An increasingly used treatment for end-stage ankle osteoarthritis is total ankle replacement (TAR). However, implant loosening and subsidence are commonly reported complications, leading to relatively high TAR failure rates. Malalignment of the TAR has often been postulated as the main reason for the high incidence of these complications. It remains unclear to what extent malalignment of the TAR affects the stresses at the bone-implant interface. Therefore, this study aims to elucidate the effect of TAR malalignment on the contact stresses on the bone-implant interface, thereby gaining more understanding of the potential role of malalignment in TAR failure.

FE models of the neutrally aligned as well as malaligned CCI Evolution TAR implant (Van Straten Medical) were developed. Separate models were developed for the tibial and talar segment, with the TAR components in neutral alignment and 5° and 10° varus, valgus, anterior and posterior malalignment, resulting in a total of 9 differently aligned TAR models. Loading conditions of the terminal stance phase of the gait cycle, when the force on the ankle joint is highest (5.2x body weight), were applied. Peak and mean contact pressure and shear stress at the bone-implant interface were analyzed. Also, stress distributions on the bone-implant interface were visualized.

In the neutrally aligned tibial and talar TAR models, peak contact pressures of respectively 98.4 MPa and 68.2 MPa, and shear stresses of respectively 49.3 MPa and 39.0 MPa were found. TAR malalignment increases peak contact pressure and shear stress on the bone-implant interface. A maximum peak contact pressure of 177 MPa was found for the 10° valgus malaligned tibial component and the highest shear stress found was 98.5 MPa for the 10° posterior malaligned talar model.

Upon TAR malalignment contact stresses increase substantially, suggesting that proper orientation of the TAR is needed to minimize peak stresses on the bone-implant interface. This is in line with previous studies, which state that malalignment considerably increases bone strains, micromotion, and internal TAR contact pressures, which might increase the risk of TAR failure. Further research is needed to investigate the relationship between increased contact stresses at the bone-implant interface and TAR failure.

Malalignment is often postulated as the main reason for the high failure rate of total ankle replacements (TARs). Only a few studies have been performed to correlate radiographic TAR malalignment to the clinical outcome, but no consistent trends between TAR alignment parameters and the clinical outcome were found. No standard TAR alignment measurement method is present, so reliable comparison between studies is difficult. Standardizing TAR alignment measurements and increasing measurable parameters on radiographs in the clinic might lead to a better insight into the correlation between malalignment and the clinical outcome. This study aims to develop and validate a tool to semi-automatic measure TAR alignment, and to improve alignment measurement on radiographs in the clinic.

A tool to semi-automatically measure TAR alignment on anteroposterior and lateral radiographs was developed and used by two observers to measure TAR alignment parameters of ten patients. The Intraclass Coefficient (ICC) was calculated and accuracy was compared to the manual measurement method commonly used in the clinic.

The tool showed an accuracy of 76% compared to 71% for the method used during follow-up in the clinic. ICC values were 0.94 (p<0.01) and higher for both inter-and intra-observer reliability.

The tool presents an accurate, consistent, and reliable method to measure TAR alignment parameters. Three-dimensional alignment parameters are obtained from two-dimensional radiographs, and as the tool can be applied to any TAR design, it offers a valuable addition in the clinic and for research purposes.

Complications after spinal fusion surgery are common, with implant loosening occurring in up to 50% of osteoporotic patients. Pedicle screw fixation strength reduces as a result of decreased trabecular bone density, whereas sublaminar wiring is less affected by these changes. Therefore, pedicle screw augmentation with radiopaque sublaminar wires (made with Dyneema Purity® Radiapque fibers, DSM Biomedical, Geleen, the Netherlands) may improve fixation strength. Furthermore, sublaminar tape could result in a gradual motion transition to distribute stress over multiple levels and thereby reduce implant loosening. The objective of this study is to test this hypothesis in a novel experimental setup in which a cantilever bending moment is applied to individual human vertebrae.

