The Biomechanics of the Transpedicular Endoscopic Approach.

STUDY DESIGN: Biomechanical cadaveric study. OBJECTIVE: The goal of this study was to analyze the effects of an endoscopic transpedicular approach with different drill diameters (6 and 8 mm) to compare them with the intact native side. In addition, the influence of bone quality on the resistance of the pedicle was investigated. SUMMARY OF BACKGROUND DATA: Clinical studies have repeatedly highlighted the benefits of endoscopic transpedicular decompression for down-migrated lumbar disc herniations. However, the biomechanical effects on pedicle stability have not been studied up to now. METHODS: Twenty-four vertebras originating from four fresh-frozen cadavers were tested under uniaxial compression load in a ramp-to-failure test: (1) the tunneled pedicle on one side, and (2) the native pedicle on the other side. Twelve lumbar vertebrae were assigned to a drill diameter of 6 mm and the other 12 to a diameter of 8 mm. RESULTS: The median ratio of sustained force for the operated side compared to the intact contralateral side is equal to 74% (63-88) for both drill diameters combined. An 8 mm transpedicular approach recorded an axial resistance of 77% (60-88) compared to the intact contralateral side ( P =0.002). A 6 mm approach resulted in an axial resistance of 72% (66-84) compared to the intact opposite side ( P =0.01). No significant difference between the two different drill diameters was recorded ( P =1). For all 3 subgroups (intact, 8 mm, 6 mm) the HU-values and the absolute resistance force showed significant correlations (intact: ρ=0.859; P <0.001; 8 mm: ρ=0.902; P <0.001; 6 mm: ρ=0.835; P <0.001). CONCLUSION: Transpedicular approach significantly reduces the axial resistance force of the pedicle, which may lead to pedicle fracture. Bone quality correlated positively with the absolute resistance force of the pedicle, whereas the influence of the drill hole diameter plays only a limited role.

Increased cranio-caudal spinal cord oscillations are the cardinal pathophysiological change in degenerative cervical myelopathy.

Introduction: Degenerative cervical myelopathy (DCM) is the most common cause of non-traumatic incomplete spinal cord injury, but its pathophysiology is poorly understood. As spinal cord compression observed in standard MRI often fails to explain a patient's status, new diagnostic techniques to assess DCM are one of the research priorities. Minor cardiac-related cranio-caudal oscillations of the cervical spinal cord are observed by phase-contrast MRI (PC-MRI) in healthy controls (HCs), while they become pathologically increased in patients suffering from degenerative cervical myelopathy. Whether transversal oscillations (i.e., anterior-posterior and right-left) also change in DCM patients is not known. Methods: We assessed spinal cord motion simultaneously in all three spatial directions (i.e., cranio-caudal, anterior-posterior, and right-left) using sagittal PC-MRI and compared physiological oscillations in 18 HCs to pathological changes in 72 DCM patients with spinal canal stenosis. The parameter of interest was the amplitude of the velocity signal (i.e., maximum positive to maximum negative peak) during the cardiac cycle. Results: Most patients suffered from mild DCM (mJOA score 16 (14-18) points), and the majority (68.1%) presented with multisegmental stenosis. The spinal canal was considerably constricted in DCM patients in all segments compared to HCs. Under physiological conditions in HCs, the cervical spinal cord oscillates in the cranio-caudal and anterior-posterior directions, while right-left motion was marginal [e.g., segment C5 amplitudes: cranio-caudal: 0.40 (0.27-0.48) cm/s; anterior-posterior: 0.18 (0.16-0.29) cm/s; right-left: 0.10 (0.08-0.13) cm/s]. Compared to HCs, DCM patients presented with considerably increased cranio-caudal oscillations due to the cardinal pathophysiologic change in non-stenotic [e.g., segment C5 amplitudes: 0.79 (0.49-1.32) cm/s] and stenotic segments [.g., segment C5 amplitudes: 0.99 (0.69-1.42) cm/s]). In contrast, right-left [e.g., segment C5 amplitudes: non-stenotic segment: 0.20 (0.13-0.32) cm/s; stenotic segment: 0.11 (0.09-0.18) cm/s] and anterior-posterior oscillations [e.g., segment C5 amplitudes: non-stenotic segment: 0.26 (0.15-0.45) cm/s; stenotic segment: 0.11 (0.09-0.18) cm/s] remained on low magnitudes comparable to HCs. Conclusion: Increased cranio-caudal oscillations of the cervical cord are the cardinal pathophysiologic change and can be quantified using PC-MRI in DCM patients. This study addresses spinal cord oscillations as a relevant biomarker reflecting dynamic mechanical cord stress in DCM patients, potentially contributing to a loss of function.

