Computerized tomography evaluation of a resorbable implant after transforaminal lumbar interbody fusion

Біоматеріал на основі полілактиду та його використання як кісткових імплантатів (аналітичний огляд літератури)

У багатьох галузях медицини широке застосування отримали імплантати з різних синтетичних та природних біоматеріалів. Серед матеріалів, що частіше використовують для створення імплантатів, полілактид (PLA), особливістю якого є біодеградація в ділянках імплантації, остеоінтеграція, здатність індукувати процеси утворення кісткової тканини та висока біосумісність з організмом. Мета огляду: проаналізувати та узагальнити дані щодо перебудови в кістці біорезорбуючих біоматеріалів на основі полілактиду та визначити тенденції розвитку проблеми. В огляді літератури подано загальну характеристику та визначено історичні віхи розвитку проблеми та використання деградуючих полімерів у кістковій хірургії. Надані дані щодо факторів, що впливають на біодеградацію в кістках цього біоматеріалу, та визначено особливості його остеоінтеграції залежно від складу. Наведено дані щодо використання PLA та співполімерів у кістковій хірургії та регенераторній медицині. Важливим напрямком майбутніх досліджень буде розробка композитних біоматеріалів на основі PLA з бажаними якостями остеоінтеграції та керованою біодеградацією. Подано нові тенденції розвитку напрямку використання в кістковій хірургії імплантатів на основі композитних матеріалів, виготовлених на основі PLA, та новітні способи створення імплантатів та композитів із використанням 3D-принтера.

Distinct fusion intersegmental parameters regarding local sagittal balance provide similar clinical outcomes: a comparative study of minimally invasive versus open transforaminal lumbar interbody fusion

Background

Most contemporary studies suggested that intersegmental parameters including disc height and local lordosis contribute to the sagittal balance of fused lumbar. Although similar clinical outcomes following MIS- and Open-TLIF were reported essentially at the early postoperative time, the comparison of local balance variables after these two different techniques was lack. The radiological differences maybe not relevant to the postoperative efficacy at an earlier post-operation stage. But during the long-term follow-up, the complications with regards to the sagittal imbalance might occur due to the distinct biomechanical properties of fusion level after MIS- and Open-TLIF.

Methods

The patients who underwent a single-level MIS- and Open-TLIF were reviewed retrospectively. The anterior disc height (ADH), posterior disc height (PDH), and segmental lordosis (SL) of the fusion segment were measured using recognition technical fluoroscopy. The mean disc height (MDH) was calculated by (ADH + PDH)/2. The relative DH was normalized by the anterior height of the upper vertebrae. The body mass index (BMI), the pain score of low back and leg visual analogue scale (VAS), Oswestry disability index (ODI), estimated blood loss, and hospital stay length was collected.

Results

A total of 88 patients undergoing a single-level TLIF (MIS and Open) were included. The pre- and post-operative ADH, PDH, MDH, and SL of MIS-TLIF group were 1.57 ± 0.33 cm, 0.79 ± 0.20 cm, 1.18 ± 0.21 cm, 7.36 ± 3.07 and 1.63 ± 0.30 cm, 1.02 ± 0.28 cm, 1.32 ± 0.24 cm, 10.24 ± 4.79 respectively. Whereas, the pre- and post-operative ADH, PDH, MDH, and SL of Open-TLIF group were 1.61 ± 0.40 cm, 0.77 ± 0.21 cm, 1.19 ± 0.24 cm, 9.05 ± 5.48 and 1.81 ± 0.33 cm, 0.98 ± 0.24 cm, 1.39 ± 0.24 cm, 12.34 ± 4,74 respectively. MIS- and Open-TLIF group showed no significant differences in low back VAS, leg VAS, and ODI both in pre-operation and post-operation (P > 0.05). The estimated blood loss and hospital stay length in the MIS-TLIF group were significantly lower than those in the Open-TLIF group (P < 0.05).

Conclusion

MIS- and Open-TLIF provided similar clinical outcomes as the respect of low back VAS, leg VAS, and ODI. MIS-TLIF significantly reduced the blood loss and length of hospital stay though. The intervertebral parameters of DH and SL were both increased significantly, Open-TLIF group presented better sagittal balance in term of ADH and SL variables. The contrast investigation of intersegmental parameters may help the surgeons to figure out the further advantages of MIS-TLIF technique, and then better manage the rehabilitation and prevent the reoperation.

The effectiveness of biodegradable instrumentation in the treatment of spinal fractures

INTRODUCTION

A variety of biodegradable implants (screws, rods, plates and cages) are available which are composed of many different biodegradable polymers with varying characteristics. The present review of animal and clinical studies examines the efficacy and safety of biodegradable implants in spinal fracture intervention.

METHODS

A review of the literature through March 2018 was performed using PubMed and Cochrane databases. Success rates were calculated according to sufficient tissue biocompatibility, solid clinical fusion and propensity for osseointegration.

