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

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

Introduction: There has been a renewed interest in metal-on-metal bearing for total hip replacement with the benefit of a larger head size and decreased incidence of dislocation. In the revision hip scenario cementation of a polyethylene liner, for a previously compromised liner fixation mechanism into a preexisting well-fixed shell or a cage, has become an accepted method to decrease the morbidity of the procedure. Perhaps Bir-mingham cementless cups could be used as cemented devices in primary and revision hip surgery where a cementless cup is not possible. Aim: To study the pull-out strength of cemented Bir-mingham sockets in an experimental model. Materials and Methods: Eight Birmingham cups were cemented into wooden blocks after they were reamed to the appropriate size allowing for a 3mm cement mantle, multiple holes drilled into the reamed sockets and cement vacuum-mixed. Cable was then threaded through the holes on the rim of the cup and the wooden block was then mounted on a metal plate and secured. Linear tension was then gradually applied on the cup through the cable. Results: The pull-out strength of the cemented Birming-ham cups was higher than the failure of the cable. The tensile load to failure for the cables ranged from 3642.6 N to 4960 N with an average load of 4286.9 N. Conclusion: The average tensile load of 4286.9 is very high compared to previous studies with cemented poly-ethylene and metal liners. This finding is very promising and might support clinical application in complex primary and revision total hip replacement

We aimed to determine the optimal method of inserting a screw into polymethylmethacrylate (PMMA) cement to enhance fixation. We performed six groups of ten axial pull-out tests with two sizes of screw (3.5 and 4.5 mm AO cortical) and three methods of insertion. Screws were placed into 'fluid' PMMA, into 'solid' PMMA by drilling and tapping, or into 'curing' PMMA with quarter-revolution turns every 30 seconds until the PMMA had hardened. After full hardening, we measured the maximum load to failure for each screw-PMMA construct. We found no significant difference in the pull-out strengths between screw sizes or between screws placed in fluid or solid PMMA. Screws placed in curing PMMA were significantly weaker: the relative strengths of solid, fluid and curing groups were 100%, 97% and 71%, respectively. We recommend the use of either solid or fluid insertion according to the circumstances and the preference of the surgeon

The effect of screw geometry on the pullout strength of Anterior Cruciate Ligament [ACL] reconstruction is well documented. Most research has looked at the effect of screw length and diameter, however other factors such as the degree of taper may also be important. Tapered screws should in theory be associated with increased pullout strength. This has not been demonstrated either clinically or in vitro before. The aim of this study was to compare the pullout strength of ACL reconstruction with a parallel against a tapered screw. A parallel and tapered screw were manufactured which were identical in all other respects. Sixty superficial digital flexors from the hind legs of sheep were harvested. The tendons were paired and combined to form a quadruple tendon reconstruction of approximately 7mm diameter as measured with graft sizer. An ACL reconstruction was performed on the proximal tibia of 30 bovine knees, which had been harvested in right and left knee pairs, using the quadruple tendon. Fifteen reconstructions were fixed using tapered screws and fifteen with non-tapered screws. The insertion torque of both tapered and non tapered screws were recorded using an instrumented torque screwdriver. The reconstructions were mounted in an Instron materials testing machine with an x-ray bearing system to eliminate horizontal forces, to ensure that the forces were all directed along the line of the tibial tunnel. The maximum pullout strengths were recorded in each case. Five knee pairs were subjected to bone densitometry scanning to ensure that any difference in pull out strength was not due to changes in bone density between right and left knee pairs. Results indicated that there was no difference between right and left knee pairs [p = 0.58] and that tapered screws were associated with significantly higher pull-out strengths [p=0.007] and insertion torques [p = 0.001]

Fixation of the glenoid component is critical to the outcome of total shoulder arthroplasty. In an in vitro study, we analysed the effect of surface design and thickness of the cement mantle on the pull-out strength of the polyethylene pegs which are considered essential for fixation of cemented glenoid components. The macrostructure and surface of the pegs and the thickness of the cement mantle were studied in human glenoid bone. The lowest pull-out forces, 20 ± 5 N, were for cylindrical pegs with a smooth surface fixed in the glenoid with a thin cement mantle. The highest values, 425 ± 7 N, were for threaded pegs fixed with a thicker cement mantle. Increasing the diameter of the hole into which the peg is inserted from 5.2 to 6.2 mm thereby increasing the thickness of the cement mantle, improved the mean pull-out force for the pegs tested

