The sacroiliac joints: evaluation using nuclear scintigraphy. Part 2: Lame horses

Review of the clinical diagnosis of sacroiliac dysfunction in horses - Challenges and limitations

Sacroiliac dysfunction (SID) is a condition seen in horses associated with poor performance that affects hind limb gait and impulsion. The condition comprises pain and dysfunction but there lacks clarity around the aetiopathogenesis and whether SID encompasses abnormal joint pathology, abnormal joint movement, abnormal regional biomechanical function, joint laxity and pain, or various combinations of these that may vary over time. Clinical assessment remains challenging for equine clinicians due to the deep location of the sacroiliac joint (SIJ) and surrounding structures which limits access for palpation, diagnostic imaging and joint-specific injection. There is no recognised single reference standard diagnostic test for SID. Clinical diagnosis has been based on ruling out other causes of hind limb lameness, along with combinations of ultrasonography, scintigraphy and periarticular anaesthesia of the SIJ. Recent studies have highlighted the lack of specificity of injections targeting the SIJ, with significant dispersal of injectate into surrounding structures including around the lumbosacral joint (LSJ). Advanced imaging modalities such as computed tomography offers promise for assessment of the structure and pathology of the SIJ and surrounding bony structures. However, there is a need to improve the understanding of the significance of anatomic variation of the sacroiliac region structures, with recent studies reporting detailed anatomic variation in groups of horses with and without SID. There are also limitations around functional assessment of the joint which is still largely reliant on a thorough clinical examination. This review aims to present an update on clinical approaches to the diagnosis of horses with SID, and to consider the challenges and limitations.

Retrospective analysis of horses with ultrasound evaluation of the sacroiliac region and response to local corticosteroid injection: 42 cases

Local injection of corticosteroids is commonly performed in horses with sacroiliac (SI) region pain and/or dysfunction, ,and ultrasound findings of normal horses and those with SI pain have also been well described. However, no studies have been performed that have evaluated if ultrasound findings, injection technique, or medications injected affect prognosis for return to function. The objectives of the current study are to determine if findings on ultrasound, injection technique, or medications injected are predictive of return to function in horses with SI region pain and/or dysfunction. Medical records were evaluated for horses that had ultrasound exam of the SI region as well as local injection with corticosteroids. A client survey was sent to determine the horse's return to performance. Logistic regression was performed to determine which variables were predictive of horses with SI pain and/or dysfunction returning to performance. A return to the same or higher level of work was found in 26 of 42 (62%) of horses after SI injections, 4 of 42 (10%) of horses returned to a lower level of work, and 12 of 42 (28%) did not return to work at any level. Horses that were injected with methylprednisolone were 4.2 times more likely to return to performance than horses injected with triamcinolone. Factors evaluated on ultrasound of the SI region did not predict whether a horse would return to performance following SI region injection.

Complications following equine sacroiliac region analgesia are uncommon: A study in 118 horses

Background

Diagnosis of sacroiliac region pain is supported by a positive response to sacroiliac region analgesia (SIRA). Varying techniques have been described for SIRA; with clinician preference often dictating method. Potential complications following SIRA include ataxia and recumbency. No study has specifically evaluated the prevalence of complications.

Objectives

To describe the complication prevalence following SIRA in a referral clinic.

Study design

Retrospective cohort study.

Methods

Review of records from horses presented to two of the authors at Rossdales, Newmarket, between January 2014 and December 2018, that underwent SIRA. Injection was performed using a blind midline approach with 20 mL mepivacaine (Intra-Epicaine 20mg/ml; Dechra) infiltrated through a straight 18 gauge 8.9cm spinal needle subdivided into four sub-locations per block.

Results

118 horses were included, with 167 individual blocks. One horse showed a mild hindlimb gait abnormality following SIRA, which resolved uneventfully over 3 hours; complication rate 1/118 horses (0.85%; 95% CI: 0,2.5%), 1/167 joints (0.60%; 95% CI: 0,1.8%). SIRA subjectively improved lameness/performance in 132/167 (79%) joints. 49/118 (42%) received bilateral SIRA with 53/118 (45%) evaluated ridden following SIRA.

