The Effects of Unitizing Nail-Plate Constructs in Distal Femur Fractures: A Biomechanical Study.

OBJECTIVES: To assess the biomechanical differences between linked and unlinked constructs in young and osteoporotic cadavers in addition to osteoporotic sawbones. METHODS: Intraarticular distal femur fractures with comminuted metaphyseal regions were created in three young matched pair cadavers, three osteoporotic matched pair cadavers, and six osteoporotic sawbones. Precontoured distal femur locking plates were placed in addition to a standardized retrograde nail, with unitized constructs having one 4.5 mm locking screw placed distally through the nail. Nonunitized constructs had seven 4.5 mm locking screws placed through the plate around the nail, with one 5 mm distal interlock placed through the nail alone. Cadaveric specimens were subjected to axial fatigue loads between 150 and 1500 N (R Ratio = 10) with 1 Hx frequency for 10,000 cycles. Sawbones were axially loaded at 50% of the ultimate load for fatigue testing to achieve runout, with testing performed with 30 and 300 N (R Ratio = 10) loads with 1 Hz frequency for 10,000 cycles. RESULTS: In young cadavers, there was no difference in the mean cyclic displacement of the unitized constructs (1.51 ± 0.62mm) compared to the non-unitized constructs (1.34 ± 0.47mm) (Figure 4A), (p = 0.722). In osteoporotic cadavers, there was no difference in the mean cyclic displacement of the unitized constructs (2.46 ± 0.47mm) compared to the non-unitized constructs (2.91 ± 1.49mm) (p =0.639). There was statistically no significant difference in cyclic displacement between the unitized and non-unitized groups in osteoporotic sawbones(p = 0.181). CONCLUSIONS: Linked constructs did not demonstrate increased axial stiffness or decreased cyclical displacement in comparison to unlinked constructs in young cadaveric specimens, osteoporotic cadaveric specimens, or osteoporotic sawbones.

A feasibility cadaver study for placing screws in various pelvic osseous fracture pathways using a robotic arm.

INTRODUCTION: The use of a robotic system for the placement of pedicle screws in spine surgeries is well documented in the literature. However, there is only a single report in the United States describing the use of a robotic system to place two screws in osseous fixation pathways (OFPs) commonly used in the treatment of pelvic and acetabular fractures in a simulated bone model. The purpose of this study was to demonstrate the use of a robotic system to place screws in multiple, clinically relevant OFPs in a cadaveric model and to quantitatively measure accuracy of screw placement relative to the preoperative plan. METHODS: A single cadaveric specimen was obtained for the purpose of this study. All surrounding soft tissues were left intact. Screws were placed in OFPs, namely iliosacral (IS), trans-sacral (TS), Lateral Compression-II (LC-II), antegrade anterior column (AC) and antegrade posterior column (PC) of the right hemipelvis using standard, fluoroscopically assisted percutaneous or mini-open technique. Following the placement of screws into the right hemipelvis using standard techniques, screws were planned and placed in the same OFPs of the contralateral hemipelvis using the commercially available ExcelsiusGPS® robotic system (Globus Medical Inc., Audubon, PA). After robotic-assisted screw placement, a post-procedure CT scan was obtained to evaluate actual screw placement against the pre-procedure plan. A custom-made image analysis program was devised to measure screw tip/tail offset and angular offset on axial and sagittal planes. RESULTS: For different OFPs, the mean tip offset, tail offset and angular offsets were 1.6 ± 0.9 mm (Range 0.0-3.6 mm), 1.4 ± 0.4 mm (Range 0.3-2.5 mm) and 1.1 ± 0.4° (Range 0.5-2.1), respectively. CONCLUSION: In this feasibility study, surgeons were able to place screws into the clinically relevant fracture pathways of the pelvis using ExcelsiusGPS® for robotic-assisted surgery. The measured accuracy was encouraging; however, further investigation is needed to demonstrate that robotic-assisted surgery can be used to successfully place the screws in the bony corridors of the pelvis to treat traumatic pelvic injuries.

Percutaneous Juxtapedicular Cement Salvage of Failed Spinal Instrumentation? Institutional Experience and Cadaveric Biomechanical Study.

