TWO MEDICAL REPORTS 1991 & 1995 (14 pages in total )
By Brian O' Ma1ley, MD
(Please see disclaimer on page 6 of 1995 Report )
A medical review of the carpal tunnel & evaluation of the possible benefits of the Flex-Rest, Inc. series of computer keyboard trays as it relates to CTS & CTD's.
1991 Report: KEYBOARD-ASSOCIATED CARPAL TUNNEL SYNDROME
The prevalence of carpal tunnel syndrome in regular risers of computer keyboards is a concern which has prompted an ergonomic approach to its prevention. As computers become more widely used, current estimates are that more than half of all office workers are keyboarding, and as the time and intensity of this workincrease, hours of data entry at rates of up to 45,000 keystrokes per hour, the reported occurrence of carpal tunnel syndrome in this setting has increased dramatically. The associated costs of disability,
therapy, job change and, not rarely, surgery, have skyrocketed.
This paper is based on an extensive review of the relevant literature. The intent is to summarize what is known about the etiology of this most common of the peripheral neropathies, andto describe how a novel keyboard support device which promotes a more comfortable typing posture, may reduce its incidence.
Carpal tunnel syndrome is a compression neuropathy of the median nerve, localized to the area of the flexor retinaculum just distal to the wrist crease. Here, the nerve and the flexor tendons share the carpal tunnel, bounded on the sides and dorsally by the carpal bones, and ventrally by the unyielding transverse carpal ligament, or flexor retinaculum. Clinically,the common result is numbness and /or paraesthesias in the median nerve distribution or in the hand diffusely. These are initially intermittant, often nocturnal, but later constant. As the neuropathy progresses, motor function is also impaired, and atrophy of the involved thenar musculature may result, with significant disability.
Numerous experimental studies have elucidated the basic mechanism of compression injury to peripheral nerves. At low levels of compression (20 to 30 mm Hg,) the earliest detectable impairment is a reduction of epineural blood flow. At pressures of 30mm fig, axonal transport is compromised, and, with time, fluid pressure within the nerve may be increased. This level of pressure on the median nerve will produce detectable electrophysiologic changes, and, more importantly, symptoms of paraesthesias in the nerve distribution. With experimental pressures of 50 to 80 mm Hg, impaired circulation within the nerve is seen, and at 80 mm Hg compression, intraneural ischemia is complete. Epineural edema is noted with 50 mm Hg compression for two hours, with development
Page (2) Medical Report by Brian O'Malley M.D. of axonal transport block possibly due to the progressively elevated endoneural fluid
pressure. Complete sensory block initially, followed by motor block, result from 60 mm Hg compression of the human median nerve. It has been shown
experimentally that ischemia, rather than simple mechanical deformation of the nerve, is
responsible for the observed changes. (Ref: Lundborg et al, J. Hand Surg,7(3):252-9, 1982;Gelberman et al, Ortho Clinics of North America, 19(1):lls-24, 1988.)
With this pathophysiology clear, numerous investigators have focused off the site of median nerve impairment, on the determinants of elevated pressures within the carpal tunnel, and on the significance of these factors in the etiology of carpal tunnel syndrome. Techniques for direct measurement of pressures within the carpal tunnel have provided convincing clinical correlation with these experimental results. The following key observations are noted:
Winn, F.J. and Habes: Carpal Tunnel Area as a Risk
Factor for Carpal Tunnel Syndrome. Muscle & Nerve 13:254-
258, 1990
Using CT scans of the wrist, the cross sectional area of the carpal tunnel was calculated. Patients were found,surprisingly,to have a larger area than controls, suggesting that other factors,possibly including such ergonomic stresses as "repetition rate, force level, ans awkward hand/wrist postures", are likely significant in the etiology of CTS. In an earlier paper, Richmasi et al (J. Hand Surg,12A:712-17, 1987) using MRI to measure the volume of the carpal tunnel, comment on the differing values obtained with this technique, which assesses true canal area, comparedwith radiologic techniques which measure the bony carpal arch. The probable contribution of the flexor tendons within the tunnel, to diminished volume and elevated pressure, is noted. This is particularly true in the distal third of the canal, where bony landmarks are unmeasureable.
