Minimising risk of tibial fracture after cementless unicompartmental knee replacement

Tibial fractures are a potential risk after unicompartmental knee replacement (UKR). The aim of this study was to (1) characterise the typical depth and positioning of saw cuts made by surgeons performing mobile UKR, and (2) to assess which bone cuts have the greatest influence on the risk of tibial fracture. In twenty four tibial sawbones used during a training course for UKR surgery the depth of the vertical and horizontal cuts and the depth and angle of the pin hole were measured. All the vertical bone cuts measured were most excessive posteirorly; cuts were 4.25±3.9mm (max:12mm) excessively deep posteriorly and 0.46±1.0mm (max:4mm) excessive anteriorly. The horizontal bone cuts posterior/anterior were not statistically different, and were excessive by 1.26±2.1mm (max:7.5mm) and 0.73±0.9mm (max:3mm), respectively. The tibial resection depth was 8.79±1.7mm on average. Of the 24 sawbones analysed, in 14 the pin hole penetrated the keel and one went through the posterior cortex. Based upon the sawbone measurements, three finite element simulations were performed; an implanted component with (1) no excessive bone cuts, (2) a vertical cut excessive 1mm anteriorly and 10mm posteriorly, (3) a horizontal cut 5 mm excessive both anteriorly and posteriorly. These preliminary experiments found the greatest bone strain in simulation (2). Therefore, to minimise the risk of tibial fracture care must be taken to ensure the vertical cut is not too deep posteriorly. One possible technique to prevent a deep vertical cut would be to saw down onto a shim inserted into a previously performed horizontal cut

Conservative Tibial Resection and Vertical Cut Minimise Risk of Tibial Plateau Fracture after UKR

Tibial fracture is a known complication after unicompartmental knee replacement (UKR) [1]. Furthermore, some studies have indicated an increased risk of tibial fracture with cementless UKR [2]. Our aim was to identify surgical factors that contribute to fracture. We examined the influence of tibial saw cuts on the risk of fracture after cementless UKR, to determine if changes in tibial preparation could minimise the risk of fracture. The range and distribution of typical saw cut positions were measured from 23 right tibial Sawbones used as part of an instructional course. Sawbones were prepared by both experienced and unexperienced orthopaedic surgeons but all had received training on the operative technique. Measured parameters were; resection depth, excessive vertical cut anterior/posterior, excessive horizontal cut anterior/posterior, pin depth and pin angle. One hundred finite element models were then created where each parameter was assigned using a random number generator within its measured distribution, and the risk of fracture assessed. Results from a multiple linear regression model indicated that a greater resection depth and a more excessive posterior vertical cut significantly increased the risk of fracture after UKR. Based upon these results, a surgical technique and instrumentation for UKR which minimises inaccuracies in the vertical cut and promotes a more conservative resection depth would be recommended to minimise the risk of tibial plateau fracture after UKR.[1] HG Pandit, DW Murray, CA Dodd, et al. (2007) Orthopedics 30: 28-31[2] JB Seeger, D Haas, S Jager et al. (2012) Knee Surg Sports Traumatol Arthrosc 20: 1087-109

Artificial Anterior Cruciate Ligament (ACL) Reconstruction for more Natural Knee Kinematics

