As the population ages, an increasing number of peopleare sustaining VCFs secondary to osteoporosis. Tradition-ally these fractures have been treated nonsurgically, butclinical implementation of operative innovations such asvertebroplasty and kyphoplasty have contributed to agrowing body of literature about percutaneous vertebralaugmentation. Despite heightened interest in VCFs, thereremains a void in scientific knowledge about the naturalhistory of these injuries, and there are no prospective ran-domized studies establishing the benefits of percutaneousvertebral augmentation procedures over nonsurgical treat-ment.35

A number of case series are available that documentthe vertebroplasty and kyphoplasty experience.10,24,25,29,35

Both procedures generally use PMMA, which polymer-izes, conferring load-bearing capacity and stiffness to thefractured vertebral segment. Vertebroplasty involves di-rect injection of PMMA into the compressed VB, where-as kyphoplasty involves the use of an inflatable balloontamp to create a void in the fractured VB while restoringits height, with the void subsequently filled with PMMA.Neither procedure delivers osteoconductive or osteoin-ductive materials for vertebral augmentation, and thus

there is no potential for remodeling or incorporation forthe injected PMMA. Although the exact mechanism bywhich these procedures provide symptomatic relief is notclear,25,28,29 restoration of vertebral stiffness and load-bear-ing capacity is thought to eliminate painful micromotionand also to restore normal sagittal alignment of the spine,counteracting the increased forward bending momentcaused by the kyphotic deformity from VCFs.

An alternative to vertebroplasty and kyphoplasty is anovel system for treatment of VCFs, which provides min-imally invasive delivery of allograft or autograft bone intoan expandable mesh graft containment device within theinvolved VB. Although PMMA provides biomechanicalstiffness and load-bearing capability, it is limited in itslack of potential for biological activity, incorporation, orremodeling once it is deposited in bone. Also, the use ofbone cement has been associated with reported cases ofmorbidity and death.

The Optimesh system (Spineology, Inc., Stillwater,MN) combines the advantages of minimally invasive sur-gical access with the ability to deliver bioactive and bio-mechanically load-bearing injectable bone graft materialinto the fractured VB, restoring vertebral height and sagit-tal alignment, providing structural stability by withstand-ing physiological loading, and allowing for incorporationof the graft material into native vertebral bone (Fig. 1). Anallograft bone graft is prepared in granular flowable form

Neurosurg Focus 18 (3):E10, 2005

A novel percutaneous system for bone graft delivery andcontainment for elevation and stabilization of vertebralcompression fractures

Technical note

SANDI LAM, M.D., AND LARRY T. KHOO, M.D.

Division of Neurosurgery and Comprehensive Spine Center, University of California at Los Angeles,California

Object. Vertebroplasty and kyphoplasty are minimally invasive procedures used to treat persistently symptomaticvertebral compression fractures (VCFs). Both interventions usually involve injection of polymethyl methacrylate(PMMA). The purpose of this technical note was to review the theory and surgical technique for a novel percutaneoussystem for fracture reduction and stabilization of VCFs by using bone graft.

Methods. This technical note highlights the Optimesh system as an alternative method of minimally invasive VCFreduction and stabilization with the delivery of a bone graft containment device. Instead of using PMMA as in verte-broplasty or kyphoplasty, this system allows the delivery of allograft and/or autograft bone, with its osteoinductive,osteoconductive, and osteogenic properties.

Conclusions. This system allows for restoration of sagittal alignment of the spine with direct control of bone graftdelivery by using a mesh graft containment device that allows for ingrowth of new bone and vascular tissue.

KEY WORDS • vertebral compression fracture • vertebroplasty • kyphoplasty •fracture reduction • percutaneous vertebral augmentation • osteoporosis

Neurosurg. Focus / Volume 18 / March, 2005 1

Abbreviations used in this paper: CT = computerized tomogra-phy; PMMA = polymethyl methacrylate; VB = vertebral body;VCF = vertebral compression fracture.

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and is thus deliverable much like PMMA, with the advan-tages of osteoconductivity with corticocancellous bonechips and osteoinductivity with demineralized bone ma-trix (Fig. 2). This mixture can also be supplemented withmorselized autograft bone or bone marrow aspirate to pro-vide further osteogenic potential. We describe the use ofthe Optimesh system for percutaneous augmentation ofvertebral fractures by delivery of an expandable bone graftcontainment device, and we outline this attractive alterna-tive to vertebroplasty and kyphoplasty, which traditional-ly use PMMA as the load-bearing vertebral augmentationmaterial (Figs. 3 and 4).