Nathan, P.A., Srinivasan, Doyle and Meadows: Location
of Inpaired sensory Conduction of the Median Nerve in Carpal
Tunnel syndrome. J Hand surg 15B: 89-92, 1990
Electrophysiologic evaluation of 1 cm segments of the median nerve in 217 hands, finding that the conduction block is often highly focal, over 1 to 2 cm in length, most often at or near the distal margin of the carpal tunnel, and that the segments of the nerve proximal to the wrist crease are affected least often. These results again cast doubt on anarrow bony carpal arch as sufficient cause for most cases of CTS.
Tanzer, R.C., Carpal-Tunnel syndrome: A clinical and Anatomical
Study. Bone and Joint surg 55A: 1744-1746, 1959
At the time of carpal tunnel repair surgery, a mercury bag was
inserted into the carpal canal. With wrist flexion andextension,
elevated pressures were measured.
Page (3) Medical Report by Brian O'Malley M.D.
Smith, E.M., Sonstegard and Anderson: Carpal Tunnel
syndrome: Contribution of Flexor Tendons. Arch Phys Ned
Rehabil 58: 379-385, 1977
Balloon catheters were inserted into the carpal tunnels of cadaver forearms. "Sizable pressure" increases were recorded as loads were applied to the flexor digitorum profundus tendons of the second and third digits, and were proportionate to the degree
of flexion of the wrist. Pressures measured in the canal were well into the range demonstrated to produce compression neuropathies. Citing the "sandwiching" of the median nerve between the flexor retinaculum and the flexor tendons, they conclude that " Tension in flexor tendons during wrist flexion may play a role in otherwise
unexplained instances of the carpal tunnel syndrome."
Gelberman, R.H., Hergenroeder, Hargens, Lundbord and
Akeson: The Carpal Tunnel Syndrome. J Bone Joint sung 63-A:
'380-383, 1981
Using a wick catheter in both patients and controls, increases inpressure were rioted within the carpal tunnel when the wrist was sustained in an extreme position of flexion or extension. In controls with no know disease or abnormality of the wrist, mean pressure with the wrist in neutral position was 2.5 mm Hg; while in patients with clinical and electrophysiologic evidence of carpal tunnel syndrome, the mean pressure was 32 mm Hg.
Marked differences in pressure within the carpal tunnel were also noted when the wrists were measured while the palmar flexion, and in extension. These differences were all statistically significant.
Position Contols Patients
Neutal position 2.5 mm Hg 32 mm Hg 90 Deg Flexion 31. mm 94 mm
90 deg. Extension 30. mm 110 mm
Following surgery, these pressures were reduced to 3.5 mm Hg, at two months, with relief of pain and paraesthesias. Thus, the symptoms and the median nerve impairment characteristic of carpal tunnel syndrome can be attributed to elevated pressure on the nerve. The authors suggest that "the marked elevations in pressure recorded
with changes in wrist position..." may account for average pressures sufficient to cause nerve injury, and particularly when these pressures are developed chronically.
Gelberman, R.H., Szabo and Mortensen: carpal Tunnel
Pressures and Wrist Position in Patients with Colles'
Fractures. J Trauma 24(8): 747-749 ,1984
Page (4) Medical Report by Brian O'Malley M.D.
Amplified on the prior research, to measure the incremental pressure rise, with degree of flexion or extension of the wrist;
Neutral Position 18 mm Hg
20 deg. Flexion 27 mm
20 deg Extension 35 mm
40 deg Flexion 47 mm
It will be noted that (although absolute pressures are higher than in the previously cited study, because these were traumatized wrists,) the rise in pressure within the carpal tunnel develops with only modest displacements from the neutral position.
