Harrington Distraction Research Articles

Biomechanical Simulation of Stresses and Strains Exerted on the Spinal Cord and Nerves During Scoliosis Correction Maneuvers

Study DesignBiomechanical analysis of the spinal cord and nerves during scoliosis correction maneuvers through numerical simulations. ObjectiveTo assess the biomechanical effects of scoliosis correction maneuvers and stresses generated on the spinal nervous structures. Background DataImportant forces are applied during scoliosis correction surgery, which could potentially lead to neurologic complications due to stresses exerted on the nervous structures. The biomechanical impact of the different types of stresses applied on the nervous structures during correction maneuvers is not well understood. MethodsThree correction techniques were simulated using a hybrid computer modeling approach, personalized to a right thoracic adolescent idiopathic scoliotic case (Cobb angle: 63°): (1) Harrington-type distraction; (2) segmental translation technique; and a (3) segmental rotation–based procedure. A multibody model was used to simulate the kinematics of the instrumentation maneuvers; a second comprehensive finite element model was used to analyze the local stresses and strains on the spinal cord and nerves. Average values of the internal medullar pressure (IMP), shear stresses, nerve compression, and strain were computed over three regions and compared between techniques. ResultsHarrington distraction maneuver generated high stresses and strains over the thoracolumbar region. In the main thoracic region, the segmental translation maneuver technique induced 15% more shear stress, 25% more strain, and 62% lower nerve compression than Harrington distraction maneuver. The segmental rotation–based procedure induced 25% lower shear stresses and 18% more strain, respectively, at the apical level, as well as 72%, 57%, and 7% lower IMP, nerve compression, and strain in the upper thoracic region, compared with Harrington distraction maneuver. ConclusionThis study quantified the relative stress induced on the spinal cord and spinal nerves for different correction maneuvers using a novel hybrid patient-specific model. Of the three maneuvers studied, the Harrington distraction maneuver induced the most important stresses over the thoracolumbar region.

PATIENT SELF-ASSESSMENT OF LONG-TERM RESULTS OF SURGERY FOR IDIOPATHIC AND CONGENITAL SCOLIOSIS

Objective. To analyze long-term results of surgical correction of idiopathic scoliosis and congenital spinal deformity using the patient self-assessment SRS-24 questionnaires. Material and Methods. The study included 121 patients operated on for idiopathic (106) and congenital (15) scoliosis using third generation segmental instrumentation (112 cases) and Harrington distraction rod (9 cases). Patients completed the SRS-24 questionnaire in 6, 12, 24 and more than 60 months after surgery. A total number of 448 questionnaires were analyzed. Results . Girls’ assessment of surgery outcome at five year follow-up was in whole higher, though they had more pronounced pain syndrome. Patients with congenital scoliosis gave lower estimates in most domains than those with idiopathic scoliosis. Segmental instrumentation in all seven domains had the advantage of the Harrington distraction rod. As the follow-up period increased the estimate of the achieved effect raised. Rib hump resection caused increase in patient self-assessment of the treatment result in all cases. Conclusion. Patient-reported outcome survey using SRS-24 questionnaire is simple, easy to interpret, and effective method. The obtained data showed the high quality of achieved results.

Spinal Sagittal Plane Deformities: Etiology, Evaluation, and Management

An aging population and an increasing number of spinal surgical procedures being performed have led to an increased number of patients presenting with spinal deformities and sagittal imbalance. Although few spine surgeons perform surgery on this patient population, most will encounter this problem in their practice. Individual spinal segments alignment is important to the overall sagittal balance. It is important to understand how these segments contribute to the global sagittal balance. Normal sagittal balance implies that the head is centered over the pelvis. When the individual is pitched forward, this is said to be a positive sagittal balance. The classic etiologies for sagittal imbalance include conditions such as ankylosing spondylitis, and Harrington distraction instrumentation. Other traditional etiologies include Zeilke and Dwyer anterior instrumentation. However, nowadays we are seeing other etiologies more frequently, including postlaminectomy deformities and iatrogenic postfusion kyphosis. Pseudoarthrosis and breakdown or fractures above or below long spinal fusions have become more common etiologies. Indications for spinal osteotomies include fixed spinal global sagittal imbalance, especially if associated with pain and disability. Surgical approaches vary depending on the nature and the etiology of the deformity, its location and the presence or absence of solid fusion in the area of intended correction. It is very important to plan the corrective procedure so that the final correction ensures the patient's spine aligns in at least neutral or negative sagittal balance.