Thirty-eight human cadaver vertebrae were stratified into four different groups: ultra-high molecular weight polyethylene sublaminar tape (ST), pedicle screw (PS), metal sublaminar wire (SW) and pedicle screw reinforced with sublaminar tape (PS+ST). The vertebrae were individually embedded in resin, and a cantilever bending moment was applied bilaterally through the spinal rods using a universal material testing machine. This cantilever bending setup closely resembles the loading of fixators at transitional levels of spinal instrumentation.

The pull-out strength of the ST (3563 ± 476N) was not significantly different compared to PS, SW or PS+ST. The PS+ST group had a significantly higher pull-out strength (4522 ± 826N) compared to PS (2678 ± 292N) as well as SW (2931 ± 250N).

The higher failure strength of PS + ST compared to PS indicates that PS augmentation with ST may be an effective measure to reduce the incidence of screw pullout, even in osteoporotic vertebrae. Moreover, the lower stiffness of sublaminar fixation techniques and the absence of damage to the cortices in the ST group suggest that ST as a stand-alone fixation technique in adult spinal deformity surgery may also be clinically feasible and offer clinical benefits.

Novel biomaterials are being developed and studied, intended to be applied as bone graft substitute materials. Typically, these materials are being tested in in vitro setups, where among others their cytotoxicity and alkaline phosphatase activity (as a marker for osteoblastic differentiation) are being evaluated. However, it has been reported that in vitro tests correlate poorly with in vivo results and therefore many promising biomaterials may not reach the clinic as a bone graft substitute product. One of the reasons for the poor correlation, may be the minimal complexity of the in vitro tests, as compared to the in vivo environment. Ex vivo models, mimicking the natural tissue environment whilst maintaining control of culture parameters, may be a promising alternative to assess biomaterials for bone formation. Assess the possibility of an ex vivo culture platform to test biomaterials on their potential to stimulate new bone formation. Osteochondral plugs (cylinders n=10, Ø 10 mm, height 15 mm) were drilled from fresh porcine knees, from the slaughterhouse. A bone defect (Ø 6 mm) was created and which was filled with a biomaterial graft (S53P4 bioactive glass (n=3); collagen sponges loaded with BMP-2 (n=3, as positive control)) or kept empty (n=4). The explants were cultured in custom-made two-chamber bioreactors for six weeks (LifeTec Group BV). Cartilage and bone were physically separated, similar to the in vivo situation, by a sealing ring. The two tissues were cultured in separate compartments, allowing for specific culture medium for each tissue. Medium was changed every 2–3 days and weekly micro computed tomography (µCT) images were obtained to longitudinally monitor the formation of new bone. An MTT assay was performed on half of the samples after six weeks of culture. The other samples were fixed for histology, to determine which cells were present after six weeks. The MTT metabolic assay showed that a number of cells in the bone were viable after six weeks. The further away from the border, the fewer living cells were observed. The cells in the cartilage also survived. No significant bone formation was observed with µCT in either of groups, even though abundant bone formation was expected in the BMP-2 group. Explanations of the negative results of the positive group might be that too few viable cells remain after six weeks, or that the cells that are still present are not able to form bone. No significant bone formation was observed in the bone defects in osteochondral explants that were cultured with, or without, biomaterials for six weeks. However, the platform showed that it is capable to successfully culture osteochondral explants for six weeks.

Histology needs to be performed to evaluate which cells were present at the end of the culture and this will be compared to the cells present directly after drilling the explants.

