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Keywords:

  • horse;
  • imaging;
  • spinal muscles;
  • multifidus;
  • back pain;
  • atrophy

Summary

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. Conflicts of interest
  9. Manufacturers' addresses
  10. References

Reasons for performing study: The multifidus muscle plays a key role in spinal stabilisation. Multifidus atrophy ipsilateral to the side of osseous pathology has been demonstrated in man and pigs but has not been investigated in horses.

Objectives: To measure cross-sectional area (CSA) left/ right symmetry of equine multifidus ultrasonographically and relate asymmetry of multifidus with osseous spinal pathology in Thoroughbred racehorses. We hypothesised that ipsilateral multifidus CSA would be reduced when osseous pathological changes are present leading to left/right asymmetry in CSA.

Materials and methods: Twenty-two racehorses presented for euthanasia for primary reasons other than back pain were examined clinically. Ultrasonographic images on left/right sides were acquired at 5 thoracolumbosacral levels and CSA's of multifidus or sacrocaudalis dorsalis calculated. At necropsy, osseous pathological of the TL spine and pelvis were recorded by spinal level, anatomical site, and graded (0–3) according to severity. The mean typical measurement error in estimating multifidus/sacrocaudalis dorsalis CSA was used to determine the significance of left/right asymmetries. An association between multifidus CSA asymmetry and asymmetrical grading of pathological lesions was sought using Pearson's χ2 analysis.

Results: All horses had significant left/right asymmetry of multifidus CSA at >2 spinal levels, most commonly at L5 with total of 74 sites affected (22 horses). Seventeen horses had severe (grade 3) pathology, 16 of these had ipsilateral atrophy of multifidus/sacrocaudalis dorsalis. There was a significant association between pathological grade and degree of multifidus asymmetry.

Conclusions: Severe osseous pathological changes were common in this population of Thoroughbred racehorses and were associated with measurable left/right asymmetry in multifidus at or close to the level of pathology.

Potential relevance: Ultrasonography of multifidus may be a useful clinical tool in diagnosis of back problems in horses.


Introduction

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. Conflicts of interest
  9. Manufacturers' addresses
  10. References

Back pain is a common problem in the performance horse. Jeffcott (1980) reported that the prevalence of back pain varied according to the type of practice: 0.9% in general veterinary practice, 13% in mixed equine practice and 47% in spinal research clinics. This is in comparison to an equine chiropractic clinic whereby 94% of cases were reported to have back dysfunction/pain (Haussler 1999a). In a survey of 11,363 registered dressage horse owners in the UK, 40% reported that their horse had a ‘back problem’ although the majority of these (80%) had not been diagnosed by a veterinary surgeon (Murray et al. 2009). Thoroughbred racehorse trainers in Sydney, Australia reported back problems to be in the top quartile of ranked conditions and one of the most common injuries preventing training and racing (Bailey et al. 1997).

The relationship between pain, pathology and spinal function has not been established in horses. Equine back pain may result from a wide variety of pathological processes. Jeffcott (1980) reviewed 443 cases identifying the major pathological lesions associated with thoracolumbar (TL) pain as: vertebral lesions 39%, soft tissue injuries 25%, sacroiliac strain 13% and nonTL lesions 13%. In the literature, the most commonly reported vertebral lesions are impingement or overriding of the dorsal spinous processes (DSPs) (Jeffcott 1979, 1980; Townsend et al. 1986; Haussler 1999b). Degenerative changes have also been reported in TL synovial intervertebral articulations (facet joints), inter-transverse joints and sacroiliac articulations (Haussler et al. 1999; Girodroux et al. 2009; Cousty et al. 2010), along with stress fractures of the vertebral lamina and pelvis in Thoroughbred racehorses (Haussler and Stover 1998). Soft tissue lesions have been reported to mainly affect the longissimus dorsi muscles and supraspinous ligament in the caudal withers and cranial lumbar regions (Jeffcott 1979, 1980; Valberg 1999; Quiroz-Rothe et al. 2002; Henson et al. 2007).

