Biomechanics of Lateral Epicondylitis

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Description/Definition[edit | edit source]

Lateral Epicondylitis, also known as ‘Tennis Elbow,’ is one of the most common upper extremity musculoskeletal disorders, causing elbow pain and dysfunction[1]. This condition is often characterized by pain and tenderness over the lateral epicondyle of the elbow and is estimated to affect 1-3% of the population, primarily the middle-aged population of both male and female[1][2]. Despite the name ‘tennis elbow,’ only 5% to 10% of affected individuals actually perform tennis[3]. Majority of injuries take place in manual labor activities involving the repetitive movement of the upper extremity[3].

Pathology/ Mechanism of Injury[edit | edit source]

Lateral epicondylitis was first classified as an inflammatory process, especially in its initial phase of injury [1][4]. However, histology has shown that lateral epicondylitis is actually a form of tendinosis; a degenerative process of the tendon[1][4]. This condition is associated with repetitive microtrauma to the extensor tendon attached at the lateral epicondylar region of the humerus, primarily the extensor carpi radialis brevis (ECRB) being the most affected muscle[1]. The supinator and other wrist extensor muscles including, the extensor carpi radialis longus, extensor digitorum, extensor digiti minimi, and extensor carpi ulnaris can also be involved[1][4]. Pain is generally due to the overloading of the extensor tendons due to gradual increase in force[4]. As force applied at the tendons increase, the tendons begin to stretch and increases stress over the extensor tendons attached at the lateral epicondyle[4]. Excess stress can cause micro-trauma, resulting in micro-tears at the attachment site[4].  Without proper rest and recovery, and overusing the extensors, multiple micro-tears can occur and eventually lead to degeneration of the tendon, also known as tendinosis[4]. As a result, pain is a common symptom and varies from intermittent and low-grade pain, to continuous and severe pain[4].

Manual Labour Activities[edit | edit source]

Lateral epicondylitis has been reported to result in pain at the lateral humeral epicondyle, involving the forearm extensors, as well as the presence of direct/ indirect tenderness over the lateral site, usually provoked by resisted extension of the wrist or 3rd finger[1][2][4]. It is known to be correlated with a variety of manual labour activities exposed to high physical loads, forceful and repetitive activities, and extreme non-neutral postures of the hand and arms[3][5][6]. Studies concluded that occupational physical factors including repetitive movements of the hands and wrists, lifting heavy loads > 5 kg, activities demanding high hand grip forces, and the use of vibrating tools all pose a risk for lateral epicondylitis [6][7]. Generally, the highest incidence rates of lateral epicondylitis, are found in occupations involved in more manual work and high demands of the upper extremity such as mechanics, butchers, painters, construction workers, etc.[5][8]. Workers exposed to high physical demands, in particular workers involved in performing manual labour requiring repetitive or constant elbow or wrist motion and lifting are at a higher risk for lateral epicondylitis compared to workers without these physical demands[6]. Other studies conducted on active workers from different manufacturing sites (i.e. electronics, automotive, medical, healthcare), found that workers exposed to longer durations of forceful exertions (> 5 times/min), and forearm supination of > 45 degrees, presented symptoms of lateral epicondylitis[5]. Modifications in physical risk factors can help reduce or prevent the risk of upper extremity MSDs[7].

Non-manual Labour Activities (Computer Use)[edit | edit source]

Lateral epicondylitis can also be present in non-manual labour jobs such as desk work[9]. Studies found that due to repetitive actions involved in computer use, typing, and gripping/squeezing the mouse for long periods of time, can cause strain to the forearm extensors and result in pain at the elbow[9]. Common risk factors for this type of work is often associated with increasing hours of mouse and keyboard use, and awkward posture involving increased wrist extension and positioning the keyboard above elbow height[10][11][12].

Recent studies show good ergonomic workstations can aid in reducing muscular strain on the forearm extensors and reduce the risk of lateral epicondylitis[11][12]. Implementing adjustable work chairs, increasing frequency work breaks, the use of arm supports, and practicing good posture, are all good methods for preventing upper extremity MSDs and reducing pain[9][10]. Recent studies conclude that the use of a wide keyboard arm support, compared to a narrow keyboard support (< 7.5 cm) can benefit in reducing the relative height above the elbow, thereby reducing wrist extension and the possible risks of elbow disorders[10][11]. Workers using keyboards placed 12 cm from the table edge and have neutral wrist posture when using the mouse, present lower risks of developing hand/ arm disorders, compared to workers using keyboards > 3.5 cm from the table edge, and radially deviate their wrist (> 5 degrees) while using the mouse[11]. Without proper rest and continuing repetitive movements of the hand, wrist and forearm, it will eventually overload the tendon and produce inflammation and pain at the elbow[9].

