Citations

This preliminary study of four elbow specimens inves tigates the relationship of articular geometry and liga mentous structures in providing stability to the elbow joint. A technique is presented that describes the con straining features of varus-valgus and distraction in extension and at 90° of elbow flexion. Valgus stability is equally divided among the medial collateral ligament, anterior capsule, and bony articulation in full extension; whereas, at 90° of flexion the contribution of the ante rior capsule is assumed by the medial collateral ligament which provides approximately 55% of the stabilizing contribution to valgus stress. Varus stress is noted to be resisted primarily by the anterior capsule (32%) and the joint articulation (55%) with only a small (14%) contribution from the radial collateral ligament. At 90° of flexion, little change is noted in the contribution to the radial collateral ligament (9%), but the anterior capsule offers only 13%, with the remaining stability (75%) arising from the joint articulation. In extension, the soft tissue resistance to distraction is provided minimally by either the radial (5%) or the medial (5%) collateral ligaments, and thus primarily originates from the anterior capsule (85%). At 90° of flexion, however, the capsule offers virtually no resistance to distraction (8%). The radial collateral ligament contributes 10% of the stability, while the medial collateral ligament ac counts for 78% of the resistance to distraction in this position. Too few specimens have been studied to form any conclusions for direct clinical applications at this time. However, the technique provides a reliable tool with additional studies for different positions and loading conditions underway. These efforts should disclose useful information that might be applied to the manage ment of chronic elbow instability, radial head or olecra non fracture, the design and implantation of elbow prostheses, or provide a rationale for other reconstruc tive procedures.

Purpose The purposes of this study were to investigate the differences between open and arthroscopic closure of the rotator interval (RI) on glenohumeral translation and range of motion. We also sought to determine if the addition of either an open or arthroscopic RI closure increases stability of the shoulder. Methods Fourteen fresh‐frozen (10 paired) cadaveric shoulder specimens were mounted in a custom testing apparatus, and glenohumeral translation and rotation were obtained by using an optoelectric tracking system (Optotrak Certus; Northern Digital, Ontario, Canada). Specimens were randomly allocated to either open (n = 7) or arthroscopic (n = 7) plication of the RI. The following were measured first with an intact and vented specimen and subsequently after an RI closure using either open or arthroscopic techniques: (1) range of motion in neutral and 90° abduction; (2) anterior and posterior translation at neutral rotation; (3) anterior translation at 90° abduction with external rotation; and (4) posterior translation at 90° flexion with internal rotation. Results Posterior stability was not improved from the intact state by either open (1.0‐mm change) or arthroscopic (0.1‐mm change) repair. The sulcus stability was improved in the open group (5.7 mm to 2.9 mm, P = .028), but not arthroscopically (5.1 to 4.1 mm, P = .499). Neutral anterior stability was improved after open repair (7.2 to 2.6 mm, P = .018), but not arthroscopically (2.3 to 2.4 mm, P = 0.5). However, anterior stability in external rotation (ER) at 90° abduction was improved in the arthroscopic repair group (5.5 to 3.1 mm, P = .006). The mean loss of ER in neutral was greater in the open group (40.8°) versus the arthroscopic group (24.4°, P = .0038). The arthroscopic group showed an 11.7° loss of ER in 90° abduction ( P = .018) versus the open group loss of 4.8°. There were no significant differences in loss of IR in either neutral or 90° abduction. Conclusions Posterior stability was not improved by either open or arthroscopic rotator interval repair, and sulcus stability only improved with the open technique. Anterior stability in neutral was improved after open repair and in the arthroscopic repair group with the arm abducted. There was a large loss of external rotation with both techniques. Clinical Relevance This study suggests that arthroscopic RI closure adds little to the overall posterior and inferior stability of the shoulder joint, although anterior stability may be improved. There is a potentially large loss of external rotation after either repair method.

