Additive manufactured osseointegrated screws with hierarchical design

Bone screws are devices used to fix implants or bones to bones.However,conventional screws are mechanically fixed with thread and often face long-term failure due to poor osseointegration.To improve osseointegration,screws are evolving from solid and smooth to porous and rough.Additive manufacturing(AM)offers a high degree of manufacturing freedom,enabling the preparation of predesigned screws that are porous and rough.This paper provides an overview of the problems currently faced by bone screws:long-term loosening and screw breakage.Next,advances in osseointegrated screws are summarized hierarchically(sub-micro,micro,and macro).At the sub-microscale level,we describe surface-modification techniques for enhancing osseointegration.At the micro level,we summarize the micro-design parameters that affect the mechanical and biological properties of porous osseointegrated screws,including porosity,pore size,and pore shape.In addition,we highlight three promising pore shapes:triply periodic minimal surface,auxetic structure with negative Poisson ratio,and the Voronoi structure.At the macro level,we outline the strategies of graded design,gradient design,and topology optimization design to improve the mechanical strength of porous osseointegrated screws.Simultaneously,this paper outlines advances in AM technology for enhancing the mechanical properties of porous osseointegrated screws.AM osseointegrated screws with hierarchical design are expected to provide excellent long-term fixation and the required mechanical strength.

Mechanical and corrosion properties of partially degradable bone screws made of pure iron and stainless steel 316L by friction welding

This paper reports a series of in vitro, ex vivo and in vivo mechanical and corrosion studies of pin and screw prototype made of friction welded pure iron and 316 L type stainless steel aiming to evaluate the applicability of the partially removable bone screws. Results showed that the pin possesses bending, tensile and torsional strengths of1706±147, 666±7 and 0.34±0.03 MPa, respectively. The pin degraded at an average weight loss rate of 17.15×10-5 g cm-2 day-1 and released Fe ions at an average concentration of 2.38 ppm. Plastic deformation induced by torsion increased the corrosion rate of the pin from 0.0014 to 0.0137 mm year-1.The maximum pull-out load of the screw prototypes was3800 N with a calculated failure strength by shear load equal to22.2 k N which is higher than the strength of the cortical bone.Detailed analysis of the rat's blood cells during 60 days of the pin implantation indicated a normal response with low neutrophils/lymphocytes ratio of 0.3-0.5. Iron ion concentration in the rat's blood slightly increased from 55 to 61 ppm without affecting the tissue recovering and healing phase. Histological evaluation confirmed the presence of macrophage cells as a normal response to the released iron particles around the iron section of the pin.

Cortical bone trajectory screws in the treatment of lumbar degenerative disc disease in patients with osteoporosis

Lumbar degenerative disc disease(DDD)in the elderly population remains a global health problem,especially in patients with osteoporosis.Osteoporosis in the elderly can cause failure of internal fixation.Cortical bone trajectory(CBT)is an effective,safe and minimally invasive technique for the treatment of lumbar DDD in patients with osteoporosis.In this review,we analyzed the anatomy,biomechanics,and advantages of the CBT technique in lumbar DDD and revision surgery.Additionally,the clinical trials and case reports,indications,advancements and limitations of this technique were further discussed and reviewed.Finally,we concluded that the CBT technique can be a practical,effective and safe alternative to traditional pedicle screw fixation,especially in DDD patients with osteoporosis.

Atlantoaxial joint fusion using anterior transarticular screw fixation and bone grafting for atlantoaxial joint instability

Objective To evaluate the clinical application of atlantoaxial joint fusion using anterior transarticular screw fixation and bone grafting for atlantoaxial joint instability. Methods Twenty-three cases of atlantoaxial joint instability were

Multitrack and multianchor point screw technique combined with the Wiltse approach for lesion debridement for lumbar tuberculosis

BACKGROUND The incidence of lumbar tuberculosis is high worldwide,and effective treatment is a continuing problem.AIM To study the safety and efficacy of the multitrack and multianchor point screw technique combined with the contralateral Wiltse approach for lesion debridement to treat lumbar tuberculosis.METHODS The C-reactive protein(CRP)level,erythrocyte sedimentation rate(ESR),visual analogue scale(VAS)score,oswestry disability index(ODI)and American Spinal Injury Association(ASIA)grade were recorded and analysed pre-and postoperatively.RESULTS The CRP level and ESR returned to normal,and the VAS score and ODI were decreased at 3 mo postoperatively,with significant differences compared with the preoperative values(P<0.01).Neurological dysfunction was relieved,and the ASIA grade increased,with no adverse events.CONCLUSION The multitrack,multianchor point screw fixation technique combined with the contralateral Wiltse approach for debridement is an effective and safe method for the treatment of lumbar tuberculosis.

