Posterior Lumbar Interbody Fusion Cages Research Articles

Vertebral Endplate Cavities (VEC) with titanium cages in posterior lumbar interbody fusion (PLIF).

Vertebral endplate cavities (VEC) have been reported with the use of Ti cages. Only few articles have recently demonstrated unfavorable radiographic changes in the form of cysts or cavities which may predispose to nonunion. The aim was to assess the prevalence of VEC in posterior lumbar interbody fusion (PLIF) using Titanium (Ti) cages, and to estimate their impact on fusion. The term "cavity" was used to describe the endplate changes. CT analysis of the VEC and fusion status following PLIFs with Ti cages was conducted by two observers. VEC were assessed according to the size, multiplicity, location, and presence of sclerosis. 42 consecutive patients with surgeries conducted on 52 levels were enrolled. There were 20 males and 22 females. The mean age was 43.6 ±10.89 years. The mean follow-up was 20.85±8.49 months. Definite union was seen in 48 levels (92.3%) by observer 1 and in 40 levels (76.9%) by observer 2. The strength of agreement was moderate. The presence of VEC was observed in 9 levels (17.3%) by observer 1 and in 12 levels (23.1%) by observer 2. The strength of agreement was moderate. The majority of VEC in the endplates were <5mm. The strength of agreement was high. The strength of agreement for location and multiplicity were moderate. The VEC was significantly correlated with the fusion status. Our study confirmed that VEC were observed following Ti cage placement after PLIF procedures. They tend to be small and might be associated with non-union. Furthermore, it reflected the limited inter-rater reliability of the assessment of both the fusion status and VEC morphology after Ti PLIF cage placement.

Biomechanical evaluation of an osteoporotic anatomical 3D printed posterior lumbar interbody fusion cage with internal lattice design based on weighted topology optimization.

In this study, we designed and manufactured a posterior lumbar interbody fusion cage for osteoporosis patients using 3D-printing. The cage structure conforms to the anatomical endplate's curved surface for stress transmission and internal lattice design for bone growth. Finite element (FE) analysis and weight topology optimization under different lumbar spine activity ratios were integrated to design the curved surface (CS-type) cage using the endplate surface morphology statistical results from the osteoporosis patients. The CS-type and plate (P-type) cage biomechanical behaviors under different daily activities were compared by performing non-linear FE analysis. A gyroid lattice with 0.25 spiral wall thickness was then designed in the internal cavity of the CS-type cage. The CS-cage was manufactured using metal 3D printing to conduct in vitro biomechanical tests. The FE analysis result showed that the maximum stress values at the inferior L3 and superior L4 endplates under all daily activities for the P-type cage implantation model were all higher than those for the CS-type cage. Fracture might occur in the P-type cage because the maximum stresses found in the endplates exceeded its ultimate strength (about 10 MPa) under flexion, torsion and bending loads. The yield load and stiffness of our designed CS-type cage fall into the optional acceptance criteria for the ISO 23089 standard under all load conditions. This study approved a posterior lumbar interbody fusion cage designed to have osteoporosis anatomical curved surface with internal lattice that can achieve appropriate structural strength, better stress transmission between the endplate and cage, and biomechanically tested strength that meets the standard requirements for marketed cages.

Technique of Biportal Endoscopic Transforaminal Lumbar Interbody Fusion.

Biportal endoscopic transforaminal lumbar interbody fusion (TLIF) may have advantages of minimally invasive fusion surgery as well as those of endoscopic surgery. The purpose of this study was to present the biportal endoscopic TLIF technique along with video presentations and a review of the literature on this technique. Basically, the biportal endoscopic TLIF technique is similar to minimally invasive TLIF with a tubular retractor. There were 2 options in the biportal endoscopic TLIF procedures. The first was the insertion of one long TLIF cage and the other was the insertion of 2 short posterior lumbar interbody fusion (PLIF) cages. After the interbody fusion procedures, percutaneous pedicles screw fixation was performed. Biportal endoscopic TLIF achieved complete neural decompression through laminectomy and facetectomy like conventional TLIF. Endplate preparation was performed completely under a clear and magnified endoscopic view. It was also feasible to insert a large TLIF cage or 2 cages for PLIF without exiting nerve root injury. Biportal endoscopic TLIF might have the advantages of endoscopic surgery as well as minimally invasive fusion surgery. Direct neural decompression, endplate preparation under endoscopic guidance, and the insertion of a large TLIF cage or 2 PLIF cages may be the merits of biportal endoscopic lumbar fusion procedures.

