Anterior Bridging Bone in a Newly Designed Cage for Lumbar Interbody Fusion: Radiographic and Finite Element Analysis.

OBJECTIVE: To evaluate the distribution of multiple anterior bridging bone (ABB) patterns using a newly designed interbody cage with 4 anterior holes that enable communication between the inside and outside of the cage and to estimate its mechanical effect by finite element analysis (FEA). METHODS: Patients underwent single-level lumbar interbody fusion using ABB cages. Two raters evaluated the distribution patterns of ABB on computed tomography scans 1 year after surgery. We defined the term H-fusion as the presence of complete anterior extracage and intracage bone bridging, with ≥1 ABBs between them. We performed finite element analysis to investigate the effect of ABB on maximal stiffness. RESULTS: The study enrolled 98 patients. ABB was most frequently observed in the medial hole of the cages (73.7%). The mean number of ABBs was 3.65, and H-fusion was observed at 135 levels (34%). Postoperative improvement in the Oswestry Disability Index was significantly higher in patients who achieved interbody fusion and H-fusion than in patients who did not. As ABB was added, the increment in the relative maximal stiffness was most affected under flexion and extension forces. CONCLUSIONS: We observed an average of 3.65 complete ABBs. Finite element analysis demonstrated that ABB could increase the stability in fused segments, especially under flexion and extension stress. Our results suggest that the ABB cage, which allows communicating cross-bridging between inside and outside of the cage, may facilitate a more stable fusion process than a conventionally designed cage.

Highly aligned carbon nanotubes and their sensor applications.

Flexible electronics comprising carbon nanotube (CNT) membranes and polymer composites are used in diverse applications, including health monitoring. Devices prepared using such electronics need to exhibit acceptable sensitivity at high strains, with the advantage of negligible hysteresis. Herein, we report a simple, physically robust method to fabricate a highly sensitive and stretchable sensor that enables the detection of pressure, strain, and human activity with facial expressions based on the highly aligned carbon nanotubes embedded in polydimethylsiloxane (PDMS). The aligned CNT network in PDMS modulates the electron conduction path in a unidirectional manner and provides multimodal mechanical sensing ability with a wide sensing range and high sensitivity. The highly aligned CNT sensor demonstrates high-pressure sensitivity (1.29 kPa-1), excellent stability and repeatability (over 10 000 cycles) with negligible hysteresis, and a good strain sensitivity over a wide range (up to 65%) with a good linear response. We confirmed the applicability of the sensor to detect small signals, such as heartbeat and pulse rate, expressions, and voice recognition, and that it could distinguish between various human motions with a very short recovery time of approximately 50 ms.

A novel design, analysis and 3D printing of Ti-6Al-4V alloy bio-inspired porous femoral stem.

The current study is proposing a design envelope for porous Ti-6Al-4V alloy femoral stems to survive under fatigue loads. Numerical computational analysis of these stems with a body-centered-cube (BCC) structure is conducted in ABAQUS. Femoral stems without shell and with various outer dense shell thicknesses (0.5, 1.0, 1.5, and 2 mm) and inner cores (porosities of 90, 77, 63, 47, 30, and 18%) are analyzed. A design space (envelope) is derived by using stem stiffnesses close to that of the femur bone, maximum fatigue stresses of 0.3σys in the porous part, and endurance limits of the dense part of the stems. The Soderberg approach is successfully employed to compute the factor of safety Nf > 1.1. Fully porous stems without dense shells are concluded to fail under fatigue load. It is thus safe to use the porous stems with a shell thickness of 1.5 and 2 mm for all porosities (18-90%), 1 mm shell with 18 and 30% porosities, and 0.5 mm shell with 18% porosity. The reduction in stress shielding was achieved by 28%. Porous stems incorporated BCC structures with dense shells and beads were successfully printed.

A comprehensive analysis of bio-inspired design of femoral stem on primary and secondary stabilities using mechanoregulatory algorithm.

