Extension Stiffness Research Articles

The Effect of Spinal Shortening After Total En Bloc Spondylectomy

A biomechanical study using human cadaveric thoracic spine specimens. To evaluate and compare the biomechanical effects of spinal shortening and cross-links in reconstruction after total en bloc spondylectomy (TES). There have been no studies that have examined the biomechanical effects of spinal reconstruction after multilevel TES or the biomechanical effects of spinal shortening in reconstruction after TES. Eight human cadaveric spines (T2-T9) were used. After the intact specimen had been biomechanically tested to determine the stiffness in compression, flexion, extension, left and right lateral bending, and left and right axial rotation, a TES at T5-6 was carried out. Three reconstruction methods were tested biomechanically (same as for the intact specimen) for their ability to restore stiffness to the specimen: (1) anterior short cage and multilevel posterior instrumentation at T3-8 with 2 cross-links (S2C), (2) anterior short cage and multilevel posterior instrumentation at T3-8 with 1 cross-link (S1C), and (3) anterior long cage and multilevel posterior instrumentation at T3-8 with 2 cross-links (L2C). A cage that was 6-10 mm shorter in height than the space created by the TES at T5-6 was selected as the "short cage" and a cage 10 mm taller in height than the short cage was selected as the "long cage" in each specimen. All 3 reconstruction methods using an anterior cage and multilevel posterior instrumentation provides a stiffer construct than that shown by the intact specimen. The reconstruction method using the 10-mm shorter cage (S2C vs. L2C) provided more stiffness than the one using the longer cage. The reconstruction using 2 cross-links (S2C vs. S1C) did not provide a stiffer construct than the one using 1 cross-link. The reconstructions using an anterior cage and multilevel posterior instrumentation provided a stiffer construct than that shown by the intact specimen. The reconstruction using a 10-mm shorter cage provided a stiffer construct than the reconstruction using the longer cage.

Hybrid III anthropomorphic test device (ATD) response to head impacts and potential implications for athletic headgear testing

The Hybrid III 50th percentile male anthropomorphic test device (ATD) is the most widely used human impact testing surrogate and has historically been used in automotive or military testing. More recently, this ATD is finding use in applications evaluating athletic helmet protectivity, quantifying head impact dosage and estimating injury risk. But ATD head–neck response has not been quantified in omnidirectional athletic-type head impacts absent axial preload. It is probable that headgear injury reduction that can be quantified in a laboratory, including in American football, boxing, hockey, lacrosse and soccer, is related to a number of interrelated kinetic and kinematic factors, such as head center of gravity linear acceleration, head angular acceleration, head angular velocity, occipito-cervical mechanics and neck stiffness. Therefore, we characterized ATD head–neck dynamic response to direct head impacts in a series of front, oblique front and lateral head impacts.Key findings were: (1) impacts producing highest ATD resultant center of gravity linear acceleration resulted in the lowest resultant occipito-cervical spine bending moment/force. (2) Resultant ATD head angular velocity and angular acceleration did not appear coupled to impact direction at lower impact energy levels; these parameters were coupled at higher energy levels. (3) The ATD had progressively increasing occipito-cervical stiffness in extension, torsion and lateral bending, respectively. Because the ATD neck influenced head and neck impact dosage parameters, testing agencies, manufacturers and researchers should consider using the Hybrid III head form attached to a neck as a means to quantify head and neck injury risks as opposed to systems that do not utilize a neck. This heightened understanding of Hybrid III ATD head–neck response, and consideration of order of stiffest axes in the lateral, oblique and extension directions, respectively, should aid in the development of head and neck injury impact testing standards.

