Journal of Orthopaedics

Background: The primary concern of LSI is radicular pain and pain due to instability.   The reduction in the disk height results in narrowing of the intervertebral foramen and there by produces compression of the emerging root. This can be relieved to a little extent by foraminotomy, but total correction of the real pathological processes could be achieved by increasing the disk height by the method of jacking of the spine so that the size of the intervertebral foramen increases and there is indirect decompression of root. Purpose of the study to understand the clinical outcome regarding the radicular pain by the technique of PLIF with distraction, instrumentation and fusion posterolaterally.
Patients And Methods: 21 patients between 2001 and 2004 who had discectemy, PLIF with posterior distraction instrumentation and posterolateral fusion were followed up for an average of 16 months. There were 12 females and 9 males. The clinical and radiological criteria of Lumbar Segmental Instability were defined for inclusion in to the study group. Clinical outcome was assessed VAS and Oswestry score.   Radiological assessment of fusion was done as the trabeculae crossing intervertebral space and graft incorporation posteriorly.
Observation And Results: 19 patients had single level PLIF, 2 patients had double level PLIF. 14 patients had double segment fusion posteriorly. Functional score was better in all cases but more so in lysis without listhesis.   There were no relation between sex and rate of fusion. At 16 months average follow up, 10 patients had graft incorporation posteriorly and 3 patients had trabeculae crossing the intervertebral disk space.   Fusion was faster at L5-S1 level.   The commonest functional spinal unit affected was L5-S1.
Discussion: LSI is a concern both for patients and surgeons, even today. Accurate preoperative identification of each component of the problem which produces a particular symptom should be addressed individually for a complete relief. The instability starts as a sclerosis of the end plates and then proceeds on to the anterior and posterior complexes, finally resulting in global instability, which makes the patient symptomatic.   It is the surgeons duty to intervene at any of these stages so that, this cascade of process can be arrested at any stage.
Conclusion: Maintaining the disk height by a posterior instrumentation with distraction prevents reduction of the disk height and thereby maintaining the size of intervertebral foramen.   This will help in reducing the radicular symptoms.

The primary concern of the Lumbar Segmental Instability (LSI) is radicular pain and pain due to instability. The radicular pain can be addressed to a little extent by foraminotomy. But, there is narrowing of the intervertebral foramen, which results partly from narrowing of the disc space, which reduces the size of the foramen. Jacking of the disk space and maintaining the disc height, increases the size of the intervertebral foramen indirectly. This can be achieved by posterior distraction, instrumentation, which can be combined with PLIF and postero lateral fusion. There is a controversy regarding the subsequent degeneration of the adjacent motion segments(7). In this method, adjacent motion segments may also be included in the fusion mass. A prospective study was performed to determine the clinical outcome of the LSI treated with posterior discectemy, PLIF and posterolateral fusion with instrumentation. Laminar hooks were used in all cases universally. No pedicular screws were used in any case. The abnormal motion segements were usually included in the fusion mass(5). But this predisposes to excessive stress in the adjacent motion segments. Abnormal motion segments adjacent to the segments which is fused are subjected to excessive stress which results in increased disc degeneration(6). And this will lead to symptoms like radiculopathy, discogenic pain, spinal canal stenosis and facet joint induced pain. The aim of the study to understand the functional outcome regarding the improvement of symptoms and understand whether fusion could be attained anteriorly and posteriorly. The technique of jacking up of the disc space, to maintain the disc height and indirectly enlarging the neural foramen and its clinical outcome regarding radiculopathy was specifically looked for.

Between July 2001 to August 2004, twenty-one patients who had PLIF with posterior instrumentation and posterolateral fusion were followed up. All cases were done by a single surgeon at a premier teaching institute in south India (Calicut Medical College). Patients between the ages of 22 to 58 were selected irrespective of sex. All cases with Lumbar segmental instability were selected. Posttraumatic and cases with infection and neoplasm were excluded. The clinical test for Lumbar segmental instability was a criteria for inclusion. The radiological criteria for LSI were more than 4 mm saggital translation and more than 10-degree saggital rotation angle. Cases with spondylolysis without listhesis , spondylolistheses, post operative LSI with progressive scoliosis, recurrent disk prolapse at the same level. Persistent radicular and non-radicular pain, in whom the clinical and radiological criteria of instability was present were included. Adjacent functional spinal units were looked for instability and radiculopathy.