THE HISTORY OF SPINAL DEFORMITY

Spinal deformity is the oldest disease known to humankind. The first record of correction of spinal deformity was documented in an Indian religious mythological book written between 3500 BC and 1800 BC. Initially, all spinal deformities were treated with the use of braces, traction, or casts. Hippocrates was the first physician to treat spinal deformities by using axial traction combined with direct pressure. Galen specifically described the anatomy of the spine and spinal nerves. The treatment of spinal deformity was greatly improved by the development of radiographic imaging by Roentgen. After x-rays became available, spinal fusions began to be used to treat scoliotic curves. Hibbs described the first spinal fusion to stabilize a deformed tuberculous spine. Soon enough, other investigators began to report on a variety of surgical techniques used to treat spinal deformity. Surgical approaches from both the posterior and anterior directions were developed and modified in an attempt to achieve durable curve corrections. Harrington's distraction rod system was a major innovation in providing a method to improve coronal plane deformity. Luque introduced segmental instrumentation, which opened up the era of modern surgical techniques for spinal deformity. This concept allowed surgeons to begin to achieve three-dimensional corrections by respecting both the sagittal and coronal curves simultaneously. The introduction of pedicle screws, throughout the thoracolumbar spine, has increased the ability of surgeons to achieve greater degrees of curve correction than had previously been possible. The history of spinal deformity is still maturing as newer procedures continue to be performed on a daily basis.

Experimental investigations on the growth of the vertebral column after dorsal spondylodesis (author's transl)

To investigate the question which growth processes take place in dorsally stiffened vertebral regions, 4 vertebral segments each were dorsally fused in twenty-one pigs, using Harrington's distraction system in 20 cases. X-ray examination and histological measurements conducted with the aid of fluorochromosequential markings showed a more or less pronounced growth of the vertebral bodies and of the fusion mass in all animals. As a rule, the sequence of vertebral bodies overgrows the fusion mass in longitudinal direction, which always results in lordosis of the stiffened region. The longitudinal growth of the vertebral bodies, and even more so of the fusion mass, decreases with increasing postoperative observation time. The fusion mass shows actual internal growth which proceeds partly in diffuse manner in all directions, in the region of the clefts, i.e. as spondyloschisis, in some cases also in the same direction as with enchondral ossification associated with columnar chondrification. The growth of the fused mass does not depend on the formation of a pseudoarthrosis, although it is probably quantitatively promoted by pseudarthroses. The stimulus to longitudinal growth of the fused mass originates from the growing vertebral bodies, with probably varying influence of tensile and compressive forces.

Harrington's operative treatment of scoliosis in combination with segmental transverse stabilization with Luque cerclage (the Harrington-Luque operation). Early results of the first 31 personal cases

Early postoperative results in 31 cases of scolioses of varying etiology using the new combination of Harrington's distraction system together with Luque's segmental wiring are presented. Starting from an average preoperative COBB angle of 70 degrees (40 degrees-120 degrees), postoperative average correction to 35 degrees (15 degrees-80 degrees) could be achieved. This represents an average correction of 49.7% (28%-73%). One deep wound infection (cleared by removal of the material) and one transient monoradicular nerve irritation complicated the follow-up in total. The superior stability of the Harrington-Luque-combination (detailed description of the operative procedure) allows the reduction of the postoperative time of external splinting to only 6 months. The Technique described can be estimated as a considerable improvement of the classical Harrington-operation and has already replaced it in our department.