Length of Lumbar Interbody Cage Using Radiological Measurements of Chinese Endplates and the Apophyseal Ring

To radiologically measure the parameters of endplates and the apophyseal ring and to suggest an applicable length for a lumbar interbody cage for Chinese patients. Twenty-four volunteers were enrolled to undergo lumbar computed tomography (CT). On the endplate plane, the diameters of the endplates (L1-S1) were measured along the axis of the cage with different lumbar interbody fusion procedures. Whereas the mid-oblique diameter (mid-OD) and maximum oblique diameter (max-OD) were defined as the minimal and maximal diameters of the endplates in transforaminal lumbar interbody fusion (TLIF), side-sagittal diameter (side-SD), mid-sagittal diameter (mid-SD), and transverse diameter (TD) represented the diameters of endplates in posterior lumbar interbody fusion (PLIF), anterior lumbar interbody fusion (ALIF); and oblique lateral interbody fusion (OLIF)/extreme lateral interbody fusion (XLIF), /direct lateral interbody fusion (DLIF), respectively. R1-R10 were the widths of the apophyseal ring covered by diameters at both ends. We used the proposed formula to calculate the cage length: 1) minimal length of TLIF cage= mid-OD- ½ (R1+ R2), 2) maximal length of TLIF cage= max-OD- ½ (R3+ R4), 3) length of PLIF cage= side-SD- ½ (R5+ R6), 4) length of OLIF/XLIF/DLIF cage= TD- ½ (R7+ R8), and 5) length of ALIF cage= mid-SD- ½ (R9+ R10). The lengths of the TLIF cage were more than 30 mm for men and 26 mm for women in L1/2-L4/5, with a large range in L5-S1. For PLIF, the lengths were 28 to 30 mm for men and 24 to 26 mm for women in L1/2-L4/5, with 26 mm and 22 mm, respectively, in L5-S1. For the OLIF/XLIF/DLIF cage, the lengths were 38 mm in L1/2 and 41 to 43 mm in L2/3-L4/5 for men and 35 mm in L1/2-L2/3 and 38 mm in L3/4-L4/5 for women. The ALIF cage lengths were 27 mm in L1/2 and L5-S1 and 29 mm in L2/3-L4/5 for men and 23 mm in L1/2 and L5-S1 and 25 mm in L2/3-L4/5 for women. The choice of an appropriate length for a lumbar interbody cage should be based on the procedure and fusion level, which can match the endplates anatomically. The size of the lumbar interbody cage is affected by many factors, and a simple calculation may not be clinically relevant.

Posterior Revision of Lumbar Interbody Fusion Cages Migration: Clinical Case Series and Literature Review

Background Data: Revision surgery for lumbar interbody cage migration is technically demanding.Cage related complication may lead to failure of fusion. Revision of such morbidity is associated with increased risk of permanent neurological insult.Purpose: To analyze the efficacy of posterior approach and iliac crest auto grafting technique in revision of migrated intervertebral cages.Study Design: Retrospective descriptive clinical case study.Patients and Methods: From January 2010 to January 2016, we operated 106 patients underwent posterior lumbar interbody fusion (PLIF) with single cage application per level for treatment of degenerative spondylolisthesis. Of these, 12 patients experiencing cage subsidence and retropulsion. In subsidence, it was graded from 0 to III. Retropulsion was considered if the cage beyond the level of the posterior longitudinal line of the index two vertebrae. Patients were assessed pre-operatively for pain and clinical functional outcome by visual analogue scale (VAS) and Oswestry disability index (ODI), respectively. Patient with VAS score ≥5; at least 20% deterioration on ODI or with the superadded neurological deficit was considered candidates for revision surgery.Results: Cage migration incidence was 11.3%, with subsidence (6.7%), and retropulsion (4.6%) of all patients. The average time for subsidence was 3.3 months (range 2 to 6 months). Five patients with grade-II and III subsidence underwent revision surgery for foraminal decompression, augmenting fixation and adding postero-lateral iliac crest bone graft. Retropulsion was encountered in 4 patients and all needed revision surgery for cage retrieval and redo fusion. Grade-I subsidence could be treated conservatively. All surgically treated patients had a good result in VAS and ODI after a second surgery which maintained during follow up with P<0.05.Conclusion: Migration of posterior lumbar interbody fusion cage into the endplates or spinal canal is usually associated with patient dissatisfaction. Revision surgery indicated for cage retropulsion or high-grade subsidence. The posterior approach is technically demanding, safe, and effective for cage migration revision surgery. (2017ESJ141)

