Comparative fixation methods of cervical disc arthroplasty versus conventional methods of anterior cervical arthrodesis: serration, teeth, keels, or screws?

A Novel Pedicle Screw Design with Variable Thread Geometry: Biomechanical Cadaveric Study with Finite Element Analysis

BACKGROUND

Pedicle screw fixation provides one of the most stable spinal constructs. Their designs together with osseous characteristics have been known to influence the screw-bone interplay during surgical maneuvers and thereafter the fusion process. Various technical modifications to enhance screw performance have been suggested. This study evaluated the pull-out strength and axial stiffness of a novel pedicle screw design with variable thread geometry and pitch.

METHODS

The newly designed triple threaded pedicle screw is tapered, and has unique out-turned flanges to hold the cancellous bone and a finer pitch at its distal and proximal end to engage the cortical bone. Five lumbar and 4 lower thoracic cadaveric vertebrae were divided into hemivertebrae. A standard cancellous pedicle screw and the newly designed pedicle screw were inserted into each hemivertebra. Axial stiffness and peak pull-out force between the screw types were compared; a finite element analysis was also performed to additionally compare the pull out under toggle forces.

RESULTS

In cadaveric study, the axial stiffness of the new screw was significantly better than that of the standard screw. However, the peak load between the screws was not statistically different. Finite element analyses suggested lesser stress at bone-implant interface for the new screw along with better axial stiffness under both co-axial and toggle forces.

CONCLUSIONS

Our novel pedicle screw design with variable thread geometry demonstrates greater axial stiffness compared with the standard screws, and therefore is likely to withstand a greater surgical manipulation.

Single level anterior cervical discectomy and fusion versus dynamic cervical implant: clinical and radiological outcome

Background

Although anterior cervical discectomy and fusion (ACDF) is considered a gold standard approach for surgical management of cervical disc herniation syndromes, the use of dynamic cervical implant (DCI) provided a novel technique that aims at reconstruction of the anterior column while facilitating controlled neck motion and reducing stress across the facet joints.

Aim of the work

The objective of this study is to evaluate the clinical and radiological outcome of the DCI surgery in comparison to that achieved with ACDF using a conventional polyethylethylketone (PEEK) cage.

Materials and methods

This is a retrospective comparative study of 30 patients, with single level cervical degenerative disc disease (DDD), managed by the authors, either by DCI (n = 15) or ACDF (n = 15). Clinical and radiologic outcomes were assessed at 1, 3, and 12 months postoperatively. Clinical scoring systems included the Visual Analog Scale for Neck (VAS-N) and Arm (VAS-A), the Neck Disability Index score (NDI), as well as the evaluation of incidence of complications and neurological deterioration postoperatively. Radiographic evaluation included the assessment of postoperative cervical implant fusion, as well as evaluating the incidence of implant migration. Study duration was for two years from October 2016 to October 2018.

Results

Both the ACDF and DCI groups showed significant clinical improvement at 12 months postoperatively regarding the clinical outcome including VAS-A, VAS-N, and NDI values (P = 0.001), while there was no significant difference on comparing between the two groups as regard the VAS-N, the VAS-A, and the NDI at 1,3 and 12 months after surgery. The ACDF group however showed better rate of implant fusion at 12 months postoperatively in contrast to the DCI group (80% and 26,7%, respectively) also, the ACDF group showed a lower rate of implant subsidence at 12 months after surgery (P = 0.002). Besides, the incidence of implant migration was relatively high in the DCI group (20%).

Conclusion

The clinical results for DCI arthroplasty for the management of single-level cervical DDD are equivalent to those for ACDF; however, though providing an immediate dynamic stability, DCI is associated with a low fusion rate, higher rates of implant subsidence, and relatively high implant migration rate. Larger series and further studies should be considered with longer follow-up periods giving special attention to these issues.

