Facet Replacement Research Articles

P71. Prospective, randomized study of lumbar facet replacement versus lumbar TLIF fusion for spondylolisthesis: 2-year outcomes

P71. Prospective, randomized study of lumbar facet replacement versus lumbar TLIF fusion for spondylolisthesis: 2-year outcomes

Mobility-Maintaining Facet Arthroplasty of the Lumbar Spine With the Second-Generation TOPS System: A Case Series.

BACKGROUND:Lumbar spinal stenosis results from spinal canal narrowing and can lead to pain and dysfunction. Until recently, surgical treatment for lumbar spinal stenosis requiring an extensive decompression, with or without spondylolisthesis, had to balance pain relief with the long-term risks of spinal instability after decompression and adjacent segment disease (ASD) after spinal fusion. Spinal motion-preserving devices aim to reduce the incidence of ASD after posterolateral fusion and consequent need for revision surgery.OBJECTIVE:To present a single-center experience with a facet replacement implant (TOPS System [TOtal Posterior Spine System], Premia Spine) designed to stabilize the spine and prevent further degeneration while maintaining a normal range of motion (ROM).METHODS:Seventeen patients received the implant after a laminotomy. Clinical assessments included surgery duration, complication rates, and visual analog score for back pain. Radiographs were used to measure ROM changes from flexion to extension and assess for any repositioning of a degenerative spondylolisthesis and segment lordosis.RESULTS:The average operative time was 102 minutes. The average visual analog score reduction was 7.5 at 3 months, 6.8 at 12 months, and 6.7 at the longest follow-up (average: 51 months, range: 26-77), demonstrating an average improvement of 81%. The preoperative and postoperative average ROMs were 8.2° and 7.4°, respectively.CONCLUSION:This series shows that the TOPS System has the potential to relieve back pain and maintain close-to-normal ROM over longer time periods without inducing ASD. The TOPS System is the first to allow the patient to settle into physiological lordosis adjustment thus presenting new treatment possibilities with mobility-maintaining dorsal instrumentation.

Mean 5-Year Follow-Up Results of a Facet Replacement Device in the Treatment of Lumbar Spinal Stenosis and Degenerative Spondylolisthesis

Flexible stabilization has been utilized to maintain spinal mobility in patients with early-stage lumbar spinal stenosis (LSS). Previous literature has not yet established any nonfusion solution as a viable treatment option for patients with severe posterior degeneration of the lumbar spine. This feasibility study evaluates the mean 5-year outcomes of patients treated with the Total Posterior Spine System (TOPS) facet replacement system in the surgical management of lumbar spinal stenosis and degenerative spondylolisthesis. Ten patients (2 men, 8 women, mean age: 59.6 years) were enrolled into a non-randomized prospective clinical study. Patients were evaluated with standing anteroposterior, lateral, flexion and extension radiographs and magnetic resonance imaging scans, back and leg pain visual analog scale scores, Oswestry Disability Index, Zurich Claudication Questionnaire and the SF-36 questionnaires, preoperatively, 6 months, 1 year, 2 years, and latest follow-up at a mean of 5 years postoperatively (range: 55-74 months). Flexion and extension standing lumbar spine radiographs were obtained at 2 years to assess range of motion at the stabilized segment. The clinical outcome scores for the cohort improved significantly across all scoring systems. Radiographs at 2 years did not reveal any loss of position or loosening of metal work. There were 2 incidental durotomies and no failures at 5 years, with no patient requiring revision surgery. The TOPS implant maintains clinical improvement and motion in the surgical management of LSS and spondylolisthesis, suggesting that it can be considered an option for these indications.

Current concepts of spondylosis and posterior spinal motion preservation for radiologists.

