Objectives. The primary stability of the cementless Oxford Unicompartmental Knee Replacement (OUKR) relies on interference fit (or press fit). Insufficient interference may cause implant loosening, whilst excessive interference could cause bone damage and fracture. The aim of this study was to identify the optimal interference fit by measuring the force required to seat the tibial component of the cementless OUKR (push-in force) and the force required to remove the component (pull-out force). Materials and Methods. Six cementless OUKR tibial components were implanted in 12 new slots prepared on blocks of solid polyurethane foam (20 pounds per cubic foot (PCF), Sawbones, Malmo, Sweden) with a range of interference of 0.1 mm to 1.9 mm using a Dartec materials testing machine HC10 (Zwick Ltd, Herefordshire, United Kingdom) . The experiment was repeated with cellular polyurethane foam (15 PCF), which is a more porous analogue for trabecular bone. Results. The push-in force progressively increased with increasing interference. The pull-out force was related in a non-linear fashion to interference, decreasing with higher interference. Compared with the current nominal interference, a lower interference would reduce the push-in forces by up to 45% (p < 0.001 One way ANOVA) ensuring comparable (or improved) pull-out forces (p > 0.05 Bonferroni post hoc test). With the more porous bone analogue, although the forces were lower, the relationship between interference and push-in and pull-out force were similar. Conclusions. This study suggests that decreasing the interference fit of the tibial component of the cementless OUKR reduces the push-in force and can increase the pull-out force. An optimal interference fit may both improve primary fixation and decrease the risk of fracture. Cite this article: S. Campi, S. J. Mellon, D. Ridley, B. Foulke, C. A. F. Dodd, H. G. Pandit, D. W. Murray. Optimal interference of the tibial component of the cementless Oxford Unicompartmental Knee Replacement. Bone Joint Res 2018;7:226–231. DOI: 10.1302/2046-3758.73.BJR-2017-0193.R1

Aims. One of the main causes of tibial revision surgery for total knee arthroplasty is aseptic loosening. Therefore, stable fixation between the tibial component and the cement, and between the tibial component and the bone, is essential. A factor that could influence the implant stability is the implant design, with its different variations. In an existing implant system, the tibial component was modified by adding cement pockets. The aim of this experimental in vitro study was to investigate whether additional cement pockets on the underside of the tibial component could improve implant stability. The relative motion between implant and bone, the maximum pull-out force, the tibial cement mantle, and a possible path from the bone marrow to the metal-cement interface were determined. Methods. A tibial component with (group S: Attune S+) and without (group A: Attune) additional cement pockets was implanted in 15 fresh-frozen human leg pairs. The relative motion was determined under dynamic loading (extension-flexion 20° to 50°, load-level 1,200 to 2,100 N) with subsequent determination of the maximum pull-out force. In addition, the cement mantle was analyzed radiologically for possible defects, the tibia base cement adhesion, and preoperative bone mineral density (BMD). Results. The BMD showed no statistically significant difference between both groups. Group A showed for all load levels significantly higher maximum relative motion compared to group S for 20° and 50° flexion. Group S improved the maximum failure load significantly compared to group A without additional cement pockets. Group S showed a significantly increased cement adhesion compared to group A. The cement penetration and cement mantle defect analysis showed no significant differences between both groups. Conclusion. From a biomechanical point of view, the additional cement pockets of the component have improved the fixation performance of the implant. Cite this article: Bone Joint Res 2022;11(4):229–238

Introduction. Cementless total knee arthroplasty (TKA) has several advantages compared to the cemented approach, including elimination of bone cement, a quicker and easier surgical technique, and potentially a stronger long-term fixation. However, to ensure the successful long-term biological fixation between the porous implant and the bone, initial press-fit stability is of great importance. Undesired motion at the bone-implant interface may inhibit osseointegration and cause failure of biological fixation. Initial stability of a cementless femoral implant is affected by implant geometry, bone press-fit dimension, and characteristics of the porous coating. The purpose of this study was to compare the initial fixation stability of two types of porous femoral implants by quantifying the pull-out force using a paired cadaveric study design. Methods. The two types of cementless TKA femoral implants evaluated in this study had identical implant geometry but different porous coatings (Figure 1). The first type had a conventional spherical-bead coating (Type A), while the second type had an innovative irregularly-shaped-powder coating (Type B). The porous coating thickness was equivalent for both types of implants, thus the dimensional press-fit with bone was also equivalent. Three pairs of cadaveric femurs were prepared using standard TKA surgical technique, with each pair of the femurs receiving one of each porous implant type. An Instron 3366 load frame (Norwood, MA, USA) was used to pull the femoral implant out from the distal femur bone (Figure 2). The testing fixture was designed to allow free rotation between the implant and the actuator. The pullout was performed under a displacement control scheme (5 mm/min). Peak pull-out force was recorded and compared between the two implant groups. Results. Mean pull-out force for the Type B porous femoral implants (512 ± 246 N) was greater than that of the Type A porous femoral implants (310 ± 185 N), although the difference was not statistically significant (p>0.05) (Figure 3). Discussion. This paired cadaveric study showed that the innovative Type B porous coating provides equivalent and potentially greater pull-out force than the conventional Type A porous coating. Lack of statistical significance could be attributed to the limited sample size. Although pull-out testing is not a physiological loading scenario for TKA implant, it provides a relevant assessment of the implant-bone press-fit stability. With all other factors the same, the greater pull-out force observed in the Type B implants is likely related to the higher roughness and friction of the new porous coating. Previous experiments have shown that the Type B porous coating has significantly greater friction against Sawbones surface (coefficient of friction 0.89) compared to Type A porous coating (coefficient of friction 0.50), which was consistent with the findings in this study. Greater initial fixation stability is more favorable in cementless TKA as it reduces the risk of interface motion and better facilitates long-term biological fixation

