Cervical spine fusion with bioabsorbable cages

Abstract

<jats:sec> <jats:title>Object</jats:title> <jats:p>Although it improves rates of fusion in surgical arthrodesis, conventional spinal instrumentation is associated with several risks, including hardware extrusion that injures adjacent anatomical structures, and disuse osteopenia as a result of stress shielding. The long-term effects of indwelling spinal instrumentation, although incompletely documented, may be detrimental. One way to avoid such problems would be to use bioabsorbable implantation devices. In this pilot study, performed in 1998 and 1999, the authors evaluated the use of a bioabsorbable interbody fusion device in a goat cervical spine model.</jats:p></jats:sec> <jats:sec> <jats:title>Methods</jats:title> <jats:p>Forty-two goats underwent two-level anterior cervical discectomy and fusion: eight received iliac crest autograft; 16 received a cage implant composed of 70:30 poly(L-lactide-co-D,L-lactide)/polyglycolic acid (70:30 PLDLLA/PGA) filled with either autograft or recombinant human bone morphogenetic protein–2 (rhBMP-2); and 18 received a cage implant composed of 85:15 PLDLLA/PGA filled with either autograft or rhBMP-2. Animals were killed at 3, 6, and 12 months postsurgery, and their cervical spines were evaluated histologically, radiographically, and physically for fusion.</jats:p> <jats:p>A primarily fibrous union was demonstrated in all animals killed at 3 months. At 6 months, bone trabeculae had become more prominent and the fibrous response less so in all cohorts. This occurred most frequently in the animals that underwent fusion with the 70:30 PLDLLA/PGA cages filled with rhBMP-2, in which 63% attained a histologically confirmed union that contained quantitatively more bone and less fibrous tissue than in the other cohorts; 63% of the unions in the aforementioned cohort were graded quantitatively as being stable.</jats:p></jats:sec> <jats:sec> <jats:title>Conclusions</jats:title> <jats:p>In this study the authors have established that the 85:15 PLDLLA/PGA cages are absorbed too quickly to be functionally useful in this model. The 70:30 PLDLLA/PGA cages worked as well as tricortical autograft when filled with cancellous autograft, and better when filled with rhBMP-2. At 6- and 12-month follow-up review, the 70:30 PLDLLA/PGA cages had not yet begun to be absorbed. There was little if any inflammatory response to these cages at 6 months. Future studies should include biomechanical and microradiographic testing, and a longer follow-up period is necessary in this model to determine when the 70:30 PLDLLA/PGA cages are absorbed.</jats:p></jats:sec>

Bioresorbable polymers: heading for a new generation of spinal cages

“…At present there are few preclinical and clinical investigations on the effect of bone growth stimulation on fusion involving cages: such studies are underway using bioresorbable cage devices in combination with bone graft substitutes such as synthetic carriers, bone morphologic proteins (BMP) or a combination of both [66,101]. Preclinical in vivo experiments demonstrated good fusion results using rhBMP-2 sponge in combination with a PLDLLA threaded cage in a small animal study [101] and clinically in a study using a Hydrosorb vertical cylinder cage [60].…”

The Performance Envelope of Spinal Implants Utilizing Thermoplastic Materials

“…Because of this it has been proposed that stiff metallic implants may shield the graft from the stress required for fusion, delaying or preventing the process. This can induce iatrogenic effects such as device-related osteopenia, intervertebral device protrusion into a neighboring vertebral body, and fracture or instability (Lippman et al 2004). Implants developed out of less stiff materials may prevent this stress shielding and foster better clinical outcomes compared to traditional devices.…”

Vordere Spondylodesen an der unteren Halswirbelsäule

“…Spongiosatransplantate kommen dagegen in der Anfertigung der vorderen Plattenspondylodesen kaum zur Anwendung [3,10,15,16,18,23,28,31,45,62]. In diesem Sinne ist die alleinige Verwendung der reinen, frischen autologen Spongiosa nur sporadisch erwähnt worden [45].…”

“…Es wurden immer neuere Plattensysteme entwickelt und es wurde nach dem besten Span gesucht. Deutlich wenig Aufmerksamkeit wurde dagegen der Sicherheit und der Schnelligkeit des biologischen Einbaus des Knochentransplantates geschenkt [1,2,3,4,13,16,18,22,23,29,33,38,39,42,50,52,57,62].…”

“…Es ist bezeichnend, dass von den zahlreichen Arbeitsgruppen, die nach dem besten Span gesucht haben, der reinen autologen/heterologen Spongiosa nur sehr wenig Aufmerksamkeit gewidmet wurde [3,10,15,16,18,23,28,31,45,62]. Sie findet zwar, genauso wie das Knochenmark [30,62], in Kombination mit verschiedenen "Kraftträgern" [3,20,16,18,23,28,31,45,62] zur Anregung der Knochenneubildung ihre beschränkte Anwendung und die damit gewonnenen Ergebnisse werden als positiv bezeichnet, ihre alleinige Verwendung bei Anfertigung der vorderen Plattenspondylodesen, sicherlich wegen der minderwertigen mechanischen Eigenschaften, wurde jedoch Die jetzt vorliegende Arbeit ist die erweiterte Version eines Referats, welches in Salzburg (10. bis 11.…”