RESULTS

49 articles (24 animal and 25 human studies) were included. In animal experiments, the overall success rate for spinal fusion was 60.3%, while the mean success rate regarding the cervical spine was 51.8% compared to 68.1% for the lumbar spine (p = 0.002). In studies involving control group(s): the mean bioabsorbable implant success rate for spinal fusion was 42% compared to 57% for conventional implants (p = 0.0016). In the lumbar spine pL-lactide acid (PLLA) had 75.2% success rate compared to poly (L-lactide-co-DL-lactide) (PLDLLA) at 53.4% (p = 0.003). In clinical studies, the overall mean success rate was 89%, while the mean success rate regarding the cervical spine was 92%, as compared to 83.6% for the lumbar spine (p = 0.001). In studies involving control group(s): the mean bioabsorbable implant success rate was 75% compared to a conventional implant mean success rate of 97% (p<0.0001). In the cervical spine PLLA had a 98.7% success rate compared to 90% with PLDLLA (p = 0.015). In the lumbar spine PLDLLA had 84.7% success rate compared to 63.6% for poly-glycolic acid (PGA) (p = 0.085).

DISCUSSION

Studies combined biodegradable and conventional implants. Polymers were used in various combinations and surface modification of the implants also varied. Comparison studies were of small sample size. Animal and clinical studies diverged. The current data are not encouraging. The end-point of assessing osseointegration varies in the studies and is indeterminate. In early stages the structure comparison of osseous restoration using biodegradable implants appears inferior to utilization of conventional cages and instrumentation. There is no statistically significant evidence supporting the efficacy of biodegradable implants replacing traditional instrumentation. There is a lack of prospective clinical trials with long-term follow-up regarding utilization of biodegradable implants and the available data does not support their routine use in spinal fracture intervention.

Comparison of the PEEK cage and an autologous cage made from the lumbar spinous process and laminae in posterior lumbar interbody fusion

Background

A prospective cohort study was performed to evaluate the clinical and radiological outcomes following posterior lumbar interbody fusion (PLIF) in patients treated with a PEEK cage compared to those treated with an autologous cage using the lumbar spinous process and laminae (ACSP).

Methods

Sixty-nine consecutive patients with lumbar degenerative disc disease were randomly assigned to either a PEEK cage (group A, n = 34) or an ACSP (group B, n = 35). Monosegmental PLIF was performed in all patients. Mean lumbar lordosis, mean disc height, visual analog scale (VAS) scores, functional outcomes, fusion rates and complication rates were recorded and compared. The patients were followed postoperatively for a minimum of 2 years.

Results

Successful radiographic fusion was documented in all patients. No flexion–extension hypermobility or pedicle screw loosening or breakage occurred during the follow-up period. No significant difference existed between the 2 groups when comparing the mean lumbar lordosis, mean disc height, visual analog scale (VAS) scores, functional outcomes, fusion rates or complication rates. Overall satisfactory results were achieved in both groups.

Conclusions

The results suggest that the ACSP appears to be equally as safe and effective as the PEEK cage.

Trial registration

ISRCTN25558534. Retrospectively registered 16/02/2016.

L5/S1 Fusion Rates in Degenerative Spine Surgery: A Systematic Review Comparing ALIF, TLIF, and Axial Interbody Arthrodesis

STUDY DESIGN

Systematic review.

OBJECTIVE

To determine the fusion rate of an anterior lumbar interbody fusion (ALIF), transforaminal lumbar interbody fusion (TLIF), and axial arthrodesis at the lumbosacral junction in adult patients undergoing surgery for 1- and 2-level degenerative spine conditions.

SUMMARY OF BACKGROUND DATA

An L5/S1 interbody fusion is a commonly performed procedure for pathology such as spondylolisthesis with stenosis; however, it is unclear if 1 technique leads to superior fusion rates.

MATERIALS AND METHODS

A systematic search of MEDLINE was conducted for literature published between January 1, 1992 and August 17, 2014. All peer-reviewed articles related to the fusion rate of L5/S1 for an ALIF, TLIF, or axial interbody fusion were included.

RESULTS

In total, 42 articles and 1507 patients were included in this systematic review. A difference in overall fusion rates was identified, with a rate of 99.2% (range, 96.4%-99.8%) for a TLIF, 97.2% (range, 91.0%-99.2%) for an ALIF, and 90.5% (range, 79.0%-97.0%) for an axial interbody fusion (P=0.005). In a paired analysis directly comparing fusion techniques, only the difference between a TLIF and an axial interbody fusion was significant. However, when only cases in which bilateral pedicle screws supported the interbody fusion, no statistical difference (P>0.05) between the 3 techniques was identified.

CONCLUSIONS

The current literature available to guide the treatment of L5/S1 pathology is poor, but the available data suggest that a high fusion rate can be expected with the use of an ALIF, TLIF, or axial interbody fusion. Any technique-dependent benefit in fusion rate can be eliminated with common surgical modifications such as the use of bilateral pedicle screws.

Exploratory meta-analysis on dose-related efficacy and morbidity of bone morphogenetic protein in spinal arthrodesis surgery

OBJECT

Bone morphogenetic protein (BMP) is frequently used for spinal arthrodesis procedures in an "off-label" fashion. Whereas complications related to BMP usage are well recognized, the role of dosage is less clear. The objective of this meta-analysis was to assess dose-dependent effectiveness (i.e., bone fusion) and morbidity of BMP used in common spinal arthrodesis procedures. A quantitative exploratory meta-analysis was conducted on studies reporting fusion and complication rates following anterior cervical discectomy and fusion (ACDF), posterior cervical fusion (PCF), anterior lumbar interbody fusion (ALIF), transforaminal lumbar interbody fusion (TLIF), posterior lumbar interbody fusion (PLIF), and posterolateral lumbar fusion (PLF) supplemented with BMP.

