On the biomechanics of ligaments and muscles throughout the range of hip motion

At the limits of the range of hip motion, impingement, subluxation and edge loading can cause osteoarthritis in natural hips or early failure hip replacements. The aim of this PhD was to investigate the role of hip joint soft tissues throughout the range of hip motion to better understand their role in preventing (or perhaps even causing) these problematic load cases. A musculoskeletal model was used to investigate the muscular contribution to edge loading and found that in the mid-range of hip motion, the lines of action of hip muscles pointed inward from the acetabular rim and thus would stabilise the hip. However, in deep hip flexion with adduction, nearly half the muscles had unfavourable lines of action which could encourage edge loading. Conversely, in-vitro tests on nine cadaveric hips found that the hip capsular ligaments were slack in the mid-range of hip motion but tightened to restrain excessive hip rotation in positions close to the limits of hip motion. This passive restraint prevented the hip from moving into positions where the muscle lines of action were found to be unfavourable and thus could help protect the hip from edge loading. The ligaments were also found to protect the hip against impingement and dislocation. Out of the labrum, the ligamentum teres and the three capsular ligaments, it was found that the iliofemoral and ischiofemoral ligaments were primary restraints to hip rotation. These two capsular ligaments should be prioritised for protection/repair during hip surgery to maintain normal hip passive restraint. Whilst this can be technically demanding, failing to preserve/restore their function may increase the risk of osteoarthritic degeneration or hip replacement failure.Open Acces

A computed tomography-based model of the infant hip anatomy for dynamic finite element analysis of hip dysplasia biomechanics

Newborns diagnosed with hip dysplasia face severe consequences when treatments fail. The Pavlik harness presents the most common worldwide treatment for correcting this medical hip abnormality in newborns, but becomes increasingly ineffective as subluxation increases. A dynamic finite element analysis on the hip joint would yield results that could provide insight to physicians as to how the Pavlik harness could be optimized to increase its success rate and develop patient-specific treatment plans. The study completes the first step in such an analysis by generating a three-dimensional model of an infant hip joint directly derived from computed tomography imaging in order to accurately represent the anatomical locations of muscle origins and insertions points as well as the unique cartilaginous characteristics of a neonate hip and femur. Such models will further enhance findings on the biomechanics of hip dysplasia that resulted from a preliminary study using computer-aided design to recreate the hip joint. In addition to the models, the orientation of the psoas tendon in a dysplastic hip through full range abduction and flexion was analyzed using a cadaveric dissection. It was determined that the psoas tendon was not an obstruction to reduction when the hip was in flexion so long as the tendon was not adherent to the hip capsule, and therefore can be disregarded in a finite element analysis or dynamic simulation that introduces flexion. The work of this thesis will lay the foundation for complex finite element analyses regarding the biomechanics of hip dysplasia in neonates as well as other hip abnormalities relevant to early child development

Dynamic testing of total hip and knee replacements under physiological conditions

Instability of total hip and knee replacements prevails as major complication. As measurements in patients are afflicted with ethical objections, this work presents a hardware-in-the-loop (HiL) approach that is capable of testing total joint stability under dynamic, reproducible and physiological conditions. An essential aspect represents its validation which includes the development of specific multibody models. In this sense, the HiL test system extends the repertoire of common approaches in orthopedic research by combining the advantages of real implant testing and model-based simulation

Collared Vs. Collarless Total Hip Arthroplasty In Both Direct Anterior And Direct Lateral Approach Surgery: A Prospective Cohort Comparison Study

Total hip arthroplasty (THA) is one of the most successful surgical procedures performed worldwide. Recent advances in implant technology and popularization of the muscle-sparing Direct Anterior (DA) approach to the hip has led to younger patients becoming candidates for hip arthroplasty surgery. Among the many considerations necessary for success in this patient population, implant design plays an important role in determining outcomes. In this thesis, we prospectively evaluated patients who received a collared or collarless fully hydroxyapatite-coated femoral stem during THA with a standard RSA protocol to assess stem migration patterns following surgery. Preliminary results indicate that collarless stems subside significantly more than collared stems within the first 2-4 post-operative weeks, with no differences in patient-reported outcome data between the two cohorts. Further study with longer-term follow-up is indicated to establish migration patterns within the first 2 post-operative years, and whether the discrepancies between cohorts manifest any clinical consequences

