Publications
41 results found
Ghouse S, Babu S, van Arkel R, et al., 2017, The influence of laser parameters and scanning strategies on the mechanical properties of a stochastic porous material, Materials & Design, Vol: 131, Pages: 498-508, ISSN: 0261-3069
Additive manufacturing enables architectured porous material design, but 3D-CAD modelling of these materials is prohibitively computationally expensive. This bottleneck can be removed using a line-based representation of porous materials instead, with strut thickness controlled by the supplied laser energy.This study investigated how laser energy and scan strategy affects strut thickness and mechanical strength of porous materials. Specimens were manufactured using varying laser parameters, 3 scan strategies (Contour, Points, Pulsing), 2 porous architectures and 2 materials (Titanium, Stainless Steel), with strut thickness, density, modulus, mechanical strength and build time measured.Struts could be built successfully as low as 15° with a minimum diameter of 0.13 mm. Strut thickness was linearly related to the specific enthalpy delivered by the laser to the melt-pool. For a given stiffness, Titanium specimens built at low power/slow speed had a 10% higher strength than those built at high power/fast speed. The opposite was found in Stainless Steel. As specimen stiffness increased, the Contour Strategy produced samples with the highest strength:stiffness and strength:weight ratio. The Points strategy offered the fastest build time, 20% and 100% faster than the Contour and Pulsing strategies, respectively. This work highlights the importance of optimising build parameters to maximize mechanical performance.
Ridzwan M, Sukjamsri C, Pal B, et al., 2017, Femoral fracture type can be predicted from femoral structure: a finite element study validated by digital volume correlation experiments, Journal of Orthopaedic Research, Vol: 36, Pages: 993-1001, ISSN: 1554-527X
Proximal femoral fractures can be categorized into two main types: Neck and intertrochanteric fractures accounting for 53% and 43% of all proximal femoral fractures, respectively. The possibility to predict the type of fracture a specific patient is predisposed to would allow drug and exercise therapies, hip protector design, and prophylactic surgery to be better targeted for this patient rendering fracture preventing strategies more effective. This study hypothesized that the type of fracture is closely related to the patient-specific femoral structure and predictable by finite element (FE) methods. Fourteen femora were DXA scanned, CT scanned, and mechanically tested to fracture. FE-predicted fracture patterns were compared to experimentally observed fracture patterns. Measurements of strain patterns to explain neck and intertrochanteric fracture patterns were performed using a digital volume correlation (DVC) technique and compared to FE-predicted strains and experimentally observed fracture patterns. Although loaded identically, the femora exhibited different fracture types (six neck and eight intertrochanteric fractures). CT-based FE models matched the experimental observations well (86%) demonstrating that the fracture type can be predicted. DVC-measured and FE-predicted strains showed obvious consistency. Neither DXA-based BMD nor any morphologic characteristics such as neck diameter, femoral neck length, or neck shaft angle were associated with fracture type. In conclusion, patient-specific femoral structure correlates with fracture type and FE analyses were able to predict these fracture types. Also, the demonstration of FE and DVC as metrics of the strains in bones may be of substantial clinical value, informing treatment strategies and device selection and design.
van arkel R, Jeffers J, amis A, 2017, Editorial Commentary: Anatomical vandalism of the hip? Hip capsular repair seems a sound adjunct to hip arthroscopic surgery, Arthroscopy-the Journal of Arthroscopic and Related Surgery, Vol: 33, Pages: 314-316, ISSN: 1526-3231
The study “Contribution of the Pubofemoral Ligament to Hip Stability: A Biomechanical Study” by Martin,Khoury, Schröder, Johnson, Gómez-Hoyos, Campos, and Palmer found that cutting the hip capsular ligament allowed alarge increase in femoral internal rotation, particularly in the flexed hip, causing subluxation to occur. In addition toproviding new data on the role of the pubofemoral ligament, it raises the question of whether hip joint surgeons shouldrepair the capsuledwhat are the likely consequences?dand whether any beneficial effects persist in long-term clinicalfollow-ups. For now, hip capsular repair seems a sound adjunct to hip arthroscopic surgery.