Initial experiences with subcutaneous Harrington distraction without spondylodesis in scoliosis

We report on a special method in the treatment of scoliosis using subcutaneous Harrington-distraction without spondylodesis. We operated 14 patients in all who were between 7 and 12 years old, in average 10 2/12 years Indication is made if scoliosis is extremely progressive, if Cobb's measure is above 50 degrees, after unsuccessful conservative treatment also including orthosis and physiotherapy, or if patients appeared to late in our department. In this technique only two incisions to make are necessary to place the Harrington roots to the cranial and caudal end of the scoliosis curve. The Harrington root can be 'needled' in subcutaneously. When in times of further growth the amount of correction gets noticeably lost the cranial hook could be tightened or the Harrington root could be changed easily. We need an orthosis (Cheneau or Milwaukee) for after treatment until in a final operation with spinal fusion is made. This method has showed good results although we had to cope with a bad prognostic starting position.

COSTAL HUMPBACK RESECTION AS A FINAL STAGE OF IDIOPATHIC SCOLIOSIS SURGICAL TREATMENT

Objective. To analyse results of multistage surgical treatment of idiopathic scoliosis including costal humpback resection. Material and Methods. From 1996 to 2005 twenty girls with idiopathic scoliosis underwent spine deformity correction with Harrington distraction rod with Drummond interspinous wires (Group I) or with Cotrel – Dubousset Horizon Instrumentation (Group II). The final long-dated stage after correction of deformity included the costal humpback resection at the convex side only. Radiologic and topographic examinations were performed, and lung vital capacity parameter was used for lung function assessment. Patients answered the Russian version of SRS-24 questionnaire after correction and at each follow-up examination. Results. In Group I the mean curvature was 81.7° ± 26.7° (range, 55–107°) before correction and 34.5° ± 13.1° after correction (primary curve correction 57.8 ± 14.1 %). Mean correction loss in dynamics before resection was 8°, after resection 4.3°. In Group II the primary curve magnitude before correction was 87.4° ± 27.1° (range, 48–126°), after correction 42.7° ± 16.9° (primary curve correction 51.9 ± 9.6 %). Average correction loss in dynamics before resection was 3.5°, after resection 2.4°. Spirometric findings presented the following dynamics: lung vital capacity before resection was 1980 ml with mean early postoperative decrease by 16.8 % and subsequent reversion to the preoperative level or increase to 2010 ml. According to the questionnaire survey 100 patients gave the consent for surgery. Conclusion. Costal humpback resection as a cosmetic intervention improves the patient’s assessment of spine deformity surgical correction result.

