Posterior Segmental Instrumentation Research Articles

Multiple and Simultaneous Spine Fractures in Ankylosing Spondylitis

A case report. To report the unique occurrence and treatment of multiple and simultaneous spine fractures in a patient with progressed ankylosing spondylitis and preexisting multilevel spine instrumentation. Ankylosing spondylitis is a complex inflammatory arthritic condition that renders the spine more susceptible to fracture than individuals who do not have ankylosing spondylitis. To our knowledge, in the patient with ankylosing spondylitis, the occurrence of nonregion-specific multiple and simultaneous spine fractures, and the role of internal instrumentation in subsequent fracture development have not been addressed in the literature. An 81-year-old white male with ankylosing spondylitis had 2 low-energy falls, resulting in 3 spine fractures. During the first fall, he had a displaced fracture at the T11-T12 level without a spinal cord injury. Fracture treatment entailed posterior instrumentation with fusion at T8-L2 and immobilization after surgery with a thoracolumbosacral orthosis brace, which led to successful healing of the injury. Approximately 2 years later, the patient had a second fall, and presented with simultaneous displaced fractures at the C6-C7 and L2-L3 levels, and an American Spinal Injury Association-A spinal cord injury. The cervical and lumbar fractures were both treated operatively via a 2-staged approach with posterior segmental instrumentation and fusion at C3-T3 and at L2-L5, respectively. A soft cervical collar and a thoracolumbosacral orthosis brace were worn after surgery. There were no intraoperative complications. Although anatomic reduction and stable fixation of the spinal injuries were achieved, the patient's neurologic status following the second injury remained unchanged. His postoperative course was complicated by pulmonary failure that ultimately resulted in death by the 3-month postoperative time. Patients with ankylosing spondylitis have a strong susceptibility to spine fracture from minor trauma, which can have devastating outcomes. Nonregion-specific multiple and simultaneous spine fractures can occur, and require thorough radiographic evaluation with imaging of the entire spinal axis, appropriate operative planning, and meticulous perioperative treatment. Preexisting internal spine instrumentation may predispose the ankylosing spondylitis spine to multiple fractures, even following a minor traumatic event. As such, the clinician should be cognizant of the possible existence of multiple and simultaneous fractures in patients with ankylosing spondylitis with preexisting internal spine instrumentation.

Pedicle Screw Fixation for Scheuermann’s Kyphosis

Scheuermann's kyphosis is an idiopathic condition of the spine, which usually presents in adolescents as hyperkyphosis of the thoracic spine. While brace therapy and observation play a role in Scheuermann's disease, frequently surgical treatment is necessary given the significant amount of deformity and back pain. In the past, surgical treatment has focused on the anterior and posterior arthrodesis with instrumentation in order to obtain correction and union. However, with the advent of thoracic pedicle screws, surgeons have recently begun to use posterior segmental instrumentation with posterior osteotomies in order to obtain acceptable correction rates. This article describes the technique of posterior instrumentation with thoracic pedicle screws for Scheuermann's kyphosis.

Proximal Junctional Kyphosis in Adolescent Idiopathic Scoliosis Following Segmental Posterior Spinal Instrumentation and Fusion