METHODS

A literature search was performed to identify studies on BMP in spinal fusion procedures reporting fusion and/or complication rates. From the included studies, a database for each spinal fusion procedure, including patient demographic information, dose of BMP per level, and data regarding fusion rate and complication rates, was created. The incidence of fusion and complication rates was calculated and analyzed as a function of BMP dose. The methodological quality of all included studies was assessed according to the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. Data were analyzed using a random-effects model. Event rates are shown as percentages, with a 95% CI.

RESULTS

Forty-eight articles met the inclusion criteria: ACDF (n = 7), PCF (n = 6), ALIF (n = 9), TLIF/PLIF (n = 17), and PLF (n = 9), resulting in a total of 5890 patients. In ACDF, the lowest BMP concentration analyzed (0.2-0.6 mg/level) resulted in a fusion rate similar to the highest dose (1.1-2.1 mg/level), while permitting complication rates comparable to ACDF performed without BMP. The addition of BMP to multilevel constructs significantly (p < 0.001) increased the fusion rate (98.4% [CI 95.4%-99.4%]) versus the control group fusion rate (85.8% [CI 77.4%-91.4%]). Studies on PCF were of poor quality and suggest that BMP doses of ≤ 2.1 mg/level resulted in similar fusion rates as higher doses. Use of BMP in ALIF increased fusion rates from 79.1% (CI 57.6%-91.3%) in the control cohort to 96.9% (CI 92.3%-98.8%) in the BMP-treated group (p < 0.01). The rate of complications showed a positive correlation with the BMP dose used. Use of BMP in TLIF had only a minimal impact on fusion rates (95.0% [CI 92.8%-96.5%] vs 93.0% [CI 78.1%-98.0%] in control patients). In PLF, use of ≥ 8.5 mg BMP per level led to a significant increase of fusion rate (95.2%; CI 90.1%-97.8%) compared with the control group (75.3%; CI 64.1%-84.0%, p < 0.001). BMP did not alter the rate of complications when used in PLF.

CONCLUSIONS

The BMP doses used for various spinal arthrodesis procedures differed greatly between studies. This study provides BMP dosing recommendations for the most common spine procedures.

Safety and efficacy of bioabsorbable cervical spacers and low-dose rhBMP-2 in multi-level ACDF

Introduction

Many options for interbody spacer and graft biologic exist for multilevel anterior cervical discectomy and fusion (ACDF). The objective of this study is to evaluate the safety and efficacy of a bioabsorbable cervical spacer (BCS) (Cornerstone HSR, Medtronic Sofamor Danek) filled with low-dose rhBMP-2 (INFUSE, Medtronic Sofamor Danek) in multilevel ACDF.

Methods

72 consecutive patients treated with a multi-level ACDF using BCS and rhBMP-2 (dosage between 0.5 to 0.7 mg per level) at a single institution were followed in an IRB-approved, prospective registry. A total of 187 levels were treated (mean = 2.6), with 37 (51%) patients undergoing a 2-level procedure and 35 (49%) undergoing a 3- or 4-level procedure. Statistical analysis included frequency and ANOVA tests. Significance was accepted for p < 0.001.

Results

Average follow-up was 13.8 months. Mean patient age was 55.3 years, 70.8% were female, and 16.7% had undergone a previous cervical procedure. 29 (40%) patients had cervical spondylitic myelopathy, 27 (38%) had radiculopathy, 15 (21%) had a combination of both, and 1 (1%) patient had a previous nonunion.

A total of 187 levels were treated with an ACDF, with 37 (51%) 2-level, 27 (38%) 3-level, and 8 (11%) 4-level cases. Average OR time, EBL, and LOS were 144 minutes, 49 mL, and 1.1 days, respectively. Major complications occurred in 5 (7%) patients: 2 returns to OR (1 nonunion, 1 seroma), 1 recurrent laryngeal nerve injury, and 2 hospital readmissions for excessive pre-vertebral swelling/dysphagia treated with steroids and observation. Minor complications occurred in 3 (4%) patients: 2 exacerbations of pre-existing medical conditions (1 atrial fibrillation, 1 COPD), and 1 hospital readmission for nausea/ headache due to narcotics.

At last follow-up, NDI improved 43% from 43.6% to 25.0%. VAS neck pain improved 60% from 5.5 to 2.2 and VAS arm pain improved 52% from 5.8 to 2.6. SF-36 PCS improved 24% from 37.5 to 46.3 and MCS improved 18% from 43.2 to 50.9. All clinical improvements were statistically significant (p < 0.001).

Patient satisfaction was high, with 97% of patients reported being satisfied with their surgical outcome, and 90% would undergo the procedure again.

Conclusion

Patients in this series experienced significant clinical improvements, low complication rates, and high patient satisfaction. Symptomatic pseudoarthrosis was rare. BCS filled with low-dose rhBMP-2 appears to be a safe and effective option in multilevel ACDF. Further investigation is warranted.

Complications of spinal fusion with utilization of bone morphogenetic protein: a systematic review of the literature

STUDY DESIGN

Systematic review.

OBJECTIVE

A systematic review was performed to identify the types of complications and complication rates associated with the use of bone morphogenetic protein (BMP) in both anterior and posterior cervical and lumbar spine surgery.

SUMMARY OF BACKGROUND DATA

There has been an increase in BMP use in various clinical situations typically in an "off-label" fashion. Associated with its use, however, have been reports of various complications.

