express.Router()问题

// 定义了一个detail.js路由文件:
const express = require('express');
const router = express.Router();
const Movie = require('../model/movie');

// 获取param
router.param('id', (req, res, next, id) => {
	next()
})

router.get('/movie/:id', function(req, res) {
	let id = req.params.id;
	Movie.findById(id, function(err, movie) {
		if(err) {
			console.log(err);
		}

		res.render('detail', {
			title: 'website ' + movie.title,
			movie: movie
		})
	});
})
module.exports = router

app.js :

const express = require('express')
const app = express()
const detail = require('./routes/detail.js')

// 失败，报错404
app.use('/movie/:id', detail)
//成功
app.use(detail)
//成功
app.get('/movie/:id', detail)

问题来了，为什么app.use(’/movie/:id’, detail)会报404错误呢？正确写法应该是怎么样呢？萌新求教