A Biomechanical Comparison of High-Tensile Strength Tape Versus High-Tensile Strength Suture for Tendon Fixation Under Cyclic Loading.

PURPOSE: To compare the biomechanical properties of high-tensile strength tape and high-tensile strength suture across 2 selected stitch techniques, the Krackow and whip stitch, in securing tendinous tissue during 5,000 cycles of nondestructive loading followed by a load to failure. METHODS: Fourteen matched pairs each of cadaveric Achilles, quadriceps, and patellar tendons (n = 84) were randomly assigned to either Krackow or whip stitch and sutured with either 2-mm high-tensile strength tape or No. 2 high-tensile strength suture. Specimens were preloaded to 20 N, cyclically loaded from 20 to 200 N for 5,000 cycles at 2 Hz, and then loaded to failure at 200 mm/min. Linear mixed models evaluated the effects of suture material and stitch technique on cyclic normalized tendon-suture elongation, total normalized tendon-suture elongation at 5,000 cycles, and maximum load at failure. RESULTS: Across all suture constructs, normalized elongation was greater during the initial 10 cycles, compared with all subsequent cycling intervals (all P < .001). There was less total normalized elongation (ß = -0.239; P = .007) and greater maximum load at failure in tape (ß = 163.71; P = .014) when used in the Krackow stitch compared with the whip stitch. CONCLUSIONS: Our findings indicate that tape used in the Krackow stitch maintains the most favorable fixation strength after enduring cyclic loading, with greater maximum load at failure. In addition, overall normalized elongation during long-term cyclic loading was predominately affected by the stitch technique used, regardless of the suture material; however, tape allowed less normalized elongation during the initial loading cycles, especially when placed in the whip stitch. CLINICAL RELEVANCE: Understanding the potential short- and long-term outcomes of suture material and stitch technique on securing tendinous tissue under repetitive stresses can help inform clinicians on optimal tendon fixation techniques for early postoperative activities.

Lumbar disc height and vertebral Hounsfield units: association with interbody cage subsidence.

OBJECTIVE: Postoperative subsidence of transforaminal lumbar interbody fusion (TLIF) cages can result in loss of lordosis and foraminal height, and potential recurrence of nerve root impingement. The objectives of this study were to determine factors associated with TLIF cage subsidence. Specifically, the authors sought to determine if preoperative disc height compared to cage height could be used to predict TLIF interbody cage subsidence, and if decreased postoperative vertebral Hounsfield units (HUs) predisposed to cage subsidence. METHODS: The authors retrospectively reviewed all patients undergoing instrumented TLIF from two institutions between July 2004 and June 2014. The preoperative disc height was measured for the operative and adjacent-level disc on MRI. The difference between cage and disc heights was measured and compared between the subsidence and nonsubsidence groups. The average HUs of the L1 vertebral body were measured on CT scans. RESULTS: Eighty-nine patients were identified with complete imaging and follow-up information. Forty-five patients (50.6%) had evidence of interbody cage subsidence on follow-up CT. The average cage subsidence was 5.5 mm (range 2.2-10.8 mm). The average implant height was significantly higher in the subsidence group compared to the nonsubsidence group (12.6 vs 11.2 mm). Additionally, the difference between cage height and preoperative adjacent-level disc height was also significantly larger in the subsidence group (3.8 vs 1.2 mm). First lumbar vertebral body (L1) HUs were significantly higher in the nonsubsidence versus the subsidence group (167.8 vs 137.71 HUs, p = 0.002). Multivariate logistic regression analysis identified suprajacent disc height and L1 HUs to be independent predictors of interbody cage subsidence. Receiver operating characteristic curves identified a suprajacent to cage height difference > 1.3 mm to have a 93.3% sensitivity for cage subsidence. CONCLUSIONS: This study is the first of its kind to demonstrate the association between vertebral body HUs and suprajacent disc height with the development of interbody cage subsidence after TLIF. The authors found that patients with lower HUs in the L1 vertebral body were more likely to experience subsidence, regardless of surgical level. Additionally, the study demonstrated that interbody cage height > 1.3 mm above the height of the suprajacent level is an independent risk factor for cage subsidence, with 93.3% sensitivity. These findings suggest that these factors may be utilized to create a template preoperatively for intraoperative cage selection.

