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SPINE Voluame 39, Number 11, pp 870-880 ©2014, Lippincott Williams & Wilkins
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Radiographical and Clinical Outcomes of Posterior Column Osteotomies in Spinal Deformity Correction Ian G. Dorward, MD,* Lawrence G. Lenke, MD,t Geoffrey E. Stoker, BS,t Woojin Cho, MD, PhD,+ Linda A. Koester, BS,t and Brenda A. Sides, MSt
Study Design. Prospectively enrolled, retrospectively analyzed case series. Objective. To evaluate a large series of pédiatrie patients/patients with adult spinal deformity undergoing surgery with posterior column osteotomies (PCOs). Summary of Background Data. Osteotomies of the posterior column (Smith-Petersen or Ponté) are used to reduce kyphosis, increase lordosis, or increase spinal flexibility. However, little focused evidence exists regarding the efficacy and safety of this technique. Methods. A total of 128 consecutive patients underwent posterior spinal fusion with PCOs with minimum 2-year follow-up. Seventyfive were primary surgical procedures; 53 were revisions. Data were collected from hospital charts, clinic notes, radiographs, and standardized questionnaires (Scoliosis Research Society-30 and Oswestry Disability Index). Results. A total of 128 patients aged 37.6 ± 21 years underwent 518 PCOs (mean, 4.0 ± 2.2 yr)with 14.4 ± 3 mean instrumentation levels, with 3-year (range, 2-6.8 yr) average follow-up. PCOs were used for kyphosis correction in 49%, scoliosis correction at the apex of a curve in 13%, and both in 38%. One hundred six patients had complete radiographical data available for evaluation. Mean kyphosis correction per PCO was 8.8° ± 7.2°, varying with patient age (10.2° for those younger than 21 yr vs. 7.7° for those
From the Departments of *Neurosurgery and tOrthopaedic Surgery, Washington University School of Medicine, St. Louis, MO; and ^Department of Orthopaedic Surgery, Albert Einstein College of Medicine, Montefiore University Hospital, Bronx, NY. Acknowledgment date; May 29, 2012. First revision date: December 10, 2012. Second revision date: August 19, 2013. Third revision date: February 12, 2014. Acceptance date: February 14, 2014. The manuscript submitted does not contain information about medical device(s)/drug(s). No funds were received in support of this work. Relevant financial activities outside the submitted work: board membership, grants/grants pending, payment for lectures, patents, royalties, travel/ accommodations/meeting expenses and fellowship grant support. Address correspondence and reprint requests to Lawrence G. Lenke, MD, Washington University School of Medicine, Department of Orthopaedic Surgery, 660 S Euclid Ave, Campus Box 8233, Saint Louis, MO 63110; E-mail: [email protected] DOI: 10.1097/BRS.0000000000000302 870
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21 yr or older, P < 0.0001) and region of the spine: thoracolumbar (T10-L2) 11.6°, lumbar (L2-S1 ) 9.4°, midthoracic (T6-T10) 7.2° and proximal thoracic (T1-T6) 3.6°. With PCOs at the apex of a curve, the maximum coronal Cobb decreased from 66° ± 21° to 31° ± 14° (P < 0.0001). Average estimated blood loss was 1419 ± 887 mL, correlating with greater age {P < 0.0001) and more instrumented levels (P < 0.0001), but not with the number of PCOs (P = 0.32). Complications occurred in 31 (24.2%) patients, including 4 radiculopathies (none attributable to PCOs). Complications did not correlate with the number of PCOs (P = 0.5). Six (4.7%) patients had loss of spinal cord monitoring or a failed wake-up test that could be attributed to overcorrection with PCOs, but none had postoperative deficits. Oswestry Disability Index scores improved (34.4 ± 17 to 23.6 ± 18, P < 0.0001), as did normalized Scoliosis Research Society-30 scores (63.7 ± 13 to 76.4 ± 15, P < 0.0001 ). Conclusion. Patients in this series undergoing posterior spinal fusion with PCOs achieved overall favorable outcomes for spinal deformity correction. The number of PCOs did not correlate with increased estimated blood lossor complications. The main technical concern was overcorrection, but neurological consequences associated with overcorrection were identified by intraoperative spinal cord monitoring and wake-up tests, and no patients experienced permanent neurological deficits related to PCOs. Key words: pédiatrie spinal deformity, adult spinal deformity, posterior spinal fusion, posterior, column osteotomies, SmithPetersen osteotomy. Ponté osteotomy, complications, outcomes.
Level of Evidence: 4 Spine 2014;39:870-880
O
steotomy of the posterior column of the spine to correct spinal deformities was first described in 1945 by Smith-Petersen.' Later modifications of the posterior column osteotomy (PCO), such as the Ponté technique, have used advances in segmental instrumentation to obtain more durable, safe, and effective results in correcting excessive kyphosis or inadequate lordosis.-'^ However, confusion regarding the nomenclature of the PCO—with names including Smith-Petersen osteotomy. Ponté osteotomy. Ponté procedure, posterior shortening osteotomy, chevron osteotomy, and segmental osteotomy—could hamper efforts at research May 2014
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Posterior Column Osteotomies • Dorward et al
Figure 1. A, A posterior column osteotomy begins with resection of the inferior facets bilaterally. B, After facetectomies, a Leksell rongeur is used to remove the spinous process and portions of the lamina. The rongeur is further used to remove the dorsal portion of the ligamentum flavum until a bulge of epidural fat is noted in the midline. C, A 3-mm Kerrison punch is used in a medial to lateral direction to remove the ligamentum flavum and bone from the lamina superiorly and the superior articular process inferiorly, continuing to the lateral extent of the foramen. D, The correction step of a posterior column osteotomy involves closure of the interval of bony resection through the bilateral facets, thereby apposing (or nearly apposing) the remaining portions of superior and inferior facet still overlying the interpedicular space. Care must be taken to inspect the foramen for any remaining bone or ligament that could result in neural compression after osteotomy closure.
and categorization. Thus, a relative paucity of recent literature exists regarding the radiographical and clinical outcomes after osteotomy of the posterior column compared with the more aggressive 3-column osteotomies (pedicle subtraction osteotomy [PSO] and vertebral column resection [VCR]). Por the sake of clarity, then, we will use the term "posterior column osteotomy" to refer to any osteotomy that involves resection of bilateral facets and the ligamentum flavum followed by posterior compression/distraction. We explored the outcomes of a large series of patients undergoing PCO to augment either kyphotic or scoliotic corrections, although a posterior-only approach. We hypothesized that PCOs not only would provide correction for pure sagittal deformities, but would also serve as a safe adjunct at the apex of scoliotic curves. We also hypothesized that complications referable to PCOs would be minimal, and that Spine
posterior-only PCOs would neither lose substantial correction nor lead to coronal decompensation.