Marin, E.L., Vernick and Friedmann: Carpal Tunnel Syndrome:
Median Nerve stress Test. Arch Phys Ned Rehabil 64:206-208,
1983
Using standard electrodiagnostic techniques, motor and sensory nerve conduction in the median nerve was compared, in CTS patients and controls, with the wrists maintained in neutral position, maximal
flexion (mean 82 deg. in controls, 76 deg. in Pts.),
and extension (mean 77 deg. in controls, 73 deg. in Pts.) controls
showed some impairment in conduction, and "all ... patients showed
considerable increment in distal latencies with extreme extension and flexion of the wrist, " accompanied in many cases by paraesthesias, within five minutes. They conclude that "position of the wrist affects distal sensory and motor latencies of the median nerve..."
Koris, M., Gelberman, Duncan, Boublick and Smith: Carpal Tunnel
Syndrome; Evaluation of a Quantitative Provocational
Diagnostic Test. Clin Orthop 251:157-61,1990.
Sensory threshold testing was performed on controls and electrodiagnostically confirmed CTS patients' hands, using force-calibrated Semmes-Weinstein monofilaments. Affected hands showed significant decrements in sensation comparing measurements in neutral position to those taken after one minute of gravity-assisted palmar flexion.
They correlate the greater susceptibility of the larger diameter, myelinated A-Beta nerve fibers, which are responsible for light touch sensation, to ischemic injury.
TO SUMMARIZE:
1. The static anatomy of the carpal tunnel does not sufficiently explain the majority of cases of CTS.
2. Pressure increases within the carpal tunnel are noted with both wrist flexion and extension, and are of a magnitude known to be capable of producing peripheral nerve ischemic injury syndromes.
Page (5) Medical Report by Brian O'Malley M.D. 3. Loading of the flexor tendons of the fingers further increases the measured intracanal pressures.
4. Electrophysiologic and setisory threshold testing confirms the neuropathic effects on the median nerve of the elevated pressures which result from flexion and extension of the wrist.
The evidence strongly suggests, then, three significant ergonomic concepts must be incorporated into any strategy for
prevention of keyboard-associated CTS. Attention to these factors will minimize the pressures which develop within the carpal tunnel, thereby sparing the median nerve the deleterious effects of those pressures. First, is maintenance of the wrist in ananatomically neutral position (defined as "the extended wrist is in line with the (dorsal) forearm": Manual of Orthopedic Surgery, American orthopedic association.) All available experimental evidence suggests that this position results in the least compression of the median nerve within the carpal tunnel. The link between ischemic compression and the functional and trophic changes observed in peripheral nerves is equally clear. It is reasonably assumed that minimizing compression-induced ischemia reduces the probability of median nerve neuropathy.
Second, is the limitation of repetitive flexion-extension stresses at the wrist. Such motions not only result in transient pressure increases, but also subject the median nerve to microtrauma at the proximal and distal margins of the flexor retinaculum. The work of Nathan et al notes the critical significance of the edges of the overlying and compressing ligament as the site of conduction blocks.
And third, is minimizing the tension developed on the flexor tendons in the wrist. As noted by Smith et al, the carpal canal pressure rises as the tendons have increasing tension applied to them, acutely compressing the median nerve. Moreover, as noted by Goldman (Goldman, RH: Cumulative traumas syndrome: An occupational hazard. Emerg Med, 25-45, Jan. 30 1991,) such reptitive strains on the tendons may result in inflammation and later hypertrophy of the sheath, further increasing pressures within the snug carpal tunnel. Although possibly transient initially, such deleterious effects become cumulative and chronic with repetitition over long work-times.
Inflammatory tenosynovitis has been strongly associated with CTS by a number of authors. Lipscomb noted evidence in more than half of his series (Lipscomb PR: Tenosynovitis of the hand and the wrist: carpal tunnel syndrome, de Quervains's disease, trigger digit. Clin Orthop 13:164-181, 1959) and Phalen noted thickening of the flexor
synovium in 203 of 212 operated wrists (Phalen, GS:The carpal tunnel syndrome:clinical
evaluation of 598 hands. Clin Orthop Rel Res 83:29, 1972.) Indeed, Mosley et al, cite flexor synovitis as the most common etiology of CTS (Mosely LH, Kalafut RN, Levinson
PD and Mokris SA: Cumulative trauma disorders and compression neuropathies of the
Page (6) Medical Report by Brian O'Malley M.D.
