Current Trends In Degenerative Adult Scoliosis

Introduction
Scoliosis in adult is defined as a deviation of more than 100 in coronal plane of the skeletally mature spine. This condition can be categorised into three types. Type I includes de novo primary degenerative scoliosis that occurs following degenerative changes in the spine which is usually asymmetric in its severity resulting in adult scoliosis. This predominantly occurs in the lumbar and thoracolumbar spine. Type II includes idiopathic adolescent scoliosis that progresses into adult years. In this case, the curve progresses due to mechanical reasons or secondary degenerative changes in the curve. Type III includes all secondary adult scoliosis with its cause either within or outside the spine. This is subdivided into Type IIIa where it is secondary to an adjacent primary curve of idiopathic, neuromuscular or congenital scoliosis, or a secondary adult scoliosis resulting from pelvic obliquity to compensate for limb length discrepancy or hip pathology or a lumbosacral transition anomaly, and Type IIIb when the scoliotic deformity occurs due to metabolic bone disease (frequently caused by osteoporosis).
Natural History
On an average the curve in degenerative adult scoliosis progresses by 3.30. Pritchell and Bortel have described radiographic risk factors that include >300 of Cobb angle, >6 mm lateral vertebral translation, grade III apical rotation, and prominent or deeply seated L5.

Pathogenesis
The asymmetric degeneration of the disc and facet joints lead to asymmetric loading of the spinal segment which in turn increase the asymmetric degeneration resulting in a vicious cycle leading on to curve progression. Further, this is compounded by bone weakness (osteoporosis) seen in the adult spine increasing progression of the curve due to asymmetric deformation and collapse of the vertebra of the affected spinal segment by asymmetric loading.

Instability of the spine results from degenerative changes affecting the various parts of the spinal column that destroys the discs, facet joints and joint capsule. This leads to facetal hypertrophy and endplate degeneration that result in narrowing of the spinal canal, and ligamentum flavum hypertrophy and calcification of joint capsules that result in narrowing of the lateral recess.

Clinical symptoms and signs
Degenerative adult scoliosis affects 6% of the population and the average age at presentation is 60 years. They typically present with back pain with radicular leg pain. Back pain may arise from the facet joint arthritis, and can be localised either at the apex of its concavity or in the counter curve from below the curve to above the curve.

Paravertebral muscle spasm can produce back pain which is diffuse in nature and may result from obliteration of lumbar lordosis. Pain radiating to the legs may be claudicant in nature and it depends on the root involvement. Radicular pain arises from compression of the nerve root on the concave side of the curve and also from stretching of the nerve root on the convex side of the curve. Rarely, they can present with neurological deficit with involvement of a single nerve root to cauda equine compression symptoms and signs.

Usually curve progression is not a significant issue in adult scoliosis but may be important in younger age. However, curve progression becomes a considerable problem once the curve reaches a certain degree as the progression of the curve continues to load asymmetrically on the osteoporotic vertebral bodies and facet joints resulting in further collapse. In addition, as age increases the co-morbidities increase and surgical intervention may become risky. Unlike, the adolescent scoliosis, adults >40 years of age rarely present with cosmesis as their main symptom. It may be occasionally seen in patients younger than 40 years of age.

Physical examination may not reveal any nerve tension signs or neurological deficit. Deformity and wasist asymmetry should be noted along with decompensation of the spine in the coronal and sagittal planes. As part if the clinical examination, hip and pelvis, and neck examination should be included along with vascular and abdominal examination as well.

Investigations
To evaluate the curve, standard posterior-anterior radiographs and lateral radiographs of the spine are needed along with full-length spine radiographs. In addition to static films, dynamic flexion and extension radiographs may be helpful to assess the translation of adjacent vertebrae. Further, these dynamic radiographs may also assess flexibility of the curve. It has been shown that L3 or L4 tilt angle, listhesis, thoracolumbar kyphosis and loss of lordosis correlate with more pain while Cobb angle, level of listhesis, sagittal pelvic tilt index and plumb line offset were not found to correlate with the visual analogue pain score.

