Mahmoud Chizari

Post-Operative Assessment of an Implant Fixation in Anterior Cruciate Ligament Reconstructive Surgery

The objective of this paper is to numerically simulate the behaviour of an anterior cruciate ligament (ACL) reconstructed knee using interference screw fixation under a single cycle loading or a cyclic loading test and to compare the numerical results with experimental tests using porcine samples of knee joint. A hyper-elastic material model was used to model the tendon graft and evaluate its elongation during continuous and cyclic tensile loading. The rigidity of the interference screw fixation was also examined using the finite element based numerical model. The finite element model uses the benefit of an anatomical 3D geometry of the tibial bone and tendon graft which was created from a CT scan of a patient.

BIOMECHANICAL TESTING PROCEDURES IN TENDON GRAFT RECONSTRUCTIVE ACL SURGERY

This paper, describes the biomedical testing of an Anterior Cruciate Ligament (ACL) reconstruction using an interference screw fixation on the bovine and porcine tissues. The harvesting procedure, experimental setup, mechanical testing, and evaluation of the tendon graft interference screw fixation are all presented throughout this study. A guideline has also been introduced to evaluate the basic mechanical properties of the bone components and the tendon graft.

MECHANICAL ASPECTS OF A SINGLE-BUNDLE TIBIAL INTERFERENCE SCREW FIXATION IN A TENDON GRAFT ACL RECONSTRUCTION

Numerical methods applicable to the tibia bone and soft tissue biomechanics of an anterior cruciate ligament (ACL) reconstructed knee are presented in this paper. The aim is to achieve a better understanding of the mechanics of an ACL reconstructed knee. The paper describes the methodology applied in the development of an anatomically detailed three-dimensional ACL reconstructed knee model for finite element analysis from medical image data obtained from a computed tomography scan. Density segmentation techniques are used to geometrically define the knee bone structure and the encapsulated soft tissues configuration. Linear and nonlinear elastic constitutive material models are implemented to mechanically characterize the behavior of the biological materials. Preliminary numerical results for the model qualitative evaluation are presented.

An analysis of the biomechanics of interference screw fixation and sheathed devices for biceps tenodesis

BACKGROUND This study aimed to evaluate the differences in biomechanical properties of biceps tenodesis when performed with sheathed versus unsheathed screws and also to investigate the effect of altering the pre-tension. METHODS Tenodesis was performed in an in vitro model using biomechanical test blocks and ovine tendons. Blocks were allocated to 1 of 5 groups which varied by method of tenodesis and cyclical loading protocol: Group A, Biosure PK screw (10-100 N), Group B: 7-8 mm Biosure Sync and Biosure PK screw (10-100 N), Group C: Biosure PK screw (10-70 N), Group D: Biosure PK (20-100 N), and Group E: custom sheath and Biosure PK screw (10-100 N). If tenodeses remained intact after 500 cycles maximum load to failure testing was performed. FINDINGS 30% of tenodeses in Group A failed prior to 500 cycles whereas none failed in the sheathed device groups (P=0.02). Using a sheathed device prevented mal-rotation. However, tenodeses in Group B were more likely to fail immediately distal to the tenodesis at a load below the anticipated maximum load to failure suggesting tendon damage during fixation. Using the custom sheath, which did not have sharp edges, resulted in a statistically significant increased maximum load to failure in Group E (348 N) when compared to Group A (228 N, mean difference 120 N, P=0.01) and Group B (253N, mean difference 95 N, P=0.0007). INTERPRETATION Sheathed devices prevent mal-rotation and increase stiffness and maximum load to failure. This is further improved by reducing tendon damage at the time of tenodesis.

RELATIVE MOTION OF TENDON LIMBS IN A LOOP TENDON GRAFT

The biomechanical data derived from the standard tensile testing machines may not be able to show the relative motion of the graft limbs. This paper uses a digital stereo image recording system, synchronized with the standard test machine, to determine the relative motion of a looped tendon graft. Bovine flexor tendon was used to create the looped graft and then the graft was passed through a tunnel in a foam block and fixed with an interference screw. The structure was then mounted in a testing machine. The tendon limbs surfaces were speckled just moments before test, and two cameras synchronized with the test machine were capturing the movements of the speckles. Following a cyclic loading from 50–250 N at 1.0 Hz for 500 cycles, a load-to-failure test was carried out at a rate of 20 mm/min. The load-displacement data and the corresponding images of the graft were used to examine the mechanical properties of the graft structure and the relative motion of the individual graft limbs. There was no significant difference between the mechanical properties of the grafts structure. The average displacement of the grafts structure was 6.95 mm, while the average relative motion between the loop limbs up to the point of the graft failure was 0.3 mm.

T-9 Evaluating the Mechanical Properties of a Tendon Graft, Using Digital Image Correlation (DIC) Technique