Biomechanical Comparison of Anterior Cervical Plate Fixation Versus Integrated Fixation Cage for Anterior Cervical Discectomy and Fusion.

STUDY DESIGN: Cadaveric, biomechanic study. OBJECTIVE: To compare the range of motion profiles of the cervical spine following one-level anterior cervical discectomy and fusion (ACDF) constructs instrumented with either an interbody cage and anterior plate or integrated fixation cage in a cadaveric model. SUMMARY OF BACKGROUND DATA: While anterior plates with interbody cages are the most common construct of fixation in ACDF, newer integrated cage-plate devices seek to provide similar stability with a decreased implant profile. However, differences in postoperative cervical range of motion between the 2 constructs remain unclear. METHODS: Six cadaveric spines were segmented into 2 functional spine units (FSUs): C2-C5 and C6-T2. Each FSU was nondestructively bent in flexion-extension (FE), right-left lateral bending (LB), and right-left axial rotation (AR) at a rate of 0.5°/s under a constant axial load until a limit of 2-Nm was reached to evaluate baseline range of motion (ROM). Matched pairs were then randomly assigned to undergo instrumentation with either the standard anterior cage and plate (CP) or the integrated fixation cage (IF). Following instrumentation, ROM was then remeasured as previously described. RESULTS: For CP fixation, ROM increased by 61.2±31.7% for FE, 36.3±20.4% for LB, and 31.7±19.1% for AR. For IF fixation, ROM increased by 64.2±15.5% for FE, 56.7±39.8% for LB, and 94.5±65.1% for AR. There was no significant difference in motion between each group across FE, LB, and AR. CONCLUSION: This biomechanical study demonstrated increased motion in both the CP and IF groups relative to the intact, un-instrumented state. However, our model showed no differences in ROM between CP and IF constructs in any direction of motion. These results suggest that either method of instrumentation is a suitable option for ACDF with respect to constructing stiffness at time zero.

Hooks Versus Pedicle Screws at the Upper Instrumented Level: An In Vitro Biomechanical Comparison.

STUDY DESIGN: Controlled laboratory study. OBJECTIVE: The aim was to compare motions at the upper instrumented vertebra (UIV) and supra-adjacent level (UIV+1) between two fixation techniques in thoracic posterior spinal fusion constructs. We hypothesized there would be greater motion at UIV+1 after cyclic loading across all constructs and bilateral pedicle screws (BPSs) with posterior ligamentous compromise would demonstrate the greatest UIV+1 range of motion. SUMMARY OF BACKGROUND DATA: Proximal junctional kyphosis is a well-recognized complication following long thoracolumbar posterior spinal fusion, however, its mechanism is poorly understood. MATERIALS AND METHODS: Twenty-seven thoracic functional spine units were randomly divided into three UIV fixation groups (n=9): (1) BPS, (2) bilateral transverse process hooks (TPHs), and (3) BPS with compromise of the posterior elements between UIV and UIV+1 (BPS-C). Specimens were tested on a servohydraulic materials testing system in native state, following instrumentation, and after cyclic loading. functional spine units were loaded in flexion-extension (FE), lateral bending, and axial rotation. RESULTS: After cyclic testing, the TPH group had a mean 29.4% increase in FE range of motion at UIV+1 versus 76.6% in the BPS group ( P <0.05). The BPS-C group showed an increased FE of 49.9% and 62.19% with sectioning of the facet joints and interspinous ligament respectively prior to cyclic testing. CONCLUSION: BPSs at the UIV led to greater motion at UIV+1 compared to bilateral TPH after cyclic loading. This is likely due to the increased rigidity of BPS compared to TPH leading to a "softer" transition between the TPH construct and native anatomy at the supra-adjacent level. Facet capsule compromise led to a 49.9% increase in UIV+1 motion, underscoring the importance of preserving the posterior ligamentous complex. Clinical studies that account for fusion rates are warranted to determine if constructs with a "soft transition" result in less proximal junctional kyphosis in vivo .

