Reverse total shoulder arthroplasty—from the most to the least common complication

Reverse total shoulder arthroplasty (RTSA) has been reported to be associated with a complication rate that is four times that of conventional total shoulder arthroplasty. It is the purpose of this article to identify and understand the most common and most serious complications of RTSA and to review current methods of prevention and treatment. The current literature was reviewed to identify type and prevalence of reported complications and to identify risk factors, preventive measures as well as technical details for management strategies for complications of RTSA. The variable accuracy of reporting and the heterogeneity of methodology in the literature limited our study, however, a definitive ranking of most to least common complication emerged. The currently identified most common complication is scapular notching. The clinically most relevant complications are infection, instability and acromial fractures. Haematoma formation used to be very frequent but can be controlled, glenoid component loosening, however, is rare when compared with conventional total shoulder replacement. In conclusion, RTSA is associated with a high rate of complications. Their incidence and the results of their treatment are inconsistently reported. To document and then prevent complications, a standardised monitoring tool including clear definitions and assessment instructions appears necessar

Posterior correction of thoracic adolescent idiopathic scoliosis with pedicle screw instrumentation: results of 48 patients with minimal 10-year follow-up

Purpose: Since early 1990s pedicle screws in thoracic spine have been used in posterior correction of adolescent idiopathic scoliosis (AIS). Long-term results are scarce. We report clinical, radiological and pulmonary function results of 48 consecutive patients with 10-year minimal follow-up. Methods: Forty-eight consecutive patients (42 females, 6 males) with 41 Lenke 1 (lumbar modifier A=19, B=8, C=14), 7 Lenke 2 (lumbar modifier A=2, B=4, C=1) were operated for AIS from posterior with pedicle screw alone instrumentation. Risser stage at the time of operation was 0-3 in 24, more than 3 in 24 patients. Mean age was 15.3years. The data were prospectively collected preoperatively, at 6weeks, 2years and 10years postoperatively. Cobb angle, sagittal and coronal balance, distal adjacent disc angle and lowest fused vertebral tilt were documented at all time-points. Choice of fusion levels is described. Not every vertebra was instrumented with pedicle screws. The implant density was average one pedicle screw per vertebra or 50%. Derotation and translation of apical vertebrae on the concave side were performed for correction. The overall outcome and the outcome of different curve types were analyzed statistically. Results: Lowest instrumented vertebra (LIV) was distal end vertebra in two-thirds of the patients and was one below distal end vertebra in one-third of the patients. The main thoracic curve correction was 63%, from 58°±12° preoperative to 21°±9° at 6weeks. The Cobb angle was 23°±10° at 2years and 26°±10° at 10years. The apical vertebral rotation improved 35%, the non-instrumented lumbar curves improved 47%, the distal adjacent disc angle decreased from 6°±3° preoperatively to −2°±4° postoperatively and the last instrumented vertebral tilt decreased from 23°±8° preoperatively to 5°±5° postoperatively. All these parameters remained stable up to 10-year follow-up. The scoliosis correction was not associated with any change in the preoperative thoracic kyphosis and lumbar lordosis. The % FVC remained unchanged with 74±21% preoperatively to 74±11% at 2years and 75±10% at 10years. The SRS-24 score was 93±18 points at 2years and 95±22 points at 10years. There were no neurological complications, no pedicle screw-related complications. Conclusion: Posterior correction of thoracic AIS with pedicle screw instrumentation is safe and produces a long-term stable correction and high patient satisfaction. An implant density of 50% is sufficient to achieve these results. LIV can be the distal end vertebra or one below the distal end vertebra depending on the position of the distal end vertebra to the centre sacral line. The preoperative pulmonary function does not change on long ter

Location of pedicle screw hold in relation to bone quality and loads

Introduction: Sufficient screw hold is an indispensable requirement for successful spinal fusion, but pedicle screw loosening is a highly prevalent burden. The aim of this study was to quantify the contribution of the pedicle and corpus region in relation to bone quality and loading amplitude of pedicle screws with traditional trajectories. Methods: After CT examination to classify bone quality, 14 pedicle screws were inserted into seven L5. Subsequently, Micro-CT images were acquired to analyze the screw's location and the vertebrae were split in the midsagittal plane and horizontally along the screw's axis to allow imprint tests with 6 mm long sections of the pedicle screws in a caudal direction perpendicular to the screw's surface. Force-displacement curves in combination with the micro-CT data were used to reconstruct the resistance of the pedicle and corpus region at different loading amplitudes. Results: Bone quality was classified as normal in three specimens, as moderate in two and as bad in two specimens, resulting in six, four, and four pedicle screws per group. The screw length in the pedicle region in relation to the inserted screw length was measured at an average of 63%, 62%, and 52% for the three groups, respectively. At a calculated 100 N axial load acting on the whole pedicle screw, the pedicle region contributed an average of 55%, 58%, and 58% resistance for the normal, moderate, and bad bone quality specimens, respectively. With 500 N load, these values were measured at 59%, 63%, and 73% and with 1000 N load, they were quantified at 71%, 75%, and 81%. Conclusion: At lower loading amplitudes, the contribution of the pedicle and corpus region on pedicle screw hold are largely balanced and independent of bone quality. With increasing loading amplitudes, the contribution of the pedicle region increases disproportionally, and this increase is even more pronounced in situations with reduced bone quality. These results demonstrate the importance of the pedicle region for screw hold, especially for reduced bone quality

