Porcine Knee Research Articles

Application of albumin-grafted scaffolds to promote neocartilage formation

This study investigates the capacity of albumin-grafted biomaterials as tissue engineering scaffolds to regenerate cartilaginous components. Porcine knee chondrocytes were seeded and cultivated in porous ternary matrix consisting of polyethylene oxide, chitin, and chitosan with surface albumin. The results revealed that the quantity of albumin did not affect the viability of porcine knee chondrocytes in the constructs. However, a high grafting concentration of albumin favored the adhesion of porcine knee chondrocytes on the scaffolding pore surface. After cultivation over 4 weeks, an increase in the concentration of albumin enhanced the quantities of porcine knee chondrocytes, glycosaminoglycans, and collagen in the constructs. The histological staining of porcine knee chondrocytes showed an active chondrocytic growth in the albumin-grafted constructs. In addition, the safranin-O staining indicated that the surface albumin could stabilize the secretion of glycosaminoglycans. Moreover, the immunochemical staining against type II collagen exhibited a regular production of collagen by phenotypic porcine knee chondrocytes in the constructs. Albumin-grafted polyethylene oxide/chitin/chitosan scaffolds can be a promising biomimetic substrate in neocartilage formation.

Mechanical stability of the femoral fixation for single‐ and double‐bundle ACL reconstruction in an in vitro experimental model

Anterior cruciate ligament ACL reconstruction using the double-bundle (DB) technique is gaining popularity. A possible weak link in the DB technique could be that two tendon grafts of smaller diameters are used. The purpose of this study was to test different femoral fixation methods and graft diameters representing single-bundle (SB) and DB ACL reconstructions and compare their biomechanical properties. We hypothesized that SB 6-mm graft constructs had inferior biomechanical properties than SB 9-mm grafts or DB 2 × 6-mm grafts. Furthermore, we hypothesized that interference (IF) screw fixation would demonstrate less elongation and a higher stiffness than Endobutton (Smith & Nephew®, Inc., Andover, Massachusetts, USA) fixation (EBF). We performed an in vitro study using porcine knees and extensor tendons. The mechanical test consisted of a cyclic test followed by a load-to-failure test. We found that 6-mm graft constructs had an ultimate failure load that was up to 40% less than both the 9-mm and 2 × 6-mm graft constructs, despite the fixation method (P-values ≥ 0.004). Comparing fixation methods, EBF was superior to IF concerning maximum load to failure (P < 0.001); IF resulted in a higher stiffness of the femur/graft complex than the EBF (P < 0.001) but no significant difference in elongation between fixation methods. Since the two graft strands are subjected to different loads in different knee flexion angles, the reduced strength of the individual graft strands in DB ACL reconstruction could be a concern.

PCL to graft impingement pressure after anatomical or non-anatomical single-bundle ACL reconstruction

Anterior cruciate ligament (ACL) graft impingement against the posterior cruciate ligament (PCL) has been postulated, but not thoroughly investigated. To evaluate PCL impingement pressure and biomechanical stability with different tibial and femoral tunnel positions in ACL reconstruction. In 15 porcine knees, the impingement pressure between ACL and PCL was measured using pressure sensitive film before and after ACL single-bundle reconstruction. ACL reconstructions were performed in each knee with three different tibial and femoral tunnel position combinations: (1) tibial antero-medial (AM) tunnel to femoral AM tunnel (AM-AM), (2) tibial postero-lateral (PL) tunnel to femoral High-AM tunnel (PL-High-AM) and (3) tibial AM tunnel to femoral High-AM tunnel (AM-High-AM). Anterior tibial translation (ATT) was evaluated after each ACL reconstruction using robotic/universal force-moment sensor testing system. There was no significant difference of the impingement pressure between AM and AM, PL-High-AM reconstructed groups and intact ACL. Only AM-High-AM ACL reconstruction group showed significantly higher impingement pressure compared with intact ACL. With regard to ATT, AM-AM group had significantly higher stiffness than PL-High-AM group. Anatomical ACL reconstruction does not cause PCL impingement and it has biomechanical advantage in ATT when compared with non-anatomical ACL reconstructions in porcine knee. For the clinical relevance, in the anatomical ACL reconstruction, no ACL-PCL impingement is found.