BACKGROUND AND OBJECTIVES: Instrumented spinal fusion constructs sometimes fail because of fatigue loading, frequently necessitating open revision surgery. Favorable outcomes after percutaneous juxtapedicular cement salvage (perc-cement salvage) of failing instrumentation have been described; however, this approach is not widely known among spine surgeons , and its biomechanical properties have not been evaluated. We report our institutional experience with perc-cement salvage and investigate the relative biomechanical strength of this technique as compared with 3 other common open revision techniques. METHODS: A retrospective chart review of patients who underwent perc-cement salvage was conducted. Biomechanical characterization of revision techniques was performed in a cadaveric model of critical pedicle screw failure. Three revision cohorts involved removal and replacement of hardware: (1) screw upsizing, (2) vertebroplasty, and (3) fenestrated screw with cement augmentation. These were compared with a cohort with perc-cement salvage performed using a juxtapedicular trajectory with the failed primary screw remaining engaged in the vertebral body. RESULTS: Ten patients underwent perc-cement salvage from 2018 to 2022 to address screw haloing and/or endplate fracture threatening construct integrity. Pain palliation was reported by 8/10 patients. Open revision surgery was required in 4/10 patients, an average of 8.9 months after the salvage procedure (range 6.2-14.7 months). Only one revision was due to progressive hardware dislodgement. The remainder avoided open revision surgery through an average of 1.9 years of follow-up. In the cadaveric study, there were no significant differences in pedicle screw pullout strength among any of the revision cohorts. CONCLUSION: Perc-cement salvage of failing instrumentation is reasonably efficacious. The technique is biomechanically noninferior to other revision strategies that require open surgery for removal and replacement of hardware. Open revision surgery may be avoided by perc-cement salvage in select cases.

Robotic-Assisted Navigation for Stereotactic Neurosurgery: A Cadaveric Investigation of Accuracy, Time, and Radiation.

BACKGROUND AND OBJECTIVES: Despite frequent use, stereotactic head frames require manual coordinate calculations and manual frame settings that are associated with human error. This study examines freestanding robot-assisted navigation (RAN) as a means to reduce the drawbacks of traditional cranial stereotaxy and improve targeting accuracy. METHODS: Seven cadaveric human torsos with heads were tested with 8 anatomic coordinates selected for lead placement mirrored in each hemisphere. Right and left hemispheres of the brain were randomly assigned to either the traditional stereotactic arc-based (ARC) group or the RAN group. Both target accuracy and trajectory accuracy were measured. Procedural time and the radiation required for registration were also measured. RESULTS: The accuracy of the RAN group was significantly greater than that of the ARC group in both target (1.2 ± 0.5 mm vs 1.7 ± 1.2 mm, P = .005) and trajectory (0.9 ± 0.6 mm vs 1.3 ± 0.9 mm, P = .004) measurements. Total procedural time was also significantly faster for the RAN group than for the ARC group (44.6 ± 7.7 minutes vs 86.0 ± 12.5 minutes, P < .001). The RAN group had significantly reduced time per electrode placement (2.9 ± 0.9 minutes vs 5.8 ± 2.0 minutes, P < .001) and significantly reduced radiation during registration (1.9 ± 1.1 mGy vs 76.2 ± 5.0 mGy, P < .001) compared with the ARC group. CONCLUSION: In this cadaveric study, cranial leads were placed faster and with greater accuracy using RAN than those placed with conventional stereotactic arc-based technique. RAN also required significantly less radiation to register the specimen's coordinate system to the planned trajectories. Clinical testing should be performed to further investigate RAN for stereotactic cranial surgery.

In vitro coupled motions of the whole human thoracic and lumbar spine with rib cage.

Study design: In vitro biomechanical study investigating the coupled motions of the whole normative human thoracic spine (TS) and lumbar spine (LS) with rib cage. Objective: To quantify the region-specific coupled motion patterns and magnitudes of the TS, thoracolumbar junction (TLJ), and LS simultaneously. Background: Studying spinal coupled motions is important in understanding the development of complex spinal deformities and providing data for validating computational models. However, coupled motion patterns reported in vitro are controversial, and no quantitative data on region-specific coupled motions of the whole human TS and LS are available. Methods: Pure, unconstrained bending moments of 8 Nm were applied to seven fresh-frozen human cadaveric TS and LS specimens (mean age: 70.3 ± 11.3 years) with rib cages to elicit flexion-extension (FE), lateral bending (LB), and axial rotation (AR). During each primary motion, region-specific rotational range of motion (ROM) data were captured. Results: No statistically significant, consistent coupled motion patterns were observed during primary FE. During primary LB, there was significant (p < 0.05) ipsilateral AR in the TS and a general pattern of contralateral coupled AR in the TLJ and LS. There was also a tendency for the TS to extend and the LS to flex. During primary AR, significant coupled LB was ipsilateral in the TS and contralateral in both the TLJ and LS. Significant coupled flexion in the LS was also observed. Coupled LB and AR ROMs were not significantly different between the TS and LS or from one another. Conclusions: The findings support evidence of consistent coupled motion patterns of the TS and LS during LB and AR. These novel data may serve as reference for computational model validations and future in vitro studies investigating spinal deformities and implants.

Are modular pedicle screws associated with a high complication rate following posterior spinal fixation?

