Quantitative Assessment of Radiocapitellar Joint Stability

Background: The radiocapitellar articulation of the elbow joint is particularly susceptible to subluxation and dislocation. Joint stability can be quantified using the stability ratio, a biomechanical parameter of joint stability defined as the ratio of the maximum dislocating force the joint can resist in relation to the joint compressive force. The purpose of this study was to biomechanically assess the stability of the radiocapitellar joint in the anterior and posterior direction across varying degrees of elbow flexion. Methods: Eight fresh-frozen cadaveric elbows, average age 68.9 years (range 61–73 years; 3 males and 5 females; 7 left and 1 right) were tested. The distal humerus and proximal radius were dissected of all soft tissues to isolate the radiocapitellar articulation. The radius and humerus were mounted on a custom jig that allows for positional adjustment and incorporates a material testing machine. Each specimen was mounted at neutral forearm position and tested at 30, 45, and 60 degrees of anatomical elbow flexion. All specimens were subjected to 10 mm of anterior–posterior displacement for 5 cycles at 20 mm per minute with 40 N of compressive load. Subluxation force, displacement at subluxation force, linear stiffness, stability ratio, and energy absorbed were calculated. Results: In all degrees of elbow flexion, the stability ratio in the posterior direction was significantly higher than the anterior direction by an average of 39.8 ± 32.6% (p < 0.025). Maximum subluxation force was also significantly higher in the posterior direction when compared to the anterior direction (p < 0.027). There was no significant difference in any other parameters. Conclusions: The stability ratio and maximum subluxation force of the radiocapitellar joint when positioned in neutral forearm rotation are significantly greater in the posterior direction when compared to the anterior direction. This finding provides quantitative insights and a biomechanical rationale for the propensity of anterior instability in the radiocapitellar joint.