Aim:The aims of this study were to define the design criteria of an artificial ACL which could reproduce the non-linear load-elongation characteristics of the native ACL, and to investigate the mechanical behaviour of a novel ACL reconstruction design consisting of a metallic elastic system and a polymeric cord.Introduction:Kinematic and survivorship studies on the ACL intact and ACL deficient knees have emphasised the importance of preserving and/or reconstructing the ACL [1], [2]. The unique mechanical properties of the ACL and the non-linear relationship between the ACL forces and the quadriceps muscle forces at different flexion angles are the key elements in providing normal kinematics.Current synthetic ACL reconstruction grafts have shown poor long-term results, mainly due to wear, creep, fatigue and mechanical failure. None of the synthetic and biological grafts used for the ACL reconstruction have been able to replicate the normal mechanical behaviour of the ACL and prevent degenerative disease progression such as osteoarthritis.Method:Desired mechanical properties of the artificial ACL were defined based the results of in vitro and in vivo biomechanical studies. Suitable materials were found for the prosthetic ACL which met the required design criteria. Implicit finite element analyses were performed on a spring-cord construct design and the output force-elongation data compared to the estimated in-vivo natural ACL properties found in the literature.Results:It was shown that an artificial ACL should have a non-linear stiffness with low resistance to the initial load (~30 Nmm-1 stiffness in the toe region) and increased stiffness under higher load (~110 Nmm-1 stiffness in the linear region). Suitable materials for the ACL reconstruction design (i.e. CoCrMo alloy and UHMWPE fibres) were identified based on their biocompatibility, strength, strain, creep and fatigue propertiesThe FEA results showed that the mechanical properties of the novel artificial ACL deisgn closely resembled that of the natural ACL at 30° of flexion. A validation test was performed on prototype samples, which supported the finite element data.ConclusionsThe non-linear force-elongation properties of the native ACL can be reproduced by an artificial ACL reconstruction system in the ACLD knees

Behaviour of Anterior Cruciate Ligament (ACL) Deficient Knees after Unicompartmental Knee Arthroplasty (UKA)

Abstract:Introduction: ACL-deficiency is a contraindication for UKA because it has been linked with early failure, in particular tibial tray loosening [1]; but a more recent study has shown no difference in the survivorship in ACL-deficient patients at 5 years post-operatively [2]. The purpose of this study was to examine the movement of ACL-deficient knees after UKA when stair climbing, to assess the function of ACL-deficient knees after UKA. Methods:This case-control study involved fluoroscopically examining 16 ACL-deficient knees (14 patients) which had undergone medial UKA. Fluoroscopy videos were taken in the sagittal plane. A matching group of 16 ACL-intact knees (13 patients) were then assessed; groups were matched for age, follow-up time, and gender, and no significant differences were found between the groups (Table 1). Starting with their leg on the step at a knee flexion angle (KFA) of 90°, patients were asked to step up, while ensuring their knee remained within the view of the fluoroscope. The patellar tendon angle (PTA) and KFA was measured on each frame of each fluoroscopic video, and the total time taken to perform the exercise was noted. The PTA is the angle between the patellar tendon and the tibial mechanical axis and it represents the anterior posterior translation of the femur relative to the tibia. In addition, patients were asked to complete three questionnaires; the Oxford Knee Score (OKS), the Tegner Activity Score (TAS) and the Visual Analogue Scale (VAS) Pain Score. Results:No differences were found in the OKS (p=0.35), TAS (p=0.15) or VAS Pain score (p=0.73) between the two groups. When the KFA was ~30° the PTA was 5° lower in the ACL-deficient group compared with the ACL-intact group (p=0.0002, Fig 1). A 2.9° reduction in PTA was also observed at a KFA of 60° (p=0.007, Fig 1). ACL-deficient group took 30.7% (13 s) longer to perform the step-up exercise on average compared to the ACL-intact group, which was significant (p=0.0007).Discussion and Conclusion:The lower PTA in the ACL-deficient knees at 30°, 40° and 60° KFA indicates increased anterior translation of the tibia. A healthy ACL resists anterior tibial translation; therefore the absence of ACL function appears to have caused knee instability at these particular angles. In addition, the increased time taken for the ACL-deficient group to step up indicates hesitancy when stair climbing and may relate to the reduced proprioception within the knee. This study highlights the importance of ACL function in maintaining knee stability after UKA. Knee instability may relate to the tibial loosening reported for ACL-deficient knees after UKA; however, no sign of loosening was observed in this study. ACL reconstruction in conjunction with UKA has been shown to restore stability and may be the best option for ACL-deficient patients with medial compartment osteoarthritis.References:[1] J Goodfellow et al., J Bone Joint Surg [Br]. 1988; 70-B(5):692-701[2] A Boissonneault et al., Knee Surg Sport Tr A. 2013;21(11):2480-

Special topic: The association between pulse ingredients and canine dilated cardiomyopathy: addressing the knowledge gaps before establishing causation.