Background: Modular pedicle screws have a separate head that can be intraoperatively assembled to the inserted shank. The aim of this study was to report associated intra- and post-operative complications and reoperation rates of posterior spinal fixations with modular pedicle screws at a single center. Methods: A retrospective, institutional chart review was performed on 285 patients who underwent posterior thoracolumbar spinal fusion with modular pedicle screw fixation between January 1, 2017, and December 31, 2019. The primary outcome was failure of the modular screw component. Other measures recorded were length of follow-up, other complications, and need for additional procedures. Results: There were 1,872 modular pedicle screws (average 6.6 per case). There were no (0.0%) screw head dissociations at the rod screw junction. There was 20.8% overall complication rate (59/285) with 25 reoperations: 6 due to non-union and rod breakage, 5 for screw loosening, 7 for adjacent segment disease, 1 for acute postoperative radiculopathy, 1 for epidural hematoma, 2 for deep surgical-site infections, and 3 for superficial surgical-site infections. Other complications included superficial wound dehiscence [8], dural tears [6], non-unions not requiring reoperation [2], lumbar radiculopathies [3], and perioperative medical complications [5]. Conclusions: This study demonstrates that modular pedicle screw fixation has reoperation rates similar to those previously reported for standard pedicle screws. There was no failure at the screw-head junction, and no increases in other complications. Modular pedicle screws present an excellent option to allow surgeons to place pedicle screws without the risk of extra complications.

Decreasing the Pedicle Screw Misplacement Rate in the Thoracic Spine With Robot-guided Navigation.

STUDY DESIGN: A retrospective chart review. OBJECTIVE: The aim of this study was to evaluate the screw accuracy of thoracic pedicle screws placed with a robot-guided navigation system. SUMMARY OF BACKGROUND DATA: Thoracic pedicles are smaller in diameter than lumbar pedicles, making pedicle screw placement difficult. Misplaced pedicle screws may present complications including decreased construct stability, and increased risks of neurological deficits and blood vessel perforation. There is a dearth of knowledge on thoracic pedicle screw accuracy placed with a robot. MATERIALS AND METHODS: A retrospective analysis of the robot-assisted placement of thoracic pedicle screws was performed. Preoperative and postoperative computed tomography (CT) scans of the implanted thoracic screws were collected to assess screw placement accuracy, pedicle breadth, and placement deviations. A CT-based Gertzbein and Robbins System was used to classify pedicle screw accuracy in 2 mm increments. A custom image overlay software was used to determine the deviations between the preoperatively planned trajectory of pedicle screws and final placement at screw entry (tail), and tip in addition to the angular deviation. RESULTS: Seventy-five thoracic pedicle screws were implanted by navigated robotic guidance in 17 patients, only 1.3% (1/75) were repositioned intraoperatively. Average patient age and body mass index were 57.5 years and 25.9 kg/m 2 , respectively, with 52.9% female patients. Surgery diagnoses were degenerative disk disease (47.1%) and adjacent segment disease (17.6%). There were zero complications, with no returns to the operating room. According to the CT-based Gertzbein and Robbins pedicle screw breach classification system, 93.3% (70/75) screws were grade A or B, 6.6% (5/75) were grade C, and 0% were grade D or E. The average deviation from the preoperative plan to actual final placement was 1.8±1.3 mm for the screw tip, 1.6±0.9 mm for the tail, and 2.1±1.5 degrees of angulation. CONCLUSIONS: The current investigation found a 93.3% accuracy of pedicle screw placement in the thoracic spine. Navigated robot assistance is a useful system for placing screws in the smaller pedicles of the thoracic spine. LEVEL OF EVIDENCE: Level III-retrospective nonexperimental study.

Does design change in total knee arthroplasty implants affect patient-reported outcomes?

PURPOSE: The purpose of this study is to compare the early results of patient-reported outcomes between two generations of a total knee system. METHODS: Between June 2018 and April 2020, 121 first-generation, cemented TKAs (89 patients) and 123 s-generation, cemented TKAs (98 patients) were performed by a single surgeon. Demographic and surgical data were collected from all patients. Starting at the 6-month follow-up, patient-reported outcome measures Knee Injury and Osteoarthritis Outcome Score, Joint Reconstruction (KOOS-JR) and Knee Society (KS) clinical and radiographic scores were prospectively recorded. This study represents a retrospective review of these prospectively collected data. RESULTS: There were no statistically significant differences between the two groups in terms of demographic variables such as age, body mass index, gender and race. KOOS-JR and Knee Society (KS) scores improved significantly (p < 0.001) from their preoperative values in both device generations. There were no differences, pre-operatively, between the two groups in terms of KOOS-JR, KS functional, KS objective, patient satisfaction, and expectation scores; however, there were statistically significant (p < 0.001) lower values of KOOS-JR and KS functional scores for first versus second generation at 6 months (81 vs. 89 and 69 vs. 74, respectively). CONCLUSION: While significant improvement in KS objective, subjective, and patient satisfaction scores were noted with both knee systems, KOOS-JR and KS function scores were significantly higher at the early (6-month) follow-up in the second-generation group. Patients responded acutely to the design change as evidenced by significantly improved patient-reported outcome scores for the second generation.

