Dairy farm worker exposure to awkward knee posture during milking and feeding tasks.

Musculoskeletal disorders are common among agricultural workers, particularly among dairy farm workers. Specifically, dairy farm workers have been identified as being at risk for knee osteoarthritis. Physical risk factors that may contribute to knee osteoarthritis include awkward postures of the knee, such as kneeling or squatting. The purpose of this study was to quantify exposure to awkward knee posture among dairy farm workers during milking and feeding tasks in two common types of milking facilities (stanchion and parlor). Twenty-three dairy farm workers performed milking and feeding tasks; 11 worked in a stanchion milking facility, and 12 worked in a parlor milking facility. An electrogoniometer was used to measure knee flexion during 30 min of the milking and feeding tasks. Milking in a stanchion facility results in a greater duration of exposure to awkward posture of the knee compared with milking in a parlor facility. Specifically, the percentage of time in >or=110 degrees knee flexion was significantly greater in the stanchion facility (X = 17.7; SE 4.2) than in the parlor facility (X = 0.05; SE 0.04; p

Giving way event during a combined stepping and crossover cutting task in an individual with anterior cruciate ligament deficiency.

STUDY DESIGN: Case study. OBJECTIVE: To compare knee kinematics and moments of nongiving way trials to a giving way trial during a combined stepping and crossover cutting activity. BACKGROUND: The knee kinematics and moments associated with giving way episodes suggest motor control strategies that lead to instability and recovery of stability during movement. METHODS AND MEASURES: A 27-year-old woman with anterior cruciate ligament deficiency reported giving way while performing a combined stepping and crossover cutting activity. A motion analysis system recorded motion of the pelvis, femur, tibia, and foot using 3 infrared emitting diodes placed on each segment at 60 Hz. Force plate recordings at 300 Hz were combined with limb inertial properties and position data to estimate net knee joint moments. The stance time, foot progression angle, and cutting angle were also included to evaluate performance between trials. RESULTS: Knee internal rotation during the giving way trial increased 3.2 degrees at 54% of stance relative to the nongiving way trials. Knee flexion during the giving way trial increased to 33.1 degrees at 66% of stance, and the knee moment switched from a nominal flexor moment to a knee extensor moment at 64% of stance. The knee abductor moment and external rotation moment during the giving way trial deviated in early stance. CONCLUSIONS: The observed response to the giving way event suggests that increasing knee flexion may enhance knee stability for this subject. The transverse and frontal plane moments appear important in contributing to the giving way event. Further research that assists clinicians in understanding how interventions can impact control of movements in these planes is necessary.

Anticipatory control of vertical lifting force and momentum during the squat lift with expected and unexpected loads.

STUDY DESIGN: Mixed, repeated measures design. OBJECTIVES: To determine if previous experience with loads of similar weight influences the anticipatory lifting force and postural adjustments during the squat lift. To examine a multijoint, functional task for coordination between stability and movement. To determine if lifting unexpected loads results in trunk loading patterns associated with greater injury risk. BACKGROUND: Workers are increasingly exposed to variability in materials handling thereby increasing the risk of injury. Understanding the control processes underlying lifting will support clinical decision making for preparing injured workers to return to realistic working conditions. METHODS AND MEASURES: Subjects (19 men, 4 women; mean age, 25.4 +/- 3.5 y) lifted a series of boxes weighing 5%, 20%, and 35% of their maximal lifting capacity. The loads were delivered via a gravity conveyor. The identical-appearing loads were ordered so that the subjects lifted several loads of similar weight, immediately followed by a lighter or heavier than expected load based on the previous lift. RESULTS: Generally, the vertical lifting force, force rate, horizontal momentum, and angular momentum increased with an increase in expected load. Higher peak lumbar extensor moments occurred with lighter than expected loads (expected 20% and lifted 5% load = 238.2 +/- 91.2 N-m; expected 35% and lifted 5% load = 278.2 +/- 101.8 N-m) compared to expected loads of similar weight (expected and lifted 5% load = 205.0 +/- 73.2 N-m). Heavier than expected loads led to eccentric trunk movements when there were large mismatches between the expected and actual loads. CONCLUSIONS: The vertical lifting forces and whole body momentum were predictively scaled according to the expected load. The loading phase relationships indicated coordination between the lifting force, force rate, horizontal momentum, and angular momentum. Trunk loading during the lifts with unexpected loads showed patterns associated with increased injury risk.

The reliability and validity of a first ray measurement device.

