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The Radiohumeral Synovial Fold: A Lateral Anatomic Landmark for Sizing Radial Head Arthroplasty
Jacob Brubacher, MD; Alexander Lampley, MD; Daniel Blizzard, MD; Grant Garrigues, MD; Marc J. Richard, MD
Duke University, Durham, NC
Intro: Radial head arthroplasty relies on accurate reproduction of native anatomy with significant clinical problems with under- or overstuffing of the radiocapitellar joint. A lateral anatomic structure to judge radial head length would be helpful as the exposure is often laterally-based.
Methods: We performed a LUCL-sparing, extensor split approach on nine cadaver elbows (Fig 1). The fold was labeled with microclips (Fig 2) and imaged with fluoroscopy with elbow in supinated AP. Traumatic injury was simulated with stripping of the humeral column and epicondyle. Fluoroscopy was repeated. A radial head replacement system (Acumed, Hillsboro, OR) was then used. Measurements from the radial head to the synovial clips were made on radiographs with intact LUCL/lateral soft tissue sleeve, after LUCL/lateral soft tissue sleeve detachment, and after radial head replacement for each specimen.
Results: Radiohumeral synovial fold was present in all specimens and found to mark the radiocapitellar joint. Distance from the subchondral surface of the radial head to the radiohumeral synovial fold was on average 1.54 mm (range 0.90 to 2.27, Std Dev 0.42). (Fig 3) Distance from proximal edge of the arthroplasty was 0.54 mm (range from 0.00 to 2.67, Std Dev 0.83) (Fig 4). With lateral ligaments disrupted the distance of radial head to the fold was average of 1.22 mm (range 0.44 to 2.29, Std Dev 0.44). We compared intact vs disrupted ligaments with a paired t-test. The mean difference between the pairs were 0.46 mm. The difference was statistically significant (p=0.031).
Conclusion: This fold was present in all specimens and averaged 1.54 mm (range 0.90 to 2.27 mm) from the radial head subchondral surface. Simulated traumatic injury to the stabilizing lateral structures showed only a 0.46 mm proximal migration of the synovial fold. We found that after replacing the radial head, using accepted clinical guidelines for sizing, the labeled fold was 0.54 mm (range from 0.00 to 2.67) from the arthroplasty. Proximity of the fold to the radial head confirms the potential benefit as a guide when sizing radial head arthroplasty.
The radiohumeral synovial fold is easily visualized from lateral approach, consistently marks the articular surface of radial head, and is not significantly altered by lateral soft tissue injury making this landmark helpful to prevent radial head overstuffing.
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