Pegs are often used in cementless total knee replacement (TKR) to improve fixation strength. Studies have demonstrated that interference fit, surface properties, bone mineral density (BMD) and viscoelasticity affect the performance of press-fit designs. These parameters also affect the insertion force and the bone damage occurring during insertion. We aimed to quantify the effect of the aforementioned parameters on the short-term fixation strength of cementless pegs. 6 mm holes were drilled in twenty-four human femora. BMD was measured using calibrated CT-scans, and randomly assigned to samples. Pegs were produced to investigate the effect of interference fit (diameters 6.5 and 7.6 mm), surface treatment (smooth and rough- porous-coating [friction coefficient: 1.4]) and bone relaxation (relaxation time 0 and 30 min) and interactions were studied using a DOE method. Two additional rough surfaced peg designs (diameters 6.2 and 7.3 mm) were included to scrutinize interference. Further, a peg based on the LCS Porocoat® (DePuy Synthes Joint Reconstruction, Leeds, UK) was added as a clinical baseline. In total seven designs were used (n = 10 for all groups). Pegs were inserted and extracted using an MTS machine (Figure 1), while recording force and displacement. Bone damage was defined as the difference between the cross-sectional hole area prior to and after the test. BMD and interference fit were significant factors for insertion force. BMD had a significant positive correlation with pull-out force and subsequent analyses were therefore normalised for BMD. . Pull-out force increased significantly with interference for both surface coatings at time 0 (p < 0.05). However, after 30 minutes the effect remained significant for rough pegs only (p < 0.05-Figure 2A). Pull-out force reduced significantly with roughness for both peg diameters at time 0 (p < 0.001). However, after 30 minutes the effect remained significant for small pegs only (p < 0.05-Figure 2A). The time dependant interaction was only significant for smooth pegs in both diameters (p < 0.05-Figure 2A). Additionally, the pull-out force increased with diameter in a non-linear manner for the rough pegs (Figure 2B). The two surface treatments were not significantly different to the clinical comparator. Interference fit was the only significant factor for bone damage. BMD was significant for insertion and pull-out forces, reinforcing the need to account for this factor in biomechanical studies and clinical practice. This study also highlights the importance of time in studying bone interactions, with surface treatment and interference showing different interaction effects with relaxation time. Although smooth pegs initially have a higher pull-out force, this effect reduces over time whereas the pullout force for rough pegs is maintained. Smooth pegs also show time sensitivity in relation to interference and the benefit of increased interference reduces over time, whereas it is maintained in rough pegs. This may be explained by different damage (compressive and abrasive) mechanisms associated with different surface treatments. In conclusion, BMD and interference fit are significant factors for initial fixation. Bone relaxation plays an important role as it reduces the initial differences between groups. Therefore, these findings should be strongly considered in the design development of cementless TKR