van arkel R, Jeffers J, 2016, In vitro hip testing in the International Society of Biomechanics coordinate system, Journal of Biomechanics, Vol: 49, Pages: 4154-4158, ISSN: 1873-2380
Many innovative experiments are designed to answer research questions about hip biomechanics, however many fail to define a coordinate system. This makes comparisons between studies unreliable and is an unnecessary hurdle in extrapolating experimental results to clinical reality. The aim of this studywas to present a specimen mounting protocol which aligns and registers hip specimens in the International Society of Biomechanics (ISB) coordinate system, which is defined by bony landmarks that are identified by palpation of the patient’s body. This would enable direct comparison between experimental testing and clinical gait analysis or radiographic studies. To represent the intact hip, four intact synthetic full-pelves with 8 full-length articulating femora were assembled and digitised to define the ISB coordinate system. Using our proposed protocol, pelvis specimens were bisected into left and right hemi-pelves and femora transected at the mid-shaft, and then mounted in bone pots to represent a typical experimental setup. Anatomical landmarks were re-digitised relative to mechanical features of the bone pots and the misalignment was calculated. The mean misalignment was found to be less than 1.5° flexion/extension, ab/adduction and internal/external rotation for both the pelves and femora; this equates to less than 2.5% of a normal range of hip motion. The proposed specimen mounting protocol provides a simple method to align in vitro hip specimens in the ISB coordinate system which enables improved comparison between laboratory testing and clinical studies. Engineering drawings are provided to allow others to replicate the simple fixtures used in the protocol.
Stephen JM, Urquhart DWJ, van Arkel RJ, et al., 2016, The use of sonographically guided botulinum toxin type A (Dysport) injections into the tensor fasciae latae for the treatment of lateral patellofemoral overload syndrome, American Journal of Sports Medicine, Vol: 44, Pages: 1195-1202, ISSN: 1552-3365
Background: Pain in the anterior and lateral parts of the knee during exercise is a common clinical problem for which current management strategies are often unsuccessful.Purpose: To investigate the effect of an ultrasound-guided botulinum toxin (BT) injection into the tensor fasciae latae (TFL), followed by physical therapy, in patients classified with lateral patellofemoral overload syndrome (LPOS) who failed to respond to conventional treatment.Study Design: Case series; Level of evidence, 4.Methods: A total of 45 patients (mean ± SD age, 32.4 ± 8.6 years) who met the inclusion criteria of (1) activity-related anterolateral knee symptoms, (2) symptoms lasting longer than 3 months, (3) a pathological abnormality confirmed by magnetic resonance imaging, and (4) previous failed physical therapy received an ultrasound-guided injection of BT into the TFL followed by physical therapy. Patient-reported outcomes were collected at 5 intervals: before the injection; at 1, 4, and 12 weeks after the injection; and at a mean 5 years after the injection. In 42 patients, relative iliotibial band (ITB) length changes were assessed using the modified Ober test at the first 4 time points. A computational model was run to simulate the effect of TFL weakening on gluteus medius (GMed) activity. Statistical analysis was undertaken using 1-way analysis of variance and paired t tests with Bonferroni post hoc correction.Results: There was a significant improvement in Anterior Knee Pain Scale scores from before the injection (61 ± 15) to 1 (67 ± 15), 4 (70 ± 16), and 12 weeks (76 ± 16) after the injection and in 87% of patients (39/45 patients available for follow-up) at approximately 5 years (from 62.9 ± 15.4 to 87.0 ± 12.5) after the injection (all P < .010). A significant effect on the modified Ober test was identified as a result of the intervention, with an increase in leg drop found at 1 (3° ± 5°), 4 (4° &
van Arkel R, Amis A, Jeffers J, 2015, The envelope of passive motion allowed by the capsular ligaments of the hip, Journal of Biomechanics, Vol: 48, Pages: 3803-3809, ISSN: 1873-2380
Laboratory data indicate the hip capsular ligaments prevent excessive range of motion, mayprotect the joint against adverse edge loading and contribute to synovial fluid replenishmentat the cartilage surfaces of the joint. However, their repair after joint preserving orarthroplasty surgery is not routine. In order to restore their biomechanical function after hipsurgery, the positions of the hip at which the ligaments engage, together with their tensionswhen they engage is required. Nine cadaveric left hips without pathology were skeletonisedexcept for the hip joint capsule and mounted in a six-degrees-of-freedom testing rig. A 5Nmtorque was applied to all rotational degrees-of-freedom separately to quantify the passiverestraint envelope throughout the available range of motion with the hip functionally loaded.The capsular ligaments allowed the hip to internally/externally rotate with a large range ofun-resisted rotation (up to 50±10°) in mid-flexion and mid-ab/adduction but this was reducedtowards the limits of flexion/extension and ab/adduction such that there was a near-zeroslack region in some positions (p<0.014). The slack region was not symmetrical; the midslackpoint was found with internal rotation in extension and external rotation in flexion(p<0.001). The torsional stiffness of the capsular ligamentous restraint averaged0.8±0.3Nm/° and was greater in positions where there were large slack regions. These dataprovide a target for restoration of normal capsular ligament tensions after joint preserving hipsurgery. Ligament repair is technically demanding, particularly for arthroscopic procedures,but failing to restore their function may increase the risk of osteoarthritic degeneration.
