Biomechanical Evaluation of a Dynamic Stabilization System for the Prevention of Proximal Junctional Failure in Adult Deformity Surgery.

STUDY DESIGN: Biomechanical spine model. Comparison of stress in the implant and the adjacent cranial segment was done with conventional rigid versus dynamic stabilization system (DS) fixation. OBJECTIVE: The aim of this study was to study stress at the proximal end of spinal fixation with a novel DS. SUMMARY OF BACKGROUND DATA: High stress at the implant bone junction may cause proximal junctional failure (PJF) in adult deformity surgery. METHODS: Five life-size spine models were instrumented with pedicle screws and a 5.5-mm Titanium rod from T8-S1. The same models were subsequently instrumented with a similar rod and DS between T8-9 pedicle screws. The spine model was loaded with 25 Nm static load cranial to the proximal fixation in six directions. Strains were measured from the proximal screws. Disc pressure was measured from the proximal instrumented segment (T8-9) and cranial adjacent segment (T7-8). RESULTS: Rigid fixation produced highest strain at T8, followed by T10 then T9. In contrast, DS fixation produced highest strain at T10, followed by T9 then T8. Strain at T8 was significantly less with DS fixation than rigid fixation (P = 0.019). The T10 screw strain was not significantly higher with DS stabilization compared to rigid fixation (P = 0.091). Rigid fixation allowed no load-sharing or pressure rise at T8-9 but an abrupt rise at T7-8. DS system permitted load-sharing and pressure rise in T8-9; the difference compared to rigid fixation was significant in flexion loading (P = 0.04) and similar trend but not significant in extension (P = 0.09). DS system produced a rise in the adjacent segment disc pressure (T7-8), which was smaller than rigid fixation but not significant. CONCLUSION: Long spinal fixation using rigid rods produces maximum stress at the proximal end screw and increases adjacent disc pressure, possibly leading to PJF. Dynamic stabilization at the cranial end segment may prevent PJF by reducing these factors.Level of Evidence: N/A.

Clinical Incidence of PJK/ASD in Adult Deformity Surgery: A Comparison of Rigid Fixation and Semirigid Fixation-Semirigid.

In the debate regarding whether rigid or semirigid fixation is better for proximal junctional kyphosis (PJK)/adult spinal deformity (ASD) correction, this presentation posits that semirigid fixation is the better approach. For ASD correction, might is not right, and a rigid approach does not solve the problems associated with PJK.

The basis of mechanical instability in degenerative disc disease: a cadaveric study of abnormal motion versus load distribution.

STUDY DESIGN: A biomechanical study in cadaveric lumbar spine. OBJECTIVE: To establish the basis of mechanical stability in degenerative disc disease from the relationship between range of motion (ROM), neutral zone motion (NZ), intradiscal pressure profile, and instantaneous axis or rotation (IAR) in advancing grades of disc degeneration. SUMMARY OF BACKGROUND DATA: The basis of mechanical instability in lumbar disc degeneration remains poorly understood. Controversy exists between abnormal motion and abnormal loading theories. METHODS: Thirty-nine lumbar motion segments were graded for staging of disc degeneration with magnetic resonance scan. These specimens were tested for ROM and NZ in a 6 df spine simulator, with 7.5 N·m unconstrained, cyclical loading. Continuous tracking of IAR was derived from ROM data. Intradiscal pressure profiles were determined using needle-mounted pressure transducer, drawn across the disc space under constant loading. RESULTS: The ROM showed insignificant change, but a trend of increase from grade I through III and a decrease with advanced degeneration. NZ increased significantly with advancing disc degeneration. Intradiscal pressure profile showed an even distribution of the load in normal discs but a depressurized nucleus and irregular spikes of excessive loading, with advancing degeneration. The IAR showed a smooth excursion in normal versus irregular jerky excursion in degenerated discs, without significant change in excursion. The center of rotation, derived from IAR, showed significantly increased vertical translation with advancing degeneration, indicating an abnormal quality of motion. CONCLUSION: The study established a basis of mechanical instability in the lumbar spine with advancing disc degeneration as an abnormal quality of motion represented by variation in IAR and center of rotation, increased NZ motion without any increase in quantity of motion, and abnormal load distribution across the disc space with spikes of high load amidst depressurized nucleus. The study cannot identify clinical instability but finds an association between the abnormal motions and the abnormal load distribution in mechanical instability. LEVEL OF EVIDENCE: N/A.