METHODS

A MEDLINE search was conducted. All articles involving complications after spine surgery in patients receiving BMP were included. Articles were excluded on the basis of the following criteria: Non-English manuscripts and nonhuman subjects. A total of 29 articles met the inclusion and exclusion criteria and were used in the analysis. For each complication identified, the incidence was calculated by pooling the subjects from the studies that reported the complication. χ tests were used to compare the incidence rates between those that had received BMP and the control groups.

RESULTS

Of the 29 articles included, 7 reported complication rates in anterior cervical fusions, 3 in posterior cervical fusions, 4 in anterior lumbar interbody fusions (ALIF), 9 in posterior/transforaminal lumbar interbody fusions (PLIF/TLIF), and 6 in posterolateral lumbar fusions. Individual complication rates when BMP was used was in the range from 0.66% to 20.1% in anterior cervical fusions, 3.5% to 14.6% in posterior cervical fusions, 2.0% to 7.3% in ALIFs, 1.5% to 21.8% in PLIF/TLIFs, and 1.4% to 8.2% in posterolateral lumbar fusions. Pseudarthrosis rates were statistically significantly lower with the utilization of BMP in all procedures except for PLIF/TLIFs, which only approached significance (P = 0.07). The only individual complication that was statistically significantly greater with BMP utilization was retrograde ejaculation in ALIFs (7.3 vs. 2.3%; P = 0.03). The rate of dysphagia/swelling in anterior cervical fusions was greater with BMP (20.1 vs. 15.6%), however this only approached statistical significance (P = 0.07).

CONCLUSION

The body of literature reports complication rates with BMP ranging from 0.66% to 21.8%. However, the only statistically significant adverse complication rate was retrograde ejaculation in the ALIF population (7.3%). Despite the increased awareness of complications associated with BMP, complication rates remain spine site specific and low. Thorough patient education should be done with the physician to make an informative use regarding BMP utilization in spinal surgery.

LEVEL OF EVIDENCE

3.

Biocomposites reinforced by fibers or tubes as scaffolds for tissue engineering or regenerative medicine

As a dynamic and hierarchically organized composite, native extracellular matrix (ECM) not only supplies mechanical support, which the embedded cells need, but also regulates various cellular activities through interaction with them. On the basis of the ECM-mimetic principle, good biocompatibility and appropriate mechanical properties are the two basic requirements that the ideal scaffolds for the tissue engineering or regenerative medicine need. Some fibers and tubes have been shown effective to reinforce scaffolds for tissue engineering or regenerative medicine. In this review, three parts, namely properties affected by the addition of fibers or tubes, scaffolds reinforced by fibers or tubes for soft tissue repair, and scaffolds reinforced by fibers or tubes for hard tissue repair are stated, which shows that tissue repair or regeneration efficacy was enhanced significantly by fiber or tube reinforcement. In addition, it indicates that these reinforcing agents can improve the biocompatibility and biodegradation of the scaffolds in most cases. However, there are still some concerns, such as the homogeneousness in structure or composition throughout the reinforced scaffolds, the adhesive strength between the matrix and the fibers or tubes, cytotoxicity of nanoscaled reinforcing agents, etc., which were also discussed in the conclusion and perspectives part.

The use of BoneWelding® technology in spinal surgery: an experimental study in sheep

The innovative BoneWelding(®) technology, where ultrasound energy bonds bioresorbable implants to bone, was tested for its feasibility in spine surgery and its local thermal effects. The three tested concepts consisted of implementation of a resorbable plating system, two converging polymer pins and suture anchors to the cervical vertebral bodies. Bioresorbable polylactide implants (PLDLLA 70/30) were inserted ventrally into the third and fourth vertebral body of seven sheep, of which six were sacrificed at 2 months and one sheep immediately after temperature measurements during implant insertion. Polymer screws were used as controls. Qualitative, semi-quantitative histological, and quantitative histomorphometrical evaluation showed excellent anchorage of the implants, new mineralized bone at the implant-bone interface, no inflammatory cell reaction or thermal damage to the adjacent bone in response to the novel insertion technology. The application of two converging pins, parallel inserted polymer pins, or fusion of the implant to the polymer plates did not affect the overall excellent tissue tolerance of the technology. Temperature increase during insertion was noticed but never exceeded 47°C for less than 1 s. The BoneWelding(®) technology was proven to be safe and easy to apply.

Osteolysis following resorbable poly-L-lactide-co-D, L-lactide PLIF cage use: a review of cases

STUDY DESIGN

Report of case series.

OBJECTIVE

To report a problem with bioabsorbable poly-L-lactide-co-D, L-lactide, PLDLLA, posterior lumbar instrumented fusion (PLIF) cage implants.

SUMMARY OF BACKGROUND DATA

Synthetic bioabsorbable implants have recently been introduced to spinal surgery and their indications and applications are still being explored. There is evidence that the use of bioabsorbable cages may be of benefit in interbody spinal fusion.

METHODS

We present a case series of nine patients who have undergone PLIF with bioabsorbable cages in the lumbar spine.

RESULTS

At follow-up over at least 1 year, four of these patients were found to have osteolysis around the implant on CT scanning. One of these patients underwent an operation to remove the cage and histology sent during surgery suggested that the implant had caused the bone loss and there was no evidence of infection. Another patient had ongoing pain in relation to the lysis, while the other two patients with lysis remained asymptomatic.

