Smith-Petersen et al. first described SPO in 1945 for correction of fixed sagittal deformity in patients with rheumatoid arthritis [22]. It has been referred to as “Chevron” osteotomy, “extension” osteotomy, or “Ponte” osteotomy. SPO involves removal of the posterior bony elements including the bilateral facet joints, inferior portion of the lamina, and inferior portion of the spinous process, and removal of the posterior ligaments at the osteotomy level (Fig. 8.2a) [4, 8, 23]. The osteotomy is closed with the axis of rotation at the posterior aspect of the disc space, which results in widening of the anterior disc space and disruption of the anterior longitudinal ligament and hence requires a mobile disc space (Fig. 8.2b). It is usually not effective if the disk space is immobile, as in the case of bridging anterior osteophytes [8]. SPO produces shortening of the posterior column and lengthening of the anterior column, with attendant risks, including vascular, neurological, pseudarthrosis, or gastrointestinal complication [4, 8, 22]. One modification of the SPO procedure is to use an interbody graft or spacer in the middle or anterior third of the disk space and then to compress posteriorly using the graft as a fulcrum; this provides a greater degree of lordosis, with less risk of compromising the neural foramina [8].

The amount of correction typically achieved with SPO is approximately 10° per level, or 1° of correction for each millimeter of bone removed [1, 4, 8, 22]. There have been reports of aggressive techniques of posterior extension osteotomy with anterior osteoclasis achieving more correction, but this is associated with higher risk of complications. SPO is typically indicated for cases with long, gradual sweeping deformity, with mobile intervertebral disc spaces, and no more than moderate elevation of SVA, features typically not associated with rigid deformities [24]. The classic indication for SPO is Scheuermann’s kyphosis, but it can be used in the treatment of mild iatrogenic fixed sagittal imbalance (6–8 cm) [8, 24]. The role of the SPO is limited in fixed sagittal deformity as these osteotomies have limited effectiveness in sharp, angular kyphosis and are not effective in the presence of anterior bridging osteophytes or across previously fused segments due to lack disc mobility. In addition, SPO is not without risks, as anterior column lengthening puts vascular structures at risk, particularly in the elderly and in patients with ankylosing spondylitis, who may have calcified major vessels [4, 8]. There is also risk of gastrointestinal complication secondary to superior mesenteric artery syndrome. Neurological complications have been reported in as high as 30 % of cases, mainly radiculopathy secondary to compression of nerve roots in the foramen from closure of the SPO [4]. Other complications include, but are not limited to, pseudarthrosis, bleeding, durotomy, and pedicle fracture. Compared with three-column osteotomies, SPOs are usually associated with less operative time, blood loss, and rates of neurological complication [25].

In an attempt to cause less disruption of the anterior column, polysegmental osteotomy (Fig. 8.3a) can be performed to correct sagittal deformity. Hehne et al. first described polysegmental lordosis osteotomy, with posterior osteotomy at each level, producing approximately 10° of correction per segment [26]. By closing multiple posterior osteotomies over multiple segments with transpedicular fixation, a more gradual correction of kyphosis is achieved with less disruption of the anterior longitudinal ligament (Fig. 8.3b) [4, 8, 23]. This technique has similar limitations as the standard SPO for correction of rigid deformities including limited effectiveness in the setting of a previously fused level, bridging anterior osteophytes, or sharp kyphosis.

PSO is typically used to correct fixed sagittal deformity with sharp or angular kyphosis in patients with SVA >8 cm and is often applied for the treatment of acquired or iatrogenic flat back, ankylosing spondylitis, and for rigid deformities that lack anterior flexibility needed for SPO to be effective [4, 23, 24]. PSO can be technically challenging, with substantial blood loss from the epidural venous plexus and cancellous bone during the osteotomy, and it is more commonly performed below the conus in the lumbar region to reduce neurological complication from thecal sac manipulation and wedge closure, but can be performed in thoracic and cervical level if indicated but with increased risk [1, 10, 24, 27]. If it is performed in thoracic or cervical spine, extra precaution should be taken when working around the spinal cord and the thecal sac should not be retracted [24]. Resecting a portion of the rib bilaterally along with the costovertebral joints during PSO in the thoracic spine can help to facilitate a safe approach to the vertebral body laterally without thecal sac retraction. PSO tends to be avoided in distal lumbar vertebra because there are fewer fixation points available distally [24]. PSO is most commonly performed at L2 or L3, as these levels are generally below the conus and have a sufficient number of fixation points distally. Nevertheless, the vertebral level of the PSO should be guided by the type and location of the pathology.

