398 - Novel Modular Disc Nucleus Prosthesis: Bench Data and Early Clinical R...

#398 Novel Modular Disc Nucleus Prosthesis: Bench Data and Early Clinical Results

Lumbar Therapies and Outcomes

Poster Presented by: P. de Muelenaere

Author(s):

P. de Muelenaere (1)
P. Asdourian (2)
A. Schwartz (3)
J. Felt (4)

(1) Brandon Regional Hospital, Brandon, MB, Canada
(2) Medstar Union Memorial Hospital, Baltimore, MD, USA
(3) Huntington Hospital, Huntington, NY, USA
(4) Vertebral Technologies, Inc., Minnetonka, MN, USA

Abstract

Background Context: Disc nucleus prostheses (DNPs) implanted via minimally invasive surgical techniques have been limited by safety and efficacy concerns. Previous DNP devices have been hampered by implant migration and subsidence issues. These concerns have been a consequence of material selection and implant geometry.

Purpose: Assess the mechanical and functional characteristics of a molded thermoset elastomeric polyurethane DNP that utilizes modular intraoperative assembly; this DNP should overcome the safety and efficacy issues that affected previous DNP devices.

BENCHTOP TESTING

Study Design/Setting: Benchtop testing performed per ASTM F2789 standards. The implant's resistance to mechanical and functional failure was evaluated using static and dynamic loading (axial, shear, and coupled).

Testing sample: Each benchtop test used 6 implants.

Methods:

Straight Axial Compression: 10M cycles; 600N axial loading at 4 HZ in 0.9% NaCl solution at 37°C.

Shear Compression: 1M cycles total; 600N at 4 HZ in 0.9% NaCl solution at 37°C; flexion/extension at ±7.5° and lateral bending at ±5°.

Expulsion testing: performed with dynamic flexion of 8° and constant loading of 1200N; Hyaluronic Acid used to increase lubricity and risk of expulsion.

Outcome analysis: Average implant height loss, wear rate, implant migration, and cycles completed were analyzed for benchtop testing. Implants were also visually inspected for functional failure during all tests.

Results: All tested parts fully retained functionality throughout testing. All implants had a height loss of < 3.2%, the highest observed wear rate was 0.09mg per million cycles, and none of the fully functional parts expulsed during testing.

CLINICAL TESTING

Study Design/Setting: A Health Canada study of 100 patients at up to 10 centers. The device will be used in patients between the ages of 21 and 60 with leg pain due to a herniated lumbar disc. Patient must have a minimum Oswestry Disability Index (ODI) score of 40% and a minimum leg pain score of 6cm on a 10cm visual analog scale (VAS).

Methods: A 2 week, 6 week, 3 month, 6 month, 12 month, and 24 month follow-up will be conducted for each implanted patient. Clinical examination, x-ray, MRI, and CT will be performed at follow-ups.

Outcome analysis: Visual Analog Pain Scale (VAS) and Oswestry Disability Index (ODI) scores will be analyzed for each patient. X-ray, MRI, and CT data will be observed for disc height and implant migration.

Results: Currently 6 patients have received implants. All have shown normalized VAS and ODI scores.

Conclusion: The modular design of this new DNP provides a large footprint through a small annulotomy. Benchtop testing has shown that the thermoset polyurethane elastomer provides fatigue, creep, expulsion, and wear resistance while maintaining a physiologic modulus. Clinical testing has shown lowered VAS and ODI scores with patients maintaining disc height.

Average Patient ODI Scores - Clinical Study