Main limitations

Small population numbers with low complication prevalence rate.

Conclusions

SIRA, using the described technique, has a low (0.85%) prevalence of complications.

Iliac auricular surface morphofunctional study in felidae

Felids show remarkable phenotypic similarities and are conservative in behavioral and ecological traits. In contrast, they display a large range in body mass from around 1kg to more than 300kg. Body size and locomotory specializations correlate to skull, limb and vertebral skeleton morphology. With an increase in body mass, felids prey selection switches from small to large, from using a rapid skull or spine lethal bite for small prey, to sustained suffocating bite for large prey. Dietary specialization correlates to skull and front limbs morphology but no correlation was found on the spine or on the hind limb. The morphology of the sacroiliac junction in relation to ecological factors remained to be described. We are presenting a study of the overall shape of the iliac auricular surface with qualitative and quantitative analyses of its morphology. Our results demonstrate that body mass, prey selection, and bite type, crucially influence the auricular surface, where no significant effect of locomotor specialization was found. The outline of the surface is significantly more elevated dorso-caudally and the joint surface shows an irregular W-shape topography in big cats whereas the surface in small cats is smoother with a C-shape topography and less of an elevated ridge. Biomechanically, we suggest that a complex auricular surface increases joint stiffness and provides more support in heavier cats, an advantage for subduing big prey successfully during a sustained bite.

Muscle glycogen concentrations and response to diet and exercise regimes in Warmblood horses with type 2 Polysaccharide Storage Myopathy

Type 1 polysaccharide storage myopathy (PSSM1) is a glycogen storage disorder of known cause whereas the basis for type 2 PSSM (PSSM2) is unknown. The same diet and exercise regime prescribed for PSSM1 is recommended for PSSM2; however, the benefit of these recommendations for PSSM2 is undocumented. The objectives of this study were to determine traits of PSSM2 Warmblood horses (WB), determine the changes in exercise responses that occur with a recommended low-starch/fat-supplemented diet and exercise regime, and determine if glycogen concentrations correspond to the severity of signs. Owners of PSSM2 WB (2008-2016), completed a retrospective questionnaire regarding their horse. Glycogen concentrations were analyzed in skeletal muscle of PSSM2 WB (n = 36) obtained prior to recommendations and in control WB with no evident myopathy (n = 23). Chi-square, Fisher's exact, McNemar's tests with Bonferroni correction and Mann Whitney testing were utilized. Abnormal exercise responses reported by owners, began at approximately 6 years of age and included a decline in performance, a reluctance to collect and reluctance to go forward in over 50% of horses. With the recommended diet and exercise regime, 80% of PSSM2 WB owners reported an overall improvement with significant decreases in the proportion of horses showing a decline in performance and rhabdomyolysis. However, 53% of PSSM2 WB were still not advancing as expected with reluctance to go forward and collect persisting in approximately one third of horses. Median muscle glycogen concentrations did not differ between PSSM2 WB and WB with no evident myopathy. PSSM2 WB with the highest glycogen concentrations were significantly more likely to show a decline in performance than those with lower glycogen concentrations. In conclusion, diet and exercise recommendations ideal for PSSM1 improve but do not eliminate the decline in performance and reluctance to go forward under saddle characteristic of PSSM2.

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.

