Structure and Innervation of the Equine Supraspinous and Interspinous Ligaments

Analysis of different techniques for injection of the interspinal space in horses

BACKGROUND

Impingement of spinous processes (SPs) is commonly diagnosed in the equine athlete. For diagnostic and therapeutic purposes, local injections are performed at the level of the space between adjacent spinous processes in affected horses.

OBJECTIVES

To assess the accuracy of different techniques for the local injection of the interspinal space in the equine thoracolumbar spine.

STUDY DESIGN

Ex vivo experimental study.

METHODS

Equine thoracolumbar spine specimens were used to compare three techniques for needle insertion (midline; bilateral abaxial; unilateral oblique), two needles (20G-1½″; 20G-3½″) and two volumes (5 mL; 20 mL) for local injection of the interspinal space. Additionally, needle insertion based on radiographic, ultrasonographic guidance, or palpation was assessed. Computed tomographic analysis and anatomical dissection were performed to evaluate the distribution of the injected volume.

RESULTS

The most accurate injection of the interspinous ligament was achieved when the midline injection method using a 20G-1½″ short needle and a volume of 5 mL was used. Wide distribution of the injected volume was observed when the bilateral abaxial injection technique was utilised. The unilateral oblique injection technique led to significantly asymmetrical unilateral distribution of the injectate. Radiographic guidance did not increase the accuracy of the injection.

CONCLUSION

The midline injection method is the most reliable technique for the targeted injection of the thoracolumbar interspinal space.

Influence of surgical intervention at the level of the dorsal spinous processes on the biomechanics of the equine thoracolumbar spine

BACKGROUND

Surgical treatment options for horses with overriding dorsal spinous processes include interspinous ligament desmotomy and partial spinous process ostectomy. The impact of spinal surgery on the three-dimensional biomechanics of the equine thoracolumbar spine and the epaxial musculature is unclear.

OBJECTIVES

To investigate the influence of interspinous ligament desmotomy and cranial wedge ostectomy on the biomechanics of the equine thoracolumbar spine and the paraspinal Musculi multifidi.

STUDY DESIGN

Ex-vivo experiments.

METHODS

Twelve equine thoracolumbar spine specimens were mounted in a custom-made mechanical test rig. Based on computed tomographic imaging, distances between dorsal spinous processes and the spinal range of motion (lateral bending, axial rotation, flexion, extension) were compared before and after desmotomy and cranial wedge ostectomy performed at two or five surgical sites. Anatomical dissection was subsequently conducted to document surgical trauma to the Musculi multifidi following desmotomy.

RESULTS

The distance between spinous processes in neutral position did not increase significantly after desmotomy (median preoperative = 7.2 mm, interquartile range [IQR] = 3.6 mm; median postoperative = 7.4 mm, IQR = 3.7 mm; p = 0.09), but increased significantly after ostectomy (median preoperative = 8.8 mm, IQR = 4.2 mm; median postoperative = 13 mm, IQR = 6.1 mm; p < 0.001). Both surgical procedures significantly increased the rotational spinal range of motion (p = 0.001), particularly at the level T14/T15 (median preoperative = 6.4°, IQR = 3.2°; median postoperative = 8.2°, IQR = 3.5°; increase = 28.1%; p = 0.02). Musculi multifidi injury was evident at all desmotomy sites.

MAIN LIMITATIONS

Ex-vivo study with limited sample size.

CONCLUSIONS

Neither interspinous ligament desmotomy nor cranial wedge ostectomy resulted in an increased range of motion during flexion, extension or lateral bending but both procedures influenced the rotational component of the equine thoracolumbar spinal mobility.

Computed tomography of the equine caudal spine and pelvis. Pathological findings in 56 clinical cases (2018-2023)

BACKGROUND

Computed tomography (CT) of the axial skeleton is increasing across many equine hospitals. CT of the pelvis and caudal spine in a large group of clinical cases has not been reported previously.

OBJECTIVE

To describe the pathological lesions identified in the caudal spine/pelvis in horses and ponies undergoing CT spine of this region.

STUDY DESIGN

A retrospective case series.

METHODS

Horses with CT imaging of the caudal spine/pelvis were included. Horses aged under 6 months and those with CT examinations performed post-mortem were excluded.

RESULTS

Fifty-six horses met the inclusion criteria. Ages ranged from 8 months to 20 years and bodyweights from 85 to 680 kg (mean 488 kg). Horses presented predominantly for lameness (30/56) and poor performance (18/56). Osseous pathology was identified in 41/56 horses; including osteoarthritis of the sacroiliac joint(s) (n: 28), pathology of the intervertebral disc joint(s) (n: 12), pelvic fractures (n: 9), osteoarthritis of the coxofemoral joint(s) (n: 8), ventral spondylosis (n: 6), acetabular rim fracture (n: 2), dislocation of coxofemoral joint(s) (n: 2), and dorsal dermal sinus of the sacrum (n: 1).