Spinal fusion is performed to eliminate motion at a degenerated or unstable segment. However, this is associated with loss of motion at the fused levels and increased stress on adjacent levels. Motion-preserving implants have been designed in effort to mitigate the limitations of fusion. This review will focus on posterior spinal motion-preserving technologies. In the cervical spine, laminoplasty is a posterior motion-preserving procedure used in the management of myelopathy/cord compression. In the lumbar spine, motion-sparing systems include interspinous process devices (also referred to as interspinous process spacers or distraction devices), posterior dynamic stabilization devices (also referred to as pedicle screw/rod fixation-based systems), and posterior element replacement systems (also referred to as total facet replacement devices). Knowledge of the intended physiologic purpose, hardware utilized, and complications is important in the assessment of imaging in those who have undergone posterior motion preservation procedures.

75. Prospective, randomized study of lumbar facet replacement and lumbar interbody fusion for spondylolisthesis

BACKGROUND CONTEXT The surgical treatment for lumbar spondylolisthesis has remained somewhat controversial. Posterior lumbar arthroplasty with facet replacement is a novel alternative to lumbar decompression and fusion. There are currently no FDA-approved devices for facet replacement. The TOPS System is a robust, pedicle screw-based biomechanical device intended to replace the facets and posterior elements following aggressive decompression. PURPOSE Lumbar facet replacement is a novel motion-preserving procedure that can be used to treat spondylolisthesis with stenosis. There is an ongoing multicenter, prospective, randomized, controlled US Food and Drug Administration (FDA) Investigation Device Exemption (IDE) trial evaluating the clinical and radiographic outcomes of an investigational facet replacement device and lumbar fusion with interbody fusion with pedicle screw fixation. STUDY DESIGN/SETTING Multicenter, prospective, randomized, US FDA Investigation Device Exemption trial. PATIENT SAMPLE The results of five high enrolling investigational sites from the prospective, randomized IDE trial comparing facet replacement (TOPS) and lumbar interbody fusion (TLiF) in the treatment of Grade I degenerative spondylolisthesis and stenosis were combined to evaluate clinical outcomes. OUTCOME MEASURES The primary clinic outcome measures included the Oswestry Disability Index (ODI) and visual analog scale (VAS) as well as re-operation rate. Patients were 2:1 randomized to artificial facet replacement vs TLIF using a monolithic PEEK interbody spacer and pedicle screw fixation. A minimum of 12 months follow-up was required for inclusion in this study. METHODS The results of five high enrolling investigational sites from the prospective, randomized IDE trial comparing facet replacement (TOPS) and lumbar interbody fusion (TLiF) in the treatment of Grade I degenerative spondylolisthesis and stenosis were combined to evaluate clinical outcomes. The primary clinic outcome measures included the Oswestry Disability Index (ODI) and visual analog scale (VAS) as well as re-operation rate. Patients were 2:1 randomized to artificial facet replacement vs TLIF using a monolithic PEEK interbody spacer and pedicle screw fixation. A minimum of 12 months follow-up was required for inclusion in this study. RESULTS A total of 129 patients have been enrolled and randomly assigned to either TOPS (n=90) or to TLIF (n= 39). A total of 63 patients were available for follow-up of at least 12 months (TOPS=47, TLIF=16). The reoperation rate for revision, removal or supplemental fixation (RRSF) for facet replacement and TLIF control was 6.7% and 12.8%, respectively. There was no significant difference between groups in baseline mean ODI (TOPS=57; TLIF=56) or VAS Back (TOPS=68; TLIF=68) and Leg scores (TOPS=83; TLIF=84). Both groups showed significant improvement in ODI (TOPS=13; TLIF=14) and VAS Back (TOPS=12; TLIF=14) and VAS Leg (TOPS=12; TLIF=10) from baseline to 12-month follow-up. At 12-month follow-up, 89% of TOPS patients and 81% of TLIF patients showed both a minimum of 15-point ODI improvement and no RRSF reoperation. CONCLUSIONS The preliminary results of this prospective, randomized study are encouraging for both TOPS and TLIF. Both lumbar facet replacement and interbody fusion groups have shown good clinical outcomes with relatively low re-operation rates. There was a trend toward lower reoperation rates with lumbar arthroplasty that did not reach clinical significance. There was no statistically significant difference between the groups in clinic outcome measures. There was a statistically significant level of improvement from baseline and last follow-up in ODI and VAS (Back and Leg) in both treatment groups. Lumbar facet replacement and lumbar interbody fusion both appear to be viable options for treatment of one-level lumbar stenosis due to degenerative spondylolisthesis. Continued enrollment with long-term follow-up is required to validate these early findings as well as to evaluate for any differences between rigid and dynamic stabilization on adjacent level disease. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.