Introduction: Knotless Suture Anchors provide numerous advantages in arthroscopic rotator-cuff (RC) repair such as, reducing the difficulties of knot tying, reducing surgical exposure, thus decreasing morbidity. The purpose of this in-vitro study was to compare the pull-out strength of three new knotless suture anchors in correlation with bone quality using the following anchors: Opus Magnum 2 -ArthroCare Co., USA; Push Lock and Swivel Lock -Arthrex Inc., USA. Material & Methods: Ten healthy and ten osteopenic macroscopically intact humeri with an average age of 51.7 and 79.5 years, respectively, were loaded with the three knotless suture anchors according to the manufacturers’ description. The healthy humeri had a mean trabecular BMD of 152.77 mgCa-HA/ml. The osteopenic humeri had a mean trabecular bone mineral density of 54.02 mgCa-HA/ml. The humeri were positioned in a custom - engineered adjustable fixation device, stabilising the direction of the pull of the sutures at an angle of 135° to the axis of the humeral shaft (Universal testing device Z010/TN2A – Zwick GmbH, Ulm, Germany). The anchors were cyclically loaded to simulate postoperative conditions. The ultimate pull-out strenngth, the initial displacement in millimeters after the first pull with 75 N and the modes of failure were recorded. Results: The mean ultimate failure loads of the Opus Magnum 2, PushLock and SwiveLock anchors in osteopenic humeri were 135.0, 102.5 and 130.0 N (p> 0.05), respectively, and in healthy humeri 142.5 N, 182.5 N and 202.5 N (p> 0.05), respectively. The initial system displacement in osteopenic humeri of the Opus Magnum 2, PushLock and SwiveLock anchors were 3.53 mm, 16.11 mm and 3.23 mm (p< 0.01), respectively, and in healthy humeri 3.71 mm, 1.98 mm, and 1.96 mm (p> 0.05), respectively. Discussion: The results of this study show that in osteopenic humeri, the Opus Magnum 2 and SwiveLock anchors display significant superiority in system displacement with an initial pull of 75N compared to the PushLock anchor in osteopenic bone, but all three anchors fail to provide significance in the ultimate failure load. PushLock anchor might cause a greater gap formation between the RC-tendon and greater tubercle interface in osteopenic humeri due to inferior gripping and therefore should not be used solely for RC repair. Due to a manufacturing flaw the suture holding fixture of the Opus Magnum 2 anchor “breaks” when a mean force of 138.75 N is applied to the system, regardless of the bone quality, thus disabling the anchor to unfold it’s properties in healthy bone. Whereas the results in osteopenic bone are comparable to the other two anchors. SwiveLock provides the best support of all three anchors in healthy humeri

The aim of this biomechanical study was to investigate the role of the dorsal vertebral cortex in transpedicular screw fixation. Moss transpedicular screws were introduced into both pedicles of each vertebra in 25 human cadaver vertebrae. The dorsal vertebral cortex and subcortical bone corresponding to the entrance site of the screw were removed on one side and preserved on the other. Biomechanical testing showed that the mean peak pull-out strength for the inserted screws, following removal of the dorsal cortex, was 956.16 N. If the dorsal cortex was preserved, the mean peak pullout strength was 1295.64 N. The mean increase was 339.48 N (26.13%; p = 0.033). The bone mineral density correlated positively with peak pull-out strength. Preservation of the dorsal vertebral cortex at the site of insertion of the screw offers a significant increase in peak pull-out strength. This may result from engagement by the final screw threads in the denser bone of the dorsal cortex and the underlying subcortical area. Every effort should be made to preserve the dorsal vertebral cortex during insertion of transpedicular screws

