Tantalum implants for posterior lumbar interbody fusion
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Lumbar interbody fusion (LIF) is the present gold standard in the surgical treatment of chronic low-back pain, with or without radiculalgia caused by degenerative disc disease, degenerative spondylolisthesis or isthmic spondylolisthesis. Interbody spinal implants enhance stability in LIF, restoring interbody height and hence segmental lordosis. A variety of intervertebral biomaterials are used: PEEK, titanium, tantalum; none, however, has demonstrated superiority over bone autograft for interbody fusion.

Tantalum is an extremely porous metal (80% porosity) with a texture close to that of cancellous bone. Its high coefficient of friction provides strong primary stability and counters secondary implant mobilization. Its rigidity transmits forces and stress to the bone, enhancing osseointegration and reducing stress-shielding effects.

Surgical technique
Under general anesthesia, the patient was positioned prone, with the abdomen free and the knees in slight flexion. On a posterior approach, bilateral complete lamino-arthrectomy allowed nerve root release with creation of a work-space for cage implantation. After complete discectomy, the vertebral endplates were freshened. Templates were used under fluoroscopic control to check cage height and length. Two cages, without bone graft, were positioned between the vertebral bodies, passing on either side of the dural sheath, away from the nerve root shoulder. Posterior internal fixation was then performed on the 2 vertebrae of the pathologic mobile spine sector, using 4 polyaxial pediculated screws connected by 2 curved titanium stems. The bone product of the laminectomy was used for posterolateral autograft. The patient was allowed to rise the next day, with a rigid thoracolumbar brace for 3 months. At 3 months, rehabilitation was initiated.

The contribution of tantalum
The coefficient of friction of tantalum provides good primary stability, unlike PEEK or titanium. This reduces the risk of secondary cage mobilization, notably in the spinal canal, and none indeed was observed in the present study. Studies of minimally invasive PLIF with tantalum implant and no complementary posterior internal fixation confirm this absence of tantalum implant mobilization. The present study showed that tantalum implants could be used as spacers to restore interbody height. Its osseointegration capacity provides a greater integrable contact surface than between bone and autologous graft in the central chamber of PEEK cages. The tantalum can then be used as a spacer in anterior fusion, avoiding the morbidity associated with autologous grafting. Unlike PEEK or titanium, tantalum is very difficult to assess on CT, due to metal artifacts, preventing CT assessment of fusion. MRI may allow reliable fusion assessment in PLIF with tantalum implant, as in PEEK. The tantalum implant is used as an integrable spacer rather than as an interbody graft for fusion, and it is bone integration rather than interbody fusion that is to be assessed.

In conclusion, PLIF with tantalum intervertebral implant without interbody bone graft provided satisfactory medium-term clinical and radiographic results. The advantages of tantalum consist of excellent primary stability and osseointegration capacity. The main drawback is the difficulty of using CT in follow-up due to metal artifacts generated by tantalum. The use of MRI is currently under assessment.

Source: https://www.sciencedirect.com/science/article/pii/S1877056820300347
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