Response of peripheral nerve to cyclic compression in a laboratory rat model.

Repetitive cyclic loading of a nerve has been proposed as a pathogenic factor in the development of occupational compression neuropathies. Little is known about the basic response of peripheral nerve to cyclic compression. We investigated the hypothesis that cyclic compression is more detrimental to nerve function than constant compression. We measured the amplitudes and velocities of distally evoked action potentials in the presence of constant or cyclic compression of the tibial nerve in rats. Seven groups were subjected to constant or cyclic compression for 6 h by a computer controlled, hydraulically activated compression chamber. Nerves were compressed with 0 (control group), 30, 60, or 90 mm Hg of constant pressure or 0-30, 20-50, or 30-60 mm Hg of cyclic compression for approximately 20,000 compression cycles. Action potentials were recorded every 15 min. The effects of cyclic compression on nerve conduction were equivalent to the effects of constant compression at the average applied pressure. Cyclic loading itself does not appear to be an important pathogenic factor in the development of nerve conduction block.

Effects of elevation on nerve function in an acute upper extremity nerve compression model.

External compression was applied to the palmar surface of the wrist over the carpal tunnel in eight healthy volunteer subjects. With the arm in the maximum elevated position, the carpal tunnel pressure was elevated to 50 mm Hg, being continuously monitored by a slit catheter inserted into the carpal canal. Sensory and motor latencies and amplitudes were evaluated at 1-min intervals. When the sensory amplitude decreased by 50% (correlating with subjective sensory changes), the hand was lowered to heart level, still maintaining the carpal tunnel pressure at 50 mm Hg. Nerve conduction velocity and amplitude monitoring continued at 30-s intervals until complete sensory block. Four subjects demonstrated a transient reversal in the sensory amplitude decline with lowering of the hand to heart level, but soon progressed to a complete sensory block. The remaining four subjects demonstrated no change in the sensory amplitude decline with lowering of the hand to heart level. Our results suggest that with moderately elevated carpal tunnel pressures, once the sensory amplitude drops by 50% and the patient starts experiencing subjective sensory changes, lowering the hand to heart level may not change the local tissue blood flow sufficiently to maintain a sustained reversal in the declining nerve function and impending nerve damage.

An apparatus to measure flexor tendon excursion and angular motion of the distal interphalangeal joint in a rabbit model.

Investigators evaluating flexor tendon adhesions have utilized visual, histological, and gross mechanical methods in reporting their results. We have developed a device to measure tendon excursion and distal interphalangeal joint motion for a small animal model. The device was tested for accuracy and reproducibility using the rabbit hindfoot. There was no statistical difference between the right and the left in 30 pairs of feet. This device provides an accurate method to quantify tendon excursion and relative adhesion formation in a rabbit model without destroying the specimen.

Effects of increased systemic blood pressure on the tissue fluid pressure threshold of peripheral nerve.

This study was designed to evaluate the functional response of the median nerve at the wrist to various degrees of acute, local compression in hypertensive patients. After measuring resting tissue fluid pressure in the carpal tunnel of the nondominant hand of nine subjects (diastolic pressures of 90 mm Hg or greater), localized pressures of 50, 60, or 70 mm Hg were applied to the palmar aspect of the wrist. Motor and sensory latencies and amplitudes of the median nerve were evaluated before compression, during 30-240 min of compression, and during the postcompression recovery phase. Sensory responses were completely blocked at a threshold tissue fluid pressure of 60-70 mm Hg, measured by the wick catheter technique. This pressure threshold was greater than the 40-50 mm Hg previously found in normotensive subjects. The tissue pressure threshold of normotensive and hypertensive subjects was consistently 30 mm Hg below diastolic blood pressure (approximately 45 mm Hg below mean arterial blood pressure). These results support the concept that ischemia is the prime mechanism of conduction block in low pressure, nerve-compression syndromes.

The operative treatment of mid-shaft clavicular non-unions.

Ten consecutive patients with clavicular non-union were treated at the University of California, Davis, Medical Center and Kaiser Permanente Hospital, Sacramento, with compression-plating and iliac bone-grafting. Seven patients were male and three were female, and their ages ranged from sixteen to sixty years. All patients achieved clinical union by ten weeks postoperatively, with no operative or postoperative complications, and had a full, painless range of motion of the ipsilateral shoulder, with an acceptable cosmetic result. In our experience, patients with symptomatic clavicular non-union may be treated by open reduction and internal fixation with a compression plate and supplemental iliac-bone graft with a high likelihood of success.

Complications of tension-band wiring of olecranon fractures.