Residual motion of different posterior instrumentation and interbody fusion constructs.

PURPOSE: To elucidate residual motion of cortical screw (CS) and pedicle screw (PS) constructs with unilateral posterior lumbar interbody fusion (ul-PLIF), bilateral PLIF (bl-PLIF), facet-sparing transforaminal lumbar interbody fusion (fs-TLIF), and facet-resecting TLIF (fr-TLIF). METHODS: A total of 35 human cadaver lumbar segments were instrumented with PS (n = 18) and CS (n = 17). Range of motion (ROM) and relative ROM changes were recorded in flexion/extension (FE), lateral bending (LB), axial rotation (AR), lateral shear (LS), anterior shear (AS), and axial compression (AC) in five instrumentational states: without interbody fusion (wo-IF), ul-PLIF, bl-PLIF, fs-TLIF, and fr-TLIF. RESULTS: Whereas FE, LB, AR, and AC noticeably differed between the instrumentational states, AS and LS were less prominently affected. Compared to wo-IF, ul-PLIF caused a significant increase in ROM with PS (FE + 42%, LB + 24%, AR + 34%, and AC + 77%), however, such changes were non-significant with CS. ROM was similar between wo-IF and all other interbody fusion techniques. Insertion of a second PLIF (bl-PLIF) significantly decreased ROM with CS (FE -17%, LB -26%, AR -20%, AC -51%) and PS (FE - 23%, LB - 14%, AR - 20%, AC - 45%,). Facet removal in TLIF significantly increased ROM with CS (FE + 6%, LB + 9%, AR + 17%, AC of + 23%) and PS (FE + 7%, AR + 12%, AC + 13%). CONCLUSION: bl-PLIF and TLIF show similarly low residual motion in both PS and CS constructs, but ul-PLIF results in increased motion. The fs-TLIF technique is able to further decrease motion compared to fr-TLIF in both the CS and PS constructs.

Role of C-reactive protein in the bone marrow of Modic type 1 changes.

Modic type 1 changes (MC1) are vertebral bone marrow lesions and associate with low back pain. Increased serum C-reactive protein (CRP) has inconsistently been associated with MC1. We aimed to provide evidence for the role of CRP in the tissue pathophysiology of MC1 bone marrow. From 13 MC1 patients undergoing spinal fusion at MC1 levels, vertebral bone marrow aspirates from MC1 and intrapatient control bone marrow were taken. Bone marrow CRP, interleukin (IL)-1, and IL-6 were measured with enzyme-linked immunosorbent assays; lactate dehydrogenase (LDH) was measured with a colorimetric assay. CRP, IL-1, and IL-6 were compared between MC1 and control bone marrow. Bone marrow CRP was correlated with blood CRP and with bone marrow IL-1, IL-6, and LDH. CRP expression by marrow cells was measured with a polymerase chain reaction. Increased CRP in MC1 bone marrow (mean difference: +0.22 mg CRP/g, 95% confidence interval [CI] [-0.04, 0.47], p = 0.088) correlated with blood CRP (r = 0.69, p = 0.018), with bone marrow IL-1ß (ρ = 0.52, p = 0.029) and IL-6 (ρ = 0.51, p = 0.031). Marrow cells did not express CRP. Increased LDH in MC1 bone marrow (143.1%, 95% CI [110.7%, 175.4%], p = 0.014) indicated necrosis. A blood CRP threshold of 3.2 mg/L detected with 100% accuracy increased CRP in MC1 bone marrow. In conclusion, the association of CRP with inflammatory and necrotic changes in MC1 bone marrow provides evidence for a pathophysiological role of CRP in MC1 bone marrow.

CD90-positive stromal cells associate with inflammatory and fibrotic changes in modic changes.

