reStav refers to both the "shin" (front of the lower leg) and the "forearm" (below the elbow). If it's necessary to make a distinction, precede the word with 'uS or DeS. reStav is more than just the shin or arm bones. The only way Maltz was aware of for referring to the bone is reStav Hom.

For legs:

Entire lower part of the leg: 'uS cha'neH
Front of lower part of the leg (shin): 'uS reStav
Back of the lower part of the leg (calf): Do'ghI'

Entire upper part of the leg (thigh): 'uS nev'ob

Unless specificity is called for, 'uS is generally left out of 'uS reStav and 'uS nev'ob; even when the context is clear, however, 'uS is seldom if ever left out of 'uS cha'neH.

'uS tends to be used with Do'ghI' only if a distinction or comparison is being made with DeS Do'ghI' (see below).

For arms:

Entire lower part of the arm (forearm): cha'neH
Outer part of the forearm (extending from the back of the hand to outer part of the elbow): DeS reStav
Inner part of the forearm (extending from the palm to the elbow pit [DeS tutren]): DeS Do'ghI'

Entire upper part of the arm: DeS nev'ob

Unless specificity is called for, DeS is generally left out of  DeS reStav and DeS nev'ob; even when the context is clear, however, DeS is seldom if ever left out of DeS Do'ghI'.

DeS tends to be used with cha'neH only if a distinction or comparison is being made with 'uS cha'neH.

Glossing reStav as "forearm" is a result of a mismatch between English and Klingon. Since English has no everyday word corresponding to either DeS reStav or DeS Do'ghI', in a nontechnical conversation, these would both probably be translated into English as simply "forearm." If one pointed to one's DeS reStav and asked "what is this called in English?" the most likely answer would be "forearm." Likewise for DeS Do'ghI'. The specificity is in Klingon only.