We encountered a high incidence of complications related to the technique of tension-band wire fixation of displaced fractures of the olecranon in a five-year retrospective study of twenty patients (twenty fractures). All had been treated with primary open reduction using the AO technique of tension-band wiring. Twenty patients were followed at least to union as determined radiographically. The most frequent complication was symptomatic prominence of the Kirschner wires at the elbow in sixteen patients. There was skin breakdown in four patients, and infection developed in one. Measurable proximal migration of the Kirschner wires, however, occurred in only three patients. Prominence of the Kirschner wires usually was due to improper seating at the time of surgery (twelve of sixteen patients). Most complications that are related to this method of fixation may be avoided by careful attention to surgical technique.

Repetitive stress injury: diagnosis or self-fulfilling prophecy?

* The vague definitions of so-called repetitive stress injuries are indicative of the fact that scientific studies have failed to show that repetitive motion causes injury. * Given the uncertainty about causation, work-related musculoskeletal disorders (WRMSDs) is a more readily accepted term to describe these phenomena. * There is little doubt that most ergonomic interventions increase comfort in the work environment, which is of great benefit to the worker. Many proponents of ergonomics assert that the elimination of certain risk factors related to force, repetition, and posture can prevent or even cure work-related musculoskeletal disorders of the upper extremity. However, there is little scientific support for this position. * Undue reliance on ergonomics to treat musculoskeletal disorders, to the exclusion of proper diagnosis and attention to medical and health risk factors, can have adverse consequences for the patient. * Science rather than politics and public policy should determine what causes injury and disease. * The failure of numerous plaintiffs in litigation regarding repetitive stress injury due to use of computer keyboards is important because, when judges and lay jurors were presented with both sides of the issue, they rejected these claims in a forum (the judicial system) that traditionally compensates individuals bringing so-called mass-tort cases.

Sensibility testing in patients with carpal tunnel syndrome.

We evaluated the sensibility of the hand preoperatively and at intervals postoperatively in twenty-three hands of twenty patients with idiopathic carpal-tunnel syndrome who underwent carpal tunnel release. Tests of sensibility included the threshold tests (vibrometry, 256-cycles-per-second vibration, and Semmes-Weinstein monofilaments) and one innervation-density test (two-point discrimination). In addition the wrist-flexion test, nerve-percussion test, and tourniquet test were performed preoperatively. Only five of the twenty-three hands had abnormal two-point discrimination and each of these also had markedly abnormal threshold-test values. Nineteen of twenty-three hands preoperatively had decreased sensibility detected by both Semmes-Weinstein monofilament testing and vibrometry. Six weeks after carpal tunnel release, all of the hands demonstrated improvement on threshold testing, and 65 per cent had normal values.

Sensibility testing in peripheral-nerve compression syndromes. An experimental study in humans.

Sensibility testing in peripheral-nerve compression syndromes was investigated in an experimental study in humans. Twelve volunteer subjects had controlled external compression of the median nerve at the carpal tunnel at a level of forty, fifty, sixty, and seventy millimeters of mercury. The subjects were then monitored for thirty to 240 minutes with four sensory tests: two-point discrimination, moving two-point discrimination, Semmes-Weinstein pressure monofilaments, and vibration. Sensory and motor conduction, subjective sensations, and motor strength were also continuously tested. The threshold tests (vibration and Semmes-Weinstein monofilaments testing) consistently reflected gradual decreases in nerve function in both subjective sensation and electrical testing, while the innervation density tests (two-point discrimination and moving two-point discrimination) remained normal until nearly all sensory conduction had ceased. Decreased muscle strength occurred late, and not until changes had already occurred in each of the sensory tests. Threshold tests of sensibility correlated accurately with symptoms of nerve compression and electrodiagnostic studies, and are being evaluated for clinical use in a variety of peripheral-nerve compression syndromes.

Results of treatment of severe carpal-tunnel syndrome without internal neurolysis of the median nerve.

Thirty-three hands (twenty-nine patients) had a release of the carpal tunnel without internal neurolysis for severe carpal-tunnel syndrome. All of the hands had increased values for two-point discrimination or thenar atrophy, or both. Twenty-three (89 per cent) of the twenty-six hands that had increased values for two-point discrimination and twenty-six (87 per cent) of the thirty hands that had an elevated result on Semmes-Weinstein testing had normal values at follow-up. Nine (90 per cent) of the ten hands that had weakness of the thenar muscles (grade-3 strength or less) regained grade-4 or 5 strength. Thirteen (65 per cent) of the twenty hands that had thenar atrophy regained normal muscle bulk. Eighteen (62 per cent) of the twenty-nine patients had complete resolution of symptoms and signs of compression of the median nerve. No significant difference was found between the results in this series of patients and those in a previously reported similar group of patients who were treated by release of the carpal tunnel combined with internal neurolysis of the median nerve.

Extra-articular fractures of the distal radius.

Extra-articular distal radius fractures frequently are undertreated. Results correlate directly with restoration of anatomy. Immobilization in plaster is an inferior method of preserving radial length and palmar tilt. Failure to maintain reduction with plaster can be predicted by the initial injury, if reduction is lost, closed reduction of the redisplaced fracture should be accompanied by external fixation.