An investigation of range of motion preservation in fusionless anterior double screw and cord constructs for scoliosis correction.

PURPOSE: To evaluate the motion-preserving properties of vertebral body tethering with varying cord/screw constructs and cord thicknesses in cadaveric thoracolumbar spines. METHODS: In vitro flexibility tests were performed on six fresh-frozen human cadaveric spines (T1-L5) (2 M, 4F) with a median age of 63 (59-to-80). An ± 8 Nm load was applied to determine range of motion (ROM) in flexion-extension (FE), lateral bending (LB), and axial rotation (AR) in the thoracic and lumbar spine. Specimens were tested with screws (T5-L4) and without cords. Single (4.0 mm and 5.0 mm) and double (4.0 mm) cord constructs were sequentially tensioned to 100 N and tested: (1) Single 4.0 mm and (2) 5.0 mm cords (T5-T12); (3) Double 4.0 mm cords (T5-12); (4) Single 4.0 mm and (5) 5.0 mm cord (T12-L4); (6) Double 4.0 mm cords (T12-L4). RESULTS: In the thoracic spine (T5-T12), 4.0-5.0 mm single-cord constructs showed slight reductions in FE and 27-33% reductions in LB compared to intact, while double-cord constructs showed reductions of 24% and 40%, respectively. In the lumbar spine (T12-L4), double-cord constructs had greater reductions in FE (24%), LB (74%), and AR (25%) compared to intact, while single-cord constructs exhibited reductions of 2-4%, 68-69%, and 19-20%, respectively. CONCLUSIONS: The present biomechanical study found similar motion for 4.0-5.0 mm single-cord constructs and the least motion for double-cord constructs in the thoracic and lumbar spine suggesting that larger diameter 5.0 mm cords may be a more promising motion-preserving option, due to their increased durability compared to smaller cords. Future clinical studies are necessary to determine the impact of these findings on patient outcomes.

An In Vitro Biomechanical Analysis of Contralateral Sacroiliac Joint Motion Following Unilateral Sacroiliac Stabilization with and without Lumbosacral Fixation.

STUDY DESIGN: Cadaveric biomechanics study. PURPOSE: This study investigated the effects of unilateral sacroiliac joint (SIJ) fixation for fusion with/without L5-S1 fixation on contralateral SIJ range of motion (ROM). OVERVIEW OF LITERATURE: SIJ fusion raises concerns that unilateral SIJ stabilization for fusion may increase contralateral SIJ mobility, leading to accelerated SIJ degeneration. Also, prior lumbosacral fixation may lead to accelerated SIJ degeneration, due to adjacent level effects. SIJ fixation biomechanics have been evaluated, showing a reduced-ROM, but SIJ fixation effects on contralateral nonfixated SIJ remain unknown. METHODS: Seven human lumbopelvic spines were used, each affixed to six-degrees-of-freedom testing apparatus; 8.5-Nm pure unconstrained bending moments applied in flexion-extension, lateral bending, and axial rotation. The ROM of left and right SIJ was measured using a motion analysis system. Each specimen tested as (1) intact, (2) injury (left), (3) L5-S1 fixation, (4) unilateral stabilization (left), (5) unilateral stabilization+L5-S1 fixation, (6) bilateral stabilization, and (7) bilateral stabilization+L5-S1 fixation. Both left-sided iliosacral and posterior ligaments were cut for injury condition to model SIJ instability before surgery. RESULTS: There were no statistical differences between fixated and contralateral nonfixated SIJ ROM following unilateral stabilization with/without L5-S1 fixation for all loading directions (p>0.930). Injured condition and L5-S1 fixation provided the largest motion increases across both joints; no significant differences were recorded between SIJs in any loading direction (p>0.850). Unilateral and bilateral stabilization with/without L5-S1 fixation reduced ROM compared with the injured condition for both SIJs, with bilateral stabilization providing maximum stability. CONCLUSIONS: In the cadaveric model, unilateral SIJ stabilization with/without lumbosacral fixation did not lead to significant contralateral SIJ hypermobility; long-term changes and in vivo response may differ.

Impaction grafting of lumbar pedicle defects: a biomechanical study of a novel technique for pedicle screw revision.