Upper extremities, p.376. In Kasden ML (ed): Occupational Hand & Upper Extremity Injuries and Diseases. Philadelphia, Hanley & Belfus, 1991.) Both repetitive finger and
wrist flexion and hyperextension have been implicated in such tendinitis; a physician will
elicit pain over the volar aspect of the wrist with each of these manipulations in making the diagnosis of digital flexor tenosynovitis. Repetitiveness of task, forcefulness of exertion,
and awkward positioning are cited by Chipman et al as the keyprime etiologic factors in mechanically induced tendinitis (Chipman JR, Kasdan ML, and Camacho DG: Tendinitis of the upper extremity. p. 404, in Kasden ML Ibid.) Therefore, reducing the frequency and force of wrist excursions in flexion and extension, can be expected to minimize both the acute and chronic pressures on the median nerve in its vulnerable section beneath the flexor retinaculum.
It has been suggested over the years, based on casual observation, that uInar deviation of the wrist is another significant provocation for CTS. More recently, proponents of the Herzog-Moss Wrist Compression Mechanism (Pinkham J: carpal tunnel sufferers find relief with ergonomic designs. occup. Health & Safety 57(9):49-53, 1988) cite the displacemefits of the carpal bones during uInar deviation as reducing the cross sectional size of the carpal tunnel and compressing the median nerve. This study, based on "CT scans and dissections", has not been published.
Contradictory evidence on this point is provided by Silverstein et al (SilJverstein BA, Fine LJ and Armstrong TJ: Occupational factors and carpal tunnel syndrome. Am J Ind Ned 11(3):343-58, 1987) in the most extensive evaluation to date of job characteristics as correlated with CTS. Detailed analysis of repetitive movements of 652 workers in a wide range of jobs, provided evidence for the primary role of highly repetitive wrist tasks in this problem. When these tasks additionally required high force, the statistical risk was even higher. However, ulnar deviation showed only a slight, and not significant, correlation with cases of CTS.
While is is intuitively attractive, the hypothesis concerning ulnar deviation must be considered tentative. Direct experimental approaches are needed to test the effect on carpal canal volume and pressure, and on median nerve function.
The FLEX-REST keyboard support device is designed in conformity with the knowledge of these basic priciples. The keyboard has been dropped below desk level, to permit the hands to be level with, or lower than, the elbows. This position reduces the
tension in the flexor tendons of the hand, which is noted to rise as the elbow flexes. At the same time, the keyboard is tilted away from the operator, (with the rear edge lower than the front,) permitting the wrists to maintain neutral position. Without this "backward tilt," a lowered standard keyboard will actually result in greater wrist extension, increasing the
Page (7) Medical Report by Brian O'Malley M.D.
risk of CTS. The uniquely adjustable angulation permits each typist to custom-configure keyboard support, according to desk and chair height, body proportion and individual comfort.
.
Furthermore, the adjustable palm-rest bar permits support of the hands during
pauses in typing, while allowing only slight wrist extension in the process. Typing and
momentary rests may alternate, with minimal change from neutral angulation. A slight
wrist flexion suffices to resume typing postion. The palm-rest bar position permits arm/hand weight to be carried at the level of the proximal thenar and hypothenar
eminences, where pressure will not be on the median nerve. Typists who are not trained to
maintain the wrists straight are actually prevented from falling into an incorrect, hyperextended posture, by the use of this palm- rest bar.
Not all professional typists develop CTS. However, screening programs, to predict who will be afflicted, at this time are in their infancy, limited to detection of the earliest symptoms and objective signs of the neuropathy. There are certainly a large number of well defined individual predispositions; rheumatoid arthritis, diabetes mellitus, alcoholism, hypothyroidism, pregnancy and obesity are among the most frequent. Many individuals with CTS have none of these; occupational stresses appear to be the only etiologic factors. It is expected that, by reducing the cumulative stress at the wrist, the FLEX-REST will provide effective prophylaxis for typists who might otherwise be destined for difficulty.
