Introduction

Transosseous flexion-distraction injuries of the spine typically require surgical intervention by stabilizing the fractured vertebra during healing with a pedicle-screw-rod constructs. As healing is taking place the load shifts from the implant back to the spine. Monitoring the load-induced deflection of the rods over time would allow quantifiable postoperative assessment of healing progress without the need for radiation exposure or frequent hospital visits. This approach, previously demonstrated to be effective in assessing fracture healing in long bones and monitoring posterolateral spinal fusion in sheep, is now being investigated for its potential in evaluating lumbar vertebra transosseous fracture healing.

Introduction. In daily clinical practice, progression of spinal fusion is typically monitored during clinical follow-up using conventional radiography and Computed Tomography scans. However, recent research has demonstrated the potential of implant load monitoring to assess posterolateral spinal fusion in an in-vivo sheep model. The question arises to whether such a strain sensing system could be used to monitor bone fusion following lumbar interbody fusion surgery, where the intervertebral space is supported by a cage. Therefore, the aim of this study was to test human cadaveric lumbar spines in two states: after a transforaminal lumbar interbody fusion (TLIF) procedure combined with a pedicle-screw-rod-construct (PSR) and subsequently after simulating bone fusion. The study hypothesized that the load on the posterior instrumentation decreases as the segment stiffens due to simulated fusion. Method. A TLIF procedure with PSR was performed on eight human cadaveric spines at level L4-L5. Strain sensors were attached bilaterally to the rods to derive implant load changes during unconstrained flexion-extension (FE), lateral bending (LB) and axial rotation (AR) loads up to ±7.5Nm. The specimens were retested after simulating bone fusion between vertebrae L4-L5. In addition, the range of motion (ROM) was measured during each loading mode. Result. The ROM decreased in the simulated bone fusion state in all loading directions (p≤0.002). In both states, the measured strain on the posterior instrumentation was highest during LB motion. Furthermore, the sensors detected a significant decrease in the load induced rod strain (p≤0.002) between TLIF+PSR and simulated bone fusion state in LB. Conclusion. Implant load measured via rod strain sensors can be used to monitor the progression of fusion after a TLIF procedure when measured during LB of the lumbar spine. However, further research is needed to investigate the influence of daily loading scenarios expected in-vivo on the overall change in implant load

Introduction. Pedicle screw loosening in posterior instrumentation of thoracolumbar spine occurs up to 60% in osteoporotic patients. These complications may be alleviated using more flexible implant materials and novel designs that could be optimized with reliable computational modeling. This study aimed to develop and validate non-linear homogenized finite element (hFE) simulations to predict pedicle screw toggling. Method. Ten cadaveric vertebral bodies (L1-L5) from two female and three male elderly donors were scanned with high-resolution peripheral quantitative computed tomography (HR-pQCT, Scanco Medical) and instrumented with pedicle screws made of carbon fiber-reinforced polyether-etherketone (CF/PEEK). Sample-specific 3D-printed guides ensured standardized instrumentation, embedding, and loading procedures. The samples were biomechanically tested to failure in a toggling setup using an electrodynamic testing machine (Acumen, MTS) applying a quasi-static cyclic testing protocol of three ramps with exponentially increasing peak (1, 2 and 4 mm) and constant valley displacements. Implant-bone kinematics were assessed with a stereographic 3D motion tracking camera system (Aramis SRX, GOM). hFE models with non-linear, homogenized bone material properties including a strain-based damage criterion were developed based on intact HR-pQCT and instrumented 3D C-arm scans. The experimental loading conditions were imposed, the maximum load per cycle was calculated and compared to the experimental results. HR-pQCT-based bone volume fraction (BV/TV) around the screws was correlated with the experimental peak forces at each displacement level. Result. The nonlinear hFE models accurately (slope = 1.07, intercept = 0.2 N) and precisely (R. 2. = 0.84) predicted the experimental peak forces at each displacement level. BV/TV alone was a weak predictor (R. 2. <0.31). Conclusion. The hFE models enable fast design iterations aiming to reduce the risk of screw loosening in low-density vertebrae. Improved flexible implant designs are expected to contribute to reduced complication rates in osteoporotic patients