Objective: Modic changes (MC) are vertebral bone marrow lesions seen on magnetic resonance images, that associate with disc degeneration and low back pain (LBP). Few studies described MC histopathology qualitatively based on a few patient samples. CD90-positive bone marrow stromal cells were shown to be pro-fibrotic in MC. We aimed to provide the first semi-quantitative histomorphometric analysis of MC bone marrow. We hypothesized a role of CD90-positive cells in MC pathomechanisms. Design: Human biopsies from Modic type 1 changes (MC1, n â€‹= â€‹8), Modic type 2 changes (MC2, n â€‹= â€‹6), and control biopsies (MC0, n â€‹= â€‹8) from adjacent vertebrae were obtained from 14 LBP patients during lumbar spinal fusion. Biopsies were processed for histology/immunohistochemistry. Inflammatory changes (oedema, inflammatory infiltrates), fibrotic changes (connective tissue, type I and III collagen, fibronectin, α-smooth muscle actin), and amount of bone marrow stromal cells (CD90, CD105) were scored. Scores for MC0, MC1, and MC2 were compared with non-parametric tests. Pairwise correlations, hierarchical clustering, and principal component analysis of histological readouts were calculated to identify most important histomorphometric MC characteristics. Results: Compared to MC0, MC1 had more connective tissue, oedema, inflammatory infiltrates, and CD90+ cells. MC2 compared to MC0 had more oedema and CD90+ cells. Scores of CD90 correlated and clustered with inflammatory and fibrotic changes. Amount of connective tissue correlated with LBP. Conclusion: Accumulation of CD90+ cells is a major characteristic of MC in patients undergoing lumbar spinal fusion and associates with inflammatory and fibrotic changes. Therefore, CD90+ cells may play an important role in the inflammatory-fibrotic pathomechanisms of MC.

Biomechanics of Transforaminal Endoscopic Approaches.

STUDY DESIGN: Biomechanical cadaveric study. OBJECTIVE: The aim of this study was to compare the effect of transforaminal endoscopic approaches with open decompression procedures. SUMMARY OF BACKGROUND DATA: Clinical studies have repeatedly highlighted the benefits of endoscopic decompression, however, the biomechanical effects of endoscopic approaches (with and without injury to the disk) have not been studied up to now. MATERIALS AND METHODS: Twelve spinal segments originating from four fresh-frozen cadavers were biomechanically tested in a load-controlled endoscopic transforaminal approach study. Segmental range of motion (ROM) after endoscopic approach was compared with segmental ROM after (1) microsurgical decompression with unilateral laminotomy and (2) midline decompression with bilateral laminotomy. In the intact state and after decompression, the segments were loaded in flexion-extension (FE), lateral shear (LS), lateral bending (LB), anterior shear (AS), and axial rotation (AR). RESULTS: Vertebral segment ROM was comparable between the two endoscopic transforaminal approaches. However, there was a-statistically nonsignificant-trend for a larger ROM after accessing via the inside-out technique: FE: +3% versus +7%, P =0.484; LS: +1% versus +12%, P =0.18; LB: +0.6% versus +9%, P =0.18; AS: +2% versus +11%, P =0.31; AR: -4% versus +5%, P =0.18. No significant difference in vertebral segment ROM was seen between the transforaminal endoscopic approaches and open unilateral decompression. Vertebral segment ROM was significantly smaller with the transforaminal endoscopic approaches compared with midline decompression for almost all loading scenarios: FE: +4% versus +17%, P =0.005; AS: +6% versus 21%, P =0.007; AR: 0% versus +24%, P =0.002. CONCLUSION: The transforaminal endoscopic intracanal technique preserves the native ROM of lumbar vertebral segments and shows a trend toward relative biomechanical superiority over the inside-out technique and open decompression procedures.

MRI appearance of adjunct surgical material used in spine surgery.

