Lateral Epicondylalgia (Part 2)
October 9th 2007 12:35
Biomechanical Factors in Acquiring Lateral Epicondylalgia
As mentioned earlier, the causes of lateral epicondylalgia could encompass a variety of factors- from cumulative trauma and biomechanical risks over the forearm and the cervical vertebrae, to the peri-articular and neurological nature of pain. These shall be discussed in this section of the discourse.
Cumulative Trauma and Overuse of the Wrist Extensor Muscles and Tendons
A common factor for acquiring lateral epicondylalgia is cumulative trauma over the wrist extensors particularly the ECRB especially on its origin. Mellor (2006) refers to this as an overuse syndrome prevalent in the fourth decade of life. Basically if an individual is exposed to an occupation or activity that involves awkward or repetitive motions of the wrist emphasizing extension, or has been doing excessive and forceful gripping activities, he would likely be one of those patients complaining of lateral elbow pain.
Why would grasping affect our wrist extensors? If we do grasping, are we not using our flexors solely instead of our extensors? The answer to the second question is no. Grasping or gripping involves synergistic contraction of both the flexors and the extensors. When our finger flexors contract to hold on to an object, our extensors stabilize the wrist into extension to prevent it from being pulled into flexion. This is what we call the tenodesis effect (Smith et al, 1999). Why is it necessary to stabilize the wrist into extension? If the wrist is pulled into flexion together with the fingers, the flexors that generate the force for us to be able to hold an object are being subjected to active insufficiency (due to excessive muscle shortening). In this condition these muscles would not be able to generate sufficient force to carry out grasping and manipulation of an object. And with this, the assumption that the wrist extensors may be affected by forceful grasping is confirmed.
But why does it seem that the extensors on the forearm are more traumatized than the flexors during forceful grasping or wrist motions? Actually both muscle groups can be traumatized due to the mentioned faulty movements, given the facts that these muscles are expected to exert great effort in stabilizing and moving a very short lever (which is the hand), and that they are inserted proximally to the lever’s axis (which is the wrist joint). If we are to consider the proximity of the muscles’ insertions to the wrist (obviously very near), we can discover why the muscles are obliged to produce relatively large amount of force in moving the wrist and the hand. Furthermore the answer to this question lies on the maximum strength nature has given these two groups of muscles. According to Matthijs et al (1994), the average maximum strength of the wrist extensors is only 5.39 kg, while the average maximum strength of the flexors is almost triple of that of the extensors-13.4 kg. Using these figures we can see how significant the difference between the strength of the two groups is. The flexors are naturally stronger than the extensors. And if there would be a mechanical insult that would inflict these forearm muscles, the first group to succumb is the extensor group.
TO BE CONTINUED>>>
As mentioned earlier, the causes of lateral epicondylalgia could encompass a variety of factors- from cumulative trauma and biomechanical risks over the forearm and the cervical vertebrae, to the peri-articular and neurological nature of pain. These shall be discussed in this section of the discourse.
Cumulative Trauma and Overuse of the Wrist Extensor Muscles and Tendons
A common factor for acquiring lateral epicondylalgia is cumulative trauma over the wrist extensors particularly the ECRB especially on its origin. Mellor (2006) refers to this as an overuse syndrome prevalent in the fourth decade of life. Basically if an individual is exposed to an occupation or activity that involves awkward or repetitive motions of the wrist emphasizing extension, or has been doing excessive and forceful gripping activities, he would likely be one of those patients complaining of lateral elbow pain.
Why would grasping affect our wrist extensors? If we do grasping, are we not using our flexors solely instead of our extensors? The answer to the second question is no. Grasping or gripping involves synergistic contraction of both the flexors and the extensors. When our finger flexors contract to hold on to an object, our extensors stabilize the wrist into extension to prevent it from being pulled into flexion. This is what we call the tenodesis effect (Smith et al, 1999). Why is it necessary to stabilize the wrist into extension? If the wrist is pulled into flexion together with the fingers, the flexors that generate the force for us to be able to hold an object are being subjected to active insufficiency (due to excessive muscle shortening). In this condition these muscles would not be able to generate sufficient force to carry out grasping and manipulation of an object. And with this, the assumption that the wrist extensors may be affected by forceful grasping is confirmed.
But why does it seem that the extensors on the forearm are more traumatized than the flexors during forceful grasping or wrist motions? Actually both muscle groups can be traumatized due to the mentioned faulty movements, given the facts that these muscles are expected to exert great effort in stabilizing and moving a very short lever (which is the hand), and that they are inserted proximally to the lever’s axis (which is the wrist joint). If we are to consider the proximity of the muscles’ insertions to the wrist (obviously very near), we can discover why the muscles are obliged to produce relatively large amount of force in moving the wrist and the hand. Furthermore the answer to this question lies on the maximum strength nature has given these two groups of muscles. According to Matthijs et al (1994), the average maximum strength of the wrist extensors is only 5.39 kg, while the average maximum strength of the flexors is almost triple of that of the extensors-13.4 kg. Using these figures we can see how significant the difference between the strength of the two groups is. The flexors are naturally stronger than the extensors. And if there would be a mechanical insult that would inflict these forearm muscles, the first group to succumb is the extensor group.
TO BE CONTINUED>>>
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