9
In 1953, Cloward 2 first described his PLIF technique as a surgical treatment option for lumbar disc disease. Al- though the PLIF procedure slowly gained acceptance thereafter, 7,12 it was not until the advent of pedicle screw spinal instrumentation that this operation became wide- ly performed. 14,15 The unilateral transforaminal approach for segmental lumbar interbody arthrodesis was first described in the 1980s by Blume 1 to address some of the complications associated with instrumented (bilateral) PLIF described by Steffee and Sitkowski. 14 In the 1990s the TLIF procedure was modified and popularized by Harms, et al. 5 The TLIF procedure is an interbody combined with a unilateral posterior (facet and/or interlaminar) arthrodesis performed with or without a bilateral posterolateral arthro- desis that is stabilized with pedicle screw instrumentation. This procedure is performed via a single midline posteri- or surgical approach. Access to the intervertebral disc is gained by a unilateral resection of the lamina, pars inter- articularis, and zygapophysial (facet) joint at the level or levels to be fused. An aggressive discectomy and inter- body arthrodesis can thus be performed unilaterally with relatively minimal medial retraction (compared with the PLIF procedure) of the traversing nerve root and thecal sac, and with essentially no retraction of the exiting nerve root. A number of materials have been used in the TLIF procedure for structural interbody support, including au- tograft and allograft bone, metal, composites, and, recent- ly, nonresorbable and resorbable polymers. In this paper the intermediate clinical results of the use of a hollow cylindrical bioabsorbable interbody spacer (HYDRO- SORB mesh; Medtronic Sofamor Danek, Inc., Memphis, TN) as well as a brief synopsis of some of the basic re- search leading to the development of the HYDROSORB material are presented. HYDROSORB is a copolymer consisting of a 70:30 ra- tio of poly-L-lactide and D,L-lactide that surgeons have started to use recently for various spinal procedures, in- cluding interbody structural support in the unilateral TLIF arthrodesis procedure (Fig. 1). Resorbable polymer im- plants, similarly to nonresorbable ones, have the advan- tage of being radiolucent, thus facilitating radiographic and imaging analysis of the status of the interbody fusion. Uniquely and perhaps more importantly, the resorbable implant slowly degrades into carbon dioxide and water over a 12- to 18-month period, which allows anterior col- umn structural support to shift gradually from the implant to the maturing interbody fusion mass. Although there have been published series that have demonstrated en- couraging preliminary results of bioabsorbable polymers in interbody fusion, 8 this is the first clinical series to be published in which the mean follow-up duration equals or exceeds the biological life expectancy of this material (18 months). Neurosurg Focus 16 (3):Article 11, 2004, Click here to return to Table of Contents Instrumented transforaminal lumbar interbody fusion with bioabsorbable polymer implants and iliac crest autograft JEFFREY D. COE, M.D. Center for Spinal Deformity and Injury, Los Gatos, California Object. The purpose of this study was to evaluate the clinical and radiographic results in 31 patients from one cen- ter who underwent instrumented transforaminal lumbar interbody fusion (TLIF) for primarily degenerative indications. Methods. Bioabsorbable polymer spacers manufactured with a copolymer of 70:30 poly(L-lactide-co-D,L-lactide) and filled with iliac crest autograft bone were used for the TLIF procedure. In this paper the details of this procedure, intermediate (1- to 2-year) clinical and radiographic outcomes, and the basic science and rationale for the use of bioab- sorbable polymers are discussed. At a mean of 18.4 months of follow up, 30 patients (96.8%) were judged to have attained solid fusions and 25 patients (81%) had good to excellent results. Three patients (9.7%) experienced compli- cations, none of which were directly or indirectly attributable to the use of the bioabsorbable polymer implant. Only one implant in one patient (3.2%) demonstrated mechanical failure on insertion, and that patient experienced no clin- ical sequelae. Conclusions. This is the first clinical series to be published in which the mean follow-up duration equals or exceeds the biological life expectancy of this material (12–18 months). Both the clinical and radiographic results of this study support the use of interbody devices manufactured from biodegradable polymers for structural interbody support in the TLIF procedure. KEY WORDS transforaminal lumbar interbody fusion bioabsorbable implant Neurosurg. Focus / Volume 16 / March, 2004 1 Abbreviations used in this paper: PLA = polylactic acid; PLIF = posterior lumbar interbody fusion; rhBMP-2 = recombinant human bone morphogenetic protein–2; Sf-36 = Short Form 36; TLIF = transforaminal lumbar interbody fusion. Unauthenticated | Downloaded 01/21/21 07:21 PM UTC

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Page 1: Instrumented transforaminal lumbar interbody fusion with ... · space. Except when sharp instruments are used, however, use of the nerve root retractor is not mandatory. A No. 15