Development of an In-Vitro Passive and Active Motion Simulator for the Investigation of Shoulder Function and Kinematics

Injuries and degenerative diseases of the shoulder are common and may relate to the joint’s complex biomechanics, which rely primarily on soft tissues to achieve stability. Despite the prevalence of these disorders, there is little information about their effects on the biomechanics of the shoulder, and a lack of evidence with which to guide clinical practice. Insight into these disorders and their treatments can be gained through in-vitro biomechanical experiments where the achieved physiologic accuracy and repeatability directly influence their efficacy and impact. This work’s rationale was that developing a simulator with greater physiologic accuracy and testing capabilities would improve the quantification of biomechanical parameters. This dissertation describes the development and validation of a simulator capable of performing passive assessments, which use experimenter manipulation, and active assessments – produced through muscle loading. Respectively, these allow the assessment of functional parameters such as stability, and kinematic/kinetic parameters including joint loading. The passive functionality enables specimen motion to be precisely controlled through independent manipulation of each rotational degree of freedom (DOF). Compared to unassisted manipulation, the system improved accuracy and repeatability of positioning the specimen (by 205% & 163%, respectively), decreased variation in DOF that are to remain constant (by 6.8°), and improved achievement of predefined endpoints (by 21%). Additionally, implementing a scapular rotation mechanism improved the physiologic accuracy of simulation. This enabled the clarification of the effect of secondary musculature on shoulder function, and the comparison of two competing clinical reconstructive procedures for shoulder instability. This was the first shoulder system to use real time kinematic feedback and PID control to produce active motion, which achieved unmatched accuracy ( These developments can be a powerful tool for increasing our understanding of the shoulder and also to provide information which can assist surgeons and improve patient outcomes

DISTAL RADIOULNAR JOINT BIOMECHANICS AND FOREARM MUSCLE ACTIVITY

Optimal management of fractures, post-traumatic arthritis and instability of the distal radioulnar joint (DRUJ) requires an understanding of the forces existing across this joint as a function of the activities of daily living. However, such knowledge is currently incomplete. The goal of this research was to quantify the loads that occur at the DRUJ during forearm rotation and to determine the effect that individual muscles have on those loads. Human and cadaver studies were used to analyze the shear (A-P), transverse (M-L) and resultant forces at the DRUJ and to determine the role that 15 individual muscles had on those forces. Data for scaling the muscles forces came from EMG analysis measuring muscle activity at nine positions of forearm rotation in volunteers during isometric pronation and supination. Muscle orientations were determined from the marked muscle origin and insertion locations of nine cadaveric arms at various stages of forearm rotation. The roles that individual muscles played in DRUJ loading were analyzed by removing the muscle of interest from the analysis and comparing the results. The EMG portion of this study found that the pronator quadratus, pronator teres, brachioradialis, flexor carpi radialis and palmaris longus contribute significantly to forearm pronation. The supinator, biceps brachii, and abductor pollicis longus were found to contribute significantly to supination. The results of the DRUJ analysis affirm that large transverse forces pass from the radius to the ulnar head at all positions of forearm rotation during pronation and supination (57.5N-181.4N). Shear forces exist at the DRUJ that act to pull the radius away from the ulna in the AP direction and are large enough to merit consideration when examining potential treatment options (7.9N-99.5N). Individual muscle analysis found that the extensor carpi radialis brevis, extensor pollicis longus, extensor carpi ulnaris, extensor indicis and palmaris longus had minimal effect on DRUJ loading. Other than the primary forearm rotators (pronator quadratus, pronator teres, supinator, biceps brachii), the muscles that exhibited the largest influence on DRUJ loading were the abductor pollicis longus, brachialis, brachioradialis, extensor carpi ulnaris, flexor carpi radialis, and flexor carpi ulnaris

Development and Validation of a Knee-Thigh-Hip LSDYNA Model of a 50th Percentile Male.

