Neutral Forearm Research Articles

Can a More Neutral Position of the Forearm When Operating a Computer Mouse Reduce the Pain Level for Visual Display Unit Operators? A Prospective Epidemiological Intervention Study

In a field study, a newly developed mouse that gives the operator a more neutral forearm position was compared with a traditional mouse using a more pronated forearm. After using the new mouse for 6 months, a significant reduction was reported regarding pain intensity and frequency for wrist/hand, forearm, shoulder, and neck (p £ .009). The control group using the traditional mouse reported only small changes in the pain level (p ³ .24). Total duration of pain the last 6 months was also significantly improved for the shoulder and forearm in the intervention group, whereas no such changes were observed in the control group. These results clearly indicate the importance of using a computer mouse with a more neutral position of the forearm.

Electromyographic Analysis of Shoulder Joint Function of the Biceps Brachii Muscle During Isometric Contraction

Surface electromyography was performed for both heads of the biceps brachii in 11 healthy men while the muscles were under 30% maximum isometric shoulder flexion and abduction. Elbow related biceps activity was minimized by using a brace locked in neutral forearm rotation. Electromyographic activity was normalized as a percentage of maximal muscle contraction during 24 shoulder motions. Electromyographic activity was detected in all motions examined, suggesting that the biceps muscle acts as a flexor and an abductor of the shoulder. Both heads of the biceps muscle had higher activities during external rotation than during internal rotation for most motions. Activities of both heads increased with arm elevation, but showed little dependence on elbow position. The long head was still active during internal rotation of the shoulder. These findings also suggest that the biceps muscle is a flexor and an abductor of the shoulder, and that the long head can act as a humeral head stabilizer in superior and anterior directions. Muscle fatigue of the biceps and the deltoid muscle also was determined at 30% of maximum isometric flexion. All muscles had significantly decreased mean power frequency and turns count, and increased amplitude and integrated electromyography. The rate of decrease in mean power frequency was larger for the biceps than for the deltoid muscle, and the rate of increase in amplitude was larger for the long head of the biceps than for the short head or for the deltoid muscle. These findings suggest that the long head of the biceps must increase its mechanical output to keep the arm in elevation to a greater extent than do the short head and the deltoid muscle. This may be one of the causes of tendinitis or rupture of the long head.

Pressure distribution in the distal radioulnar joint

Measurement of the pressure distribution within the distal radioulnar joint was performed in fresh cadaver forearms at varying positions of forearm rotation. Axial loads of 0 N, 36 N, and 89 N were applied to the wrist flexors and extensors. At neutral forearm rotation and application of 89 N axial load, an average of 12.5% of the sigmoid notch area was in contact with the ulna. Analysis of the pressure plots reveals that in pronation, the pressure was concentrated in the dorsal portion of the sigmoid notch and that in supination the pressure was distributed in the palmar portion.

Posterolateral elbow joint instability: The basic kinematics

Thirty-five osteoligamentous elbows were included in a study on the kinematics of posterolateral elbow joint instability during the pivot shift test (PST) before and after separate ligament cuttings in the lateral collateral ligament complex (LCLC). Division of the annular ligament or the lateral ulnar collateral ligament caused no laxity during the PST. Division of the lateral collateral ligament caused maximal laxity of 4° and 23° during forced PST in valgus and external rotation (supination), respectively. Cutting of the LCLC at the ulnar or the humeral insertion was necessary for any PST stressed elbow joint laxity to occur. Total division of the LCLC induced a maximal laxity of 7.9° and 37° during forced PST in valgus and external rotation (supination), respectively. This study suggests the lateral collateral ligament to be the primary soft tissue constraint to PST stress and the annular ligament and the lateral ulnar collateral ligament to be only secondary constraints. This study indicates that the integrity of the medial collateral elbow ligaments should be evaluated during forced valgus in pronation or neutral forearm rotation. Furthermore an isometric lateral collateral ligament reconstruction was shown to correct the joint laxity introduced by total LCLC transection.

The interosseous membrane of the forearm: Anatomy and function

The anatomic detail of the interosseous membrane was studied by dissection of 20 preserved cadaveric specimens. The interosseous membrane was found to be a complex structure consisting of a central band, accessory bands, a proximal interosseous band, and membranous portions. The central band, a stout ligamentous structure, was found in all specimens. Fibers of the central band originate on the radius and are oriented distal and ulnar an average of 21 degrees to the longitudinal axis of the ulna. Accessory bands were of less substance than the central band but were present in all specimens. The number of accessory bands ranged from 1 to 5. The proximal interosseous band is located on the dorsal surface only, and its fibers run counter to the central band. It shares a point of origin with the central band on the radius. This structure was present in 17 of 20 specimens. Since the central band was the most dominant and consistent structure, we chose to analyze the strain in the central band in 6 preserved specimens. Maximum strain in the central band of the intact specimen occurs in neutral forearm rotation. Once the radial head is removed, the percent strain universally increases throughout the arc of forearm rotation and peak strain shifts to pronation.

