Body parts+adjective requiring possessive adjective

[michael rivers]

I know body parts are generally preceded by the definite article.

But I've heard that when the body part is qualified by an adjective, this rule is flexible.

Is it correct to say the definite article is always replaced by a possesive adjective when an adjective qualifies a body part? 

Elle a haussé ses lourdes epaules 

I've heard "droite" and "gauche" may be exceptions to the above rule but I'm not sure why.

Would this rule also apply when one performs an action on a part of another person's body?

Ils lui ont essuyé le visage

would become 

Ils lui ont essuyé son visage sale.

[George Hunt]

Well all rules have exceptions ,but I think you have the gist of this.

As for "la main droite" etc  the reason seems to be that the phrase is so compact and common that it falls into  the category of unqualified body parts.

Not sure what other examples of this there are,but it does make sense  to me

You might also have "avec sa main droite abimée il a réussi à ouvrir la porte" Or "la main droite abimée .....etc". 

I think either would work.

[Chantal Savignat]

Ils lui ont essuyé le visage

would become

Ils lui ont essuyé son visage sale. (1)   =  Ils ont essuyé son visage sale (2)

The form (2) is better. (1) is not really wrong but not used.

Yes I never thought about that before. But Yes when an adjective qualifies a body part the definite article is always replaced by a possessive adjective except for "droite" and "gauche".

Even for another person's body.

"avec sa main droite abimée il a réussi à ouvrir la porte" Or "avec la main droite abimée..."

Yes the two forms are correct, I think it's because of "droite".