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Biomedical subjects

M M Panjabi

Publications and source records attributed to M M Panjabi.

At least 73 records · Page 4Linked to original sources
PubMed1997

Multidirectional stabilizing potential of BAK interbody spinal fusion system for anterior surgery.

Improvement in laparoscopic surgery requires spinal-fusion devices appropriately designed for this technique. The BAK interbody fusion device (Spine Tech Inc., Minneapolis, MN, U.S.A.), which consists of two titanium screw cages, meets this requirement. Multidirectional stabilizing potential of this device was investigated by using an in vitro human cadaveric model. Four fresh-frozen human lumbosacral spine specimens (L5-S1) were used. The flexibility test consisted of applying six pure moments (flexion, extension, bilateral axial torques, and lateral bending moments) and measuring the ensuing three-dimensional motion. Moments were applied in four load steps: 0, 2.5, 5.0, 7.5, and 10.0 Nm, and for three load and unload cycles. Motion of the top vertebra was recorded during the third load cycle by using a three-dimensional optoelectronic motion-measurement system. The motion parameters studied were the ranges of motion (ROM) and the neutral zone (NZ). Comparing the ROM of the intact specimen and after the fixation, all motions except extension were reduced significantly (p < 0.005). Average percentage decrease in ROM were 45.8% in flexion, 40.4% in axial rotation, and 65.6% in lateral bending. The only significant changes in NZ were a 255.7% increase in extension, a 90.9% increase in axial rotation, and a 70.8% decrease in lateral bending. This biomechanical study revealed that the BAK system provided decreases in ROM in all directions except in extension. The increased NZ in extension and axial rotation is most likely related to the positioning of the implant. Because these implants were placed from the anterior, damage to anterior annulus and anterior longitudinal ligament is inevitable. For clinical relevance, the patients undergoing this surgical procedure should avoid extension motions.

Adult↗
PubMed1997

Functional morphology of the spinal canal after endplate, wedge, and burst fractures.

Changes in the canal diameter during physiological motions are important considerations in the treatment of patients who have a burst fracture with the presence of bony fragments, but without neurologic deficit. In this in vitro study, the changes in the soft-canal diameter of the thoracolumbar region, when intact and after different fractures, was investigated under several different loading conditions. The soft-canal diameter was clearly identified on the lateral radiographs by attaching a series of steel balls to the posterior longitudinal ligament and ligamentum flavum in the midsagittal plane. Endplate, wedge, and burst fractures were produced incrementally in 19 three-vertebrae human cadaveric spine specimens by high-speed impacts. After each injury, a series of functional lateral radiographs were taken. The minimal canal diameter (MCD) was obtained by digitizing the images of the steel balls on radiographs using a custom-designed computer program. In the intact specimens, the MCD at the disc level changed significantly in flexion, extension, and compression, when compared with the MCD in the unloaded neutral position. However, the changes were small. The MCD after endplate and wedge fractures changed in a similar way. However, after the burst fracture, the MCD at the bone fragment level increased remarkably by a distraction force. It also significantly improved by an anterior shear force in comparison to the corresponding MCD in the neutral position. However, this change was smaller than the change due to the distraction force.

Biomechanical Phenomena↗
PubMed1996

Effects of posture and structure on three-dimensional coupled rotations in the lumbar spine. A biomechanical analysis.

STUDY DESIGN: A biomechanical lumbar spine model was constructed to simulate three-dimensional spinal kinematics under the application of pure moments. Parametric analysis of the model allowed for the estimation of how much of the coupled motions could be predicted by the lumbar lordosis and the intrinsic mechanical properties of the spine. OBJECTIVES: To evaluate the relative effects of lordosis and intrinsic mechanical spine properties on the magnitude and direction of coupled rotations. SUMMARY OF BACKGROUND DATA: Clinical evidence suggests that abnormal coupled motion in the lumbar spine may be an indicator of low back disorders. METHODS: The biomechanical lumbar spine model consisted of five vertebrae separated by intervertebral joints that provided three rotational degrees of freedom. In vitro experimental data, obtained from nine fresh-frozen (L1-S1) cadaveric specimens, were used to establish the mechanical properties of the intervertebral joints. Two different submodels were considered in simulating the three-dimensional intervertebral rotations in response to the applied moments. In the first, it was assumed that the coupled motions were generated solely as a result of the vertebral orientation caused by lordosis. In the second, additional intrinsic motion coupling was assumed. RESULTS: Intervertebral coupling was partially predicted by lumbar lordosis; however, the inclusion of intrinsic mechanical coupling dramatically improved the simulation of the intervertebral rotations (root mean square error < 1 degree). Comparison of the results from the two models demonstrated that the lumbar lordosis and intrinsic mechanical properties of the spine had about an equal effect in predicting the coupling between axial rotation and lateral bending. In contrast, coupled flexion, associated with lateral bending, was almost fully accounted for by the presence of lumbar lordosis. CONCLUSIONS: The lumbar lordosis and intrinsic mechanical properties of the spine were equally important in predicting the magnitude and direction of the coupled rotations.

