19 results found
Doyle R, van Arkel R, Muirhead-Allwood S, et al., 2020, Impaction technique influences implant stability in low density bone model, Bone & Joint Research, Vol: 9, ISSN: 2046-3758
Aims: Cementless acetabular cups rely on press-fit fixation for initial stability. In certain cases initial stability is more difficult to obtain (such as during revision). No current study evaluates how a surgeon’s impaction technique (mallet mass, mallet velocity and number of strikes) may affect cup fixation. This study seeks to answer the following research questions:(1) How does impaction technique affect a) bone strain generation and deterioration (and hence implant stability); b) seating in different density bones? (2) Can an impaction technique be recommended to minimize risk of implant loosening while ensuring seating of the acetabular cup? Methods: A custom drop tower was used to simulate surgical strikes seating acetabular cups into synthetic bone. Strike velocity and drop mass were varied. Synthetic bone strain was measured using strain gauges and stability was assessed via push out tests. Polar gap was measured using optical trackers. Results: A phenomenon of strain deterioration was identified if an excessive number of strikes were used to seat a cup. This effect was most pronounced in low density bone at high strike velocities. Polar gap was reduced with increasing strike mass and velocity. Conclusions: A high mallet mass with low strike velocity resulted in satisfactory implant stability and polar gap while minimizing the risk of losing stability due to over-striking. Extreme caution not to over-strike must be exercised when using high velocity strikes in low density bone for any mallet
Doyle R, van Arkel R, Jeffers J, 2019, The effect of impaction energy on dynamic bone strains, fixation strength and seating of cementless acetabular cups, Journal of Orthopaedic Research, Vol: 37, Pages: 2367-2375, ISSN: 0736-0266
Seating a cementless acetabular cup via impaction is a balancing act; good cup fixation must be obtained to ensure adequate bone in‐growth and cup apposition, while acetabular fracture must be avoided. Good impaction technique is essential to the success of hip arthroplasty. Yet little guidance exists in the literature to inform surgeons on ‘how hard’ to hit. A drop rig and synthetic bone model were used to vary the energy of impaction strikes in low and high density synthetic bone, while key parameters such as dynamic strain (quantifying fracture risk), implant fixation and polar gap were measured. For high energy impaction (15 J) in low density synthetic bone a peak tensile strain was observed during impaction that was up to 3.4x as large as post‐strike strain, indicating a high fracture risk. Diminishing returns were observed for pushout fixation with increasing energy. 85% of the pushout fixation achieved using a 15 J impaction strike was attained by using a 7.5 J strike energy. Similarly polar gap was only minimally reduced at high impaction energies. Therefore it is suggested that higher energy strikes increase fracture risk, but do not offer large improvements to fixation or implant‐bone apposition. It may difficult be for surgeons to accurately deliver specific impaction energies, suggesting there is scope for operative tools to manage implant seating.
