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Biomedical subjects

K N An

Publications and source records attributed to K N An.

At least 181 records · Page 10Linked to original sources
PubMed1994

Malrotation of the humeral component of the capitellocondylar total elbow replacement is not the sole cause of dislocation.

Malrotation of the humeral component of the capitellocondylar total elbow replacement is thought but not proved to be one of the major causes of postoperative dislocation. The purpose of this study was to quantitate the effect of malrotation of the humeral component on the kinematics and laxity of the capitellocondylar total elbow prosthesis. Eleven fresh previously frozen elbows were used. With the humeral component in optimal position, external rotation, or internal rotation, movements of the elbow with neutral, valgus, and varus loading were monitored with an electromagnetic tracking device. When the humeral component was positioned in external rotation, the ulna was more valgus and supinated than when the component was in optimal position, and when the component was in internal rotation the ulna was more valgus in extension and more supinated in flexion. Malrotation in external rotation decreased valgus-varus laxity, and malrotation in internal rotation increased rotational laxity. Only one elbow became dislocated, despite constant severe maltracking between the components in all of the specimens. We concluded that although malrotation of the humeral component influences the laxity and causes maltracking, it is not the primary cause of postoperative dislocation. The contribution of other factors should be investigated.

Aged↗
PubMed1994

Lumbrical muscle incursion into the carpal tunnel during finger flexion.

Carpal tunnel syndrome is one of the many so-called cumulative trauma disorders thought by some to be related to the performance of repetitive tasks in the work-place. The cause of this disorder is unknown. We have observed lumbrical muscle incursion into the carpal tunnel during finger flexion. This study was conducted to determine the amount of this incursion in normal wrists. Five cadaver upper limbs were analyzed radiographically with radiopaque markers on the flexor retinaculum and the lumbrical muscle origins in four finger positions: full extension, 50% flexion, 75% flexion, and 100% finger flexion. The lumbrical muscle origins were an average of 7.8 mm distal to the carpal tunnel in full finger extension. They moved an average of 14 mm into the carpal tunnel with 50% finger flexion, 25.5 mm with 75% flexion, and 30 mm with 100% flexion. Abnormal lumbrical muscles have been cited as a possible cause of carpal tunnel syndrome. These findings suggest that lumbrical muscle incursion during finger flexion is a normal occurrence and is a possible cause of work-related carpal tunnel syndrome.

Carpal Bones↗
PubMed1994

Lateral stability of proximal interphalangeal joint replacement.

The lateral stability of the cadaver proximal interphalangeal joint was studied with an electromagnetic tracking system before and after implant replacement. Ten middle fingers were retrieved and randomly divided into two groups for joint replacement with either a silicone rubber flexible finger joint implant or a custom surface replacement prosthesis. Each finger was mounted on a fixture that allowed loading of the proximal interphalangeal joint with tension through the flexor, extensor, and intrinsic tendons. For the intact proximal interphalangeal joint under lateral stress, lateral angulation averaged 4 degrees in extension and 8 degrees with the joint in 60 degrees of flexion. Although lateral angulation increased after surface replacement prosthesis implantation when the joint was flexed more than 20 degrees, comparison with the intact joint showed no statistical difference. With the silicone implant, lateral angulation became more pronounced even in the extended position and showed a significant difference when the proximal interphalangeal joint was flexed more than 20 degrees.

Cadaver↗
PubMed1994

Material properties of the plantar aponeurosis.

Material properties of the plantar aponeurosis were determined by a two-dimensional video tracking method to simultaneously measure the aponeurosis deformation. Failure loads averaged 1189 +/- 244 N and were higher in men. Average stiffness of the intact fascia was 203.7 +/- 50.5 N/mm at a loading rate of 11.12 N/sec and it did not vary significantly for the loading rates of 11.12 to 1112 N/sec. The high tensile loads required for failure were consistent with clinical and biomechanical studies and indicated the importance of the aponeurosis in foot function and arch stability.

Aged↗
PubMed1994

Motion and laxity of the capitellocondylar total elbow prosthesis.