ABNORMAL IMAGING FINDINGS OF THE FEMORAL THIRD TROCHANTER IN 20 HORSES

Injuries involving the femoral third trochanter are an uncommon but important source of equine lameness; however, clinical localization can be challenging. The purpose of this retrospective study was to describe ultrasonographic and scintigraphic findings in a group of horses with presumed third trochanter injury. Medical records of an equine referral hospital were searched from 2004-2014, and 20 horses met the inclusion criteria. Lesions consistent with third trochanter fracture were identified with ultrasound in 14/20 horses. Onset of lameness was acute (11), insidious (2), or unknown (1). All but one horse was lame at presentation, ranging from Grade 2-4/5. Ultrasound was the primary diagnostic modality in 5/14 horses with fragmentation, while scintigraphic findings of intense (3), moderate (5), and mild (1) increased radiopharmaceutical uptake (IRU) prompted ultrasonographic examinations in 9/14 fractured horses. A nondisplaced fracture was suspected in an additional horse with intense IRU and negative ultrasound findings. In the remaining five horses, imaging findings included only mild IRU. Lameness was localized to other regions in these cases. Six of 12 fractured horses with available outcome data were returned to function after a prolonged rehabilitation of 8-18 months. Scintigraphic findings helped to direct focused ultrasound exams in the majority of fracture cases. Horses with evidence of third trochanter fracture had similar clinical characteristics to that reported for pelvic fractures and authors therefore recommend ultrasonographic examination of both regions, especially when scintigraphy is unavailable. Prognosis for return to function in horses of the current study was less favorable than previously reported.

Pressure algometry to quantify muscle pain in racehorses with suspected sacroiliac dysfunction

REASONS FOR PERFORMING STUDY

Despite the prevalence of orthopaedic injuries to horses, there is no objective means of quantifying the intensity of musculoskeletal pain.

HYPOTHESES

Mechanical nociceptive thresholds (MNT) can be measured repeatably by pressure algometry in horses and MNTs are correlated with both severity of clinical signs and subjective scores of muscle pain on palpation in horses with suspected sacroiliac dysfunction (SID).

METHODS

The technique of pressure algometry and its repeatability was tested at 4 anatomical sites on either side of the thoracolumbar and pelvic region in 12 Thoroughbreds in training. In a second series of 15 racing Thoroughbreds, using a different set of landmarks, pain on palpation was assessed by pressure algometry. Horses were grouped based on clinical scores of SID as normal (n = 5), mild (n = 5), moderate (n = 4) and severe (n = 1) suspected SID and scored for muscle pain response by manual palpation.

RESULTS

Pressure algometry was shown to be a repeatable measure of MNTs. Horses with suspected SID had significantly lower mean MNT when sites and horses were pooled and showed greater differences in mean algometer measurements between left and right sides, compared to control horses. A significant correlation was found between mean pressure algometry measurements and both suspected SID grade and muscle pain response on palpation.

CONCLUSION AND POTENTIAL RELEVANCE

Horses with suspected SID displayed lower MNTs compared to control horses, especially in the pelvic region. This supports a potential role for pressure algometry in providing an objective means of quantifying musculoskeletal pain reflected as a reduced MNT associated with SID and its response to physiotherapy or other treatments.

Ultrasonographic examination of the equine sacroiliac region

REASONS FOR PERFORMING STUDY

Little information exists about the normal ultrasonographic appearance of the equine sacroiliac region, but knowledge of the ultrasonographic anatomy is necessary to understand the possible pathological changes in sacroiliac diseases.

OBJECTIVES

The normal ultrasonographic appearance of soft tissues and bony structures of the sacroiliac region in horses was studied in order to establish clinically relevant reference parameters.

METHODS

Thirteen cadaver specimens were examined using a transcutaneous approach above the tubera sacrale to image the dorsal sacroiliac ligament and the tendon of the longissimus dorsi muscle. A rectal approach was used to outline the sacroiliac joint and its adjacent structures. Thirteen sound horses with no history of back pain were examined following the same protocol as for the post mortem examinations.

RESULTS

The tendon of the longissimus dorsi muscle can clearly be distinguished from the dorsal sacroiliac ligament, especially in longitudinal images. Transrectal examination of the sacroiliac joint consists of evaluation of the bony surfaces of the sacrum and ilium in comparison with the contralateral side.

CONCLUSIONS

Ultrasonographic examination of the sacroiliac region provided clear images of the caudomedial border of the sacroiliac joint and its adjacent structures and is a useful aid in the diagnosis of sacroiliac joint diseases and adjacent lesions. The study has shown ultrasonography to be a useful method for examining and differentiating the longissimus dorsi muscle and the dorsal sacroiliac ligament at the level of the tubera sacrale.

