A Passive Ankle Dorsiflexion Testing System for an In Vivo Model of Overuse-induced Tendinopathy

Our work addresses the mechano-biological factors involved in the initiation and progression of overuse induced tendinopathy. The questions we are trying to answer include what factors of exercise, such as frequency, magnitude, and duration of load affect the tendon's response to injury? Current tools such as mechanical measures, histology, and biological assays to evaluate outcome measures are centered and limited to end-of-stage tissue harvesting.

With this model, we can explore in vivo continuous measurements with tools such as ultrasound and MRI. In the field, in vivo models load the tendon in physiologically relevant manners while ex vivo models allow for the measurement of biological responses to injuries. Our protocol combines these two measures for direct measurement of tendon stresses and strains during injuries and the associated biological changes.

We've established an adaptive system to induce tendon injuries, which allows for simultaneous exploration of mechanical and biological factors. Having established this model, future directions include assessing different parameters, therapeutic avenues, and rehabilitation measures. To begin, connect the microcontroller, torque sensor, 3D electromagnetic positioning, and orientation system to a computer.

Turn on the 3D electromagnetic positioning and orientation system. Now turn on the computer, launch MATLAB, and load the code files. Initiate the PDIMFC software to connect the 3D electromagnetic positioning, orientation system, and MATLAB program.

Click on the Connect option and proceed with continuous P and O followed by Start Stock Export Function. Attach and turn on a water-based heating element to the platform to maintain the temperature. to immobilize the left hind limb, tape two splints to place the knee in full extension.

Lightly dorsiflex the ankle by pushing on the toes to ensure that the ankle rotation occurs due to the isolated tendon rather than involving surrounding soft tissues and tension. Then secure the anesthetized animal in a prone position onto the full body platform. Using a nose cone attachment, administer 2.5%isoflurane to sustain anesthesia.

Use zip ties to secure the ankle onto the joint actuator. Attach another zip tie around the toes. Secure the knee split with two zip ties and adjust the axle to position the ankle in full plantar flexion.

Turn on the power supply. To run the system's code, click Run in MATLAB for each code section corresponding to the specific loading test. Now cycle the ankle 50 times, subjecting it to a load equivalent to 15%of the ultimate tensile stress based on the Achilles tendon's ex vivo pull-to-failure tests.

Perform an initial calibration of the tendon by dorsiflexing it three times to an angle of 12 degrees. Incrementally dorsiflex the ankle to increasing angles until the exponential region of the curve is reached, or a maximum angle of 40 degrees is attained. Perform five cyclic mechanical measurements at the final obtained angle for a preloading baseline.

Execute the cyclic fatigue loading regimen for the desired number of cycles. Calculate the slope of the loading portion of the hysteresis curve every 50 cycles. Then conduct five preloading cyclic mechanical measurements at the initially chosen angle to measure tendon mechanical properties prior to cyclic loading.

Carefully detach the zip ties and splint from the animal. Safely transfer the animal back to the recovery chamber and continuously monitor it until it regains adequate consciousness. Once conscious, return the animal to its cage.

Stress-strain curves depicted reduced in vivo tendon mechanical properties with the increasing number of applied cycles. Hematoxylin, eosin, and Masson's trichrome-stained images of tendon samples demonstrated that increasing the number of cycles applied results in more rounded cells, hyper cellularity, fiber disruption, and fiber crimping.