How fast pain, numbness, and paresthesia resolves after lumbar nerve root decompression: a retrospective study of patient's self-reported computerized pain drawing.

STUDY DESIGN: A single-center retrospective study. OBJECTIVE: To compare the speed of recovery of different sensory symptoms, pain, numbness, and paresthesia, after lumbar nerve root decompression. SUMMARY OF BACKGROUND DATA: Lumbar radiculopathy is characterized by different sensory symptoms like pain, numbness, and paresthesia, which may resolve at different rates after surgical decompression. METHODS: Eighty-five cases with predominant lumbar radiculopathy treated surgically were reviewed. Oswestry Disability Index score, 36-Item Short Form Health Survey scores (Physical Component Summary and Mental Component Summary), and pain drawing at preoperative and at 6 weeks, 3 months, 6 months, and 1-year follow-up were reviewed. Recovery rate between different sensory symptoms were compared in all patients, and between the short-term compression (<6 mo) and long-term compression groups. RESULTS: At baseline, 73 (85.8%) patients had pain, 63 (74.1%) had numbness, and 38 (44.7%) had paresthesia; 28 (32.9%) had all these 3 component of sensory symptoms. Mean pain score improved fastest (55.3% at 6 wk); further resolution until 1 year was slow and not significant compared with each previous visit. Both numbness and paresthesia scores showed a trend of faster recovery during the initial 6-week period (20.5% and 24%, respectively); paresthesia recovery reached a plateau at 3 months postoperatively, but numbness continued a slow recovery until 1-year follow-up. Both Oswestry Disability Index score and Physical Component Summary scores (54.02 ± 1.87 and 26.29 ± 0.93, respectively, at baseline) improved significantly compared with each previous visits at 6 weeks and 3 months postoperatively, but further improvement was insignificant. Mental Component Summary showed a similar trend but smaller improvement. The short-term compression group had faster recovery of pain than the long-term compression group. CONCLUSION: In lumbar radiculopathy patients after surgical decompression, pain recovers fastest, in the first 6 weeks postoperatively, followed by paresthesia recovery that plateaus at 3 months postoperatively. Numbness recovers at a slower pace but continues until 1 year. LEVEL OF EVIDENCE: 4.

Pedicle screw-based posterior dynamic stabilization: literature review.

Posterior dynamic stabilization (PDS) indicates motion preservation devices that are aimed for surgical treatment of activity related mechanical low back pain. A large number of such devices have been introduced during the last 2 decades, without biomechanical design rationale, or clinical evidence of efficacy to address back pain. Implant failure is the commonest complication, which has resulted in withdrawal of some of the PDS devices from the market. In this paper the authors presented the current understanding of clinical instability of lumbar motions segment, proposed a classification, and described the clinical experience of the pedicle screw-based posterior dynamic stabilization devices.

New treatments and imaging strategies in degenerative disease of the intervertebral disks.

Magnetic resonance (MR) imaging in patients with persistent low back pain and sciatica effectively demonstrates spine anatomy and the relationship of nerve roots and intervertebral disks. Except in cases with nerve root compression, disk extrusion, or central stenosis, conventional anatomic MR images do not help distinguish effectively between painful and nonpainful degenerating disks. Hypoxia, inflammation, innervation, accelerated catabolism, and reduced water and glycosaminoglycan content characterize degenerated disks, the extent of which may distinguish nonpainful from painful ones. Applied to the spine, "functional" imaging techniques such as MR spectroscopy, T1ρ calculation, T2 relaxation time measurement, diffusion quantitative imaging, and radio nucleotide imaging provide measurements of some of these degenerative features. Novel minimally invasive therapies, with injected growth factors or genetic materials, target these processes in the disk and effectively reverse degeneration in controlled laboratory conditions. Functional imaging has applications in clinical trials to evaluate the efficacy of these therapies and eventually to select patients for treatment. This report summarizes the biochemical processes in disk degeneration, the application of advanced disk imaging techniques, and the novel biologic therapies that presently have the most clinical promise.

Precision of lumbar intervertebral measurements: does a computer-assisted technique improve reliability?