Magnesium calcium alloys are promising candidates for an application as biodegradable osteosynthesis implants [1,2]. As the success of most internal fracture fixation techniques relies on safe anchorage of bone screws, there is necessity to investigate the holding power of biodegradable magnesium calcium alloy screws. Therefore, the aim of the present study was to compare the holding power of magnesium calcium alloy screws and commonly used surgical steel screws, as a control, by pull-out testing. Magnesium calcium alloy screws with 0.8wt% calcium (MgCa0.8) and conventional surgical steel screws (S316L) of identical geometries (major diameter 4mm, core diameter 3mm, thread pitch 1mm) were implanted into both tibiae of 40 rabbits. The screws were placed into the lateral tibial cortex just proximal of the fibula insertion and tightened with a manual torque gauge (15cNm). For intended pull-out tests a 1.5mm thick silicone washer served as spacer between bone and screw head. Six animals with MgCa0.8 and four animals with S316L were followed up for 2, 4, 6 and 8 weeks, respectively. Thereafter the rabbits were sacrificed. Both tibiae were explanted, adherent soft tissue and new bone was carefully dissected around the screw head. Pull-out tests were carried out with an MTS 858 MiniBionix at a rate of 0.1mm/sec until failure of the screw or the bone. For each trial the maximum pull-out force [N] was determined. Statistical analysis was performed (ANOVA, Student's t-test). Both implant materials were tolerated well. Radiographically, new bone was detected at the implantation site of MgCa0.8 and S316L, which was carefully removed to perform pull-out trials. Furthermore, periimplant accumulations of gas were radiographically detected in MgCa0.8. The pull-out force of MgCa0.8 and S316L did not significantly differ (p = 0.121) after two weeks. From 6 weeks on the pull-out force of MgCa0.8 decreased resulting in significantly lower pull-out values after 8 weeks. Contrary, S316L pull-out force increased throughout the follow up. Thus, S316L showed significantly higher pull-out values than MgCa0.8 after 4, 6 and 8 weeks (p<0.001). MgCa0.8 showed good biocompatibility and pull-out values comparable to S316L in the first weeks of implantation. Thus, its application as biodegradable osteosynthesis implant is conceivable. Further studies are necessary to investigate whether the reduced holding power of MgCa0.8 is sufficient for secure fracture fixation. In addition, not only solitary screws, but also screw-plate-combinations should be examined over a longer time period. Acknowledgements. The study is part of the collaborative research centre 599 funded by the German Research Foundation

Surgeons treating fractures with many small osteochondral fragments have often expressed the clinical need for an adhesive to join such fragments, as an adjunct to standard implants. If an adhesive would maintain alignment of the articular surfaces and subsequently heal it could result in improved clinical outcomes. However, there are no bone adhesives available for clinical indications and few pre-clinical models to assess safety and efficacy of adhesive biomaterial candidates. A bone adhesive candidate based on water, α-TCP and an amino acid phosphoserine was evaluated in-vivo in a novel murine bone core model (preliminary results presented EORS 2019) in which excised bone cores were glued back in place and harvested @ 0, 3, 7, 14, 28 and 42days. Adhesive pull-out strength was demonstrated 0–28 days, with a dip at 14 days increasing to 11.3N maximum. Histology 0–42 days showed the adhesive progressively remodelling to bone in both cancellous and cortical compartments with no signs of either undesirable inflammation or peripheral ectopic bone formation. These favourable results suggested translation to a large animal model. A porcine dental extraction socket model was subsequently developed where dental implants were affixed only with the adhesive. Biomechanical data was collected @ 1, 14, 28 and 56 days, and histology at 1,14,28 and 56 days. Adhesive strength assessed by implant pull-out force increased out to 28 days and maintained out to 56 days (282N maximum) with failure only occurring at the adhesive bone interface. Histology confirmed the adhesive's biocompatibility and osteoconductive behavior. Additionally, remodelling was demonstrated at the adhesive-bone interface with resorption by osteoclast-like cells and followed by new bone apposition and substitution by bone. Whilst the in-vivo dental implant data is encouraging, a large animal preclinical model is needed (under development) to confirm the adhesive is capable of healing, for example, loaded osteochondral bone fragments. Acknowledgements: The murine study was supported, in part, by the Swedish Foundation for Strategic Research (#RMA15-0110)

Abstract. Approximately 20% of primary and revision Total Knee Arthroplasty (TKA) patients require multiple revisions, which are associated with poor survivorship, with worsening outcomes for subsequent revisions. For revision surgery, either endoprosthetic replacements or metaphyseal sleeves can be used for the repair, however, in cases of severe defects that are deemed “too severe” for reconstruction, endoprosthetic replacement of the affected area is recommended. However, endoprosthetic replacements have been associated with high complication rates (high incidence rates of prosthetic joint infection), while metaphyseal sleeves have a more acceptable complication profile and are therefore preferred. Despite this, no guidance exists as to the maximal limit of bone loss, which is acceptable for the use of metaphyseal sleeves to ensure sufficient axial and rotational stability. Therefore, this study assessed the effect of increasing bone loss on the primary stability of the metaphyseal sleeve in the proximal tibia to determine the maximal bone loss that retains axial and rotational stability comparable to a no defect control. Methods. to determine the pattern of bone loss and the average defect size that corresponds to the clinically defined defect sizes of small, medium and large defects, a series of pre-operative x-rays of patients with who underwent revision TKA were retrospectively analysed. Ten tibiae sawbones were used for the experiment. To prepare the bones, the joint surface was resected the typical resection depth required during a primary TKA (10mm). Each tibia was secured distally in a metal pot with perpendicular screws to ensure rotational and axial fixation to the testing machine. Based on X-ray findings, a fine guide wire was placed 5mm below the cut joint surface in the most medial region of the plateau. Core drills (15mm, 25mm and 35mm) corresponding to small, medium and large defects were passed over the guide wire allowing to act at the centre point, before the bone defect was created. The test was carried out on a control specimen with no defect, and subsequently on a Sawbone with a small, medium or large defect. Sleeves were inserted using the published operative technique, by trained individual using standard instruments supplied by the manufacturers. Standard axial pull-out (0 – 10mm) force and torque (0 – 30°) tests were carried out, recording the force (N) vs. displacement (mm) curves. Results. A circular defect pattern was identified across all defects, with the centre of the defect located 5mm below the medial tibial base plate, and as medial as possible. Unlike with large defects, small and medium sized defects reduced the pull-out force and torque at the bone-implant interface, however, these reductions were not statistically significant when compared to no bony defect. Conclusions. This experimental study demonstrated that up to 35mm radial defects may be an acceptable “critical limit” for bone loss below which metaphyseal sleeve use may still be appropriate. Further clinical assessment may help to confirm the findings of this experimental study. This study is the first in the literature to aim to quantify “critical bone loss” limit in the tibia for revision knee arthroplasty. Declaration of Interest. (a) fully declare any financial or other potential conflict of interest

