ACL injuries often have an acutely swollen knee, and an inability to walk on the affected leg. Diagnosis is made through clinical examination as doctor does a range of movement and addditional tests. MRI confirms the diagnosis.
However he may have done some other damage. It all depends on his presentation. If there is any problem with flexing or straightening the knee, or put full weight on it. Or there is any swelling or tenderness then he would need someone to have a look. The degree of injury will vary depending what speed he was travelling, the angle he went over etc.
Depending what he has done, treatment may be rest, elevation, ice and compression and return to mobility with exercises.
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