Bleecker, Margit L. MD, PhD; Celio, Mark A. MA; Barnes, Sheryl K. MAc, OTR/L
Many workers use computers for increasingly more hours and not at ergonomic workstations or employing ergonomic technique. Laboratory studies have measured the biomechanical stress on the upper extremities that occurs with keyboard/mouse use. Just the act of typing increases carpal tunnel pressure (CTP) that is further aggravated if the keyboard is struck with more force than necessary or if the palm is leaning on the wrist rest while typing.1–3 Mouse use increases CTP when the wrist is maintained in extension and when force is applied on the mouse buttons.3–5 Carpal tunnel pressure is also made worse by repeated mouse dragging tasks.4 Increased muscle activity in the shoulder occurs with mouse use next to the number keypad or on an elevated primary worksurface.6–8 Keyboard and mouse use is also associated with increased muscle activity in forearm extensors because of full pronation of the forearm.9 The clinical outcomes of prolonged exposure to these biomechanical stressors from keyboard/mouse use have received little attention.
In 1993, Pascarelli and Kella10 reported on 53 patients with soft-tissue injuries related to keyboard use that focused on keyboard technique as the source of the symptoms. At that time, only two persons were using a mouse and 14 had begun keyboard use on a manual typewriter, whereas 33 were trained on an electric typewriter or computer keyboard. The most frequent upper extremity diagnoses were lateral/medial epicondylitis, de Quervain syndrome, and carpal tunnel syndrome (CTS). By 2001, Pascarelli and Hsu11 examined a larger group of computer users and the major health outcomes were neck and shoulder posture and neurogenic thoracic outlet syndrome (TOS).
Occupational epidemiological studies of keyboard/mouse users have primarily used the outcome of pain in the neck and/or upper extremities and its association with exposure.12 Some studies found a dose–effect relationship between duration of keyboard/mouse use and hand-arm symptoms,12–17 whereas others reported a dose–effect relationship with symptoms in the neck/shoulder area.18–21
Studies of students in secondary school and undergraduate and graduate programs found that over 50% had current upper extremity pain associated with computer use, most commonly in the neck/shoulder area that interfered with sleep and required use of medication.22–27 Computer use greater than 3 hours a day had significant odds of reporting symptoms that increased across quartiles of exposure.28
Despite considerable literature about what constitutes an ergonomic workstation and good work practices, workers, management, and health care providers are frequently unfamiliar with these ergonomic principles or do not effectively use them as part of the intervention. In the clinical setting, upper extremity disorders associated with intensive keyboard/mouse use are frequently addressed only with conservative medical management and work restriction or surgery. This approach may relieve symptoms but does not address the working condition that caused the problem. The Medical-Ergonomic Program was a natural progression from medical management programs developed for the meatpacking and the newspaper industries (MLB), where symptom onset was linked to the inciting ergonomic stressor in the workplace. Correction of the ergonomic stressors along with conservative medical management had a high rate of symptom resolution. The Medical-Ergonomic Program in the clinical setting identified the ergonomic stressor(s) associated with the upper extremity medical condition(s) and addressed both in the course of medical management. This allowed for follow-up of the identified conditions and response to the implementation of ergonomic intervention besides educating patients about ergonomic principles regarding their workstation and keyboard/mousing techniques. The following is a case series of 56 patients who presented with upper extremity symptoms and with occupational exposure to intensive keyboard/mouse use.
Patients in this case series are from our Medical-Ergonomic Program at the Center for Occupational and Environmental Neurology and included individuals with upper extremity/neck symptoms associated with intensive keyboard/mouse use at work and who did not have underlying medical conditions or hobbies to account for their symptoms. Patients were referred by the employer or the insurance company or were self-referred. The usual medical history was obtained and also an occupational history. If clinically indicated after the examination, nerve conduction studies were performed. Patients received treatment for their diagnoses and had an ergonomic evaluation at a training workstation with appropriate changes made to their overall technique and their own workstation setup.
