J. small Anim. Pract. (1976) 17, 583-592.
Lateral spinal decompression in the dog K . G . B R A U N D , * T. K . F. T A Y L O R , P . G H O S H AND
A. A. S H E R W o o D t
Departments of Veterinary Surgery* and Mechanical Engineering, t University of Sydney, and Raymond Purves Research Laboratories, Royal North Shore Hospital of Sydney, N.S.W., Australia
ABSTRACT As an adjunct to the thoracolumbar surgical management of intervertebral disc prolapse in the dog, a lateral decompressive technique is described which permits removal of the prolapsed intervertebral disc material and prophylactic disc fenestration at the same time. INTRODUCTION The surgical management of thoracolumbar intervertebral disc disorder in the dog has centred around two procedures-disc fenestration and spinal cord decompression. The choice of which procedure to use has usually been determined by the clinical status of the animal: decompression being the procedure of choice in animals presented with severe spinal cord involvement as evidenced by complete paraplegia and loss of voluntary control of micturition. This syndrome may be seen in any breed but particularly in those animals with chondodystrophoid traits (Hansen, 1952; Braund et al., 1975), being secondary to Type I (Hansen, 1952) or Type I11 (Funkquist, 1962a) disc prolapse. I n those cases with less severe sensori-motor disturbances (thoracolumbar spinal pain, unilateral or bilateral hind limb paresis, ataxia), characteristic of Type I1 disc protrusion (Hansen, 1952), intervertebral disc fenestration alone is routinely employed (Olsson, 1951; Leonard, 1960; Yturraspe & Lumb, 1973; Flo & Brinker, 1975). In the surgical management of an animal paralysed as a result of intervertebral disc prolapse in the thoraco-lumbar region, a number of objectives are apparent, including decompression of the spinal cord and removal of the prolapsed disc Requests for reprints: Dr K. G. Braund, Department of Small Animal Surgery and Medicine, School of Veterinary Medicine, Auburn University, Auburn? Alabama 36830, U.S.A.
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material. The two spinal cord decompression procedures routinely employed in the dog are hemilaminectomy (Redding, 1951 ; Hoerlein, 1952b, 1956) and dorsal laminectomy (Funkquist, 1962b; Trotter, Brasmer & delahunta, 1975). While the degree of cord decompression afforded by these two procedures is comparable (Hoerlein, 1965, 197l ) , only the hemilaminectomy approach safely permits both cord decompression and removal of the prolapsed disc material at the same time. Prolapsed material cannot be totally removed from the vertebral canal using the dorsal decompression procedures without significant risk of further loss of cord function (Funkquist, 1962b), due to the cord manipulation required to reach the disc material via this dorsal approach. A certain degree of cord manipulation is also frequently inevitable via the hemilaminectomy exposure with potential untoward neurological sequellae, due to vertebral canal entry from a dorso-lateral direction, necessitated by the original dorsal mid-line approach. I n 1970, a lateral approach to the canine thoracolumbar spine, similar to that described by Seeman (1968)) was evaluated in these laboratories during the course of experimental instrumentational studies on thirty pure-bred Beagles and Greyhounds, the description and results of which are reported elsewhere (Braund, 1972). The use of a similar lateral approach for intervertebral disc fenestration in dogs has recently been published (Flo & Brinker, 1975). This paper is a preliminary report on the surgical management of the paralytic disc syndrome in the dog using a lateral decompressive procedure. This approach enables the surgeon to decompress effectively the spinal cord, remove the prolapsed disc material without cord manipulation and to fenestrate prophylactically adjacent discs a t the same time. SURGICAL PROCEDURE After standard anaesthetic induction-maintenance the animal is placed in lateral recumbency and the skin over the entire trunk, from the mid-thoracic region to the iliac wing (extending dorsally to the mid-line, and 4-6 in laterally) is surgically prepared. A skin incision is made approximately 2 in lateral to the dorsal mid-line, the length of which will depend upon the radiographic localization of the offending disc. I t may be continued from the T9-TI0 vertebral level through L5-L6. The incision is extended through the superficial subcutaneous tissues, deep lumbodorsal fascia and sub-fascial adipose layers to expose the laterally-lying iliocostalis muscle mass. The tips of the lumbar transverse processes are readily palpable (Fig. 1) and are exposed by blunt dissection. The thin fibrous periosteum on the dorsal surfaces of the transverse processes is then elevated to the junction with the vertebral body. I n the case of lumbar disc prolapse, the iliocostalis and mediallylying longissimus muscle mass between the exposed transverse processes, is separated from the inter-transverse ligament and retracted dorsally, thus exposing
LATERAL SPINAL DECOMPRESSION I N T H E DOG
FIG.1. The laterally-lying iliocostalismuscle mass is partially retracted dorsally to permit palpation of the tips of the lumbar transverse processes (diagramatic representation).