In 1953, Cloward2 first described his PLIF techniqueas a surgical treatment option for lumbar disc disease. Al-though the PLIF procedure slowly gained acceptancethereafter,7,12 it was not until the advent of pedicle screwspinal instrumentation that this operation became wide-ly performed.14,15 The unilateral transforaminal approachfor segmental lumbar interbody arthrodesis was firstdescribed in the 1980s by Blume1 to address some ofthe complications associated with instrumented (bilateral)PLIF described by Steffee and Sitkowski.14 In the 1990sthe TLIF procedure was modified and popularized byHarms, et al.5

The TLIF procedure is an interbody combined with aunilateral posterior (facet and/or interlaminar) arthrodesisperformed with or without a bilateral posterolateral arthro-desis that is stabilized with pedicle screw instrumentation.This procedure is performed via a single midline posteri-or surgical approach. Access to the intervertebral disc isgained by a unilateral resection of the lamina, pars inter-articularis, and zygapophysial (facet) joint at the level orlevels to be fused. An aggressive discectomy and inter-body arthrodesis can thus be performed unilaterally withrelatively minimal medial retraction (compared with thePLIF procedure) of the traversing nerve root and thecal

sac, and with essentially no retraction of the exiting nerveroot. A number of materials have been used in the TLIFprocedure for structural interbody support, including au-tograft and allograft bone, metal, composites, and, recent-ly, nonresorbable and resorbable polymers. In this paperthe intermediate clinical results of the use of a hollowcylindrical bioabsorbable interbody spacer (HYDRO-SORB mesh; Medtronic Sofamor Danek, Inc., Memphis,TN) as well as a brief synopsis of some of the basic re-search leading to the development of the HYDROSORBmaterial are presented.

HYDROSORB is a copolymer consisting of a 70:30 ra-tio of poly-L-lactide and D,L-lactide that surgeons havestarted to use recently for various spinal procedures, in-cluding interbody structural support in the unilateral TLIFarthrodesis procedure (Fig. 1). Resorbable polymer im-plants, similarly to nonresorbable ones, have the advan-tage of being radiolucent, thus facilitating radiographicand imaging analysis of the status of the interbody fusion.Uniquely and perhaps more importantly, the resorbableimplant slowly degrades into carbon dioxide and waterover a 12- to 18-month period, which allows anterior col-umn structural support to shift gradually from the implantto the maturing interbody fusion mass. Although therehave been published series that have demonstrated en-couraging preliminary results of bioabsorbable polymersin interbody fusion,8 this is the first clinical series to bepublished in which the mean follow-up duration equals orexceeds the biological life expectancy of this material (18months).

Neurosurg Focus 16 (3):Article 11, 2004, Click here to return to Table of Contents

Instrumented transforaminal lumbar interbody fusion withbioabsorbable polymer implants and iliac crest autograft

JEFFREY D. COE, M.D.

Center for Spinal Deformity and Injury, Los Gatos, California

Object. The purpose of this study was to evaluate the clinical and radiographic results in 31 patients from one cen-ter who underwent instrumented transforaminal lumbar interbody fusion (TLIF) for primarily degenerative indications.

Methods. Bioabsorbable polymer spacers manufactured with a copolymer of 70:30 poly(L-lactide-co-D,L-lactide)and filled with iliac crest autograft bone were used for the TLIF procedure. In this paper the details of this procedure,intermediate (1- to 2-year) clinical and radiographic outcomes, and the basic science and rationale for the use of bioab-sorbable polymers are discussed. At a mean of 18.4 months of follow up, 30 patients (96.8%) were judged to haveattained solid fusions and 25 patients (81%) had good to excellent results. Three patients (9.7%) experienced compli-cations, none of which were directly or indirectly attributable to the use of the bioabsorbable polymer implant. Onlyone implant in one patient (3.2%) demonstrated mechanical failure on insertion, and that patient experienced no clin-ical sequelae.

Conclusions. This is the first clinical series to be published in which the mean follow-up duration equals or exceedsthe biological life expectancy of this material (12–18 months). Both the clinical and radiographic results of this studysupport the use of interbody devices manufactured from biodegradable polymers for structural interbody support in theTLIF procedure.

KEY WORDS • transforaminal • lumbar interbody fusion • bioabsorbable implant

Neurosurg. Focus / Volume 16 / March, 2004 1

Abbreviations used in this paper: PLA = polylactic acid; PLIF =posterior lumbar interbody fusion; rhBMP-2 = recombinant humanbone morphogenetic protein–2; Sf-36 = Short Form 36; TLIF =transforaminal lumbar interbody fusion.