Adult scoliosis often requires interventional radiographic procedures in addition. They include sequential discograms to assess morphology of the disc and concordant pain response; facet blocks, epidural blocks both as diagnostic and therapeutic response; and a myelogram preferably combined with a CT scan when there are larger magnitude curves with a significant dynamic component. A spiral CT with a myelogram and MRI scan are more useful to evaluate the adult degenerative scoliosis so as to obtain a clear understanding of the pathology.

Figure 1: Adult degenerative scoliosis - PA radiograph showing significant lumbar degeneration with scoliosis. Figure 2: Adult degenerative scoliosis - Lateral radiograph revealing lumbar kyphosis

Management
To aid in therapeutic decision in adult degenerative scoliosis some authors have given treatment rationale based on the severity of the curve in the coronal and sagittal planes, the degree of stenosis and the amount of subluxation. The severity of the curve in coronal plane is grade I if the curve is 100 - 250, II if 260 - 350, III if 360 - 450, and IV if >450 or >3 cm deviation from CVA. In the sagittal plane it is grade I if -400 to -600, II if -200 to -390, III if 00 to -190, and IV if frank kyphosis. The stenosis is graded into mild, moderate and severe. The subluxation is graded into grade I if <2 mm, II if 2 - 5 mm, III if 5 - 10 mm, and IV if >10 mm.

Conservative management
Conservative management may be indicated in grades I and II of coronal and sagittal plane deformity with mild to moderate stenosis and grades I and II of subluxation. Non-operative management consists of analgesics and anti-inflammatories, epidural steroids, physiotherapy exercises focusing on aerobic conditioning exercises and flexibility exercises, and thoracolumbar orthosis (TLO) or thoracolumbosacral orthosis (TLSO). TLO/TLSO may also be useful to decide on surgical management by using them temporarily for stabilisation of the spine and noting the pain response.

Isolated decompression procedures
Decompression alone may be performed in minor curves (grades I and II) with <2 mm subluxation but with significant stenosis. Isolated decompression procedures give pain relief from neurologic compression but run the risk of destabilising the spine. This is especially true when performed at the bottom of a rigid curve usually at L4/5 or L5/S1. The rigid curve may decompensate these segments in translation and may tip off the balance resulting in complete disability for the patient.

Decompression with fusion
To overcome the instability of the spine following decompression alone, fusion is mostly indicated along with decompression procedures. Fusion may be only posterior with or without instrumentation, or a combined anterior and posterior fusion with instrumentation. Decompression with posterior fusion is indicated in curves of smaller magnitude with short segment involvement (grades II and III) with grade III translation and moderate to severe stenosis. In these cases fusion of the lumbar spine at “adequate” lordosis in the presence of a severe thoracic kyphosis above may still lead to a flat back syndrome. Insufficient correction of lordosis is the cause of failure for this procedure, and correction of the lordosis leads to relief of back pain and successful fusion than correction of scoliosis.

Decompression with anterior and posterior spinal fusion with instrumentation is indicated in larger magnitude curves with long segment involvement (grade IV curves), severe stenosis, and grade IV subluxation. Overall, combined anterior and posterior fusion has better fusion rates, superior correction of deformity and improved functional outcome at the expense of increased risk, morbidity and technical difficulty.

Inclusion of sacrum/pelvis in fusion
The most critical segment to consider for fusion is the lumbosacral junction. As it takes all the movement, it is difficult to fuse L5/S1 junction and may result in pseudoarthrosis or failure of fusion. The impact of including the sacrum in fusion not only affects the iloiosacral joints but also the hip joints leading to overload of these joints and thereby accelerate the degenerative process in them. In posterior fusion surgeries, sacral screws alone may be inadequate and distal fixation below S1 screws may be indicated. It has been shown that distal fixation to S1 screw reduces 70% strain on the S1 screw, reducing the incidence of pseudoarthrosis. Successful fusion at L5/S1 may be achieved by distal fixation below S1 screw with anterior strut grafting at L5/S1. Translaminar screw fixation may be used where correction is not the goal as it is simple, less traumatic and minimally invasive. However, a pedicular system is the treatment of choice for long fixation and correction.