It must be noted that several other cumulative trauma syndromes related to protracted keyboard use have been described. Although less dramatic than carpal tunnel syndrome, the sheer frequency of these injuries makes them significant occupational hazards. Each will be noted, with particular reference to how the FLEX-REST
addresses the problem preventively.
Prolonged tension on the muscles of the neck is a frequent cause of lateral neck and posterior shoulder pain. The increased incidence of cervicobrachial disorders in keyboard operators has been noted (Mosely et al, op cit.) The trapezii, primarily, and levator scapulae, to a lesser degree, are subject to the stress of carrying the weight of the upper extremities during typwriting, while maintining an almost constant functional position (Travell, J.G, and Simons, Myofascial Pain and Dysfunction. Baltimore, Williams and Wilkins, 1983: pp.189, 342.) The FLEX-REST provides an arm support device, the adjustable palm -rest bar, enabling the typist to utilize the many brief pauses during data entry (while checking work, readinq source material, etc.) to unload the shoulder girdle. Interruption of sustained muscle tension is recognized as effective in the prevention of fatigue and strain. As previousl,y noted, a desirable neutral position for the wrists is maintained during such rests. Further protection from overuse strains of the trapezii comes from the lowered keyboard position (ibid p. 198.)
Page (8) Medical Report by Brian O'Malley M.D.
The deltoid muscles show increases in strain as the type writer keyboard is raised, according to Lundervold (in Travell and Simons, ibid, p. 433 ) The development of active
trigger points there may result in deep deltoid area pain, and limited range of
motion of the shoulder.
Stresses on the myofascial units of thee elbow are greater as the degree of elbow flexion increases. So too, is tension on the cubital tunnel of the medial elbow, containing the ulnar nerve, this is the site of another common compression neuropathy affecting the hands. Not only is there compression of the nerve during elbow flexion; it is stretched as much as 3 cm. (Pechan J et a1, cited in Kasden ML op cit.)
With respect to each of these stresses, the lowered and backward-tilted keyboard provides a more comfortable and less traumatic positioning for the operator.
In summary, the FLEX-REST keyboard support device:
Encourages maintenance of a neutral wrist position, both while typing and during pauses, in order to prevent transient pressure increases within the carpal canal.
- Minimizes repetitive flexion-extension motions, to limit flexor tendon microtrauma, which causes the swelling and chronic pressure elevations of tendinitis, and;
-Maintains the forearms in a lowered position which further reduces the stress and tension on the finger flexors.
The fulfillment of these ergonomic criteria, which are so amply supported by a wealth of research evidence, can be expected to reduce the incidence of carpal tunnel syndrome in at-risk professional typists.
Rev. 3/25/91
Page (1) of 1995 Medical Report by Brian O'Malley M.D. UPDATE 1995
"Recent studies on the significance of wrist and arm position in the
pathogenesis of carpal tunnel syndrome." .
Brian O'Malley, M.D.
MARCH 1995
Our understanding of the mechanism of injury in carpal tunnel syndrome is
becoming much clearer, as numerous researchers around the world focus their attention on
this disorder. This attention is spurred on by the apparantly epidemic scale of workplace-
related disability, particularly in regular keyboard users. Carpal tunnel syndrome has now
become synonymous with "power" keyboarding... "flying fingers" is now seen as
potentially crippling. " (Chong L "Solving "White Collar" pain problems. " Occupational
Health and Safety, 1993 62 (9)11&20.
In the present paper, I will update my earlier work ("Keyboard-associated carpal
tunne syndrome. " 1991) with summaries of the relevant findings of the recent research.
The evidence suggests a unifying hypothesis regarding the pathophysiology of carpal
tunnel syndrome.
