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

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

Aims. To draw a comparison of the pullout strengths of buttress thread, barb thread, and reverse buttress thread bone screws. Methods. Buttress thread, barb thread, and reverse buttress thread bone screws were inserted into synthetic cancellous bone blocks. Five screw-block constructs per group were tested to failure in an axial pullout test. The pullout strengths were calculated and compared. A finite element analysis (FEA) was performed to explore the underlying failure mechanisms. FEA models of the three different screw-bone constructs were developed. A pullout force of 250 N was applied to the screw head with a fixed bone model. The compressive and tensile strain contours of the midsagittal plane of the three bone models were plotted and compared. Results. The barb thread demonstrated the lowest pullout strength (mean 176.16 N (SD 3.10)) among the three thread types. It formed a considerably larger region with high tensile strains and a slightly smaller region with high compressive strains within the surrounding bone structure. The reverse buttress thread demonstrated the highest pullout strength (mean 254.69 N (SD 4.15)) among the three types of thread. It formed a considerably larger region with high compressive strains and a slightly smaller region with high tensile strains within the surrounding bone structure. Conclusion. Bone screws with a reverse buttress thread design will significantly increase the pullout strength. Cite this article: Bone Joint Res 2021;10(2):105–112

Objectives. Screw plugs have been reported to increase the fatigue strength of stainless steel locking plates. The objective of this study was to examine and compare this effect between stainless steel and titanium locking plates. Methods. Custom-designed locking plates with identical structures were fabricated from stainless steel and a titanium alloy. Three types of plates were compared: type I unplugged plates; type II plugged plates with a 4 Nm torque; and type III plugged plates with a 12 Nm torque. The stiffness, yield strength, and fatigue strength of the plates were investigated through a four-point bending test. Failure analyses were performed subsequently. Results. For stainless steel, type II and type III plates had significantly higher fatigue strength than type I plates. For titanium, there were no significant differences between the fatigue strengths of the three types of plates. Failure analyses showed local plastic deformations at the threads of screw plugs in type II and type III stainless steel plates but not in titanium plates. Conclusion. The screw plugs could increase the fatigue strength of stainless steel plates but not of titanium plates. Therefore, leaving screw holes open around fracture sites is recommended in titanium plates. Cite this article: L-W. Hung, C-K. Chao, J-R. Huang, J. Lin. Screw head plugs increase the fatigue strength of stainless steel, but not of titanium, locking plates. Bone Joint Res 2018;7:629–635. DOI: 10.1302/2046-3758.712.BJR-2018-0083.R1

Objectives. Bisphosphonates (BP) are the first-line treatment for preventing fragility fractures. However, concern regarding their efficacy is growing because bisphosphonate is associated with over-suppression of remodelling and accumulation of microcracks. While dual-energy X-ray absorptiometry (DXA) scanning may show a gain in bone density, the impact of this class of drug on mechanical properties remains unclear. We therefore sought to quantify the mechanical strength of bone treated with BP (oral alendronate), and correlate data with the microarchitecture and density of microcracks in comparison with untreated controls. Methods. Trabecular bone from hip fracture patients treated with BP (n = 10) was compared with naïve fractured (n = 14) and non-fractured controls (n = 6). Trabecular cores were synchrotron scanned and micro-CT scanned for microstructural analysis, including quantification of bone volume fraction, microarchitecture and microcracks. The specimens were then mechanically tested in compression. Results. BP bone was 28% lower in strength than untreated hip fracture bone, and 48% lower in strength than non-fractured control bone (4.6 MPa vs 6.4 MPa vs 8.9 MPa). BP-treated bone had 24% more microcracks than naïve fractured bone and 51% more than non-fractured control (8.12/cm. 2. vs 6.55/cm. 2. vs 5.25/cm. 2. ). BP and naïve fracture bone exhibited similar trabecular microarchitecture, with significantly lower bone volume fraction and connectivity than non-fractured controls. Conclusion. BP therapy had no detectable mechanical benefit in the specimens examined. Instead, its use was associated with substantially reduced bone strength. This low strength may be due to the greater accumulation of microcracks and a lack of any discernible improvement in bone volume or microarchitecture. This preliminary study suggests that the clinical impact of BP-induced microcrack accumulation may be significant. Cite this article: A. Jin, J. Cobb, U. Hansen, R. Bhattacharya, C. Reinhard, N. Vo, R. Atwood, J. Li, A. Karunaratne, C. Wiles, R. Abel. The effect of long-term bisphosphonate therapy on trabecular bone strength and microcrack density. Bone Joint Res 2017;6:602–609. DOI: 10.1302/2046-3758.610.BJR-2016-0321.R1

