Michael F. O'brien

Unilateral transforaminal posterior lumbar interbody fusion (TLIF): indications, technique, and 2-year results.

A prospective analysis of consecutive cases of lumbar fusion using the unilateral transforaminal posterior lumbar interbody fusion (TLIF) technique with pedicle screw fixation. The objective of the study was to assess the clinical and radiographic outcome of TLIF and describe the technique and indications in the treatment of degenerative disease of the lumbar spine. Forty patients treated with TLIF for degenerative diseases of the lumbar spine were followed up for a minimum of 2.5 years (mean: 36 months; range: 30–42 months). Twenty-three patients had degenerative disc disease alone, 13 had associated isthmic or degenerative spondylolisthesis, and 4 had recurrent disc herniations at the L4–L5 level. Thirty-six (90%) had solid fusions radiographically at latest follow-up. Seventy-nine percent had excellent or good clinical outcomes. Our patients demonstrated high fusion rates and patient satisfaction.

Accuracy and efficacy of thoracic pedicle screws in curves more than 90

Study Design. Retrospective study of large-magnitude thoracic curves (≥90°) treated with pedicle screw constructs. Objective. To evaluate the results of pedicle screw constructs for thoracic curves ≥ 90° in terms of sagittal and coronal correction/efficacy, as well as accuracy and safety of thoracic pedicle screw placement. Summary of Background Data. Thoracic pedicle screw constructs continue to become increasingly more common; however, the debate continues about the safety and efficacy of these constructs because of their perceived increased risk of neurologic injury and the increased cost of spinal instrumentation. Methods. Since 1998, all patients with adolescent idiopathic scoliosis, or adult progression of adolescent idiopathic scoliosis, a thoracic curve ≥ 90° and a minimum 2-year follow-up who were treated with pedicle screw constructs were included in this study. Standing anteroposterior (or posteroanterior), lateral and bending preoperative radiographs, and anteroposterior (or posteroanterior) and lateral postoperative radiographs were evaluated for curve magnitude, flexibility, and postoperative correction to assess the efficacy of these constructs in the immediate postoperative period and at latest follow-up. Postoperative CT scans were evaluated for screw accuracy using established 2-mm increments (intrapedicular, 0–2 mm breach, 2–4 mm breach, > 4 mm breach). Preoperative plans were also reviewed to evaluate the ability to place a pedicle screw at each planned level in these large-magnitude curves. Results. Twenty patients with thoracic curves ≥ 90° and an average follow-up of 3.3 years (range, 2.0–5.2 years) were included in the study. All patients underwent a posterior spinal fusion with a pedicle screw only construct. The average preoperative main thoracic curve measured 100.2° (range, 90°–133°), with an average side-bender of 71.6° (29% flexibility). The average postoperative main thoracic curve was 32.3° (68% correction). A total of 352 thoracic screws were placed in the 20 cases (17.6 screws/case). Screw accuracy (either intrapedicular or <2 mm breach) was 96.3% (339 of 352 screws) by postoperative CT scanning. Ten screws were considered to have a breach between 2 and 4 mm (3 medial, 7 lateral), while three screws were > 4 mm (2 medial, 1 lateral). The two medial screws were the only placed screws that were removed (0.57%). Overall, 94% of planned screws (352 of 374 screws) were placed according to the preoperative plan. There were no incidences of screw or instrumentation failure. Of note, there was a temporary decrease in motor-evoked potentials during curve correction in 2 cases; however, there were no identifiable neurologic complications. Conclusions. Thoracic pedicle screw constructs can be safely used for large-magnitude curves. Curve correction (68%) is powerful for these curves, which are stiff and difficult to manage. Correction should be performed carefully with consideration given to convex compression for cases with concomitant hyperkyphosis for these “at risk” spinal cords. Screw accuracy (96.3%) was excellent in this review. The authors found that screws can consistently be placed according to the preoperative plan even in these large-magnitude curves.

Pedicle morphology in thoracic adolescent idiopathic scoliosis: is pedicle fixation an anatomically viable technique?