Surgical Treatment for Scoliosis in Marfan Syndrome

Review of results of patients with Marfan syndrome treated with instrumented posterior fusion alone for scoliosis. To analyze the results of surgical treatment for scoliosis in Marfan syndrome. Few studies have been reported in the literature on surgical treatment for scoliosis in Marfan syndrome, analyzing long-term results of posterior instrumented fusion. Twenty-three patients with Marfan syndrome with a mean age of 17 years (range, 11-31 years) were treated surgically from 1982 to 1995 for scoliosis, using a posterior instrumented fusion alone (Harrington rod with sublaminar wires in the first 16 cases, and a more recent hybrid instrumentation in the remaining 7 cases). All of the patients received a long posterior instrumented fusion, including 12.3 levels on average (range, 9-17), extending the fusion area to vertebrae that were neutral and stable in both coronal and sagittal planes before surgery. Patients were analyzed as two different groups (Group 1 and Group 2) according to the different posterior instrumentations employed: Group 1 included 16 patients treated by the Harrington distraction rod technique with sublaminar wires, while Group 2 included 7 patients treated using more recent hybrid instrumentations. Presentation features, complications, and results were analyzed. At a minimum follow-up of 7 years (maximum, 18 years), all 23 patients were reviewed. The mean age was 26.8 years (range, 20-38 years). The average preoperative scoliosis value of 69.91 degrees was initially corrected to 38.17 degrees, averaged 40.89 degrees 1 year after surgery, and was finally equal to 44.09 degrees at the last follow-up. Differences in terms of scoliosis correction achieved with different instrumentations (Groups 1 and 2) did not reach statistical significance. In Group 2 patients, the percentage of postoperative correction was slightly lower (44.23%) than that of Group 1 (46.55%) but remained more stable at the last follow-up (40.97% vs. 36.38% of Group 1). There were 11 complications in 10 of the 23 patients (43.4%); two complications occurred in 1 patient. Intraoperatively, dural tears occurred in 2 cases (8.6%). Pseudarthrosis with instrumentation failure in 2 cases (8.6%) required revision surgery. Five (21.7%) distal hook dislodgements with moderate loss of scoliosis correction, 1 (4.3%) mild loss of correction without instrumentation failure, and 1 asymptomatic cervicothoracic junctional kyphosis. did not require surgery. All complications occurred among the 16 Group 1 patients, treated using the Harrington rod instrumentation with sublaminar wires. These results seemed to demonstrate that a satisfactory stabilization of scoliosis can be achieved by posterior instrumentation alone in patients with Marfan syndrome. Instrumented posterior fusion should be extended to include vertebrae that are neutral and stable in both coronal and sagittal planes before surgery, in order to ensure stabilization of the deformity and reduce the risks of decompensation of the spine.

Minimum 20-year follow-up results of Harrington rod fusion for idiopathic scoliosis

We evaluated the outcome of spinal fusion with a single Harrington distraction rod in patients with idiopathic scoliosis. At follow-up visits a minimum of 20 years post-surgery, we studied 24 patients who had been operated on by the same surgeon. The Scoliosis Research Society (SRS) Instrument and an additional questionnaire of our own, along with an invitation for a follow-up visit, were originally mailed to 28 consecutive patients of the surgeon. The SRS Instrument has seven domains dealing with back pain, general self-image, self-image after surgery, general function, function in terms of level of activity, function after surgery, and degree of satisfaction with the surgery. The length of time between surgery and the follow-up visit averaged 22.9 years (20.2-27.3). The mean age at surgery and follow-up were 15.8 (13-22) and 38.8 (35-48) years, respectively. Twenty-four patients sent back the completed questionnaires and 16 of them participated in the clinic and radiographic follow-up. To assess the meaning of the questionnaires' results, a control group of the same sex, age and geographic provenance was selected from our outpatients without scoliosis. The average follow-up score on the SRS Instrument for the patients was 100.8 (78-110). When we compared the study and control groups, no significant differences in the single SRS domain scores were observed. The mean Cobb angle and rib cage deformity before surgery were 70.46 degrees (40-120) and 36.4 mm (20-60 mm), respectively, whereas on follow-up they were 41.23 degrees (16-75) and 22.3 mm (5-50 mm), respectively. These long-term results lead us to consider Harrington fusion a procedure that produces a long-lasting high degree of self-reported post-operative satisfaction.

Prevention and management of iatrogenic flatback deformity.

The most common cause of iatrogenic flatback syndrome is Harrington distraction instrumentation extending into the lower lumbar spine. Other common causes and exacerbating factors include failure to enhance regional lordosis during lumbar fusion for degenerative spondylosis, development of pseudarthrosis or postoperative loss of correction, development of kyphosis at the thoracolumbar junction, development of degeneration and decompensation cephalad or caudad to a prior fusion, and hip flexion contractures. Prevention of flatback syndrome involves preoperative assessment of sagittal balance, avoidance of distraction instrumentation and extension of long fusions into the lower lumbar spine, enhancement of physiologic lordosis during lumbar fusions, and intraoperative positioning with the hips extended. Treatment of flatback syndrome involves corrective pedicle subtraction or Smith-Petersen osteotomies with segmental instrumentation. Polysegmental osteotomies and vertebral column resection may be utilized in cases of sloping global sagittal imbalance and related severe coronal imbalance, respectively. Following surgical treatment, sagittal balance is generally improved with fair-to-good clinical outcomes, high patient satisfaction, and moderately high perioperative complication rates.