In a key study entitled "Soft-Tissue Injuries Related to Use of the Computer
Keyboard," Pascarelli and Kella studied 53 subjects, each of whom had spent the
major portion of their day at a computer keyboard, each disabled from performing
their work by pain, or by sensory or movement disorder of the upper extremity. Most
common complaints were forearm pan, more often extensor than flexor, as well as
elbow, wrist, hand, and thumb pain.
On examination, myositis of the extensor and/or flexor forearm was found in
80%; epicondylitis of the elbow in 33%; carpal tunnel syndrome in 28%; and
Deouervain's disease of the wrist in 22%.
The most common aberrant wrist position noted, in their videotaped study of
these 53 patients, was dorsiflexion (extension) in 43%. They observe that
"malpositioning the wrist during use of the hand can lead to a variety of injuries. " The
exaggerated extension of the wrist results in "increased friction and shearing of the
flexor tendons in or near the carpal tunnel," as well as for the extensor tendons, on the
other side of the wrist, below the extensor retinaculum. This causes an increased
work load for the forearm muscles which power the fingers. Combined with the high-
frequency repetitive nature of this effort, this positioning "contributes to the muscle
injury characteristic of CID'S (cumulative trauma disorders) with swelling,
tendemess, pain, loss of dexterity and endurance, and ensuing microscopic changes in
muscles which appear to result in shortening ofthe muscle bundles. "
Page (2) of 1995 Medical Report by Brian O'Malley M.D.
They emphasize the critical importance of what they term "intrinsic
ergonomics", poor technique, deconditioned (physical) state, and postural
misaligmnent; in the production of CID injury.
(Pascarelli, EF; Kella JJ. Soyt-tissue injuries related to use of the computer
keyboard A clinical study of 53 severely injured persons. Kathryn and Gilbert Miller
Health Care institute for Performing Artists, St. Luke's/Roosevelt Hospital Center,
New York NY J Occup Med. 1993; 35(5): 322-532.
Accumulating evidence that wrist position is a critical determinant of median nerve
functions comes from a variety of clinical observations.
A study of upper extremity cumulative trauma disorders in sign language
interpreters, found deviations of the wrist from the neutral position to be a significant
biomechanical risk factor. (Omer GE Jr. Median nerve compression at the wrist.
Carrie Tingley Hospital, Albuquerque, New Mexico. Hand Clin 1992 May;8(2):317-
24)
A wrist flexion-extension exercise was used in conjunction with nerve
conduction studies in the median distribution as a provocative test. With only four
minutes of this action, symptoms were elicited in half the patients and distal sensory
latency was significant increased. (Clifford JC and lsraels H; Provocative exercise
maneuver; its effect on nerve conduction studies in patients with carpal tunnel
syndrome; Department of Physical Medicine and Rehabilitation, University of
Western Ontario, London, Canada. Arch Phys Med Rehabil 1994 Jan; 75(1):8-11).
A prospective, blind trial comparing symptom relief of CTS with wrist
splinting in neutral, versus 20 degrees extension, found superior relief with the neutral
positioning. (Burke DT; Burke MM; Stewart GW. Cambre A Splinting for carpal
tunnel qyndtome: in search of the optimal angle. Department of Medicine; Louisiana
State University Medical Center; New Orleans Arch Phys Med Rehabil 1994
Nov; 75(11):1241-4.
A series of investigations has served to bring a much more clear picture of the
anatomic and pathophysiologic changes that occur within the carpal canal with deviation
of the wrist.
Precise open measurements of the carpal canal arch during surgery for CTS
demonstrated a reduction in transverse diameter with wrist flexion and extension.
With the flexor retinaculum intact, the trapezium and hammate bones moved closer
together with wrist deviation.
Page (3) 1995 Medical Report by Brian O'Malley M.D.
(Garcia-Elias M. Sanchez-Freijo JM; Salolo JM;
Lluchal. Dynamic changes of the transverse carpal arch during flexion-extension of
the wrist: effects of sectioning the transverse carpal ligament Department of
Orthopedic Surgery, Hospital General de Catalunya, Sant Cugat del Valles,
Barcelona, Spain. J Hand Surg (Am) 1992. Nov;17(6):1017-9.