In vitro analysis of circumferential joint replacement, including bilateral facet joint replacement with lateral lumber disc prosthesis: a parametric investigation of disc sizing.

Lateral lumbar disc prosthesis (LLDP) is an innovative device used to restore motion in select patients through a lateral retroperitoneal approach. No in vitro biomechanical studies have been published. Further, the potential for in toto circumferential joint restoration when use of this anterior disc is combined with facet replacement remains unqualified but signifies a potentially interesting clinical direction. Researchers conducted a biomechanical feasibility study of an LLDP designed to investigate parameters of disc sizing used with bilateral facet joint replacement in a cadaveric model. Tested constructs at L4-L5 included (1) intact, (2) LLDP, (3) LLDP+ wide discectomy, (4) LLDP+ bilateral facetectomy, and (5) LLDP+ bilateral facet joint replacement (BFJR). Investigators tested instrumented constructs (2-5) with an LLDP at compact-fit and lax-fit heights and used raw data to perform statistical analysis by repeated measures analysis of variance (ANOVA), along with Student-Newman-Keuls post hoc analysis (p≤0.05). Increased height of the LLDP resulted in significantly less motion compared with intact. Widening the discectomy while using lax-fit sizing led to motion similar to intact in flexion-extension. As expected, motion was greater with lax-fit height than with compact-fit height in all loading modes and constructs, as is noted with a widened discectomy. The L4-L5 center of rotation was maintained regardless of placement of the LLDP. After bilateral facetectomy, reconstruction of the three-joint complex achieved by combining the LLDP with BFJR may provide a viable alternative to current clinical treatment regimens.

In vitro measurement of load-sharing in spinal implants

Efficient load-sharing in the spinal column relies on the proper working of the components of the Functional Spinal Unit (FSU). Due to various reasons such as trauma, ageing and diseases, these components or even the entire FSU can get degenerated or injured during a person’s lifetime. Spinal column reconstruction surgerieswere created with the aimto restore the functioning of the diseased or injured spine. Several spinal implants are available today for the surgeon to aid in this process. There are three major categories of these devices: anterior stabilization devices, posterior stabilization devices and motion preservation devices. This review highlights thein vitro researchdone on these devices,over the past five decades, to evaluate their ability to effectively share loads at the operated level of the spinal column. Some conclusions have been drawn based on this research.Dynamic anterior cervical plates are more successful at maintaining load-sharing after graft subsidence and anterior stabilization devices can be used to provide support to posterior stabilization devices during severe anterior column injuries. Motion preservation devices, specifically cervical disc prostheses and facet replacement systems,show great potential in maintaining physiologicalloads in the spinal column. Further clinical investigation of all these implants would help to identify the contributing factors for their success or failure post-surgery. It would also aid in determining the requirements of an ideal spine stabilization device which perfectly mimics the physiological load-sharing properties of the FSU and its components.

Simple facet joint repair with dynamic pedicular system: Technical note and case series.

Purpose:Facet joints are important anatomical structures for the stability of spine. Surgical or degenerative damage to a facet joint may lead to spinal instability and causes clinical problems. This article explains the importance of facet joints, reviews facet replacement systems, and describes a simple and effective method for facet replacement after surgical removal of facet joints.Materials and Methods:Ten patients were operated with the diagnosis of unilateral nerve root compression secondary to facet degeneration. The hypertrophic facet joints were removed with microsurgical techniques and the roots were decompressed. Then, a unilateral artificial facet joint was created using two hinged screws and a dynamic rod.Results:The clinical outcome of all the patients was determined good or excellent at second and last follow-up (mean 13.3 months) controls using visual analog scale (VAS) and Oswestry Disability Index (ODI) scores. Radiological evaluations also demonstrated no implant-related complications.Conclusions:The authors suggest that, if removal of a facet joint is necessary to decompress the nerve roots, the joint can be replaced by a construct composed of two hinged screws connected by a dynamic rod. This simple system mimics the function of a normal facet joint and is an effective technique for unilateral facet joint replacement.

