Effect of Elbow Position on Grip Strength in the Evaluation of Lateral Epicondylitis
By Dorf, Erik R Chhabra, A Bobby; Golish, S Raymond; McGinty, Jasmin L; Pannunzio, Michael E
Purpose: This study evaluated the maximum grip strength in a position of elbow extension versus flexion as a diagnostic tool in the assessment of a patient with suspected lateral epicondylitis (LE). Methods: From our database we identified 81 patients with grip strength measurements and the diagnosis of LE. From these patient records we collected grip strength measurements with the elbow in full extension and with the elbow in 90[degrees] of flexion for the affected and the healthy extremity. We then compared 2 values: the pretreatment grip strength in flexion and extension for the affected extremity and the pretreatment grip strengths of the nonaffected extremity compared with the affected extremity. Grip strengths were compared with paired and unpaired 2-tailed t tests.
Results: Grip strength was no different in flexion and extension for the healthy extremity and 29% stronger in flexion than in extension for the affected extremity. The affected arm averaged 50% of the strength of the healthy arm in extension and 69% of the strength of the healthy arm in flexion. These differences were statistically significant. An 8% difference in grip strength between flexion and extension was found to be 83% accurate in distinguishing the affected from the unaffected extremities.
Conclusions: The measurement of extension grip strength is a useful objective tool to aid in the diagnosis of LE. In patients with LE, the grip strength decreases as one moves from a position of flexion to a position of extension. (J Hand Surg 2007;32A:882-886. Copyright (c) 2007 by the American Society for Surgery of the Hand.)
Type of study/level of evidence: Diagnostic III.
Key words: Tennis elbow, lateral humeral epicondylitis, hand strength, grip.
In patients with lateral epicondylitis (LE), pain at the lateral epicondyle during power grip occurs because the extensor carpi radialis longus and the extensor carpi radialis brevis (ECRB) must work to counteract the flexion moment generated at the wrist by the digital and wrist flexors. Snijders et al1 measured the electrical activity of the wrist extensors at the elbow in 8 healthy patients while gripping and found that as grip strength increased, so did extensor muscle activity. This increase in extensor muscle activity maintains the wrist in a position of slight extension, allowing the digital flexors to function near their ideal length-tension relationship and thus generate maximal grip strength.
Because the motor units for the wrist cross the elbow, their length and muscle tension are affected by elbow position. Several studies have been performed to evaluate the difference in grip strength between positions of elbow flexion and extension in healthy adults. Although results vary, these studies generally show higher values for grip strength measurements with the elbow in full extension (Gs-E) than for grip strength measurements recorded with the elbow in 90[degrees] of flexion (Gs-F).2-5
Numerous studies have used grip strength as an outcome measure for the evaluation and treatment of LE without controlling for elbow position.6-8 DeSmet and Fabry9 and DeSmet et al10 acknowledged the importance of elbow position on grip strength in patients with LE. We currently use a hydraulic hand dynamometer (Jamar, Preston Rolyan, Bolingbrook, IL) as part of the initial assessment of all patients presenting to our clinic with elbow pain. This study evaluated the maximum grip strength in a position of elbow extension versus flexion as a diagnostic tool in the assessment of a patient with suspected LE. This objective tool can be used by surgeons or primary care physicians to support the suspected diagnosis, or in the case of a negative test result, indicate the need for further work-up.
Materials and Methods
We reviewed the charts of all patients who presented to our hand clinic and were given the diagnosis of LE based on the physical examination findings by 1 of 2 fellowship-trained, attending hand surgeons from January 2001 to October 2004. Within this group of 107 patients, measurements of Gs-F and Gs-E were available for 81 patients. In 47 the dominant hand was affected, in 23 the nondominant hand was affected, in 3 no dominance was expressed, and 7 had both sides affected. Forty patients had grip strength measurements of both extremities. Forty-one patients had only grip strength measurements for the affected extremity. For each patient, we recorded handedness, Gs-F, and Gs-E. Patients then were assigned an anonymous identification code and their names and medical record numbers were omitted from the database. This study was approved by our hospital’s institutional review board.
