Pinch force and forearm-muscle load during routine colonoscopy: a pilot study.

BACKGROUND AND OBJECTIVE: Overuse injuries of the hand, wrist, forearm, and shoulder are common among endoscopists and may be from repetitive pinching and gripping forces or awkward posturing. In this pilot study, we evaluated distal upper-extremity musculoskeletal load during colonoscopy (1) to confirm the feasibility of performing ergonomic measurements in endoscopists and (2) to identify tasks that may contribute to overuse injuries. DESIGN AND SUBJECTS: Three experienced gastroenterologists were evaluated during 3 colonoscopies each. SETTING: Veterans Affairs Medical Center, San Francisco, California. MAIN OUTCOME MEASUREMENT: Right-thumb pinch force using a thumb-force sensor and bilateral forearm-muscle activity using electromyography. RESULTS: The mean duration of the 9 colonoscopies was 19.5 minutes. The highest mean (SD) right-thumb peak pinch forces occurred during left (10.4 [4.1] N) and right (10.1 [4.5] N) colon insertion, which exceeded the injury threshold of 10 N. Mean peak forearm-muscle activity was also greatest during left and right colon insertion. Activity of the left abductor pollicis longus, left extensor carpi radialis, and right extensor carpi radialis exceeded the American Conference of Industrial Hygienists (ACGIH) hand activity level (HAL) action limit. The left extensor carpi radialis was at the ACGIH HAL threshold limit. LIMITATIONS: The small sample size, no force measurement for the left thumb, and all the gastroenterologists were men. CONCLUSION: The pinch forces and forearm-muscle loads applied during routine colonoscopy may pose a risk for overuse injuries at the elbow and wrist.

MMP-1, IL-1beta, and COX-2 mRNA expression is modulated by static load in rabbit flexor tendons.

Tendon cells respond to their mechanical environment by synthesizing and degrading the surrounding matrix. This study examined how expression of genes associated with tendon degeneration is affected by static loads. Forty flexor tendons from 10 New Zealand White rabbits were harvested and secured in a tissue loading system. A static load of 0, 2, 4, or 6 MPa was applied to tendons for 20 h. MMP-1, IL-1beta, COX-2, GAPDH, and 18s mRNA expression was measured by qRT-PCR. MMP-1 expression in tendons loaded to 6 MPa was significantly increased 259% compared to tendons loaded to 4 MPa. Relative to a 0 MPa load, IL-1beta expression was inhibited with load at 4 MPa (48%) while COX-2 expression was increased at 6 MPa (219%). A polynomial regression analysis found a significant positive correlation between creep and expression of MMP-1 (R(2) = 0.53, p < 0.001) and IL-1beta (R(2) = 0.55, p < 0.001). The results of this study indicate that moderate load inhibits IL-1beta and high load stimulates COX-2 relative to stress shielding. MMP-1 expression is up-regulated with high loads compared to moderate loads. The correlation between creep and expression suggests that the pathway for MMP-1 and IL-1beta expression, leading eventually to tendon degeneration, may be regulated by the biomechanical factor creep.

Evaluation of gene expression through qRT-PCR in cyclically loaded tendons: an in vivo model.

An in vivo rabbit animal model for the tendinopathy, epicondylitis, was used to examine the effects of repetitive load on the expression of various genes associated with matrix remodeling. Following 80 h of cumulative load, tissue from the distal and proximal regions of the flexor digitorum profundus tendon was collected. Quantitative RT-PCR was used to asses mRNA levels of collagenase-1 (MMP-1), stromelysin (MMP-3), vascular endothelial growth factor (VEGF), connective tissue growth factor (CTGF), cyclooxygenase-2 (COX-2), interleukin-1beta (IL-1beta), type III collagen (COL-III) and fibronectin (FBRN). No significant differences in expression levels were found between loaded and unloaded limbs at either region of the tendon. The findings were unexpected as the same model has already demonstrated an increase in the density of cells staining for VEGF and CTGF. Different regulatory mechanisms between mRNA and protein expression or localized changes missed due to homogenization of the tissue samples, may explain the discrepancy in findings.

