Mechanical evidence of cervical facet capsule injury during whiplash: a cadaveric study using combined shear, compression, and extension loading.

STUDY DESIGN: A comparison of cervical facet capsule strain fields in cadaveric motion segments exposed to whiplash-like loads and failure loads. OBJECTIVES: To compare the maximum principal strain in the facet capsular ligament under combined shear, bending, and compressive loads with those required to injure the ligament. SUMMARY OF BACKGROUND DATA: The cervical facet capsular ligament is thought to be an anatomic site for whiplash injury, although the mechanism of its injury remains unclear. METHODS: Motion segments from seven female donors were exposed to quasi-static flexibility tests using posterior shear loads of 135 N applied to the superior vertebra under four compressive axial preloads up to 325 N. The right facet joint was then isolated and failed in posterior shear loading. The Lagrangian strain field in the right facet capsular ligament was calculated from capsular displacements determined by stereophotogrammetry. Statistical analyses examined the effect of axial compression on motion segment flexibility, and compared maximum principal capsular strain between the flexibility and failure tests. RESULTS: Capsular strain increased with applied shear load but did not vary with axial compressive load. The maximum principal strain reached during the flexibility tests was 61% +/- 33% of that observed in subcatastrophic failures of the isolated joints. Two specimens reached strains in their flexibility tests that were larger than their corresponding strains at subcatastrophic failure in the failure tests. CONCLUSIONS: The cervical facet capsular ligaments may be injured under whiplash-like loads of combined shear, bending, and compression. The results provide a mechanical basis for injury caused by whiplash loading.

The influence of surface padding properties on head and neck injury risk.

A validated computational head-neck model was used to understand the mechanical relationships between surface padding characteristics and injury risk during impacts near the head vertex. The study demonstrated that injury risk can be decreased by maximizing the energy-dissipating ability of the pad, choosing a pad stiffness that maximizes pad deformation without bottoming out, maximizing pad thickness, and minimizing surface friction. That increasing pad thickness protected the head without increasing neck loads suggests that the increased cervical spine injury incidence previously observed in cadaveric impacts to padded surfaces relative to lubricated rigid surfaces was due to increased surface friction rather than pocketing of the head in the pad.

An anatomical investigation of the human cervical facet capsule, quantifying muscle insertion area.

Facet capsule injury has been hypothesised as a mechanism for neck pain. While qualitative studies have demonstrated the proximity of neck muscles to the cervical facet capsule, the magnitude of their forces remains unknown owing to a lack of quantitative muscle geometry. In this study, histological techniques were employed to quantify muscle insertions on the human cervical facet capsule. Computerised image analysis of slides stained with Masson's trichrome was performed to characterise the geometry of the cervical facet capsule and determine the total insertion area of muscle fibres into the facet capsule for the C4-C5 and C5-C6 joints. Muscle insertions were found to cover 22.4+/-9.6% of the capsule area for these cervical levels, corresponding to a mean muscle insertion area of 47.6+/-21.8 mm2. The magnitude of loading to the cervical facet capsule due to eccentric muscle contraction is estimated to be as high as 51 N. When taken in conjunction with the forces acting on the capsular ligament due to vertebral motions, these forces can be as high as 66 N. In that regard, these anatomical data provide quantitative evidence of substantial muscle insertions into the cervical facet capsular ligament and provide a possible mechanism for injury to this ligament and the facet joint as a whole.

A biomechanical, radiologic, and clinical comparison of outcome after multilevel cervical laminectomy or laminoplasty in the rabbit.

STUDY DESIGN: A rabbit model was used to compare clinical outcome, radiographic changes, and biomechanical flexibility after cervical laminectomy and open-door laminoplasty. OBJECTIVE: This study tested the hypothesis that radiographic changes and biomechanical flexibility could explain the differences in clinical outcome after cervical laminectomy and laminoplasty. SUMMARY OF BACKGROUND DATA: Although multilevel cervical laminoplasty is thought to have advantages over cervical laminectomy, clinical outcome studies have been contradictory, and no experimental study has examined the possible mechanisms for the differences after healing. METHODS: Twenty-four New Zealand White rabbits were randomized into four groups: normal, sham, C3-C6 wide laminectomy, and C3-C6 open-door laminoplasty. Clinical, radiographic, and biomechanical data were collected and compared up to 3 months after surgery. RESULTS: Laminectomy had a statistically significant poorer clinical outcome when compared with laminoplasty after 3 months of healing. Radiologic analysis showed statistically significant angular deformity in the laminectomy group compared with laminoplasty and control groups at 3 months. In contrast, biomechanical measures of flexibility, neutral zone, and range of motion showed only small differences between any of the groups at any time. CONCLUSIONS: The presence of deformity, and not a change in flexibility, is responsible for the differences in clinical outcome observed after laminectomy compared with laminoplasty in this model.

