Incidence and prognostic factors of postoperative C5 palsy after cervical OPLL surgery: a nationwide prospective multicenter study.

This prospective multicenter study examined the incidence, risk factors, and recovery course of C5 palsy after surgery for cervical ossification of the posterior longitudinal ligament in 482 patients treated at 28 institutions between 2015 and 2017. C5 palsy was defined as a postoperative decline of at least one grade in deltoid MMT strength. Overall, 6.0% of patients developed C5 palsy, with notable variation by surgical procedure: 4.0% after anterior decompression and fusion, 4.6% after laminoplasty, and 11.8% after posterior decompression and fusion. Nearly half of the affected patients developed symptoms on the day of surgery, and deltoid strength dropped from a mean of 4.7 preoperatively to 2.3 at onset. Over the following two years, 81% of patients regained their preoperative motor function. Better outcomes were observed in younger individuals and in those without concurrent biceps brachii weakness, whereas older patients and those with multimuscle involvement showed less favorable recovery. These findings clarify the expected clinical course of C5 palsy after OPLL surgery and highlight patient factors that may help guide prognosis and perioperative counseling.