Adult↗
PubMed1996

Internal architecture of the thoracic pedicle. An anatomic study.

STUDY DESIGN: In this study, data are presented that provide the surgeon with additional information about the internal structure of the thoracic pedicle, which is especially useful for pedicle screw fixation in the thoracic spine. OBJECTIVES: To quantify the internal structure of the pedicle in the thoracic spine. SUMMARY OF BACKGROUND DATA: There are many studies describing the external dimensions of the thoracic pedicle (i.e., pedicle height, pedicle width, and pedicle axis in the transverse and sagittal planes). However, there is little reliable information concerning the internal structure of the pedicle. METHODS: Eighteen thoracic vertebrae were attached to a thin-sectioning machine and both pedicles were cut in six 1.0-mm thin slices. Slides of contact radiographs were rear-projected to a digitizer and the internal and external borders of the pedicle were digitized. Using special computer software, two external dimensions (i.e., pedicle height and pedicle width) and four internal dimensions (i.e., cortical thicknesses of the superior, inferior, medial, and lateral walls) were calculated. RESULTS: The cancellous core was more than twice as large as the cortical shell, with a range from 65.6% to 78.6% with respect to the pedicle height, and 61.3% to 71.6% with respect to the pedicle width. The medial wall was between two and three times thicker than the lateral wall throughout all the pedicle slices and thoracic levels. These differences were highly significant (P < 0.001). CONCLUSIONS: The thoracic pedicle is a complex three-dimensional structure that is mostly filled with cancellous bone. The medial wall is significantly thicker than the lateral wall, which could explain the fact that most of the pedicle fractures related to pedicle screw insertion occur laterally.

Adult↗
PubMed1996

Subfailure injury of the rabbit anterior cruciate ligament.

Ligamentous injuries range in severity from a simple sprain to a complete rupture. Although sprains occur more frequently than complete failures, only a few studies have investigated the phenomena of these subfailure injuries. The purpose of our study was to document the changes in the load-deformation curve until the failure point, after the ligament has been subjected to an 80% subfailure stretch. Thirteen paired fresh rabbit bone-anterior cruciate ligament-bone preparations were used. One of the pairs (control) was stretched until failure; the other (experimental) was first stretched to 80% of the failure deformation of the control and then stretched to failure. Comparisons were made between the load-deformation curves of the experimental and control specimens. The nonlinear load-deformation curves were characterized by eight parameters: failure load (Ffail), failure deformation (Dfail), energy until failure (Efail), deformations measured at 5, 10, 25, and 50% of the failure load (D5, D10, D25, and D50, respectively), and stiffness measured at 50% of the failure force (K50). There were no significant differences in the values for Ffail, Dfail, and Efail between the experimental and control ligaments (p > 0.33). In contrast, the deformation values were all larger for the experimental than the control ligaments (p > 0.01). The deformations D5, D10, D25, and D50 (mean +/- SD) for the control were 0.36 +/- 0.13, 0.49 +/- 0.23, 0.81 +/- 0.35, and 1.23 +/- 0.41 mm. The corresponding deformations for the experimental ligaments were, respectively, 209, 186, 153, and 130% of the control values. K50 was also greater for the experimental ligament (125.0 +/- 41.7 N/mm compared with 108.7 +/- 31.4 N/mm, p < 0.03). These findings indicate that even though the strength of the ligament did not change due to a subfailure injury, the shape of the load-displacement curve, especially at low loads, was significantly altered. Under the dynamic in vivo loading conditions of daily living, this may result in increased joint laxity, additional loads being applied to other joint structures, and, with time, to joint problems.

Animals↗
PubMed1996

On improving the accuracy of instrumented spatial linkage system.

Calibration is important for improving the accuracy of instrumented spatial linkage (ISL) in the application of biomechanical studies. The assumption of the linear performance of the potentiometer transducer has limited the improvement of the linkage accuracy. We present a non-linear numerical calibration procedure and double potentiometer design to improve the accuracy of ISL. Through the use of a three-degree-of-freedom linkage, the non-linear calibration procedure and the double potentiometer design were shown to be effective in reducing the ISL errors. The error, i.e. standard deviation for the angle decreased from +/-0.38 degree to +/-0.12 degree while the same for the translation decreased from +/-0.41 to +/-0.16 mm. A high-accuracy linkage system using low-cost potentiometers could be constructed by using our calibration method and double potentiometer design.

