Biomedical subjects

King H Yang

Publications and source records attributed to King H Yang.

At least 19 recordsLinked to original sources

PubMed2006

Computer simulation and validation of the Archimedes Lever hypothesis as a mechanism for aortic isthmus disruption in a case of lateral impact motor vehicle crash: a Crash Injury Research Engineering Network (CIREN) study.

OBJECTIVES: Can aortic isthmus disruption occurring in a lateral motor vehicle crash (LMVC) be explained by the Archimedes Lever Hypothesis, where the intrathoracic aorta, super-pressurized by the thoracic impact force, functions as a rigid lever system? The long arm of this lever system is the proximal aorta-aortic arch, the short arm is the aortic isthmus fixed distally at the descending aorta, and the fulcrum is at the great vessels, especially the left subclavian artery. METHODS: The theory was tested by a simulation technique using a computer-based finite element numerical model system. This simulation model included the dynamics of the crashed vehicles, the direction of force impact, and the structure of the thorax and intrathoracic viscera, including the entire intrathoracic aorta. The specific patient whose data were entered into the model was chosen from a study of 34 LMCV aortic injuries (AIs). The model was constrained by patient and vehicle data from this surviving case. RESULTS: Three sequential lateral thoracic levels impacted by the vehicle side structures were selected. At each level, the maximum mean intra-aortic pressure was 50 to 100 ms after impact, the structure dynamics of the actual crash and the resultant vehicle deformation were simulated; only when the lateral impact was induced in a transverse plane including the first 4 ribs at the level of the aortic arch/isthmus system, with intra-aortic pressures from 200 to 500 mm Hg, were AI-compatible stresses and deformations in the aortic wall achieved at the isthmus. CONCLUSIONS: In LMVC AI, the simulation suggests that the aorta functions as an Archimedes Lever System in which the magnified force mediated by the long lever arm produces sufficient strain on the short lever arm to rupture the aorta at the isthmus.

Accidents, Traffic↗

PubMed2006

Effect of assumed stiffness and mass density on the impact response of the human chest using a three-dimensional FE model of the human body.

The mass density, Young's modulus (E), tangent modulus (Et), and yield stress (sigma y) of the human ribs, sternum, internal organs, and muscles play important roles when determining impact responses of the chest associated with pendulum impact. A series of parametric studies was conducted using a commercially available three-dimensional finite element (FE) model, Total HUman Model for Safety (THUMS) of the whole human body, to determine the effect of changing these material properties on the predicted impact force, chest deflection, and the number of rib fractures and fractured ribs. Results from this parametric study indicate that the initial chest apparent stiffness was mainly influenced by the stiffness and mass density of the superficial muscles covering the torso. The number of rib fractures and fractured ribs was primarily determined by the stiffness of the ribcage. Similarly, the stiffness of the ribcage and internal organs contributed to the maximum chest deflection in frontal impact, while the maximum chest deflection for lateral impact was mainly affected by the stiffness of the ribcage. Additionally, the total mass of the whole chest had a moderately effect on the number of rib fractures.

Computer Simulation↗

PubMed2005

Dynamic evaluation of contact pressure and the effects of graft harvest with subsequent lateral release at osteochondral donor sites in the knee.

PURPOSE: To dynamically evaluate contact pressure about the periphery of the lateral femoral condyle in intact knees, to qualify the effects of osteochondral donor graft harvest on this contact pressure, and to quantify the effects of lateral release on contact pressure after graft harvest. TYPE OF STUDY: Cadaveric analysis. METHODS: Digital electronic pressure-sensing cells were used to measure contact pressure over the periphery of the lateral femoral condyle in 10 fresh-frozen knee specimens. Nonweightbearing resistive extension was simulated as the knees were placed through a functional range of motion. Dynamic pressure readings were evaluated over intact cartilage, around the rims of four 5-mm osteochondral defects, and after lateral release. RESULTS: The pressure cells were all subjected to contact pressures as the knees were placed through a functional range of motion. Average maximal contact pressure progressed distally as the knees were flexed. The creation of 5-mm osteochondral defects did not lead to a significant increase in rim stress concentration over the surrounding cartilage. Lateral release resulted in small decreases in contact pressure over the osteochondral defects. CONCLUSIONS: The creation of 5-mm donor defects about the lateral aspect of the lateral femoral condyle does not lead to significant alterations in local contact pressure. CLINICAL RELEVANCE: Our biomechanical findings may have important implications relating to cartilage restoration using osteochondral autografting procedures. Donor-site morbidity may be minimized if donor-site defects are limited to 5 mm and smaller.

