function (1–5). Equine exercise programs routinely incorporate ground poles and training devices for the similar goals of increasing spinal and core stability and strength (6–8). The multifidus muscle has been an area of focus due to atrophy associated with disease (9). To date, there have been no reports on the activity of the multifidus muscle in horses in relation to therapeutic exercises. Our objectives were to use electromyography to determine the average work performed and peak muscle activity of the multifidus in horses trotting, trotting over ground poles, trotting while wearing a resistance band-based training device and trotting while wearing the training device over ground poles. We hypothesized that ground poles and the training device would each increase average work performed and peak multifidus muscle activity. Right and left cranial thoracic locations showed significant increased muscle work and peak activation when horses were trotted over ground poles versus without. The peak activation was significantly greater in horses trotting over poles in both lumbar regions, but there was no significant change in peak activation in either location due to the training device. When the influence of the training device was investigated without ground poles, left caudal thoracic muscle work and peak activity, and right lumbar muscle work were significantly lower when using the training device, as compared to without. When the training device was combined with trotting over ground poles, both left and right caudal thoracic regions showed significantly lower muscle work and peak activity when the device was used. There was no significant difference between with and without the device in either left or right lumbar muscle work. In conclusion, implementing ground poles can be an effective strategy to increase the activation of the multifidus muscle, however, caution should be taken when incorporating the use of a resistance band training device as muscle work and peak activation were significantly reduced in most locations. Further study should be performed in regards to the training device to determine its effects on epaxial musculature.

Clinical assessment and grading of back pain in horses

Background

The clinical presentation of horses with back pain (BP) vary considerably with most horse's willingness to take part in athletic or riding purpose becoming impossible. However, there are some clinical features that are directly responsible for the loss or failure of performance.

Objectives

To investigate the clinical features of the thoracolumbar region associated with BP in horses and to use some of the clinical features to classify equine BP.

Methods

Twenty-four horses comprised of 14 with BP and 10 apparently healthy horses were assessed for clinical abnormality that best differentiate BP from normal horses. The horses were then graded (0–5) using the degree of pain response, muscular hypertonicity, thoracolumbar joint stiffness and overall physical dysfunction of the horse.

Results

The common clinical features that significantly differentiate horses with BP from non-BP were longissimus dorsi spasm at palpation (78.6%), paravertebral muscle stiffness (64.3%), resist lateral bending (64.3%), and poor hindlimb impulsion (85.7%). There were significantly (p < 0.05) higher scores for pain response to palpation, muscular hypertonicity, thoracolumbar joint stiffness and physical dysfunction among horses with BP in relation to non-BP. A significant relationship exists between all the graded abnormalities. Based on the cumulative score, horses with BP were categorized into mild, mild-moderate, moderate and severe cases.

Conclusions

BP in horse can be differentiated by severity of pain response to back palpation, back muscle hypertonicity, thoracolumbar joint stiffness, physical dysfunctions and their cumulative grading score is useful in the assessment and categorization of BP in horses.

A comparative study of breed differences in the anatomical configuration of the equine vertebral column

The importance of the equine thoracolumbar vertebral column in orthopaedic disorders is well recognized and diagnostic imaging becomes more feasible, but little is known about variations in the anatomical configuration within breeds. In this descriptive post-mortem study, anatomical variations in three widely differing breeds: Warmblood horses, Shetland ponies and semi-feral Konik horses are described. The caudal cervical (C), thoracic (T), lumbar (L) and sacral (S) regions of the vertebral column of 30 Warmblood horses, 29 Shetland ponies and 18 Konik horses were examined using computed tomography and visualized by volume rendering. Homologous/morphologic variations in the caudal cervical area were frequently seen in Warmblood horses (43%), which was significantly more than in the other breeds (p < 0.001). The as standard described equine formula of 18 T, 6 L and 5 S vertebrae was seen in 78% of Konik horses, but only in 53% Warmblood horses and 38% Shetland ponies, which was significantly different (p < 0.05). Overall, Shetland ponies showed a higher tendency of thoracoization, lumbarization and more variations in the number of vertebrae and pairs of ribs. Ankylosed intertransverse joints (ITJs) between transverse processes of the lumbar vertebrae were most common between the second last and last lumbar vertebra and prevalence was significantly higher in Shetland ponies (61%), than in Warmblood horses (38%) and Konik horses (7%) (p < 0.0001). Cranial to the second last lumbar vertebra there were fewer ITJs ankylosed (14%) in Warmblood horses (p < 0.0095), and this decrease in number of ankylosed ITJs was different compared to the change in ankylosed ITJs in Shetland ponies (p < 0.005). ITJs occurred asymmetrically in 15% (12/77) of the cases. A limitation of the study was that clinical data of the horses were only incompletely available, precluding any conclusions about the potential clinical implications of anatomical variations. Knowledge of variation in osseous anatomy of the equine thoracolumbar vertebral column is important for the interpretation of diagnostic imaging. To assess the functional importance and clinical relevance of this variation, follow-up studies are necessary.