Aims. Anchorage of pedicle screw rod instrumentation in the elderly spine with poor bone quality remains challenging. Our study aims to evaluate how the screw bone anchorage is affected by screw design, bone quality, loading conditions, and cementing techniques. Methods. Micro-finite element (µFE) models were created from micro-CT (μCT) scans of vertebrae implanted with two types of pedicle screws (L: Ennovate and R: S. 4. ). Simulations were conducted for a 10 mm radius region of interest (ROI) around each screw and for a full vertebra (FV) where different cementing scenarios were simulated around the screw tips. Stiffness was calculated in pull-out and anterior bending loads. Results. Experimental pull-out strengths were excellently correlated to the µFE pull-out stiffness of the ROI (R. 2. > 0.87) and FV (R. 2. > 0.84) models. No significant difference due to screw design was observed. Cement augmentation increased pull-out stiffness by up to 94% and 48% for L and R screws, respectively, but only increased bending stiffness by up to 6.9% and 1.5%, respectively. Cementing involving only one screw tip resulted in lower stiffness increases in all tested screw designs and loading cases. The stiffening effect of cement augmentation on pull-out and bending stiffness was strongly and negatively correlated to local bone density around the screw (correlation coefficient (R) = -0.95). Conclusion. This combined experimental, µCT and µFE study showed that regional analyses may be sufficient to predict fixation strength in pull-out and that full analyses could show that cement augmentation around pedicle screws increased fixation stiffness in both pull-out and bending, especially for low-density bone. Cite this article: Bone Joint Res 2021;10(12):797–806

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

Aims. To develop an early implant instability murine model and explore the use of intermittent parathyroid hormone (iPTH) treatment for initially unstable implants. Methods. 3D-printed titanium implants were inserted into an oversized drill-hole in the tibiae of C57Bl/6 mice (n = 54). After implantation, the mice were randomly divided into three treatment groups (phosphate buffered saline (PBS)-control, iPTH, and delayed iPTH). Radiological analysis, micro-CT (µCT), and biomechanical pull-out testing were performed to assess implant loosening, bone formation, and osseointegration. Peri-implant tissue formation and cellular composition were evaluated by histology. Results. iPTH reduced radiological signs of loosening and led to an increase in peri-implant bone formation over the course of four weeks (timepoints: one week, two weeks, and four weeks). Observational histological analysis shows that iPTH prohibits the progression of fibrosis. Delaying iPTH treatment until after onset of peri-implant fibrosis still resulted in enhanced osseointegration and implant stability. Despite initial instability, iPTH increased the mean pull-out strength of the implant from 8.41 N (SD 8.15) in the PBS-control group to 21.49 N (SD 10.45) and 23.68 N (SD 8.99) in the immediate and delayed iPTH groups, respectively. Immediate and delayed iPTH increased mean peri-implant bone volume fraction (BV/TV) to 0.46 (SD 0.07) and 0.34 (SD 0.10), respectively, compared to PBS-control mean BV/TV of 0.23 (SD 0.03) (PBS-control vs immediate iPTH, p < 0.001; PBS-control vs delayed iPTH, p = 0.048; immediate iPTH vs delayed iPTH, p = 0.111). Conclusion. iPTH treatment mediated successful osseointegration and increased bone mechanical strength, despite initial implant instability. Clinically, this suggests that initially unstable implants may be osseointegrated with iPTH treatment. Cite this article: Bone Joint Res 2022;11(5):260–269

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)

Purpose: The purpose of our work was to assess sutures, suturing techniques, and suture anchors used in rotator cuff surgery in order to explore weak parts in our repair. Material and Methods: Ten types of sutures, four types of suturing techniques and eight types of sutures anchors commonly used in shoulder surgery were tested. Vicryl, Ticron, Dexon, PDS, Panacryl, Ethibond, Durabraid, Fiberwire, HiFi and Orthocord sutures were tested. Simple, mattress, massive cuff tear (MCT) technique and modified Mason Allen. (MMA) suturing technique in ex-vivo ovine healthy rotator cuff were tested. Four metallic and four bioabsorbable anchors: Arthrex, Smith+Nephew, Linvatec, Mitek and bio respectively were tested. Their pull-out strength and failure mode was determined in ex-vivo ovine humeral heads. Materials Testing Machine and attached load cell run with Emperor Software (MEC-MESIN, UK) was used for the tests with application of tensile load(60mm/min). Load and displacement were recorded at a sampling rate of 100 Hz and breaking load and stiffness were recorded. Results: The suture mean breaking strength (N) was: Vicryl 89.0, Ticron 70.9, Dexon 111.7, PDS 92.9, Panacryl 52.9, Ethibond 64.5, Durabraid 72.6, Fiber-wire 127.2, HiFi 163.0 and Orthocord 141.8. The mean suture stiffness (N/mm) was: Vicryl 3.4, Ticron 3.0, Dexon 2.4, PDS 1.2, Panacryl 0.7, Ethibond 2.5, Durabraid 3.1, Fiberwire 9.7, HiFi 11.1, and Orthocord 6.9. The technique’s mean breaking strength (N) was: simple 54.1, mattress 102.8, MCT 194.0, MMA 227.7 and their mean stiffness (N/mm) was: simple 10.4, mattress 13.1, MCT 26.0 and MMA 18.9. The anchors had mean pull-out strength (N): Arthrex 534.0 and Smith & Nephew 574.0, Linvatec 707.2N, Mitek 736.4N and Arthrex Bio 257.4, Linvatec Bio 305.2, Mitek Bio 359.6, S& N Bio 330.6. Often either in metallic (10/20) or in bioabsorbable anchors (11/20) the eyelet fails first. Conclusion: Modern non absorbable sutures (HiFi Orthocord Fiberwire) have higher breaking strength and stiffness than absorbable ones (p< 0.05). MCT suturing technique, arthroscopically applicable, and MMA technique, which is most commonly used in open surgery have no great differences in strength and stiffness (p=0.046 and p=0.352 respectively). Both of them have higher strength and stiffness than simple and mattress technique (p< 0.05). Metallic anchors have a higher pull-out strength than bioabsorbable ones (p< 0.05) and the eyelet is a weak point in both

