What is the potential serious pitfall of performing flexion-extension studies in the acute setting?

Paraspinous muscle spasm may mask instability due to ligamentous injury in the acute setting (false negative). Instability may develop after muscular spasm resolves (described as delayed instability, which is really a mis-nomer). If evaluation for ligamentous injury is desired, it may be prudent to discharge the patient in a cervical collar and perform a flexion-extension study in 1 to 2 weeks.