Design of intramedullary prostheses to prevent bone loss: predictions based on damage-stimulated remodelling

The adaptation of bone around intramedullary fixated prostheses, such as the femoral component of the hip joint or the radial component of the elbow joint, is well documented in follow-up studies. Bone adaptation takes the form of proximal bone atrophy accompanied, in some cases, by distal bone hypertrophy. A mechanistic model has been formulated to predict bone adaptation based on the concept that the continuous processes of damage and repair regulate bone adaptation. We apply the model to investigate the significance of two features of intramedullary prosthesis design on bone adaptation: prosthesis Young's modulus and the presence of a prosthesis collar. Results, as well as indicating some characteristics of accumulative-damage stimulated bone adaptation, predict that a low Young's modulus stem will very much reduce the extent of bone loss whereas the presence of a collar will have no significant effect. The results predict that a collarless low stiffness prosthesis is one possible approach for improving the secondary stability of intramedullary-fixated orthopaedic implants.     

The role of the biceps brachii in shoulder elevation.

The biceps brachii is a bi-articular muscle affecting motion at the shoulder and elbow. While its' action at the elbow is well documented, its role in shoulder elevation is less clear. Therefore, the purpose of this project was to investigate the influence of shoulder and elbow joint angles on the shoulder elevation function of the biceps brachii. Twelve males and 18 females were tested on a Biodex dynamometer with the biceps brachii muscle selectively stimulated at a standardized level of voltage. The results indicated that both shoulder and elbow joint angles influence the shoulder joint elevation moment produced by the biceps brachii. Further analysis revealed that the elevation moment was greatest with the shoulder joint at 0 degrees and the elbow flexed 30 degrees or less. The greatest reduction in the elevation moment occurred between shoulder angles of 0 degrees and 30 degrees . The shoulder elevation moment was near zero when shoulder elevation reached or exceeded 60 degrees regardless of elbow angle. These results clarify the role of the biceps in shoulder elevation, as a dynamic stabilizer, and suggest that it is a decelerator of the arm during the throwing motion.     

Bone formation induced by a novel form of mechanical loading on joint tissue.

Because of insufficient mechanical loading, exposure to weightlessness in space flight reduces bone mass. In order to maintain bone mass in a weightless condition, we investigated a novel form of mechanical loading--joint loading. Since some part of gravity-induced loading to our skeletal system is absorbed by viscoelastic deformation of joint tissues, we hypothesized that deformation of joint tissues would generate fluid flow in bone and stimulate bone formation in diaphyseal cortical bone. In order to test the hypothesis, we applied directly oscillatory loading to an elbow joint of mice and conducted bone histomorphometry on the diaphysis of ulnae. Using murine femurs ex vivo, streaming potentials were measured to evaluate a fluid flow induced by joint loading. Bone histomorphometry revealed that compared to no loading control, elbow loading increased mineralizing surface, mineral apposition rate, and bone formation rate 3.2-fold, 3.0-fold, and 7.9-fold, respectively. We demonstrated that joint loading generated a streaming potential in a medullar cavity of femurs. The results support a novel mechanism, in which joint loading stimulates effectively bone formation possibly by generating fluid flow, and suggest that a supportive attachment to joints, driven passively or actively, would be useful to maintain bone mass of astronauts during an exposure to weightlessness.     

Elbow joint biomechanics for preclinical evaluation of total elbow prostheses

Total elbow arthroplasty is a clinically successful procedure, yet long-term implant survival rates have historically lagged behind those reported for total hips and knees. Clinical complications associated with implant wear, osteolysis, stem loosening and device fracture have been implicated as reasons for limited long-term survivorship. Unfortunately, there is little published information on the biomechanics and method(s) for preclinical evaluation of total elbow prostheses that could provide insight into the mechanisms of failure. Additionally, there are no consensus testing standards or summaries of loading profiles of the humero-ulnar joint associated with a range of activities of daily living. Such data would facilitate the standardized preclinical assessment of total elbow devices such is commonplace for other large joints. The objective of the work here is therefore to provide a comprehensive review of elbow joint biomechanics as it relates to preclinical evaluation of total elbow implants. This summary includes a review of elbow joint forces, kinematics, the types and frequency of humero-ulnar joint motions associated with activities of daily living and clinical outcomes, as well as proposing a methodology for deriving humero-ulnar joint reaction force magnitudes and vector orientations as a function of a known mass/force at the hand. From these data, a scalable, bi-axial loading profile is proposed as a foundation for the development of clinically relevant, laboratory simulations for assessment of total elbow prostheses performance.     