Description of Technique

As with most vertebroplasty and kyphoplasty proce-dures, the patient is positioned prone on a radiolucent ta-ble with adequate padding. Intraoperative image guidanceis essential in this procedure to localize and delineate theextent of the fracture, and to guide instrument placement,minimize the risk of neural and soft-tissue injury, avoidpedicle disruption, assess fracture reduction, and assessvolume and placement of bone graft (Fig. 5). Biplanar flu-oroscopy is typically adequate for visualization during thisprocedure. If available, CT guidance may also be usedintraoperatively in place of fluoroscopy or to supplementthis modality in patients with difficult anatomy.2,9,28

Choice of anesthesia must be made jointly by the anes-thesia team and the surgical team, taking into account thepatient’s overall medical condition and the surgeon’s tech-nical considerations for the case.43 Because routine verte-

broplasty and kyphoplasty are often performed with thepatient receiving sedation and local anesthesia and re-maining awake to give feedback, this is similarly feasiblefor the Optimesh procedure performed by an experiencedsurgeon.

Sterile technique is crucial as in all surgical cases. Thepatient is thus prepared and draped in a sterile fashion.The procedure begins by gaining access to the central–anterior portion of the VB with the aid of intraoperativeimage guidance. This can be achieved using a transpedic-ular or posterolateral/parapedicular approach. Currentlythe standard working channel for the Optimesh systemhas an outer diameter of 8 mm and an inner diameter of7.75 mm; thus the parapedicular approach is advocated toavoid pedicle disruption and spinal canal intrusion.

The guide pin is directed to the entry point at the supe-rior and lateral margin of the pedicle on the anteroposteri-or fluoroscopy projection, and at the posterior part of the

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Fig. 1. Photograph showing the Optimesh graft containment de-vice in its unfilled state (left), and in its filled state (right).

Fig. 2. Photograph showing allograft bone material prepared forthe bone filling tube.

Fig. 3. Preoperative and postoperative lateral x-ray films show-ing a VCF, with some restoration of VB height after implantationof the Optimesh device filled with allograft bone.

Fig. 4. Preoperative and postoperative CT scans of three-levelOptimesh implantations for treatment of three vertebral fractures.

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VB at the junction of the pedicle on the lateral projection(Fig. 6). A stab incision is made laterally based on fluoro-scopic localization of the target level, usually 5 to 10 cmlaterally from the midline depending on the level, and theguide pin is advanced into the VB with the aid of biplanarfluoroscopic guidance. When the tip of the guide pin isin the central-middle part of the VB, a cannulated drillis used to prepare this entrance channel, into which thefixed-diameter working portal is placed. The position ofthe working portal is confirmed by fluoroscopic visualiza-tion to direct the proper placement of working tools and ofthe Optimesh device. Once the working portal is placed, itcan be connected to the fixed bar system that attaches tothe operating table. The portal is thus conveniently held ina fixed position for the remainder of the procedure.

Next, a small-diameter expandable reamer is passedthrough the working channel to the appropriate depth.This tool is available in various diameter models (5, 8, and10 mm); these cutting blades can be serially expanded,controlled by a knob at the proximal end of the instru-

ment, and produce cavities as large as 14, 22, and 25 mm,respectively. The cutting blades are retracted when thereamer is to be passed in or out through the fixed workingcannula (Fig. 7). The Optimesh graft containment deviceis then passed through the tube (Fig. 8) into the cavity cre-ated by the reamer, and its position is confirmed with theaid of fluoroscopy. At this point, the Optimesh expand-able mesh balloon may be filled with the graft materialof choice, including PMMA, autograft bone, or allograftbone. The Musculoskeletal Transplant Foundation (Edi-son, NJ) has produced an allograft mixture specifically foruse with the Optimesh system, and it is available in pre-filled tubes. The graft material is loaded into long metalcylinders and delivered sequentially into and filling theOptimesh container that expands in situ within the VB.While packing the graft into the cavity with a tamp andmallet, the graft delivery tube should be rotated 90˚ at reg-ular intervals to ensure even distribution of the graft mate-rial toward all directions in the cavity (Fig. 9). Increasingresistance from the cavity is transmitted through the col-umn of graft material as the graft becomes packed moreand more tightly. This correlates with fluoroscopy imagesas the cavity becomes more radiopaque and the VB frac-ture is reduced (Fig. 10). Once a sufficient amount of graftmaterial has been delivered based on tactile cues from thefilling system and visual assessment of the VB with imageguidance, the Optimesh bag is detached from the distal tipof the cannula, and all instruments are withdrawn. Thesurgical wound is small, and can be closed by the sur-geon’s chosen method.