BACKGROUND CONTEXT: Early postoperative MR images are frequently necessary after spine surgery. The appearance of commonly used adjunct hemostatic agents and dural sealants in MR images has not been systematically evaluated. PURPOSE: The purpose of this experimental study was to systematically analyze and describe the characteristics of the most commonly applied hemostatic agents and dural sealants in spine surgery on early postoperative MR images. STUDY DESIGN: Cadaver Study METHODS: Four commonly applied dural sealants (Duraseal, Bioglue, Tachosil, Tisseel) and five commonly used hemostatic agents (Surgiflo, Bonewax, , Spongostan, Gelfoam, Avitene) were investigated. The experimental setting involved a human cadaver where a standard left-sided laminotomy was performed on nine levels of the thoracolumbar spine, and the materials were separately applied and mixed with fresh blood or water for hemostatic and dural sealants, respectively. The cadaver model was scanned at a 3 Tesla MRI and the imaging findings for all materials were compared to the surrounding tissue and systematically reported. RESULTS: All investigated dural sealants and hemostatic agents were distinguishable from the surrounding tissue on MR images with different appearances on the MR sequences. A detailed atlas for the identification of the materials in postoperative spine MRI was established. CONCLUSION: Commonly used hemostatic agents and dural sealants can be successfully identified on early postoperative spine MRI. CLINICAL SIGNIFICANCE: Knowledge about MRI appearances of commonly used adjunct surgical materials helps in interpretation of postoperative imaging and supports clinical decision making.

Occipitopexy as a Fusionless Solution for Dropped Head Syndrome: A Case Report.

CASE: A 68-year-old woman suffered from an irradiation-induced dropped head syndrome (DHS). Fusion surgery was vehemently rejected by the patient. A new surgical method, avoiding fusion, was invented and performed to treat her DHS. This novel surgical technique of "occipitopexy"-a ligamentous fixation of the occiput to the upper thoracic spine-is described in detail. One year postoperatively, the patient was very satisfied, able to maintain a horizontal gaze, and rotate her head 20° to each side. CONCLUSION: This is the first report describing "occipitopexy" as an alternative to cervicothoracic fusion for patients with flexible DHS.

Biomechanical performance of bicortical versus pericortical bone trajectory (CBT) pedicle screws.

PURPOSE: The cortical bone trajectory (CBT) is an alternative to the traditional pedicle screw trajectory (TT) in posterior spinal instrumentation, enhancing screw contact with cortical bone and therefore increasing fixation strength. Additional to the trajectory, insertion depth (pericortical vs. bicortical placement) could be a relevant factor affecting the fixation strength. However, the potential biomechanical benefit of a bicortical placement of CBT screws is unknown. Therefore, the aim of this study was to quantify the fixation strength of pericortical- versus bicortical-CBT (pCBT versus bCBT) screws in a randomized cadaveric study. METHODS: Pedicle screws were either placed pericortical or bicortical with a CBT in 20 lumbar vertebrae (2 × 20 instrumented pedicles) from four human spine cadavers by using patient-specific templates. Instrumented specimens underwent physiological cyclic loading testing (1'800'000 cycles, 10 Hz), including shear and tension loads as well as bending moments. Translational and angular displacements of the screws were quantified and compared between the two techniques. RESULTS: There was a slight decrease in translational (0.2 mm ± 0.09 vs. 0.24 mm ± 0.11) and angular displacements (0.06° ± 0.05 vs. 0.13° ± 0.11) of bCBT screws when compared with pCBT screws after 1'800'000 cycles. However, the results were non-significant (p > 0.05). CONCLUSION: The authors do not recommend placing CBT screws bicortically, as no relevant biomechanical advantage is gained while the potential risk for iatrogenic injury to structures anterior to the spine is increased.

Surgical Process Modeling for Open Spinal Surgeries.

