Spine loading characteristics of patients with low back pain compared with asymptomatic individuals

STUDY DESIGN

Patients with low back pain and asymptomatic individuals were evaluated while performing controlled and free-dynamic lifting tasks in a laboratory setting.

OBJECTIVE

To evaluate how low back pain influences spine loading during lifting tasks.

SUMMARY OF BACKGROUND DATA

An important, yet unresolved, issue associated with low back pain is whether patients with low back pain experience spine loading that differs from that of individuals who are asymptomatic for low back pain. This is important to understand because excessive spine loading is suspected of accelerating disc degeneration in those whose spines are damaged already.

METHODS

In this study, 22 patients with low back pain and 22 asymptomatic individuals performed controlled and free-dynamic exertions. Trunk muscle activity, trunk kinematics, and trunk kinetics were used to evaluate three- dimensional spine loading using an electromyography- assisted model in conjunction with a new electromyographic calibration procedure.

RESULTS

Patients with low back pain experienced 26% greater spine compression and 75% greater lateral shear (normalized to moment) than the asymptomatic group during the controlled exertions. The increased spine loading resulted from muscle coactivation. When permitted to move freely, the patients with low back pain compensated kinematically in an attempt to minimize external moment exposure. Increased muscle coactivation and greater body mass resulted in significantly increased absolute spine loading for the patients with low back pain, especially when lifting from low vertical heights.

CONCLUSIONS

The findings suggest a significant mechanical spine loading cost is associated with low back pain resulting from trunk muscle coactivation. This loading is further exacerbated by the increases in body weight that often accompany low back pain. Patient weight control and proper workplace design can minimize the additional spine loading associated with low back pain.

Relevance of Cobb method in progressing sagittal plane spinal deformity

Non-traumatic, progressing sagittal plane deformities are uncommon, but can lead to neurological deficit if untreated. The currently used Cobb method in assessing sagittal spinal curves is based on measuring the tilt of the end vertebrae. This study describes a method which quantifies the apex of the sagittal curve based on the apical quality as measured by the radius of curvature. Both this and the Cobb methods are compared to determine which has relevance in determining neurological deficit. Radiographs of 36 consecutive patients diagnosed with congenital kyphosis were reviewed. Twenty-four had normal neurology and 12 had neurological deficit as a result of sagittal curve progression. Both groups of patients had their weight bearing lateral radiographs analysed to measure the sagittal curve by the usual Cobb method and the Radius of Curvature method. There was no difference for the Cobb values for negative neurology and patients with positive neurological deficit (p = 0.3). There was a difference in these two groups when the radius of curvature method was used (p < 0.0005). The Radius of Curvature method has more relevance than Cobb method in quantifying sagittal plane deformity in congenital kyphosis when assessing neurological deficit.

Premature vertebral endplate ossification and mild disc degeneration in mice after inactivation of one allele belonging to the Col2a1 gene for Type II collagen

STUDY DESIGN

Skeletal tissues of mice with an inactivated allele of the Col2a1 gene for Type II collagen ("heterozygous knockout") were studied.

OBJECTIVE

To determine whether a heterozygous inactivation of the Col2a1 gene has a role in the etiology of spine disorders such as disc degeneration.

SUMMARY OF BACKGROUND DATA

Mutations in the COL2A1, COL11A1, COL11A2, and COL9A2 genes have been linked to spine disorders. However, the mechanism by which genetic factors lead to disc degeneration still are largely unknown.

METHODS

Spine tissues were studied using radiograph analyses; conventional, quantitative, and polarized light microscopy; immunohistochemistry for the major extracellular components, and in situ hybridization for procollagens alpha1(I) and alpha1(II). Voluntary running activity also was monitored in half of the mice.

RESULTS

As the findings showed, 1-month-old heterozygous knockout mice had shorter limb bones, skulls, and spines, as well as thicker and more irregular vertebral endplates, which calcified earlier than in the control mice. They also had a lower concentration of glycosaminoglycans in the anulus fibrosus, in the endplates, and in the vertebral bone than the controls. These features in the heterozygous knockout mice were compensated by the age of 15 months. However, the long bones and skulls of the mature heterozygous mice remained shorter than those of the controls. Gene-deficient mice used the running wheel less. However, physical exercise did not induce any marked structural changes in the skeleton.