Amputation, Surgical↗

PubMed2005

Concussion in professional football: brain responses by finite element analysis: part 9.

OBJECTIVE: Brain responses from concussive impacts in National Football League football games were simulated by finite element analysis using a detailed anatomic model of the brain and head accelerations from laboratory reconstructions of game impacts. This study compares brain responses with physician determined signs and symptoms of concussion to investigate tissue-level injury mechanisms. METHODS: The Wayne State University Head Injury Model (Version 2001) was used because it has fine anatomic detail of the cranium and brain with more than 300,000 elements. It has 15 different material properties for brain and surrounding tissues. The model includes viscoelastic gray and white brain matter, membranes, ventricles, cranium and facial bones, soft tissues, and slip interface conditions between the brain and dura. The cranium of the finite element model was loaded by translational and rotational accelerations measured in Hybrid III dummies from 28 laboratory reconstructions of NFL impacts involving 22 concussions. Brain responses were determined using a nonlinear, finite element code to simulate the large deformation response of white and gray matter. Strain responses occurring early (during impact) and mid-late (after impact) were compared with the signs and symptoms of concussion. RESULTS: Strain concentration "hot spots" migrate through the brain with time. In 9 of 22 concussions, the early strain "hot spots" occur in the temporal lobe adjacent to the impact and migrate to the far temporal lobe after head acceleration. In all cases, the largest strains occur later in the fornix, midbrain, and corpus callosum. They significantly correlated with removal from play, cognitive and memory problems, and loss of consciousness. Dizziness correlated with early strain in the orbital-frontal cortex and temporal lobe. The strain migration helps explain coup-contrecoup injuries. CONCLUSION: Finite element modeling showed the largest brain deformations occurred after the primary head acceleration. Midbrain strain correlated with memory and cognitive problems and removal from play after concussion. Concussion injuries happen during the rapid displacement and rotation of the cranium, after peak head acceleration and momentum transfer in helmet impacts.

Brain Concussion↗

PubMed2005

Motion Analysis of the Mandible during Low-Speed, Rear-End Impacts using High-Speed X-rays.

There has been much debate over "whiplash"-induced temporomandibular joint (TMJ) dysfunction following low-speed, rear-end automobile collisions. While several authors have reported TMJ injury based on case studies post collision, there has been little biomechanical evidence showing that rear-end impact was the primary cause of such injury. The purpose of this study was to measure the relative translation between the upper and lower incisors in cadavers subjected to low-speed, rearend impacts. High-speed x-ray images used for this analysis were reported previously for the analysis of cadaveric cervical spine kinematics during low-speed, rear-end impacts. The cadavers were positioned at various seatback angles and body postures, producing an overall picture of various seating scenarios. Of the 38 tests conducted using 10 cadavers, there were seven tests from three cadavers in which the positions of the upper and lower incisors could be tracked with precision using imageprocessing software. The relative protrusion, retrusion, and mouth opening were computed from these seven sets of data, providing a better understanding of TMJ motion. Based on this limited data, the average maximum protrusion, retrusion and mouth opening were 1.6+/-1.8, 1.1+/-0.7, and 1.2+/-1.2 mm, respectively. These values appear to fall within normal physiological limits experienced during daily activities such as mastication. It is concluded that low-speed, rear-end automobile collisions do not appear to create the motion required to initiate injury to the TMJ.

