Review of Diagnosis and Treatment of Lumbosacral Pain in Sport and Race Horses
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The lumbosacral joint is the most mobile intervertebral joint between the cranial thoracic area and the pelvis. Rectal ultrasonographic examination of this joint can easily be performed in routine practice, and it aids identification of several types of injuries as well as differential diagnosis with sacroiliac lesions. Treatment of lumbosacral pain has been considerably improved using ultrasonography-guided injections with a craniodorsal approach of the joint both on the left and right sides.
1. Introduction
Objective assessment of back and pelvic pain and clear identification of the cause(s) of the pain are not easy in horses. Osteoarticular thoracolumbar lesions have been described and documented in horses [1-5]. Several papers have been published on the clinical and nuclear scintigraphic evaluation of the sacroiliac joints [6-8]. Ultrasonographic examination of the sacroiliac joint has also been described [4,9]. Little attention has been given to the lumbosacral junction in the literature, whereas lesions have been documented in clinical cases and confirmed post-mortem in experimental studies [4,9-11].
Low back pain is suspected in a number of horses presenting poor performance with hindlimb stiffness, lack of propulsion, and discomfort during sport exercises such as short turns, jumping, and dressage exercises. In racehorses, low back pain is a cause of poor propulsion; it is also the cause of irregular gait at high speed in trotters.
The objectives of this paper are to attract attention to the clinical incidence of lumbosacral injuries in sport and racehorses, to show the diagnostic value of rectal ultrasonographic examinations of this area, and to show how ultrasonography-guided injections of the lumbosacral junction improve the practitioner's ability to help affected patients.
2. Anatomy and Biomechanics
The lumbosacral joint establishes the junction between the last lumbar vertebra (L6) and the first sacral vertebra (S1; Fig. 1). It is composed of five separate joints (Fig. 2). In the median plane, a symphysis is made of the last intervertebral disc (L6D; Fig. 3 and Fig. 4); this disc is usually thicker in the craniocaudal area and smaller in a dorsoventral axis between the first thoracic vertebra and the sacrum. Dorsally, there are two small synovial joints on the left and the right between the last articular processes (AP) of L6 and the cranial AP of S1. Finally, the transverse processes of L6 and S1 articulate on each side through a synovial lumbosacral intertransverse joint. The dorsal and ventral aspects of this joint are covered by an intertransverse ligament (Fig. 3 and Fig. 5).
Figure 1. Ventral aspect of the lumbosacral junction. On this specimen, there is an ankylosis between the last two lumbar vertebrae. 1, L5; 2, L6; 3, S1; 4, left ilium; 5, right ilium.
Figure 2. Cranial aspect of the pelvic part of the lumbosacral junction showing the five articular surfaces of the sacrum. 1, vertebral head of the S1; 2, sacral articular surface of the left lumbosacral intertransverse joint; 3, sacral articular surface of the right lumbosacral intertransverse joint; 4, surface of the left articular process of S1; 5, surface of the right articular process of S1; 6, left ilium; 7, right ilium.
Figure 3. Ventral aspect of the left part of the lumbosacral junction showing the intervertebral discs and ligaments. 1, L6; 2, S1; 3, left ilium; 4, lumbosacral intervertebral disc; 5, ventral longitudinal ligament; 6, ventral lumbosacral intertransverse ligament; 7, ventral sacroiliac ligament.
Figure 4. Median section of the lumbosacral junction. 1, L6; 2, S1; 3, lumbosacral intervertebral disc; 4, ventral longitudinal ligament; 5, dorsal longitudinal ligament; 6, vertebral canal; 7, dura mater; 8, spinal cord.
Figure 5. Paramedian section of the lumbosacral junction and sacroiliac joint. 1, transverse process of the L6; 2, transverse process of the S1; 3, ilium wing; 4, lumbosacral intertransverse joint; 5, ventral lumbosacral intertransverse ligament; 6, sacroiliac joint.
Several congenital and anatomical variations can be seen in the lumbosacral area of horses [4,12]. The most common ones are the intervertebral ankylosis between L6 and fifth lumbar vertebra (L5) and the sacralization of L6 resulting in a lumbosacral ankylosis. Fusion between two vertebras results in a concentration of the mobility and biomechanical stresses in the adjacent joint(s).