Differences of the Morphology of Subaxial Cervical Spine Endplates between Chinese and White Men and Women

Objective. The aim of this comparative anatomical study was to specifically investigate endplate morphology differences between Chinese and White men and women. Materials and Methods. Three-dimensional cervical endplate models were constructed using computed tomography imaging of 41 healthy Chinese and 24 White subjects. The morphologic measurements of cervical endplate included linear parameters (EPWu: upper endplate width; EPDu: upper endplate depth; EPWl: lower endplate width; and EPDl: lower endplate depth) and area parameters with a digital measuring system. Results. All linear parameters showed a constant increase from C3 to C7 except for EPDl in both the Chinese and the White subjects. An increase trend was observed on area parameters in both Chinese and White subjects. The ratio of EPWl/EPDl was smaller in Chinese females than in White females at C3, C4, and C6 levels (P < 0.05). The ratio of EPWl/EPDl was significantly different between the Chinese and White men at C4-5 levels (P < 0.05). Conclusions. Our data indicates that the morphology of subaxial cervical spine endplates between Chinese and White men and women is different in most of the linear and area parameters. This information could provide guidelines for the design of CDA implants and the improvement of surgical techniques.

In-vivo study of osseointegration in Prestige LP cervical disc prosthesis

Background

A study was designed to quantify the extent of porous osseointegration at the prosthesis-bone interface in the Prestige LP prosthesis containing a plasma-sprayed titanium coating.

Methods

Using an anterior surgical approach, cervical disc arthroplasty was performed in 8 mature male goats at the C3-C4 segment, followed by implantation of the Prestige LP prosthesis. The vertebral specimens were examined using microcomputed tomograph for histomorphometric quantification, and proceeded by routine paraffin processing for histological observation. Hence, the porous osseointegration at the prosthesis-bone interface was evaluated based on histologic and histomorphometric analyses.

Results

At 6 months after surgery, there was no evidence of prosthesis migration, loosening, subsidence, or neurologic or vascular complications. Based on gross histologic analysis, there was excellent porous ingrowth at the prosthesis–bone interface, without significant histopathologic changes. Histomorphometric analysis at the prosthesis-bone interface indicated the mean porous ingrowth of 48.5% ± 10.4% and the total ingrowth range of 36.6 to 59.8%.

Conclusions

As the first comprehensive in vivo investigation into the Prestige LP prosthesis, this project established a successful animal model in the evaluation of cervical disc arthroplasty. Moreover, histomorphometric analysis of porous ingrowth at the prosthesis-bone interface was more favorable for cervical disc arthroplasty with the Prestige LP prosthesis compared to historical reports of appendicular total joint arthroplasty.

Electronic supplementary material

The online version of this article (10.1186/s12891-018-1957-2) contains supplementary material, which is available to authorized users.

Anterior Lumbar Interbody Fusion Integrated Screw Cages: Intrinsic Load Generation, Subsidence, and Torsional Stability

OBJECTIVE

To perform a repeatable idealized in vitro model to evaluate the effects of key design features and integrated screw fixation on unloaded surface engagement, subsidence, and torsional stability.

METHODS

We evaluated four different stand-alone anterior lumbar interbody fusion (ALIF) cages with two, three, and four screw designs. Polyurethane (saw-bone) foam blocks were used to simulate the vertebral bone. Fuji Film was used to measure the contact footprint, average pressure, and load generated by fixating the cages with screws. Subsidence was tested by axially loading the constructs at 10 N/s to 400 N and torsional load was applied +/-1 Nm for 10 cycles to assess stability. Outcome measures included total subsidence and maximal torsional angle range.

RESULTS

Cages 1, 2, and 4 were symmetrical and produced similar results in terms of contact footprint, average pressure, and load. The addition of integrated screws into the cage-bone block construct demonstrated a clear trend towards decreased subsidence. Cage 2 with surface titanium angled ridges and a keel produced the greatest subsidence with and without screws, significantly more than all other cages ( P < 0.05). Angular rotation was not significantly affected by the addition of screws ( P < 0.066). A statistically significant correlation existed between subsidence and reduced angular rotation across all cage constructs ( P = 0.018).

CONCLUSION

Each stand-alone cage featured unique surface characteristics, which resulted in differing cage-foam interface engagement, influencing the subsidence and torsional angle. Increased subsidence significantly reduced the torsional angle across all cage constructs.

Evaluation of mobility and stability in the Discover artificial disc: an in vivo motion study using high-accuracy 3D CT data

OBJECT

Artificial disc replacement (ADR) devices are unlike implants used in cervical fusion in that they are continuously exposed to stress not only within the implant site but also at their site of attachment to the adjacent vertebra. An imaging technique with higher accuracy than plain radiography and with the possibility of 3D visualization would provide more detailed information about the motion quality and stability of the implant in relation to the vertebrae. Such high-accuracy studies have previously been conducted with radiostereometric analysis (RSA), which requires implantation of tantalum markers in the adjacent vertebrae. The aim of this study was to evaluate in vivo motion and stability of implanted artificial discs. A noninvasive analysis was performed with CT, with an accuracy higher than that of plain radiographs and almost as high as RSA in cervical spine.

