Richard J. van Arkel

Hip abduction can prevent posterior edge loading of hip replacements

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.

Design and preliminary testing of a novel concept low depth hydropower device

This paper introduces a new type of kinetic hydropower generator, ideally suited to relatively small shallow rivers and channels. The design utilizes rectangular hydroplanes (‘sails’) moving around the device. The device extracts energy from a flow of water using an elongated vertical axis turbine, where a series of sails are mounted between two belts at the top and bottom of the device, rotating in the horizontal plane.

The Use of Sonographically Guided Botulinum Toxin Type A (Dysport) Injections Into the Tensor Fasciae Latae for the Treatment of Lateral Patellofemoral Overload Syndrome

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° ± 5°), and 12 (7° ± 6°) weeks after the injection compared with before the injection (all P < .010). Simulating a progressive reduction in TFL strength resulted in corresponding increases in GMed activity during gait. Conclusion: An injection of BT into the TFL, combined with physical therapy, resulted in a significant improvement of symptoms in patients with LPOS, which was maintained at 5-year follow-up. This may result from reduced lateral TFL/ITB tension or to an increase in GMed activity in response to inhibition of the TFL.

The envelope of passive motion allowed by the capsular ligaments of the hip.

Laboratory data indicate the hip capsular ligaments prevent excessive range of motion, may protect the joint against adverse edge loading and contribute to synovial fluid replenishment at the cartilage surfaces of the joint. However, their repair after joint preserving or arthroplasty surgery is not routine. In order to restore their biomechanical function after hip surgery, the positions of the hip at which the ligaments engage together with their tensions when they engage is required. Nine cadaveric left hips without pathology were skeletonised except for the hip joint capsule and mounted in a six-degrees-of-freedom testing rig. A 5 N m torque was applied to all rotational degrees-of-freedom separately to quantify the passive restraint 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 of un-resisted rotation (up to 50±10°) in mid-flexion and mid-ab/adduction but this was reduced towards the limits of flexion/extension and ab/adduction such that there was a near-zero slack region in some positions (p<0.014). The slack region was not symmetrical; the mid-slack point was found with internal rotation in extension and external rotation in flexion (p<0.001). The torsional stiffness of the capsular ligamentous restraint averaged 0.8±0.3 N m/° and was greater in positions where there were large slack regions. These data provide a target for restoration of normal capsular ligament tensions after joint preserving hip surgery. Ligament repair is technically demanding, particularly for arthroscopic procedures, but failing to restore their function may increase the risk of osteoarthritic degeneration.

Additive manufactured push-fit implant fixation with screw-strength pull out

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.

In vitro hip testing in the International Society of Biomechanics coordinate system

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 study was 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.

Reduced tibial strain-shielding with extraosseous total knee arthroplasty revision system

Highlights • A novel extracortical support system for revision of failed knee prostheses.• Shown to reduce metaphyseal stress-shielding versus intramedullary stem fixation.• Reduces bone loss and enables bone grafting of defects after implant loosening.• Enables use of conventional prosthesis in a revision scenario.

Femoral fracture type can be predicted from femoral structure: A finite element study validated by digital volume correlation experiments

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.