Graft Characteristics

The Optimesh container is a hollow, expandable meshballoon for retention and containment of bone graft orbone graft substitutes. The mesh material is a woven poly-ester (Dacron) that is also used in other applications suchas vascular grafts. The finely woven mesh restricts leak-age of graft material outside of the cavity but at the sametime theoretically allows passage of liquids, cells, pro-teins, and other macromolecules, as well as vascular, os-teoconductive, and osteoinductive ingrowth.18,19 The struc-tural component of the Optimesh graft comes from its

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Fig. 5. Photograph showing skin markings derived from fluoro-scopic localization.

Fig. 6. Left: Photograph showing the trajectory of the guide pin for a parapedicular approach. Center: Lateral spine x-ray film demon-strating the guide pin position for a parapedicular approach. Right: Anteroposterior x-ray film demonstrating the guide pin position for aparapedicular approach.

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granular mechanical properties. The Optimesh systemtakes advantage of the unique characteristics of granularmaterials like bone graft in its finely ground and mor-selized form, creating the tools and conditions for deliveryof the morselized bone graft through a small access portal.After the cavity is filled, further application of pressurecan cause a granular material to change phase from aflowable liquid to a rigid solid. In its solid phase, the bonegraft material is thus able to withstand physiological com-pression loads and not flow back through the access por-tal.18,19

The surgeon may choose between a variety of graftmaterials, including combinations of autograft, allograftalone, allograft with bone marrow aspirate, allograft with

bone morphogenic proteins, autograft extended withallograft, autograft with other bone graft extenders, orPMMA. There are preprocessed allograft mixtures thatmeet the specific flow characteristics of the Optimesh sys-tem graft delivery tubes and that are commercially avail-able through a collaboration with the MusculoskeletalTransplant Foundation. The dry mix is a demineralizedbone matrix and freeze-dried corticocancellous chip mix-ture that is hydrated with the patient’s blood or bone mar-row aspirate immediately before application. Ground au-tograft may also be added to this mixture. Prefilled tubeshave recently been developed that are ready for implanta-tion into the Optimesh balloon without mixing.

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Fig. 7. Upper: Photograph showing an expandable reamer.Center: Lateral spine x-ray film showing the expandable reamerinside the VB with blades in the retracted position. Lower: La-teral spine x-ray film showing the expandable reamer inside theVB with blades in the deployed position.

Fig. 8. Photograph showing the Optimesh device about to be in-serted into the working portal.

Fig. 9. Photograph showing the surgeon filling the cavity withallograft bone through the bone filling tube. Pressure is exertedfirmly with a mallet.

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DISCUSSION

Although Optimesh is in its infancy in terms of clinicalimplementation, this unique system combines minimallyinvasive surgical access with the ability to restore sagittalalignment of the spine and deliver an osteoinductive andosteoconductive intravertebral load-bearing bone graftthat is expandable in situ for controlled delivery of acontained biological bone-filling material. The modulusof the solid Optimesh graft is close to that of bone, unlikethe stiffer characteristics of solid PMMA.36,44 This maytheoretically have an impact on reducing the relative riskof subsequent fracture in adjacent vertebral segments af-ter treatment with Optimesh and allograft compared withvertebroplasty or kyphoplasty and bone cement, but thiswould need to be further investigated with biomechanicalstudies and prospective clinical studies.8,13,16,23

With the increasing clinical implementation of verte-broplasty and kyphoplasty, there have been a number ofserious complications,26 a large percentage of which arerelated to the use of bone cement in these procedures,3–6,11,

12,14,15,20,28,31,42,45 and others that are related to misplacementof instruments. Cement leakage has been well described,occurring both through cortical defects and through thevenous system. Complications associated with percuta-neous vertebral augmentation procedures include hypo-tension,5,15,37 pulmonary embolism,4,6,34 pulmonary cementembolism,1,3,14,27 cerebral cement embolism,31 adult respi-ratory distress syndrome,41 paraplegia due to spinal cordcompression from cement leakage into the spinal ca-nal,7,20,32 intravascular leakage and extension of cement,1,11

