Joseph J. Crisco

Mechanical behavior of the human lumbar and lumbosacral spine as shown by three-dimensional load-displacement curves.

The lumbar region is a frequent site of spinal disorders, including low-back pain, and of spinal trauma. Clinical studies have established that abnormal intervertebral motions occur in some patients who have low-back pain. A knowledge of normal spinal movements, with all of the inherent complexities, is needed as a baseline. The present study documents the complete three-dimensional elastic physical properties of each lumbar intervertebral level from the level between the first and second lumbar vertebrae through the level between the fifth lumbar and first sacral vertebrae. Nine whole fresh-frozen human cadaveric lumbar-spine specimens were used. Pure moments of flexion-extension, bilateral axial torque, and bilateral lateral bending were applied, and three-dimensional intervertebral motions were determined with use of stereophotogrammetry. The motions were presented in the form of a set of six load-displacement curves, quantitating intervertebral rotations and translations. The curves were found to be non-linear, and the motions were coupled. The ranges of motion were found to compare favorably with reported values from in vivo studies.

Biomechanical evaluation of lumbar spinal stability after graded facetectomies.

In an in vitro experiment using fresh human lumbar functional spinal units, the effects of the division of the posterior ligaments (consisting of the supraspinous/ interspinous ligaments) and graded facetectomies were investigated. The graded facetectomies consisted of unilateral and bilateral medial facetectomies, and unilateral and bilateral total facetectomies. Six kinds of moments were applied and ranges of motion (ROM) and neutral zones (NZ) were determined three-dimensionally by stereophotogrammetric methods. Range of motion was not affected by the division of the supraspinous/interspinous ligaments for all load modes. In flexion, ROM increased slightly after unilateral medial facetectomy. In right axial rotation, ROM increased after left unilateral total facetectomy. Range of motion was not affected, even by bilateral total facetectomies, in extension and lateral bendings. This study suggested that medial facetectomy does not affect lumbar spinal stability, and conversely, total facetectomy, even created unilaterally, makes the lumbar spine unstable.

Biomechanical evaluation of four different posterior atlantoaxial fixation techniques.

Four different techniques for posterior atlantoaxial fusion were tested in vitro: 1) wire fixation with one median graft (Gallie type); 2) wire fixation with two bilateral grafts (Brooks type); 3) transarticular screw fixation (Magerl); and, 4) two bilateral posterior clamps (Halifax). The experiment was designed to determine the immediate three-dimensional stability of the spinal construct. Ten fresh human cadaveric specimens were tested intact, injured, and instrumented with each of the fixation techniques. The injury consisted of a severe soft tissue injury model, in which the alar, transverse, and capsular ligaments were transected. The three-dimensional motions of C1 relative to C2 were measured as the specimens were subjected to loads of pure moments in flexion-extension, axial rotation, and lateral bending. Each fixation technique significantly decreased motion in all directions, as compared to the intact and injured spines. We found that the Gallie system generally allowed significantly more rotation in flexion, extension, axial rotation, and lateral bending than the other three fixation techniques. There was generally no significant difference between the amount of rotation with the other three fixation techniques. However, the Magerl technique tended to allow the least rotation. The anteroposterior translation of two points on C1 were about equal for all fixation techniques.

Disc degeneration affects the multidirectional flexibility of the lumbar spine.

Study Design An in vitro biomechanical investigation using human lumbar cadaveric spine specimens was undertaken to determine any relationship between intervertebral disc degeneration and nonlinear multidirectional spinal flexibility. Summary of Background Data Previous clinical and biomechanical studies have not established conclusively such a relationship. Methods Forty-seven discs from 12 whole lumbar spina specimens were studied under the application of flexion-extension, axial rotation, and lateral bending pure moments. Three flexihility parameters were defined (neutral zone (NZ), range of motion (ROM), and neutral zone ratio (NZR = NZROM)) and correlated with the macroscopic and radiographic degeneration. Results and Conclusions In flexion-extension, the ROM decreased and NZR increased with degeneration. In axial rotation, NZ and NZR increased with degeneration. In lateral binding, the ROM significantly decreased and the NZR increased with degeneration. In all three loading directions, the NZR increased, indicating greater joint laxity with degeneration.