Objectives. Cement augmentation of pedicle screws could be used to improve screw stability, especially in osteoporotic vertebrae. However, little is known concerning the influence of different screw types and amount of cement applied. Therefore, the aim of this biomechanical in vitro study was to evaluate the effect of cement augmentation on the screw pull-out force in osteoporotic vertebrae, comparing different pedicle screws (solid and fenestrated) and cement volumes (0 mL, 1 mL or 3 mL). Materials and Methods. A total of 54 osteoporotic human cadaver thoracic and lumbar vertebrae were instrumented with pedicle screws (uncemented, solid cemented or fenestrated cemented) and augmented with high-viscosity PMMA cement (0 mL, 1 mL or 3 mL). The insertion torque and bone mineral density were determined. Radiographs and CT scans were undertaken to evaluate cement distribution and cement leakage. Pull-out testing was performed with a material testing machine to measure failure load and stiffness. The paired t-test was used to compare the two screws within each vertebra. Results. Mean failure load was significantly greater for fenestrated cemented screws (+622 N; p ⩽ 0.001) and solid cemented screws (+460 N; p ⩽ 0.001) than for uncemented screws. There was no significant difference between the solid and fenestrated cemented screws (p = 0.5). In the lower thoracic vertebrae, 1 mL cement was enough to significantly increase failure load, while 3 mL led to further significant improvement in the upper thoracic, lower thoracic and lumbar regions. Conclusion. Conventional, solid pedicle screws augmented with high-viscosity cement provided comparable screw stability in pull-out testing to that of sophisticated and more expensive fenestrated screws. In terms of cement volume, we recommend the use of at least 1 mL in the thoracic and 3 mL in the lumbar spine. Cite this article: C. I. Leichtle, A. Lorenz, S. Rothstock, J. Happel, F. Walter, T. Shiozawa, U. G. Leichtle. Pull-out strength of cemented solid versus fenestrated pedicle screws in osteoporotic vertebrae. Bone Joint Res 2016;5:419–426

Sufficient primary stability of the acetabular cup is essential for stable osseous integration of the implant after total hip arthroplasty. By means of under-reaming the cavities press-fit cups gain their primary stability in the acetabular bone stock. These metal-backed cups are inserted intra-operatively using an impact hammer. The aim of this experimental study was to obtain the forces exerted by the hammer both in-vivo and in-vitro as well as to determine the resulting primary stability of the cups in-vitro. Two different artificial bone models were applied to simulate osteoporotic and sclerotic bone. Polymeth-acrylamid (PMI, ROHACELL 110 IG, Gaugler & Lutz, Germany) was used as an osteoporotic bone substitute, whereas a composite model made of a PMI-Block and a 4 mm thick (cortical) Polyvinyl chloride (PVC) layer (AIREX C70.200, Gaugler & Lutz, Germany) was deployed to simulate sclerotic bone. In all artificial bone blocks cavities were reamed for a press-fit cup (Trident PSL, Size 56mm, Stryker, USA) using the original surgical instrument. The impactor of the cup was equipped with a piezoelectric ring sensor (PCB Piezotronics, Germany). Using the standard surgical hammer (1.2kg) the acetabular cups were implanted into the bone substitute material by a male (95kg) and a female (75kg) surgeon. Subsequently, primary stability of the implant (n=5) was determined in a pull-out test setup using a universal testing machine (Z050, Ziwck/Roell, Germany). For validation the impaction forces were recorded intra-operatively using the identical press-fit cup design. An average impaction force of 4.5±0.6kN and 6.3±0.4kN using the PMI and the composite bone models respectively were achieved by the female surgeon in vitro. 7.4±1.5kN and 7.7±0.8kN respectively were obtained by the male surgeon who reached an average in-vivo impaction force of 7.5±1.6kN. Using the PMI-model a pull-out force of 298±72N and 201±112N were determined for the female and male surgeons respectively. However, using the composite bone model approximately half the pull-out force was measured for the female surgeon (402±39N) compared to the male surgeon (869±208N). Our results show that impact forces measured in-vitro correspond to the data recorded in-vivo. Using the osteoporotic bone model the pull-out test revealed that too high impaction forces affect the pull-out force negatively and hence the primary implant stability is reduced, whereas higher impact forces improve primary stability considerably in the sclerotic bone model. In conclusion, the amount of impaction force contributes to the quality of the obtained primary cup stability substantially and should be adjusted intra-operatively according to the bone quality of each individual patient