ACADIA® Facet Replacement System IDE Study: Preliminary Outcomes at Two- and Four-Years Postoperative

ACADIA® Facet Replacement System IDE Study: Preliminary Outcomes at Two- and Four-Years Postoperative

Motion preservation surgery in the spine.

The primary goal of motion preservation surgery in the spine is to maintain normal or near normal motion in an attempt to prevent adverse outcomes commonly seen with conventional spinal fusion, most notably the development of adjacent-level degenerative disc disease. Several different surgical approaches have been developed to preserve motion in the lumbar spine, including total disc replacement, partial disc (nucleus) replacement, interspinous spacers, dynamic stabilization devices, and total facet replacement devices. The design of devices varies greatly. The devices are created using a similar rationale but are unique in design relative to their lumbar counterparts.

Postero-lateral disc prosthesis combined with a unilateral facet replacement device maintains quantity and quality of motion at a single lumbar level.

BackgroundMechanically replacing one or more pain generating articulations in the functional spinal unit (FSU) may be a motion preservation alternative to arthrodesis at the affected level. Baseline biomechanical data elucidating the quantity and quality of motion in such arthroplasty constructs is non-existent.PurposeThe purpose of the study was to quantify the motion-preserving effect of a posterior total disc replacement (PDR) combined with a unilateral facet replacement (FR) system at a single lumbar level (L4-L5). We hypothesized that reinforcement of the FSU with unilateral FR to replace the resected, native facet joint following PDR implantation would restore quality and quantity of motion and additionally not change biomechanics at the adjacent levels.Study DesignIn-vitro study using human cadaveric lumbar spines.MethodsSix (n = 6) cadaveric lumbar spines (L1-S1) were evaluated using a pure-moment stability testing protocol (±7.5 Nm) in flexion-extension (F/E), lateral bending (LB) and axial rotation (AR). Each specimen was tested in: (1) intact; (2) unilateral FR; and (3) unilateral FR + PDR conditions. Index and adjacent level ROM (using hybrid protocol) were determined opto-electronically. Interpedicular travel (IPT) and instantaneous center of rotation (ICR) at the index level were radiographically determined for each condition. ROM, ICR, and IPT measurements were compared (repeated measures ANOVA) between the three conditions.ResultsCompared to the intact spine, no significant changes in F/E, LB or AR ROM were identified as a result of unilateral FR or unilateral FR + PDR. No significant changes in adjacent L3-L4 or L5-S1 ROM were identified in any loading mode. No significant differences in IPT were identified between the three test conditions in F/E, LB or AR at the L4-L5 level. The ICRs qualitatively were similar for the intact and unilateral FR conditions and appeared to follow placement (along the anterior-posterior (AP) direction) of the PDR in the disc spaceConclusionBiomechanically, quantity and quality of motion are maintained with combined unilateral FR + PDR at a single lumbar spinal level.

Does Treatment with the ACADIA® Facet Replacement Device Provide Sustained Relief of Stenotic Leg Pain?

Does Treatment with the ACADIA® Facet Replacement Device Provide Sustained Relief of Stenotic Leg Pain?

Stem fracture after total facet replacement in the lumbar spine: a report of two cases and review of the literature