A retrospective study. To analyze the long-term proximal junctional change in adolescent idiopathic scoliosis (AIS) following segmental posterior spinal instrumentation and fusion 5 years or more after surgery. No study has concentrated on time-dependent long-term proximal junctional change in AIS following segmental posterior spinal instrumentation and fusion after 5 years postoperation. Risk factors for developing proximal junctional kyphosis (PJK) are unknown. A total of 193 consecutive AIS patients with a minimum 5-year follow-up (average, 7.3 years; range, 5-16.7 years) treated with segmental posterior spinal instrumentation and fusion were evaluated. Radiographic measurements analyzed included sagittal Cobb angle at the proximal junction on preoperative, early postoperation, 2-year postoperation, and final follow-up (> or = 5 years) by standing long cassette radiographs. Postoperative Scoliosis Research Society (SRS)-24 outcome scores were also evaluated. Abnormal PJK was defined as the final proximal junctional sagittal Cobb angle between the lower endplate of the uppermost instrumented vertebra and the upper endplate of two vertebrae supra-adjacent, which was > 10 degrees and at least 10 degrees greater than the preoperative measurement. The incidence of PJK at 7.3 years postoperation was 26% (50 of 193 patients). The average proximal junctional angle increased 15.2 degrees until 2 years postoperation and then increased 1.7 degrees until final follow-up in the PJK group (n = 50). Factors that were statistically significant for PJK development were as follows: a thoracoplasty procedure (P = 0.001), preoperative hyperkyphotic thoracic alignment (T5-T12 > 40 degrees) (P = 0.015), and hybrid instrumentation (proximal hooks and distal pedicle screws) compared with the hooks only group (P = 0.029). The number of fused vertebrae more than 11 was also related with PJK (P = 0.08). The level of the uppermost instrumented vertebra did not affect the PJK incidence. SRS-24 outcome scores did not demonstrate any significant differences (P = 0.54 for total score and P = 0.49 for self-image subscale) between the PJK and non-PJK groups. The incidence of proximal junctional kyphosis at 7.3 years postoperation was 26% and did not progress significantly after 2 years postoperation. Risk factors for developing PJK were an associated thoracoplasty, hybrid instrumentation (proximal hooks and distal pedicle screws), and a preoperative larger sagittal thoracic Cobb angle (T5-T12 > 40 degrees). The SRS-24 outcome instrument was not affected by PJK.

Spinal deformity in neurofibromatosis type-1: diagnosis and treatment.

Spinal deformity is the commonest orthopaedic manifestation in neurofibromatosis type-1 and is categorized into dystrophic and non-dystrophic types. Management should be based on a meticulous assessment of the spine with plain radiography and magnetic resonance imaging (MRI) to rule out the presence of dysplastic features that will determine prognosis and surgical planning. MRI of the whole spine should also be routinely obtained to reveal undetected intraspinal lesions that could threaten scheduled surgical interventions. Non-dystrophic curvatures can be treated with similar decision-making criteria to those applied in the management of idiopathic scoliosis. However, close observation is necessary due to the possibility of modulation with further growth and due to the increased reported risk of pseudarthrosis after spinal fusion. The relentless progressive nature of dystrophic curves necessitates aggressive operative treatment, which often has a significant toll on the quality of life of affected patients through their early childhood. Bracing of dystrophic curves has been unsuccessful. Combined anterior/posterior spinal arthrodesis including the entire structural component of the deformity is indicated in most cases, particularly in the presence of associated sagittal imbalance. This should be performed using abundant autologous bone graft and segmental posterior instrumentation to minimize the risk of non-union and recurrence of the deformity.

P23. Thoracolumbar junctional analysis in patients fixed to T12 vs L1 in adolescent idiopathic scoliosis: is there any difference?

BACKGROUND CONTEXT: Is there any difference in the distal junctional change between fusions ending to T12 vs L1 as the lowest instrumented vertebra (LIV) in adolescent idiopathic scoliosis (AIS) undergoing segmental posterior spinal instrumentation?

Debate: Resolved, a 55° Right Thoracic Adolescent Idiopathic Scoliotic Curve Should Be Treated by Posterior Spinal Fusion and Segmental Instrumentation Using Thoracic Pedicle Screws

Debate: Resolved, a 55° Right Thoracic Adolescent Idiopathic Scoliotic Curve Should Be Treated by Posterior Spinal Fusion and Segmental Instrumentation Using Thoracic Pedicle Screws

Debate: Resolved, a 55° Right Thoracic Adolescent Idiopathic Scoliotic Curve Should Be Treated by Posterior Spinal Fusion and Segmental Instrumentation Using Thoracic Pedicle Screws

From *Washington University School of Medicine, Saint Louis, Missouri; ‡Medical University of South Carolina, Charleston, South Carolina. Address correspondence and reprint requests to Carl L. Stanitski, M.D., 96 Jonathan Lucas Street, Charleston, SC 19425, USA. (e-mail: [email protected]).