Objective. This study compared the primary stability of two commercially available acetabular components from the same manufacturer, which differ only in geometry; a hemispherical and a peripherally enhanced design (peripheral self-locking (PSL)). The objective was to determine whether altered geometry resulted in better primary stability. Methods. Acetabular components were seated with 0.8 mm to 2 mm interference fits in reamed polyethylene bone substrate of two different densities (0.22 g/cm. 3. and 0.45 g/cm. 3. ). The primary stability of each component design was investigated by measuring the peak failure load during uniaxial pull-out and tangential lever-out tests. Results. There was no statistically significant difference in seating force (p = 0.104) or primary stability (pull-out p = 0.171, lever-out p = 0.087) of the two components in the low-density substrate. Similarly, in the high-density substrate, there was no statistically significant difference in the peak pull-out force (p = 0.154) or lever-out moment (p = 0.574) between the designs. However, the PSL component required a significantly higher seating force than the hemispherical cup in the high-density bone analogue (p = 0.006). Conclusions. Higher seating forces associated with the PSL design may result in inadequate seating and increased risk of component malpositioning or acetabular fracture in the intra-operative setting in high-density bone stock. Our results, if translated clinically, suggest that a purely hemispherical geometry may have an advantage over a peripherally enhanced geometry in high density bone stock. Cite this article: Bone Joint Res 2013;2:264–9

Introduction: The geometry of uncemented press-fit ace-tabular cups is important in achieving primary stability to ensure bony ingrowth. This study compares the in vitro primary stability of two widely used designs. Methods: The primary stability of two uncemented ace-tabular cup designs (true hemispheric and peripherally enhanced) with the same 52mm diameter and produced by the same manufacturer, was tested in vitro. Polyethylene blocks of low and high density -representing softer and harder bone- were reamed using the manufacturers’ reamers. The cups were seated using an Instron 5800R machine. Peak failure loads and moments during uniaxial pull-out and tangential lever-out tests were used as measures of primary stability. Eighty tests were performed. Results: Low density substrate: no difference between the two designs for seating force or stability, with the substrate under-reamed by 2mm. High density substrate: the cups could not be adequately seated with a 2mm under-ream. Seating was achieved with 1mm under-ream for the hemispheric and 1mm over-ream for the peripherally enhanced design. There was a statistically significant difference in seating forces, with the hemispheric cup requiring less force (6264±1535N vs 7858±2383N, p< 0.05). There was a statistically significant difference in the stability ratio of pull-out force to seating force, favouring the hemispheric cup. Discussion: No difference was seen in the low density substrate between the 2 cups. In the high density, the hemispheric design had better characteristics (lower seating force and higher pull-out force to seating force ratio) than the peripherally enhanced design, which are more favourable in clinical settings

Infections are the most uneventfull complications after tumor resection and implantation of a maegaendopros-thesis.Silver-coating of megaendoprosthesis has become a regular procedure in our department since last year in tumor cases. Especially in revision cases with high risk of infection they play a major role in preventing adhesion of bacteria. The successful reduction in infection rates show the effectiveness of the coating but still leave the question “how much coating do we need?” and “how much coating can be tolerated. Latest research concentrated on the coating of the stems, since they can still be the source of the infection if everything else is coated by silver already. Summarised so far, our experience in a rabbit model, a phase I Trial in humans and prelimnary results in Phase II Trials in humans showed no toxic side effects. Driven so far it seems to be sensible to extent the silver coating. So far, the coating is limited to all areas without joint movement or bone contact. An Animal trial was performed anylising the osteointegrative properties of an silver-coated stem versus an regular Titanium stem in 17 dogs. After 12 months of regular X-Ray Analysis a Pull-out test and a concentration analysis has been done. Results showed high significantly (p< 0.001) an osteointegration in 8 out of 8 titanium stems with an average pull-out force of 3764 Newton (Range 1755– 5967 Newton). Silver-coated stems showed no signs of Osteointegration in all 9 out of 9 femurs. The average pull-out force was 21 Newton (Range 0– 186 Newton). A cemented control could resist a pull out force of 350 Newton. Analysis of the silver concentration directly in the first millimeter of the bone-implant interface and the second millimeter showed highly elevated silver levels. The silver concentration in the bone-implant interface at Titanium stems ranged from 0.3 to 3502 parts per Billion (ng/g) compared to silver-coated stems ranging from 303 to 2.418.800 ppb parts per Billion (ng/g). Discussion: Sharing the histologic picture and reactions of the osteoblasts to the silver-coating there are several possible reasons for failed osteointegration. We want o discuss wether these has to be considered as a toxic response or just an adverse reaction. In summary, surgeons have to decide in the future how much silver they need in each individual case concerning intramedullary infection prophylaxis. The balance between loosening or infection should be based on long term expectations, taking into account that even after successful resection of a tumor an ongoning infection can lead to loosening of a limb or even life. Apart from intramedullary use, we recommend silver as a safe adjuvant therapy in all suited patients undergoing endoprosthetic reconstruction after tumor resection

