Postoperative analysis of patients who received the Universal 2 total wrist implant system

Third-generation total wrist arthroplasty devices have provided joint stability, relief from pain and increased wrist motion for patients suffering from severe arthritis. While reports of clinical follow-up appointments describe improved wrist function, the improvement in overall upper extremity function and patient perception remains a question. Therefore, the purpose of this study was to assess the upper extremity function in patients that received the Universal 2 total implant system. Eight patients participated in the complete protocol, which included testing activities of daily living as well as surveys to assess patient perception. The findings of the current study suggest that although patients exhibit motion that exceeds the needed amount, many still have a perceived disability.     

Biomechanical analysis of the Universal 2 implant in total wrist arthroplasty: a finite element study

Little is known about the mechanics of in vivo loading on total wrist prostheses where many studies have looked at the mechanics of other types of arthroplasty such as for the hip and the knee which has contributed to the overall success of these types of procedures. Currently surgeons would prefer to carry out arthrodesis on the wrist rather than consider arthroplasty as clinical data have shown that the outcome of total wrist arthroplasty is poorer than compared to the hip and knee. More research is needed on the loading mechanisms of the implants in order to enhance the design of future generation implants. This study looks at the load transfer characteristics of the Universal 2 implant using a finite element model of a virtually implanted prosthesis during gripping. The results showed that the loading on the implant is higher on the dorsal and ulnar aspect than on the volar and radial aspect of the implant. The whole load is transmitted through the radius and none through the ulna.     

The hominoid wrist joint

In a previous study of the primate wrist joint the author has shown that this articulation is uniquely modified in the Pongidae by the interposition of a meniscus between the ulnar styloid process and the carpus. This meniscus (which in gibbons contains a bony lunula) partially isolates the ulnar styloid process in a proximal synovial compartment. The human wrist joint is clearly derived from such an articulation, the proximal synovial compartment persisting as the prestyloid recess. The present paper is concerned with observations on a wider range of hominoid material. A spectrum of variations is demonstrated, largely the result of a tendency for the neomorphic meniscus to be incorporated as an integral component of the proximal articular surface, thereby progressively excluding the ulnar styloid process from the wrist joint and constricting the entrance to the proximal synovial compartment. The unique construction of the hominoid wrist joint is considered to be a specialization facilitating pronation-supination. Such free rotatory movement is a necessary prerequisite for true brachiation, and the obvious phylogenetic implication is that Homo has shared a brachiating ancestry with the Pongidae. This is convincing evidence in favour of the view that a period of brachiation provided the essential apprenticeship for the complex locomotor activities of bipedal, tool-using man.     

Dynamics of wrist rotations

Understanding the dynamics of wrist rotations is important for many fields, including biomechanics, rehabilitation and motor neuroscience. This paper provides an experimentally based mathematical model of wrist rotation dynamics in Flexion-Extension (FE) and Radial-Ulnar Deviation (RUD), and characterizes the torques required to overcome the passive mechanical impedance of wrist rotations. We modeled the wrist as a universal joint with non-intersecting axes. The equations of motion of the hand rotating about the wrist joint include inertial, damping, and stiffness terms, with parameter values based on direct measurements (stiffness) or measurements combined with data available in the literature (inertia, damping). We measured the wrist kinematics of six young, healthy subjects making comfortable and fast-paced wrist rotations (±15° in FE, RUD, and combinations) and inserted these kinematic data into the model of wrist rotation dynamics. With this we quantified the torques required to overcome the impedance of wrist rotations and evaluated the relative importance of individual impedance terms as well as interactions between the degrees of freedom. We found that the wrist's passive stiffness is the major impedance the neuromuscular system must overcome to rotate the wrist. Inertia and passive damping only become important for very fast movements. Unlike elbow and shoulder reaching movements, inertial interaction torques are negligible for wrist rotations. Interaction torques due to stiffness and damping, however, are significant. Finally, we found that some model terms (inertial interaction torques, axis offset, and, for moderately sized rotations, non-linearities) can be neglected with little loss of accuracy, resulting in a simple, linear model useful for studies in biomechanics, motor neuroscience, and rehabilitation.     

Results of treatment of extensive volar wrist lacerations: the spaghetti wrist

A series of 38 volar wrist lacerations is reviewed with regard to epidemiologic aspects and results. In general, return of tendon function was quite good, and return of nerve function in this series was also satisfying. We attribute the generally good results to immediate repair of all structures, microscopic repair of significant arterial injuries, microscopic grouped fascicular nerve repair, early mobilization (dynamic splinting and intensive occupational therapy), and a generally youthful group of patients. Review of this series has strengthened our opinion that aggressive primary repair of all injured structures is appropriate for these extensive lacerations.     

Epithelioid hemangioendothelioma of the wrist

A rare case of epithelioid hemangioendothelioma occurring at the wrist is reported. No mitoses were seen in the tissue examined, but the cell type could not be identified by frozen section. Based on the report, the remaining neoplasm was resected and no structures vital to hand function were sacrificed. There has been no recurrence of the tumor in 3 1/2 years.     

