Spinal Osteotomy

Anatomy and Physiology

These are posterior approach osteotomies, and a proper understanding of spinal anatomy is critical. This includes bony anatomy, facet complex, disc, and ligament structures. Furthermore, it remains important to understand the 3D anatomical component of the deformity in a sagittal, coronal, axial, and rotational view.

PCO (SPO or Ponte osteotomy) refers to the removal of the facet joints, lamina, and posterior ligaments (supraspinous, intraspinous ligaments, and ligamentum flavum). The correction is through the disc space and is considered an anterior column lengthening procedure.

The SPO generally is labeled as an SRS-Schwab classification 1 and the Ponte osteotomy an SRS-Schwab classification 2. Often used interchangeably, the nomenclature regarding Ponte Osteotomy is specifically for more aggressive posterior resection of the thoracic spine, generally for kyphosis. SPO historically addresses the lumbar spine for ankylosing spondylitis.

PSO represents a three-column osteotomy in which the pedicles and portions of the body are resectioned in a wedge-type fashion. The posterior spine is shortened as the osteotomy is closed and compressed in its final stages. This is an SRS-Schwab classification 3. An extended PSO would fall into SRS-Schwab classification 4.

A VCR represents an aggressive removal of the vertebral body. A thin rim of bone can be left anteriorly to protect the great vasculature. This is an SRS-Schwab classification 5 with an extended version into the adjacent disc space as an SRS-Schwab classification 6.

Indications

PCOs can be performed overall multiple levels allowing for a smooth or harmonious restoration of sagittal balance. Generally, one level of PCO will result in 10 degrees of correction. Approximately 1 mm of resection will result in 1 degree of correction. This is ideal for cases of gradual correction, such as in Scheuermann Kyphosis. It also can be used as an adjunct at additional levels during more complex deformity corrections.

PSO is best suited for patients with a significant and rigid sagittal imbalance. The PSO can result in approximately 30 degrees of correction with maximum bony resection. They are best performed at the apex of a sharp deformity.

VCR is best suited for the most complex spinal deformities. This includes rigid multiplanar deformity, fixed coronal imbalance, hemivertebra excisions, and sharp angular deformities. Correction of up to 35 to 60 degrees can be obtained.[4][5][6]

Contraindications

Three-column osteotomy should be reserved for those patients with significant rigid deformity. Furthermore, the patient’s functional status, bone quality, medical co-morbidities, and overall quality-of-life goals should be merit consideration. 

Equipment

A variety of spinal navigation or adjunct technology can aid in the safe delivery of spinal instrumentation. These include the use of c-arm fluoroscopy, CT image guidance, robotic technology, dynamic surgical guidance, and combinations of the above technology. The decision is largely guided by the surgeon’s comfort and preference as well as realities of cost and availability. New technologies and improving technologies are emerging. 

Neuromonitoring for maximal expiratory pressure, somatosensory evoked potential, and spontaneous and triggered EMG is extremely beneficial.

Personnel

There is a growing debate among spinal specialists regarding the availability of one or two specialized spinal surgeons during osteotomy procedures. Regardless, the lead surgeon should be a spinal surgeon well trained and comfortable with complex deformity management. Having a dedicated anesthesia team is also essential. Furthermore, there will need to be a neuromonitoring team that includes a monitoring technician, plus a neurologist (generally off-site). For complex adult cases, proper integration with the medicine or critical care teams is important. 

For complex pediatric cases, interprofessional care is vital. This can include spine surgeon(s), primary pediatrician, dietary specialist, physical therapist, cardiologist, pulmonologist, gastroenterologist, child life specialists, and social workers as appropriate. 

Preparation

Significant pre-operative planning by the surgeon must be undertaken. For complex deformity correction, this can occur with the help of formal 3D models. A growing quantity of literature documents that team-based care is necessary for these cases to improve operative outcomes, reduce blood loss, and prevent infection. During the case, it becomes important for the surgeon to communicate and realize the portion of the procedure where he or she could stop and stage the operation if necessary. This can become a safety check.

From the patient’s perspective, all medical co-morbidities should be controlled. Meeting with the pre-operative team to ensure proper medical management in the adult population is critical. This is even more vital in the pediatric population, who might be prone to respiratory issues and malnutrition pre-operatively. Certain patients in the pediatric population benefit from gravity traction for a prolonged period prior to surgery. There should be an absolute emphasis on proper discussion with the patient and the patient’s family to manage and describe proper expectations for the pre-operative, operative, and post-operative course.