Tension band wire fixation for anterior cruciate ligament avulsion fracture: biomechanical comparison of four fixation techniques

The purpose of this study is to design a new fixation method to treat tibial eminence fractures and assess its stability compared with conventional fixation methods. Eighty fresh porcine knees were stripped of all soft tissue, leaving intact only the femur-anterior cruciate ligament (ACL)-tibia complex. A standardized type III fracture was simulated at the anterior cruciate ligament attachment region using an osteotome. Then, the 80 specimens were randomly divided into 4 groups consisting of 20 knees each. The bony fragments were, respectively, fixed with sutures, steel wire, screws, and the newly designed tension band wire. All specimens were subsequently tested on a Material Testing Machine at a load rate of 60 mm/min. The statistically significant difference between the methods in terms of ultimate failure load, yield load, and displacement of the fragment under single-cycle loading and cyclic loading were analysed. Steel wire encircling K-wire fixation showed significantly higher maximum loads, yield loads, and less displacement than all the other fixation methods tested. Specimens fixed with steel wire had the second highest maximal load followed by fixation with the cannulated screw. The lowest maximal load was observed in the group using PDS II suture. The ultimate strength of tension band wire fixation of tibial eminence fractures in these specimens was significantly greater than those of the other three fixation methods. Tension band wire fixation of eminence fractures appears to provide biomechanical advantages over the other three fixation methods; hence, it is a practical alternative to conventional fixation techniques.

Structural properties of a new fixation strategy in double bundle ACL reconstruction: the MiniShim

Double-bundle reconstruction of the ACL has become the focus of scientific and clinical interest in the last years. However, there is still a discussion about the most appropriate technique for graft fixation. Both, extracortical fixation systems like the Endobutton and aperture fixation by interference screws have advantages as well as disadvantages. Aim of this study was to analyze the biomechanical properties of a new small wedge shaped implant (MiniShim, Karl Storz, Germany) for the fixation of a soft tissue graft in double bundle ACL reconstruction and to compare it to an aperture fixation by interference screw and an extracortical fixation. Porcine knees and flexor tendons were used for this study. 5 and 6mm tunnels were drilled. The following fixation strategies were tested: 4 and 5mm MiniShim (Karl Storz Germany), 6mm interference screw (MegaFix, Karl Storz, Germany), hybridfixation by FlippTack (FlippTack, Karl Storz, Germany) and MiniShim and hybridfixation by FlippTack and 6mm interference screw. All fixation strategies were tested with a 5 and 6mm tendon graft. Maximum load, yield load and stiffness were recorded using a material testing machine. Load was applied in line with the bone tunnel. Grafts were cyclically preconditioned between 0 and 20N for 10 cycles before the graft-bone-complex was loaded to failure. Statistical evaluation was performed using SPSS Version 11.0. Load to failure for the 5mm graft was 81.1 and 118.0N for the 4 and 5mm MiniShims. Fixation by interference screw reached 237.4N. The extracortical fixation resulted in a load to failure of 471.7N. Load to failure for the 6mm tendon grafts was 52.0 and 92.8N for the 4 and 5mm MiniShims. Fixation by interference screw resulted in a load to failure of 214.0N. Extracortical fixation failed at 451.7N. The difference between MiniShim and interference screw was statistically significant. Load to failure was significantly higher for extracortical fixation compared to fixation by MiniShim or interference screw. Hybrid fixation showed higher fixation strength compared to fixation by interference screw or MiniShim alone. This difference was statistically significant. Stiffness was significantly higher for fixation by interference screw compared to extracortical fixation and fixation by MiniShim. Four different modes of failure could be seen. All 4mm MiniShims failed by slippage of the tendon past the MiniShim. In the 5mm group the fixation failed by pullout of the MiniShim or the tendon past the MiniShim. Hybrid fixation failed by rupture of the linkage material. When the graft was fixed by an interference screw failure occurred by rupture of the tendon at the fixation side. Hybrid fixation using the MiniShim provides biomechanical properties strong enough to withstand the forces occurring during rehabilitation and comparable to the fixation strength provided by interference screw. While fixation by MiniShim alone does not provide sufficient fixation strength in double bundle ACL reconstruction, hybridfixation using a cortical fixation by FlippTack is an alternative to aperture fixation by interference screw concerning primary stability.