The surgical technique was disk excision, posterior instrumentation with laminar hooks with distraction and jacking of the disk height along with PLIF at abnormal functional spinal units with facet joints and inter transverse fusion. Expandable stand-alone cages were used wherever possible. Standing AP, Lat, flexion-extension lateral, and rotation lateral views were taken pre operatively. In the lateral X ray, neutral flexion and extension were measured for AP translation, disk height and saggital rotation angle at the abnormal functional spinal units. LSI due to degeneration was classified according to University of California at Los Angeles grading scale. Grade I – No disc degeneration; Grade II – Mild, Grade III – Moderate, Grade IV – Severe. Grade III and IV were only included in this study. The radiological involvement of the intervertebral disk were assessed with Saraste Classification (Table 1) (8).

Stage I A	Normal disk height without dehydration
Stage I B	Normal disk height with dehydration
Stage II	Disk height decreased by less than 50%
Stage III	Disk height decreased at least by 50%
Stage IV	Disk height obliterated

Stages II, III and IV were included in this study. The variables like age, sex, pre op degree of LSI were compared with the post op results. Diagnostic variables were assessed with functional outcome. Pre op functional evaluation was done with visual analogue scale and Oswestry score.

The patients were regularly followed up with clinical and radiological assessment and persistence of symptoms work status functional status, pain medication, neurological status was documented. Fusion was assessed radiologically as trabeculae crossing intervertebral disk and graft incorporation posteriorly.

The study group included 21 patients with 12 females and 9 males. The average age was 40 (Range 22-58). The average duration of follow up was 16 months (ranging from 4 months to 28 months). All cases were operated PLIF with minced Iliac crest graft, Posterior instrumentation with posterolateral fusion, except in one case treated with expandable cage, PLIF and no posterior instrumentation along with posterolateral fusion with floating intertransverse bone graft. 2 patients had double level PLIF. Posterolateral fusion was done in 2 levels in 14 cases, 3 levels in 6 cases and 4 levels in 2 cases. Single level PLIF was done in 19 cases. The instrumentation extended 4 segments in 2 cases, 3 segments in 6 cases, 2 segments in 14 cases. Single level posterior instrumentation was not done in any cases. The condition of the adjacent spinal units were abnormal cephalad single level 14 patients, caudad and cephalad one each in 6 cases, abnormal caudad 1 and cephalad 2 cases. Number segments to be included in the fusion mass depended on the pre operative assessment. The clinical tests for segmental instability were positive in all cases. Sagital translation was 5 mm in 3 cases, 8 mm in 12 cases and 10 mm in 6 cases and 11 mm in 1 case. Saggital rotation angle was 12 degrees in 3 cases, 14 degrees in 13 cases, 15 degrees in 6 cases. Average disk height was 7 mm pre operatively. Average disk height post operatively was 13 mm.

Spondylolysis without listhesis	12
Spondylolisthesis	6
Post Operative LSI	1
Progressive scoliosis with LSI	1
Persistent radicular pain	1