POTENTIAL RELEVANCE

Diagnostic ultrasound is available to most practitioners. These reference ultrasound parameters may help to improve the diagnosis of sacroiliac diseases.

Structural and biomechanical aspects of equine sacroiliac joint function and their relationship to clinical disease

Pain originating from the sacroiliac joint (SIJ) in horses has long been associated with poor performance, yet specific diagnosis of sacroiliac dysfunction (SID) has been difficult to achieve. Clinical presentation of SID appears to fall into two categories. The first, presenting as pain and poor performance, is responsive to local analgesia of periarticular structures with poorly defined pathology. The second presents primarily as poor performance with bony pathological changes as a result of chronic instability. Diagnostic tests based on biomechanics as well as manual provocation for SIJ pain have formed the basis of tests currently used to diagnose SIJ dysfunction in humans. This review summarises the anatomy and biomechanics of the equine SIJ and current biomechanical, innervation and motor control concepts in human SID. The relationship between abnormal SIJ motion and altered neuromotor control with clinical disease of the equine SIJ are discussed. Future utilisation of these principles to develop new diagnostic and management tools for the equine SID is promising.

Skeletal scintigraphy in the horse: Current indications and validity as a diagnostic test

Gamma scintigraphy is a well established imaging modality, which in equine practice is predominantly used in the investigation of lameness and suspected musculoskeletal problems. Whilst there is a growing literature on the indications for scintigraphy in the horse, there has been little emphasis so far on identifying the validity of scintigraphy as a diagnostic test. In particular, to what extent can the results of a scintigraphic examination be trusted? In this opinionated review the current indications for skeletal scintigraphy in the horse are considered and its validity as a diagnostic test reviewed. It is concluded that in the majority of published studies, inherent biases in study design make it difficult to assess accurately the validity of skeletal scintigraphy in the horse. Further well designed, prospective studies are required to assess the validity of skeletal scintigraphy as a diagnostic tool, particularly in horses with subtle alterations in radiopharmaceutical uptake.

Femoral asymmetry in the Thoroughbred racehorse

OBJECTIVE

To investigate the occurrence of geometrical asymmetries in the macro-architecture of left and right femurs from Thoroughbred racehorses previously used in competitive training and racing in New South Wales, Australia.

METHODS

Detailed postmortem measurements were made of 37 characteristics of left and right femurs from eleven Thoroughbred racehorses euthanased for reasons unrelated to the study. Measurements focused on articulating surfaces and sites of attachment of muscles and ligaments known to be associated with hindlimb locomotion.

RESULTS

Five measurements were significantly larger in left compared to right femurs (P < 0.05). The regions showing significant differences between left and right limbs were proximal cranial and overhead medio-lateral widths, greater trochanter depth, depth of the fovea in the femoral head and distal inter-epicondylar width.

CONCLUSION

The left-right differences in femoral morphology were associated with sites of muscle and ligament attachment known to be involved with hindlimb function in negotiating turns. These differences may be the result of selection pressure for racing performance on curved race tracks and/or adaptations related to asymmetrical loading of the outside hindlimb associated with repeated negotiation of turns on such tracks.

The sacroiliac joints: evaluation using nuclear scintigraphy. Part 1: The normal horse

REASONS FOR PERFORMING STUDY

Sacroiliac (SI) disease is recognised as a cause of poor hindlimb action but differential diagnosis is often difficult.

HYPOTHESES

That in clinically normal horses there would be a significant difference in the ratio of radiopharmaceutical uptake (RU) between the fifth lumbar vertebra (L5) and each tuber sacrale (TS) and between L5 and each SI joint; and that these ratios would alter with age, but ratios would be bilaterally symmetrical.