The motion and laxity of the capitellocondylar unconstrained total elbow prosthesis were assessed, with use of an electromagnetic tracking device and stimulated muscle-loading, after implantation in seventeen cadaveric elbows. The axis of motion of the elbows with the capitellocondylar implants averaged 2.1 +/- 2.3 degrees more varus angulation than that of the intact elbows. This difference may be attributed to the design of the implant, as the 5-degree-valgus humeral component used in this study has a smaller valgus inclination than the articular surface of the distal aspect of the humerus. Although the maximum valgus-varus laxity of the capitellocondylar elbow prostheses was, on the average, 4.3 +/- 2.4 degrees greater than normal (with simulated muscle-loading), the data must be interpreted in light of the fact that this in vitro study did not allow for soft-tissue healing. The prosthetic components tracked well, and there were no dislocations or malarticulations provided that appropriate soft-tissue tensioning and positioning of the components had been achieved at the time of implantation. Sectioning of either the medial or the lateral collateral ligament resulted in gross instability of the joint after capitellocondylar arthroplasty. The ulnar attachment of the medial collateral ligament was found to be vulnerable to injury during the positioning of the ulnar component of this implant.

Aged↗
PubMed1994

Displaced intra-articular fractures of the calcaneus treated non-operatively. Clinical results and analysis of motion and ground-reaction and temporal forces.

Twenty-seven patients who had a unilateral displaced intra-articular fracture of the calcaneus were managed with a cast instead of with reduction or an operation. The clinical result after a mean of six years (range, two to ten years) was excellent in five patients, good in five, fair in seven, and poor in ten. The sixteen patients who were re-examined for this study and for whom the gait was analyzed demonstrated abnormalities in ground-reaction force with regard to vertical force (F3) and temporal force factors (T2, T3, T6, and T9). Analysis of temporal and distance factors showed a trend toward a decreased proportion of single-limb support on the involved side. Three-dimensional motion analysis of the ankle and hindfoot was performed with electrogoniometers as the subject walked on a level surface, on a 10-degree side-slope, and up and down stairs. Motion was decreased in the sagittal, coronal, and transverse planes during walking on level ground and on a side-sloping surface. Significant decreases in motion in these planes were also seen during walking up and down stairs. Although these patients did not have a subsequent reconstructive operation, most had a residual functional deficit.

Ankle Joint↗
PubMed1994

Four axial structural and material test machine.

Structural tests of complex motion segments, such as those found in numerous joints in the body, require a flexible test bed capable of coordinated multiple axis control and a thorough understanding of the forces and moments. Past experience with such tests on the wrist, elbow, foot and spine joints pointed to the inadequacies of conventional test machines not designed for such purposes. Therefore, a PC-based four-axial benchtop test machine suited for more flexible, sophisticated, biomechanical testing has been developed and built. The test machine consists of a rigid aluminum frame incorporating three translational and one rotational axis driven by micro-stepping motors. The tester is controlled by an industry standard 486 PC including a motor indexer and analog-to-digital (A-D) board. The custom motion control software (not limited to four channels) is designed to accommodate both stepper and servo controllers in displacement or load control modes, or a feedback mode utilizing any number of A-D inputs to control axis velocity. Each axis can act independently, or dependently as a function of another axis. A six-component load cell was also incorporated for force and moment measurement. This new test machine has been found to be quite feasible and easy to operate in the analysis of joint constraint and laxity measurement.

Biomechanical Phenomena↗
PubMed1994

Biomechanics of the elbow and forearm.

The elbow joint functions as a link between the shoulder and wrist providing an exceptional amount of stability and motion. The elbow joint should not be considered a simple hinge joint; rather there are important out-of-plane motions that affect implant design and surgical reconstruction of the elbow. Forearm rotation, which occurs as the radius wraps around the ulna, guided by the soft tissues at the wrist and elbow joints, also contributes to upper extremity mobility. Force transmission in the forearm is a complex interaction of the radius, ulna, and interosseous membrane. Forces at the wrist affect the transmission of force through the forearm to the elbow joint. During some activities, forces at the elbow joint can reach several times body weight. These motion, stability, and force interactions allow for the forearm's function. It should be recognized that an event at the elbow joint affects the forearm and the wrist, and conversely injury or disease at the wrist joint can affect the elbow.

Biomechanical Phenomena↗
PubMed1994

Dynamic anterior stabilisers of the shoulder with the arm in abduction.

