Surgical Reconstruction of Degenerative Scoliosis

History:
The patient is a 56 year-old female who presented complaining of severe lower back pain. She had previously had two lumbar surgeries for leg pain and back pain; the first surgery was a decompression to alleviate pressure on her nerve roots and the second surgery was an instrumentation and fusion of L3-L4 for instability of the area after surgery. She reported that she got significant leg pain after the first surgery but has had debilitating back pain since that has not improved. She has had extensive physical therapy and pain management with no relief. She is still working as a nurse but has had to curtail her hours because of pain. She has no other medical problems but smokes 1 pack of cigarettes per day.

Physical examination showed the patient to have markedly decreased range of motion throughout her lumbar spine. She had no weakness or numbness in her legs and had symmetric reflexes bilaterally. While ambulating, she walked with a markedly pitched-forward gait.

Radiographs revealed a significant degenerative scoliosis with broken instrumentation and no evidence of a fusion at the L3/4 level. In addition, her spinal alignment in the lateral plane was almost completely straight with a dramatic loss of lumbar lordosis.

AP - Note the subluxations at L2/3 and L4/5 with disc tilting and no stabilizing osteophytes.	Lateral - 10° lordosis. Note the broken screw at L3.

Surgical Considerations:
The patient has several problems that need to be addressed. They include:

1. Broken right L3 screw
2. Probable pseudarthrosis at L3/4
3. Poor posterior fusion bed with coral debris
4. Loss of lumbar lordosis
5. Rotatory subluxations L2/3 and L4/5
6. Degenerative scoliosis
   

The treatment choices for this problem include reaugmentation of fusion, redo posterior spinal instrumentation and fusion, anterior spinal instrumentation and fusion, or a combined anterior and posterior instrumentation and fusion.

Of all of the choices, it was felt that the only option that would effectively address all of the problems was a combined anterior and posterior procedure. Given the amount of rotatory subluxation at the levels above and below the prior fusion, extension of the instrumentation posteriorly was important. With the poor posterior fusion bed combined with the loss of lumbar lordosis and a nicotine history, anterior structural grafting was also an important adjunct. Prior to any surgical undertaking, the patient was told that she needed to quit smoking; this was verified with urine cotinine levels that will show degradation products of nicotine over a period of time. The degenerative scoliosis from T12 to L5 is also an important consideration in picking levels to be fused.

Surgery:
The surgery was carried out in two stages done on the same day. The first stage was an anterior thoracoabdominal approach done through the left flank. The 9th rib was harvested for use as autogenous bone graft. Thorough anterior discectomies were done for all levels from T12 to S1 except for the L1/2 disc space which was angled towards the right, not allowing good access to the disc. Structural grafting was then done with Harms cages and autograft at all levels. The structural grafting provided an important bone interface for fusion as well as restoration of a more physiologic lumbar lordosis.

After the anterior procedure, the patient was turned prone and a posterior exposure was done. The instrumentation was removed and the fusion mass was explored; there was prolific reactive tissue about the coral on both sides of the spine with no evidence of a fusion. After a thorough debridement of the spine, pedicle screws were established at each level from T12 to S1. To protect the S1 screws and the L5/S1 fusion, iliac screws were also placed bilaterally. The L1/2 disc space was accessed via a transforaminal approach on the right, which allowed Harms cages to be placed in the L1/2 disc. Finally, all pedicle and iliac screws were connected to two rods. The patient tolerated the procedure well and lost a total of 800 cc of blood. Throughout the case spinal cord monitoring was used and remained unchanged from baseline. The patient was in the hospital for a total of 6 days and then went to a rehabilitation facility for 1 more week.

Post-op Radiographs:

Discussion:
Degenerative de novo scoliosis is a condition that usually presents after the age of 40. It is thought to be equally distributed between men and women, but females predominate in our experience. The etiology of degenerative scoliosis is thought to be asymmetric disc and facet joint degeneration without any stabilizing osteophytes. As the degeneration progresses more rapidly on one side, a vicious cycle ensues where the degenerating side bears more of the loads than the non-degenerated side causing more rapid degeneration and imbalance.

While the imbalance in the coronal plane is well-recognized, most of these patients have sagittal decompensation as well. This patient has a loss of lumbar lordosis with a sagittal Cobb measurement of T12-S1 of -10°. These patients have more sagittal decompensation than the typical patient with either lumbar stenosis or degenerative spondylolisthesis. The sagittal balance is an important factor in surgical decision-making in these patients, especially if lumbar back pain is a major complaint.

The curve patterns in degenerative scoliosis usually show two lumbar curves, one upper curve and one lower curve. The transitional area is usually the L3/4 disc with a lateral tilt of the L4/5 disc into the lower curve. Rotatory subluxations are an important hallmark of degenerative scoliosis and are often seen at L2/3, L3/4 and/or L4/5. The L5/S1 disc rarely shows any subluxation.

Surgery for degenerative scoliosis encompasses a wide spectrum ranging from a simple decompression to a multilevel anterior/posterior instrumentation and fusion. A decompression would be most appropriate for a patient with severe stenosis without major coronal or sagittal imbalance. The presence of bridging osteophytes also speaks to the stability of the spine and that a decompression may be feasible without destabilizing the spine.

Posterior instrumentation and fusion is appropriate for patients with severe stenosis who have a relatively flexible deformity without much sagittal imbalance. These patients will often have moderate subluxations that, if decompressed without stabilization, would worsen. A combined procedure is usually necessary for patients who have severe coronal and sagittal imbalance that is stiff and with severe subluxations.

While the appropriate surgical levels for idiopathic scoliosis are relatively well-agreed-upon, there is no similar system for picking the appropriate surgical levels in degenerative scoliosis. General rules for picking levels to be fused are to end a fusion in the stable zone. A common mistake is to end a fusion next to a level that has rotatory subluxation. This will almost invariably lead to worsening of the subluxation and a poor surgical result.