INTRODUCTION

Growth-guidance constructs are an alternative to growing rods for the surgical treatment of early onset scoliosis (EOS). In growth-guidance systems, free-sliding anchors preserve longitudinal spinal growth, thereby eliminating the need for surgical lengthening procedures. Non-segmental constructs containing ultra-high molecular weight polyethylene (UHMWPE) sublaminar wires have been proposed as an improvement to the traditional Luque trolley. In such a construct, UHMWPE sublaminar wires, secured by means of a knot, serve as sliding anchors at the proximal and distal ends of a construct, while pedicle screws at the apex prevent rod migration and enable curve derotation. Ideally, a construct with the optimal UHMWPE sublaminar wire density, offering the best balance between providing adequate spinal fixation and minimizing surgical exposure, is designed preoperatively for each individual patient. In a previous study, we developed a parametric finite element (FE) model that potentially enables preoperative patient-specific planning of this type of spinal surgery. The objective of this study is to investigate if this model can capture the decrease in range of motion (ROM) after spinal fixation as measured in an experimental study.

Background

Bio-Active Glass (BAG) is a promising bone graft substitute for large bone defect reconstruction because of its favourable osteoconductive, antibacterial and angiogenic properties. Potentially, it could also mechanically reinforce the defect, thus making it suitable for load-bearing defects. However, the mechanical properties of the reconstructive layer consisting of BAG/bone allograft mixtures are unknown. The goals of this study therefore were, first, to measure the mechanical properties of different BAG/bone graft mixtures and, second, to investigate to what extent such mixtures could reinforce distal tibial defects using micro-FE analysis and high-resolution CT scans.

Background

Implant stability and is an important factor for adequate bone remodelling and both are crucial in the long-term clinical survival of total hip arthroplasty (THA). Assessment of early bone remodelling on X-rays during the first 2 years post-operatively is mandatory when stepwise introduction of a new implant is performed. Regardless of fixation type (cemented or cementless), early acetabular component migration is usually the weakest link in THA, eventually leading to loosening. Over the past years, a shift towards uncemented cup designs has occurred. Besides the established hydroxyapatite (HA) coated uncemented cups which provide ongrowth of bone, new uncemented implant designs stimulating ingrowth of bone have increased in popularity. These cups initiate ingrowth of bone into the implant by their open metallic structure with peripheral pores, to obtain a mechanical interlock with the surrounding bone, thereby stabilising the prosthesis in an early stage after implantation. This retrospective study assessed bone remodelling, osseointegration and occurrence of radiolucency around a new ingrowth philosophy acetabular implant.

Background

Finite element (FE) models have become a standard pre-clinical tool to study biomechanics of spine and are used to simulate and evaluate different strategies in scoliosis treatment: examine their efficacy as well as the effect of different implant design parameters. The goal of this study is to investigate, in a system of rods and laminar wires, the effect of the number of wires and their pre-stress on whole spine stiffness.

Chronic osteomyelitis is historically treated in a two stage fashion with antibiotic-loaded polymethylmethacrylate (PMMA) as local antibacterial therapy. However, two-stage surgeries are associated with high morbidity, long hospitalization and high treatment costs. In recent years new biomaterials were developed that allow to change this treatment algorithm. S53P4 bioactive glass is such a novel biodegradable antibacterial bone graft substitute that enables a one-stage surgery in local treatment of chronic osteomyelitis. This study aimed to explore the eradication of infection and bone healing capacities of S53P4 bioactive glass in clinical practice.

In this prospective longitudinal outcome study, clinical applicability of S53P4 bioactive glass in treatment of patients with chronic osteomyelitis was assessed. All patients with clinically, haematologically and radiologically evident chronic osteomyelitis were included. All patients were treated with an extensive debridement surgery, S53P4 bioactive glass implantation and systemic antibiotic administration. Primary endpoint of this study is eradication of infection. During follow-up eradication was analysed based on clinical outcomes, blood samples (inflammatory parameters) and radiological outcomes. The secondary endpoint, bone healing, is assessed using conventional radiographic images of the treated region.