Implications of the neuroanatomy of the equine thoracolumbar vertebral column with regional anaesthesia and complications following desmotomy of the interspinous ligament

Impinging/overriding dorsal spinous processes (DSPs) of the thoracolumbar vertebrae are a common cause of poor performance in horses. In the last five decades, numerous surgical treatments have been reported on, from transverse transection of the affected DSPs, and endoscopic resection of the affected DSPs, to transection of the interspinous ligament. Until recently, cosmetic outcomes have been reported as good to excellent in studies. However, a previously unreported complication of neurogenic atrophy of the contralateral epaxial muscle following desmotomy of the interspinous ligament has been recently reported. The authors hypothesised that this was because of a more lateral approach than previously described, resulting in the scissors being too far across midline and transecting a nerve in the region. Considering this finding, we have reviewed the literature on the neuroanatomy of the thoracolumbar region in the horse. Literature on the neuroanatomy of the horse is lacking when compared with that of humans and companion animals, with most of the work extrapolated from companion animals. Based on the current literature, we hypothesise that transection of an intermediate branch of the dorsal spinal nerve supplying the m. longissimus is potentially the cause of the post-operative neurogenic atrophy. The lack of detailed knowledge of the neural anatomy of the equine back has resulted in the role of local anaesthesia in localising pain in the equine back being poorly understood. The wide variation in techniques used for localising back pain may explain why some horses suffering from poor performance or an abnormal gait because of back pain improve to local anaesthesia of the back while others do not. This review article highlights a lack of anatomical knowledge regarding the equine thoracolumbar region in the literature despite diagnostic local anaesthesia, medication, and surgery in this area being relatively common.

Accelerometric Changes before and after Capacitive Resistive Electric Transfer Therapy in Horses with Thoracolumbar Pain Compared to a SHAM Procedure

Simple Summary

Capacitive resistive electric transfer (CRET), a radiofrequency at 448 kHz, has been shown to result in increased muscle oxygenation and flexibility in the quadriceps muscle of human beings. In this study, 18 sport horses with thoracolumbar pain were divided into two homogenous groups: CRET (n = 9), subjected to four sessions of CRET during two consecutive weeks and SHAM (n = 9), subjected to the same sessions but with the device off. Clinical examination and accelerometry were made at the beginning and at the end of the study. A Mann-Whitney test and a Wilcoxon matched pair test were used to compare between SHAM and CRET groups and before and after the intervention, respectively. CRET horses showed a reduction of 1 degree in thoracolumbar pain (p = 0.002) and of 2 degrees in epaxial muscle pain (p = 0.03). SHAM horses had a reduction of 1 degree in thoracolumbar pain (p = 0.01). CRET horses presented increased dorsoventral power at walk and trot (p < 0.002), probably reflecting increased dorsoventral movement and flexibility. Such changes were not found in SHAM horses. No changes were found in the dorsoventral displacement of the center of gravity in either group. Our study demonstrated that sport horses with mild to moderate thoracolumbar pain could improve clinically and biomechanically after CRET therapy.