The predominant sign of back pain in horses is loss of performance (Jeffcott 1980, 1999; Jeffcott et al. 1982; Denoix 1998, 1999; Haussler 1999a; Peham et al. 2001). The insidious nature of the back pain syndrome makes it a difficult condition to diagnose. Presenting signs vary from overt lameness or pain responses on palpation of the back, to subtle gait alterations or behavioural changes (Denoix and Dyson 2003). There is a strong association between lameness and back problems (Landman et al. 2004) which may pose a diagnostic challenge. Due to variability in presenting signs and altered kinematics of the back and limbs as a result of back pain and or lameness (Gomez-Alvarez et al. 2007a,b, 2008) back pain may be underdiagnosed.

Pathoanatomical diagnosis is complicated by the complex anatomy of the area, the inherent difficulties in using diagnostic equipment in the equine vertebral column and the need to use a variety of ancillary aids, including invasive techniques such as infiltration of local anaesthetic to confirm the clinical problem (Jeffcott 1980; Jeffcott et al. 1982; Denoix 1998, 1999; Gellman 1998; Holm et al. 2006). Horses suspected of having back pain are often treated on the basis of clinical examination only, with the treatment response being used to determine the need for further investigations, such as ultrasonography, radiography, scintigraphy and thermography (Munroe 2009). As in man, pathoanatomical diagnosis in horses may be complicated by the high prevalence of pathological changes (Jeffcott 1980; Haussler 1999b; Girodroux et al. 2009). Determining the significance in terms of pain and dysfunction may be the more important diagnostic approach and this is achieved in human medicine by examination of the multifidus muscle (Hides et al. 2008).

The multifidi provide intersegmental stabilisation and stiffen the spine, contributing two-thirds of the total increase in spinal stiffness imparted by muscular action (Wilke et al. 1995). In vivo studies in pigs confirmed that the multifidi are also a major stabiliser of the quadrupedal lumbar spine (Kaigle et al. 1995). In human back pain patients, multifidus is reduced in cross-sectional area (CSA) on the ipsilateral side and at the same intervertebral level where pathology is present (Hides et al. 1994). In a recent study the density of multifidus/erector spinae was associated with facet joint osteoarthritis, spondylolisthesis and disc narrowing (Kalichman et al. 2009). This also occurs within 3 days after a unilateral experimental lesion to an intervertebral disc in pigs (Hodges et al. 2006). Further, multifidus does not automatically resume its normal function following recovery from or resolution of an episode of acute back pain (Hides et al. 1996). Specific physiotherapeutic interventions are required to restore the size and function of multifidus after an episode of acute back pain in people and these interventions reduce the rate of recurrence of injury from 84% in untreated controls to 30% (Hides et al. 2001). In horses, generalised secondary atrophy of the epaxial muscles, especially longissimus dorsi and gluteus medius have been reported in horses with back pain (Jeffcott et al. 1982; Quiroz-Rothe et al. 2002) although changes in multifidus have not been reported.

In the field of human physiotherapeutic rehabilitation, ultrasonography has emerged as an invaluable tool for objective assessment and management of low back and pelvic girdle pain and dysfunction (Jull and Richardson 2000; Pietrek et al. 2000; Richardson et al. 2002; Hodges and Cholewicki 2007; Whittaker et al. 2007). Ultrasonographic measurements of multifidus CSA and function has proven to be a reliable, objective guide in the assessment, management and prevention of recurrence of back pain in man (Hides et al. 2008). Several measurements of muscle size provide a method of direct assessment of muscle function by indicating whether the muscle is of normal size, atrophied or hypertrophied, which is very important in rehabilitation for monitoring effectiveness of treatment over time (Rantanen et al. 1993; Stokes et al. 2005; Whittaker et al. 2007). Ultrasonography is used extensively in equine veterinary practice and many practitioners already have an ultrasound machine. The objective of this study was to investigate whether atrophy or asymmetry of multifidus occurs in association with pathological changes in the equine thoracolumbosacral spine. This study is based on the hypothesis that the human physiotherapeutic approach to back pain can be applied to the horse and that the use of ultrasonography to measure epaxial muscle size, especially multifidus, will be valuable in developing assessment tools and management strategies in horses suffering from back syndromes. The experimental hypothesis was that severe osseous pathological changes identified at necropsy in the thoracolumbosacral spine are associated with reduced multifidus CSA on the ipsilateral side at the same intervertebral level.

