Introduction. The combined incubation of a composite scaffold with bone marrow stromal cells in a perfusion bioreactor could make up a novel hybrid graft material with optimal properties for early fixation of implant to bone. The aim of this study was to create a bioreactor activated graft (BAG) material, which could induce early implant fixation similar to that of allograft. Two porous scaffold materials incubated with cells in a perfusion bioreactor were tested in this study. Methods and Materials. Two groups of 8 skeletally mature female sheep were anaesthetized before aspiration of bone marrow from the iliac crest. For both groups, mononuclear cells were isolated, and injected into a perfusion bioreactor (Millenium Biologix AG, Switzerland). Scaffold granules Ø∼900–1500 μm, ∼88% porosity) in group 1, consisted of hydroxyapatite (HA, 70%) with -tricalcium-phosphate (−TCP, 30%) (Danish Technological Institute, Denmark). The granules were coated with poly-lactic acid (PLA) 12%, in order to increase the mechanical strength of the material (Phusis, France). Scaffold granules Ø∼900–1400 μm, 80% porosity) in group 2 consisted of pure HA/-TCP (Fin Ceramica, Italy). For both groups, cells were incubated in the bioreactor for 2 weeks. Fresh culture medium supplemented with dexamethasone and ascorbic-acid was added every third or fourth day. Porous titanium alloy implants with diameter=length=10mm (Biomet, USA) were inserted bilaterally in each of the distal femurs of the sheep; thus 4 implants in each sheep. The concentric gap (2 mm) surrounding the implant was filled with 1) BAG (autogenous), 2) granules, 3) granules+bone marrow aspirate (BMA, autologous) or 4) allograft. The sheep were euthanized after 6 weeks. Distal femurs were removed and implant-bone samples were divided in two parts. The superficial part was used for mechanical testing and micro-CT scanning, and the profound part for histomorphometry. Push-out tests were performed on an 858 Bionix MTS hydraulic materials testing machine. Shear mechanical properties between implant and newly generated bone were calculated to assess implant fixation. Results were assessed by One-way ANOVA. P-values less than 0.05 were considered significant. Results. One sheep in group 1 had to be euthanized after 4 weeks (excluded). One implant in each group was loosened and could not undergo push-out test (excluded). Group 1: No significant differences regarding failure energy (kJ/m2, p=0.44) or ultimate shear strength (MPa, p=0.17) could be seen. Shear stiffness (MPa) was significantly higher for the allograft group (p=0.04). Group 2: No significant differences regarding failure energy (p=0.11) or shear stiffness (p=0.52) could be seen. Ultimate shear strength was significantly higher for allograft (p=0.04). Results from μ-CT scanning and histomorphometry are pending. Discussion and Conclusion. The present study shows a possible effect of bioreactor activated bone substitute on early implant fixation. We are currently working on bone microarchitecture surrounding implant and histomorphometry. These results will aid in determining if BAG could make up a promising alternative for allograft as bone graft material

Objectives. Osteochondral injuries, if not treated adequately, often lead to severe osteoarthritis. Possible treatment options include refixation of the fragment or replacement therapies such as Pridie drilling, microfracture or osteochondral grafts, all of which have certain disadvantages. Only refixation of the fragment can produce a smooth and resilient joint surface. The aim of this study was the evaluation of an ultrasound-activated bioresorbable pin for the refixation of osteochondral fragments under physiological conditions. Methods. In 16 Merino sheep, specific osteochondral fragments of the medial femoral condyle were produced and refixed with one of conventional bioresorbable pins, titanium screws or ultrasound-activated pins. Macro- and microscopic scoring was undertaken after three months. . Results. The healing ratio with ultrasound-activated pins was higher than with conventional pins. No negative heat effect on cartilage has been shown. Conclusion. As the material is bioresorbable, no further surgery is required to remove the implant. MRI imaging is not compromised, as it is with implanted screws. The use of bioresorbable pins using ultrasound is a promising technology for the refixation of osteochondral fractures

