Innovation and New Technologies in Spine Surgery, Circa 2020: A Fifty-Year Review.

Spine surgery (lumbar, cervical, deformity, and entire spine) has increased in volume and improved in outcomes over the past 50 years because of innovations in surgical techniques and introduction of new technologies to improve patient care. Innovation is described as a process to add value or create change in an enterprise's economic or social potential. This mini review will assess two of three assessments of innovation in spine surgery: scientific publications and patents issued. The review of both scientific publications and issued patents is a unique assessment. The third assessment of innovation: regulatory clearances of medical devices and equipment for spine surgery and their evolution over time, will also be discussed.

Contribution of Round vs. Rectangular Expandable Cage Endcaps to Spinal Stability in a Cadaveric Corpectomy Model.

BACKGROUND: Expandable cages are gaining popularity in anterior reconstruction of the thoracolumbar spine following corpectomy as they can provide adjustable distraction and deformity correction. Rectangular, rather than circular, endcaps provide increased resistance to subsidence by spanning the apophyseal ring; however their impact on construct stability is not known. The objective of this study was to investigate the contribution of expandable corpectomy cage endcap shape (round vs. rectangular) and fixation method (anterior plate vs. posterior pedicle screws) to the stability of an L1 sub-total corpectomy construct. METHODS: Eight fresh-frozen cadaveric specimens (T11-L3) were subjected to multi-directional flexibility testing to 6 N·m with a custom spine simulator. Test conditions were: intact, L1 sub-total corpectomy defect, expandable cage (round endcap) alone, expandable cage (round endcap) with anterior plate, expandable cage (round endcap) with bilateral pedicle screws, expandable cage (rectangular endcap) alone, expandable cage (rectangular endcap) with anterior plate, expandable cage (rectangular endcap) with bilateral pedicle screws. Range-of-motion across T12-L2 was measured with an optoelectronic system. RESULTS: The expandable cage alone with either endcap provided significant stability to the corpectomy defect, reducing motion to intact levels in flexion-extension with both endcap types, and in lateral bending with rectangular endcaps. Round endcaps allowed greater motion than intact in lateral bending, and axial rotation ROM was greater than intact for both endcaps. Supplemental fixation provided the most rigid constructs, although there were no significant differences between instrumentation or endcap types. CONCLUSIONS: These results suggest anterior-only fixation may be adequate when using an expandable cage in a sub-total corpectomy application and choice of endcap type may be driven by other factors such as subsidence resistance.

Biomechanical stability of lateral interbody implants and supplemental fixation in a cadaveric degenerative spondylolisthesis model.

STUDY DESIGN: In vitro cadaveric biomechanical study of lateral interbody cages and supplemental fixation in a degenerative spondylolisthesis (DS) model. OBJECTIVE: To investigate changes in shear and flexion-extension stability of lateral interbody fusion constructs. SUMMARY OF BACKGROUND DATA: Instability associated with DS may increase postoperative treatment complications. Several groups have investigated DS in cadaveric spines. Extreme lateral interbody fusion (XLIF) cages with supplemental fixation have not previously been examined using a DS model. METHODS: Seven human cadaveric L4-L5 motion segments were evaluated using flexion-extension moments to ±7.5 N·m and anterior-posterior (A-P) shear loading of 150 N with a static axial compressive load of 300 N. Conditions were: (1) intact segment, (2) DS simulation with facet resection and lateral discectomy, (3) standalone XLIF cage, (4) XLIF cage with (1) lateral plate, (2) lateral plate and unilateral pedicle screws contralateral to the plate (PS), (3) unilateral PS, (4) bilateral PS, (5) spinous process plate, and (6) lateral plate and spinous process plate. Flexion-extension range of motion (ROM) data were compared between conditions and with results from a previous study without DS simulation. A-P shear displacements were compared between conditions. RESULTS: Flexion-extension ROM after DS destabilization increased significantly by 181% of intact ROM. With the XLIF cage alone, ROM decreased to 77% of intact. All conditions were less stable than corresponding conditions with intact posterior elements except those including the spinous process plate. Under shear loading, A-P displacement with the XLIF cage alone increased by 2.2 times intact. Bilateral PS provided the largest reduction of A-P displacement, whereas the spinous process plate alone provided the least. CONCLUSION: This is the first in vitro shear load testing of XLIF cages with supplemental fixation in a cadaveric DS model. The variability in sagittal plane construct stability, including significantly increased flexion-extension ROM found with most fixation conditions including bilateral PS may explain some clinical treatment complications in DS with residual instability. LEVEL OF EVIDENCE: N/A.

