Hip replacements often lead to one leg ending up a little longer than the other, requiring patients to wear special shoes and causing long-term discomfort. Researchers at the Fraunhofer Institute for Machine Tools and Forming Technology IWU in Chemnitz, Germany have developed a system to be able to make hip implants very accurate.
The team use an optical tool to measure the length of of patients’ legs before the surgery and a specially developed hip implant that can be made longer or shorter. Pre-operative software lets the researchers adjust the length of the implant to match the patient’s anatomy as it will look like following surgery. The team developed the three components to work together as a unified system that can be quickly introduced into existing surgical workflows.
Here are some details about how the measurements are taken, according to Fraunhofer:
First, a plastic box with optical markers on its surface is attached to the patient’s tibia. Holding the limb in extension, the surgeon then takes the leg by the heel and lifts it upward. During this maneuver, a 3D camera is used to record the circular motion described by the optical markers on the patient’s shin. In essence, it’s like using a mathematical compass to draw circles around a point, which in this case is the hip joint around which the leg rotates. In this analogy, the optical markers correspond to the tip of the pencil. After provisionally inserting the implant, a second measurement is carried out. The software program compares the two rotational measurements to verify that the leg length remains the same before and after the intervention. If a difference is detected, the length inequality must be corrected.