Introduction and Objective. Posterior and transforaminal lumbar interbody fusion (PLIF, TLIF) represent the most popular techniques in performing an interbody fusion amongst spine surgeons. Pseudarthrosis, cage migration, subsidence or infection can occur, with subsequent failed surgery, persistent pain and patient’ bad quality of life. The goal of revision fusion surgery is to correct any previous technical errors avoiding surgical complications. The most safe and effective way is to choose a naive approach to the disc. Therefore, the anterior approach represents a suitable technique as a salvage operation. The aim of this study is to underline the technical advantages of the anterior retroperitoneal approach as a salvage procedure in failed PLIF/TLIF analyzing a series of 32 consecutive patients. Materials and Methods. We performed a retrospective analysis of patients’ data in patients who underwent ALIF as a salvage procedure after failed PLIF/TLIF between April 2014 to December 2019. We recorded all peri-operative data. In all patients the index level was exposed with a minimally invasive anterior retroperitoneal approach. Results. Thirty-two patients (average age: 46.4 years, median age 46.5, ranging from 21 to 74 years hold- 16 male and 16 female) underwent salvage ALIF procedure after failed PLIF/TLIF were included in the study. A minimally invasive anterior retroperitoneal approach to the lumbar spine was performed in all patients. In 6 cases (18.7%) (2 infection and 4 pseudarthrosis after stand-alone IF) only anterior revision surgery was performed. A posterior approach was necessary in 26 cases (81.3%). In most of cases (26/32, 81%) the posterior instrumentation was overpowered by the anterior cage without a previous revision. Three (9%) intraoperative minor complications after anterior approach were recorded: 1 dural tear, 1 ALIF cage subsidence and 1 small peritoneal tear. None vascular injuries occurred. Most of patients (90.6%) experienced an improvement of their clinical condition and at the last follow-up no mechanical complication occurred. Conclusions. According to our results, we can suggest that a favourable clinical outcome can firstly depend from technical reasons an then from radiological results. The removal of the mobilized cage, the accurate endplate and disc space preparation and the cage implant eliminate the primary source of pain reducing significantly the axial pain, helping to realise an optimal bony surface for fusion and enhancing primary stability. The powerful disc distraction given by the anterior approach allows inserting large and lordotic cages improving the optimal segmental lordosis restoration

We performed a biomechanical study on human cadaver spines to determine the effect of three different interbody cage designs, with and without posterior instrumentation, on the three-dimensional flexibility of the spine. Six lumbar functional spinal units for each cage type were subjected to multidirectional flexibility testing in four different configurations: intact, with interbody cages from a posterior approach, with additional posterior instrumentation, and with cross-bracing. The tests involved the application of flexion and extension, bilateral axial rotation and bilateral lateral bending pure moments. The relative movements between the vertebrae were recorded by an optoelectronic camera system. We found no significant difference in the stabilising potential of the three cage designs. The cages used alone significantly decreased the intervertebral movement in flexion and lateral bending, but no stabilisation was achieved in either extension or axial rotation. For all types of cage, the greatest stabilisation in flexion and extension and lateral bending was achieved by the addition of posterior transpedicular instrumentation. The addition of cross-bracing to the posterior instrumentation had a stabilising effect on axial rotation. The bone density of the adjacent vertebral bodies was a significant factor for stabilisation in flexion and extension and in lateral bending

In case of spine tumors, when en bloc vertebral column resection (VCR) is indicated and feasible, the segmental defect should be reconstructed in order to obtain an immediate stability and stimulate a solid fusion. The aim of this study is to share our experience on patients who underwent spinal tumor en bloc VCR and reconstruction consecutively. En bloc VCR and reconstruction was performed in 138 patients. Oncological and surgical staging were performed for all patients using Enneking and Weinstein-Boriani-Biagini systems accordingly. Following en bloc VCR of one or more vertebral bodies, a 360° reconstruction was made by applying posterior instrumentation and anterior implant insertion. Modular carbon fiber implants were applied in 111 patients, titanium mesh cage implants in 21 patients and titanium expandable cages in 3 patients; very recently in 3 cases we started to use custom made titanium implants. The latter were prepared according to preoperative planning of en bloc VCR based on CT-scan of the patient, using three dimensional printer. The use of modular carbon fiber implant has not leaded to any mechanical complications in the short and long term follow-up. In addition, due to radiolucent nature of this implant and less artifact production on CT and MRI, tumor relapse may be diagnosed and addressed earlier in compare with other implants, which has a paramount importance in these group of patients. We did not observe any implant failure using titanium cages. However, tumor relapse identification may be delayed due to metal artifacts on imaging modalities. Custom- made implants are economically more affordable and may be a good alternative choice for modular carbon fiber implants. The biocompatibility of the titanium make it a good choice for reconstruction of the defect when combined with bone graft allograft or autograft. Custom made cages theoretically can reproduce patients own biomechanics but should be studied with longer follow-up