Journal Article↗

PubMed2005

Numerical Investigations of Interactions between the Knee-Thigh-Hip Complex with Vehicle Interior Structures.

Although biomechanical studies on the knee-thigh-hip (KTH) complex have been extensive, interactions between the KTH and various vehicular interior design parameters in frontal automotive crashes for newer models have not been reported in the open literature to the best of our knowledge. A 3D finite element (FE) model of a 50(th) percentile male KTH complex, which includes explicit representations of the iliac wing, acetabulum, pubic rami, sacrum, articular cartilage, femoral head, femoral neck, femoral condyles, patella, and patella tendon, has been developed to simulate injuries such as fracture of the patella, femoral neck, acetabulum, and pubic rami of the KTH complex. Model results compared favorably against regional component test data including a three-point bending test of the femur, axial loading of the isolated knee-patella, axial loading of the KTH complex, axial loading of the femoral head, and lateral loading of the isolated pelvis. The model was further integrated into a Wayne State University upper torso model and validated against data obtained from whole body sled tests. The model was validated against these experimental data over a range of impact speeds, impactor masses and boundary conditions. Using Design Of Experiment (DOE) methods based on Taguchi's approach and the developed FE model of the whole body, including the KTH complex, eight vehicular interior design parameters, namely the load limiter force, seat belt elongation, pretensioner inlet amount, knee-knee bolster distance, knee bolster angle, knee bolster stiffness, toe board angle and impact speed, each with either two or three design levels, were simulated to predict their respective effects on the potential of KTH injury in frontal impacts. Simulation results proposed best design levels for vehicular interior design parameters to reduce the injury potential of the KTH complex due to frontal automotive crashes. This study is limited by the fact that prediction of bony fracture was based on an element elimination method available in the LS-DYNA code. No validation study was conducted to determine if this method is suitable when simulating fractures of biological tissues. More work is still needed to further validate the FE model of the KTH complex to increase its reliability in the assessment of various impact loading conditions associated with vehicular crash scenarios.

Journal Article↗

PubMed2005

Development of a Three-Dimensional Finite Element Chest Model for the 5(th) Percentile Female.

Several three-dimensional (3D) finite element (FE) models of the human body have been developed to elucidate injury mechanisms due to automotive crashes. However, these models are mainly focused on 50(th) percentile male. As a first step towards a better understanding of injury biomechanics in the small female, a 3D FE model of a 5(th) percentile female human chest (FEM-5F) has been developed and validated against experimental data obtained from two sets of frontal impact, one set of lateral impact, two sets of oblique impact and a series of ballistic impacts. Two previous FE models, a small female Total HUman Model for Safety (THUMS-AF05) occupant version 1.0Beta (Kimpara et al. 2002) and the Wayne State University Human Thoracic Model (WSUHTM, Wang 1995 and Shah et al. 2001) were integrated and modified for this model development. The model incorporated not only geometrical gender differences, such as location of the internal organs and structure of the bony skeleton, but also the biomechanical differences of the ribs due to gender. It includes a detailed description of the sternum, ribs, costal cartilage, thoracic spine, skin, superficial muscles, intercostal muscles, heart, lung, diaphragm, major blood vessels and simplified abdominal internal organs and has been validated against a series of six cadaveric experiments on the small female reported by Nahum et al. (1970), Kroell et al. (1974), Viano (1989), Talantikite et al. (1998) and Wilhelm (2003). Results predicted by the model were well-matched to these experimental data for a range of impact speeds and impactor masses. More research is needed in order to increase the accuracy of predicting rib fractures so that the mechanisms responsible for small female injury can be more clearly defined.

Journal Article↗

PubMed2005

Characteristics of PMHS Lumbar Motion Segments in Lateral Shear.