The osteointegration of a new three-dimensional reticular titanium material, Trabecular Titanium™, was assessed using a bilateral cancellous (distal femur, proximal tibia) and cortical (tibia diaphysis) bone drill hole model in 18 sheep. TT is a novel Ti6Al4V material characterized by a high open porosity and composed of multi-planar regular hexagonal cells. Two 5.0 mm diameter, 12 mm long cylinders (TT1 & TT2) of two different porosities (TT1:650 μm, TT2:1250 μm) were tested and compared to two solid predicate 5.0 mm diameter, 12 mm long Ti cylinders (PT1 & PT2) coated with porous Ti (PT1: vacuum-plasma spray coating; PT2: inert-gas shielding arc spray coating). Each implant type was surgically implanted at 4 separate locations in each sheep (16 implants per sheep). Three timepoints of 4, 16 and 52 weeks (n=6 sheep per timepoint) were used. Bone-implant interface was analyzed ex vivo by the determination of: 1) the shear strength (SS) measured during a push out test, 2) the percentage of bone in-growth (%B) using histomorphometry, 3) the bone apposition rate using fluorochrome labelling analysis and 4) the bone-implant contact using backscattered scanning electron microscopy (SEM). An ANOVA with a Bonferroni Post hoc test were used to detect differences between tested and predicate implants. P values 0.05 were considered significant. At 4 weeks, 5 out of the 6 TT1 could be pushed out of the cortical bone (COB) samples. The remaining TT1 collapsed during testing. All TT1 could be pushed of the cancellous bone (CAB) samples. Four out of the 6 TT2 could be pushed out of CAB and of the COB samples. At 16 and 52 weeks, only one TT1 and one TT2 could be pushed out of the bone samples, the remaining implants collapsed during testing. All the PTs were successfully pushed out at all timepoints. The mean %B of PT1 and PT2 did not significantly increase over time. For both materials, the mean %B ranged between 1.7% and 4.4% at 4 weeks and between 5.7% and 6.5% at 52 weeks. The mean %B of TT1 significantly increased over time in both COB (10.2% at 4 weeks, 46.2% at 16 weeks, 50.5% at 52 weeks) and CAB (5.8%, 23.9%, 24.3%). Similarly, the mean %B of TT2 significantly increased over time in both COB (7.8%, 48.6%, 65%) and CAB (4.5%, 24.1%, 38.6%). Bone apposition rates for the TT implants remained superior to 2 μm/day for the entire duration of the study. SEM showed an intimate bone-implant contact for all implant types at all timepoints. At 16 and 52 weeks, histomorphometry revealed an extensive osteointegration of the TT specimens. Bone-implant interface strength was so high for the TT implants that they could not be pushed out of the bone samples. The results of this study would indicate that the TT implants provide a good scaffold for bone in-growth

Kirschner wires are commonly used in paediatric fractures, however, the requirement for removal and the possibility of pin site infection provides opportunity for the development of new techniques that eliminate these drawbacks. Bioabsorbable pins that remain in situ and allow definitive closure of skin at the time of insertion could provide such advantages. Three concurrent studies were performed to assess the viability of bioabsorbable pins across the growth plate. (1) An epidemiological study to identify Kirschner wire infection rates. (2) A mechanical assessment of a bioabsorbable pin compared to Kirschner wires in a simulated supracondylar fracture. (3) The insertion of the implants across the physis of sheep to assess effects of the bioabsorbable implant on the growth plate via macroscopic, pathohistological and micro-CT analysis. An infection rate of 8.4% was found, with a deep infection rate of 0.4%. Mechanically the pins demonstrated comparable resistance to extension forces (p=) but slightly inferior resistance to rotation (p=). The in vivo component showed that at 6 months: there was no leg length discrepancy (p=0.6), with micro-CT evidence of normal physeal growth without tethering, and comparable physeal width (p=0.3). These studies combine to suggest that bioabsorbable pins do not represent a threat to the growth plate and may be considered for physeal fracture fixation