Biomechanical Analysis of Multilevel Posterior Cervical Spinal Fusion Constructs.

STUDY DESIGN: Controlled Laboratory Study. OBJECTIVE: To compare multilevel posterior cervical fusion (PCF) constructs stopping at C7, T1, and T2 under cyclic load to determine the range of motion (ROM) between the lowest instrumented level and lowest instrumented-adjacent level (LIV-1). SUMMARY OF BACKGROUND DATA: PCF is a mainstay of treatment for various cervical spine conditions. The transition between the flexible cervical spine and rigid thoracic spine can lead to construct failure at the cervicothoracic junction. There is little evidence to determine the most appropriate level at which to stop a multilevel PCF. METHODS: Fifteen human cadaveric cervicothoracic spines were randomly assigned to 1 of 3 treatment groups: PCF stopping at C7, T1, or T2. Specimens were tested in their native state, following a simulated PCF, and after cyclic loading. Specimens were loaded in flexion-extension), lateral bending, and axial rotation. Three-dimensional kinematics were recorded to evaluate ROM. RESULTS: The C7 group had greater flexion-extension motion than the T1 and T2 groups following instrumentation (10.17±0.83 degree vs. 2.77±1.66 degree and 1.06±0.55 degree, P <0.001), and after cyclic loading (10.42±2.30 degree vs. 2.47±0.64 degree and 1.99±1.23 degree, P <0.001). There was no significant difference between the T1 and T2 groups. The C7 group had greater lateral bending ROM than both thoracic groups after instrumentation (8.81±3.44 degree vs. 3.51±2.52 degree, P =0.013 and 1.99±1.99 degree, P =0.003) and after cyclic loading. The C7 group had greater axial rotation motion than the thoracic groups (4.46±2.27 degree vs. 1.26±0.69 degree, P =0.010; and 0.73±0.74 degree, P =0.003) following cyclic loading. CONCLUSION: Motion at the cervicothoracic junction is significantly greater when a multilevel PCF stops at C7 rather than T1 or T2. This is likely attributable to the transition from a flexible cervical spine to a rigid thoracic spine. Although this does not account for in vivo fusion, surgeons should consider extending multilevel PCF constructs to T1 when feasible. LEVEL OF EVIDENCE: Not applicable.

Biomechanical Comparison of Anatomic Restoration of the Ulnar Footprint vs Traditional Ulnar Tunnels in Ulnar Collateral Ligament Reconstruction.

BACKGROUND: Current techniques for ulnar collateral ligament (UCL) reconstruction do not reproduce the anatomic ulnar footprint of the UCL. The purpose of this study was to describe a novel UCL reconstruction technique that utilizes proximal-to-distal ulnar bone tunnels to better re-create the anatomy of the UCL and to compare the biomechanical profile at time zero among this technique, the native UCL, and the traditional docking technique. HYPOTHESIS: The biomechanical profile of the anatomic technique is similar to the native UCL and traditional docking technique. STUDY DESIGN: Controlled laboratory study. METHODS: Ten matched cadaveric elbows were potted with the forearm in neutral rotation. The palmaris longus tendon graft was harvested, and bones were sectioned 14 cm proximal and distal to the elbow joint. Specimen testing included (1) native UCL testing performed at 90° of flexion with 0.5 N·m of valgus moment preload, (2) cyclic loading from 0.5 to 5 N·m of valgus moment for 1000 cycles at 1 Hz, and (3) load to failure at 0.2 mm/s. Elbows then underwent UCL reconstruction with 1 elbow of each pair receiving the classic docking technique using either anatomic (proximal to distal) or traditional (anterior to posterior) tunnel locations. Specimen testing was then repeated as described. RESULTS: There were no differences in maximum load at failure between the anatomic and traditional tunnel location techniques (mean ± SD, 34.90 ± 10.65 vs 37.28 ± 14.26 N·m; P = .644) or when including the native UCL (45.83 ± 17.03 N·m; P = .099). Additionally, there were no differences in valgus angle after 1000 cycles across the anatomic technique (4.58°± 1.47°), traditional technique (4.08°± 1.28°), and native UCL (4.07°± 1.99°). The anatomic group and the native UCL had similar valgus angles at failure (24.13°± 5.86° vs 20.13°± 5.70°; P = .083), while the traditional group had a higher valgus angle at failure when compared with the native UCL (24.88°± 6.18° vs 19.44°± 5.86°; P = .015). CONCLUSION: In this cadaveric model, UCL reconstruction with the docking technique utilizing proximal-to-distal ulnar tunnels better restored the ulnar footprint while providing valgus stability comparable with reconstruction with the docking technique using traditional anterior-to-posterior ulnar tunnel locations. These results suggest that utilization of the anatomic tunnel location in UCL reconstruction has similar biomechanical properties to the traditional method at the time of initial fixation (ie, not accounting for healing after reconstruction in vivo) while keeping the ulnar tunnels farther from the ulnar nerve. Further studies are warranted to determine if an anatomically based UCL reconstruction results in differing outcomes than traditional reconstruction techniques. CLINICAL RELEVANCE: Current UCL reconstruction techniques do not accurately re-create the ulnar UCL footprint. The UCL is a dynamic constraint to valgus loads at the elbow, and a more anatomic reconstruction may afford more natural joint kinematics. This more anatomic technique performs similarly to the traditional docking technique at time zero, and the results of this study may offer a starting point for future in vivo studies.