Fibrin glue does not improve the fixation of press-fitted cell-free collagen gel plugs in an ex vivo cartilage repair model

Adequate graft fixation over a certain time period is necessary for successful cartilage repair and permanent integration of the graft into the surrounding tissue. The aim of the present study was to test the primary stability of a new cell-free collagen gel plug (CaReS(®)-1S) with two different graft fixation techniques over a simulated early postoperative period. Isolated chondral lesions (11mm diameter by 6mm deep) down to the subchondral bone plate were created on the medial femoral condyle in 40 porcine knee specimens. The collagen scaffolds were fixed in 20 knees each by press-fit only or by press-fit+fibrin glue. Each knee was then put through 2,000 cycles in an ex vivo continuous passive motion model. Before and after the 2,000 motions, standardized digital pictures of the grafts were taken. The area of worn surface as a percentage of the total collagen plug surface was evaluated using image analysis software. No total delamination of the scaffolds to leave an empty defect site was recorded in any of the knees. The two fixation techniques showed no significant difference in worn surface area after 2,000 cycles (P=n.s.). This study reveals that both the press-fit only and the press-fit+fibrin glue technique provide similar, adequate, stability of a type I collagen plug in the described porcine model. In the clinical setting, this fact may be particularly important for implantation of arthroscopic grafts.

Arthroscopic Fixation of Matrix-Associated Autologous Chondrocyte Implantation: Importance of Fixation Pin Angle on Joint Compression Forces

The aim of the study was to investigate the effect of pin fixation perpendicular and 30° tilted to the matrix surface on the joint compression forces. In a porcine knee model, joint compression forces were recorded with a digital pressure sensor above the medial meniscus and with axial compression of 100 N by use of a material testing machine. The forces were recorded for an intact femoral condyle, as well as a standardized cartilage defect of 25 × 20 mm, after matrix-associated autologous chondrocyte implantation (m-ACI) (BioSeed C; Biotissue Technologies, Freiburg, Germany), fixed by use of a conventional suture technique and pin fixation with a biodegradable pin perpendicular and 30° tilted to the matrix surface. In knees with cartilage defects, the peak compression forces (mean, 824 kPa) were significantly increased compared with the intact knee joint (564 kPa). After m-ACI implantation with a chondral suture (581.3 kPa) and perpendicular pin fixation, the joint compression forces of the cartilage defect were significantly decreased (630.7 kPa). There were no significant differences compared with the intact knee. After 30° tilted pin insertion, mean joint compression forces were significantly increased (1,740 kPa). This study shows that after chondral suture and perpendicular pin fixation, there are no increased compression forces in the knee joint in comparison to an intact knee. Thirty degree tilted pin insertion contributes to increased joint compression forces. A tilted insertion during pin fixation in m-ACI should be avoided because it may lead to increased joint compression forces, especially after cartilage defect lesions on the tibial side.

Accurate three-dimensional registration of magnetic resonance images for detecting local changes in cartilage thickness

The purpose of this study is to develop a three-dimensional registration method for monitoring knee joint disease from magnetic resonance (MR) image data sets. A global optimization technique was used for identifying anatomically corresponding points of knee femur surfaces (bone cartilage interfaces). In a first pre-registration step, we used the principal axes transformation to correct for different knee joint positions and orientations in the MR scanner. In a second step, we presented a global search algorithm based on Lipschitz optimization theory. This technique can simultaneously determine the translation and rotation parameters through searching a six-dimensional space of Euclidean motion metrics (translation and rotation) after calculating the point correspondences. The point correspondences were calculated by using the Hungarian algorithm. The accuracy of registration was evaluated using 20 porcine knees. There were 300 corresponding landmark points over the 20 pig knees. We evaluated the registration accuracy by measuring the root-mean-square distance (RMSD) error of corresponding landmark points between two femur surfaces (two time-points). The results show that the average RMSD was 1.22 ± 0.10 mm (SD) by the iterative closest point (ICP) method, 1.17 ± 0.10 mm the by expectation-maximization-ICP method, 1.02 ± 0.06 mm by the genetic method, and 0.93 ± 0.04 mm by the proposed method. Compared with the other three registration approaches, the proposed method achieved the highest registration accuracy.