Biomechanical Comparison of Polymeric Spinal Cages Using Ct Based Finite Element Method

Interbody fusion devices are gaining acceptance as a treatment method of mainly for disc degeneration diseases and other medical conditions. Posterior lumbar interbody fusion (PLIF) cage is used in the procedure to maintain stability and promote fusion between vertebrae. Poly lactic acid (PLA) is assumed to be the alternative material which could provide cheaper material and lower production cost. However, these implants often cause subsidence failure at the endplate, resulting in injury risk and mechanical instability during fusion. In this study, the stress behavior of PLIF cage made by two different materials, Polyether ether ketone (PEEK) and PLA; was studied using finite element method (FEM). By implementing bilateral cages between vertebral bone L4 and L5, and conducting 6 different motion activities onto the model, the stress distribution of L4-L5, and cage bodies was predicted. Simulation results predicted that the cage subsidence occurred at both materials, with an overall of higher cage-endplate stresses for PEEK, in comparison to PLA and controlled configurations. In addition, the stress distribution in PLA cage was better and the maximum von Mises stress was approximately 3 times lower than PEEK cage. Further investigation of PLA cage’s mechanical properties should be done experimentally to determine the accuracy and reliability of the simulation.

Does impaction of titanium-coated interbody fusion cages into the disc space cause wear debris or delamination?

Background ContextA large number of interbody fusion cages are made of polyetheretherketone (PEEK). To improve bone on-growth, some are coated with a thin layer of titanium. This coating may fail when subjected to shear loading. PurposeThe purpose of this testing was to investigate whether impaction of titanium-coated PEEK cages into the disc space can result in wear or delamination of the coating, and whether titanium cages with subtractive surface etching (no coating) are less susceptible to such failure. Study Design/SettingA biomechanical study was carried out to simulate the impaction process in clinical practice and to evaluate if wear or delamination may result from impaction. Materials and MethodsTwo groups of posterior lumbar interbody fusion cages with a similar geometry were tested: n=6 titanium-coated PEEK and n=6 surface-etched titanium cages. The cages were impacted into the space in between two vertebral body substitutes (polyurethane foam blocks). The two vertebral body substitutes were fixed in a device, through which a standardized axial preload of 390 N was applied. The anterior tip of the cage was positioned at the posterior border of the space between the two vertebral body substitutes. The cages were then inserted using a drop weight with a mass representative of a surgical hammer. The drop weight impacted the insertion instrument at a maximum speed of about 2.6 m/s, which is in the range of the impaction speed in vivo. This was repeated until the cages were fully inserted. The wear particles were captured and analyzed according to the pertinent standards. ResultsThe surface-etched titanium cages did not show any signs of wear debris or surface damage. In contrast, the titanium-coated PEEK cages resulted in detached wear particles of different sizes (1–191 µm). Over 50% of these particles had a size <10 µm. In median, on 26% of the implants' teeth, the coating was abraded. Full delamination was not observed. ConclusionsIn contrast to the surface-etched implants, the titanium-coated PEEK implants lost some coating material. This was visible to the naked eye. More than half of all particles were of a size range that allows phagocytosis. This study shows that titanium-coated implants are susceptible to impaction-related wear debris.

Would an Anatomically Shaped Lumbar Interbody Cage Provide Better Stability? An In Vitro Cadaveric Biomechanical Evaluation

