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Biomechanics

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The biomechanical research project supported by the Hungarian Scientific Research Fund (OTKA) became a reality through the collaboration between the Budapest University of Technology and Economics and the National Center for Spinal Disorders. The purpose of the study is to examine the recently developed new surgical techniques for the spine from the biomechanical standpoint and to find biomechanical explanations for the still unknown causes of mechanical complications following prevailing surgical techniques.  With the help of biomechanical tests and computer modeling, we will compare the effects of various surgical techniques from the standpoint of their effect on the physical aspects of the spinal column.  The results will help us understand the development of these complications and, with the help of improved techniques will, ultimately, help us avoid them. 

 

Phases of Biomechanical Testing Supported by OTKA

1. Biomechanical testing of the adjacent segment disease
As a consequence of the great number of fusion surgeries performed at the National Center for Spinal Disorders, a large number of patients have returned with complaints of adjacent segment disease.   This leads to the necessity of biomechanical evaluation of clinical advantages, if any, of non-fusion and motion-preserving stabilization systems over rigid fusion techniques since these have as yet not been unequivocally proven.
 
1.1 Examination of the adjacent segment disease  with motion analysis
In examining the adjacent segment disease problem, we use motion evaluation in in vivo patients in order to determine the effect of a surgical technique on the motion aspect of the adjacent segments, the shape of the entire spine, the status of the median and the degree of the spine's biological curvature. We further examine compensating movements and the presence and degree of abnormal movements.
 
The study includes surgical techniques used at the National Center for Spinal Disorders in its clinical practice.  The minimal number of cases in the fusion and non-fusion patient groups and the patients who underwent motion-preserving stabilization, number 50 persons per group.

Examination procedure:
-       In vivo follow-up motion examination before and after surgery. Recording the spine's shape, mobility and muscle function. Checking the musculature of the neighboring segments immediately after surgery and then at given intervals of time.
-       Evaluation of measurement results, comparison from the standpoint of the surgical techniques applied and comparison with the numerical simulation results in point 1.2.
-        Follow-up and assessment period needed for all pertinent data would be over the OTKA set time limit. The expected average minimal follow-up time is 2 years. Since these are considered short term results, we wish to continue the study beyond the tender's 4-years. 
 
Personal and material conditions of the study, ethical permit:
The motion examinations are carried out through the joint efforts of a spine surgeon, x-ray assistant, radiologist, physiotherapist and assistant psychologist. A laptop, a Spinal Mouse for assessing spine motion, the ZEBRIS motion analysis system and a WinSpine computer program is required. The study is subject to a Scientific Research Ethics Committee permit that has been obtained.
 
Expected benefits of the study:
If the results show that the non-fusion and the motion preserving stabilizing systems have a preventive effect on the degeneration of the intervertebral discs of the neighboring segments, there would be significantly less complaints following surgery and a reduction in the number of subsequent surgeries signifying serious improvement and financial savings in the surgical treatment of degenerative diseases of the spine.
 
2. Biomechanical examination of new surgical techniques for degenerative diseases of the spine including osteoporosis
Numerous spinal stabilizing surgeries for intervertebral disc degeneration with osteoporosis are performed at the National Center for Spinal Disorders. The treatment has great significance as a national health issue and the biomechanical examination of the effectiveness of new surgical techniques, therefore, is of special importance.
 
2.1 The National Center for Spinal Disorders has, for several years, been applying in its practice the surgical method based on biomechanical experiments using spacers made out of bone cement.  
The essence of this, a relatively new method worldwide, is that, in cases of spine stabilizing fusion surgeries for the osteoporotic spine, bone cement is used instead of metal to replace part of the intervertebral disc that had been removed and crushed bone in the other part for ossification.  The advantages of this method is that during the fast solidification process, the cement not only covers a larger area but fits the surface of the osteoporotic, degenerated and uneven end plates more precisely than the metal spacer, thus, decreasing the depression in the osteoporotic surroundings observed following the use of conventional spacers.
 
Our goal is to show the new method's effectiveness through in vitro mechanical solidity examination as follows:
-          Using conventional fusion techniques and new cementing methods, the experimental segment samples are prepared and the intervertebral space filled - anteriorly, posteriorly, completely - simulating various cases and using cement of differing mechanical properties.
-          In the biomechanical laboratory, under constant and cyclic pressure, measure the stability and loading capacity of segments fused conventionally and with discoplasty, and examine end plate compression, cement migration, screw loosening as well as the cement's quality and the effect of its placement.  
-        The experimental results obtained following the comparative evaluation will also be compared with the numeric simulation results described in point 2.2 
 
Personal and material conditions of the study, ethical permit:
The biomechanical tests are carried out through the joint efforts of a spine surgeon, a biomechanical engineer and an assistant. Surgical instruments, mechanical examining machine and a laptop are required. The study is subject to a Scientific Research Ethics Committee permit which is yet to be obtained.
 