Evaluation of rotational instability in the anterior cruciate ligament deficient knee using triaxial accelerometer: a biomechanical model in porcine knees

To measure the acceleration in multiple directions of the rotational instability in ACL deficient models using porcine knees. Ten porcine knees were tested with ACL intact and tear models. The pivot shift test was performed manually, and the acceleration of the pivot shift phenomenon was recorded by the use of a triaxial accelerometer. Tests were repeated in four different ACL states: (1) intact; (2) partial AM deficient; (3) complete AM deficient, and (4) complete ACL (AMandPL) deficient. The acceleration in three directions and the magnitude of acceleration were measured to evaluate rotational instability and compare between different ACL conditions. Significantly increased accelerations were observed in the complete deficient ACL model, while the partial ACL tear models demonstrated a slight increase without statistical significance. The accelerometer detected stepwise increases in the acceleration with the extent of ACL tear. Additionally, the PL bundle exhibited the largest contribution for rotational instability (80.4%) when compared with the AM (19.5%) bundles. Triaxial accelerometer could serve as a quantitative evaluation of rotational instability. The present study demonstrated that PL bundle has the most important contribution for rotational instability (80.4%) when compared to IM bundle (0.01%) and AM bundle (19.5%) in porcine knee model.

Structural properties of a new device for graft fixation in cruciate ligament reconstruction: the shim technique

In ACL reconstruction using a soft tissue graft, aperture fixation with interference screws (IFS) can lacerate and rotate the graft and cause primary tunnel widening. To overcome these downsides, a new wedge-shaped implant (MegaShim, Karl Storz, Germany) was developed. We hypothesized that aperture fixation of hamstring ACL reconstruction using the MegaShim technique shows comparable structural properties when compared to interference screw fixation. In a porcine knee model, ACL reconstructions with a tunnel diameter of 6, 7, 8 and 9mm were performed and human hamstring grafts were fixed using the MegaShim technique (group I). In group 2, grafts were fixed in a hybrid fixation using a MegaShim and cortical flip button (FlippTack, Karl Storz, Germany). Interference screw graft fixation served as a control group (group III). Maximum load, yield load and stiffness were recorded using material testing machine. Grafts were cyclically preconditioned between 0 and 20N for 10 cycles before the graft-bone complex was loaded to failure. Statistical evaluation was performed using SPSS Version 11.0. Mean maximum load to failure for the hybrid fixation was significantly higher than after interference screw or MegaShim fixation. The difference between MegaShim and interference screw fixation showed no significant difference for 6 and 7mm sizes. An 8 and 9mm MegaShim fixation resulted in significantly lower ultimate failure load compared to interference screw fixation. Stiffness of grafts fixed using 6mm MegaShim was significantly lower than grafts fixed with hybrid or interference screw fixation, whereas no significant differences were found in the 7, 8, and 9mm fixations. Aperture fixation using the MegaShim technique provides comparable structural properties compared to interference screw fixation. Hybrid fixation using MegaShim and cortical flip button results in significantly higher ultimate failure loads than both aperture fixation approaches. Smaller grafts (6mm) showed significantly lower ultimate failure load and stiffness than interference screw fixation. The "MegaShim technique" is an alternative to interference screw fixation concerning initial fixation strength.

A biomechanical comparison of tibial back side fixation between suspensory and expansion mechanisms in trans-tibial posterior cruciate ligament reconstruction

Soft tissue grafts have attracted increasing attention in anterior cruciate ligament (ACL) reconstruction and offer a number of advantages Therefore, it can also be attractive for trans-tibial PCL reconstruction, if four-strand hamstring or two-strand tibialis grafts could be converted for this use. We intended to investigate the biomechanical properties of fixation devices that are frequently used for the soft tissue graft in the trans-tibial PCL reconstruction.Thirty-six fresh adult porcine knees were used in this study. Porcine digital extensor tendons were used as two-stranded soft tissue grafts. The tibial side of the PCL was fixed using a bio-TransFix of suspensory mechanism (TransFix system®: Arthrex, Naples, FL, USA) device (group I) or a RIGIDFIX of expansion mechanism (RIGIDFIX system®: Mitek, Johnson & Johnson, USA) device (group II). We performed biomechanical testing to identify maximum failure load, stiffness, and displacement for both devices.Maximum mean failure loads in groups I and II were 907.3 ± 142.2 and 701.9 ± 101.5 N, respectively ( p = 0.03). Stiffness was 65.6 ± 16.8 and 63.1 ± 15.1 N/mm, respectively ( p = 0.85). Mean displacements were 23.9 ± 6.0 and 19.8 ± 7.9 mm, respectively ( p = 0.37).Suspensory and expansion mechanisms used for tibial back side fixation in the trans-tibial PCL reconstruction using soft tissue grafts showed acceptable biomechanical properties and could be a good choice in case of short multi-stranded soft tissue graft.