Between 2011 and 2016, 25 patients were included in this study, with a mean follow-up of 23 months (range 4 – 57). Hospital stay was short with a mean of 18 days (range 4 – 40) and patients required an average of 1,4 surgeries (range 1 – 4). The inflammatory parameter C-reactive protein (CRP) showed a normalization after a mean duration of 46 days (range 0 – 211). At the end of follow-up haematological and clinical outcomes showed eradication of infection in 24 (96%) of all patients. Radiologically none of all patients showed persisting signs of infection and bone healing was observed in 22 (88%) patients based on changes on conventional radiographic images. One patient had a persistent infection without any bone healing, this patient had an infected non-union prior to surgery. There were two other patients with an initial infected non-union fracture which was not consolidated at last follow-up, although they had successful infection treatment. Another patient had a femoral fracture after surgery that needed additional surgery which did not interfere with eradication of infection. Four (16%) of all patients had initial wound healing problems related to compromised skin and/or soft tissue prior to surgery.

Based on the results of our clinical experience, S53P4 bioactive glass can successfully be used in a one-stage procedure for treatment of chronic osteomyelitis. Eradication of infection was successful in almost all patients and so far no patients required a second surgery due to infection recurrence. Bone healing (incorporation of the bioactive glass) was seen in all patients except for the patients with an initial infected non-union fracture. As a consequence of these results, we changed our institutional protocol for treatment of chronic osteomyelitis to a one-stage approach instead of a two-step approach.

Total ankle replacement (TAR) is increasingly used in the treatment of end-stage ankle arthropathy, but much debate exists about the clinical result. The goals of present study are: 1) to provide an overview of the clinical outcome of 58 TAR's in a single centre and 2) to assess the association between radiological characteristics and clinical outcome.

We reviewed a prospective included cohort of 58 TAR's in 54 patients with a mean age of 66.9 (range 54–82) and a mean follow-up of 21.6 months (range 1.45–66.0). The TAR's where performed by a single surgeon in a single centre (MUMC) between 2010 and 2015, using the CCI ankle replacement. A standard surgical protocol and standardized post-op rehabilitation was used. Patients were followed-up pre-op and at 1 day, 6 weeks, 3–6–12 months and yearly thereafter post-op. The AOFAS and range of motion (ROM) were assessed and all complications, re-operations and the presence of pain were recorded. Radiographic assessment consisted of the estimation of prosthesis alignment, migration, translation and radiolucent lines using the Rippstein protocol (1). The clinical outcome was compared with a systematic review of TAR outcome.

Ten intra-operative complications occurred and 9 were malleolar fractures. Post-operative complications occurred in 20 out of the 54 patients (37.0%). Impingement (5/54 patients), deep infection (4/54 patients), delayed wound healing (3/54 patients) and minor nerve injuries (3/54 patients) were the most frequently recorded. 18 patients (31.0%) underwent one or more re-operations and 12 of these 18 patients underwent a component revision (mostly the PE insert) or a conversion to arthrodesis. Despite the complications and revisions, the functional outcome improved. Radiologically 15.8% of the TAR's were positioned in varus and 1.8% in valgus. Migration in the frontal and sagittal plane is seen in 3 and 2 TAR's respectively. Radiolucency is significantly increasing with the follow-up time (p=0.009). Migration in the frontal plane is significantly associated with conversion to arthrodesis (p=0.005) and migration in the sagittal plane to revision of a component or conversion to arthrodesis (p=0.04). Finally, pain is significantly associated with re-operations (p=0.023) and complications (p=0.026). Remarkable is that the clinical outcome is independent of the direct post-op alignment of the TAR.

The complication-, re-operation and revision or conversion to arthrodesis rates makes the clinical outcome of TAR still questionable favourable. Especially the complication and re-operation incidences are greater than found in the systematic review. However, it is remarkable that the minor complications and re-operations not related to the TAR are not often mentioned in the literature. Radiographic characteristics could be of value in predicting this clinical outcome and thereby influence the post-operative handling. In conclusion, our results show relatively high incidences of complications (37.0%) and re-operations (31.0%) when minor complications and re-operations are included. TAR clinical outcome can be predicted by radiographic migration characteristics and pain.