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Indications for the TLIF procedure include mechanicallow-back pain related to degenerative disc disease with orwithout disc herniation, isthmic or degenerative spondy-lolisthesis, spinal stenosis with instability, degenerativescoliosis, and failed previous lumbar surgery. This lastindication occurs most commonly in patients with recalci-trant low-back pain after discectomy for disc herniation,which results in instability of one or more levels inpatients whose disease has failed to respond to a compre-hensive 3- to 6-month nonsurgical treatment program.5,9

CLINICAL MATERIAL AND METHODS

Surgical Procedure

The patient is placed prone on a suitable spine frameor table with the hips in maximum extension, helping tomaintain lumbar lordosis; this position affords partial re-duction of an isthmic or degenerative spondylolisthesis,when present. A standard midline approach is used. Care-ful subperiosteal dissection is extended to the tips of thetransverse processes of the levels included in the fusion.Through the same incision, one iliac crest is exposed butmuscles are left attached. A small window is made in theposterior iliac crest and an adequate amount of cancellousbone is removed from between the cortical tables of thecrest to use for bone grafts. The fascia over the iliac crestis closed with interrupted sutures. I routinely reconstructthe iliac defect with coralline hydroxyapatite granules anddemineralized bone matrix, and am aware of little or nopostoperative donor site pain associated with this method.

The pedicles are cannulated and radiopaque markersare placed therein. A localizing radiograph is then ob-tained to verify pedicle cannulation and to confirm levelidentification. The pedicles are tapped in preparation forscrew placement. At this point the transverse processesare decorticated and iliac crest bone is used to perform theintertransverse (posterolateral) fusion. Multiaxial pediclescrews are then inserted at the appropriate levels and prop-er placement is confirmed with subsequent radiographicimaging and direct electrical stimulation of the screwsperformed while recording electromyographic responses

in the myotomes of the adjacent exiting nerve roots(evoked electromyographic responses).

The side of the spine selected for the TLIF is chosen onthe basis of preoperative radicular symptoms and/or imag-ing studies. Generally the most symptomatic and/or dis-eased side is selected for the transforaminal approach; thatis, if a disc herniation or foraminal stenosis is present andis predominantly one-sided, that side is chosen. If symp-toms are bilaterally equal, an approach on the left side isused. Rods are contoured in lordosis and cut approximate-ly 0.5 to 1 cm longer than usual to allow for disc space dis-traction. The rod and locking screws are inserted into themultiaxial screw heads, bilateral distraction is applied, andthe locking screws are tightened.

Alternatively, particularly on the side of the TLIF ap-proach, a device designed to distract the heads of the mul-tiaxial pedicle screws while maintaining wide access tothe foramen can be used, facilitating access to the inter-vertebral disc between the heads of the multiaxial screws(Fig. 2). After distraction has been applied, a 10-mm oste-otome and Kerrison rongeurs are used to remove the infe-rior articular process and upper portion of the superior ar-ticular process on the side chosen for the TLIF. Theipsilateral pars interarticularis and the caudal and medialaspect of the ipsilateral lamina are resected. At this stageof the procedure, except at levels with bilateral spondylol-ysis, the cephalad lamina is left intact to protect the at-tached pedicles during distraction, and the midline laminaand spinous process are left intact to prevent excessive re-traction of the traversing nerve root and thecal sac.

Exposure of the underlying disc space is facilitatedby removal of the lateral margin of the ligamentum fla-vum. Identifying the exiting nerve root inferior and medi-al to the upper (cephalad) instrumented pedicle as well asthe superior and medial aspect of the lower (caudal) onehelps orient the surgeon because the remainder of theanatomy is consistent in relations to these structures. Epi-dural bleeding is frequently encountered at this point dur-ing separation of the nerve root from epidural fat and ve-nous plexus. An irrigating bipolar electrocautery deviceis useful in controlling epidural bleeding and throm-bin-soaked Gelfoam and cottonoids also can be used if

J. D. Coe

2 Neurosurg. Focus / Volume 16 / March, 2004

Fig. 1. Left: Photograph showing two identically sized cylindrical interbody fusion spacers, both 10 mm tall and 13mm in diameter, with 2-mm-thick walls (both manufactured by Medtronic Sofamor Danek, Inc., Memphis, TN). The de-vice on the left side of the panel is the HYDROSORB spacer, which is manufactured from a bioabsorbable polymer. Thedevice on the right side is a titanium mesh cage (Pyramesh). Right: Photograph showing a HYDROSORB bioabsorb-able spacer mounted on an angled inserter that is designed to allow insertion of the device into the prepared disc space(contralateral to the side of the anular window) during the TLIF procedure. Photographs are reprinted with permissionfrom Slack, Inc.