STUDY DESIGN: Comparison of intra- and interobserver reliability of digitized manual and computer-assisted intervertebral motion measurements and classification of "instability." OBJECTIVE: To determine if computer-assisted measurement of lumbar intervertebral motion on flexion-extension radiographs improves reliability compared with digitized manual measurements. SUMMARY OF BACKGROUND DATA: Many studies have questioned the reliability of manual intervertebral measurements, although few have compared the reliability of computer-assisted and manual measurements on lumbar flexion-extension radiographs. METHODS: Intervertebral rotation, anterior-posterior (AP) translation, and change in anterior and posterior disc height were measured with a digitized manual technique by three physicians and by three other observers using computer-assisted quantitative motion analysis (QMA) software. Each observer measured 30 sets of digital flexion-extension radiographs (L1-S1) twice. Shrout-Fleiss intraclass correlation coefficients for intra- and interobserver reliabilities were computed. The stability of each level was also classified (instability defined as >4 mm AP translation or 10° rotation), and the intra- and interobserver reliabilities of the two methods were compared using adjusted percent agreement (APA). RESULTS: Intraobserver reliability intraclass correlation coefficients were substantially higher for the QMA technique THAN the digitized manual technique across all measurements: rotation 0.997 versus 0.870, AP translation 0.959 versus 0.557, change in anterior disc height 0.962 versus 0.770, and change in posterior disc height 0.951 versus 0.283. The same pattern was observed for interobserver reliability (rotation 0.962 vs. 0.693, AP translation 0.862 vs. 0.151, change in anterior disc height 0.862 vs. 0.373, and change in posterior disc height 0.730 vs. 0.300). The QMA technique was also more reliable for the classification of "instability." Intraobserver APAs ranged from 87 to 97% for QMA versus 60% to 73% for digitized manual measurements, while interobserver APAs ranged from 91% to 96% for QMA versus 57% to 63% for digitized manual measurements. CONCLUSION: The use of QMA software substantially improved the reliability of lumbar intervertebral measurements and the classification of instability based on flexion-extension radiographs.

Instant axis of rotation of L4-5 motion segment--a biomechanical study on cadaver lumbar spine.

The instant axis of rotation (IAR) is an important kinematic property to characterise of lumbar spine motion. The goal of this biomechanical study on cadaver lumbar spine was to determine the excursion of the IAR for flexion (FE), lateral bending (LB) and axial rotation (AR) motion at L4-5 segment. Ten cadaver lumbar spine specimens were tested in a 6 degrees-of-freedom spine tester with continuous clyclical loading using pure moment and follower pre-load, to produce physiological motion. The specimens were x-rayed and CT scanned prior to testing to identify marker position. Continuous motion tracking was done by Optotrak motion capture device. A continuous tracking of the IAR excursion was calculated from the continuous motions capturedata using a computer programme. IAR translates forward in flexion and backwards in extension with mean excursion of 26.5 mm (+/- 5.6 SD). During LB motion, IAR translates laterally in the same direction, and the mean excursion was 15.35 mm (+/- 8.75 SD). During axial rotation the IAR translates in the horizontal plane in a semicircular arc, around the centre of the vertebral body, but the IAR translates in the opposite direction of rotation. The IAR excursion was faster and larger during neutral zone motion in FE and LB, but uniform for AR motion. This is the first published data on the continuous excursion of IAR of a lumbar motion segment. The methodology is accurate and precise, but not practicable for in vivo testing.

Intraoperative ketamine reduces perioperative opiate consumption in opiate-dependent patients with chronic back pain undergoing back surgery.

