Validation of a Redundant Robotic Manipulator for Shoulder in Vitro Biomechanical Testing.

Cadaveric joint simulators are commonly used to explore native and pathological joint function as well as to test medical devices. Recently, robotic manipulators have been proposed as a new gold standard for in vitro biomechanical testing as they offer higher possibilities than Universal Testing Machines in terms of degrees of freedom (DOF). However, current protocols remain conducted in extra-corporal conditions by fixing one segment of a diarthrodial joint while mobilising the other segment. Moreover, induced motions are commonly not specimen-specific and do not respect related joint kinematic constraints and physiologic boundaries. In this study, using a 7 DOF redundant robotic manipulator, an intra-corporal condition protocol was defined. This protocol allows 1) the analysis of the shoulder girdle full kinematic chain, 2) the replication of specimen-specific humerus motions initially induced by an operator. On the 10 shoulders tested, the robotic manipulator was able to perform requested end-effector motions with a reliability of 0.28 ± 0.57 mm and 0.15 ± 0.25°, and a fidelity of 0.27 ± 0.56 mm and 0.22 ± 0.28°. This protocol will be used in the future to explore joint function as well as to test medical devices, on the shoulder girdle and potentially other joints.

In Vitro Human Joint Models Combining Advanced 3D Cell Culture and Cutting-Edge 3D Bioprinting Technologies

Joint-on-a-chip is a new technology able to replicate the joint functions into microscale systems close to pathophysiological conditions. Recent advances in 3D printing techniques allow the precise control of the architecture of the cellular compartments (including chondrocytes, stromal cells, osteocytes and synoviocytes). These tools integrate fluid circulation, the delivery of growth factors, physical stimulation including oxygen level, external pressure, and mobility. All of these structures must be able to mimic the specific functions of the diarthrodial joint: mobility, biomechanical aspects and cellular interactions. All the elements must be grouped together in space and reorganized in a manner close to the joint organ. This will allow the study of rheumatic disease physiopathology, the development of biomarkers and the screening of new drugs.

Facet Joints of the Spine: Structure–Function Relationships, Problems and Treatments, and the Potential for Regeneration

The zygapophysial joint, a diarthrodial joint commonly referred to as the facet joint, plays a pivotal role in back pain, a condition that has been a leading cause of global disability since 1990. Along with the intervertebral disc, the facet joint supports spinal motion and aids in spinal stability. Highly susceptible to early development of osteoarthritis, the facet is responsible for a significant amount of pain in the low-back, mid-back, and neck regions. Current noninvasive treatments cannot offer long-term pain relief, while invasive treatments can relieve pain but fail to preserve joint functionality. This review presents an overview of the facet in terms of its anatomy, functional properties, problems, and current management strategies. Furthermore, this review introduces the potential for regeneration of the facet and particular engineering strategies that could be employed as a long-term treatment.

Current Therapeutic Strategies for Stem Cell-Based Cartilage Regeneration

The process of cartilage destruction in the diarthrodial joint is progressive and irreversible. This destruction is extremely difficult to manage and frustrates researchers, clinicians, and patients. Patients often take medication to control their pain. Surgery is usually performed when pain becomes uncontrollable or joint function completely fails. There is an unmet clinical need for a regenerative strategy to treat cartilage defect without surgery due to the lack of a suitable regenerative strategy. Clinicians and scientists have tried to address this using stem cells, which have a regenerative potential in various tissues. Cartilage may be an ideal target for stem cell treatment because it has a notoriously poor regenerative potential. In this review, we describe past, present, and future strategies to regenerate cartilage in patients. Specifically, this review compares a surgical regenerative technique (microfracture) and cell therapy, cell therapy with and without a scaffold, and therapy with nonaggregated and aggregated cells. We also review the chondrogenic potential of cells according to their origin, including autologous chondrocytes, mesenchymal stem cells, and induced pluripotent stem cells.

Bone Biology

This chapter introduces readers to the basics of understanding bone’s functions, which include calcium homeostasis and enabling movement, bone’s components, such as the collagen, and bone’s organization, such as the Haversian system found in cortical bone. The focus of this chapter is on explaining concepts of bone remodeling, which is thought to prevent fractures and other bone damage, and repair, which can take place at macro-levels and micro-levels. Wolff’s Law of bone remodeling, which was initially focused on trabecular bone changes, is discussed in terms of bone’s response to forces that result in strains and stresses. Finally, diarthrodial joint remodeling and repair are discussed; cartilage cells were once thought to be static, yet now they are known to also respond to stresses.

Use of Robotic Manipulators to Study Diarthrodial Joint Function

Diarthrodial joint function is mediated by a complex interaction between bones, ligaments, capsules, articular cartilage, and muscles. To gain a better understanding of injury mechanisms and to improve surgical procedures, an improved understanding of the structure and function of diarthrodial joints needs to be obtained. Thus, robotic testing systems have been developed to measure the resulting kinematics of diarthrodial joints as well as the in situ forces in ligaments and their replacement grafts in response to external loading conditions. These six degrees-of-freedom (DOF) testing systems can be controlled in either position or force modes to simulate physiological loading conditions or clinical exams. Recent advances allow kinematic, in situ force, and strain data to be measured continuously throughout the range of joint motion using velocity-impedance control, and in vivo kinematic data to be reproduced on cadaveric specimens to determine in situ forces during physiologic motions. The principle of superposition can also be used to determine the in situ forces carried by capsular tissue in the longitudinal direction after separation from the rest of the capsule as well as the interaction forces with the surrounding tissue. Finally, robotic testing systems can be used to simulate soft tissue injury mechanisms, and computational models can be validated using the kinematic and force data to help predict in vivo stresses and strains present in these tissues. The goal of these analyses is to help improve surgical repair procedures and postoperative rehabilitation protocols. In the future, more information is needed regarding the complex in vivo loads applied to diarthrodial joints during clinical exams and activities of daily living to serve as input to the robotic testing systems. Improving the capability to accurately reproduce in vivo kinematics with robotic testing systems should also be examined.

Glutaraldehyde Fixation of Bovine Humeral Head Articular Cartilage Maintains Functional Frictional Response

Hemiarthroplasty is a surgical procedure that replaces the injured half of a diarthrodial joint (such as the hip or shoulder) with a smooth impermeable metal surface, leaving the apposing healthy cartilage layer intact. In 2006, more than 260,000 hip and shoulder hemiarthroplasties were performed in the United States alone [1]. Hemiarthroplasties are often revised to total arthroplasties, due in part to premature erosion of the intact, initially healthy cartilage [2]. Recent theoretical and experimental studies [3, 4] have shown that the low friction and wear of healthy diarthrodial joints depend critically upon sustained, elevated pressure of the interstitial water within the porous cartilage. Because this fluid pressure is continuous across the porous-permeable cartilage contact interface, the impermeable bearing surface implanted in hemiarthroplasty may substantially disrupt the natural lubrication of the apposing healthy cartilage [5]. Motivated by the established clinical success of implanting glutaraldehyde-treated porcine and bovine heart valves and pericardial grafts in humans, the objective of this study was to investigate whether a novel bioprosthetic hemiarthroplasty, utilizing a glutaraldehyde-treated cartilage xenograft, can reproduce the sustained low friction of a healthy natural diarthrodial joint. The specific aim of this study was to measure and compare the 24 h in-vitro frictional response of a bovine shoulder joint with that of a bioprosthetic hemiarthroplasty consisting of a glutaraldehyde-treated humeral head and an untreated, native cartilage glenoid.