OBJECTIVE: The two most common revision options available for the management of loose pedicle screws are larger-diameter screws and cement augmentation into the vertebral body for secondary fixation. An alternative revision method is impaction grafting (pedicoplasty) of the failed pedicle screw track. This technique uses the impaction of corticocancellous bone into the pedicle and vertebral body through a series of custom funnels to reconstitute a new pedicle wall and a neomedullary canal. The goal of this study was to compare the biomechanics of screws inserted after pedicoplasty (impaction grafting) of a pedicle defect to those of an upsized screw and a cement-augmented screw. METHODS: For this biomechanical cadaveric study the investigators used 10 vertebral bodies (L1-5) that were free of metastatic disease or primary bone disease. Following initial screw insertion, each screw was subjected to a pullout force that was applied axially along the screw trajectory at 5 mm per minute until failure. Each specimen was instrumented with a pedicoplasty revision using the original screw diameter, and on the contralateral side either a fenestrated screw with cement augmentation or a screw upsized by 1 mm was inserted in a randomized fashion. These revisions were then pulled out using the previously mentioned methods. RESULTS: Initial screw pullout values for the paired upsized screw and pedicoplasty were 717 ± 511 N and 774 ± 414 N, respectively (p = 0.747) (n = 14). Revised pullout values for the paired upsized screw and pedicoplasty were 775 ± 461 N and 762 ± 320 N, respectively (p = 0.932). Initial pullout values for the paired cement augmentation and pedicoplasty were 792 ± 434 N and 880 ± 558 N, respectively (p = 0.649). Revised pullout values for the paired cement augmentation and pedicoplasty were 1159 ± 300 N and 687 ± 213 N, respectively (p < 0.001). CONCLUSIONS: Pedicle defects are difficult to manage. Reconstitution of the pedicle and creation of a neomedullary canal appears to be possible through the use of pedicoplasty. Biomechanically, screws that have been used in pedicoplasty have equivalent pullout strength to an upsized screw, and have greater insertional torques than those with the same diameter that have not been used in pedicoplasty, yet they are not superior to cement augmentation. This study suggests that although cement augmentation appears to have superior pullout force, the novel pedicoplasty technique offers promise as a viable biological revision option for the management of failed pedicle screws compared with the option of standard upsized screws in a cadaveric model. These findings will ultimately need to be further assessed in a clinical setting.

A Dual-Screw Technique for Vertebral Compression Fractures via Robotic Navigation in the Osteopenic Lumbar Spine: An In-Vitro Biomechanical Analysis.

STUDY DESIGN: Biomechanical cadaveric study. OBJECTIVES: Multi-rod constructs maximize posterior fixation, but most use a single pedicle screw (PS) anchor point to support multiple rods. Robotic navigation allows for insertion of PS and cortical screw (CS) within the same pedicle, providing 4 points of bony fixation per vertebra. Recent studies demonstrated radiographic feasibility for dual-screw constructs for posterior lumbar spinal fixation; however, biomechanical characterization of this technique is lacking. METHODS: Fourteen cadaveric lumbar specimens (L1-L5) were divided into 2 groups (n = 7): PS, and PS + CS. VCF was simulated at L3. Bilateral posterior screws were placed from L2-L4. Load control (±7.5Nm) testing performed in flexion-extension (FE), lateral bending (LB), axial rotation (AR) to measure ROM of: (1) intact; (2) 2-rod construct; (3) 4-rod construct. Static compression testing of 4-rod construct performed at 5 mm/min to measure failure load, axial stiffness. RESULTS: Four-rod construct was more rigid than 2-rod in FE (P < .001), LB (P < .001), AR (P < .001). Screw technique had no significant effect on FE (P = .516), LB (P = .477), or AR (P = .452). PS + CS 4-rod construct was significantly more stable than PS group (P = .032). Stiffness of PS + CS group (445.8 ± 79.3 N/mm) was significantly greater (P = .019) than PS (317.8 ± 79.8 N/mm). Similarly, failure load of PS + CS group (1824.9 ± 352.2 N) was significantly greater (P = .001) than PS (913.4 ± 309.8 N). CONCLUSIONS: Dual-screw, 4-rod construct may be more stable than traditional rod-to-rod connectors, especially in axial rotation. Axial stiffness and ultimate strength of 4-rod, dual-screw construct were significantly greater than rod-to-rod. In this study, 4-rod construct was found to have potential biomechanical benefits of increased strength, stiffness, stability.

Selecting the lowest instrumented vertebra in a multilevel posterior cervical fusion across the cervicothoracic junction: a biomechanical investigation.