The purpose of this study was to determine the characteristics of eighteen lumbar spine motion segments subjected to lateral shear forces under quasi-static (0.5 mm/s) and dynamic (500 mm/s) test conditions. The quasi-static test was also performed on the lumbar spine of a side impact anthropomorphic test device, the EuroSID-2 (ES-2). In the quasi-static tests, the maximum force before disc-endplate separation in the PMHS lumbar motion segments was 1850 +/- 612 N, while the average linear stiffness of PMHS lumbar motion segments was 323 +/- 126 N/mm. There was a statistically significant difference between the quasi-static (1850 +/- 612 N) and dynamic (2616 +/- 1151 N) maximum shear forces. The ES-2 lumbar spine (149 N/mm) was more compliant than the PMHS lumbar segments under the quasi-static test condition.

Journal Article↗

PubMed2005

Injury patterns and sources of non-ejected occupants in trip-over crashes: a survey of NASS-CDS database from 1997 to 2002.

The objective of this study was to investigate the main injury patterns and sources of non-ejected occupants (i.e. no full/partial ejection) during trip-over crashes, using the NASS-CDS database. Specific injury types and sources of the head, chest, and neck were identified. Results from this study suggest that cerebrum injuries, especially subarachnoid hemorrhage, rib fractures, lung injuries, and cervical spine fractures need to be emphasized if cadaveric tests or numerical simulations are designed to study rollover injury mechanisms. The roof has been identified as the major source for head and neck injuries. However, changing the roof design alone is not likely to improve rollover safety. Instead, the belt restraint systems, passive airbags, roof structure, and new innovations need to be considered in a systematic manner to provide enhanced rollover occupant protection.

Accidents, Traffic↗

PubMed2004

Osteochondral defects in the human knee: influence of defect size on cartilage rim stress and load redistribution to surrounding cartilage.

PURPOSE: To determine the influence of osteochondral defect size on defect rim stress concentration, peak rim stress, and load redistribution to adjacent cartilage over the weightbearing area of the medial and lateral femoral condyles in the human knee. METHODS: Eight fresh-frozen cadaveric knees were mounted at 30 degrees of flexion in a materials testing machine. Digital electronic pressure sensors were placed in the medial and lateral compartments of the knee. Each intact knee was first loaded to 700 N and held for 5 seconds. Dynamic pressure readings were recorded throughout the loading and holding phases. Loading was repeated over circular osteochondral defects (5, 8, 10, 12, 14, 16, 18, and 20 mm) in the 30 degrees weightbearing area of the medial and lateral femoral condyles. RESULTS: Stress concentration around the rims of defects 8 mm and smaller was not demonstrated, and pressure distribution in this size range was dominated by the menisci. For defects 10 mm and greater, distribution of peak pressures followed the rim of the defect with a mean distance from the rim of 2.2 mm on the medial condyle and 3.2 mm on the lateral condyle. An analysis of variance with Bonferroni correction revealed a statistically significant trend of increasing radius of peak pressure as defect size increased for defects from 10 to 20 mm (P = .0011). Peak rim pressure values did not increase significantly as defects were enlarged from 10 to 20 mm. Load redistribution during the holding phase was also observed. CONCLUSIONS: Rim stress concentration was demonstrated for osteochondral defects 10 mm and greater in size. This altered load distribution has important implications relating to the long-term integrity of cartilage adjacent to osteochondral defects in the human knee. Although the decision to treat osteochondral lesions is certainly multifactorial, a size threshold of 10 mm, based on biomechanical data, may be a useful adjunct to guide clinical decision making.

Aged↗

PubMed2004

A proposed injury threshold for mild traumatic brain injury.