Debate: Resolved, a 55 degrees right thoracic adolescent idiopathic scoliotic curve should be treated by posterior spinal fusion and segmental instrumentation using thoracic pedicle screws: Pro: Thoracic pedicle screws should be used to treat a 55 degrees right thoracic adolescent idiopathic scoliosis.

Debate: Resolved, a 55 degrees right thoracic adolescent idiopathic scoliotic curve should be treated by posterior spinal fusion and segmental instrumentation using thoracic pedicle screws: Pro: Thoracic pedicle screws should be used to treat a 55 degrees right thoracic adolescent idiopathic scoliosis.

The posterior approach for lumbar and thoracolumbar adolescent idiopathic scoliosis: posterior shortening and pedicle screws.

Prospective clinical case series. Lumbar and thoracolumbar adolescent idiopathic scoliosis has traditionally been treated with an anterior approach and instrumentation. This anterior method often has had problems with kyphosis, pseudarthrosis, and loss of correction. The senior author has had good results treating these same lumbar and thoracolumbar curves posteriorly with wide posterior release and segmental instrumentation. In this series of his evolving technique, he adds pedicle screws as the sole anchor in the thoracolumbar/lumbar curves. To prospectively evaluate outcomes, coronal and sagittal radiographic results, balance parameters, complications, and reoperations in a group of consecutive patients with lumbar and thoracolumbar adolescent idiopathic scoliosis. These patients were surgically treated with wide posterior release and segmental posterior screw instrumentation with 2-year minimum follow-up (range 26-47 months). Sixty-two consecutive patients with thoracolumbar and lumbar adolescent idiopathic scoliosis were treated with a wide posterior release and segmental pedicle screw instrumentation limited to the curve defined by the Cobb measurement. The patients were evaluated clinically and radiographically at intervals up to 36 months. There was 2-year minimum follow-up. One patient was lost to follow-up. Of the remaining 61 patients, there were 51 Lenke 5 Type curves, 7 Lenke Type 3C curves, and 3 Lenke Type 6 curves. Only the curve defined by the Cobb measurement was fused. A total of 613 pedicle screws were placed safely. Average coronal correction of the thoracolumbar/lumbar curves was from 52 degrees to 10 degrees (80%). In the sagittal plane, lumbar lordosis was normalized from 41 degrees with a wide range (20 degrees -70 degrees ) to 42 degrees with a normal range (34 degrees -47 degrees ). There were no pseudoarthroses, no reoperations, no infections, no problems with screw placement, and excellent maintenance of correction at last follow-up. The lowest instrumented vertebrae had 81% correction of coronal angulation, center sacral line to lowest instrumented vertebrae was improved from 2.4 cm to 0.7 cm, and apex to center sacral line was improved from 5.2 cm to 1.5 cm. The C7 plumb line to center sacral line was also improved from 2.5 cm to 0.6 cm, illustrating the centering of the trunk. Wide posterior release and segmental pedicle screw instrumentation has excellent radiographic and clinical results with minimal complications. There were no pseudoarthroses and no reoperations.

