Sciatic Spinal Deformity-Lumbosacral List: An Unusual Presentation

Morgan P. Lorio, Avi J. Bernstein, and Edward H. Simmons
Department of Orthopedic Surgery. State University of New York at Buffalo, Buffalo, New York, U.S.A.

Sciatic spinal deformity or lumbosacral list has received little attention in the literature. The phenomenon was first described in 1881 by Remak, but it was not until 1942 that Duncan and Hoen made the association between disk herniation and lumbosacral list. Since that time, the literature concerning this topic has been sparse and the terminology inconsistent. A case of lumbosacral list associated with disk herniation is presented with documented resolution after surgery. The pathogenesis of the list is described with a comprehensive review of the literature.

It is often observed that patients presenting with significant back pain and/or sciatica assume abnormal postures (3). When considering lumbosacral list, the distinction between a temporary involuntary scoliosis and a correctable lean must be made. Arangio et al. (1) defined lumbosacral list as “… a temporary, clinically appreciable, lateral deviation attitude in the normally straight vertical line of the lumbosacral spine.” The distinction between lumbosacral list and lumbosacral scoliosis concerns the correctable nature of the list once the offending painful stimulus is removed (4). Lumbosacral list has received a number of designations, including alternating lumbar scoliosis (16), alternating sciatic scoliosis (2), sciatic scoliotic list (15), trunk list (14), gravity-induced trunk list (9), “wind swept” spine (8), and lumbosacral list (1), which we deem the most appropriate. The Scoliosis Research Society recognizes lumbosacral list as a nonstructural scoliosis secondary to nerve root irritation, either due to herniation of the nucleus pulposus or tumor (23).

The rest of the differential regarding nonstructural scoliosis includes postural scoliosis, hysterical scoliosis, leg length discrepancy, contractures about the hip, or visceral inflammatory lesions such as appendicitis. The association of significant back pain and/or leg pain in a typical sciatic distribution easily rules out these other etiologies. These other nonstructural etiologies also can be distinguished radiographically because of their tendency toward long sweeping curves as opposed to the sharp short angular curve that is often restricted to a single level in lumbosacral lists. A typical patient presents with severe acute onset of back pain and/or leg pain in a sciatic distribution and fulfills several of McCulloch’s criteria (10). Classical teaching has focused attention on the predictability of the anatomic location of the disk herniation, including the segmental level of disk herniation and the topographical position of the disk herniation in relation to the nerve root. The following case report illustrates a number of points.

CASE REPORT

Fig. 1 Preoperative posterior standing view of patient. Note marked sciatic spinal deformity with right lumbosacral list

A.B., a 45-year-old housewife, presented with a 1~ year history of mechanical low-back pain brought on initially by a lifting strain. Her chief complaint was left low-back pain of moderate intensity that radiated to the left thigh, recurred periodically, and improved with rest. Two years previously, the patient “turned to pick up something oft’a table” and had a severe episode of low-back pain. This episode improved with 2 months of bed rest. She had recurrent episodes of symptoms 9 and 14 months later, each episode improving with recumbency. She had pain aggravated by bending, lifting, sitting, and prolonged standing. Her pain improved with recumbency resting on her side with her hips and knees flexed. On initial physical examination the patient stood erect. She was treated with a flexion exercise program and a lumbosacral corset with improvement over the ensuing month.

The patient returned 3 months later in severe distress complaining of left-sided low-back pain with radiation to the left lower extremity. On physical examination. she stood with a markedly abnormal posture. She leaned forward and listed to the right side, away from the side of the pain (Fig. 1). Forward flexion was markedly limited with reversal of spinal rhythm noted on returning to the upright position. Extension and left-sided bending caused increasing pain. She demonstrated left calf weakness on fatigue testing as well as grade 4 strength of her left peroneal muscles. There was diminished sensation to pin prick along the lateral border of the left foot. Straight leg raising on the left was limited to 30° with reproduction of sciatic pain and a positive bowstring test result. Contralateral straight leg raising was normal. Her left Achilles reflex was absent.

Plain radiographs showed 12 thoracic vertebrae and ribs. Lumbosacral radiographs demonstrated a 30° right lumbosacral list and six lumbar vertebrae. Magnetic resonance imaging demonstrated a large extruded disk herniation at the L5-6 level on the left (Fig. 2).

It was anticipated that the herniation would be lateral to the nerve root based on the patient’s right-sided lumbosacral list. However, at operation a massive extrusion of disk material was seen in the axilla of the S1 root, that is. between the S1 root and the dural sac. The extrusion consisted of a large loose fragment along with multiple smaller fragments contiguous with the major disk herniation. Disk material had herniated through the annulus as well as the posterior longitudinal ligament. A complete diskectomy was performed with a free fat graft placed in the laminectomy defect and an L5-6 bilateral posterolateral spinal fusion.

Postoperatively, the patient noted immediate relief of her left lower extremity pain with resolution of her lumbosacral list (Fig. 3). She had normal sensation and early return of motor strength. Postoperative radiographs confirmed complete resolution of the sciatic spinal deformity with incorporation of bone graft.