Traumatic brain injuries constitute a significant portion of injury resulting from automotive collisions, motorcycle crashes, and sports collisions. Brain injuries not only represent a serious trauma for those involved but also place an enormous burden on society, often exacting a heavy economical, social, and emotional price. Development of intervention strategies to prevent or minimize these injuries requires a complete understanding of injury mechanisms, response and tolerance level. In this study, an attempt is made to delineate actual injury causation and establish a meaningful injury criterion through the use of the actual field accident data. Twenty-four head-to-head field collisions that occurred in professional football games were duplicated using a validated finite element human head model. The injury predictors and injury levels were analyzed based on resulting brain tissue responses and were correlated with the site and occurrence of mild traumatic brain injury (MTBI). Predictions indicated that the shear stress around the brainstem region could be an injury predictor for concussion. Statistical analyses were performed to establish the new brain injury tolerance level.

Acceleration↗

PubMed2004

Below Knee Impact Responses using Cadaveric Specimens.

Knee injuries represent about 10% of all injuries suffered during car crashes. Efforts to assess the injury risk to the posterior cruciate ligament (PCL) have been based on a study available in the literature (Viano et al., 1978), in which only two of the five knees tested had PCL ruptures. The aims of the current study were to repeat the study with a higher number of samples, study the effects of other soft tissues on knee response, and assess the adequacy of the experimental setup for the identification of a PCL tolerance. A total of 14 knees were tested using a high-speed materials testing machine. Eight were intact knees (with the patella and all the muscular and ligamentous structures), three were PCL-only knees (patella and all the muscular and ligamentous structures other than the PCL removed), and the last three were PCL-only knees with the tibia protected from bending fracture. Of the eight intact knees tested, only one had PCL mid substance rupture, one had a partial articular fracture of the tibia below the plateau, and six had simple transverse fracture of the tibial metaphysis. Of the three PCL-only knees without tibial protection, one had PCL mid substance rupture, one had avulsion at the posterior intercondylar attachment point, and the last one had a simple oblique fracture of the tibial metaphysis. Of the three PCL only knees with tibia protection, two had PCL mid-substance ruptures and the third one had an avulsion at the tibial insertion site with partial articular fracture of the lateral plateau. Overall, the results of the current study were similar to those observed by Viano et al. (1978). The average displacement at failure for all PCL related injuries was 17.2+/-2.8 mm for the current study (n=6) and 16.2+/-3.9 mm for Viano et al. (1978) (n=4). This value is higher than the Injury Assessment Reference Value of 15 mm proposed by Mertz (1984) and used in various regulations. Both studies suggest that the existence of the soft tissues other than the PCL affect the injury outcome and that the intact knee would suffer predominantly tibial metaphyseal fractures possibly due to bending. Consequently, it is concluded that the current experimental setup can produce isolated PCL injuries but the data available are inadequate to characterize PCL tolerance. A Hybrid III knee equipped with a ball bearing knee slider was also tested using a pendulum setup. Apart from the initial higher stiffness, the overall response of this knee lies within the force-deflection corridors defined using the response of the cadaver knees with PCL mid-substance failure.

Journal Article↗

PubMed2004

The influence of surrogate blood vessels on the impact response of a physical model of the brain.

Cerebral blood vessels are an integral part of the brain and may play a role in the response of the brain to impact. The purpose of this study was to quantify the effects of surrogate vessels on the deformation patterns of a physical model of the brain under various impact conditions. Silicone gel and tubing were used as surrogates for brain tissue and blood vessels, respectively. Two aluminum cylinders representing a coronal section of the brain were constructed. One cylinder was filled with silicone gel only, and the other was filled with silicone gel and silicone tubing arranged in the radial direction in the peripheral region. An array of markers was embedded in the gel in both cylinders to facilitate strain calculation via high-speed video analysis. Both cylinders were simultaneously subjected to a combination of linear and angular acceleration using a two-segment pendulum. Marker motion was tracked, and maximum shear strain (MSS) and maximum principal strain (MPS) were calculated using markers clustered in groups of three. Four test series were conducted. Peak angular acceleration varied from 2,600 to 26,000 rad/s2, and peak angular speed varied from 17 to 29 rad/s. For a given impact condition, the test-to-test variation of these values was less than 5.5%. For all clusters, the peak MSS and peak MPS for both physical models were less than 26% and 32%, respectively. For 90% of the cluster locations, the absolute value of the difference in peak MSS and peak MPS between the physical models was 4% and 6%, respectively. In the physical model with tubing, strain tended to decrease in the periphery (near to the tubing), while it tended to increase toward the center (away from the tubing). Strain amplitudes were found to be sensitive to the peak angular speeds. In general, this study suggests that the vasculature could influence the deformation response of the brain.