G020014 2電極電気インピーダンス計測における軟骨組織の受動的電気特性([G02001]バイオエンジニアリング部門一般セッション(1))

The purpose of this study was to investigate the relationship between mechanical properties and passive electrical property for articular cartilage. In the present study, the magnitude of admittance IYI was used to evaluate passive electrical property. Cartilage specimens without subchondral bone were taken from porcine knee joints with biopsy punch with 6 mm diameter. The specimen of 1.2 mm thickness was firstly prepared and its magnitude of admittance IY1 was measured. This specimen was then sliced from 1.2 mm to 0.9 mm thickness and then again from 0.9 mm to 0.6 mm, and its magnitude of admittance I11 was measured at each thickness. The magnitude of admittance IYI for the specimen of 1.2 mm thickness was measured under 20 and 40 °C. The magnitude of admittance III is constant at high frequencies and variation of the saturated value with thickness and temperature of the specimen were observed at high frequencies. These results showed that passive electrical property of cartilage can be evaluated by the magnitude of admittance III at high frequencies. Electric impedance measurement and stress-relaxation test were carried out for the same specimens of 1.2 mm thickness to evaluate relationship between the passive electrical property and mechanical properties obtained using three elements model. The magnitude of admittance 1/1 showed a significant negative correlations with elastic modulus El(r = -0.704, P<0.05), elastic modulus E2(r = -0.704, P<0.05), and viscosity coefficient ri(r = -0.689, P<0.05) respectively. These results showed that mechanical property of articular cartilage can be estimated by using an electric impedance method.

Investigating the effects of anterior tibial translation on anterior knee force in the porcine model: Is the porcine knee ACL dependent?

This study sought to determine anterior force in the porcine knee during simulated 6-degree-of-freedom (DOF) motion to establish the role of the anterior cruciate ligament (ACL). Using a 6-DOF robot, a simulated ovine motion was applied to porcine hind limbs while recording the corresponding forces. Since the porcine knee is more lax than the ovine knee, anterior tibial translations were superimposed on the simulated motion in 2 mm increments from 0 mm to 10 mm to find a condition that would load the ACL. Increments through 8 mm increased anterior knee force, while the 10 mm increment decreased the force. Beyond 4 mm, anterior force increases were non-linear and less than the increases at 2 and 4 mm, which may indicate early structural damage. At 4 mm, the average anterior force was 76.9 ± 10.6 N (mean ± SEM; p < 0.025). The ACL was the primary restraint, accounting for 80-125% of anterior force throughout the range of motion. These results demonstrate the ACL dependence of the porcine knee for the simulated motion, suggesting this model as a candidate for studying ACL function. With reproducible testing conditions that challenge the ACL, this model could be used in developing and screening possible reconstruction strategies.

Biomechanical comparison of three anatomic ACL reconstructions in a porcine model

Different tunnel configurations have been used for double-bundle (DB) anterior cruciate ligament (ACL) reconstruction. However, controversy still exists as to whether three-tunnel DB with double-femoral tunnels and single-tibial tunnel (2F-1T) or with single-femoral tunnel and double-tibial tunnels (1F-2T) better restores intact knee biomechanics than single-bundle (SB) ACL reconstruction. The purpose was to compare the knee kinematics and in situ force in the grafts among SB and two types of three-tunnel DB ACL reconstructions performed in an anatomic fashion. Twenty-four porcine knees were subjected to an 89-N anterior tibial load (simulated KT-1000 test) at 30°, 60°, and 90° of flexion and to a 4-Nm internal tibial torque and 7-Nm valgus torque (simulated pivot-shift test) at 30° and 60° of flexion. The resulting knee kinematics and in situ force in the ACL or replacement grafts were measured using a robotic system for (1) ACL-intact, (2) ACL-deficient, and (3) three ACL reconstructed knees: SB; DB 2F-1T; and DB 1F-2T. During the simulated pivot-shift test, the DB grafts more closely restored the in situ force in the intact ACL at low flexion angle than the SB graft. There were no significant differences in knee kinematics between SB and DB ACL reconstruction. The DB 2F-1T reconstruction did not show a significant difference in knee kinematics or in situ force when compared to the DB 1F-2T technique. The in situ force in the ACL is better restored with an anatomic three-tunnel DB reconstruction in response to the simulated pivot-shift test at low flexion angle when compared to an anatomic SB reconstruction. Both three-tunnel DB ACL reconstructions performed in an anatomic fashion had similar biomechanical behavior. As long as it is performed anatomically, DB ACL reconstruction could be better alternative than SB ACL reconstruction, no matter which three-tunnel procedure, 2F-1T or 1F-2T, is used.