Because of the presence of intertransverse joints (Fig. 2, Fig. 3, and Fig. 5), the lumbosacral junction is specialized in flexion and extension [13-15]. There is a wide variation between horses in the amount of motion for the last two lumbar intervertebral joints (range = 5 - 20°). Intervertebral kinematic analysis showed that the center of rotation of this joint is closer to the disc than in other thoracolumbar joints [13]. This results in less shearing but more compression and traction [14] (Fig. 6). Lateroflexion is limited by the contact between the transverse processes. As the intertransverse ligaments are stretched in flexion and extension, a small amount of rotation is only possible for a neutral position of the lumbosacral joint [14].
Figure 6. Median section of the lumbosacral junction in flexion.Note that the lumbosacral intervertebral disc presents a degenerative appearance with cavitation. In flexion, its dorsal fibers are stretched, while the ventral fibers are relaxed and prolapsed ventrally.Between the vertebral arches, the flavum (interarcual) ligament is stretched. 1, L6; 2, S1; 3, lumbosacral intervertebral disc; 4, vertebral canal; 5, flavum (interarcual) ligament.
3. Complaints: Anamnesis
Back pain is a common complaint in sport and racehorses. A number of different problems specifically related to low back pain involve the lumbosacral junction.
In all disciplines, the horse exhibits stiff gaits, especially before warming up, and reduction of hindlimb propulsion.
In sport horses, lack of engagement, lack of propulsion, reduction of lumbosacral mobility during jumping, defensiveness during collected gaits, asymmetrical lateral bending, asymmetric canter, reluctance to change lead at canter, and defensiveness during backing up and lateral work are often reported. Racehorses may show a reduction of action and a lack of propulsion; in trotters, an asymmetrical gait at high speed is also present. The large majority of these horses do not show any hindlimb lameness.
Many of these manifestations can be found in horses having thoracolumbar lesions such as osteoarthrosis of the AP [5,9] or sacroiliac lesions [16]. Therefore, a complete clinical and imaging evaluation of the thoracolumbar and lumbosacroiliac areas is always performed on the affected patients.
4. Clinical Examination
During physical examination, muscle atrophy involving the erector spinae muscle and the gluteal muscles can be identified in the lumbosacral area. However, a number of horses with lumbosacral lesions do not present any muscle atrophy. Some horses with lumbosacral pain show a reduction of flexion and extension movements during active mobilization, which is induced by digital stimulation; pressure over the tuber sacrale causes more frequent sinking (flexion) of the hindlimb in trotters than in sport horses.
Dynamic evaluation is first performed at the walk. Horses with lumbosacral pain may show a restricted gait with short strides, especially on short circles. During examination from the side at trot, the passive flexion and extension movements of the lumbosacral joint can be assessed as well as the gait amplitude, engagement, and propulsion. If lameness is present, it will be investigated using a classical approach, but horses with lumbosacral pain often do not present any hindlimb asymmetry during walking and trotting.
Cantering in a deep footing is useful for assessing the power and strength of the hind legs. Dissociation or engagement of the hindlimbs or wrong placement of the inside hindlimb is often seen in horses with lumbosacral or sacroiliac problems. Cantering is also useful in assessing the active alternative lumbosacral movements [15]; lumbosacral flexion takes place during hindlimb engagement, and extension is synchronic with hindlimb propulsion. Examination of the horse being ridden or driven may help to highlight gait abnormalities and reduced motion in the lumbosacral area.
5. Diagnostic Imaging
Our routine diagnostic approach to low back pain in horses includes a complete radiographic examination of the thoracolumbar spine down to the fourth lumbar vertebra (L4) on the standing sedated patient [3] and a rectal ultrasonographic evaluation of the pelvis, which includes the lumbosacral junction, the caudal part of the lumbar spine (from L4 to L6), and the sacroiliac joints [9]. Radiographic examination of the lumbosacral joint can be performed with a ventrodorsal projection under general anesthesia. However, this view cannot be done in routine practice and has limited clinical ability to identify degenerative lesions because of superimposition of abdominal viscera. In some cases, nuclear scintigraphy is also used to help localize bone pathology in theses areas. This paper is focused on the ultrasonographic data involving the lumbosacral junction.
