Common Occupational Hand and Arm Disorders: a Primer for the Luthier

Common Occupational Hand and Arm Disorders: A Primer for the Luthier

By David H. Lang MD

Introduction

The study of occupational disorders is a science. These disorders have significant social, financial, legal and personal ramifications. The past several decades have seen an astonishing increase in the amount of occupationally related injuries. Musculoskeletal disorders attributed to workplace cumulative trauma increased nine to ten fold between 1981 and 1991 and account for approximately 60% of all work related injuries.[1] These statistics have occurred despite the activities of various government work safety organizations. They continue to increase.

There are no studies specific to occupational disorders in luthiers. There is, however, no reason to believe that luthiers are somehow immune from these disorders. Personal communication with several luthiers has demonstrated that these various disorders do exist commonly among those in lutherie.

This article will present a useful informational overview of common occupational hand and arm disorders for the luthier. It will attempt to cover the topic by reviewing germane hand anatomy, ergonomic principles and practice, common overuse disorders with respect to symptoms and treatment, as well as present basic guidelines of when to seek out medical advise. This article is not intended to provide a prescription for self-diagnosis and treatment. Some of these disorders can lead to serious downtime and incapacity even when treated appropriately. Please use it as an informational guide.

Definitions

Any meaningful discussion of work related disorders require the definition of terms to be used. The following is a list of terms and their definitions in layman’s language used in this article and in the literature on work related injuries.

Cumulative Trauma Disorder (CTD)

Any disorder believed to be related to repetitive force or strain over time. This is a very general term without precise medical meaning and should largely be avoided for its lack of precision. Equivalent terms include repetitive strain injury and repetitive motion disorders.

Musculoskeletal Disorder of the Workplace (MSD)

This term includes a myriad of disorders that are believed to occur as a in the context of work. These same disorders can also commonly occur outside the workplace unrelated to work. However, when these disorders occur as a result of workplace exposure MSD applies.

Ergonomics

The science dedicated to decreasing the risk of musculoskeletal disorders due to abnormal stresses and exposures by improving body position and tool design by task.

Unique Needs of the Luthier

Unfortunately, most luthiers cannot completely eliminate risks of workplace disorders. Few of the tools of our art were designed to minimize trauma and have remained unchanged in design for hundreds of years. The hand builder is probably at the most risk- especially if volumes are high and hours are long. The CNC builder is probably at less risk due to less direct exposure. One only needs to consider the chisel, the backsaw, the graver and the sanding bowl as typical tools. These tools are used with the wrist in a deviated or non-straight position. It is hard to imagine how these tools of our art could be modified to keep our wrists in a proper ergonomically correct position. There are countless examples of ergonomically poor positions assumed while building instruments. Many of these high-risk postures can be modified to decrease risk while some cannot.

Overview of Hand Anatomy for the Luthier

Photo 1

The hand is truly one of the architectural marvels in nature. Its design allows transmission of light and incredibly large forces, execution of gross and graceful movement and communication by gesture or touch. 30 bones, approximately 30 muscles, several dozen joints and three nerves do all of this. The main purpose of the arm is mostly to position the hand in space and transmit force to the hand.

The finger is a linkage of three bones (phalanges) and one metacarpal bone in the palm. Two muscles that originate in the forearm and one in the palm flex each finger. One muscle in the forearm and two in the hand extend each finger. Each finger contributes about twenty-five percent of total handgrip strength.

The thumb is unique to mammals. Its structure and ability to oppose the thumb is unique to primates. This ability to oppose our thumb is a combination of flexing and rotating the thumb about its axis. Opposition allows pinching between the thumb and fingertips, gripping and firm grasping. The thumb accounts functionally for approximately one-half of the hand. It has two phalanges and one metacarpal. One muscle flexes the thumb, seven muscles extend it, three muscles allow for opposition and one serves the pinch function.

The wrist is of sort of universal joint composed of eight carpal bones, the two forearm bones, and a myriad of ligaments and complex joints. It allows flexion, extension, hand and forearm rotation as well as deviation of the hand toward the thumb and small finger. The bones of the wrist are as a group assembled in a arch which is bridged by a ligament forming the carpal tunnel.

In general, muscles that extend or straighten the fingers, thumb and wrist lie on the back (dorsal) side of the forearm. Muscles that flex the fingers, thumb and wrist lie on the front (palmer) side of the forearm.