Background context A randomized controlled multicenter investigational device exemption clinical trial comparing the total facet arthroplasty system (TFAS) (Archus Orthopedics, Redmond, WA, USA) with posterior fusion was discontinued because of financial reasons. To our knowledge, no clinical outcomes or complications have yet been presented for the TFAS, and no device-related complications have been reported for any other lumbar facet replacement system. Purpose To report and discuss two cases of stem fracture after total facet replacement in the lumbar spine. Study design Case report and literature review. Patient sample A 55-year-old man with a body mass index (BMI) of 40 underwent total facet replacement at L4–L5 for Grade 1 spondylolisthesis with stenosis. After 9 months of pain relief, he experienced gradually increasing pain and radiographs showed a broken stem. A 60-year-old woman with a BMI of 31 underwent total facet replacement at L4–L5 for Grade 1 spondylolisthesis with stenosis. She experienced stem fracture 27 months postoperatively. Outcome measures Visual analog scale for pain, Oswestry Disability Index for function, and computed tomography and X-ray for imaging. Results After TFAS stem breakage, both patients underwent interbody fusion through a transpsoas approach and have done well over 24- and 12-month follow-up periods, respectively. Conclusions These are the first cases of stem fracture reported after total facet replacement in the lumbar spine. Biomechanics of TFAS stem breakage may be similar to those of pedicle screw breakage, including fatigue and three-point bending stress. Further biomechanical studies and failure analyses however are needed for adequate understanding to improve the biomechanics of dynamic pedicle–based devices.

Influence of an Auxiliary Facet System on Lumbar Spine Biomechanics

In vitro biomechanical study investigating L4-L5 kinematics and intradiscal pressure (IDP) with a facet replacement system. To assess the influence of the Auxiliary Facet System (AFS). Posterior dynamic systems are used in the treatment of low back pain to avoid adjacent segment degeneration. Facet replacement systems are supposed to stabilize a lumbar segment after facetectomy and neural decompression, and to provide an intersegmental range of motion (ROM). The AFS is fixed by 4 pedicle screws, linked by 2 angulated rods, a polyaxial connector, and a crosslink. Flexibility tests were conducted on 6 human cadaver specimens (L3-S1) using a load testing device and the Polaris system. The specimens were loaded by steps of 1 Nm to 10 Nm in flexion/extension, lateral bending, and axial rotation. The following configurations were investigated: intact segment, instrumented, instrumented plus medial facetectomy, and facetectomy alone. The sagittal mean center of rotation (MCR) was calculated, and IDPs were measured in flexion/extension. The ROM of the intact segment was 10.9° (9.4°-15.5°) in flexion/extension, 9.5° (6.8°-12.1°) in lateral bending, and 4.7° (3.4°-6.0°) degrees in axial rotation. Medial facetectomy and instrumentation led to -6% of ROM in flexion/extension and +1% lateral bending. Medial facetectomy without implant led to +106% of axial rotation (P = 0.028). The instrumentation reduced axial rotation to -38% (P = 0.028). This decrease was because of the presence of the cross-link. The MCR was located around the middle of the superior L5 endplate in intact and instrumented specimens. It moved cranial after facetectomy without instrumentation. The implant decreased the maximal IDP during flexion/extension to -17% (P = 0.028). The AFS had a minor influence on flexion/extension and lateral bending, and the MCR kept physiologic. Bilateral facetectomy yielded an increase in axial rotation, which was stabilized by the implant. The AFS seemed to reduce IDPs.

Prospective US IDE Trial: Interim Results for the Treatment of Symptomatic Lumbar Spinal Stenosis with Facet Replacement in 100 Patients Enrolled at 15 Centers

Patients presenting with radiculopathy and/or neurogenic claudication secondary to lumbar spinal stenosis with or without spondylolisthesis often receive destabilizing decompressions that require arthrodesis. Alterations in lumbar biomechanics due to fusion have the potential to accelerate degenerative changes at adjacent levels. Facet replacement as an alternative to fusion may provide the required stability and preserve adjacent level biomechanics thereby mitigating the risk of accelerated degenerative changes.