TREATMENT OF IDIOPATHIC SCOLIOSIS BY HARRINGTON INSTRUMENTATION

An adolescent idiopathic right-sided thoracolumbar scoliosis has been correctedsurgically with Harrington distraction and compression instrumentation with posteriorfusion for the first time in Nepal.Key Words: Idiopathic scoliosis, Harrington system.

Pediatric spinal deformities

Pediatric spinal deformity results from multiple conditions including congenital anomalies, neuromuscular disorders, skeletal dysplasia, and developmental disorders (idiopathic). Pediatric spinal deformities can be progressive and cause pulmonary compromise, neurological deficits, and cardiovascular compromise. The classification and treatment of these disorders have evolved since surgical treatment was popularized when Harrington distraction instrumentation was introduced. The advent of anterior-spine instrumentation systems has challenged the concepts of length of fusion needed to arrest curvature progression. Segmental fixation revolutionized the surgical treatment of these deformities. More recently, pedicle screw-augmented segmental fixation has been introduced and promises once again to shift the standard of surgical therapy. Recent advances in thoracoscopic surgery have made this technique applicable to scoliosis surgery. Not only has surgical treatment progressed but also the classification of different forms of pediatric deformity continues to evolve. Recently, Lenke and associates proposed a new classification for adolescent idiopathic scoliosis. This classification attempts to address some of the shortcomings of the King classification system. In this article the authors review the literature on pediatric spinal deformities and highlight recent insights into classification, treatment, and surgery-related complications.

The effect of surgery and remodelling on spinal canal measurements after thoracolumbar burst fractures.

Bone fragments in the spinal canal after thoracolumbar spine injuries causing spinal canal narrowing is a frequent phenomenon. Efforts to remove such fragments are often considered. The purpose of the present study was to evaluate the effects of surgery on spinal canal dimensions, as well as the subsequent effect of natural remodelling, previously described by other authors. A base material of 157 patients operated consecutively for unstable thoracolumbar spine fractures at Sahlgrenska University Hospital in Gothenburg during the years 1980-1988 were evaluated, with a minimum of 5-years follow-up. Of these, 115 had suffered burst fractures. Usually the Harrington distraction rod system was employed. Patients underwent computed tomography (CT) preoperatively, postoperatively and at follow-up. From digitized CT scans, cross-sectional area (CSA) and mid-sagittal diameter (MSD) of the spinal canal at the level of injury were determined. The results showed that the preoperative CSA of the spinal canal was reduced to 1.4 cm2 or 49% of normal, after injury. Postoperatively it was widened to 2.0 cm2 or 72% of normal. At the time of follow-up, the CSA had improved further, to 2.6 cm2 or 87%. The extent of widening by surgery depended on the extent of initial narrowing, but not on fragment removal. Remodelling was dependent on the amount of bone left after surgery. The study shows that canal enlargement during surgery is caused by indirect effects when the spine is distracted and put into lordosis. Remodelling will occur if there is residual narrowing. Acute intervention into the spinal canal, as well as subsequent surgery because of residual bone, should be avoided.

Aspects of spinal deformity in familial dysautonomia (Riley-Day syndrome).