Study Design. A radiographic study of thoracic pedicle anatomy in a group of adolescent idiopathic scoliosis (AIS) patients. Objective. To investigate the anatomic constraints of the thoracic pedicles and determine whether the local anatomy would routinely allow pedicle screw insertion at every level. Summary of Background Data. In spite of the clinical successes reported with limited thoracic pedicle screw-rod constructs for thoracic AIS, controversy exists as to the safety of this technique. Material and Methods. Twenty-nine patients with right thoracic AIS underwent preoperative thoracic CT scans and plain radiographs. Anatomic parameters were measured from T1 to T12. Results. Information on 512 pedicles was obtained. The transverse width of the pedicles from T1 through T12 ranged from 4.6–8.25 mm. The medial pedicle to lateral rib wall transverse width from T1 through T2 ranged from 12.6 to 17.9 mm. Measured dimensions from the CT scans showed the actual pedicle width to be 1–2 mm larger than would have been predicted from the plain radiographs. Age, Risser grade, curve magnitude, and the amount of segmental axial rotation did not correlate with the morphology or size of the thoracic pedicles investigated. In no case would pedicle morphology have precluded the passage of a pedicle screw. Conclusion. Based on the data identified in this group of adolescent patients, it is reasonable to consider pedicle screw insertion at most levels and pedicle-rib fixation at all levels of the thoracic spine during the treatment of thoracic AIS.

A biomechanical study of regional endplate strength and cage morphology as it relates to structural interbody support

Study Design. An in vitro biomechanical investigation to quantify the endplates resistance to compressive loads, in the thoracic and lumbar spine. Comparisons were made to determine the regional strength of the endplate, the optimal size and geometry of interbody support, and the effects of endplate removal on structural strength. Objectives. To biomechanically assess the regional variation of endplate strength in the thoracic and lumbar spine, the optimal geometry and cross-sectional area for structural interbody support, and endplate preparation techniques with respect to endplate failure or subsidence. Summary of Background Data. Anterior column interbody support plays an important role in spinal reconstruction. Subsidence of interbody structural support is a common problem and may be related to regional weakness of the endplate, the size and/or geometry of structural support, and the preparation of the endplate. Biomechanical data related to these issues should be of importance to spine surgeons and reduce the risk of subsidence and its inherent complications. Methods. The indentation tests were performed in three subgroups, each with a different set of test variables. The first test consisted of 65 vertebrae at six different endplate test positions using a 9.53-mm diameter indenter. The second test was performed on 48 vertebrae at a central endplate test site using three hollow and two solid cylindrical indenters of varying diameter. The third test was done using 24 vertebrae with the endplate intact, partially removed, or fully removed. All tests were run using human cadaveric specimen using both the superior and inferior endplates. The maximum load to failure (MLF) was determined for each test performed. Results. For all levels tested, the highest MLF occurred in the posterolateral region of the endplate. The lowest value occurred in the central and anterocentral regions for levels T7–L5 and T1–T6, respectively. Hollow indenters with a small diameter had the lowest MLF, whereas solid large-diameter indenters had the highest MLF. The ultimate compressive strength for all hollow indenters was significantly higher than all solid indenters. There was a significant reduction in the endplate strength with the complete removal of the endplate. Conclusions. The posterolateral region of the endplate provides the greatest resistance to subsidence while the central region provides the least resistance. A larger-diameter solid support has the greater MLF and the lower the risk of subsidence, suggesting a more efficient transfer of force to the endplate with the hollow indenters. Parameters such as the geometry of structural support and the position and preparation of the endplate can influence the resistance of an interbody support to subside. Partial removal of the endplate may provide both, for adequate mechanical advantage and a highly vascular site for fusion.