Biomechanical evaluation of stand-alone lumbar polyether-ether-ketone interbody cage with integrated screws.

BACKGROUND CONTEXT: Stand-alone interbody cages with integrated screws potentially provide a biomechanically stable solution for anterior lumbar interbody fusion (ALIF) that alleviates the need for additional exposure for supplemental fixation, thereby reducing the chance of additional complications and morbidity. PURPOSE: To compare the stability of a stand-alone anterior interbody fusion system with integrated fixation screws against traditional supplemental fixation methods and to evaluate the difference between three and four fixation screws in the stand-alone cage. STUDY DESIGN: In vitro cadaveric biomechanical study. METHODS: Eight cadaveric lumbar spines (L2-sacrum) were tested using a flexibility protocol consisting of three cycles to ±7.5 Nm in flexion-extension, lateral bending, and axial rotation. The conditions evaluated were intact spine; polyether-ether-ketone cage (zero integrated screws) at L4-L5; cage (zero screws)+bilateral pedicle screws (PS); cage (three screws); cage (four screws); cage (zero screws)+anterior plate; and cage (three screws)+spinous process plate. Motion at the index level was assessed using an optoelectronic system. RESULTS: The cage without integrated screws reduced the motion in flexion-extension and lateral bending (p<.001) compared with that in the intact spine. In axial rotation, mean range of motion (ROM) was 8% greater than in intact spine (p>.962). The addition of three integrated screws reduced ROM significantly compared with the cage without screws in all motion planes (p<.001). A fourth screw had no statistically significant effect on the ROM, although there was a trend toward less motion with four screws compared with three. In flexion-extension, the cage with three integrated screws and the spinous process plate was the most rigid condition. There was no significant difference from the bilateral PS (p=.537); however, this was more rigid than all other conditions (p<.024). The most stable condition in lateral bending and axial rotation was the cage with bilateral PS. In lateral bending, the cage (three or four screws) was not significantly different from the cage with anterior plate or the cage (three screws) with spinous process plate fixation; however, only the latter condition was statistically comparable with bilateral PS. In axial rotation, there were no significant differences between the conditions that included integrated screws or supplemental fixation (p>.081). CONCLUSIONS: Biomechanical testing revealed that the stand-alone cage with integrated screws provides more immediate stability than a cage alone and provides equivalent stability to ALIF constructs with supplemental fixation in lateral bending and axial rotation. Additional flexion-extension rigidity of the anterior cage maybe realized by the addition of a spinous process plate that was found to be as stable as supplemental bilateral PS.

Lordosis restoration after anterior longitudinal ligament release and placement of lateral hyperlordotic interbody cages during the minimally invasive lateral transpsoas approach: a radiographic study in cadavers.

OBJECT: In the surgical treatment of spinal deformities, the importance of restoring lumbar lordosis is well recognized. Smith-Petersen osteotomies (SPOs) yield approximately 10° of lordosis per level, whereas pedicle subtraction osteotomies result in as much as 30° increased lumbar lordosis. Recently, selective release of the anterior longitudinal ligament (ALL) and placement of lordotic interbody grafts using the minimally invasive lateral retroperitoneal transpsoas approach (XLIF) has been performed as an attempt to increase lumbar lordosis while avoiding the morbidity of osteotomy. The objective of the present study was to measure the effect of the selective release of the ALL and varying degrees of lordotic implants placed using the XLIF approach on segmental lumbar lordosis in cadaveric specimens between L-1 and L-5. METHODS: Nine adult fresh-frozen cadaveric specimens were placed in the lateral decubitus position. Lateral radiographs were obtained at baseline and after 4 interventions at each level as follows: 1) placement of a standard 10° lordotic cage, 2) ALL release and placement of a 10° lordotic cage, 3) ALL release and placement of a 20° lordotic cage, and 4) ALL release and placement of a 30° lordotic cage. All four cages were implanted sequentially at each interbody level between L-1 and L-5. Before and after each intervention, segmental lumbar lordosis was measured in all specimens at each interbody level between L-1 and L-5 using the Cobb method on lateral radiography. RESULTS: The mean baseline segmental lordotic angles at L1-2, L2-3, L3-4, and L4-5 were -3.8°, 3.8°, 7.8°, and 22.6°, respectively. The mean lumbar lordosis was 29.4°. Compared with baseline, the mean postimplantation increase in segmental lordosis in all levels combined was 0.9° in Intervention 1 (10° cage without ALL release); 4.1° in Intervention 2 (ALL release with 10° cage); 9.5° in Intervention 3 (ALL release with 20° cage); and 11.6° in Intervention 4 (ALL release with 30° cage). Foraminal height in the same sequence of conditions increased by 6.3%, 4.6%, 8.8% and 10.4%, respectively, while central disc height increased by 16.1%, 22.3%, 52.0% and 66.7%, respectively. Following ALL release and placement of lordotic cages at all 4 lumbar levels, the average global lumbar lordosis increase from preoperative lordosis was 3.2° using 10° cages, 12.0° using 20° cages, and 20.3° using 30° cages. Global lumbar lordosis with the cages at 4 levels exhibited a negative correlation with preoperative global lordosis (10°, R = -0.756; 20°, -0.730; and 30°, R = -0.437). CONCLUSIONS: Combined ALL release and placement of increasingly lordotic lateral interbody cages leads to progressive gains in segmental lordosis in the lumbar spine. Mean global lumbar lordosis similarly increased with increasingly lordotic cages, although the effect with a single cage could not be evaluated. Greater global lordosis was achieved with smaller preoperative lordosis. The mean maximum increase in segmental lordosis of 11.6° followed ALL release and placement of the 30° cage.