Laparoscopic heller myotomy and anterior fundoplication for achalasia results in a high degree of patient satisfaction.

HYPOTHESIS: Laparoscopic Heller myotomy with anterior fundoplication will alleviate the symptoms of achalasia and result in excellent patient satisfaction. DESIGN: Retrospective study of consecutive patients who underwent laparoscopic Heller myotomy with anterior fundoplication for achalasia between October 1995 and July 1999. A telephone survey assessed symptoms and satisfaction. Patients were asked to quantitate their symptoms on a scale of 0 to 3 (0 = none; 1, mild; 2, moderate; and 3, severe). SETTING: University referral center. PATIENTS: Twenty-four patients who underwent laparoscopic Heller myotomy with anterior fundoplication for achalasia. MAIN OUTCOME MEASURES: Postoperative symptoms and satisfaction. RESULTS: Twenty-one patients (88%) were successfully contacted. Mean follow-up was 16.5 months. The laparoscopic approach was successful in all but 3(88%). The mean dysphagia score was 2.81 preoperatively and 0.81 postoperatively (P<.000). The mean chest pain score was 1. 57 preoperatively and 0.86 postoperatively (P<.015). The mean supine regurgitation score was 2.10 preoperatively and 0.57 postoperatively (P<.000). The mean upright regurgitation score was 1.57 preoperatively and 0.52 postoperatively (P<.000). The mean heartburn score was 1.57 preoperatively and 0.57 postoperatively (P<.000). Postoperatively, 18 (86%) of 21 patients could swallow bread without difficulty and 17 (89%) of 19 patients could eat meat without difficulty (2 were excluded as they were vegetarians). Twenty (95%) of 21 patients reported improvement after the operation. CONCLUSIONS: Laparoscopic Heller myotomy with anterior fundoplication significantly relieves the symptoms of achalasia without causing the symptoms of gastroesophageal reflux disease. This procedure results in excellent overall patient satisfaction.

Quantifying skeletal muscle properties in cadaveric test specimens: effects of mechanical loading, postmortem time, and freezer storage.

Investigators currently lack the data necessary to define the state of skeletal muscle properties within cadaveric specimens. The purpose of this study is to define the temporal changes in the postmortem properties of skeletal muscle as a function of mechanical loading and freezer storage. The tibialis anterior of the New Zealand white rabbit was chosen for study. Modulus and no-load strain were found to vary significantly from live after eight hours postmortem. Following the changes that occur during rigor mortis, a stable region of postmortem, post-rigor properties occurred between 36 to 72 hours postmortem. A freeze-thaw process was not found to have a significant effect on the post-rigor response. The first loading cycle response of post-rigor muscle was unrepeatable but stiffer than live passive muscle. After preconditioning, the post-rigor muscle response was repeatable. The preconditioned post-rigor response was less stiff than the live passive response due to a significant increase in no-load strain. Failure properties of postmortem muscle were found to be significantly different from live passive muscle with a significant decrease in failure stress (61 percent) and energy (81 percent), while failure strain was unchanged. These results suggest that the post-rigor response of cadaveric muscle is unaffected by freezing but sensitive to even a few cycles of mechanical loading.

The cervical facet capsule and its role in whiplash injury: a biomechanical investigation.

STUDY DESIGN: Cervical facet capsular strains were determined during bending and at failure in the human cadaver. OBJECTIVE: To determine the effect of an axial pretorque on facet capsular strains and estimate the risk for subcatastrophic capsular injury during normal bending motions. SUMMARY OF BACKGROUND DATA: Epidemiologic and clinical studies have identified the facet capsule as a potential site of injury and prerotation as a risk factor for whiplash injury. Unfortunately, biomechanical data on the cervical facet capsule and its role in whiplash injury are not available. METHODS: Cervical spine motion segments were tested in a pure-moment test frame and the full-field strains determined throughout the facet capsule. Motion segments were tested with and without a pretorque in pure bending. The isolated facet was then elongated to failure. Maximum principal strains during bending were compared with failure strains, by paired t test. RESULTS: Statistically significant increases in principal capsular strains during flexion-extension loading were observed when a pretorque was applied. All measured strains during bending were significantly less than strains at catastrophic joint failure. The same was true for subcatastrophic ligament failure strains, except in the presence of a pretorque. CONCLUSIONS: Pretorque of the head and neck increases facet capsular strains, supporting its role in the whiplash mechanism. Although the facet capsule does not appear to be at risk for gross injury during normal bending motions, a small portion of the population may be at risk for subcatastrophic injury.

