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Logo of nihpaAbout Author manuscriptsSubmit a manuscriptHHS Public Access; Author Manuscript; Accepted for publication in peer reviewed journal;
 
J Orthop Sports Phys Ther. Author manuscript; available in PMC 2013 August 8.
Published in final edited form as:
PMCID: PMC3738021
NIHMSID: NIHMS478184

Relationships between Biomechanics, Tendon Pathology, and Function in Individuals with Lateral Epicondylosis

Abstract

Study Design

Single cohort descriptive and correlational study.

Objectives

To investigate the relationships between tendon pathology, biomechanical measures, and self-reported pain and function in individuals with chronic lateral epicondylosis.

Background

Lateral epicondylosis has a multi-factorial etiology and its pathophysiology is not well understood. Consequently, treatment remains challenging and those with lateral epicondylosis are prone to recurrence. While tendon pathology, pain system changes, and motor impairments due to lateral epicondylosis are considered related, their relationships have not been thoroughly investigated.

Methods

Twenty-six participants with either unilateral (n = 11) or bilateral (n=15) chronic lateral epicondylosis participated in this study. Biomechanical (grip strength, rate of force development, and electromechanical delay), tendon pathology (magnetic resonance imaging [MRI] and ultrasound), and self-reported pain and function (Patient-rated Tennis Elbow Evaluation [PRTEE]) measurements were made. Partial Spearman correlations, adjusting for covariates (age, gender, weight, and height), were used to evaluate the relationship between self-reported pain, function, and biomechanical and tendon pathology measures.

Results

Statistically significant correlations between biomechanical measures and PTREE measures ranged in magnitude from 0.44 to 0.68 (P<0.05), but no significant correlation was observed between tendon pathology (MRI and ultrasound) measures and PRTEE (r = −0.02 – 0.31, P>.05). Rate of force development had a stronger correlation (0.54 – 0.68, P<0.05) with self-reported function score than grip strength (r = 0.35 – 0.47, P<.05) or electromechanical delay (r = 0.5, P<.05).

Conclusion

Biomechanical measures (pain free grip strength, rate of force development, electromechanical delay) have the potential to be used as outcome measures to monitor progress in lateral epicondylosis. In comparison, the imaging measures (MRI and ultrasound) were useful for visualizing the pathophysiology of lateral epicondylosis. However, the severity of the pathophysiology was not related to pain and function, indicating that imaging measures may not provide the best clinical assessment.

Keywords: grip strength, hand function, rate of force development, tennis elbow

Lateral epicondylosis (LE) is a prevalent and costly musculoskeletal disorder of the common extensor tendon characterized by degeneration of the tendon, and pain at the lateral aspect of the elbow is frequently reported.23,26 In addition, biomechanical and sensorimotor deficits can occur and adversely impact upper extremity function.4, 8 These functional deficits may interfere with occupational tasks and activities of daily living resulting in significant individual and occupational costs.16,48 Because the pathophysiology of LE is not well understood, treatment remains challenging and LE is prone to recurrence.11,13

Tendon changes due to LE include dense populations of fibroblasts, vascular hyperplasia, and disorganized collagen.28,39,43 The common extensor tendon origin in individuals with LE is usually thickened and shows increased signal intensity on magnetic resonance images (MRI). The region of greatest signal abnormality is usually at the origin of the extensor carpi radialis brevis tendon from the lateral epicondyle of the humerus. The areas of increased signal intensity within the diseased tendon usually correspond to areas of mucoid degeneration and neovascularization on histopathologic analysis.27,43,46 Ultrasound also has been used to study LE, and findings include the presence of intratendinous calcification, tendon thickening, adjacent bone irregularity, focal hypoechoic regions, and diffuse heterogeneity of the common extensor tendon.9,10,33

Pain is the primary symptom of LE.23 The pain experience in patients with LE may be due to changes in the nervous system as a result of neuronal tissue changes as well as nociceptive and non-nociceptive processes.13,35 In patients with LE, pain can be assessed using pressure-pain threshold and self-reported measures such as the visual analog scale and the Patient-rated Tennis Elbow Evaluation (PRTEE).12,45,50,53 PRTEE is a commonly used, valid, reliable, and sensitive clinical instrument for assessment of pain and disability in individuals with chronic LE.32,40,45

Pain free grip strength is the most commonly assessed motor impairment,5,49,52 and recently the effects of LE on reaction time,4,5,42 rate of force development, and electromechanical delay have been investigated.7 Rate of force development is considered to be a measure of the ability to rapidly generate strength and is associated with higher functional performance.1,47 Electromechanical delay represents time duration of the excitation contraction coupling in the muscle and the time to take-up the slack in the elastic structures of the muscle tendon unit.30 Chourasia et al7 found lower rate of force development and longer electromechanical delay in individuals with LE compared to controls. In addition, Bisset et al4,5 reported higher reaction times in individuals with LE compared to controls.

