Biomechanical response to ladder slipping events: Effects of hand placement.

Ladder falling accidents are a significant, growing and severe occupational hazard. The factors that contribute to falls from ladders and specifically those that influence the motor response from ladder falls are not well understood. The aims of this research were to determine the effects of hand placement (rung versus rail) on muscle activation onset and peak activity timing in response to slipping on a ladder and to sequence the timing of events following slip initiation. Fifteen unexpected slips from 11 experienced ladder climbers were induced with a freely spinning rung under the foot, while subjects were randomly assigned to a rung versus rail hand grasping strategy. EMG onset time and peak activity time from five bilateral muscles (semitendinosis, vastus lateralis, triceps, biceps and anterior deltoid) were analyzed. Results indicated that significantly slower muscle activation onset and peak response times occurred during rail hand placement, suggesting that grasping ladder rungs may be preferable for improving the speed of the motor response. The triceps muscle activated and reached peak activity earlier in the slip indicating that subjects may initially extend their arms prior to generating hand forces. The study also revealed that slips tended to occur around the time that a foot and hand were in motion and there were just two points of contact (one hand and the slipping foot).

Biomechanics of Lower Limbs during Walking among Candidates for Total Knee Arthroplasty with and without Low Back Pain.

The effect of joint pathologies, such as unilateral knee osteoarthritis (UKOA) or low back pain (LBP), on bilateral gait symmetry has gained increased attention during the past decade. This study is the first to compare gait patterns between patients with UKOA and LBP in combination and with UKOA only. Temporal, kinematic, and kinetic variables were measured bilaterally during gait stance phase in 31 subjects with UKOA and LBP (Group I) and 11 subjects with only UKOA (Group II). Group I patients exhibited less hip rotation in the affected limb (A) than in the nonaffected (NA) limb during walking in contrast to Group II patients. Group I patients had minimal bilateral differences in hip abduction and flexion, but Group II patients displayed significantly larger values in the NA limb compared to the A limb for both parameters. Hip flexion patterns were significantly different between Groups I and II. Subjects in both groups adapted gait patterns that minimized vertical ground reaction force, knee flexion motion, and stance time on the UKOA affected limb. The distinct kinematic gait patterns that were revealed in this study may provide clinical value for assessment of patients with UKOA in conjunction with LBP.

Effects of foot placement, hand positioning, age and climbing biodynamics on ladder slip outcomes.

Ladder falls frequently cause severe injuries; yet the factors that influence ladder slips/falls are not well understood. This study aimed to quantify (1) the effects of restricted foot placement, hand positioning, climbing direction and age on slip outcomes, and (2) differences in climbing styles leading to slips versus styles leading to non-slips. Thirty-two occupational ladder users from three age groups (18-24, 25-44 and 45-64 years) were unexpectedly slipped climbing a vertical ladder, while being assigned to different foot placement conditions (unrestricted vs. restricted toe clearance) and different hand positions (rails vs. rungs). Constraining foot placement increased the climber's likelihood of slipping (p < 0.01), while younger and older participants slipped more than the middle-aged group (p < 0.01). Longer double stance time, dissimilar and more variable foot and body positioning were found in styles leading to a slip. Maintaining sufficient toe clearance and targeting ladder safety training to younger and older workers may reduce ladder falls. Practitioner Summary: Ladder falls frequently cause severe occupational fall injuries. This study aims to identify safer ladder climbing techniques and individuals at risk of falling. The results suggest that ladders with unrestricted toe clearance and ladder climbing training programmes, particularly for younger and older workers, may reduce ladder slipping risk.

A retrospective study of the relationship between back pain and unilateral knee osteoarthritis in candidates for total knee arthroplasty.

The purpose of this study was to determine the presence and temporal relationship between back pain and knee osteoarthritis (OA). All subjects were candidates for unilateral total knee arthroplasty (TKA) to relieve knee pain related to OA, and information regarding the prevalence of back pain was collected via questionnaires. A total of 42 subjects with unilateral knee OA responded to the questionnaires, and 74% of subjects reported chronic back pain, which first occurred approximately 10 years before their becoming candidates for TKA. All but 1 subject reported the onset of back pain prior to TKA candidacy, and less than 15% of subjects felt that their worst back pain occurred after the onset of knee OA. The results of this study are a first step toward quantifying the temporal relationship between back pain and unilateral knee OA, and future studies will look to assess potential risk factors for knee OA such as strength, biomechanical, and anatomical asymmetry.

Symmetry of ground reaction forces and muscle activity in asymptomatic subjects during walking, sit-to-stand, and stand-to-sit tasks.

In addition to walking, essential activities of daily living include the ability to rise from a seated position and sit from a standing position. Although many high-quality studies have been performed on these common functional tasks, the objective of the current research is to quantify symmetry indices (SI) of ground reaction force (GRF) and electromyographical (EMG) variables between the non-dominant (ND) and dominant (D) sides of the body in asymptomatic subjects during walking, sit-to-stand, and stand-to-sit tasks. Thirty-five healthy subjects consented to participate in the study that included collection of bilateral GRF and muscle activity of the back, trunk, and legs during the stance phase of walking and sit-stand tasks. No significant differences in SI values between the ND and D sides of the body were found, indicating that asymptomatic subjects walk, stand up, and sit down in a rather symmetric manner. Gait stance time, peak vertical GRF at heel strike, and peak vertical GRF during the entire sit-stand cycle were found to be "perfectly symmetrical" with SI values equal to 1. Future studies will involve similar analyses to determine the level of asymmetry among symptomatic subjects.

Effect of orientation on measured failure strengths of thoracic and lumbar spine segments.

Substantial research has been performed over many years to determine the compressive failure limits of spinal motion segments. However, the majority of studies have not considered the natural alignment of the spine, testing only for pure compression loads. This study tested 27 motion segments, ranging from the T6/T7 to L4/L5 levels, from 13 human cadaveric spines. The segments were oriented in either the neutral position, based on Harrison posterior tangent angles, or in-line axially. Load was applied at a low rate, reducing dynamic effects and in contrast to previous studies, until failure was observed. Force and deformation were measured during testing, with the normalized parameters of stress and strain calculated post-test. Failure forces, adjusted for bone mineral density, were found to decrease by 11% in lumbar segments when oriented while thoracic segment adjusted failure force also decreased by 4.5%. Similarly, orientation decreased failure stress by 12% for lumbar segments and increased it by 25% for thoracic segments. Some correlation was found between failure strength and bone mineral density. After testing, all segments were visually examined to determine the failure mode, and DXA and radiographic scans were performed. Oriented segments exhibited different fracture characteristics than non-oriented segments. The results indicate that segment orientation has a significant effect on failure strength, stress, and strain, and should be considered when determining appropriate load limits.