CONCLUSION

Mice with heterozygous knockout of Col2a1 show subtle early skeletal manifestations that bear some resemblance to those of human spine disorders.

[The biomechanics of kyphosis]

Kyphosis is a dorsally convex curvature of the spine in the sagittal plane. A pathological kyphosis of the thoracic spine has a Cobb angle greater than 50 degrees. It occurs when the anterior and/or posterior load-transferring elements of the spine are overloaded or damaged. Wedge-shaped vertebral bodies may be found at one or several levels. A wedge-shaped vertebral body increases the curvature of the spine and moves the centre of gravity of the body parts above of the corresponding vertebral body in a ventral direction. This increases the flexion-bending moment acting on the spine. In the case of a wedge-shaped deformation of a vertebral body, the relative increase of the flexion moment is a function of the wedge angle and of the original position of the centre of gravity of the upper body.

Mechanical and pathologic consequences of induced concentric anular tears in an ovine model

STUDY DESIGN

Relations between induced concentric tears in the sheep disc and the mechanics of the intervertebral joint and vertebral body bone were analyzed.

OBJECTIVE

To examine the effect of concentric disc tears on the mechanics of the spine.

SUMMARY OF BACKGROUND DATA

Degeneration of the intervertebral disc results in changes to the mechanics and morphology of the spine, but the effect of concentric disc tears is unknown.

METHODS

In this study, 48 merino wethers were subjected to surgery, and discs were randomly selected for either a needlestick injury or induction of a concentric tear in the anterior and left anterolateral anulus. Sheep were randomly assigned to groups for killing at 0, 1, 3, 6, 12, and 18 months. From each sheep, two spine segments were mechanically tested: one with a needlestick injury and one with a concentric tear. Macroscopic disc morphology was assessed by three axial slices of the disc. Sagittal bone slices were taken from cranial and caudal vertebral bodies for histologic analysis.

RESULTS

Induced concentric tears decrease the stiffness of intact spine segments in left bending and the disc alone in flexion. In all other mechanical tests, the needlestick injury had the same effect as the induced concentric tear. In the isolated disc, the disc stiffness at 6 months was increased for right bending, as compared with the response at 1 month. This was associated with increased anterior lamellar thickening and increased vertebral body bone volume fraction.

CONCLUSIONS

Concentric tears and needlestick injury in the anterior anulus lead to mechanical changes in the disc and both anular lamellar thickness and vertebral body bone volume fraction. A needlestick injury through the anulus parallel to the lamellae produces progressive damage.

[Analysis of the changes of temporomandibular joint under repeated +Gz stress]

Changes of temporomandibular joint (TMJ) under repeated +Gz stress were discussed. From the etiological point of view in TMJ, many papers in the fields of aviation medicine, microcirculation, maxillofacial surgery and bone surgery were reviewed. +Gz forces can cause inadequacy of blood of oxygen supply to TMJ area. This situation can be worsened by release of free radical agent and cellular factors, ischemia/reperfusion injury, and/or hemorrheologic changes. Furthermore, G-induced injury of cervical muscles and spine may break the maxillofacial muscle chain balance. In addition to the above factors, mental stress may do harm to TMJ. This paper introduced the researches on this area in an attempt to enlighten the concern about TMJ responses to increased +Gz acceleration forces.

Misdiagnosis in vertebral osteomyelitis: problems and factors

One hundred and one cases diagnosed with vertebral osteomyelitis were evaluated for misdiagnosis and both factors and outcomes of misdiagnosis were assessed. There were 67 patients with tuberculous spondylitis and 34 patients with pyogenic vertebral osteomyelitis. Misdiagnosis occurred in 33.7 per cent of the cases. The average delayed diagnosis time was 2.6 months (range, 0.2 to 12). Age between 60 to 70 years was the most frequent group for misdiagnosis, while the most frequent area of misdiagnosis was the lumbar spine. Metastatic carcinoma, spinal stenosis, herniated nucleus palposus and back strain were common initial misdiagnoses. The factors, age group, absence of fever and positive straight leg raising test (SLRT) were associated with misdiagnosis in univariate analysis and multivariate analysis (odds ratio 3.40 (95%CI:1.07-11.94), 3.47 (95%CI:1.20-10.05), and 24.47 (95%CI:2.18-274.28), respectively) Misdiagnosis was statistically significantly associated with the result of treatment. This paper emphasizes that the elderly age group, absence of fever and positive SLRT are the independent factors which increase the risk of misdiagnosis of vertebral osteomyelitis.