FIG. 2. The fibrous periosteum on the dorsal surfaces of the transverse processes has been elevated and the iliocostalis and longissimus muscle mass separated from the intertransverse ligament, and retracted dorsally. With further retraction, the lateral aspects of the intervertebral disc and segmental vessels and nerve are exposed (inset) (diagramatic representation).
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completely the transverse processes and lateral aspect of the vertebral bodies adjacent to the involved disc (Fig. 2). The periosteum is further elevated to the dorsal border of the diarthrodial vertebral articulations and the epaxial muscle mass retracted dorsally to expose the intervertebral foramen, segmental nerve and vessels (Fig. 3). The tendinous attachments of the epaxial musculature to the accessory processes are divided, and the thin connective tissue membrane covering the intervertebral foramen is carfully incised where it attaches to the cranial and caudal vertebral notches, and fine-tipped rongeur forceps or a high-speed air drill can be used to remove the pedicle bone from adjacent vertebral segments. The amount of bone removed will be determined by each individual case. I n our experience, removal of approximately half of the pedicle from adjacent vertebral segments, extending ventrally from the floor of the vertebral canal to, but not including, the diarthrodial articulations, dorsally (i.e. in line with the dorsal limits of the intervertebral foramen) provides effective cord decompression (Figs 3, 4 and 5). The accessory process of the cranial vertebral segment is also routinely removed. If the disc lesion is located between the caudal thoracic vertebral segments
FIG. 3. The periosteum has been elevated to the dorsal border of the diarthrodial articulation, and the epaxial muscle mass retracted to expose the intervertebral foramen, emanating spinal nerve, vessels and intervertebral disc. The extent of bone to be excised is outlined (diagramatic representation).
LATERAL SPINAL DECOMPRESSION I N T H E D O G
FIG.4. Approximately half of the pedicle from adjacent vertebrae has been excised, extending from the floor of the canal to the dorsal limits of the diarthrodial articulation, exposing the spinal cord, segmental nerve and vessels and intervertebral disc (diagramatic representation).
FIG.5. This cross-sectional illustration demonstrates the route for the proposed periosteal elevation (on the left). The dorsal retraction of the epaxial muscle mass and excised pedicular bone are shown on the right. B
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(TIO-T13), the muscular leaves of the iliocostalis system joining the ribs are readily exposed by extending the incision of the deep lumbo-dorsal fascia cephalad. These muscle leaves can be easily retracted dorsally and the periosteum from the underlying ribs elevated to the junction of the ribs with the thoracic vertebrae, in the same manner as for the lumbar transverse processes. The intercostal and foraminal areas are then exposed by retraction of the epaxial musculature to the level of the diarthrodial joints and decompression achieved in the manner previously described in the lumbar region. Thus, effective spinal cord decompression can be performed a t any vertebral level from T10-TI I through L5-L6. Provided sub-periosteal elevation is used, bleeding is minimal or absent, and as the muscle planes have not been transgressed, muscle trauma is also minimal. Potential bleeding may occur from two main sources : (i) vessels which penetrate the intercostal and intertransverse ligaments supplying the spinal epaxial musculature; (ii) segmental vessels located a t the intervertebral foramina. The former vessels (usually one or two in number, situated at the caudal margin of each rib or transverse process) can be identified and localized by careful separation of the muscle mass from the intercostal or intertransverse ligament. Usually it is not necessary to ligate these vessels once they have been isolated, since they easily stretch with dorsal retraction of the muscle mass. Careful dissection is required around the foramina1 region in order to avoid damage to the second group of vessels. Only infrequently has ligation been necessary in our experience. Lateral cord decompression provides direct visualization of the ventro-lateral aspects of the spinal cord and ventral floor of the vertebral canal, including the ipsilateral longitudinal vertebral venous sinus and dorsal root ganglia. As the surgeon is able to work at a level ventral to the spinal cord, the segmental canal floor can be quickly and safely explored for prolapsed disc material which can then be removed without jeopardizing the neural tissues. Curved, straight-edged tartar scrapers have proved satisfactory for this procedure. The involved disc, together with adjacent discs, can then be fenestrated as a prophylactic procedure (usually from T11 through L4) since discs in this region are most frequently implicated in prolapse in the dog (Hansen, 1952; Hoerlein, 1952a, 1965, 1971). The technique for disc fenestration using the lateral approach is described in detail by Flo & Brinker (1975). A haemostatic agent (Gelatin Sponge) is routinely placed over the decompression site adjacent to the cord, so as to promote formation of an interposing membrane between the dura mater and muscle in order to prevent dural adhesions and periradicular fibrosis (La Rocca & Macnab, 1974). The epaxial musculature returns to its original position once retraction is released. The incision is closed with simple, single-interrupted sutures, apposing the deep lumbodorsal fascia and subcutaneous tissues using 210 chromic catgut, and skin margins with 310 silk. An abdominal dressing is applied to prevent soilage to the incision, for 4-5 days.