BACKGROUND: Ketamine is an N-methyl-d-aspartate receptor antagonist that has been shown to be useful in the reduction of acute postoperative pain and analgesic consumption in a variety of surgical interventions with variable routes of administration. Little is known regarding its efficacy in opiate-dependent patients with a history of chronic pain. We hypothesized that ketamine would reduce postoperative opiate consumption in this patient population. METHODS: This was a randomized, prospective, double-blinded, and placebo-controlled trial involving opiate-dependent patients undergoing major lumbar spine surgery. Fifty-two patients in the treatment group were administered 0.5 mg/kg intravenous ketamine on induction of anesthesia, and a continuous infusion at 10 microg kg(-1) min(-1) was begun on induction and terminated at wound closure. Fifty patients in the placebo group received saline of equivalent volume. Patients were observed for 48 h postoperatively and followed up at 6 weeks. The primary outcome was 48-h morphine consumption. RESULTS: Total morphine consumption (morphine equivalents) was significantly reduced in the treatment group 48 h after the procedure. It was also reduced at 24 h and at 6 weeks. The average reported pain intensity was significantly reduced in the postanesthesia care unit and at 6 weeks. The groups had no differences in known ketamine- or opiate-related side effects. CONCLUSIONS: Intraoperative ketamine reduces opiate consumption in the 48-h postoperative period in opiate-dependent patients with chronic pain. Ketamine may also reduce opioid consumption and pain intensity throughout the postoperative period in this patient population. This benefit is without an increase in side effects.

Biomechanical evaluation of the kinematics of the cadaver lumbar spine following disc replacement with the ProDisc-L prosthesis.

STUDY DESIGN: Biomechanical study of the ProDisc-L in a cadaveric model under pure moment loading. OBJECTIVE.: To determine the kinematic properties of a lumbar spine motion segment and the adjacent level following ProDisc-L disc replacement in the cadaveric spine. SUMMARY OF BACKGROUND DATA: Total disc replacement is intended to preserve native motion, in an attempt to prevent accelerated adjacent segment degeneration. The quality and quantity of the motion following TDR may have important consequences on the facet joints of the same motion segment, as well as the motion at the prosthetic component interface. METHODS: Ten cadaveric lumbar spines were radiographed (L3-L5) and tested under pure moments (+10 Nm to -10 Nm) with an applied follower load (200 N). Load-deformation was tested in flexion/extension, lateral bending (LB), and axial rotation (AR). Range of Motion (ROM) data were recorded. Superior adjacent disc pressure (L3-L4) was measured using subminiature pressure transducers. The L4-L5 disc was subsequently instrumented with a ProDisc-L. Radiographs and biomechanical tests were repeated. RESULTS: Disc replacement significantly reduced extension (ROM 2.2 degrees +/- 0.5 degrees before and 1.2 degrees +/- 0.7 degrees after instrumentation) (P = 0.001), but not flexion (ROM 5.6 degrees +/- 3.1 degrees before and 6.2 degrees +/- 1.2 degrees after) (P = 0.34). Combined flexion/extension motion was marginally reduced (P = 0.517). LB ROM (7.4 degrees +/- 2.0 degrees ) was marginally reduced (P = 0.072) following instrumentation (6.2 degrees +/- 2.5 degrees ), while ROM in AR (3.4 degrees +/- 1.1 degrees ) was significantly increased (4.4 degrees +/- 1.2 degrees ) (P = 0.001). Superior adjacent segment ROM was preserved.No significant differences in disc pressure were observed at the adjacent motion segment before (199 kPa at maximum flexion and 171 kPa at maximum extension) or after disc replacement (252 kPa and 208 kPa, respectively). CONCLUSION: In cadaveric spines, ROM of operated and adjacent motion segments was preserved following ProDisc-L insertion. Excision of the anterior anulus may increase laxity, which is taken up by the restoration of disc height and lordosis, at the cost of a moderate loss of flexion/extension motion. Adjacent segment kinematics were unaffected following TDR.

Development of a 4-axis load cell used for lumbar interbody load measurements.

Numerous studies have assessed lumbar interbody fusion, but little data from direct interbody load measurements exists. This manuscript describes an interbody fusion cage with integrated 4-axis load cell that can simulate implant heights of 13, 15, 17, 19 and 21 mm. The calibrated load cell was accurate to within 7.9% for point compressive loads over the central 8 mm x 8 mm region, but up to 26.8% for eccentric loads on the outer 16 mm x 16 mm rim of the device (although typically errors were less than half). Anterior-posterior shear and lateral shear loads did not affect compressive load measurement (<1.0% and <3.5%, respectively). Moments calculated from 4 load sensing corner pillars demonstrated errors below 2.3% in lateral bending and 2.1% in flexion-extension. Although this device does not have the accuracy of other much larger corpectomy implants, it incorporates four channels of load and simulates multiple implant heights, making for a favorable comparison in this restricted space. This device has immediate use in cadaveric testing, providing data previously not attainable, and serves as a novel technological step towards an implantable interbody device with multi-axis load sensing capability. As per the authors' knowledge, no such device has previously been described.