A modification of the classic clinical diagnostic maneuver, Phalen's test,
performed with the wrist held in full extension, rather than full flexion, for one
minute, was shown to cause significantly higher intracarpal canal hydrostatic pressure.
Patients with CTS and normal controls each showed median sensory response
prolongation; although the patients showed significantly greater impairment.
(Wemer RA ; Bir C; Arnstrong TJ Reverse Phalen's maneuver m an aid in
diagnosing carpal tunnel syndrome. Department of Physical Medicine and
Rehabilitation,, University of Michigan Medical Center, Ann Arbor. Arch Physmed
Rehabil 1994 Jul; 75(7): 783-6
In a study designed to evaluate the clinical maneuvers used to provoke CTS
symptoms, researchers found that direct pressure over the carpal canal could
reproduce symptoms in a mean of 9 seconds (with 150 mm Hg pressure) to 19
seconds (with only 100 mm Hg pressure.)
(Williams TM Mackinnon SE, Novak CB, McCabe S, Kelly L. Verification of
the Pressure provocative test in carpal tunnel syndrome. University of Toronto,
Ontario, and Washington University, St. Louis, MO. Ann Plast Surg 1992;29:8-11.)
The pressure within the carpal canal was continuously measured in twenty-
two CTS patients and six controls. Patients with early and intermediate, active CTS
had higher pressures in neutral than controls. Full flexion raised the pressures; full
extension raised them even higher. After a one-minute exercise consisting of repeated
flexion-extension, the pressures in the CTS patients remained elevated above baseline
for at least ten minutes, while the control wrists showed no elevation in carpal canal
pressure.
Of interest, the group of patients with advanced CTS did not show the
pressure increases, suggesting that the chronic nerve damage in this setting, with
fibrosis and deymelination, no longer involves the same active vascular and/or
inflammatory process.
(Szabo RM Chidgey LK Stress carpal tunnel pressures in patients with
carpal tunnel syndrome and normal patients. Dept orthopedic Surgery, Univ, of
California, Davis and University Flordai, Gainsville. J Hand Surg 1989;14A:624-
7. )
Page(4) 1995 Medical Report by Brian O'Malley M.D.
In a ground breaking study &om Japan, high-resolution MRI scans of the wrist
were performed, using a contrast agent which demonstrates tissue vascular supply, to
study the perfusion of the intact, live median nerve. Patients with CTS and controls
were studied, with wrists in neutral, flexed, and extended positions. Normal controls
had a gradual uptake of contrast over time in the nerve, consistent with adequate
perfusion of the tissue. In patients with CTS, scanning suggested the development of
ischemia in the median nerve, as the wrist was repositioned from neutral to either
flexion or extension. This radiologic change was accompanied by an aggravation of
CTS symptoms. Edema or ischemia was noted in nearly all of these nerves in the
neutral position. The images showed no compression of the median nerve by the
flexor retinaculum.
The authors suggest that this work supports the theory of Sunderland, that the
primmy cause of CTS is impairment of median nerve vascular supply, progressing
from venous congestion, to anoxic endothelial damage and nerve eden4 to impaired
blood supply and hypoxia.
(Sugimoto H; Miyaji N; Ohsawa T Carpal tunnel qmdrome; evaluation of
median nerve circulation with @vnamic contrast-enhanced MR imaging. Department
of Radiology, Jichi Medical School, Tochigi-ken, Japan. Radiology 1994
Feb;190(2) :459-66.