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DISCUSSION There would appear to be three main objectives in the surgical management of severe spinal cord derangement secondary to intervertebral disc protrusion : (i) Adequate spinal cord decompression. Cord compression secondary to acute and semi-acute disc prolapse is usually due to a combination of prolapsed disc material and the accompanying inflammatory response (Olsson, 1958) and possible extradural haemorrhage (Griffiths, 1972a). Following cord concussion and, frequently, contusion secondary to intervertebral disc prolapse, localized segmental cord oedema occurs (Hoerlein, 1952a, 1953, 1971; Jubb & Kennedy, 1970) with potential development of severe malacic changes (Wright & Palmer, 1969; Griffiths, 1972a,b). The value of prompt surgical decompression has been well documented in both experimental (Tarlov, 1957) and clinical (Funkquist, 1962a,b; Hoerlein, 1952b, 1956, 1965, 1971) studies. (ii) Removal of the prolapsed disc material. Due to the danger of producing further neurological deficit secondary to cord manipulation in the dorsal decompressive procedure described by Funkquist & Schantz (1962), decompression alone is usually performed, whereas removal of the prolapsed disc material at the same time as decompression is by far the preferable alternative (Hoerlein, 1952b, 1971). Removal ofprolapsed material undoubtedly helps to alleviate the attendant inflammatory response which can exacerbate and maintain the clinical syndrome (Olsson, 1958). Although small prolapsed fragments may be partially or completely resorbed over a few days (Hoerlein, 1971), clinical experience indicates that the material may remain epidurally indefinitely, especially if calcified, in which case the mass may become circumscribed (Parker, Park & Richie, 1973). Failure to remove the prolapsed material may result in long term neurological sequellae, including the possibility of vascular compression, leading to focal cord ischaemia (Wright & Palmer, 1969), and periodic compression of a pre-existing displaced cord, by spinal movement. (iii) Prophylactic intervertebral discfenestration. Without complete enucleation of the nucleus pulposus of both the affected disc and related discs in the thoracolumbar region (Tll-L4), as advocated by Hoerlejn (1952b, 1971), the possibility of prolapse recurrence is high. I n a series of dogs with disc disorder surgically managed by decompression alone, a recurrence rate of more than 20% was noted during the following 3-6 months (Funkquist, 196213). When prophylactic fenestration has been performed at the same time as decompression, recurrence rate is minimal in long term follow-up (Hoerlein, 1965, 1971). The surgical technique described in this paper fulfills all three objectives. In addition, it is considered to possess the following advantages : (a) I t is a relatively simple and quick approach to the lateralaspectsof the neurovertebral axis. The time required for pedicle removal and fenestration of the affected disc rarely takes longer than 30 minutes, and the entire procedure, including adjacent disc fenestration (T11-L4) and wound closure, can usually
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be completed within 1 hour. Although the dorso-lateral approach employed for hemilaminectomy also permits the aforementioned surgical criteria, our experience indicates that these criteria may be more readily accomplished using the lateral approach. (b) The procedure do'es not require further disruption of the spinal stability by removal of the dorsal vertebral elements, an integral part of the surgical technique in dorsal bilateral decompressive operations (Funkquist, 1962b; Trotter et al., 1975). (c) Decompression can be achieved without resorting to excessive bone resection. Since half the pedicle bone from each adjacent vertebra is removed, the amount of cord decompression approximates that produced by hemilaminectomy. However, in cases of per-acute disc prolapse resulting in multi-segmental cord oedema and swelling, more radical bone removal can be accomplished by craniocaudal and/or dorsal extension. I n conjunction with decompression, durotomy (Parker & Smith, 1974) and normothermic and/or hypothermic cord irrigation (Tator & Deecke, 1973; Smith & Parker, 1975) can also be performed. A potential complication arising from dorsal decompression is secondary cord compression from fibrotic cicitrization, especially if radical laminectomy is performed (Funkquist & Schantz, 1962; Trotter et aZ., 1975). Further effects of radical laminectomy on vertebral axis stability and intervertebral disc metabolism have recently been examined (Taylor, Ghosh & Braund, 1976). (d) I t allows the surgeon to work ventrally to the spinal cord with the dural sac in full view. Any compressing disc material can be pulled down, away from the cord, thus avoiding cord manipulation (spinal cord compromised by prolapsed disc material, with or without an inflammatory reaction, tolerates handling poorly, no matter how gentle the manipulation). I t is this factor (not inherent in any other decompressive procedure) which has led to widespread acceptance of the lateral approach in human orthopaedic and neurosurgical circles for anteriorly (ventrally) placed compressive lesions in the thoracic spine, notably, disc prolapse and angular kyphosis (Hulme, 1960; Taylor, 1970). T o date, thoracolumbar cord decompression using this method has been performed successfully, without relevant complication, in a clinical trial of twenty chondrodystrophoid and non-chondrodystrophoid dogs presented with the paralytic disc syndrome. Detailed clinical appraisal of this technique, including longterm follow-up data, will be published at a later date. ACKNOWLEDGMENTS
The financial support of the National Health and Medical Research Council, together with the F. H. Loxton Research Committee, University of Sydney, is acknowledged. The clinical trial was conducted a t the University of Sydney Veterinary School, and a t Auburn University School of Veterinary Medicine, Auburn, Alabama, USA. We are grateful to Dr B. F. Hoerlein, Department
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Head, Small Animal Surgery and Medicine, Auburn University, Auburn, AIabama, USA for his comments and suggestions concerning this manuscript. We thank Ms Nadine Harper for the illustrations.