Familial dysautonomia (FD) is a rare autosomal recessive disease occurring in Jews of Ashkenazi descent, with only some 500 recognized cases. The causative gene was identified on chromosome 9. FD is of considerable orthopedic interest, because of the prevalence of skeletal deformity. About 90% of surviving dysautonomic children will develop a spinal curvature, commonly a scoliosis. The scoliotic curve is usually kyphotic rather than lordotic, and appears during the first decade of life. Fifty-one of the 90 reported cases of familial dysautonomia in Israel involved patients who were seen at the scoliosis clinic for assessment and treatment of their spinal deformities. Most of the patients presented with a scoliotic deformity associated in 37 cases with an increased thoracic kyphosis. In our series orthotic treatment and physiotherapy were found to be minimally successful at best. Surgical treatment of the spine was performed in 13 of 51 patients in this series. A retrospective review of these patients' charts and radiographs was carried out. Six years of follow-up are reported. The primary indication for surgery was progression of the spinal curve. Only posterior spinal fusions were performed. Anterior transthoracic procedures were avoided in spite of the significance of the kyphotic deformity, because of the frequency of pulmonary complications. Harrington distraction and compression instrumentation was used. Three-millimeter compression rods were used in a distraction mode in thin, young children. "Harri-Luque" segmental sublaminar wiring technique and Wisconsin spinous process segmental wiring was used in some. In all cases, the spine fusion was supplemented by bank bone only, to avoid the additional trauma of graft removal. We believe that surgical intervention is advantageous, if done early in the evolution of spinal deformity. Greater technical difficulties and a higher complication rate were encountered in this series relative to the problems usually seen after spinal deformity surgery in children; this is all the more important in a disease in which general anesthesia is an additional major complicating factor. It is hoped that the improved physical condition now seen after early gastrostomy and fundoplication will aid in reducing this high complication rate. Only a small degree (about 25%) of correction was achieved in the majority of patients. Some of this apparent rigidity derived from the inability to apply sufficient instrumental corrective force because of the friable osteoporotic bone. After surgery, there was a marked decrease in the frequency of pneumonia and an improvement in the degree of ataxia, for reasons not understood, which led to an obvious improvement in the quality of life.

Scoliosis elasticity assessed by manual traction: 49 juvenile and adolescent idiopathic cases.

We assessed preoperative curve elasticity in 49 consecutive patients with juvenile or adolescent idiopathic scoliosis who were operated on with Harrington distraction rods. Preoperatively, the curve was determined from posteroanterior radiographs taken in the standing position and in the supine position, with traction. In the latter, the radiographs were taken at the moment of maximal traction when one technician applied traction to the ankles and another to the wrists. The scoliotic curve in the 10 patients with juvenile scoliosis averaged 59 degrees and 32 degrees in the standing and supine positions with traction, respectively. Immediately postoperatively, the curve averaged 19 degrees. 39 patients with adolescent scoliosis had a scoliotic curve which averaged 58 degrees in the standing position and 32 degrees in the supine position with traction. The mean postoperative measurement was 21 degrees. These findings suggest that manual traction is a simple and reliable means of predicting the minimal correction of the scoliotic curve to be expected, using Harrington distraction rods.

Posterior instrumentation and anterior interbody fusion for tuberculous kyphosis of dorsal and lumbar spines.

Thirty-nine adults and five children with active spinal tuberculosis and resulting kyphosis of the dorsal and lumbar spine who had combined posterior instrumentation and anterior interbody fusion were observed to determine whether the corrected spinal deformity could be maintained until solid fusion. To evaluate the effectiveness of the combined two-stage procedure for treating kyphosis due to active spinal tuberculosis. Until 1970, with all methods of treatment, kyphosis due to active spinal tuberculosis tended to increase during therapy. Most of the patients treated with these methods were not happy with this residual kyphosis, even though their disease was arrested or cured. Kyphosis became their main concern regarding further treatment. A combined two-stage procedure, under the cover of 18 months of triple chemotherapy, was used for all patients. For posterior stabilization, the Harrington distraction system, Rush nails or Steinmann pins and wires, and Texas Scottish Rite Hospital instrumentation were used. The diagnosis of successful interbody fusion was made if there was no loss of correction, no graft resorption or graft bed resorption, and if there was visible graft remodeling, such as trabeculation between the graft beds and graft and the graft hypertrophy. In the 39 adults, average preoperative, immediate postoperative, and last follow-up kyphosis angles were 37 degrees, 16 degrees, and 18 degrees, respectively. In four children, the average preoperative, immediate postoperative, and last follow-up kyphosis angles were 55 degrees, 28 degrees, and 31 degrees, respectively. The loss of correction did not exceed 3 degrees. For one-segment spondylodesis, the average fusion times were 4 months in adults and 3.5 months in children. For a two-segment fusion, the average fusion times were 6 months in adults and 6.3 months in children. Posterior instrumental stabilization and anterior interbody fusion were found helpful in arresting the disease early, providing early fusion, preventing progression of kyphosis, and correcting the kyphosis.

