Kinematic investigation of normal MCP joint

The Influence of the Abduction Joints of Four Fingers to Grasp: Experimental and Simulated Verification

The thumb is the most important finger of the human hand and has a great influence on grasp manipulations. However, the extent to which joints other than the thumb joints affect the grasp, and thus, which joints should be included in a prosthetic hand, remains an open issue. In this paper, we focus on the metacarpophalangeal joints of the four fingers, except the thumb, which can generate flexion/extension and abduction/adduction motions. The contribution of these joints to grasping was evaluated in four aspects: grasp size, grasp force, grasp quality and grasp success rate. Six subjects participated in experiments with respect to the maximum grasp size and grasp force. The results show that possessing abduction mobility of the metacarpophalangeal joints can increase the grasp size by 4.67 ± 1.93 mm and the grasp force by 5.27 ± 4.25 N. Then, the grasping quality and success rate were tested in a simulation platform and using a robotic hand, respectively. The results show that grasp quality was promoted by 76.7% in the simulated environment with abduction mobility compared to without abduction mobility, whereas the grasp success rate was promoted by 68.3%. We believe that the results of this work can benefit the understanding of hand function and prosthetic hand design.

Proposal of a New Dynamic Distraction Device to Treat Complex Periarticular Fractures of the Metacarpophalangeal Joint of Long Finger

Background: Complex periarticular fractures of the metacarpophalangeal joint (MCPJ) are often challenging to treat. Conservative and operative treatments are often burdened with stiffness, loss of function, and poor clinical outcome. These phenomena could be a direct consequence of long period of immobilization. To promote a short time of immobilization and a quick return to daily activities, it is mandatory to stabilize the fracture maintaining the active range of motion (AROM) of the ray. A simple solution is to reduce the fragments by means of dynamic ligamentotaxis. The authors propose a new dynamic distraction device (DDD) for the MCPJ. Methods: The DDD for the MCPJ was made of Kirschner wires bent and connected to counteract dislocation forces and to allow mobilization of the joint. The DDD was tested on a cadaver model under a simulated load in physiological conditions, and also in metacarpal and proximal phalanx (P1) fracture patterns. The effectiveness of the device was evaluated under fluoroscopy. Results: The data showed that DDD is able to achieve fracture reduction through ligamentotaxis and primary fragments stability and to avoid secondary dislocation during AROM of complex periarticular fractures of the MCPJ. Conclusions: The frame could be an alternative option to treat periarticular fractures of the MCPJ. The DDD implant has several advantages: It is time efficient because assembly and application take only few minutes. Furthermore, it is very versatile; indeed, it can be used in all metacarpal and phalanx bones, even in the central rays.

Joint Manipulation: Toward a General Theory of High-Velocity, Low-Amplitude Thrust Techniques

OBJECTIVE

The objective of this study was to describe the initial stage of a generalized theory of high-velocity, low-amplitude thrust (HVLAT) techniques for joint manipulation.

METHODS

This study examined the movements described by authors from the fields of osteopathy, chiropractic, and physical therapy to produce joint cavitation in both the metacarpophalangeal (MCP) joint and the cervical spine apophysial joint. This study qualitatively compared the kinetics, the similarities, and the differences between MCP cavitation and cervical facet joint cavitation. A qualitative vector analysis of forces and movements was undertaken by constructing computer-generated, simplified graphical models of the MCP joint and a typical cervical apophysial joint and imposing the motions dictated by the clinical technique.

RESULTS

Comparing the path to cavitation of 2 modes of HVLAT for the MCP joint, namely, distraction and hyperflexion, it was found that the hyperflexion method requires an axis of rotation, the hinge axis, which is also required for cervical HVLAT. These results show that there is an analogue of cervical HVLAT in one of the MCP joint HVLATs.

CONCLUSIONS

The study demonstrated that in a theoretical model, the path to joint cavitation is the same for asymmetric separation of the joint surfaces in the cervical spine and the MCP joints.

Dimensions of the Metacarpo-Phalangeal Joint with Particular Reference to Joint Prostheses

Sixty metacarpo-phalangeal joints were dissected and investigated to determine the shape, size and position of the articular surfaces with respect to the medullary canals of the metacarpal and the phalanx.

