# OPF/PMMA Page System as an Alternative Approach for the Treatment of Vertebral Correctomy
## 2 Materials and Methods
### Kinematic Motion Testing on Spine  
The testing protocol was approved by the Mayo Clinic institutional review board (IRB) (ID: 16-004936). One cadaveric torso was obtained from the anatomy department in our institution. Screening radiographs were used to ensure no fractures, implants, or significant anatomical anomaly was present in the spine. The lumbar region was chosen as this region has the largest vertebrae in the spinal column and frequently undergoes minimally invasive surgeries such as correctomy. The lumbar spine (L\({}_{1}\)-Sacrum) was dissected from the torso leaving the ligaments and muscles surrounding the spine intact. The specimen was then kept frozen at \(-20\)\({}^{\circ}\)C and thawed overnight at room temperature (65 F) in preparation testing. PMMA resin, k-wires, and screws were used to embed the uppermost vertebral body (L\({}_{1}\)) and sacrum in circular acrylic fixtures. The potted specimen was then attached to a custom spine simulator which has been previously designed and implemented on various studies [16; 17; 18]. The spine simulator device has two passive axes of translation in the transverse plane and a third distal axial stage under load control using a pneumatic system. Stepper motors can generate motions in flexion/extension, lateral bending, and axial rotation, and forces and moments are measured using a 6-component load cell (JR3, Woodland, CA, USA) [16].  
Three-dimensional kinematic measurements were obtained using an Optotrak Certus optoelectric data acquisition system (Northern Digital Inc., Waterloo, ON, Canada) with a 3-camera unit and accompanying software (MotionMonitor, Innovative Sports Training Inc., Chicago, IL, USA). Before testing, active motion markers were attached to the L\({}_{2}\), L\({}_{4}\), L\({}_{5}\), and sacrum levels of the spine. The L\({}_{3}\) vertebra was left markerless as this is the level that was removed to mimic correctomy. Fiberglass pins were inserted into each vertebral body and Optotrak sensors were rigidly secured to the pins with aluminum connecting elements. These markers allowed for motion capture of each level as the spine was tested. After marker placement, the spine was placed in the spine simulator and tested in flexion/extension and right/left lateral bending with a pure moment of 7.5 Nm, as previously described [16]. A follower load was not implemented in this study. A follower load is a load that is added to the testing equipment by means of cables to mimic the weight of the torso. Sensor position and moment data from the load cell were synchronized and simultaneously recorded using the MotionMonitor software. Load and displacement data were collected for a total of 4 motion cycles. Spine kinematics for flexion/extension and left/right lateral bending were obtained in the following sequence: (1) intact spine; (2) intact spine with bilateral pedicle screws and instrumented rods at the L\({}_{2}\) and L\({}_{4}\) vertebral levels; (3) correctomy of the L\({}_{3}\) vertebral body with bilateral pedicle screws and rods at the L\({}_{2}\) and L\({}_{4}\) vertebral levels; (4) correctomy of the L\({}_{3}\) vertebral body with bilateral pedicle screws and rods at the L\({}_{2}\) and L\({}_{4}\) vertebral levels, and OPF/PMMA cage. Conditions 1, 3, and 4 are shown in Figure 2. The total angular ROMs (flexion/extension and left/right lateral bending) were determined for the L\({}_{2}\)/L\({}_{4}\) spine segment, to locally analyze the motion of the segment affected by the OPF/PMMA cage; and for the L\({}_{2}\)/Sacrum to analyze the global motion of the spine. Custom-made Matlab codes were developed to obtain outcome data for each motion, each level, and each condition.