Clinical Criteria Used for Upper Extremity Diagnoses
Carpal tunnel syndrome required primary symptoms of paresthesias in the median nerve distribution (frequently noted upon awakening), shaking hand-relieved symptoms, complaints of decreased grip strength, and dropping items. Diminished pin sensation in the median nerve (index finger compared to fifth digit) distribution and positive Tinel or Phalen. Weakness in the abductor pollicis brevis was not a requirement. Nerve conduction studies had to show prolonged median sensory nerve peak latencies and/or prolonged median mid-palmar latency with normal ulnar nerve sensory studies.29
Cubital tunnel syndrome included sensitivity to palpation of the ulnar nerve at the elbow with a positive Tinel sign. Nerve conduction studies had focal slowing in the ulnar nerve motor conduction velocity across the elbow with absolute slowing of less than 50 m/s and motor conduction velocity across the elbow was more than 10 m/s slower than motor conduction velocity in the forearm segment.30 If the physical examination was positive for ulnar nerve irritation at the elbow but the nerve conduction study was normal, the diagnosis was ulnar neuritis.
De Quervain's tenosynovitis required a positive Finkelstein test consisting of pain over the radial styloid when the thumb was held tightly and the wrist is bent in the ulnar direction. The involved tendons are the abductor pollicis longus and extensor pollicis brevis, where they enter the fibro-osseous sheath at the distal radius.
Lateral epicondylitis needed focal pain where the inflamed tendon of the extensor muscles (most commonly the extensor carpi radialis) in the forearm attached to the lateral epicondyle of the humerus. Pain increased with elbow extension and wrist flexion or resisted wrist and finger extension.
Impingement syndrome of the supraspinatus tendon was present when shoulder abduction with the thumb pointing to the floor produced pain and decreased range of motion (Neer's impingement sign). There frequently is pain in the subacromial area or over the upper lateral arm were the supraspinatus inserts onto the humerus.
Myofascial Pain Syndrome (MPS) is the diagnosis applied to overused muscles with active trigger points (TrP). When the motor endplate region in a muscle becomes dysfunctional from overload and fatigue, a nodule (TrP) develops at the motor end plate that is located in a taut band. The taut band may be felt by rubbing lightly across the direction of the muscle fiber. With an active TrP there is spontaneous pain, and with a latent TrP there is pain when pressure is applied. An active TrP and latent TrP keep the muscle shortened that may be appreciated by visual inspection and by palpable increased tension in the muscle. TrPs have referred pain, for instance an active TrP in the forearm extensors may refer pain down the dorsum of the forearm to the wrist, hand and include the middle and ring fingers. The involved muscle is weakened, and pain prevents it from reaching a full stretch.31
Thoracic outlet syndrome in the setting of keyboard/mouse use is usually the result of compression of the lower roots of the brachial plexus and subclavian/axillary artery/vein by a shortened anterior scalene, middle scalene, and/or pectoralis minor muscles from their involvement in MPS. The patient reports inability to work with arms at or above shoulder height because of the onset of fatigue, pain, or paresthesias in the ulnar distribution in the upper extremity. Adson's maneuver or elevated arm stress test (with arm in “surrender” position, the hand is slowly opened and closed for 3 minutes producing patient's usual symptoms) are positive. With neurogenic TOS, nerve conduction studies showed a diminished amplitude in the medial antebrachial cutaneous nerve to less than 6.1 μV or the interside amplitude ratio greater than 1.8.32 The diagnosis of TOS could be made with a positive history and examination as TOS may result from compromise of only a vascular structures though this is less common than neurogenic TOS.33
The therapeutic modalities employed included trigger point and myofascial release, cryotherapy (counter irritant with menthol and plant extracts, ice, ethyl chloride, etc), and heat (heat packs, topical agents containing capsaicin, arnica cream, etc). Corrective tape that can stretch to 30% to 40% of the resting length and once applied will last for 3 to 5 days. The purpose of the tape was for mechanical correction whereby mechanoreceptors are stimulated from the high tension and downward pressure of the tape. The second approach was fascia correction that focused on “holding” the myofascial release in the position obtained.34 Management of neuropathic pain included acupuncture, transcutaneous electrical nerve stimulation (TENS), Salonpas patches (Hisamitsu Pharmaceutical Co., Inc, Saga Tosu, Japan), Lidoderm patches (Endo Pharmaceuticals, Inc, Chadds Ford, PA) and a topically applied mixture of wintergreen alcohol with aspirin. Wrist and elbow splints for nocturnal use and wristlets for work35 were recommended as needed. The nocturnal wrist splints for CTS held the wrist in the neutral position and not in the functional position.36 A home stretching program included posture reeducation.