Abstract

Capacitive resistive electric transfer (CRET), a radiofrequency at 448 kHz, increases flexibility in quadricep muscles of human athletes. To assess whether CRET would result in clinical and biomechanical improvements in horses with thoracolumbar pain, 18 sport horses were divided into two groups: CRET (n = 9), subjected to four CRET sessions, during two consecutive weeks, and SHAM (n = 9), subjected to the same procedure with the device off. Clinical examination and accelerometry were performed before and after the four sessions. During the study, horses were in training and in active competition, and did not receive any other treatment. Mann-Whitney and a Wilcoxon matched pair tests were used to compare between the SHAM and CRET groups and before and after the intervention, respectively. CRET horses showed increased dorsoventral (p < 0.002), mediolateral and total power (p < 0.01) after the intervention, suggesting increased back flexibility. SHAM horses did not show any of these modifications after the intervention. No changes were found in the dorsoventral displacement of the gravity center in either group. Thoracolumbar pain decreased one degree after CRET (p = 0.002), and it did not change after SHAM. Epaxial muscle pain decreased two degrees after CRET (p = 0.03) and one degree after SHAM (p = 0.01). These results reflected that CRET therapy would increase back flexibility and decrease thoracolumbar and epaxial pain.

Functional Electrical Stimulation (FES) and the Effect on Equine Multifidi Asymmetry

Asymmetry of the multifidi has been correlated with scoliosis and back pain in humans and has been investigated as a factor in equine back pain as well. The purpose of this study was to determine if FES would affect the symmetry of equine thoracolumbar multifidi when compared to controls. Twelve horses received 24 FES treatments bilaterally over the thoracolumbar region for 8 weeks. Twelve additional control horses received no FES treatments. Ultrasonographic measurements of the cross-sectional area (CSA) of the multifidi of the treatment horses at seven thoracolumbar levels were compared to determine the change in left and right asymmetry post-FES. The same measurements during the same period were also taken in the control group. All measurements were blinded for evaluation. Statistical significance was assessed utilizing two-sided, matched-pairs t-tests, and Welch's (unequal variances) t-test (alpha = 0.05). Multiple comparisons were accounted for using the Sidak correction. A significant improvement in multifidi asymmetry was observed, post-FES, at all seven thoracolumbar levels, with no evidence of asymmetry improvement in the control group. The difference between mean improvements of the treatment and control groups was statistically significant (P < .001). FES significantly improved the symmetry of equine multifidi, and evidence was provided for the effectiveness of FES at each of seven thoracolumbar levels. The improvement in symmetry appeared to result from increases, decreases, and maintenance of the CSA of the left and right multifidi in various combinations. The FES protocol used in this study has the potential to improve spinal function and assist in reducing back pain in horses.

Gymnastic Training of Hippotherapy Horses Benefits Gait Quality When Ridden by Riders with Different Body Weights

The objective was to evaluate the effects of gymnastic training on stride characteristics of walk and trot in therapy horses carrying riders of different weights. Eighteen horses used for therapeutic riding 5 days/week were randomly divided into 2 groups. Nine horses performed gymnastic (GYM) exercises after therapeutic riding on 4 days/week for 3 months, 9 horses did no additional exercises (SED). On days 0 and 90, an inertial sensor mounted to the girth on the ventral midline was used to evaluate stride characteristics when horses were ridden at walk (1.3 m/second) and trot (3.0 m/second) by able-bodied riders representing rider: horse body weight ratios (BWRs) 15%, 20%, and 25%. On day 0, the measured variables did not differ significantly between sedentary (SED) and GYM groups, but on day 90, the following statistically significant results were found: GYM-trained horses had higher regularity for all BWRs at walk and 15% and 20% BWRs at trot. Higher stride symmetry was found in GYM-trained horses carrying 25% BWRs at walk and all rider weights at trot. Dorsoventral displacement was higher in GYM-trained horses when carrying 20% and 25% BWRs at walk and 25% BWRs at trot. Dorsoventral power was lower in SED-trained versus GYM-trained horses carrying 15% BWR at walk and 20% BWR at trot. A more regular and symmetrical stride with a larger range of dorsoventral trunk motion is likely to provide a better therapeutic riding experience.

