In vitro biomechanical evaluation of a strutted intradiscal spacer for lumbar discectomy

Abstract

Background: Discectomy plus implantation of a strutted intradiscal spacer has been shown to reduce reoperations and reherniations versus discectomy alone following lumbar disc herniation. This study explored the underlying biomechanics of the intradiscal spacer.

Methods: Six fresh-frozen cadaveric lumbar spine specimens (L2 to L5) from three donors were used. Following box annulotomy to simulate disc herniation, a discectomy was performed. One segment from each donor was randomly assigned to either an untreated control group or the test group where an intradiscal spacer was implanted. A six degree of freedom universal spine tester assessed range of motion (RoM) in flexion/extension, lateral bending and axial rotation in the native state in load controlled [±7.5 Nm] and intervals up to 60,000 cycles. Disc height was measured on fluoroscopy for multiple timepoints. The segments were also analyzed to detect possible reherniation during the cycling loading.

Findings: Following 60,000 cycles, the mean percentage RoM increase versus the intact state was less for discectomy plus the intradiscal spacer versus discectomy alone for lateral bending (170.7 ± 10.0 vs. 222.5 ± 33.3 %), flexion/extension (178.5 ± 6.1 vs. 204.6 ± 44.3 %) and axial rotation (284.4 ± 127.2 vs. 362.3 % ± 240.4 %). Mean overall disc height loss versus the annulotomy state was also less with the intradiscal spacer versus discectomy alone (-19.3 ± 3.7 vs. -29.1 ± 6.1 %). There was no evidence of device subsidence or migration.

Interpretation: This study helps to explain the clinical observation that insertion of a strutted intradiscal spacer following discectomy reduces reherniation rate by mechanically limiting the increase in RoM and disc height loss following lumbar discectomy.

Keywords: Cadaver study; Disc repair; Intradiscal spacer; Lumbar disc herniation; Reherniation.