Biomechanical Comparison of Cervical Spine Reconstructive Techniques After a Multilevel Corpectomy of the Cervical Spine

An in vitro biomechanical study of several reconstructive techniques after a two-level cervical corpectomy. To evaluate, compare, and quantitate the stability of several reconstructive strategies (anterior, posterior, or anterior/posterior with or without instrumentation) after a multilevel cervical corpectomy. Several clinical and biomechanical studies have questioned the stability of stand-alone long-segment anterior plate fixation after a multilevel (>or=2) corpectomy. The large cantilever forces generated within the stabilized construct, particularly at the caudal screw-bone interface, have led to plate and screw dislodgement and the need for further surgical intervention. The addition of posterior segmental instrumentation has been shown to improve overall stability and decrease local stresses on the anterior fusion construct (graft and plate). Seven fresh-frozen cadaveric human cervical spines (C1-T1) were harvested. The C1-C2 and C7-T1 vertebral bodies were embedded in poly-methylmethacrylate (PMMA). Three VICON cameras tracked three-dimensional segmental motions at the ends of the fusion construct after a two-level corpectomy and placement of a strut graft with or without instrumentation. Pure moments (flexion/extension, lateral bending, and axial rotation) were applied to the C1 level of each specimen. The motion segments were loaded to a maximum of 2 Nm using dead weights. Testing was first performed on the intact specimens. Then, a two-level corpectomy at the C4 and C5 levels was performed. A PMMA strut graft was then placed into the corpectomy site. Biomechanical testing was then repeated among three different reconstruction techniques: 1) anterior cervical locking plate (PEAK; Depuy-Acromed, Raynham, MA) with dual unicortical screw fixation at C3 and C6; 2) posterior cervical instrumentation (Summit; Depuy-Acromed) using a 3.0-mm rod with segmental lateral mass screw fixation from C3 to C6; and 3) a combined anterior-posterior instrumentation using the anterior PEAK plate and posterior Summit rod system. In all pure moments tested (flexion/extension/lateral bending/axial rotation) the combined anterior-posterior instrumentation reconstruction model and the posterior-only instrumentation model were significantly more rigid than the anterior-only instrumentation model (P < 0.05). Interestingly, no statistically significant difference was noted between the combined anterior plate/posterior instrumentation model and the posterior instrumentation-only model. The biomechanical results obtained suggest that posterior segmental instrumentation confers significant stability to a multilevel cervical corpectomy regardless of the presence or absence of anterior instrumentation. In cases in which the stability of a multilevel reconstruction procedure is tenuous, the surgeon should strongly consider the placement of segmental posterior instrumentation to significantly improve the overall stability of the fusion construct.

P68. Pedicle augmenter in treating burst fracture

HYPOTHESIS: Burst fracture with unstable biomechanics and cord compression may need surgery. The classical surgery of anterior and posterior approaches may cause suffering in the aged patient. Transpedicular bone graft only had about 33% anterior fusion rate. The short segment posterior instrumentation alone had about 20% implant failure rate. The long segment posterior fusion decreased the spine ROM. The new pedicle-augmenter may be an easier option to reconstruct the vertebral bodies through pedicles, which may replace the role of anterior approach in burst fracture and ensure the success of short segment fusion.

Radiographic outcomes using freeze-dried cancellous allograft bone for posterior spinal fusion in pediatric idiopathic scoliosis.

The senior author (A.G.) has gained extensive experience using freeze-dried cancellous allograft chips to obtain solid posterior fusion in patients with adolescent idiopathic scoliosis. The purpose of this study is to determine whether this form of allograft bone will yield successful fusion rates and maintain a minimal loss of curve correction when combined with current segmental posterior spinal instrumentation systems. Radiographs of 55 patients were evaluated by two masked reviewers using a previously devised grading system. At an average follow-up of 39 months (minimum 24 months), the overall fusion rate was 92.7% and the loss of curve correction was 3.4 degrees. The results of this study show that freeze-dried allograft chips yield successful fusion rates and only minimal loss of curve when combined with current posterior spinal instrumentation systems in patients with pediatric idiopathic scoliosis.

Factors predicting hospital stay, operative time, blood loss, and transfusion in patients undergoing revision posterior lumbar spine decompression, fusion, and segmental instrumentation.