Quasi passive bounding of a quadruped model with articulated spine

The motion of spine in passive quadrupedal bounding and its effect on leg behavior were presented in this paper. First, a simplified sagittal plane model of quadruped mammals was introduced. The model's body contained one articulated spine joint. Next, a control method was developed to obtain symmetrical bounding of the model. In this method, the spine joint was locked when the spine reached its maximum bend. It was held until vertical velocity became opposite in value. These actions resulted in a specific type of bounding, which was defined as quasi passive bounding. Despite its simplicity, this system captures properties of real animals. Plenty of bounding conditions were considered in the analysis of system kinetics. Passive bounding of the model with stiff spine was also analyzed. A comparison of the maximum leg compression between the two models suggests the use of spine joint for legged systems at a high speed. Moreover, to obtain realistic motion of quadruped mammals, evolution of the spine joint angle shows that trunk stiffness in extension is greater than that in flexion.

Density, elastic and magnetic properties of Co–Fe–Ta–Si metallic glasses by theory and experiment

Ab initio molecular dynamics simulations were employed to study the density, elastic and magnetic properties of Co–Fe–Ta–Si metallic glass thin films . A density of 8.03 g cm −3 , a Young’s modulus of 187 GPa and a volume magnetization of 0.089 μ B Å −3 were calculated and validated by thin film experiments. The extensive stiffness of this glass may be related to the existence of strong (Fe,Co)–Si clusters as revealed by ab initio chemical short-range order data.

Apport de l’IRM cube 3D dans le diagnostic des ruptures partielles du LCA

In anterior cruciate ligament (ACL) reconstruction, success depends on several factors: patient selection; surgical technique, taking account of associated meniscal and ligamentous lesions; and postoperative rehabilitation. Improved hamstring-tendon graft preparation and fixation techniques now provide results in terms of laxity and retear comparable to patellar tendon graft, which has long been the gold-standard for patients with strong functional demand, despite its higher risk of extension stiffness and anterior pain. Apart from a few exceptional preferential indications, such as hamstring tendon in growing children and patients whose lifestyle or occupation involves frequent kneeling and patellar tendon in case of severe medial laxity associated with ACL tear, either graft may be used for ACL reconstruction. The keypoints in the procedure are good tunnel positioning and hence good mastery of the surgical technique, and treatment of all associated lesions, and especially of occult meniscal lesions and rotational laxity due to anterolateral ligament deficiency, which requires associated extra-articular plasty. Graft choice is secondary and not a key to success.

The surgical treatment of knee stiffness following anterior cruciate ligament reconstruction

Knee stiffness following anterior cruciate ligament (ACL) reconstruction remains a common complication, which can substantially impair knee function. The aim of this study was to assess the effectiveness of arthroscopic arthrolysis, in conjunction with manipulation under anaesthetic (MUA), in treating stiffness post-ACL reconstruction. We reviewed the records of 18 patients who underwent arthroscopic arthrolysis to treat established stiffness following primary isolated ACL reconstruction. Eight of these patients underwent concomitant MUA at time of arthrolysis. The median time between reconstruction and arthrolysis was nine months. Seven patients had arthrolysis performed within eight months of reconstruction, while 11 patients underwent arthrolysis greater than eight months postreconstruction. Following arthrolysis, the mean extension loss improved from 7° to 1°. In patients with mild extension stiffness (prearthrolysis extension deficits <10°), the mean improvement to extension was 3°. In patients with severe extension stiffness (prearthrolysis extension deficit ≥10°), the mean improvement to extension was 10°. Arthroscopic arthrolysis was significantly more effective in restoring extension loss if carried out within eight months of the primary reconstruction (P < 0.03). In the patients who underwent MUA at time of arthrolysis, the mean flexion loss improved from 16° to 4°. In conclusion, arthroscopic arthrolysis, in conjunction with MUA, is an effective treatment for knee stiffness post-ACL reconstruction but ideally should be carried out within eight months.