On reference ultrasound scans (Fig. 7) performed in the median plane, the ventral bone surfaces of L6 and S1 are regular and smooth. Between the vertebral fossa of L6 and the vertebral head of S1, the L6D is a 2- to 4-mm-thick homogenous echogenic structure. The ventral aspect of this disc is moderately convex and limited by the ventral longitudinal ligament. Dorsally, the disc is separated from the vertebral canal by the dorsal longitudinal ligament. Because the disc makes an acoustic window, the vertebral canal and its content (dura mater, cerebrospinal fluid, and epidural space with lumbar spinal nerves roots) can be seen.
Figure 7. Reference median ultrasonographic scan of the lumbosacral junction of a 10-yr-old selle français male used for show jumping. Note the normal lumbosacral angulation and the homogenous echogenicity as well as the moderate ventral prolapsus of the lumbosacral intervertebral disc. 1, L6; 2, S1; 3, lumbosacral intervertebral disc; 4, ventral longitudinal ligament; 5, dorsal longitudinal ligament; 6, vertebral canal.
On reference ultrasound scans performed in a paramedian plane, the normal lumbosacral intertransverse joint (Fig. 8) appears as a small anechogenic gap between the two regular hyperechogenic bone surfaces of the adjacent transverse processes of L6 and S1.
Figure 8. Reference paramedian ultrasonographic scan of the intertransverse lumbosacral joint of an 8-yr-old French trotter female used for racing. Note the regularity of the articular margins. 1, transverse process of the L6; 2, transverse process of the S1; 3, lumbosacral intertransverse joint space; 4, origin of the cranial gluteal artery.
Abnormal findings of the lumbosacral junction detected with ultrasonography include:
- congenital abnormalities such as lumbosacral ankylosis (sacralization of L6; Fig. 9) or intervertebral ankylosis between L5 and L6
- disc degenerative lesions, especially of the lumbosacral disc (these lesions include fissuration, cavitation [Fig. 10], ventral herniation [Fig. 11], and dystrophic mineralization [Fig. 12])
- intervertebral malalignment (spondylolisthesis) of the lumbosacral joint or the joint between L5 and L6 (Fig. 13)
- lumbosacral intertransverse osteoarthrosis (periarticular osteophytes or remodeling can be seen on the joint margins [Fig. 14 and Fig. 15])
Figure 9. Median ultrasonographic image of the lumbosacral junction of a 5-yr-old French trotter male used for racing. A congenital reduction of the lumbosacral intervertebral disc is present and associated with lumbosacral ankylosis (sacralization of L6).1, L6; 2, S1; 3, lumbosacral intervertebral disc.
Figure 10. Median ultrasonographic scan of the lumbosacral junction and post- mortem examination of a 6-yr-old French trotter female. (A) Median ultrasonographic scan; the dorsal part of the L6D is completely anechogenic (arrow head). (B) Median post-mortem section of the corresponding frozen specimen; degeneration and frozen hemorrhagic fluid are present in the dorsal part of L6D.Note the intervertebral ankylosis between the last two lumbar vertebrae (arrow head). (C) Thawed post-mortem specimen showing fiber degeneration and hemorrhagic fluid in the dorsal part of L6D. (D) Cranial aspect of the vertebral head of the S1 and disc material after transection of L6D and separation of the adjacent vertebrae.An extensive disc degeneration is present in the center of L6D.The fluid induced a dorsal herniation of the disc (arrow head) in the vertebral canal close to the left intervertebral foramen. 1, L6; 2, S1; 3, L6D.
Figure 11. Median ultrasonographic scan of the lumbosacral junction of a 5-yr-old selle français female used for show jumping. The L6D has an heterogenous echogenicity with echogenic spots compatible with mineralization; also, it shows a clear ventral herniation limited by the ventral longitudinal ligament. 1, L6; 2, S1; 3, lumbosacral intervertebral disc.
Figure 12. Median ultrasonographic scan of the lumbosacral junction of an 8-yr-old selle français male used for show jumping. The ventral surface of the lumbosacral intervertebral disc is completely hyperechogenic; this image is indicative of dystrophic mineralization or bone metaplasia. 1, L6; 2, S1; 3, lumbosacral intervertebral disc.
Figure 13. Median ultrasonographic scan of the lumbosacral junction of a 3-yr-old French trotter female used for racing. The ventral surface of the S1 is clearly displaced ventrally compared with the ventral aspect of the L6. This finding is indicative of a ventral subluxation of the sacrum. The lumbosacral intervertebral space is completely collapsed, which indicates that the intervertebral disc is degenerating. 1, L6; 2, S1; 3, lumbosacral intervertebral disc.