DISCUSSION

FIG. 2. Sagittal (A) and axial (B) MRI views of lumbosacral spine showing large extrusion of the L5-6 disk on the left, in keeping with sequestration. Sagittal view also shows loss of signal density at L5-6 with the suggestion of some change at L4-5. However, diskography demonstrated a normal disk at the L4-5 level.

Predicting the anatomic location of a disk herniation based on a patient’s lumbosacral list has been reported (6,11,13,18). White and Panjabi (21) supported Finneson’s lumbosacral list hypothesis (6) in which the location of a disk herniation can be predicted from physical examination and knowledge of the laterality of the painful complaint. The suppositions are as follows: (a) increasing pain with lateral leaning results from increased stretch of the nerve root in relationship to the disk herniation; (b) increasing pain with contralateral leaning implicates an axillary herniation; and (c) increasing pain with ipsilateral leaning implicates a disk herniation lateral to the nerve root. Our patient’s intraoperative findings of a left L5-6 axillary disk herniation and clinical examination of right lumbosacral list with impaired left lateral lean contradict this hypothesis.

Porter (14) reviewed 100 patients with lumbosacral list and low-back pain with or without leg pain. Forty-nine of those patients satisfied three or more of McCulloch’s criteria. Twenty patients (20 of 49 or 40%) failed conservative management and required diskectomy. Porter found no consistency between lumbosacral list laterality and the topographical relationship of the disk herniation to the nerve root either axillary or lateral. Porter’s study is small, but it does point out the complexity of nerve root compression. Compression is a result of the degree of disk herniation combined with the anatomy of the superior articular facet that may be deformed by osteophyte formation and degeneration.

FIG. 3. Postoperative standing posterior view of patient showing erect posture with disappearance of lumbosacral list.

Arangio et al. (1) recently described two methods to objectively measure the degree of lumbosacral list, intercrestal line method (ICL). and interspinous line method (ISL). ICL measures lumbosacral list, but it does not correct for leg length discrepancy and, there-fore. can be inconsistent. Arangio et al. included patients with leg length discrepancies in their studies. Frymoyer et al. (7) described an ISL method to evaluate the degree of lumbosacral list, which was then modified by Arangio et al. Unfortunately ISL is inconsistent when comparing patients of different sizes or different listing segmental levels. In our experience the amount of lateral bend due to the lumbosacral list can be quantitated via Cobb-angle measurement of the sciatic spinal deformity radiographically (12) and the plumb line clinically (Fig. 4).

Weitz (20) reviewed 300 bending studies and felt that he could accurately determine the segmental level of disk herniation based on the bending radiographs. One hundred eight of the 300 patients (36%) had impaired bending. Of these 108, 31% went on to have myelography and/or surgery. The findings corresponded to the predicted level in all patients. Weitz demonstrated that the angular deformity of lumbosacral list is constant and localized to one disk space on lateral bending radiographs. We feel that an impaired lateral lean is related to a wide spectrum of pathology, including disk herniation, mechanical instability, spinal stenosis, and facet arthritis.

It has been noted that patients with an L4-5 disk herniation have a more significant list than at the L5-S1 level. This is related to the ability of the L4-5 level to rotate 7°-8° in the coronal plane as compared with l°-3° at the L5-S1 level (19,22). Our patient had a significant list, which may be attributed to her having six lumbar vertebrae and an L5-6 disk herniation. It is also commonly demonstrated that lumbosacral list is related to upright posture. Porter and Miller (14) stated in their series that lumbosacral list was abolished in patients with gravity removed, either lying in a recumbent position or hanging from a bar. This mechanism is probably related to unloading of the disk space, thereby decreasing intradiskal pressure.

The lumbosacral list is caused by an as yet undefined spastic reflex designed to splint the involved disk (5) and thus diminish the painful stimulation that results from disk herniation. In some patients this mechanism is so effective that the list persists after resolution of the pain. Alternating lists have bVen described (2,16); however, the pathologic anatoifly was not determined in these cases. We hypothesize-that alternating list is related to a central disk herniation or an extruded mobile fragment.

The pain-relieving phenomenon of lumbosacral list may be explained biomechanically by decreasing nerve root tension from the protruding mass, widening of the neural foramen with respect to a large disk herniation, or simply decompressing the mass effect of the disk herniation by opening up the disk space on the symptomatic side. In a review of 113 patients with back and/or leg pain, Khuffash and Porter (9) found an equal frequency of the presentation of list and cross-leg pain. Thirty percent of patients with list alone eventually required surgery. Forty-eight percent of patients with cross-leg pain alone required surgery. In patients with a lumbosacral list and cross-leg pain, 58% eventually required surgical intervention. They associated lumbosacral list and cross-leg pain with a poor prognosis for conservative management.

We conclude that radiographic study of the lumbosacral list may determine the segmental level of the disk herniation. Magnetic resonance imaging is the most accurate noninvasive means of investigating disk herniation (17). Laterality of the lumbosacral list does not indicate the relationship of the disk herniation to the nerve root, either axillary or lateral. Nevertheless, the lumbosacral list remains an important clinical sign.

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