Influence of Interpersonal Geometrical Variation on Spinal Motion Segment Stiffness

A validated finite element model of an L3-L4 motion segment is used to analyze the effects of interpersonal differences in geometry on spinal stiffness. The objective of this study is to determine which of the interpersonal variations of the geometry of the spine have a large effect on spinal stiffness. This will improve patient-specific modeling. The parameters that define the geometry of a motion segment are vertebral height, disc height, endplate width, endplate depth, spinous process length, transverse process width, nucleus size, lordosis angle, facet area, facet orientation, and the cross-sectional areas of the ligaments. All these parameters differ between patients. The influence of each parameter on spinal stiffness is largely unknown and such knowledge would greatly help in patient-specific modeling of the spine. The range of interpersonal variation of each of the geometric parameters was set at mean±2SD (covering 95% of the population). Subsequently, we determined the effect of each of these ranges on the bending stiffness in flexion, extension, axial rotation, and lateral bending. Disc height had the largest influence; a maximal disc height reduced the spinal stiffness to 75-86% of the mean motion segment stiffness, and a minimal disc height increased the spinal stiffness to 154-226% of the mean motion segment stiffness. Lordosis angle, transversal and longitudinal facet angle, endplate depth, and area of the capsular ligament also had a substantial influence (>5%) on the stiffness, but considerable less than the influence of the disc height. Ligament areas, nucleus size, spinous process length, and length of processes are of negligible effect (<2%) on the stiffness. The disc height should be accurately determined in patients to estimate the spinal stiffness. Ligament areas, nucleus size, spinous process length, and transverse process width do not need patient-specific modeling.

Treatment of distal humeral fractures using conventional implants. Biomechanical evaluation of a new implant configuration

BackgroundIn the face of costly fixation hardware with varying performance for treatment of distal humeral fractures, a novel technique (U-Frame) is proposed using conventional implants in a 180° plate arrangement. In this in-vitro study the biomechanical stability of this method was compared with the established technique which utilizes angular stable locking compression plates (LCP) in a 90° configuration.MethodsAn unstable distal 3-part fracture (AO 13-C2.3) was created in eight pairs of human cadaveric humeri. All bone pairs were operated with either the "Frame" technique, where two parallel plates are distally interconnected, or with the LCP technique. The specimens were cyclically loaded in simulated flexion and extension of the arm until failure of the construct occurred. Motion of all fragments was tracked by means of optical motion capturing. Construct stiffness and cycles to failure were identified for all specimens.ResultsCompared to the LCP constructs, the "Frame" technique revealed significant higher construct stiffness in extension of the arm (P = 0.01). The stiffness in flexion was not significantly different (P = 0.16). Number of cycles to failure was found significantly larger for the "Frame" technique (P = 0.01).ConclusionsIn an in-vitro context the proposed method offers enhanced biomechanical stability and at the same time significantly reduces implant costs.

La voie d’abord postérieure transtricipitale dans les luxations invétérées du coude

Neglected elbow dislocation is a rare injury but is still frequent in our country. Authors report 12 cases of neglected elbow dislocation with stiffness in extension. All patients were treated by open reduction using a posterior approach and plasty of tricipital tendon. Authors describe the interest of the posterior approach for treatment of neglected elbow dislocation with stiffness in extension.

The effect of three-dimensional geometrical changes during adolescent growth on the biomechanics of a spinal motion segment

During adolescent growth, vertebrae and intervertebral discs undergo various geometrical changes. Although such changes in geometry are well known, their effects on spinal stiffness remains poorly understood. However, this understanding is essential in the treatment of spinal abnormalities during growth, such as scoliosis.A finite element model of an L3–L4 motion segment was developed, validated and applied to study the quantitative effects of changing geometry during adolescent growth on spinal stiffness in flexion, extension, lateral bending and axial rotation. Height, width and depth of the vertebrae and intervertebral disc were varied, as were the width of the transverse processes, the length of the spinous process, the size of the nucleus, facet joint areas and ligament size. These variations were based on average growth data for girls, as reported in literature.Overall, adolescent growth increases the stiffness with 36% (lateral bending and extension) to 44% (flexion). Two thirds of this increase occurs between 10 and 14 years of age and the last third between 14 years of age and maturity.Although the height is the largest geometrical change during adolescent growth, its effect on the biomechanics is small. The depth increase of the disc and vertebrae significantly affects the stiffness in all directions, while the width increase mainly affects the lateral bending stiffness. Hence, when analysing the biomechanics of the growing adolescent spine (for instance in scoliosis research), the inclusion of depth and width changes, in addition to the usually implemented height change, is essential.