Design of thoracolumbosacral orthosis (TLSO) braces using CT/MR

The field of orthotics has gained scientific attention over the last few years. Its objective is to correct, adjust, or modify the operation of human limbs, joints, or muscles. Thoracolumbosacral orthosis (TLSO) braces are used by scoliosis and postoperative patients who need back correction and/or support. The anatomic dimensions for TLSO braces have been acquired mainly by casting the patient. Casting is a time-proven method for obtaining surface geometry, but it can be inconvenient in certain situations. For example, casting might not be suitable for postoperative and trauma patients owing to the risk of further injury. Such prohibitive cases can still be handled safely by X-ray CT or MR scanning. This article presents an alternative method for data acquisition of TLSO patients' anatomic dimensions using CT/MRI. The experimental results show the method to be statistically accurate, efficient, and feasible compared with the conventional casting method.

Factors that influence outcome in bracing large curves in patients with adolescent idiopathic scoliosis

STUDY DESIGN

A retrospective review of 51 patients with adolescent idiopathic scoliosis (AIS) treated with a Boston brace for curves ranging from 36 degrees to 45 degrees.

OBJECTIVES

To determine what radiographic or clinical observations may be predictive of outcome.

SUMMARY OF BACKGROUND DATA

Patients with AIS who are braced for curves >35 degrees are less likely to respond to conservative treatment than patients of similar maturity with smaller curves.

METHODS

Skeletally immature patients with AIS with no history of prior treatment were treated with a Boston brace. Cobb angles, vertebral tilt angles, coronal decompensation, apical vertebral translation(s), apical vertebral rotation, lateral trunk shift, rib vertebral angle difference, pelvic tilt, and the lumbar pelvic relationship (LPR) were measured at brace prescription, initial in-brace, brace discontinuation, and follow-up.

RESULTS

At the time of brace discontinuation, 31 patients (61%) were judged treatment successes. With follow-up observation, an additional eight patients progressed beyond 5 degrees, and a total of 16 patients (31%) required surgical correction. Only patients with double curves were found to have radiographic values predictive of outcome. The LPR angle, the association between the thoracic curve vertebral tilt angles and the amount of in-brace correction of the Cobb angle, were significant predictors. A patient's reported wear schedule significantly influenced outcome.

CONCLUSIONS

Patients with a double curve pattern in which the thoracic curve is >35 degrees and the LPR angle is >12 degrees are significantly more likely to demonstrate curve progression. In-brace correction for double curves of at least 25% and a patient's ability to wear the orthosis >18 hours/day significantly increased the likelihood of success.

Validity, reliability, and responsiveness of the fingertip-to-floor test

OBJECTIVE

To evaluate the validity, reliability, and responsiveness of the fingertip-to-floor test to assess total mobility when bending forward in standing position.

DESIGN

Experimental, prospective, correlational.

SETTING

Rehabilitation and radiology departments in a university hospital in France.

PARTICIPANTS

Ten patients (6 women, 4 men; mean age, 42yr) with chronic low back pain (LBP) in the validity study; 32 LBP patients (16 women, 16 men; mean age, 52yr) in the reliability study; and 72 LBP patients (22 women, 50 men; mean age, 30yr) in the responsiveness study.

INTERVENTIONS

Dynamic radiographs and fingertip-to-floor test.

MAIN OUTCOME MEASURES

For the validity study, 2 lateral radiographs of the upper dorsal spine, 1 in neutral position, and then 1 in full trunk flexion, were made. Validity was assessed by means of Spearman's correlation coefficient. Reliability was studied by using intraclass correlation coefficient (ICC) and the Bland and Altman method. Responsiveness was assessed by the effect size and the standardized response mean (SRM).

