Interference in intradiscal pressure measurement using a needle‐type pressure transducer

Abstract

The invasive needle‐type pressure transducer is widely used in the measurement of intradiscal pressure (IDP). However, the protocol for measuring IDP is not a standard procedure. Most of the in vitro studies employ an anterior insertion of the transducer while most of the in vivo studies employ a lateral insertion. The interference between transducer and disc needs to be understood before comparing the results of the two different protocols. Sixteen porcine one‐motion segments (T9–10, T11–12) were used. The transducers were inserted into the disc from either the anterior site (N = 9) or the lateral site (N = 7). All specimens had axial compressive force applied on eight locations along the mid‐sagittal line on the top of the cast to simulate flexion, neutral, and extension bending moments. The effects of bending moment and alignment of pressure transducers on the IDP were analyzed. Both the alignment of the transducer and bending moment affect the measurement of IDP. The IDP measured by an anterior‐inserted‐transducer (ant‐IDP) declined gradually from flexion through neutral to extension. The IDP measured by a lateral‐inserted‐transducer (lat‐IDP) during flexion and extension is higher than the IDP measured during the neutral condition. The ant‐IDP is higher than the lat‐IDP during flexion and neutral, but lower during extension. The ant‐IDP may be overestimated, compared to lat‐IDP, during flexion and neutral but underestimated during extension. We suggest that lateral insertion of transducer may be a better choice for both in vivo and in vitro IDP measurement.