The ergonomic evaluation performed by the occupational therapist (S.K.B.) determined the presence of ergonomic stressors that could contribute to the upper extremity symptoms and diagnoses. Table 1 is a checklist that evaluated posture and keyboard/mousing technique that was influenced by aspects of the workstation setup such as location of the keyboard tray, monitor, and adequacy of seating support. The ergonomic setup (Table 1) was explored individually. It was important during this process for patients to feel and perceive the symptoms that accompany keyboarding/mousing activities. Feeling symptoms allows for the recognition of how the ingrained habits need to be changed. For example, many patients with neck and shoulder symptoms typed with arms fully extended only to complain that their shoulders and neck were getting tight while demonstrating their typing technique. It was at this symptomatic moment that a more ergonomically appropriate keyboard placement was instituted closer to the patient at elbow height with shoulders relaxed, elbows at the side, and neutral wrist position. The patient was able to notice the immediate change in their symptoms changing both the mindset and the body memory for the task of typing. They returned to their own workstation, ready to make changes, and with the body memory of how it felt to type comfortably. A similar approach was used for the other items on the checklist in Table 1.
All analyses were completed using SPSS v.16.0 (SPSS, Inc, Chicago, IL). Descriptive statistics and graphics were performed to check for extreme outliers and determine whether each variable of interest was appropriate for use in parametric statistical analysis. Cases were stratified according to age into a younger group (Age ≤ 35; n = 20) and an older group (Age > 35; n = 36).
Table 2 presents demographic data for the whole group and stratified by age. Overall the patient group was highly educated with occupations that included administrative assistants, architect, claims examiner, communication specialists, editors, journalists, lawyers, programmers, reporters, and systems engineers. All had jobs with intensive keyboard/mouse use, upper extremity symptoms were usually present for many weeks, and as expected more years of employment existed in the older group. Only patients in the younger group reported routine daily use of a computer in college. Men made up the majority of the younger group (80%) but the minority of the older group (33%). Body mass index (BMI) was elevated (≥25) in 39.3% of the whole group.
Symptoms were reported more frequently in the hand/wrist, shoulder/neck, and forearm region with similar prevalence in both age groups (Table 3). It was common for patients to have more than one upper extremity diagnoses with 92% having between two to five diagnoses. The distribution of diagnoses was 1 diagnosis in 1 (2%), 2 diagnoses in 10 (18%), 3 diagnoses in 20 (35%), 4 diagnoses in 12 (21%), 5 diagnoses in 10 (18%), 6 diagnoses in 2 (4%), and 7 diagnoses in 1 (2%).
The most prevalent diagnosis was MPS of the shoulder/neck muscles followed by MPS in the forearm extensor muscles (Table 4). More patients had MPS in the shoulder/neck and forearm than symptoms in these areas because the examination found latent trigger points with shortened muscles that were not reported by the patient since spontaneous pain was not present. Of the 10 diagnoses in Table 4 only cubital tunnel syndrome was different by age, as it was not present in the younger group.
The gender prevalence for CTS was 32% in male patients and 54% in female patients. Patients with CTS (n = 24) had a mean BMI of 26.0 ± 4.74 compared to the rest of the group (n = 32) with a mean BMI of 23.9 ± 3.64.