Workload When Using a Mouse as an Input Device

A newly developed mouse, which seemed to give the operator a more neutral forearm position was compared with a traditional mouse. The muscle load was recorded by electromyography from the extensor digitorum communis, extensor carpi ulnaris, and trapezius muscles. The muscle load of the forearm was significantly less when using the new mouse compared with the traditional one. This was true for the extensor digitorum communis regarding the static (p = .0005) and the median (p = .001) values of the amplitude distribution function (ADF) and the number of periods per minute when the muscle load was below 1% of maximum voluntary contraction (p = .03). The same dear tendency was also found regarding the static muscle load from the extensor carpi ulnaris (p = .06). These results indicate the need for reducing the pronation of the forearm when, working with a mouse.

Biceps activity during shoulder motion: an electromyographic analysis.

Electromyographic responses in 44 shoulders from 30 subjects were examined. Fourteen shoulders from 13 patients had documented rotator cuff tears. The remaining volunteers had normal cuff integrity by history and examination. Electromyographic responses were recorded from the long head of the biceps, brachioradialis (elbow control), and from the supraspinatus (shoulder control). Elbow related biceps activity was minimized by using a brace locked in neutral forearm rotation and 100 degrees flexion. Analysis of normal and rotator cuff deficient data was performed in a masked fashion and electromyographic activity normalized as a percent of maximal muscle contraction during 10 shoulder motions based on the scapular plane. Normal shoulders in all ranges of active motion exhibited significant supraspinatus activity (20%-50% maximum muscle contraction). The response followed patterns expected for a shoulder stabilizer. In contrast, with every normal shoulder, biceps and brachioradialis activity remained insignificant (1.7%-3.6% maximum muscle contraction) and did not follow a patterned response. In patients with rotator cuff tears, biceps activity remained low (1.6%-4.4% maximum muscle contraction). As opposed to previous studies using electromyography about the shoulder, this trial examined shoulder specific biceps activity by relaxing the elbow. No significant biceps activity was observed in any shoulder, including patients with rotator cuff tears. Given these findings, any function of the long head of the biceps in shoulder motion does not involve active contractions.

Rotational laxity and stiffness of the radiocarpal joint

Objective. To investigate the constraint and potential mechanism of torque transmission across the wrist joint. Design. In vitro experiment using human cadaveric specimens. Background. Transmission of torque from the forearm to the hand requires rotational stability at the wrist. Better appreciation of the constraints would have applicability to several clinical problems where the stability is compromised. Methods. Thirteen fresh-frozen cadaveric specimens were used in this experiment to investigate the rotational laxity and stiffness of the radiocarpal joint in unloaded and axially loaded (100 N) conditions, and three forearm orientations in a neutral, pronation (60 °), or supination (60 °) position. Results. In pronation or supination, there was no difference between loaded and unloaded conditions in primary or total laxity at a maximum torque of 2.3 Nm. Unloaded specimens showed a mean total rotational laxity of 42.1 °. Supination or pronation of the forearm caused a decrease in laxity with respect to neutral forearm rotation (35 ° and 41.6 ° versus 49.6 ° respectively). The primary rotational laxity accounted for half of the total laxity. With axial compression, total rotational laxity did not change, but primary laxity dropped to 50% of its unloaded value. The primary stiffness was very low — approximately 11% of the secondary stiffness. Conclusion. The ligamentous structures and the joint articulation restricted excessive axial rotation of the wrist. However, a laxity of approximately 20 ° was identified for normal wrists.

The stabilizing mechanism of the distal radioulnar joint during pronation and supination

A biomechanical cadaver study was performed to determine the roles of the stabilizing structures of the distal radioulnar joint during pronation and supination. Subluxation and dislocation of the radius with respect to the ulna were evaluated in seven cadaver forearms placed in supination, pronation, and neutral forearm rotation. The amount of subluxation was measured with all structures intact, and after sectioning in various sequences the dorsal and palmar radioulnar ligaments, the distal portion of the interosseous membrane including the pronator quadratus, and the entire interosseous membrane. After sectioning two of any four structures, the distal radioulnar joint remained stable. When the interosseous membrane was disrupted first, the dorsal radioulnar ligament was found to be more important than the palmar radioulnar ligament in stabilizing the distal radioulnar joint in pronation, and conversely the palmar radioulnar ligament was more important than the dorsal radioulnar ligament in supination. Dislocation, and frequently diastasis, occurred only with sectioning of all four structures. This suggests that all four structures contribute to stability of the distal radioulnar joint.