Effect of Caudal Traction on Mechanical Nociceptive Thresholds of Epaxial and Pelvic Musculature on a Group of Horses With Signs of Back Pain

Direct muscular attachment from lumbar vertebrae to the caudal vertebrae of the tail suggests that caudal traction, also described as a tail pull, may affect lumbar vertebral segments and/or associated soft tissues in horses. Traction is a commonly used human manual therapy technique used for pain relief and anecdotally observed to relieve pain in horses. However, research is lacking validating the efficacy of manual caudal traction on the horse. The objective of this study was to determine if caudal traction has an effect on mechanical nociceptive thresholds (MNTs) in a group of horses with clinical signs of back pain. Pressure algometry was used to measure MNTs of five bilateral anatomical sites in the epaxial and pelvic musculature of 11 horses referred to physiotherapy because of clinical signs of back pain. Measurements were recorded both before and immediately after traction. A significant difference (P ≤ .05) was identified between mean before and after caudal traction algometry measurements in all described sites. The percentage of MNT increase was highest in the thoracic region (83%) compared with the lumbar (50%) and the pelvic (52.4%) regions. These results support an effect of caudal traction in increasing MNTs in the thoracolumbar and pelvic regions in horses. Further research to determine the clinical effect of this technique is warranted.

Myelopathy and Reactive Microgliosis and Astrogliosis in Equine Back Pain

Equine chronic back pain (CBP) has been linked to different pathologic processes, which directly or indirectly involve spinal structures. Thus, making diagnosis and management very challenging with most horses with the condition recommended for early retirement from athletic activity. This study described the spinal cord lesions and the development of reactive microgliosis and astrocytosis in the spinal cords of horse with CBP. Thoracolumbar spinal cord segments from three horses euthanized because of unresolved CBP were dissected and grossly and histopathologically examined. The expression of activated microglia and astrocytes were demonstrated immunohistochemically using polyclonal rabbit anti-Iba-1 and anti-glial fibrillary acidic protein antibodies, respectively. All horses had radiological evidence of varying degrees of kissing spine involving six to nine vertebrae with the majority of the lesions graded between 2 and 5. Grossly, there was myelomalacia with intramedullary hemorrhages. The gray matters of the spinal cords were characterized by hemorrhagic malacic lesions with medullary disintegration. Reactive microgliosis and astrocytosis were evident in the spinal dorsal horns. White matter lesions include axonal swollen and/or loss, satellitosis, and varying degrees of dilation of myelin sheaths with some containing macrophages. In conclusion, the presence of reactive microgliosis and astrogliosis in the spinal dorsal horn indicates that they are possible precipitating factors in the development of equine CBP.

The Effect of Kinesiotape on Flexion-Extension of the Thoracolumbar Back in Horses at Trot

Kinesiotape theoretically stimulates mechanoreceptive and proprioceptive sensory pathways that in turn may modulate the neuromuscular activity and locomotor function, so alteration of activation, locomotion and/or range of motion (ROM) can be achieved. The aim of this study was to determine whether kinesiotape applied to the abdominal muscles would affect the ROM in flexion-extension (sagittal plane) in the thoracolumbar back of horses at trot. The study design was a paired experimental study, with convenient sample. Each horse was randomly placed in the control or the intervention group and then the order reversed. Eight horses trotted at their own preferred speed in hand on a straight line, 2 × 30 m. Optical motion capture was used to collect kinematic data. Paired t-tests, normality tests and 1-Sample Wilcoxon test were used to assess the effects of the kinesiotape. No statistical significance (p < 0.05) for changes in flexion-extension of the thoracolumbar back in trot was shown in this group of horses. Some changes were shown indicating individual movement strategies in response to stimuli from the kinesiotape. More research in this popular and clinically used method is needed to fully understand the reacting mechanisms in horses.

Inter- and Intra-Rater Reliability of Soft Tissue Palpation Scoring in the Equine Thoracic Epaxial Region

Back pain is a significant factor for horses and is challenging for professionals to diagnose, with assessment frequently using subjective tools such as manual palpation. Reliable and valid objective measures are required and use of a pressure algometer (PA) has been investigated as an assessment tool; however, it has limitations, and other more realistic methods may be better suited for the task. The aim of the study was to establish inter- and intra-rater reliability for PA, FlexiForce Sensor (FFS), and manual palpation for equine epaxial soft tissue, measuring mechanical nociception threshold responses. In group 1, 10 horses underwent three repeated tests with PA and FFS, and once for manual palpation, with three Association of Chartered Physiotherapists in Animal Therapy (ACPAT) Chartered Physiotherapists in the right thoracic epaxial region. Group 2 followed the same protocol using one ACPAT Chartered Physiotherapist and 22 horses. The order of palpation was randomly applied for each test and each experimenter. Manual palpation showed excellent interrater reliability with no significant differences between scores (P = .64; intraclass correlation coefficient [ICC] 90.0%). PA (P = .002) and FFS (P = .025) scores significantly differed between experimenters. Intrarater testing showed significant differences (P = .014) with horses increasing sensitivity over repeated PA measures. The FFS showed no significant differences (P = .347; ICC 94.7%) in repeated measures with excellent reliability and consistency. The PA showed a lack of consistency in intrarater reliability conflicting with previous research findings, whereas the FFS showed greater reliability in comparison; however, it proved difficult to use in clinical practice. Manual palpation by physiotherapists was shown to have excellent interrater reliability when using a categorical scoring system.