Duration of time needed for fusion 16 months in 10 cases of fusions attained posteriorly, 3 patients in the same duration developed interbody fusion. Laminar hooks and rods were used in all cases. Expandable cage in one case, cross-links were used in all cases. Routine posterior decompression, foraminotomy, posterolateral fusion were done in all cases. Radiologically trabeculae crossing the intervertebral disk were seen in 3 cases and graft incorporation posteriorly was seen in 10 cases. Average pre op VAS (visual analogue scale) 80% , post operative VAS 30%. Pre op Oswestry scope 35, and post op 85. No significant correlation between the age and fusion were obtained. (P = >0.35) There was no relation between the sex and fusion. There was a relation between diagnosis and fusion – fusion was better with Spondylolysis without listhesis. P=<0.01). functional outcome was better in cases of Lysis without listhesis (n=12). VAS pre op 90% and post op VAS 20%. Oswestry Pre op 30 and post op 95. Functional assessment for spondylolistheses VAS 75% pre op, 35% postop. Oswestry pre op 40, post op 80. Oswestry and VAS were improved in the cases were adjacent functional spinal units were included in the fusion mass. Commonest functional spinal unit affected was L1 (14 cases) and in L4-5 in seven cases.

Lumbar segmental Instability is a concern both for patients and surgeons even today. Accurate pre op identification of each component of the problem, which produces a particular symptom, should be addressed individually for a complete relief. Instability in a particular functional spinal unit starts as sclerosis of the end plates with disk space narrowing, initial hypertrophy of the ligament of flavum and PLL. Later on there is translation listhesis, and angulations indirectly narrowing the intervertebral foramen and compressing the root, which may result in spinal canal stenosis, facet joint arthritis, capsular ligament laxity of the facet joint with facetal instability resulting in facet induced pain and discogenic pain and claudication and neurological deficit from global spinal instability in a particular functional spinal unit. It is the surgeons duty to intervene at any of these stages to reverse this cascade of processes, so that the symptoms can be reversed. Instability should be addressed by instrumentation, which later on should be taken over by fusion both interbody and posterolaterally. Otherwise, the implant will fail in the long run. Canal compromise should be addressed by decompression. In this study, stress is given to maintain the disk height by the technique of jacking up the disk space so that this will indirectly increase the size of the intervertebral foramen and decompressing the root, thus relieving the radiculopathy. Adjacent functional spinal units are usually abnormal and should be included in the fusion mass to avoid re operation for LSI at the adjacent functional spinal unit. Accelerated degeneration of the adjacent segments was described in literature(1,2,3,5). Once a particular functional spinal unit is fused, more stress occurs at the adjacent spinal unit, accelerating degeneration and LSI(4).

42.9% of patients were males, 57.1% were females. Females were commonly affected (n=12). 90.5% patients with single level PLIF and 9.5% patients with double level PLIF. 95.6% were treated with posterior instrumentation, PLIF and PL fusion. 4.7% were treated with anterior stand-alone cage and posterior floating graft without posterior instrumentation. The common LSI was at L5-S1 level (n=14). (66.7%). At 16 months average follow up 14.2% fusion achieved in PLIF. 47.6% fusion achieved posterolaterally. 8 out of 10 cases of posterolateral fusion were at L5-S1. Three out of 21 cases of fusion were at L5-S1 anteriorly. 80% of posterolateral fusion attained was at L5-S1. 66.66% of fusion by PLIF was at L5-S1. Early fusion was seen at L5-S1 compared to L4-5 , probably due to better mechanical stabilization to the sacrum, which is immobile. 57.1% of the cases were spondylolysis with listhesis. 28.5% cases were spondylolistheses. L5-S1 level (n=14) were commonly affected – 66.7%. L4-5 (n=7) was affected in 33.33% of cases. VAS improved from 90% to 20% in Lysis without listhesis.

Distraction – instrumentation helps in maintaining the disk height results in preventing the compression between the 2 vertebrae, which results in further narrowing of the disk space and foraminal narrowing. The traditional method of pedicular screws used to compress the vertebrae together reduces the disk height that narrows the intervertebral foramen. This could be a reason for persistent radicular symptoms even after achieving solid fusion. The better symptomatic results in this study may be due to either decompression of the root or decompression of the dura but this could also be due to a short term nature of the study and only by a long term follow up any further conclusion could be made.

Maintaining the disk height by a posterior instrumentation with distraction prevents reduction of the disk height and thereby maintaining the size of intervertebral foramen. This will help in reducing the radicular symptoms.

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