球状关节是的人类上肢骨骼可以在肩部自由旋转，这也是汽车车轮在转向柱的操控下转向的关键所在。

Ball and socket joints let your arm bones rotate at the shoulders and also allow the wheels of your car to be turned through the steering column.

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与自由驾驶相比，上肢制动使得乡村和城市路段上的驾驶过程更加小心，对于速度和横向移位的调整能力减弱。

Limb immobilisation led to more cautious rural and urban driving, with less adjustment of speed and lateral road position than when unrestricted.

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结论上肢中28个自由度中，当合理地选择其中8 ~ 9个自由度时，即可恢复上肢的大部分功能。

Conclusion By properly choosing 8-9 among 28 freedoms of arm, an artificial limb can mainly restore the function of arm.

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