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needed. Once hemostasis is achieved, the underlying discspace (lateral one third), dural sac, and exiting nerve rootshould be readily visible. The exiting nerve root rarelyneeds retraction except at the L5–S1 level. Gentle use ofan angled nerve root retractor protects the dural sac andfacilitates exposure and access to the underlying discspace. Except when sharp instruments are used, however,use of the nerve root retractor is not mandatory.

A No. 15 blade scalpel is used to create an anular win-dow. The medial border of the window is at the lateralmargin of the dural sac, and the lateral border is the later-al edge of the visible anulus. The incised anulus is re-moved with a pituitary rongeur. A 0.25-in osteotome or abox chisel is used to enlarge the window and remove pos-terior osteophytes, allowing easy access to the disc space.Specialized straight and angled osteotomes, pituitaryrongeurs, rasps, and curettes are used to elevate and re-move disc material and cartilaginous endplate (Fig. 3). Atthis point, additional distraction of the pedicle instrumen-tation can be applied, relying on ligamentotaxis and tactilefeedback to prevent overdistraction. The disc space is irri-gated with bacitracin-containing saline and then rein-spected to confirm complete removal of disc material. Adisc spanner or other measuring device is inserted to de-

termine the appropriate size of the bioabsorbable polymercage, which should be 0.5 to 1 mm shorter than the span-ner measurement to allow for lordosis when compressionis applied to the posterior instrumentation; 13-mm-diame-ter cages with heights ranging from 8 to 12 mm are mostcommonly used.

A 10-mm angled osteotome is used to decorticate onlythe anterior one third of the adjacent endplates. This de-cortication provides an excellent graft bed adjacent to theanterior anulus. The posterior two thirds of the adjacentendplates are less aggressively decorticated in order toprovide support for the cages. Previously harvested iliaccrest bone graft then is packed tightly into the anterior onethird of the disc space with a bone tamp. In multilevelcases, crushed cancellous allograft as well as iliac crestand local autograft (“morcellized” laminectomy and spi-nous process bone) is used for this step. Two HYDRO-SORB bioabsorbable polymer cages packed with iliaccrest autograft are then inserted into the disc space (Fig. 4left). The first spacer is inserted into the posterior inter-body interspace and maneuvered across the disc space tothe contralateral side by using an angled insertion deviceas well as straight and angled impactors (Fig. 4 right). Thesecond spacer is inserted into the ipsilateral posterior disc

Neurosurg. Focus / Volume 16 / March, 2004

Instrumented TLIF with bioabsorbable implants

3

Fig. 2. Left: Photograph showing the distractor. This device is designed to distract the heads of the multiaxial pedi-cle screws while maintaining wide access to the foramen. Right: Intraoperative photograph showing the distractor insitu. Note how the intervertebral disc can be easily approached between the heads of the multiaxial screws. Photographsare reprinted with permission from Slack, Inc.

Fig. 3. Photograph showing a left-facing angled and serrated curette that facilitates preparation of the vertebral end-plate during the TLIF procedure. Not shown are similar straight and right-facing serrated curettes. Photograph is reprint-ed with permission from Slack, Inc.

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space (Fig. 5), and distraction is then released. Direct in-spection of the spacer and palpation with the use of an ele-vator are performed to ensure that the ipsilateral cage iscontained within the intervertebral space. Ideally, the de-vices should be placed in the posterior one third of the discspace. This provides structural support close to the centerof rotation for the motion segment, and allows later radio-graphic assessment of fusion anterior to the cages.

Additional levels are treated as necessary. If distractorswere used, the rods are inserted and compression is thenapplied to lock the cages in place and maximize seg-mental lordosis. Device placement and stability are againconfirmed by inspection and palpation with straight andangled elevators. Further decompression, as indicated, isthen performed. The contralateral facet and any residualcontralateral lamina are decorticated and packed with the

remaining autograft bone, and one or two crosslinks areplaced to connect the rods on each side. The wound isclosed in layers over closed suction drainage to completethe procedure.

Patients are mobilized on postoperative Day 1 andare usually discharged from the hospital on Day 4; noexternal orthosis is required. For the first 6 weeks postop-eratively, patients are encouraged to walk as much aspossible. Physical therapy, beginning with aquatic condi-tioning exercises and progressing to land-based therapywith strengthening and aerobic exercises, is then progres-sively instituted. By 6 months, patients are allowed to re-sume full activities as tolerated. Typically, solid fusion isconfirmed radiographically at 12 months postoperatively.

Patient Population

Between December 2001 and September 2002, 31 pa-tients (22 men and 9 women) with a mean age of 45.5years (range 30–64 years) underwent the TLIF procedureat a total of 58 levels (mean 1.9 levels per patient, rangeone–three levels). This procedure was performed for avariety of lumbar conditions. Two 13 � 8 to 12–mm HY-DROSORB bioabsorbable spacers were used per in-terbody fusion level for anterior column support (116 to-tal spacers were implanted). Two more patients under-went posterior fusion at one additional level (transitionalL5–S1) without supplemental anterior column support.One patient with a Grade I isthmic spondylolisthesis atL5–S1 (below a previous anterior fusion from L2–4 for anL-3 burst fracture) underwent the TLIF procedure at L4–5and L5–S1 with instrumentation and posterior fusion fromL2–S1 (Fig. 6).