Expected benefits:
The new, exceptionally simple and economic fusion strategy has the potential of bringing about significant advances in the surgical treatment of the evermore serious national health problem - the degenerative diseases of the spine complicated by osteoporosis  

3. Biomechanical assessment of the new methods of cementing the osteoporotic vertebrae
The conventional method used for strengthening vertebrae compressed due to osteoporosis entails injecting cement into the bony substance of the vertebrae. The disadvantage to this technique is that the cement will migrate into the surrounding tissues when placed under loading pressure.   Several new cementing techniques have appeared of late. We plan the experimental mechanical examination of two of these new methods.

3.1.  Comparative assessment of methods of cementing vertebrae based on pressure experiments.
One of the new methods entails the placement of a balloon into the compressed vertebra. The balloon is first blown up to create a round cavity in the spongeous matter of the vertebra, then removed and cement pushed into the cavity. The cement thus introduced into the cavity will remain in the cavity and not migrate into the surrounding tissues and not allow unwanted side effects to develop.
 
Another new method includes pressing blended cement pulp, turned viscous with heat energy, into the compressed vertebral body.   The viscous cement will not spread into the surrounding tissues thus not allowing dangerous side effects to this develop in this case either.  Biomechanical assessment is planned for these two new technical methods based on in vitro pressure experiments.
 
Research procedure:
-          Cementing cadaver vertebrae with conventional, balloon and energy treated cementing methods.
-          Prepare CT scan images to determine cement distribution.
-          Prepared vertebrae are placed under unidirectional pressure test and cyclic loading to the point of fracture followed by a CT scan.
-          The experimental results obtained following the comparative evaluation will also be compared with the numeric simulation results described in point 3.2.

Personal and material conditions of the study, ethical permit:
The pressure experiments are carried out through the joint efforts of a spine surgeon, a biomechanical engineer and an assistant. Surgical instruments, cement compressor, heating instrument, mechanical testing machine and a laptop are required. The study is subject to a Scientific Research Ethics Committee permit which is yet to be obtained.

Possible benefits of the research:
Insofar as the examination proves the effectiveness of the new cementing techniques, the appropriate solidity and loading capacity of the vertebrae, and the side effects of conventional cementing could be avoided, this would then signify a step forward in the surgical treatment of degenerative diseases of the spine accompanied by osteoporosis.
 
4. Biomechanical analysis of conservative treatments
Conservative therapy (physiotherapy, stretching) plays a very important part in the prevention of surgery with its goal of regaining muscle balance, decreasing abnormal movements, attaining proper posture and stopping pain.   Biomechanical assessment has become important in evaluating whether demonstrable benefits or possible dangers exist in certain conservative therapies.

4.1.  Examination of the effectiveness of physiotherapy with motion analysis
All patients of the National Center for Spinal Disorders take part in physiotherapy prior to surgery.   The purpose of motion assessment is to gain information regarding the measure of healthy motion, loading capacity and muscle balance attained following physiotherapy. We will determine the shape of the spine, the degree of curvature, the median line, motion, the interrelationship of segments, the activity of surface muscles surrounding the spine and the extent of muscle strength. Comparative mechanical analysis will be done with patients referred to the National Center for Spinal Disorders for physiotherapy.   The patients will be compared to healthy patients of the same age.
 
The research procedure:
Examination of motion and muscle balance in the healthy person and in patients undergoing physiotherapy, before and, at intervals, during treatment.   Comparison of healthy and patient results.
Follow the healing process, the time frame of which might exceed the time allotted by OTKA.
 
Personal and material conditions of the study, ethical permit:
The motion analysis study is carried out through the joint efforts of a spine surgeon, a physiotherapist and a biomechanical engineer. A laptop, the ZEBRIS motion analysis system, a WinSpine computer program, the Spinal Mouse motion measuring instrument as well as a surface electromyograph (emg) instrument is required. The study is subject to a Scientific Research Ethics Committee permit which has been obtained.
 
Benefits:
The effectiveness of physiotherapy interpreted numerically may have a benefit in preventing the necessity of surgery.