METHODS

Twenty-eight patients with ADR were included from a larger cohort of a randomized controlled trial comparing treatment of cervical radiculopathy with ADR or anterior cervical decompression and fusion. Surgical levels included C4–7; 18 patients had 1-level surgery and 10 patients had 2-level surgery. Follow-up time ranged from 19 to 50 months, with an average of 40 months. Two CT volumes of the cervical spine, 1 in flexion and 1 in extension, were obtained in each patient and then spatially registered using a customized imaging tool, previously used and validated for the cervical spine. Motion between the components in the artificial disc, as well as motion between the components and adjacent vertebrae, were calculated in 3 planes. Intraclass correlation (ICC) between independent observers and repeatability of the method were also calculated.

RESULTS

Intrinsic motion, expressed as degrees in rotation and millimeters in translation, was detectable in a majority of the ADRs. In the sagittal plane, in which the flexion/extension was performed, sagittal rotation ranged between 0.2° and 15.8° and translation between 0.0 and 5.5 mm. Eight percent of the ADRs were classified as unstable, as motion between at least 1 of the components and the adjacent vertebra was detected. Five percent were classified as ankylotic, with no detectable motion, and another 8% showed very limited motion due to heterotopic ossification. Repeatability for the motion in the sagittal plane was calculated to be 1.30° for rotation and 1.29 mm for translation (95% confidence level), ICC 0.99 and 0.84, respectively. All 3 patients with unstable devices had undergone 1-level ADRs at C5–6. They all underwent revision surgery due to increased neck pain, and instability was established during the surgery.

CONCLUSIONS

The majority of the artificial discs in this study showed intrinsic mobility several years after implantation and were also shown to be properly attached. Implant instability was detected in 8% of patients and, as all of these patients underwent revision surgery due to increasing neck pain, this might be a more serious problem than heterotopic bone formation.

Failure analysis of C-5 after total disc replacement with ProDisc-C at 1 and 2 levels and in combination with a fusion cage: finite-element and biomechanical models

OBJECT

The purpose of this study was to evaluate the failure risk of cervical vertebrae after total disc replacement with a keel-design prosthesis (ProDisc-C), taking into consideration the effects of vertebral body height, multilevel replacement, and the association with an adjacent fusion cage. Although promising clinical results have been reported for the ProDisc-C, some clinical studies have reported vertebral body–splitting fractures at single- and multilevel arthroplasty sites. This implant has central keels to provide solid initial stability, and some authors associate the potential risk of vertebral body failure with the keel design, especially in patients with small vertebral body height or when the implant is used at multiple levels.

METHODS

The study was performed using a specimen-specific C4–6 cervical-segment finite-element model to assess the compressive strains on the C-5 vertebral body for each cervical segment configuration, and synthetic polyurethane models to experimentally predict the compressive load at failure for 3 vertebral body heights.

RESULTS

The use of a keeled ProDisc-C prosthesis at multiple levels or in combination with a fusion cage increases by a factor of 2–3 the compressive strains at the C-5 vertebral body relative to single-level arthroplasty. All implanted segment configurations tested demonstrated a continuum of the load at failure and the vertebral body height, but no significant differences were found between the 3 vertebral body heights in each segment configuration.

CONCLUSIONS

The use of a keeled ProDisc-C prosthesis at 2 adjacent levels or combined with a fusion cage presented the lowest load-at-failure values, 2 times higher on average than the ones occurring during physiological tasks. This fact indicates an identical and limited risk of vertebral body failure for these 2 segment configurations, whereas vertebral body height appears to slightly affect this risk. However, for some tasks that place higher physical demands on the neck, beyond what was represented by our models, there may also be risk of microdamage initiation, which is not present in the single-level arthroplasty.