Garner A, van Arkel RJ, Cobb J, 2019, Classification of combined partial knee arthroplasty, Bone and Joint Journal, Vol: 101B, Pages: 922-928, ISSN: 2049-4394
AimsThere has been a recent resurgence in interest in combined partial knee arthroplasty (PKA) as an alternative to total knee arthroplasty (TKA). The varied terminology used to describe these procedures leads to confusion and ambiguity in communication between surgeons, allied health professionals, and patients. A standardized classification system is required for patient safety, accurate clinical record-keeping, clear communication, correct coding for appropriate remuneration, and joint registry data collection.Materials and MethodsAn advanced PubMed search was conducted, using medical subject headings (MeSH) to identify terms and abbreviations used to describe knee arthroplasty procedures. The search related to TKA, unicompartmental (UKA), patellofemoral (PFA), and combined PKA procedures. Surveys were conducted of orthopaedic surgeons, trainees, and biomechanical engineers, who were asked which of the descriptive terms and abbreviations identified from the literature search they found most intuitive and appropriate to describe each procedure. The results were used to determine a popular consensus.ResultsSurvey participants preferred “bi-unicondylar arthroplasty” (Bi-UKA) to describe ipsilateral medial and lateral unicompartmental arthroplasty; “medial bi-compartmental arthroplasty” (BCA-M) to describe ipsilateral medial unicompartmental arthroplasty with patellofemoral arthroplasty; “lateral bi-compartmental arthroplasty” (BCA-L) to describe ipsilateral lateral unicompartmental arthroplasty with patellofemoral arthroplasty; and tri-compartmental arthroplasty (TCA) to describe ipsilateral patellofemoral and medial and lateral unicompartmental arthroplasties. “Combined partial knee arthroplasty” (CPKA) was the favoured umbrella term.ConclusionWe recommend bi-unicondylar arthroplasty (Bi-UKA), medial bicompartmental arthroplasty (BCA-M), lateral bicompartmental arthroplasty (BCA-L), and tricompartmental arthroplasty (
Logishetty K, van Arkel RJ, Ng KC, et al., 2019, Hip capsule biomechanics after arthroplasty - the effect of implant, approach and surgical repair, Bone and Joint Journal, Vol: 101-B, Pages: 426-434, ISSN: 2049-4394
AimsThe hip’s capsular ligaments passively restrain extreme range of movement (ROM) by wrapping around the native femoral head/neck. We determined the effect of hip resurfacing arthroplasty (HRA), dual-mobility total hip arthroplasty (DM-THA), conventional THA, and surgical approach on ligament function.Materials and MethodsEight paired cadaveric hip joints were skeletonized but retained the hip capsule. Capsular ROM restraint during controlled internal rotation (IR) and external rotation (ER) was measured before and after HRA, DM-THA, and conventional THA, with a posterior (right hips) and anterior capsulotomy (left hips).ResultsHip resurfacing provided a near-native ROM with between 5° to 17° increase in IR/ER ROM compared with the native hip for the different positions tested, which was a 9% to 33% increase. DM-THA generated a 9° to 61° (18% to 121%) increase in ROM. Conventional THA generated a 52° to 100° (94% to 199%) increase in ROM. Thus, for conventional THA, the capsule function that exerts a limit on ROM is lost. It is restored to some extent by DM-THA, and almost fully restored by hip resurfacing. In positions of low flexion/extension, the posterior capsulotomy provided more normal function than the anterior, possibly because the capsule was shortened during posterior repair. However, in deep flexion positions, the anterior capsulotomy functioned better.ConclusionNative head-size and capsular repair preserves capsular function after arthroplasty. The anterior and posterior approach differentially affect postoperative biomechanical function of the capsular ligaments.
El Daou H, Ng KC, van Arkel R, et al., 2019, Robotic hip joint testing: Development and experimental protocols, Medical Engineering and Physics, Vol: 63, Pages: 57-62, ISSN: 1350-4533
The use of robotic systems combined with force sensing is emerging as the gold standard for in vitro biomechanical joint testing, due to the advantage of controlling all six degrees of freedom independently of one another. This paper describes a novel robotic platform and the experimental protocol used for hip joint testing. An experimental protocol implemented optical tracking and registration techniques in order to define the position of the hip joint centre of rotation (COR) in the coordinate system of the robot's end effector. The COR coordinates defined the origin of the task-related coordinate system used to control the robot, with a hybrid force/position law to simulate standard clinical tests. The axes of this frame were defined using the International Society of Biomechanics (ISB) anatomical coordinate system.Experiments were carried out on two cadaveric hip joint specimens using the robotic testing platform and a mechanical testing rig previously developed and described by our group. Simulated internal-external and adduction/abduction laxity tests were carried out with both systems and the resulting peak range of motion (ROM) was measured. Similarities and differences were observed in these experiments, which were used to highlight some of the limitations of conventional systems and the corresponding advantages of robotics, further emphasising their added value in vitro testing.