Calibration↗
PubMed1995

Validity of the three-column theory of thoracolumbar fractures. A biomechanic investigation.

STUDY DESIGN: This study validated the three-column theory of fractures by correlating the multidirectional instabilities and the vertebral injuries to each of the three columns, using a biomechanic trauma model. OBJECTIVES: The objective was to validate the three-column theory as applied to the thoracolumbar fractures. SUMMARY OF BACKGROUND DATA: The widely used three-column theory of fractures for classification and evaluation was based on retrospective analysis of radiographs. No biomechanic study, using realistic spinal fractures and multidirectional instability measurements, was available. METHODS: Using 16 fresh cadaveric thoracolumbar human spine specimens, two groups of burst fractures were produced by either simple axial compression or flexion-compression, using a high-speed trauma model. Multidirectional flexibility was measured before and after the trauma, thus quantifying the instability of the burst fracture. Computed tomography scans were taken after the fracture, and a newly developed injury scoring scheme quantified the injuries to the anterior, middle, and posterior columns. Statistical correlations were obtained between the flexibility parameters and injuries to each of the three columns. RESULTS: In the axial compression group, the middle column injury, compared with the other two columns, showed the highest correlations to eight of the nine flexibility parameters (average R2 = 0.77). In the flexion-compression group, again the middle column injury showed the highest correlations to eight of the nine flexibility parameters (average R2 = 0.85). CONCLUSIONS: The results of this study supported the three-column theory of the thoracolumbar fractures and bolstered the concept of the middle column being the primary determinant of mechanical stability of this region of the spine.

Adult↗
PubMed1995

Fracture pattern and instability of thoracolumbar injuries.

Spinal fractures are common in the thoracolumbar region. Assessment of fracture instability is often made from fracture pattern seen on plain radiographs or CT scans. The purpose of this in vitro study was to correlate three-dimensional flexibility to each fracture type, i.e., endplate, wedge, and burst. Ten fresh cadaveric human spine specimens (T11-L1) were incrementally impacted in a high-speed trauma apparatus until a fracture occurred. All fractures were produced by the same mechanism (axial compression/flexion load). The occurrence of a fracture was monitored by lateral radiographs of the specimen, whose canal was lined with 1.6-mm steel balls. After each impact, the specimen was studied for its flexibility in flexion, extension, left and right lateral bindings, and left and right axial rotations. The flexibility was determined in response to the application of maximum pure moments of 7.5 Nm. Each moment was applied individually and in three load cycles. Parameters of neutral zone (NZ) and range of motion (ROM) were computed. Average flexion-extension ROM (and NZ) for intact, endplate, wedge, and burst fracture were respectively, 12.7 degrees (1.3 degrees), 13.9 degrees (1.7 degrees), 19.2 degrees (3.2 degrees), 22.0 degrees (6.0 degrees). The average lateral bending ROM (NZ) were 12.6 degrees (1.2 degrees), 13.6 degrees (1.9 degrees), 19.1 degrees (3.7 degrees), 27.2 degrees (9.8 degrees). The average axial rotation ROM (NZ) were 4.7 degrees (0.4 degree), 6.1 degrees (0.7 degrees), 7.1 degrees (1.0 degree), 12.9 degrees (3.1 degrees).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1995

Normal motion of the lumbar spine as related to age and gender.

The CA-6000 Spine Motion Analyzer was used to measure the lumbar spine's range of motion (ROM). One hundred and four asymptomatic volunteers were examined to obtain normal values for flexion/extension, lateral bending, and axial rotation. A detailed error analysis was conducted to investigate the inter- and intraobserver reliability of the measurement equipment, the differences between passive and active examination, the effects of stretching exercises before examination, and the diurnal changes related to lumbar spine ROM. Subjects were divided into groups by age and gender. Values for each group were compared with respect to age and gender. The measurements were found to be consistent and repeatable. Stretching exercises were observed to increase ROM. Passive examination was recommended to achieve maximum ROM. ROM was observed to increase during the course of the day. A normative database was established showing significantly decreased motion as age increased, but no gender differences were discovered. The validity of the axial rotation values due to fixation difficulties is questioned.

Adult↗
PubMed1995

In vivo axial rotations and neutral zones of the thoracolumbar spine.