Biomechanical analysis in a human cadaveric model of spinous process fixation with an interlaminar allograft spacer for lumbar spinal stenosis: Laboratory investigation.

OBJECT: Traditional posterior pedicle screw fixation is well established as the standard for spinal stabilization following posterior or posterolateral lumbar fusion. In patients with lumbar spinal stenosis requiring segmental posterior instrumented fusion and decompression, interlaminar lumbar instrumented fusion (ILIF) is a potentially less invasive alternative with reduced morbidity and includes direct decompression assisted by an interlaminar allograft spacer stabilized by a spinous process plate. To date, there has been no biomechanical study on this technique. In the present study the biomechanical properties of the ILIF construct were evaluated using an in vitro cadaveric biomechanical analysis, and the results are presented in comparison with other posterior fixation techniques. METHODS: Eight L1-5 cadaveric specimens were subjected to nondestructive multidirectional testing. After testing the intact spine, the following conditions were evaluated at L3-4: bilateral pedicle screws, bilateral laminotomy, ILIF, partial laminectomy, partial laminectomy plus unilateral pedicle screws, and partial laminectomy plus bilateral screws. Intervertebral motions were measured at the index and adjacent levels. RESULTS: Bilateral pedicle screws without any destabilization provided the most rigid construct. In flexion and extension, ILIF resulted in significantly less motion than the intact spine (p < 0.05) and no significant difference from the laminectomy with bilateral pedicle screws (p = 0.76). In lateral bending, there was no statistical difference between ILIF and laminectomy with unilateral pedicle screws (p = 0.11); however, the bilateral screw constructs were more rigid (p < 0.05). Under axial rotation, ILIF was not statistically different from laminectomy with unilateral or bilateral pedicle screws or from the intact spine (p > 0.05). Intervertebral motions adjacent to ILIF were typically lower than those adjacent to laminectomy with bilateral pedicle screws. CONCLUSIONS: Stability of the ILIF construct was not statistically different from bilateral pedicle screw fixation following laminectomy in the flexion and extension and axial rotation directions, while adjacent segment motions were decreased. The ILIF construct may allow surgeons to perform a minimally invasive, single-approach posterior decompression and instrumented fusion without the added morbidity of traditional pedicle screw fixation and posterolateral fusion.

Teaching medical device design using design control.

The design of medical devices requires an understanding of a large number of factors, many of which are difficult to teach in the traditional educational format. This subject benefits from using a challenge-based learning approach, which provides focused design challenges requiring students to understand important factors in the context of a specific device. A course was designed at San Diego State University (CA, USA) that applied challenge-based learning through in-depth design challenges in cardiovascular and orthopedic medicine, and provided an immersive field, needs-finding experience to increase student engagement in the process of knowledge acquisition. The principles of US FDA 'design control' were used to structure the students' problem-solving approach, and provide a format for the design documentation, which was the basis of grading. Students utilized a combination of lecture materials, industry guest expertise, texts and readings, and internet-based searches to develop their understanding of the problem and design their solutions. The course was successful in providing a greatly increased knowledge base and competence of medical device design than students possessed upon entering the course.

Biomechanical analysis and review of lateral lumbar fusion constructs.