Correa T, Pal B, van Arkel R, et al., 2018, Reduced tibial strain-shielding with extraosseous total knee arthroplasty revision system, Medical Engineering and Physics, Vol: 62, Pages: 22-28, ISSN: 1350-4533
BackgroundRevision total knee arthroplasty (RTKA) has poorer results than primary total knee arthroplasty (TKA), and the prostheses are invasive and cause strain-shielding of the bones near the knee. This paper describes an RTKA system with extracortical fixation. It was hypothesised that this would reduce strain-shielding compared with intramedullary fixation.MethodsTwelve replica tibiae were prepared for full-field optical surface strain analysis. They were either left intact, implanted with RTKA components with cemented intramedullary fixation stems, or implanted with a novel design with a tibial tray subframe supported by two extracortical fixation plates and screw fixation. They were loaded to simulate peak walking and stair climbing loads and the surface strains were measured using digital image correlation. The measurements were validated with strain gauge rosettes.ResultsCompared to the intact bone model, extracortical fixation reduced surface strain-shielding by half versus intramedullary fixation. For all load cases and bone regions examined, the extracortical implant shielded 8–27% of bone strain, whereas the intramedullary component shielded 37–56%.ConclusionsThe new fixation design, which offers less bone destruction than conventional RTKA, also reduced strain-shielding. Clinically, this design may allow greater rebuilding of bone loss, and should increase long-term fixation.
van Arkel R, Ng KCG, Muirhead-Allwood S, et al., 2018, Capsular ligament function after total hip arthroplasty, Journal of Bone and Joint Surgery, American Volume, Vol: 100, Pages: e94-e94, ISSN: 0021-9355
Background: The hip joint capsule passively restrains extreme range of motion, protecting the native hip against impingement, dislocation, and edge-loading. We hypothesized that following total hip arthroplasty (THA), the reduced femoral head size impairs this protective biomechanical function.Methods: In cadavers, THA was performed through the acetabular medial wall, preserving the entire capsule, and avoiding the targeting of a particular surgical approach. Eight hips were examined. Capsular function was measured by rotating the hip in 5 positions. Three head sizes (28, 32, and 36 mm) with 3 neck lengths (anatomical 0, +5, and +10 mm) were compared.Results: Internal and external rotation range of motion increased following THA, indicating late engagement of the capsule and reduced biomechanical function (p < 0.05). Internal rotation was affected more than external. Increasing neck length reduced this hypermobility, while too much lengthening caused nonphysiological restriction of external rotation. Larger head sizes only slightly reduced hypermobility.Conclusions: Following THA, the capsular ligaments were unable to wrap around the reduced-diameter femoral head to restrain extreme range of motion. The posterior capsule was the most affected, indicating that native posterior capsule preservation is not advantageous, at least in the short term. Insufficient neck length could cause capsular dysfunction even if native ligament anatomy is preserved, while increased neck length could overtighten the anterior capsule.Clinical Relevance: Increased understanding of soft-tissue balancing following THA could help to prevent instability and improve early function. This study illustrates how head size and neck length influence the biomechanical function of the hip capsule in the early postoperative period.
van Arkel R, Ghouse S, Milner P, et al., 2018, Additive manufactured push-fit implant fixation with screw-strength pull out, Journal of Orthopaedic Research, Vol: 36, Pages: 1508-1518, ISSN: 0736-0266
Additive manufacturing offers exciting new possibilities for improving long-term metallic implant fixation in bone through enabling open porous structures for bony ingrowth. The aim of this research was to investigate how the technology could also improve initial fixation, a precursor to successful long-term fixation. A new barbed fixation mechanism, relying on flexible struts was proposed and manufactured as a push-fit peg. The technology was optimized using a synthetic bone model and compared with conventional press-fit peg controls tested over a range of interference fits. Optimum designs, achieving maximum pull-out force, were subsequently tested in a cadaveric femoral condyle model. The barbed fixation surface provided more than double the pull-out force for less than a third of the insertion force compared to the best performing conventional press-fit peg (p < 0.001). Indeed, it provided screw-strength pull out from a push-fit device (1,124 ± 146 N). This step change in implant fixation potential offers new capabilities for low profile, minimally invasive implant design, while providing new options to simplify surgery, allowing for one-piece push-fit components with high levels of initial stability.
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.
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.
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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