Towards the quantification of end-feel for the assessment of passive joint motion

Abstract

Passive joint stability tests require the relative displacement of articular components in a specific translation or rotation. Subjective interpretations of these tests include the evaluation of 'end-feel' leading to diagnoses and treatment protocols. However, the clinical concept of end-feel has not been defined in quantitative terms, making communication between individuals ambiguous. The purpose of this paper is to suggest a definition of end-feel and a generalizable approach that can be used to quantify end-feel. In order to describe the force–displacement properties of the joint, single points alone appear to be inadequate, as may methods using average stiffness. The force–displacement properties of a joint can be represented as a continuous mathematical function. Evaluating the first derivative and the second derivative of the force–displacement function improves the description of joint properties compared to single point methods. The second derivative, the rate of change of stiffness, may be indicative of the onset of constraints and the sharpness with which restraints come into play. Therefore, we suggest that the second derivative of the force–displacement curve is most likely to contain important clinical information; however, validation of this proposal must still be carried out. New concepts proposed in this paper include the use of kinanthropometric normalization to adjust tests for the subject's body weight. Directions for future research include the documentation of diagnostic criteria, elucidating relationships between instability and symptoms, and determination of the efficacy of treatment regimes.

Keywords:

• FORCE–DISPLACEMENT ANALYSIS
• JOINT INSTABILITY
• MANUAL THERAPY
• ORTHOPAEDIC ASSESSMENT