These arms seem to break on massage tables all the time. I printed mine in Onyx (carbon fiber reinforced Nylon) on a Markforge with strong triangle infill. I'd love to hear if its strong enough with other types of filaments and printers.

The part was 3D scanned and modified to have a solid arm. The original injection moulded part has a series of holes running along the arm to reduce its plastic volume. I removed these holes to make the part stronger for 3D printing. The bottom of the part was made flat for good bed adhesion when printing with FDM. The part was mirrored to replicate the other headrest strut.
The 3D scanner I used was a structured light einscan pro 2X. I used chalk paint to get a good exposure when scanning the part. The scan was modified with Meshmixer.