STUDY DESIGN: Biomechanical study and the review of literature on lumbar interbody fusion constructs. OBJECTIVE: To demonstrate the comparative stabilizing effects of lateral interbody fusion with various supplemental internal fixation options. SUMMARY OF BACKGROUND DATA: Lumbar interbody fusion procedures are regularly performed using anterior, posterior, and more recently, lateral approaches. The biomechanical profile of each is determined by the extent of resection of local supportive structures, implant size and orientation, and the type of supplemental internal fixation used. METHODS: Pure moment flexibility testing was performed using a custom-built 6 degree-of-freedom system to apply a moment of ±7.5 Nm in each motion plane, while motion segment kinematics were evaluated using an optoelectronic motion system. Constructs tested included the intact spine, stand-alone extreme lateral interbody implant, interbody implant with lateral plate, unilateral and bilateral pedicle screw fixation. These results were evaluated against those from literature-reported biomechanical studies of other lumbar interbody constructs. RESULTS: All conditions demonstrated a statistically significant reduction in range of motion (ROM) as a percentage of intact. In flexion-extension, ROM was 31.6% stand-alone, 32.5% lateral fixation, and 20.4% and 13.0% unilateral and bilateral pedicle screw fixation, respectively. In lateral bending, the trend was similar with greater reduction with lateral fixation than in flexion-extension; ROM was 32.5% stand-alone, 15.9% lateral fixation, and 21.6% and 14.4% unilateral and bilateral pedicle screw fixation. ROM was greatest in axial rotation; 69.4% stand-alone, 53.4% lateral fixation, and 51.3% and 41.7% unilateral and bilateral pedicle screw fixation, respectively. CONCLUSION: The extreme lateral interbody construct provided the largest stand-alone reduction in ROM compared with literature-reported ALIF and TLIF constructs. Supplemental bilateral pedicle screw-based fixation provided the overall greatest reduction in ROM, similar among all interbody approach techniques. Lateral fixation and unilateral pedicle screw fixation provided intermediate reductions in ROM. Clinically, surgeons may evaluate these comparative results to choose fixation options commensurate with the stability requirements of individual patients.

Evaluation of a bioresorbable polylactide sheet for the reduction of pelvic soft tissue attachments in a porcine animal model.

In an adult porcine model, the effectiveness of a bioresorbable film to minimize soft tissue attachment to the pelvic viscera was evaluated at 4-week and 12-week endpoints. Following a transperitoneal laparotomy through a midline incision, the bladder and uterus were abraded in all animals to promote soft tissue attachment to the viscera. Control animals received no further treatment. The experimental group animals were treated with bioresorbable polylactide (PLa) sheets, 0.02 mm thick, one between the bladder and the abdominal wall, and a second sheet between the bladder and the uterus. Quantitative assessment of the severity and location of soft tissue attachments, and qualitative histologic assessment were performed at 4 and 12 weeks post-operatively. Statistically significant differences in the quantitative soft tissue attachment scores were observed in comparing the PLa film treated animals versus the control animals, at both the 4-week and 12-week time points. In the control animals, the formation of numerous thick fibrous bands was observed at both time points. Histology revealed no adverse reaction to the bioresorbable PLa barrier film. The bioresorbable PLa sheet provided an effective barrier between adjacent anatomical structures and minimized soft tissue attachments to the device when in contact with the viscera as compared to the control groups. Surgical dissection planes between the abdominal wall and adjacent soft tissues were maintained with the use of the PLa sheet at both time points.

Use of polylactide resorbable film as a barrier to postoperative peridural adhesion in an ovine dorsal laminectomy model.

OBJECT: The purpose of this study was to evaluate the performance of a resorbable polylactide film in the sheep posterior spine in the presence of a combined laminectomy and durotomy defect. METHODS: A resorbable polylactide film was used to cover the combined defects in the eight sheep used in this study. Two surgical levels were performed in each animal, with randomly assigned control and treated sites. Each surgical level consisted of a full laminectomy followed by a needle-induced durotomy. The treated levels received a resorbable polylactide film cut to size and tucked in under the laminar defect. At 8 to 10 weeks postoperatively, results of myelography and visual dye infiltration showed complete healing of the durotomies for all sites. In addition, evaluation of gross dissection based on volume and tenacity scores as well as histological findings indicates decreased posterior dural adhesions for sites treated with resorbable polylactide film. CONCLUSIONS: The results of this investigation support previous studies in which the use of a resorbable polylactide film was found to be effective in reducing posterior dural adhesions in the spine with no apparent safety issues related to impaired dural healing.