Mechanical Properties of the Human Cervical Spine as Shown by Three-dimensional Load–displacement Curves

Study Design. The mechanical properties of multilevel human cervical spines were investigated by applying pure rotational moments to each specimen and measuring multidirectional intervertebral motions. Objectives. To document intervertebral main and coupled motions of the cervical spine in the form of load–displacement curves. Summary of Background Data. Although a number of in vivo and in vitro studies have attempted to delineate normal movement patterns of the cervical spine, none has explored the complexity of the whole cervical spine as a three-dimensional structure. Methods. Sixteen human cadaveric specimens (C0–C7) were used for this study. Pure rotational moments of flexion–extension, bilateral axial torque, and bilateral lateral bending were applied using a specially designed loading fixture. The resulting intervertebral motions were recorded using stereophotogrammetry and depicted as a series of load–displacement curves. Results. The resulting load–displacement curves were found to be nonlinear, and both rotation and translation motions were coupled with main motions. With flexion–extension moment loading, the greatest degree of flexion occurred at C1–C2 (12.3°), whereas the greatest degree of extension was observed at C0–C1 (20.2°). With axial moment loading, rotation at C1–C2 was the largest recorded (56.7°). With lateral bending moments, the average range of motion for all vertebral levels was 7.9°. Conclusions. The findings of the present study are relevant to the clinical practice of examining motions of the cervical spine in three dimensions and to the understanding of spinal trauma and degenerative diseases.

Analysis of real-time head accelerations in collegiate football players.

Objective: To measure and analyze head accelerations during American collegiate football practices and games. Methods: A newly developed in-helmet 6-accelerometer system that transmits data via radio frequency to a sideline receiver and laptop computer system was implemented. From the data transfer of these accelerometer traces, the sideline staff has real-time data including the head acceleration, the head injury criteria value, the severity index value, and the impact location. Data are presented for instrumented players for the entire 2003 football season, including practices and games. Setting: American collegiate football. Subjects: Thirty-eight players from Virginia Techs varsity football team. Main Outcome Measurements: Accelerations and pathomechanics of head impacts. Results: A total of 3312 impacts were recorded over 35 practices and 10 games for 38 players. The average peak head acceleration, Gadd Severity Index, and Head Injury Criteria were 32 g ± 25 g, 36 g ± 91 g, and 26 g ± 64 g, respectively. One concussive event was observed with a peak acceleration of 81 g, a 267 Gadd Severity Index, and 200 Head Injury Criteria. Because the concussion was not reported until the day after of the event, a retrospective diagnosis based on his history and clinical evaluation suggested a mild concussion. Conclusions: The primary finding of this study is that the helmet-mounted accelerometer system proved effective at collecting thousands of head impact events and providing contemporaneous head impact parameters that can be integrated with existing clinical evaluation techniques.

The intersegmental and multisegmental muscles of the lumbar spine. A biomechanical model comparing lateral stabilizing potential.

The intersegmental and multisegmental musculature of the lumbar spine was studied in a biomechanical model to compare their lateral stabilizing potential. By approximating the active and passive behavior of the stretch reflex as a variable stiffness spring whose stiffness was proportional to activation, the critical muscle stiffness required for mechanical stability was calculated. The model demonstrated that the intersegmental muscles were the least efficient at laterally stabilizing the spine. At any given load, multisegmental muscles were more efficient, and their efficiency increased with the number of segments spanned. The most efficient muscles were those that originated from the pelvis, spanning the maximum number of segments. The muscular model was unstable, regardless of the muscular stiffness, when any vertebral segment was devoid of muscle. Moreover, when the load on the spine is increased, buckling can be prevented most efficiently with the pelvic muscles and least efficiently with the intersegmental muscles.