Materials and methods

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. Conflicts of interest
  9. Manufacturers' addresses
  10. References

The study was approved by the Animal Experiments Ethics Committee, Faculty of Medicine, Chinese University of Hong Kong and covered by license DH/ORIH/8/2/8/Pt.2 issued by the Department of Health, the Government of the Hong Kong SAR.

Subjects

Twenty-two Thoroughbred racehorses (mass: 493.2 ± 25.5 kg; age 6.2 ± 1.9 years; height 164.8 ± 3.7 cm) from the HKJC presented for euthanasia for primary reasons other than back pain were recruited. Retrospective clinical history was obtained from clinical case files to determine whether the horse had any prior history of back pain and or had been treated by a veterinarian, chiropractor and/or physiotherapist for back pain/spinal dysfunction.

Ultrasonographic evaluation

Ultrasonographic images of the left and right multifidus muscles were acquired at 4 TL locations (T13, L1, L3, L5) and of the sacrocaudalis dorsalis (SCD) muscles, the caudal continuation of multifidus, at the level of the third sacral vertebra (S3) (Fig 1). Ultrasonographic examination1 was performed with the horses lightly sedated and standing in stocks using standard skin preparation methods and different curvilinear probes (5–10 MHz) dependant on the depth of penetration required. Three ultrasonographic images were acquired at each level on the left and right sides and were stored using the software on the ultrasound machine. Image analysis to measure multifidus/SCD CSA was performed 3 times for each image using proprietary software2.

image

Figure 1. Ultrasound images of multifidus (M), sacrocaudalis dorsalis medialis (SM) and sacrocaudalis dorsalis lateralis (SL) muscles at the levels of (left to right) the 13th thoracic vertebra (T13), the 1st and 5th lumbar vertebra (L1, L5) and the 3rd sacral vertebra (S3). The vertebral spinous process (SP) is seen forming the medial border of these muscles. Longissimus dorsi (L) lies on the lateral side in the thoracolumbar region and biceps femoris (B) is on the lateral side at S3. The ventral border at T13 is the costovertebral joint (CVJ), at L5 the transverse process (TP) and at S3 the lateral sacral crest (LS). The middle gluteal (MG) and iliocostalis (I) muscles are also shown.

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Pathological evaluation

A full necropsy was performed. Gross soft tissue lesions of muscle, ligament and fascia were noted and photographed. The thoracolumbar spine and sacropelvis were removed intact. The soft tissues were removed by gross dissection then a steel rod was passed through the spinal canal and fixed at both ends to maintain vertebral alignment. The spine was boiled to remove all remaining soft tissues and was stored until examination for evidence of gross bone pathology by one of the investigators (NCS) who was blinded to the identity using a coding system.

When pathological changes were found the following data were recorded: TL level of the lesion, side of occurrence (left, right, bilateral) and the anatomical site. The sites were classified as vertebral body or end plate; facet joint or articular process; dorsal spinous process or lumbar transverse process; lumbosacral complex (intertransverse joints, lumbosacral joint) and sacroiliac complex (CSA of the sacroiliac joint and presence of degenerative joint disease of the sacral and iliac joint surfaces). The following pathological abnormalities were sought: fractures; spondylosis; evidence of lysis and/or periosteal new bone formation (determined by the presence of an irregular cavity in or irregular, porous bone on the periosteal surface of the bone); or other lesions. Each lesion was graded according to severity on a scale of 0–3 in noncumulative fashion; 0: no pathological changes; 1: mild changes; 2: moderate changes and 3: severe changes (Stecher 1962; Jeffcott 1980; Townsend et al. 1986; Haussler et al. 1999). Active new bone formation was considered a major finding and was required in order to grade a lesion as severe.

Statistical analysis

To calculate symmetry/asymmetry between left vs. right multifidus/SCD CSA the mean typical measurement error was established for each spinal level based on 3 measures at that level and side for each horse. The minimal detectable difference outside of the measurement error was established using coefficients of variation (CV) of 4, 8 and 12% (95% CI) for each level across all horses (Hopkins 2000). Pearson's Chi-squared analysis was used to determine whether there was an association between the presence of significant left/right asymmetry of multifidus/SCD CSA at a specific spinal level and the presence of asymmetrical osseous pathology grades at that level within individual horses. Pearson's Chi-squared analysis was also used to determine if there was an association between pathological grade (1–3) and spinal asymmetry of multifidus/SCD CSA at each spinal level to determine if left/right asymmetry in multifidus/SCD CSA was associated with left/right asymmetry of pathological grade at the same level and to determine whether a significant reduction in multifidus/SCD CSA was associated with a higher asymmetrical grade of pathology on the same side and at the same level within an individual horse.