Single focal grade IV cartilage lesion in the knee has a poor healing capacity. Instead these lesions often progress to severe and generalized osteoarthritis that may result in total knee replacement. Current treatment modalities aim at biological repair and, although theoretically appealing, the newly formed tissue is at the best cartilage-like, often fibrous or fibrocartilaginous. This at the expense of sophisticated laboratory resources, delicate surgery and strict compliance from patients. An alternative may be small implants of biomaterial inserted to replace the damaged cartilage. We investigated the response of the opposing tibia cartilage to a metallic implant inserted at different depth into the surrounding cartilage level. Methods. The medial femoral condyle of both knees of 12 sheep, 70–90kg, 2 year of age and from the same breeder, was operated. A metallic implant with an articulating surface of 316L stainless steel, diameter of 7mm, HA plasma sprayed press-fit peg and a tailored radius and contour to the sheep femoral condyle was placed at the most weight-bearing position. The level of the implant was aimed flush, 0,3 and 0,8 mm below surrounding cartilage. The animals were stabled indoors, allowed to move freely and euthanized after 6 and 12 weeks. Postoperatively the knees were high resolution photographed for macroscopic evaluation. The position and depth of the implant were analysed using a laser scan device. Tibial and femoral condyles specimen were decalcified and slices were prepared for microscopic evaluation. Implant position and cartilage damage was assessed from two independent observers using a macroscopic ICRS score and a modified histologic score according to Mankin. Results. 22 tibia condyles showed a variety of cartilage damage ranging from severe damage down to subchondral bone to an almost pristine condition. There was a strong correlation between implant position and damage to opposing cartilage surface. Mankin score correlated significantly with implant position (p<0.001 regression analysis, r. 2. =.45) as did the ICRS score (p<0.001, regression analysis, r. 2. =.67). Implants sitting proud were associated with poor Mankin score. There was no difference between 6-week and 3-months knees. Conclusion. By precise postoperative measurement we have shown that significant imprecision occur; this has never before been studied. We found a distinct correlation between implant position and cartilage damage. These results suggest that further studies of metallic implants, inserted into cartilage defects with the utmost precision regarding the surrounding cartilage, may be warranted

Aims

The modified Radiological Union Scale for Tibia (mRUST) fractures score was developed in order to assess progress to union and define a numerical assessment of fracture healing of metadiaphyseal fractures. This score has been shown to be valuable in predicting radiological union; however, there is no information on the sensitivity, specificity, and accuracy of this index for various cut-off scores. The aim of this study is to evaluate sensitivity, specificity, accuracy, and cut-off points of the mRUST score for the diagnosis of metadiaphyseal fractures healing.

Secondary fracture healing processes are strongly influenced by interfragmentary motion. Shear movement is assumed to be more critical than axial movement, however experimental results are controversial. Numerical fracture healing models allow to simulate the fracture healing process with variation of single input parameters and under comparable normalized mechanical conditions. Therefore, a direct comparison of different in vivo scenarios is possible. The aim of this study was to simulate fracture healing under several axial and shear movement scenarios and compare their respective time to heal. We hypothesize that shear movement is always more critical than axial loading. For the presented study, we used a corroborated numerical model for fracture healing in sheep. Numerous variations of the movement amplitude, the fracture gap size and the musculoskeletal loads were simulated for comparable axial compressive and shear load cases. In all simulated cases, axial compressive load had less inhibitory influences on the healing process than shear load. Therefore, shear loading is more critical for the fracture healing outcome in general. Thus, our findings suggest osteosynthesis implants to be optimized to limit shear movements under musculoskeletal loading

