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Biomedical subjects

Jacek Cholewicki

Publications and source records attributed to Jacek Cholewicki.

12 recordsLinked to original sources
PubMed2003

Trunk muscle recruitment patterns in patients with low back pain enhance the stability of the lumbar spine.

STUDY DESIGN: A comparative study of trunk muscle recruitment patterns in healthy control subjects and patients with chronic low back pain was conducted. OBJECTIVE: To assess trunk muscle recruitment in patients with low back pain. SUMMARY OF BACKGROUND DATA: Conflicting evidence has been reported on the level and pattern of trunk muscle recruitment in patients with low back pain. The disparities can be explained partly by methodologic differences. It was hypothesized that trunk muscle recruitment patterns may be altered in patients with low back pain to compensate for reduced spinal stability. METHODS: For this study, 16 patients with low back pain and 16 matched control subjects performed slow trunk motions about the neutral posture and isometric ramp contractions while seated upright. Ratios of electromyographic amplitudes and estimated moment contributions of antagonist over agonist muscles and of segmentally inserting muscles over muscles inserting on the thorax and pelvis only were calculated. In addition, model simulations were performed to assess the effect of changes in muscle recruitment on spinal stability. RESULTS: The ratios of antagonist over agonist, and of lumbar over thoracic erector spinae electromyographic amplitude and estimated moment contributions were greater in the patients than in the control subjects. The simulation model predicted that these changes would effectively increase spinal stability. CONCLUSIONS: Trunk muscle recruitment patterns in patients with low back pain are different from those in healthy control subjects. The differences are likely to be functional with respect to enhancement of spinal stability in the patients.

Adult↗
PubMed2003

The effects of visual input on postural control of the lumbar spine in unstable sitting.

Postural control of the lumbar spine in unstable sitting was quantified through the analysis of the center of pressure (CoP) movement recorded by a force plate situated underneath a seat that incorporated a hemisphere. Thirteen healthy subjects were tested under conditions of increasing seat instability and elimination of visual input. The purpose of this study was to determine the relative effects of visual input and support surface instability on open and closed loop postural control mechanisms in sitting and to determine the association between traditional summary statistics and random walk analysis of CoP movement. The effects of the seat instability level and visual input on the CoP movement parameters were tested with a two-factor, repeated measures ANOVA (p<0.01). In all summary statistics CoP movement parameters increased significantly due to the seat instability level and lack of visual input. The random walk analysis identified two regions, short- and long-term, which has been postulated to represent open and closed loop control mechanism, respectively. While short-term scaling exponents were independent from visual input, CoP displacement in the short-term region was significantly increased in the eyes closed condition. Summary statistic of CoP total path length per second correlated highly with critical point coordinates and short-term diffusion coefficients. The CoP movement in the long-term region was consistent with a closed loop control mechanisms. The findings of visual influence on what is assumed as an open-loop control mechanism does not, at face value, support the hypothesis that two separate mechanisms are working to achieve postural control.

Adult↗
PubMed2003

Trunk muscle activation in low-back pain patients, an analysis of the literature.

This paper provides an analysis of the literature on trunk muscle recruitment in low-back pain patients. Two models proposed in the literature, the pain-spasm-pain model and the pain adaptation model, yield conflicting predictions on how low- back pain would affect trunk muscle recruitment in various activities. The two models are outlined and evidence for the two from neurophsysiological studies is reviewed. Subsequently, specific predictions with respect to changes in activation of the lumbar extensor musculature are derived from both models. These predictions are compared to the results from 30 clinical studies and three induced pain studies retrieved in a comprehensive literature search. Neither of the two models is unequivocally supported by the literature. These data and further data on timing of muscle activity and load sharing between muscles suggest an alternative model to explain the alterations of trunk muscle recruitment due to low-back pain. It is proposed that motor control changes in patients are functional in that they enhance spinal stability.

Adaptation, Physiological↗
PubMed2003

Coordination of muscle activity to assure stability of the lumbar spine.

The intention of this paper is to introduce some of the issues surrounding the role of muscles to ensure spine stability for discussion -- it is not intended to provide an exhaustive review and integration of the relevant literature. The collection of works synthesized here point to the notion that stability results from highly coordinated muscle activation patterns involving many muscles, and that the recruitment patterns must continually change, depending on the task. This has implications on both the prevention of instability and clinical interventions with patients susceptible to sustaining unstable events.

Biomechanical Phenomena↗
PubMed2003

The effect of increased peripheral suture purchase on the strength of flexor tendon repairs.

PURPOSE: Previous studies have hypothesized unequal load sharing between peripheral and core sutures in flexor tendon repairs. Most commonly peripheral sutures are placed very near the repair site and characteristically fail before the core strands. We hypothesized that placement of the peripheral sutures farther from the repair site would better optimize load sharing and resist suture pullout, yielding a stronger overall repair. METHODS: To test the hypothesis we developed a mathematical model of the load sharing between core and peripheral sutures. By using this model we predicted that placement of peripheral sutures 2 mm from the repair site would optimize the balance of load between core and peripheral sutures. We then divided and repaired 27 flexor digitorum profundus tendons in 6 ways (core plus peripheral or peripheral sutures only at 1 mm, 2 mm, or 3 mm from the repair site). Tendons were clamped to a custom-built linear loading machine and distracted to failure. RESULTS: There was a clinically and statistically significant increase in strength with an increased distance of the peripheral suture from the repair site showing that core sutures augmented by a 2-mm peripheral repair were stronger than those performed with 1-mm peripheral repairs (50.8 vs 37.1 N). CONCLUSIONS: A peripheral stitch placement approximately 2 mm from the repair site represents a simple modification that can significantly increase the ultimate strength of flexor tendon repairs.