Results

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. Conflicts of interest
  9. Manufacturers' addresses
  10. References

Pathology

Osseous pathology was found at all spinal levels examined (84) and all horses had mild or moderate changes at each level with at least one lesion that was grade 2 or greater. Evidence of severe (grade 3) spinal pathology was found in 17/22 horses (77%). All horses had at least one osseous lesion of grade 1 or higher at each spinal level (T13, L1, L3, L5, S3), comprising 36 levels with grade 1 lesions, 47 levels with grade 2 lesions, and 33 levels with grade 3 lesions (Table 1). At T13 there was a higher prevalence of grade 1 lesions (16/22 horses), with L5 having the greatest number of grade 3 osseous pathological lesions (12/22).

Table 1. Pathological grades of osseous lesions for the 5 spinal levels at which ultrasonographic images of multifidus or sacrocaudalis dorsalis were evaluated
LevelGrade 1Grade 2Grade 3Total
T13165122
L178722
L3612422
L5371222
S3313622
Total354530110

While none of the horses was subjected to euthanasia as a direct result of back pain, 15 horses (68%) had a prior history of back pain previously treated by veterinarians, chiropractors and/or physiotherapists. Within this group, 12 (80%) had a grade 3 spinal lesion. Of the 7 horses without any specific history of back pain 6/7 (86%) had a grade 3 lesion. A complete clinical examination was able to be performed in 20/22 horses, 18 showed clinical signs of TL-pelvic back pain just prior to euthanasia. Not all ultrasonographic CSA images could be analysed at some levels due to poor image quality.

The mean typical measurement error was established for each level across all horses resulting in minimal detectable difference in multifidus/SCD CSA between the left and right sides of 0.6 cm2 for CV 4%; 1.2 cm2 for CV 8% and 1.8 cm2 for CV 12%. Table 2 shows the number of horses with significant left/right differences in multifidus/SCD CSA at each level using CVs of 4, 8 or 12%. For comparison with pathological changes a CV 4% (0.6 cm2) was used to determine left/right asymmetry.

Table 2. Number of horses showing left/right asymmetry of multifidus or sacrocaudalis dorsalis at 5 spinal levels based on 4, 8 and 12% coefficients of variation (CV) and the total number of horses with ultrasound scans of these muscles at each level
 T13L1L3L5S3Total
CV 4% (0.6 cm2)981118955
CV 8% (1.2 cm2)46713636
CV 12% (1.8 cm2)12511423
Number of horses with images121914221885

Association between osseous pathology and muscle asymmetry

Analysis of the relationship between osseous pathology grades and the presence of asymmetries in ultrasonographic CSA are shown in Figure 2 with grade 1 osseous lesions associated with asymmetrical multifidus/SCD CSA at 12/24 sites; grade 2 24/31 sites; and grade 3 at 18/26 sites. When the maximum pathological grade was calculated for each level examined, there was no significant association between the grade of pathology and symmetry/asymmetry of multifidus or SCD CSA; however, there was a trend at L1: P = 0.06. Of the 84 levels examined 55 were symmetrical left-right within grade of multiple osseous pathologies; 27 had symmetrical left/right multifidus CSA and 28 asymmetrical, there was no significance between the groups (P = 0.82). However, 29 spinal levels showed left/right asymmetry in the pathological grade and this was significantly associated with left/right asymmetry in multifidus CSA (P = 0.04). Twenty levels showed left/right asymmetries in both multifidus/SCD CSA and pathological grade. Asymmetry in multifidus/SCD CSA had a significant association with the occurrence of grade 3 pathological lesions but not with grade 1 or grade 2 lesions. When asymmetrical pathological lesions of grades 1 and 2 were combined, there was a trend (P = 0.07) toward an association with asymmetry in multifidus/SCD CSA.