The coated porous section of stem surface is initially filled with callus that undergoes osseointegration process, which develops a bond between stem and bone, lessens the micromotions and transfers stresses to the bone, proximally. This phenomenon attributes to primary and secondary stabilities of the stems that exhibit trade-off the stem stiffness. This study attempts to ascertain the influence of stem stiffness on peri-prosthetic bone formation and stress shielding when in silico models of solid CoCr alloy and Ti alloy stems, and porous Ti stems (53.8 GPa and 31.5 GPa Young's moduli) were implanted. A tissue differentiation predictive mechanoregulation algorithm was employed to estimate the evolutionary bond between bone and stem interfaces with 0.5-mm- and 1-mm-thick calluses. The results revealed that the high stiffness stems yielded higher stress shielding and lower micromotions than that of low stiffness stems. Contrarily, bone formation around solid Ti alloy stem and porous Ti 53.8 GPa stem was augmented in 0.5-mm- and 1-mm-thick calluses, respectively. All designs of stems exhibited different rates of bone formation, diverse initial micromotions and stress shielding; however, long-term bone formation was coherent with different stress shielding. Therefore, contemplating the secondary stability of the stems, low stiffness stem (Ti 53.8 GPa) gave superior biomechanical performance than that of high stiffness stems.

Influence of functionally graded pores on bone ingrowth in cementless hip prosthesis: a finite element study using mechano-regulatory algorithm.

Cementless hip prostheses with porous outer coating are commonly used to repair the proximally damaged femurs. It has been demonstrated that stability of prosthesis is also highly dependent on the bone ingrowth into the porous texture. Bone ingrowth is influenced by the mechanical environment produced in the callus. In this study, bone ingrowth into the porous structure was predicted by using a mechano-regulatory model. Homogenously distributed pores (200 and 800 [Formula: see text]m in diameter) and functionally graded pores along the length of the prosthesis were introduced as a porous coating. Bone ingrowth was simulated using 25 and 12 [Formula: see text]m micromovements. Load control simulations were carried out instead of traditionally used displacement control. Spatial and temporal distributions of tissues were predicted in all cases. Functionally graded pore decreasing models gave the most homogenous bone distribution, the highest bone ingrowth (98%) with highest average Young's modulus of all tissue phenotypes approximately 4.1 GPa. Besides this, the volume of the initial callus increased to 8.33% in functionally graded pores as compared to the 200 [Formula: see text]m pore size models which increased the bone volume. These findings indicate that functionally graded porous surface promote bone ingrowth efficiently which can be considered to design of surface texture of hip prosthesis.

Polydeoxyribonucleotide improves tendon healing following achilles tendon injury in rats.

Tendon injuries are major musculoskeletal disorders. Polydeoxyribonucleotide activates the adenosine receptor subtype A2A, resulting in tissue growth and neogenesis. This experimental study confirms that polydeoxyribonucleotide can improve secretion of various growth factors, promote collagen synthesis, and restore tensile strength of the Achilles tendon in a rat model with Achilles tendon injury. Thirty-six male Sprague-Dawley rats, aged 7 weeks, were divided into two groups, and the Achilles tendon was transected and repaired using the modified Kessler's method. In the experimental group (n = 18), the rats received daily intraperitoneal administration of polydeoxyribonucleotide (8 mg/kg/day for 1, 2, or 4 weeks). The control groups received the same amount of normal saline. The rats were euthanized at 1, 2, and 4 weeks, and tissues from the repair site were harvested. The cross-sectional area of the tendon was significantly increased at 2 and 4 weeks in polydeoxyribonucleotide group (p = 0.008 and p = 0.017, respectively). Moreover, tendons in the polydeoxyribonucleotide group were more resistant to mechanical stress at 2 and 4 weeks (p = 0.041 and p = 0.041, respectively). The staining levels of collagen type I in the experimental group were significantly stronger at 2 and 4 weeks (p = 0.026 and p = 0.009, respectively). Furthermore, higher expression levels of fibroblast growth factor, vascular endothelial growth factor, and transforming growth factor ß1 were detected in the experimental group at 4 weeks (p = 0.041, p = 0.026, and p = 0.041, respectively). This study confirms that polydeoxyribonucleotide can improve the tensile strength of the rats' Achilles tendon following injury and repair. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1767-1776, 2018.

Comparison of Flexor Tendon Suture Techniques Including 1 Using 10 Strands.