Introduction. ACL reconstruction using hamstring tendons has gained general acceptance. However, it has been recommended to seek a tight fit of the tendon in the bone canal in order to provide circumferential contact and healing of the graft, and to prevent secondary tunnel widening. Recent findings show, that the graft dynamically adapts to pressure in the canal resulting in a potentially loose graft-bone contact. It was the goal of this study to understand the viscoelastic behaviour of hamstring grafts under pressure and to develop a new method for tendon pre-conditioning to reduce the graft volume before implantation, in order to reduce the necessary bone canal diameter to accommodate the same graft. Material and Methods. Flexor digitorum tendons of calf and extensor digitorum tendons of adult sheep were identified to be suitable as ACL grafts substitutes for human hamstring tendons in vitro. The effect of different compression forces on dimensions and weight of the grafts were determined. Further, different strain rates (1mm/min vs 10mm/min), compression methods (steady compression vs. creep) and different compression durations(1, 5, 10min) 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 (25% of initial volume) reached a plateau at 6000N. 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. With a strain rate of 1mm/min no macroscopic destruction was documented, however with 10mm/min some parts were ruptured. During all pressure tests, considerable amounts of liquid were pressed out from the tendons, and if the graft was submersed in saline solution overnight, the volume reduction was mostly reversible. Conclusion. Compression reduces the dimensions of the ACL graft reversibly, to the greatest part by squeezing out of interstitial water. It is reasonable to assume that this effect also occurs if tendons are under constant pressure in the body, such as at the bend where entering a bone tunnel or under the pressure of interference screws. This in vitro experiment suggests that preconditioning of a 8mm hamstring graft is achieved best by creeping compression with 6kN at a strain rate of 1mm/min. By using this technique, indeed a canal of approximately 10–15% less diameter (i.e. 7 instead of 8mm) may be drilled for the same tendon, resulting in a tight fit of the graft in the bone

In the assessment of fracture healing by monitoring stiffness with vibrational analysis or instrumented external fixators, it has been assumed that there is a workable correlation between stiffness and strength. We used four-point bending tests to study time-related changes in stiffness and strength in healing tibial fractures in sheep. We aimed to test the validity of the measurement of stiffness to assess fracture strength. At each duration of healing examined, we found marked variations in stiffness and strength. Stiffness was shown to be load-dependent: measurements at higher loads reflected ultimate strength more accurately. There was a biphasic relationship between stiffness and strength: at first there was a strong correlation regardless of loading conditions, but in the second phase, which included the period of ‘clinical healing’, stiffness and strength were not significantly correlated. We conclude that the monitoring of stiffness is useful primarily in assessing progress towards union but is inherently limited as an assessment of strength at the time of clinical union. Any interpretation of stiffness must take into account the load conditions

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. MATERIALS AND METHODS. This study included 6 Tesselaar sheep, age 7±2months. Two pedicle screws (Legacy system, Medtronic) were placed at lumbar level. Four consecutive laminae were attached to two titanium bars (4.5 mm) using 3 mm diameter UHMWPE (Dyneema Purity®) on the left side and 5 mm diameter on the right side. The sublaminar wires were fixed with a double loop sliding knot and tightened with a tensioning device. As a control, in one animal titanium sublaminar wires (Atlas cable, Medtronic) were applied. After sacrifice the spine of the animals was harvested. Radiographs were taken and CT scans were performed. The vertebrae were dissected and placed in formaldehyde for macroscopic and histological evaluation. RESULTS. The animals were sacrificed after a (minimal) postoperative period of 15 weeks. One animal developed a wire fistula and one animal died the first postoperative day due to complications of the anesthesia. None of the 3 or 5 mm knots loosened and no neurological complications occurred. An average of 8.7 mm growth was seen over the segment operated on. Computed tomography confirmed the preserved stability. Even though no decortication was performed, variable bone bridges with fused levels were seen on CT. Macroscopic and histological analysis showed no inflammation at lamina and dura levels containing Dyneema Purity®, with the exception of the case with the fistula where it was observed locally. DISCUSSION. This pilot animal model study shows that the UHMWPE laminar wire made by Dyneema Purity® has good handling and tensioning properties and can provide sufficient stability in fusionless spinal instrumentation while allowing substantial growth. The examined model showed to be a feasible spinal study model, without occurrence of neurological problems. Reactive periostal bone formation with fusion levels led to some restrictions in this model. In the future it will be necessary to test the described construction in a large animal scoliosis model

