Having no technical knowledge of surgery I wouldn't dare offer an answer here, and don't even feel qualified to assess fvasconcellos's answer, which looks wholly convincing to me, but just browsing out of interest I did find "narcotic bow" offered as a straight equivalent for "arco de Kocher". I don't know whether this has any validity or will be of any use, but I offer it for what it's worth:
[PDF] fluoroscopica 2009.cdr
Arco de Kocher. Narcotic bow. Posabrazos. Armrests. Hombreras. Shoulders positioners. Soporte lateral. Side support. Cabezal en U. U Head holder ...
www.surmed.com.ar/fluo_Folleto.pdf