Patients with TOS (n = 30) had positive electrodiagnostic findings supporting neurogenic TOS in 22 (11 younger and 11 older), whereas 8 had vascular TOS, with a positive history and examination but no electrodiagnostic findings for TOS.
CONSERVATIVE MEDICAL MANAGEMENT
Conservative medical management was similar in both age groups with posture reeducation for rounded shoulders and chin jutting forward in 98%, home stretching and strengthening program in 98%, myofascial and trigger point release in 96%, topical cyrotherapy in 79%, nocturnal splints in 66%, acupuncture in 59%, corrective taping for 45%, topical agents for heat in 32%, and the TENS unit for pain management in 27%.
As posture was a major problem, this was addressed in all patients as part of their home program and during therapy. The focus was on stretching for shortened muscles involved in MPS. It was important not to aggravate this condition with resistive exercises such as weight lifting. Patients were taught to perform acupressure over trigger points to release them using tennis balls, tools for deep pressure massage or digital pressure. Corrective taping was successful when used for mechanical and fascia correction. Overall patients obtained more relief with topical cooling agents than heat. The use of nocturnal splints was primarily for the diagnoses of CTS, de Quervain, cubital tunnel syndrome, and ulnar neuritis. Acupuncture, TENS, and topical agents were beneficial in treating pain.
ERGONOMIC STRESSORS AND EFFECTIVE INTERVENTIONS
The prevalence of ergonomic stressors was similar in both age groups and is discussed below, whereas the effective interventions are listed in Table 5.
Mouse technique in 89% involved improper placement of the mouse that resulted in shoulder abduction, flexion, or external rotation with elbows not at the side. Wrist was in extension and mouse was clutched with too much force. Typing technique in 88% included leaning on the wrist rest while typing, using too much force when striking keys, thumbs held in extension, frequent ulnar deviation of the wrist, and typing with straight fingers. Adjustable keyboard tray if present was too high or absent in 84%, resulting in hiked shoulders and dropped wrists over the edge of the keyboard. Monitor location in 51% was either too high resulting in neck extension or too far away resulting in leaning forward and chin protrusion or the monitor was not aligned with the keyboard resulting in a nonneutral neck position. Chair support for upper or lower back was inadequate in 75% and armrests were usually too high. Work methodology for 73% reported no breaks. Symptoms at deadlines were present in 57%. Increased workload for a variety of reasons such as coworker absence, downsizing of workforce, or a new project on top of existing work load explained why some older patients (55%) developed symptoms after years on the job symptom free. Handwriting was a problem in 54% because of small circumference of writing utensil thereby increasing pinch force. Intensive keyboard data entry in 20% lacked upper extremity support to offload upper extremities.
After conservative medical treatment and ergonomic intervention 19 of 20 younger patients and 31 of 36 older patients improved. One younger patient and 6 older patients had persistent symptoms, or they required surgery. Overall CTS responded to conservative medical intervention and removal of the ergonomic stressors. Carpal tunnel syndrome required surgery when the condition was too advanced at the time of entry into the Medical-Ergonomic Program. Once symptoms responded to treatment, an important guideline for the patient was to pay attention to symptom onset in the future, as they may revert to old habits. Depending upon symptom location, they were now able to go through a checklist of potential causes and intervene early to reverse the onset of symptoms.