MATERIALS AND METHODS Patients Institutional review hoard approval was obtained prior to initiation of the study and the project deemed minimal risk given its retrospective nature. We reviewed a database of prospectively enrolled adult and pédiatrie patients who underwent posterior spinal fusion for the treatment of scoliosis, kyphosis, sagittal imbalance, prior surgery requiring multilevel reconstruction, or a combination of the ones mentioned earlier. We included 128 patients who underwent at least 1 PCO and had a minimum 2-year clinical/radiographicai follow-up. We excluded patients who underwent anterior approaches www.spinejournal.com
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Figure 2. A 33-year-old female with a history of aT12 fracture and previous T4-L2 PSF with subsequent instrumentation removal presents with progressive kyphosis. She underwent T2-L3 PSF with PCOs at 5 levels, yielding a 6 1 % correction rate. A, Preoperative AP radiograph. B, Postoperative AP radiograph. C, Preoperative lateral radiograph. D, Postoperative lateral radiograph. E, Preoperative posterior clinical photograph. F, Postoperative posterior clinical photograph. G, Preoperative lateral clinical photograph. H, Postoperative lateral clinical photograph. PCO indicates posterior column osteotomy; PSF, posterior spinal fusion; AP anteroposterior. 872
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Figure 3. A 47-year-old female with adult idiopathic scoliosis and only 8% curve flexibility underwent T3-L4 PSF with apical PCOs at 6 levels. Surgery yielded a 52% correction rate. A, Preoperative AP radiograph. B, Postoperative AP radiograph. C, Preoperative lateral radiograph. D, Postoperative lateral radiograph. E, Preoperative posterior clinical photograph. F, Postoperative posterior clinical photograph. G, Preoperative lateral clinical photograph. H, Postoperative lateral clinical photograph. PCO indicates posterior column osteotomy; AP, anteroposterior; PSF, posterior spinal fusion. Spine
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1 AB Lb 1 ^ ;^»ïï^Tl f-,,
Posterior Column Osteotomies • Dorward et al
, Jg^jgïgJJte N = 128
Age at surgery* (yr)
37.6 ± 2 1 (5.6-82.1)
Sex Male
39(30.5)
Female
89 (69.5)
Operative diagnosis Adolescent idiopathic scoliosis
18(14.1}
Adult idiopathic scoliosis
29 (22.6)
Congenital kyphoscoliosis
3 (2.3)
Degenerative scoliosis
6(4.7)
Fixed sagittal imbalance
26(20.3)
Neuromuscular/syndromic
21 (16.4)
Scheuermann kyphosis
21 (16.4)
Post-traumatic kyphosis
4(3.1)
Primary surgery
76 (59.4)
Revision surgery
52 (40.6)
Plane of PCO correction Sagittal only
63 (49.2)
Coronal only
17(13.3)
Both planes
48(37.5)
PCOs performed Total
518(100)
Through fused segment
. 104(20.1)
Through pseudarthrosis
35 (6.8)
Primary PCO Length of follow-up* (mo)
379(73.2) 35.8 ± 19(24.0,81.6)
'Values indicate mean ± standard deviation (range). Values indicate number (%) unless otherwise specified. PCO indicates posterior column osteotomy.
for release and/or fusion at PCO levels, or other concomitant osteotomies (PSO or VCR). Patient records were reviewed and data were abstracted and analyzed. Research was performed at Washington University School of Medicine. Radiographical Review Of the 128 patients, 22 had incomplete radiographical records available thus were excluded. We evaluated standing 36-inch anteroposterior and lateral radiographs at 3 time points: preoperative, initial (within 1-8 wk) postoperative, and final postoperative (2-year or later follow-up). Preoperative evaluations also included hyperextension lateral and anteroposterior side-bending radiographs. All radiographical measurements conformed to the recommendations of the Spinal Deformity Study Group.** In addition to standard measurements, we measured Cobb angles for each individual 874
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PCO level on lateral radiographs and for segments of contiguous PCOs on both lateral and anteroposterior radiographs. Regions of the spine in which PCOs were performed were defined as proximal thoracic (T1-T6), midthoracic (from T6-T10), thoracolumbar (T10-L2) and lumbar (L2-S1). For data analysis, PCOs were categorized as being used for either sagittal correction or coronal correction. Osteotomies falling into the sagittal correction group were clearly defined in the operative summary as being used for reduction of kyphosis or creation of greater lordosis. Outcomes Oswestry Disability Scores and Scoliosis Research Society Scores (22, 24, 29, or 30 converted to a 100-point percentage scale for the purposes of standardization) were used to evaluate patient outcomes.
Data Analysis A biostatistician assisted in all aspects of statistical analysis, which was generated using SAS version 9.1.3 of the SAS System for Linux (SAS Institute Inc., Cary, NC). For radiographical data featuring repeat measurements at different time points, longitudinal analyses were performed using mixed model repeated measures analysis of variance. If initial analyses detected significant change over time between groups, statistical contrasts were used to determine at which time point the change occurred, and, further, to test the null hypothesis that the changes between time points in the group in question were the same as corresponding changes in other groups. Data sets with significant heterogeneity of variance across time points and groups were analyzed using rank- or log-transformed data. For complications and other clinical variables deemed non-normally distributed, differences between groups were assessed using nonparametric tests such as the Wilcoxon sign rank test. For small samples of categorical data, the Fisher exact test was used. PCO Procedure The PCO technique as used in this series is depicted step-bystep in Figure 1. Principle indications for PCOs were ( 1 ) reducing kyphosis or increasing lordosis (Figure 2); or (2) increasing the flexibility of a stiff scoliosis (Figure 3) to enable correction via other maneuvers, that is, rod derotation techniques. For sagittal plane correction, the number and location of PCOs were generally selected on the basis of previous findings that 10° of correction can be obtained per PCO.^ Although few firm rules were used when deciding between PCO, PSO, or VCR for the patients in this series, some general principles were followed. PCOs were chosen in cases with more gradual/ less angular curves because focal and/or angular deformities more readily lend themselves to correction with PSO (sagittal plane in the lumbar spine) or VCR (sagittal or coronal plane in the thoracic spine). PCOs were also chosen only when the disc spaces were presumed mobile enough to allow for correction. PCOs were favored over PSO or VCR when they seemed May 2014
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90- T— 80"
10'
PreOp
Hyperextension
Initial PostOp Final PostOp
PreOp
|
Maximum Cobb Angles
Hyperextension
Initial PostOp | Final PostOp j
PCO Segment Cobb Angles Sagittal Plane
Figure 4. Sagittal plane Cobb angle changes for the maximum Cobb angle and Cobb angle over regions of contiguous PCOs. Data shown are means with 95% confidence intervals. The P values above each Cobb angle category refer to the difference between that Cobb angle measurement and the preoperative Cobb angle. PCO indicates posterior column osteotomy; preop, preoperative; postop, postoperative.
sufficient to effect adequate correction without subjecting a patient to the expected increase in morbidity associated with a more extensive 3-column osteotomy. During every procedure, intraoperative monitoring with neurogenic or transcranial motor evoked potentials (MEPs) were used. In addition, if no perturbations in monitoring were noted during the case, a full wake-up test was still performed
Figure 5. Mean correction afforded by PCOs based on region of the spine in which they are performed: proximal thoracic (T1-T6, 3.6° ± 10.0° of correction), midthoracic (T6-T10, 7.2° ± 5.8°), thoracolumbar (T10-L2, 11.6° ± 7.2°), lumbar (L2-L5, 9.4° ± 5.2°). PCO indicates posterior column osteotomy.
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at the end of the procedure to document that no change in neurological function had occurred.