Implant loosening is one of the primary mechanisms of failure for hip, knee, ankle and shoulder arthroplasty. Many established implant fixation surfaces exist to achieve implant stability and fixation. More recently, additive manufacturing technology has offered exciting new possibilities for implant design such as large, open, porous structures that could encourage bony ingrowth into the implant and improve long-term implant fixation. Indeed, many implant manufacturers are exploiting this technology for their latest hip or knee arthroplasty implants. The purpose of this research is to investigate if the design freedoms offered by additive manufacturing could also be used to improve initial implant stability – a precursor to successful long-term fixation. This would enable fixation equivalent to current technology, but with lower profile fixation features, thus being less invasive, bone conserving and easier to revise. 250 cylindrical specimens with different fixation features were built in Ti6Al4V alloy using a Renishaw AM250 additive manufacturing machine, along with 14 specimens with a surface roughness similar to a conventional titanium fixation surface. Pegs were then pushed into interference fit holes in a synthetic bone material using a dual-axis materials testing machine equipped with a load/torque-cell (figure 1). Specimens were then either pulled-out of the bone, or rotated about their cylindrical axis before being pulled out to quantify their ability to influence initial implant stability. It was found that additively manufactured fixation features could favourably influence push-in/pull-out stability in one of two-ways: firstly the fixation features could be used to increase the amount pull-out force required to remove the peg from the bone. It was found that the optimum fixation feature for maximising pull-out load required a pull-out load of 320 N which was 6× greater than the least optimum design (54 N) and nearly 3× the maximum achieved with the conventional surface (120 N). Secondly, fixation features could also be used to decrease the amount of force required to insert the implant into bone whilst improving fixation (figure 2). Indeed, for some designs the ratio of push-in to pull-out was as high as 2.5, which is a dramatic improvement on current fixation surface technology, which typically achieved a ratio between 0.3–0.6 depending on the level of interference fit. It was also found that the additively manufactured fixation features could influence the level of rotational stability with the optimum design resisting 3× more rotational torque compared to the least optimum design. It is concluded that additive manufacturing technology could be used to improve initial implant stability either by increasing the anchoring force in bone, or by reducing the force required to insert an implant whilst maintaining a fixed level of fixation. This defines a new set of rules for implant fixation using smaller low profile features, which are required for minimally invasive device design

Summary. These data suggest that PTH treatment for stimulation of bone healing after trauma is not much dependent on mechanical stimulation and therefore, roughly equal treatment effects might be expected in the upper and lower extremities in humans. Introduction. Stimulation of bone formation by PTH is known to, in part, act via increased mechanosensitivity. Therefore, unloading should decrease the response to PTH treatment in uninjured bone. This has served as a background for speculations that PTH might be less efficacious for human fracture treatment in unloaded limbs, e.g. for distal radial fractures. We analyzed if the connection with mechanical stimulation also pertains to bone formation after trauma in cancellous bone. Methods. 20 male SD rats, 8 weeks old, had one hind leg immobilised via Botox injections. At 10 weeks of age the rats received bilateral screw implants into their proximal tibiae. Half of the rats were given daily injections of 5µg/kg PTH(1–34). After two weeks of healing, the tibias and femurs were harvested. Mechanical testing of screw fixation (pull-out) and µCT of the cancellous bone of the distal femurs was performed. Results. The pull-out forces served as a read-out for cancellous bone formation after trauma. PTH more than doubled the pull-out force in the unloaded limbs (from 14 to 30 N), but increased it by less than half in the loaded (from 30 to 44 N). These force values are not limited by a ceiling effect, and the difference in relative effect of PTH was significant (p = 0.03). Discussion/Conclusion. PTH appeared to exert a greater effect on bone healing in the unloaded limbs, compensating for the lack of mechanical stimulation. These data suggest that PTH treatment for stimulation of bone healing after trauma is not much dependent on mechanical stimulation. Therefore, roughly equal treatment effects might be expected in the upper and lower extremities in humans