To receive a diagnosis of LE, patients were required to have tenderness over the ECRB or the common extensor origin and at least 2 of the 3 following criteria: (1) pain with resisted wrist extension, (2) pain with resisted middle finger extension, and (3) pain with the elbow extended and the wrist flexed and pronated (Mills test).11,14 Exclusion criteria for this study included patients with other pathology contributing to lateral elbow pain such as known cervical radiculopathy, radiocapitellar joint instability, or degeneration. Patients who had received surgical treatment for LE previously also were excluded from the study. Grip strengths were measured in the seated position with a hydraulic hand dynamometer (Jamar) by the attending surgeon or a resident orthopedic surgeon. Measurements were taken both with the elbow in 90[degrees] of flexion, and with the elbow fully extended in front of the patient. Care was taken to ensure accurate limb positioning. Measurements were taken for the affected extremity only (41 patients) or for both the affected and healthy extremities (40 patients). Loss of grip strength from flexion to extension was recorded as a relative value as follows:
The Gs-F was compared with the Gs-E within the affected extremity for all patients. For patients who had grip strength data for an unaffected extremity, we compared the maximum Gs-F and Gs-E between the extremities. A t test was used with a 1- or 2-tailed distribution, either paired or unpaired. Patients who were affected bilaterally were eliminated from the comparison analysis.
To estimate a cut-off value to determine how much grip strength loss is significant, we computed a 2 x 2 contingency table that compared the loss of strength for affected extremities with pain- free extremities for all 40 patients with unilateral disease. The table was computed for multiple cut-off values. The sensitivity and specificity were computed from the table for each cut-off value. Chi- squared analysis was used for the contingency table results, and a ? value of less than .05 was considered significant. Power analysis was performed using post hoc analysis with the noncentral distribution theory. Data analysis was performed with statistical software (SPSS; SPSS Inc., Chicago, IL). Power analysis also was performed with statistical software (GPOWER; Heinrich Heine University, Dusseldorf, Germany).
When comparing grip strength within the healthy arm, we found that Gs-F was no different than Gs-E; however, when comparing measurements within the affected arm we found that on average the Gs- F exceeded the Gs-E by 29% (p < .01) (Table 1).
When comparing a patient’s healthy extremity with their own affected extremity, we found that the Gs-E for the affected side was on average only 50% of the Gs-E for the healthy side, and we found that the Gs-F for the affected side was on average 69% of the Gs-F for the healthy side (p < .01) (Table 2).
Table 1. Differences in Flexion and Extension Grip Strengths
The loss of grip strength between flexion and extension in a single extremity was considered as a test to distinguish an extremity with LE from a painfree extremity. With a 5% decrease in the Gs-E the sensitivity was 83% and the specificity was 80%. With an 8% decrease in the Gs-E the sensitivity was 80% and the specificity was 85%. With a 10% decrease in the Gs-E the sensitivity was 78% and the specificity was 90%. Figure 1 shows the tradeoff between the sensitivity and specificity for multiple cut-off values. The results of the contingency table analysis were significant using the chi-squared test (p < .001). Post hoc power analysis showed that a group of 40 patients was sufficient to achieve 99% power for a p value of less than .05, assuming a large effect size (Cohen's w > 0.5).
DeSmet and Fabry9 are the only investigators who have provided clinical insight into the effect of elbow position on grip strength in patients with LE. They evaluated the Gs-E and the Gs-F in 55 consecutive patients with chronic LE. All of their patients had symptoms for more than 6 months and had been treated nonsurgically with various treatment modalities. They found a statistically significant mean grip strength loss of 43% from flexion to extension for the pathologic side, with a less than 2% difference for the control side. They performed a further prospective study in 17 patients with a minimum of 1 year of follow-up evaluation after surgery for LE. In their second study they found that the Gs-E and the Gs-F both improved significantly after surgery, and that an increased Gs-E correlated with a good clinical outcome.10
Table 2. Comparison of Affected Versus Unaffected Extremities Although DeSmet’ s observations4 were similar to ours, they offered no insight into why the ECRB is affected differently in different elbow positions, or why the ECRB is affected more than other wrist extensors. In an effort to explain this. Lieber et al15 performed a study that evaluated the length of the ECRB sarcomere through various degrees of elbow flexion. In their evaluation of 13 patients they found a biphasic change in sarcomere length as the elbow was moved from a fully extended position to a position of 90[degrees] of flexion. Sarcomere length was maximal with the elbow at 90[degrees] of flexion, and minimal between 30[degrees] of flexion and 60[degrees] of flexion. The sarcomere length again lengthened at full extension. In another study, Lieber et al16 examined the unique architecture of the wrist flexors and extensors and found that each flexor and extensor could be differentiated uniquely based on the fiber length to muscle length ratio, pennate angle, and muscle length with 100% accuracy. Lieber et al16 postulated that because of the unique architecture of the ECRB and because the ECRB sits close to the center of rotation of the elbow, it is exposed to eccentric muscle contracture through a range of elbow position and thus may be more prone to injury than the extensor carpi radialis longus. A position of full extension places the ECRB in a particularly vulnerable position with regard to muscle tension, thus exacerbating the symptoms of LE more than a position of elbow flexion.