The need for measuring the mobility of the first ray has been identified. The purpose of this study was to test the reliability and validity of a device built to measure the relative vertical displacement of the first ray. Twenty fresh frozen cadaver feet were sampled (mean age of donor was 70+/-13 years). Dorsal mobility of the first ray was measured by device over three trials of repeated loading using 20 N, 35 N, 55 N and 85 N of force. Radiographs served as the criterion standard for validation of the device. Vertical displacement was measured from x-ray by a digitizing procedure that recorded movement of the first ray during loading. Reliability of the device assessed by intraclass correlation coefficients (ICC) was .98 with standard errors of the measurement calculated to be 0.35 mm. A correlation of agreement value of .97 was determined for the two methods of measurement. Analysis of variance testing found a significant interaction between force and method of measurement. Tukey post-hoc analysis found no difference (F<1.70) between the two methods of measuring first ray displacement in cadaver specimens when the force applied did not exceed 55 N. At 85 N of force (F = 10.05), unwanted movement of the second metatarsal caused the device to overestimate the amount of displacement that occurred specific to the first ray. This measure of first ray mobility should help clinicians and researchers to better investigate foot pathology resulting from faulty mechanics of the first ray.

Physiological measurements of walking and running in people with transtibial amputations with 3 different prostheses.

STUDY DESIGN: A 3-factor (foot type, speed, and mode of ambulation) repeated-measures experimental design was used. OBJECTIVES: To compare the differences in energy expenditure, gait efficiency, and relative exercise intensity in persons with transtibial amputations with various prostheses. BACKGROUND: There is a need for improved prosthetic designs to accommodate physically active persons with lower-extremity amputations. METHODS AND MEASURES: We used progressive speeds of treadmill walking (53.64, 67.05, 80.46, 93.87, and 107.28 m/min) and running (120.69, 134.1, and 147.51 m/min) with 3 different types of prostheses: the Solid Ankle Cushion Heel (SACH) foot, the Flex-Foot (FF), and the Re-Flex Vertical Shock Pylon (VSP) prosthesis. Five physically active men with unilateral transtibial amputations served as subjects (aged 31.6 +/- 4.28 years). RESULTS: The following statistically significant differences (improvements) between the Re-Flex VSP versus the FF and the SACH foot were found. Energy cost: walking (5%), running (11%); gait efficiency: walking (6%), running (9%); relative exercise intensity: walking (4%), running (5%). However, we found no significant differences between the FF and the SACH. CONCLUSIONS: The Re-Flex VSP appears to have a positive effect on energy cost, efficiency, and relative exercise intensity compared with the other prosthetic foot types during walking and running.

Weight-bearing immobilization and early exercise treatment following a grade II lateral ankle sprain.

STUDY DESIGN: Case study. OBJECTIVES: To describe a protocol used in the rehabilitation of a grade II lateral ankle sprain, emphasizing brief immobilization with a removable boot, weight bearing as tolerated, and progression of early exercise. BACKGROUND: The optimum conservative treatment of severe grade II ankle sprains remains undefined. Short-term benefits of early mobilization have won favor over immobilization by casting; however, pain and ankle joint instability often linger. The timing of weight bearing as a variable that influences recovery has largely been ignored when either treatment is considered. METHODS AND MEASURES: The patient was a 17-year-old girl who had sustained a left ankle inversion sprain while playing high school basketball. The sprained ankle was placed in an immobilizer boot for 1 week, and weight bearing was encouraged. She received instructions for active exercise and for resistive exercise with elastic tubing. Volumetric and active range of motion measurements and gait observation provided indicators of rehabilitation progress. A digital inclinometer was used to measure active range of motion in the sagittal plane. Vertical ground reaction forces recorded with an instrumented treadmill documented gait symmetry. RESULTS: The patient responded well to the course of treatment, returning to full participation in basketball 2 weeks after the injury. The injured ankle had 29% (19 degrees) less active range of motion than the nonimpaired ankle at the beginning of physical therapy. The injured ankle also displaced 50 mL more water compared with the nonimpaired ankle at the start of treatment. Four weeks after beginning treatment, the sprained ankle had 4 degrees less active range of motion and displaced 5 mL more water compared with the nonimpaired ankle. As a college athlete, the patient has remained free of subjective complaints of ankle pain, instability, and swelling. CONCLUSION: Weight-bearing immobilization combined with early exercise provided safe and effective treatment for this patient, who suffered a grade II lateral ankle sprain.