Clinical outcome scales for use in a rabbit model of cervical myelopathy.

This study determined the ability of an upper extremity Tarlov scale, a lower extremity Tarlov scale, and the Durham scale to predict the development of myelopathy and the likelihood of survival in a rabbit model of surgical treatments for cervical spondylotic myelopathy. Forty-eight rabbits were evaluated using the scales after cervical spinal surgery. Logistic regression analysis revealed that all three scales could predict the occurrence of myelopathy. However, only the Durham and lower extremity Tarlov scales also predicted the likelihood of survival. The Durham scale is offered as a useful predictor of myelopathy and survival in an animal model of surgical treatments for cervical spondylotic myelopathy. The lower extremity Tarlov scale is also a useful predictor of outcome; however, the upper extremity Tarlov scale is not recommended.

Inertial properties and loading rates affect buckling modes and injury mechanisms in the cervical spine.

Cervical spine injuries continue to be a costly societal problem. Future advancements in injury prevention depend on improved physical and computational models which, in turn, are predicated on a better understanding of the responses of the neck during dynamic loading. Previous studies have shown that the tolerance of the neck is dependent on its initial position and its buckling behavior. This study uses a computational model to examine the mechanical factors influencing buckling behavior during impact to the neck. It was hypothesized that the inertial properties of the cervical spine influence the dynamics during compressive axial loading. The hypothesis was tested by performing parametric analyses of vertebral mass, mass moments of inertia, motion segment stiffness, and loading rate. Increases in vertebral mass resulted in increasingly complex kinematics and larger peak loads and impulses. Similar results were observed for increases in stiffness. Faster loading rates were associated with higher peak loads and higher-order buckling modes. The results demonstrate that mass has a great deal of influence on the buckling behavior of the neck, particularly with respect to the expression of higher-order modes. Injury types and mechanisms may be substantially altered by loading rate because inertial effects may influence whether the cervical spine fails in a compressive mode, or a bending mode.

Tensile properties of the human muscular and ligamentous cervical spine.

Tensile neck injuries are amongst the most serious cervical injuries. However, because neither reliable human cervical tensile tolerance data nor tensile structural data are currently available, the quantification of tensile injury risk is limited. The purpose of this study is to provide previously unavailable kinetic and tolerance data for the ligamentous cervical spine and determine the effect of neck muscle on tensile load response and tolerance. Using six male human cadaver specimens, isolated ligamentous cervical spine tests (occiput - T1) were conducted to quantify the significant differences in kinetics due to head end condition and anteroposterior eccentricity of the tensile load. The spine was then separated into motion segments for tension failure testing. The upper cervical spine tolerance of 2400 +/- 270 N (occiput-C2) was found to be significantly greater (p < 0.01) than the lower cervical spine tolerance of 1780 +/- 230 N (C4-C5 and C6-C7 segments). Data from these experiments were used to develop and validate a computational model of the ligamentous spine. The model predicted the end condition and eccentricity responses for the tensile force-displacement relationship. Cervical muscular geometry data derived from cadaver dissection and MRI imaging were used to incorporate a muscular response into the model. The cervical musculature under maximal stimulation increased the tolerance of the cervical spine from 1800 N to 4160 N. In addition, the cervical musculature resulted in a shift in the site of injury from the lower cervical spine to the upper cervical spine and offers an explanation for the mechanism of upper cervical spine tension injuries observed clinically. The results from this study predict a range in tensile tolerance from 1.8 - 4.2 kN based on the varying role of the cervical musculature.

Experimental and computational characterization of three-dimensional cervical spine flexibility.