The results show that the articular surfaces of the metacarpo-phalangeal joint have a single centre of rotation in the sagital plane and in the transverse plane. The joints of the little and ring fingers have radii of curvature in the sagital and transverse planes, which are almost equal (within 1.6 per cent) while those radii of the middle finger varied by 9 per cent. The index finger had a variation in radius from the sagital to the transverse plane of almost 13 per cent; the sagital plane radius being the greatest. This observation is the opposite of the other joints where the transverse radius is the greater one.

The overall widths of the metacarpal heads were seen to vary from 13 mm in the little finger of females to 17 mm in the index finger of males (average).

The medullary canals had axes which were not coincident with the centre of rotation of the joint but up to 3 mm displaced from it. These dimensional differences have important implications in prosthesis design.

Evaluation of joint type modelling in the human hand

This short communication presents preliminary results from an extensive investigation of joint modelling for the human hand. We use finger and hand movement data recorded from both hands of 110 subjects using passive reflective markers on the skin. Furthermore, we use data which was recorded from a single Thiel-fixated cadaver hand using also passive reflective markers but fixed to the bone. Our data clearly demonstrate that, for wrist and finger joints, hinge joint models are sufficiently accurate to describe their movement in Cartesian space.

The effect of wrist surgery on the kinematic consistency of joint axis reconstruction in a static posture

Three-dimensional analysis of wrist motion is a growing focus in orthopedic research, however, our understanding of its validity (accuracy and reliability) remains limited. Nine human cadavers were tested to estimate wrist joint axes alignment in a postural static pose. The objective was to investigate a rater's ability to reliably align three skin- tracked wrist joint coordinate system (WJCS) definitions across baseline and reconstructive wrist states (intact, mid-carpal arthrodesis, and proximal-row carpectomy). Two WJCSs (legacy, anatomic) were based on palpated bony landmarks and the third (functional) was based on both landmarks and passive flexion-extension motion. A coordinate frame based on the anatomic definition was tracked with bone pins and served as a reference. Each WJCS was tested in each wrist state and in three forearm position (45° pronation, neutral, 45° supination). The angular offset about each axis of the WJCS frames were calculated with respect to the reference in flexion-extension, radial-ulnar deviation, and pronation-supination for every iteration. Reliability and root mean square deviation values were analyzed across wrist states. Our data suggest that no WJCS is uniformly more reliable than another. The functional WJCS definition was most consistent across intact and post-operative states for pronation-supination offset, but this was dependent on rater interpretation. It still however offers the practical benefit of requiring fewer landmarks.

Comparison Between Healthy and Reduced Hand Function Using Ranges of Motion and a Weighted Fingertip Space Model

Detection and quantification of changes in hand function are important for patients with loss of function and clinicians who are treating them. A recently developed model, the weighted fingertip space (WFS) quantifies the hand function of individuals in three-dimensional space and applies kinematic weighting parameters to identify regions of reachable space with high and low hand function. The goal of this research was to use the WFS model to compare and contrast the functional abilities of healthy individuals with the abilities of individuals with reduced functionality due to arthritis (RFA). Twenty two individuals with no reported issues with hand function and 21 individuals with arthritis affecting the hand were included in the research. Functional models were calculated from the ranges of motion and hand dimension data for each individual. Each model showed the volume of reachable space for each fingertip of each hand, the number of ways to reach a point in space, the range of fingertip orientations possible at each point, and the range of possible force application directions (FADs) at each point. In addition, two group models were developed that showed how many individuals in both the healthy and RFA groups were able to reach the same points in space. The results showed differences between the two groups for the range of motion (ROM) measurements, the individual model calculations, and the group models. The ROM measurements showed significant differences for the joints of the thumb, extension of the nonthumb metacarpophalangeal (MCP) joints, and flexion of the distal interphalangeal (DIP) joints. Comparing the models, the two groups qualitatively showed similar patterns of functional measures in space, but with the RFA group able to reach a smaller volume of space. Quantitatively, the RFA group showed trends of smaller values for all of the calculated functional weighting parameters and significantly smaller reachable volume for all of the fingers. The group models showed that all healthy individuals were able to reach an overlapping space, while 18 of 21 RFA individuals were able to reach similar spaces. Combined, the results showed that the WFS model presents the abilities of the hand in ways that can be quantitatively and qualitatively compared. Thus, the potential of this hand model is that it could be used to assess and document the changes that occur in hand function due to rehabilitation or surgery, or as a guide to determine areas most accessible by various populations.