Fourteen normal male subjects with mean age 23 (range 20-32) years and mean body weight of 69.6 kg underwent right and left axial rotation in a special machine--axial rotation tester (AROT). The AROT was designed and fabricated such as to allow uninhibited coupled axial rotation and lateral flexion while preventing flexion and extension. The range of rotation (ROR) and neutral zone (NZ) were recorded during active rotation (.A), active rotation with blindfold (.B), and passive rotation with blindfold (.P). Finally, bilateral axial rotation was tested with 6, 12, 18, 24, 30, and 36 Nm rotary torque (.T). There was no significant difference between ROR.A and ROR.B, both being approximately 140 degrees. However, there was a significant difference between NZ.A and NZ.B (p < 0.01). ROR.P was approximately 30 degrees greater than ROR.A. The trunk structures showed a nonlinear viscoelastic behavior with progressive rotary torque application. The neutral zone in axial rotation did not show significant difference between different loads. It is reported that the rotary neutral zone varies between subjects, and it is suggested to be contributory to spinal laxity.

Adult↗
PubMed1995

Dynamic canal encroachment during thoracolumbar burst fractures.

In the burst fractures seen clinically, often poor correlation exists between the neurological deficit and the canal encroachment measured on post-trauma radiographic images. The purpose of the present study was to determine whether the dynamic canal encroachment during the trauma is greater than the static canal encroachment posttrauma. We successfully produced burst fractures in nine of 15 fresh human cadaveric thoracolumbar spine specimens (T11-L1). The specimens were incrementally impacted in a high-speed trauma apparatus until fracture occurred. During the trauma, dynamic canal encroachments were measured using three specially designed transducers placed in the canal at the levels of the superior end-plates of the T12 and L1 and the T12/L1 disk. After the trauma, residual static spinal canal encroachments were measured from the radiographs of the specimens that were prepared with 1.6-mm diameter steel balls lining the canal in the midsagittal plane. We found that the average canal diameter was 16.6 +/- 1.3 mm and the static canal encroachment was 18.0% of the canal diameter. The corresponding dynamic canal encroachment was 33.3%. Thus, the dynamic canal encroachment was 85% more than the static measurement. The clinical significance of this study lies in providing awareness to the clinician that the dynamic canal encroachment is significantly greater than the static canal encroachment seen on posttrauma radiographs or computed tomography scans. The finding may also explain the clinical observation of poor correlation between the canal encroachment measured radiographically and the neurological deficit.

Adult↗
PubMed1994

On the understanding of clinical instability.

STUDY DESIGN: Three-dimensional flexibility changes due to the application of an external fixator at C4-C5 were studied in cervical spine specimens. OBJECTIVES: To evaluate the biomechanical effects of applying a cervical external fixator to a patient using an in vitro model. SUMMARY OF BACKGROUND DATA: There is controversy regarding the relationship between the changes in spinal motion and clinical instability. METHODS: Using fresh cadaveric C4-C7 specimens, multidirectional flexibility was measured at all vertebral levels, before and after the fixator application at C4-C5, C5-C6, and C4-C6. RESULTS: The average ranges of motion for flexion, extension, lateral bending, and axial rotation were 8.3 degrees, 7.2 degrees, 5.3 degrees, and 5.6 degrees, which decreased by 40%, 27%, 32%, and 58%, respectively, because of the fixator application. The corresponding neutral zones were 3.4 degrees, 3.4 degrees, 3.0 degrees, and 2.0 degrees, which decreased by 76%, 76%, 54% and 69%, respectively. The decreases with the fixation at C4-C5 were similar to those for fixation at C5-C6. CONCLUSIONS: This in vitro study documented that the application of an external fixator to the cervical spine decreases the intervertebral motion in general, and decreases flexion, extension and torsional neutral zones in particular. The findings help explain the clinical instability of the spine and support the hypothesis that the neutral zone is more closely associated with the clinical instability than is the range of motion.

Adult↗
PubMed1994

The role of plate and screw fixation in occipitocervical fusion in rheumatoid arthritis.