PURPOSE: To compare mechanical properties of a multistrand suture technique for flexor tendon repair with those of conventional suture methods through biomechanical and clinical studies. METHODS: We describe a multistrand suture technique that is readily expandable from 6 to 10 strands of core suture. For biomechanical evaluation, 60 porcine flexor tendons were repaired using 1 of the following 6 suture techniques: Kessler (2-strand), locking cruciate (4-strand), Lim/Tsai's 6-strand, and our modified techniques (6-, 8-, or 10-strand). Structural properties of each tenorrhaphy were determined through tensile testing (ultimate failure load and force at 2-mm gap formation). Clinically we repaired 25 flexor tendons using the described 10-strand technique in zones I and II. Final follow-up results were evaluated according to the criteria of Strickland and Glogovac. RESULTS: In the biomechanical study, tensile properties were strongly affected by repair technique; tendons in the 10-strand group had approximately 106%, 66%, and 39% increased ultimate load to failure (average, 87 N) compared with those in the 4-, 6-, and 8-strand groups, respectively. Tendons in the 10-strand group withstood higher 2-mm gap formation forces (average, 41 N) than those with other suture methods (4-strand, 26 N; 6-strand, 27 N; and 8-strand, 33 N). Clinically, we obtained 21 excellent, 2 good, and 2 fair outcomes after a mean of 16 months (range, 6-53 mo) of follow-up. No patients experienced poor results or rupture. CONCLUSIONS: The 10-strand suture repair technique not only increased ultimate strength and force at the 2-mm gap formation compared with conventional suture methods, it also showed good clinical outcomes. This multistrand suture technique can greatly increase the gap resistance of surgical repair, facilitating early mobilization of the affected digit. TYPE OF STUDY/LEVEL OF EVIDENCE: Therapeutic IV.

The isometry of two different paths for remnant-preserving posterior cruciate ligament reconstruction.

PURPOSE: It is reported that the length of the posterior cruciate ligament (PCL) fibres increases as the knee flexes, and the magnitude of the length change reaches up to 9.8 mm throughout the range of motion, which exceeds the range of failure strain. Therefore, we postulated that a compensatory mechanism must be recruited to overcome this large strain in order to maintain physiologic function as a key component of joint kinematics. Our main objective was to compare the length change pattern for the linear distance between the femoral and tibial tunnels with the length change patterns derived from a real isometer test of different curvatures. METHODS: We utilized ten intact cadaveric knees and created a vertical femoral tunnel (5 mm medial to the roof of the intercondylar notch and 5 mm proximal from the articular margin) and lateral tibial tunnels (5 mm proximal to the posterior bony ridge on the lateral side of the PCL fibre) and performed a 3D-CT scan at 0º, 30º, 60º, 90º, and 120º. The distances between the femoral and tibial tunnels were calculated from the 3D coordinates. Real isometry was checked both (1) over the PCL and (2) under the PCL using an isometer with an accuracy of 0.1 mm. RESULTS: The path over the PCL had the longest intra-articular length, followed by the path under the PCL, and the lengths measured by CT, respectively. The path over the PCL had a more curved path compared with the path under the PCL and the lengths measured by CT. The lengths measured by CT showed significantly larger excursion than the real isometer test. The path over the PCL showed the least excursion through the range of motion, followed by the path under the PCL, and the lengths measured by CT, respectively. CONCLUSION: Our findings suggested that a more curved PCL path has better isometry because the curvature of the PCL compensates for the length change between 0º and 60º flexion. In remnant preservation PCL reconstruction, the passage of graft over the PCL would have increased intra-articular length and better isometry compared with straight under the PCL path. LEVEL OF EVIDENCE: Basic science study.

How isometric are the anatomic femoral tunnel and the anterior tibial tunnel for anterior cruciate ligament reconstruction?