The stabilising effects on the glenohumeral joint of each of the rotator-cuff muscles and of the biceps were studied with the arm in abduction and external rotation in 13 cadaver shoulders. The muscles were loaded one at a time with forces proportional to their cross-sectional areas. We recorded the positions of the humeral head before and after the application to the humerus of an anterior force of 1.5 kg. When the capsule was intact, the anterior displacement with the subscapularis loaded was significantly larger than with the other muscles loaded (p = 0.0009). With the capsule vented, the displacement with the biceps loaded was significantly smaller than that with the subscapularis loaded (p = 0.0052). After creating an imitation Bankart lesion, the displacement with the biceps loaded was significantly less than with any of the rotator-cuff muscles loaded (p = 0.0132). We conclude that in the intact shoulder, the subscapularis is the least important anterior stabiliser, and that the biceps becomes more important than the rotator-cuff muscles as stability from the capsuloligamentous structure decreases. Strengthening of the biceps as well as the rotator-cuff muscles should be part of the rehabilitation programme for anterior shoulder instability.

Adult↗
PubMed1994

Pull-out strength of screws from polymethylmethacrylate cement.

We aimed to determine the optimal method of inserting a screw into polymethylmethacrylate (PMMA) cement to enhance fixation. We performed six groups of ten axial pull-out tests with two sizes of screw (3.5 and 4.5 mm AO cortical) and three methods of insertion. Screws were placed into 'fluid' PMMA, into 'solid' PMMA by drilling and tapping, or into 'curing' PMMA with quarter-revolution turns every 30 seconds until the PMMA had hardened. After full hardening, we measured the maximum load to failure for each screw-PMMA construct. We found no significant difference in the pull-out strengths between screw sizes or between screws placed in fluid or solid PMMA. Screws placed in curing PMMA were significantly weaker: the relative strengths of solid, fluid and curing groups were 100%, 97% and 71%, respectively. We recommend the use of either solid or fluid insertion according to the circumstances and the preference of the surgeon.

Biomechanical Phenomena↗
PubMed1994

Biomechanics of wheelchair propulsion by able-bodied subjects.

The mechanical parameters of wheelchair propulsion were measured using 10 able-bodied participants. A roller system connected to a Cybex Isokinetic Machine was designed for measurement of the torque and angular displacement of the wheels during propulsion. The peak torque, angular displacement, work, and angular impulse were measured and calculated. Three types of wheelchairs, one from each of the following categories based on popularity, were evaluated: (1) lightweight, collapsible, nonadjustable Everest and Jennings Premier II (EJ); (2) lightweight, collapsible, adjustable Quickie II (Q2); and (3) lightweight, rigid-framed, adjustable Quickie GPV (Q1). Significant differences were found in certain mechanical parameters with propulsion of the three different types of wheelchairs. The work performed by each single stroke and the angular impulses are higher for the Q2 and Q1 than those of the EJ. These findings support the concept that wheelchair design and dimensions relative to the anthropometry of the user have great influence on the characteristics of wheelchair propulsion.

Adult↗
PubMed1993

Hand position affects elbow joint load during push-up exercise.

Electromagnetic motion sensors and a piezoelectric force plate were used to record simultaneously upper-extremity motion and forces in nine healthy male subjects during push-ups in six different hand positions. The intersegmental loading pattern on the elbow joint during a push-up exercise was investigated. The importance of hand position on these loads was examined. Peak forces exerted on the elbow joint along the forearm axis averaged 45% of the body weight for the 'normal' hand position and were significantly decreased if hands were positioned either 'apart' or 'superior' from 'normal'. The peak torque in the 'normal' position tended to produce elbow flexion and was 2305.9 N cm, or 56% of the maximal isometric extensor torque, which was significantly different from hands 'apart' and hand 'together' at 29 and 71% of the maximal isometric torque, respectively. The maximum torque about the forearm axis tended to produce forearm pronation with a mean value of 315.4 N cm (35% of the maximal isometric supinator torque). The maximum valgus torque at the elbow opposed by the medial ligamentous structure was 1241 N cm and was significantly increased if the hand was positioned superiorly. The valgus torque increased by 42% for the one-handed push-up under simulated fall condition. The results of this analysis give an insight into the biomechanics of a normal elbow and to its load-carrying capacity. The data may be extrapolated to the design of rehabilitation programs and possibly to the mechanisms of forearm injury during a fall.

Adult↗
PubMed1993

Excursion of prime wrist tendons.