[Ref. Sunderland S The nerve lesion in the carpal tunnel syndrome. J Neural
Neurosurg Psychiatry 1976; 39:615-26. ]
A synthesis of these research findings may be suggested. The cross-sectional area
of the carpal tunnel is decreased as the wrist deviates from neutral, with a resultant
increase in the intracanal pressure. Repetitive motions add a dynamic component of
tendon swelling, further increasing tissue pressure. As previously noted by Gelberman et
a1, pressures as low as 20-30 mm Hg are sufficient to cause nerve ischemia, and the
median nerve in CTS patients is subjected to pressures well above this with wrist
deviation. During and after prolonged ischemia, permeability of the vascular endothelium
increases, and edema of the nerve develops. This, of course, further accelerates the rise in
presure, and vascular compromise worsens. Over time, nerve injury results in irreversible
axonal degeneration, fibrosis and demyelination. The poor outcomes of surgical correction
at this stage are a disappointment to patient and surgeon alike.
[Ref Gelberman RH et al. "Carpal tunnel Syndrome". A scientific basis for
clinical care. Ortho Clin NAmer 1988 Jan, 19(1):115-24.]
It has long been noted that the threshold for compression neuropathy is
lowered by injury elsewhere to the same nerve. This is referred to a double (or
multiple) crush syndrome.
With particular respect to the median nerve; compression above to the wrist
may be produced in the proximal forearm.
Page (5) 1995 Medical Report by Brian O'Malley M.D.
Contraction of the pronator teres muscle occurs with forearm supination and
in increased by elbow flexion. Contraction effort of the flexor digitorum superficialis
muscles is exaggerated by typing with the wrist extended. Both actions tend to cause
pressure increases and median nerve compression proximally. Abnormal tension in the
muscles of the neck and shoulder area may further contribute to the problem and the
symptom complex.
(MacKinnon SE, Novak CB. Clinical Commentarv: Pathogenesis of
cumulative trauma disorder. Division of Plastic Surgery, Department of Surgery,
Washington University School ofmedicine, St. Louis, MO. J Hand Surg1994
Sept;19A :873-881.
The overwhelming evidence from years of clinical study is that the neutral position
of the wrist is associated with the lowest pressure on the median nerve. To this, we can
now add as ergonomically desirable that elbow flexion is minimized. Indeed, with a goal
of the alleviation ofthe entire symptom complex of upper extremity cumulative trauma
disorder, the facilitation of a posture which reduces muscle tension and abnorma1joint
positioning is a rational step.
The Flex-Rest user sits with shoulders retracted and dropped, elbows partially
extended. With the positioning of the lowered keyboard and in conjunction with the aid
of the negative tilted keyboard combined with an adjustable palm rest,wrists are
maintained in neutral position Although no preventive strategy known to medicine is
I00% perfect in reducing CTD's (cummulative trama disorders), the material cited, suggests in the battle againstkeyboard-associated upper extremity CTD the use of the Rex-Rest , places the odds for better health, on the side of the keyboard operator.
Brian O'Malley , M.D.
Provincetown Medical Group
Provincetown, Ma. 02657
Medical School
Suny Health Sciences Center, Brooklyn , New York
M.D. Cum Laude 1974
Internship and Residency: .
New England Deaconess Hospital, Boston, Massachusetts, 1974-77
(Internal Medicine )
Certification:
National Board of Medical Examiniers 1975
American Board of lnternal Medicine 1977
(con't next page)
Page (6) 1995 Medical Report by Brian O'Malley M.D.
Hospital Staff Affiliations:
New England Baptist Hospital, Boston, Massachusetts
Special Assistant to Charles Fager, M.D.,
Lahey Clinic Department of Neurosurgery, 1977.
New England Deaconess Hospital, Boston, Massachusetts
Active staff, Department of Medicine, 1978.
Cape Cod Hospital, Hyannis, Massachusetts,
Courtesy Staff, Department of Medicine, 1979.
Memberships:
Alpha omega Alpfia Honor Medical Society; Election 1973
Massachusetts Medical Society
Important note: This is report is an opinion only and makes no claims as to medical treatments or cures for the treatment of CTS (carpal tunnel syndrome), or any other medical situation. Always seek the advise of your own personal professional health care provider if you are experiencing a potential medical problem. We can not respond to specific health questions as they must be directed to your primary care health provider to insure your best health.
Flex-Rest, Inc.
Worcester, Ma. 01605
Product Page & Medical Report: http:\\www.flexrest.com