Unilateral and Bilateral Sacropelvic Fixation Result in Similar Construct Biomechanics

In vitro biomechanical investigation of lumbosacropelvic spinal instrumentation. Determine whether unilateral iliac fixation, with or without an L6 to S1 interbody graft, provides equivalent biomechanical stability compared with bilateral iliac fixation. Recent clinical evidence has shown improved clinical outcomes of unilateral iliac fixation compared with bilateral instrumentation that contradicts biomechanical data supporting bilateral instrumentation, although no specific investigation has compared unilateral versus bilateral instrumentation. Sixteen porcine spines were instrumented with bilateral segmental pedicle screws from L1 to S1 and 5.5-mm titanium rods. Spines were randomized to either have an intact L6 to S1 disc space (n = 8/group) or a full discectomy and intervertebral cage at L6 to S1 (n = 8/group). Four reflective noncolinear markers were attached to both L6 and S1. Spines were tested with bilateral ilium, unilateral ilium, and sacrum-only fixation in flexion, extension, lateral bending, and axial torsion between +/-7.0 Nm. L6 to S1 range of motion (degrees) and mechanical stiffness (Nmm/degrees) were compared between groups with a 2-way analysis of variance (P < 0.05). No significant differences were found in construct stiffness or L6 to S1 motion between unilateral or bilateral fixation for any test direction and both demonstrated significantly less L6 to S1 motion compared with sacrum-only fixation for all tests (all P values <0.005). Bilateral fixation was significantly stiffer than sacrum-only fixation in flexion and extension (P < 0.0001). The interbody cage significantly decreased construct stiffness in extension, lateral bending, and axial torsion (P < 0.002), and significantly increased L6 to S1 motion in torsion compared with an intact disc (P < 0.03). There were no biomechanical differences between bilateral and unilateral iliac screw fixation. Intervertebral cage with full discectomy was significantly less stiff than intact. This study provides biomechanical data to correlate with improved clinical outcomes using unilateral iliac screw fixation, and evidence contraindicating full discectomy with intervertebral cage placement.

Arthrography in extension stiffness of the knee joint

In the present paper the authors point out in the importance of arthrography in the preoperative diagnosis of stiffness of the knee joint; their findings are based on a study of 29 cases. The majority of the roentgenograms show the knees of patients who subsequently underwent surgical arthrolysis. The technique and special features of the procedure are described. The evaluated contrast films may be classified in three groups, the first including joints with a residual mobility of up to 50 degrees, the second including those with between 50 and 90 degrees and the third those with more than 90 degrees. Typical for the first group is an obliteration of the upper recessus and an omega-shaped form in AP films. Films from Group 2 only show constrictions of the recessus suprapatellaris. In the third group only slight changes are found, which in some cases could only be assessed more accurately by comparison with the healthy side. In cases of knee-joint stiffness due to extra-articular causes there is no correlation between the arthrogram and the range of mobility. The authors conclude that X-rays of the interior of the joint using contrast medium can be a valuable help in planning surgical treatment for fibrotically stiffened knee joints.

Bilateral Medial Tibiofemoral Joint Stiffness in Full Extension and 20° of Knee Flexion

The valgus stress test is used clinically to assess injury to the medial knee structures in 2 positions: full extension and some degree of flexion. The amount of flexion used to "isolate" the medial collateral ligament is not consistent in the literature, but most studies have shown that stiffness of the ligaments was consistent between the limbs. To determine (1) if the stiffness of the medial knee structures was the same bilaterally, and (2) if the stiffness was different in full extension compared with 20 degrees of knee flexion. Criterion standard, before-after design. University research laboratory. Both knees of 45 healthy and active volunteers (26 females, 19 males; age = 23.2 +/- 3.96 years, height = 170.6 +/- 7.75 cm, mass = 74.2 +/- 15.14 kg) were studied. A valgus force of 60 N was applied to the lateral aspect of both knees in full extension and in 20 degrees of flexion. The slope of the force-strain line of the medial knee during a valgus force was calculated using the LigMaster arthrometer. Slope means in full extension were 16.1 +/- 3.3 (right knee) and 15.8 +/- 3.1(left knee). Means for 20 degrees of flexion were 12.2 +/- 3.1 (right) and 11.7 +/- 2.8 (left). Stiffness was greater when the knee was in full extension versus 20 degrees of flexion (t(44) = 12.04, P < .001). No difference was noted between the slopes of the 2 knees in extension (t(44) = 0.74, P = .46) or in flexion (t(44) = 1.2, P = .27). These findings support the use of the contralateral knee as a control. Further, the valgus stress test should be performed in full extension and in some degree of flexion to assess the different restraining structures of the medial tibiofemoral joint.