Summary. Metastatic spinal disease is a common entity of much debate in terms of ideal surgical treatment. The introduction of MIS can be a game-changer in the treatment of MSD due to less peri-operative morbidity and allowing earlier radiotherapy and/or chemotherapy. Introduction. Less invasive techniques have always been welcome for management of patients with ‘Metastatic Spinal Disorders’. This is because these patients can be poor candidates for extensive / major invasive surgery even though radiologically, there may be an indication for one. The aim of the treatment with Minimal Invasive Fixation (MIS) systems is mainly for ‘pain relief’ than to radically decrease tumour burden or to achieve near total spinal cord decompression, which could be major presentations in these patients. These procedures address the ‘spinal instability’ very well and they can address pain associated with compression fractures resulting from metastatic disease from a solid organ as well as multiple myeloma with minimal complications. These procedures can be combined with radiology and chemotherapy without much concern for wound problems in the way of infection or dehiscence. They also have a great advantage of timing of adjunct therapy closer to the index procedure. The disadvantage, however, are they do not allow thorough decompression of the spinal cord. There could also be problem in addressing patients who have severe vertebral height loss or loss of integrity of the anterior column where anterior column reconstruction may be required. There is a risk of inadequate fixation or implant loosening or failure. We aim to examine the results of MIS surgery in our department and support the rationale for its use. Patients and Methods. We prospectively collected data of patients who underwent MIS posterior instrumentation for MSD. Between June 2011 and December 2012, 10 patients presented with acute motor deficit, instability and/or threatening radiological features. Effectiveness of MIS was assessed in terms of operative parameters and clinical outcomes. Results. No patient suffered intra-operative complications. The median surgical time was 198 minutes (range: 149 – 403), median blood loss was 100 ml (range: 60 – 400). All patients maintained full neurological function and reported effective pain reduction. All patients were discharged with a median hospital stay was 13 days (range: 4 – 45) post-surgery. 9 patients started oncological treatment as planned. The median time in 7 patients who had radiotherapy post-surgery was 23 days (range: 20 – 40). Chemotherapy was initiated in 4 patients at a median of 9 days post-surgery (range: 6 – 23). No patient as yet has required open procedure due to progression of the disease. Discussion/Conclusion. We have shown that satisfactory outcomes are achievable with MIS in a selected group of patients with MSD. While our results are limited by small study size, we have been able to improve patient quality of living through minimally invasive intervention. By reducing surgical morbidity and enabling early implementation of oncological treatment, MIS has the potential to re-evaluate multi-disciplinary decision making for early surgery in MSD

Summary. This is the first ever study to report the successful elimination of malignant cells from salvaged blood obtained during metastatic spine tumour surgery using a leucocyte depletion filter. Introduction. Catastrophic bleeding is a significant problem in metastatic spine tumour surgery (MSTS). However, intaoperative cell salvage (IOCS) has traditionally been contraindicated in tumour surgery because of the theoretical concern of promoting tumour dissemination by re-infusing tumour cells into the circulation. Although IOCS has been extensively investigated in patients undergoing surgery for gynaecological, lung, urological, gastrointestinal, and hepatobiliary cancers, to date, there is no prior report of the use of IOCS in MSTS. We conducted a prospective observational study to evaluate whether LDF can eliminate tumour cells from blood salvaged during MSTS. Patients & Methods. After Institutional Review Board (IRB) approval, 21 consecutive patients with metastatic spinal tumours from a known epithelial primary (defined as originating from breast, prostate, thyroid, renal, colorectal, lung, nasopharyngeal) who were scheduled for MSTS were recruited with informed consent. During surgery, a IOCS device (Dideco, Sorin Group, Italy) was used to collect shed blood from the operative field. Salvaged blood was then passed through a leucocyte depletion filter (RS1VAE, Pall Corporation, UK). 15-ml specimens of blood were taken from each of three consecutive stages: (i) operative field prior to cell saver processing (Stage A); (ii) transfusion bag post-cell saver processing (Stage B); (iii) filtered blood after passage through LDF (Stage C). Cell blocks were prepared by the pathology department using a standardised laboratory protocol. From each cell block, 1 haematoxylin and eosin (H&E) slide, and 3 slides each labelled with one of the following monoclonal mouse cytokeratin antibodies AE1/3, MNF 116 and CAM 5.2 were prepared. The cytokeratin antibodies are highly sensitive and specific markers to identify tumour cells of epithelial origin. These slides were read by one of two consultant pathologists who were provided full access to information on operative notes, but were blinded to the actual stages from which the slides were derived. Results. One case was excluded when the final diagnosis was revised to infection instead of metastatic spine tumour. Of the remaining cases, 7/21 tested positive for tumour cells in Stage A, 2 positive in Stage B. No specimen tested positive for tumour cells in Stage C. In 5 cases, posterior instrumentation without tumour manipulation was performed. Discussion/Conclusion. In this first-ever study of cell saver use in spine tumour surgery, we prove that leucocyte-depletion filters (LDF) can effectively eliminate tumour cells from blood salvaged during MSTS. It is now possible to conduct a clinical trial to evaluate IOCS-LDF use in MSTS. Our results are consistent with published results of similar studies performed on IOCS and LDF use outside the field of orthopaedic surgery. Spinal metastases originate from a myriad of primary cancers across various organ systems. If LDF can remove tumour cells from blood salvaged during surgery for spinal metastasis of different histological origin, then the finding can likely be extrapolated to several other fields of surgery where IOCS and LDF have not yet been attempted such as: neurosurgery, otolaryngology and general musculoskeletal oncology. Our results form a proof-of-concept for a paradigm shift in thinking regarding autotransfusion during spine tumour surgery