Technique or Treatment

Posterior Column Osteotomy

• Pedicle screw fixation
• Removal of the lamina, facet, and posterior ligaments (supraspinous, intraspinous, and ligamentum flavum)
• Posterior-only release with compression during rod placement to restore kyphosis
• Requires a mobile disc space anteriorly

Pedicle Subtraction Osteotomy

• Generally requires pedicle screw fixation at least two levels above and two levels below the PSO.
• Posterior elements are widely exposed.
• A detachment of the paravertebral muscles from the lateral portion of the vertebral body occurs after resection of the transverse process. Attention must be paid to the segmental vessels, which course the lateral wall of the vertebral body.
• Resection of the inferior articulating process the level above, pars, and the superior/inferior facets of the PSO level is performed. This technique also removes the lamina.
• Pedicles are resected either with a bone scalpel, osteotomy, or high-speed eggshell drilling.
• The temporary rod can be placed in cases of significant kyphosis or instability.
• The lateral portion of the pedicle and vertebral body, as well as the thin rim of the posterior vertebral body, are left for last.
• The posterior wall of the vertebral body can be taken down with a down-pushing curette or a deformity-specific instrument. Great care is taken not to violate the thecal sac anteriorly.
• The osteotomy is then closed with posterior compression.
• Final rod placement is then obtained with a minimum three rod and usually four-rod construct across the PSO.

Vertebral Column Resection

• Generally requires pedicle screw fixation at least four levels above and four levels below the VCR.
• Posterior elements are widely exposed.
• A detachment of the paravertebral muscles from the lateral portion of the vertebral body occurs after resection of the transverse process; Attention must be paid to the segmental vessels, which course the lateral wall of the vertebral body.
• The posterior elements are removed completely. The exiting nerve root should be well exposed and, at the thoracic level, it may be tied off.
• Resection of the rib head is also necessary at the thoracic levels, generally up to 4 cm.
• Pedicles are resected either with a bone scalpel, osteotomy, or high-speed eggshell drilling. The vertebral body is then removed in piecemeal, generally leaving a very thin rim of cortical bone anteriorly.
• A temporary rod is placed as the pedicles are resected.
• The lateral portion of the pedicle and vertebral body, as well as the thin rim of the posterior vertebral body, are left for last.
• The posterior wall of the vertebral body can be taken down with a down-pushing curette or a deformity-specific instrument. Great care is taken not to violate the thecal sac anteriorly.
• The osteotomy is then closed with posterior compression.
• Final rod placement is then obtained with a four-rod construct across the VCR.

Complications

Complications for adult spinal deformity range from 10.5% to 96%. The prospective multicenter Scoli-RISK-1 Study noted an immediate decline in lower extremity motor strength in 22.18% of patients undergoing complex spinal deformity surgery for adult scoliosis. At six months, this largely improved, with 20.52% noting an improvement in preoperative strength at 10.82% showing an improvement. Revision spinal surgery increases these risks.[7][8][9]

Three-column osteotomy by nature of the spinal deformity and the invasiveness of the procedure has an increased complication rate. In one series from the International Spine Study Group, 78.0% of patients had complications following three-column osteotomy for adult deformity. Sixty-one percent of patients had a significant complication. Another study illustrated that 108 adults treated with a PSO for kyphotic deformity had an 11.1% rate of neurologic deficit. In children, Lenke et al. found a 40% overall rate of complications and an 11.4% rate of neurological complications. 

Complications can include iatrogenic injury to the spinal cord, nerves, durotomy, infection, or pseudomeningocele. It also can include injury to the neighboring structures such as pneumothorax, pleural effusion, large vessel injury, abdominal injury, or medical sequelae such as deep vein thrombosis, myocardial infarction, or pneumonia.

Following the surgery, the patient must be monitored for instrumentation failure as well as the development of proximal junctional kyphosis or proximal junctional failure.

Clinical Significance

Improving technology has put a large reliance on posterior approach surgery for spinal deformity. Therefore, spinal osteotomy is a powerful tool for the spinal deformity surgeon to correct spinal deformity through a single approach. As such, this has become more integrated into training programs, and more familiarity with the techniques is becoming common. It remains important to recognize the morbidity platform associated with these procedures and the absolute need for continuity of interprofessional care.

Enhancing Healthcare Team Outcomes

Many patients have various degrees of spinal deformity. The patient should be encouraged first to seek physical therapy to increase joint mobility and muscle strength for those who have symptoms. Surgery is the last resort for spinal deformities. Spinal osteotomy is an umbrella term for techniques used by spinal surgeons to correct spinal deformity. They can be performed on pediatric or adult patients. The purpose is to establish normal range spinal curvature, relieve pain, and improve quality of life. These can be broken down into posterior column osteotomy (PCO), including Ponte osteotomy and Smith-Petersen osteotomy (SPO), pedicle subtraction osteotomy (PSO), or vertebral column resection (VSR). The SRS-Schwab classification nomenclature grades osteotomies from 1 to 6 by the amount of bone or disc removal. The overall prognosis for patients who undergo correction of the spine is fair. There are several complications that can be serious and lead to disability. Thus, an interprofessional team approach to care is necessary in these cases, including all clinicians (MDs, DOs, NPs, PAs), therapists, specialists (spinal, orthopedic, neurologic), and specialized nursing staff; this approach to care will yield the best possible results. [Level5]