RESULTS Patient demographic characteristics are depicted in Table 1. Mean follow-up was 3.0 years (range, 2-6.8 yr). A total of 128 patients underwent a mean of 4.0 ± 2.2 PCOs and 14.4 ± 3 mean levels of instrumentation. A total of 321 PCOs were performed for sagittal correction. Cobb angles for the maximal measured kyphosis decreased from 64° ± 22° preoperatively to 47° ± 13° at initial postoperative evaluation (P < 0.0001). We noted an increase to 52° ± 15° in the maximum Cobb angle from initial to final evaluation (P < 0.0001; Figure 4), which was largely because of increased kyphosis proximal to the upper instrumented vertebra. The mean sagittal correction per PCO between preoperative and final postoperative radiographs for all regions of the spine was 8.8° ± 7.2°, and varied with spinal region (P < 0.0001; Figure 5) and patient age (10.2° ± 7.8° per level for patients younger than 21 yr vs. 7.7° ± 6.3° for those 21 yr or older, P < 0.0001). For all patients undergoing PCOs for sagittal correction, sagittal balance improved from 3.2 ± 5.8 cm preoperatively to - 0 . 5 ± 6.7 cm at the final postoperative evaluation (P < 0.0001). Of note, this analysis of sagittal imbalance did not include strictly patients with uncompensated fixed sagittal-imbalance syndrome; all patients with local kyphosis or hypolordosis were included, which is why the average preoperative sagittal vertical axis was only 3.2 cm. With PCOs at the apex of a scoliotic curve (51% of the patients overall; Figure 6), the maximum coronal Cobb angle www.spinejournal.com
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Posterior Column Osteotomies • Dorward et al
Figure 6. Coronal plane Cobb angle changes. Data shown are means with 95% confidence intervals. The P values above each Cobb angle category refer to the difference between that Cobb angle measurement and the preoperative Cobb angle. Preop indicates preoperative; postop, postoperative.
decreased from 66° ± 21° preoperatively to 30° ± 14° at initial postoperative evaluation and 31° ± 14° at ñnal evaluation (F < 0.0001), for a 53% correction rate and no loss of correction (P = 0.78). Overall, 7.0° of coronal correction were obtained at each PCO level. Coronal balance did not change from preoperative to flnal postoperative radiographs (2.68 ± 3.36 cm to 2.04 ± 1.62 cm, P = 0.099). Of the 128 patients, only 6 (4.7%) showed coronal decompensation of more than 3 cm, and only 1 (0.78%) showed decompensation of more than 4 cm (a 5.6cm decompensation was present in a patient who experienced pseudarthrosis at non-PCO levels). Mean estimated blood loss increased with increasing patient age (P < 0.0001) and with more instrumented levels (? < 0.0001). However, a greater number of PCOs (P = 0.32) did not correlate with greater estimated blood loss. Intraoperative complications and monitoring or wake-up test issues are depicted in Table 2. Six (4.7%) patients lost spinal cord monitoring signals intraoperatively; 1 event was because of transient hypotension, responding rapidly to fluid resuscitation and pressors, and another event was because of a technical prohlem with monitoring. In addition, 2 patients who did not lose MEPs nonetheless failed a wake-up test. Thus, in 6 patients, either monitoring loss or wake-up test failure was attributed to overcorrection with PCOs. None of these patients, however, experienced postoperative neurological deficits, thanks to the rapid efforts to address the issue of possible overcorrection by immediate lessening/reversal of the correction. Table 3 lists both early and late complications. Thirty-eight complications occurred in 31 (24.2%) patients. These complications included 4 conflrmed pseudarthroses (1 at a PCO level). Four (3.1%) patients experienced radiculopathy with motor weakness, although in 3, the site of deficit was clearly distant from and unrelated to the PCOs. One patient died secondary to a failed reintubation attempt during an acute episode of respiratory failure. The occurrence of complications did not correlate with the number of PCOs (P = 0.5). 876
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The patients in this series experienced substantial improvements in both Oswestry Disability Index (34.4 ± 17 preoperatively vs. 23.6 ± 18 at final follow-up, P < 0.0001) and Scoliosis Research Society scores (63.7 ± 13 preoperatively vs. 76.4 ± 15 at final follow-up, P < 0.0001) (Figure 7).
DISCUSSION Osteotomy of the posterior column of the spine has evolved considerably since its introduction. Smith-Petersen et al^ described a technique involving resection of the superior and inferior facets, the ligamentum flavum, and the spinous processes, followed hy osteotomy closure. From this method sprang the 2 general approaches for generating lordosis of the spine. The first approach—an opening wedge osteotomy— involved embracing the anterior longitudinal ligament (ALL) rupture and anterior opening that occurred in some of the original patients studied hy Smith-Petersen.^^" The second approach was to perform a posterior bony resection at multiple levels followed by judicious osteotomy closure, leading to a more harmonious generation of lordosis with reduced morhidity.*^"'"* The latter approach culminated in the Ponté method, involving posterior element osteotomies at multiple levels followed by posterior rod reduction and compression in patients with long, gradual kyphoses such as those with Scheuermann kyphosis.^-^ Confusion exists as to which eponym—Smith Petersen or Ponté—is most appropriate. Some authors suggest that a Smith-Petersen osteotomy is through a previously fused segment and involves ALL rupture, whereas a Ponté osteotomy is used through a "virgin" or previously unfused segment.'^' However, Smith-Petersen et a? descrihed the technique for patients with ankylosed facets hut no history of spinal surgery, and some of them seem to have retained an intact ALL at the conclusion of the procedure. It has also heen stated that the Smith-Petersen osteotomy is performed at a single level, whereas the Ponté osteotomy is a multilevel procedure,'^ although Smith-Petersen's original series did include patients with osteotomies at multiple levels. May 2014
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877
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MnM3È^ÊÊÊÊÊ Complications
Posterior Column Osteotomies • Dorward et al
^
^
^
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No. (%) Early complications (within 30 d of surgery) Surgical complications Durotomy
2(1.6)
Radiculopathy with weakness
4(3.1)
Pressure-related thigh numbness
1 (0.8)
Wound infection requiring reoperation
4(3.1)
Other (retained drain fragment)
1 (0.8)
Medical complications Death due to respiratory failure
1 (0.8)
Ogilvie syndrome
1 (0.8)
Acute renal failure
1 (0.8)
Elevated troponin
1 (0.8)
Sepsis
2(1.6)
Urinary tract infection
1 (0.8)
Respiratory failure
3 (2.3)
Pneumonia
2(1.6)
DVT/PE
5 (3.9)
¿ate complications (more than 30 d after surgery) Adjacent segment disease, proximal
2(1.6)
Pseudarthrosis
4(3.1)
Late infection requiring reoperation
3 (2.3)
Persistent radiculopathy with weakness
1 (0.8)
DVT indicates deep vein thrombosis; PE puimonary embolism.
That being said, the technique of using multiple osteotomies put forth by Ponté of the posterior column to achieve correction via reduction of pedicle screws into a precontoured metallic rod is the most accurate representation of the technique commonly used today. Because of the lack of consensus regarding the nomenclature of these osteotomies, and with the hopes of reducing confusion and tendentiousness associated with eponyms, we have described the method in simple anatomic terms: the posterior column osteotomy or PCO. This term applies to any osteotomy involving resection of bilateral facets and ligamentum flavum plus/minus any portion of the spinous processes or laminae, followed by posterior compression to create lordosis, reduce kyphosis, or engender increased flexibility of a stiff spinal deformity. This term could be applied regardless of the cause of the deformity or the presence of an existing fusion. Anatomic and Radiographical Considerations PCO is distinct from PSO and VCR in that the compression phase of the osteotomy leads to some degree of widening of the anterior disc space because of the fact that the fulcrum of the compression rests somewhere in the mid-disc.'*''^ Recent evidence has confirmed that the interval between the anterior margins of adjacent endplates widens by 2.2 mm after PCO."* However, using segmental instrumentation with pedicle 878
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PieOp
PcstOp
O D I Scores
|A|
PieOp
PostOp
SRS Scores
Figure 7. Outcomes according to normalized (percentage of total possible) ODI and SRS-30 scores. Data shown are means with 95% confidence intervals. ODI indicates Oswestry Disability Index; SRS-30, Scoliosis Research Society-30; preop, preoperative; postop, postoperative.