A biomechanical cadaveric study of lumbar spine segments. To compare the immediate stability provided by parallel-shaped and anatomically shaped carbon fiber interbody fusion I/F cages in posterior lumbar interbody fusion (PLIF) and transforaminal lumbar interbody fusion (TLIF) constructs with posterior pedicle screw instrumentation. Few biomechanical data are available on the anatomically shaped cages in PLIF and TLIF constructs. Twenty human lumbar segments were tested in flexion-extension (FE) (8 N m flexion, 6 N m extension), lateral bending (LB) (± 6 N m), and torsional loading (± 5 N m). Each segment was tested in the intact state and after insertion of interbody cages in one of 3 constructs: PLIF with 2 parallel-shaped or anatomically shaped cages and TLIF with 1 anatomically shaped cage. All cages received supplementary pedicle screw fixation. The range-of-motion (ROM) values after cage insertion and posterior fixation were compared with the intact specimen values using analysis of variance and multiple comparisons with Bonferroni correction. All constructs significantly reduced segmental motion relative to intact (P < 0.001). The motion reductions in FE, LB, and axial rotation were 85 ± 15%, 83 ± 18%, and 67 ± 6.8% for the PLIF construct using parallel cages, 79 ± 5.5%, 87 ± 10%, and 66 ± 20% for PLIF using anatomically shaped cages, and 90 ± 6.8%, 87 ± 12%, and 77 ± 22% for TLIF with an anatomically shaped cage. In FE and LB, the reductions in the ROM caused between the 3 constructs were equivalent (P > 0.05). In axial rotation, the TLIF cage provided significantly greater limitation in the ROM compared with the parallel-shaped PLIF cage (P = 0.01). The parallel-shaped and anatomically shaped I/F cages provided similar stability in a PLIF construct. The greater stability of the TLIF construct was likely due to a more anterior placement of the TLIF cage and preservation of the contralateral facet joint.

The use of beta-tricalcium phosphate and bone marrow aspirate as a bone graft substitute in posterior lumbar interbody fusion

Due to the disadvantages of iliac crest bone and the poor bone quality of autograft gained from decompression surgery, alternative filling materials for posterior lumbar interbody fusion cages have been developed. β-Tricalcium phosphate is widely used in cages. However, data regarding the fusion rate of β-TCP assessed by computer tomography are currently not available. A prospective clinical trial involving 34 patients (56.7 years) was performed: 26 patients were treated with single-level, five patients double-level and three patients triple-level PLIF filled with β-TCP and bone marrow aspirate perfusion, and additional posterior pedicle screw fixation. Fusion was assessed by CT and X-rays 1 year after surgery using a validated fusion scale published previously. Functional status was evaluated with the visual analogue scale and the Oswestry Disability Index before and 1 year after surgery. Forty-five levels in 34 patients were evaluated by CT and X-ray with a follow-up period of at least 1 year. Clinically, the average ODI and VAS for leg and back scores improved significantly (P < 0.001). CT assessment revealed solid fusion in 12 levels (26.67%) and indeterminate fusion in 15 levels (34.09%). Inadequate fusion (non-union) was detected in 17 levels (38.63%). The technique of PLIF using β-TCP yielded a good clinical outcome 1 year after surgery, however, a high rate of pseudoarthrosis was found in this series therefore, we do not recommend β-TCP as a bone graft substitute using the PLIF technique.

Management of Deep Wound Infection After Posterior Lumbar Interbody Fusion With Cages

To evaluate long-term treatment outcome of patients with infected posterior lumbar interbody fusion (PLIF) managed with surgical debridement and or prolonged antiobiotic treatment without removal of the interbody cages. Between 1996 and 1999, 8 out of 111 patients who underwent PLIF were diagnosed with deep wound infection (7.2%). All infected patients were clinically followed for at least 2 years after completion of the antibiotic treatment. Longer follow-up of at least 6 years duration was performed by a telephone interview. Six patients were managed with surgical debridement, wound irrigation, and primary closure of the wound. None of the patients required removal of the instrumentation. In 2 patients, the PLIF cages were repositioned in the face of infection. All 8 patients received 4 to 6 weeks of intravenous antibiotic therapy followed by another 6 to 9 weeks of oral antibiotic administration. At 2-year follow-up, no clinical or laboratory signs of recurrent infection were evident. Four of the 8 patients reported improved clinical status compared with their prefusion status. At 6-year follow-up, 3 patients had minimal disability according to the Oswestry Disability Index and 2 patients had moderate disability with residual leg pain. In cases of postoperative deep wound infection after PLIF with cages, removal of the interbody implants is not necessary. Treatment is composed of prolonged antibiotic therapy guided by antimicrobial susceptibility of the isolated bacteria and supplemented with extensive surgical debridement if needed.

