Simulating Fall-Induced Wrist Fractures Using a Cadaveric Human Forearm Specimen

Begin with a human cadaver forearm specimen to model fall-induced wrist fractures.

Remove soft tissue from the upper forearm to expose the radius and ulna.

Cut the forearm bones at a fixed location.

Position the forearm in pronation so the radius crosses over the ulna, matching wrist orientation during a fall.

Pour self-curing resin around the exposed bones and let it cure to immobilize the specimen.

Secure the specimen in a compression testing machine.

Position the palm flat against the loading plate and apply a controlled force to ensure full contact.

Next, apply a higher downward force while recording actuator displacement and the resulting force from contact with the specimen.

On the force–displacement curve, the initial linear region represents wrist stiffness in the elastic region, followed by the yield point where plastic deformation begins, and ultimately the peak force that represents the maximum load-bearing capacity.

After fracture, the curve drops sharply, indicating a loss of resistance to loading.

Calculate the area under the force–displacement curve to quantify the work associated with each of these force–displacement values.

To begin, collect fresh frozen forearm specimens that have been disarticulated at the elbow from an anatomical donation registry. Place the specimen on an absorbent pad to thaw at room temperature for 18 to 20 hours.

After thawing, remove any packaging and absorbent pads from the specimen. Place the specimen on an absorbent pad for dissection.

Next, with a ruler and marker, measure and mark the location three inches proximally from the styloid process of the ulna. Use a scalpel, surgical scissors, and rat-tooth forceps, and remove all soft tissue proximal to the marked location to expose the radius and ulna.

Measure and mark the location six inches proximally from the styloid process of the ulna on the exposed radius and ulna. Then, dissect and remove the radius and ulna sections proximal to this location. Place the proximal end of the exposed radius and ulna into a table vise and tighten. With an oscillating saw or handsaw, cut the exposed bone at the six-inch mark.

For specimen mounting, first seal the bottom of a three-inch by three-inch by three-inch square aluminum extrusion section with aluminum foil and laboratory tape. Place the specimen against the wrist mounting fixture and secure it using trigger clamps.

Position the radius and ulna so that they cross each other, mimicking a pronated hand position. Center the specimen with the proximal end of the radius and ulna approximately 0.25 inches from the bottom of the extrusion.

Now, mix self-curing acrylic per manufacturer specifications. Fill the extrusion to 0.25 to 0.50 inches from the top.

After the acrylic has cured for 15 minutes, proceed for biomechanical testing. For biomechanical testing, place the biaxial stage on the material testing machine stage. Secure the bottom portion with four M10 screws and the top portion with four M8 screws. Attach the extrusion holder to the top portion of the biaxial stage using three M8 screws.

Then, fix the 10-kilonewton load cell to the actuator with six M10 screws. Secure a three-inch by three-inch loading platen to the load cell with six M8 screws. Now, insert the load and torsion transducers into the material testing machine frame and turn on the machine.

Launch the material testing machine software and perform the required system calibration of the load cell and set system limits. Raise the actuator to its highest position to allow full use of the range of motion.

Place the square extrusion section of the mounted specimen into the extrusion holder on the material testing machine stage. Then tighten the two M4 set screws to secure the specimen.

Move the biaxial stage to align the specimen with the actuator from left to right. Align the specimen from front to back so that the loading platen covers the breadth of the palm.

Now, lower the material testing machine frame so that the loading platen is nearly touching the palm of the specimen. Monitor the measured load in the software to ensure no force is applied to the specimen.

Review the testing setup before fracture induction to ensure that all screws on the plate are fully tightened. Use an Absolute Ramp Function to pre-load the specimen at a Loading rate of 0.33 millimeters per second until a force value of two newtons is reached.

Next, use the Absolute Ramp Function to pre-load the specimen at 0.33 millimeters per second until a force of 50 newtons is reached. Move away from the specimen at the same rate until a force of 10 newtons is reached. Inspect the specimen before resuming or canceling the test when prompted.

Ensure that the specimen wrist remains in extension with the loading platen in contact. Click Resume in the pop-up prompt window.

Then use the Absolute Ramp Function to load the specimen at a rate of 3.3 millimeters per second until failure occurs, with an End-of-ramp load value of 5000 newtons, adjusted for the load cell capacity.

After fracture induction, raise the material testing machine frame and loosen the set screws. Remove the specimen and cured self-curing acrylic from the aluminum extrusion.

Collect a radiograph of the wrist to confirm successful fracture induction. Analyze the force-displacement graph to assess stiffness, yield point, maximum force, fracture force, work to maximum force, and work to fracture force before further testing or disposal.