Influence of Medial Support Screws on the Maintenance of Fracture Reduction after Locked Plating of Proximal Humerus Fractures

Background： Technical aspects of the correct placement of medial support locking screws in the locking plate for proximal humerus fractures remain incompletely understood. This study was to evaluate the clinical relationship between the number of medial support screws and the maintenance of fracture reduction after locked plating of proximal humerus fractures. Methods： We retrospectively evaluated 181 patients who had been surgically treated for proximal humeral fractures （PHFs） with a locking plate between September 2007 and June 2013. All cases were then subdivided into one of four groups as follows： 75 patients in the medial cortical support （MCS） group, 26 patients in the medial multiscrew support （MMSS） group, 29 patients in the medial single screw support （MSSS） group, and 51 patients in the 11o medial support （NMS） group. Clinical and radiographic evaluations included the Constant-Murley score （CM）, visual analogue scale （VAS）, complications, and revision surgeries. The neck-shaft angle （NSA） was measured in a true anteroposterior radiograph immediately postoperation and at final follow-up. One-way analysis of variance or KruskaI-Wallis test was used for statistical analysis of measurement data, and Chi-square test or Fisher＇s exact test was used for categorical data. Results： The mean postoperative NSAs were 133.46°± 6.01°, 132.39° ± 7.77°. 135.17° ± 10.15°, and 132.41° ± 7.16° in the MCS, MMSS, MSSS, and NMS groups, respectively, and no significant differences were found （F = 1.02, P= 0.387）. In the final follow-up, the NSAs were 132.79° ±6.02°, 130.19° ± 9.25°, 131.28° ± 12.85°, and 127.35° ± 8.50° in the MCS, MMSS, MSSS, and NMS groups, respectively （F = 4.40, P = 0.008）. There were marked differences in the NSA at the final follow-up between the MCS and NMS groups （P = 0.004）. The median （interquartile range [IQR]） NSA losses were 0.0° （0.0-1.0）°, 1.3° （0.0-3.1）°, 1.5° （ 1.0-5.2）°, and 4.0° （ 1.2 -7.1 ）° in the MCS, MMSS, MSSS, and NMS groups, respectively （H = 60.66, P 〈 0.001 ）. There were marked differences in NSA loss between the MCS and the other three groups （MCS vs. MMSS, Z = 3.16, P = 0.002; MCS vs. MSSS, Z = 4.78, P 〈 0.001; and MCS vs. NMS, Z = 7.34, P 〈 0.001）. There was also significantly less NSA loss observed in the MMSS group compared to the NMS group （Z = -3.16, P = 0.002）. However, there were no significant differences between the MMSS and MSSS groups （Z = -1.65, P = 0.225） or the MSSS and NMS groups （Z =- 1.21, P = 0.099）. The average CM scores were 81.35 ± 9.79, 78.04± 8.97, 72.76 ± 10.98, and 67.33 ± 12.31 points in the MCS, MMSS, MSSS, and NMS groups, respectively （F = 18.68, P 〈 0.001）. The rates of excellent and good CM scores were 86.67%, 80.77%, 65.52%, and 43.14% in the MCS, MMSS, MSSS, and NMS groups, respectively （ X^2 = 29.25, P 〈 0.001 ）. The median （IQR） VAS scores were 1 （0-2）, l （0 2）,2 （ 1-3）, and 3 （1-5） points in the MCS, MMSS, MSSS, and NMS groups, respectively （H = 27.80, P 〈 0.001）. Functional recovery was markedly better and VAS values were lower in the MCS and MMSS groups （for CM scores： MCS vs. MSSS, P 〈 0.001 ; MCS vs. N MS. P 〈 0.001; MMSS vs. MSSS, P= 0.031 and MMSS vs. NMS, P 〈 0.001 and for VAS values： MCS vs. MSSS, Z=3.31, P = 0.001： MCS vs. NMS, Z = 4.64, P 〈 0.001; MMSS vs. MSSS, Z = -2.09, P = 0.037： and MMSS vs. NMS, Z=-3.16, P = 0.003）.Conclusions： Medial support screws might help enhance mechanical stability and maintain fracture reduction when used to treat PHFs with medial metaphyseal comminution or malreduction.