screws and gentle posterior compression along bilateral rods allows controlled anterior lengthening without substantial risk of ALL rupture. Indeed, in this series we observed no clinical evidence of ALL rupture and no associated visceral complications in any patients. Regarding the radiographical results yielded by PCOs, previous reports have suggested a range of 9.3° to 10.7° of sagittal correction per level, with another general rule of thumb being to expect 1° of correction for every millimeter of bone resected.^'^'^ In this study, we found a mean correction of 8.8° with any PCO. PCOs were more effective in younger individuals and were associated with most correction when used in the thoracolumbar and lumbar regions. The greater correction with PCOs in younger patients may pertain to the biomechanical mechanism of correction: because PCOs require mobility of the disc space, the greater hydration of the nucleus pulposus and elasticity of the annulus in younger patients may enable greater correction to occur. One concern with PCOs that has been previously highlighted in the literature is the potential for coronal decompensation toward the concavity, with some authors suggesting that PCOs should not be used in the presence of a coronal plane deformity.'^ In a study by Cho et aP., 13.3% of patients experienced coronal decompensation of more than 4 cm; however, that coronal decompensation predominantly affected patients who did not have a posterior-only approach for PCO (i.e., an anterior release and fusion was used). In the current series of more than 4 times as many patients, only 1 patient experienced a coronal decompensation of more than 4 cm (which stemmed from a pseudarthrosis and failure of May 2014
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Posterior Column Osteotomies • Dorward et al
instrumentation). Thus, it does not seem that coronal decompensation poses a meaningful concern in the use of PCOs through a posterior-only approach. It also seems that the literature has not sufficiently addressed the use of PCOs at the apex of scoliotic deformities. With PCOs used in this fashion, we obtained a correction rate of more than 53% for maximum coronal Cobb angles. To prove the efficacy of PCOs in this regard, we would of course need a control group undergoing similar deformity corrections without the benefit of PCOs.
This study does have several limitations. First, its retrospective design leaves it vulnerable to the various biases inherent in such studies. Second, the lack of a control group means that we cannot make sound judgments as to the safety and efficacy of PCOs relative to either other osteotomies or the use of no osteotomy at all. Third, highly experienced surgeons at a high-volume deformity center treated these patients, and as such, the results generated may not be generalizable to all spinal surgery practices.
Complications
CONCLUSION
Six patients experienced either a loss of monitoring signals or a failed wake-up test that was attributed to overcorrection with PCOs. PCOs, although not as powerful as PSO or VCR in terms of focal deformity correction, remain a potent tool that must be used with caution. It is paramount to use some form of somatosensory evoked potential and MEP to recognize and rapidly remediate insults to the spinal cord. Not having monitoring available, or being unable to obtain signals on a patient, should remain a relative contraindication to performing PCOs or any type of osteotomy. Aside from the potential for overcorrection, this series suggests that PCOs pose little risk of complications when performed carefully. Patients undergoing a greater number of PCOs did not experience increased blood loss or complications. No patients experienced durotomy, nerve root deficit, spinal cord deficit, or other complications related directly to PCOs, and no patients experienced unexpected complications such as superior mesenteric artery syndrome, as have been reported previously." In evaluating the complication rates associated with PCOs, the largest previous set of data comes from the Smith et aP° report on 135 patients from the Scoliosis Research Society Morbidity and Mortality Database regarding the correction of thoracolumbar fixed sagittal deformity. We had a similar rate of overall complications (24.2% vs. 28.1% in Smith et aP") and neurological deficit (3.1% vs. 3.7%), a lower rate of durotomy (1.6% vs. 6.7%), and a higher rate of wound infections (5.5% vs. 1.1%) and deep vein thrombosis/pulmonary embolism (3.9% vs. 0.7%).^« Our 24.2% overall complication rate, 5.5% infection rate, and 2.3% PJK rate also compared favorably with other recent evaluations of PCOs in the literature.^-' Certain elements of the PCO technique warrant emphasis to improve safety. First, meticulous dissection and bone removal helps prevent injury to the dura, spinal cord or nerve roots. Second, the bilateral facetectomies must be complete and the foramina entirely unroofed, because the osteotomy closure involves contraction of the neural foramina that could lead to nerve root impingement by any remnants of the overlying facets. Third, the osteotomy closure must be judicious, to avoid excessive anterior lengthening of the disc space and resultant violation of the anterior longitudinal ligament. Fourth, the PCOs must be performed efficiently to reduce associated blood loss and avoid unnecessarily protracting the procedure.
Spinal fusion with PCOs through a posterior-only approach was associated with effective correction for both sagittal and coronal plane deformities. The mean sagittal correction per PCO was 8.8°, but was greatest in the thoracolumbar and lumbar regions. Younger patients also obtained greater correction. The main technical concern with PCOs was overcorrection, but resultant neurological consequences were identified by intraoperative MFPs and wake-up tests, and no patients experienced permanent neurological deficits related to PCOs. Coronal decompensation was not encountered even when PCOs were used at the apex of coronal plane deformities.
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Limitations
Key Points •
The use of PCOs seems safe and effective for spinal deformity correction.
•
The number of PCOs was not correlated with greater complications or blood loss at surgery.
•
The sagittal plane correction afforded by PCOs varies by the region of the spine, with thoracolumbar and lumbar PCOs associated with the greatest correction. Younger patients also experienced greater correction from PCOs.
•
The greatest risk of PCOs seems to be overcorrection of deformity, with the potential for spinal cord injury. However, in this series strict utilization of neuromonitoring and wakeup testing identified and allowed us to address neurological perturbations, and no patients experienced spinal cord deficits from PCOs.
References 1. Smith-Petersen MN, Larson CB, Aufranc OE. Osteotomy of the spine for correction of flexion deformity in rheumatoid arthritis. J Bone Joint Surg Am 1945;27:1-11. 2. Geek MJ, Macagno A, Ponte A, et al. The Ponte procedure: posterior-only treatment of Scheuermann's kyphosis using segmental posterior shortening and pedicle screw instrumentation. / Spinal Disord Tech 2007;20:586-93. 3. Ponte A, Vero B, Siccardi GL, ed. Surgical Treatment of Scheuermann's Hyperkyphosis. Bologna, Italy: Aulo Gaggi; 1984. 4. O'Brien MF, Kuklo TR, Blanke KM, et al. Radiographic Measurement Manual. Spinal Deformity Study Group. Memphis, TN: Medtronic Sofamor Danek; 2004. www.spinejournal.com
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5. Cho KJ, Bridwell KH, Lenke LG, et al. Comparison of SmithPetersen versus pedicle suhtraction osteotomy for the correction of fixed sagittal imbalance. Spine (Phila Fa 1976) 2005;30:2030-7. 6. La Chapelle E. Osteotomy of the lumhar spine for correction of kyphosis in a case of ankylosing spondylarthritis. / Bone Joint Surg Am 1946;28:851-8. 7. Herbert JJ. Vertebral osteotomy: technique, indications, and results. J Bone Joint Surg Am 1948;30:680-9. 8. Herbert JJ. Vertebral osteotomy for kyphosis, especially in MarieStrumpell arthritis; a report on fifty cases. / Bone Joint Surg Am 1959;41:291-302. 9. Law A. Osteotomy of the spine. / Bone Joint Surg Am 1962;44: 1199-206. 10. McMaster MJ. A technique for lumbar spinal osteotomy in ankylosing spondylitis. / Bone Joint Surg Br 1985;67:204-10. 11. Camargo FP, Cordeiro EN, Napoli MM. Corrective osteotomy of the spine in ankylosing spondylitis. Experience with 66 cases. Clin Orthop RelatRes 1986;208:157-67. 12. Wilson MJ, Turkell JH. Multiple spinal wedge osteotomy; its use in a case of Marie-Strumpell spondylitis. Am J Surg 1949;77:777-82. 13. Hehne HJ, Zieike K, Böhm H. Polysegmental lumbar osteotomies and transpedicled fixation for correction of long-curved kyphotic deformities in ankylosing spondylitis. Report on 177 cases. Clin Orthop Relat Res 1990;258:49-55.