MAIN LIMITATIONS

The relationship between CT imaging findings and clinical signs in horses remains unclear. Further work is required to describe the relationship between congenital, developmental, and acquired changes in the caudal spine and pelvis, and clinical signs.

CONCLUSIONS

CT of the caudal spine and pelvis can be utilised in horses and ponies for diagnosing a range of clinical disorders that may be causing 'lumbosacroiliac pain', poor performance, hindlimb lameness, and stiffness. The pathologies we observed were diverse and many patients had multiple lesions.

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.

Computed tomographic study analysing functional biomechanics in the thoracolumbar spine of horses with and without spinal pathology

To better understand physiological and pathological movement patterns in the equine thoracolumbar spine, investigation of the biomechanics on a segmental level requires a constant moment. A constant moment along the spinal column means that the same torque acts on each vertebral segment, allowing the range of motion of different segments to be compared. The aims of this study were to investigate the range of motion of the equine thoracolumbar spine in horses with and without spinal pathology and to examine whether the pressure between the spinous processes depends on the direction of the applied moment. Thoracolumbar spine specimens (T8-L4) of 23 horses were mounted in a custom-made mechanical test rig to investigate spinal biomechanics during lateral bending, axial rotation, flexion and extension using computed tomographic imaging. Results were compared between horses with spondylosis, overriding spinous processes and specimens free of gross pathology. The interspinous space pressure was additionally determined using a foil sensor. The median lateral bending between T9 and L3 was 3.7°-4.1° (IQR 5.4°-8.0°). Maximum rotational movement with inconsistent coupled motion was observed at T9-T16 (p < 0.05). The dorsoventral range of motion was greatest in segments T9-T11 (p < 0.05). Spondylosis and overriding spinous processes restricted spinal mobility, depending on the severity of the condition. There was no significant difference in interspinous pressure during motion (p = 0.54). The biomechanical study confirmed that the range of motion of intervertebral joints depends on the anatomical position of the joint and the direction of the moment applied. Restricted mobility was evident in the presence of different grades of overriding spinous processes or spondylosis. A better understanding of equine spinal biomechanics in horses with spinal pathology facilitates individual rehabilitation.

Description of an Ultrasound-Guided Erector Spinae Plane Block and Comparison to a Blind Proximal Paravertebral Nerve Block in Cows: A Cadaveric Study

Simple Summary

One of the most common surgical procedures performed in cattle is abdominal surgery, and this procedure is routinely performed in the standing adult animal. This procedure is performed using local anaesthetic techniques in order to eliminate pain and reduce the need for chemical and physical restraints. One of the most common locoregional anaesthetic techniques is the proximal paravertebral nerve block, in which a local anaesthetic is used to desensitize the nerves providing sensation to the flank region. The use of ultrasound-guided techniques has been demonstrated in multiple species, including humans, to be more accurate, safe and efficacious than traditional blind techniques. The aim of this paper was to develop an ultrasound-guided block that would target the nerves desensitized in the paravertebral nerve block of the flank. Additionally, our study aimed to evaluate the two techniques (blind and ultrasound-guided) in cow cadavers. The use of ultrasound guidance resulted in an apparent improvement in accuracy, and the blind technique remains a reliable approach. Further studies are warranted to develop and to evaluate the ultrasound-guided technique in live animals.

Abstract

The proximal paravertebral nerve block is commonly used to provide anaesthesia to the flank during standing surgical procedures in adult cattle. It has been reported that additional anaesthetic infiltration may be necessary to provide complete anaesthesia. In humans as well as animal species, another technique—the ultrasound (US)-guided erector spinae plane block (ESPB)—has been described. The goal of the present study was to develop and investigate an US-guided ESPB in comparison to a blind proximal paravertebral nerve block (PPNB) in cow cadavers. In 10 cadaver specimens, injections of methylene blue-lidocaine (1:1) were performed at the level of T13, L1 and L2 vertebras, on one side doing an ESPB block and, on the other side, a PPNB. Five cadavers were injected with high (40 mL per injection for PPNB and 20 mL for ESPB) and five with low (20 and 15 mL, respectively) volumes of injectate. For the ESPB, the ultrasound probe was oriented craniocaudally, and the ventral-cranial aspect of the articular processes (T13, L1 and L2) was targeted for injection. The dye spreading was evaluated by dissection. The landmarks for US-guided injection were easily visualized; however, injections were accidentally performed at T12, T13 and L1. Nevertheless, L2 was stained in 60% of ESPBs. Epidural spreading was observed with both techniques and all volumes. Viscera puncture was reported in two PPNBs. The ESPB resulted in similar nerve staining compared to the PPNB while using a lower volume of injectate. Even better staining is expected with a T13-L2 instead of a T12-L1 ESPB approach. Further studies are warranted to evaluate the clinical efficacy.

Ultrasound-guided erector spinae plane block in horses: a cadaver study

OBJECTIVES

To describe dye distribution and spinal nerve involvement after a simulated erector spinae plane (ESP) block performed on fresh equine cadavers.

STUDY DESIGN

Experimental cadaver study.