PURPOSE: The purpose of this study was to evaluate the isometry of an anatomic femoral tunnel and anterior tibial tunnel positions. METHODS: Tibial tunnels were made at 2 different locations in 10 cadaveric knees: the conventional tunnel and a more anterior position. Three-dimensional computed tomography (CT) scanning was then performed at 0°, 30°, 60°, 90°, and 120°. After removal of the anterior cruciate ligament from its femoral attachment, the 2 different femoral tunnels were marked at (1) the vertical femoral tunnel point and (2) the anatomic femoral tunnel point. After scans were repeated for coordinate transformation, the change in length between the tunnels was calculated with imaging software (OsiriX, version 3.2; Apple, Cupertino, CA) and the center of rotation for the femoral tunnels was calculated with a least squares fitting algorithm. RESULTS: The conventional tibial tunnel-vertical femoral tunnel combination showed the least excursion as knee flexion angle changed. The vertical femoral tunnel combination groups showed a trend toward increasing length as the knee flexion angle increased. In contrast, the anatomic femoral tunnel combination groups displayed a trend toward decreased length with increasing knee flexion. At less than 30° of flexion, the tibial anterior-anatomic femoral tunnel showed the least excursion. CONCLUSIONS: The anatomic femoral tunnel was nonisometric, and the differences in isometry for each tunnel type were explained primarily by differences in relations between the centers of rotation of tunnels and tunnel position. When a femoral anatomic tunnel is chosen for anterior cruciate ligament reconstruction, the anterior tibial tunnel offers greater isometric benefits than the conventional tibial tunnel, especially in near full extension. CLINICAL RELEVANCE: The distance between anatomic femoral and tibial tunnels is greatest in full extension and decreases with flexion. This would result in graft laxity. The surgeon should give consideration to a more anterior tibial tunnel position, which shows less excursion in early flexion.

Evaluation of tunnel position of posterolateral corner reconstruction using 3-dimensional computed tomogram.

PURPOSE: To evaluate the isometry of different tunnel positions in posterolateral corner (PLC) reconstruction using 3-dimensional computed tomography. METHODS: In 10 fresh-frozen cadaveric knees, fibular tunnels were made from the anterodistal surface of the fibular neck to the posteroproximal fibular tip. Tibial tunnels were made from just medial to the Gerdy tubercle to a point 1 to 1.5 cm medial to the proximal tibiofibular joint. Femoral condyles were marked at 3 different locations: (1) epicondyle, (2) 5 mm distal-anterior to the epicondyle, and (3) 18 mm distal-anterior to the epicondyle. All specimens were scanned by computed tomography at different ranges of motion. Relative length changes between the tunnels were calculated by use of medical imaging software, and the center of rotation (COR) of each distal tunnel was obtained by use of a least-squares circle-fitting algorithm. RESULTS: The anterior fibular tunnel to lateral epicondyle and the posterior fibular or posterior tibial tunnel to 5 mm distal-anterior to the lateral epicondyle showed the best results in terms of isometry. The COR of the posterior fibular tunnel is distal and anterior to the epicondyle, whereas the COR of the posterior tibial tunnel is distal and slightly posterior to the epicondyle (8.4 mm away from the epicondyle, with a -8.4° angle along the longitudinal axis of the femur). The COR of the anterior fibular tunnel is located posterior and distal to the epicondyle. CONCLUSIONS: Contrary to our hypothesis, the distal tunnels for PLC reconstruction each have different isometric points. The isometric point of the posterior fibular tunnel is distal and anterior to the epicondyle, whereas the isometric points of the posterior tibial and anterior fibular tunnels are distal and posterior to the epicondyle. CLINICAL RELEVANCE: The isometric pattern of each tunnel combination should be considered in PLC reconstruction; currently, popliteus tendon reconstruction is non-isometric.

Accuracy and reliability of length measurements on three-dimensional computed tomography using open-source OsiriX software.

There is a growing interest in three-dimensional computed tomography (3D-CT) as a research tool for the study of bone, joint anatomy, and kinematics. However, when CT data are processed and handled manually using image processing programs to yield 3D image and coordinate value, systematic and random errors should be validated. We evaluated the accuracy and reliability of length measurement on CT with OsiriX software. 3D-CT scans were made of 14 frozen pig knees with five transosseous holes in the metaphyseal portion of femur. The lengths between tunnel orifices were measured using Mitutoyo Digimatic digital calipers to establish the gold standard, and with the OsiriX program in 3D multi-planar reformatting mode for comparison. All measurements were recorded by a principal (replicate 1, trial 1) and a secondary observer (replicate 2, trial 1) and were repeated once by each observer (trial 2). The mean differences between OsiriX and real measurements were less than 0.1 mm in both replicates, and maximum differences were less than 0.3 mm. There were no significant differences between the replicates and real measurements (p=0.544 and 0.622 for replicates 1 and 2, respectively). The intraclass correlation coefficients (ICC) were very high between trials and between replicates (ICC=0.998 and 0.999, respectively). For kinematic analysis of the knees, length measurements on 3D-CT using OsiriX program can be used as alternatives to real measurements with less than 0.3-mm accuracy and very high reliability.