150RTG1S Rabbit Knee Tester

Stiffness and swelling are common side effects after knee surgery or injury. Through use of tedious physical therapy, patients strive to recover full range of motion after months and in rare cases even years. These common complications are the driving force behind a new 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 surgery or injury.

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. For this study, he 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.

Problem Solving to Improve Design

Pursuing a deep understanding of the Dr.’s application needs, TestResources engineers studied his requirements and proposed a new tester design. Engineers noticed the previous study’s 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. 
Customer Quote

Delivering Educated Solutions 

Keeping Dr. Fertala’s requirements in mind, TestResources engineered a solution focused on precision and freedom of motion. TestResources followed good rules of design to configure a 150RTG1S 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. 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 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 150RTG1S Torsion Test Machine to research improving painful knee recoveries. For this study, Dr. Fertala will measure 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.