In patients with focal fixed-angle sagittal deformity, PSO is typically performed at the level of kyphosis; however in the absence of focal thoracolumbar kyphosis, lumbar PSO is the preferred option. In addition to providing greater correction of deformity, PSO has an advantage over SPO, as it does not require a mobile anterior segment or disc space and can be performed in patients with circumferential fusion across multiple segments, previous laminectomy, or area of rotation, although these features do potentially increase the technical difficulty and the risk of complications [24]. The extensive cancellous bony contact secondary to wedge osteotomy increases stability and reduces the risk of pseudarthrosis. Also, by performing an asymmetrical wedge resection osteotomy correction of both sagittal and coronal plane deformity can be achieved. Extended PSO is a modification that involves extension of the bony resection cranially to include the rostral vertebral endplate with removal of the rostral intervertebral disc. The wedge osteotomy is closed over the vertebral endplate of the rostral vertebral body providing a greater degree of correction [3, 4, 7]. If necessary, an interbody spacer can be placed in the middle or anterior third of the disc space to act as a fulcrum to help prevent compromise of the neural foramina.

The degree of deformity correction with PSO has been studied in multiple cadaveric, clinical, and radiographic studies. Li et al. obtained a mean of 36.4° correction with standard PSO and a mean of 48.5° correction with the modified extended PSO in a cadaveric study [4, 28]. Multiple clinical studies have shown deformity correction between 26.2° and 40.1°, with an average correction of 32° with PSO [1, 2, 4, 11, 23, 24, 29, 30]. The expected correction for PSO in the thoracic spine is less than in the lumbar spine, likely due to the shorter heights of thoracic versus lumbar vertebral bodies.

MacLennan first described vertebral column resection in 1922 for treatment of severe scoliosis [31]. Suk et al. developed the posterior-only approach for VCR, with complete resection of one or more vertebral segments through a posterior-only approach, with the goal of achieving sagittal and coronal balance with shortening of the spinal column [32–34]. This technique involves stabilization of the vertebral column with transpedicular screw fixation, followed by compete resection of all posterior elements at the level of the VCR, the vertebral body at the apex of deformity, and the adjacent rostral and caudal intervertebral discs [34]. In most cases, anterior fusion is performed via the posterior approach with structural support using an anterior cage that preserves anterior column height and enhances the degree of correction [4].

VCR is a complex procedure with significant risk of morbidity and neurological injury, especially when performed in the thoracic and upper lumbar region, as the spinal cord and conus may be vulnerable to injury during vertebral body resection, and they may be already compromised secondary to the deformity [31]. Therefore, VCR is generally reserved for severe, complex, rigid three-dimensional deformities that are not amenable to treatment with other techniques. It is primarily used for severe fixed sagittal deformity with severe coronal plane deformities, congenital kyphosis, hemivertebra, L5 spondyloptosis, and resection of spinal tumor [4, 6]. Suk et al. [34] reported correction of 61.9° in the coronal plane and 45.2° in the sagittal plane, whereas Lenke et al. [35, 36] in their two studies, noted major curve improvements of 57–61° in scoliosis cases, 45–56° in global kyphosis, 59–51° in angular kyphosis and a combined 98–109° in kyphoscoliosis cases. VCR remains the most powerful method for three-dimensional deformity correction, but this technique is associated with relatively higher risk of morbidity and neurological injury [25].

