Looking at past studies, Dr. Fertala found that his predecessors used a unique testing device created to measure the effectiveness of drug therapy on rabbit knees by carefully measuring free-motion torque and range of motion in knee joints. Dr. Fertala wanted a more accurate machine to perform these measurements, so he enlisted the help of TestResources to engineer a similar tester. Stiffness and swelling are common side effects after injury or knee surgery. Patients strive to recover full range of motion after months and in rare cases even years of physical therapy. These common complications are the driving force behind a study being conducted by Dr. Andrzej Fertala at Thomas Jefferson University. Dr. Fertala aims to reduce patient recovery time by studying the use of drug therapy to minimize stiffness after injury or surgery.
The Challenge: Unique Application Requirements
For this study, Dr. Fertala needs precise measurements accurate enough to differentiate a healthy rabbit knee from an injured knee, and to analyze performance based on drug dosages and various periods of healing. The machine should also allow a complex knee joint to freely flow in a natural angle when bending.
The Design: Re-Engineering Existing Systems to Provide Budget-Friendly Solutions
Pursuing a deep understanding of the Dr.’s application needs, TestResources' application engineers studied his requirements carefully. While reviewing the previous study's tester, the engineers noticed the tester had design qualities which could be improved upon.
- The current rack and pinion solution could create unwanted noise in the load reading.
- The tester used load cell and movement arm calculations to estimate torque measurements. As Dr. Fertala’s primary parameter, it would be better to avoid using calculations to find torque measurements.
- Frictional errors could occur due to a complex load train with several bearings.
The Solution: Torsion Test Machine for Rabbit Knees
Keeping Dr. Fertala’s requirements in mind, TestResources engineered and proposed a solution that focused on precision and freedom of motion. TestResources followed good rules of design to configure a Torsion Test Machine specifically designed for testing rabbit knees. This solution allowed for:
- Precise torque measurements with a torque motor directly under the torque cell in lieu of a rack and pinion solution. The accuracy of the machine shows consistent torque values down to smaller than 0.01 Nm.
- More exact data results with a high-resolution digital encoder for angle measurement.
- Five degrees of freedom to allow the knee to follow natural bending motions.
- Noise reduction with the elimination of all bearings and joints between the specimen
and the torque cell. - Lower expenses due to improved design practices.
Researching Recovery
Dr. Fertala will use the TestResources Torsion Test Machine to research improving painful knee recoveries. For this study, Dr. Fertala will measure the range-of-motion angle of the knee joint up to 0.2 Nm knee torque, in flexion and extension, to create precise hysteresis plots of torque vs. angle.
