Mi lavis la manojn: la for the owner, and aches

The rule: la, not mia

English marks the owner of every body part: my hands, his head. Esperanto usually does not. PMEG, the standard reference grammar:

Ofte oni uzas la anstataŭ poseda pronomo, se la kunteksto klare montras, kiu la posedanto estas. Tio aparte ofte okazas, kiam oni parolas pri korpopartoj, vestaĵoj aŭ parencoj.

Often one uses la instead of a possessive pronoun if the context clearly shows who the owner is. That happens especially often with body parts, clothing and relatives.

PMEG's examples cover all three:

• Li levis la kapon. - He raised his head.
• La randon de la ĉapelo li ofte ektuŝas per la mano. - He often touches the brim of his hat with his hand.
• Diru al la patro, ke mi estas diligenta. - Tell Father I am diligent.

La patro there is the speaker's father. PMEG glosses li levis la kapon as = li levis sian kapon: the same meaning.

It is a preference, not a law. Mi lavis miajn manojn. is correct, only heavier than it needs to be.

Al si: making the owner explicit

When the bare la could leave a doubt, put the owner after al. With he, she and they that is the reflexive al si:

• Ŝi lavis al si la piedojn. - She washed her feet. (PMEG's example)
• Li rompis al si la brakon. - He broke his arm.

Al ŝi or al li there would mean another woman's feet, another man's arm. The reflexive explains why.

When the possessive comes back

When whose it is matters, the possessive does real work:

• La kuracisto ekzamenis miajn manojn, ne viajn. - The doctor examined my hands, not yours.
• Ŝi tenis mian manon. - She held my hand. Two people, two sets of hands.

The test: if you could drop the English my and lose nothing, use la. If dropping it raises the question "whose?", keep the possessive.

Saying that something hurts

Three forms are standard. With the verb dolori (to hurt), the body part is the subject:

The Reta Vortaro (ReVo), the main online dictionary, remarks that modern usage seems to prefer lia kapo doloras to the older la kapo doloras lin, which you will meet in early texts.

The body part is the subject, so it takes no -n, and doloris is the same for one bone or many (Esperanto verbs never change for person or number):

• Doloris miaj ostoj post la longa vojaĝo. - My bones ached after the long journey.

The compound noun works for any body part: kapdoloro (headache), dentodoloro (toothache), ventrodoloro (stomach ache). This is ordinary compounding.

Mistakes English speakers make