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

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.

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.

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.

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.