The Incidence, Risk Factors, and Complications Associated With Surgical Delay in Multilevel Fusion for Adult Spinal Deformity.

STUDY DESIGN: Retrospective database review. OBJECTIVES: The incidence and risk factors for surgical delay of multilevel spine fusion for adult spinal deformity (ASD), and the complications corresponding therewith, remain unknown. The objectives of this study are to assess the incidence and risk factors for unexpected delay of elective multilevel spinal fusions on the date of surgery as well as the postoperative complications associated with these delays. METHODS: We conducted a retrospective review of the ACS-NSQIP database on patients undergoing elective spinal instrumentation of greater than 7 levels for ASD between the years 2005 and 2015. Preoperative risk factors for delay and postoperative complications were compared between the cohorts of patients with and without surgical delays. RESULTS: Multivariate analysis of 1570 (15.6%) patients identified advanced age, male sex, American Society of Anesthesiologists (ASA) Class 4, and history of smoking as independent risk factors for delay. Patients experiencing surgical delay demonstrated longer operative times, increased intraoperative bleeding, longer hospitalizations, and significantly higher rates of postoperative complications. Patients experiencing delay demonstrated an almost 7-fold increase in mortality rate (3.4% vs 0.5%, P < .001). CONCLUSIONS: Delays in elective surgical care for spinal deformity are negatively related to patient outcomes. Advanced age, male sex, increased ASA class, and a history of smoking cigarettes place patients at risk for surgical delay of multilevel spinal fusion. Patients experiencing surgical delay are at higher risk for postoperative complications, including a 7-fold increase in mortality. These findings suggest that ASD surgery should be postponed in patients experiencing a delay, until modifiable risk factors can be medically optimized, and perhaps postponed indefinitely in those with nonmodifiable risk factors.

Development of an in vitro test method to simulate intra-operative impaction loading on lumbar intervertebral body fusion devices.

Intervertebral body fusion devices (IBFDs) are commonly used in the treatment of various spinal pathologies. Intra-operative fractures of polyether-ether-ketone (PEEK) implants have been reported in the literature and to the FDA as device-related adverse events. The device and/or implant inserter failures typically occur during device impaction into the disc space and require implant removal and replacement. These additional steps may cause further complications along with increased surgical time and cost. Currently, there are no standardized test methods that evaluate clinically relevant impaction loading conditions on IBFDs. This study aims to develop an in vitro test method that would evaluate implant resistance to failure during intra-operative impaction. To achieve this, (1) surgical implantations of IBFDs were simulated in nine lumbar cadaver specimens by three different orthopedic spine surgeons (n = 3/surgeon). Impact force and mallet speed data were acquired for each surgeon. (2) Based on the acquired surgeon data, a benchtop mechanical test setup was developed to differentiate between two TLIF IBFD designs and two inserter designs (for a total of four IBFD-inserter combinations) under impaction loading. During implant insertion, impact force measurements indicated that lumbar IBFDs are subjected to high energy forces that may exceed their mechanical strength. Our test method successfully replicated clinically-relevant loading conditions and was effective at differentiating failure parameters between different implant and inserter instrument designs. The mechanical test method developed shows promise in its ability to assess impaction resistance of IBFD/inserter designs and evaluate potential risks of device failure during intraoperative loading.