Improving the fretting biocorrosion of Ti6Al4V alloy bone screw by decorating structure optimised TiO2 nanotubes layer

TiO2 nanotubes(NT)has been demonstrated its potential in orthopaedic applications due to its enhanced surface wettability and bio-osteointegration.However,the fretting biocorrosion is the main concern that limited its successfully application in orthopaedic application.In this study,a structure optimised thin TiO2 nanotube(SONT)layer was successfully created on Ti6Al4V bone screw,and its fretting corrosion performance was investigated and compared to the pristine Ti6Al4V bone screws and NT decorated screw in a bone-screw fretting simulation rig.The results have shown that the debonding TiO2 nanotube from the bone screw reduced significantly,as a result of structure optimisation.The SONT layer also exhibited enhanced bio-corrosion resistance compared pristine bone screw and conventionally NT modified bone screw.It is postulated that interfacial layer between TiO2 nanotube and Ti6Al4V substrate,generated during structure optimisation process,enhanced bonding of TiO2 nanotube layer to the Ti6Al4V bone screws that leading to the improvement in fretting corrosion resistance.The results highlighted the potential SONT in orthopaedic application as bone fracture fixation devices.

Bone cement enhanced pedicle screw fixation combined with vertebroplasty for elderly patients with malignant spinal tumors

Background Older patients with malignant spinal tumors are difficult to treat because they have many co-morbidities including osteoporosis. The purpose of this research is to discuss the technique and clinical outcome of bone cement enhanced pedicle screw fixation combined with vertebroplasty （the Sandwich Procedure） for elderly patients with severe osteoporosis and malignant spinal tumors. Methods This study includes 28 consecutive elderly patients with malignant thoracic or lumbar spinal tumors. There were nine patients with myelomas, and 19 patients with metastatic bone tumors. The Sandwich Procedure began with curettage of the tumor and a vertebroplasty with bone cement （polymethyl methacrylate, PMMA）, followed by PMMA enhanced pedicle screw fixation. Patients were evaluated with the visual analogue scale （VAS）, oswestry disability index （ODI）, American Spinal Cord Injury Association （ASIA） neurological function classification, and the radiographic degree of kyphosis （Cobb angle）. Data were analyzed using paired t-test to compare the pre- and post-operative values. The complications, local recurrences, and the survival status were also recorded. Results There was no operative mortality, and the mean operative time was 210 minutes （range 150-250 minutes）. The average blood loss was 1550 ml （range 650-3300 ml）. The average amount of cement for vertebroplasty was 3.6 ml （range 3-5 ml）. The VAS, ODI, and ASIA scores were significantly improved after surgery （P 〈0.05）. However, we found no differences between the pre and post-operative Cobb angles. The shortest survival time was 3 months, and we found no evidence of local recurrence in this group of patients. Conclusion The Sandwich Procedure is a safe operation and provides symptomatic relief in these difficult patients, permitting further treatment with chemotherapy or radiotherapy.

Ultrafine-grained Nb-Cu immiscible alloy implants for hard tissue repair:Fabrication,characterization,and in vitro and in vivo evaluation

