Research the tendon excursion method used to calculate moment arms. Given that d
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Question
Research the tendon excursion method used to calculate moment arms. Given that data included the change in tendon length of the Posterior Tibial Tendon and the kinematic of the foot. Create a flow chart of how you would calculate the moment arms based on this method.Research the tendon excursion method used to calculate moment arms. Given that data included the change in tendon length of the Posterior Tibial Tendon and the kinematic of the foot. Create a flow chart of how you would calculate the moment arms based on this method.
Explanation / Answer
Developing accurate estimates for muscle-tendon parameters is important for use in biomechanical studies. The muscle moment arm is one such parameter transforming the force developed by a muscle into a moment about a joint. Current methods for estimating muscle-tendon moment arm (MA) include the tendon excursion method and the center-of-rotation method. These methods have been adapted for in vitro and in vivo MA studies of the lower extremity.
The tendon excursion method is based on the principle of virtual work, which relates tendon excursion and the angular change in joint position. This requires two measurements of tendon length for each moment arm that is computed. Although in theory the angular change should be small to approximate the instantaneous moment arm, in practice, however, large displacements are generally used to overcome the influence of measurement error on the resulting moment arm. For example, Maganaris and colleagues used a 15-degree angular change in joint position when approximating the Achilles tendon moment arm using the tendon excursion method. In doing so, the moment arm is more representative of an average value rather than a specific value at particular joint angle. An obvious limitation of using a large angular change is that it is not possible to determine the moment arm at the limits of a joint’s range of motion. This is particularly relevant at the ankle since plantar flexion strength is greatest when the ankle is dorsiflexed.
Method to calculate moment arms based on the tendon excursion method
Fresh frozen cadaveric lower extremities.
The ankle joint and all tarsal joints fixed in the neutral positions by screws.
A line passing the most inferior tip of the calcaneus and the plantar end of the medial sesamoid kept in a vertical position to an axis of the tibia.
The extrinsic muscles (the extensor hallux longus muscle (EHL) and the flexor hallucis longus muscle (FHL)) and the intrinsic muscles (the extensor hallucis brevis muscle (EHB), the abductor hallucis muscle (ABD), the oblique head (ADD-o) and the transverse head (ADD-t) of the adductor hallucis muscle, and the medial head (FHBm) and the lateral head (FHB-l) of the flexor hallucis brevis muscle) identified. Those were cut at their musclotendinous junction. Dacron braided suture lines were attached to the proximal ends of the cut tendons. The tibia securely anchore to the foot-supporting frame on the jig. Pulleys fixed at proximal ends of the origins of the intrinsic muscles.
Dacron lines sutured to the intrinsic muscle tendons threaded through the pulleys.
The lines threaded through separate guide holes in the vertical frame.
Each tendon loaded with 250g to take up the slack in the tendons during tendon excursions.
The lines were routed around the pulleys of the rotary precision potentiometers to measure voltage produced by the tendon-wire unit during movement.
The voltage automatically convert to values of the tendon excursions by computer software.
A dual-axis electrogoniometer mounted on the calcaneus and the great toe to monitor motion of the first MTP joint.
The values of the first MTP angles calibrate to an accuracy of 0.1 degree and tendon excursion values rounded to 0.1 mm.
The first MTP joint, guide by a metal bar, is move through full flexion to full extension in the sagittal plane.
Tendon excursions from 40 degrees flexion to 60 degrees of extension used to analyze differences of excursions and moment arms between the tendons.
An average of four measurements in each subject used for the analysis.
Tendon moment arms calculated according to the formula that excursion along an arc on a circle equals the radius of the circle multiplied by the subtended angle of the arc in radians.
Moment arms of the first MTP joint motions derived from excursions of the tendons during 100 degrees of flexion-extension defined as the average moment arm.
Instantaneous moment arm at a certain angle calculate using excursions from the certain angle minus 5 degrees to plus 5 degrees.
Differences of averages of excursions and moment arms between the tendons analyze by a two-way ANOVA
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