Aims: The new Fixclips are used with 0.8mm to 3.0mm diameter wires and screws to þx osteotomies and fractures. This study deals with the biomechanical properties of the þxclip system. Methods: The range of normally accepted screw tightness was established by using a torque screwdriver at surgery. The mechanical grip-strength over this torque range was measured using a Hounsþeld Tensometer in the laboratory. The þxation was simulated using Tufnol material and the effect of additional clips on the grip strength and the stability of the construct was assessed. Results: Pull out force depends on the wire size and varied linearly over the clinical range of screw torque (0.25 to 3Nm) with values from 50 N to 900 N. An additional clip increases the pull-out force upto 3000N and the adjusting the distance also affects the test results. The strength increased with the distance between the clips and a maximum was obtained at a distance of 4.5cms between the clips. Conclusions: The system is modular and is designed to lie slightly off the bone causing minimal damage to the underlying periosteum and hence less disturbance to blood supply. The system is cost effective, less time consuming and mechanically reliable and stable for the given clinical situations. It has signiþcant advantage over the existing methods of þxation especially in paediatric orthopaedic and trauma situations

Introduction: Conventional cancellous screws have proven purchase in healthy bone, but may be prone to loosening in osteoporotic bone. Locking screws have become a popular choice to combat loosening. A new screw design has optimized thread form to gain better purchase into poor quality bone. The purpose of this study was to evaluate the maximum stripping torque and pull-out strength of the PERI-LOCTM 5.0mm Osteopenia Bone Screw using an osteopenic model. Methods: Stripping Torque: PERI-LOCTM 5.0mm Osteopenia Bone Screws were inserted through a One-Third Tubular B-plate into a pre-drilled pilot hole to a depth of 20mm. Rotational loading was applied manually using a hex driver until torque reached a peak value. The maximum torque value due to screw head contact with the plate was measured using a torque-meter and denoted as the stripping torque. This same procedure was used for TC-100TM 4.0mm Cancellous Bone Screws, which were inserted through a TC-100TM Standard Tubular Plate. Pull-Out Strength: PERI-LOCTM 5.0mm Osteopenia Bone Screws were inserted to a depth of 20 mm into an osteopenic model. Axial pull-out was then conducted on a MTS testing frame by applying a tensile load along its longitudinal axis at a rate of 0.2 in/min. The maximum pull-out force was recorded. This same procedure was used for TC-100TM 4.0mm Cancellous Bone Screws. The test set-up is shown in Figure 1. Discussion: The PERI-LOCTM 5.0mm Osteopenia Bone Screws showed a 34% increase in stripping torque and a 40% increase in pull-out strength (p < < 0.01 at á = 0.05 in both instances) as compared to clinically successful bone screws. Conclusions: When tested in an osteopenic bone model, the PERI-LOCTM 5.0mm Osteopenia Bone Screw provided superior stripping torque and pull-out strength as compared to conventional cancellous bone screws. The increased torque generation during insertion of PERI-LOCTM 5.0mm Osteopenia Bone Screws provides better fracture reduction, as compared to conventional screws. These findings indicate that the use of the improved thread design is advantageous in poor quality bone

Purpose: As proposed by Marnay, posterior fixation of the spine with self-stabilising forceps facilitates the operative procedure. These forceps enable lamolaminal, pediculolaminal, or pediculotransverse fixations. We developed a method for posterior fixation of the spine where a self-stabilising forceps links the lateral forceps hook to a medial hook allowing a bilateral hold on the segment for better fixation and correction. The aim of this work was to evaluate the contribution of the self-stabilising forceps compared with standard hooks during reduction movements. Material and methods: Pull-out tests were conducted on five different holds using a supratransversal hook, a sublaminal hook, a pediculotransversal forceps, and a pediculolaminal forceps (Spine-Evolution), and a bipediculolaminal hook mounted on two vertebrae (Sofamor-Danek). The tests were performed on anatomic specimens. The test procedure was a reduction of a kyphosis of the upper part to the tested segment. Fourteen measurements were made for each implant. Results: Pull-out force (N) was (mean, range): supratrans-versal hook (24, 8-40) < pediculotransvers forceps (154, 80-280) < supralaminal hook (360, 120–560) < pediculolam-inal forceps (491, 440–550) < bipediculolaminal forceps on two vertebrae (711, 400–800). The differences were significant. Discussion: These results must be considered under the experimental conditions. Fixation with a supratransversal hook did not produce a reliable hold. The pediculotransversal forceps failed in one case due to fracture of a weak transversal mass. The supralaminal hook exhibited more consistent pull-out resistance. In most of the cases, pull-out occurred by fracture of the posterior arch. The bilateral self-stabilising forceps demonstrated the greatest pull-out resistance. During the five tests made with this forceps, the test was limited by the weakness of the osteosynthesis rods used so the maximal resistance to pull-out could not be measured (> 800 N). Conclusion: The self-stabilising pediculolaminal forceps provides greater pull-out resistance than hooks alone. The self-stabilizing bipediculolaminal forceps allows a new surgical strategy for segmentary fixation with promising potential