Paralysie des muscles intrinsèques des doigts longs

Intrinsic muscles of the fingers are the interosseous, lumbricals and hypothenar muscles. Their main action is metacarpophalangeal (MP) flexion and interphalangeal (IP) extension. If extrinsic muscles remain active, intrinsic paralysis results in a claw deformity: MP hyperextension and IP flexion. Bouvier's test is positive if IP extension is actively possible when MP hyperextension is passively prevented. Surgical operations to correct claw deformity are divided into passive and active palliative procedures. Passive palliative procedures are tenodeses and capsuloplasties. Active palliative procedures have either a proximal action (MP flexion only): lasso and direct interosseous activation, or a distal action (MP flexion and IP extension). When Bouvier's maneuver is positive, a simple claw deformity may be treated by a passive procedure and/or an active palliative with proximal action procedure. This last procedure should be preferably indicated on index and middle finger if a few muscular motors are available. When claw deformity is complicated by MP stiffness in extension, a capsulectomy-capsuloplasty is indicated. When Bouvier's test is negative, and passive IP extension is possible, an active palliative with distal action procedure is indicated. Even when there is no claw deformity, intrinsic paralysis may be treated by an active palliative with proximal action procedure, in order to stabilize pinch and grasp. Capsuloplasties, lassos and interosseous activation procedures were all invented by Eduardo Zancolli.

Mechanical Comparison in Cadaver Specimens of Three Different 90-Degree Double-Plate Osteosyntheses for Simulated C2-Type Distal Humerus Fractures With Varying Bone Densities

To investigate the bone-implant-anchorage of 90-degree double-plate osteosynthesis in simulated complete intra-articular distal humerus fractures using conventional reconstruction plates (CRP), locking compression plates (LCP), and distal humerus plates (DHP), depending on the bone mineral density (BMD) of the cadaver specimens. Groups (CRP, LCP, DHP, n=8; LCP, DHP, n=13) in distal humerus cadaver bones were created based on BMD. The fracture model was an unstable intraarticular distal humerus fracture with a transverse osteotomy gap representing metaphyseal comminution (AO type 13-C2.3). Flexion and extension stiffness as well as cycles until failure due to screw pullout under cyclic loading were evaluated. Estimates of BMD values, below which failure was likely to occur, were determined. Stiffness values were not significantly different between groups (extension: P=0.881, flexion: P=0.547). Under cyclic loading, consistent screw pullout failure occurred at BMD values below about 400 mg/cm for CRP and below about 300 mg/cm for LCP constructs. Comparing BMD-matched groups of 8 and 13 specimens respectively, the failure rate was significantly lower for the DHP (0/8) than for the CRP (5/8; P=0.026) and tended to be lower for the DHP (0/13) as compared to the LCP (4/13; P=0.096). Bone-implant anchorage was different between locking and nonlocking plate constructs and depended on BMD. While in good bone quality implant choice was not critical, both locking plates provided superior resistance against screw loosening as compared to the CRP at low BMD values (<420 mg/cm). Based on our laboratory results, we conclude that locking plates such as the LCP and DHP are constructs designed to keep anatomical reduction in the presence of comminution and poor bone quality in a low intra-articular fracture of the distal humerus.