To allow continuous and simultaneous measurements of tendon excursion and joint rotation angles, we developed a system using an electric potentiometer and an electromagnetic tracking device. Instantaneous moment arms of each tendon could then be calculated on the basis of the slope of the curve between tendon excursion and joint angular displacement. Five prime wrist motor tendons were studied on freshly frozen cadavers. Calculated tendon moment arms were found to be consistent throughout a full range of flexion-extension wrist motion and radioulnar deviation and corresponded closely to the anatomic location and orientation of the tendons. The flexor carpi ulnaris tendon provided the largest moment contribution to the wrist joint. Forearm rotation did not affect the function of the wrist tendon except for the extensor carpi ulnaris. During flexion-extension motion, the excursion of the extensor carpi ulnaris decreased significantly from 10 to 4 mm, with the forearm in neutral and pronated positions. During radioulnar deviation, the excursion of the extensor carpi ulnaris increased from 14 to 17 mm with the forearm in supinated and pronated positions.

Aged↗
PubMed1993

Stability and constraint of the proximal interphalangeal joint.

The kinematics of the intact proximal interphalangeal joint of 12 fresh cadaver index fingers were measured by means of an electromagnetic tracking system. The specimens were then randomly divided into two groups for ligament sectioning in two different sequences and for testing under lateral stress. Lateral stress of the intact proximal interphalangeal joints produced an average of 5 degrees of adduction and 9 degrees of supination motion throughout the arc of flexion/extension. Maximum lateral angulation was 15 degrees under 1 kg of force (30 N cm) applied at the distal end of the middle phalanx. Joint angulation increased to 20 degrees after total sectioning of the collateral ligament. Joint laxity was greatly reduced in full extension, in full flexion, and when the muscles were loaded. The proximal interphalangeal joint remained stable when one half of the collateral ligament was left intact. The results indicate that lateral stability of the proximal interphalangeal joint is provided primarily by the collateral ligament. When the lateral stress test is normal in proximal interphalangeal joint extension, an additional test in 20 to 30 degrees of flexion should be considered to avoid a false-negative result. Angulation greater than 20 degrees is abnormal and indicates a loss of collateral ligament integrity.

Electromagnetic Phenomena↗
PubMed1993

Anatomy of trapeziometacarpal ligaments.

The stabilizing ligaments of the thumb trapeziometacarpal joint were identified and studied during anatomic dissections of 30 hand specimens. Five main ligamentous structures were identified: (1) the anterior oblique ligament, (2) the ulnar collateral ligament, (3) the first intermetacarpal ligament, (4) the posterior oblique ligament, and (5) the dorsoradial ligament. It was observed that the anterior oblique ligament is the primary stabilizer of the trapeziometacarpal joint and is taut in abduction, extension, and pronation. The first intermetacarpal, ulnar collateral, and posterior oblique ligaments appear to be secondary stabilizers. In every specimen, the first intermetacarpal, ulnar collateral, and posterior oblique ligaments merged to form a force nucleus at the base of the first metacarpal. The dorsoradial ligament did not play a primary or secondary role in thumb stability. The clinical correlation of this anatomic study suggests that, at the minimum, the reconstruction of a primary thumb trapeziometacarpal ligament (anterior oblique ligament) is essential in the treatment of degenerative arthritis to maintain thumb stability.

Aged↗
PubMed1993

Intraarticular pressure of the shoulder.

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 H2O 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.

Cadaver↗
PubMed1993

In vitro stability of an unconstrained total elbow prosthesis. Influence of axial loading and joint flexion angle.

Total elbow arthroplasty is often used to replace elbow joints that have been severely damaged by arthritis or trauma. A great disparity of designs exists, however, in currently available elbow prostheses. This study evaluated the intrinsic stability of one popular resurfacing implant, the Capitellocondylar (Johnson and Johnson Orthopaedics, Inc., New Brunswick, NJ) total elbow. The in vitro response of this unconstrained prosthesis to valgus-varus and supination-pronation loading was investigated using a materials testing machine. The influence of compressive loading and flexion angle on the intrinsic stability of the prosthesis was studied. The Capitellocondylar prosthesis was found to have little intrinsic constraint, relying on external forces for component stabilization. Dislocations were common at 111 N of compressive loading, while larger loads progressively stabilized the prosthesis. Joint flexion angle had little influence on the intrinsic constraint of the implant except to increase varus stability at lower flexion angles. The Capitellocondylar total elbow prosthesis, as designed by F. C. Ewald, behaves as an unconstrained implant. Adequate soft tissue supports, which are properly balanced to provide controlled loading, are essential to prevent instability of this arthroplasty.

Biomechanical Phenomena↗