INTRODUCTION. Autologous bone grafts are considered gold standard in the repair of bone defects. However they are limited in supply and are associated with donor site morbidity. This has led to the development of synthetic bone graft substitute (BGS) materials, many of which have been reported as being osteoinductive. The structure of the BGS is important and bone formation has been observed in scaffolds with a macroporous morphology. Smaller pores termed ‘strut porosity’ may also be important for osteoinduction. The aim of this study was to compare the osteoinductive ability of one silicate-substituted calcium phosphate (SiCaP) with differing strut porosities in an ectopic ovine model. Our hypothesis was that SiCaP with greater strut porosity would be more osteoinductive. METHODS. The osteoinduction of SiCaP BGS with two different strut porosities (AF and AF++) was investigated. The materials had an identical chemical composition and morphological structure but differing strut porosity (AF=22.5%, AF++=47%). Implants were inserted into the paraspinal muscles in skeletally mature sheep. Procedures were carried out in compliance with UK Home Office regulations. There were 12 implants in each group. Implants remained in vivo for 8 and 12 weeks and on retrieval were prepared for undecalcified histology. Sections were stained and examined using light microscopy. A line intersection method was used to quantify bone, implant and implant surface/bone contact within seven random regions of interest along each implant. A Mann-Whitney U test was used for statistical analysis where p values < 0.05 were considered significant. RESULTS. Bone formation was observed to be greater in the AF++ group at 8 (AF=0.2%+/−0.15; AF++=0.44%+/−0.12) and significantly higher at 12 weeks (AF=1.33% +/−0.84; AF++=6.17%+/−1.51) (p=0.04). Significantly higher implant surface/bone contact was observed in the AF++ group at 8 (AF=0.67%+/−0.52; AF++=3.30%+/−1.17) (p=0.04) and 12 weeks (AF=3.06%+/−1.89; AF++=21.82%+/−5.59) (p=0.01). The % implant measured was less in the AF++ group at 8 (AF=39.06%+/−1.26; AF++=33.09%+/−2.14) and 12 weeks (AF=36.05% +/−3.55; AF++=30.60%+/−2.29) but this was not significant. Histology revealed bone formation within BGS strut pores measuring < 50um. Endochondral and intramembranous ossification were also observed in both groups. DISCUSSION. The results indicate that higher strut porosity promotes greater osteoinduction in SiCaP materials. This could be attributed to the micropores providing a greater surface area for the action of growth factors and osteoblasts leading to the formation of bone at an earlier time point. Endochondral ossification was an unusual finding as this is usually associated with bone formation secondary to Bone Morphogenetic proteins (BMPs). This suggests that the osteoinductive mechanisms by SiCaP may involve cytokines such as BMPs

Aims

In this randomized study, we aimed to compare quality of regenerate in monolateral versus circular frame fixation in 30 patients with infected nonunion of tibia.

Aims

The Intraosseous Transcutaneous Amputation Prosthesis (ITAP) may improve quality of life for amputees by avoiding soft-tissue complications associated with socket prostheses and by improving sensory feedback and function. It relies on the formation of a seal between the soft tissues and the implant and currently has a flange with drilled holes to promote dermal attachment. Despite this, infection remains a significant risk. This study explored alternative strategies to enhance soft-tissue integration.

Objectives

Bisphosphonates are widely used as first-line treatment for primary and secondary prevention of fragility fractures. Whilst they have proved effective in this role, there is growing concern over their long-term use, with much evidence linking bisphosphonate-related suppression of bone remodelling to an increased risk of atypical subtrochanteric fractures of the femur (AFFs). The objective of this article is to review this evidence, while presenting the current available strategies for the management of AFFs.