First in man in-situ augmented reality pedicle screw navigation

Background Augmented reality (AR) is a rising technology gaining increasing utility in medicine. By superimposing the surgical site and the operator's visual field with computer-generated information, it has the potential to enhance the cognitive skills of surgeons. This is the report of the first in man case with "direct holographic navigation" as part of a randomized controlled trial. Case description A pointing instrument was equipped with a sterile fiducial marker, which was used to obtain a digital representation of the intraoperative bony anatomy of the lumbar spine. Subsequently, a previously validated registration method was applied to superimpose the surgery plan with the intraoperative anatomy. The registration result is shown in situ as a 3D AR hologram of the preoperative 3D vertebra model with the planned screw trajectory and entry point for validation and approval by the surgeon. After achieving alignment with the surgery plan, a borehole is drilled and the pedicle screw placed. Postoperativ computer tomography was used to measure accuracy of this novel method for surgical navigation. Outcome Correct screw positions entirely within bone were documented with a postoperative CT, with an accuracy similar to current standard of care methods for surgical navigation. The patient was mobilized uneventfully on the first postoperative day with little pain medication and dismissed on the fourth postoperative day. Conclusion This first in man report of direct AR navigation demonstrates feasibility in vivo. The continuation of this randomized controlled study will evaluate the value of this novel technology

Interference screws should be shorter than the hamstring tendon graft in the bone tunnel for best fixation

Purpose: Interference screw fixation of hamstring tendon grafts in bone has to overcome the challenges that tendons have a slippery surface and viscoelastically adapt under pressure. As the typical failure mode of the graft is to slip past the interference screw, it was hypothesized that the position and configuration of the graft end may be of influence on the fixation strength. Methods: Different configurations of the graft ending and its effect to primary fixation with interference screws after viscoelastic adaptation were tested in six groups: I: graft and the screw inserted at the same depth, II/III: the graft overlaps the tip of the screw (interference screw of 28 and 19mm in length, respectively), IV: strengthening of the graft ending with additional suture knots, V: Endopearl, respectively, and VI: effect of partial retraction of the screw after excessive insertion. In vitro tests were performed with fresh calf tendon grafts and interference screws in bone tunnels (fresh porcine distal femur) all of 8mm in diameter. Results: The relative position of the graft ending to the tip of the interference screw thereby was recognized as a significant factor on pullout forces. Further strengthening at the graft endings with additional suture knots or an Endopearl device could improve primary hold as well. Conclusions: Better fixation strength is achieved if the tip of interference screw does not extend past the end of a tendon graft. Enforcement of the tendon end with sutures or an implant can further improve fixatio

Real-time assessment of anteroposterior stability of spinal segments

PURPOSE While anteroposterior instability of spinal segments is regarded as an important biomechanical aspect in the clinical evaluation of lumbar pathologies, the reliability of the available diagnostic tools is limited and an intraoperative method to quantify stability is lacking. The aim of this study was to develop and validate an instrument to measure the anteroposterior stability of a spinal segments in real-time. METHODS Torsi of five fresh-frozen human cadavers were used for this study. After pedicle screw insertion, a specifically modified reposition tool composed with load and linear sensors was used to measure the segmental anteroposterior motion caused by 100 N anterior and posterior force during 5 loading cycles on either side of the instrumentation by two different operators. The spinal segments were then resected from the torsi and anteroposterior loading with ± 100 N was repeated in an advanced biomechanical spine testing setup as a reference measurement. The Inter-correlation coefficient (ICC) was used for validation of the "intraoperative" device. RESULTS Inter-operator repeatability of the measurements showed an ICC of 0.93 (p < 0.0001) and the bilateral (left-right) comparison had an ICC of 0.73 (p < 0.0001). The ICC resulting from the comparison to the reference measurement was 0.82 (p < 0.0001) without offset correction, and 0.9 (p < 0.0001) with offset correction. The ICC converged at this value already after two of the five performed loading cycles. CONCLUSION An accurate and reliable measurement tool is developed and validated for real-time quantification of anteroposterior stability of spinal segments and serves as a basis for future intraoperative use

Spine Biomechanics in the Work of Aristotle (384 - 322 BC)