Resting Orientations of Dinosaur Scapulae and Forelimbs: A Numerical Analysis,with Implications for Reconstructions and Museum Mounts

The inclination of the scapular blade and the resting pose of the forelimb in dinosaurs differ among reconstructions and among skeletal mounts. For most dinosaurian taxa, no attempt has previously been made to quantify the correct resting positions of these elements. Here, we used data from skeletons preserved in articulation to quantify the resting orientations of the scapula and forelimb in dinosaurs. Specimens were included in the study only if they were preserved lying on their sides; for each specimen the angle between forelimb bones at a given joint was included in the analysis only if the joint was preserved in articulation. Using correlation analyses of the angles between the long axis of the sacrum, the first dorsal centrum, and the scapular blade in theropods and Eoraptor, we found that vertebral hyperextension does not influence scapular orientation in saurischians. Among examined taxa, the long axis of the scapular blade was found to be most horizontal in bipedal saurischians, most vertical in basal ornithopods, and intermediate in hadrosauroids. We found that in bipedal dinosaurs other than theropods with semilunate carpals, the resting orientation of the elbow is close to a right angle and the resting orientation of the wrist is such that the hand exhibits only slight ulnar deviation from the antebrachium. In theropods with semilunate carpals the elbow and wrist are more flexed at rest, with the elbow at a strongly acute angle and with the wrist approximately at a right angle. The results of our study have important implications for correct orientations of bones in reconstructions and skeletal mounts. Here, we provide recommendations on bone orientations based on our results.     

Shoulder muscle function depends on elbow joint position: an illustration of dynamic coupling in the upper limb

Shoulder muscle function has been documented based on muscle moment arms, lines of action and muscle contributions to contact force at the glenohumeral joint. At present, however, the contributions of individual muscles to shoulder joint motion have not been investigated, and the effects of shoulder and elbow joint position on shoulder muscle function are not well understood. The aims of this study were to compute the contributions of individual muscles to motion of the glenohumeral joint during abduction, and to examine the effect of elbow flexion on shoulder muscle function. A three-dimensional musculoskeletal model of the upper limb was used to determine the contributions of 18 major muscles and muscle sub-regions of the shoulder to glenohumeral joint motion during abduction. Muscle function was found to depend strongly on both shoulder and elbow joint positions. When the elbow was extended, the middle and anterior deltoid and supraspinatus were the greatest contributors to angular acceleration of the shoulder in abduction. In contrast, when the elbow was flexed at 90°, the anterior deltoid and subscapularis were the greatest contributors to joint angular acceleration in abduction. This dependence of shoulder muscle function on elbow joint position is explained by the existence of dynamic coupling in multi-joint musculoskeletal systems. The extent to which dynamic coupling affects shoulder muscle function, and therefore movement control, is determined by the structure of the inverse mass matrix, which depends on the configuration of the joints. The data provided may assist in the diagnosis of abnormal shoulder function, for example, due to muscle paralysis or in the case of full-thickness rotator cuff tears.     

ELBOW AND WRIST INJURIES IN SPORTS

Any disabling injury of the elbow or wrist should be studied roentgenographically for evidence of fracture which may not be otherwise evident but which may cause permanent disability unless the joint is immobilized for healing.“Tennis elbow” may be treated with physical therapy and analgesic injection but may require splinting or tendon stripping. Elbow sprain can occur in the growing epiphysis but is rare in adults. A jarring fall on the hand may cause fracture or dislocation at the elbow.Full extension of the joint should be restored gradually by active exercise rather than passive or forcible stretching.Fracture at the head of the radius may cause joint hemorrhage with severe pain which can be relieved by aspiration. A displacing fracture at the head of the radius requires removal of the head to prevent arthritic changes. Myositis ossificans contraindicates operation until after it has cleared.Healing of wrist fractures may be facilitated by exercise of the shoulder and elbow while the wrist is still in a cast. Fractures of the navicular bone are difficult to detect even roentgenographically and splinting may have to be done on clinical evidence alone.     