Figure 1. Difference in grip strength considered as a test to distinguish an extremity with LE from a pain-free extremity. The sensitivity and specificity of the test were calculated for various values of grip strength (boxes, [black square]). The x-axis is the false-positive rate (FP) or 1 -specificity. The y-axis is the true- positive rate (TP) or the sensitivity. As one moves from left to right on the x-axis, the sensitivity increases and the specificity decreases. TP, true-positive rate; FP, false-positive rate.
Our work corroborates the work of DeSmet and Fabry9,10 and adds further clinical relevance to the work of Lieber.15,16 Although we offer no scientific evidence linking the works of DeSmet, Fabry, and Lieber, we have shown that patients who have LE by classic physical examination findings are likely to have significant differences between the Gs-F and the Gs-E. This finding may be secondary to the unique architecture of the ECRB and its relative position proximal to the elbow joint as elucidated by Lieber.15,16
In our study, loss of grip strength between flexion and extension in a single extremity was considered as a test to distinguish an extremity with LE from a pain-free extremity. We found that an 8% decrease from the Gs-F to the Gs-E was 80% sensitive and 85% specific. Implementing a 15% cut-off value (per DeSmet and Fabry9) showed a 70% sensitivity and a 98% specificity. In any diagnostic study, the choice of cut-off value is a judgment in which sensitivity is traded for specificity. Here, grip strength is used to distinguish LE from a pain-free extremity. When grip strength is used to diagnose LE in all painful extremities, we would expect grip strength to be equally sensitive but perhaps somewhat less specific.
The relative decrease in grip strength in a position of elbow extension is a diagnostic tool that should be used in the context of an extremity with suspected LE. The addition of this tool to the classic signs and symptoms of tennis elbow gives the doctor additional objective evidence implicating LE as the cause of a patient’s pain. In addition, the finding of decreased grip strength in a position of elbow extension provides further evidence supporting the diagnosis of LE in patients for whom the diagnosis is not entirely clear. Conversely, the objective findings of our study also may be useful in ruling out the diagnosis of LE in patients with other potential sources of elbow pain.
Our study had several limitations. First, there was a selection bias from our patient population. Because we are a tertiary referral center, many of our patients have failed one or multiple therapeutic modalities. In addition, our extremities were chosen retrospectively based on the diagnosis of LE. Although the diagnosis was made primarily by using the patient’s history and physical examination findings, the attending surgeons were likely to use the information from the grip strength measurements to aid in the diagnosis, and thus inadvertently may have selected for our group patients with a marked difference between the Gs-F and the Gs-E. In addition, we lacked control data. Although we had 81 patients with measurements for the affected limb, we only had bilateral data for 40 patients and thus we were forced to compare 2 different groups in several instances.
We did not evaluate the effect of elbow position on grip strength in patients who ultimately were found to have other conditions that also might present with lateral elbow pain, such as radial tunnel syndrome, radiocapitellar arthritis, radial head/neck fracture, or rheumatoid arthritis. Although we did not find any evidence in the literature to suggest that similar differences in the Gs-F versus the Gs-E would be seen in those conditions, further investigation is warranted to determine what other pathology about the elbow might produce the positional differences in grip strength we found in patients with LE.
Despite these limitations, there is a statistically relevant correlation between a relative decrease in the Gs-E and the diagnosis of LE. This retrospective review provides preliminary data to support a prospective study to evaluate the predictive value of differential grip strength measurements in the evaluation and treatment of LE. Our prospective arm seeks to evaluate grip strengths in flexion and extension for all patients who present with elbow pain to better support the specificity of this test for the diagnosis of LE.
The authors would like to acknowledge Dr. David P. Green for his training in the use and evaluation of grip strength assessments in patients with suspected LE.
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Erik R. Dorf, MD, A. Bobby Chhabra, MD, S. Raymond Golish, MD, PhD, Jasmin L. McGinty, MD, Michael E. Pannunzio, MD
From the University of Virginia Hand Center, Charlottesville, VA, and the Reconstructive Hand Surgeons of Indiana, Carmel, IN.
Received for publication March 16, 2007; accepted March 17, 2007.
No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article.
Support was received from the Orthopaedic Research Education Foundation and the NIH/N1AMS (AR49407).
Corresponding author: Michael E. Pannunzio, MD, Reconstructive Hand Surgeons of Indiana, 1 342 1 Old Meridian St, Suite 200, Carmel, IN 46032.
Copyright (c) 2007 by the American Society for Surgery of the Hand
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(c) 2007 Journal of Hand Surgery, The. Provided by ProQuest Information and Learning. All rights Reserved.