Changes in the flexor digitorum profundus tendon geometry in the carpal tunnel due to force production and posture of metacarpophalangeal joint of the index finger: an MRI study

BACKGROUND

Carpal tunnel syndrome is a disorder caused by increased pressure in the carpal tunnel associated with repetitive, stereotypical finger actions. Little is known about in vivo geometrical changes in the carpal tunnel caused by motion at the finger joints and exerting a fingertip force.

METHODS

The hands and forearms of five subjects were scanned using a 3.0 T magnetic resonance imaging scanner. The metacarpophalangeal joint of the index finger was placed in: flexion, neutral and extension. For each joint posture subjects either produced no active force (passive condition) or exerted a flexion force to resist a load (~4.0 N) at the fingertip (active condition). Changes in the radii of curvature, position and transverse plane area of the flexor digitorum profundus tendons at the carpal tunnel level were measured.

RESULTS

The radius of curvature of the flexor digitorum profundus tendons, at the carpal tunnel level, was significantly affected by posture of the index finger metacarpophalangeal joint (P<0.05) and the radii was significantly different between fingers (P<0.05). Actively producing force caused a significant shift (P<0.05) in the flexor digitorum profundus tendons in the ventral (palmar) direction. No significant change in the area of an ellipse containing the flexor digitorum profundus tendons was observed between conditions.

INTERPRETATION

The results show that relatively small changes in the posture and force production of a single finger can lead to significant changes in the geometry of all the flexor digitorum profundus tendons in the carpal tunnel. Additionally, voluntary force production at the fingertip increases the moment arm of the FDP tendons about the wrist joint.

Human hand modelling: kinematics, dynamics, applications

An overview of mathematical modelling of the human hand is given. We consider hand models from a specific background: rather than studying hands for surgical or similar goals, we target at providing a set of tools with which human grasping and manipulation capabilities can be studied, and hand functionality can be described. We do this by investigating the human hand at various levels: (1) at the level of kinematics, focussing on the movement of the bones of the hand, not taking corresponding forces into account; (2) at the musculotendon structure, i.e. by looking at the part of the hand generating the forces and thus inducing the motion; and (3) at the combination of the two, resulting in hand dynamics as well as the underlying neurocontrol. Our purpose is to not only provide the reader with an overview of current human hand modelling approaches but also to fill the gaps with recent results and data, thus allowing for an encompassing picture.

Effects of the index finger position and force production on the flexor digitorum superficialis moment arms at the metacarpophalangeal joints - a magnetic resonance imaging study

BACKGROUND

The purpose of this study was to use magnetic resonance imaging to measure the moment arm of the flexor digitorum superficialis tendon about the metacarpophalangeal joint of the index, middle, ring, and little fingers when the position and force production level of the index finger was altered. A secondary goal was to create regression models using anthropometric data to predict moment arms of the flexor digitorum superficialis about the metacarpophalangeal joint of each finger.

METHODS

The hands of subjects were scanned using a 3.0 T magnetic resonance imaging scanner. The metacarpophalangeal joint of the index finger was placed in: flexion, neutral, and extension. For each joint configuration subjects produced no active force (passive condition) and exerted a flexion force to resist a load at the fingertip (active condition).

RESULTS

The following was found: (1) The moment arm of the flexor digitorum superficialis at the metacarpophalangeal joint of the index finger (a) increased with the joint flexion and stayed unchanged with finger extension; and (b) decreased with the increase of force at the neutral and extended finger postures and did not change at the flexed posture. (2) The moment arms of the flexor digitorum superficialis tendon of the middle, ring, and little fingers (a) did not change when the index metacarpophalangeal joint position changed (P>0.20); and (b) The moment arms of the middle and little fingers increased when the index finger actively produced force at the flexed metacarpophalangeal joint posture. (4) The moment arms showed a high correlation with anthropometric measurements.

INTERPRETATION

Moment arms of the flexor digitorum superficialis change due to both changes in joint angle and muscle activation; they scale with various anthropometric measures.