Currently available fracture fixation devices that were originally developed for healthy bone are often not effective for patients with osteoporosis. Resulting outcomes are unsatisfactory, with longer recovery times, often requiring re-surgery for failed cases. One major issue is the design of bone screws, which can loosen or pull-out from osteoporotic bone. Design improvements are possible, but the development of new screws is a lengthy and expensive process due to the manufacture of the complex geometry involved. The aim of this research was to validate our currently available 3D printing technology in the design, manufacture and testing of screws. Three standard wood screw designs were reverse-engineered using computational modelling and then fabricated in polymeric resin using 3D rapid prototyping on a Stereolithography (SLA) machine. The original metal screws and the 3D screws (n=5 of each) were then inserted into a synthetic bone block (Sawbones, PCF5) representing the mechanical properties of severely osteoporotic cancellous bone. Pull-out tests were conducted in accordance with ASTM 543-13. The three metal screws exhibited pull-out strengths of 125, 74 and 118 N respectively. The 3D printed screws by comparison showed pull-out strengths approximately 15–20 % lower than their metal counterparts. However, when the results were normalised to the material tested, showing the relative changes to the first design, the pattern of results in the metal and 3D printed groups were almost identical (within 3 % of each other), showing excellent correlation. This study is the first to show that 3D Rapid Prototyping can be used in the pre-clinical testing of orthopaedic screws. The methodology provides a cheaper, faster development process for screws, allowing huge scope for development and improvement. Future work will include expanding the study to include more screw configurations as well as testing in higher density foams to compare performance in healthier bone

Introduction: The use of self-tapping screws has become increasingly popular since it allows for a rapid screw placement avoiding the tapping step during ORIF of fractures.. While sharing the same basic principle of cutting flutes and partial threads at the tip, at least four types of screw design is currently available, varying in the number and shape of cutting flutes. The purpose of this biomechanical study was to research for any significant difference between the various self-tapping screws. Material and Methods: Three different designs of 4.5-mm self-tapping screws and one standard 4.5 screw serving as control were compared for pull-out strength after insertion into an adult human non-embalmed cadaveric humeri. All specimens were machined to a 5 mm uniform cortical thickness. Four equidistant 3.2 mm holes were drilled into each specimen by an MTS mounted drill. All screws were inserted randomly in one of the four positions using a hand screwdriver. The cortical bone specimen was secured between two metal plates to the base of a MTS machine while a uniaxial tensile force was applied to the jig for screw removal at a rate of 0.833 mm/sec until holding power had decreased to 25 % of the maximum. Load displacement curves were recorded. Resulting data was analyzed using paired student-t tests. P values of less then 0.05 were considered statistically significant. Results: The mean load-to-failure was 97.4167N (S.D. 13.29924) for the Synthes control screw, 69.2333N (S.D. 4.48360) for the Synthes self-tapping screw, 67.15 (S.D. 11.23864) for the Stryker self-tapping screw, and 55.0667 (S.D. 8.59271) for the ODI self-tapping screw. A significant difference was found between the mean pull-out strength of the Synthes control screw when compared to each of the three self-tapping screws (Pairs 1–3, P < 0.05). Furthermore, the mean pull-out strength of the ODI self-tapping screw was found to be significantly less than Stryker self-tapping screw (Pair 6, P < 0.05). There was no significant difference between Synthes self-tapping screws and Stryker self-tapping screws (Pair 5, P < 0.05). Discussion and conclusion: Self tapping screws with three short cutting flutes performed better than those with two long cutting flutes. Despite of the different designs and length of the cutting flutes in self-tapping screws, they all have less pull out strength than regular screws