Spinal canal restoration by posterior distraction or anterior decompression in thoracolumbar spinal fractures and its influence on neurological outcome.

Thirty consecutive patients who had suffered unstable fractures and dislocations of the thoracolumbar spine mostly associated with neurologic impairment and bony encroachment on the spinal canal were treated either with Harrington distraction rods combined with sublaminar wires or with the Zielke-VDS device. These patients were subsequently assessed for neurologic outcome, spinal canal clearance, sagittal and coronal spinal deformity correction preoperatively and postoperatively with a minimum follow-up of 26 months. In the follow-up evaluation, the patients who underwent surgery with Harrington rods showed an overall improvement of their neurologic function of 90.9%, whereas all patients who underwent the Zielke operation improved. Preoperatively, positive correlations were found between the level of injury and Frankel grades; the cord lesion tended to demonstrate more severe neurologic deficit when compared with cauda equina ones (P < 0.001). Furthermore, dislocation accompanying the injury resulted in a more severe neurological deficit (P < 0.05). Harrington rods and Zielke device offer sufficient initial correction of the frontal spinal deformity but did not significantly either restore or maintain sagittal plane alignment. The Harrington series showed an overall improvement of the segmental kyphosis of 26% (NS), with a subsequent loss of correction of 7.38% (NS) on the follow-up observation. The Zielke device produced an immediate, much better correction of the segmental posttraumatic kyphosis of 45% (NS), but a loss of correction of 22.9% (NS) was measured in the follow-up evaluation. Correction of the anterior and posterior vertebral height was shown to be better for the Zielke patient group.(ABSTRACT TRUNCATED AT 250 WORDS)

Three-dimensional simulation of Harrington distraction instrumentation for surgical correction of scoliosis.

Harrington distraction rod surgery on six female patients with idiopathic scoliosis was simulated in three-dimensional osseoligamentous finite element models with individual geometry taken from preoperative stereo roentgenographic reconstructions of the spine and ribcage and compared with the measured outcome. Boundary conditions at the ends of the spine were used to maintain pelvis and head alignment. Published material and flexibility properties were used. The amount of hook distraction was calculated from measured changes in the distance between the hook sites (range, 13-27 mm). Initial simulations underestimated the Cobb angle correction by an average 6%. They underestimated the spinal elongation by 36% and predicted an average 12 degrees increase in kyphosis angle compared with an actual 10 degrees average decrease. Agreement for sagittal plane changes improved in five cases when the beams representing the motion segments were displaced posteriorly. In the sixth case (with the rod applied over a lordotic spinal region), agreement was improved with the motion segment beams displaced anteriorly. The amount of the beam displacement that gave the best agreement was variable, and we were not able to predict it for each individual. Both measured and simulated changes in vertebral transverse plane rotations and in rib angulations were small. The greatest source of errors in these simulations appeared to be inadequate representation of in vivo motion segment behavior by in vitro measured stiffness properties.

Three-dimensional simulations of harrington distraction rod for scoliosis surgery

Three-dimensional simulations of harrington distraction rod for scoliosis surgery