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14. Halm H, Metz-Stavenhagen P, Zieike K. Results of surgical correction of kyphotic deformities of the spine in ankylosing spondylitis on the basis of the modified arthritis impact measurement scales. Spine (Phila Pa 1976) 1995;20:1612-9. 15. Macagno AE, O'Brien ME. Thoracic and thoracolumbar kyphosis in adults. Spme (Phila Pa 1976) 2006;31:S161-70. 16. Wang MY, Berven SH. Lumbar pedicle subtraction osteotomy. Neurosurgery 2007;60:ONS140-6. 17. Gill JB, Levin A, Burd T, et al. Corrective osteotomies in spine surgery. / Bone Joint Surg Am 2008;90:2509-20. 18. Cho W, Lenke LG, Bridwell KH, et al. The effect of posterior shortening and anterior lengthening using Smith-Petersen osteotomy (SPO) for kyphosis correction. Presented at the 17th International Meeting on Advanced Spine Techniques (IMAST). Toronto, Ontario, Canada, July 13-16, 2011. 19. Papagelopoulos PJ, Klassen RA, Peterson HA, et al. Surgical treatment of Scheuermann's disease with segmental compression instrumentation. Clin Orthop Relat Res 2001;385: 139-49. 20. Smith JS, Sansur CA, Donaldson WE III, et al. Short-term morbidity and mortality associated with correction of thoracolumbar fixed sagittal plane deformity: A report from the Scoliosis Research Society Morbidity and Mortality Committee. Spine (Phila Pa 1976) 2011;36:958-64.
May 2014
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SPINE Voluame 39, Number 11, pp 870-880 ©2014, Lippincott Williams & Wilkins
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Radiographical and Clinical Outcomes of Posterior Column Osteotomies in Spinal Deformity Correction Ian G. Dorward, MD,* Lawrence G. Lenke, MD,t Geoffrey E. Stoker, BS,t Woojin Cho, MD, PhD,+ Linda A. Koester, BS,t and Brenda A. Sides, MSt
Study Design. Prospectively enrolled, retrospectively analyzed case series. Objective. To evaluate a large series of pédiatrie patients/patients with adult spinal deformity undergoing surgery with posterior column osteotomies (PCOs). Summary of Background Data. Osteotomies of the posterior column (Smith-Petersen or Ponté) are used to reduce kyphosis, increase lordosis, or increase spinal flexibility. However, little focused evidence exists regarding the efficacy and safety of this technique. Methods. A total of 128 consecutive patients underwent posterior spinal fusion with PCOs with minimum 2-year follow-up. Seventyfive were primary surgical procedures; 53 were revisions. Data were collected from hospital charts, clinic notes, radiographs, and standardized questionnaires (Scoliosis Research Society-30 and Oswestry Disability Index). Results. A total of 128 patients aged 37.6 ± 21 years underwent 518 PCOs (mean, 4.0 ± 2.2 yr)with 14.4 ± 3 mean instrumentation levels, with 3-year (range, 2-6.8 yr) average follow-up. PCOs were used for kyphosis correction in 49%, scoliosis correction at the apex of a curve in 13%, and both in 38%. One hundred six patients had complete radiographical data available for evaluation. Mean kyphosis correction per PCO was 8.8° ± 7.2°, varying with patient age (10.2° for those younger than 21 yr vs. 7.7° for those
From the Departments of *Neurosurgery and tOrthopaedic Surgery, Washington University School of Medicine, St. Louis, MO; and ^Department of Orthopaedic Surgery, Albert Einstein College of Medicine, Montefiore University Hospital, Bronx, NY. Acknowledgment date; May 29, 2012. First revision date: December 10, 2012. Second revision date: August 19, 2013. Third revision date: February 12, 2014. Acceptance date: February 14, 2014. The manuscript submitted does not contain information about medical device(s)/drug(s). No funds were received in support of this work. Relevant financial activities outside the submitted work: board membership, grants/grants pending, payment for lectures, patents, royalties, travel/ accommodations/meeting expenses and fellowship grant support. Address correspondence and reprint requests to Lawrence G. Lenke, MD, Washington University School of Medicine, Department of Orthopaedic Surgery, 660 S Euclid Ave, Campus Box 8233, Saint Louis, MO 63110; E-mail: [email protected] DOI: 10.1097/BRS.0000000000000302 870
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21 yr or older, P < 0.0001) and region of the spine: thoracolumbar (T10-L2) 11.6°, lumbar (L2-S1 ) 9.4°, midthoracic (T6-T10) 7.2° and proximal thoracic (T1-T6) 3.6°. With PCOs at the apex of a curve, the maximum coronal Cobb decreased from 66° ± 21° to 31° ± 14° (P < 0.0001). Average estimated blood loss was 1419 ± 887 mL, correlating with greater age {P < 0.0001) and more instrumented levels (P < 0.0001), but not with the number of PCOs (P = 0.32). Complications occurred in 31 (24.2%) patients, including 4 radiculopathies (none attributable to PCOs). Complications did not correlate with the number of PCOs (P = 0.5). Six (4.7%) patients had loss of spinal cord monitoring or a failed wake-up test that could be attributed to overcorrection with PCOs, but none had postoperative deficits. Oswestry Disability Index scores improved (34.4 ± 17 to 23.6 ± 18, P < 0.0001), as did normalized Scoliosis Research Society-30 scores (63.7 ± 13 to 76.4 ± 15, P < 0.0001 ). Conclusion. Patients in this series undergoing posterior spinal fusion with PCOs achieved overall favorable outcomes for spinal deformity correction. The number of PCOs did not correlate with increased estimated blood lossor complications. The main technical concern was overcorrection, but neurological consequences associated with overcorrection were identified by intraoperative spinal cord monitoring and wake-up tests, and no patients experienced permanent neurological deficits related to PCOs. Key words: pédiatrie spinal deformity, adult spinal deformity, posterior spinal fusion, posterior, column osteotomies, SmithPetersen osteotomy. Ponté osteotomy, complications, outcomes.