Chiari I Malformation Associated with Syringomyelia and Scoliosis : A Twenty-Year Review of Surgical and Nonsurgical Treatment in a Pediatric Population

Study Design. Retrospective review of patients with Chiari I malformation with or without associated scoliosis. Objectives. Determine the effect of decompression of Chiari I malformation with syringomyelia on stabilization or improvement of associated scoliosis. Summary of Background Data. Chiari malformations are often associated with spinal deformities, including scoliosis. Studies have suggested a causal relation between syringomyelia and scoliosis. Methods. Patients with Chiari I malformation and syringomyelia with or without scoliosis treated over the last 20 years were reviewed. Patients with any other anomalies were excluded. Scoliotic curves were classified by magnitude and curve type. All patients were treated with surgical decompression of the Chiari malformation with or without drainage of the syringomyelia. Results. Twenty-five patients were identified, ranging in age from 19 months to 16.5 years. Nineteen patients (76%) had associated scoliosis. The majority of the patients with scoliosis (13 of 19) sought treatment for spinal deformity, and only 6 had for pain or neurologic symptoms. Eleven of 19 patients with scoliosis (58%) underwent fusion. Eight of 19 (42%) patients have not undergone fusion: 3 have experienced progress, 1 remains in a stable condition, and 4 have experienced improvement of curvature since undergoing decompression. The mean age of patients who experienced progress after decompression was 14.5 years, compared to 6 years for patients who experienced improvement. Conclusion. Early decompression of Chiari I malformation with syringomyelia and scoliosis resulted in improvement or stabilization of the spinal deformity in 5 cases. Each of these patients underwent decompression before 8 years of age and before the curve was severe. However, this series represents a few patients demonstrating this trend, and further follow-up and investigation are warranted.

Comparison of manual and digital measurements in adolescent idiopathic scoliosis.

Study Design. Comparison of manual and digital measurement of radiographic parameters in patients with adolescent idiopathic scoliosis (AIS). Objective. To assess the reliability of digital measures as compared to manual measures in the evaluation of AIS. Summary of Background Data. Radiographic parameters are critical to the evaluation of patients with AIS, and are frequently used to monitor curve progression and guide treatment decisions. The reliability of many of the more common radiographic measures has only recently been elucidated for both manual and digital measures. However, a comparative analysis of manual versus digital measures has been performed only for coronal Cobb angles. The inter-technique reliability of these parameters will have increasing importance as digital radiographic viewing and analysis become commonplace. Methods. There were 2 independent, blinded observers that measured 30 complete sets of preoperative (posterior-anterior, lateral, and both side-bending) and postoperative (posterior-anterior and lateral) radiographs on 4 different occasions. For the first 2 iterations, manual measurements were taken using the same pencil and protractor. For the last 2 iterations, measurements of digitized radiographs were taken on a software measurement program (PhDx, Albuquerque, NM). Coronal measures included the main thoracic and thoracolumbar/lumbar standing and side-bending Cobb angles, apical vertebral translation, coronal balance, T1 tilt angle, lowest instrumented vertebrae angle, angulation of the disc inferior to the lowest instrumented vertebrae, apical Nash-Moe vertebral rotation, and Risser grade. Sagittal parameters included T2–T5 and T5–T12 regional thoracic kyphosis, T2–T12 thoracic kyphosis, T10–L2 thoracolumbar junction sagittal curvature, T12–S1 lumbar lordosis, and global sagittal balance. The technique-dependent measurement variability and the inter-technique (manual vs. digital), intraobserver reliability were evaluated for each radiographic parameter (within 3°). Results. Digital measurement showed decreased intraobserver variability for many (9 of 15) of the radiographic parameters assessed. Likewise, digital measures indicated good or excellent correlation with the absolute values obtained with manual measurement for many (10 of 15) parameters. All but 1 of those parameters having moderate-to-poor correlation had been previously shown to have poor reliability, regardless of measurement technique. Statistically significant differences between measurement variability were noted for 6 measures, including 2 favoring digital and 4, manual. Significant differences in the absolute values were noted for 5 measures, determined at a difference of 3°. However, the differences in both parameter variability and absolute values tended to be small and of little clinical significance for manual versus digital measurement. Conclusions. Digital measurement showed improved measurement precision and good correlation with manual measurements for the majority of AIS parameters. Absolute differences between manual and digital measurements were generally small. Therefore, digital measures are acceptable as a valid technique for scoliosis evaluation. The importance of digital versus manual measurement reliability will increase as digital radiographic viewing becomes more prevalent.

Analysis of patient and parent assessment of deformity in idiopathic scoliosis using the Walter Reed Visual Assessment Scale.