Nine patients in this series had undergone previous de-compressive lumbar surgery at one or more of the surgi-cally treated levels. One patient had undergone a previousTLIF procedure with implantation of metallic cages atL3–4 and L4–5 3 years before her TLIF procedure atL5–S1 with HYDROSORB spacers. In all patients in thisseries low-back pain was their predominant complaint,

J. D. Coe

4 Neurosurg. Focus / Volume 16 / March, 2004

Fig. 4. Left: Photograph showing two HYDROSORB spacers loaded on straight and angled inserters and packedwith autologous bone graft in preparation for insertion into the prepared intervertebral disc space. Right: These straightand angled impactors are used to adjust the implant position after insertion. To avoid cracking the HYDROSORB im-plants, it is important to avoid excessive force when using these impactors. Photographs are reprinted with permissionfrom Slack, Inc.

Fig. 5. Intraoperative photograph showing a HYDROSORBbioabsorbable spacer visualized through the anular window afterinsertion. The top of the photograph is oriented medial, left is ori-ented caudally. Photograph is reprinted with permission fromSlack, Inc.

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with varying degrees of radicular pain and neurologicalsymptoms. All patients in this series underwent at least 12months of nonsurgical care before receiving surgery.

Twenty-one patients (67%) underwent treatment forwork-related disorders of the lumbar spine. All patients inthis series had some component of degenerative disc dis-ease. A complete listing of the other diagnoses is shown inTable 1. The most cephalad level undergoing operation inthis series was L2–3. The distribution of fused levels isshown in Table 2. The mean estimated blood loss was1070 ml (range 350–3500 ml) and the mean postoperativelength of stay was 5.1 days (range 2–11 days).

Lumbar radiographs with anteroposterior, lateral, and

Ferguson views were obtained at 2 weeks and at 3, 6,12, and 24 months postoperatively. Lateral standing flex-ion–extension films were obtained as well, beginning withthe 6-month set. Fusion status was judged on the 12-month (and when available, the 24-month) films based onthe criteria listed in Table 3. The clinical results of thisstudy were analyzed using the method of Prolo, et al.12

Additionally, the SF-36 outcomes instrument was admin-istered preoperatively in all patients, 12 months postoper-atively in 19 patients, and 24 months postoperatively infour patients. The preoperative and 12-month postopera-tive scores were compared and analyzed for the purposesof this study.

Neurosurg. Focus / Volume 16 / March, 2004

Instrumented TLIF with bioabsorbable implants

5

Fig. 6. This 41-year-old man with isthmic Grade I spondylolisthesis had undergone an anterior decompression, tita-nium mesh cage implantation, fusion, and instrumentation for an L-3 burst fracture with neurological deficit (whichresolved postoperatively) 6 years before a lifting injury that rendered his spondylolisthesis symptomatic. Upper Left:Lateral radiograph demonstrating the anterior implants spanning L2–3. Upper Center: A detailed lateral radiograph ofthe lumbosacral junction indicating the loss of intervertebral disc height in addition to the spondylolisthesis. UpperRight: Lateral radiograph obtained 2 weeks postoperatively demonstrating the restoration of the L5–S1 intervertebral discheight and partial reduction of the spondylolisthesis as well as the posterior transpedicular implants spanning L2–S2.Note that the lordosis between L-3 and S-1 is preserved. Preoperative discography had indicated that the L4–5 disc wastoo degenerated and symptomatic not to be included in the fusion. Lower Left: Postoperative anterior–posterior radio-graph obtained at 2 weeks. Lower Right: Lateral radiograph obtained 1 year postoperatively indicating solid interbodyfusion at L4–5 and L5–S1 with preservation of disc height and lumbar lordosis.

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RESULTS

The mean follow-up duration in this series was 18.4months (range 16–24 months). Four postoperative com-plications were noted in three patients (9.7%) and arelisted in Table 4. None of these complications was attri-butable to the use of the bioabsorbable polymer. In onepatient (3.2%) one cracked implant was noted immediate-ly after insertion. No subsidence or other evidence of fur-ther structural failure has been observed subsequently inthis patient and he was judged to have attained solid fu-sion at his most recent follow-up visit. No patient has dis-played evidence of allergic or inflammatory reactionsto the polymer. Specifically, there have been no adverseevents related either directly or indirectly to use of thebioabsorbable implants.