Comminuted distal radius fractures.

Comminuted displaced fractures of the distal end of the radius pose a significant treatment challenge. The goal of treatment is to restore functional, painless motion of the wrist and fingers. Although satisfactory results correlate to a large extent with obtaining and maintaining normal anatomy, excessive distraction and a flexed wrist position with external fixation cause more harm than good, even if the anatomy is restored.

Carpal tunnel syndrome.

Attention in the press and in trade publications has created a widespread public awareness of carpal tunnel syndrome, the most frequently encountered peripheral compression neuropathy. Diagnosis and treatment is facilitated by familiarity with its stages of presentation, association with various pathologies, and appropriated use of predictive tests. Controversial issues in operative management are explored based on the introduction of some new techniques and some old ideas.

Common tendinitis problems in the hand and forearm.

Although common and often transitory, tendinitis involving the hand and forearm may be disabling. Most tendinitis conditions will respond to conservative measures. The hand surgeon's best tools to obtain a swift and successful resolution include a careful history and physical examination, coupled with and appreciation of the anatomy of the commonly affected sites.

Kienböck's disease.

Recent anatomic and biomechanical studies have contributed to a better understanding of Kienb ock 's disease. The operative alternative, if based on a classification of the severity of disease, should provide a more logical and systematic approach to patients with this difficult problem.

Carpal tunnel syndrome. A scientific basis for clinical care.

The series of experimental studies reviewed in this article supports a classification of median nerve compression at the wrist into early, intermediate, advanced, and acute nerve compression. The findings correlate well with experimental studies on the pathophysiology of nerve compression. A patient-specific management approach is recommended based upon the clinical and electrophysiologic findings which can be correlated with previously demonstrated intraneural pathologic changes.

Semitubular blade plate for fixation in the proximal humerus.

Rigid internal fixation is frequently difficult to obtain in the proximal humerus, as osteoporotic bone and small fracture fragments may preclude firm purchase of plates and/or screws. We describe our clinical results using a semitubular plate, fashioned into a blade plate device, for fixation of four displaced fractures and three osteotomies of the proximal humerus. All patients were clinically and radiographically united by 4 months postoperatively and had a functional range of motion. The strength of this fixation was compared to that of an AO "T" plate in an oblique subcapital osteotomy model using 10 matched pairs of human humeri. No statistically significant difference could be demonstrated between the two fixation methods with regard to load to failure, yield load, energy absorbed to failure, or stiffness. As a consequence of these studies, we believe the semitubular blade plate expands the options available for challenging fixations in the proximal humerus.

Innervation of the lumbrical muscles.

It has long been recognized that the first and second lumbricals are normally innervated by the median nerve, whereas the third and fourth lumbricals are innervated by the ulnar nerve (Sunderland and Ray, 1946). However, the courses of the motor nerves, particularly to the first two lumbricals and their loci of insertion, have not been clearly described. Because this information may be useful to a surgeon operating in the palm, we undertook a cadaver study to define more precisely the pathways of innervation of the lumbrical muscles.

Early mobilization following carpal tunnel release. A prospective randomized study.

A prospective randomized study was undertaken of 50 consecutive patients undergoing surgery for idiopathic carpal tunnel syndrome to determine the value of splintage of the wrist following open carpal tunnel release. Patients were randomized to either be splinted for 2 weeks following surgery or to begin range-of-motion exercises on the first post-operative day. Subjects were evaluated at 2 weeks, 1 month, 3 months, and 6 months after surgery by motor and sensory testing, physical examination, and a questionnaire. Variables assessed included date of return to activities of daily living, dates of return to work at light duty and at full duty, pain level, grip strength, key pinch strength, and occurrence of complications. Patients who were splinted had significant delays in return to activities of daily living, return to work at light and full duty, and in recovery of grip and key pinch strength. Patients with splinted wrists experienced increased pain and scar tenderness in the first month after surgery; otherwise there was no difference between the groups in the incidence of complications. We conclude that splinting the wrist following open release of the flexor retinaculum is largely detrimental, although it may have a role in preventing the rare but significant complications of bowstringing of the tendons or entrapment of the median nerve in scar tissue. We recommend a home physiotherapy programme in which the wrist and fingers are exercised separately to avoid simultaneous finger and wrist flexion, which is the position most prone to cause bowstringing.

Acute carpal tunnel syndrome.

Although the carpal tunnel is open at both ends, it has the physiologic properties of a closed compartment bounded by synovium proximally and distally. When the intracarpal canal interstitial pressure rises above a critical threshold pressure, capillary blood flow is reduced below the level required for median nerve viability. Acute carpal tunnel syndrome is recognized frequently as occurring secondary to wrist trauma and infrequently due to a variety of infectious, rheumatologic, and hematologic disorders. This condition warrants prompt recognition and the treatment is early carpal tunnel release.