Extracorporeal shockwave therapy raises mechanical nociceptive threshold in horses with thoracolumbar pain

BACKGROUND

Although extracorporeal shockwave therapy (ESWT) is a common treatment for horses with back pain, effects on mechanical nociceptive threshold (MNT) and multifidus muscle cross sectional area (CSA) in the spine are unknown.

OBJECTIVES

To evaluate effects of ESWT on spinal MNT and multifidus muscle CSA in horses with thoracolumbar pain.

STUDY DESIGN

Non-randomised trial.

METHODS

Thoracolumbar spines of 12 horses with thoracolumbar pain were radiographed to document existing pathology. Each horse received three ESWT treatments, 2 weeks apart (days 0, 14, 28). Palpation scores were documented (days 0, 45 and 65). Ultrasonographic CSA of left and right multifidus muscles was recorded at T12, T14, T16, T18, L3 and L5 (days 0, 45 and 65). MNT was measured at the same spinal sites every 7 days (day 0-56).

RESULTS

Mechanical nociceptive threshold in 10/12 horses (83%) was greater at each time point compared with day 0 (P < 0.05). Mechanical nociceptive threshold increased at all time points at six sites in 2/12 (16%), at five sites in 3/12 (25%), at four sites in 4/12 (33%) and at one site in 1/12 (8%; P < 0.05). Mechanical nociceptive threshold average per cent  increase from day 0 to 56 was 64% for the thoracic region (T12-T18) and 29% for the lumbar region (L3-L5). There was no statistical difference in MNT from day 35 to 56 (P = 0.25). A bimodal analgesic trend was observed following ESWT. Degree of radiographic change was not associated with response to treatment. No significant change in multifidus muscle CSA was observed.

MAIN LIMITATIONS

Small study size and lack of control group.

CONCLUSIONS

Three treatments of ESWT 2 weeks apart raised MNT over a 56-day period in horses with back pain, but did not influence change in CSA of the multifidus muscle. While ESWT appears justifiable for analgesia, physiotherapeutic techniques may be necessary in conjunction for concurrent muscle rehabilitation.

Changes in Structure and Function of the Back Muscles in Low Back Pain: Different Time Points, Observations, and Mechanisms

Spinal health depends on optimal back muscle performance, and this is determined by muscle structure and function. There has been substantial research evaluating the differences in structure and function of many back muscles, including the multifidus and erector spinae, but with considerable variation in results. Many studies have shown atrophy, fat infiltration, and connective tissue accumulation in back muscles, particularly deep fibers of the multifidus, but the results are not uniform. In terms of function, results are also somewhat inconsistent, often reporting lower multifidus activation and augmented recruitment of more superficial components of the multifidus and erector spinae, but, again, with variation between studies. A major recent observation has been the identification of time-dependent differences in features of back muscle adaptation, from acute to subacute/recurrent to chronic states of the condition. Further, these adaptations have been shown to be explained by different time-dependent mechanisms. This has substantial impact on the rationale for rehabilitation approaches. The aim of this commentary was to review and consolidate the breadth of research investigating adaptation in back muscle structure and function, to consider explanations for some of the variation between studies, and to propose how this model can be used to guide rehabilitation in a manner that is tailored to individual patients and to underlying mechanisms. J Orthop Sports Phys Ther 2019;49(6):464-476. doi:10.2519/jospt.2019.8827.