Facet Replacement: Three-Year Follow-up on a Multicenter Study

Facet Replacement: Three-Year Follow-up on a Multicenter Study

Kinematics of total facet replacement (TFAS-TL) with total disc replacement

Background Total disc replacement (TDR) and total facet replacement (TFR) have been the focus of recent kinematics evaluations. Yet their concurrent function as a total joint replacement of the lumbar spine's 3-joint complex has not been comprehensively reported. This study evaluated the effect of a TFR specifically designed to replace the natural facets and supplement the function with the natural disc and with TDR. The ability to replace degenerated facets to complement a pre-existing or simultaneously implanted TDR may allow surgeons to completely address degenerative pathologies of the 3-joint complex of the lumbar spine. We hypothesized that TFR would reproduce the biomechanical function of the natural facets when implanted in conjunction with TDR. Methods Lumbar spines (L1-5, 51.3 ± 14.2 years, N = 6) were tested sequentially as follows: (1) intact, (2) after TDR implantation, and (3) after TFR implantation in conjunction with TDR, all at L3-4. Specimens were tested in flexion-extension (+ 8 Nm to − 6 Nm), lateral bending (± 6 Nm), and axial rotation (± 5 Nm). A 400 N compressive follower preload was applied during flexion-extension tests. Three-dimensional segmental motion was recorded and analyzed using analysis of variance in Systat (Systat Software Inc., Chicago, Illinois) and multiple comparisons with Bonferroni correction. Results The TDR implantation (TDR + natural facets) allowed similar lateral bending ( P = .66), but it generally increased flexion-extension ( P = .06) and axial rotation ( P < .05) range of motion (ROM) at the implanted level compared to intact. The TFR + TDR (following replacement of the natural facets with TFR) decreased ROM to levels similar to intact in lateral bending ( P = .70) and axial rotation ( P = .23). The TFR + TDR flexion-extension ROM was reduced in comparison to intact and TDR + natural facets ( P < .05). Conclusions The TFR with TDR was able to restore stability to the lumbar segment after bilateral facetectomy, while allowing near-normal motions in all planes.

Posterior Pedicle Fixation-based Dynamic Stabilization Devices for the Treatment of Degenerative Diseases of the Lumbar Spine

Literature review. To provide a comprehensive review of the available literature reporting clinical results of using pedicle-based posterior dynamic stabilization systems in the lumbar spine. A literature search was performed using a number of key words including: posterior dynamic stabilization, facet replacement, pedicle fixation. There is a wide array of pedicle-based, posterior dynamic stabilization systems available. Purported indications are also varied, spanning from degenerative disk disease to reconstruction after laminectomy for spinal stenosis. Short-term and mid-term clinical results of some of these devices are available. For many others, clinical studies are still underway or have just begun. For the spine community to draw sound conclusions that a posterior dynamic device is better than fusion, results from multiple, similarly designed, independently funded trials must be compiled, compared, and contrasted.

L5 – S1 Segmental Kinematics After Facet Arthroplasty

Background Facet arthroplasty is a motion restoring procedure. It is normally suggested as an alternative to rigid fixation after destabilizing decompression procedures in the posterior lumbar spine. While previous studies have reported successful results in reproducing normal spine kinematics after facet replacement at L4-5 and L3-4, there are no data on the viability of facet replacement at the lumbosacral joint. The anatomy of posterior elements and the resulting kinematics at L5-S1 are distinctly different from those at superior levels, making the task of facet replacement at the lumbosacral level challenging. This study evaluated the kinematics of facet replacement at L5-S1. Methods Six human cadaveric lumbar spines (L1-S1, 46.7 ± 13.0 years) were tested in the following sequence: (1) intact (L1-S1), (2) complete laminectomy and bilateral facetectomy at L5-S1, and (3) implantation of TFAS-LS (Lumbosacral Total Facet Arthroplasty System, Archus Orthopedics, Redmond, Washington) at L5-S1 using pedicle screws. Specimens were tested in flexion (8Nm), extension (6Nm), lateral bending (LB, ± 6Nm), and axial rotation (AR, ± 5Nm). The level of significance was α = .017 after Bonferroni correction for three comparisons: (1) intact vs. destabilized, (2) destabilized vs. reconstructed, and (3) intact vs. reconstructed. Results Laminectomy-facetectomy at L5-S1 increased the L5-S1 angular range of motion (ROM) in all directions. Flexion-extension (F-E) ROM increased from 15.3 ± 2.9 to 18.7 ± 3.5 degrees ( P < .017), LB from 8.2 ± 1.8 to 9.3 ± 1.6 degrees ( P < .017), and AR from 3.7 ± 2.0 to 5.9 ± 1.8 degrees ( P < .017). The facet arthroplasty system decreased ROM compared to the laminectomy-facetectomy condition in all tested directions ( P < .017). The facet arthroplasty system restored the L5-S1 ROM to its intact levels in LB and AR ( P > .017). F-E ROM after the facet arthroplasty system implantation was smaller than the intact value (10.1 ± 2.2 vs. 15.3 ± 2.9 degrees, P < .017). The load-displacement curves after the facet arthroplasty system implantation at L5-S1 were sigmoidal, and quality of motion measures were similar to intact, demonstrating graded resistance to angular motion in F-E, LB and AR. Conclusions The facet arthroplasty system was able to restore stability to the lumbosacral segment after complete laminectomy and bilateral facetectomy, while also allowing near-normal kinematics in all planes. While F-E ROM after the facet arthroplasty system implantation was smaller than the intact value, it was within the physiologic norms for L5-S1. These results are consistent with previous studies of facet arthroplasty at L3-L4 and L4-L5 and demonstrate that TFAS technology can be adapted to the lumbosacral joint with functionality comparable to its application in superior lumbar levels.