RESULTS

The Spearman's correlation coefficient for trunk flexion assessed by the test and the radiologic measure was excellent (r(s) = -.96). The intra- and interobserver reliability were excellent (ICC = .99). The Bland and Altman method showed no systematic trend. The values observed for the test were .97 for SRM and .87 for effect size.

CONCLUSIONS

Because the fingertip-to-floor test has excellent validity, reliability, and responsiveness, it can be used in clinical practice and therapeutic trials.

Trabecular shear stress in human vertebral cancellous bone: intra- and inter-individual variations

Correlation of the mean and standard deviation of trabecular stresses has been proposed as a mechanism by which a strong relationship between the apparent strength and stiffness of cancellous bone can be achieved. The current study examined whether the relationship between the mean and standard deviation of trabecular von Mises stresses can be generalized for any group of cancellous bone. Cylindrical human vertebral cancellous bone specimens were cut in the infero-superior direction from T12 of 23 individuals (inter-individual group). Thirty nine additional specimens were prepared similarly from the T4-T12 and L2-L5 vertebrae of a 63 year old male (intra-individual group). The specimens were scanned by micro-computed tomography (microCT) and trabecular von Mises stresses were calculated using finite element modeling. The expected value, standard deviation and coefficient of variation of the von Mises stress were calculated form a three-parameter Weibull function fitted to von Mises stress data from each specimen. It was found that the average and standard deviation of trabecular von Mises shear stress were: (i) correlated with each other, supporting the idea that high correlation between the apparent strength and stiffness of cancellous bone can be achieved through controlling the trabecular level shear stress variations, (ii) dependent on anatomical site and sample group, suggesting that the variation of stresses are correlated to the mean stress to different degrees between vertebrae and individuals, and (iii) dependent on bone volume fraction, consistent with the idea that shear stress is less well controlled in bones with low BV/TV. The conversion of infero-superior loading into trabecular von Mises stresses was maximum for the tissue at the junction of the thoracic and lumbar spine (T12-L1) consistent with this junction being a common site of vertebral fracture.

Verbal categories for classification of spinal postures and their respective angular values registered by photographs and electrogoniometry

The perception of posture may allow workers to discern sensations associated with physical overload and potential tissue damage. In an occupational context, the classification of body postures in ranges of amplitude has been useful for researchers and ergonomists interested in evaluating the exposure of workers to uncomfortable and potentially harmful postures. In this paper we describe measurements, using photographs and electrogoniometry of the angle of flexion of the trunk and of the thoracolumbar segment, respectively, adopted according to the verbal categories of mild, moderate, and severe flexion, as requested by the experimenter. The results showed no differences between the groups of subjects, but significant differences occurred in the classification of the movement amplitude per verbal categories.

Plaster of Paris as bone substitute in spinal surgery

In order to assess the effectiveness of calcium sulphate (plaster of Paris; POP) as a substitute for autologous bone graft, we performed lumbar intervertebral fusion in mature sheep using POP and a variety of other graft materials, and reviewed the literature. The osteoconductivity of the POP grafts was compared to that of grafts carried out with autogenous iliac crest, frozen allogeneic bone, and ProOsteon 500 coralline bone. We also compared the osteogenicity of POP to admixtures of autogenous iliac crest bone with POP and coralline bone, and to an osteoinductive demineralized sheep bone preparation (DBM). The substrates were loaded into tubular titanium mesh, implanted into excavated disc spaces and recovered after a period of 4 months. Fusion mass segments tested in flexion and tension showed that POP was equal to autogenous bone and most other substrates. The POP fusions were significantly tougher than the DBM fusions, even though histomorphometry failed to reveal differences in the amount of trabecular bone. We conclude that POP can be used to achieve a biomechanically stable interbody lumbar vertebral fusion. In addition, our literature review indicated that POP can be used as a vehicle for local delivery of antibiotics in bone infections.