Stabilization with the Dynamic Cervical Implant: a novel treatment approach following cervical discectomy and decompression

OBJECT

Although cervical total disc replacement (TDR) has shown equivalence or superiority to anterior cervical discectomy and fusion (ACDF), potential problems include nonphysiological motion (hypermobility), accelerated degeneration of the facet joints, particulate wear, and compromise of the mechanical integrity of the endplate during device fixation. Dynamic cervical stabilization is a novel motion-preserving concept that facilitates controlled, limited flexion and extension, but prevents axial rotation and lateral bending, thereby reducing motion across the facet joints. Shock absorption of the Dynamic Cervical Implant (DCI) device is intended to protect adjacent levels from accelerated degeneration.

METHODS

The authors conducted a prospective evaluation of 53 consecutive patients who underwent DCI stabilization for the treatment of 1-level (n = 42), 2-level (n = 9), and 3-level (n = 2) cervical disc disease with radiculopathy or myelopathy. Forty-seven patients (89%) completed all clinical and radiographic outcomes at a minimum of 24 months. Clinical outcomes consisted of Neck Disability Index (NDI) and visual analog scale (VAS) scores, neurological function at baseline and at latest follow-up, as well as patient satisfaction. Flexion-extension radiography was evaluated for device motion, implant migration, subsidence, and heterotopic ossification. Cervical sagittal alignment (Cobb angle), functional spinal unit (FSU) angle, and range of motion (ROM) at index and adjacent levels were evaluated with WEB 1000 software.

RESULTS

The NDI score, VAS neck and arm pain scores, and neurological deficits were significantly reduced at each postoperative time point compared with baseline (p < 0.0001). At 24 months postoperatively, 91% of patients were very satisfied and 9% somewhat satisfied, while 89% would definitely and 11% would probably elect to have the same surgery again. In 47 patients with 58 operated levels, the radiographic assessment showed good motion (5°-12°) of the device in 57%, reduced motion (2°-5°) in 34.5%, and little motion (0-2°) in 8.5%. The Cobb and FSU angles improved, showing a clear tendency for lordosis with the DCI. Motion greater than 2° of the treated segment could be preserved in 91.5%, while 8.5% had a near segmental fusion. Mean ROM at index levels demonstrated satisfying motion preservation with DCI. Mean ROM at upper and lower adjacent levels showed maintenance of adjacent-level kinematics. Heterotopic ossification, including 20% minor and 15% major, had no direct impact on clinical results. There were 2 endplate subsidences detected with an increased segmental lordosis. One asymptomatic anterior device migration required reoperation. Three patients underwent a secondary surgery in another segment during follow-up, twice for a new disc herniation and once for an adjacent degeneration. There was no posterior migration and no device breakage.

CONCLUSIONS

Preliminary results indicate that the DCI implanted using a proper surgical technique is safe and facilitates excellent clinical outcomes, maintains index-and adjacent-level ROM in the majority of cases, improves sagittal alignment, and may be suitable for patients with facet arthrosis who would otherwise not be candidates for cervical TDR. Shock absorption together with maintained motion in the DCI may protect adjacent levels from early degeneration in longer follow-up.

ISASS Policy Statement - Cervical Artificial Disc

Morgan Lorio, MD, FACS, Chair, ISASS Task Force on Coding & Reimbursement

The ISASS Task Force reached out to Domagoj Coric, MD to provide a timely summation on cervical disc arthroplasty given his special interest and recent IASP championship of this innovative technology to insure enhanced spine patient access. The ISASS Task Force is pleased with this step towards published ISASS societal policy and applauds Dr. Coric's effort; if ISASS is to continue to succeed we must continually harness the voluntary talents and energies of our members with gratitude.

Pullout strength of bone-patellar tendon-bone allograft bone plugs: a comparison of cadaver tibia and rigid polyurethane foam

PURPOSE

To compare the load-to-failure pullout strength of bone-patellar tendon-bone (BPTB) allografts in human cadaver tibias and rigid polyurethane foam blocks.

METHODS

Twenty BPTB allografts were trimmed creating 25 mm × 10 mm × 10 mm tibial plugs. Ten-millimeter tunnels were drilled in 10 human cadaver tibias and 10 rigid polyurethane foam blocks. The BPTB anterior cruciate ligament allografts were inserted into these tunnels and secured with metal interference screws, with placement of 10 of each type in each material. After preloading (10 N), cyclic loading (500 cycles, 10 to 150 N at 200 mm/min) and load-to-failure testing (200 mm/min) were performed. The endpoints were ultimate failure load, cyclic loading elongation, and failure mode.