OBJECTIVE: Posterior cervical fusion is a common surgical treatment for patients with myeloradiculopathy or regional deformity. Several studies have found increased stresses at the cervicothoracic junction (CTJ) and significantly higher revision surgery rates in multilevel cervical constructs that terminate at C7. The purpose of this study was to investigate the biomechanical effects of selecting C7 versus T1 versus T2 as the lowest instrumented vertebra (LIV) in multisegmental posterior cervicothoracic fusion procedures. METHODS: Seven fresh-frozen cadaveric cervicothoracic spines (C2-L1) with ribs intact were tested. After analysis of the intact specimens, posterior rods and lateral mass screws were sequentially added to create the following constructs: C3-7 fixation, C3-T1 fixation, and C3-T2 fixation. In vitro flexibility tests were performed to determine the range of motion (ROM) of each group in flexion-extension (FE), lateral bending (LB), and axial rotation (AR), and to measure intradiscal pressure of the distal adjacent level (DAL). RESULTS: In FE, selecting C7 as the LIV instead of crossing the CTJ resulted in the greatest increase in ROM (2.54°) and pressure (29.57 pound-force per square inch [psi]) at the DAL in the construct relative to the intact specimen. In LB, selecting T1 as the LIV resulted in the greatest increase in motion (0.78°) and the lowest increase in pressure (3.51 psi) at the DAL relative to intact spines. In AR, selecting T2 as the LIV resulted in the greatest increase in motion (0.20°) at the DAL, while selecting T1 as the LIV resulted in the greatest increase in pressure (8.28 psi) in constructs relative to intact specimens. Although these trends did not reach statistical significance, the observed differences were most apparent in FE, where crossing the CTJ resulted in less motion and lower intradiscal pressures at the DAL. CONCLUSIONS: The present biomechanical cadaveric study demonstrated that a cervical posterior fixation construct with its LIV crossing the CTJ produces less stress in its distal adjacent discs compared with constructs with C7 as the LIV. Future clinical testing is necessary to determine the impact of this finding on patient outcomes.

Robotic-assisted spine surgery allows for increased pedicle screw sizes while still improving safety as indicated by elevated triggered electromyographic thresholds.

The present study used triggered electromyographic (EMG) testing as a tool to determine the safety of pedicle screw placement. In this Institutional Review Board exempt review, data from 151 consecutive patients (100 robotic; 51 non-robotic) who had undergone instrumented spinal fusion surgery of the thoracic, lumbar, or sacral regions were analyzed. The sizes of implanted pedicle screws and EMG threshold data were compared between screws that were placed immediately before and after adoption of the robotic technique. The robotic group had significantly larger screws inserted that were wider (7 ± 0.7 vs 6.5 ± 0.3 mm; p < 0.001) and longer (47.8 ± 6.4 vs 45.7 ± 4.3 mm; p < 0.001). The robotic group also had significantly higher stimulation thresholds (34.0 ± 11.9 vs 30.2 ± 9.8 mA; p = 0.002) of the inserted screws. The robotic group stayed in the hospital postoperatively for fewer days (2.3 ± 1.2 vs 2.9 ± 2 days; p = 0.04), but had longer surgery times (174 ± 37.8 vs 146 ± 41.5 min; p < 0.001). This study demonstrated that the use of navigated, robot-assisted surgery allowed for placement of larger pedicle screws without compromising safety, as determined by pedicle screw stimulation thresholds. Future studies should investigate whether these effects become even stronger in a later cohort after surgeons have more experience with the robotic technique. It should also be evaluated whether the larger screw sizes allowed by the robotic technology actually translate into improved long-term clinical outcomes.

A Retrospective Analysis of Pedicle Screw Placement Accuracy Using the ExcelsiusGPS Robotic Guidance System: Case Series.

BACKGROUND: Robotic guidance has become widespread in spine surgery. Although the intent is improved screw placement, further system-specific data are required to substantiate this intention for pedicle screws in spinal stabilization constructs. OBJECTIVE: To determine the accuracy of pedicle screws placed with the aid of a robot in a cohort of patients immediately after the adoption of the robot-assisted surgery technique. METHODS: A retrospective, Institutional Review Board-approved study was performed on the first 100 patients at a single facility, who had undergone spinal surgeries with the use of robotic techniques. Pedicle screw accuracy was graded using the Gertzbein-Robbins Scale based on pedicle wall breach, with grade A representing 0 mm breach and successive grades increasing breach thresholds by 2 mm increments. Preoperative and postoperative computed tomography scans were also used to assess offsets between the objective plan and true screw placements. RESULTS: A total of 326 screws were analyzed among 72 patients with sufficient imaging data. Ages ranged from 21 to 84 years. The total accuracy rate based on the Gertzbein-Robbins Scale was 97.5%, and the rate for each grade is as follows: A, 82%; B, 15.5%; C, 1.5%; D, 1%; and E, 0. The average tip offset was 1.9 mm, the average tail offset was 2.0 mm, and the average angular offset was 2.6°. CONCLUSION: Robotic-assisted surgery allowed for accurate implantation of pedicle screws on immediate adoption of this technique. There were no complications attributable to the robotic technique, and no hardware revisions were required.

A quantitative accuracy assessment of the use of a rigid robotic arm in navigated placement of 726 pedicle screws.