BIOMECHANICS OF THE NORMAL AND DISEASED METACARPOPHALANGEAL JOINT: IMPLICATIONS ON THE DESIGN OF JOINT REPLACEMENT IMPLANTS

The metacarpophalangeal (MCP) joint is crucial for hand function, but is frequently affected by arthritis, leading to pain and disability. This paper reviews the biomechanics of the normal and diseased joint in order to help consider the design of improved MCP joint replacement implants. The normal MCP joint enables a large range of motion in flexion/extension and abduction/adduction as well as a few degrees of rotation. A normal joint typically allows 90° flexion, with a grip strength of up to 672 N. The diseased joint has a reduced range of motion (typically 30° flexion) and reduced hand strength compared to the normal joint. Current MCP joint replacement implants generally try to recreate the range of motion of the normal joint; however, many designs are prone to fracture, as they are unable to withstand the conditions of the diseased joint. It may be beneficial for future implant designs to provide just a functional range of motion. Future designs of MCP joint replacement implants need to be more durable and last longer. Careful consideration of the diseased joint, rather than the normal joint, may help to better define the requirements for such implants.

Surface replacement arthroplasty of the proximal interphalangeal and metacarpophalangeal joints: The current state

Surface replacement arthroplasty for proximal interphalangeal joint and metacarpophalangeal joints are becoming popular. Low profile, anatomically designed implants limit the amount of bone removed but need preservation of the collateral ligaments. Pyrocarbon and cobalt-chrome stemmed unconstrained implants on ultra-high molecular weight polyethylene are the two commonly available bearing surfaces. The indications for small joint arthroplasty are degenerative, post-traumatic or rheumatoid arthritis. Early results are encouraging, primarily in patient satisfaction and pain relief, but are based on low numbers. The main concerns are progressive loss of range due to implant settling, dislocation, squeaking and poor osteo-integration with the appearance of a radiolucent line at the bone-implant interface. Our experience suggests that metacarpophalangeal joint replacements consistently give good results.

The influence of concentric and eccentric loading on the finger pulley system

In this study we investigated the influence of the loading condition (concentric vs. eccentric loading) on the pulley system of the finger. For this purpose 39 cadaver finger (14 hands, 10 donors) were fixed into an isokinetic loading device. The forces in the flexor tendons and at the fingertip were recorded. In the concentric loading condition A2 and A4 ruptures as well as alternative events such as fracture of a phalanx or avulsion of the flexor tendons were almost equally distributed, whereas the A2 pulley rupture was the most common event (59%) in the eccentric loading condition and alternative events were rare (23.5%). The forces in the deep flexor tendon, the fingertip and in the pulleys were significantly lower in the eccentric loading condition. As the ruptures occurred at lower loads in the eccentric than in the concentric loading condition it can be concluded that friction may be an advantage for climbers, supporting the holding force of their flexor muscles but may also increase the susceptibility to injury.

Nonrheumatoid metacarpophalangeal joint arthritis. Unconstrained pyrolytic carbon implants: indications, technique, and outcomes

Unconstrained pyrolytic surface replacement arthroplasty provides the benefits of a more natural center of rotation with preservation of native ligamentous joint stability. Initial short-term results show excellent motion, pain relief, and restoration of pinch and grip strength. These results are encouraging, and suggest that pyrolytic carbon arthroplasty may be a reasonable option for joint salvage in patients suffering from MP joint osteoarthritis.

Optimum tool handle diameter for a cylinder grip

The ideal diameter for a tool handle for males and females has been determined using an existing biomechanical model of the hand validated in previous works. The model estimates a 33-mm optimum diameter tool handle for the general population (males and females). When the optimum diameter for a tool handle is selected, the muscles exert the minimum force needed to hold the tool and perform gripping activities. Optimal handle design reduces the force required for gripping a tool, protects the underlying joint structures, and reduces the risk of developing cumulative trauma associated with repetitive task requiring high grip forces and awkward postures. This article provides a design parameter for optimal tool diameter to aid the therapist in the selection of assistive devices, built-up handles, or for the fabrication of a tool handle.

Five-year results of a new total replacement prosthesis for the finger metacarpo-phalangeal joints

An unconstrained surface metacarpophalangeal joint replacement was developed with metal metacarpal and polyethylene phalangeal components, fixed by uncemented finned polyethylene plugs which allowed some metacarpal component motion. Clinical and radiological results in 13 joints in eight patients are presented after 5 years. One infection required revision at 3 months. There were no further complications. At final review there were no implant failures. Two of 13 joints showed lucency around the phalangeal component and one showed 2mm subsidence of the metacarpal component. No other adverse radiological features were observed. Seven patients had no pain and one had minor discomfort. Joint movement had improved from an arc of 27 degrees to 60 degrees and disability, assessed using the P.E.M. questionnaire, had improved from 77% to 9%.

