Elbow flexor and extensor muscle weakness in lateral epicondylalgia. Clinical commentary.

Elbow flexor and extensor muscle weakness in lateral epicondylalgia.

Coombes BK, Bisset L, Vicenzino B. Elbow flexor and extensor muscle weakness in lateral epicondylalgia. Br J Sports Med. 2012;46:449-453.

Abstract

Background

Lateral epicondylalgia; lateral (LE) is one of the common and complex elbow problems in athletes as well as in the general population.¹ Pain with reduced grip strength and weakness of muscles mainly wrist extensors are the cardinal signs of LE.² Many studies have focused on the strength of upper limb (UL) kinetic chain segments such as MCP, wrist, and shoulder associated with LE.^3-6 But surprisingly, elbow flexors and extensors are not evaluated by any studies yet, despite its biomechanical importance in UL kinetic chain, functional movements, and sporting activities.

Objective

To identify and evaluate the possible elbow flexor and extensor muscles weakness associated with LE compared to the healthy population.

Methods:

One hundred and fifty participants were recruited for a cross-sectional study. Inclusion criteria were: unilateral elbow pain over lateral epicondyle for longer than six weeks, pain aggravated with palpation, gripping and resisted wrist and/or finger extension. Exclusion criteria were: elbow pain due to other conditions such as carcinogenic, radiohumeral or neurological, recent fractures, corticosteroid injections or physiotherapy treatment. Fifty-four healthy participants were recruited as age and gender-matched controls.

All the participants were tested for the isometric elbow extension and flexion strength on both affected and unaffected sides with 30 seconds intervals alternatively. Controls were also tested on both sides. Strength was measured at the level of ulna styloid process in Newton(N) by using a digital dynamometer attached to a purpose-built apparatus, in a standing position with elbow flexed at 90⁰ and forearm in neutral rotation. Participants were not allowed to do any extraneous movements like trunk or scapular movements. They were instructed to keep their wrist and fingers relaxed during the test. Data were analyzed by performing analysis of covariance (ANCOVA) by using SPSS 19. The covariates were; age, gender, and BMI of the participants.

Results:

Strength differences (affected–unaffected) greater than 2.09 and 3.14 N for extensor and flexor respectively were considered significant with 95% confident and represent true change.

Results revealed significant side difference between lateral epicondylalgia and control groups. Elbow extensor strength (-6.54N, 95% CI, -11.43 to -1.65, p = 0.008, SMD -0.45) and flexor strength (-11.26 N, 95% CI, -11.59 to -2.94, p = -0.009, SMD -0.46). However, within LE group, only extensor strength deficit between sides was significant with -2.94 N difference results.

Conclusion

Patients with unilateral lateral epicondylalgia have weaker elbow flexor and extensor muscles strength in comparison to healthy population. This deficit should be considered for the evaluation, performance enhancement, injury prevention and better therapeutic prognosis of LE.

Commentary

Introduction

Lateral epicondylalgia (lateral epicondylitis) is presented with a relatively uncomplicated clinical picture to diagnose in most of the cases.⁷ However, it has been emerged as more complex, multi-structural pathology rather than a simple lesion at common extensor tendon origin at lateral epicondyle.^1,7 Because of high incidence rate among athletes as well as in general population, complex pathophysiology, lack of conclusively determined evidence-based approach of management and high recurrence rate have shouted the need of more research on LE. Although research on LE extends across anatomical, biomechanical and clinical literatures,⁷ most of the studies have focused on physical impairments found during clinical examinations and effort to propose the most successful rehabilitation approaches based on the reduction of pain and thereby addressing the physical impairments such as muscles weakness, stiffness and/or functional impairments.² Many studies have reported marked weakness of wrist flexion and extension, grip strength, fingers extension and shoulder abduction, internal and external rotation strength.^3,5,6,8 However, much surprisingly, this paper is the first study to evaluate elbow flexor and extensor strength in LE compared to a healthy individual. In my opinion, elbow being an important segment in upper limb kinetic chain, its biomechanical and functional importance in upper limb movement and its proximation to injury site may support the importance and possible clinical implications of this study in lateral epicondylitis treatment.