Figure 3: Postoperative PA radiograph revealing pedicle screw implants and good correction of scoliosis Figure 4: Postoperative lateral radiograph revealing good correction of lumbar kyphosis and a resultant lumbar lordosis in relation to thoracic kyphosis

Special problems to be considered in adult scoliosis

1. Length of fusion
Fusion should be avoided in general as much as possible, however it is an integral part in treating adult scoliosis. The length of fusion can be determined by preoperative discography, facet joint blocks and temporary orthosis. Patients should be warned that fusing a segment of spine might lead to accelerated degeneration in the adjacent segments due to abnormal overload. New trends include dynamic fixation and disc arthroplasty, however their results in adult scoliosis need to be evaluated.

2. Spinal segments adjacent to the level of fusion
Long segment fusion may act as a significant lever arm for the segments above and below. If there is a rigid spine which is either developed physiologically or following a fusion surgery at younger age for childhood scoliosis, this may result in decompensation above the fused lumbar spine resulting in overall imbalance of the spine and severe disability to the patient. Mid-lumbar or thoracolumbar curves may have a short compensatory curve at L5/S1or L4/5 with an oblique take-off. This compensatory curve may not correct with correction and fusion above L3/4 or L4/5 resulting in decompensation of the spine.

3. Inclusion of lumbosacral segment:
L5/S1 junction may be normal while first considering fusion above this level. However, there is increased chance of rapid deterioration or degenereation following fusion up to L5 as the entire load is taken at the L5/S1 junction. Further, pseudoarthrosis is common at this level, and distal fixation with a possible anterior fusion should be considered bearing in mind they have their own increased risks in general terms.

4. Previous scoliosis surgery:
Many juvenile/adolescent scoliosis treated with Harrington rod instrumentation 20-25 years ago now end up with degenerative adult scoliosis that is so complex and multifactorial, and may need overall rebalancing of the spine by single or multiple osteotomies.

5. Age and associated co-morbidities
These are important factors determining the general outcome of the patients. Further as the procedures involved aggravate the morbidity in these patients, the pre- and peri-operative management remains challenging in spite of advances in anaesthesiology. This has to be considered in patients younger than 50 years, and if there is significant curve progression with no other symptoms, still surgery may be considered just to prevent performing major surgeries at a later age with poor medical condition.

6. Osteoporosis
The surgical implants are difficult to be anchored to a weak bone and hence, new implants with larger screw diameter with better purchase and augmentation with cement are considered.

Complications
Pseudoarthrosis especially at L5/S1 junction is not rare (5% – 30%). Wound infection, nerve root deficits, urinary tract infection, cerebrovascular accident, venous thromboembolism, and pelvic fractures have been reported.

Recurrence of nerve compression, back pain, flat back syndrome, and failed back surgery syndrome are other known complications.

Outcome
In general, pain reduction after appropriate surgery has been reported between 70% and 80%. There is improvement in age-matched general outcome in >70% of the patients after surgery.

References

  1. Aebi M. The adult scoliosis. Eur Spine J. 2005; 14(10): 925-48.
  2. Alegre GM, Gupta MC, Bay BK, Smith TS, Laubach JE. S1 screw bending moment with posterior spinal instrumentation across the lumbosacral junction after unilateral iliac crest harvest. Spine. 2001; 26(18): 1950-5.
  3. Bridwell KH, Dewald RL, editors. Adult scoliosis and related deformities. 2nd edition. The textbook of spinal surgery, vol.1. Philadelphia: Lippincott-Raven; 1997. pp 777-95.
  4. Bridwell KH. Where to stop the fusion distally in adult scoliosis: L4, L5 or the sacrum? In: Pritchard DJ, editor. Instructional Course Lectures, vol. 45. Rosemont (IL): AAOS; 1996.pp 101-7.
  5. Grubb SA, Lipscomb HJ, Suh PB. Results of surgical treatment of painful adult scoliosis. Spine 1994; 19(14): 1619- 27.
  6. Gupta MC. Degenerative scoliosis. Options for management. Orthop Clin N Am. 2003; 34: 269-79.
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