Measuring first ray mobility with a new device.

First ray hypermobility has been linked to many abnormal conditions in the foot. First metatarsal vertical displacement is proportional to the measurement of first ray dorsiflexion. A new device that measures first ray mobility has been built and tested. The device applies a dorsiflexing force to the head of the first metatarsal and measures the amount of vertical displacement that results. The design and instrumentation of the device is described. A safe and reliable testing procedure for measuring maximal first ray displacement is discussed. Clinicians could use this measure when selecting treatment options for patients who suffer foot pathologies resulting from faulty mechanics of the first ray.

Comparison of vertical ground reaction forces during overground and treadmill walking.

PURPOSE: The purpose of this study was to compare vertical ground reaction forces walking overground with vertical foot-belt forces for treadmill gait. METHODS: Twenty-four subjects walked overground and on a treadmill at three speeds (slow, normal, and fast), and at comparable cadences and stride length at each of the speeds. Treadmill and overground vertical force curves were normalized to 100% of stance time and compared using Person's product moment correlation. Selected measures from vertical force records were compared between the two modes of locomotion via repeated measures ANOVA (P < 0.05). Post-hoc analysis consisted of paired t-tests with Bonferroni correction. All comparisons were made across conditions (treadmill vs overground) at each of the three walking speeds. RESULTS: The pattern of reaction forces were similar. Correlation between curves were 0.998, 0.983, and 0.983 for the slow (1.03-1.05 m.s-1), normal (1.40-1.44 m.s-1) and fast (1.65-1.71 m.s-1) walking trials. Small (5-9%) but significant differences in force magnitude for the two forms of locomotion were evident during mid-stance for normal (P = 0.00009) and fast (P = 0.0007) walking speeds and in late stance for normal (P = 0.0014) and fast (P = 0.0005) trials. CONCLUSIONS: Although the patterns of the vertical reaction forces for the two forms of locomotion were nearly identical, small but significant differences in selected force magnitudes were evident. The interpretation of locomotion data collected on a treadmill should consider that forces during mid- and late-stance may be different than if the subject walked overground.

Measurement of dorsal mobility in the first ray: elimination of fat pad compression as a variable.

Previous designs for a device to measure first ray mobility have included compression of the first metatarsal fat pad as part of the measurement of displacement or have failed to standardize the force applied to the head of the first metatarsal. In this investigation, assessment of vertical mobility of the first ray of both feet in 14 volunteers was determined using a device that applied dorsiflexing force to the first metatarsal. First ray displacement was measured initially from the plantar surface and then from the dorsal aspect of the head of the first metatarsal. The difference between plantar- and dorsal-surface-measured vertical displacement was highly significant. This study suggests that mobility of the first ray measured from the dorsal aspect of the first metatarsal head eliminated compression of the plantar fat pad from being interpreted as part of the measurement of displacement.

Muscle function and gait in patients with knee osteoarthritis before and after muscle rehabilitation.

Patients with knee osteoarthritis (OA) have reduced functional capacity and muscle function that improves significantly after quantitative progressive exercise rehabilitation (QPER). The effects of these changes on the biomechanics of walking have not been quantified. Our goal was to quantify the effects of knee OA on gait before and after QPER. Bilateral kinematic and kinetic analyses were performed using a standard link-segment analysis on seven women (60.9 +/- 9.4 years) with knee OA. All functional capacity, muscle function and gait variables were initially reduced compared to age-matched controls. Muscle strength, endurance and contraction speed were significantly improved (55%, 42% and 34%, respectively) after 2 months of QPER (p < 0.05), as were function (13%), walking time (21%), difficulty (33%) and pain (13%). There were no significant changes in the gait variables after QPER. To use the QPER improvements to the best advantage, gait retraining may be necessary to "re-programme' the locomotor pattern.

Effects of leg length discrepancies on the forces at the hip joint.

The authors questioned whether leg length discrepancies of the magnitude ordinarily seen after total hip reconstruction (<2 cm) would substantially alter hip joint forces. Using conventional gait analysis techniques to ascertain intersegmental resultant hip forces and moments, the authors used lifts to simulate leg length discrepancies of 2.3, 3.5, and 6.5 cm in 7 normal subjects. The 2.3-cm lift produced no changes. On the side of the lift (long limb), the 3.5- and 6.5-cm lifts modestly decreased mean peak intersegmental resultant hip forces by 6% and 12%, respectively, but not moments. The changes were, however, variable, with a few subjects showing increases and the rest showing decreases in selected forces or moments. On the side opposite to the lift (short limb), the 3.5- and 6.5-cm lifts increased mean peak intersegmental resultant hip forces by 2% to 12%, but not moments except in 1 case (8%). It is concluded that leg length discrepancies of the sort commonly seen after total hip reconstruction would likely cause no substantial changes in hip forces.