 

Discussion

This is a well designed and controlled study investigating the strength of elbow flexor and extensor muscles in lateral epicondylalgia. The findings of this study are in line with previous studies of wrist, forearm, and shoulder muscle strength in LE participants.^3,5,6,8 By recruiting the participants from the general community through media advertisements and a matching control group according to age, gender and dominant arm has increased the generalizability of this study.⁹ Also, a number of participants under study (n=150) and control group (n=54) and comparison of the affected limb with same side limb of the control group have improved validity and reliability of the report.¹⁰ The authors have well controlled the effect of dominance bias in the result by comparing the same side strength between LE and control group. Lower elbow extensor deficit and failure to detect elbow flexor deficits within LE group and relatively higher deficit compared to control group demonstrated by this study have a clinical value that assessment of elbow strength by comparison between sides may underestimate true deficit in the result which may provide the wrong picture of muscle strength and hence resulting in incomplete rehabilitation. Although this study is not able to provide conclusive mechanism of relationship between elbow muscle strength impairment and LE, several previous studies on upper limb musculature imbalance, upper limb kinetic chain, functional biomechanics of joints of upper limb, moment arm of muscles crossing elbow joint, muscular activity, overuse or disuse of muscles suggest the possible relationship between elbow muscles weakness in LE.

 

A global upper limb (UL) weakness exists and is highly possible in patients with the presentation of lateral epicondylalgia.³ Alizadehkhaitayat et al³ integrated the electromyographic activity of UL musculature along with strength tests to assess the role of muscular imbalance in the pathophysiology of LE. Although this study didn’t study elbow muscles activity, in particular, the report has concluded that there is widespread UL weakness in LE and is associated with muscle activation imbalance mainly of Extensor Carpi Radialis (ECR). In UL kinetic chain, strength or motor deficits at particular segments may be dissembled in short-term by the compensation at other segments but when this compensation remains for a longer period, it may lead to overactivity, fatigue and hence muscle weakness with decreased performance.^11,12 Significant rotator cuff weakness observed by Alizadehkhaitayat et al³ in LE patients suggests the involvement of UL kinetic chain which may create a global UL muscular weakness or imbalance. Since there is a close kinetic relation between elbow and shoulder,¹² elbow muscles may be involved in compensation activity for the weakness/imbalance of ECR and other forearm muscles in LE. Kibler¹³ has demonstrated the essential link and importance of muscular balance or coordination of musculoskeletal components of scapula, shoulder, elbow, and wrist during the tennis stroke that transfers force generated from the legs and trunk movement as energy to more rapidly moving distal segments of wrist and hand. However, the strength pattern of elbow muscle group in LE has never been investigated, which is a big gap to fill. So, this paper may be a big step forward to fill this gap.

 

Although many reports have suggested an etiological relationship between muscle imbalance and tennis elbow, it is not well defined yet about the possible muscle imbalances over the wrist-elbow-shoulder segments.⁴ Several studies have reported shoulder muscle imbalance in lateral epicondylalgia, which can result in a compensatory overuse of elbow joint and its components.^4,11,12 These report may suggest to the possible elbow muscle imbalance in LE caused by faulty joint mechanics in UL chain which may result in elongated or shortened muscles and hence weak and unused.⁴ Based on the moment arm measurement, An et al¹⁴ have demonstrated Brachioradialis, Biceps, Brachialis, and Extensor carpi radialis as the major flexors of the elbow joint. This report may indicate the possible overuse of biceps and other muscles to compensate for the weakness of ECR associated with LE during UL elbow flexion movements. The weakness of muscle can lead to compensatory overuse of other muscles, thereby developing a state of failure of agonist-antagonist relationship or balance.^15,16 This overuse, in turn, develop muscle imbalance causing a diminished participation of antagonist muscle, triceps in this case that leads to disuse atrophy.⁴ So, the UL muscular imbalance associated with LE may support the findings of this paper that weakness of elbow extensors and flexors exist in LE.

 

Recently lucado et al¹⁷ studied the potential pathomechanical factor in the etiology of LE in female tennis players and suggested the possible mechanical involvement of UL musculature that are not directly associated with symptomatic site in the development of LE. They demonstrated a small significant difference in elbow muscles compare to wrist and shoulder muscles which are in consistent with Coombes et al study. However, Lucado et al¹⁷ showed more significant weakness by side within the LE group in elbow flexors    (-10.2N, affected–unaffected) rather than elbow extensors. This may be due to the tennis players as the participants in the study that they may have maintained the triceps strength during their training and tennis playing as elbow extensors are more active than flexors to generate force during tennis strokes.¹⁸ As Coombes et al, this study cannot suggest the possible relationship between the muscle weakness and LE as this difference may be the result as much as for the cause of injury. But either way, these findings may have potential clinical value in terms of complete rehabilitation of this population, especially in case of athletes before they go back to high muscular balance and force demanding sports like tennis.