In one patient (3.2%) a nonunion developed as deter-mined by obvious motion on flexion–extension lateral ra-diographs obtained after increasing reports of low-backpain at 9 months postsurgery; this patient has undergonesubsequent revision surgery. The outcome in the remain-ing 30 patients (96.8%), however, has progressed to asolid fusion, as illustrated in Fig. 7.

According to the criteria of Prolo, et al.,12 25 (80.6%) ofthe 31 patients had good to excellent results, five (16.1%)had a fair result, and one (3.2%), the only patient in thisseries with a nonunion, had a poor result (assessed beforehis revision surgery; see Table 5). The SF-36 outcomesanalysis demonstrated a statistically significant improve-ment in the 12-month mean pain scores and the 12-monthmean physical function scores, compared with the preop-erative scores assessed according to the same scales (Fig.8). Other SF-36 scores showed improvement, but onlysome results reached statistical significance.

DISCUSSION

Surgical procedures that include both posterolateral andinterbody fusion have demonstrated high fusion rates andgood clinical results.7,11–13,15 These procedures have distinctadvantages including anterior column load sharing, largesurface areas for fusions, restoration of a normal sagittalprofile, and the achievement of passive foraminal decom-pression. The posterior unilateral transforaminal approachallows the surgeon to address all of these issues concur-rently via one approach without the need for a secondanterior incision and its associated morbidity and compli-cations (particularly vascular complications in all patientsand retrograde ejaculation in male patients). Comparedwith the PLIF, the TLIF has the advantage of requiring ex-posure and manipulation of the neural elements (for thepurpose of achieving interbody fusion) on only one sideper level, and even that only minimally.

A number of interbody devices have been used for thisprocedure, including structural allograft, structural auto-graft, titanium mesh, cylindrical threaded devices, andboth resorbable and nonresorbable polymers. I believethat there are some definite advantages of using resorbablepolymers, including the facilitation of imaging to assessfusion (an advantage shared with nonresorbable polymersand bone) and the unique bioresorption process, whichallows the anterior column fusion mass to share the loadprogressively with the posterior column.

J. D. Coe

6 Neurosurg. Focus / Volume 16 / March, 2004

TABLE 1Diagnoses in 31 patients who underwent TLIF procedures*

Diagnosis No. of Patients (%)

degenerative disc disease 31 (100.0)disc herniation 24 (77.4)spinal stenosis 18 (58.1)failed previous lumbar op 10 (32.3)isthmic spondylolisthesis 2 (6.5)degenerative spondylolisthesis 1 (3.2)prior unrelated lumbar op 1 (3.2)

* Because all patients had multiple diagnoses, the totals exceed 100%.

TABLE 2Levels fused in 31 patients who underwent TLIF procedures*

Levels No. of Patients (%)

oneL2–3 2 (6.5)L3–4 0 (0.0)L4–5 2 (6.5)L5–S1 6 (19.4)subtotal 10 (32.3)

twoL3–5 1 (3.2)L4–S1 14 (45.2)subtotal 15 (48.4)

three L3–5 5 (16.1)L2–4 1 (3.2)subtotal 6 (19.4)

* Only levels with interbody fusion are included.

TABLE 3Fusion criteria used for 31 patients who underwent TLIF procedures

Criteria

Solid Fusion Nonunion

bridging interbody & intertransverse bone absence of bridging interbody & intertransverse boneno motion on lat flexion–extension radiographs presence of motion on lat flexion–extension radiographsabsence of continuous interbody radiolucent lines one or more continuous interbody radiolucent linessubsidence to �75% of original disc space height subsidence to �75% of original disc space height

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Currently, there are two Food and Drug Administra-tion–approved resorbable materials that are most com-monly used in orthopedic and/or neurosurgical applica-tions. The first is a copolymer of poly-L-lactic acid andpolyglycolic acid that retains 70% of its strength for 6to 9 weeks, with nearly complete loss of strength at 12weeks, and essentially complete resorption (mass loss)within 12 months. The other is a copolymer of poly-L-lac-tide and D,L-lactide, which retains approximately 70%strength for 6 to 9 months and is resorbed between 18 and36 months. HYDROSORB is made of the latter copoly-mer, which is believed to have the ideal spinal implantcharacteristics, including a slow degradation with reten-tion of strength over a sufficiently long period to providestability while the interbody fusion mass matures and pro-gressively assumes anterior column loading over time(load sharing).

