Partial Disc Replacement Research Articles

Biomechanical evaluation of a novel nucleus pulposus prosthesis in canine cadaveric spines

Partial disc replacement is a new surgical technique aimed at restoring functionality to degenerated intervertebral discs (IVDs). The aim of the present study was to assess biomechanically the behaviour of a novel nucleus pulposus prosthesis (NPP) in situ and its ability to restore functionality to the canine IVD after nuclectomy alone or after combined dorsal laminectomy and nuclectomy. Nine canine T13-L5 specimens (L2L3 group) and 10 L5-Cd1 specimens (LS group) were tested biomechanically in the native state, after nuclectomy (L2L3 group) or after combined dorsal laminectomy and nuclectomy (LS group), and after insertion of the NPP. Range of motion (ROM), neutral zone (NZ), and neutral zone stiffness (NZS) were determined in flexion/extension, lateral bending, and axial rotation. Nuclectomy alone and combined dorsal laminectomy and nuclectomy caused significant instability in all motion directions. Implantation of the NPP resulted in significant restoration of the parameters (ROM, NZ, and NZS) towards the native state; however, fragmentation/herniation of the NPP occurred in 47% of the cases. In conclusion, the NPP has the ability to improve functionality of the nuclectomized canine IVD. The high rate of NPP failure requires modifications directed at the integrity of the NPP and its confinement to the nuclear cavity.

Mature runt cow lumbar intradiscal pressures and motion segment biomechanics

Background context The optimal animal model for in vivo testing of spinal implants, particularly total or partial disc replacement devices, has not yet been determined. Mechanical and morphological similarities of calf and human spines have been reported; however, limitations of the calf model include open growth plates and oversized vertebrae with growth. Mature runt cows (Corrientes breed) may avoid these limitations. Purpose This study compared vertebral morphology and biomechanical properties of human and runt cow lumbar motion segments. Study design In vivo disc pressure measurements were obtained in six mature runt cows at L4–L5. In vitro evaluation was performed on these same segments and repeated on 12 human motion segments. Methods Disc pressures were measured in vivo in runt cow (Corrientes breed) L45 discs using a percutaneous transducer with the animal performing various activities. These motion segments were then harvested and morphologic and biomechanical evaluations (disc pressure in compression, flexibility tests to 7.5 Nm) were performed on both cow and male human L23 and L45 segments. Results The transverse lumbar disc dimensions were slightly smaller for (mixed gender) cow versus (male) humans, but were within the range of reported (mixed gender) human values. The mean±SD disc height was smaller for runt cow (7±1 mm) versus human discs (13±2 mm, p<.001). The vertebral bodies of the cow were approximately twice as tall as the human. In vitro testing revealed significantly greater disc pressure response to applied axial loading in the runt cow versus humans (1.27±0.18 vs. 0.84±0.15 kPa/N, respectively) but similar overall stiffness (2.15±0.71 vs. 1.91±0.94 kN/mm, respectively). Runt cow and human segment flexibility curves were similar with the following exceptions: runt cow stiffness was ∼40% greater in torsion (p<.05), runt cow segment lateral bending motion was greater versus humans (range of motion by 30%, neutral zone by 100%; both p<.05), and flexion range of motion tended to be smaller in runt cow versus human specimens (by ∼40%, p=NS). In vivo, the standing disc pressure in the runt cow was 0.80±0.24 MPa. Conclusions Although no animal replicates the human motion segment, the runt cow lumbar spine had a number of biomechanical and morphological measurements within the range of human values. The closed physes and temporally stable morphology of the mature runt cow may make this model more suitable versus standard calf models for human intradiscal implant studies.

Antidegenerative Effects of Partial Disc Replacement in an Animal Surgery Model

In vivo degenerative changes of rabbit intervertebral discs after partial disc replacements were evaluated radiologically and histologically in a controlled trial. To demonstrate the therapeutic effects of partial disc replacement in an animal surgical model. Although some authors reported that partial disc replacements have beneficial clinical outcomes, there are few controlled animal studies in which the therapeutic effects of this procedure have been demonstrated. The implants for partial disc replacements were made of poly (vinyl alcohol) hydrogel and rod-shaped. The L2-L3 or L3-L4 intervertebral discs of Japanese white rabbits were pierced with a 2.0-mm Kirschner wire and implants were inserted into the holes. For comparative purposes, the adjacent discs underwent sham treatments or control treatments in which the disc was pierced but no implant was inserted. Sixty discs from 30 rabbits were analyzed radiologically and histologically for degenerative changes at 1, 3, or 6 months after surgery. Radiologic analysis revealed that significantly less disc height was lost with the replacement treatment than with the control treatment. Change in disc height after the replacement treatment was not significantly different from that after the sham treatment. Histologic degeneration of the replaced discs was delayed in comparison with that of the control discs but progressed with time. The antidegenerative effects of partial disc replacement surgery were demonstrated by quantitative radiologic and histologic analyses. Degeneration of the anulus fibrosus after the replacement treatment was delayed by preserving disc height and occupying the space of the nucleus pulposus. Properly designed implants and minimally invasive techniques are necessary for long-term success.

5:31 46. Partial disc replacement in the baboon lumbar spine

5:31 46. Partial disc replacement in the baboon lumbar spine

P52. Partial disc replacement in the lumbar spine

P52. Partial disc replacement in the lumbar spine

Partial Disc Replacement with the PDN Prosthetic Disc Nucleus Device

The aim of this study was to evaluate the efficacy of the PDN prosthetic disc nucleus device for the treatment of chronic discogenic back pain caused by degenerative disc disease. Among the 48 patients who underwent nucleus replacement surgery from January 2001 through May 2002, 46 patients were followed >6 months. The mean Oswestry Disability Index score was 58.9% preoperatively, and it improved to 18% at the 1-year follow-up. Visual Analogue Pain Scale scores improved from a preoperative mean of 8.5 to 3.1 after 1 year. The mean Prolo Scale score also improved from 5.2 preoperatively to 7.2 at 1 year. Major complications included four cases of device migration, requiring revision surgery, and infection in one patient. According to MacNab's criteria, results were excellent in 5 patients (10.9%), good in 31 (67.4%), fair in 3 (6.5%), and poor in 7 (15.1%). The overall clinical success rate was 78.3%. Nucleus replacement with the PDN device seemed to be effective in treating patients with chronic discogenic back pain caused by degenerative disc disease.