 

Kelly et al⁶ performed the electromyographic and cinematographic analysis of elbow function in tennis players with subacute LE and demonstrated the significant higher activity of ECRL during the preparation phase (28% compared with 13% MMT) and during ball impact (89% compared with 43% MMT) in injured athletes than in an uninjured group. A cinematographic study on tennis players with no LE done by Giangarra et al⁸ showed no flexion in the elbow with the elbow facing to the ground and wrist in a neutral position during ball impact during backhand stroke whereas increased flexion of the elbow (leading elbow) and extended wrist were seen in athletes with LE. This may suggest that LE may cause weakness of elbow extensors and hence athletes with LE are unable to maintain elbow extension compared to athletes without LE. Kelly⁶ also reported the significant overactivity of pronator teres during ball impact and early follow-through phases in LE athletes causing exaggerated pronation of forearm at ball impact. The cinematographic presentation of leading elbow may be due to the increased activity of biceps muscles as powerful supinator to balance the exaggerated pronator activity for stabilizing the racquet during ball impact. Small significant elbow flexors weakness reported in Lucado¹⁷ study with female players may be due to the fatigue of biceps muscles because of overuse of it to prevent excessive pronation of the forearm.

 

Clinical implications

The clinical implications of this study are relatively more important in the management of LE. Although some studies have included elbow muscles strengthening exercises in the rehabilitation of LE, many previous studies emphasized the forearm muscles and grip strengthening exercises only.² This study has definitely rooted the clinical importance of evaluation and functional rehabilitation of elbow muscles and whole UL strength deficits along with forearm muscles and grip strength in the complete program of lateral epicondylitis treatment. Also, it clearly shows the evidence for the possible increased strength of dominant arm compared to non-dominant side and importance of regaining of this increased strength in dominant arm, especially in athletes group for complete rehabilitation and reduces recurrence rate in LE.¹⁹

 

Limitations and future considerations

This study has assessed only isometric elbow muscle strength in particular elbow, shoulder and wrist positions. So, future studies should consider various aspects of motor function in order to fully understand the functional motor deficits of elbow muscles in LE. Also more reliable methods like surface and fine wire EMG to examine muscle imbalance and twitch interpolation, a technique to assess if muscle is contracting fully or not during the muscle test by the superimposition of an electrical stimulus to examine muscular activity²⁰ should be used to improve the reliability of the findings of the study.

 

As LE is more common in athlete group (tennis players, badminton, baseball players etc), future studies should be done in athlete groups as well to determine the effect of elbow muscles weakness in LE in sports performance. Also, impact analysis study⁹ and possible mechanotherapeutic effect of exercise interventions²¹ should be considered in future studies to determine the relevance of UL muscles strengthening exercises in tissue healing, recovery and return to full sporting action following LE injury.

 

Conclusion

This study has failed to establish the causal relationship between its findings of elbow muscles weakness and lateral epicondylalgia. However, it has definitely spotlighted the necessity of more studies on this aspect which has important clinical implications in the assessment and lateral epicondylitis treatment.  Previous studies done on UL muscle imbalance, upper limb kinetic chain relation, anatomical study, moment arms of different muscles across the elbow joint and their functions and functional biomechanics of upper limb movement have also supported the possible association of elbow muscles weakness with LE. The results of this study have clearly shown the significant upper limb musculature imbalance associated with LE which is in consistent with previous studies and encourages the physiotherapists to include whole upper limb rehabilitation including elbow flexors and extensors rather than focusing only in the forearm muscles in lateral epicondylitis treatment. Also this study is able to aware physiotherapists about the possible effect of side dominance-related differences during the strength measurement and comparison between the sides of a patient with unilateral presentation of lateral epicondylalgia. More systematic and scientific studies are necessary to determine the conclusive causal relationship between elbow muscles strength impairment and LE, its effect in functional movement of upper limb which may be milestone to define and establish mechanotherapeutic effects of exercises in LE and hence to develop more effective and complete lateral epicondylitis treatment program. With the findings of this study and other studies discussed, I am convinced with the possible elbow flexors and extensors strength impairment in patients with LE and shall be including strengthening and stretching exercises of all upper limb muscles according to need after careful assessment of shoulder, arm, forearm and hand muscles during lateral epicondylitis treatment.

 

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