Vertebral reconstruction with cortical allograft: long-term evaluation

Reconstruction of large anterior vertebral column defects is indicated in a number of pathological conditions including tumor, infection, trauma and post-traumatic deformity. Several substitutes and techniques are available for the functional restoration of the vertebral column. Vascularized bone transfers, autografts, allografts or xenografts have been used, as well as metal or ceramic implants. All of these bear potential advantages and drawbacks in terms of associated morbidity of graft harvesting, disease transmission, mechanical failure, implant incorporation and overall long-term clinical outcome. In the present paper we report our experience with the use of freeze-dried, gamma-irradiated, cortical allograft for the reconstruction of large, anterior segmental defects of the spine, involving at least one vertebral body with its two adjacent discs. Cortical allografts were used in 67 cases operated for a variety of conditions. No case of disease transmission, infection or long-term mechanical graft failure occurred in our entire series, with a mean follow-up of 31 months. Fusion and mechanical stability was reliably obtained. Specific advantages include the absence of donor site morbidity, the possibilities for exact trimming to the size of the defect, superior mechanical strength as compared to available autograft, and reliable fusion with the host bone with partial bone remodeling, preventing fatigue failure. We conclude that freeze-dried, irradiated cortical allografts are safe and effective for anterior reconstruction of the spine.

The use of plate fixation in anterior surgery of the degenerative cervical spine: a comparative prospective clinical study

The method of anterior mono- or bisegmental cervical spine fusion is a well-established procedure for degenerative conditions of the cervical spine. While the early reports promote fusion with bone graft alone, recent studies report superior results with the addition of anterior plating. The objective of this study was to evaluate the influence of using plates in anterior cervical spine fusion in a prospective study. Fifty candidates for anterior monoor bisegmental cervical spine fusion were randomly and prospectively selected and assigned to a plated and a non-plated group. After a minimum follow-up of 22 months, patients were clinically and radiologically examined. The reduction in pain, improvement in neurology and functional assessment showed a significant improvement in both groups compared to the preoperative values. The total neurological score improved significantly in both groups, but the changes were greater in the group with plates. There was no significant difference between the groups for fusion rating, but graft quality (graft height) was significantly better in the plated group. We conclude that the overall data do not suggest better results with plating in mono- or bisegmental anterior spine fusions. Indications for additional internal fixation are restricted to special conditions with increased instability, insufficient bone quality or inappropriate graft placing.

Porous tricalcium phosphate and transforming growth factor used for anterior spine surgery

Harvesting autologous bone graft from the iliac crest is associated with considerable secondary morbidity. Bone graft substitutes such as porous ceramics are increasingly used for spinal surgery. This paper presents the results of an animal study in which beta-tricalcium phosphate (beta-TCP) bone substitutes were used for anterior spinal surgery in sheep and baboons. The presented baboon study also investigated the effect of impregnating the ceramic material with transforming growth factor (TGF). In the first study, using the sheep model, a stand-alone instrumented anterior fusion was performed. The animals were randomized into three treatment groups: autologous bone, beta-TCP granules, and sham group. The results were analyzed biomechanically and histologically at three survival intervals: 8, 16 and 32 weeks. An additional animal group was added later, with ceramic pre-filled implants. In the second study, a baboon model was used to assess the osteointegration of a 15-mm-diameter porous beta-TCP block into the vertebral body. The experiment was partially motivated by a new surgical procedure proposed for local bone graft harvest. Three treatment groups were used: beta-TCP plug, beta-TCP plug impregnated with TGF-beta3, and a sham group with empty defect. The evaluation for all animals included computer tomograms at 3 and 6 months, as well as histology at 6 months. In the sheep model, the mechanical evaluation failed to demonstrate differences between treatment groups. This was because massive anterior bone bridges formed in almost all the animals, masking the effects of individual treatments. Histologically, beta-TCP was shown to be a good osteoconductor. While multiple signs of implant micromotion were documented, pre-filling the cages markedly improved the histological fusion outcomes. In the baboon study, the beta-TCP plugs were completely osteointegrated at 6 months. For the group that used ceramic plugs impregnated with TGF-beta3, no incremental advantage was seen as a result of this particular application. However, TGF-beta3 is a potent growth factor at a very low dose. Not only does it speed up the ceramic material resorption, but it is also responsible for massive regional new bone formation. More experiments are required to better understand the biological effects of this growth factor in relation to bone formation, and to be able to take clinical advantage of them.