RESULTS

No difference in ultimate failure load existed between grafts inserted into rigid polyurethane foam blocks (705 N) and those in cadaver tibias (669 N) (P = .69). The mean rigid polyurethane foam block elongation (0.211 mm) was less than that in tibial bone (0.470 mm) (P = .038), with a smaller standard deviation (0.07 mm for foam) than tibial bone (0.34 mm).

CONCLUSIONS

All BPTB grafts successfully completed 500 cycles. The rigid polyurethane foam block showed less variation in test results than human cadaver tibias.

CLINICAL RELEVANCE

Rigid polyurethane foam blocks provide an acceptable substitute for human cadaver bone tibia for biomechanical testing of BPTB allografts and offer near-equivalent results.

High prevalence of heterotopic ossification after cervical disc arthroplasty: outcome and intraoperative findings following explantation of 22 cervical disc prostheses

OBJECT

Cervical disc arthroplasty (CDA) has been increasingly used for the treatment of cervical disc herniations. However, the impact of CDA on adjacent-segment degeneration and the degree of heterotopic ossification (HO) of the treated segment remain a subject of controversy. Due to a product failure of the Galileo-type disc prosthesis, 22 of these devices were explanted. The radiological and clinical course in each case was investigated in detail with an emphasis on the incidence of HO and facet joint degeneration 18 months following the operation. Intraoperative findings regarding ossification and implant fixation were documented. Thus, the authors were able to describe the true rate of adjacent-segment degeneration and HO following CDA and the clinical relevance thereof.

METHODS

In all 22 patients, functional radiographic imaging was performed prior to surgery, 3 and 12 months after surgery, and prior to disc prosthesis explantation. At all time points, the range of motion (ROM) in the operated and adjacent segments was determined. A motion index was calculated using the preoperative and all postoperative ROMs (preoperative ROM/postoperative ROM). Computed tomography was used preoperatively to measure the height of the index segment, extent of HO, and the degree of the progression of facet arthrosis, and was used postoperatively prior to prosthesis explantation. Patients completed clinical questionnaires that included a visual analog scale and the Neck Disability Index.

RESULTS

The motion index of the index segment declined gradually from 1.4 at 3 months postoperative to 1.2 prior to explantation, while the motion index of the adjacent upper segment increased from 0.9 to 1.3. The mean ROM of the index segment was 10.4° ± 6.7°, and fusion was observed in 2 (9%) of the 22 patients. Prosthesis migration was present in 3 patients (13.6%). Severe HO (Grades 3 and 4) was present in 17.4%. Computed tomography showed a significant increase of segmental height of the index segment (1.6 ± 1.1 mm, p = 0.035), and a significant increase of left-sided lateral osteophytes (1.7 ± 2.1 mm, p = 0.009). The incidence of severe osteophyte formation (> 2 mm) occurred in 40%. Intraoperative findings reflected the results from CT, with primary lateral proliferation of osteophytes found in approximately 25% of patients. The mean visual analog scale scores were 3.8 ± 2.7 (neck) and 2.4 ± 2.5 (arms), and the mean Neck Disability Index score was 30 ± 22. No correlation was found between radiological and clinical parameters.

CONCLUSIONS

In this study, a higher incidence of HO after CDA could be demonstrated using CT, compared with studies using fluoroscopy only. However, patient selection and/or the operative technique might have contributed to the high prevalence of osteophyte formation. Thus, the exact indication for CDA has to be reconsidered. Because implant migration was detected, using fixation in the present CDA model appears suboptimal.

Biomechanical evaluation of a novel total cervical prosthesis in a single-level cervical subtotal corpectomy model: an in vitro human cadaveric study

BACKGROUND

Anterior cervical subtotal corpectomy and fusion provides extensive decompression in the treatment of cervical myelopathy. However, early adjacent segment degeneration may arise due to the abnormal kinematics. To the best of our knowledge, this is the first report on a newly-designed total cervical prosthesis (TCP) to preserve the normal kinematics of cervical spine. The purpose of this study was to compare the cervical range of motion (ROM) of TCP with anterior cervical plating (ACP) in a single-level cervical subtotal corpectomy model.

STUDY DESIGN

An in vitro biomechanical study of a novel total cervical prosthesis (TCP) using a cadaveric model.