Cervical spine trauma.

Cervical spine trauma is a common problem with a wide range of severity from minor ligamentous injury to frank osteo-ligamentous instability with spinal cord injury. The emergent evaluation of patients at risk relies on standardized clinical and radiographic protocols to identify injuries; elucidate associated pathology; classify injuries; and predict instability, treatment and outcomes. The unique anatomy of each region of the cervical spine demands a review of each segment individually. This article examines both upper cervical spine injuries, as well as subaxial spine trauma. The purpose of this article is to provide a review of the broad topic of cervical spine trauma with reference to the classic literature, as well as to summarize all recently available literature on each topic. IDENTIFICATION OF REFERENCES FOR INCLUSION: A Pubmed and Ovid search was performed for each topic in the review to identify recently published articles relevant to the review. In addition prior reviews and classic references were evaluated individually for inclusion of classic papers, classifications and previously unidentified references.

Outcome of local bone versus autogenous iliac crest bone graft in the instrumented posterolateral fusion of the lumbar spine.

STUDY DESIGN: Retrospective, comparative study of clinical and radiologic outcome with independent, blinded observer. OBJECTIVES: To compare the clinical and radiologic outcome of instrumented posterolateral lumbar fusion using local bone versus autogenous iliac crest bone graft (ICBG). SUMMARY OF BACKGROUND DATA: There is no published report of outcome of posterolateral spinal fusion using local bone alone for degenerative disorders of the lumbar spine. MATERIALS AND METHODS: Seventy-six cases (male 26, female 50) of spinal stenosis, operated during 1996 and 1997 by the senior author, were reviewed. All the cases had decompression and posterior spinal fusion with pedicle screw instrumentation. Forty cases had only local bone graft obtained from decompression, morselized in a bone mill, and 36 cases had autogenous ICBG. Mean age was 60 years (range, 27-83 years). Fusion was performed at one level in 51 (67%), two levels in 16 (21%), three levels in 5 (7%), and four or more levels in 4 cases (5%). Minimum follow-up was 2-years (mean, 28 years; range, 24-72 months). An independent, blinded radiologist rated plain radiographs as fused, indeterminate, or nonunion. RESULTS: There was no difference in age, sex, and diagnosis between the two groups. Overall fusion rate was higher in the ICBG group (75%, 27 of 36) compared with the local bone group (65%, 26 of 40) but not significantly different (P = 0.391). Analyzed separately according to the number of fusion levels, the local bone group achieved similar fusion rate ( approximately 80%) in single-level fusion but a much smaller fusion rate in multilevel fusion (20% vs. 66%, P = 0.029) compared with the ICBG group. Mean improvement in the Oswestry Disability Inventory was 36% in the local bone group and 32% in the ICBG group. There was no significant difference in overall clinical outcome between the two groups. There was no correlation between fusion status and clinical outcome. Blood loss and hospital stay were significantly less in the local bone group; however, blood losswas more significantly related to the sum total number of segments undergoing decompression and fusion. CONCLUSIONS: Use of local bone graft alone achieved a similar fusion rate in single-level fusion but a much smaller fusion rate in multilevel fusion compared with the ICBG group. Local bone graft alone achieved a similar clinical outcome but less morbidity irrespective of number of fusion level.

Fulcrum assisted soft stabilization system: a new concept in the surgical treatment of degenerative low back pain.