Ｇａｌｅａｚｚｉ骨折の治療経験

We report 10 cases of acute Galeazzi fracture-dislocations which we treated during a three years period. The mean age of the patients was 51.4 years, and six of them had classical Galeazzi fractures, and four had Galeazzi-equivalent fractures. Three fractures were treated by closed reduction and percutaneous pinning, three with open reduction and internal plate fixation, three with external fixation and bone graft, and one with open reduction and internal K-wire fixation.All fractures were evaluated using Kanazawa's criteria. Results were judged to be excellent in five cases, fair in three, and poor in two. The two poor in two. The two poor cases were older women, one with osteoporosis the other with a comminuted fracture of the distal third of the radius.Computerized tomography was valuable in diagnosing subluxation of the distal RU joint.Postoperative temporary K-wire fixation of the distal RU joint in the neutral forearm position was effective.

The distal radioulnar ligaments: A biomechanical study

The mechanical roles of the triangular fibrocartilage have been examined in three experiments. Kinematic analysis by a stereophotogrammetric method revealed that the palmar radioulnar ligament was taut in supination and that the dorsal radioulnar ligament was taut in pronation. In full pronation, the palmar radioulnar ligament decreased to an average of 71% of its length in tension. In full supination, the dorsal radioulnar ligament decreased to an average of 90% of its length. Mechanical testing of the triangular fibrocartilage under axial load disclosed a significant laxity (mean: 10.4 mm), which was decreased in pronation. Transverse loading tests demonstrated that the triangular fibrocartilage is less stiff in neutral forearm rotation. Study of the material properties of the palmar and dorsal parts of the triangular fibrocartilage showed these structures to be strong ligaments with material properties similar to those of the radiocarpal ligaments.

The effect of the radial head and prosthetic radial head replacement on resisting valgus stress at the elbow.

Five fresh nonembalmed elbows were tested for resistance to valgus stress in their anatomic state, after radial head resection, and after insertion of Silastic and polymethylmethacrylate (PMMA) radial head replacements. The resistance to valgus stress was found to be reduced an average of 28% after radial head resection. The PMMA and Silastic implants restored valgus stiffness an average of 86% and 78% respectively, as compared to intact elbow values for corresponding flexion angles. Testing in pronation, supination and neutral forearm rotation demonstrated no difference in valgus stiffness. For each elbow, resistance to valgus stress was greatest at full extension and dropped approximately 30% at all other flexion angles as compared to corresponding full extension value. These data support the concept of the radial head as a stabilizer to valgus stress in the in vitro elbow. Further, this data demonstrated the ineffectiveness of current radial head replacement systems in restoring this biomechanical function and suggest that the use of a stiffer implant material may be beneficial in resisting valgus stress. Additional testing is indicated to determine the performance of a stiffer implant at the clinical and biological levels.

Anterior marginal articular fracture of distal radius

Dr. John Larkin: A 38-year-old white male laborer was involved in an automobile collision and was thrust against the instrument panel of his vehicle. The back of his wrist struck the panel and the patient reports that his wrist was palmar flexed forcibly at the time of his injury. He sustained a contusion of the scalp and a fractured wrist. Examination in the emergency ward at the Massachusetts General Hospital showed no evidence of brain damage or significant systemic injury. X-ray films showed a volar marginal fracture of the distal articular surface of the radius with anterior subluxation of the distal fragment and of the carpal bones (Fig 1). An axillary block was performed and reduction of the fracture was attempted. The wrist was positioned in 25° of wrist dorsiflexion and neutral forearm rotation, as is recommended in most standard fracture textbooks. Follow-up x-ray films showed persistent anterior subluxation of

Anterior Marginal Articular Fracture of Distal Radius

Dr. John Larkin: A 38-year-old white male laborer was involved in an automobile collision and was thrust against the instrument panel of his vehicle. The back of his wrist struck the panel and the patient reports that his wrist was palmar flexed forcibly at the time of his injury. He sustained a contusion of the scalp and a fractured wrist. Examination in the emergency ward at the Massachusetts General Hospital showed no evidence of brain damage or significant systemic injury. X-ray films showed a volar marginal fracture of the distal articular surface of the radius with anterior subluxation of the distal fragment and of the carpal bones (Fig 1). An axillary block was performed and reduction of the fracture was attempted. The wrist was positioned in 25° of wrist dorsiflexion and neutral forearm rotation, as is recommended in most standard fracture textbooks. Follow-up x-ray films showed persistent anterior subluxation of