REFERENCES BRAUND,K.G. (1972) Experimental models for the investigation of abnormal physical forces on the canine intervertebral disc. MVSc thesis, University of Sydney. K.G. GHOSH,P., TAYLOR, T.K.F. & LARSEN,L.H. (1975) Morphological studies on BRAUND, the canine intervertebral disc. The assignment of the beagle to the achondroplastic classification. Res. Vet. Sci. 19, 167. W.O. (1975) Lateral fenestration of thoracolumbar discs. J . Am. An. Hosp. FLO,G.L. & BRINKLER, Ass. 11, 619. FUNKQUIST, B. (1962a) Thoracolumbar disc protrusion with severe cord compression in the dog. I Clinical and patho-anatomic observations with special reference to the rate of development of the symptoms of motor loss. Acta vet. scand. 3,256. FUNKQUIST, B. (1962b) Thoracolumbar disc protrusion with severe cord compression in the dog. 111. Treatment by decompressive laminectomy. Acta vet. scand. 3, 344. FUNKQUIST, B. & SCHANTZ, B. (1962) Influence of extensive laminectomy on the shape of the spinal canal. Acta 07th. scand., Supplement 56. GRIFFITHS, I.R. (1972a) The extensive myelopathy of intervertebral disc protrusions in dogs (“The ascending syndrome”). 3. small Anim. Pract. 13, 425. GRIFFITHS, I.R. (1972b) Some aspects of the pathology and pathogenesis of the myelopathy caused by disc protrusions in the dog. 3. Neurol., Neurosurg. Psych. 35,403. HANSEN, H.J. (1952) A pathologic-anatomical study on disc degeneration in the dog. Acta orth. scand., Supplement 1 1. HOERLEIN, B.F. (1952a) Intervertebral discprotrusiotrr in the dog. A clinical and pathological study. PhD thesis, Cornell University. HOERLEIN, B.F. (1952b) The treatment of intervertebral disc protrusions in the dog. Proc. Am. vet. med. Ass. 206, 1952. HOERLEIN, B.F. (1 953) Intervertebral disc protrusions in the dog. 111. Radiological diagnosis. Am. 3. vet. Res. 19, 260. HOERLEIN, B.F. (1956) Further evaluation of the treatment of disc protrusion paraplegia in the dog. 3. Am. vet. med. Ass. 129, 495. HOERLEIN, B.F. (1965) Canine Neurology-Diagnosis and Treatment, 1st Edn. W. B. Saunders CO., Philadelphia. HOERLEIN, B.F. (197I ) Canine Neurology-Diagnosis and Treatment, 2nd Edn. W. B. Saunders CO., Philadelphia. HULME,A. (1960) The surgical approach to thoracic intervertebral disc lesions. 3. Neurol., Neurosurg. P.ych. 23, 133. JUBB, K.V.F. & KENNEDY, P.C. (1970) Pathology of Domestic Animals, 2nd Edn. New York, Academy Press. LAROCCA,H. & MACNAB,I. (1974) The laminectomy membrane-studies in its evolution, characteristics, effects and prophylaxis in dogs. 3.BoneJoint Surg. 56-By 545. LEONARD, E.P. (1960) Orthopedic Surgery ofthe Cat and Dog. W. B. Saunders Co., Philadelphia. OLSSON, S-E. (1951) On disc protrusion in the dog. Acta orth. scand., Supplement 8. OLSSON, S-E. (1958) The dynamic factor in spinal cord compression. A study on dogs with special reference to cervical disc protrusions. 3.Neurosurg. 15, 308. PARKER,A.J., PARK,R.D. & RICHIE,D.A. (1973) An unusual case of chronic cord compression. 3.Am. An. Hosp. Ass. 9, 382.