Objectives

A successful outcome following treatment of nonunion requires the correct identification of all of the underlying cause(s) and addressing them appropriately. The aim of this study was to assess the distribution and frequency of causative factors in a consecutive cohort of nonunion patients in order to optimise the management strategy for individual patients presenting with nonunion.

Objectives

Small animal models of fracture repair primarily investigate indirect fracture healing via external callus formation. We present the first described rat model of direct fracture healing.

We hypothesised that cells obtained via a Reamer–Irrigator–Aspirator (RIA) system retain substantial osteogenic potential and are at least equivalent to graft harvested from the iliac crest. Graft was harvested using the RIA in 25 patients (mean age 37.6 years (18 to 68)) and from the iliac crest in 21 patients (mean age 44.6 years (24 to 78)), after which ≥ 1 g of bony particulate graft material was processed from each. Initial cell viability was assessed using Trypan blue exclusion, and initial fluorescence-activated cell sorting (FACS) analysis for cell lineage was performed. After culturing the cells, repeat FACS analysis for cell lineage was performed and enzyme-linked immunosorbent assay (ELISA) for osteocalcin, and Alizarin red staining to determine osteogenic potential. Cells obtained via RIA or from the iliac crest were viable and matured into mesenchymal stem cells, as shown by staining for the specific mesenchymal antigens CD90 and CD105. For samples from both RIA and the iliac crest there was a statistically significant increase in bone production (both p < 0.001), as demonstrated by osteocalcin production after induction.

Medullary autograft cells harvested using RIA are viable and osteogenic. Cell viability and osteogenic potential were similar between bone grafts obtained from both the RIA system and the iliac crest.

Cite this article: Bone Joint J 2013;95-B:1269–74.

Between October 2001 and February 2002, 324 healthcare workers were screened for methicillin-resistant Staphylococcus aureus (MRSA) by nose and throat swabs. A positive finding led to activation of a standardised control programme for the affected person who was immediately excluded from work. Family members of those who were MRSA-positive were offered screening free of charge. An eradication programme was carried out in the permanent carriers. MRSA was found in 17 (5.3%) healthcare workers, 11 of whom proved to be permanent carriers, and six temporarily colonised. Three children of a positive healthcare worker showed nasopharyngeal MRSA, the acquisition of which occurred within the hospital. The standardised eradication programme for carriers was successful in most cases but failed in two individuals, whereupon systemic antibiotics were used successfully. The decolonised carriers, observed for more than one year, remained MRSA negative.

Isolation precautions in hospitals do not always prevent hospital staff and their families from acquiring MRSA. The identification of affected employees is difficult because in most cases only asymptomatic colonisation occurs. Screening and eradication can be complicated and costly, and for the affected employees the occupational consequences can be far-reaching as they have no guaranteed legal protection.

Most animal studies indicate that early irrigation and debridement reduce infection after an open fracture. Unfortunately, these studies often do not involve antibiotics. Clinical studies indicate that the timing of initial debridement does not affect the rate of infection but these studies are observational and fraught with confounding variables. The purpose of this study was to control these variables using an animal model incorporating systemic antibiotics and surgical treatment.

We used a rat femur model with a defect which was contaminated with Staphylococcus aureus and treated with a three-day course of systemic cefazolin (5 mg/kg 12-hourly) and debridement and irrigation, both of which were initiated independently at two, six and 24 hour time points. After 14 days the bone and hardware were harvested for separate microbiological analysis.

No animal that received antibiotics and surgery two hours after injury had detectable bacteria. When antibiotics were started at two hours, a delay in surgical treatment from two to six hours significantly increased the development of infection (p = 0.047). However, delaying surgery to 24 hours increase the rate of infection, but not significantly (p = 0.054). The timing of antibiotics had a more significant effect on the proportion of positive samples than earlier surgery. Delaying antibiotics to six or 24 hours had a profoundly detrimental effect on the infection rate regardless of the timing of surgery. These findings are consistent with the concept that bacteria progress from a vulnerable planktonic form to a treatment-resistant biofilm.