Modern operating rooms are becoming increasingly advanced thanks to the emerging medical technologies and cutting-edge surgical techniques. Current surgeries are transitioning into complex processes that involve information and actions from multiple resources. When designing context-aware medical technologies for a given intervention, it is of utmost importance to have a deep understanding of the underlying surgical process. This is essential to develop technologies that can correctly address the clinical needs and can adapt to the existing workflow. Surgical Process Modeling (SPM) is a relatively recent discipline that focuses on achieving a profound understanding of the surgical workflow and providing a model that explains the elements of a given surgery as well as their sequence and hierarchy, both in quantitative and qualitative manner. To date, a significant body of work has been dedicated to the development of comprehensive SPMs for minimally invasive baroscopic and endoscopic surgeries, while such models are missing for open spinal surgeries. In this paper, we provide SPMs common open spinal interventions in orthopedics. Direct video observations of surgeries conducted in our institution were used to derive temporal and transitional information about the surgical activities. This information was later used to develop detailed SPMs that modeled different primary surgical steps and highlighted the frequency of transitions between the surgical activities made within each step. Given the recent emersion of advanced techniques that are tailored to open spinal surgeries (e.g., artificial intelligence methods for intraoperative guidance and navigation), we believe that the SPMs provided in this study can serve as the basis for further advancement of next-generation algorithms dedicated to open spinal interventions that require a profound understanding of the surgical workflow (e.g., automatic surgical activity recognition and surgical skill evaluation). Furthermore, the models provided in this study can potentially benefit the clinical community through standardization of the surgery, which is essential for surgical training.

Hand or foot train-of-four tests and surgical site muscle relaxation assessed with multiple motor evoked potentials: A prospective observational study.

BACKGROUND: Intra-operative muscle relaxation is often required in orthopaedic surgery and the hand train-of-four (TOF) test is usually used for its quantification. However, even though full muscle relaxation is claimed by anaesthesiologists based on a TOF count of zero, surgeons observe residual muscle activity. OBJECTIVE: The aim of the study was to assess if hand or foot TOF adequately represents intra-operative muscle relaxation compared with multiple motor evoked potentials. DESIGN: Prospective observational study. SETTING: A single-centre study performed between February 2016 and December 2018 at the Balgrist University Hospital, Zurich, Switzerland. PATIENTS: Twenty patients scheduled for elective lumbar spinal fusion were prospectively enrolled in this study after giving written informed consent. INTERVENTIONS: To assess neuromuscular blockade (NMB) with the intermediate duration nondepolarising neuromuscular blocking agent rocuronium, hand TOF (adductor pollicis) and foot TOF (flexor hallucis brevis) monitoring, and muscle motor evoked potentials (MMEPs) from the upper and lower extremities were assessed prior to surgery under general anaesthesia. Following baseline measurements, muscle relaxation was performed with rocuronium until the spinal surgeon observed sufficient relaxation for surgical intervention. At this timepoint, NMB was assessed by TOF and MMEP. MAIN OUTCOME MEASURES: The primary outcome was to determine the different effect of rocuronium on muscle relaxation comparing hand and foot TOF with the paraspinal musculature assessed by MMEP. RESULTS: Hand TOF was more resistant to NMB and had a shorter recovery time than foot TOF. When comparing MMEPs, muscle relaxation occurred first in the hip abductors, and the paraspinal and deltoid muscles. The most resistant muscle to NMB was the abductor digiti minimi. Direct comparison showed that repetitive MMEPs simultaneously recorded from various muscles at the upper and lower extremities and from paraspinal muscles reflect muscle relaxation similar to TOF testing. CONCLUSION: Hand TOF is superior to foot TOF in assessing muscle relaxation during spinal surgery. Hand TOF adequately represents the degree of muscle relaxation not only for the paraspinal muscles but also for all orthopaedic surgical sites where NMB is crucial for good surgical conditions. TRIAL REGISTRATION: ClinicalTrials.gov (NCT03318718).

Ultrasound-guided interventions with augmented reality in situ visualisation: a proof-of-mechanism phantom study.

BACKGROUND: Ultrasound (US) images are currently displayed on monitors, and their understanding needs good orientation skills. Direct overlay of US images onto the according anatomy is possible with augmented reality (AR) technologies. Our purpose was to explore the performance of US-guided needle placement with and without AR in situ US viewing. METHODS: Three untrained operators and two experienced radiologists performed 200 US-guided punctures: 100 with and 100 without AR in situ US. The punctures were performed in two different phantoms, a leg phantom with soft tissue lesions and a vessel phantom. Time to puncture and number of needle passes were recorded for each puncture. Data are reported as median [range] according to their non-normal distribution. RESULTS: AR in situ US resulted in reduced time (median [range], 13 s [3-101] versus 14 s [3-220]) and number of needle passes (median [range], 1 [1-4] versus 1 [1-8]) compared to the conventional technique. The initial gap in performance of untrained versus experienced operators with the conventional US (time, 21.5 s [3-220] versus 10.5 s [3-94] and needle passes 1 [1-8] versus 1 [1, 2]) was reduced to 12.5 s [3-101] versus 13 s [3-100] and 1 [1-4] versus 1 [1-4] when using AR in situ US, respectively. CONCLUSION: AR in situ US could be a potential breakthrough in US applications by simplifying operator's spatial orientation and reducing experience-based differences in performance of US-guided interventions. Further studies are needed to confirm these preliminary phantom results.