A retrospective chart review was conducted for 112 patients who underwent revision posterior lumbar spine decompression, fusion, and segmental instrumentation. To ascertain factors predicting hospital stay, operative time, blood loss, and transfusion in patients undergoing revision posterior lumbar spine decompression, fusion, and segmental instrumentation. Posterior lumbar spine decompression and fusion with segmental instrumentation is a common procedure in the treatment of degenerative lumbar spine disorders. Many patients undergoing this procedure have had previous lumbar spine surgery, yet little is known about the factors predicting hospital stay, operative time, blood loss, and transfusion. The charts of 112 patients (53 men and 59 women) with degenerative lumbar spinal stenosis who underwent revision surgery from March 1992 to June 1999 were reviewed. Their average age was 54 years (range, 27-84 years). All the surgeries included decompression and fusion with segmental instrumentation. The patients' demographics, comorbid conditions, factors related to previous lumbar spine surgery, diagnosis, number of levels fused, and preoperative hemoglobin and hematocrit were collected and used as the independent variables. Multiple regression analysis was used to ascertain factors predicting length of hospital stay, operative time, intraoperative blood loss, and transfusion. The mean length of hospital stay was 6 +/- 2.4 days, the operative time 280 +/- 62 minutes, the estimated intraoperative blood loss 1073 +/- 716 mL, and the total volume of blood transfused 1.04 +/- 1.17 U. For 63% of the patients, a blood transfusion was needed. Increasing age was the significant predictor for hospital stay (P < 0.001). The factors predicting operative time were number of levels fused (P < 0.001), diagnosis of degenerative scoliosis (P < 0.05), and excessive body weight (P < 0.01). The factors predicting intraoperative blood loss were number of levels fused (P < 0.01), body weight (P < 0.001), and high preoperative hemoglobin (P < 0.001). Both logistic and linear regression analysis showed that the factors predicting blood transfusion were number of levels fused (P < 0.01), age (P < 0.05), and low preoperative hemoglobin (P < 0.001). Other factors associated with hospital stay and blood transfusion were unemployment associated with three or more comorbid conditions and complications. The women had less intraoperative blood loss (P < 0.01), but received more transfused blood than the men (P < 0.01). Number of levels fused and age seem to be the most significant factors predicting hospital stay, operative time, intraoperative blood loss, and transfusion in patients undergoing revision posterior lumbar spine decompression, fusion, and segmental instrumentation.