In vivo evaluation of bioresorbable polylactide implants for cervical graft containment in an ovine spinal fusion model.

OBJECT: An in vivo study was conducted in an ovine model to investigate the biomechanical changes after the animals underwent single-level anterior cervical discectomy followed by fusion in which autologous tricortical graft was used and implantation of cervical plates for which bioresorbable polymer screws and plates were used. The specific aims of the study were to evaluate whether implant failure or screw backout would occur over time and to measure the change in stiffness at the treated level at various postoperative time periods (3, 6, and 12 months). METHODS: A total of 58 x-ray films were evaluated over the 12-month survival period. No screw breakage or displacement was observed in any animal during the temporal radiographic analysis. Radiographically confirmed fusion appeared to be complete at all time periods longer than 6 months. The biomechanical testing demonstrated dramatic reductions in range of motion at the fusion level in the animals allowed to survive for 6 and 12 months, indicating complete fusion after 6 months. CONCLUSIONS: The bioresorbable polymer cervical graft containment system appears to provide a safe and effective alternative for cervical fusion, and warrants further clinical evaluation for its use in single-level anterior cervical discectomy and fusion without postoperative orthosis.

MacroPore resorbable devices in craniofacial surgery.

Resorbable polymer implants have become a compelling option in the treatment of acquired and congenital craniofacial deformities. The resorbable polylactide (PLa) and polyglycolide (PGa) polymers in particular have demonstrated excellent safety profile sin multiple in vitro, animal, and clinical studies and are currently being used in a wide variety of craniofacial applications. In this article, the authors discuss the biomaterial properties of PLa and PGa resorbable implants and provide an overview of the use of these polymers in craniofacial surgery. They conclude by relating their experience with an ongoing clinical series using MacroPore PLDLa and FRP implants for various applications,including Le Fort osteotomies, midface/monobloc internal distraction, and craniosynostosis reconstruction.

Use of polylactide resorbable film as an adhesion barrier.

OBJECT: The present investigation evaluates two thicknesses of a resorbable polylactic acid (PLA) barrier film as an adhesion barrier to posterior spinal scar formation. METHODS: A readily contourable, thin film was placed directly over the dura. The thick film was placed above the lamina defect to act as a physical barrier inhibiting the prolapse of soft tissue into the epidural space. Through a combination of gross dissection with and without scar scores, quantitative analysis of collagen adjacent to the scar site, and histological evaluation, the resorbable adhesion barrier membranes were found to be effective treatment for reduction of posterior adhesions. CONCLUSIONS: The gross dissection demonstrated that both thicknesses of resorbable PLA barrier films created a controlled dissection plane, facilitated access to the epidural space, and provided a reduction in the tissue adherent to the dura.

Evaluation of 70/30 poly (L-lactide-co-D,L-lactide) for use as a resorbable interbody fusion cage.

OBJECT: Titanium lumbar interbody spinal fusion devices are reported to be 90% effective in cases requiring single-level lumbar interbody arthrodesis, although radiographic determination of fusion has been debated. METHODS: Using blinded radiographic, biomechanical, histological, and statistical measures, researchers in the present study evaluated a radiolucent 70/30 poly(L-lactide-co-D,L-lactide) interbody fusion device packed with autograft or recombinant human bone morphogenetic protein-2 on a collagen sponge in 25 sheep at 3, 6, 12, 18, and 24 months. A trend of increased fusion stiffness, radiographic fusion, and histologically confirmed fusion was demonstrated at 3 months to 24 months postimplantation. Device degradation was associated with a mild to moderate chronic inflammatory response at all postoperative sacrifice times. CONCLUSIONS: Use of this material in interbody fusion may be a viable alternative to metals.

Feasibility of a resorbable anterior cervical graft containment plate.

In this article the authors review the history of anterior cervical plating for one- and two-level discectomy for degenerative disease and provide background justification for the design and testing of a cervical plate composed of a resorbable material. The design of the plate is discussed with special reference to modifications of its design and tools compared with metallic plates that are necessary because of the different mechanical properties of the less rigid material. The cadaveric and animal in vivo testing methodologies are described, and a novel testing method for reliably quantifying graft containment is also described. Data from a representative sample are presented. Advantages and disadvantages of resorbable plating are discussed.

Bioabsorbable anterior lumbar plate fixation in conjunction with cage-assisted anterior interbody fusion.