Wherever a nerve or tendon crosses a joint a strap like or belt like structure known as a retinaculum is present. This retinaculum functions as a guide for one or more structures as they cross the joint. Analogous structures would be a cable guide on the brake cable of a bicycle or the line loops on a fly rod. In all cases the guide holds the moving structure against the structural element and prevents bowstringing. These structural features have implications in hand disorders such as carpal tunnel and the trigger finger. Additionally, whenever a tendon crosses a joint or passes under a retinaculum the tendon is covered with a lubricating tissue known as synovium. Synovium is a wispy thin, exceedingly slippery tissue which functions in health as “grease” and thickens with inflammation in disease states. It is this diseased synovium that underlies most of the work related disorders and their symptoms.

Ergonomic Principles and Practice for the Luthier

The science of ergonomics is the study of designing the tool or the job task to fit the person doing the task. Unfortunately, there is no one single ergonomic factor that has been shown to cause or for that matter prevent repetitive-motion disorders. In general there are four goals in ergonomics that are widely accepted to improve ergonomic design of work places and tools. Those goals are decrease the force needed to perform the task, avoid awkward positions while performing the task, avoid repetition when able to do so, and decrease exposure to vibration.

Methods of decreasing the force needed to use a tool most often start by modifying the tool handle. For firm or power grip the optimum diameter handle is one that can be gripped with the thumb not quite touching the finger tips. In general, this represents a diameter of about 1 _ to 2 inches.

Photo 2 Appropriate handle diameter and length

This is dependant on hand size. Small hands need smaller tool handles for power grip. For precision or pinching work the tool handle should be about _ inch in diameter.

Photo 3 Precision pinch tool size

The tool handle should be at least 5” long for power grip and at least 4” long for precision pinch. No tool should end with the handle pushing into the hollow part of the palm.

Photo 4 Tool hand should not end in middle of palm

Most hand tools will be the most comfortable when they weigh less than two pounds. Precision tools are usually much lighter. A comfortable tool is usually a “correct” tool.

Hand and arm position are frequently poor with hand tools. In general, it is preferred to work with the wrist in a neutral position (not bent) and avoid sustained or repetitive extremes of thumb, finger and wrist positioning. Furthermore, it is preferred to keep the arms and elbows to the side of the body. The hand should not be used in positions that widely spread the hand and fingers. All work should be done limiting reaching to 1 _ to 2 feet at most and keep work at waist height. Place parts in vises clamps or fixtures to avoid clumsy tool or hand positions. Use power tools when appropriate to avoid repetition.

Photo 5 Example of poor wrist position

Photo 6 Example of good wrist position

Repetition is inherent in musical instrument building. Probably the most direct method of reducing repetition is by automation of repetitive tasks. Less obvious methods of reducing repetition is by taking breaks and rotating workers or tasks that cause symptoms of pain or strain. Learning to recognize the physical signs of straining and taking a break before or immediately after symptoms of strain develop is helpful.

Prolonged exposure to vibration has been implicated in the development of disorders of tendons, blood vessels and especially nerves. Short term or prolonged disturbances in sensation in the hand can be caused by prolonged exposure to vibration of power tools. This problem can be avoided by decreasing exposure to the offending power tool, switching to hand tools and using anti-vibration padding such as sorbothane.

In short, there is no such thing as an ideal ergonomic tool or work station . The ideal ergonomic tool is one that is comfortable for the user, minimizes prolonged stresses on the hand and arm and avoids awkward positioning of joints. Adherence to these principles and common sense will probably go further toward preventing or minimizing repetitive motion problems than adherence to a strict ergonomic formulas and protocols.

Common Overuse Disorders

Workplace Nerve Injuries

Injury to nerves in the arm and hand is extremely common in the work place. Aside from lacerated nerves the so-called nerve compression syndromes are a common workplace injury. Nerve compression or “pinched nerve” is usually attributed to a combination of factors. Tasks requiring sustained force, awkward position and repetition are most commonly cited as causes for nerve compression. The nerve compression is usually due to swelling of surround tissue (synovium) or due to mechanical stress locally applied to the nerve during work tasks. Common disorders such as diabetes and thyroid disease can predispose a worker to these disorders at the workplace. These diseases are thought to “weaken” the nerves and make them more susceptible to nerve compression. The most common work related nerve compression injuries other than lacerations are carpal tunnel syndrome, cubital tunnel syndrome and bowler’s thumb.

Carpal Tunnel Syndrome

Carpal tunnel syndrome (CTS) is by far the most common of all overuse conditions of the hand. It is responsible for 30-50% of all reported workplace injuries and affects about one million people each year. In the workplace it is felt to be caused by any combination of repetition and sustained awkward positions of the wrist which in turn leads to inflammation and swelling of the synovium surrounding the median nerve. The median nerve passes through the wrist through the carpal tunnel and supplies sensation to the thumb, index, long and ring fingers. The median nerve also controls several of the muscle of the thumb. The carpal tunnel is a literal tunnel bounded by the wrist bones forming an arch which is covered by a ligament (a retinaculum). The median nerve travels through this tunnel with the tendons and synovium of the fingers. If the synovium swells the nerve is “pinched” and leads to symptoms.