Concerns about the safety of bioabsorbable deviceshave been addressed in several basic science stud-ies.3,4,6,10,16,17 The biocompatibility of PLA has been demon-strated in both dural and neural tissues within the spinalcord by Lundgren, et al.10 Gautier, et al.,4 have shown thatthe presence of PLA has no effect on neuronal cells, non-neuronal cells, or axonal growth. Likewise, De Medi-naceli, et al.,3 have demonstrated biocompatibility withperipheral nerves on both gross and histological examina-tion. It has also been demonstrated that pH changes areabsent in the degradation of PLA implants placed in thefemoral shafts of sheep.17

The mechanical properties of HYDROSORB haveshown 100% retention of strength at 3 months, 90% at 6months, 70% at 9 months, and 50% at 12 months.6 Re-sorption of PLA occurs by bulk hydrolysis into carbondioxide and water; thus there are no detrimental degrada-tion products.6

In 2002 Toth and coworkers16 published a study inwhich they used stand-alone resorbable threaded inter-body spine implants to compare autograft against rhBMP-2 implants. In their study they demonstrated no significantinflammatory response related to the polymer and gradualreplacement of the polymer spacer by precursors of os-seous tissue and ultimately bone, indicating good biocom-patibility in the 12-, 18-, and 24-month groups of sheep. Inthe 12-month group, two of four sheep (one with auto-graft, one with rhBMP-2) achieved fusion and two (onewith autograft and one with rhBMP-2) did not achievefusion, ostensibly because of increased segmental mobili-ty related to mechanical degradation of the resorbablepolymer spacers. In the 18- and 24-month groups, howev-er, all five sheep (three with autograft and two withrhBMP-2) went on to attain solid fusion determined bothradiographically and histologically.

Only preliminary clinical results of the use of cylindri-cal HYDROSORB bioabsorbable spacers have been re-ported to date.8,9 Lowe and Coe8 reported the preliminaryresults in a combined (two-center) series of 60 patientswho underwent the TLIF procedure for implantation ofHYDROSORB mesh cages. Early clinical results werefound to be encouraging in that study, but the follow-upduration was short (mean 4.7 months; longest follow-upperiod only 9 months). No complications attributable tothe use of the resorbable implants were noted, however.

This is the first series in which the clinical results ofinterbody fusion with spacers manufactured from 70:30poly(L-lactide-co-D,L-lactide) copolymer are reported af-ter a follow-up period that equals or exceeds the biologi-cal life expectancy of the material (12–18 months). All

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TABLE 4Complications in 31 patients who underwent TLIF

Complication No. of Patients (%)

superficial wound infection 1 (3.2)deep wound infection* 1 (3.2)transient foot drop 1 (3.2)persistent foot drop* 1 (3.2)

* These two complications occurred in a single patient.

Fig. 7. This 39-year-old man underwent a single-level TLIF fordegenerative disc disease and a central disc herniation. UpperLeft: Preoperative lateral radiograph. Upper Right: Lateral radio-graph obtained 2 weeks postoperatively. Lower Left: Lateral ra-diograph obtained 6 months postoperatively. Note that the discspace height is well preserved with only minimal loss of lordoticangulation of the intervertebral endplates. Note also that the bonedensity throughout the entire disc space is well preserved, indicat-ing probable progression toward solid arthrodesis. Lower Right:A solid trabeculated interbody fusion in the posterior two thirds ofintervertebral disc space is demonstrated in a lateral radiographobtained 12 months postoperatively. Note the absence of kyphosisand subsidence compared with the 6-month film.

TABLE 5Clinical results in 31 patients who underwent TLIF procedures*

Clinical ProloResult Score No. of Patients (%)

excellent 9–10 6 (19.4)good 7–8 19 (61.3)fair 5–6 5 (16.1)poor 2–3 1 (3.2)

* According to the criteria of Prolo, et al.

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of the procedures were performed by the same surgeonat one institution, with 100% follow up. Clinical resultsare equivalent to those published in comparable seriesin which nonresorbable spacers were used for interbodystructural support. This is particularly noteworthy becausemore than two thirds of the patients in this series werefrom a traditionally difficult-to-treat patient population(those with Worker’s Compensation claims).7,11–13,15

Limitations of this study include a relatively small se-ries size (31 patients), lack of a control group in whichnonresorbable implants were used, and a relatively shortfollow-up duration for long-term assessment of clinicalresults. Nevertheless, this series represents the largest oneinvolving the clinical use of bioabsorbable polymer inter-body implants yet published in which the mean follow-upduration exceeds 18 months.

The future of bioabsorbable technology in spinal sur-gery appears to be quite exciting. Bone morphogeneticprotein appears to be well suited for use in combinationwith resorbable polymer interbody implants.16 I beganto use rhBMP-2 clinically in lieu of iliac crest autograftwith HYDROSORB mesh interbody spacers in the fall of2002. In more than 30 cases treated so far, the blood losshas been less, the length of stay has been shorter, and,most significantly, fusion has been achieved earlier than inthe cases reported in the present series. Results in thesepatients will be formally reported when at least 1 year offollow up has been achieved in most of them.