The menisci function within the knee as load distributors, shock absorbers and secondary stabilisers. The medial meniscus has been shown to carry as much as 50% of the load across the medial compartment, and the lateral meniscus 70% of its compartmental load. After total meniscectomy, joint contact areas decrease by approximately 75%, and peak local contact stresses increase by as much as 235%. Meniscectomy may lead to a 14 times increase in the risk of arthritis at 20 years. Axial load across the knee is converted into hoop stresses along the circumferential collagen fibres within the meniscus. Strong and stiff attachment of both meniscal horns, via the insertional ligaments, to the tibia is essential. Disruption of the circumferential fibre arrangement will defunction the meniscus. Preservation of meniscal tissue, where possible and appropriate, is now accepted practice. Most techniques for meniscal repair have been validated in vitro by testing radial pull-out strengths. However, meniscal tissue is highly anisotropic, with little strength in the radial direction, perpendicular to the circumferential collagen fibres. Physiological forces in the radial direction, across the menisci, are probably only very small. Therefore, mechanical evaluation of radial pull-out strengths is probably of little clinical significance. The role of different repair techniques, and the significance of gapping across repair sites under cyclical loading will be discussed

The intermittent administration of parathyroid hormone (PTH) increases the formation of bone by stimulating osteoblastic activity. Our study evaluates the possibility that intermittent treatment with PTH (1-34) may also enhance the implant-bone fixation of stainless-steel screws. Twenty-eight rats received one screw in either one (n = 8) or in both (n = 20) proximal tibiae. We administered either PTH (1-34) in a dosage of 60 μg/kg/day (n = 14) or vehicle (n = 14) over a period of four weeks. At the end of this time, the degree of fixation was assessed by measuring the removal torque on one screw in each rat (n = 28) and the pull-out strength on the contralateral screw (n = 20). PTH increased the mean removal torque from 1.1 to 3.5 Ncm (p = 0.001) and the mean pull-out strength from 66 to 145 N (p = 0.002). No significant differences in body-weight or ash weight of the femora were seen. Histological examination showed that both groups had areas of soft tissue at the implant-bone interface, but these appeared less in the PTH group. These results indicate that intermittent treatment with PTH may enhance the early fixation of orthopaedic implants

Clinically applied methods of assessing implant fixation and implant loosening are of sub-optimal precision, leading to the risk of unsecure indication of revision surgery and late recognition of bone defects. Loosening diagnosis involving measuring the eigenfrequencies of implants has its roots in the field of dentistry. The changing of the eigenfrequencies of the implant-bone-system due to the loosening state can be measured as vibrations or structure-borne sound. In research, vibrometry was studied using an external shaker to excite the femur-stem-system of total hip replacements and to measure the resulting frequencies by integrated accelerometers or by ultrasound. Since proper excitation of implant components seems a major challenge in vibrometry, we developed a non-invasive method of internal excitation creating an acoustic source directly inside the implant. In the concept proposed for clinical use, an oscillator is integrated in the implant, e.g. the femoral stem of a total hip replacement. The oscillator consists of a magnetic or magnetisable spherical body which is fixed on a flat steel spring and is excited electromagnetically by a coil placed outside the patient. The oscillator impinges inside the implant and excites this to vibrate in its eigenfrequency. The excitation within the bending modes of the implant leads to a sound emission to the surrounding bone and soft tissue. The sound waves are detected by an acoustic sensor which is applied on the patient's skin. Differences in the signal generated result from varying level of implant fixation. The sensor principle was tested in porcine foreleg specimens with a custom-made implant. Influence of the measurement location at the porcine skin and different levels of fixation were investigated (press-fit, slight loosening, advanced loosening) and compared to the pull-out strength of the implant. Evaluation of different parameters, especially the frequency spectrum resulted in differences of up to 12% for the comparison between press-fit and slight loosening, and 30% between press-fit and advanced loosening. A significant correlation between the measured frequency and the pull-out strength for different levels of fixation was found. Based on these findings, an animal study with sensor-equipped bone implants was initiated using a rabbit model. The implants comprised an octagonal cross-section and were implanted into a circular drill hole at the distal femur. Thereby, definite gaps were realized between bone and implant initially. After implantation, the bone growth around the implant started and the gaps were successively closed over postoperative period. Consequently, since the tests had been started with a loose implant followed by its bony integration, a reverse loosening situation was simulated. In weekly measurements of the eigenfrequencies using the excitation and sensor system, the acoustic signals were followed up. Finally, after periods of 4 and 12 weeks after implantation, the animals were sacrificed and pull-out tests of the implants were performed to measure the implant fixation. The measured implant fixation strengths at the endpoint of each animal trial were correlated with the acoustic signals recorded