Incidence and Risk Factors of Acute Patellar Tendon Rupture, Repair Failure, and Return to Activity in the Active-Duty Military Population.

BACKGROUND: Patellar tendon ruptures have a reported incidence of 0.68 per 100,000 person-years in the general population. The epidemiology of surgically treated patellar tendon ruptures in the US military has yet to be reported, which would provide opportunity for identification of risk factors for these otherwise healthy and active patients. PURPOSE: To determine the incidence of patellar tendon rupture in the Military Health System (MHS) population and to analyze demographic patterns, surgical fixation methods, and rerupture rates. STUDY DESIGN: Case-control study; Level of evidence, 3. METHODS: We utilized the MHS Data Repository (MDR) to identity active-duty military servicemembers surgically treated for patellar tendon rupture between 2010 and 2015. Records were reviewed for demographic information, injury characteristics, fixation technique, and occurrence of rerupture. Risk factors for rupture were calculated using Poisson regression based on population counts and demographic data obtained in the MDR. Risk factors for rerupture and return to duty were analyzed via univariate analysis and multivariate regression. RESULTS: A total of 504 operatively treated primary patellar tendon repairs in 483 patients were identified, with an overall incidence of 6 per 100,000 person-years. Mean age was 33.6 years (range, 17-54 years) and 98% of patients were male. Fixation method was 81% bone tunnels and 7% suture anchors, and 12% were unknown. Black race had a higher relative rate ratio for rupture compared with the race categories White (9.21; P < .0001) and Other (3.27; P < .0001). The rupture rate was higher in 35- to 44-year-old patients compared with those aged 18 to 24 years (P < .0001), 25 to 34 years (P < .0001), and 45 to 64 years (P = .004). Return to full previous level of activity occurred in 75.8% of patients, 14.6% returned to activity with limitations, and 9.5% were medically separated. The rerupture rate was 3%. Fixation method, tobacco usage, body mass index, and race were not significant risk factors for rerupture. CONCLUSION: The incidence of patellar tendon rupture in the US military population is substantially higher than has been reported in the civilian population. Among military personnel, men, Black servicemembers, and those aged 35 to 44 years were at highest risk for patellar tendon rupture. Three-quarters of patients were able to return to full activity without limitations. The rerupture rate was low and unaffected by fixation method.

Higher Paraspinal Muscle Density Effect on Outcomes After Anterior Cervical Discectomy and Fusion.

STUDY DESIGN: Retrospective cohort study. OBJECTIVES: Studies in the lumbar spine suggest a correlation between sarcopenia and worse patient outcomes. The purpose of this study was to determine whether paraspinal Goutalier grade of fat degeneration is associated with patient-reported outcomes in patients undergoing anterior cervical discectomy and fusion (ACDF). METHODS: We performed a retrospective review of a prospective cohort of patients undergoing 1- to 3-level ACDF at a single institution between the years 2011-2014. We utilized preoperative magnetic resonance images to classify patients into Goutalier grades. Patient-reported outcomes, including Neck Disability Index (NDI), RAND score, and EQ-5D score were collected and analyzed according to patients' Goutalier grade. RESULTS: We identified 69 patients for inclusion. A total of 29 patients were classified as Goutalier 0-1 (group 1), 29 were Goutalier 1.5-2 (group 2), and 11 were Goutalier 2.5-4.0 (group 3). All Goutalier groups experienced significant improvement in all 3 outcome scores. Average postoperative NDI scores were 25.3 in group 1, 13.9 in group 2, and 25.1 in group 3 (P = .02). The percentage of patients in each group reporting worse disability after surgery was 17.2%, 3.3%, and 9.1%, respectively (P = .05). No statistically significant difference was seen between groups in postoperative EQ-5D (P = .07) or RAND scores (P > .05). CONCLUSIONS: The present study is the first to assess the association between cervical paraspinal muscle Goutalier grade and patient-reported outcomes following ACDF. Based on our study, patients with worse cervical paraspinal degeneration may benefit from improved symptom relief in comparison to patients with a lesser degree of degeneration undergoing ACDF.

