Toward Generality of a Framework for Quantifying Biomechanical Stability: Demonstration on the Ankle

This paper presents a mathematical description and experimental investigation of using an industrial robot to evaluate biomechanical stability in human cadaveric ankle specimens. We previously proposed a methodology and parameterizable task-space motion framework for biomechanical investigations of shoulders. The present study aimed to demonstrate the generality and application of our framework to replicate an ankle test protocol from the literature, and to experimentally evaluate the replicated test protocol. Stability tests in cadaveric studies can be performed by applying a known force or torque to the joint, and measuring the resulting linear or angular motion. The relative stability between joint states can be determined by comparing the magnitude of motion, for example, between the intact, injured, or surgically repaired states. Increased joint motion between states can be interpreted as decreased stability, whereas decreased joint motion can be interpreted as increased stability. Comparing the motion between different states can be used to investigate the effects of soft tissue or bony structures on stability. The replicated protocol was tested in a technical pilot study using a fresh frozen human cadaveric ankle specimen. The specimen was tested in the intact state and in three subsequent injury states. This pilot study demonstrated that the framework could successfully be parameterized to conduct tests on the ankle joint. The expected trend for subsequent injury states was progressive instability, and the observed trends from experimental testing aligned with this prior expectation. However, additional work on the framework is necessary to make it truly generalized.