In Vivo Measurement of Intradiscal Pressure Changes Related to Spinal Manual Therapy in an Animal Model: A Feasibility Study

Research Objectives To determine the feasibility of recording in vivo intradiscal pressure (IDP) during spinal manual therapy (SMT) using commercially available and custom-made clinical devices in a feline intravertebral disc model. Design Experimental study. Setting Basic laboratory. Participants Adult male felines (5.3-6.4 kg). Interventions All experiments were reviewed and approved by the Institutional Animal Care and Use Committee. Anesthesia was induced with isoflurane and maintained with sodium pentobarbital (Nembutal; 35 mg/kg intravenously). Miniature pressure catheters (Millar SPR-1000) were inserted into the L4-L5 disc via the left intervertebral foramen using an 18-gauge needle secured with cyanoacrylate. The Activator IV device (Activator Methods Int. Ltd., Phoenix AZ) with an attached impedance head including a dynamic load cell (Model 208C04; PCB, NY) and a tri-axial accelerometer was used to deliver spinal manipulative thrusts onto the L4 vertebrae at a device setting of 2 (2-3ms thrust duration, average force ∼ 81N). A custom-made motorized device having a hinged platform in which the caudal portion moved in cyclical downward and upward pattern (15, 20, or 30 degrees) at a fixed rate of 0.14Hz was used to deliver spinal mobilization. Main Outcome Measures Intradiscal pressure (IDP; kPa). Results Baseline IDP was ∼6 kPa. Activator IV manipulative impulses yielded similar peak IDP (16.7 - 18.0 kPa), with the initial spinal manipulative impulse IDP peak typically being slightly less than subsequent impulses. Peak IDP pressures during table flexion were consistently between 14.0 - 14.7 kPa. Conclusions IDP for each distinct type of SMT was uniform throughout the intervention delivery supporting the feasibility of in vivo recordings in a feline intravertebral disc model for future mechanistic studies involving manual therapy and pathological disc models. Author(s) Disclosures Authors declare no conflicts.