A Multicenter Evaluation of the Feasibility, Patient/Provider Satisfaction, and Value of Virtual Spine Consultation During the COVID-19 Pandemic.

OBJECTIVE: To assess the feasibility, patient/provider satisfaction, and perceived value of telehealth spine consultation after rapid conversion from traditional in-office visits during the COVID-19 pandemic. METHODS: Data were obtained for patients undergoing telehealth visits with spine surgeons in the first 3 weeks after government restriction of elective surgical care at 4 sites (March 23, 2020, to April 17, 2020). Demographic factors, technique-specific elements of the telehealth experience, provider confidence in diagnostic and therapeutic assessment, patient/surgeon satisfaction, and perceived value were collected. RESULTS: A total of 128 unique visits were analyzed. New (74 [58%]), preoperative (26 [20%]), and postoperative (28 [22%]) patients were assessed. A total of 116 (91%) visits had successful connection on the first attempt. Surgeons felt very confident 101 times (79%) when assessing diagnosis and 107 times (84%) when assessing treatment plan. The mean and median patient satisfaction was 89% and 94%, respectively. Patient satisfaction was significantly higher for video over audio-only visits (P < 0.05). Patient satisfaction was not significantly different with patient age, location of chief complaint (cervical or thoracolumbar), or visit type (new, preoperative, or postoperative). Providers reported that 76% of the time they would choose to perform the visit again in telehealth format. Sixty percent of patients valued the visit cost as the same or slightly less than an in-office consultation. CONCLUSIONS: This is the first study to demonstrate the feasibility and high patient/provider satisfaction of virtual spine surgical consultation, and appropriate reimbursement and balanced regulation for spine telehealth care is essential to continue this existing work.

A Case Report of Rapid Aseptic Intervertebral Disc Destruction After Lumbar Microdiscectomy: A Case Report.

CASE: A previously healthy military recruit underwent routine microdiscectomy after lumbar disc herniation. After a period of improvement, he developed recurrent pain without repeat injury. Advanced imaging showing loss of marrow signal, and disc height was concerning for discitis. Inflammatory markers remained negative. Conservative treatment without antibiotics led to symptom resolution. CONCLUSION: This case demonstrates an unusual complication after lumbar microdiscectomy in a healthy individual. The recurrent symptoms and imaging changes were likely secondary to aseptic discitis and rapid degeneration rather than infection. A stepwise approach is critical for determining the cause of pain exacerbation after spinal procedures.

The effect of lumbar corticosteroid injections on postoperative infection in lumbar arthrodesis surgery.

We sought to characterize the association between lumbar corticosteroid injections and postoperative infection rate for patients in the Military Health System undergoing lumbar arthrodesis. The Military Health System Data Repository was searched for all patients undergoing lumbar arthrodesis from 2009 to 2014. Current Procedural Terminology (CPT) codes were used to identify the subset of patients who also received preoperative lumbar corticosteroid injections. These patients were stratified by timing, type, and number of injections. Infection rates were compared to the control group of patients who did not receive preoperative lumbar corticosteroid injections. The search identified 3403 patients who had undergone lumbar arthrodesis from 2009 to 2014 within the Military Health System. 612 patients had received lumbar corticosteroid injections prior to surgery (348 epidural, 264 facet). The control group consisted of the remaining 2791 patients. Overall post-operative infection rate was 1.47% with an infection rate in the injection group of 1.14% versus 1.54% in the control group. When stratified by time, infection rates ranged from 0% to 1.85% in the injection groups. No differences between injection and control groups reached statistical significance in any subgroup analysis. Post-operative infection rate is not significantly increased in patients receiving lumbar corticosteroid injections (LCSIs) prior to lumbar arthrodesis. No differences were observed in infection rates based on timing, type, or number of injections prior to surgery.