Level of Evidence: 4 Spine 2014;39:870-880
O
steotomy of the posterior column of the spine to correct spinal deformities was first described in 1945 by Smith-Petersen.' Later modifications of the posterior column osteotomy (PCO), such as the Ponté technique, have used advances in segmental instrumentation to obtain more durable, safe, and effective results in correcting excessive kyphosis or inadequate lordosis.-'^ However, confusion regarding the nomenclature of the PCO—with names including Smith-Petersen osteotomy. Ponté osteotomy. Ponté procedure, posterior shortening osteotomy, chevron osteotomy, and segmental osteotomy—could hamper efforts at research May 2014
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Posterior Column Osteotomies • Dorward et al
Figure 1. A, A posterior column osteotomy begins with resection of the inferior facets bilaterally. B, After facetectomies, a Leksell rongeur is used to remove the spinous process and portions of the lamina. The rongeur is further used to remove the dorsal portion of the ligamentum flavum until a bulge of epidural fat is noted in the midline. C, A 3-mm Kerrison punch is used in a medial to lateral direction to remove the ligamentum flavum and bone from the lamina superiorly and the superior articular process inferiorly, continuing to the lateral extent of the foramen. D, The correction step of a posterior column osteotomy involves closure of the interval of bony resection through the bilateral facets, thereby apposing (or nearly apposing) the remaining portions of superior and inferior facet still overlying the interpedicular space. Care must be taken to inspect the foramen for any remaining bone or ligament that could result in neural compression after osteotomy closure.
and categorization. Thus, a relative paucity of recent literature exists regarding the radiographical and clinical outcomes after osteotomy of the posterior column compared with the more aggressive 3-column osteotomies (pedicle subtraction osteotomy [PSO] and vertebral column resection [VCR]). Por the sake of clarity, then, we will use the term "posterior column osteotomy" to refer to any osteotomy that involves resection of bilateral facets and the ligamentum flavum followed by posterior compression/distraction. We explored the outcomes of a large series of patients undergoing PCO to augment either kyphotic or scoliotic corrections, although a posterior-only approach. We hypothesized that PCOs not only would provide correction for pure sagittal deformities, but would also serve as a safe adjunct at the apex of scoliotic curves. We also hypothesized that complications referable to PCOs would be minimal, and that Spine
posterior-only PCOs would neither lose substantial correction nor lead to coronal decompensation.
MATERIALS AND METHODS Patients Institutional review hoard approval was obtained prior to initiation of the study and the project deemed minimal risk given its retrospective nature. We reviewed a database of prospectively enrolled adult and pédiatrie patients who underwent posterior spinal fusion for the treatment of scoliosis, kyphosis, sagittal imbalance, prior surgery requiring multilevel reconstruction, or a combination of the ones mentioned earlier. We included 128 patients who underwent at least 1 PCO and had a minimum 2-year clinical/radiographicai follow-up. We excluded patients who underwent anterior approaches www.spinejournal.com
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Posterior Column Osteotomies • Dorward et al
Figure 2. A 33-year-old female with a history of aT12 fracture and previous T4-L2 PSF with subsequent instrumentation removal presents with progressive kyphosis. She underwent T2-L3 PSF with PCOs at 5 levels, yielding a 6 1 % correction rate. A, Preoperative AP radiograph. B, Postoperative AP radiograph. C, Preoperative lateral radiograph. D, Postoperative lateral radiograph. E, Preoperative posterior clinical photograph. F, Postoperative posterior clinical photograph. G, Preoperative lateral clinical photograph. H, Postoperative lateral clinical photograph. PCO indicates posterior column osteotomy; PSF, posterior spinal fusion; AP anteroposterior. 872
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Figure 3. A 47-year-old female with adult idiopathic scoliosis and only 8% curve flexibility underwent T3-L4 PSF with apical PCOs at 6 levels. Surgery yielded a 52% correction rate. A, Preoperative AP radiograph. B, Postoperative AP radiograph. C, Preoperative lateral radiograph. D, Postoperative lateral radiograph. E, Preoperative posterior clinical photograph. F, Postoperative posterior clinical photograph. G, Preoperative lateral clinical photograph. H, Postoperative lateral clinical photograph. PCO indicates posterior column osteotomy; AP, anteroposterior; PSF, posterior spinal fusion. Spine
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873
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1 AB Lb 1 ^ ;^»ïï^Tl f-,,
Posterior Column Osteotomies • Dorward et al
, Jg^jgïgJJte N = 128
Age at surgery* (yr)
37.6 ± 2 1 (5.6-82.1)
Sex Male
39(30.5)
Female
89 (69.5)
Operative diagnosis Adolescent idiopathic scoliosis
18(14.1}
Adult idiopathic scoliosis
29 (22.6)
Congenital kyphoscoliosis
3 (2.3)
Degenerative scoliosis
6(4.7)
Fixed sagittal imbalance
26(20.3)
Neuromuscular/syndromic
21 (16.4)
Scheuermann kyphosis
21 (16.4)
Post-traumatic kyphosis
4(3.1)
Primary surgery
76 (59.4)
Revision surgery
52 (40.6)
Plane of PCO correction Sagittal only
63 (49.2)
Coronal only
17(13.3)
Both planes
48(37.5)
PCOs performed Total
518(100)
Through fused segment
. 104(20.1)
Through pseudarthrosis
35 (6.8)
Primary PCO Length of follow-up* (mo)
379(73.2) 35.8 ± 19(24.0,81.6)
'Values indicate mean ± standard deviation (range). Values indicate number (%) unless otherwise specified. PCO indicates posterior column osteotomy.
for release and/or fusion at PCO levels, or other concomitant osteotomies (PSO or VCR). Patient records were reviewed and data were abstracted and analyzed. Research was performed at Washington University School of Medicine. Radiographical Review Of the 128 patients, 22 had incomplete radiographical records available thus were excluded. We evaluated standing 36-inch anteroposterior and lateral radiographs at 3 time points: preoperative, initial (within 1-8 wk) postoperative, and final postoperative (2-year or later follow-up). Preoperative evaluations also included hyperextension lateral and anteroposterior side-bending radiographs. All radiographical measurements conformed to the recommendations of the Spinal Deformity Study Group.** In addition to standard measurements, we measured Cobb angles for each individual 874
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PCO level on lateral radiographs and for segments of contiguous PCOs on both lateral and anteroposterior radiographs. Regions of the spine in which PCOs were performed were defined as proximal thoracic (T1-T6), midthoracic (from T6-T10), thoracolumbar (T10-L2) and lumbar (L2-S1). For data analysis, PCOs were categorized as being used for either sagittal correction or coronal correction. Osteotomies falling into the sagittal correction group were clearly defined in the operative summary as being used for reduction of kyphosis or creation of greater lordosis. Outcomes Oswestry Disability Scores and Scoliosis Research Society Scores (22, 24, 29, or 30 converted to a 100-point percentage scale for the purposes of standardization) were used to evaluate patient outcomes.
Data Analysis A biostatistician assisted in all aspects of statistical analysis, which was generated using SAS version 9.1.3 of the SAS System for Linux (SAS Institute Inc., Cary, NC). For radiographical data featuring repeat measurements at different time points, longitudinal analyses were performed using mixed model repeated measures analysis of variance. If initial analyses detected significant change over time between groups, statistical contrasts were used to determine at which time point the change occurred, and, further, to test the null hypothesis that the changes between time points in the group in question were the same as corresponding changes in other groups. Data sets with significant heterogeneity of variance across time points and groups were analyzed using rank- or log-transformed data. For complications and other clinical variables deemed non-normally distributed, differences between groups were assessed using nonparametric tests such as the Wilcoxon sign rank test. For small samples of categorical data, the Fisher exact test was used. PCO Procedure The PCO technique as used in this series is depicted step-bystep in Figure 1. Principle indications for PCOs were ( 1 ) reducing kyphosis or increasing lordosis (Figure 2); or (2) increasing the flexibility of a stiff scoliosis (Figure 3) to enable correction via other maneuvers, that is, rod derotation techniques. For sagittal plane correction, the number and location of PCOs were generally selected on the basis of previous findings that 10° of correction can be obtained per PCO.^ Although few firm rules were used when deciding between PCO, PSO, or VCR for the patients in this series, some general principles were followed. PCOs were chosen in cases with more gradual/ less angular curves because focal and/or angular deformities more readily lend themselves to correction with PSO (sagittal plane in the lumbar spine) or VCR (sagittal or coronal plane in the thoracic spine). PCOs were also chosen only when the disc spaces were presumed mobile enough to allow for correction. PCOs were favored over PSO or VCR when they seemed May 2014
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90- T— 80"
10'
PreOp
Hyperextension
Initial PostOp Final PostOp
PreOp
|
Maximum Cobb Angles
Hyperextension
Initial PostOp | Final PostOp j
PCO Segment Cobb Angles Sagittal Plane
Figure 4. Sagittal plane Cobb angle changes for the maximum Cobb angle and Cobb angle over regions of contiguous PCOs. Data shown are means with 95% confidence intervals. The P values above each Cobb angle category refer to the difference between that Cobb angle measurement and the preoperative Cobb angle. PCO indicates posterior column osteotomy; preop, preoperative; postop, postoperative.