Figure 14. Paramedian ultrasonographic scan of the right lumbosacral intertransverse joint of a 9-yr-old Dutch Warmblood male used for show jumping. The ventral aspect of the articular margins is irregular because of the presence of periarticular osteophytes. Synovial membrane thickening and/or ventral lumbosacral intertransverse desmopathy make a hypoechogenic area (arrow head) at the ventral aspect of the joint space (compare with figure 8). 1, transverse process of the L6; 2, transverse process of the S1; 3, lumbosacral intertransverse joint space.
Figure 15. Ventral aspect of the lumbosacral junction of an anatomical bone specimen showing periarticular bone remodeling on the ventral margins of the lumbosacral intertransverse joints (arrow heads). There is an ankylosis between the L5 and the L6. 1, L5; 2, L6; 3, S1; 4, left ilium; 5, right ilium.
Differential diagnosis between lumbar, lumbosacral, and sacroiliac conditions is based on radiographic examination of the lumbar spine, rectal ultrasonographic examination of the ventral aspect of the caudal part of the lumbar spine and sacroiliac joints, and, in some cases, nuclear scintigraphic examination.
Abnormal radiographic findings in the lumbar vertebral column include kissing of the spinous processes, especially between L4 and L6, osteoarthrosis of the AP (common condition), and ventrolateral spondylosis on the vertebral bodies (rare condition).
Abnormal findings seen at the ventral aspect of the sacroiliac joint as assessed with ultrasonography include bone remodeling of the sacrum and/or ilium, periarticular osteophytes of the auricular surfaces, and ventral sacroiliac ligament desmopathy or enthesopathy.
Nuclear scintigraphic examinations are performed using a dorsal approach to the pelvis (camera horizontal), a dorsocaudal approach (camera parallel to the sacrum), and two symmetrical dorsolateral approaches (camera parallel to the coxal bone). When the ilium is superimposed to the lumbosacral joint, the location of increased radiopharmaceutical uptake (IRU) must be established carefully. IRU over the auricular surfaces of the sacroiliac joint is related to osteoarticular disease of this joint. IRU can be seen between the auricular surfaces and tuber sacrale, where it is correlated either to the insertion of the interosseus sacroiliac ligament or the lumbosacral joint. IRU detected cranially to the auricular surfaces corresponds to the transverse processes of the L6 and the adjacent intertransverse joints.
6. Treatment
The specific treatment of lumbosacral pain is ultrasonography-guided injection of steroids. This treatment can be associated to systemic medication and regional intradermal injections (IDI; mesotherapy).
Systemic Treatment
Treatment of lumbosacral pain with non-steroidal anti-inflammatory drugs (NSAIDs) is usually disappointing. When bone lesions are identified, especially involving the intertransverse joint, tiludronate is indicated. This drug is injected intravenously in slow-rate infusion at the total dose of 1 mg/kg body weight.
Local Injections
Pain associated with lumbosacral joint injuries is treated by deep paramedian injections of corticosteroids (flumethasone [a], total dose of 4 mg; dexamethasone [b], total dose of 10 mg; methylprednisolone acetate [c], total dose of 200 mg), sometimes in association with Sarapin [d] or local anesthetic solutions. Injections are made on both sides using ultrasonographic guidance (Fig. 16) and 15-cm-long × 1-mm-diameter needles [e].
Figure 16. Ultrasonography-guided injection of the lumbosacral junction. (A) After aseptic preparation of the injection site, the probe is placed in a paramedian position over the iliac crest. The needle is placed cranially in the same plane to be imaged in the ultrasound beam. A sterile glove is placed over the probe, and acoustic contact is obtained with alcohol. (B) A paramedian ultrasonographic scan of the procedure shows the needle going under the ilium wing to the dorsal aspect of the intertransverse lumbosacral joint (compare with figure 5). 1, ilium wing; 2, transverse process of the L5; 3, gluteus medius muscle; 4, needle.
For needle penetration through the skin, the site is located on a transverse line joining the cranial aspect of two tuber coxae, 4 cm apart from the median plane. On each site, a 5 x 5-cm area is clipped short and prepared aseptically.
The ultrasonographic guidance is performed using a 3.5 - 7.5 MHz convex probe, usually set to a 6-MHz frequency. A sterile glove is placed over the probe; contact acoustic gel is used between the probe and glove. Acoustic contact between the probe (covered with the glove) and skin is achieved using alcohol.