Posterior compact Cotrel-Dubousset instrumentation for occipitocervical, cervical and cervicothoracic fusion

The authors report on 32 consecutive patients with instability at the craniocervical, cervical and cervicothoracic regions suffering from various pathologies, who were treated with posterior instrumentation and fusion using the posterior hooks-rods-plate cervical compact Cotrel-Dubousset (CCD) instrumentation alone or, in three patients, in combination with anterior operation. The patients were observed postoperatively for an average of 31 months (range 25-44 months) and evaluated both clinically and radiographically using the following parameters: spine anatomy and reconstruction, sagittal profile, neurologic status, functional level, complications and status of arthrodesis. All patients but one (who died) achieved a solid arthrodesis based on plain and flexion/extension roentgenograms. Cervical lordosis (skull-C7) and cervicothoracic kyphosis (C7-T2) was improved by instrumentation towards a physiological lateral curve by an average of 33% (P<0.05) and 28% (P<0.05) respectively. Anterior vertebral olisthesis was reduced in the craniocervical and cervicothoracic region, by 73% and 90% respectively. At final follow-up there was an improvement of the neurologic Frankel status by an average of 1.2 grades and of myelopathy in 75% of the operated patients. Good to excellent functional results were seen in 77% of the operated patients, while acute and chronic pain was reduced by an average of 2.4 grades, on a scale of 0-3, in operated patients. No neurovascular or pulmonary complications arose from surgery. There was no significant change in lateral spine profile and olisthesis at the latest follow-up evaluation. There were no instrument-related failures. One patient requested hardware removal in the hope of reducing postoperative pain in the cervicothoracic region. The poor and fair results were related to the lack of improvement of neurologic impairment and myelopathy. The results of this study demonstrate that cervical CCD instrumentation applied in the region of the skull to the upper thoracic region for various disorders is a simple and safe instrumentation that restores lateral spine alignment, improves the potential for a solid fusion and offers sufficient functional results in the vast majority of the operated patients. However, the use of hooks in spinal stenosis is contraindicated.

Stiffness and neuromuscular reflex response of the human spine to posteroanterior manipulative thrusts in patients with low back pain

BACKGROUND

Studies investigating posteroanterior (PA) forces in spinal stiffness assessment have shown relationships to spinal level, body type, and lumbar extensor muscle activity. Such measures may be important determinants in discriminating between patients who are asymptomatic and those who have low back pain. However, little objective evidence is available concerning variations in PA stiffness and their clinical significance. Moreover, although several studies have assessed only load input in relation to stiffness, a more complete assessment based on dynamic stiffness measurements (force/velocity) and concomitant neuromuscular response may offer more information concerning mechanical properties of the low back.

OBJECTIVE

To determine the stiffness and neuromuscular characteristics of the symptomatic low back.

STUDY DESIGN

This study is a prospective clinical study investigating the in vivo mechanical and muscular behavior of human lumbar spinal segments to high loading rate PA manipulative thrusts in research subjects with low back pain (LBP).

METHODS

Twelve men and 10 women, aged 15 to 73 years (mean age of 42.8 +/- 17.5 years) underwent physical examination and completed outcome assessment instruments, including Visual Analog Scale, Oswestry Low Back Disability Index, and SF-36 health status questionnaires. Clinical categorization was made on the basis of symptom frequency and LBP history. A hand-held spinal manipulation device, equipped with a preload control frame and impedance head, was used to deliver high-rate (<0.1 millisecond) PA manipulative thrusts (190 N) to several common spinal landmarks, including the ilium, sacral base, and L5, L4, L2, T12, and T8 spinous and transverse processes. Surface, linear-enveloped, electromyographic (sEMG) recordings were obtained from electrodes (8 leads) located over the L3 and L5 paraspinal musculature to monitor the bilateral neuromuscular activity of the erector spinae group during the PA thrusts. Maximal-effort isometric trunk extensions were performed by the research subjects before and immediately after the testing protocol to normalize sEMG data. The accelerance or stiffness index (peak acceleration/peak force, kg-1) and composite sEMG neuromuscular reflex response were calculated for each of the thrusts.