image

Figure 2. Scatterplot showing the relationship between osseous pathological grades and the presence of asymmetries in ultrasonographic CSA of multifidus or sacrocaudalis dorsalis. Osseous lesions were associated with asymmetrical multifidus or sacrocaudalis dorsalis CSA at 12/24 sites for grade 1 lesions; 24/31 sites for grade 2 lesions; and 18/26 sites for grade 3 lesions. The graph plots horse on the x-axis and spinal level on the y-axis. Triangles represent no significant left-right difference in ultrasound CSA (CV 4%: 0.6 cm). Squares represent significant left-right difference in ultrasound CSA (CV 4%: 0.6 cm).White fill represents grade 1 osseous lesions, grey fill represents grade 2, black fill grade 3.

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When the pathology was asymmetrical, the side with the higher pathological grade corresponded with the smaller multifidus/SCD CSA at 18/20 levels and this relationship was highly significant (P = 0.0003) (Table 3). Figure 3 is an example at L5 where the right osseous pathology (facet and neural arch fracture, with incomplete vertebral body spondylosis) matches the right reduction in CSA (left mean CSA 15.07 cm2 s.d. 0.21; right mean CSA 11.21 cm2 s.d. 0.24; absolute difference: 3.86 cm2). This is a very large left/right difference, significant even when using 12% CV (1.8 cm2) limits.

Table 3. Horses and levels that had left-right asymmetries of both osseous pathology grade and ultrasonographic (US) multifidus cross sectional area (CSA) based on a 4% coefficient of variation (CV: 95% CI)
HorseOsseous pathologyUltrasound asymmetryLevelOsseous pathology
Max gradeLeft gradeRight gradeAbs diffRatioMatchMax/level
  1. For the US multifidus CSA, the difference is calculated by subtracting right CSA from left. The ratio is the difference between left and right CSA divided by the larger (left or right) CSA. Match indicates whether the side with maximal pathology grade matches with the side with smaller multifidus CSA. The osseous pathology does not include central lesions if the grade was lower than that for the unilateral pathology. R. right; L. left; US: ultrasound; SID: sacroiliac disease; VB: vertebral body; TP: transverse process; IT: intertransverse joint; #: fracture; TC: tuber coxae; OA: osteoarthritis.

191011.131.11YesS3R. SID
102120.901.08YesL1R. VB marginal osteophytes
103131.971.17YesL5R. Active facet ankylosis, old facet #. Note: DSP and TP fused smooth ankylosis, ventral VB bone spurs and osteophytes
143133.861.34YesL5R. Facet and neural arch #. Note: L5.6. incomplete ankylosis, VB spondylosis (osteophytes, ventral lipping)
173131.471.29YesL1R. Facet OA, large periarticular osteophytes visible on US
183131.141.09YesS3R. SID Note: R. TC # one month prior, acute L TC #
5220−1.820.86YesS3L. SID
10221−0.681.07YesS3L. SID
203230.131.01YesS3R. SID
223230.651.05YesS3R. SID, joint completely destroyed, chronic ilial #
9332−0.860.93YesL1L. Facet severe cleft # with obvious proliferation in the neural canal
9332−2.510.80YesL3L. Facet cleft #
123233.001.29YesL3R. TP active ankylosis
15331−1.720.86YesL5L. IT active incomplete ankylosis. Note: R. IT smooth ankylosis; VB grade 3 eburnation and proliferation
17332−1.450.81YesL3L. Facet cleft #
19332−0.900.91YesL3L. Facet cleft #: Note OA IT
21131−3.500.75YesL5L. Facet cleft #
22332−1.750.86YesL5L. Complete facet # Note: L6 facet cleft #; unable to assess joint as ankylosed TP; old # R L5 TP smooth ankylosis
72211.201.11NoL5L. Facet OA Note: severe R. L3/4 facet #, R. TP almost complete smooth ankylosis
83320.631.06NoL5L. IT and LS OA Note: Grade2. L/R. facets clefts OA
image

Figure 3. Left and right ultrasound images of multifidus (M) cross-sectional area (CSA) at the 5th lumbar vertebra in Horse 14. The right osseous pathology (facet and neural arch fracture, with incomplete vertebral body spondylosis) matches the right reduction in CSA (left mean CSA 15.07 cm2s.d. 0.21; right mean CSA 11.21 cm2s.d. 0.24; absolute difference: 3.86 cm2.