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PARKER, A.J. & SMITH,C.W. (1974) Functional recovery from spinal cord trauma following incision ofspinal meninges in dogs. Res. Vet. Science, 16,276. REDDING, R.W. (1951) Laminectomy in the dog. Am. J . vet. Res. 12, 123. SEEMANN, C.W. (1968) Lateral approach for thoracolumbar disc fenestration. Modern vet. Pract. 49, 73. SMITH,C.W. & PARKER,A.J. (1975) Functional recovery from spinal cord trauma following normothermic irrigation in dogs. Res. Vet. Science, 19, 224. TARLOV, I.M. (1 957) Spinal Cord Compression. Thomas, Springfield, Illinois. TATOR, C.H. & DEECKE,L. (1973) Value of normothermic perfusion, hypothermic perfusion and durotomy in the treatment of experimental acute spinal cord trauma. 3. Neurosurg. 39, 52. TAYLOR, T.K.F. (1970) Resection of the apex of the kyphos in the management of incomplete traumatic paraplegia. J . Bone Joint Surg. 54-B,202. TAYLOR, T.K.F., GHOSH,P. & BRAUND, K.G. (1976) The effect of spinal fusion on intervertebral disc composition-an experimental study. 3. surg. Res. (in press). TROTTER, E.J., BRASMER, T.H. & DELAHUNTA, A. (1975) Modified deep dorsal laminectomy in the dog. Cornell Vet. 65,402. WRIGHT,F.E. & PALMER, A.C. (1969) Morphological changes caused by pressure on the spinal cord. Path. vet. 6, 355. YTURRASPE, D.J. & LUMB,W.V. (1973) Thoracolumbar intervertebral disc fenestration. 3. Am. vet. med. Ass. 162, 1037.
Lateral spinal decompression in the dog K . G . B R A U N D , * T. K . F. T A Y L O R , P . G H O S H AND
A. A. S H E R W o o D t
Departments of Veterinary Surgery* and Mechanical Engineering, t University of Sydney, and Raymond Purves Research Laboratories, Royal North Shore Hospital of Sydney, N.S.W., Australia
ABSTRACT As an adjunct to the thoracolumbar surgical management of intervertebral disc prolapse in the dog, a lateral decompressive technique is described which permits removal of the prolapsed intervertebral disc material and prophylactic disc fenestration at the same time. INTRODUCTION The surgical management of thoracolumbar intervertebral disc disorder in the dog has centred around two procedures-disc fenestration and spinal cord decompression. The choice of which procedure to use has usually been determined by the clinical status of the animal: decompression being the procedure of choice in animals presented with severe spinal cord involvement as evidenced by complete paraplegia and loss of voluntary control of micturition. This syndrome may be seen in any breed but particularly in those animals with chondodystrophoid traits (Hansen, 1952; Braund et al., 1975), being secondary to Type I (Hansen, 1952) or Type I11 (Funkquist, 1962a) disc prolapse. I n those cases with less severe sensori-motor disturbances (thoracolumbar spinal pain, unilateral or bilateral hind limb paresis, ataxia), characteristic of Type I1 disc protrusion (Hansen, 1952), intervertebral disc fenestration alone is routinely employed (Olsson, 1951; Leonard, 1960; Yturraspe & Lumb, 1973; Flo & Brinker, 1975). In the surgical management of an animal paralysed as a result of intervertebral disc prolapse in the thoraco-lumbar region, a number of objectives are apparent, including decompression of the spinal cord and removal of the prolapsed disc Requests for reprints: Dr K. G. Braund, Department of Small Animal Surgery and Medicine, School of Veterinary Medicine, Auburn University, Auburn? Alabama 36830, U.S.A.