Objectives. This study evaluates the Walter Reed Visual Assessment Scale (WRVAS) compared with clinical parameters and written descriptions of the deformity from idiopathic scoliosis patients and their parents. Summary of Background Data. The WRVAS demonstrates seven visible aspects of spinal deformity in an analogue scale. Higher scores reflect worsening deformity. Materials and Methods. The WRVAS was administered to 182 idiopathic scoliosis patients at four centers in conjunction with open-ended questions about patients’ and their parents’ perceptions of their spinal deformity. The open-ended responses were categorized as either “deformity noted” or “no deformity noted.” Results. WRVAS scores strongly correlate with curve magnitude (P = 0.01) and clearly differentiates curves of 30° or more from lesser curves. Among treatment groups, patients with surgery recommended had significantly higher scores than that of other patients. The instrument differentiated those noting no deformity from those noting a deformity. The correlation between patients’ and parents’ scores was high (Spearman’s rho = 0.8). When a deformity was noted, parents gave higher scores than did their children for rib prominence, shoulder level, scapular rotation, and the total score, but not for the other dimensions. Conclusions. Increasing scores of the WRVAS are strongly correlated with curve magnitude lending construct validity to this type of assessment tool. Patients with “surgery recommended” report more visible deformity on the scale than observed, braced, and postoperative patients, supporting the hypothesis that surgery improves the perceived appearance. Parents perceive more deformity of the ribs and shoulders more than did the patients, but other aspects of the deformity are identified equally. WRVAS scores correlate significantly with curve magnitude and treatment. Parents and patients have similar scores, but with parents perceiving more deformity of the ribs and shoulders than patients.

Reliability analysis for manual adolescent idiopathic scoliosis measurements

Study Design. Manual radiographic measurement analysis. Objectives. To determine the intraobserver and interobserver reliability of numerous radiographic process measures used in the assessment of adolescent idiopathic scoliosis. Summary of Background Data. Analysis of scoliosis requires a thorough radiographic evaluation to completely assess the deformity. Numerous radiographic process measures have been studied extensively and used for outcomes assessment and thus become the de facto standard of care. However, many of these measures have not been evaluated to determine the reliability and reproducibility. Validation of radiographic process measures is necessary to compare these measures with patient-focused outcome measures, as well as to permit valid comparison of different surgical techniques. Methods. Thirty complete sets of long-cassette scoliosis radiographs (anteroposterior [AP], lateral and side-bending preoperative and AP, and lateral postoperative) were analyzed by three independent experienced observers on two separate occasions. Coronal image measures included the coronal Cobb angles, side-bending Cobb, apical vertebral translation, coronal balance, T1 tilt, lowest instrumented vertebrae (LIV) tilt, angulation of the disc below the LIV, apical vertebral rotation (Nash-Moe),and Risser sign; sagittal measures included T2–T5, T5–T12, T2–T12, T10–L2, T12–S1, and sagittal balance. Intraobserver and interobserver reliability for each measure was then assessed. Results. The vast majority of the radiographic process measures assessed demonstrated good to excellent or excellent intraobserver and interobserver reliability. However, the angulation of the disc below the LIV demonstrated only fair interobserver reliability for postoperative measurements (rho = 0.59). Likewise, Risser grade measurements reflected good intraobserver (0.81–0.99) but only fair interobserver reliability (0.60–0.70). Apical vertebral rotation assessed by the technique of Nash and Moe produced good intraobserver reliability before surgery (0.74–0.85) but only fair reliability after surgery (0.50–0.85). The interobserver reliability for apical Nash-Moe rotation was fair to poor (0.53–0.59). For T2–T5 regional kyphosis, intraobserver (0.22–0.83) and interobserver (0.33–0.47) reliability was generally poor. Overall, the reliability of postoperative measurements tended to be decreased relative to preoperative values, likely due to instrumentation overlying radiographic landmarks. Conclusions. Most of the radiographic process measures evaluated in this study demonstrated good or excellent reliability. The reliability of measuring the angulation of the disc below the LIV, the apical Nash-Moe rotation, and Risser grading was decreased relative to other measures. The reliability of measuring T2–T5 regional kyphosis was disappointing and poor. With regards to the other 13 measures assessed, our findings support the use of these process measures obtained by experienced deformity surgeons via manual measurement for routine clinical and academic purposes.