ANIMALS

A group of 11 adult equine cadavers.

METHODS

The spinal region surrounding the sixteenth thoracic vertebra (Th16) of one cadaver was removed and underwent magnetic resonance imaging. In 10 adult equine cadavers [body weight, 549 ± 58 kg (mean ± standard deviation)], 0.2 mL kg^-1 of a 50:1 2% lidocaine/dye solution was injected bilaterally (n = 20 injections) into the fascial plane between the transverse process of Th16 and the erector spinae muscles. An in-plane ultrasound-guided technique with a convex transducer was used to guide injection. Dissection was performed immediately following injection. The craniocaudal and lateral extent of dye distribution was measured (cm) and the number of vertebral bodies involved were counted (n = 20). Abdominal and thoracic cavities as well as the epidural space were also examined for presence of dye (yes/no) (n = 20). Further dissection was performed to evaluate if staining of the dorsal and ventral rami of the spinal nerves and sympathetic chain occurred (n = 14).

RESULTS

The thoracolumbar fascia was stained in 17/20 (85%) injections and three injections terminated intramuscularly. Multisegmental staining of the dorsal rami was observed in the 14 injections in which staining was evaluated. Ventral rami staining was observed in 3/14 injections where staining was evaluated. Epidural migration was observed in 4/20 (20%) injections. No evidence of dye was found in the thoracic and abdominal cavities or on the sympathetic chain.

CONCLUSIONS AND CLINICAL RELEVANCE

The ESP block may prove beneficial to desensitize structures innervated by the dorsal rami of the thoracic spinal nerves. Further investigation is necessary to evaluate complications caused by epidural contamination.

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.

Anatomy and Ultrasound-Guided Injection of the Medial Branch of the Dorsal Ramus of the Cervical Spinal Nerves in the Horse: A Cadaveric Study

OBJECTIVE

 The aim of this study was to describe the anatomy of the nerves supplying the cervical articular process joint and to identify relevant anatomical landmarks that could aid in the ultrasound-guided location and injection of these nerves for diagnostic and therapeutic purposes.

STUDY DESIGN

 Twelve cadaveric equine necks were used. Five necks were dissected to study the anatomy of the medial branch of the dorsal ramus of the cervical spinal nerves 3 to 7. Relevant anatomical findings detected during dissections were combined with ultrasonographic images obtained in one other neck. Six additional necks were used to assess the accuracy of ultrasound-guided injections of the medial branch with blue dye.

RESULTS

 Each examined cervical articular process joint, except for C2 to C3, presented a dual nerve supply. The articular process joints were found to be in close anatomical relationship with the medial branch of the dorsal ramus of the cervical spinal nerve exiting from the intervertebral foramen at the same level, and with the medial branch of the dorsal ramus of the cervical spinal nerve exiting from the intervertebral foramen one level cranial to the articular process joint of interest. A total of 55 nerves were injected under ultrasonographic guidance, 51 of which were successfully stained.

CONCLUSION

 The current study provided new detailed information regarding the innervation of the cervical articular process joint. The medial branches of the dorsal rami of the cervical spinal nerves were injected with an accuracy that would be of clinical value. Our study offers the foundations to develop new diagnostic and therapeutic techniques for pain management in cervical articular process joint arthropathy in horses.

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.

Long-term outcome and effect of diagnostic analgesia in horses undergoing interspinous ligament desmotomy for overriding dorsal spinous processes

OBJECTIVE

To report the long-term outcome of horses treated with interspinous ligament desmotomy (ISLD) for pain associated with overriding dorsal spinous processes (ORDSP) and determine the influence of preoperative diagnostic analgesia on long-term outcome.

STUDY DESIGN

Retrospective study.

ANIMALS

Eighteen horses.

METHODS

Data were collected from horses presenting for ISLD to the University of Pennsylvania New Bolton Center between January 2013 and May 2018. Follow-up of ≥3 months postsurgically was obtained from the owner, trainer, or referring veterinarian. Long-term improvement was compared between horses that improved with diagnostic analgesia presurgically and horses that did not undergo diagnostic analgesia presurgically by using a χ² test. Univariate logistic regression was used to test associations between long-term improvement and independent variables.

RESULTS

Clinical signs had improved in 13 of 18 horses at long-term follow-up (median, 14.5 months; range, 3-57). Clinical signs improved in nine of 10 horses responding to diagnostic analgesia but only in four of eight horses that did not undergo diagnostic analgesia (χ² [1], N = 18) = 3.55; P = .06). Although the likelihood of long-term improvement increased with prior diagnostic analgesia (odds ratio = 6.3; 95% confidence interval = 0.73, 55.0; P = .09), it did not reach statistical significance.

CONCLUSION

A higher proportion of horses experienced long-term improvement in clinical signs after ISLD when horses responding to preoperative diagnostic analgesia were compared with horses that were not tested.

CLINICAL SIGNIFICANCE

This study provides some evidence to support the use of diagnostic analgesia in conjunction with clinical examination for identification of clinically relevant ORDSP.