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material. The two spinal cord decompression procedures routinely employed in the dog are hemilaminectomy (Redding, 1951 ; Hoerlein, 1952b, 1956) and dorsal laminectomy (Funkquist, 1962b; Trotter, Brasmer & delahunta, 1975). While the degree of cord decompression afforded by these two procedures is comparable (Hoerlein, 1965, 197l ) , only the hemilaminectomy approach safely permits both cord decompression and removal of the prolapsed disc material at the same time. Prolapsed material cannot be totally removed from the vertebral canal using the dorsal decompression procedures without significant risk of further loss of cord function (Funkquist, 1962b), due to the cord manipulation required to reach the disc material via this dorsal approach. A certain degree of cord manipulation is also frequently inevitable via the hemilaminectomy exposure with potential untoward neurological sequellae, due to vertebral canal entry from a dorso-lateral direction, necessitated by the original dorsal mid-line approach. I n 1970, a lateral approach to the canine thoracolumbar spine, similar to that described by Seeman (1968)) was evaluated in these laboratories during the course of experimental instrumentational studies on thirty pure-bred Beagles and Greyhounds, the description and results of which are reported elsewhere (Braund, 1972). The use of a similar lateral approach for intervertebral disc fenestration in dogs has recently been published (Flo & Brinker, 1975). This paper is a preliminary report on the surgical management of the paralytic disc syndrome in the dog using a lateral decompressive procedure. This approach enables the surgeon to decompress effectively the spinal cord, remove the prolapsed disc material without cord manipulation and to fenestrate prophylactically adjacent discs a t the same time. SURGICAL PROCEDURE After standard anaesthetic induction-maintenance the animal is placed in lateral recumbency and the skin over the entire trunk, from the mid-thoracic region to the iliac wing (extending dorsally to the mid-line, and 4-6 in laterally) is surgically prepared. A skin incision is made approximately 2 in lateral to the dorsal mid-line, the length of which will depend upon the radiographic localization of the offending disc. I t may be continued from the T9-TI0 vertebral level through L5-L6. The incision is extended through the superficial subcutaneous tissues, deep lumbodorsal fascia and sub-fascial adipose layers to expose the laterally-lying iliocostalis muscle mass. The tips of the lumbar transverse processes are readily palpable (Fig. 1) and are exposed by blunt dissection. The thin fibrous periosteum on the dorsal surfaces of the transverse processes is then elevated to the junction with the vertebral body. I n the case of lumbar disc prolapse, the iliocostalis and mediallylying longissimus muscle mass between the exposed transverse processes, is separated from the inter-transverse ligament and retracted dorsally, thus exposing
LATERAL SPINAL DECOMPRESSION I N T H E DOG
FIG.1. The laterally-lying iliocostalismuscle mass is partially retracted dorsally to permit palpation of the tips of the lumbar transverse processes (diagramatic representation).
FIG. 2. The fibrous periosteum on the dorsal surfaces of the transverse processes has been elevated and the iliocostalis and longissimus muscle mass separated from the intertransverse ligament, and retracted dorsally. With further retraction, the lateral aspects of the intervertebral disc and segmental vessels and nerve are exposed (inset) (diagramatic representation).
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completely the transverse processes and lateral aspect of the vertebral bodies adjacent to the involved disc (Fig. 2). The periosteum is further elevated to the dorsal border of the diarthrodial vertebral articulations and the epaxial muscle mass retracted dorsally to expose the intervertebral foramen, segmental nerve and vessels (Fig. 3). The tendinous attachments of the epaxial musculature to the accessory processes are divided, and the thin connective tissue membrane covering the intervertebral foramen is carfully incised where it attaches to the cranial and caudal vertebral notches, and fine-tipped rongeur forceps or a high-speed air drill can be used to remove the pedicle bone from adjacent vertebral segments. The amount of bone removed will be determined by each individual case. I n our experience, removal of approximately half of the pedicle from adjacent vertebral segments, extending ventrally from the floor of the vertebral canal to, but not including, the diarthrodial articulations, dorsally (i.e. in line with the dorsal limits of the intervertebral foramen) provides effective cord decompression (Figs 3, 4 and 5). The accessory process of the cranial vertebral segment is also routinely removed. If the disc lesion is located between the caudal thoracic vertebral segments
FIG. 3. The periosteum has been elevated to the dorsal border of the diarthrodial articulation, and the epaxial muscle mass retracted to expose the intervertebral foramen, emanating spinal nerve, vessels and intervertebral disc. The extent of bone to be excised is outlined (diagramatic representation).
LATERAL SPINAL DECOMPRESSION I N T H E D O G
FIG.4. Approximately half of the pedicle from adjacent vertebrae has been excised, extending from the floor of the canal to the dorsal limits of the diarthrodial articulation, exposing the spinal cord, segmental nerve and vessels and intervertebral disc (diagramatic representation).