The effects of unilateral knee immobilization on lower extremity gait mechanics.

The purpose of this study was to identify the effects of knee immobilization on uninvolved lower extremity joints during gait. Video and force platform data were collected for seven subjects walking normally (N) and with the knee fixed at three flexion angles: 0 degrees (B00), 10 degrees (B10), and 20 degrees (B20). A bilateral, sagittal plane link-segment model was used to determine lower limb kinematic and kinetic measures. Mean data from three normal and five braced gait trials were compared using one-way repeated measures ANOVA (P < 0.05). Significant increases in involved limb (IL) ankle generation work (J.kg-1) during propulsion were evident: (N = 0.249, B00 = 0.295, B10 = 0.293, B20 = 0.308). There were significant increases in peak IL hip power (W.kg-1) in early stance (N = 0.638, B00 = 1.056, B10 = 1.018, B20 = 1.097) and in IL hip absorption work (J.kg-1) during late stance (N = 0.049, B00 = 0.080, B10 = 0.082, B20 = 0.079). The hip of the uninvolved limb (UL) displayed significant increases in generation work (J.kg-1) in early stance (N = 0.089, B00 = 0.183, B10 = 0.149, B20 = 0.179). Normal kinematic and kinetic patterns of other joints were changed with knee immobilization. The major effects were increases in the magnitude of IL peak hip and ankle joint kinetic measures. Fixing the knee in 10 degrees of flexion resulted in the fewest significant changes in normal gait mechanics.

Anterior tibial translation during progressive loading of the ACL-deficient knee during weight-bearing and nonweight-bearing isometric exercise.

Many protocols for rehabilitating the knee following anterior cruciate ligament (ACL) injury or repair call for the use of both weight-bearing and nonweight-bearing exercises. However, not much is known about the strain these exercises place on the passive restraining mechanisms. The purpose of this study was to examine the effect of progressive loading of the knee extensors on anterior tibial translation during weight-bearing and nonweight-bearing isometric exercise. Fourteen subjects diagnosed as ACL-deficient via arthroscopic surgery participated in the study. An arthrometer was used to measure anterior tibial translation during weight-bearing and nonweight-bearing exercises with the knee in 20 degrees of flexion and with a quadriceps load equivalent to 25, 50, 75, and 100% of body weight. Hamstring muscle activations during all testing were monitored to eliminate the possibility of substantial cocontractions. During the weight-bearing exercise, anterior tibial translation was found to be significantly less than that measured during the Lachman's evaluation and the 50, 75, and 100% nonweight-bearing exercises. For the nonweight-bearing exercises, anterior tibial translation was either equivalent to or greater than the Lachman's evaluation. During the weight-bearing exercises, anterior tibial translation was not different under the different loading conditions. During the nonweight-bearing exercises, anterior tibial translation progressively increased with increased loading. The results from this study imply that weight-bearing exercises minimize strain to the passive restraining structures whereas nonweight-bearing exercises will strain these structures, and the magnitude of this strain appears to be proportional to the knee extensor moment.

Dynamic stability in the elderly: identifying a possible measure.

BACKGROUND: The purpose of this research was to assess the ability of trunk acceleration measures to discriminate between the walking patterns of elderly individuals with and without stability problems. METHODS: Twenty volunteers, aged 65 and over, and 19 younger volunteers, all of whom were free of abnormalities or problems that could affect their gait, were recruited for this study. A triaxial accelerometry system was mounted directly over the spine of the upper trunk. Forty seconds of walking data were collected. Using a heel contact switch to define the beginning of the gait cycle, harmonic analyses of each of the 3 acceleration measures were performed on 10 strides. The ratio of summed amplitudes of the even and odd harmonics (index of smoothness) was calculated for each stride and averaged across 10 strides. One-way analyses of variance were used to compare harmonic ratios between groups. Relationships between variables were tested using a correlation analysis. RESULTS: The scores of individuals with stability problems were shown to be significantly different from the younger controls and the older individuals without stability problems for the anterior/posterior and vertical harmonic ratio and peak acceleration measures. CONCLUSION: The results from this research demonstrate that trunk acceleration measures offer the possibility of being able to identify unstable elderly individuals.