Clinical investigation of back disorders in horses: A retrospective study (2002-2017)

Background and Aim:

Back disorder is an ailment that often affects athletic and riding horses. Despite the rapidly growing equine athletic and equestrian activities, there is no documentation on the nature of equine back disorder (EBD) in Malaysian horses. The purpose of this study was to characterize EBD cases presented to University Veterinary Hospital, Universiti Putra Malaysia, between 2002 and 2017.

Materials and Methods:

The compilation of data was based on signalment, case history, duration of clinical signs, anatomical location of the pain, method of diagnosis, type of EBD, treatment, and outcome. The diagnosis of EBD was based on a history of poor performance, clinical examination findings, radiography, and, where applicable, necropsy.

Results:

A total of 181 diagnosed cases of EBDs were identified. The age of horses ranged from 5 to 22 years. The EBD cases were more prevalent in male than female horses and predominantly in geldings (60.77%). Thoroughbred, Arab, Polo pony, and Warmblood also recorded the most EBD cases among breeds. The discipline of horses tended to influence the development of EBDs, with patrolling horses recording the highest frequency. Most EBD cases were of the primary type (92.27%), with the main causes being soft-tissue lesions (57.48%), vertebral lesions (18.56%), tack-associated problems (16.77%), and neurological lesions (7.19%). The common treatments employed were administration of nonsteroidal anti-inflammatory agents, 1 to 3-month rest, warm and cold compression therapy, massage therapy, exercise adjustment, as well as correction of ill-saddle fit.

Conclusion:

Most EBDs in this study were associated with soft-tissue lesions. Among vertebral lesions, kissing spines were the most common cause of EBDs in horses in Malaysia.

Two Multicenter Surveys on Equine Back-Pain 10 Years a Part

Despite back-pain being a common cause of poor performance in sport horses, a tailored diagnostic workflow and a consolidated therapeutic approach are currently lacking in equine medicine. The aim of the study was to assess the evolution in the veterinarian approach to diagnose and treat back-pain over a 10 years period. To investigate this topic, two surveys were addressed to equine veterinarians working in practice throughout Europe 10 years apart (2006 and 2016). The answers were organized in an Excel dataset and analyzed. There were 47 respondents in 2006 and 168 in 2016, from 8 European Countries. The main reasons for examining horses with back-pain were poor performance (76%), behavioral issues (68%), and lameness (50%). When assessing back pain, 97% of respondents applied careful digital pressure over paravertebral muscles, 90% of them used digital back mobilization, and 69% was detecting areas of localized heat. The use of diagnostic analgesia to confirm the source of pain was rarely employed. Radiography and ultrasonography were the most frequent diagnostic imaging modalities used to investigate the causes of back-pain in both surveys. Obtaining a definitive diagnosis in horses with back-pain is considered challenging due to the reduced accessibility of the area and the variability in the pain manifestations. Corticosteroids injections were used for local treatments by 80% of respondents in 2006 and 92% in 2016. Recently, ultrasonography has been extensively used during the injections of the vertebral articular facets and sacroiliac joints region. The use of complementary therapies was restricted to a low percentage of respondents in the first survey (20%) but it increased over the decade. In 2016, a wider percentage of respondents considered osteopathy (40%), kinesiotherapy (29%), and acupuncture (22%) when treating back disorders compared to 2006. The structural differences of the two surveys did not enable a direct data comparison. Based on the results of this surveys, however, veterinarians should be sensitized to the back-pain problems and seek to integrate findings from clinical research studies in their daily practice.

A simple method of equine limb force vector analysis and its potential applications

BACKGROUND

Ground reaction forces (GRF) measured during equine gait analysis are typically evaluated by analyzing discrete values obtained from continuous force-time data for the vertical, longitudinal and transverse GRF components. This paper describes a simple, temporo-spatial method of displaying and analyzing sagittal plane GRF vectors. In addition, the application of statistical parametric mapping (SPM) is introduced to analyse differences between contra-lateral fore and hindlimb force-time curves throughout the stance phase. The overall aim of the study was to demonstrate alternative methods of evaluating functional (a)symmetry within horses.