CONCLUSIONS

PLDLLA cage, which has high osteolytic nature, is considered not suitable as a fusion cage.

Effect of side holes in cervical fusion cages: a finite element analysis study

The objective of this study was to investigate the effect of side holes on the predicted von Mises stress levels in cervical spinal fusion cages subjected to compressive loading. Models with between zero and ten side holes were developed. Finite element analysis (FEA) was used to simulate compression of the cage, made from the polymer PEEK (polyetheretherketone), between two adjacent vertebrae. The analyses were validated by experimental tests. In all of the models, the von Mises stress was highest at the cage–vertebrae interface with peak stresses of between 14 and 18 MPa. Increasing the Young’s modulus of the vertebrae from 12 to 30 GPa increased the peak stress on average by 29 per cent. The stresses in the models were lower than the compressive strength of PEEK (118 MPa), and are well within the PEEK fatigue strength reported (60 MPa at 10 million cycles). This study suggests that the number of side holes had a negligible effect on the stress distribution within the cage; the stress magnitudes were fairly constant across all of the models and did not change substantially with the number of holes. Hence, a cervical cage with side holes is unlikely to fail in compression.

Minimal access versus open transforaminal lumbar interbody fusion: meta-analysis of fusion rates

STUDY DESIGN

A quantitative meta-analysis was conducted on published studies reporting fusion rates after open or minimally invasive/mini-open transforaminal lumbar interbody fusion (TLIF) procedures for single or multilevel degenerative disease including stenosis with spondylolisthesis and degenerative disc disease.

OBJECTIVES

The primary aim of this study was to establish benchmark fusion rates for open TLIF and minimally invasive TLIF (mTLIF) based on published studies. A secondary goal was to review complication rates for both approaches.

SUMMARY OF BACKGROUND DATA

Lumbar fusion for the treatment of degenerative disease has evolved from a purely posterior noninstrumented approach to a combination of anterior and/or posterior surgery with instrumentation. The increasingly popular transforaminal approach has advanced to incorporate minimally invasive spinal techniques. There currently exist no controlled comparisons between open TLIF and mTLIF.

METHODS

A Medline search was performed to identify studies reporting fusion rate on open TLIF or mTLIF with instrumentation. A database including patient demographic information, fusion rate, and complication rate was created. Fusion and complication rates were pooled according to whether TLIF was performed with open or minimally invasive technique. Publication bias was assessed with Egger's test, and adjustments were performed using Duval and Tweedie's Trim and Fill algorithm.

RESULTS

Twenty-three articles were identified that fit inclusion criteria. In each of the 23 studies, TLIF was performed with pedicle fixation and fusion was evaluated using radiograph or computed tomography scan at minimum 6-month follow-up. Overall, the studies included 1028 patients, 46.8% of which were female. The mean age of all patients was 49.7 (range, 38-64.9), and mean follow-up interval for assessment of fusion was 26.6 months (range, 6-46 months). The usage of recombinant bone morphologic protein was higher in the mTLIF group (50% vs. 12%). Mean fusion rate from 16 studies (716 patients) of open TLIF was 90.9%, whereas mean fusion rate from 8 studies (312 patients) of mTLIF was 94.8%. Complication rate was 12.6% and 7.5% for open and mTLIF, respectively.

CONCLUSION

Fusion rates for both open and mTLIF are relatively high and in similar ranges. Complication rates are also similar, with a trend toward mTLIF having a lower rate. This analysis provides clear benchmarks for fusion rates in open and mTLIF procedures for spine surgeons.

Posterior lumbar interbody fusion using non resorbable poly-ether-ether-ketone versus resorbable poly-L-lactide-co-D,L-lactide fusion devices. Clinical outcome at a minimum of 2-year follow-up

Previous papers on resorbable poly-L-lactide-co-D,L-lactide (PLDLLA) cages in spinal fusion have failed to report adequately on patient-centred clinical outcome measures. Also comparison of PLDLLA cage with a traditionally applicable counterpart has not been previously reported. This is the first randomized prospective study that assesses clinical outcome of PLDLLA cage compared with a poly-ether-ether-ketone (PEEK) implant. Twenty-six patients were randomly assigned to undergo instrumented posterior lumbar interbody fusion (PLIF) whereby either a PEEK cage or a PLDLLA cage was implanted. Clinical outcome based on visual analogue scale scores for leg pain and back pain, as well as Oswestry Disability Index (ODI) and SF-36 questionnaires were documented and analysed. When compared with preoperative values, all clinical parameters have significantly improved in the PEEK group at 2 years after surgery with the exception of SF-36 general health, SF-36 mental health and SF-36 role emotional scores. No clinical parameter showed significant improvement at 2 years after surgery compared with preoperative values in the PLDLLA patient group. Only six patients (50%) in the PLDLLA group showed improvement in the VAS scores for leg and back pain as well as the ODI, as opposed to 10 patients (71%) in the PEEK group. One-third of the patients in the PLDLLA group actually reported worsening of their pain scores and ODI. Three cases of mild to moderate osteolysis were seen in the PLDLLA group. Following up on our preliminary report, these 2-year results confirm the superiority of the PEEK implant to the resorbable PLDLLA implant in aiding spinal fusion and alleviating symptoms following PLIF in patients with degenerative spondylolisthesis associated with either canal stenosis or foramen stenosis or both and emanating from a single lumbar segment.