Accurate measurement of the biomechanical properties of tendon grafts such as stiffness, Youngs modulus and ultimate strength has important implications in the surgical repair of anterior cruciate ligament injuries. However, the mechanical behaviour of the tendon is complex and difficult to model. The data from the grip-to-grip displacement reported by the standard testing machines may not be an accurate way to determine the mechanical properties of tendon. The goal of this study was to verify the biomechanical property of an anterior cruciate ligament model tendon graft using the experimental data obtained from the standard tensile loading testing machines with a non-invasive digital imaging correlation (DIC) method. In this study the in vitro mechanical properties of the 10 bovine digital flexor tendon constructs was determined. Each construct consisted of a synthetic foam block where the tendon was doubled over an Endo-button loop and fixed with a round head Arthrex ® interference screw. The diameter of the tunnel and interference screw was the same as the diameter of the doubled tendon. The samples were secured and tested in a custom-made apparatus that was mounted in a LOS (Losenhausen, Maschinenbau AG Dusseldorf) uniaxial testing machine. Samples were pre-conditioned and cyclically loaded. A final tensile load to failure was applied to the failure. Experimental measurements were carried out using a DIC system, including two cameras and Vic3D (Limess GmbH, Pforzheim, Germany) software. The technique utilizes two similarly speckled images, which were captured by a solid state video camera, to represent the states of the object before and after deformation. By analyzing any pair of consecutive speckle images with the DIC technique, displacements between the corresponding load levels, incremental displacements and strain of the speckled pattern were obtained. At the beginning of the test, the contour was uniform with same displacement in axial direction, for both limbs of the tendon which verifies that the sample stretched fairly uniformly. By increasing the load the result of displacement in different limbs was slightly different. This meant that there was a relative motion between the limbs and can be concluded that the fixation force is not equal for both strand in the tunnel. At the maximum load, the maximum vertical strain was 0.42 and the shear strain was 0.26. Our results have shown that DIC provides a novel and reliable technique for assessing the biomechanical properties of a tendon graft. This in turn may help clinicians to accurately determine the mechanical properties of tendon grafts used in surgical repair such as a single bundle and a double bundle anterior cruciate ligament repair.

The Kinematics of the Hip Joint with Femoroacetabular Impingement May Be Affected by the Thickness of the Articular Cartilage

The abnormalities in the shape and orientation of the femoral head and neck or the acetabulum are important morphological characteristics of femoroacetabular impingement (FAI). Concerns exist about the effect of damaged cartilage on the kinematics of the affected hip joint. The current study is aiming to track the motion of a femur bearing a cam deformity, with healthy or damaged articular cartilage. This may prove useful in understanding the changes occurring in a hip joint with cam-type FAI, as arthritis develops and progresses. A three-dimensional (3D) model of the left hip joint of a male patient diagnosed with FAI was obtained from pre-operative Computerised Tomography (CT) data using density segmentation techniques in Mimics 13.1 (Materialise NV). The kinematics of FAI was analysed in Abaqus 6.9 (Simulia Dassault Systems) using a finite element method. The translation and rotation parameters were defined in a single step for each one of three cases: healthy cartilage, 2mm (one-sided thinning) and 4mm (two-sided thinning) worn-out articular cartilage. As the acetabulum and femur came into contact, the penetrations were detected and the contact constraints were applied according to the penalty constraint enforcement method. The results of the analysis showed that thinning of the cartilage at the hip joint adversely affects impingement, as range of motion was decreased with progressive thinning of the articular cartilage.

ESTIMATING MATERIAL PROPERTY AND FAILURE OF A LIVING CELL; NUMERICAL STUDY

This paper presents finite element modelling of the deformation of a detached living cell subjected to microinjection and through the simulation, an investigation of the material properties of the cell components. The model is verified using images of the deformed cell as well as the measured penetration forces in the tests reported in the open literature. It is hoped that the modelling in this context will help to quantitatively evaluate the mechanical properties of the cells, and in particular, the failure strain of the cell cortex when penetration occurs.

In vivo Kinematics Assessment of Bulged Disk Cervical Vertebral

Objective: On a cervical disk, the bulge may be produced in the poster lateral direction when there is a combination of lateral bending and compression loading. Although attempts have been made to measure the kinematics of intact vertebral spine but has not been compared with a vertebral spine when the dicks are bulged. The study aims to investigate the effect of a bulged disk on the kinematics of a cervical spine during a flexionextension motion then flexion-extension of five subject patients who had history of bulged disk in their cervical spine were studied. All patients had bulged disk at C5/C6 level. Design: This study uses a three dimensional model of cervical vertebras which was created from CT data of the subject patients. Flexion-extension range of motion of each subject patients was recorded using a fluoroscopic imaging method. Then motion of the cervical vertebra next to bulged disk were tracked using a 2D-to-3D registration method. The result of this measurement was compared with motion of intact cervical spines obtained by previous researchers. Results: The range of motion for normal C5/C6 is less than bulged C5/C6. Conclusion: The kinematics of flexion-extension motion for bulged intervertebral disk and the normal intervertebral disks are different.

THE PLANE RADIOGRAPH OF THE KNEE FOR HIGH TIBIAL OSTEOTOMY ASSESSMENT IS IN CONTRAST TO STANDING ALIGNMENT VIRTUALLY ELABORATED HANDLING BASED PRE-OPERATION PLANNING

High Tibial Osteotomy (HTO) is a popular approach among contemporary corrective lower extremity procedures. As a surgical method in the HTO, the Open-Wedge High Tibial Osteotomy (OWHTO) preserves leg length, avoids dissection near the nerve and allows for fine-tuning of the angle by gradually inserting a wedge into a tibia. Nowadays, the gold standard approach to the OWHTO is based on the patient’s Long-Leg Radiograph (LLR) assessment. These standard weight bearing views of the lower extremity have their own practical advantages. This study aims to closely look at existing gold standard OWHTO planning method and assess its accuracy compared to a true patient’s weight bearing posture. The study attempts to introduce a method which can be used as a template for the HTO planning and has less weakness than the existing method. This method will assess the lower limb weight bearing three-dimensionally using a patient specific Computer Tomography (CT) data. The method has been validated using a Standing Alignment Virtually Elaborated Handling (SAVEH) of the lower limb using fluoroscopy giving an in vivo dynamic weight bearing analysis of the knee. The outcome of typical examples on assessment of the natural mechanical axis of the knee using proposed method has shown more accuracy than common two-dimensional LLR image control method. The study concluded that looking at the OWHTO without any address of the real three-dimensional orientation of the knee bones specially during standing phase of gait may be a missing point of view on OWHTO surgery.