cement toxicity,11 epidural hematoma,35 dural tear,1 and in-fection.40,46 There is also the hypothetical risk of thermalinjury from the exothermic reaction during PMMA poly-merization, a process that has resulted in a measurable in-crease in temperature in animal studies,38 although no clin-ical cases of thermal injury have been reported.11,28 Thesecement-related complications may be eliminated with theOptimesh system, which gives the option for use of allo-graft or autograft preparations in place of PMMA or otherbone cements. There remain risks related to anesthesiaand surgical instrumentation, as with any procedure. Intheory, the reaming and manipulation of the VB during theapproach, cavity creation, and fracture reduction may ex-pose the patient to the same risks of embolism from thebone marrow, fat, and air as in kyphoplasty (especial-ly during balloon inflation) and other orthopedic ream-ing,11,17,33 but this complication has not been encounteredin clinical implementation of Optimesh procedures todate. There may be a risk of extrusion of the bone graftmaterial as well, but with a discrete cavity created toreceive it, the presence of the graft containment mesh, andthe design adapted to take advantage of the granularmechanics of the filling material, the risk of extrusion ap-pears to be minimized. As the VB cavity and graft con-tainment mesh are filled and exposed to the exertionof pressure, the flowable state of the graft material in thetube changes to a solid state, thus preventing the back-flow of graft material through the bone defect created forthe working cannula, and also making the graft immedi-ately ready to handle physiological loading stresses of thespine.18,19

Kyphoplasty has been reported to allow for injectionof PMMA under lower pressures than are required duringvertebroplasty,21,22,30 with the packing of the cancellousbone at the periphery toward the endplates being thoughtto aid in protecting against transcortical cement extravasa-tion, and with the void created by the inflatable balloontamp representing a lower-pressure cavity than direct in-jection into the fracture site as is done in vertebroplasty.This also enables the cement to be inserted in a morecured form.30 Thus, proponents of kyphoplasty state that itallows superior control of PMMA delivery. The Optimeshgraft containment system allows for even more control ofthe graft material, because the mesh bag with its finelywoven configuration prevents frank extravasation.

The ability of the Optimesh system to restore VBheight mechanically can be observed in animal studiesand in clinical cases (unpublished data). Although bothbone graft and PMMA can technically fill a void createdin bone, the biological advantage of bone graft is obviouswith the osteoconductive and osteoinductive potential inthe Optimesh graft. Especially in younger patients, inwhom there is higher demand and longer expected useof the intravertebral stabilization construct, this newminimally invasive approach to delivering both solutionsfor fracture reduction and stabilization with potential forgraft incorporation provides a viable option for achievinga good long-term result. Minimally invasive techniquessuch as kyphoplasty have been called useful in certaintraumatic VB fracture patterns.39 Similarly, Optimesh isalso well suited for traumatic VB fractures, and in Europeit has been used successfully for such cases with and with-out posterior instrumented fusion.

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Fig. 10. Lateral spine x-ray film showing bone graft materialfilling the Optimesh graft containment device inside the cavity cre-ated by the expandable reamer.

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Click here to view Video Clip 1:An example of such a constructis provided in a three-dimensional rotating image in the attachedmovie file.

CONCLUSIONS

The Optimesh system is a novel implantable and ex-pandable device that can be delivered with a minimally in-vasive surgical approach to reduce and stabilize VCFs byusing biologically active allograft or autograft bone in-stead of PMMA. This procedure is approved by the Foodand Drug Administration for intravertebral use in VCFsand offers an exciting and promising alternative to mini-mally invasive stabilization procedures in which bonecement is used. This system allows for the restoration ofsagittal alignment of the spine with direct control of bonegraft delivery by using a mesh graft containment devicethat allows for ingrowth of new bone and vascular tissue.Small retrospective case reviews are being conducted,currently only with anecdotally favorable results, but thispowerful modality, which has the ability to restore VBheight and achieve solid stabilization with minimally in-vasive delivery of osteoconductive and osteoinductivebone graft warrants larger-scale prospective studies.

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embolism during spinal instrumentation surgery. A prospectivestudy using transoesophageal echocardiography. J Bone JointSurg Br 85:90–94, 2003

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38. Verlaan JJ, Oner FC, Verbout AJ, et al: Temperature elevationafter vertebroplasty with polymethyl-methacrylate in the goatspine. J Biomed Mater Res B Appl Biomater 67:581–585,2003

39. Verlaan JJ, van Helden WH, Oner FC, et al: Balloon vertebro-plasty with calcium phosphate cement augmentation for directrestoration of traumatic thoracolumbar vertebral fractures.Spine 27:543–548, 2002

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Manuscript received January 18, 2005.Accepted in final form February 28, 2005.Address reprint requests to: Sandi Lam, M.D., Comprehensive

Spine Center, Division of Neurosurgery, University of California atLos Angeles, 1245 16th Street, Suite 220, Santa Monica, CA 90404.email: salam@mednet.ucla.edu.

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