Experience in reoperation of lumbar spinal surgery using posterior lumbar interbody fusion cage

To investigate the indications and surgical techniques of reoperative lumbar spinal surgery using posterior lumbar interbody fusion cage. Seventeen cases underwent reoperative lumbar spinal surgery using posterior lumbar interbody fusion cage. The surgical methods included decompression of lumbar canal, dural and radicular conglutination release, discectomy, posterior insertion of lumbar interbody fusion cage, pedicle screw instrumentation, posterolateral lumbar fusion. Periodical follow-up was conducted for 18 months (12 - 43 months). The clinical effect was evaluated by the Macnab's criterion, and the outcome of lumbar interbody fusion was evaluated according to the Brantigan's criterion. Twenty-seven cages were implanted into twenty-three disc spaces (cage at L(3 - 4) in 5 cases, cage at L(4 - 5) in 8 cases, and cage at L(5)-S(1) in 4 cases). All postoperative patients ambulated after two weeks. No wound healing problems and nerve injury were found. Dural rupture occurred in 5 cases, but without occurrence of cerebrospinal fluid leakage. According to the Macnab's criterion, the preoperative lower extremity radicular symptoms and neurogenic claudication were effectively relieved in 15 cases (88.2%), and the outcomes were good or excellent in 15 cases (88.2%). According to the Brantigan's criterion no evidence of implant failure was found, and interbody fusion could be achieved about 6 months in all patients. No additional operation was needed for involved segments, and the surgical outcomes could be maintained. A good and effective method, use of posterior lumbar interbody fusion cage in reoperative lumbar spinal surgery eliminates neural compression and the discogenic pain, restore the lumbar alignment, and accomplish the internal fixation and anterior column fusion of lumbar vertebrae simultaneously.

In Vitro Stabilizing Effect of a Transforaminal Compared With Two Posterior Lumbar Interbody Fusion Cages

An in vitro biomechanical flexibility test on different lumbar interbody fusion cages using monosegmental lumbar spine specimens. To investigate the stabilizing effect of a transforaminal lumbar interbody fusion (TLIF) cage compared with two established posterior lumbar interbody fusion (PLIF) cages. TLIF using interbody fusion cages is gaining more and more popularity in the treatment of degenerative disc disease. However, only little is known on its biomechanical behavior. Eighteen intact human lumbar spine segments were tested for flexibility in a specially designed spine tester. Pure moments were applied in the three main planes, and range of motion and neutral zone were determined. Then, TLIF using the sickle-shaped MOON cage (AMT AG), PLIF using the cubic Stryker cages (Stryker Orthopaedics), or PLIF using the threaded BAK cages (Zimmer Spinetech) was carried out and the specimens tested again. The stability after implantation of the MOON TLIF cage did not significantly differ from that after implantation of the cubic Stryker PLIF cages (P > 0.05). In contrast, the threaded BAK PLIF cages had a significantly higher primary stability than both the MOON TLIF and the Stryker PLIF cages in lateral bending, flexion, and extension (P < 0.05) but not in axial rotation (P > 0.05). In terms of its stabilizing effect, TLIF using the MOON cage can be recommended as an alternative to PLIF using the cubic Stryker cages. Compared with the threaded BAK PLIF cages, however, the MOON TLIF cage provides a lower primary stability in lateral bending, flexion, and extension.

Posterior lumbar interbody fusion using recombinant human bone morphogenetic protein type 2 with cylindrical interbody cages