Histology of tissues within retrieved human titanium mesh cages

Daisuke Togawa, MD, PhD, Thomas W. Bauer, MD, PhD, Cleveland, OH, USA; Gary L. Lowery, MD, PhD, Phoenix, AZ, USAIntroduction: The use of vertically placed titanium mesh intervertebral body fusion cages is controversial, and there is little histological documentation of the contents of these cages in the human spine. The purpose of this study is to describe the contents of a series of retrieved, clinically failed human titanium mesh cages, with special reference to the viability of bone graft and the presence of debris.Methods: Ten Titanium Surgical Mesh Cages (Harma; DePuy AcroMed, Raynham, MA) retrieved from nine patients were analyzed. Preoperative diagnoses of these nine adult patients included disease conditions in the sagittal plane: spondylosis (eight), discogenic disease (five) and stenosis (two). The spinal levels treated were C4–6 (one patient), C5–6 (three patients), L3–4 (one patient) and L4–5 (four patients). The cages had been packed with autograft (local, n=4; iliac crest, n=4), autograft (iliac crest) in combination with hydroxyapatite granules (Interpore Cross International, Irvine, CA; n=1) or hydroxyapatite only (n=1). Cage implantation was performed with anterior and posterior segmental instrumentation (plates, pedicle screws and cross-links). Indications for cage retrieval included failed fusion (n=8) or failed fusion with hardware failure (n=2). The cages had been in situ from 2 to 47 months (mean, 25 months). Specimens were fixed in 70% ethanol, dehydrated, embedded in plastic and sectioned without decalcification. Sections were reviewed qualitatively, and the approximate percent of area in the cage occupied by viable bone, necrotic bone (graft), fibrocartilage, fibrous tissue and bone graft substitute were visually estimated. Particles of metal debris were estimated by a semiquantitative scoring system ranging from 0 to 4. Spearman's rank-order correlation analysis was used to test correlations between duration in situ and the percentage of viable bone, fibrocartilage and the extent of debris.Results: The cage with 2 months duration in vivo showed only fragments of necrotic bone (graft) surrounded by fibrous tissue. All other cages showed evidence of vascular ingrowth and areas of histologically viable bone, almost certainly representing incorporating bone graft. We estimate an average viable bone area of approximately 32% (range, 0% to 80%). The lateral openings of these cages contained approximately 81% fibrous tissue or fibrocartilage (range, 30% to 100%). In spite of the relatively small number of cases, there is a significant correlation between the duration in situ and the proportion of viable bone (p=.03, r=0.69). At least a few particles of debris were present in 8 of 10 cages, but with the numbers available we did not identify a significant correlation between the debris score and duration in situ (p=.36). There was no bone apposition directly to the inner surface of any cage. Instead, a membrane of either fibrous tissue or fibrocartilage separated bone from the inside of each cage. Fibrocartilage in the cages was of two types. Fibrocartilage of probable intervertabral disk origin ranged from 0% to 70% of the available area (average, 22%), and there was no significant correlation between duration and the proportion of fibrocartilage (p=.20). In addition, several cages contained small seams of fibrocartilage connecting segments of bone in a pattern that suggests uniaxial motion. There was only focal bone apposition to the hydroxyapatite granules present in one cage.Discussion: In spite of the likelihood of motion in vivo, almost all of these cages showed evidence of at least some bone graft incorporation. The presence of fibrous tissue and necrotic bone (graft), however, suggests that the incorporation was still incomplete. To the best of our knowledge, the seams of fibrocartilage connecting segments of viable bone have not been previously described in this location. A few particles of debris were present in most cages, but there is no histologic evidence of particle-induced bone resorption or inflammation. The study of clinically successful cages retrieved at autopsy would help clarify the safety and efficacy of these intervertebral body fusion cages.

Interbody cages: be careful what you pack

Interbody cages: be careful what you pack

One-Stage Posterior Hemivertebra Resection and Correction Using Segmental Posterior Instrumentation

A retrospective study of 12 patients with congenital kyphoscoliosis caused by a single hemivertebra who underwent one-stage posterior hemivertebra resection and correction by posterior segmental instrumentation. To evaluate the surgical outcomes of 12 patients with hemivertebra treated by hemivertebra resection by single posterior approach and correction with segmental posterior instrumentation. Congenital scoliosis caused by hemivertebra causes extremely severe curves in some patients. Posterior fusion or posterior and anterior hemi-epiphysiodesis is performed to prevent progression of the deformity. The results of these procedures have been variable and not promising, especially in an adolescent patient with fixed kyphoscoliotic deformity. Hemivertebra resection offers more certain results and better correction of the deformity. To date, hemivertebra resection is performed by anterior and posterior approaches either by one-stage or two-stage operation. Few reports have been published describing a procedure consisting of one-stage posterior hemivertebra resection and correction of the deformity by segmental posterior instrumentation. A total of 12 patients with a single hemivertebra between the ages 8-24 years who underwent operative treatment were evaluated for a minimum of 2 years. All patients had a single nonincarcerated hemivertebra [T9 (1 patient), T10 (2), T11 (2), T12 (4), and L1 (3)]. After posterior hemivertebra resection, segmental posterior instrumentation was used for correction of the kyphoscoliotic deformity [CD (4 patients), Kaneda SR (2), and ISOLA (6)]. Radiographic evaluations were conducted on the preoperative, postoperative, and follow-up standing posteroanterior and lateral radiographs. All 12 patients had kyphoscoliotic deformity. Preoperative scoliosis averaging 49 degrees was corrected to 18 degrees (correction rate, 64%). Preoperative kyphosis of 40 degrees was corrected to 17 degrees of kyphosis. Trunk shift of 23 mm was improved to 3 mm. Correction loss was 2 degrees in the frontal plane and 3 degrees in the sagittal plane, and no patients showed more than 5 degrees of correction loss. No intraoperative complications were noted. Solid fusion was obtained in all patients, and no implant failure was verified at the final radiographic evaluations. This study indicated that correction of kyphoscoliosis caused by a single hemivertebra can be effectively conducted by one-stage posterior hemivertebra resection and correction using segmental posterior instrumentation. The operation was safe, and no associated adverse complications were noted. This procedure is best indicated for adolescent patients with a structural kyphoscoliotic deformity caused by a thoracic or thoracolumbar single hemivertebra.