Our case series of intense keyboard/mouse users compared to the initial study of Pascarelli and Kella10 had increased prevalence of CTS (43% vs 28%), involvement of shoulder/neck muscles (88% vs 43%), forearm extensor muscles (80% vs 45%), and lateral epicondylitis (20% vs 17%) and decreased prevalence for de Quervain (13% vs 36%). Pascarelli and Kella had no cases of ulnar nerve impairment at the elbow, TOS, or impingement syndrome as we found. Nevertheless, when we compare our present results to Pascarelli and Hsu series of upper extremity complaints in keyboard/mouse users in 2001,11 pain in the forearm extensors was similar (80% vs 73%), along with impingement syndrome (11% vs 12%), whereas TOS (54% vs 70%) and cubital tunnel syndrome (14% vs 54%) was higher in their series and finally CTS (43% vs 8%) was much higher in our series. The Pascarelli and Hsu (2001) diagnoses were based upon history and physical examination with no electrodiagnostic testing that may have accounted for some of the differences. In the original Pascarelli and Kella10 study, the presence of median nerve compression in CTS was confirmed with electrodiagnostic studies.
Posture. As in the Pascarelli and Hsu study,11 poor posture was a major ergonomic stressor in our patients. Rounded shoulders associated with a shortened pectoralis minor that may compress the neurovascular bundle, as it is traveling into the arm and produce symptoms of TOS. A shortened anterior and middle scalene muscle from the maintenance of the neck/chin forward posture may also directly compress the brachial plexus and axillary/subclavian artery. The shortened anterior and middle scalene muscles can also elevate the first rib causing the nerves and blood vessels to be stretched over the rib and compressed behind the clavicle resulting in symptoms of TOS.
Myofascial pain syndrome, the most common etiology for symptoms in our group of patients was not unexpected, as some muscle groups were overloaded and fatigued from constant use. For those not familiar with the condition, the intensity of the discomfort from active TrPs reported by the patient such as deep throbbing, stabbing, burning, knife-like, and cramping may seem unrealistic. Even latent TrPs once palpated may generate significant pain.31
MPS shoulder/neck. Myofascial pain syndrome in the shoulder/neck muscles was commonly present in the upper extremity controlling the mouse, as the shoulder was frequently in abduction and/or flexion. This arm position was elevating the scapula and rotating it laterally and anteriorly, which resulted in the development of trigger points in muscles surrounding the scapula from chronic activation, namely, the levator scapula, the rhomboids, the upper and middle trapezius, and the supraspinatus. Correcting this stressor with mouse positions that kept the shoulder relaxed at the side had dramatic results. Another ergonomic stressor for the shoulder/neck region was using a keyboard positioned too high or from using armrests that were too high for support when typing. A prospective study of newly hired computer users reported a 10% prevalence of neck/shoulder symptoms at entry and 57.5% incidence rate at 12 month follow-up.20 A second publication with this population found neck/shoulder symptoms produced by keying with elevated elbows that was corrected by lowering the armrests.37 By contrast in our patients, the presence of armrests interfered with typing posture and technique and did not allow the shoulder neck area to relax leading to increased MPS in the shoulder/neck area. Many chairs do not have armrests that can be adequately lowered, and therefore they were removed. Nevertheless, in our patients with intensive keyboard/mouse use such as data entry or working on deadline, dynamic arm supports adjusted to the correct height provided symptom relief because of reduced static muscle load, as demonstrated by Odell et al.38
MPS Forearm Extensors. Myofascial pain syndrome involving the forearm extensor muscles resulted from forearms maintained in full pronation and wrists in extension. Intramuscular electromyography recording from the extensor carpi radialis muscle found higher amplitudes of motor unit action potentials in full pronation than in the better semipronated position.9 Extensor carpi radialis activity was also increased with wrist extension,9 a position commonly maintained with mouse use. The split keyboard supported by other studies39,40 allowed for tenting of the keyboard that placed the forearm in a semipronated position and decreased wrist extension. The NUDATA study found the incidence of right forearm pain related to intensive use of the mouse and keyboard.16
Carpal tunnel pressure. Magnetic resonance imaging studies of carpal tunnel dimensions with different postures found wrist extension resulted in the smallest carpal tunnel area and carpal tunnel volume compared to the neutral position.41 Wrist extension greater than 32.7° during mouse use increases CTP beyond that known to influence nerve function (30 mm Hg).4,5 Increased CTP is further aggravated by repeated dragging tasks4 that required force applied to mousing buttons and to the side of the mouse.3 Small changes in fingertip load on the mouse buttons translates to large increases in CTP.3 This may explain the increased risk of CTS in the right hand with time spent gripping a mouse device.17,42 These risk factors for increased CTP were present in 89% of our patients.