A 3D biomechanical model of the hand for power grip

A three-dimensional scalable biomechanical model of the four fingers of the hand to evaluate power grip is proposed. The model has been validated by means of reproducing an experiment in which the subjects exerted the maximal voluntary grasping force over cylinders of different diameters. The model is used to simulate the cylinder grip for two hand sizes and for five different handle diameters. The reduction of the muscle forces using different handle diameters has been studied. The model can be applied to the design and evaluation of handles for power grip and to the study of power grasp for normal and abnormal hands.

A test procedure for artificial finger joints

This paper highlights the lack of an agreed testing standard for artificial finger joints. It reviews the anatomy, pathology and biomechanics of finger joints as well as the various designs of finger prostheses and the machines used to test them. While pre-implantation testing should be fundamental, increasing regulation of the biomedical engineering industry will further demand testing of prostheses to pre-agreed standards. Standards relating to the testing of other artificial joints are reviewed before possible parameters for testing finger prostheses are offered.

A 3-D dynamic model of human finger for studying free movements

The purpose of this work is to develop a 3D inverse dynamic model of the human finger for estimating the muscular forces involved during free finger movements. A review of the existing 3D models of the fingers is presented, and an alternative one is proposed. The validity of the model has been proved by means of two simulations: free flexion-extension motion of all joints, and free metacarpophalangeal (MCP) adduction motion. The simulation shows the need for a dynamic model including inertial effects when studying fast movements and the relevance of modelling passive forces generated by the structures studying free movements, such as the force exerted by the muscles when they are stretched and the passive action of the ligaments over the MCP joint in order to reproduce the muscular force pattern during the simulation of the free MCP abduction-adduction movements.

Implant arthroplasty of the hand: retrospective and prospective considerations

Small joint arthroplasty has lagged behind the development of that in large joints because of their small sizes, different shapes, presence within kinetic chains, complex soft tissue investments, presence of adjacent rays, secondary displacement and contracture, and the differing requirements of degenerative and rheumatoid arthritis. Prosthetic development must take into consideration range of motion, stability, tendon moment arms, fixation, ease of implantation, biocompatibility, wear and strength characteristics, and soft tissue reconstruction. The metacarpophalangeal, interphalangeal, and trapeziometacarpal joints each present different problems in the design of kinematic equivalent prostheses. One-piece polymeric designs have advantages in cost, adaptability, and known performance but show degradation of function with time. Total joint designs have the potential of better simulating normal joint function but have shown tendencies to subsidence, loosening, and breakage. The rigidity of hinge joints limits the damping of out-of-plane forces and places greater stress on bone-stem interfaces, whereas global designs have poor constraint features.

A new concept for a metacarpophalangeal prosthesis: consequence on joint biomechanics

OBJECTIVE

The purpose of this work was to establish whether surface replacement non-constrained prostheses can duplicate the normal biomechanics of the metacarpophalangeal joint.

DESIGN

A series of mathematical models.

BACKGROUND

A non-constrained prostheses has been designed for the replacement of the metacarpophalangeal joint. It uses the concept of surface replacement in that it attempts to replicate the anatomy of the original cartilage surfaces. The centre of rotation of the prosthesis is also sited at the same position as in the natural joint to maintain the balance between the flexor and extensor tendon forces, such that the prosthesis duplicates the biomechanics of the normal joint. Due to the unique dimensions of each joint that may present for surgery, the four sizes of prosthesis that are available for implantation may not always produce an exact replication of the joint kinematics. These situations were examined to establish whether the biomechanics of the joint can indeed be restored.

METHODS

Mathematical models for each size of prosthesis implanted into a range of different sized metacarpophalangeal joints were developed. The prosthetic and cartilage surface profiles were compared and the balance between the tendon forces was examined.

RESULTS

Differences in size that may occur between the surface profiles of the normal joint and prosthesis, together with any relocation of the centre of rotation, would have negligible effects on the normal joint biomechanics.

CONCLUSIONS

All four sizes of the non-constrained prosthesis can duplicate the normal biomechanics of the joint and hence provide normal function.