Scoliosis correction maintenance in skeletally immature patients with idiopathic scoliosis. Is anterior fusion really necessary?

A retrospective evaluation of the occurrence of the crankshaft phenomenon in skeletally immature patients with idiopathic scoliosis. To determine what factors, if any, contribute to a decreased occurrence of crankshaft phenomenon in patients treated with posterior surgery only. Reports have described the progression of scoliotic deformity, termed the crankshaft phenomenon, in a region of solid posterior arthrodesis in skeletally immature patients. This has led some authors to advocate the use of concomitant anterior discectomy and fusion to prevent crankshaft. From 1989 through 1994, 18 Risser 0 patients with thoracic or thoracolumbar idiopathic scoliosis underwent Isola (De Puy-Acromed, Raynham, MA) posterior instrumentation and fusion. They were assessed for evidence of the crankshaft phenomenon, identified by coronal plane deformity progression of 10 degrees or more, or a rib vertebra angle difference of 10 degrees or more. The average age of the patients was 12.5 years (range, 10.5-15.5 years), and the average follow-up period was 39 months (range, 24-68 months). Eleven patients (10 girls and 1 boy) had closed triradiate cartilage at the time of surgery. Their average Cobb angle was 62 degrees before surgery, 21 degrees after surgery, and 22 degrees at follow-up assessment. No patients in this group met the criteria for crankshaft. Seven patients (6 girls and 1 boy) had open triradiate cartilage at the time of surgery. Their average Cobb angle was 62 degrees before surgery, 18 degrees after surgery, and 20 degrees at follow-up evaluation. No patient had a 10 degrees or more increase in rib vertebra angle difference. One patient had more than a 10 degrees increase in her Cobb angle (11 degrees) from postoperative to latest follow-up assessment. Her instrumentation construct, performed in 1989, used sublaminar wires as the caudal anchors. Hooks and pedicle screws are now used. Two of the seven patients with open triradiate cartilage underwent surgery during or before their peak height velocity and displayed no evidence of crankshaft. No deaths, neurologic complications, or infections occurred in either group. These findings suggest that scoliotic deformity progression can be prevented in skeletally immature patients with idiopathic scoliosis as young as 10 years of age with the use of stiff segmental posterior instrumentation, without the necessity of concomitant anterior arthrodesis.

Spontaneous lumbar curve coronal correction after selective anterior or posterior thoracic fusion in adolescent idiopathic scoliosis.