sufficient to effect adequate correction without subjecting a patient to the expected increase in morbidity associated with a more extensive 3-column osteotomy. During every procedure, intraoperative monitoring with neurogenic or transcranial motor evoked potentials (MEPs) were used. In addition, if no perturbations in monitoring were noted during the case, a full wake-up test was still performed
Figure 5. Mean correction afforded by PCOs based on region of the spine in which they are performed: proximal thoracic (T1-T6, 3.6° ± 10.0° of correction), midthoracic (T6-T10, 7.2° ± 5.8°), thoracolumbar (T10-L2, 11.6° ± 7.2°), lumbar (L2-L5, 9.4° ± 5.2°). PCO indicates posterior column osteotomy.
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at the end of the procedure to document that no change in neurological function had occurred.
RESULTS Patient demographic characteristics are depicted in Table 1. Mean follow-up was 3.0 years (range, 2-6.8 yr). A total of 128 patients underwent a mean of 4.0 ± 2.2 PCOs and 14.4 ± 3 mean levels of instrumentation. A total of 321 PCOs were performed for sagittal correction. Cobb angles for the maximal measured kyphosis decreased from 64° ± 22° preoperatively to 47° ± 13° at initial postoperative evaluation (P < 0.0001). We noted an increase to 52° ± 15° in the maximum Cobb angle from initial to final evaluation (P < 0.0001; Figure 4), which was largely because of increased kyphosis proximal to the upper instrumented vertebra. The mean sagittal correction per PCO between preoperative and final postoperative radiographs for all regions of the spine was 8.8° ± 7.2°, and varied with spinal region (P < 0.0001; Figure 5) and patient age (10.2° ± 7.8° per level for patients younger than 21 yr vs. 7.7° ± 6.3° for those 21 yr or older, P < 0.0001). For all patients undergoing PCOs for sagittal correction, sagittal balance improved from 3.2 ± 5.8 cm preoperatively to - 0 . 5 ± 6.7 cm at the final postoperative evaluation (P < 0.0001). Of note, this analysis of sagittal imbalance did not include strictly patients with uncompensated fixed sagittal-imbalance syndrome; all patients with local kyphosis or hypolordosis were included, which is why the average preoperative sagittal vertical axis was only 3.2 cm. With PCOs at the apex of a scoliotic curve (51% of the patients overall; Figure 6), the maximum coronal Cobb angle www.spinejournal.com
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Posterior Column Osteotomies • Dorward et al
Figure 6. Coronal plane Cobb angle changes. Data shown are means with 95% confidence intervals. The P values above each Cobb angle category refer to the difference between that Cobb angle measurement and the preoperative Cobb angle. Preop indicates preoperative; postop, postoperative.
decreased from 66° ± 21° preoperatively to 30° ± 14° at initial postoperative evaluation and 31° ± 14° at ñnal evaluation (F < 0.0001), for a 53% correction rate and no loss of correction (P = 0.78). Overall, 7.0° of coronal correction were obtained at each PCO level. Coronal balance did not change from preoperative to flnal postoperative radiographs (2.68 ± 3.36 cm to 2.04 ± 1.62 cm, P = 0.099). Of the 128 patients, only 6 (4.7%) showed coronal decompensation of more than 3 cm, and only 1 (0.78%) showed decompensation of more than 4 cm (a 5.6cm decompensation was present in a patient who experienced pseudarthrosis at non-PCO levels). Mean estimated blood loss increased with increasing patient age (P < 0.0001) and with more instrumented levels (? < 0.0001). However, a greater number of PCOs (P = 0.32) did not correlate with greater estimated blood loss. Intraoperative complications and monitoring or wake-up test issues are depicted in Table 2. Six (4.7%) patients lost spinal cord monitoring signals intraoperatively; 1 event was because of transient hypotension, responding rapidly to fluid resuscitation and pressors, and another event was because of a technical prohlem with monitoring. In addition, 2 patients who did not lose MEPs nonetheless failed a wake-up test. Thus, in 6 patients, either monitoring loss or wake-up test failure was attributed to overcorrection with PCOs. None of these patients, however, experienced postoperative neurological deficits, thanks to the rapid efforts to address the issue of possible overcorrection by immediate lessening/reversal of the correction. Table 3 lists both early and late complications. Thirty-eight complications occurred in 31 (24.2%) patients. These complications included 4 conflrmed pseudarthroses (1 at a PCO level). Four (3.1%) patients experienced radiculopathy with motor weakness, although in 3, the site of deficit was clearly distant from and unrelated to the PCOs. One patient died secondary to a failed reintubation attempt during an acute episode of respiratory failure. The occurrence of complications did not correlate with the number of PCOs (P = 0.5). 876
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The patients in this series experienced substantial improvements in both Oswestry Disability Index (34.4 ± 17 preoperatively vs. 23.6 ± 18 at final follow-up, P < 0.0001) and Scoliosis Research Society scores (63.7 ± 13 preoperatively vs. 76.4 ± 15 at final follow-up, P < 0.0001) (Figure 7).
DISCUSSION Osteotomy of the posterior column of the spine has evolved considerably since its introduction. Smith-Petersen et al^ described a technique involving resection of the superior and inferior facets, the ligamentum flavum, and the spinous processes, followed hy osteotomy closure. From this method sprang the 2 general approaches for generating lordosis of the spine. The first approach—an opening wedge osteotomy— involved embracing the anterior longitudinal ligament (ALL) rupture and anterior opening that occurred in some of the original patients studied hy Smith-Petersen.^^" The second approach was to perform a posterior bony resection at multiple levels followed by judicious osteotomy closure, leading to a more harmonious generation of lordosis with reduced morhidity.*^"'"* The latter approach culminated in the Ponté method, involving posterior element osteotomies at multiple levels followed by posterior rod reduction and compression in patients with long, gradual kyphoses such as those with Scheuermann kyphosis.^-^ Confusion exists as to which eponym—Smith Petersen or Ponté—is most appropriate. Some authors suggest that a Smith-Petersen osteotomy is through a previously fused segment and involves ALL rupture, whereas a Ponté osteotomy is used through a "virgin" or previously unfused segment.'^' However, Smith-Petersen et a? descrihed the technique for patients with ankylosed facets hut no history of spinal surgery, and some of them seem to have retained an intact ALL at the conclusion of the procedure. It has also heen stated that the Smith-Petersen osteotomy is performed at a single level, whereas the Ponté osteotomy is a multilevel procedure,'^ although Smith-Petersen's original series did include patients with osteotomies at multiple levels. May 2014
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Posterior Column Osteotomies • Dorward et al
^
^
^
^
No. (%) Early complications (within 30 d of surgery) Surgical complications Durotomy
2(1.6)
Radiculopathy with weakness
4(3.1)
Pressure-related thigh numbness
1 (0.8)
Wound infection requiring reoperation
4(3.1)
Other (retained drain fragment)
1 (0.8)
Medical complications Death due to respiratory failure
1 (0.8)
Ogilvie syndrome
1 (0.8)
Acute renal failure
1 (0.8)
Elevated troponin
1 (0.8)
Sepsis
2(1.6)
Urinary tract infection
1 (0.8)
Respiratory failure
3 (2.3)
Pneumonia
2(1.6)
DVT/PE
5 (3.9)
¿ate complications (more than 30 d after surgery) Adjacent segment disease, proximal
2(1.6)
Pseudarthrosis
4(3.1)
Late infection requiring reoperation
3 (2.3)
Persistent radiculopathy with weakness
1 (0.8)
DVT indicates deep vein thrombosis; PE puimonary embolism.