Articular morphology of the proximal ulna in extant and fossil hominoids and hominins

Extant hominoids share similar elbow joint morphology, which is believed to be an adaptation for elbow stability through a wide range of pronation-supination and flexion-extension postures. Mild variations in elbow joint morphology reported among extant hominoids are often qualitative, where orangutans are described as having keeled joints, and humans and gorillas as having flatter joints. Although these differences in keeling are often linked to variation in upper limb use or loading, they have not been specifically quantified. Many of the muscles important in arboreal locomotion in hominoids (i.e., wrist and finger flexors and extensors) take their origins from the humeral epicondyles. Contractions of these muscles generate transverse forces across the elbow, which are resisted mainly by the keel of the humeroulnar joint. Therefore, species with well-developed forearm musculature, like arboreal hominoids, should have more elbow joint keeling than nonarboreal species. This paper explores the three- and two-dimensional morphology of the trochlear notch of the elbow of extant hominoids and fossil hominins and hominoids for which the locomotor habitus is still debated. As expected, the elbow articulation of habitually arboreal extant apes is more keeled than that of humans. In addition, extant knuckle-walkers are characterized by joints that are distally expanded in order to provide greater articular surface area perpendicular to the large loads incurred during terrestrial locomotion with an extended forearm. Oreopithecus is characterized by a pronounced keel of the trochlear notch and resembles Pongo and Pan. OH 36 has a morphology that is unlike that of extant species or other fossil hominins. All other hominin fossils included in this study have trochlear notches intermediate in form between Homo and Gorilla or Pan, suggesting a muscularity that is less than in African apes but greater than in humans.     

Alterations in the adhesion behavior of osteoblasts by titanium particle loading: inhibition of cell function and gene expression

Total joint replacement prostheses are required to withstand corrosive environments and sustain millions of loading and articulation cycles during their term of implantation. Wear debris generation has been implicated as one of the primary causes of periprosthetic osteolysis and subsequent implant loosening in total joint replacements. Particulate debris consisting of metals, polyethylene, ceramics, and bone cement have each been shown to provoke a biological response in joint tissues. The major cell types within the interfacial granulomatous fibrous tissues consist of fibroblasts, macrophages, lymphocytes, and foreign-body giant cells. Osteoblasts are one of the principal cell types in the bone tissue adjacent to prostheses, maintaining physiologic bone remodeling through the balanced coordination of bone formation and resorption in concert with osteoclasts. To date the phenomenon of osteoblast phagocytosis of titanium particles has been suggested, but has not been sufficiently studied or confirmed. This study seeks to clarify the influence of titanium particles on osteoblast adhesion, deformability, proliferation, and gene expression profile. These studies were accomplished by performing biorheological testing, Northern blot analysis and RNase protection assay. The uptake of metallic particles by the osteoblast resulted in a particle-filament complex formation, which induced a series of variations in cell function. Understanding these variations is critical to expanding our knowledge of implant loosening and elucidating the nature of prosthetic joint failure. This study suggests that the impact of titanium particles on osteoblast function and subsequent implant loosening may have been previously underestimated.     

Olecranon orientation as an indicator of elbow joint angle in the stance phase,and estimation of forelimb posture in extinct quadruped animals

Reconstruction of limb posture is a challenging task in assessing functional morphology and biomechanics of extinct tetrapods, mainly because of the wide range of motions possible at each limb joint and because of our poor knowledge of the relationship between posture and musculoskeletal structure, even in the extant taxa. This is especially true for extinct mammals such as the desmostylian taxa Desmostylus and Paleoparadoxia. This study presents a procedure that how the elbow joint angles of extinct quadruped mammals can be inferred from osteological characteristics. A survey of 67 dried skeletons and 113 step cycles of 32 extant genera, representing 25 families and 13 orders, showed that the olecranon of the ulna and the shaft of the humerus were oriented approximately perpendicular to each other during the stance phase. At this angle, the major extensor muscles maximize their torque at the elbow joint. Based on this survey, I suggest that olecranon orientation can be used for inferring the elbow joint angles of quadruped mammals with prominent olecranons, regardless of taxon, body size, and locomotor guild. By estimating the elbow joint angle, it is inferred that Desmostylus would have had more upright forelimbs than Paleoparadoxia, because their elbow joint angles during the stance phase were approximately 165° and 130°, respectively. Difference in elbow joint angles between these two genera suggests possible differences in stance and gait of these two mammals. J. Morphol. 2009. © 2009 Wiley‐Liss, Inc.     

