Intradiscal pressure measurements in normal discs, compressed discs and compressed discs treated with axial posterior disc distraction: an experimental study on the rabbit lumbar spine model

Abstract

Intervertebral disc (IVD) pressure measurement is an appropriate method for characterizing spinal loading conditions. However, there is no human or animal model that provides sufficient IVD pressure data. The aim of our study was to establish physiological pressure values in the rabbit lumbar spine and to determine whether temporary external disc compression and distraction were associated with pressure changes. Measurements were done using a microstructure-based fibreoptic sensor. Data were collected in five control rabbits (N, measurement lying prone at segment L3/4 at day 28), five rabbits with 28 days of axial compression (C, measurement at day 28) and three rabbits with 28 days of axial compression and following 28 days of axial distraction (D, measurement at day 56). Disc compression and distraction was verified by disc height in lateral radiographs. The controls (N) showed a level-related range between 0.25 MPa-0.45 MPa. The IVD pressure was highest at level L3/4 (0.42 MPa; range 0.38-0.45) with a decrease in both cranial and caudal adjacent segments. The result for C was a significant decrease in IVD pressure (0.31 MPa) when compared with controls (P=0.009). D showed slightly higher median IVD pressure (0.32 MPa) compared to C, but significantly lower levels when compared with N (P=0.037). Our results indicate a high range of physiological IVD pressure at different levels of the lumbar rabbit spine. Temporary disc compression reduces pressure when compared with controls. These data support the hypothesis that temporary external compression leads to moderate disc degeneration as a result of degradation of water-binding disc matrix or affected active pumping mechanisms of nutrients into the disc. A stabilization of IVD pressure in discs treated with temporary distraction was observed.

Fig. 1

The samba sensor principle

Fig. 2

a Radiographic verification of correct sensor placement inside the nucleus pulposus of L2/3 segment adjacent to a loaded disc. b Lateral Radiograph of the lumbar spine before application of load. Note the processus transversus located laterally the intervertebral discs. Median physiological disc height at L3/4 was 2.01 mm. c Lateral radiograph of the lumbar spine after application of temporary disc loading. Note slight endplate reactions at the loaded segment and the significant disc height reduction (1.47 mm, P=0.009 vs N). d Lateral radiograph of the lumbar spine after application of temporary disc loading and axial distraction. Note the disc height re-establishment (2.02 mm, P=0.836 vs N)

Fig. 3

Intervertebral disc pressure measurements (MPa) in healthy control discs (N) with standard deviations, n=5, spine level TH11/12-L5/6

Fig. 4

Intervertebral disc pressure measurements (MPa) and standard deviation at spine level L3/4: comparison between controls (N1–N5, median), compressed (C1–C5, median) and distracted (D1–D3, median) discs. In both C and D, IVD pressure was significantly reduced compared to controls (C: P=0.009; D: P=0.037) while no significant difference was found between C and D (P=0.852)