Carpal tunnel syndrome. Individuals with CTS have CTP more than 30 mm Hg in a neutral wrist position.43,44 Preoperatively, when patients with CTS had more precise intracarpal pressure measurements at the level of the hook of the hamate, the mean resting pressure was 56 mm Hg and a mean pressure during maximum grip force of 1151 mm Hg.45 Forty-three percent in our group of patients had CTS and all had stressors for increased CTP, as described in the previous paragraph, from incorrect mousing and keyboard techniques.
Body mass index. Gender and BMI were not risk factors for CTS in this small group of patients. In 1582 patients younger than 63 years, BMI was a significant independent risk factor for CTS.46 In another study that focused on BMI and distal median nerve function, asymptomatic obese subjects (mean BMI: 35.5) compared to a thin reference group (mean BMI: 22.5) found no difference between the groups for CTP or the size of the median nerve at the wrist. Nevertheless, the median sensory peak latency was more prolonged in the high BMI group and correlated with cross-sectional area of the median nerve and with carpal tunnel pressure, a finding usually associated with CTS and not asymptomatic obese subjects.47
Much of the epidemiological literature trying to establish a relationship between keyboard/mouse use and onset of symptoms in the upper extremities/neck will frequently use pain as the outcome.16,18,19,21 Early in the development of MPS, the symptom of interest is tightness/motor dysfunction with a latent TrP that does not produce spontaneous pain. Patients may notice tightness/stiffness of the forearm extensors and in the muscles around the right scapula/neck area. Unless the latent TrPs are identified on examination, the involvement of these muscle groups will go unnoticed. Therefore, by using pain as the outcome, the latent TrP has to progress to an active TrP that has spontaneous pain. Also, MPS involving the muscles of the upper back, neck, and shoulder region are impossible to separate by region as trigger points from one area frequently refers to another.31 For example, the levator scapula, a muscle usually involved on the side of mouse use has its origin on the superior angle of the scapula and inserts on the transverse processes of cervical vertebrae 1 through 4 with active trigger points that radiate to the neck and shoulder.
The variability in the epidemiological literature may be due to how outcomes are defined and the large range in exposure of the ergonomic stressor. When mean mouse use was 6.1 hours per week and keyboard use 1.3 hours per week, there was no association between mouse use and neck/shoulder problems.18 This was a much lower exposure than in our patients suggesting enough recovery time occurred to prevent the development of chronic neck and shoulder pain. In contrast, 2826 students, aged 16 to 18 years, that used computers 31 hours a week complained of headaches and neck/shoulder problems related to computer use. When computer use was more than 56 hours per week, neck and shoulder symptoms increased dramatically with the addition of eyestrain and forearm symptoms in the female students.23 The addition of forearm symptoms in female students may reflect that women use a higher percentage of their strength with computer tasks.48,49 In graduate students, years of computer use and time spent using a computer more than 10 hours a week was associated with the development of pain within an hour of computing.22 Significant problems in our younger patients younger than 35 years could be related to the increased use of keyboard/mouse during their years in college, placing them at increase risk for upper extremity/neck problems when they entered the workforce and increased their daily keyboard/mouse use.
This clinical case series has limitations as all patients had reached a symptom severity that medical treatment was sought. The limited dose–effect relationship may reflect that all the patients were intensive keyboard/mouse users and the size of the group was small. Nevertheless, these patients did not have medical conditions or hobbies known to be associated with the outcomes. The ergonomic evaluation identified many stressors supported by the literature that when corrected had significant impact upon the patient's symptoms. Educating the patients was essential, as it empowered them to intervene at symptom onset in the future if there was a reoccurrence.
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