An ex vivo continuous passive motion model in a porcine knee for assessing primary stability of cell-free collagen gel plugs

BackgroundPrimary stability of cartilage repair constructs is of the utmost importance in the clinical setting but few continuous passive motion (CPM) models are available. Our study aimed to establish a novel ex vivo CPM animal model and to evaluate the required motion cycles for testing the mechanical properties of a new cell-free collagen type I gel plug (CaReS®-1S).MethodsA novel ex vivo CPM device was developed. Full-thickness cartilage defects (11 mm diameter by 6 mm deep) were created on the medial femoral condyle of porcine knee specimens. CaReS®-1S was implanted in 16 animals and each knee underwent continuous passive motion. After 0, 2000, 4000, 6000, and 8000 motions, standardized digital pictures of the grafts were taken, focusing on the worn surfaces. The percentage of worn surface on the total CaReS®-1S surface was evaluated with image processing software.ResultsSignificant differences in the worn surface were recorded between 0 and 2000 motion cycles (p < 0.0001). After 2000 motion cycles, there was no significant difference. No total delamination of CaReS®-1S with an empty defect site was recorded.ConclusionThe ex vivo CPM animal model is appropriate in investigating CaReS®-1S durability under continuous passive motion. 2000 motion cycles appear adequate to assess the primary stability of type I collagen gels used to repair focal chondral defects.

Cartilage viability and catabolism in the intact porcine knee following transarticular impact loading with and without articular fracture

Posttraumatic arthritis commonly develops following articular fracture. The objective of this study was to develop a closed joint model of transarticular impact with and without creation of an articular fracture that maintains the physiologic environment during loading. Fresh intact porcine knees were preloaded and impacted at 294 J via a drop track. Osteochondral cores were obtained from the medial and lateral aspects of the femoral condyles and tibial plateau. Chondrocyte viability was assessed at days 0, 3, and 5 postimpact in sham, impacted nonfractured, and impacted fractured joints. Total matrix metalloproteinase (MMP) activity, aggrecanase (ADAMTS-4) activity, and sulfated glycosaminoglycan (S-GAG) release were measured in culture media from days 3 and 5 posttrauma. No differences were observed in chondrocyte viability of impacted nonfractured joints (95.9 ± 6.9%) when compared to sham joints (93.8 ± 7.7%). In impacted fractured joints, viability of the fractured edge was 40.5 ± 27.6% and significantly lower than all other sites, including cartilage adjacent to the fractured edge (p < 0.001). MMP and aggrecanase activity and S-GAG release were significantly increased in specimens from the fractured edge. This study showed that joint impact resulting in articular fracture significantly decreased chondrocyte viability, increased production of MMPs and aggrecanases, and enhanced S-GAG release, whereas the same level of impact without fracture did not cause such changes.

Anterior cruciate ligament reconstruction with bone-hamstring-bone hybrid procedure

Dear Editors,We read the article ‘‘Augmentation of autologous ham-string graft during anterior cruciate ligament reconstructionusing the bone chip technique’’ by Nha et al. [3] with greatinterest. We would like to commend the authors on theirwork.ACL reconstruction with bone-hamstring-bone (BHB) isa hybrid procedure that lacks the disadvantages of thebone-patellar tendon-bone and semitendinosus and gracilistendon methods while retaining the advantages of thesemethods. Nha et al. [3] described very interesting techniqueto augment the thickness of the hamstring tendon graftduring ACL reconstruction using cancellous bone chipsfrom the femoral intercondylar notch. But this technique isnot new, it should be noted that this technique was pub-lished several years ago. Liu et al. [1] in 1995 measured theinitial fixation strength of a new graft, bone-hamstring-bone (BHB), for reconstruction of the anterior cruciateligament (ACL) in 79 porcine knees and compared it withthat of the normal porcine ACL and of the bone-patellartendon-bone (BPB) graft. Takeuchi et al. [4] in 2002described composite graft prepared by folding the gracilisand the semitendinosus tendons twice and flanking the endsby bone blocks obtained from the tibia. Milankov et al. [2]in 2007 use two cancellous bone cylinders, were taken outof the tibial tunnel, by use of a cancellous bone extractor,and fixed to both ends of the graft by use of sutures. Oneend of the graft was put into a pressing device to achieve agraft diameter of 9 or 10 mm, and then the other end waspressed. By doing so, very strong end parts of the graftwere obtained.We also believe, when using the AM portal techniquefor creation femoral tunnel, it is rarely needed to makenotchplastic, so the usage of bone from that place is notnecessary because it leads to additional damage. It is betterto use cancellous bone cylinders taken out of the tibialtunnel.References