Frequency and Location of Head Impact Exposures in Individual Collegiate Football Players

CONTEXT Measuring head impact exposure is a critical step toward understanding the mechanism and prevention of sport-related mild traumatic brain (concussion) injury, as well as the possible effects of repeated subconcussive impacts. OBJECTIVE To quantify the frequency and location of head impacts that individual players received in 1 season among 3 collegiate teams, between practice and game sessions, and among player positions. DESIGN Cohort study. SETTING Collegiate football field. PATIENTS OR OTHER PARTICIPANTS One hundred eighty-eight players from 3 National Collegiate Athletic Association football teams. INTERVENTION(S) Participants wore football helmets instrumented with an accelerometer-based system during the 2007 fall season. MAIN OUTCOME MEASURE(S) The number of head impacts greater than 10 g and location of the impacts on the players helmet were recorded and analyzed for trends and interactions among teams (A, B, or C), session types, and player positions using Kaplan-Meier survival curves. RESULTS The total number of impacts players received was nonnormally distributed and varied by team, session type, and player position. The maximum number of head impacts for a single player on each team was 1022 (team A), 1412 (team B), and 1444 (team C). The median number of head impacts on each team was 4.8 (team A), 7.5 (team B), and 6.6 (team C) impacts per practice and 12.1 (team A), 14.6 (team B), and 16.3 (team C) impacts per game. Linemen and linebackers had the largest number of impacts per practice and per game. Offensive linemen had a higher percentage of impacts to the front than to the back of the helmet, whereas quarterbacks had a higher percentage to the back than to the front of the helmet. CONCLUSIONS The frequency of head impacts and the location on the helmet where the impacts occur are functions of player position and session type. These data provide a basis for quantifying specific head impact exposure for studies related to understanding the biomechanics and clinical aspects of concussion injury, as well as the possible effects of repeated subconcussive impacts in football.

Euler stability of the human ligamentous lumbar spine. Part II: Experiment.

The lateral backing and postbuckling behaviour of the intact and injured whole human lumbar spine was experimentally studied using six fresh cadaveric specimens. The ligamentous lumbar spine was loaded in axial compression and the lateral rotation of each vertebra was recorded. At the point of the load application, the most superior vertebrae, the specimens were constrained to move in the frontal plane since sagittal plane buckling will not occur due to the lumbar lordosis. The average load required to buckle an intact whole lumbar specimen was 88 N, and significantly decreased with injury. Once the spines had buckled, the postbuckling behaviour was recorded. These results were compared to theoretical predictions of a model (see Part I). The model was demonstrated to be in excellent agreement with the experimental results.

A Muscle Contusion Injury Model: Biomechanics, Physiology, and Histology

We developed a reproducible muscle contusion injury and studied its effect on contractile function, histology, and passive failure. An instrumented drop-mass tech nique (mass, 171 g; height, 102 cm; spherical radius, 6.4 mm) delivered a single impact to the posterior sur face of the gastrocnemius muscle in one limb of 40 male Wistar rats. On Day 0, the impact significantly (N = 12, P < 0.01) decreased maximum tetanic tension to 63% of the contralateral control value. Histologic examina tion demonstrated extravasation of erythrocytes, edema, myofiber disruption, and vacuolation of myofi bers. Passive failure initiated at the site of injury. At 2 days, tetanic tension was 75% of controls (N = 11, P < 0.01). Histologically, acute inflammation and pha gocytosis were noted. Tetanic tension at 7 days was 81 % of controls (N = 8, P < 0.01). Vimentin staining indicated a dramatic increase in myoblast activity. Con tractile strength was near normal at 24 days. Histologic examination showed complete regeneration of normal striated muscle fibers. No vimentin activity was found. No passive failures initiated at the injury site. Contusion injury produced a significant deficit in contractile func tion that continually diminished with gross histologic evi dence of degeneration, regeneration, and normalization at the injured muscle fibers.