Background: Spine biomechanics is a field of applied research aiming to unravel the biomechanical understanding of the spine and its disorders and to understand the implications of their interventional therapy to improve clinical practice, physical performance and daily living. Its scientific whereabouts can be traced in the work of Aristotle, who discussed physical and biological concepts of spine biomechanics in a series of treatises.Results: The authors searched the Thesaurus Linguae Graecae archive for original texts written in Greek and attributed to Aristotle and selected excerpts of medical and biological treatises that elaborate on spine biomechanics.Discussion: While many of his theories have become outdated, his methodology and rationale remain relevant for contemporary researchers and clinicians. Here, the relevant content of passages of the corpus aristotelicum related to spine biomechanics and discuss their practical implications are presented. Keywords: aristotle; humanities; philosophy; spine biomechanic

Kinematics of the Cervical Spine Under Healthy and Degenerative Conditions: A Systematic Review

Knowledge of spinal kinematics is essential for the diagnosis and management of spinal diseases. Distinguishing between physiological and pathological motion patterns can help diagnose these diseases, plan surgical interventions and improve relevant tools and software. During the last decades, numerous studies based on diverse methodologies attempted to elucidate spinal mobility in different planes of motion. The authors aimed to summarize and compare the evidence about cervical spine kinematics under healthy and degenerative conditions. This includes an illustrated description of the spectrum of physiological cervical spine kinematics, followed by a comparable presentation of kinematics of the degenerative cervical spine. Data was obtained through a systematic MEDLINE search including studies on angular/translational segmental motion contribution, range of motion, coupling and center of rotation. As far as the degenerative conditions are concerned, kinematic data regarding disc degeneration and spondylolisthesis were available. Although the majority of the studies identified repeating motion patterns for most motion planes, discrepancies associated with limited sample sizes and different imaging techniques and/or spine configurations, were noted. Among healthy/asymptomatic individuals, flexion extension (FE) and lateral bending (LB) are mainly facilitated by the subaxial cervical spine. C4-C5 and C5-C6 were the major FE contributors in the reported studies, exceeding the motion contribution of sub-adjacent segments. Axial rotation (AR) greatly depends on C1-C2. FE range of motion (ROM) is distributed between the atlantoaxial and subaxial segments, while AR ROM stems mainly from the former and LB ROM from the latter. In coupled motion rotation is quantitatively predominant over translation. Motion migrates caudally from C1-C2 and the center of rotation (COR) translocates anteriorly and superiorly for each successive subaxial segment. In degenerative settings, concurrent or subsequent lesions render the association between diseases and mobility alterations challenging. The affected segments seem to maintain translational and angular motion in early and moderate degeneration. However, the progression of degeneration restrains mobility, which seems to be maintained or compensated by adjacent non-affected segments. While the kinematics of the healthy cervical spine have been addressed by multiple studies, the entire nosological and kinematic spectrum of cervical spine degeneration is partially addressed. Large-scale in vivo studies can complement the existing evidence, cover the gaps and pave the way to technological and clinical breakthroughs

Viscoelastic adaptation of tendon graft material to compression: biomechanical quantification of graft preconditioning

Purpose: The tensile viscoelastic behaviour of tendon tissue is of central biomechanical importance and well examined. However, the viscoelastic tendon adaptation to external compression, such as when a tendon graft is fixated with an interference screw, has not been investigated before. Here, we quantify this adaptive behaviour in order to develop a new method to mechanically precondition tendon grafts and to better understand volumetric changes of tendinous tissue. The hypothesis of this study was that under compressive loads, tendon grafts will undergo a temporary volumetric (and therefore diametric) reduction, due to the extrusion of water from the tendon. Methods: Compressive testing was performed on a material testing machine and load applied through the use of a custom-made mould, with a semi-circular cross section to accommodate the tendon graft. The effects of different compressive forces on the length, diameter and weight of tendon grafts were measured by calipers and a weighing scale, respectively. Further, different strain rates (1 vs. 10mm/min) (n=6, per rate), compression method (steady compression vs. creep) (n=15 for each method) and different compression durations (1, 5, 10min) (n=5 for each duration) were tested to identify the most effective combination to reduce graft size by preserving its macroscopic structure. Results: The effect of compression on volume reduction (75% of initial volume and weight) reached a plateau at 6,000N on an 8-mm tendon bundle. Length thereby increased by approximately 10%. Both steady compression and creeping were able to reduce dimensions of the graft; however, creeping was more effective. There was no difference in effect with different durations for compression (p>0.05) in both methods. Conclusion: The viscoelastic behaviour of hamstring tendon grafts under pressure allows preconditioning of the grafts for reduction of volume and diameter and therefore to drill a smaller bone tunnel, retaining more of the original bone. At the same time, the collagen content of the transplant is preserved and a tight fit of the transplant in the bone tunnel achieve