Large index-fingertip forces are produced by subject-independent patterns of muscle excitation

Are fingertip forces produced by subject-independent patterns of muscle excitation? If so, understanding the mechanical basis underlying these muscle coordination strategies would greatly assist surgeons in evaluating options for restoring grasping. With the finger in neutral ad- abduction and flexed 45 degrees at the MCP and PIP, and 10 degrees at DIP joints, eight subjects attempted to produce maximal voluntary forces in four orthogonal directions perpendicular to the distal phalanx (palmar, dorsal, lateral and medial) and in one direction collinear with it (distal). Forces were directed within 4.7 +/- 2.2 degrees (mean +/- S.D.) of target and their magnitudes clustered into three distinct levels (p < 0.05; post hoc pairwise RMANOVA). Palmar (27.9 +/- 4.1 N), distal (24.3 +/- 8.3 N) and medial (22.9 +/- 7.8 N) forces were highest, lateral (14.7 +/- 4.8 N) was intermediate, and dorsal (7.5 +/- 1.5 N) was lowest. Normalized fine-wire EMGs from all seven muscles revealed distinct muscle excitation groups for palmar, dorsal and distal forces (p < 0.05; post hoc pairwise RMANOVA). Palmar force used flexors, extensors and dorsal interosseous; dorsal force used all muscles; distal force used all muscles except for extensors; medial and lateral forces used all muscles including significant co-excitation of interossei. The excitation strategies predicted to achieve maximal force by a 3-D computer model (four pinjoints, inextensible tendons, extensor mechanism and isometric force models for all seven muscles) reproduced the observed use of extensors and absence of palmar interosseous to produce palmar force (to regulate net joint flexion torques), the absence of extensors for distal force, and the use of intrinsics (strong MCP flexors) for dorsal force. The model could not predict the interossei co-excitation seen for medial and lateral forces, which may be a strategy to prevent MCP joint damage. The model predicts distal force to be most sensitive to dorsal interosseous strength, and palmar and distal forces to be very sensitive to MCP and PIP flexor moment arms, and dorsal force to be sensitive to the moment arm of and the tension allocation to the PIP extensor tendon of the extensor mechanism.

Chronic post-traumatic radial instability of the metacarpophalangeal joint of the finger. Long-term results of ligament reconstruction

Chronic painful post-traumatic instability of the radial collateral ligament complex of the metacarpophalangeal joint of a finger was treated by tendon graft reconstruction in 24 patients. Seventeen patients (20 joints) were available for a retrospective study at a mean follow-up time of 105 months. Eighty percent of the joints showed excellent or good results, with relief of pain, return of adequate stability, a near normal range of motion and absence of degenerative changes.

The virtual hand. The Pulvertaft Prize Essay for 1996

Virtual reality technologies are now at a stage in which the various disciplines can be brought together to construct a virtual human hand. Devices can be constructed to record multiple joint positions accurately in clinical environments. Joint prostheses may be tested virtually before undergoing clinical trials, albeit in a simple way at present, but may eventually be incorporated into a virtual model of the hand and driven by goniometric gloves. This will allow more detailed analyses of implant in situ behaviour. These exciting developments will provide a huge advance in our understanding of the functions of the real hand and also a potential way of assessing outcomes in a simple and repeatable fashion. We are on the edge of a new era in hand surgery when the computer scientist, biomechanic, control engineer, hand therapist and surgeon will be able to alternate between the virtual and the real world in producing better outcomes for patients.

Reconstruction with tenodesis in an adult flatfoot model. A biomechanical evaluation of four methods

Six fresh-frozen adult cadaveric specimens were mounted in an Instron materials testing machine with use of a cemented intramedullary rod. Angular relationships between the first metatarsal and the talus were recorded with a sonic digitizer. A flatfoot deformity was created by dividing the talonavicular joint capsule (superiorly, medially, and inferiorly), the spring ligament, the anteromedial aspect of the subtalar joint capsule, and the plantar fascia. Angular displacement in the sagittal and transverse planes was recorded at no load and at 100, 350, and 700-newton plantar loads. Each specimen was subjected to four different reconstructions with tenodesis, and the angular relationship between the first metatarsal and the talus was measured at the four levels of load. A reconstruction with use of the peroneus longus tendon was performed by preserving its insertion into the first metatarsal, rerouting the tendon and passing it from medial to lateral through a calcaneal bone tunnel, and anchoring it to the lateral aspect of the calcaneus. A reconstruction with the tibialis tendon was performed by passing the medial third of the tendon from dorsal to plantar through the navicular and from medial to lateral through the calcaneal bone tunnel and securing it to the lateral aspect of the calcaneus. The reconstruction with the tibialis anterior tendon was repeated with the tendon graft routed along the medial aspect of the navicular, directly through the calcaneal bone tunnel. The fourth reconstruction was done with use of an Achilles tendon allograft.(ABSTRACT TRUNCATED AT 250 WORDS)