Objectives. The aim of this study was to systematically review the literature on measurement of muscle strength in patients with femoroacetabular impingement (FAI) and other pathologies and to suggest guidelines to standardise protocols for future research in the field. Methods. The Cochrane and PubMed libraries were searched for any publications using the terms ‘hip’, ‘muscle’, ‘strength’, and ‘measurement’ in the ‘Title, Abstract, Keywords’ field. A further search was performed using the terms ‘femoroacetabular’ or ‘impingement’. The search was limited to recent literature only. Results. A total of 29 articles were reviewed to obtain information on a number of variables. These comprised the type of device used for measurement, rater standardisation, the type of movements tested, body positioning and comparative studies of muscle strength in FAI versus normal controls. The studies found that hip muscle strength is lower in patients with FAI; this is also true for the asymptomatic hip in patients with FAI. Conclusions. Current literature on this subject is limited and examines multiple variables. Our recommendations for achieving reproducible results include stabilising the patient, measuring isometric movements and maximising standardisation by using a single tester and familiarising the participants with the protocol. Further work must be done to demonstrate the reliability of any new testing method. Cite this article: E. Mayne, A. Memarzadeh, P. Raut, A. Arora, V. Khanduja. Measuring hip muscle strength in patients with femoroacetabular impingement and other hip pathologies: A systematic review. Bone Joint Res 2017;6:66–72. DOI: 10.1302/2046-3758.61.BJR-2016-0081

Objectives. Our objective was to predict the knee extension strength and post-operative function in quadriceps resection for soft-tissue sarcoma of the thigh. Methods. A total of 18 patients (14 men, four women) underwent total or partial quadriceps resection for soft-tissue sarcoma of the thigh between 2002 and 2014. The number of resected quadriceps was surveyed, knee extension strength was measured with the Biodex isokinetic dynamometer system (affected side/unaffected side) and relationships between these were examined. The Musculoskeletal Tumor Society (MSTS) score, Toronto Extremity Salvage Score (TESS), European Quality of Life-5 Dimensions (EQ-5D) score and the Short Form 8 were used to evaluate post-operative function and examine correlations with extension strength. The cutoff value for extension strength to expect good post-operative function was also calculated using a receiver operating characteristic (ROC) curve and Fisher’s exact test. Results. Extension strength decreased when the number of resected quadriceps increased (p < 0.001), and was associated with lower MSTS score, TESS and EQ-5D (p = 0.004, p = 0.005, p = 0.006, respectively). Based on the functional evaluation scales, the cutoff value of extension strength was 56.2%, the equivalent to muscle strength with resection of up to two muscles. Conclusion. Good post-operative results can be expected if at least two quadriceps muscles are preserved. Cite this article: A. Tanaka, Y. Yoshimura, K. Aoki, M. Kito, M. Okamoto, S. Suzuki, T. Momose, H. Kato. Knee extension strength and post-operative functional prediction in quadriceps resection for soft-tissue sarcoma of the thigh. Bone Joint Res 2016;5:232–238. DOI: 10.1302/2046-3758.56.2000631