With the introduction of air bags, occupant safety in frontal car crashes has been improved for upper regions of the body, such as the head and thorax. These improvements, however, have not helped improve the safety for the lower extremities, increasing their percentage of injuries in car crashes. Though lower extremity injuries are usually not life threatening, they can have long lasting physical and psychosocial consequences. An LSDYNA finite element model of the knee-thigh-hip (KTH) of a 50th percentile adult male was developed for exploring the mechanics of injuries to the KTH during frontal crash crashes. The model includes a detailed geometry of the bones, the mass of the soft tissue, and a discrete element representation of the ligaments and muscles of the KTH. The bones were validated using physical tests obtained from the National Highway Traffic and Safety Administration\u27s (NHTSA) test database. The geometry, the material properties and the failure mechanisms of bone materials were verified. A validation was also performed against a whole-body cadaver test to verify contributions of passive muscle and ligament forces. Failure mechanisms in the tests and simulations were compared to ensure that the model provides a useful tool for exploring fractures and dislocations in the KTH resulting from frontal vehicle crashes. The validated model was then used to investigate injury mechanisms during a frontal car crash at different occupant positions. The role of muscle forces on these fracture mechanisms was explored and simulations of frontal impacts were then reproduced with the KTH complex at different angles of thigh flexion, adduction and abduction. Results show that the failure mechanism of the lower limb can significantly depend on the occupant position prior to impact. Failure mechanisms in the simulations were compared to results found in literature to ensure the model provides a useful tool for predicting fractures in the lower limb resulting from out-of-position frontal vehicle crashes. The FE model replicate injury criteria developed for ligament failure and suggested lowering the actual used axial femur force threshold for KTH injures both in neutral and out-of-position KTH axial impacts

Effects of Scapular Notching and Bone Remodelling on Long-Term Fixation of the Glenoid Component in Reverse Shoulder Arthroplasty

Reverse shoulder arthroplasty (RSA) has been a proposed surgical treatment for severe rotator cuff deficiency associated with arthritis. Favourable clinical results for this type of prosthesis have been reported from short- and mid-term follow-up studies. However, the high revision rate (5% - 33%) at long-term follow up (i.e. greater than 6 years) is a concern. One of the principal factors leading to RSA failure is glenoid component loosening with an incidence of 5% - 38%. Therefore, one objective of this project is to investigate factors leading to long-term glenoid loosening. As various glenosphere positions have been proposed to minimize scapular notching, the other objective is to predict fixation strengths associated with these new surgical techniques. Scapular notching is one of the most frequently reported complications for Delta RSA, due to the high postoperative incidence of 50% to 96%. In this thesis, the study of scapular notching showed negative effects on the inferior screw safety and safety of the bone close to the screw. The study of initial stability showed that scapular notching may not destroy the good environment for bony ingrowth. Strain-induced bone remodelling has been an important factor for the bone loss after hip and knee joint prosthesis implantations. Effects of this factor on the bone loss after Delta RSA implantations were investigated. The results showed that bone resorption was considerable in the region close to the back of metagelene and the middle stem with a mean reduction of postoperative bone apparent density of approximately 63% at 8-year follow up. Thereby, postoperative bone loss could be caused by three factors: strain-induced bone resorption, scapular notching and osteolysis induced by the polyethylene wear particles. In this study, prosthesis fixations in the case of inferior positioning and downward tilting of the glenosphere were assessed using two parameters: strain-induced bone resorption and initial stability. It was found that inferior positioning may lead to early bone resorption due to the inferior shift of postoperative glenohumeral force. The downward tilting may cause significant increase of bone-prosthesis micromotions and may result in poor initial stabilities of glenoid prosthesis