STUDY DESIGN: An experimental study on cadaver spine and spine model for biomechanical evaluation of a novel dynamic stabilization device. OBJECTIVES: First, to test the hypothesis that in dynamic stabilization of a lumbar spine using pedicle screws and ligament, addition of a fulcrum in front of the ligament can unload the disc. Second, to determine the relationship between the length and stiffness of the fulcrum and the ligament on disc unloading, lordosis and motion preservation. SUMMARY OF BACKGROUND DATA: Activity related low back pain may be attributable to abnormal disc loading or abnormal movement. Spinal fusion addresses both the mechanisms, but it has limitations. Soft stabilization with Graf ligament restricts abnormal movement but increases the disc pressure. The Dynesys system uses a plastic cylinder around the ligament to prevent overloading the disc, but it restricts extension and loses lordosis. METHODS: A novel dynamic stabilization system (fulcrum assisted soft stabilization or FASS) was developed in which a flexible fulcrum was placed in front of a ligament between the pedicle screws. It was hypothesized that the fulcrum should transform the compressive force of a ligament behind into a distraction force in front and unload the disc. Three spine models were developed using wooden blocks for vertebral bodies and neoprene rubber of different hardness for disc. Their load-deformation character was tested and compared with that of the cadaver spine in a spine tester. The spine model with the closest load-deformation property to cadaver spine was then tested for the effect of a FASS system, consisting of high density polythene rod as fulcrums and rubber "O" rings as ligaments. The disc pressure in the spine models were recorded with strain gauge in the center. RESULTS: Application of ligaments alone across the pedicle screws increased the disc pressure, produced a lordosis, and reduced the range of motion. Application of fulcrums reduced the disc pressure and maintained the lordosis. Increasing the fulcrum length resulted in progressive unloading of the disc but increased stiffness of the motion segment. As the fulcrum length approximated the height of the motion segment, the lordosis was lost, and the disc was completely unloaded. Decreasing the lateral bending stiffness of the fulcrum had minimal effect on disc unloading and motion-segment stiffness. CONCLUSION: The novel FASS system can unload the disc, control the range of motion, and maintain lordosis. These parameters may be controlled with a suitable combination of ligament and fulcrum system. The study provides an indication toward the desirable biomechanical properties of the fulcrum and ligament for future development of a clinically applicable prototype.

Degenerative spondylolisthesis: review of current trends and controversies.

STUDY DESIGN: A literature-based review. OBJECTIVES: To review management and controversies and to present authors recommendations. SUMMARY OF BACKGROUND DATA: There is considerable controversy regarding indication for surgery, role for decompression alone, and decompression with fusion with or without instrumentation. METHODS: Review of English language medical literature. RESULTS: The condition may stabilize itself with the collapse of the disc spaces and osteophytes but may continue to progress in nearly a third of the cases. It may cause predominantly back pain due to segmental instability, or radicular pain/neurogenic claudication secondary to root entrapment or spinal stenosis. When conservative treatment fails, the mainstay of surgical treatment is decompressive laminectomy and fusion, with or without instrumentation. CONCLUSIONS: Decompression primarily relieves radicular symptoms and neurogenic claudication whereas fusion primarily relieves back pain by elimination of instability. The goals for instrumentation are to promote fusion and to correct deformity. Fusion has a better long-term outcome than decompression alone. There is evidence that instrumentation improves fusion rate but does not improve clinical outcome in a relatively short-term follow-up. However, outcome of pseudarthrosis cases deteriorates over time and solid fusion produces better long-term outcome. The benefit of instrumentation comes with a price of higher postoperative morbidity and complication rate. Bone morphogenetic proteins are being tried to increase the rate of fusion, without increasing the complication rate, but the cost is prohibitive. More recently, dynamic stabilization with instrumentation but without fusion has been introduced as an alternative treatment. The current trends of surgical treatment and controversies are discussed.

Neglected spinal injuries.

Neglected spinal injuries secondary to overlooked diagnosis may result in serious medical and medicolegal problems. These are not uncommon but are reported infrequently in the medical literature. I studied the incidence, causes, and consequences of neglected spinal injuries and recommendations for prevention and treatment by reviewing the literature found in a Medline search. Overlooked spinal injuries are most frequently seen in unconscious or intoxicated patients and in polytrauma patients with distracting remote injuries. These are 4.5 times more frequent in the cervical spine compared with the thoracolumbar spine. The most common cause is failure to obtain radiographs. Other causes include a failure to recognize the injury or the fact that the initial studies may fail to show the injuries. Use of computed tomography and magnetic resonance imaging scans as screening tests may be good ways to diagnose these injuries, but their use is limited by cost and availability. The most serious consequence of overlooked spinal injuries is progressive neural deficit. More frequently they result in progressive deformity and persistent pain requiring surgical intervention that most likely could have been avoidable, often with an unsatisfactory outcome. Untreated or inadequately treated spinal injuries with late presentation are more often seen in the developing world. Unfortunately, reports on these cases are published rarely. Their brief report in the current study is based on search of nonindexed medical journals using in Internet search engine and personal communications.