A micromechanical model for extension of a tightly packed bundle of aligned short fibres

Micromechanical models for the interaction between discrete short fibres in idealized bundles are developed and are used to investigate fibre strain profiles, slippage behaviour with increasing extension, bundle load-extension, and tangent stiffness properties. The modeling approach permits abutting fibres to interact by elastic surface shear forces in gripping regions and inelastic frictional slip in slipping regions, where transition from gripping to slipping at a contact position occurs as a linear elastic–perfectly plastic function of the interfibre relative displacement. Results show that for typical staple fibre dimensions and physical properties, a short fibre composite model for the fibre strain profile provides a good approximation to the average fibre strain profile occurring along fibres embedded in bundles. For one fibre assembly considered, results for bundle tangent stiffness indicate that, with increasing extension, average bundle stiffness may be expected to decrease from about 0.8 to 0.5 relative to a bundle of similar but continuous fibres, with 0.5 being reached at the point of collapse by localized slippage.

Thompson's quadricepsplasty for stiff knee

Background:Stiffness of the knee after trauma and/or surgery for femoral fractures is one of the most common complications and is difficult to treat. Stiffness in extension is more common and can be reduced by vigorous physiotherapy. If it does not improve then quadricepsplasty is indicated. The present study was undertaken to evaluate the results of Thompsons quadricepsplasty.Materials and Methods:Twenty-two male patients (age range 20-45 years) with posttraumatic knee stiffness following distal femoral fractures underwent Thompson's quadricepsplasty where knee flexion range was less than 45°. The index injury in these patients was treated with plaster cast (n=5), plates (n=3), intramedullary nailing (n=3) and external fixator for open fractures (n=9). Thompson's quadricepsplasty was performed in all the patients using anterior approach, with incision extending from the upper thigh to the tibial tubercle. Release of rectus femoris from underlying vastus intermedius and release of intraarticular adhesions were performed. After surgery the patients needed parenteral analgesia for three days and then oral analgesics for three weeks. Active assisted knee mobilization exercises was started on the first postoperative day. Continuous passive motion machine was used from the same day. Supervised physiotherapy was continued in hospital for six weeks followed by intensive knee flexion and extension exercise including cycling at home for atleast another six months.Results:Out of 22 patients, 20 had excellent to good results and two patients had poor results using criteria devised by Judet. One poor result was due to peroperative fracture of patella which was then internally fixed and hence the flexion of knee could not be started immediately. There was peroperative avulsion of tibial tuberosity in another patient who finally gained less than 50° knee flexion and hence a poor result.Conclusion:Thompsons quadricepsplasty followed by a strict and rigourous postoperative physiotherapy protocol successfully increases the range of knee flexion.

Biomechanical and Clinical Evaluation of a Novel Technique for Surgical Repair of Spondylolysis in Adolescents

A biomechanical comparison of a novel spondylolysis repair technique method to established spondylolysis repair constructs accompanied by a case series of 5 adolescent patients with spondylolysis treated with this technique. To provide retrospective data on these patients treated with an intralaminar link construct, as well as present comparative biomechanical data on this construct and that of an intact spine, lytic spine, and known methods of repair. Spondylolysis is a unilateral or bilateral defect in the pars interarticularis, and most commonly occurs at L5 and less frequently at L4. Surgical treatment may be indicated in patients with persistent pain and impairment despite conservative treatment. Unlike posterolateral fusion, direct pars repairs may benefit adolescents by sparing motion segments. Biomechanical testing of 5 cadaver lumbar spines was completed to provide comparative biomechanical data on this intralaminar link construct, and that of an intact spine, destabilized spondylolytic spine, Scott wiring technique, pedicle screw-cable system, and the pedicle screw-rod-hook constructs. There were 5 adolescent patients with spondylolysis treated with multiaxial pedicle screws, with a modular linkage that passes beneath the spinous process of the same segment. Biomechanical evaluation of the intralaminar link construct showed the least displacement (across pars defect) followed by the pedicle screw-rod-hook system, Scott wiring, and, finally, the pedicle screw-cable system. Interbody flexion and extension stiffness was highest for pedicle screw-rod-hook followed by normal, intralaminar link construct, Scott wiring, pedicle screw-cable system, and, finally, the destabilized spine. Interbody torsional stiffness was highest for pedicle screw-rod-hook followed by intralaminar link construct, normal, pedicle screw-cable system, Scott wiring, and lytic spine. Retrospective follow-up (average 4.6 years) of patients showed complete radiographic healing or pain relief in all 5 patients. There was 1 patient with solid healing of L3 spondylolysis who later had onset pain despite evidence of solid fusion on computerized tomographic images. In this patient, pain resolved after implant removal. Biomechanical evaluation of the intralaminar link construct showed excellent stability of a spondylolytic defect in comparison to established methods. Clinical follow-up of this method reflects the results of biomechanical testing with excellent clinical results.