Augmented reality navigation for spinal pedicle screw instrumentation using intraoperative 3D imaging.

BACKGROUND CONTEXT: Due to recent developments in augmented reality with head-mounted devices, holograms of a surgical plan can be displayed directly in the surgeon's field of view. To the best of our knowledge, three dimensional (3D) intraoperative fluoroscopy has not been explored for the use with holographic navigation by head-mounted devices in spine surgery. PURPOSE: To evaluate the surgical accuracy of holographic pedicle screw navigation by head-mounted device using 3D intraoperative fluoroscopy. STUDY DESIGN: In this experimental cadaver study, the accuracy of surgical navigation using a head-mounted device was compared with navigation with a state-of-the-art pose-tracking system. METHODS: Three lumbar cadaver spines were embedded in nontransparent agar gel, leaving only commonly visible anatomy in sight. Intraoperative registration of preoperative planning was achieved by 3D fluoroscopy and fiducial markers attached to lumbar vertebrae. Trackable custom-made drill sleeve guides enabled real-time navigation. In total, 20 K-wires were navigated into lumbar pedicles using AR-navigation, 10 K-wires by the state-of-the-art pose-tracking system. 3D models obtained from postexperimental CT scans were used to measure surgical accuracy. MF is the founder and shareholder of Incremed AG, a Balgrist University Hospital start-up focusing on the development of innovative techniques for surgical executions. The other authors declare no conflict of interest concerning the contents of this study. No external funding was received for this study. RESULTS: No significant difference in accuracy was measured between AR-navigated drillings and the gold standard with pose-tracking system with mean translational errors between entry points (3D vector distance; p=.85) of 3.4±1.6 mm compared with 3.2±2.0 mm, and mean angular errors between trajectories (3D angle; p=.30) of 4.3°±2.3° compared with 3.5°±1.4°. CONCLUSIONS: In conclusion, holographic navigation by use of a head-mounted device achieve accuracy comparable to the gold standard of high-end pose-tracking systems. CLINICAL SIGNIFICANCE: These promising results could result in a new way of surgical navigation with minimal infrastructural requirements but now have to be confirmed in clinical studies.

Shunt age-related complications in adult patients with suspected shunt dysfunction. A recommended diagnostic workup.

BACKGROUND: Patients admitted for suspicion of shunt dysfunction (SD) often show unspecific symptoms and require time-consuming, expensive and even invasive diagnostics involving significant radiation exposure. The purpose of this retrospective study was to analyse the current diagnostic procedures and to propose a process optimisation. METHOD: As all patients admitted for suspicion of SD receive imaging studies, we searched for adult patients receiving neuroimaging in the period from January 2010 to July 2013, analysing referring diagnosis, clinical signs, products, diagnostic process and final diagnosis. Recursive partitioning was used to define time intervals for differentiating types of SD. RESULTS: A total of 148 patients, aged 18-89 (mean, 54) years, were studied. Forty-two percent were referred by a hospital or rehabilitation centre, 30% by general practitioners and 24% were self-referrals. The admission diagnosis was in the majority "shunt dysfunction" only. Further differentiations were rarely made. An SD was confirmed in 46% of the patients. In 17%, the symptoms were based on another cause and in 37% they could not be clearly attributed to any specific disorder. Abdominal dislocations (2%) and shunt infections (5%) were found within the first 6 months. Over- (3%) and under-drainage (14%) were the most frequent complications during the first 4 years. Disconnections (13%) occurred generally 4 years or more after implantation. Only shunt obstruction (9%) showed no temporal pattern. CONCLUSIONS: Symptoms of SD remain mostly unspecific. This study showed that the type of SD depends on the time interval from implantation. We propose a workup strategy for patients with SD based on the temporal profile.