That being said, the technique of using multiple osteotomies put forth by Ponté of the posterior column to achieve correction via reduction of pedicle screws into a precontoured metallic rod is the most accurate representation of the technique commonly used today. Because of the lack of consensus regarding the nomenclature of these osteotomies, and with the hopes of reducing confusion and tendentiousness associated with eponyms, we have described the method in simple anatomic terms: the posterior column osteotomy or PCO. This term applies to any osteotomy involving resection of bilateral facets and ligamentum flavum plus/minus any portion of the spinous processes or laminae, followed by posterior compression to create lordosis, reduce kyphosis, or engender increased flexibility of a stiff spinal deformity. This term could be applied regardless of the cause of the deformity or the presence of an existing fusion. Anatomic and Radiographical Considerations PCO is distinct from PSO and VCR in that the compression phase of the osteotomy leads to some degree of widening of the anterior disc space because of the fact that the fulcrum of the compression rests somewhere in the mid-disc.'*''^ Recent evidence has confirmed that the interval between the anterior margins of adjacent endplates widens by 2.2 mm after PCO."* However, using segmental instrumentation with pedicle 878
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PieOp
PcstOp
O D I Scores
|A|
PieOp
PostOp
SRS Scores
Figure 7. Outcomes according to normalized (percentage of total possible) ODI and SRS-30 scores. Data shown are means with 95% confidence intervals. ODI indicates Oswestry Disability Index; SRS-30, Scoliosis Research Society-30; preop, preoperative; postop, postoperative.
screws and gentle posterior compression along bilateral rods allows controlled anterior lengthening without substantial risk of ALL rupture. Indeed, in this series we observed no clinical evidence of ALL rupture and no associated visceral complications in any patients. Regarding the radiographical results yielded by PCOs, previous reports have suggested a range of 9.3° to 10.7° of sagittal correction per level, with another general rule of thumb being to expect 1° of correction for every millimeter of bone resected.^'^'^ In this study, we found a mean correction of 8.8° with any PCO. PCOs were more effective in younger individuals and were associated with most correction when used in the thoracolumbar and lumbar regions. The greater correction with PCOs in younger patients may pertain to the biomechanical mechanism of correction: because PCOs require mobility of the disc space, the greater hydration of the nucleus pulposus and elasticity of the annulus in younger patients may enable greater correction to occur. One concern with PCOs that has been previously highlighted in the literature is the potential for coronal decompensation toward the concavity, with some authors suggesting that PCOs should not be used in the presence of a coronal plane deformity.'^ In a study by Cho et aP., 13.3% of patients experienced coronal decompensation of more than 4 cm; however, that coronal decompensation predominantly affected patients who did not have a posterior-only approach for PCO (i.e., an anterior release and fusion was used). In the current series of more than 4 times as many patients, only 1 patient experienced a coronal decompensation of more than 4 cm (which stemmed from a pseudarthrosis and failure of May 2014
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Posterior Column Osteotomies • Dorward et al
instrumentation). Thus, it does not seem that coronal decompensation poses a meaningful concern in the use of PCOs through a posterior-only approach. It also seems that the literature has not sufficiently addressed the use of PCOs at the apex of scoliotic deformities. With PCOs used in this fashion, we obtained a correction rate of more than 53% for maximum coronal Cobb angles. To prove the efficacy of PCOs in this regard, we would of course need a control group undergoing similar deformity corrections without the benefit of PCOs.
This study does have several limitations. First, its retrospective design leaves it vulnerable to the various biases inherent in such studies. Second, the lack of a control group means that we cannot make sound judgments as to the safety and efficacy of PCOs relative to either other osteotomies or the use of no osteotomy at all. Third, highly experienced surgeons at a high-volume deformity center treated these patients, and as such, the results generated may not be generalizable to all spinal surgery practices.
Complications
CONCLUSION
Six patients experienced either a loss of monitoring signals or a failed wake-up test that was attributed to overcorrection with PCOs. PCOs, although not as powerful as PSO or VCR in terms of focal deformity correction, remain a potent tool that must be used with caution. It is paramount to use some form of somatosensory evoked potential and MEP to recognize and rapidly remediate insults to the spinal cord. Not having monitoring available, or being unable to obtain signals on a patient, should remain a relative contraindication to performing PCOs or any type of osteotomy. Aside from the potential for overcorrection, this series suggests that PCOs pose little risk of complications when performed carefully. Patients undergoing a greater number of PCOs did not experience increased blood loss or complications. No patients experienced durotomy, nerve root deficit, spinal cord deficit, or other complications related directly to PCOs, and no patients experienced unexpected complications such as superior mesenteric artery syndrome, as have been reported previously." In evaluating the complication rates associated with PCOs, the largest previous set of data comes from the Smith et aP° report on 135 patients from the Scoliosis Research Society Morbidity and Mortality Database regarding the correction of thoracolumbar fixed sagittal deformity. We had a similar rate of overall complications (24.2% vs. 28.1% in Smith et aP") and neurological deficit (3.1% vs. 3.7%), a lower rate of durotomy (1.6% vs. 6.7%), and a higher rate of wound infections (5.5% vs. 1.1%) and deep vein thrombosis/pulmonary embolism (3.9% vs. 0.7%).^« Our 24.2% overall complication rate, 5.5% infection rate, and 2.3% PJK rate also compared favorably with other recent evaluations of PCOs in the literature.^-' Certain elements of the PCO technique warrant emphasis to improve safety. First, meticulous dissection and bone removal helps prevent injury to the dura, spinal cord or nerve roots. Second, the bilateral facetectomies must be complete and the foramina entirely unroofed, because the osteotomy closure involves contraction of the neural foramina that could lead to nerve root impingement by any remnants of the overlying facets. Third, the osteotomy closure must be judicious, to avoid excessive anterior lengthening of the disc space and resultant violation of the anterior longitudinal ligament. Fourth, the PCOs must be performed efficiently to reduce associated blood loss and avoid unnecessarily protracting the procedure.
Spinal fusion with PCOs through a posterior-only approach was associated with effective correction for both sagittal and coronal plane deformities. The mean sagittal correction per PCO was 8.8°, but was greatest in the thoracolumbar and lumbar regions. Younger patients also obtained greater correction. The main technical concern with PCOs was overcorrection, but resultant neurological consequences were identified by intraoperative MFPs and wake-up tests, and no patients experienced permanent neurological deficits related to PCOs. Coronal decompensation was not encountered even when PCOs were used at the apex of coronal plane deformities.
Spine
Limitations
Key Points •
The use of PCOs seems safe and effective for spinal deformity correction.
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The number of PCOs was not correlated with greater complications or blood loss at surgery.
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The sagittal plane correction afforded by PCOs varies by the region of the spine, with thoracolumbar and lumbar PCOs associated with the greatest correction. Younger patients also experienced greater correction from PCOs.
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The greatest risk of PCOs seems to be overcorrection of deformity, with the potential for spinal cord injury. However, in this series strict utilization of neuromonitoring and wakeup testing identified and allowed us to address neurological perturbations, and no patients experienced spinal cord deficits from PCOs.
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May 2014
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