MATERIALS AND METHODS

After evaluation of the ROM of the 14 human cadaveric cervical spines (C(2)-T(1)) (intact group), single-level subtotal corpectomy models at the C(5) levels were performed. All specimens were randomized, instrumented with ACP (n = 7) and TCP (n = 7) from C(4) to C(6). All specimens were tested for flexion/extension, lateral bending, and axial rotation loading. The ROM of implanted segments (C(4)-C(6)) and adjacent segments (C(3)/C(4) and C(6)/C(7)) were monitored, respectively.

RESULTS

TCP was found to accurately recapitulate the preoperative ROM both in the adjacent segments (C(3)/C(4) and C(6)/C(7)) and the implanted segments (C(4)-C(6)). In the adjacent segments, no significant difference was found in ROM(C3/C4) between the TCP group and the intact group in flexion, extension, and lateral bending. In the implanted segments, TCP preserved well the ROM(C4-C6), with 5.29° in flexion, 12.27° in extension, 8.95° in right lateral bending, and 7.50° in left lateral bending. In contrast, the mean ROM(C4-C6) in the ACP group was lower than those in the TCP group and the intact group significantly in all directions (P < 0.05). In addition, compared with the ACP group, the mean ROM(C3-C7) in TCP group increased by 32.6% (P = 0.034) in flexion, 62.9% (P = 0.008) in extension, 24.8% (P > 0.05) in lateral bending, and 36.0% (P < 0.01) in rotation. Compared with the intact group, the TCP group showed moderate decrease in flexion and moderate increases in extension, lateral bending, and rotation. But no significant differences were detected (P > 0.05).

CONCLUSIONS

Biomechanical analyses suggest that TCP preserves ROM in the implanted segments after cervical subtotal corpectomy. TCP will not induce compensatory motion in the adjacent segments, thus may possibly help prevent adjacent segment degeneration.

Comparative safety of simultaneous and staged anterior and posterior spinal surgery

STUDY DESIGN

Analysis of population-based national hospital discharge data collected for the Nationwide Inpatient Sample.

OBJECTIVE

To study perioperative outcomes of circumferential spine surgery performed on either the same or different days of the same hospitalization.

SUMMARY OF BACKGROUND DATA

Circumferential spine fusion surgery has been linked to an increased adjusted risk in perioperative morbidity and mortality compared with procedures involving only 1 site. To minimize these risks, some surgeons elect to perform the 2 components of this procedure in separate sessions during the same hospitalization. The value of this approach is uncertain.

METHODS

Data collected between 1998 and 2006 for the Nationwide Inpatient Sample were analyzed. Hospitalizations during which a circumferential noncervical spine fusion was performed were identified. Patients were divided into those who had their anterior and posterior portion performed on the same and those performed on different days of the same hospitalization. The prevalence of patient and health care system-related demographics was evaluated. Frequencies of procedure-related complications and mortality were determined. Multivariate regression models were created to identify whether timing of procedures was associated with an independent increase in risk for adverse events.

RESULTS

We identified a total of 11,265 entries for circumferential spine fusion. Of those, 71.2% (8022) were operated in 1 session. Complications were more frequent among staged- versus same-day surgery patients (28.4% vs. 21.7%, P < 0.0001). The incidence of venous thrombosis and adult respiratory distress syndrome also increased among staged candidates, while the trend toward higher mortality (0.5% vs. 0.4%) did not reach significance. In the regression model, staged circumferential spine fusions were associated with a 29% increase in the odds morbidity and mortality compared with same-day procedures.

CONCLUSION

Staging circumferential spine surgery procedures during the same hospitalization offers no mortality benefit and may even expose patients to increased morbidity.

Cervical and lumbar spinal arthroplasty: clinical review

In contrast to cervical and lumbar fusion procedures, the principal aim of disk arthroplasty is to recapitulate the normal kinematics and biomechanics of the spinal segment affected. Following decompression of the neural elements, disk arthroplasty allows restoration of disk height and maintenance of spinal alignment. Based on clinical observations and biomechanical testing, the anticipated advantage of arthroplasty over standard arthrodesis techniques has been a proposed reduction in the development of symptomatic ALD. In this review of cervical and lumbar disk arthroplasty, we highlight the clinical results and experience with standard fusion techniques, incidence of ALD in the population of patients with surgical fusion, and indications for arthroplasty, as well as the biomechanical and clinical outcomes following arthroplasty. In addition, we introduce the devices currently available and provide a critical appraisal of the clinical evidence regarding arthroplasty procedures.