Cadaver↗
PubMed2002

Effects of the abdominal belt on muscle-generated spinal stability and L4/L5 joint compression force.

The goals of this study were (1) to determine the effects of abdominal belts on muscle-generated active lumbar spine stability, (2) to determine their effect on the subsequent joint compression force at L4/L5 and (3) to determine whether the effective stability of the spine could be predicted by the active spine stability and belt condition. Electromyographic (EMG) and trunk stiffness data from a previously reported experiment in which 10 subjects performed quick-release tasks (perturbation) with and without an abdominal belt were used as inputs to biomechanical models to estimate the active spine stability and effective stability of the spine, respectively. The subjects exerted isometric trunk flexion, extension and lateral bending trials at 0 and 80% of maximum intra-abdominal pressure when the resisted force was suddenly released. Wearing an abdominal belt had no significant effect on either the muscle-generated lumbar spine stability or the L4/L5 joint compression force in any direction. The effective stability of the spine was adequately predicted by the active spine stability and the effect of the belt, which accounted for approximately 34% of the effective spine stability. The study demonstrated that the abdominal belt contributed to the passive stability of the lumbar spine and did not change the active stability for tests performed within the same experimental session.

Adult↗
PubMed2002

Can increased intra-abdominal pressure in humans be decoupled from trunk muscle co-contraction during steady state isometric exertions?

The purpose of the present study was to investigate whether increased intra-abdominal pressure (IAP) can be achieved without elevating the overall trunk muscle co-contraction that causes increased spine compression force. Ten subjects performed isometric trunk flexion, extension, and lateral bending exertions while generating 0%, 40% and 80% of their maximal IAP or while co-contracting trunk muscles without consciously raising IAP. An additional three subjects performed a variety of ramp IAP, co-contraction and isometric exertion tasks while holding their breaths and while exhaling. An 18 degree-of-freedom, electromyogram (EMG)-assisted biomechanical model was used to quantify trunk muscle co-contraction with calculations of spine compression force and stability. Spine stability and compression force increased proportionally with increased IAP regardless of whether the subjects intentionally generated IAP or consciously avoided it. This increase was accomplished with significantly greater co-contraction of 12 major trunk muscles. The EMG activation of all muscles was highly correlated with IAP and intra-thoracic pressure (ITP) ( r from 0.59 to 0.95). Activity of the thoracic erector spinae correlated the best with ITP ( r=0.81), which in turn was correlated with IAP ( r=0.91). It was not possible to co-contract trunk muscles without generating IAP and ITP, or conversely to generate IAP without trunk muscle co-contraction and increased ITP.

Abdominal Cavity↗
PubMed2002

Relative contribution of trunk muscles to the stability of the lumbar spine during isometric exertions.

OBJECTIVE: To compare the relative contribution of various trunk muscles to the stability of the lumbar spine. DESIGN: Quantification of spine stability with a biomechanical model. BACKGROUND: Modern low back rehabilitation techniques focus on muscles that stabilize the lumbar spine. However, the relative contribution of various trunk muscles to spine stability is currently unknown. METHODS: Eight male subjects performed isometric exertions in trunk flexion, extension, lateral bending, and axial rotation, and isometric exertions under vertical trunk loading and in a lifting hold. Each isometric trial was repeated three times at 20%, 40%, and 60% of the maximum trunk flexion force or with a load of 0%, 20%, 40%, and 60% of body weight for the latter two exertions. Surface EMG data from 12 major trunk muscles were used in the biomechanical model to estimate stability of the lumbar spine. A simulation of each trial was performed repeatedly with one of the 10 major trunk muscle groups removed from the model. RESULTS: Relative contribution of each muscle to spine stability was significantly affected by the combination of loading magnitude and direction (3-way interaction). None of the removed muscles reduced spine stability by more than 30%. CONCLUSIONS: A single muscle cannot be identified as the most important for the stability of the lumbar spine. Rather, spine stability depends on the relative activation of all trunk muscles and other loading variables. RELEVANCE: This study will improve our understanding of individual trunk muscles' contribution to overall stability of the lumbar spine.

Adult↗
PubMed2002

Neuromuscular function in athletes following recovery from a recent acute low back injury.