Comparison of closed and open kinetic chain exercise in the anterior cruciate ligament-deficient knee.

The purpose of this study was to quantify the amount of anterior tibial displacement occurring in anterior cruciate ligament-deficient knees during two types of rehabilitation exercises: 1) resisted knee extension, an open kinetic chain exercise; and 2) the parallel squat, a closed kinetic chain exercise. An electrogoniometer system was applied to the anterior cruciate ligament-deficient knee of 11 volunteers and to the uninvolved normal knee in 9 of these volunteers. Anterior tibial displacement and the knee flexion angle were measured during each exercise using matched quadriceps loads and during the Lachman test. The anterior cruciate ligament-deficient knee had significantly greater anterior tibial displacement during extension from 64 degrees to 10 degrees in the knee extension exercise as compared to the parallel squat exercise. In addition, the amount of displacement during the Lachman test was significantly less than in the knee extension exercise, but significantly more than in the parallel squat exercise. No significant differences were found between measurements in the normal knee. We concluded that the stress to the anterior cruciate ligament, as indicated by anterior tibial displacement, is minimized by using the parallel squat, a closed kinetic chain exercise, when compared to the relative anterior tibial displacement during knee extension exercise.

Acoustic myography as an indicator of force during sustained contractions of a small hand muscle.

To test the hypothesis that muscle sound amplitudes would remain constant during sustained submaximal isometric contractions, we recorded acoustic myograms from the abductor digiti minimi muscle in 12 subjects at 15, 25, 50, and 75% of a maximum voluntary contraction (MVC). Muscle sounds were detected with an omni-directional electret microphone encased in closed-cell foam and attached to the skin over the muscle. Acoustic amplitudes from the middle and end of the sustained contractions were compared with the amplitudes from the beginning of contractions to determine whether acoustic amplitudes varied in magnitude as force remained constant. Physiological tremor was eliminated from the acoustic signal by use of a Fourier truncation at 14 Hz. The amplitudes of the acoustic signal at a contraction intensity of 75% MVC remained constant, reflecting force production over time. At 50% MVC, the root-mean-square amplitude decreased from the beginning to the end of the contraction (P less than 0.05). Acoustic amplitudes increased over time at 15 and 25% MVC and were significantly higher at the end of the contractions than at the beginning (P less than 0.05). Alterations in the acoustic amplitude, which reflect changes in the lateral vibrations of the muscle, may be indicative of the different recruitment strategies used to maintain force during sustained isometric contractions.

A three-dimensional musculoskeletal model for gait analysis. Anatomical variability estimates.

Three-dimensional coordinates defining the origin and insertion of 40 muscle units, and bony landmarks for osteometric scaling were identified on dry bone specimens. Interspecimen coordinate differences along the anterior-posterior axis of the pelvis and the long bone axes of the pelvis, femur and leg were reduced by scaling but landmark differences along the other axes were not. The coordinates were mapped to living subjects using close-range photogrammetry to locate superficial reference markers. The error of predicting the positions of internal coordinates was assessed by comparing joint centre locations calculated from local axes defining the orientation of segments superior and inferior to a joint. A difference was attributed to: anatomical variability not accounted for by scaling; errors in identifying and placing reference landmarks; the accuracy of locating markers using photogrammetry and error introduced by marker oscillation during movement. Anatomical differences between specimens are one source of error in defining a musculoskeletal model but larger errors are introduced when such models are mapped to living subjects.

EMG profiles during normal human walking: stride-to-stride and inter-subject variability.

The EMG patterns for 16 muscles involved in human walking are reported along with stride-to-stride and inter-subject variability measures. These profiles and measures were developed for basic researchers and clinical investigators as a baseline reference of motor patterns and for use in the diagnosis of gait pathologies. Evident from a comparison of these patterns were some fundamental aspects of the neuromuscular control and the mechanical demands of walking. These comparisons can be summarized as follows: (1) The distal support muscles (soleus, tibialis anterior, gastrocnemii) are the most active muscles, the more proximal muscles are least active. (2) The least variable EMG patterns, as quantified by the normalized inter-subject variability measures, are seen in the most distal single joint muscles, the most variable are the more proximal muscles. The EMGs of the biarticulate muscles, both proximal and distal, exhibit higher variability than the EMGs of the single joint muscles. (3) The detailed patterns and levels of EMG activity demonstrate the different mechanical tasks of each muscle over the gait cycle.