CONCLUSIONS

In this study I have evaluated the clinical and radio-graphic results in 31 patients from one center who under-

went instrumented TLIF for primarily degenerative in-dications. Cylindrical bioabsorbable polymer spacersmanufactured with a 70:30 copolymer of poly L-lactideand D,L-lactide (HYDROSORB) and packed with iliaccrest autograft bone were used to stabilized the spine. Ata mean of 18.4 of months follow up, 30 patients (96.8%)were judged to have attained solid fusions and 25 patients(81%) had good to excellent results. Three patients (9.7%)experienced complications, none of which were directlyor indirectly attributable to the use of the bioabsorbablepolymer implant. Only one implant in one patient (3.2%)demonstrated mechanical failure on insertion; there wereno clinical sequelae. This is the first clinical series to bepublished in which the mean follow-up duration equals orexceeds the biological life expectancy of this material(12–18 months). Both the clinical and radiographic resultsof this study support the use of interbody devices manu-factured from biodegradable polymers for structural inter-body support in the TLIF procedure.

Acknowledgment

I thank Sarmad Pirzada, M.D., M.P.H., for his assistance in pre-paring the SF-36 data reported in this paper.

References

1. Blume HG: Unilateral posterior lumbar interbody fusion: sim-plified dowel technique. Clin Orthop 193:75–84, 1985

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3. De Medinaceli L, al Khoury R, Merle M: Large amounts ofpolylactic acid in contact with divided nerve sheaths have no

J. D. Coe

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Fig. 8. Bar graph showing SF-36 data in 19 of 31 patients in whom 12-month postoperative mean scores are com-pared with preoperative mean scores. Note that there were statistically significant improvements in the mean pain andphysical function scores.

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adverse effects on regeneration. J Reconstr Microsurg 11:43–49, 1995

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5. Harms J, Jeszenszky D, Stoltze D, et al: True spondylolisthesisreduction and monosegmental fusion in spondylolisthesis, inBridwell KH, DeWald RL (eds): The Textbook of Spinal Sur-gery, ed 2. Philadelphia: Lippincott-Raven, 1997, Vol 2, pp1337–1347

6. Hollinger JO, Battistone GC: Biodegradable bone repair ma-terials. Synthetic polymers and ceramics. Clin Orthop 207:290–305, 1986

7. Lin PM, Cautilli RA, Joyce MF: Posterior lumbar interbodyfusion. Clin Orthop 180:154–168, 1983

8. Lowe TG, Coe JD: Bioresorbable polymer implants in the uni-lateral transforaminal lumbar interbody fusion procedure. Or-thopedics 25 (Suppl 10):S1179–S1183, 2002

9. Lowe TG, Tahernia AD: Unilateral transforaminal posteriorlumbar interbody fusion. Clin Orthop 394:64–72, 2002

10. Lundgren D, Nyman S, Mathisen T, et al: Guided bone regen-eration of cranial defects, using biodegradable barriers: an ex-perimental pilot study in the rabbit. J Craniomaxillofac Surg20:257–260, 1992

11. Newman MH, Grinstead GL: Anterior lumbar interbody fusionfor internal disc disruption. Spine 17:831–833, 1992

12. Prolo DJ, Oklund SA, Butcher M: Toward uniformity in evalu-ating results of lumbar spine operations. A paradigm applied toposterior lumbar interbody fusions. Spine 11:601–606, 1986

13. Shirado O, Zdeblick TA, McAfee PC, et al: Biomechanicalevaluation of methods of posterior stabilization of the spine andposterior lumbar interbody arthrodesis for lumbosacral isthmicspondylolisthesis. A calf-spine model. J Bone Joint Surg Am73:518–526, 1991

14. Steffee AD, Sitkowski DJ: Posterior lumbar interbody fusionand plates. Clin Orthop 227:99–102, 1988

15. Suk SI, Lee CK, Kim WJ, et al: Adding posterior lumbar inter-body fusion to pedicle screw fixation and posterolateral fusionafter decompression in spondylolytic spondylolisthesis. Spine22:210–220, 1997

16. Toth JM, Wang M, Scifert JL, et al: Evaluation of 70/30 D,L-PLa for use as a resorbable interbody fusion cage. Orthopedics25 (Suppl 10):S1131–S1140, 2002

17. van der Elst M, Dijkema AR, Klein CP, et al: Tissue reaction onPLLA versus stainless steel interlocking nails for fracture fixa-tion: an animal study. Biomaterials 16:103–106, 1995

Manuscript received January 19, 2004.Accepted in final form February 4, 2004.Address reprint requests to: Jeffrey D. Coe, M.D., 360 Dar-

danelli Lane Suite 1F, Los Gatos, California 95032.

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