Objectives. The most prevalent disorders of the shoulder are related to the muscles of rotator cuff. In order to develop a mechanical method for the evaluation of the rotator cuff muscles, we created a database of isometric force generation by the rotator cuff muscles in normal adult population. We hypothesised the existence of variations according to age, gender and dominancy of limb. Methods. A total of 400 healthy adult volunteers were tested, classified into groups of 50 men and women for each decade of life. Maximal isometric force was measured at standardised positions for supraspinatus, infraspinatus and subscapularis muscles in both shoulders in every person. Torque of the force was calculated and normalised to lean body mass. The profiles of mean torque-time curves for each age and gender group were compared. Results. Our data showed that men gradually gained maximal strength in the fifth decade, and showed decreased strength in the sixth. In women the maximal strength was gained in the fourth decade with gradual decline to the sixth decade of life. The dominant arm was stronger in most of the tested groups. The torque profiles of the rotator cuff muscles in men at all ages were significantly higher than that in women. Conclusions. We found previously unrecognised variations of rotator cuff muscles’ isometric strength according to age, gender and dominancy in a normal population. The presented data may serve as a basis for the future studies for identification of the abnormal patterns of muscle isometric strength in patients with pathology of the rotator cuff muscles. Cite this article: Bone Joint Res 2013;2:214–19

Objectives. Taper junctions between modular hip arthroplasty femoral heads and stems fail by wear or corrosion which can be caused by relative motion at their interface. Increasing the assembly force can reduce relative motion and corrosion but may also damage surrounding tissues. The purpose of this study was to determine the effects of increasing the impaction energy and the stiffness of the impactor tool on the stability of the taper junction and on the forces transmitted through the patient’s surrounding tissues. Methods. A commercially available impaction tool was modified to assemble components in the laboratory using impactor tips with varying stiffness at different applied energy levels. Springs were mounted below the modular components to represent the patient. The pull-off force of the head from the stem was measured to assess stability, and the displacement of the springs was measured to assess the force transmitted to the patient’s tissues. Results. The pull-off force of the head increased as the stiffness of the impactor tip increased but without increasing the force transmitted through the springs (patient). Increasing the impaction energy increased the pull-off force but also increased the force transmitted through the springs. Conclusions. To limit wear and corrosion, manufacturers should maximize the stiffness of the impactor tool but without damaging the surface of the head. This strategy will maximize the stability of the head on the stem for a given applied energy, without influencing the force transmitted through the patient’s tissues. Current impactor designs already appear to approach this limit. Increasing the applied energy (which is dependent on the mass of the hammer and square of the contact speed) increases the stability of the modular connection but proportionally increases the force transmitted through the patient’s tissues, as well as to the surface of the head, and should be restricted to safe levels. Cite this article: A. Krull, M. M. Morlock, N. E. Bishop. Maximizing the fixation strength of modular components by impaction without tissue damage. Bone Joint Res 2018;7:196–204. DOI: 10.1302/2046-3758.72.BJR-2017-0078.R2

Objectives. There remains conflicting evidence regarding cortical bone strength following bisphosphonate therapy. As part of a study to assess the effects of bisphosphonate treatment on the healing of rat tibial fractures, the mechanical properties and radiological density of the uninjured contralateral tibia was assessed. Methods. Skeletally mature aged rats were used. A total of 14 rats received 1µg/kg ibandronate (iban) daily and 17 rats received 1 ml 0.9% sodium chloride (control) daily. Stress at failure and toughness of the tibial diaphysis were calculated following four-point bending tests. Results. Uninjured cortical bone in the iban group had a significantly greater mean (standard deviation (. sd. )), p < 0.001, stress at failure of 219.2 MPa (. sd. 45.99) compared with the control group (169.46 MPa (. sd. 43.32)) following only nine weeks of therapy. Despite this, the cortical bone toughness and work to failure was similar. There was no significant difference in radiological density or physical dimensions of the cortical bone. Conclusions. Iban therapy increases the stress at failure of uninjured cortical bone. This has relevance when normalising the strength of repair in a limb when comparing it with the unfractured limb. However, the 20% increase in stress at failure with iban therapy needs to be interpreted with caution as there was no corresponding increase in toughness or work to failure. Further research is required in this area, especially with the increasing clinical burden of low-energy diaphyseal femoral fractures following prolonged use of bisphosphonates. Cite this article: Bone Joint Res 2015;4:99–104