Hip simulators are regularly used by researchers to assess total hip arthroplasty (THA) implants, range of motion, stability, and alignment of acetabular cup and stem. Previous papers have described three types of simulators: three-dimensional protractors, biaxial rocking motion (BRM) protractors, and single-axis prosthetic range-of-motion (PROM) devices. We have developed a new hip simulator in which the ROM device is completely automated in three independent axes (elevation, internal/external rotation, and plane of elevation). Coupled with the simulator, we used a FaroArm Gold Series coordinate measuring machine (CMM) to accurately align the implant components. The results show that the methodology and alignment setup are accurate and repeatable. With this simulator and digitizer, we are able to study the characteristics of numerous THA implants at various orientations of the pelvis, acetabular cup, stem, and femur.

A fracture healing monitoring system with external fixators was analysed using the finite element method. Pin displacement and side bar strain under axial and side loading were evaluated at various stages of simulated fracture healing. In general, a recovery of rigidity at the fracture site of up of 25 percent of intact bone could be sensitively predicted. Effects of cross-sectional distribution and length of callus at the fracture site on pin displacement and side bar strain were studied. Alterations of fixation configuration, such as component failure during the healing process, were found to have relatively little effect on pin displacement but a rather larger effect on side bar strain. In general, the assessment of fracture healing by monitoring the deformation of external fixation devices is a useful idea. However, in practice, great care must be taken to fully understand the implication of the monitoring system before drawing conclusions on such measurements.

In biomechanics, the knowledge of accurate location of a joint center is essential because equilibration of the external loads and muscular forces about the joint is performed about this specific point. This paper focuses on the location of centers of gleno-humeral joint and scapulo-thoracic joint in a subject moving their arm in the scapular plane with a magnitude of 120°. Biplanar radiography with successive exposures has been used locating anatomical axes of bones. Geometric models of bones were defined allowing access to bone morphology by superposing model projections onto X-ray imaged bone contours. Functional models were used so as to represent the behavior in motion of shoulder joints. These techniques allowed us to access to results describing the linear and angular relative displacements of the shoulder bones between two different postures. The gleno-humeral and scapulo-thoracic finite joint centers (F H and F S ) are first defined through the location of the corresponding helical axis of motion (HAM) moving the joint from positions occupied in initial and final postures. The gleno-humeral and scapulo-thoracic mean joint centers (M H and M S ) are then calculated using a new technique, which defines that each joint center has the point having the smallest migrations while moving continuously from initial to final postures. This allows for the analysis of the linear and angular clearances, which affect joint center migration. The whole continuous movement has been parsed into several steps to test the stability of the mean joint center throughout the motion.

The tenosynovium in the human carpal tunnel is connected to the flexor tendons and the median nerve by the subsynovial connective tissue (SSCT). The most common histological finding in carpal tunnel syndrome (CTS), a compression neuropathy of the median nerve, is noninflammatory fibrosis of the SSCT. The relationship, if any, between the fibrosis and nerve pathology is unknown, although some have speculated that a change in the SSCT volume or stiffness might be the source of the compression. Yet, while animal models have been used to study the physiology of nerve compression, so far none have been used to study the relationship of the SSCT pathology to the neurophysiological abnormalities. The purpose of this study was to identify animal models that might be appropriate to study the interaction of SSCT and nerve function in the development of CTS. The front paws of a rat, rabbit, dog, and baboon were dissected. The carpal tunnel anatomy and SSCT of these animals were also examined by light and scanning microscopy and compared to the relevant human anatomy and ultrastructure. The carpal tunnel anatomy and contents of the baboon and rabbit are similar to humans. The canine carpal tunnel lacks the superficial flexor tendons and the rat carpal tunnel is very small. The human, baboon, and rabbit specimens had very similar organization of the SSCT, and content of the carpal canal. We conclude that, while both the baboon and rabbit would be good animal models to study the relationship of the SSCT to CTS, the rabbit is likely to be more practical, in terms of cost and animal care concerns.