FIG.5. This cross-sectional illustration demonstrates the route for the proposed periosteal elevation (on the left). The dorsal retraction of the epaxial muscle mass and excised pedicular bone are shown on the right. B
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(TIO-T13), the muscular leaves of the iliocostalis system joining the ribs are readily exposed by extending the incision of the deep lumbo-dorsal fascia cephalad. These muscle leaves can be easily retracted dorsally and the periosteum from the underlying ribs elevated to the junction of the ribs with the thoracic vertebrae, in the same manner as for the lumbar transverse processes. The intercostal and foraminal areas are then exposed by retraction of the epaxial musculature to the level of the diarthrodial joints and decompression achieved in the manner previously described in the lumbar region. Thus, effective spinal cord decompression can be performed a t any vertebral level from T10-TI I through L5-L6. Provided sub-periosteal elevation is used, bleeding is minimal or absent, and as the muscle planes have not been transgressed, muscle trauma is also minimal. Potential bleeding may occur from two main sources : (i) vessels which penetrate the intercostal and intertransverse ligaments supplying the spinal epaxial musculature; (ii) segmental vessels located a t the intervertebral foramina. The former vessels (usually one or two in number, situated at the caudal margin of each rib or transverse process) can be identified and localized by careful separation of the muscle mass from the intercostal or intertransverse ligament. Usually it is not necessary to ligate these vessels once they have been isolated, since they easily stretch with dorsal retraction of the muscle mass. Careful dissection is required around the foramina1 region in order to avoid damage to the second group of vessels. Only infrequently has ligation been necessary in our experience. Lateral cord decompression provides direct visualization of the ventro-lateral aspects of the spinal cord and ventral floor of the vertebral canal, including the ipsilateral longitudinal vertebral venous sinus and dorsal root ganglia. As the surgeon is able to work at a level ventral to the spinal cord, the segmental canal floor can be quickly and safely explored for prolapsed disc material which can then be removed without jeopardizing the neural tissues. Curved, straight-edged tartar scrapers have proved satisfactory for this procedure. The involved disc, together with adjacent discs, can then be fenestrated as a prophylactic procedure (usually from T11 through L4) since discs in this region are most frequently implicated in prolapse in the dog (Hansen, 1952; Hoerlein, 1952a, 1965, 1971). The technique for disc fenestration using the lateral approach is described in detail by Flo & Brinker (1975). A haemostatic agent (Gelatin Sponge) is routinely placed over the decompression site adjacent to the cord, so as to promote formation of an interposing membrane between the dura mater and muscle in order to prevent dural adhesions and periradicular fibrosis (La Rocca & Macnab, 1974). The epaxial musculature returns to its original position once retraction is released. The incision is closed with simple, single-interrupted sutures, apposing the deep lumbodorsal fascia and subcutaneous tissues using 210 chromic catgut, and skin margins with 310 silk. An abdominal dressing is applied to prevent soilage to the incision, for 4-5 days.
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DISCUSSION There would appear to be three main objectives in the surgical management of severe spinal cord derangement secondary to intervertebral disc protrusion : (i) Adequate spinal cord decompression. Cord compression secondary to acute and semi-acute disc prolapse is usually due to a combination of prolapsed disc material and the accompanying inflammatory response (Olsson, 1958) and possible extradural haemorrhage (Griffiths, 1972a). Following cord concussion and, frequently, contusion secondary to intervertebral disc prolapse, localized segmental cord oedema occurs (Hoerlein, 1952a, 1953, 1971; Jubb & Kennedy, 1970) with potential development of severe malacic changes (Wright & Palmer, 1969; Griffiths, 1972a,b). The value of prompt surgical decompression has been well documented in both experimental (Tarlov, 1957) and clinical (Funkquist, 1962a,b; Hoerlein, 1952b, 1956, 1965, 1971) studies. (ii) Removal of the prolapsed disc material. Due to the danger of producing further neurological deficit secondary to cord manipulation in the dorsal decompressive procedure described by Funkquist & Schantz (1962), decompression alone is usually performed, whereas removal of the prolapsed disc material at the same time as decompression is by far the preferable alternative (Hoerlein, 1952b, 1971). Removal ofprolapsed material undoubtedly helps to alleviate the attendant inflammatory response which can exacerbate and maintain the clinical syndrome (Olsson, 1958). Although small prolapsed fragments may be partially or completely resorbed over a few days (Hoerlein, 1971), clinical experience indicates that the material may remain epidurally indefinitely, especially if calcified, in which case the mass may become circumscribed (Parker, Park & Richie, 1973). Failure to remove the prolapsed material may result in long term neurological sequellae, including the possibility of vascular compression, leading to focal cord ischaemia (Wright & Palmer, 1969), and periodic compression of a pre-existing displaced cord, by spinal movement. (iii) Prophylactic intervertebral discfenestration. Without complete