Summary. Pyogenic spondylodiscitis is an uncommon but severe spinal infection. In majority of cases treatment is based on intravenous antibiotics and rigid brace immobilization. Posterior percutaneous spinal instrumentation is a safe alternative procedure in relieving pain, preventing deformity and neurological compromise. Introduction. Pyogenic spondylodiscitis (PS) is an uncommon but severe spinal infection. Patients affected by a non-complicated PS and treatment is based on intravenous antibiotics and rigid brace immobilization with a thoracolumbosacral orthosis (TLSO) suffices in most cases in relieving pain, preventing deformity and neurological compromise. Since January 2010 we started offering patients percutaneous posterior screw-rod instrumentation as alternative approach to TLSO immobilization. The aim of this study was to evaluate safety and effectiveness of posterior percutaneous spinal instrumentation for single level lower thoracic (T9-T12) or lumbar pyogenic spondylodiscitis. Materials and Methods. Retrospective cohort analysis on 27 patients diagnosed with PS who were offered to choose between 24/7 TLSO rigid bracing for 3 to 4 months and posterior percutaneous screw-rod instrumentation bridging the infection level followed by soft bracing for 4 weeks after surgery. All patients underwent antibiotic therapy. Fifteen patients chose conservative treatment, 12 patients chose surgical treatment. Patients were seen at 1, 3, 6, 9 months after diagnosis. Erythrocyte sedimentation rate (ESR), C-reactive protein (CRP) and complete blood count were measured at each follow-up visit. Segmental kyphosis was measured at diagnosis and at 9 months. VAS, SF-12, and EQ-5D questionnaires were recorded at each follow-up visit. Baseline groups’ demographic characteristics were assessed using independent sample t-tests for continuous variables and χ2 tests for frequency variables. Results. Complete healing was achieved in all patients, no difference was observed in healing time between the two groups (77.3±7.2 days vs 80.2±4.4). Instrumentation failure and screw loosening was not observed in any patient. In both group CRP and ESR decreased accordingly with response to antibiotic therapy. Surgically treated patients had significantly lower VAS scores at 1 month (3.05±0.57 in surgery group vs 5.20±1.21 in TLSO group) and 3 months (2.31±0.54 in surgery group vs 2.85±0.55 in TLSO group) post-diagnosis. Both groups had similar trends toward fast recovery in both mental (MCS) and physical components (PCS) of SF-12 questionnaire, surgically treated patients showed steeper and statistically significative improvement at 1 month (37.83±4.57 MCS in surgery group vs 24.52±3.03 MCS in TLSO group and 35.46±4.43 PCS in surgery group vs 27.07±4.45 PCS in TLSO group, p<0.001), 3 months (52.94±3.82 MCS in surgery group vs 39.45±4.92 MCS in TLSO group and 44.93±3.73 PCS in surgery group vs 35.33±6.44 PCS in TLSO group, p<0.001), and 6 months (54.93±3.56 MCS in surgery group vs 49.99±5.82 MCS in TLSO group) post-diagnosis, no statistically significant differences were detected at the other time points (9 months post-diagnosis). EQ-5D index was significantly higher in surgery patients at 1 month (0.764±0.043 in surgery group vs 0.458±0.197 in TLSO group) and 3 months (0.890±0.116 in surgery group vs 0.688±0.142 in TLSO group); no statistically significant changes were observed in segmental kyphosis between the two groups. Conclusion. Posterior percutaneous spinal instrumentation is a safe, feasible, and effective procedure in relieving pain, preventing deformity and neurological compromise. Surgical stabilization was associated with faster recovery, lower pain scores, and improved quality of life compared with TLSO conservative treatment at 1 and 3 months after diagnosis