Abstract
Summary
Consistent load distributions with over-sizing of radial head implants show minimal variance in interosseus ligament (IOL) and triangular-fibrocartilage complex (TFCC) tension, both of which are essential in distribution of load at the elbow.
Introduction:Changes in loading distribution at the elbow have not been studied with radial head (RH) arthroplasty. Difficulty arises concerning distribution variability between loading methods and magnitudes, and with implant oversizing.
Method
RC joint capsule were exposed using the Kocher approach in seven fresh-frozen cadaver Humeri. Specimens were loaded axially in an MTS machine with humeri at 90° and wrist neutral. The arms were cycled in load control between 13N–130N until steady-state was reached for each trial. After loading in neutral, the arms were rotated to 60° supination (60S) and 60° pronation (60P), the test repeated. The radial head was excised and Co-Cr implant inserted. Sizings 0mm, +2mm, +4mm were simulated using 2mm plastic spacers on the stem. A Tekscan pressure map transducer at RC recorded loading. The recorded Tekscan loads were organised according to sizing (native, 0mm, +2mm, +4mm) for each specimen. The max/min load values were recorded and the difference, ΔL was calculated. The Max and ΔL values from each sizing were percentage paired with the respective native value. The ΔL values were used to discern load distribution. A linear regression was done using the RC loading plotted against the applied load to visualise the change of load distribution with changing applied loads. Data was analyzed using one-way analysis of variance.
Result
Max load values and percent pairings are shown (one-way Anova). There was a direct relationship between loading at the RC joint and sizing of the radial head implant. The loading increases with over-sizing of the RH implant. Implant RC loading differences (ΔL) were compared percent paired with native values, and as total values. One-way ANOVA comparisons can be seen showing a trend. A linear regression was done (RC v. Applied load) showing a linear relation between loading at the RC joint and sizing of the radial head implant for all forearm positions.
Conclusion
Linear relation between RC and applied load shows consistent distribution at any load. Equivalence of ΔL values indicate consistent distribution with implant oversizing. Consistent load distributions with over-sizing show minimal variance in interosseus ligament (IOL) and triangular-fibrocartilage complex (TFCC) tension, both of which are essential in distribution of load at the elbow. The TFCC and IOL loading are both reliant on radius position in relation to the ulna. It can be inferred that with minimal change in IOL and TFCC loading, there is little radial translation resulting from additional RH length.