OBJECT: An in vitro biomechanical study was conducted to determine the effects of anterior stabilization on cage-assisted lumbar interbody fusion biomechanics in a multilevel human cadaveric lumbar spine model. METHODS: Three spine conditions were compared: harvested, bilateral multilevel cages (CAGES), and CAGES with bioabsorbable anterior plates (CBAP), tested under flexion-extension, lateral bending, and axial rotation. Measurements included vertebral motion, applied load, and bending/rotational moments. Application of anterior fixation decreased local motion and increased stiffness of the instrumented levels. Clinically, this spinal stability may serve to promote fusion. CONCLUSIONS: Coupled with the bioabsorbability of the plating material, the bioabsorbable anterior lumbar plating system is considered biomechanically advantageous.

Use of a resorbable sheet in iliac crest reconstruction in a sheep model.

OBJECT: Iliac crest bone graft harvesting can result in major complications, the rates of which range from approximately 6 to 8%. The objective of this study was to evaluate the postoperative regeneration of iliac crest donor defects in an animal model after harvesting a full-thickness tricortical graft. METHODS: In skeletally mature sheep, a tricortical iliac crest graft was harvested. The graft sites were allowed to heal unprotected or protected with the resorbable polylactic acid sheet material, MacroPore OS Protective Sheeting. After 6 months of healing, the sites were assessed by examination of undecalcified histological sections. Histomorphometric measurements of the original defect area, the area of new bone within the defect site, and the percentage of defect filled with new bone were quantified for both control and protected groups. In all histological sections, new bone growth within the defect sites appeared normal, with no observed excessive inflammatory cells. The developing bone tissue appeared to be remodeling normally. For the unprotected sites, the area of new bone averaged 16.3 mm2 (+/- 7.2 mm2), and the percentage of the defect area filled with bone averaged 10.7% (+/- 6.5%). In the protected sites, the area of new bone averaged 64.8 mm2 (+/- 11.6 mm2) and the percentage of the defect area filled with bone averaged 25.9% (+/- 1.6%). Both differences in area of new bone growth and percentage of defect area filled were statistically significant. Literature review has indicated that regeneration of donor site defects is desirable. CONCLUSIONS: Based on the results of the present study, MacroPore resorbable Protective Sheeting can improve bone regeneration significantly within the donor site following tricortical iliac crest graft harvesting.

Resorbable posterolateral graft containment in a rabbit spinal fusion model.

OBJECT: The authors studied the effect of a resorbable graft containment device in a rabbit posterolateral lumbar spinal fusion model. METHODS: Twenty rabbits were divided into four groups: autologous bone graft (ABG), ABG with the MacroPore containment device (ABG + MP), demineralized bone matrix (DBM), and DBM with the containment device (DBM + MP). Fusion mass was assessed at 6 weeks with high-resolution radiography and volumetric computerized tomography. The graft containment device was associated with alteration of the fusion mass structure and significant enhancement of fusion mass volume (ABG versus ABG + MP, p = 0.027; DBM versus DBM + MP, p = 0.043). CONCLUSIONS: A bioabsorbable protective graft containment device successfully enhanced posterolateral spinal fusion mass volume.

Feasibility of a resorbable anterior cervical graft containment plate.

In this article we review the background of anterior cervical plating for one- and two-level diskectomy for degenerative disease and provide background justification for the design and testing of a cervical plate composed of a resorbable material. The design of the plate is discussed with special reference to modifications of implant design and implant tools compared with metallic plates that are necessary because of the different mechanical properties of the less rigid material. Our cadaveric and animal in vivo testing methodologies are described and a novel testing method for reliably quantifying graft containment is also described. Data from a representative sample are presented. Advantages and disadvantages of resorbable plating are discussed.

Bioabsorbable anterior lumbar plate fixation in conjunction with anterior interbody fusion cages.

An in vitro biomechanical study was conducted to determine the effects of anterior stabilization on lumbar interbody cage fusion biomechanics in a multilevel human cadaveric lumbar model. Three spine conditions were compared: harvested, bilateral multilevel cages (CAGES), and CAGES with bioabsorbable anterior plates (CBAP), tested under flexion/extension, lateral bending, and axial rotation. Measurements included vertebral motion, applied load, and bending/rotational moments. Application of anterior fixation decreased local motion and increased stiffness of the instrumented levels. Clinically, this spinal stability may serve to promote fusion. Coupled with the bioabsorbability of the plating material, the bioabsorbable anterior lumbar plating system is considered biomechanically advantageous.