BACKGROUND: Traditional minimally invasive fluoroscopy-based techniques for pedicle screw placement utilize guidance, which may require fluoroscopic shots. Computerized tomography (CT) navigation results in more accurate screw placement. Robotic surgery seeks to establish access and trajectory with greater accuracy. OBJECTIVE: This study evaluated the screw placement accuracy of a robotic platform. METHODS: Demographic data, preoperative/postoperative CT scans, and complication rates of 127 patients who underwent lumbosacral pedicle screw placement with minimally invasive navigated robotic guidance using preoperative CT were analyzed. RESULTS: On the GRS scale, 97.9% (711/726) of screws were graded A or B, 1.7% (12/726) of screws graded C, 0.4% (3/726) of screws graded D, and 0% graded E. Average offset from preoperative plan to final screw placement was 1.9 ± 1.5 mm from tip, 2.2 ± 1.4 mm from tail and 2.9 ± 2.3° of angulation. CONCLUSIONS: Robotic-assisted surgery utilizing preoperative CT workflow with intraoperative fluoroscopy-based registration improves pedicle screw placement accuracy within a patient's pedicles.

Factors Affecting the Accuracy of Pedicle Screw Placement in Robot-Assisted Surgery: A Multicenter Study.

STUDY DESIGN: Retrospective multicenter. OBJECTIVE: The aim was to investigate the factors involved in, and their relative contributions to, the overall accuracy of robot-assisted pedicle screw placement. SUMMARY OF BACKGROUND DATA: Robot-assisted surgery has reportedly resulted in greater accuracy for placement of pedicle screws than conventional methods. There are many potential factors affecting the accuracy of pedicle screws placed with a robot. No study has investigated these factors in a robust way. MATERIALS AND METHODS: Radiographic and clinical data of three centers were pooled. Preoperative and postoperative computerized tomographies were obtained by all three centers to assess the accuracy of the placed screws. The primary outcome measured was accuracy of pedicle screws placed with the robot. The authors performed a multivariate regression analysis to determine the significant patient-related and screw-related variables and their relative contribution to the overall accuracy. In addition, an ordinal regression analysis was conducted to investigate the effects of different variables on accuracy of robot-placed screws graded by Gertzbein-Robbins grading system (GRS). RESULTS: The total contribution of all studied variables to overall accuracy variation as measured by offsets between the placed and planned screws was only 18%. Obesity, long constructs, female gender, surgeon, and vertebral levels were among the factors that had small contributions to the different screw offsets. For GRS grades, significant variables were gender (Log odds: 0.62, 95% CI: 0.38-0.85), age (Log odds: 0.02, 95% CI: 0.01-0.03), length of constructs (Log odds: 0.07, 95% CI: 0.02-0.11), screw diameter (Log odds: 0.55, 95% CI: 0.39-0.71), and length of the screws (Log odds: 0.03, 95% CI: 0.01-0.05). However, these variables too, regardless of their significant association with the accuracy of placed screws, had little contribution to overall variability of accuracy itself (only about 7%). CONCLUSION: The accuracy of screws placed with robotic assistance, as graded by GRS or measured offsets between planned and placed screw trajectories, is minimally affected by different patient-related or screw-related variables due to the robustness of the robotic navigation system used in this study. LEVEL OF EVIDENCE: Level III.

Laterally placed expandable interbody spacers with and without adjustable lordosis improve patient outcomes: A preliminary one-year chart review.