The biocompatible metallic implants with strong osteointegration often lack the ability of anti-infection.The biocompatible niobium(Nb)containing the antibacterial copper(Cu),the obtained Nb-Cu alloy,could be a potential candidate to solve this issue.To test this hypothesis,ultrafine-grained Nb-Cu immiscible alloys were fabricated via mechanical alloying and spark plasma sintering.The aim of this study was to investigate the microstructure,mechanical properties,magnetic susceptibility,corrosion behavior,ion release,and the bactericidal activity,biocompatibility and osteogenic potential of the Nb-Cu alloys in vitro and their osteogenesis and osteointegration ability in vivo with a comparison with pure Nb.The rat cranial defect model and the bone screws insertion in rabbit femoral bone were used to evaluate the osteogenesis and osteointegration ability,respectively.The results showed that after the addition of 3 wt.%of Cu,the compressive strength was significantly improved from 1.57 GPa to 2.21 GPa and the magnetic susceptibility slightly decreased.The Nb-3 wt.%Cu(Nb-3Cu)alloy exhibited higher corrosion resistance than pure Nb in Hank’s solution and strong bactericidal activity against both E.coli and S.aureus.In vitro,the Nb-3Cu alloy showed comparable biocompatibility with pure Nb.The addition of 3 wt.%Cu also significantly enhanced the expression of osteogenesis-related genes(RUNX2,ALP,COLA1 and OCN)of pre-osteoblasts.In vivo,the Nb-3Cu alloy promoted bone regeneration at the defect sites and showed enhanced osteointegration after 12 weeks of implantation.Such a good combination of high mechanical strength and corrosion resistance,strong antibacterial activity and improved osteogenesis and osseointegration ability enables the present Nb-3Cu alloy a promising candidate for heavy load-bearing hard tissue repair.

Experience in surgical treatment of typeⅡodontoid fractures:A report of two cases and review of the literature

Two cases of typeⅡodontoid fractures were reported to share our experience in surgery treatment of such cases.A 33-year-old woman with comminuted typeⅡodontoid fracture and a 42-year-old man with fracture end hardened typeⅡodontoid fracture received surgical treatment in our hospital.Though imaging examination suggested that these two patients were suitable for anterior screw fixation,we encountered difficulties during the operation.The two patients eventually underwent posterior C1–C2 fusion surgery and recovered well.According to the experience of these two cases,we found that the fracture line angle and the degree of comminution are two important factors affecting surgical decision-making.Although anterior screw fixation is the ideal choice for typeⅡodontoid fractures with anterior superior to posterior inferior fracture line,it may not be the best choice for comminuted or fracture end hardened typeⅡodontoid fractures.

Applied anatomy of the lower cervical pedicle screw insertion

Objective: To ascertain an accurate approach to inserting the pedicle screw into C3-C7 segments of the cervical vertebra.Methods: Anatomic morphology of lateral mass and pedicle, and their anatomic relationship with the adjacent tissue were observed on C3-C7 segments of 25 adult embalmed cadavers (50 sides).Results: 1 ) The inferior edge of the base of the posterior tubercle of the transverse process and the inferior edge of the pedicle were connected with each other on 25 adult embalmed cadavers (50 sides ). The transverse section which passed through the median point between the superior edge and the inferior edge of the base of the posterior tubercle of the transverse process, and the transverse section which passed through the central axis between the superior edge and the inferior edge of the pedicle, were in the same horizontal plane. The superior and inferior position of placing the pedicle screw was determined by this transverse section, which passed through the median point between the superior and the inferior edge of the base of the posterior tubercle of the transverse process. 2 ) There was a directed internaldownwards "triangular sulcule" between the base of the posterior tubercle of the transverse process and the anterolateral edge of the inferior articular process. The anterior wall of the triangular sulcule was the base of the posterior tubercle of the transverse process, the posterior wall was the anterolateral edge of the inferior articular process, and the bottom of the sulcule was connected with the interior edge of the pedicle. The vertical length between the top of triangle and the planes of inferior edge of the pedicle was (2.78 ± 1.71 ) mm. The inferior edge of the cervical pedicle could be detected using a blunt probe along the "triangular sulcule" between the base of the posterior tubercle of the transverse process and the anterolateral edge of the inferior articular process in surgical operation. 3 )The lateral fovea of the articular process was observed on all lateral masses (50 sides ). The internal and external position of the entrance point could depend on anatomic landmarks: the lateral edge of the lateral fovea of the articular process. The horizontal length between the lateral fovea of the articular process and the entrance point was (3.14 ± 1.45 ) mm. 4 ) The diameter of pedicle screw,about (2.78 ± 1.71 ) mm, was the transverse diameter of the cancellous bone of the greatest narrow part of the cervical pedicle.Conclusions: The median point between the superior edge and the inferior edge of the base of the posterior tubercle of the transverse process, the lateral fovea of the articular process, and the triangular sulcule between the base of the posterior tubercle of the transverse process and the anterolateral edge of inferior articular process, are easy to be exposed and identified in surgical operation. The pedicle screw can be precisely inserted through this method.