Journal Article↗

PubMed2004

Effect of Head-Neck Position on Cervical Facet Stretch of Post Mortem Human Subjects during Low Speed Rear End Impacts.

The purpose of this study was to determine the effect of head-neck position on cervical facet stretch during low speed rear end impact. Twelve tests were conducted on four Post Mortem Human Subjects (PMHS) in a generic bucket seat environment. Three head positions, namely Normal (neutral), Zero Clearance between the head and head restraint, and Body Forward positions were tested. A high-speed x-ray system was used to record the motion of cervical vertebrae during these tests. Results demonstrate that: a) The maximum mean facet stretch at head restraint contact occurs at MS4 and MS5 for the Body Forward condition, b) The lower neck flexion moment, prior to head contact, shows a non-linear relationship with facet stretch, and c) "Differential rebound" during rear end impact increases facet stretch.

Journal Article↗

PubMed2003

Failure of human cervical endplates: a cadaveric experimental model.

STUDY DESIGN: An in vitro biomechanical study using a servohydraulic testing machine on cadaveric endplates. OBJECTIVES: To characterize the effects of bone mineral density, endplate geometry, and preparation technique on endplate failure load. SUMMARY OF BACKGROUND DATA: The effects of endplate preparation methods on failure loads are only partly characterized in the literature. Endplate burring has been recommended to increase fusion rates. However, graft subsidence may complicate anterior reconstruction procedures. METHODS: After radiographic screening, 21 cadaveric cervical spines underwent dual-energy x-ray absorptiometry scanning to quantify mineral content. Endplate geometry was calculated in 55 randomly selected endplates from the inferior C2 to the superior T1 levels. These vertebrae were embedded in polyester resin and randomly left intact, perforated, or burred. The cervical endplates were loaded at a rate of 0.2 mm/s on an Instron materials tester with an attached 9 mm diameter polycarbonate rod (an area of 64 mm2). A stepwise, univariate linear regression was used to compare the point of endplate failure with the vertebral level, endplate area, gender, age, bone mineral density, and preparation technique. RESULTS: Mean bone mineral density, as measured by dual-energy x-ray absorptiometry, was 0.713 g/cm2 (+/- 0.173 g/cm2). Mean endplate area was calculated at 323 mm2. A mean compressive force of 754 N (+/- 445 N) was required before endplate failure. Trends toward increasing compressive loads were noted with decreasing endplate area and increasing bone mineral density. Increasing age (P = 0.0203), caudal vertebral level (P < 0.0001), endplate burring (P = 0.0068), and female gender (P = 0.0452) were associated with significantly lower endplate fracture loads in compression. CONCLUSIONS: Bone quality was predictive of endplate compressive failure loads. Intact endplates failed at significantly higher loads than their perforated or burred counterparts.

Aged↗

PubMed2003

Effects of a cervical compression plate on graft forces in an anterior cervical discectomy model.