METHODS

GRF and kinematic data were collected from 10 horses trotting over a series of four force plates (120 Hz). The kinematic data were used to determine clean hoof contacts. The stance phase of each hoof was determined using a 50 N threshold. Vertical and longitudinal GRF for each stance phase were plotted both as force-time curves and as force vector diagrams in which vectors originating at the centre of pressure on the force plate were drawn at intervals of 8.3 ms for the duration of stance. Visual evaluation was facilitated by overlay of the vector diagrams for different limbs. Summary vectors representing the magnitude (VecMag) and direction (VecAng) of the mean force over the entire stance phase were superimposed on the force vector diagram. Typical measurements extracted from the force-time curves (peak forces, impulses) were compared with VecMag and VecAng using partial correlation (controlling for speed). Paired samples t-tests (left v. right diagonal pair comparison and high v. low vertical force diagonal pair comparison) were performed on discrete and vector variables using traditional methods and Hotelling's T2 tests on normalized stance phase data using SPM.

RESULTS

Evidence from traditional statistical tests suggested that VecMag is more influenced by the vertical force and impulse, whereas VecAng is more influenced by the longitudinal force and impulse. When used to evaluate mean data from the group of ten sound horses, SPM did not identify differences between the left and right contralateral limb pairs or between limb pairs classified according to directional asymmetry. When evaluating a single horse, three periods were identified during which differences in the forces between the left and right forelimbs exceeded the critical threshold (p < .01).

DISCUSSION

Traditional statistical analysis of 2D GRF peak values, summary vector variables and visual evaluation of force vector diagrams gave harmonious results and both methods identified the same inter-limb asymmetries. As alpha was more tightly controlled using SPM, significance was only found in the individual horse although T2 plots followed the same trends as discrete analysis for the group.

CONCLUSIONS

The techniques of force vector analysis and SPM hold promise for investigations of sidedness and asymmetry in horses.

Core Training and Rehabilitation in Horses

The central body axis or core is a key component in controlling body posture and providing a stable platform for limb movements and generation of locomotor forces. Persistent dysfunction of the deep stabilizing muscles seems to be common in horses indicating a need for core training exercises to restore normal function. Core training should be performed throughout the horse's athletic career to maintain a healthy back and used therapeutically when back pain is identified. This article reviews the structure and function of the equine thoracolumbar spine with special reference to function, dysfunction, conditioning, and rehabilitation of the core musculature.

Introduction to Equine Physical Therapy and Rehabilitation

Physical therapy (physiotherapy, or PT) can be broadly defined as the restoration of movement and function and includes assessment, treatment, and rehabilitation. This review outlines the history, definition, and regulation of PT, followed by the core scientific principles of PT. Because musculoskeletal physiotherapy is the predominant subdiscipline in equine PT, encompassing poor performance, back pain syndromes, other musculoskeletal disorders, and some neuromuscular disorders, the sciences of functional biomechanics, neuromotor control, and the sensorimotor system in the spine, pelvis, and peripheral joints are reviewed. Equine PT also may involve PT assessment and treatment of riders.

Comparison of cross sectional area and fat infiltration of the epaxial muscles in dogs with and without spinal cord compression

This study investigated the cross sectional area (CSA) and fat infiltration of the epaxial muscles in Dachshunds with compressive spinal cord lesions due to intervertebral disc herniation (IVDH) and in dogs with non-compressive spinal cord lesions with fibrocartilaginous embolism (FCE). The CSA and fat infiltration of the multifidi and longissimus dorsi muscles were determined from T1 weighted magnetic resonance images. Difference in CSA and fat infiltration between the lesion- and non-lesion side in the Dachshunds was assessed using mixed model analysis. Difference in CSA and fat infiltration between Dachshunds and FCE dogs was analysed with independent sample t-tests. There was no difference in CSA or fat infiltration between sides in the Dachshunds. FCE dogs had greater CSA (multifidus P = 0.036, longissimus P < 0.001) and less fat infiltration compared to Dachshunds (longissimus P = 0.017). Duration of neurological deficits, age, body size and conformation are likely to have influenced the difference between the groups.

The interrelationship of lameness, saddle slip and back shape in the general sports horse population

REASONS FOR PERFORMING STUDY

Saddle slip is usually blamed on saddle fit, crooked riders or horse shape, but may reflect hindlimb lameness. There are no studies of the frequency of occurrence of saddle slip and risk factors within a tested sample population of the general sports horse population.

OBJECTIVES

To quantify the frequency of saddle slip and to describe the association with lameness, thoracolumbar shape/symmetry, crooked riders and ill-fitting saddles.

