Biomedical subjects

B A MacWilliams

Publications and source records attributed to B A MacWilliams.

7 recordsLinked to original sources

PubMed1999

Hamstrings cocontraction reduces internal rotation, anterior translation, and anterior cruciate ligament load in weight-bearing flexion.

Strengthening of the hamstrings is often recommended following injury and reconstruction of the anterior cruciate ligament. It has been suggested that hamstrings activity stabilizes the knee and reduces anterior cruciate ligament load during weight-bearing flexion; however, the effects of hamstrings cocontraction on the kinematics and mechanics of the normal knee have not been assessed at physiological load levels. The aim of this study was to determine whether the addition of hamstrings force affects knee rotations, translations, and joint and quadriceps force during flexion with loads at physiological levels applied to the muscles and joints. Eight cadaveric knee specimens were tested with a servohydraulic mechanism capable of applying controlled dynamic loads to simulate quadriceps and hamstrings muscle forces throughout a physiological range of motion. A constant vertical load of physiologic magnitude was applied to the hip, and quadriceps force was varied to maintain equilibrium throughout flexion. Two conditions were tested: no hamstrings force and a constant hamstrings force equivalent to the vertical load. Hamstrings force significantly reduced internal rotation (p<0.0001) and anterior translation (p<0.0001), increased quadriceps force (p<0.0001) and normal resultant force on the tibia (p<0.0001), and reversed the direction of the shear force on the tibia (p<0.0001). These results suggest that hamstrings strengthening following anterior cruciate ligament injury may benefit anterior cruciate ligament-deficient and reconstructed knees by reducing the load in the ligament; however, they also imply that this comes at the expense of efficiency and higher patellofemoral and joint forces.

Aged↗

PubMed1999

Defining flatfoot.

Pes planus is a term frequently used in describing flatfoot; however, no study has objectively defined flatfoot. We evaluated the single leg stance footprint of 40 feet in 21 people with no history of foot problems, using pressure-sensitive film and a Harris mat. The medial and lateral aspects of the forefoot, midfoot, and hindfoot were assessed. The midfoot was further analyzed by dividing the medial midfoot force by the total midfoot force. The mean medial midfoot force/total midfoot force was 11.1% (SD = 6.5%). Pes planus was defined as the medial midfoot force/total midfoot force > 24.0% (mean + 2 SD). A population associated with pes planus (124 feet in 63 patients with Marfan syndrome) was then evaluated in the same fashion. Although the mean medial midfoot force/total midfoot force was not statistically different (16.0%), a distinct group of patients (25%) had forces that were outside the range of normal midfoot forces.

Adult↗

PubMed1998

Variation of arterial compliance within the cardiac pressure pulse.

Past investigations of in vivo arterial behavior have concentrated on determining material properties based upon the maximum and minimum pressure and diameter measured over a pulse cycle. A new in vivo technique, based upon continuous measurement of pressure and flow, has been developed to study arterial compliance throughout the pulse cycle. Compliance in the abdominal aorta of rats showed different behavior during the rising and falling portion of the pressure pulse. Previous investigations of canine arteries which used different methods are consistent with these findings. This study demonstrates the utility of a new measurement technique and shows some trends in compliance within the pulse cycle which have neither been revealed by static tests nor by dynamic tests which focused on pulse averaged values.

Animals↗

PubMed1998

A repeatable alignment method and local coordinate description for knee joint testing and kinematic measurement.

A method for aligning cadaver knee specimens to a mechanical testing rig and determining local anatomical coordinate systems using landmarks identifiable on plane X-rays is introduced. Three sequential rotational alignments arc used to position the femur and tibia relative to the coordinate system of the testing mechanism. To validate this methodology five independent observers aligned the same knee specimen. The maximum error in the alignment orientations of the tibia and femur was 2.2 from the mean. These small misalignments produced variations of up to 4.7 in tibio-femoral rotations measured during knee flexion. Kinematic measurements of 15 specimens aligned using this procedure indicate that knee alignment is reproducible and physiologically relevant.

Biomechanical Phenomena↗

PubMedDate not supplied

Plantar pressure and radiographic changes after distal calcaneal lengthening in children and adolescents.

Eleven feet (nine patients) with symptomatic flatfoot deformities of various etiologies that had failed nonoperative treatment underwent distal calcaneal lengthenings. Pre- and postoperative plantar pressure measurements and radiographic parameters were compared and a postoperative clinical evaluation was performed using the AOFAS ankle and hindfoot scoring system. Follow-up ranged from 4 to 20 months (mean, 11.1 months). Plantar pressure parameters including contact area, mean, and peak pressures indicated significant lateral shifts in the weight-bearing surface of the foot. The most significant radiographic changes were an improvement in the talonavicular coverage angle (mean, 17.3 degrees) on the anteroposterior view and an improvement in the talo-first metatarsal angle (16.2 degrees) on the lateral view. The average postoperative American Orthopedic Foot and Ankle Society score was 90 with seven excellent, three good, and one poor results.

Adolescent↗

PubMedDate not supplied

Characteristic ground-reaction forces in baseball pitching.

Overhand throwing requires contributions from and interaction between all limb segments. Most previous investigations have concentrated on the throwing arm itself, yet poor mechanics at the arm may originate in the lower extremities. Multicomponent ground-reaction forces of both the push-off and landing limbs were measured in six collegiate and one high school level baseball pitchers. Full body kinematics were simultaneously recorded to correlate phases in the pitching cycle with the force data. Pitchers were found to generate shear forces of 0.35 body weight in the direction of the pitch with the push-off leg and to resist forces of 0.72 body weight with the landing leg. Wrist velocity was found to correlate highly with increased leg drive. This study validates the clinical impression that the lower extremity is an important contributor to the throwing motion. Based on this study, strengthening of the lower extremities could be inferred to be important both to enhance performance and to avoid injury.

Adolescent↗

PubMedDate not supplied

The foot in Marfan syndrome: clinical findings and weight-distribution patterns.

The feet of Marfan patients are typically described as pes planovalgus. We evaluated the single-leg-stance footprint of 124 feet in 63 patients with the Marfan syndrome by using pressure-sensitive film and a Harris mat. Forty feet in 21 people with no history of foot problems were evaluated as normal controls. The medial and lateral aspects of the fore-, mid-, and hindfoot were assessed. The midfoot was further analyzed by dividing the medial midfoot force by the total midfoot force. The mean medial midfoot force/total midfoot force (MM/TM) in the control population was 11.1% (SD, 6.5%). Pes planus was defined as the MM/TM force > 24.0% (mean + 2 SD). The mean MM/TM force in the Marfan group was not statistically different (16.0%) from controls. The distribution, however, revealed two distinct types of weight-bearing patterns. Of the Marfan group, 74.8% had medial forces within the standard distribution of the normal control population. Only 25.2% of the Marfan patients had forces that were outside the range of normal midfoot forces and were defined as pes planus. Analysis of the patient's ligamentous laxity and the foot function in the Marfan population revealed no statistically significant correlation to the type of weight-bearing pattern of the foot.

Adult↗