Posterior lumbar interbody fusion using nonresorbable poly-ether-ether-ketone versus resorbable poly-L-lactide-co-D,L-lactide fusion devices: a prospective, randomized study to assess fusion and clinical outcome

STUDY DESIGN

A prospective randomized clinical study. OBJECTIVE.: To assess fusion, clinical outcome, and complications.

SUMMARY OF BACKGROUND DATA

Resorbable poly-L- lactide-co-D,L-lactide (PLDLLA) cages intended to aid spinal interbody fusion have been introduced into clinical practice within the last decade. Although early case series show promising results with respect to fusion rate, worries persist with regards to efficacy and potential risks of early failure of these implants. Despite widespread clinical application this is the first randomized prospective study to assess clinical and radiologic outcomes of PLDLLA cage compared with a traditionally applicable counterpart.

METHODS

Twenty-six patients were randomly assigned to undergo instrumented posterior lumbar interbody fusion whereby either a nonresorbable poly-ether-ether-ketone (PEEK) cage or a resorbable PLDLLA cage was implanted to aid fusion. Fusion rate, subsidence, and clinical outcome based on visual analog scale scores for leg pain and back pain, as well as Oswestry Disability Index and SF-36 questionnaires were documented and analyzed. Complications and adverse events were recorded.

RESULTS

Fusion rate was significantly higher with the PEEK cage compared with PLDLLA cage (Fisher exact test, P = 0.0302). Rate of subsidence was significantly higher with the PLDLLA cage compared to PEEK cage (Fisher exact test, P = 0.0414). The PEEK group demonstrated greater improvement in the Oswestry Disability Index compared with the PLDLLA group (Fisher exact test, P = 0.1414). Two cases of mild to moderate osteolysis were seen in the PLDLLA group.

CONCLUSION

Our results strongly suggest that PLDLLA cage proffers a lower rate of fusion compared with PEEK cage, and also confirms that the efficacy of PLDLLA cage in enhancing interbody spinal fusion is yet to be established. The higher rate of subsidence and occurrence of osteolysis seen in association with PLDLLA cages in this study remain worrisome.

Position of interbody spacer in transforaminal lumbar interbody fusion: effect on 3-dimensional stability and sagittal lumbar contour

STUDY DESIGN

Biomechanical study.

OBJECTIVE

To test 2 different intervertebral positions of a semilunar cage and their effects on 3-dimensional stability and segmental lordosis in a model of transforaminal lumbar interbody fusion (TLIF).

SUMMARY OF BACKGROUND DATA

In his original TLIF description, Harms recommended decortication of endplates, followed by placement of mesh cages in the middle-posterior intervertebral third. Subsequent studies presented conflicting recommendations: anterior placement of the spacer-cage for better load-sharing versus placement on the stronger posterolateral endplate regions.

METHODS

Six human lumbar spinal functional units were first tested intact. TLIF was performed using a semilunar poly-ether-ether-ketone cage randomly inserted in the anterior (TLIF-A) or posterior (TLIF-P) disc space. Pedicle screws and rods were added. Unconstrained pure moments in axial-torsion, lateral-bending (LB), and flexion-extension (FE) were applied under 0.05 Hz and +/-5 Nm sinusoidal waveform. Segmental motions were recorded. Range of motion (ROM) and neutral zone (NZ) were calculated. Pairwise comparisons were made using nonparametric Wilcoxon-matched pairs signed rank sum test with statistical significance set at P<0.05.

RESULTS

TLIF-A and TLIF-P significantly decreased ROM (P<0.05) of the intact spinal functional unit, in FE and LB. In axial-torsion, decrease of ROM after TLIF procedures was not significant (P>0.05). Delta-ROM between TLIF-A and TLIF-P was not significant (P>0.05). TLIF-A and TLIF-P significantly decreased NZ in LB (P<0.05). In FE, TLIF-P significantly decreased NZ (P<0.05); TLIF-A showed a trend toward significance (P=0.09). Delta-NZ between TLIF-A and TLIF-P was not significant (P>0.05). Segmental lordosis of TLIF-A and TLIF-P on C-arm views showed angle differences within the range of measurement error of Cobb angles.

CONCLUSIONS

Difference in ROM and NZ between anterior (TLIF-A) or posterior (TLIF-P) positions was not statistically significant. Similarly, both positions did not influence segmental lordosis.

Time-dependent mechanical strength of 70/30 Poly(L, DL-lactide): shedding light on the premature failure of degradable spinal cages

STUDY DESIGN

In vitro studies on the mechanical strength of 70/30 poly(l,dl-lactic acid) (70/30 PLDLLA) cages.

OBJECTIVE

To evaluate the effect of loading rate, humidity, temperature, and continuous static loading on the strength of 70/30 PLDLLA, to elucidate the mechanism of premature failure of degradable spinal cages observed in earlier studies.

SUMMARY OF BACKGROUND DATA

Degradable 70/30 PLDLLA cages have been designed to withstand mechanical loads in a goat lumbar spine for at least 6 months. Yet mechanical failure was observed after only 3 months in vivo. We hypothesize that this observation can be related to the time-dependent nature of the polymer.

METHODS

Degradable 70/30 PLDLLA cages were loaded to failure at loading rates between 10 and 10 mm/s under standard loading conditions (in air at room temperature: +/-23 degrees C). The experiments were also done at body temperature (37 degrees C) and under wet conditions. Furthermore, we determined the time-to-failure for 70/30 PLDLLA cages subjected to loads well below their instantaneous mechanical strength.