L5 - s1 segmental kinematics after facet arthroplasty.

BackgroundFacet arthroplasty is a motion restoring procedure. It is normally suggested as an alternative to rigid fixation after destabilizing decompression procedures in the posterior lumbar spine. While previous studies have reported successful results in reproducing normal spine kinematics after facet replacement at L4-5 and L3-4, there are no data on the viability of facet replacement at the lumbosacral joint. The anatomy of posterior elements and the resulting kinematics at L5-S1 are distinctly different from those at superior levels, making the task of facet replacement at the lumbosacral level challenging. This study evaluated the kinematics of facet replacement at L5-S1.MethodsSix human cadaveric lumbar spines (L1-S1, 46.7 ± 13.0 years) were tested in the following sequence: (1) intact (L1-S1), (2) complete laminectomy and bilateral facetectomy at L5-S1, and (3) implantation of TFAS-LS (Lumbosacral Total Facet Arthroplasty System, Archus Orthopedics, Redmond, Washington) at L5-S1 using pedicle screws. Specimens were tested in flexion (8Nm), extension (6Nm), lateral bending (LB, ± 6Nm), and axial rotation (AR, ± 5Nm). The level of significance was α = .017 after Bonferroni correction for three comparisons: (1) intact vs. destabilized, (2) destabilized vs. reconstructed, and (3) intact vs. reconstructed.ResultsLaminectomy-facetectomy at L5-S1 increased the L5-S1 angular range of motion (ROM) in all directions. Flexion-extension (F-E) ROM increased from 15.3 ± 2.9 to 18.7 ± 3.5 degrees (P < .017), LB from 8.2 ± 1.8 to 9.3 ± 1.6 degrees (P < .017), and AR from 3.7 ± 2.0 to 5.9 ± 1.8 degrees (P < .017). The facet arthroplasty system decreased ROM compared to the laminectomy-facetectomy condition in all tested directions (P < .017). The facet arthroplasty system restored the L5-S1 ROM to its intact levels in LB and AR (P > .017). F-E ROM after the facet arthroplasty system implantation was smaller than the intact value (10.1 ± 2.2 vs. 15.3 ± 2.9 degrees, P < .017). The load-displacement curves after the facet arthroplasty system implantation at L5-S1 were sigmoidal, and quality of motion measures were similar to intact, demonstrating graded resistance to angular motion in F-E, LB and AR.ConclusionsThe facet arthroplasty system was able to restore stability to the lumbosacral segment after complete laminectomy and bilateral facetectomy, while also allowing near-normal kinematics in all planes. While F-E ROM after the facet arthroplasty system implantation was smaller than the intact value, it was within the physiologic norms for L5-S1. These results are consistent with previous studies of facet arthroplasty at L3-L4 and L4-L5 and demonstrate that TFAS technology can be adapted to the lumbosacral joint with functionality comparable to its application in superior lumbar levels.