The procedure is routinely performed by two operators: the first operator holds the probe, and the second operator places the needle in the ultrasound beam.
To place the needle under the ilium wing, the needle is directed to the medial part of the lumbosacral intertransverse joint. In the first step, the ilium wing is imaged ultrasonographically. The second step consists of inserting the needle cranially to the probe at a point located in the prolongation of the ilium wing (Fig. 16b). During the third step, the needle is placed in the ultrasound beam and directed just under the ilium wing but slightly more vertical. Because of the hyperechogenic appearance of the ilium wing, the needle is no longer visible caudally to the ilium crest.
Correction of the orientation of the needle must be done if the needle goes in the gluteus medius muscle dorsally to the ilium wing or if it is orientated too vertically in the direction of the transverse process of L5. When placed properly, the needle is inserted until bone contact; then, the injection is made.
Mesotherapy
Mesotherapy consists of multiple IDIs made with short and thin needles [f] (5-mm-long) in the dermatomes corresponding to the site of the lesion(s).
Mesotherapy is based on the theory of the gait control of pain, which states that pain takes place in the dorsal horn of the spinal cord grey mater. According to this theory, types I and II nerve fibers coming from the skin have collateral fibers that can inhibit the conduction of information in the spinothalamic fasciculus, transmitting painful information from deep structures of the same spinal segment to the thalamus and cerebrum.
After aseptic preparation of the skin, mesotherapeutic injections are usually made using a local anaesthetic solution (i.e., lidocaine [g], 140 mg, for a volume of 7 ml) and a short acting corticosteroid (i.e., dexamethasone [h], 15 mg, for a volume of 7 ml). According to the principle of mesotherapy, injection with only saline solution may also have beneficial effects. Because most horses are sensitive to the procedure, the patient is placed in stocks, and the use of a twitch and sedation are recommended. A multi-injector [i] is used. These IDIs are performed at the level of the lumbosacral junction and caudal to it over the croup, taking into account the caudal orientation of the segmental nerves (cranial and caudal clunium nerves). Two to three rows of injections are made on each side of the median plane.
After either local injections or mesotherapy, the horse is restricted to light work in lunge for a couple of days. Normal training is progressively resumed over 3 - 5 days. A substantial improvement is anticipated within 7 - 14 days. If improvement is limited, mesotherapy should be repeated 2 - 3 wk after the first treatment. The expected duration of improvement varies between 3 and 12 mo. Ideally, a maximum of two local infiltrations should be performed per year, either alternately or in conjunction with mesotherapy.
Training Management
In conjunction with the medical treatment to reduce pain, modification of the training program is an essential part of the management of low back and lumbosacral problems. The aims of the exercise management are to avoid further muscle atrophy and to develop back proprioceptive control and joint stability. Rest is contraindicated, except in untreatable horses that are not improved by any kind of treatment and management. A progressive warm up of the horse, starting at a walk, is highly recommended. Then, progressive active mobilization of the lumbosacral junction is performed at slow canter rather than at trot, which can induce passive uncontrolled movements of this area. Dressage exercises, jumping exercises, or faster gaits will be progressively introduced after 15 - 20 min or when the horse is warm and relaxed.
Footnotes
- Cortexilar solution, Pfizer, 91400 Orsay, France.
- Voren Suspension injectable, Boehringer Ingelheim, 75116 Paris, France.
- Depomédrol, Pharmacia, 78280 Guyancourt, France.
- Sarapin, High Chemical Company, Levittown, PA 19056.
- BD Spinal Needle 20GX6, 0.9 x 150 mm, BD Medical Systems, Franklin Lakes, NJ 07417.
- Ago ipodermico sterile per mesoterapia, 0.4 x 4 mm, PIC Indolor, 20070 Grandate, Italy.
- Xylovet, CEVA Santé Animale, 33501 Libourne, France.
- Dexadreson, Intervet SA, 49071 Beaucouze, France.
- Multi-injector without needles, RI.MOS.srl, 29 41037 Mirandola, Italy.
1. Peterson ME, Ferguson DC. Thyroid Diseases. In: Ettinger SJ (Ed). Textbook of Veterinary Internal Medicine, Vol. 27. Philadelphia: WB Saunders and Co, 1990; 1632-1675.
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