Genetic covariation of pelvic organ and elbow mobility in twins and their sisters.

A range of environmental risk factors, with childbirth the most notable, have been associated with the development of pelvic organ prolapse and urinary incontinence. However, indications of genetic influence (positive family histories, ethnic differences) have prompted research into the heritability of measures of pelvic organ descent and joint mobility, which have also been associated with prolapse and incontinence. Genes appear to influence about half of the variation in these measures and, furthermore, the pelvic organ measures are associated with elbow hyperextension at a phenotypic level (r approximately .2). We examined these measures in young, nulligravid women to determine if their association is due to a common genetic source. Data were collected from 178 Caucasian female co-twins and non-twin sisters, 50 of whom returned to be retested, which allowed reliability to be estimated and unreliable variance to be isolated in the multivariate analyses. Structural equation modeling was used to estimate genetic associations between latent elbow and bladder mobility factors for which heritabilities were estimated to be 0.80 and 0.64 respectively. The association between these factors appeared to be mediated by common genes (genetic r = .48, non-shared environmental r = -.06), with genes influencing latent elbow mobility accounting for 14% of the variation in latent bladder mobility. We speculate that genes influencing connective tissue structure may underlie this association.     

Elbow flexor evoked twitch contractile properties in untrained men and women and male bodybuilders

The influence of elbow joint angle on elbow flexor isometric evoked twitch contractile properties was assessed in 15 young women (F), 18 young men (M) and 11 male bodybuilders (BB). Measurements were made at elbow joint angles of 1.31, 1.57, 1.83, 2.09, 2.36, 2.62 and 2.88 rad (3.14 rad =180° =full extension). The largest peak twitch torque values [mean (SE) N · m] in F [3.77 (0.20)], M [10.38 (0.68)] and BB [11.38 (1.05)] occurred at 2.88 rad. Peak torque was progressively smaller at smaller joint angles, but the decline from 2.88 to 1.31 rad was greater in M (68%) and BB (76%) than F (59%). Thus, the magnitude of intergroup differences in peak twitch torque (PT) was joint angle dependent. Twitch time to peak torque (TPT) was influenced in a complex way by joint angle in the three groups; BB had the lowest values at small joint angles but the highest values at the largest angles. Half-relaxation time (HRT) generally increased from the smallest to largest joint angles in a pattern that did not differ significantly among the three groups. Maximum rates of twitch torque development and relaxation showed the same pattern of results as PT; indicating that these time-related measures were more sensitive to joint angle effects on PT than on TPT or HRT. The results of this study indicate that careful consideration should be given to the selection of joint angles in the measurement of evoked twitch contractile properties for the purpose of making group comparisons or investigating the effects of interventions such as training.     

Dependence of elbow joint stiffness measurements on speed,angle, and muscle contraction level

Elbow joint stiffness is critical to positioning the hand. Abnormal elbow joint stiffness may affect a person's ability to participate in activities of daily living. In this work, elbow joint stiffness was measured in ten healthy young adults with a device adapted from one previously used to measure stiffness in other joints. Measurements of elbow stiffness involved applying a constant-velocity rotational movement to the elbow and measuring the resultant displacement, torque, and acceleration. Elbow stiffness was then computed using a previously-established model for joint stiffness. Measurements were made at two unique elbow joint angles, two speeds, and two forearm muscle contraction levels. The results indicate that the elbow joint stiffness is significantly affected by both rotational speed and forearm muscle contraction level.     

Biomechanical influences of pin placement and elbow angle on hinge alignment and joint distraction of bridged elbow-pin-fixator construct