enucleation of the nucleus pulposus of both the affected disc and related discs in the thoracolumbar region (Tll-L4), as advocated by Hoerlejn (1952b, 1971), the possibility of prolapse recurrence is high. I n a series of dogs with disc disorder surgically managed by decompression alone, a recurrence rate of more than 20% was noted during the following 3-6 months (Funkquist, 196213). When prophylactic fenestration has been performed at the same time as decompression, recurrence rate is minimal in long term follow-up (Hoerlein, 1965, 1971). The surgical technique described in this paper fulfills all three objectives. In addition, it is considered to possess the following advantages : (a) I t is a relatively simple and quick approach to the lateralaspectsof the neurovertebral axis. The time required for pedicle removal and fenestration of the affected disc rarely takes longer than 30 minutes, and the entire procedure, including adjacent disc fenestration (T11-L4) and wound closure, can usually
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be completed within 1 hour. Although the dorso-lateral approach employed for hemilaminectomy also permits the aforementioned surgical criteria, our experience indicates that these criteria may be more readily accomplished using the lateral approach. (b) The procedure do'es not require further disruption of the spinal stability by removal of the dorsal vertebral elements, an integral part of the surgical technique in dorsal bilateral decompressive operations (Funkquist, 1962b; Trotter et al., 1975). (c) Decompression can be achieved without resorting to excessive bone resection. Since half the pedicle bone from each adjacent vertebra is removed, the amount of cord decompression approximates that produced by hemilaminectomy. However, in cases of per-acute disc prolapse resulting in multi-segmental cord oedema and swelling, more radical bone removal can be accomplished by craniocaudal and/or dorsal extension. I n conjunction with decompression, durotomy (Parker & Smith, 1974) and normothermic and/or hypothermic cord irrigation (Tator & Deecke, 1973; Smith & Parker, 1975) can also be performed. A potential complication arising from dorsal decompression is secondary cord compression from fibrotic cicitrization, especially if radical laminectomy is performed (Funkquist & Schantz, 1962; Trotter et aZ., 1975). Further effects of radical laminectomy on vertebral axis stability and intervertebral disc metabolism have recently been examined (Taylor, Ghosh & Braund, 1976). (d) I t allows the surgeon to work ventrally to the spinal cord with the dural sac in full view. Any compressing disc material can be pulled down, away from the cord, thus avoiding cord manipulation (spinal cord compromised by prolapsed disc material, with or without an inflammatory reaction, tolerates handling poorly, no matter how gentle the manipulation). I t is this factor (not inherent in any other decompressive procedure) which has led to widespread acceptance of the lateral approach in human orthopaedic and neurosurgical circles for anteriorly (ventrally) placed compressive lesions in the thoracic spine, notably, disc prolapse and angular kyphosis (Hulme, 1960; Taylor, 1970). T o date, thoracolumbar cord decompression using this method has been performed successfully, without relevant complication, in a clinical trial of twenty chondrodystrophoid and non-chondrodystrophoid dogs presented with the paralytic disc syndrome. Detailed clinical appraisal of this technique, including longterm follow-up data, will be published at a later date. ACKNOWLEDGMENTS
The financial support of the National Health and Medical Research Council, together with the F. H. Loxton Research Committee, University of Sydney, is acknowledged. The clinical trial was conducted a t the University of Sydney Veterinary School, and a t Auburn University School of Veterinary Medicine, Auburn, Alabama, USA. We are grateful to Dr B. F. Hoerlein, Department
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Head, Small Animal Surgery and Medicine, Auburn University, Auburn, AIabama, USA for his comments and suggestions concerning this manuscript. We thank Ms Nadine Harper for the illustrations.
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PARKER, A.J. & SMITH,C.W. (1974) Functional recovery from spinal cord trauma following incision ofspinal meninges in dogs. Res. Vet. Science, 16,276. REDDING, R.W. (1951) Laminectomy in the dog. Am. J . vet. Res. 12, 123. SEEMANN, C.W. (1968) Lateral approach for thoracolumbar disc fenestration. Modern vet. Pract. 49, 73. SMITH,C.W. & PARKER,A.J. (1975) Functional recovery from spinal cord trauma following normothermic irrigation in dogs. Res. Vet. Science, 19, 224. TARLOV, I.M. (1 957) Spinal Cord Compression. Thomas, Springfield, Illinois. TATOR, C.H. & DEECKE,L. (1973) Value of normothermic perfusion, hypothermic perfusion and durotomy in the treatment of experimental acute spinal cord trauma. 3. Neurosurg. 39, 52. TAYLOR, T.K.F. (1970) Resection of the apex of the kyphos in the management of incomplete traumatic paraplegia. J . Bone Joint Surg. 54-B,202. TAYLOR, T.K.F., GHOSH,P. & BRAUND, K.G. (1976) The effect of spinal fusion on intervertebral disc composition-an experimental study. 3. surg. Res. (in press). TROTTER, E.J., BRASMER, T.H. & DELAHUNTA, A. (1975) Modified deep dorsal laminectomy in the dog. Cornell Vet. 65,402. WRIGHT,F.E. & PALMER, A.C. (1969) Morphological changes caused by pressure on the spinal cord. Path. vet. 6, 355. YTURRASPE, D.J. & LUMB,W.V. (1973) Thoracolumbar intervertebral disc fenestration. 3. Am. vet. med. Ass. 162, 1037.
