Fig. 1

Calculation method of the CSA of the lumbar multifidus muscle on MRI. Note: The Philips MRI machine uses T2-weighted phase imaging of the L4-5 axial intervertebral space level of the lumbar spine surgery segment to select the cross-sectional boundary of the multifidus muscle by freehand tracing, and the system generates area values for area calculations. a (left) Patient, female, 58 years old, L4-5 intervertebral disc herniation, preoperative L4-5 disc level multifidus muscle CSA tracing method and area value (133.54 mm²). b (right) The method and area value (134.85mm²) of the CSA of the multifidus muscle in the L4-5 disc 6 months after surgery. A represents the CSA of the multifidus muscle (mm²); P indicates the perimeter of the scribed area (mm); M indicates the average gray value of the scribed area; SD indicates the standard deviation of the gray value of the scribed area