Joint distraction and mobilization with a hinged external fixator preserves elbow stability and mobility. However, the alignment of both elbow and fixator hinges was the initial prerequisite of the arthrodiatasis technique. The main goal of this study was to numerically evaluate the kinematic influence of the device, surgery, and joint factors on hinge alignment. The kinetic effects of the pins placement and elbow angle on concentric distraction and mobilization were also discussed. A unilaterally hinged elbow-fixator system with a 14 links and 10 degrees-of-freedom was instrumented into a humeroulnar model. The Denavit–Hartenberg method with the homogeneous transformation matrixes was applied to perform kinematic analysis of the linkage system. The predicted results revealed that the concurrence of hinge alignment (i.e., kinematic) and concentric distraction (i.e., kinetic) necessitates two telescopic tubes orthogonal to the elbow hinge. The degrees-of-freedom arrangement of the fixator articulators plays a significant role in hinge alignment. After joint distraction, two hinges might be misaligned due to the difference in the structural rigidity of the pins, fixator, and stiffened elbow. Furthermore, those two prerequisite are interactive and sensitive to elbow angle, fixator design, and pin placement of the bridged elbow-pin-fixator construct. In addition, the ideally concentric distraction might occur only at an elbow angle of 120° owing to the ulnar anatomy. Meticulous planning is necessary for such highly technically demanding surgery.     

Development of an image-based technique to examine joint congruency at the elbow

Identifying joint contact in articular joints is important for both the biomechanical investigation of joint mechanics and the study of osteoarthritis. The purpose of this study is to develop a proximity mapping technique to non-invasively determine joint congruency, as a surrogate of joint contact. To illustrate the capabilities of this algorithm, a cadaveric upper extremity was positioned at varying degrees of elbow flexion. This technique was validated using a gold standard experimental casting technique. The pattern of the cast showed an excellent agreement with the generated proximity map using the inter-bone distance algorithm. The results from this study agree with the results of previous studies examining joint contact at the elbow both in the location and in the tracking of the joint contact throughout elbow flexion. Ultimately, this technique will lead to an increased understanding of the effect of malalignment and instability of the joint on contact mechanics.     

Muscle moment arm and normalized moment contributions as reference data for musculoskeletal elbow and wrist joint models

A geometric musculoskeletal model of the elbow and wrist joints was developed to calculate muscle moment arms throughout elbow flexion/extension, forearm pronation/supination, wrist flexion/extension and radial/ulnar deviation. Model moment arms were verified with data from cadaver specimen studies and geometric models available in the literature. Coefficients of polynomial equations were calculated for all moment arms as functions of joint angle, with special consideration to coupled muscles as a function of two joint angles. Additionally, a “normalized potential moment (NPM)” contribution index for each muscle across the elbow and wrist joints in four degrees-of-freedom was determined using each muscle's normalized physiological cross-sectional area (PCSA) and peak moment arm (MA). We hypothesize that (a) a geometric model of the elbow and wrist joints can represent the major attributes of MA versus joint angle from many literature sources of cadaver and model data and (b) an index can represent each muscle's normalized moment contribution to each degree-of-freedom at the elbow and wrist. We believe these data serve as a simple, yet comprehensive, reference for how the primary 16 muscles across the elbow and wrist contribute to joint moment and overall joint performance.     

ISB recommendation on definitions of joint coordinate systems of various joints for the reporting of human joint motion--Part II: shoulder, elbow, wrist and hand

In this communication, the Standardization and Terminology Committee (STC) of the International Society of Biomechanics proposes a definition of a joint coordinate system (JCS) for the shoulder, elbow, wrist, and hand. For each joint, a standard for the local axis system in each articulating segment or bone is generated. These axes then standardize the JCS. The STC is publishing these recommendations so as to encourage their use, to stimulate feedback and discussion, and to facilitate further revisions. Adopting these standards will lead to better communication among researchers and clinicians.     

Individual muscle force parameters and fiber operating ranges for elbow flexion-extension and forearm pronation-supination

We have quantified individual muscle force and moment contributions to net joint moments and estimated the operating ranges of the individual muscle fibers over the full range of motion for elbow flexion/extension and forearm pronation/supination. A three dimensional computer graphics model was developed in order to estimate individual muscle contributions in each degree of freedom over the full range of motion generated by 17 muscles crossing the elbow and forearm. Optimal fiber length, tendon slack length, and muscle specific tension values were adjusted within the literature range from cadaver studies such that the net isometric joint moments of the model approximated experimental joint moments within one standard deviation. Analysis of the model revealed that the muscles operate on varying portions of the ascending limb, plateau region, and descending limb of the force-length curve. This model can be used to further understand isometric force and moment contributions of individual muscles to net joint moments of the arm and forearm and can serve as a comprehensive reference for the forces and moments generated by 17 major muscles crossing the elbow and wrist.