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

Aims. Orthopaedic surgery requires grafts with sufficient mechanical strength. For this purpose, decellularized tissue is an available option that lacks the complications of autologous tissue. However, it is not widely used in orthopaedic surgeries. This study investigated clinical trials of the use of decellularized tissue grafts in orthopaedic surgery. Methods. Using the ClinicalTrials.gov (CTG) and the International Clinical Trials Registry Platform (ICTRP) databases, we comprehensively surveyed clinical trials of decellularized tissue use in orthopaedic surgeries registered before 1 September 2022. We evaluated the clinical results, tissue processing methods, and commercial availability of the identified products using academic literature databases and manufacturers’ websites. Results. We initially identified 4,402 clinical trials, 27 of which were eligible for inclusion and analysis, including nine shoulder surgery trials, eight knee surgery trials, two ankle surgery trials, two hand surgery trials, and six peripheral nerve graft trials. Nine of the trials were completed. We identified only one product that will be commercially available for use in knee surgery with significant mechanical load resistance. Peracetic acid and gamma irradiation were frequently used for sterilization. Conclusion. Despite the demand for decellularized tissue, few decellularized tissue products are currently commercially available, particularly for the knee joint. To be viable in orthopaedic surgery, decellularized tissue must exhibit biocompatibility and mechanical strength, and these requirements are challenging for the clinical application of decellularized tissue. However, the variety of available decellularized products has recently increased. Therefore, decellularized grafts may become a promising option in orthopaedic surgery. Cite this article: Bone Joint Res 2023;12(3):179–188

Aims. There are concerns regarding nail/medullary canal mismatch and initial stability after cephalomedullary nailing in unstable pertrochanteric fractures. This study aimed to investigate the effect of an additional anteroposterior blocking screw on fixation stability in unstable pertrochanteric fracture models with a nail/medullary canal mismatch after short cephalomedullary nail (CMN) fixation. Methods. Eight finite element models (FEMs), comprising four different femoral diameters, with and without blocking screws, were constructed, and unstable intertrochanteric fractures fixed with short CMNs were reproduced in all FEMs. Micromotions of distal shaft fragment related to proximal fragment, and stress concentrations at the nail construct were measured. Results. Micromotions in FEMs without a blocking screw significantly increased as nail/medullary canal mismatch increased, but were similar between FEMs with a blocking screw regardless of mismatch. Stress concentration at the nail construct was observed at the junction of the nail body and lag screw in all FEMs, and increased as nail/medullary canal mismatch increased, regardless of blocking screws. Mean stresses over regions of interest in FEMs with a blocking screw were much lower than regions of interest in those without. Mean stresses in FEMs with a blocking screw were lower than the yield strength, yet mean stresses in FEMs without blocking screws having 8 mm and 10 mm mismatch exceeded the yield strength. All mean stresses at distal locking screws were less than the yield strength. Conclusion. Using an additional anteroposterior blocking screw may be a simple and effective method to enhance fixation stability in unstable pertrochanteric fractures with a large nail/medullary canal mismatch due to osteoporosis. Cite this article: Bone Joint Res 2022;11(3):152–161

Aims. Poly(methyl methacrylate) (PMMA)-based bone cements are the industry standard in orthopaedics. PMMA cement has inherent disadvantages, which has led to the development and evaluation of a novel silorane-based biomaterial (SBB) for use as an orthopaedic cement. In this study we test both elution and mechanical properties of both PMMA and SBB, with and without antibiotic loading. Methods. For each cement (PMMA or SBB), three formulations were prepared (rifampin-added, vancomycin-added, and control) and made into pellets (6 mm × 12 mm) for testing. Antibiotic elution into phosphate-buffered saline was measured over 14 days. Compressive strength and modulus of all cement pellets were tested over 14 days. Results. The SBB cement was able to deliver rifampin over 14 days, while PMMA was unable to do so. SBB released more vancomycin overall than did PMMA. The mechanical properties of PMMA were significantly reduced upon rifampin incorporation, while there was no effect to the SBB cement. Vancomycin incorporation had no effect on the strength of either cement. Conclusion. SBB was found to be superior in terms of rifampin and vancomycin elution. Additionally, the incorporation of these antibiotics into SBB did not reduce the strength of the resultant SBB cement composite whereas rifampin substantially attenuates the strength of PMMA. Thus, SBB emerges as a potential weight-bearing alternative to PMMA for the local delivery of antibiotics. Cite this article: Bone Joint Res 2021;10(4):277–284

