Office of Technology Transfer – University of Michigan

Ball Joint Center Locating Method Using Data From Attached Inertial Measurement Unit

Technology #5410

Joint Center Locating Using Inertial Measurements

Researchers from the University of Michigan Mechanical Engineering Department have developed a technology that determines the center of rotation of joints by using inertial measurement units. The technology can be used to determine knee, hip, and elbow pivot points for locating orthotic and prosthetic devices. The alignment system does not require external equipment such as MRI, CT, or specialized camera setups, allowing it to be used in operating rooms. Additionally, the device is simple to use, unlike the other methods that require a skilled operator. These factors combine to create a much lower cost method for determining the center of rotation of joints. Tests have been performed that have validated the ability of the device and method to locate centers of rotation as accurately as competing methods.

Joint Center Locating

Prosthetic devices, especially knee and hip joints, need to be carefully aligned to ensure that weight is properly distributed during use. The challenge presented to physicians is locating the center of rotation of the joint for placement during surgery. Current methods involve expensive, large camera setups that require skilled operators, using CT or MRI scanners, or having a surgeon locate the center by feel. These methods are costly, require specialized equipment, or are imprecise. With 500,000 knee arthroplasty procedures per year in the US, reaching 3.5 million by 2030 (8.5% CAGR), and over 200,000 hip replacements in the US per year, there is a substantial market for a product that could better locate a joint’s center of rotation.

Applications and Advantages


  • Knee arthroplasty
  • Hip replacement
  • Knee brace alignment


  • Compact enough for us in the operating room
  • Low cost
  • High accuracy and precision
  • Non-invasive