STUDY DESIGN: Observational case control design. OBJECTIVES: To examine muscle response to sudden trunk loading in athletes with and without a recent history of acute low back injury (LBI). BACKGROUND: Impaired neuromuscular function is associated with chronic low back pain. This study examined whether such impairment persists after recovery from an acute LBI. METHODS AND MEASURES: Seventeen athletes who had a recent history of acute LBI and 17 matched healthy controls were tested. At the time of testing (mean = 56 days postinjury, range = 7-120 days postinjury), all athletes were symptom free and had returned to regular competition. Subjects performed isometric exertions in trunk flexion, extension, and left and right lateral bending against a trunk restraining cable. Upon reaching the target isometric force, the cable was released to impose sudden loading on the lumbar spine. Surface EMG signals from 12 major trunk muscles were recorded. The shut-off and switch-on latencies and number of muscles responding to sudden loading were compared between the 2 groups. RESULTS: In all 4 testing directions, the athletes with a recent history of acute LBI shut off significantly fewer muscles and did so with delayed latency. On average, the injured subjects shut off 4.0 out of 6.0 (SD = 1.3) muscles compared to 4.6 out of 6.0 (SD = 1.3) muscles in the control group. The average muscle shut-off latency was 71 (SD = 31) milliseconds for the injured and 50 (SD = 21) milliseconds for the control subjects. No differences were found in number or latency of muscles switching on. CONCLUSIONS: These objective measures of neuromuscular function indicated an altered muscle response pattern to sudden trunk loading in athletes following their clinical recovery from a recent acute LBI.

Acute Disease↗
PubMed1998

Critical load of the human cervical spine: an in vitro experimental study.

OBJECTIVE: To determine the critical load of the osteoligamentous cervical spine in frontal plane. DESIGN: Whole human cervical spine specimens were loaded in axial compression with increasing force until the point of buckling. BACKGROUND: The osteoligamentous cervical spine and the surrounding muscles support the weight of the head and the external loads applied to it. Critical load is the maximum compressive force that the spinal column can sustain before buckling. Critical loads have been obtained for the osteoligamentous thoracolumbar spine (without the rib cage) and the lumbar spine. Critical load of the cervical spine has not yet been determined. METHODS: When a compressive force is applied to the cervical spine, it bends in the sagittal plane producing greater lordosis. The determination of critical load in Euler's sense requires blocking of this sagittal plane bending. A special apparatus was developed that constrained such bending in the sagittal plane, but allowed complete freedom of the spine motion in the frontal plane. Experiments were conducted to determine the axial force-lateral bending curves of whole cervical spine specimens. Critical load values were obtained from these curves. As an alternative to this method, bending stiffness in the frontal plane was experimentally determined and the critical load was computed using Euler's theory of columns. RESULTS: Based upon the study of seven spine specimens (CO-T1), the critical load for the human cervical spine was found to be 10.5 (3.8) N obtained by direct experimentation. The average critical load calculated with the Euler theory using bending stiffness data, was 11.9 (2.0), but there were large individual differences when compared with the experimental results. CONCLUSIONS: The critical load of the osteoligamentous human cervical spine is about one-fifth to one-quarter the weight of the average head.

Journal Article↗
PubMed1998

Mechanism of whiplash injury.

OBJECTIVE: To propose a different hypothesis of whiplash injury mechanism based on a series of experimental studies summarized in this communication. DESIGN: A series of biomechanical studies simulating whiplash trauma using isolated human cadaveric spine specimens. BACKGROUND: Whiplash injuries are on the rise as reported in several recent studies, due primarily to the increased traffic density. Although the symptoms associated with whiplash have been described, our understanding of the injury mechanism remains poor. The prevailing view of neck hyper-extension causing the injury has not been supported by recent experimental studies. METHODS: Eight fresh human cadaveric cervical spine specimens were prepared and traumatized to varying degrees under controlled conditions using a bench-top model of whiplash trauma. Before and after each trauma, the specimen was studied by functional radiography and flexibility test to document changes in the anatomic alignment and biomechanical properties at each level indicating injuries sustained. At the end of all testing, CT-scans, MRI and cryomicrotome images were obtained. During each trauma, relative motions of all intervertebral joints were recorded with a high speed movie camera. Elongations of the vertebral artery and several capsular ligaments were also monitored during the trauma using specially designed transducers. RESULTS: The hyper-extension hypothesis of injury mechanism was not supported by these studies. We found a distinct bi-phasic kinematic response of the cervical spine to whiplash trauma. In the first phase, the spine formed an S-shaped curve with flexion at the upper levels and hyper-extension at the lower levels. In the second phase, all levels of the cervical spine were extended, and the head reached its maximum extension. The occurrence of anterior injuries in the lower levels in the first phase was confirmed by functional radiography, flexibility tests and imaging modalities. The largest dynamic elongation of the capsular ligaments was observed at C6-C7 level during the initial S-shaped phase of whiplash. Similarly, the maximum elongation of the vertebral artery occurred during the S-shape phase of whiplash. CONCLUSION: We propose, based upon our experimental findings, that the lower cervical spine is injured in hyperextension when the spine forms an S-shaped curve. Further, this occurs in the first whiplash phase before the neck is fully extended. At higher trauma accelerations, there is a tendency for the injuries to occur at the upper levels of the cervical spine. Our findings provide truer understanding of whiplash trauma and may help in improving the diagnosis, treatment, and prevention of these injuries.

Journal Article↗