Recognition and treatment of the proximal thoracic curve in adolescent idiopathic scoliosis treated with Cotrel-Dubousset instrumentation.

Study Design. A retrospective radiographic and clinical review of a consecutive series of patients with adolescent idiopathic scoliosis (AIS) instrumented/fused with Cotrel-Dubousset instrumentation (CDI) was undertaken. Objective. The authors determined criteria when the upper thoracic curve should be instrumented/fused in AIS treated with CDI and assessed the results of surgical treatment. Summary of Background Data. Failure to recognize and include the upper left thoracic curve in the instrumentation/fusion of a lower right thoracic idiopathic scoliosis may produce shoulder imbalance and coronal decompensation. Patients with an elevated left shoulder clinically or a positive T1 tilt radiographically usually require instrumentation/fusion of the proximal thoracic curve. However, the upper left thoracic curve may be structural and require inclusion in the instrumentation/fusion when the shoulders clinically are level or even if the right shoulder is elevated preoperatively when using CDI. Methods. The authors compared 27 patients with AIS with structural upper thoracic curves that were instrumented with CDI to T2 (Group I) to 27 patients with King Type III curves treated with CDI that did not have the upper thoracic curve instrumented/fused (Group II). Results. The distinguishing Group I preoperative criteria indicating a structural upper thoracic curve included a proximal thoracic curve greater than 30° that corrected to no better than 20° on sidebending; ≥ Grade I rotation or ≥ 1 cm translation present at the apex of this curve; any elevation of the left shoulder or tilt of T1 into the concavity of the upper thoracic curve; or when the transitional vertebra between the two curves is at T6 or below. Conclusions. When these aforementioned criteria are present and surgical correction with CDI is planned, we recommend extending the instrumentation up to T2 to produce level shoulders and maintain coronal balance.

Restoration of Thoracic Kyphosis After Operative Treatment of Adolescent Idiopathic Scoliosis: A Multicenter Comparison of Three Surgical Approaches

Study Design. Multicenter analysis of 3 groups of patients who underwent surgical treatment for adolescent idiopathic scoliosis (AIS). Objective. To evaluate 3 surgical approaches to determine the modality that has the greatest influence on improving thoracic kyphosis. Summary of Background Data. AIS is characterized by thoracic hypokyphosis which may be restored to normal to varying degrees with surgery. Methods. A multicenter retrospective AIS surgical database was reviewed. Patients with only a structural main thoracic curve (Lenke 1, 2, or 3), and instrumentation of only the main thoracic curve were included. Lateral radiographs were analyzed to determine sagittal plane measurements before surgery, after surgery at 6 to 8 weeks, 1 year, and 2 years. The 3 groups were compared and statistical significance was defined as P < 0.05. Results. Three groups were analyzed: (1) ASF group (n = 135), Anterior spinal fusion and instrumentation, (2) PSF-Hybrid group (n = 86), PSF with proximal hooks, ± apical wires and distal pedicle screws, and 3) PSF-Hooks group (n = 132), PSF with only hooks. All groups had similar preoperative coronal main thoracic curve magnitudes (ASF: 50.6°, PSF-Hybrid: 49.1°, PSF-Hooks: 52.0°) and thoracic kyphosis (ASF: 23.7°, PSF-Hybrid: 19.3°, PSF-Hooks: 21.9°). After surgery, the T5–T12 kyphosis was greater in the ASF group (25.1°) compared with PSF-Hooks (19.0°) and PSF-Hybrid (18.5° (P < 0.05). At 1 year, thoracic kyphosis (T5–T12) remained greater in the ASF group (28.8°) compared with PSF-Hooks (22.6°) and PSF-Hybrid (20.2°) (P < 0.05), and was also greater at 2 years (29.9° vs. 23.8.8° and 19.7°) (P < 0.05). Kyphosis at the thoracolumbar junction was not seen in the PSF-Hybrid group. Lumbar lordosis increased only in the ASF group in response to the increase in thoracic kyphosis. Conclusion. ASFI is the best method to restore thoracic kyphosis when compared with posterior approaches using only hooks or a hybrid construct in the treatment of thoracic adolescent idiopathic scoliosis.