Biomechanical function of a balloon nucleus pulposus replacement system: A human cadaveric spine study

Abstract

With recent advances in motion-sparing techniques in spine surgery, disc nucleus replacement (DNR) has been introduced as a viable method to restore the biomechanical functions of the spine. Several methods of DNR have been proposed in the literature. However, the risk of device migration or extrusion is a major issue that should be addressed for a successful DNR. DNR using a balloon nucleus (BN) filled with pressurized fluid may be capable of reducing such risks while preserving the advantages of DNR. The objective of this study was to investigate the biomechanical functionalities of the human cadaveric lumbar motion segments with a custom made BN filled with saline at internal fluid pressure of 0.3 or 0.6 MPa in terms of axial and rotational flexibilities of the L4-L5 motion segment. Axial flexibility was quantified by the axial displacement resulting from an axial compressive force of 400 N while the rotational flexibility by the range of motions determined as the rotational angles in response to a pure moment of 6.0 Nm in flexion, extension, and right- and left-lateral bending directions. These tests were performed successively on the motion segment in the following conditions: intact, post nucleotomy, implanting BN with 0.3 MPa, and BN with 0.6 MPa. The nucleotomy was found to significantly increase both the axial and rotational flexibilities while the implantation of the BN reduced the axial and rotational flexibilities to those of the intact segment. The axial and rotational flexibilities of the segment with the BN with 0.3 MPa were greater than those of the segment with the BN with 0.6 MPa. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:167-173, 2018.

Bionate Lumbar Disc Nucleus Prosthesis: Biomechanical Studies in Cadaveric Human Spines

“…After nucleotomy, compared to the intact nucleus, motion range recovery is not complete in our nucleus replacement, as reported with other nucleus implant devices. ,,,− The most significant improvement is in lateral bending, axial torsion, and flexion-extension, as in our nucleus replacement. Therefore, in this area, there is still room for improvement.…”

“…Nucleus replacement technology, available since the 90’ (PDN, Raymedica Inc., Minneapolis, USA), had good clinical results initially, followed by complications related to subsidence and extrusion. − As a result, many other implants have been created, ,,− only a few reaching the market, ,− and most are no longer in use. The reason is that although they achieve biomechanical restoration close to but not equal to an intact intervertebral disc, ,,,− extrusion and subsidence are not fully solved yet. ,,,, …”

“…In addition, some of these materials fracture or break under cycling loading . Some designs have an outside bag that prevents the spillage of implant debris, but the injected core-curing process poses another challenge. , …”

“…45 Some designs have an outside bag that prevents the spillage of implant debris, but the injected core-curing process poses another challenge. 51,53 Implants with an uneven load distribution have a higher subsidence risk, 56 which is minimized in those with a central void cavity. 65 Without this space, implants are stiffer and apply higher stresses on the adjacent endplates.…”

“…32 − 35 As a result, many other implants have been created, 7 , 8 , 36 − 44 only a few reaching the market, 10 , 45 − 50 and most are no longer in use. The reason is that although they achieve biomechanical restoration close to but not equal to an intact intervertebral disc, 24 , 26 , 36 , 51 − 56 extrusion and subsidence are not fully solved yet. 32 , 33 , 45 , 57 , 58 …”