Cyclic loading inhibits expression of MMP-3 but not MMP-1 in an in vitro rabbit flexor tendon model.

BACKGROUND: Gene expression analysis is useful for assessing cellular behavior and may improve our understanding of the initial cellular response to mechanical load leading to tendon degeneration. This study assessed gene expression of MMP-1 and MMP-3, genes associated with matrix degradation, in tendons exposed to cyclic loads within physiologic range. METHODS: Six flexor tendons from each of ten New Zealand White rabbits were harvested and randomly assigned to one of the following six groups: load deprived for 18h; cyclically loaded for 18h to a peak stress of 2MPa; 3MPa; 4MPa; 5MPa; or snap frozen in liquid nitrogen. MMP-1, MMP-3 and 18s mRNA expression was measured by qRT-PCR. FINDINGS: No significant differences in MMP-1 mRNA expression levels were found between loading groups. MMP-3 expression was significantly inhibited (57%) in tendons cyclically loaded to a peak stress of 4MPa in comparison to load deprived tendons, however, when peak stress was increased to 5MPa, expression was no longer significantly lower compared to stress shielded tendons. INTERPRETATION: The results suggest a 'U' shape relationship between load and MMP-3 expression. The lack of change in MMP-1 expression with loading was unexpected as inhibition of MMP-1 in response to mechanical load has been demonstrated in previous studies. In conclusion, we demonstrate that MMP-3 expression is modulated by cyclic load and is sensitive to load magnitude. MMP-1 mRNA expression is not significantly modulated by cyclic load in this model.

In vitro system for applying cyclic loads to connective tissues under displacement or force control.

Overuse is thought to be the primary cause of chronic tendon injuries, in which forceful or repetitive loading results in an accumulation of micro-tears leading to a maladaptive repair response. In vitro organ culture models provide a useful method for examining how specific loading patterns affect the cellular response to load which may explain the early mechanisms of tissue injury associated with tendinopathies and ligament injuries. We designed a novel tissue loading system which employs closed-loop force feedback, capable of loading six tissue samples independently under force or displacement control. The system was capable of applying loads up to 40 N at rates of 100 N s(-1) and frequencies of 2 Hz, well above loads and rates measured in rabbit tendons in vivo. Loading parameters such as amplitude, rate, and frequency can be controlled while biomechanical factors such as creep, force relaxation, tangent modulus and Young's modulus can be assessed. The system can be used to examine the relationship between each loading parameter and biomechanical factors of connective tissues maintained in culture which may provide useful information regarding the etiology of overuse injuries.

Thumb force and muscle loads are influenced by the design of a mechanical pipette and by pipetting tasks.

Work involving pipetting is associated with elevated rates of musculoskeletal disorders of the hand and wrist. The purpose of this study was to quantify thumb loading and muscle activity and determine if they varied among pipetting tasks. Fourteen experienced participants performed nine pipetting tasks while surface electromyography was measured for the extensor pollicis brevis, abductor pollicis longus, flexor pollicis longus, and abductor pollicis brevis muscles. For five tasks, participants used a pipette instrumented to measure the thumb force applied to the plunger. High-precision tasks significantly increased static muscle activity but reduced peak thumb force on average 5% as compared with low-precision tasks. Pipetting high-viscosity fluids increased peak thumb forces on average 11% as compared with pipetting low-viscosity fluids. Use of a latch pipette increased muscle activity of three muscles. We conclude that pipette design and pipetting tasks can influence applied thumb force and muscle activity. We recommend that pipettes be designed to limit applied peak forces and that pipette users be instructed in use patterns that will reduce applied forces. Actual or potential applications of this research include modifications to pipette designs and worker training in order to reduce hand pain associated with pipetting.