Many of these occupational cases often result in at least one other upper extremity MSD of the shoulder, hand or wrist, along with lateral epicondylitis. It is suggested that lateral epicondylitis not only affects the elbow or forearm region, but also adjacent body regions of the shoulder, hands and wrist due to the repetitive and strenuous use of the upper extremity[5].

Skilled vs. Unskilled Tennis Players[edit | edit source]

Although lateral epicondylitis is termed as ‘tennis elbow,’ this condition can be common in other racket sports involving strenuous upper extremity use and repetitive movement of the arm[13]. However, it is also estimated that one-half of all tennis players will suffer from tennis elbow at one point or another[14]. Tennis players primarily involve the use of wrist extensors in all stroke actions (i.e. serve, forehand, and single-and-doubled-handed backhand strokes), which can be an explanation for the cause of this condition[15][16]. All strokes involve the wrist extensors, primarily the ECRB muscle which show high activity throughout the stroke actions, especially during the acceleration phase before ball-racket impact[16][17]. High wrist extensor activity, along with high force and high speed at the elbow, can place increased stress at the elbow site which may be a reason for symptoms of this condition[15][16][18]. Factors including player experience, player ability, racket type, and stroke mechanics can play a role in the risk of developing lateral epicondylitis[14]. Inexperienced/ novice players have a higher chance of developing lateral epicondylitis based on faulty stroke techniques compared to skilled/experienced tennis players[14]. During a single-handed backhand swing, skilled players tend to impact the ball in a hyper-extended wrist (~ 23 degrees from neutral) and continue to place the wrist in extension throughout impact[17][19]. However, novice players will impact the ball with the wrist in flexion (~ 13 degrees), while maintaining the wrist in flexion following impact[17][19]. These results indicate that skilled players activate concentric (shortening) contractions of the wrist extensors during impact, while novice players will contract eccentrically (lengthen)[17]. As the wrist is repeatedly in a flexed position, the wrist extensors are rapidly stretched and ultimately lead to tendon overload and aggravation of the tendons attached at the lateral epicondyle[17][19]. Since eccentric contractions are more common in muscle injury, novice players are at a higher risk of developing lateral epicondylitis due to the eccentric contractions of the forearm extensors[17]. Given the wrist extensors already lengthened due to the flexed wrist position in novice players, the extensors may stretch beyond the plateau of the length-tension relationship. As a result, exposing connective tissue of the extensors to high loads from the ball-racket impact and pose a risk of injury[17].

Doubled-handed Backhand vs. Single-handed Backhand[edit | edit source]

Studies have also suggested that the double-handed backhand stroke is preferred over the single-handed backhand stroke, as a result of a helping arm (non-dominant) providing support for the dominant arm, which can aid in transferring energy to the other arm[20]. Studies suggest players who perform the double-handed backhand stroke over the single-handed stroke rarely develop lateral epicondylitis[20]. The dominant arm in a double-handed backhand stroke exhibits greater pronation than the single-handed backhand[20]. The pronator teres muscle demonstrates a greater activity during the acceleration phase and may be a biomechanical advantage in reducing risk of injury[20]. Because the dominant arm shares the racket, the non-dominant arm may cause more rotation as the racket moves forward, which will create more pronation of the dominant arm[20]. As the arm is more pronated, the elbow ligaments are wound more tightly in this position, providing more arm stability and strength, and allowing forces to be transmitted at the elbow rather than being absorbed by the tissues of the elbow[20]. Because there is a lack of a non-dominant arm support in the single-handed stroke, a “leading elbow” position of the dominant arm can occur, seen in improper stroke techniques[20]. As a result, the arm is less pronated, allowing more laxity of the lateral elbow ligaments, producing higher risk of injury[20].

Due to these findings, it is considered that players using a double-handed backhand stroke, as well as practicing proper stroke techniques can benefit from preventing upper extremity MSDs and lateral epicondylitis[17][19][20].

Summary[edit | edit source]

  • Lateral epicondylitis is common upper extremity MSDs in athletes and work-related activities
  • Involves the forearm extensors, primarily the extensor carpi radialis brevis (ECRB)
  • Characterized by pain and tenderness over the lateral epicondyle of the humerus
  • Due to micro-trauma of the extensor tendons from repetitive movement of the upper extremity
  • Common in manual labour activities involving high physical exposure, constant elbow flexion/extension, forearm supination, heavy lifting, wrist bending/twisting, and long durations of forceful exertions
  • Common in non-manual labour jobs (i.e. desk jobs) involving repetitive and long hours of mouse and keyboard use, and awkward postures
  • Changes or modification in workstations, breaks, and use of arm supports can help limit risk of LE
  • Novice tennis players more common developing LE than skilled players due to faulty stroke mechanics
  • Novice players will eccentrically contract forearm extensors while skilled players will concentrically contract extensors
  • Double-handed backhand strokes are preferred over single-handed backhand strokes
  • Proper stroke techniques can help reduce risk of LE

References[edit | edit source]

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