RESULTS

The mechanical strength of 70/30 PLDLLA cages was lower for lower loading rates, higher temperature, and higher humidity. The cages already failed within less than 5 minutes when statically loaded at 75% of their strength, and within 1 day when loaded at about 50% of their strength. Extrapolation predicts cage failure at 3 months when loaded at 25% of their strength.

CONCLUSION

Premature failure of 70/30 PLDLLA cages, as observed in vivo in earlier studies, is owing to mechanical loading and the time-dependent mechanical properties of the material. The standards for mechanical testing of implants made of strongly time-dependent materials like polylactide should be reconsidered.

Bioabsorbable interbody spacers

Bioabsorbable polymers have been used in surgery for more than four decades. With increased reliability and decreased incidence of complications, their application has become widespread. Although their role in spinal surgery continues to evolve, the theoretic biomechanical and biologic advantages over contemporary metallic and composite implant materials make bioabsorbable interbody spacers an attractive alternative. The lack of artifact on postoperative imaging studies and the ability to load share across fusion sites in a time-dependent manner can lead to more accurate fusion assessment and increased fusion rates. The preliminary data from small, short-term studies are promising. However, larger studies with long-term follow-up are lacking. The theoretic advantages of bioabsorbable materials must be tempered by the lack of long-term clinical evidence of their benefit. Until the results of more studies in human spinal applications become available, the precise indications for the use of bioabsorbable interbody spacers will continue to evolve.

Lumbar body fusion with a bioresorbable cage in a goat model is delayed by the use of a carboxymethylcellulose-stabilized collagenous rhOP-1 device

The purpose of this study was to evaluate the efficacy of recombinant human osteogenic protein-1 (rhOP-1) with a carboxymethylcellulose-stabilized collagenous carrier as a bone graft substitute for instrumented lumbar spinal fusion in an established goat model. Twenty goats received a resorbable poly-L-lactic acid (PLLA) interbody cage packed with either rhOP-1 and its carrier or autologous bone graft. The carrier material was bovine collagen type-1 stabilized with carboxymethylcellulose. The fusion segments were retrieved at 3 or 6 months postimplantation and evaluated by radiographic and histologic analyses. The rhOP-1 graft substitute, used in combination with the resorbable PLLA cage, showed inferior results as compared to autologous bone graft in the goat lumbar fusion model. Whereas four out of five segments from the autograft group were fused after 6 months, none of the four segments receiving the rhOP-1 graft substitute were fused at this time point. Bone ingrowth into the cage was delayed or absent in the experimental group, whereas all autograft specimens showed advanced bone ingrowth (3 months) or fusion (6 months). We suggest that the fusion process was inhibited, because cells were unable to penetrate the rhOP-1 graft material. This led to delayed bone formation and in some cases inadequate tissue formation.

Fibre reinforced bioresorbable composites for spinal surgery

Composites containing different amounts of beta-tricalcium phosphate (beta-TCP) embedded in a poly-lactide (PLA70) matrix with and without poly-lactide (PLA96) fibre reinforcement were studied and the feasibility of using these composites in spinal fusion implants was examined. Compressive yield strength was measured in two directions: parallel to (83-97 MPa) and perpendicular to (108-123 MPa) the laminated structure of the composites. In the parallel direction, the addition of beta-TCP decreased compressive yield strength while in the perpendicular direction this was increased when compared to plain specimens (p<0.05). Fibre reinforcement had no significant effect on compressive yield strength (p<0.05), but did increase impact strength by 127-216% for notched specimens (parallel direction) and by about 65% for un-notched specimens (perpendicular direction) (p<0.05). A 24 week in vitro analysis of implant prototypes in simulated body fluid revealed a decrease in compressive yield strength, which was greater for the samples containing 50 wt.% beta-TCP than for those containing 25 wt.% beta-TCP. After 12 weeks incubation the composites retained 66-99% of their initial compressive strength, depending on composition. After 24 weeks incubation the lowest compressive strength was 51% (56 MPa: 50/50) and the highest was 94% (90 MPa: 75/25) of the initial value. Calcium phosphate precipitation on the surfaces of the materials in vitro was also observed. The initial compressive strengths of the studied composites were comparable to materials used in spinal fusion applications, but adequate strength retention behaviour needs to be confirmed before undertaking clinical experiments.

Radiographic, histologic, and chemical evaluation of bioresorbable 70/30 poly-L-lactide-CO-D, L-lactide interbody fusion cages in a goat model

STUDY DESIGN

A study of lumbar interbody fusion using polylactic acid-based bioresorbable fusion cages in a goat model.

OBJECTIVE

To evaluate the effect of polylactic acid polymer composition, and internal stabilization on the rate and quality of interbody fusion.

SUMMARY OF BACKGROUND DATA

A spinal cage should provide an appropriate biomechanical environment to facilitate interbody fusion. Previous studies have shown that bioresorbable polylactic acid-based cages can provide adequate stability for spinal fusion. However, at present and to our knowledge, the best bioresorbable materials, optimal cage stiffness, and desired period over which the cage should biodegrade are unknown.