METHODS

Dorsal scintigraphic images of the SI region of 15 horses, selected randomly from the clinic database, were analysed by 2 of the authors, comparing noncorrected and motion-corrected images. To determine scintigraphic anatomy, the scintigraphic images of 10 Thoroughbred horses were superimposed over a ventrodorsal radiographic image of an isolated pelvis. Dorsal scintigraphic images of 40 clinically normal horses age 3-16 years were evaluated using subjective examination, profile analysis and quantification using regions of interest.

RESULTS

The tubera sacrale were seen as 2 well-defined oval regions immediately to the left and right of the midline, abaxial to which were larger, approximately oval areas with less RU, representing uptake in the SI joints. The definition between the SI region and the TS was more obvious in younger horses. Nonmotion-corrected images were often not of diagnostic quality or could be misinterpreted as abnormal. There were significant differences in RU between the TS and SI joints compared to L5, and decreased RU in the tubera sacrale with increasing age, but no change of uptake in the SI joint region and no effect of gender on RU. There was a high degree of left-right symmetry of the TS and SI joint regions.

CONCLUSIONS AND POTENTIAL RELEVANCE

The scintigraphic images of horses with suspected sacroiliac joint disease should be compared with images of normal horses of comparable age. In normal horses, there was a high degree of symmetry; therefore, marked left-right asymmetry is likely to be abnormal.

Pain associated with the sacroiliac joint region: a clinical study of 74 horses

REASONS FOR PERFORMING STUDY

There has been no large study of horses with suspected sacroiliac (SI) joint region pain in which the clinical diagnosis has been supported by either abnormal radiopharmaceutical activity in the SI joint region or by periarticular infiltration of local anaesthetic solution.

OBJECTIVES

To describe the clinical features of horses with SI joint region pain, to document the age, breed, sex, discipline, size and conformation of affected horses and to compare these with the author's (SD) normal case population and to document the results of infiltration of local anaesthetic solution around the SI joint region.

METHODS

Horses were selected for inclusion in the study based upon the exclusion of other causes of lameness or poor performance, together with clinical signs suggestive of SI joint pain and abnormal radiopharmaceutical activity in the SI joint region and/or a positive response to periarticular infiltration of local anaesthetic solution.

RESULTS

Sacroiliac joint region disease was identified in 74 horses between November 1997 and March 2002. Dressage and showjumping horses appeared to be at particular risk (P < 0.001). Affected horses were generally slightly older than the normal clinic population (P < 0.0001), taller at the withers (P < 0.0001) and of greater bodyweight (P < 0.01). There was a significant effect of breed (P < 0.001), with a substantially higher proportion of Warmblood horses (51%) in the SI pain group compared to the normal clinic population (29%). There was no correlation between conformation and the presence of SI joint region pain. The tubera sacrale appeared grossly symmetrical in most (95%) horses. Poor development of the epaxial muscles in the thoracolumbar region and asymmetry of the hindquarter musculature were common. Twenty-six horses (35%) showed restricted flexibility of the thoracolumbar region and 10 (16%) had an exaggerated response to pressure applied over the tubera sacrale. Fourteen horses (19%) were reluctant to stand on one hindlimb for prolonged periods. The majority of horses (75%) had a straight hindlimb flight and only 18% moved closely behind or plaited. In all horses restricted hindlimb impulsion was the predominant feature; invariably this was most obvious when the horse was ridden. Stiffness, unwillingness to work on the bit and poor quality canter were common. Sacroiliac joint region pain was seen alone (47%), or in conjunction with thoracolumbar pain (16%), hindlimb lameness (20%), forelimb lameness (7%) or a combination of problems (10%). Seventy-three horses (99%) had abnormalities of the SI joint region identified using nuclear scintigraphy. Infiltration of local anaesthetic solution around the SI joint region produced profound improvement in gait in all 34 horses in which it was performed.

CONCLUSIONS AND POTENTIAL RELEVANCE

Careful clinical examination combined with scintigraphic evaluation of the SI joint region and local analgesia can enable a more definitive diagnosis of SI joint region pain than has previously been possible.