['Elevated serum levels of creatine kinase (CK) reflect skeletal muscle injury, which may lead to renal dysfunction following surgery. High CK levels are known to occur after neurosurgical interventions, especially following lateral positioning, but a consensus on possible risk factors is still lacking. Here we investigate risk factors for postoperative CK excess in a patient population at high risk (lateral position) with a special focus on the influence of intraoperative neurophysiological monitoring (IONM), particularly Motor Evoked Potentials (MEPs).', 'We analyzed patient charts from elective surgeries in lateral position between 2010 and 2012 and where IONM was performed and where postoperative CK-levels were available. In these patients, the anesthesia regimen excluded muscle relaxants. Patient charts were reviewed retrospectively for patient characteristics, CK levels and indicators of renal dysfunction. The MEP response intensity was measured. These patients were compared to a matched (age, BMI, surgery duration) control group of patients operated with IONM, but operated in prone or supine position.', 'We included 96 patients (55 female, mean age 50years). The maximal CK level (CKmax) occurred on postoperative days 2 or 3 (mean 1763U/L). In a multivariate linear regression model, log(CKmax) correlated positively with duration of surgery (p<0.001) and BMI (p=0.007), and negatively with age (p=0.007), but not with MEP response intensity (p=0.481). We did not observe impaired renal function.'] Is elevated serum creatine kinase after neurosurgeries in lateral position with intraoperative neurophysiological monitoring associated with OP duration , BMI and age?