Activation characteristics of back- and trunk muscles after vertebral fractures and instabilities after lumbar spinal fusion

Status:

completed 05/2010

Aims:

Before and after scheduled vertebral fusion surgery it was planned to investigate the impact of different accesses (ventral vs. dorsal) on segmental control of back muscles. Furthermore, ventral trunk muscles were involved in these investigations. Analyses were performed during exactly metered static loading tasks of the upper body. The gathered data was compared with clinical course and muscle fiber characteristics from back muscles that were obtained during the respective operations.

Activities/Methods:

The metered exposure of the trunk was carried out by tilting the patient in well defined angle levels. With this defined forces act on the trunk. The identification of activation patterns was carried out by Surface EMG. For this back extension muscles were measured virtually continuous by using a finely subdivided electrode grid. According to international recommendations the remaining trunk muscles were measured selectively at representative recording sites. Histological characteristics of muscle substances accruing from the surgical treatment were analysed. Correlations between clinical course, SEMG data and histology was calculated.

Results:

Patients who underwent lumbar spinal fusion after traumatic vertebral fractures during static (application of graded forces on the trunk) as well as dynamic testing (walking on a treadmill at different speeds) were investigated. Trunk muscle function was evaluated by multichannel Surface EMG (SEMG). A specific feature of the investigation consisted of a continuous investigation of paravertebral muscles with 16 electrodes on each side, starting at L5 level by using electrode strips. As a part of the project normative data were established with a group of healthy volunteers (n=56).
Although, patients were characterized by a large inter-individual variability systematic differences to the controls could be established. Static investigation: Patients showed increased SEMG amplitudes for the whole paraspinal region. Their amplitude force characteristic was distorted for the abdominal as well as the paraspinal muscles (only males). Especially males developed side differences from prevailing left sided amplitudes at caudal regions to right sided dominance at cranial regions. Dynamic investigation: Mean amplitude levels in patients were diminished for many paravertebral region and all abdominal muscles. The spatial amplitude distribution along the spine was corrupted. Amplitude peaks at heel strike also were reduced, in contrast, the low level amplitudes during stance phases were increased. Differently from controls, who with increasing speeds only showed an increase of their paraspinal amplitude peaks, in patients all amplitudes went up if walking speed increased. Therefore, a less phasic activation pattern of the paravertebral muscles could be identified in patients, which, caused by the continuous activity may lead to muscular fatigue and therefore finally result in recurring vertebral instabilities.

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