Cervical spine behavior for generalized loading is often characterized using a full three-dimensional flexibility matrix. While experimental studies have been aimed at determining cervical motion segment behavior, their accuracy and utility have been limited both experimentally and analytically. For example, the nondiagonal terms, describing coupled motions, of the matrices have often been omitted. Flexibility terms have been primarily represented as constants despite the known nonlinear stiffening response of the spine. Moreover, there is presently no study validating the flexibility approach for predicting vertebral motions; nor have the effects of approximations and simplifications to the matrix representations been quantified. Yet, the flexibility matrix currently forms the basis for all multibody dynamics models of cervical spine motion. Therefore, the purpose of this study is to fully quantify the flexibility relationships for cervical motion segments, examine the diagonal and nondiagonal components of the flexibility matrix, and determine the extent to which multivariable relationships improve cervical spine motion prediction. To that end, using unembalmed human cervical spine motion segments, a full battery of flexibility tests were performed for a neutral orientation and also following an axial pretorque. Primary and coupled matrix components were described using linear and piecewise nonlinear incremental constants. An additional approach utilized multivariable incremental relationships to describe matrix terms. Measured motions were predicted using structural flexibility methods and were evaluated using RMS error of the difference between the predicted and measured responses. Results of this study provide a full set of flexibility relationships describing primary and coupled motions for C3-C4 and C5-C6 motion segment levels. Analysis of these data indicates that a flexibility matrix using incremental responses describing primary and coupled motions offers improved predictions over using linear methods (p<0.01). However, there is no significant improvement using more generalized nonlinear terms represented by the multivariable functional approach (p<0.2). Based on these findings, it is suggested that a multivariable approach for flexibility is more demanding experimentally and analytically while not offering improved motion prediction.

Human Cervical Motion Segment Flexibility and Facet Capsular Ligament Strain under Combined Posterior Shear, Extension and Axial Compression.

The cervical facet capsular ligaments are thought to be an important anatomical site of whiplash injury, although the mechanism by which these structures may be injured during whiplash remains unclear. The purpose of this study was to quantify the intervertebral flexibility and maximum principal strain in the facet capsular ligament under combined shear, bending and compressive loads similar to those which occur during whiplash loading. Two motion segments (C3-4 and C5-6) from seven female donors (50 +/- 10 years) were exposed to quasi-static posterior shear loads of 135 N applied to the superior vertebra on four occasions while under compressive axial preloads of 0 N, 45 N, 197 N and 325 N. Vertebral body motions and the full Lagrangian strain field in the right facet capsular ligament were measured using stereophotogrammetry. After flexibility testing, the right facet joint of each motion segment was isolated and failed in posterior shear. Differences in the kinematic response of the vertebrae and maximum principal strain in the capsular ligaments under the four axial preloads were tested using repeated-measures ANOVA's for each load step. Although significant differences were observed at two axial load levels in the kinematic sequence (197 N and 325 N), neither the regressed flexibility nor the maximum principal strain in the facet capsular ligament varied significantly with axial compression (p > 0.14). Maximum principal strain during the flexibility tests reached 61 +/- 33 percent of the maximum principal strain observed in sub-catastrophic failures of the isolated joints. Two of the thirteen specimens reached strains in their flexibility tests which were larger than their corresponding strains at sub-catastrophic failure in the failure tests. These results suggest that the cervical facet capsular ligaments may be injured under combined shear, bending and compression load levels that occur in rear-end impacts.

Surface friction in near-vertex head and neck impact increases risk of injury.

A computational head-neck model was developed to test the hypothesis that increases in friction between the head and impact surface will increase head and neck injury risk during near-axial impact. The model consisted of rigid vertebrae interconnected by assemblies of nonlinear springs and dashpots, and a finite element shell model of the skull. For frictionless impact surfaces, the model reproduced the kinematics and kinetics observed in near-axial impacts to cadaveric head-neck specimens. Increases in the coefficient of friction between the head and impact surface over a range from 0.0 to 1.0 resulted in increases of up to 40, 113, 9.8, and 43% in peak post-buckled resultant neck forces, peak moment at the occiput-C1 joint, peak resultant head accelerations, and HIC values, respectively. The most dramatic increases in injury-predicting quantities occurred for COF increases from 0.0 to 0.2, while further COF increases above 0.5 generally produced only nominal changes. These data suggest that safety equipment and impact environments which minimize the friction between the head and impact surface may reduce the risk of head and neck injury in near-vertex head impact.

Laparoscopic resection of esophageal epiphrenic diverticulum.