In July 2018, the Food and Drug Administration warned about a possible relationship between dilated cardiomyopathy (DCM) in dogs and the consumption of dog food formulated with potatoes and pulse ingredients. This issue may impede utilization of pulse ingredients in dog food or consideration of alternative proteins. Pulse ingredients have been used in the pet food industry for over 2 decades and represent a valuable source of protein to compliment animal-based ingredients. Moreover, individual ingredients used in commercial foods do not represent the final nutrient concentration of the complete diet. Thus, nutritionists formulating dog food must balance complementary ingredients to fulfill the animal's nutrient needs in the final diet. There are multiple factors that should be considered, including differences in nutrient digestibility and overall bioavailability, the fermentability and quantity of fiber, and interactions among food constituents that can increase the risk of DCM development. Taurine is a dispensable amino acid that has been linked to DCM in dogs. As such, adequate supply of taurine and/or precursors for taurine synthesis plays an important role in preventing DCM. However, requirements of amino acids in dogs are not well investigated and are presented in total dietary content basis which does not account for bioavailability or digestibility. Similarly, any nutrient (e.g., soluble and fermentable fiber) or physiological condition (e.g., size of the dog, sex, and age) that increases the requirement for taurine will also augment the possibility for DCM development. Dog food formulators should have a deep knowledge of processing methodologies and nutrient interactions beyond meeting the Association of American Feed Control Officials nutrient profiles and should not carelessly follow unsubstantiated market trends. Vegetable ingredients, including pulses, are nutritious and can be used in combination with complementary ingredients to meet the nutritional needs of the dog

Attention bias to emotional faces varies by IQ and anxiety in Williams syndrome

Individuals with Williams syndrome (WS) often experience significant anxiety. A promising approach to anxiety intervention has emerged from cognitive studies of attention bias to threat. To investigate the utility of this intervention in WS, this study examined attention bias to happy and angry faces in individuals with WS (N=46). Results showed a significant difference in attention bias patterns as a function of IQ and anxiety. Individuals with higher IQ or higher anxiety showed a significant bias toward angry, but not happy faces, whereas individuals with lower IQ or lower anxiety showed the opposite pattern. These results suggest that attention bias interventions to modify a threat bias may be most effectively targeted to anxious individuals with WS with relatively high IQ

A systematic review of the barriers and facilitators impacting patient enrolment in clinical trials for lung cancer

Purpose. Clinical research trials are needed to enhance the medical care and treatment for lung cancer, which remains the leading cause of cancer-related deaths worldwide. While clinical trials allow for the development of novel therapies to treat cancer, the recruitment of lung cancer patients to trials is low. This review aimed to identify and synthesise the available literature concerning barriers and facilitators affecting lung cancer patients’ decisions to enrol in clinical trials to guide future cancer research efforts. Methods. Four databases were systematically searched: Academic Search Complete, CINHAL, PubMed, and PsycINFO in August 2023. A supplemental grey literature search was also conducted alongside this. Articles were quality appraised using CASP and JMI checklists, and results were narratively synthesised. Results. Eighteen articles of varied design met the inclusion criteria, and results were mapped onto the Capability, Opportunity, and Motivation Behaviour (COM-B) Model to help structure and conceptualise review findings. Evidence suggests that the decision to enrol in a trial is multifaceted and informed by: when and how study information is presented, travel and trial eligibility, and altruistic hopes and fears. Conclusions. There is need to address the many different concerns that lung cancer patients have about participating in a clinical trial through the supply of accessible and timely trial information, and via the reduction of travel, expansion of study eligibility criteria, and recognition of a person's altruistic wishes, hopes, fears, and family-oriented concerns. Future research should aim to work alongside lung cancer patients, clinicians, and other stakeholders to increase research accessibility