Even though potential benefits of surgery for adult scoliosis patients have been shown in multiple studies [37–42], these procedures are not benign and need careful planning and understanding of the risks and benefits by both patients and surgeons [40]. Smith et al. reviewed the SRS morbidity and mortality database for cases of thoracolumbar fixed sagittal plane deformity (FSPD) and analyzed the short-term complication rates in patients undergoing osteotomy, based on correction technique, surgical approach, surgeon experience, patient age, and history of prior surgery [25]. A total of 578 cases of FSPD were identified, of which 402 (70 %) were treated with an osteotomy, including 215 with PSO, 135 with SPO, 19 with anterior discectomy with corpectomy (ADC), 18 with VCR, and 15 with unspecified osteotomies. There were 170 complications (29.4 %) in 130 patients, and a mortality rate of 0.5 %. The more common complications included durotomy (5.9 %), wound infection (3.8 %), neurological deficit (3.8 %), implant failure (1.7 %), wound hematoma (1.6 %), epidural hematoma (1.4 %), and pulmonary embolism (1 %). The overall complication rates associated with cases including an osteotomy were significantly higher than those not requiring osteotomy (34.8 % vs. 17 %), and this remained significant after adjusting for patient age, surgeon experience and history of prior surgery. There was a progressive increase in complication rates with more aggressive osteotomy, from no osteotomy (17.0 %), to SPO (28.1 %), to PSO (39.1 %), to VCR (61.1 %). In addition, there was a higher rate of complication in patients who underwent revision procedures (24.5 % versus 18.2 %). These risks should be carefully considered in patient counseling and surgical planning. To what degree a patient needs to be corrected and how much he or she can tolerate varies with each individual. Evaluation of this risk–benefit balance should be personalized, with careful discussion with the patient. When considering surgical treatment, one should carefully consider patient age, overall health of the patient, severity of the symptoms, impact on patient quality of life, and willingness of the patient to accept the risk of surgery. A recent multicenter study has looked into the risk factors for major perioperative complication in adult spinal deformity surgery and found significantly higher rates of complications were associated with staged and combined anterior–posterior surgeries [43]. Although these complex surgical procedures have been shown on average to be significantly beneficial in treating these patients, surgery is not necessarily indicated for every patient with sagittal deformity, and nonoperative methods should generally be the first line of treatment.

The main indication for PSO is fixed sagittal imbalance that needs more than 30° correction of lumbar lordosis [11]. Many of these patients have a history of previous fusion and a rigid flat back that requires three-column osteotomy for alignment correction. Patients with sharp angular kyphosis, ankylosing spondylitis with cervicothoracic kyphosis or thoracolumbar kyphosis, and progressive untreated idiopathic scoliosis may require PSO for adequate correction of deformity.

PSO is a technically demanding procedure, with relatively longer operative time and blood loss in comparison with SPO. When considering PSO, the patient’s overall health should be properly assessed to evaluate if he or she can tolerate the procedure. Patients with fixed sagittal deformity with severe coronal plane deformity may benefit more with a VCR. Similarly, patients with a gradual curve and an SVA <8 cm, or requiring only 10° to 20° of lordosis correction may be better treated with one or more SPOs, which are relatively less morbid.

All patients with spinal deformity should have a global assessment of the spine with long cassette (36-in.) standing posteroanterior (PA) and lateral radiographs, with the hips and knees fully extended, arms flexed and hands positioned along the clavicle, head facing forward, and feet placed shoulder width apart [44]. The pelvis and hip joints should be included in the film to demonstrate the true extent of the deformity. Changes in the joint angle of the lower extremity may change the sagittal alignment; hence, it is important to follow strict standard protocols for patient X-ray positioning. The lateral radiographs should include C2 to the pelvis along with femoral head. The sagittal parameters, including SVA, regional spinal alignment (lumbar lordosis and thoracic kyphosis), and pelvic parameters, including pelvic incidence and pelvic tilt, should be measured. On the PA view, the margins of the rib cage and the pelvis along with the femoral heads should be clearly visible. Coronal curves and coronal imbalance should be measured. Visualization of the ribs aids in identifying associated rib cage deformity and helps in the assessment of vertebral body rotation at the apex of the coronal curve. These radiographs can be complemented with additional studies including flexion/extension views, side bending views, supine full-length views, and use of traction or bolster radiographs to assess flexibility. Flexibility should be evaluated in all curves that are considered for surgical correction, as it helps in predicting the magnitude of curve correction that can be achieved, the number of spinal levels needed to be fused, and the need of osteotomy [12].

Advanced imaging studies, including computed tomography (CT), CT myelograms, and/or magnetic resonance imaging (MRI), are typically required to evaluate the bony anatomy, spinal canal, neural elements, vascular anatomy, and discs. Preoperative MRI and/or CT myelogram can be particularly important in patients with neurological symptoms or deficits. CT myelogram can be particularly useful in the setting of previous instrumentation, since it is often less affected by imaging artifact compared with MRI.

Dual energy X-ray absorptiometry (DEXA) scans provide valuable information regarding bone density, and patients should be treated for osteoporosis prior to surgery if feasible. Patients with kyphoscoliosis with increased SVA but low PT (inability to compensate) should be evaluated for hip or lower extremity pathology, such as hip deformity or hip flexion contracture before considering surgical correction, as failure to diagnose these pathologies can lead to poor postoperative outcome. These patients are usually referred for preoperative physical therapy for better spinopelvic alignment prior to surgical fusion. The Thomas test is helpful in the assessment of hip flexure contracture [15].