Retrospective review of anterior and posterior fusions for treatment of adolescent idiopathic thoracic scoliosis. To evaluate both the instrumented thoracic and the spontaneous lumbar curve corrections after treatment of the primary thoracic scoliosis by either anterior or posterior fusion. Recent reports of thoracic scoliosis fusions have concentrated on the thoracic correction obtained by posterior segmental instrumentation systems. Coronal decompensation occurring because of curve progression with imbalance of the unfused lumbar spine has also been investigated. No report comparing spontaneous lumbar curve response after selective anterior versus posterior thoracic scoliosis fusions are available. One hundred twenty-three cases of primary thoracic-compensatory lumbar adolescent idiopathic scoliosis were treated by selective thoracic instrumentation and fusion with either an anterior (n = 70) or posterior (n = 53) single approach. Thoracic and lumbar Cobb measurements and lumbar apical translation parameters were assessed before surgery, 1 week after surgery, and 2 years after surgery on upright coronal radiographs. All patients had a minimum 2-year follow-up. At 2-year follow-up, the percentage of thoracic curve correction was superior for the anterior (58%) versus the posterior (38%) group (P < 0.05), whereas the spontaneous lumbar curve correction was also superior for the anterior (56%) group versus the posterior (37%) group for all curve types investigated (P < 0.05). Both treatment groups consistently improved lumbar apical positioning after the thoracic fusion procedure. Spontaneous lumbar curve correction occurs consistently after both selective anterior and posterior thoracic fusion implying intrinsic ability of the lumbar spine to follow thoracic spine correction. In the current study, using multisegmented hook-rod systems posteriorly with intentional limitation of posterior thoracic correction to avoid decompensation, instrumented thoracic and spontaneous lumbar curve correction was statistically better after anterior thoracic instrumentation and fusion, with the results most dramatic for lumbar curve Type C (true King II curves).

Stability of posterior spinal instrumentation and its effects on adjacent motion segments in the lumbosacral spine.

An in vitro biomechanical analysis of three anterior instability patterns was performed using calf lumbosacral spines. Stiffness of the constructs was compared, and segmental motion analyses were performed. To clarify the factors that alter the stability of the spinal instrumentation and to evaluate the influence of instrumentation on the residual intact motion segments. Recently, many adverse effects have been reported in fusion augmented with rigid instrumentation. Only few reports are available regarding biomechanical effects of stability provided by spinal instrumentation and its effects on residual adjacent motion segments in the lumbar-lumbosacral spine. Eighteen calf lumbosacral spine specimens were divided into three groups according to instability patterns--one-level, two-level, and three-level disc dissections. Six constructs were cyclically tested in rotation, flexion-extension, and lateral bending of intact spines, of destabilized spine, and of spines with four segmental posterior instrumentation systems used to extend the levels of instability (Cotrel-Dubousset compression hook and three transpedicular screw fixation systems). During each test, stiffness values and segmental displacements were measured. The rigidity of the instrumented construct increased as the fixation range became more extensive. Although application of the instrumentation effectively reduced the segmental motion of the destabilized vertebral level, the motion at the destabilized level tended to increase as the number of unstable vertebral levels increased, and the fixation range of the instrumentation became more extensive. Instrumented constructs produced higher segmental displacement values at the upper residual intact motion segment when compared with those of the intact spine. In contrast, the instrumented constructs decreased their segmental displacement values at the lower residual intact motion segment with higher magnitude of the translational (shear) motion taking place compared with the intact spine in flexion-extension and lateral bending. These changes in the motion pattern became more distinct as the fixation range became more extensive. As segmental spinal instrumentation progresses from one level to three levels, the overall torsional and flexural rigidity of the system increases. However, segmental displacement at the site of simulated instability becomes more obvious. Application of segmental instrumentation changes the motion pattern of the residual intact motion segments, and the changes in the motion pattern become more distinct as the fixation range becomes more extensive and as the rigidity of the construct increases.

Clotting parameters in patients with adolescent idiopathic scoliosis undergoing posterior spinal fusion and instrumentation.

Thirty-six patients, 9 males and 27 females, average age 13.2 years, undergoing posterior fusion and segmental instrumentation surgery for idiopathic adolescent scoliosis were studied for abnormalities of platelet count (PC), prothrombin time (PT) and partial thromboplastin time (PTT). Intraoperative and immediate postoperative values were obtained at 2, 4, 6, 12, 24, and 48 hours. All patients showed diminution of platelet counts during the study period, but mean values were reduced below normals only at 4 hours after operation. The PT was significantly elevated in all patients intraoperatively and for the first 24 hours postoperatively, with return to normal by 48 hours. The PTT levels were essentially unaffected at any time.