BACKGROUND/OBJECTIVES: Minimally invasive lateral lumbar interbody fusion (MIS LLIF) has been employed to treat degenerative disc disease, with reduced complication profiles in comparison to other open anterior and posterior techniques. The technique permits the use of larger, coronal-spanning interbody spacers to restore height and alignment. However, large static spacers have historically been associated with iatrogenic complications during trialing and insertion. Developments in expandable technology have the potential for incrementally larger increases in both height and lordosis in a controlled expansion in situ, minimizing endplate violation. However, further clinical and radiographic data are needed to investigate the effect of expansion technology. METHODS: A retrospective, single-surgeon chart review was performed on 103 consecutive patients, all of whom underwent MIS LLIF surgery at 1-2 contiguous level(s) with expandable spacers [66/103 patients were implanted with lordotically actuated (adjustable lordosis) spacers, and 37/103 with non-adjustable lordosis spacers]. Clinical and radiographic functional outcomes were collected and compared at both preoperative and postoperative time points up to 12-month follow-up. Parametric and nonparametric tests were utilized when they were appropriate, with a P value < 0.05 being significant. RESULTS: One-hundred twenty-five levels were instrumented on 103 consecutive cases. Average age was 58.2 ± 12.1 years; 42.1% (45/107) were female; 78.6% (81/103) were 1-level cases; 21.4% (22/103) were 2-level cases; 44.8% (56/125) were performed at L4-L5 and 34.4% (43/125) at L3-4. Average estimated blood loss was 24.6 ± 12.3cc. Mean operative time was 61.0 ± 19.1 min, and mean fluoroscopic time was 28.2 ± 14.6 s. Visual Analog Scale (VAS) back and leg pain scores decreased significantly by an average of 6.5 ± 1.3 points at 12 months (P < 0.001). Oswestry Disability Index (ODI) scores significantly decreased at final follow-up by a mean of 62.0 ± 12.4 points (P < 0.001). Lumbar lordosis significantly improved by a mean of 3.1 ± 8.8°, while segmental lordosis significantly improved by 3.9 ± 3.1° at 12 months (P < 0.001). Anterior, middle, and posterior disc heights all experienced significant increases at 12 months by averages of 5.1 ± 3.1, 4.5 ± 2.9, and 2.4 ± 2.2 mm, respectively (P < 0.001). Neuroforaminal height significantly increased at 12 months by a mean of 3.7 ± 3.7 mm (P < 0.001). There was 99% fusion at all levels, with no findings of radiolucency and 1% pseudarthrosis observed. Only 1 (1/125, 0.8%) case of subsidence and 7 (7/125, 5.6%) cases of suspected, asymptomatic radiographic adjacent segment degeneration were reported, with no secondary revision surgeries through 12-month follow-up. CONCLUSION: Significant improvement of disc height, neuroforaminal height, segmental lordosis, and indirect decompression was achieved and maintained up to 1-year follow-up from baseline. Clinical outcomes were significantly improved based on appreciable decreases in VAS pain and ODI scores at final follow-up. Minimal complications were reported, with significant radiographic and patient reported outcomes observed. The use of expandable spacers, with and without adjustable lordosis, was shown to improve outcomes for the studied patient population.

A Critical Analysis of Lateral Versus Central Endpoint in Distal Tibia Nailing: Does It Affect Alignment?

OBJECTIVES: To evaluate the effect of a traditional "center-center" end point for distal tibia nailing in comparison with a lateral-of-center end point on fracture malalignment in a cadaver model. METHODS: Nine matched pairs of human cadaveric lower-extremity specimens were used to model the effect of nail end point on fracture alignment in extra-articular distal tibia fractures. After simulation of the fracture through a standardized osteotomy, 1 member of each pair was fixed with an intramedullary nail using a "center-center" end point, whereas a lateral-of-center end point was used for the other member of the pair. Specimens were stripped of soft tissue, and digital calipers were used to measure fracture translation and gap medially, laterally, anteriorly, and posteriorly. Coronal plane angulation at each fracture was measured on the final mortise image. RESULTS: The average coronal angulation was 7.0 degrees of valgus (with a SD of 4.1) in central-end point specimens versus 0.2 degrees of valgus (SD = 1.5) in lateral-end point specimens ( P < 0.001). Lateral-end point specimens also demonstrated significantly less fracture gap medially (mean 0.2 vs. 3.1 mm for central-end point specimens, P < 0.001), anteriorly (mean 0.1 vs. 1.3 mm, P = 0.003), and posteriorly (mean 0.3 vs. 2.2 mm, P = 0.003). Lateral-end point specimens also showed less lateral translation (mean 0.6 vs. 1.6 mm, P = 0.006). CONCLUSIONS: Lateral-of-center nail end points may help surgeons restore native alignment in extra-articular distal tibia fractures and avoid valgus malalignment.

Fixation Strength of Modified Iliac Screw Trajectory Compared to Traditional Iliac and S2 Alar-Iliac Trajectories: A Cadaveric Study.

OBJECTIVE: Traditional iliac (TI) screws require extensive dissection, involve offset-connectors, and have prominent screw heads that may cause patient discomfort. S2 alar-iliac (S2AI) screws require less dissection, do not need offset connectors, and are less prominent. However, the biomechanical consequences of S2AI screws crossing the alar-iliac joint is unknown. The present study investigates the fixation strength of a modified iliac (MI) screw, which has a more medial entry point and reduced screw prominence, but does not cross the alar-iliac joint. METHODS: Eighteen sacropelvic spines were divided into 3 groups (n = 6): TI, S2AI, and MI. Each specimen was fixed unilaterally with S1 pedicle screws and pelvic fixation according to its group. Screws were loaded at ±10 Nm at 3Hz for 1000 cycles. Motion of each screw and rod strain above and below the S1 screw was measured. RESULTS: Toggle of the S1 screw was lowest for the TI group, followed by the MI and S2AI groups, but there were no significant differences (P = 0.421). Toggle of the iliac screw relative to the pelvis was also lowest for the TI group, followed by the MI group, and was greatest for the S2AI group, without significant differences (P = 0.179). Rod strain was similar across all groups. CONCLUSIONS: No statistically significant differences were found between the TI, S2AI, and MI techniques with regard to screw toggle or rod strain. Advantages of the MI screw include its lower profile and a medialized starting point eliminating the need for offset-connectors.