Background context In a large series of human patients undergoing open anterior lumbar interbody fusion with a tapered titanium fusion cage, recombinant human bone morphogenetic protein type 2 (rhBMP-2) on an absorbable collagen sponge carrier has been shown to decrease operative time and blood loss, to promote osteoinduction and fusion and to be a safe and effective substitute for iliac crest harvesting. Purpose The purpose of the study was to determine the clinical and radiographic outcomes in patients treated for single-level degenerative lumbar disc disease with a posterior interbody fusion, using stand-alone cylindrical threaded titanium fusion cages with either autogenous bone graft or rhBMP-2 and an absorbable collagen sponge carrier. Study design/setting A prospective, randomized, nonblinded, 2-year pilot study at 14 investigational sites. Patient sample Between March 1999 and December 1999, 67 patients with symptomatic, single-level degenerative lumbar disc disease of at least 6 months' duration underwent a single-level posterior lumbar interbody fusion using two paired cylindrical threaded titanium fusion devices. Patients were randomly assigned to one of two groups: one (n=34 patients) received rhBMP-2 on a collagen sponge carrier; the other (n=33 patients) autogenous iliac crest bone graft. Outcome measures Clinical outcomes were measured using low back and leg pain numerical rating scales, the Short Form (SF)–36, Oswestry Low Back Pain Disability Questionnaire and work status. Plain radiographs and computed tomographic scans were used to evaluate fusion at 6, 12 and 24 months after surgery. Methods In this prospective nonblinded study, 67 patients were randomly assigned to one of two groups who underwent interbody fusion using two cylindrical threaded fusion cages: the investigational group (34 patients), who received rhBMP-2 on an absorbable collagen sponge, and a control group (33 patients), who received autogenous iliac crest bone graft. Clinical data were collected and analyzed by a commercial entity. Results The mean operative time and blood loss for the investigational rhBMP-2 group was 2.6 hours and 322.8 ml, respectively. For the autograft control group, these values were 3.0 hours and 372.7 ml. The differences were not significant. Although not statistically different, at 24 months, the investigational group's fusion rate of 92.3% was higher than the control's at 77.8%. At all postoperative intervals, the mean Oswestry, back and leg pain scores and physical components of the SF-36 improved in both treatment groups compared with preoperative scores, but no significant differences were found between groups. A statistically significant difference in the change in back pain was found at 24 months for the investigational group. In the control group, two adverse events related to harvesting of the iliac crest graft occurred in two patients (6.1%). Conclusions This small multicenter, randomized, nonblinded trial showed few statistically significant differences between the study groups. Both groups showed comparable improvements on outcome scores. Overall results show that the use of rhBMP-2 can eliminate the need for harvesting iliac crest graft and may be an equivalent replacement for autograft for use in successful posterior lumbar interbody fusions. Further studies of the use of rhBMP-2 in posterior lumbar interbody fusion cage procedures are needed.

Stabilizing effect of posterior lumbar interbody fusion cages before and after cyclic loading.

The function of interbody fusion cages is to stabilize spinal segments primarily by distracting them as well as by allowing bone ingrowth and fusion. An important condition for efficient formation of bone tissue is achieving adequate spinal stability. However, the initial stability may be reduced due to repeated movements of the spine during everyday activity. Therefore, in addition to immediate stability, stability after cyclic loading is of remarkable relevance; however, this has not yet been investigated. The object of this study was to investigate the immediate stabilizing effect of three different posterior lumbar interbody fusion cages and to clarify the effect of cyclic loading on the stabilization. Before and directly after implantation of a Zientek, Stryker, or Ray posterior lumbar interbody fusion cage, 24 lumbar spine segment specimens were each evaluated in a spine tester. Pure lateral bending, flexion-extension, and axial rotation moments (+/- 7.5 Nm) were applied continuously. The motion in each specimen was measured simultaneously. The specimens were then loaded cyclically (40,000 cycles, 5 Hz) with an axial compression force ranging from 200 to 1000 N. Finally, they were tested once again in the spine tester. In general, a decrease of movement in all loading directions was noted after insertion of the Zientek and Ray cages and an increase of movement after implantation of a Stryker cage. In all three cage groups greater stability was demonstrated in lateral bending and flexion than in extension and axial rotation. Reduced stability during cyclic loading was observed in all three cage groups; however, loss of stability was most pronounced when the Ray cage was used.

Stabilizing effect of posterior lumbar interbody fusion cages before and after cyclic loading

The function of interbody fusion cages is to stabilize spinal segments primarily by distracting them as well as by allowing bone ingrowth and fusion. An important condition for efficient formation of bone tissue is achieving adequate spinal stability. However, the initial stability may be reduced due to repeated movements of the spine during everyday activity. Therefore, in addition to immediate stability, stability after cyclic loading is of remarkable relevance; however, this has not yet been investigated. The object of this study was to investigate the immediate stabilizing effect of three different posterior lumbar interbody fusion cages and to clarify the effect of cyclic loading on the stabilization. Before and directly after implantation of a Zientek, Stryker, or Ray posterior lumbar interbody fusion cage, 24 lumbar spine segment specimens were each evaluated in a spine tester. Pure lateral bending, flexion-extension, and axial rotation moments (± 7.5 Nm) were applied continuously. The motion in each specimen was measured simultaneously. The specimens were then loaded cyclically (40,000 cycles, 5 Hz) with an axial compression force ranging from 200 to 1000 N. Finally, they were tested once again in the spine tester. In general, a decrease of movement in all loading directions was noted after insertion of the Zientek and Ray cages and an increase of movement after implantation of a Stryker cage. In all three cage groups greater stability was demonstrated in lateral bending and flexion than in extension and axial rotation. Reduced stability during cyclic loading was observed in all three cage groups; however, loss of stability was most pronounced when the Ray cage was used.