Design of a non-constrained, non-cemented, modular, metacarpophalangeal prosthesis

A non-constrained, non-cemented, modular prosthesis for replacement of the metacarpophalangeal joints of the fingers has been developed. The prosthesis is of a surface design which is modular in construction and is implanted into the bones with a press fit. The prosthesis is designed to be implanted into patients with traumatic injuries, post-traumatic osteoarthritis and into patients with rheumatoid arthritis at an early stage in the disease where the muscles and ligaments that surround the joint are still functional and can provide joint stability.

Biomechanics of the human flexor tendon sheath investigated by tenography

Tenography has been performed on eight detached fingers and two intact hands of cadavers. Bulging and overlapping of synovial pockets between the ligamentous structures during flexion, their flattening during extension and the continuous change in expansion of the proximal cul de sac suggests a possible mixing mechanism for the synovial fluid. During flexion and extension a physiological joint-type bowstringing of the flexor tendons was observed at the PIP and DIP joints. This finding supports the theory that the flexor tendon moment arm is increased at these joints.

An instrumented glove for monitoring MCP joint motion

A lycra glove has been instrumented with novel low-profile electrogoniometers to measure index and middle finger metacarpophalangeal (MCP) flexion/extension motion. It is lightweight and comfortable to wear, enabling portable, unobtrusive measurement of joint usage about the home or work environment. Preliminary results have shown it to be of comparable accuracy to existing clinical measurements. Many applications are envisaged in the fields of ergonomics, orthopaedics and rehabilitation.

Metacarpophalangeal joint prostheses: a review of past and current designs

The anatomy and biomechanics of the metacarpophalangeal (MCP) joint are briefly described. Hinge, flexible and surface designs of past and current MCP prosthetic joints are reviewed, outlining their respective advantages and disadvantages. Although existing prostheses can restore cosmetic appearance and relieve pain, none can equal the stability and versatility of the natural joint. Delayed reconstructive surgery may be partly responsible for the mediocre results experienced, since the later the surgery the worse will be the condition of the muscles and ligaments surrounding the joint. These are the structures responsible for strength, movement and stability of the joint. From a mechanical viewpoint it may be desirable to operate at an earlier stage of the disease than is currently indicated, but this is a clinical decision. Some design aspects, namely fixation and wear, require a different approach when designing an MCP prosthesis from that adopted in the case of prosthetic hips and knees.

Excursion of the flexor digitorum profundus tendon: a kinematic study of the human and canine digits

The most common problem following primary flexor tendon repair is the failure of the tendon apparatus to glide, secondary to the formation of adhesions. Early motion following tendon repair has been shown to be effective in reducing adhesions between the tendon and the surrounding sheath. Therefore, it is important to determine the amount of flexor tendon excursion along the digit during joint motion. In this study, the excursion between the flexor digitorum profundus (FDP) tendon and the sheath was examined in both human and canine digits. Based on roentgenographic measurements and joint kinematic analysis, the motion of the bones, the FDP tendon, and the sheath were measured with respect to joint rotations. It was found that the canine flexor tendon apparatus behaved similarly to that of the human for the motions studied. The amount of tendon excursion was very small in regions distal to the joint in motion (approximately 0.1 mm/10 degrees of joint rotation). There was little displacement of the sheath (0.2-0.3 mm), except at the metacarpal joint region during metacarpophalangeal (MCP) joint motion and at the proximal interphalangeal (PIP) joint region during PIP joint motion. Tendon excursion relative to the tendon sheath was the largest in zone II during PIP joint rotation (1.7 mm/10 degrees of joint rotation). These results suggest that PIP joint motion may be most effective in reducing adhesions following tendon repair in zone II.

A mechanical study of six digital pulley reconstruction techniques: Part I. Mechanical effectiveness

A laboratory study on fresh-frozen human cadaver limbs compared six types of flexor tendon pulley reconstruction in the fingers. The reconstructions used were those described by (1) Bunnell, (2) Karev, (3) Weilby, and (4) Lister, and two types developed by us that have not been previously described. The pulleys were studied in specific configurations to determine their effectiveness in transforming tendon excursion into finger flexion. In each finger, comparison was made between the amount of tendon excursion required for full flexion with an intact pulley system versus the various types of reconstructed pulleys. The ratio of these two values was defined as the mechanical effectiveness of the pulley reconstruction. The Karve reconstruction was most effective at 108.2%, which was significantly different from the other five reconstructions (p less than 0.01). The remaining reconstructions ranged in effectiveness from 80.0% to 88.5%.

