A mobile device to quantify the forces and angles required to overcome knee arthrofibrosis in the clinic

Knee arthrofibrosis, a condition where scar tissue limits motion of the knee, is encountered after 4-35% of ligament surgeries. It is treated either by manually manipulating the knee to break scar tissue or with further surgery. The work herein sought to design, build and evaluate a means of quantifying the forces and angles required to overcome arthrofibrosis during knee manipulation. Physicians are thought to rely upon several cues including the a) initial resting angle of the upper and lower leg, b) torques and angles at the break point of scar tissue, and c) maximum angle and torque following manipulation. To quantify these cues, the device was built to be mobile and attach to a common knee brace. Fixtures were designed to afford normal physician postures and manual control of torque. The device utilizes load cells, rotary potentiometers, 3D printed parts and integrated circuits. Graphical user interfaces on a mobile phone allow in-the-loop evaluation and a database is used for subsequent, offline analysis. A preliminary clinical study with four participants shows the device can measure maximum torque of 31 Nm, rotational angles of 130 degrees, and combine both measures to differentiate knee stiffness over a range of motion.