Biomechanical evaluation of the ventral and lateral surface shear strain distributions in central compared with dorsolateral placement of cages for lumbar interbody fusion

The purpose of this study was to measure and compare the ventral and lateral surface strain distributions and stiffness for two types of interbody cage placement: 1) central placement for anterior lumbar interbody fusion (ALIF); and 2) dorsolateral placement for extraforaminal lumbar interbody fusion (ELIF). Two functional spine units were obtained for testing in each of 13 cadaveric spines, yielding 26 segments (three of which were not used because of bone abnormalities). Bilateral strain gauges were mounted adjacent to the endplate on the lateral and ventral walls of each vertebral body in the 23 motion segments. Each segment was cyclically tested in compression, flexion, and extension in the following conditions: while intact, postdiscectomy, and instrumented with interbody fusion cages placed using both insertion techniques. No significant differences were observed between ALIF and ELIF in compressive stiffness, bending stiffness in flexion and extension (p > or = 0.1), ventral and lateral strain distribution during the intact tests (p > or = 0.24), and during the flexion tests after fusion (p > or = 0.22). In compression, higher ventral and lower lateral strain was observed in the ALIF than in the ELIF group (ventral, p = 0.05; lateral, p = 0.04), and in extension, higher ventral (p = 0.01) and higher lateral strain (p = 0.002) was observed in the ELIF than in the ALIF group. Preservation of the ventral anulus and dorsolateral placement of the interbody cages during ELIF allow alternate load transfer pathways through the dorsolateral vertebral wall and ventral anulus that are not observed following ALIF. These may be associated with a lower incidence of subsidence and a higher rate of fusion due to a more concentrated application of bone healing-enhancing compression forces during the fusion and healing process.

SPIRE spinous process stabilization plate: biomechanical evaluation of a novel technology

The authors studied the biomechanical properties of a novel spinous process stabilization plate (CD HORIZON SPIRE Spinal System) and present the results in comparison with those of other posterior fixation methods. Ten functional cadaveric lumbar segments were subjected to nondestructive quasistatic loading forces in 10 different conditions: intact, destabilized (discectomy), fitted with spinous process plate (SPP) alone, with anterior-column support (ACS) alone, ACS with SPP, ACS with posterior translaminar facet screw (PTFS) fixation, ACS with unilateral pedicle screw and rod (UPSR) fixation, ACS with bilateral pedicle screw and rod (BPSR) fixation, UPSR alone, or BPSR alone. Stiffness and range of motion (ROM) data were compared using a repeated-measures, one-way analysis of variance. The construct with greatest mean limitation of flexion-extension ROM was ACS/SPP at 4.14 degrees whereas it was 5.75 degrees for ACS/UPSR fixation, 5.03 degrees for ACS/BPSR fixation, and 10.13 degrees for the intact spine. The SPIRE plate alone also provided greater flexion and extension stiffness, with less ROM than other posterior stabilization options. Fixation with BPSR with or without ACS resulted in the stiffest construct in lateral bending and axial rotation. The SPP and UPSR fixation groups were equivalent in resisting lateral bending and axial rotation forces with or without ACS. The SPIRE plate effectively stabilized the spine, and the test results compare favorably with other fixation techniques that are more time consuming to perform and have greater inherent risks.