Symptomatic esophageal epiphrenic diverticula are usually repaired with a diverticulectomy and esophagomyotomy via a left thoracotomy with substantial postoperative pain and morbidity. If a laparoscopic approach could be shown to be safe and effective, the decrease in postoperative pain and potentially shorter hospital stay would make this technique beneficial. We report three cases repaired via a transabdominal approach. The first two cases were done laparoscopically. The third case was attempted laparoscopically and completed via a midline laparotomy, demonstrating that thoracotomy is not necessary even if laparoscopy is not possible. All three patients had long-standing debilitating symptoms refractory to standard nonsurgical therapies (botulinum toxin injection, pneumatic dilation, antispasmodic medication) with abnormal esophageal motility. There was one intraoperative complication of a left pneumothorax that required neither laparotomy nor thoracostomy. An esophagram on the first postoperative day demonstrated no extravasation and good flow into the stomach. The postoperative course was uneventful for all three patients, with the laparoscopic patients discharged on the second postoperative day and the laparotomy patient discharged on the seventh postoperative day. In conclusion, laparoscopic repair of symptomatic esophageal epiphrenic diverticula is a safe and effective technique with minimal postoperative pain and morbidity. It should be considered as an alternative to the traditional transthoracic approach, and may become the standard technique.

The influence of strain rate on the passive and stimulated engineering stress--large strain behavior of the rabbit tibialis anterior muscle.

The passive and stimulated engineering stress-large strain mechanical properties of skeletal muscle were measured at the midbelly of the rabbit tibialis anterior. The purpose of these experiments was to provide previously unavailable constitutive information based on the true geometry of the muscle and to determine the effect of strain rate on these responses. An apparatus including an ultrasound imager, high-speed digital imager, and a servohydraulic linear actuator was used to apply constant velocity deformations to the tibialis anterior of an anesthetized neurovascularly intact rabbit. The average isometric tetanic stress prior to elongation was 0.44 +/- 0.15 MPa. During elongation the average stimulated modulus was 0.97 +/- 0.34 MPa and was insensitive to rate of loading. The passive stress-strain responses showed a nonlinear stiffening response typical of biologic soft tissue. Both the passive and stimulated stress-strain responses were sensitive to strain rate over the range of strain rates (1 to 25 s-1). Smaller changes in average strain rate (1 to 10, and 10 to 25 s-1) did not produce statistically significant changes in these responses, particularly in the stimulated responses, which were less sensitive to average strain rate than the passive responses. This relative insensitivity to strain rate suggests that pseudoelastic functions generated from an appropriate strain rate test may be suitable for the characterization of the responses of muscle over a narrow range of strain rates, particularly in stimulated muscle.

An improved method for finite element mesh generation of geometrically complex structures with application to the skullbase.

An automated method has been developed to generate finite element meshes of geometrically complex structures from CT images using solely hexahedral elements. This technique improves upon previous voxel-based mesh reconstruction approaches by smoothing the irregular boundaries at model surfaces and material interfaces. Over a range of mesh densities, RMS error in surface Von Mises stress was higher in the unsmoothed circular ring models (0.11-0.24 MPa) than in the smoothed models (0.080-0.15 MPa) at each mesh density. The element-to-element oscillation in surface element stress, as measured by the average second spatial derivative of Von Mises stress along the outer surface of the ring, was higher in the unsmoothed models (11.5-15.0 kPa mm-2) than in the smoothed models (4.0-6.8 kPa mm-2). Similarly, in a human skullbase model, the element-to-element oscillation in surface Von Mises stress was higher in the unsmoothed model (5.52 kPa mm-2) than in the smoothed model (1.83 kPa mm-2). Using this technique, finite element models of complex geometries can be rapidly reconstructed which produce less error at the surface than voxel-based models with discontinuous surfaces.

The effects of padded surfaces on the risk for cervical spine injury.

STUDY DESIGN: This is an in vitro study comparing cervical spine injuries produced in rigid head impacts and in padded head impacts. OBJECTIVES: To test the hypothesis that deformable impact surfaces pose a greater risk for cervical spine injury than rigid surfaces using a cadaver-based model that includes the effects of the head and torso masses. SUMMARY OF BACKGROUND DATA: It is widely assumed that energy-absorbing devices that protect the head from injury also reduce the risk for neck injury. However, this has not been demonstrated in any experimental or epidemiologic study. On the contrary, some studies have shown that padded surfaces have no effect on neck injury risk, and others have suggested that they can increase risk. METHODS: Experiments were performed on 18 cadaveric cervical spines to test 6 combinations of impact angle and impact surface padding. The impact surface was oriented at -15 degrees (posterior impact), 0 degree (vertex impact), or +15 degrees (anterior impact). The impact surface was either a 3-mm sheet of lubricated Teflon or 5 cm of polyurethane foam. RESULTS: Impacts onto padded surfaces produced significantly larger neck impulses (P = 0.00023) and a significantly greater frequency of cervical spine injuries than rigid impacts (P = 0.0375). The impact angle was also correlated with injury risk (P < 0.00001). CONCLUSIONS: These experiments suggest that highly deformable, padded contact surfaces should be used carefully in environments where there is the risk for cervical spine injury. The results also suggest that the orientation of the head, neck, and torso relative to the impact surface is of equal if not greater importance in neck injury risk.

