Spinal Loads VS. Body Position
It is very difficult to study actual forces through the spine in a living human being short of cutting one open and implanting a sensor, which is essentially what they did, and this is why the study's are so limited.
The results are not looking for precision as much as perspective.
Measured Loads On A Vertebral Body Replacement During Sitting
BACKGROUND CONTEXT:
Sitting is frequently assumed to cause high spinal loads because people with sedentary work often suffer from low back pain. It is assumed that the posture while sitting, as well as several seat parameters, also affects the spinal loads.
PURPOSE:
To measure the loads on a spinal implant for different upper body inclinations, backrest declinations, seat heights, types of seat, and arm positions.
STUDY DESIGN:
Loads on a vertebral body replacement during sitting were measured in five patients with telemeterized implants.
METHODS:
The telemeterized vertebral body replacement measures all six load components. It was implanted into five patients suffering from compression fractures of a lumbar vertebral body. Loads were measured when the patients were sitting on a stool and inclining their upper body between 15° flexion and 10° extension in steps of 5°; on a chair with an adjustable backrest that allowed declination angles between 108° and 180°; on an office chair while the seat height was varied between 40 and 60 cm in steps of 5 cm; and successively on seven different types of seats. The effect of the arm position was also studied.
RESULTS:
The resultant implant force was increased on the average by 48% for 15° flexion and decreased by 19% for 10° extension of the trunk. When sitting on a chair with an adjustable backrest, the loads decreased with an increasing backrest declination angle. The seat height had in most cases only a minor effect on implant loads. In comparison to sitting on a stool, the loads were reduced when sitting on a bench (7%) or a stool with a padded wedge (9%), a knee stool (19%), a chair (35%), and an office chair (41%). Sitting on a physiotherapy ball increased the loads by 7%. Placing the hands on the thighs reduced the implant loads on the average by 19% in comparison to arms hanging on the sides.
CONCLUSION:
Spinal loads can be reduced by leaning against the backrest, placing the arms on the armrest or the thighs, and by decreasing the flexion angle of the upper body.
Spinal Loads During Position Changes
BACKGROUND:
Recommendations exist how patients should change from one body position to another in order to keep the spinal loads low. However, until now it is not clear whether the loads are in fact lower if the patients follow these recommendations. The aim was to measure the loads while changing the body position.
METHODS:
Telemeterized vertebral body replacements have been inserted into 5 patients who had a severe compression fracture of a lumbar vertebral body. The acting loads were measured during a changing of the body position while lying and when moving from lying to sitting, from sitting to standing and vice versa.
FINDINGS:
When the lying patients changed their position according to the physiotherapist's recommendations, the resultant force was nearly as high as it was during relaxed standing. Otherwise, the force was nearly twice as high. Changing from a lateral lying position to sitting and vice versa caused forces of about 180% of those seen for standing when the recommendations were heeded. Without instructions, the loads were about 70% higher. Use of a trapeze bar mounted to the bed did not increase the loads. Rising from a chair with the arms hanging down laterally led to average resultant forces of 380% related to standing. Placing the hands on armrests reduced this value to 180%.
INTERPRETATION:
High forces may act on the spine when changing from one body position to another. These loads can be minimized when following the physiotherapist's instructions and when supporting the upper body by the arms.
Sources: https://www.ncbi.nlm.nih.gov/pubmed/21775218 & https://www.ncbi.nlm.nih.gov/pubmed/22571842