STUDY DESIGN

Nonrandom, cross-sectional survey using convenience sampling.

METHODS

Five hundred and six sports horses in normal work were assessed prospectively. Thoracolumbar shape/symmetry were measured at predetermined sites; the presence of lameness (in hand and/or ridden) and saddle slip was recorded. Descriptive statistics, univariable and multiple logistic regression were performed to assess the relationship between horse-saddle-rider factors and saddle slip.

RESULTS

The frequency of lameness, quadrilaterally reduced cranial phase of the stride or stiff, stilted canter was 45.7%, saddle slip 12.3%, left-right thoracolumbar shape asymmetries ≥ coefficient of variance of 8% (1.2 cm) 0.6%; and 103 of 276 riders (37.3%) sat crookedly. The saddle consistently slipped to one side in 24.4% of horses with hindlimb lameness alone, 45.5% of horses with concurrent hindlimb and forelimb lameness, compared with 5.4% with forelimb lameness, 17.4% with stiff, stilted canter, 20% with quadrilaterally reduced cranial phase of stride and 5.5% nonlame horses. Nineteen horses (30.6%) with saddle slip had no detectable hindlimb lameness; however, 14 had a gait abnormality, particularly in canter. Multivariable analysis revealed that saddle slip was significantly associated with hindlimb lameness and gait abnormalities (odds ratio [OR] = 52.62, 95% confidence interval [CI] 17.3-159.7), a saddle fitted with even contact and uniform flocking (OR = 15.49, 95% CI 1.9-125.5), riders sitting crookedly (OR = 6.32, 95% CI 2.9-13.7), a well-balanced saddle (OR = 3.05, 95% 1.4-6.9) and large back shape ratio at T18 (OR = 1.2, 95% 1.1-1.3).

CONCLUSIONS

Many horses with hindlimb and/or forelimb lameness go unrecognised. Saddle slip may be a sign of hindlimb lameness. Education of the equestrian population to identify lameness and saddle slip is required. The Summary is available in Chinese - see Supporting information.

Muscle fibre type distribution of the thoracolumbar and hindlimb regions of horses: relating fibre type and functional role

BACKGROUND

Although the majority of equine muscles have a mixed fibre type distribution indicative of diverse functional roles, the predominance of a fibre type can indicate the primary function of a muscle. The deep epaxial musculature has an important role in core spinal stability in humans, reflected as a predominantly muscle fibre type (MFT) I or postural fibre type. The fibre type of the deep epaxial musculature has not been determined in horses. The objective of the study was to determine the MFT distribution in selected muscles of thoracolumbar and hindlimb region of horses. This included deep epaxial and hypaxial muscles that were hypothesised to have a postural stabilising role. A second objective was to examine differences in MFT distribution between horses bred for endurance (Arabian) and sprinting (Quarter horse). Muscle biopsy samples were obtained from selected thoracolumbar and hind limb muscles of 5 Quarter horses, 4 Arabians, and 2 Thoroughbreds. The myosin heavy chain distribution was determined by gel electrophoresis. Mann-Whitney rank test was used to compare the proportional MFT and differences between breeds.

RESULTS

Mm. sacrocaudalis dorsalis medialis and diaphragm had the highest proportion of MFT-I. The remaining deep epaxial muscles and the hypaxial muscle m. psoas minor had approximately equal MFT I and II proportions. Mm. psoas major, iliocostalis, longissimus dorsi and the hind limb muscles contained mostly MFT-IIX. The fibre type distribution was similar between Arabians and Quarter horses, although Quarter horses had more MFT-IIX fibres in psoas major (P = 0.02) while Arabians had more MFT-I fibres in m. longissimus dorsi (P = 0.03).

CONCLUSIONS

The fibre type distribution of the deep epaxial muscles, mm psoas minor and diaphragm varied from approximately equal MFT-I and II proportions to predominantly MFT-I suggesting a postural stabilising role possibly important in core spinal stability. In contrast the fibre type proportions of mm psoas major, iliocostalis, longissimus dorsi and the hind limb muscles were mainly MFT-II suggesting a locomotory role. Knowledge of fibre type distribution in such a clinically important area can direct diagnosis, prevention and treatment of muscular or neuromotor dysfunction.