van Arkel RJ, Pal B, Darton H, et al., 2015, Biomechanics of Joints, Experimental Research Methods in Orthopedics and Trauma, Editors: Simpson, Augat, Publisher: Thieme Medical Publishers, ISBN: 9783131731111
This book provides a comprehensive summary of all current research methodologies for translational and pre-clinical studies in biomechanics and orthopedic trauma surgery.
van Arkel RJ, Amis AA, Cobb JP, et al., 2015, The capsular ligaments provide more hip rotational restraint than the acetabular labrum and the ligamentum teres, Bone & Joint Journal, Vol: 97B, Pages: 484-491, ISSN: 2049-4394
In this in vitro study of the hip joint we examined which soft tissues act as primary and secondary passive rotational restraints when the hip joint is functionally loaded. A total of nine cadaveric left hips were mounted in a testing rig that allowed the application of forces, torques and rotations in all six degrees of freedom. The hip was rotated throughout a complete range of movement (ROM) and the contributions of the iliofemoral (medial and lateral arms), pubofemoral and ischiofemoral ligaments and the ligamentum teres to rotational restraint was determined by resecting a ligament and measuring the reduced torque required to achieve the same angular position as before resection. The contribution from the acetabular labrum was also measured. Each of the capsular ligaments acted as the primary hip rotation restraint somewhere within the complete ROM, and the ligamentum teres acted as a secondary restraint in high flexion, adduction and external rotation. The iliofemoral lateral arm and the ischiofemoral ligaments were primary restraints in two-thirds of the positions tested. Appreciation of the importance of these structures in preventing excessive hip rotation and subsequent impingement/instability may be relevant for surgeons undertaking both hip joint preserving surgery and hip arthroplasty.
van Arkel RJ, Modenese L, Phillips ATM, et al., 2013, Hip Abduction Can Prevent Posterior Edge Loading of Hip Replacements, Journal of Orthopaedic Research, Vol: 31, Pages: 1172-1179, ISSN: 1554-527X
Edge loading causes clinical problems for hard-on-hard hip replacements, and edge loading wear scars are present on the majority of retrieved components. We asked the question: are the lines of action of hip joint muscles such that edge loading can occur in a well-designed, well-positioned acetabular cup? A musculoskeletal model, based on cadaveric lower limb geometry, was used to calculate for each muscle, in every position within the complete range of motion, whether its contraction would safely pull the femoral head into the cup or contribute to edge loading. The results show that all the muscles that insert into the distal femur, patella, or tibia could cause edge loading of a well-positioned cup when the hip is in deep flexion. Patients frequently use distally inserting muscles for movements requiring deep hip flexion, such as sit-to-stand. Importantly, the results, which are supported by in vivo data and clinical findings, also show that risk of edge loading is dramatically reduced by combining deep hip flexion with hip abduction. Patients, including those with sub-optimally positioned cups, may be able to reduce the prevalence of edge loading by rising from chairs or stooping with the hip abducted.
Van Arkel R, Amis A, 2013, (i) Basics of orthopaedic biomechanics, Orthopaedics and Trauma, Vol: 27, Pages: 67-75, ISSN: 1877-1327
An outline of the basic principles of orthopaedic biomechanics is presented. Joint moments, muscle moment arms, in vivo forces, contact stresses and joint stability are all discussed with recent clinical examples to demonstrate their importance. These clinical examples focus on the hip and the knee and include: the effects of femoral offset and reducing the abductor moment arm on hip arthroplasty, how the knee adduction moment causes an asymmetric load distribution between the condyles, the magnitude of in vivo forces and their implications for wear, the consequences of meniscectomy on cartilage contact stresses, extreme contact stresses caused by edge loading in hip replacements, the effect of femoral head size and capsular repair in total hip replacement stability, knee medial rotation and the role of the anterior cruciate ligament in joint stability. © 2013 Elsevier Ltd.
van Arkel R, Owen L, Allison S, et al., 2011, Design and preliminary testing of a novel concept low depth hydropower device, MTS/IEEE Oceans 2011
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