METHODS

Interbody fusions were performed at L3-L4 level in 35 skeletally mature Dutch milk goats. Titanium and poly-L-lactide-CO-D,L-lactide (PLDLLA) cages were implanted at random as stand-alone cages. In addition, PLDLLA cages were implanted with anterior fixation. The goats were euthanized at 3, 6, or 12 months. Radiographic, magnetic resonance imaging, histologic, and histomorphometric analyses were performed on retrieved segments. Chemical analysis was used to assess degradation of the retrieved PLDLLA cages. Beforehand, chemical and mechanical degradation of the PLDLLA cages were assessed in vitro.

RESULTS

At 3 months, bone graft was almost completely remodeled. Endochondral bone formation was observed in all specimens. At 6 months, 50% of the PLDLLA stand-alone cages and 83% of the PLDLLA anterior fixation cages were fused. At 12 months, 38% of the PLDLLA stand-alone and 83% of the titanium cages realized fusion. A very mild and dispersed foreign body reaction was seen in all PLDLLA specimens. E-beam sterilized PLDLLA cages degraded more rapidly in vivo as compared to both, PLDLLA cages in vitro, and ethylene oxide sterilized poly-L-lactic acid cages in vivo.

CONCLUSIONS

Within the 3-6-month period, PLDLLA stand-alone cages provided insufficient mechanical stability, which manifested as cracking and deformation of the cages and lower fusion rates. This result implies that within this time, additional stabilization is required; supplemental internal fixation proved sufficient to obtain successful fusion. In all cases, only a mild host response was seen, indicating good biocompatibility.

Paramedian approach for transforaminal lumbar interbody fusion with unilateral pedicle screw fixation. Technical note and preliminary report on 47 cases

Lumbar fusion is a commonly performed procedure for a variety of pathological conditions, and it is frequently used in the treatment of degenerative lumbar instability that is refractory to medical management. Pedicle screws and interbody devices have been used for internal fixation to promote arthrodesis, prevent nonunion, and facilitate early mobilization. Recently, attempts have been made to reduce the morbidity associated with lumbar fusion by using a variety of minimally invasive techniques. Many minimally invasive lumbar fusion procedures require specialized retractors, implants, image guidance systems, or insertion instruments. Other minimally invasive techniques are primarily applied to an ideal patient population (thin, healthy, and with no previous surgery). The authors describe their experience with a paramedian approach for minimally invasive transforaminal lumbar interbody fusion (TLIF) with unilateral pedicle screw (PS) fixation. This procedure requires only standard implants, instruments, and retractors, with direct visualization for all aspects of the procedure. The authors describe encouraging early results in a challenging patient population in which there was a high incidence of obesity, medical comorbidities, and previous surgery at the same level. The paramedian approach for TLIF performed using unilateral lumbar PSs has yielded successful outcomes in this series of 47 patients, and further study of this technique may help define its role as a minimally invasive procedure for spinal fusion.

Bioresorbable polymers: heading for a new generation of spinal cages

The use of polymer-based bioresorbable materials is now expanding to the realm of spinal interbody fusion. Bioresorbable polymers have important advantages over metals, because they are temporary, much less stiff, and radiolucent. Most promising is a group of alpha-polyesters, in particular polylactide acids (PLAs). Their biocompatibility is excellent, and they have sufficient stiffness and strength to provide initial and intermediate-term stability required for bone healing. However, polylactides have characteristics that make them vulnerable to complications if not properly controlled. Degradation rate strongly depends on polymer type, impurities, manufacturing process, sterilization, device size, and the local environment. The fact that larger implants degrade faster is contra-intuitive, and should be considered in the design process. Also optimal surgical techniques, such as careful bone bed preparation, are required for a successful application of these materials. The purpose of this paper is to highlight the specific properties of these bioresorbable polymers and to discuss their potential and limitations. This is illustrated with early preclinical and clinical data.Bioresorbable cage technology is just emerging: their time-engineered degradation characteristics allow controlled dynamization in interbody applications, facilitating spinal fusion. Their radiolucency improves image assessment of fusion healing. Acceptance and use of bioresorbable implants may increase as further research and clinical studies report on their safety, efficacy, and proper usage.

Bone morphogenetic proteins: from structure to clinical use

Bone morphogenetic proteins (BMPs) are multi-functional growth factors belonging to the transforming growth factor ss superfamily. Family members are expressed during limb development, endochondral ossification, early fracture, and cartilage repair. The activity of BMPs was first identified in the 1960s but the proteins responsible for bone induction were unknown until the purification and cloning of human BMPs in the 1980s. To date, about 15 BMP family members have been identified and characterized. The signal triggered by BMPs is transduced through serine/threonine kinase receptors, type I and II subtypes. Three type I receptors have been shown to bind BMP ligands, namely: type IA and IB BMP receptors and type IA activin receptors. BMPs seem to be involved in the regulation of cell proliferation, survival, differentiation and apoptosis, but their hallmark is their ability to induce bone, cartilage, ligament, and tendon formation at both heterotopic and orthotopic sites. This suggests that, in the future, they may play a major role in the treatment of bone diseases. Several animal studies have illustrated the potential of BMPs to enhance spinal fusion, repair critical-size defects, accelerate union, and heal articular cartilage lesions. Difficulties in producing and purifying BMPs from bone tissue have prompted the attempts made by several laboratories, including ours, to express these proteins in the recombinant form in heterologous systems. This review focuses on BMP structure, molecular mechanisms of action and significance and potential applications in medical, dental and veterinary practice for the treatment of cartilage and bone-related diseases.