Aims. Mechanical stimulation is a key factor in the development and healing of tendon-bone insertion. Treadmill training is an important rehabilitation treatment. This study aims to investigate the benefits of treadmill training initiated on postoperative day 7 for tendon-bone insertion healing. Methods. A tendon-bone insertion injury healing model was established in 92 C57BL/6 male mice. All mice were divided into control and training groups by random digital table method. The control group mice had full free activity in the cage, and the training group mice started the treadmill training on postoperative day 7. The quality of tendon-bone insertion healing was evaluated by histology, immunohistochemistry, reverse transcription quantitative polymerase chain reaction, Western blotting, micro-CT, micro-MRI, open field tests, and CatWalk gait and biomechanical assessments. Results. Our results showed a significantly higher tendon-bone insertion histomorphological score in the training group, and the messenger RNA and protein expression levels of type II collagen (COL2A1), SOX9, and type X collagen (COL10A1) were significantly elevated. Additionally, tendon-bone insertion resulted in less scar hyperplasia after treadmill training, the bone mineral density (BMD) and bone volume/tissue volume (BV/TV) were significantly improved, and the force required to induce failure became stronger in the training group. Functionally, the motor ability, limb stride length, and stride frequency of mice with tendon-bone insertion injuries were significantly improved in the training group compared with the control group. Conclusion. Treadmill training initiated on postoperative day 7 is beneficial to tendon-bone insertion healing, promoting biomechanical strength and motor function. Our findings are expected to guide clinical rehabilitation training programmes. Cite this article: Bone Joint Res 2023;12(5):339–351

Aims. Several artificial bone grafts have been developed but fail to achieve anticipated osteogenesis due to their insufficient neovascularization capacity and periosteum support. This study aimed to develop a vascularized bone-periosteum construct (VBPC) to provide better angiogenesis and osteogenesis for bone regeneration. Methods. A total of 24 male New Zealand white rabbits were divided into four groups according to the experimental materials. Allogenic adipose-derived mesenchymal stem cells (AMSCs) were cultured and seeded evenly in the collagen/chitosan sheet to form cell sheet as periosteum. Simultaneously, allogenic AMSCs were seeded onto alginate beads and were cultured to differentiate to endothelial-like cells to form vascularized bone construct (VBC). The cell sheet was wrapped onto VBC to create a vascularized bone-periosteum construct (VBPC). Four different experimental materials – acellular construct, VBC, non-vascularized bone-periosteum construct, and VBPC – were then implanted in bilateral L4-L5 intertransverse space. At 12 weeks post-surgery, the bone-forming capacities were determined by CT, biomechanical testing, histology, and immunohistochemistry staining analyses. Results. At 12 weeks, the VBPC group significantly increased new bone formation volume compared with the other groups. Biomechanical testing demonstrated higher torque strength in the VBPC group. Notably, the haematoxylin and eosin, Masson’s trichrome, and immunohistochemistry-stained histological results revealed that VBPC promoted neovascularization and new bone formation in the spine fusion areas. Conclusion. The tissue-engineered VBPC showed great capability in promoting angiogenesis and osteogenesis in vivo. It may provide a novel approach to create a superior blood supply and nutritional environment to overcome the deficits of current artificial bone graft substitutes. Cite this article: Bone Joint Res 2023;12(12):722–733

