I can understand why "splint" is called 夾板 in Chinese, but I am having a hard time understanding why it's also called 副木. Does anyone know the origin of this terminology? Thank you!
副木 (or 副子、副え木) is a Japanese loanword. The meanings of 副木 in Japanese are:
To add a tree as a support to prevent plants from falling over.
A board used to hold a broken bone in place. A splint.
Wood used to reinforce the joints in the human body and joints of building materials.
An entry in 世界大百科事典 第２版 says:
This name comes from the fact that wooden boards have been used as splints since ancient times. Currently, wooden materials are often used only for emergency treatment because they do not have the plasticity to conform to the shape of the limb.
副木 entered Chinese no later than the New Culture Movement. The paragraph below is an excerpt from Lu Xun's translation of The Rout by the Russian novelist Alexander Fadeyev in 1930.
He looked iat his delicate, emaciated fingers, at his legs, fettered by the splints, under the blanket; and the old grievances he had tried hard to repress blazed up in him with new force, and his heart ached with pain and distress.
Lu Xun had little knowledge in Russian and he translated the novel based on a Japanese translation of the Russian original. The word 副木 is taken directly from the Japanese translation.
副木 is not old-fashioned as a medical term.
副 is often used for terms of assistance or second in command. You see it used for people such as copilots, associate professors, deputies etc. However it is also sometimes used for items in a similar vein, like back up generators or supplementary/assisting items etc.
木 is literally wood but in this case can be interpreted as saying wooden or stick.
So this term is literally dissected into saying that it is a wooden assistance device, or an auxilary/secondary (bone/limb) made of wood.
In my opinion 副木 is a little old fashioned, like taping a literal stick to the side of someones leg or arm as emergency treatment or in the past. At least that is the mental image it gives me vs a proper modern splint or plaster.