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Discussion

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. Conflicts of interest
  9. Manufacturers' addresses
  10. References

Left/right asymmetry of osseous pathological lesion grade was associated with asymmetrical multifidus/SCD CSA at the same spinal level, with the side having the higher grade of pathology corresponding with the smaller multifidus/SCD CSA. Further, this asymmetry was associated with severe lesions showing active bone remodelling as opposed to other lesions of a lower severity (grades 1 and 2). Across all levels examined for pathology the prevalence of severe pathology was very high (80%) and all horses in the study had moderate or mild changes. While this finding is in agreement with the high prevalence of pathological lesions in Thoroughbred horses examined following catastrophic racecourse injuries (Haussler and Stover 1998; Haussler et al. 1999), it has not been possible to determine which lesions are painful or performance-limiting and which lesions are incidental or benign. In this study, the combination of severe pathology and multifidus/SCD atrophy or asymmetry strongly suggests that the lesions are clinically significant, although further work is required to investigate the relationship with pain. Ultrasonography is a noninvasive tool potentially able to differentiate active from the highly prevalent incidental osseous changes in the equine spine.

The prevalence of a prior history of back pain was also high considering the age (mean 6 years) and previous prevalence estimates, but is in agreement with figures reported for specialist back or chiropractic practice (Haussler 1999a). These findings highlight the importance of back pathologies and back pain in the racing population.

In the current study, the extremely high prevalence of multiple grades and types of pathology across all spinal levels was problematic for the analysis of asymmetry data due to the multiple variables affecting multifidus CSA. None of the levels examined ultrasonographically received grade 0 for osseous pathology on both left and right sides at that level or at the next level. At many levels, pathology was bilateral or on the midline (facet joint osteoarthritis, DSP impingement, degenerative disc disease, vertebral spondylosis, sacroiliac disease). It is uncertain whether these osseous pathologies cause bilateral atrophy of multifidus and SCD complex. It is also only possible to compare left-right symmetry at the same level in each horse because CSA along the length of the vertebral column varies within and between horses (McGowan et al. 2007).

Despite these concerns, across the 22 horses examined, 55 levels had significant left/right multifidus/SCD CSA asymmetry. This type of asymmetry was not present in young horses (unbroken Australian stock horses and Thoroughbreds in prerace training), and is less prevalent in mature Standardbreds and other aged horses that are not ex-racehorses (McGowan et al. 2007). These findings further support that asymmetry of multifidus/SCD measured ultrasonographically may be an important diagnostic indicator of severe osseous pathology in horses and warrants further investigation in different populations of horses.

While the multifidi have a key role in the stability of the lumbar spine in man (Moseley et al. 2002), it is the role of the mutifidi proprioceptive and preparatory function (neuromotor control) of the spine that is important in preventing unwanted vertebral motion and the occurrence or recurrence of back pain in man (reviewed in Hodges and Cholewicki 2007). In horses multifidus has similar muscular anatomy and structure and is thought to play a similar role in stabilising the spine (Stubbs et al. 2006). Similarly, the innervation of the multifidus in horses is similar to man, further supporting the similar role this muscle plays in the equine spine (Vandeweerd et al. 2007). Each lumbar articular facet and multifidus is innervated by the medial branches of the dorsal rami of the spinal nerves at the same level and one level cranially. Since the fascicles of multifidus from each spinal level cross between 1 and 4 intervertebral joints, an osseous pathological lesion can potentially affect the CSA up to 4 levels further caudally. However, this effect at 4 levels caudally may be insignificant due to only one fascicle crossing this level that originated at the level of the pathology (Stubbs et al. 2006). This important neuromotor control role of the multifidi probably explains why this group of muscles demonstrate atrophy most closely correlated with back pain syndromes in people (Hides et al. 2008). Ultrasonography is relatively inexpensive, portable, easy to use and enables rapid analysis by an experienced practitioner. Both objective and subjective scales of measurement are used (Genovese et al. 1997; Reef 1998; Pickersgill et al. 2001). These include comparison of contralateral tissues and determination of echogenicity using grey scale analysis and predetermined ordinal scales (Gillis et al. 1993; Martinoli et al. 1993; Tsukiyama et al. 2005). However, several inherent difficulties associated with the image acquisition and analysis process for measuring size of multifidus were highlighted in this study. At some levels poor image quality either during the acquisition and/or image analysis processes precluded analysis. However, in all 22 horses, multifidus CSA could be measured at L5 which is of particular interest as this is the region of maximal dorsoventral motion in the horse's TL spine (Townsend et al. 1983). It was also the site where the greatest number of grade 3 lesions occurred. In some cases, artifacts were due to pathology, such as excessive bony proliferation of the dorsal spinous process and/or interspinous ligament attachment, or a change in spinous process morphology with increased mediolateral angulation of the spinous process which was frequently associated with overriding dorsal spinous processes at that level. Another source of artifact was the presence of adipose tissue along the lateral border of the spinous process and within the deeper fascicles of multifidus at the level of the pathology and associated with reduced multifidus CSA. The ability of newer ultrasound machines to identify fat will facilitate identification of these changes in the future.

