Evaluation of the Seesaw Test as New Diagnostic Test for Thumb CMC Osteoarthritis

Background: The seesaw test consists of flexion and extension of the thumb metacarpal on the trapezium, with continuous axial pressure to keep the metacarpal base reduced in the carpometacarpal (CMC) joint. We aim to evaluate this maneuver compared with the grind test. Methods: We prospectively enrolled 80 participants from March 2017 to March 2018 at a single institution, excluding those who had previous thumb surgery or pathology. Each participant underwent both seesaw and grind tests by 2 independent examiners. We included 24 patients with a mean age of 73 years in the CMC osteoarthritis group (Eaton stages 2-4) and 44 patients with a mean age of 66 years in the control group (Eaton stages 0 and 1). We calculated the sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and multirater κ measure. Results: The seesaw test had a higher sensitivity than the grind test (42%-71% vs 13%-17%), but a lower specificity (82%-86% vs 91%-98%). The PPV was more consistent between examiners for the seesaw test (63%-68% vs 42%-80%), and the NPV was higher (73%-84% vs 66%-68%). There was a slight agreement between the attending surgeon and the fellow performing the grind test (κ = 0.08) and a moderate agreement between the attending surgeon and the fellow performing the seesaw test (κ = 0.59). Conclusions: The seesaw test is superior to the grind test, with a much higher sensitivity, slightly lower specificity, more consistent PPV, and slightly higher NPV. Therefore, the seesaw test could be a valuable addition or even replacement for the grind test, and we recommend considering it in daily practice.