INTRODUCTION

Surgical correction of spinal deformities in the growing child can be applied with or without fusion. Sublaminar wiring, first described by Luque, allows continuation of growth of the non-fused spine after correction of the deformity. Neurological complications and wire breakage are the main clinical problems during the introduction and removal of currently used sublaminar wires. In this pilot study a posterior hybrid construction with the use of a medical-grade UHMWPE (Dyneema Purity®) sublaminar wire was assessed in an ovine model. We hypothesized that such a hybrid construction can safely replace current titanium laminar wires, while providing sufficient stability of the non-fused spinal column with preservation of growth.

Introduction: Ponseti and Friedman suggest that curve type is genetically determined and that curve types do not change throughout its course. In current clinical practice scoliosis is seen as a more dynamic process. Therefore we like to postulate that the natural history of idiopathic scoliosis can change during growth when left untreated.

Aim of the Study: This study focused on the shift of curve patterns as result of age, especially in patients younger than ten years. It was assessed whether age is a factor in the dynamic progression of idiopathic scoliosis. We evaluated patients records as well as radiographic images and clinical measures.

Materials and Methods: 48 Patients with idiopathic scoliosis who visited the scoliosis team between 1990 and 2007 were included. The criteria for inclusion were a curve less than 30° and not treated with brace or operative procedures. Curve pattern changes were classified according to the Scoliosis Research Society classification and the Lenke classification.

Results: The forty-eight patient records demographics consisted of eleven males and thirty-seven females. Their mean age at the start of follow-up was 11,2 years (range 4–17). Mean follow-up lasted 3,4 years (range 1–11,2). Thirteen patients were diagnosed with juvenile idiopathic scoliosis and thirty-five patients were diagnosed with an adolescent idiopathic scoliosis. Eight from the forty-eight patients, showed curve pattern changes according the SRS classification: six females and two males. Six of the thirtteen patients with juvenile scoliosis showed a shift of the scoliosis curves (46%). Two of the thirty-five patients with the adolescent scoliosis showed a shift of the scoliosis curves (6%; p< 0,05).

In eleven patients with juvenile scoliosis(84,6%) there was a shift in the Lenke classification, while this only occurred in eighttteen patients with adolescent scoliosis(51,4%) (p< 0,05). No curve pattern changes occurred in two patients with juvenile idiopathic scoliosis(15,4%) and in twelve patients of the adolescent idiopathic scoliosis(34,3%) (p< 0,05).

Conclusion: There is evidence that idiopathic scoliosis has an genetic origin, but not all elements of the scoliosis formation can be explained. We found changes in curve patterns which suggest that idiopathic scoliosis is not a fixed deformity, but a dynamic process especially in patients younger than 10 years.

Introduction: The aim of this study was to compare the clinical, radiological and functional outcome results of the Scorpio PS TKA prosthesis with either a mobile (MB) or fixed bearing (FB) Pe insert. We hypothesized that the MB group would perform better over time in clinical and functional outcome as well as showing a reduction in anterior knee pain occurrence.

Methods: In a prospective, randomised, single centre, multi surgeon clinical study, a total of 100 patients were enrolled equally divided between MB and FB groups. A standard surgical protocol was used for implanting the Scorpio knee prosthesis with either an MB or FB insert. Post-op rehabilitation was standardized and unrelated to insert type. Patients were assessed pre-op and after 3–6-12–24 months post-op. RAND-36 and Knee Society Score (KSS), were assessed as well as pain measurement during functional testing (chair rise and stair climb) using Visual Analogue Scale (VAS) scale. X-rays were assessed for implant positioning, migration, radiolucent lines and patella tilt (using a Skyline view in 30–60 and 90 degrees).

Results: Both tests groups showed a statistical significant decrease of VAS pain score over time (p < 0.01). No significant differences were seen between both groups at any time point. results did show the MB group to have less pain the first postoperative year in both chair rise test and stair climb test tests. No statistically significant differences were found in total range of motion between the two groups. Repeated measures tests showed a significant improvement over time for both groups for KSS and most RAND 35 subscores. There were no significant differences between groups at any given follow up moment. Within 8 out of 9 RAND 36 subdivisions showed the MB group to score non significantly better the first postoperative year. After one year the differences disappeared. Radiology showed stable implants with no progressive radiolucent lines in all patients. No significant differences in patellar tilting were found.