The symptoms of carpal tunnel syndrome can include pain, disturbance of sensation, weakness and swelling. The pain of CTS can affect the fleshy part of the thumb base and the fingers, the wrist and occasionally the elbow or shoulder. The sensation disturbance usually affects the thumb index and long and ring finger.

Photo 7 Distribution of abnormal sensation in CTS

Photo 8 Site of compression in CTS

It usually does not effect the small finger or the back of the hand. The sensory disturbance is usually felt as numbness or tingling on the thumb side of the hand. This can occur during sleep, especially in the early morning hours, during driving, reading or while working. Patients will often complain of weakness clumsiness or frequent accidental dropping of objects. Some with carpal tunnel syndrome will complain of swelling of the hand. In severe cases the numbness in the hand can be constant and the weakness in the hand can lead to muscle loss that is permanent.

Cubital Tunnel Syndrome

Cubital tunnel syndrome is the second most common type of “pinched” nerve in the hand and arm. It is due to a combination of repetitious elbow flexion and extension and/or sustained elbow flexion. This is due to a pinching of the nerve at the elbow at the site coloquieally known as the funny bone. The common sensation due to striking this area is due to striking a nerve (not a bone) called the ulnar nerve. The pinching of the ulnar nerve causes the symptoms of cubital tunnel. Similar to carpal tunnel the ulnar nerve travel around the inside of the elbow under a retinaculum.

The symptoms of cubital tunnel can include elbow and forearm pain, numbness in the small and ring finger and weakness or clumsiness in the hand. Most people with cubital tunnel syndrome complain of numbness on the small finger side of the hand. Like CTS, cubital tunnel can range from minor occasional symptoms to constant symptoms and permanent functional loss.

Bowler’s Thumb

Bowler’s thumb is numbness and possibly pain due to direct compression of the nerves in the thumb or finger. In bowlers it is due to pinching of the nerves in the thumb on the edge of the drilled thumb hole on the ball. Direct injury to the nerve in the fingers can occur due to tool holding which pinches the nerve between the tool and the firm bony structures of the finger or thumb. This is a relatively rare problem.

Common Workplace Tendon Injuries

Trigger Finger

A trigger finger is medically known by the descriptive medical term stenosing tenosynovitis. Stenosis refers to a constriction or closing down. Teno means tendon. Synovitis is inflammation or swelling of the synovium. A trigger finger is essentially tendonitis of the finger tendons. This results in enlarged synovium catching beneath a retinaculum of the finger. This presents as pain in the finger and/or palm in early cases and a catching or locking of the involved finger when making a tight fist. Often individuals with a trigger finger will complain of a single finger locked in the fist position upon arising in the morning which painfully unlocks when pulled upon. Usually the pain of a trigger finger is located between the palm crease (life line) and the finger. Often a trigger finger feels as if it is double jointed.

Photo 9 Normal finger tendon and synovium

Photo 10 Locked finger with swollen synovium

Trigger fingers usually begin after unusually repetitious or strenuous use of the hand and finger. Often pain is the first and only sign of a problem. The trigger finger then typically progresses to clicking. This disorder affect fingers and thumbs. Several medical problems can present with a trigger finger. Most notable are diabetes and inflammatory arthritis. Most trigger fingers are not due to these diseases.

DeQuarvain’s Tenosynovitis

Dequarvain’s tenosynovitis is in many ways analogous to the trigger finger. It is due to repetitious or strenuous wrist movement. It seems to occur particularly often in repetitive movements of deviation of the wrist alternatively toward the small finger and thumb. This side to side movement elicits tenosynovitis of two of the wrist tendons as they pass under a retinaculum on the back of the wrist. Local pain is the first sign. This pain can be come quite disabling and can prevent even light use of the hand and wrist.

Photo 11 Location of tenderness in Dequarvain’s tenosynovitis)

Tennis Elbow

Tennis elbow is known medically as lateral epicondylitis. Unfortunately, this painful condition does not only occur in individuals that play racquet sports. It is thought to be due repetitious use of the wrist and elbow in a fashion that causes inflammation of the muscles that extend the wrist at their attachment at the elbow. These muscles attach at the outside point of the elbow (epicondyle). This is the typical location of the pain. Sometimes tennis elbow causes the elbow to feel stiff. Most often it is a long lasting condition that waxes and wanes over many months

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Work Place Disorders of Blood Vessels