COUPLED SPINE MOTIONS, SPINE LOADING AND RISK OF OCCUPATIONALLY-RELATED LOW BACK DISORDERS

Fadi A. FATHALLAH

Low back disorders are considered to be one of the most prevalent musculoskeletal disorders in industry. Several epidemiological and in‑vitro studies have implicated Combined motions and loads of the back to constitute highly undesirable lifting situations. However, up to this date, there were no studies that quantitatively assessed trunk coupled or combined motions of industrial workers and the corresponding 3‑D spinal loading under these complex conditions. In‑vivo assessment of spinal coupled motions and loading could provide us with better insights about the mechanism(s) which compromise the integrity of the spinal structure.

This study consisted of three main phases including: a surveillance phase, a laboratory phase, and a modeling phase. In the surveillance phase, trunk continuous coupled motions of three risk groups within "work place" categories were quantified and compared. Elevated levels of combined lateral and twisting velocities at extreme sagittal flexion angles were patterns unique to both the medium and high risk groups. However, coupled positions did not provide consistent patterns for distinguishing among risk groups. Furthermore, workplace factors had an effect on coupled motion patterns, suggesting an interactive nature among risk factors. Lastly, including information about trunk coupled dynamic factors into models of industrial LBD risk could enhance the sensitivity and specificity of these models.

The laboratory phase consisted of a controlled experiment to assess the trunk muscular response under various whole‑body free‑dynamic coupled and symmetric lifting and lowering conditions. Substantial coactive patterns were observed under most conditions, especially during coupled exertions. Therefore, it was found essential to include all ten monitored muscles in the modeling efforts of quantifying spinal loading.

In the modeling phase, the Biodynamics Laboratory EMG‑assisted model was advanced to deal with whole‑body free‑dynamic lifting situations. An apparatus/method was developed to determine the essential continuous location and orientation of L5/S1 in 3‑D space. Situations involving extreme sagittal flexion and extreme asymmetric postures subjected the spine to elevated loading that could potentially lead to injury. Ignoring the role of shear forces during typical MMH lifting tasks could result in underestimation of the complete spinal loading.