There are several different ways of preparing the femoral canal prior to cementing a hip prosthesis. This study investigated the mechanical strength of the cement-bone interface of four different types of preparation determined by the maximum tensile force required to separate a cemented prosthesis from its cancellous bone origin. Forty-eight fresh-frozen ox femora were prepared for hip arthroplasty, In a four-way comparison, groups of eleven femora were prepared by irrigation using. syringe injected normal saline;. hydrogen-peroxide soaked gauze;. pulse-lavage brushing; and. pulse-lavage brushing and hydrogen-peroxide soaked gauze combination. Specimens were secured to a Material-test System (MTS), and the femoral implant pulled from the femur uni-axially at a rate of 5mm/min. The ‘pull-out strength’ was defined as the maximum tension recorded by the MTS during separation. Cement interdigitation was also inspected for each technique by microscopy of eight bone-implant transverse sections taken from prepared specimens. Following an analysis of variance and pair-wise Fisher comparison, the average pull-out strength of the cemented prosthesis was significantly higher (P< 0.001) using pulse-lavage brushing (mean 8049.2 N), and pulse-lavage brushing in combination with hydrogen-peroxide soaked gauze (mean 8489.1 N), than with normal saline irrigation (mean 947.1 N) or hydrogen-peroxide soaked gauze preparation (mean 1832.6 N). Prosthesis pull-out strength following pulse-lavage brushing in combination with hydrogen-peroxide soaked gauze was not significantly different (P> 0.05) than preparing with pulse-lavage brushing alone. Low and high power microscopy of specimen transverse sections revealed the greatest levels of cement penetration in specimens prepared using pulse-lavage brushing. This study demonstrated that one of the most effective preparations of the femoral canal for optimal mechanical fixation between cement and cancellous bone is pulse- lavage brushing. The use of hydrogen-peroxide soaked gauze in femoral canal preparation, either alone or in combination with pulse-lavage brushing, may not significantly improve prosthesis fixation

To assess the current literature on suture anchor placement for the purpose of identifying factors that lead to suture anchor perforation and techniques that reduce the likelihood of complications. Three databases (PubMed, Ovid MEDLINE, EMBASE) were searched, and two reviewers independently screened the resulting literature. Methodological quality of all included papers was assessed using Methodological Index for Non-Randomized Studies criteria and the Cochrane Risk of Bias Assessment tool. Results are presented in a narrative summary fashion using descriptive statistics. Fourteen studies were included in this review. Four case series (491 patients, 56.6% female, mean age 33.9 years), nine controlled cadaveric/laboratory studies (111 cadaveric hips and 12 sawbones, 42.2% female, mean age 60.0 years), and one randomized controlled trial (37 hips, 55.6% female, mean age 34.2 years) were included. Anterior cortical perforation by suture anchors led to pain and impingement of pelvic neurovascular structures. The anterior acetabular positions (three to four o'clock) had the thinnest bone, smallest rim angles, and highest incidence of articular perforation. Drilling angles from 10° to 20° measured off the coronal plane were acceptable. The mid-anterior (MA) and distal anterolateral (DALA) portals were used successfully, with some studies reporting difficulty placing anchors at anterior locations via the DALA portal. Small-diameter (< 1 .8-mm) suture anchors had a lower in vivo incidence of articular perforation with similar stability and pull-out strength in biomechanical studies. Suture anchors at anterior acetabular rim positions (3–4 o'clock) should be inserted with caution. Large-diameter (>2.3-mm) suture anchors increase the likelihood of articular perforation without increasing labral stability. Inserting small-diameter (< 1 .8-mm) all-suture suture anchors (ASAs) from 10° to 20° using curved suture anchor drill guides, may increase safe insertion angles from all cutaneous portals. Direct arthroscopic visualization, use of fluoroscopy, distal-proximal insertion, and the use of nitinol wire can help prevent articular violation