Discussion: Our hypothesis, that the MB prostheses would provide a better ROM and less anterior knee pain, was not confirmed by the results. In our study the MB group showed less decrease in ROM immediately postop. This phenomenon was also seen by Harrington et al. The MB prosthesis regained its ROM after surgery earlier than the FB implants. This difference could potentially be attributed to the implant design and its kinematics. This advantage did not persist and the FB group slowly leveled. In conclusion, our study does not show any clear advantages in terms of function, pain, ROM, general health, radiological evaluation, KSS and RAND 36 of MB compared with FB TKA at a follow-up of 2 years.

Introduction: The purpose of this study was to evaluate the long-term clinical and radiological outcome of instrumented femoral revisions after failed total hip arthroplasties using the impaction bone grafting technique with morsellized bone chips in combination with a cemented polished stem.

Methods: Thirty-three consecutive femoral reconstructions were performed between November 1991 and February 1996 using the X-Change femoral impaction system with fresh frozen morsellized bone grafts and a cemented polished Exeter stem. All patients were prospectively followed. The learning curve with this new technique is included in this report. This technique was used in twenty-four women and nine men; the average age at surgery was sixty-three years (range 33–82). Femoral bone stock defects were classified according to the Endoklinik classification as grade 1 in three hips, grade 2 in fourteen hips, grade 3 in twelve hips and grade 4 in four hips. At a minimal eight years follow-up no patient was lost to follow-up, but eight patients died (at 0.5, 3.5, 3.5, 7.0, 7.0, 7.5 and 9.0 after reconstruction). All were followed until death, none of these deaths was related to the surgery, and none had a re-revision

Results: No femoral reconstruction was re-rerevised at a mean follow-up of 10.4 years (range 8 to 13 years). However, there were three femoral fractures during follow-up (at 3, 6 and 22 months), all at the level of tip of the prostheses. All healed after plating, all femoral implants were left in situ. The average Harris hip score improved from 49 prior to surgery to 85 at review (68–100). The average migration of the stem within the cement mantle was three mm (0–14 mm), most migration was seen in the first year. Radiologically, there were no failures. With an endpoint of femoral revision for any reason, with endpoint aseptic loosening or with endpoint radiological loosening the survival rate using the Kaplan-Meier analysis was hundred per cent in all situations (one-sided 95% C.I. 100–91.3 %)

Conclusions Femoral revision using bone impaction grafting with fresh frozen bone grafts and a cemented polished stem showed an excellent survival at eight to thirteen years follow-up.

Aims: The effects of bone graft washing and bone graft particle size on initial cup stability in an acetabular model were studied. Methods: From fresh human femoral heads large (8–12 mm) and small (2–4) grafts were produced. Four different groups were tested; large washed, large unwashed, small washed and small unwashed. An AAOS type 3 combined defect was reconstructed in a synthetic acetabular model using a metal mesh and screws. Bone grafts were impacted in a standardized way using a hammer and metal impactors. Cement was pressurized and a PE cup was inserted. Cups were dynamically loaded with 1500 N and 3000 N for 15 minutes using an MTS-device, RSA was used to calculate 3-D cup migrations. Next a lever-out test of the cup was done in a displacement (16¡/minute) controlled test. After testing CT scans of the cups were made to quantify cement layer roughness, as a measurement of cement penetration. Results: Cups reconstructed with large washed bone grafts migrated signiþcantly less during mechanical compression and withstood signiþcantly higher lever-out moments. Washing improved cup stability for both small and large grafts, however only signiþcantly for the larger bone grafts. A signiþcantly higher cement penetration depth was found for all large bone grafts, washing did not inßuence cement penetration depth. Discussion: For acetabular revisions with bone impaction grafting we recommend to use large washed bone grafts.