2 sentences

1. 他摔倒时撞到了后脑。

   tā shuāi​dǎo shí zhuàng​dào le hòu​nǎo.

   He hit the back of his head when he fell.

   Source: Dong Chinese Dictionary

2. 医生说这次撞击伤到了他的后脑，幸好没有影响平衡感。

   yī​shēng shuō zhè cì zhuàng​jī shāng dào le tā de hòu​nǎo, xìng​hǎo méi​yǒu yǐng​xiǎng píng​héng​gǎn.

   The doctor said the impact injured the back of his head, but fortunately, it didn't affect his sense of balance.

   Source: Dong Chinese Dictionary