The clinical outcome and radiographic analysis of 82 patients undergoing total hip arthroplasty using a titanium acetabular component coated with a new proprietary Titanium Porous Coating inserted without cement are reported. All total hip replacements were performed by a single surgeon and utilized a porous coated, cementless femoral component. Pre clinical testing was carried out in an animal model to evaluate the new porous coating. THR was performed using a cementless acetabular component of the same geometrical design inserted without cement. The component is coated with a new proprietary Titanium Porous Coating wherein the non-spherical bead itself is also porous. This creates a “lava rock” type of structure and gives variability in the pore sizes that aids in the in-growth and apposition of bone (fig 5). The inter-bead pore size: the pore size between each non-spherical bead = 200–525 μm while the Intra-bead pore size: the pore size within each non-spherical bead = 25–65 μm. The resulting surface is extremely rough and provides a robust initial “bite” or “stick” to the bone. Clinical results were evaluated using the Harris Hip score and were recorded prospectively preoperatively and at 6 weeks, 6 months, and 1 year postoperatively. Radiographs were evaluated for component migration, subsidence, and cortical and cancellous biologic response as well as zonal analysis of radiolucent lines, using the Muller THR template. Pre-clinical animal testing of the new porous coating was carried out in 50 sheep using a metacarpal intramedulary implant (similar to a hip stem) designed to function as a Percutaneous Osseointegrated Prosthesis (POP) for amputees and evaluated Apposition Bone Index (ABI) (fig 1), Mineral Apposition Rate (MAR) (fig 2),% Bone In-growth (fig 3), and Axial Pull-out Force (fig 4). Sheep were sacrificed at time points of 0, 3, 6, 9, and 12 months to measure and evaluate the above parameters. Human clinical and radiographic follow up averaged 10.5 months (range 2–18 months). There were 39 females and 43 males. Average age was 59 years. The clinical results were excellent with respect to both pain and function at mid term follow up. Patient satisfaction was high. Radiographic analysis showed no migration or change in the angle of inclination at latest follow up. Femoral component subsidence was detected in 2 cases and averaged 1.8 mm. No polyethylene wear was detected. No hips dislocated. No hips underwent additional surgery. Pre-clinical test data demonstrated excellent mechanical and biological attributes. Average tensile strength of the coating surpassed the FDA minimum requirement by 3X. Animal testing in the sheep showed no evidence of stem loosening or need for revision after 12 months, and corroborated well with clinical results. Correlation between the pre-clinical testing and the human experience was exceptional. Application of a new titanium porous coating utilizing a proprietary dual pore size structure to the surface of the acetabular component provides an extremely rough surface and robust initial fixation during cementless THR. Excellent early clinical and radiographic results are demonstrated. The addition of this new type of porous coating to other arthroplasty components may confer additional clinical advantages

Purpose: The purpose of this experimental study was to compare fixation with hooks and screws inserted posteriorly. A digitalized analysis using finite element analysis was applied. Material and methods: We used seven human thoracic spines for this experimental study. We identified 49 pairs of two vertebrae. Traction was applied to rupture, the maximal force at rupture measured with an Instron. Fixations were made with four pedicle screws and two pediculolaminar clamps. For the digitalized study, the modellised vertebra was composed of 63000 nodes and 14000 elements. Calculations were made in the elastic domain using the finite elements abacus method. Results: Traction on the peidculolaminar clamp produced a fracture at the base of the pedicles in all cases. When screw fixation was used, there was a medial fissuration of the base of the pedicle. For hooks, pull-out force was 1108±510 Newtons. It was 820±418 Newtons for the 4-mm diameter screws and 1395±425 Newtons for the 5-mm screws. T5–T6 and T7–T8 assemblies ruptured more easily. The screw model demonstrated a concentration of the stress forces at the medial level of the pedicle, inside the spinal canal. Use of a long screw did not reduce stress significantly. The hook model demonstrated maximal stress force at the lower level of the pedicles. Discussion and conclusion: From a mechanical point of view, screw fixation is best, but this type of fixation did not fulfil all expectations. The results showed that the force for 4-mm screws is 23% weaker than for hooks and that 5-mm screws only provide a 12% better force than hooks. There are two mechanisms for pull-out, stripping of the bone threads, or rupture of the pedicles. The bone thread strips when the screw threads do not penetrate the cortical bone sufficiently because the screw is too small. On the contrary, larger screws risk injuring the pedicle. Pedicle rupture is observed for much higher stress force and constitutes the upper limit of resistance. This leads us to hypothesise that in most cases, screw pull-out occurs by bone thread stripping. Screws are less effective if they cannot be correctly anchored in the cortical, probably the cause of their relative weakness. The screw diameter should be chosen to adapt to the diameter of each pedicle. Stress forces would be transmitted better from the screw to the pedicle. The vertebrae are exposed to greater stress forces with hooks. The digitalised study confirmed that use of long screws crossing the entire vertebra did not provide a sufficient diminution of stress on the pedicles to justify their use

Aims

Aseptic loosening is the most common cause of failure following cemented total knee arthroplasty (TKA), and has been linked to poor cementation technique. We aimed to develop a consensus on the optimal technique for component cementation in TKA.