Ligament stability of the metacarpophalangeal joint: a biomechanical study

Capsuloligamentous contributions to metacarpophalangeal joint stability were obtained from load-displacement tests on the joints of 15 human cadavers. The contribution of each ligament to joint stability was obtained by measuring the reduction of load that induced a given joint displacement after sequential ligamentous sectioning. Four modes of joint displacement were examined: distal distraction, dorsopalmar dislocation, abduction-adduction rotations, and supination-pronation rotations. This study demonstrated that both radial and ulnar collateral ligaments play primary roles in stabilizing the metacarpophalangeal joint in all four modes of joint displacement. The accessory collateral ligaments contribute primarily to abduction-adduction rotational stability, but contribute little to stabilizing dorsopalmar dislocation or axial (supination-pronation) rotations. The palmar plate prevents dorsal dislocation only at full extension. The dorsal capsule has a moderate contribution to stability in distraction and supination-pronation rotations.

Alumina ceramic finger implants: a preliminary biomaterial and clinical evaluation

An alumina ceramic hinge-type finger prosthesis, composed of alumina ceramics and high-density polyethylene, is described. Biomaterial evaluations, including flexion-extension tolerance, stretching, twisting, extraction tests, and histologic examinations of affinity for bone, demonstrated that this implant has characteristics superior to those of previous finger implants. Eighteen proximal interphalangeal joints and 13 metacarpophalangeal joints have been replaced with this alumina ceramic finger implant. Follow-up studies (12 to 31 months) have been most encouraging with satisfactory functional recovery and no fracture or dislocation of the implants.

The laboratory development of a new metacarpophalangeal prosthesis

The paper describes the design and laboratory testing of a new metacarpophalangeal prosthesis. The novel features of the new design include the joining of pairs of prostheses by common hinge-pins and the inclusion of bearings within the proximal phalanges. The common hinge-pins are designed to prevent the recurrence of ulnar drift by sharing the forces on one finger with a neighbouring joint, and together with the intramedullary bearings to prevent potentially loosening torques from acting on the fixation of the components.

Resultant finger joint loads in selected activities

The intersegmental loads transmitted by the proximal interphalangeal (PIP) and metacarpophalangeal (MCP) joints of the index finger are presented in activities involving application of a twisting moment by the hand. Twenty normal subjects, ten males and ten females were included in the studies. A six component load transducer was incorporated in each of the two fixtures representing a water tap and a jar cap 70mm in diameter and the maximal loading on the fingers was monitered in applying an isometric twisting moment to these structures. Two different hand configurations were studied for each activity: the spatial position and orientation of the finger segments were determined using two orthogonally positioned still cameras, and specially designed stick markers were utilized to highlight anatomical landmarks. The results confirm the use of the finger in a complex three-dimensional manner with no significant differences between the male and female subjects. Forces recorded in the jar cap activity were larger than those applied in the tap activity, the maximum being around 100 N and in general the abduction/adduction moments developed at both joints were of comparable magnitude to flexion/extension. Torques as high as 0.6 Nm and 1.0 Nm were calculated at the PIP and MCP joints respectively.

Biomechanical evaluation of metacarpophalangeal joint prosthesis designs

A laboratory biomechanical analysis of metacarpophalangeal joint prosthesis designs was done with fresh cadaver finger rays. The center of rotation, range of motion, tendon excursion, and fingertip force were determined on the specimens before and after implanting Swanson, Niebauer, Steffee II, St. Georg-Buchholz, Schultz, and modified Strickland prostheses. Their biomechanical behavior varied considerably and none duplicated the normal metacarpophalangeal (MP) joint. Each has design characteristics that may be clinically advantageous as well as disadvantageous. Irrespective of the design, the studies done cannot be divorced from the following factors: (1) implant material properties--silicone rubber implants buckled with tendon loading; this deformity created a significant flexor mechanical advantage and an extensor mechanical disadvantage; (2) implant fixation--freely movable implant stems dampened part of the applied load; braided suture provided inadequate immediate fixation; (3) implantation technique--the articulated prostheses can be technically unforgiving; errors in technique resulted in alteration of their biomechanical behavior.