Aims. To determine whether half-threaded screw holes in a new titanium locking plate design can substantially decrease the notch effects of the threads and increase the plate fatigue life. Methods. Three types (I to III) of titanium locking plates were fabricated to simulate plates used in the femur, tibia, and forearm. Two copies of each were fabricated using full- and half-threaded screw holes (called A and B, respectively). The mechanical strengths of the plates were evaluated according to the American Society for Testing and Materials (ASTM) F382-14, and the screw stability was assessed by measuring the screw removal torque and bending strength. Results. The B plates had fatigue lives 11- to 16-times higher than those of the A plates. Before cyclic loading, the screw removal torques were all higher than the insertion torques. However, after cyclic loading, the removal torques were similar to or slightly lower than the insertion torques (0% to 17.3%), although those of the B plates were higher than those of the A plates for all except the type III plates (101%, 109.8%, and 93.8% for types I, II, and III, respectively). The bending strengths of the screws were not significantly different between the A and B plates for any of the types. Conclusion. Removing half of the threads from the screw holes markedly increased the fatigue life of the locking plates while preserving the tightness of the screw heads and the bending strength of the locking screws. However, future work is necessary to determine the relationship between the notch sensitivity properties and titanium plate design. Cite this article: Bone Joint Res 2020;9(10):645–652

Aims. This study examined whether systemic administration of melatonin would have different effects on osseointegration in ovariectomized (OVX) rats, depending on whether this was administered during the day or night. Methods. In this study, a titanium rod was implanted in the medullary cavity of one femoral metaphysis in OVX rats, and then the rats were randomly divided into four groups: Sham group (Sham, n = 10), OVX rat group (OVX, n = 10), melatonin day treatment group (OVX + MD, n = 10), and melatonin night treatment group (OVX + MN, n = 10). The OVX + MD and OVX + MN rats were treated with 30 mg/kg/day melatonin at 9 am and 9 pm, respectively, for 12 weeks. At the end of the research, the rats were killed to obtain bilateral femora and blood samples for evaluation. Results. Micro-CT and histological evaluation showed that the bone microscopic parameters of femoral metaphysis trabecular bone and bone tissue around the titanium rod in the OVX + MD group demonstrated higher bone mineral density, bone volume fraction, trabecular number, connective density, trabecular thickness, and lower trabecular speculation (p = 0.004) than the OVX + MN group. Moreover, the biomechanical parameters of the OVX + MD group showed higher pull-out test and three-point bending test values, including fixation strength, interface stiffness, energy to failure, energy at break, ultimate load, and elastic modulus (p = 0.012) than the OVX + MN group. In addition, the bone metabolism index and oxidative stress indicators of the OVX + MD group show lower values of Type I collagen cross-linked C-telopeptide, procollagen type 1 N propeptide, and malondialdehyde (p = 0.013), and higher values of TAC and SOD (p = 0.002) compared with the OVX + MN group. Conclusion. The results of our study suggest that systemic administration with melatonin at 9 am may improve the initial osseointegration of titanium rods under osteoporotic conditions more effectively than administration at 9 pm. Cite this article: Bone Joint Res 2022;11(11):751–762

Aims. To verify whether secretory leucocyte protease inhibitor (SLPI) can promote early tendon-to-bone healing after anterior cruciate ligament (ACL) reconstruction. Methods. In vitro: the mobility of the rat bone mesenchymal stem cells (BMSCs) treated with SLPI was evaluated by scratch assay. Then the expression levels of osteogenic differentiation-related genes were analyzed by real-time quantitative PCR (qPCR) to determine the osteogenic effect of SLPI on BMSCs. In vivo: a rat model of ACL reconstruction was used to verify the effect of SLPI on tendon-to-bone healing. All the animals of the SLPI group and the negative control (NC) group were euthanized for histological evaluation, micro-CT scanning, and biomechanical testing. Results. SLPI improved the migration ability of BMSCs and upregulated the expression of genes related to osteogenic differentiation of BMSCs in vitro. In vivo, the SLPI group had higher histological scores at the tendon-bone interface by histological evaluation. Micro-CT showed more new bone formation and bone ingrowth around the grafted tendon in the SLPI group. Evaluation of the healing strength of the tendon-bone connection showed that the SLPI group had a higher maximum failure force and stiffness. Conclusion. SLPI can effectively promote early tendon-to-bone healing after ACL reconstruction via enhancing the migration and osteogenic differentiation of BMSCs. Cite this article: Bone Joint Res 2022;11(7):503–512