RESULTS

Posteroanterior stiffness obtained at the sacroiliac joints, transverse processes, or spinous processes was not different for subjects grouped according to LBP chronicity. However, in those with frequent or constant LBP symptoms, there was a significantly increased spinous process (SP) stiffness index (7.0 kg-1) (P <.05) in comparison with SP stiffness index (6.5 kg-1) of subjects with only occasional or no LBP symptoms. Subjects with frequent or constant LBP symptoms also reported significantly greater scores on the visual analog scale (P =.001), Oswestry (P =.001), and perceived health status (P =.03) assessments. The average SP stiffness index was 6.6% greater (P <.05) and 19.1% greater (P <.001) than the average sacroiliac stiffness index and average transverse process stiffness index, respectively.

CONCLUSIONS

This study is the first to assess erector spinae neuromuscular reflex responses simultaneously during spinal stiffness examination. This study demonstrated increased spinal stiffness index and positive neuromuscular reflex responses in subjects with frequent or constant LBP as compared with those reporting intermittent or no LBP.

Surface EMG activity of the back musculature during axial spinal unloading using an LTX 3000 Lumbar Rehabilitation System

Electromyographic (EMG) analysis has been used successfully to identify back muscle impairment in patients with low back pain. EMG signals from normal subjects during axial spinal unloading using an LTX 3000 device were obtained and spectral parameters of the electromyographic (EMG) signal were analyzed. The purpose of the study was to determine the optimal time for effective traction using the LTX 3000 rehabilitation device. These data will serve as a baseline for future studies to help assess back muscle function in low back patients undergoing rehabilitation. Three time points during axial spinal unloading were compared to pre-unloading to detect alterations in median power frequency (MPF), root-mean-square (RMS) and rectified integrated EMG (riEMG) during axial spinal unloading. There were reductions of riRMG during 0-10 minutes of axial spinal unloading in all muscle groups, followed by an increase in riEMG value from 10 to 15 minutes. A similar trend was seen in the RMS values. The MPF did not change during the course of unloading, indicating that there was likely no change in fatigue properties of the paraspinal muscles during axial spinal unloading. The optimal time for effective axial spinal unloading on the basis of muscle activity was determined to be 10 minutes of axial spinal unloading, and a back assessment procedure was presented that uses surface EMG electrodes to objectively characterize muscle activity and relative fatigue properties. Future studies will use this methodology to assess treatment outcome in a chronic low back pain population.

Posterior-only unit rod instrumentation and fusion for neuromuscular scoliosis

STUDY DESIGN

A retrospective study to determine the efficacy of posterior-only unit rod instrumentation and fusion in a skeletally immature neuromuscular scoliosis population.

OBJECTIVE

To determine whether the posterior-only approach to this population adequately addresses the concerns of correction of scoliosis and pelvic obliquity, maintenance of that correction over time, and the incidence of crankshaft phenomenon.

SUMMARY OF BACKGROUND DATA

Controversy exists regarding the need for anterior release to improve curve flexibility and the need to obtain an anterior arthrodesis in those skeletally immature patients at risk for crankshafting with continued anterior growth.

METHODS

From 1992 through 1997, 28 consecutive skeletally immature patients with neuromuscular scoliosis underwent posterior-only unit rod instrumentation and fusion for the treatment of progressive, symptomatic spinal deformities. Preoperative, immediate postoperative, and final follow-up radiographs were analyzed with respect to scoliosis and pelvic obliquity correction, maintenance of that correction over time, and the development of the crankshaft phenomenon as evidenced by loss of correction and/or increased rib-vertebral angle difference. The average age of the patients was 12.8 years and the average follow-up was 58 months with a minimum of 2 years.

RESULTS

Twenty-six patients were available for final follow-up. The initial Cobb angle correction averaged 66%, with 75% of the pelvic obliquity corrected. These corrections were maintained over time. Before surgery 27 of 28 patients were Risser 0, 1, or 2. The triradiate cartilage was open in nine patients, and five patients were < or =10 years of age. At the final follow-up 22 of the 26 patients were Risser 5 and 4 were Risser 4. There was one patient with increased rib-vertebral angle difference over the length of follow-up, with no loss of frontal or sagittal plane alignment.

CONCLUSIONS

These results indicate that even in the very young neuromuscular patient, acceptable amounts of curve correction can be achieved and maintained with posterior-only unit rod instrumentation and fusion. The biomechanical stiffness of this construct seemed to be able to prevent the crankshaft phenomenon in the majority of those patients at risk.