The importance of abductor pollicis longus in wrist motions: A physiological wrist simulator study

The abductor pollicis longus (APL) is one of the primary radial deviators of the wrist, owing to its insertion at the base of the first metacarpal and its large moment arm about the radioulnar deviation axis. Although it plays a vital role in surgical reconstructions of the wrist and hand, it is often neglected while simulating wrist motions in vitro. The aim of this study was to observe the effects of the absence of APL on the distribution of muscle forces during wrist motions. A validated physiological wrist simulator was used to replicate cyclic planar and complex wrist motions in cadaveric specimens by applying tensile loads to six wrist muscles – flexor carpi radialis (FCR), flexor carpi ulnaris, extensor carpi radialis longus (ECRL), extensor carpi radialis brevis, extensor carpi ulnaris (ECU) and APL. Resultant muscle forces for active wrist motions with and without actuating the APL were compared. The absence of APL resulted in higher forces in FCR and ECRL – the synergists of APL – and lower forces in ECU – the antagonist of APL. The altered distribution of wrist muscle forces observed in the absence of active APL control could significantly alter the efficacy of in vitro experiments conducted on wrist simulators, in particular when investigating those surgical reconstructions or rehabilitation of the wrist heavily reliant on the APL, such as treatments for basal thumb osteoarthritis.     

Effects of wrist position and contraction on wrist flexors H-reflex, and its functional implications.

In order to determine whether joint position exerts a powerful influence on length-tension regulation in multiarticulate wrist flexors, three wrist positions (neutral, flexion and extension) and four levels of flexor contraction [0%, 10%, 20% and 30% maximum voluntary contraction (MVC)] were manipulated. There were significant differences in H-reflex amplitudes according to wrist positions and levels of flexor contraction. H-reflex increased linearly as a function of contraction in all three wrist positions. H-reflex was consistently larger in the wrist flexion than in the wrist extension position. The strength of the relationship (omega2) indicated that wrist position had a greater effect on H-reflex than force of muscle contraction. The interaction between wrist flexors contraction and joint position was significant only in the wrist flexion position. Trend analysis showed that, in the wrist flexion position, a low level of contraction was sufficient to maximally facilitate the H-reflex; however, a quadratic component was seen at higher contraction levels. The above findings may reflect the length-tension relationship of the multiarticulate wrist flexors. Therefore, this paper will discuss the functional implications related to the larger H-reflex in flexion position and the depressed H-reflex in the wrist extension position.     

Dynamics of wrist and forearm rotations

Human movement generally involves multiple degrees of freedom (DOF) coordinated in a graceful and seemingly effortless manner even though the underlying dynamics are generally complex. Understanding these dynamics is important because it exposes the challenges that the neuromuscular system faces in controlling movement. Despite the importance of wrist and forearm rotations in everyday life, the dynamics of movements involving wrist and forearm rotations are currently unknown.     

The effects of wrist motion and hand orientation on muscle forces: A physiologic wrist simulator study

Although the orientations of the hand and forearm vary for different wrist rehabilitation protocols, their effect on muscle forces has not been quantified. Physiologic simulators enable a biomechanical evaluation of the joint by recreating functional motions in cadaveric specimens. Control strategies used to actuate joints in physiologic simulators usually employ position or force feedback alone to achieve optimum load distribution across the muscles. After successful tests on a phantom limb, unique combinations of position and force feedback – hybrid control and cascade control – were used to simulate multiple cyclic wrist motions of flexion-extension, radioulnar deviation, dart thrower’s motion, and circumduction using six muscles in ten cadaveric specimens. Low kinematic errors and coefficients of variation of muscle forces were observed for planar and complex wrist motions using both novel control strategies. The effect of gravity was most pronounced when the hand was in the horizontal orientation, resulting in higher extensor forces (p < 0.017) and higher out-of-plane kinematic errors (p < 0.007), as compared to the vertically upward or downward orientations. Muscle forces were also affected by the direction of rotation during circumduction. The peak force of flexor carpi radialis was higher in clockwise circumduction (p = 0.017), while that of flexor carpi ulnaris was higher in anticlockwise circumduction (p = 0.013). Thus, the physiologic wrist simulator accurately replicated cyclic planar and complex motions in cadaveric specimens. Moreover, the dependence of muscle forces on the hand orientation and the direction of circumduction could be vital in the specification of such parameters during wrist rehabilitation.     

A musculoskeletal model to estimate the relative changes in wrist strength due to interacting wrist and forearm postures

Wrist rotations about one wrist axis (e.g. flexion/extension) can affect the strength about another wrist axis (e.g. radial/ulnar deviation). This study used a musculoskeletal model of the distal upper extremity, and an optimization approach, to quantify the interaction effects of wrist flexion/extension (FE), radial/ulnar deviation (RUD) and forearm pronation/supination (PS) on wrist strength. Regression equations were developed to predict the relative changes in strength from the neutral posture, so that the changes in strength, due to complex and interacting wrist and forearm rotation postures, can be incorporated within future ergonomics assessments of wrist strength.