Injection Molding of Degradable Interference Screws into Polymeric Mold

Nowadays the need for faster development cycle can be found all over in the industry. Rapid prototyping has become a common tool in product development, but available materials in these technologies can not always substitute the materials needed for product. Rapid tooling makes it possible to produce a small series of a product with the same technology and materials as that of the final product. In our work we have used the Polyjet technology (Objet Geometries Ltd.) to produce mold for the injection molding of biodegradable interference screws. Our goal was to produce enough quantity of interference screws for biomechanical measurements, with a technology that is more cost efficient than selective laser sintering (SLS). Two types of mold materials were tested. The first mold was prepared from Fullcure720, an acrylic based, UV curing resin on an Object ALARIS machine. The second mold was prepared with resin casting from AH-12/T-58 (100:40) epoxy resin filled with 25 m% Al2O3 powder. For injection molding Natureworks 3051D polylactide (PLA) was used. After injection molding the weight and the geometry of the screws were measured. The results showed that the molds can withstand 5-10 injection cycles, and the screws manufactured meet the requirements for biomechanical tests on porcine knees.

A novel and non-destructive method to examine meniscus architecture using 9.4 Tesla MRI

SummaryObjectiveTo investigate the ability of high-field (9.4 T) magnetic resonance (MR) imaging to delineate porcine knee meniscal tissue structure and meniscal tears.Materials and methodsPorcine knees were obtained from a local abattoir, and eight medial menisci with no visible defects were dissected. Lesions simulating longitudinal tears were created on two of the menisci. MR images of the menisci were obtained at 9.4 T using a three-dimensional (3D)-FLASH sequence. A detailed 3D internal architecture of the intact and injured menisci was demonstrated on high-resolution MR images.ResultsHigh-resolution 3D MR imaging allowed visualisation of internal architecture of the meniscus and disruption to the internal structural network in damage models. The architecture of the porcine knee meniscus revealed by the MR scans appeared similar to the structures visualised by histology in previously reported studies.ConclusionHigh-field MRI is a non-destructive technique to examine the internal structural components and damage/wear of meniscal tissue. It has tremendous potential in the field of functional cartilage/meniscus biomechanics and biotribology.

Stiffer Fixation of the Tibial Double-Tunnel Anterior Cruciate Ligament Complex Versus the Single Tunnel: A Biomechanical Study

The primary objective of this study was to evaluate the difference in graft pullout forces, stiffness, and failure mode of double-bundle anterior cruciate ligament (ACL) reconstruction of the tibial insertion by use of a single tunnel compared with a double-tunnel technique with interference screw fixation. ACL reconstruction on the tibial side was performed on 40 fresh-frozen porcine knees (mean bone mineral density of 0.64 g/cm(2) measured by dual-energy x-ray absorptiometry scan), randomly assigned to the single- or double-tunnel group. Interference screw fixation of the soft-tissue graft was used for both types of tibial reconstruction. Maximum failure load, stiffness, and failure mode were recorded. There was no significant difference in maximum failure load between the single-tunnel group (400 +/- 26 N) and double-tunnel group (440 +/- 20 N). Stiffness of the tibial tunnel complex was significantly higher in the double-tunnel group (76 +/- 3 N/mm) than in the single-tunnel group (62 +/- 4 N/mm) (P = .013). All but 2 grafts (38 of 40) failed by slippage of the tendon past the interference screw. There was significantly stiffer fixation of the tibial double-tunnel ACL complex when compared with the single tunnel. Our study did not show a different failure mode for the double-tunnel reconstruction compared with the single-tunnel reconstruction. This study shows a biomechanical advantage with no potential deleterious side effects for fixation of the ACL with a double-tunnel technique on the tibial side.