In 2 horses the side of significantly reduced CSA did not match the side of the higher pathological grade, both at L4/L5, where the higher grade of pathology was on the left side (grade 2). The transverse processes of L4/L5 on the left side were undergoing active ankylosis and the intertransverse joint on the right was already ankylosed with smooth bone (grade 1). In addition, there was a mild degree of overriding of the dorsal spinous processes (grade 1). However, there was also a severe fracture of the facet joint at L3/L4 on the same side as the reduced multifidus CSA. As previously stated, multifidus crosses between 1 and 4 intervertebral discs (Stubbs et al. 2006), thus the L3/L4 facet fracture may account for the multifidus atrophy more caudally on that side. The other horse in which the pathological grade did not match the ultrasonographic asymmetry also had a grade 3 lesion on the left and a grade 2 lesion on the right. Bilateral L4/L5 facet degenerative joint disease was evident (grade 2) with moderate periarticular osteophytes and moderate asymmetry in the size of the facet joint/articular pillar, the right one being larger than the left, and this may have been the source of the multifidus asymmetry. However, the left side was graded higher due to the presence of marked intra-articular bone erosions of the inter-transverse joints (grade 3 left, grade 2 right). It is also uncertain whether these types of pathology result in atrophy of multifidus/SCD in the lumbosacral region as ultrasonographic CSA evaluation is not possible between L6–S2 due to the position of the ilium.

The lesions most commonly associated with both severe changes and multifidus asymmetry were stress fractures of the facet joints and/or associated degenerative joint disease. Pelvic fractures, sacroiliac dysfunction and lumbosacral degenerative joint disease were less common. Only one horse had overriding dorsal spinous processes as the primary finding and this horse had no asymmetry of its multifidus or history of back pain. Facet joint pathology was detected on the ultrasound images in many cases using the same technique as for the CSA of multifidus and represents an area where pathology may be directly imaged in affected horses. This is consistent with recent practice trends demonstrating the value of musculoskeletal system ultrasonography of the back (Denoix 1999; Lamas and Head 2009).

This study indicates a clear association between osseous pathological findings at necropsy and objective ultrasonographic measurements showing atrophy and asymmetry of multifidus CSA at the same level and on the same side of the spine. It is concluded that ultrasonography of the epaxial muscles is a promising noninvasive tool for detecting spine pathology, likely to be associated with back pain in horses and for monitoring the response to treatment. The fact that atrophy of multifidus persisted in association with chronic pathological lesions suggests that in horses, as in man, there is a potential need for physiotherapeutic strategies for strengthening and recruiting this muscle during treatment and rehabilitation.

Acknowledgements

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. Conflicts of interest
  9. Manufacturers' addresses
  10. References

The authors appreciate the cooperation of the Hong Kong Jockey Club, particularly colleagues in the Department of Veterinary Clinical Services, without which this study would not have been possible. P.H. is supported by a fellowship from the National Health and Medical Research Council of Australia.

References

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. Conflicts of interest
  9. Manufacturers' addresses
  10. References
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  • Cousty, M., Retureau, C., Tricaud, C., Geffroy, O. and Caure, S. (2010) Location of radiological lesions of the thoracolumbar column in French trotters with and without signs of back pain. Vet. Rec. 166, 41-45.
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