Purpose Large rotator cuff tears present a challenge to orthopaedic surgeons. Because tissue may be insufficient or of inadequate quality to undergo repair, a variety of materials have been used as adjuncts. Human dermal tissue may be processed to render it acellular, and thus less immunogenic, but with the extracellular matrix left intact, creating a collagen scaffold with favorable characteristics. Because of these traits, use in rotator cuff repair was proposed. Methods A canine model for a full‐thickness infraspinatus tendon tear was used. Tendon was excised from the bony interface to the myotendinous junction, and a human acellular dermal matrix graft (experimental) or the autologous excised tendon (control) was used to bridge the defect. Animals were sacrificed, and shoulders were evaluated histologically and biomechanically. Results At time 0, strength of control and experimental repairs was similar. At 6 weeks, the strength of the experimental repair was half that of the control side. Strength of control specimens remained the same at 6 and 12 weeks, but by 12 weeks, the strength of the experimental repair was equal to that of the control. Histologically, cells infiltrated the control and experimental specimens by 6 weeks; chronic inflammation was consistent with surgery and repair. At 6 months, control and experimental specimens mimicked normal tendon structure grossly and histologically. Conclusions Use of human acellular dermal matrix as a patch is a viable option in this model of large rotator cuff defects. Within 6 weeks, histologic evidence of native cell infiltration and neotendon development was observed. Within 12 weeks, the strength of the dermal matrix graft repair was equivalent to that of autologous tendon. At 6 months, control and graft specimens mimicked normal tendon structure grossly and histologically. Clinical Relevance This study provides in vivo animal data to support the use of this acellular dermal matrix graft for repair of full‐thickness rotator cuff defects. Additional studies are indicated to determine the role of this material in the treatment of humans with rotator cuff tears.

Summary Nine fresh frozen cadaveric shoulders were used to examine the changes in intraarticular pressure (IAP) of the shoulder joint and the position of the humeral head under various loads to determine the relationship between these parameters. All the soft tissues superficial to the rotator cuff were removed. The position of the humerus relative to the scapula was monitored using an electromagnetic tracking system before and after venting the capsule with 0, 0.5, and 1.0 kg of load applied to the humerus inferiorly in addition to the weight of the arm. Simultaneously, the IAP was monitored using a pressure transducer before venting the capsule. Venting had a significant effect on the position of the humeral head: the positions of the head after venting were significantly lowered in all loading conditions. The average IAP was −76 cm H 2 O without load, and the value decreased in a linear fashion with increased load; the correlations were significant in four of six shoulders without dislocation. The correlations were less significant between the pressure and the position, and there were no significant correlations between the load and the position. IAP, which is determined primarily by the load applied, is important to stabilize the shoulder inferiorly. Because IAP is intimately related to the external load and the response is specific to individuals, examination of IAP response to external load may be helpful in characterizing various instabilities of the shoulder.

The effect of external force environment on the healing of a partial thickness injury to canine flexor tendon was studied. A 50% laceration was made in either the fibrocartilaginous (compressive) zone or in the tendinous (tensile) zone of canine flexor digitorum profundus tendons. After three or six weeks, the tendons were harvested. An optical method for determining zone-specific material properties showed that, in response to injury, the structural stiffness decreased in the tensile zone of the tendon but increased in the compressive zone. The mechanical properties and failure mechanism of canine tendon and their changes in response to injury vary according to tendon zone, and differences in the healing process in mechanically specialised zones of the flexor tendon are discussed.

Despite the use of wrist guards during skate- and snowboard activities, fractures still occur at the wrist or at further proximal locations of the forearm. The main objectives of this study were to conduct a human subject testing under simulated falling conditions for measurement of the impact force on the hand, to model wrist guards as a shock isolator, to construct a linear mass-spring-damper model for quantification of the impact force attenuation (Q-ratio) and energy absorption (S-ratio), and to determine whether wrist guards play a role of an efficient shock isolator. While the falling direction (forward and backward) significantly influenced the impact responses, use of wrist guards provided minimal improvements in the Q- and S-ratios. It was suggested based on the results under the submaximal loading conditions that protective functions of the common wrist guard design could be enhanced with substantial increase in the damping ratio so as to maximize the energy absorption. This would bring forth minor deterioration in the impact force attenuation but significant increase in the energy absorption by 19%, which would help better protection against fall-related injuries of the upper extremity.