STUDY DESIGN: An ex vivo biomechanical study using an instrumented distractor and load cells in a cadaveric multilevel discectomy construct was conducted. OBJECTIVE: To demonstrate that a dynamic cervical plate can be used to increase compressive load on interbody grafts in a multilevel discectomy specimen. SUMMARY OF BACKGROUND DATA: Cervical plating is used to decrease pseudarthrosis, graft extrusion, and graft subsidence in multilevel anterior discectomy procedures. Plating may shield a graft as it resorbs and may reverse normal loading mechanics. METHODS: Preoperative disc height was measured in five cadaveric spines. A three-level discectomy was performed. The disc spaces were opened with a distractor instrumented with strain gauges to allow the introduction of spacers fixed rigidly to subminiature load cells. Distraction was removed, and immediate compressive forces were measured by the load cells. An external compressor was applied followed by a cervical plate. The specimen then was placed in a loading frame, and final compressive forces were measured. RESULTS: A mean 116.5 N distractive force was required to insert grafts into all three levels. No significant relation between preoperative disc height and distractive or compressive forces was noted. Release of the distractor yielded an immediate compressive load on each graft. The compressor significantly increased graft compression. After plate application, the external compressor was removed. Graft compression did not significantly decrease. In the loading frame, an increase in compressive load was noted. CONCLUSIONS: Preoperative disc height was not related to the compressive force on the graft. Compressive force can be increased and maintained with a dynamic plating system.

Aged↗

PubMed2003

Neck kinematics in rear-end impacts.

The purpose of this study was to document the kinematics of the neck during low-speed rear-end impacts. In a series of experiments reported by Deng et al (2000), a pneumatically driven mini-sled was used to study cervical spine motion using six cadavers instrumented with metallic markers at each cervical level, a 9-accelerometer mount on the head, and a tri-axial accelerometers on the thorax. A 250-Hz x-ray system was used to record marker motion while acceleration data were digitized at 10,000 Hz. Results show that, in the global coordinate system, the head and all cervical vertebrae were primarily in extension during the entire period of x-ray data collection. In local coordinate systems, upper cervical segments were initially in relative flexion while lower segments were in extension. Facet joint capsular stretch ranged from 17 to 97%. In the vertical direction, the head and T1 accelerated upward almost instantaneously after impact initiation while there was delay for the head in the horizontal direction. This combination was the result of a force vector which was pointed in the forward and upward direction to generate an extension moment. Upward ramping of the torso was larger in tests with a 20-deg seatback angle. The study concluded that the kinematics of the neck is rather complicated and greatly influenced by the large rotations of the thoracic spine. Significant posterior shear deformation was found, as evidenced by the large facet capsular stretch. Although the neck forms a "mild" S-shaped curve during whiplash, using its shape as an injury mechanism can be misleading because the source of pain is likely to be located in the facet capsules.

Acceleration↗

PubMed2002

Effects of disc height and distractive forces on graft compression in an anterior cervical discectomy model.

STUDY DESIGN: An in vitro biomechanical study using a calibrated distractor and a subminiature load cell in a cadaver anterior cervical discectomy construct was conducted. OBJECTIVE: To study the interrelations of preoperative disc height, graft height, and compressive and distractive forces in an anterior cervical discectomy model. SUMMARY OF BACKGROUND DATA: The effects of graft size on compressive and distractive forces in a discectomy model remain unknown. Larger grafts afford neural decompression through anterior column distraction. This distraction may subject the graft and vertebral bodies to excessive loads, increasing graft fracture, and subsidence risk. METHODS: Disc height was measured radiographically in 18 specimens. A Smith-Robinson discectomy was performed, and the superior and inferior ends of the specimens were embedded in polyester resin. Distraction was applied through a calibrated Caspar distractor to measure the distractive force applied while steel spacers rigidly fixed to a subminiature load cell were introduced. After distraction was removed, immediate compressive force was measured. RESULTS: Distractive forces of 112.4 N and 189.9 N were required to insert the 6-mm and 8-mm grafts, respectively. When this distractive force was removed, immediate compressive loads of 8.8 N and 21.5 N on the graft were noted. When a compressive load of 45 N was applied in a loading frame, measured graft loads of 16.2 N and 29.2 N also increased. No statistically significant relation was observed between preoperative disc height and distractive force or compression of the graft. Significantly lower distractive and compressive forces were associated with insertion of the 6-mm rather than 8-mm graft. CONCLUSIONS: Significantly higher distractive and compressive forces were recorded with larger grafts. Preoperative disc height was not an accurate predictor of graft loads.

Aged↗