STUDY DESIGN: In a clinical retrospective study, the results of occipitocervical fusion in patients with rheumatoid arthritis were studied and analyzed. OBJECTIVES: The results of two different operative techniques were compared. The advantages of screw fixation compared with wiring techniques in this population of patients were investigated. SUMMARY OF BACKGROUND DATA: Numerous different implants have been presented in the literature for occipitocervical fusion in patients with rheumatoid arthritis. The use of wires being the standard fixation technique. METHODS: Occipitocervical fusion was performed in patients with rheumatoid arthritis: 26 patients with the wiring technique and 33 patients with a new Y-plate fixation. The results were compared at a follow-up period of 24 months and 50 months, respectively. Clinical and radiologic results were investigated. RESULTS: The atlantodental distance could be significantly better reduced in the group with the Y-plate fixation and the neurologic improvement in the wiring group was 40%, whereas in the Y-plate fixation 86% of neurologic improvement was observed. Pseudarthrosis was seen in 27% of the wiring technique and in 6% in the plate and screw fixation technique. CONCLUSIONS: In occipitocervical fusion for patients with rheumatoid arthritis, the screw and plate fixation technique provides superior results than other techniques using wire fixations.

Arthritis, Rheumatoid↗
PubMed1994

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 spine specimens were studied under the application of flexion-extension, axial rotation, and lateral bending pure moments. Three flexibility parameters were defined (neutral zone (NZ), range of motion (ROM), and neutral zone ratio (NZR = NZ/ROM)) 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 bending, the ROM significantly decreased and the NZR increased with degeneration. In all three loading directions, the NZR increased, indicating greater joint laxity with degeneration.

Adult↗
PubMed1994

Anular incision technique on the strength and multidirectional flexibility of the healing intervertebral disc.

STUDY DESIGN: This study used a sheep model to biomechanically analyze the healing strength of the anulus fibrosus after two types of anular incisions. OBJECTIVE: This study evaluated whether the type of anular incision made at the time of lumbar discectomy plays a role in the subsequent healing strength of the anulus and the biomechanical flexibility of the corresponding motion segment. METHODS: Two types of anular incision, a full thickness removal of a box or window of anulus and a full thickness straight transverse slit through the anulus, were made in the intervertebral discs of 18 adult sheep. After healing times of 2, 4, and 6 weeks, the intervertebral discs were tested versus control levels for strength of anular healing and biomechanical flexibility of the corresponding motion segment. RESULTS: The box incised discs showed a significantly greater loss in strength during the early healing phase (2 to 4 weeks) and a longer response before recovering anular strength when compared with the slit-incised discs. The type of incision also affected the multidirectional flexibility of the motion segments in a differentiated manner. Larger amounts of motion were seen with the box incision when compared with the slit incision at all time periods and in all pure moments. CONCLUSION: The technique of anular incision plays a definite role in the timing and strength of subsequent anular healing. The box incision through the anulus led to significantly weaker healing than did the slit incision in the early healing phase (2-4 weeks). Also, larger amounts of motion were seen in the vertebral motion segments of those discs undergoing box incision when compared with slit or control levels.

Animals↗
PubMed1994

Thoracolumbar burst fracture. A biomechanical investigation of its multidirectional flexibility.

Assessment of clinical instability of thoracolumbar burst fractures remains controversial and subjective. The purpose of the study was to obtain objective measures of acute instability of these fractures. Thirteen fresh cadaveric human spine specimens (T11-L1) were subjected to high-speed axial trauma, resulting in burst fractures in 10 specimens. Multidirectional flexibilities were measured when the specimen was intact and after the trauma. The average ranges of motion of the burst fractures, measured as percentages of the corresponding intact values at 7.5 Newton-meters, were 202%, 403%, 266%, and 462% for flexion/extension, axial rotation, lateral bending, and tension/compression, respectively. For the neutral zone motion parameter, the motions of the burst fracture were even greater: 670%, 1650%, 779%, and 650%, respectively. All of the increases were significant (P < 0.05). The clinical significance of the study lies in its finding of high multidirectional acute instability of the thoracolumbar burst fracture, especially in axial rotation.

Adult↗
PubMed1994

The value of functional computed tomography in the evaluation of soft-tissue injury in the upper cervical spine.

A functional rotatory computed tomography (CT) study of 423 whiplash patients with cervical spine soft-tissue injury was undertaken to determine its diagnostic value. The results are correlated with previous CT studies on normal subjects, and an evaluation of paradox motion, in which the lower vertebra rotates more than the vertebra immediately superior to it, is given. Asymmetrical left/right rotation reached the pathological value in 36% of the patient population at the level of C0-1. Twice as many patients had hypermobile rotation to the left as compared with the right, perhaps indicating that the right alar ligament is more often damaged in injuries involving the whiplash mechanism. A higher percentage of pathological values for hypermobile rotation was found at the level of C0-1 than at C1-2. Patients exhibiting paradox rotation had a significantly higher amount of rotation to the contralateral side than did those who exhibited no paradox rotation. These findings validate the use of functional rotatory CT in the evaluation of soft-tissue damage of the upper cervical spine resulting from whiplash injury.

Adolescent↗