Acute experimental colitis decreases colonic circular smooth muscle contractility in rats.

Distal colitis decreases the contractility of the underlying circular smooth muscle. We examined how time after injury and lesion severity contribute to the decreased contractility and how colitis alters the calcium-handling properties of the affected muscle. Distal colitis was induced in rats by intrarectal administration of 4% acetic acid. Contractile responses to acetylcholine, increased extracellular potassium, and the G protein activator NaF were determined for circular muscle strips from sham control and colitic rats at days 1, 2, 3, 7, and 14 postenemas. Acetylcholine stimulation of tissues from day 3 colitic rats was performed in a zero calcium buffer, in the presence of nifedipine, and after depletion of intracellular stores of calcium. The colitis was graded macroscopically as mild, moderate, or severe. Regardless of agonist, maximal decrease in force developed 2 to 3 days posttreatment, followed by a gradual return to control by day 14. The inhibitory effect of colitis on contractility increased with increasing severity of inflammation. Limiting extracellular calcium influx had a greater inhibitory effect on tissues from colitic rats; intracellular calcium depletion had a greater inhibitory effect on tissues from control animals. The data suggest that both lesion severity and time after injury affect the contractile response of circular smooth muscle from the inflamed distal colon. Impaired utilization of intracellular calcium may contribute to the decreased contractility.

The biomechanics of cervical spine injury and implications for injury prevention.

Most catastrophic cervical spinal injuries occur as a result of head impacts in which the head stops and the neck is forced to stop the moving torso. In these situations the neck is sufficiently fragile that injuries have been reported at velocities as low as 3.1 m/s with only a fraction of the mass of the torso loading the cervical spine. Cervical spinal injury occurs in less than 20 ms following head impact, explaining the absence of a relationship between clinically reported head motions and the cervical spinal injury mechanism. In contrast, the forces acting on the spine at the time of injury are able to explain the injury mechanism and form a rational basis for classification of vertebral fractures and dislocations. Fortunately, most head impacts do not result in cervical spine injuries. Analysis of the biomechanical and clinical literature shows that the flexibility of the cervical spine frequently allows the head and neck to flex or extend out of the path of the torso and escape injury. Accordingly, constraints which restrict the motion of the neck can increase the risk for cervical spine injury. These observations serve as a foundation on which injury prevention strategies, including coaching, helmets, and padding, may be evaluated.

Strength and stability of posterior lumbar interbody fusion. Comparison of titanium fiber mesh implant and tricortical bone graft.

STUDY DESIGN: A paired comparison was done of the bending flexibility and compression strength of tricortical bone graft and titanium fiber mesh implants in a human cadaver model of posterior lumbar interbody fusion. OBJECTIVES: To test the hypothesis that a titanium fiber mesh implant and a tricortical bone graft provide adequate and equal mechanical strength and stability in posterior lumbar interbody fusion constructs. SUMMARY OF BACKGROUND DATA: Although studies of posterior lumbar interbody fusion constructs have been performed, the authors are unaware of any study in which the strength and stability of a titanium fiber mesh implant are compared with those of tricortical bone graft for posterior lumbar interbody fusion in the human cadaver lumbar spine. METHODS: Changes in neutral zone and range of motion were measured in a bending flexibility test before and after placement of posterior lumbar interbody fusion constructs. Tricortical bone graft and titanium fiber mesh implant construct stability than were compared in a paired analysis. The constructs than were loaded to failure to evaluate construct strength as a function of graft material and bone mineral density. RESULTS: The posterior lumbar interbody fusion procedure produced statistically significant decreases in neutral zone when compared with the intact spine. No statistically significant differences in neutral zone, range of motion, or strength were detected between the two implants. Construct strength correlated strongly with bone mineral density. CONCLUSIONS: Posterior lumbar interbody fusion procedures result in equal or improved acute stability for titanium fiber mesh implants and tricortical bone graft implants when used without additional posterior stabilization.