While tendon pathology, pain system changes, and motor impairments due to LE are considered related, their relationship has not been investigated thoroughly. For example, Clarke et al9 observed a positive association between ultrasound findings and improvements in self-reported pain and function but changes in motor performance were not evaluated. Similarly, Bisset et al4,5 investigated the effects of various interventions for LE on global improvement, grip strength, and sensorimotor measures but did not assess morphological changes in the common extensor tendon.

It is noteworthy that the majority of studies on LE use an eligibility criterion of only including patients with LE of the dominant arm, excluding those with bilateral LE or unilateral LE of the non-dominant arm.5,42 It is important that the relationships between the various components of LE are investigated in a heterogeneous sample. This may help to gain a better understanding of LE to improve assessment and treatment outcomes.

The overall objective of this study was to evaluate the relationships between self-reported pain and function (PRTEE) with biomechanical (grip strength, rate of force development, and electromechanical delay) and tendon pathology (MRI and ultrasound imaging) measures in individuals with LE. Secondary analyses evaluated the relationships between biomechanical and tendon pathology measures. This information may help provide a better understanding of the effect of LE on function and its association with biomechanical measures.

METHODS

Participants

Twenty-nine patients with LE were recruited and enrolled from various outpatient clinics in Madison, Wisconsin, USA from June 2009 to February 2010. These patients were participating in a therapeutic trial investigating the efficacy of prolotherapy for LE. Diagnostic criteria for LE included the presence of lateral elbow pain for more than 3 months, tenderness to palpation over the lateral epicondyle and/or extensor mechanism, and pain present on at least 2 of the following provocation tests: pain with resisted extension of the wrist or fingers, pain with resisted supination, pain with passive stretch of the wrist extensors or supinator muscle. Exclusion criteria consisted of: coexisting or previous medical history of rheumatoid or inflammatory arthritis, chronic pain diagnoses, diabetes mellitus, pregnancy, systemic nervous disease, neuropathy, or acute trauma to the fingers or hands. Additional exclusion criteria were prior upper extremity injury, concurrent upper extremity injury, unresolved litigation, and co-morbidities that could interfere with ability to participate in the study. Two participants were excluded because they reported concurrent upper extremity injury. Data from 1 participant was excluded because of instrumentation malfunction. Of the 26 eligible participants, 11 had unilateral symptoms, while 15 had bilateral symptoms (TABLE 1).

TABLE 1
Participant demographics (n = 26)

Informed consent was obtained for all participants participating in this study in accordance with University of Wisconsin-Madison human subjects institutional review board guidelines.

Self-reported Measures

Patient-rated Tennis Elbow Evaluation questionnaire

Participants completed the PRTEE, a condition-specific questionnaire that assesses both elbow pain and function. PRTEE has good test-retest reliability, although reliability is less for patients with work related (ICC=0.80) than non-work-related (ICC=0.94) LE.40 It has also been used to determine the effects of different interventions for LE.18,19

The PRTEE consists of 2 subscales: pain and function. The pain subscale has 5 items and the function subscale has 10 items. Each subscale is scored from 0 to 50, with 0 being the best score and 50 the worst score. The PRTEE composite score is the sum of the pain and function subscales and ranges from 0 to 100, with 0 being the best score and 100 the worst score.

Visual analog scale (VAS)

All participants were asked to rate the average lateral elbow pain intensity for the previous week using a 10 cm line ranging from “0 = no pain” to “10 = most pain”.

Biomechanical Measures

Biomechanical measures included pain free grip strength, rate of force development, and electromechanical delay. These measures were collected bilaterally and the results have been reported elsewhere.7 For the correlational analyses reported in this paper, only the results from the affected arm are used. In case of bilaterally affected participants, the results from the more affected arm, as determined by the VAS scores, were used. When both arms were equally affected, the results from the dominant arm were used.

Pain free Grip Strength

Pain free grip strength is a valid and reliable (intraclass correlation coefficient [ICC] = 0.97) measure and is commonly used in research and clinical assessment of LE.4,5,49,51 For testing, as recommended for evaluation of grip strength in patients with LE,14,15 the participants were seated in a chair with the elbow in an extended position. The participants were then instructed to squeeze the BASELINE® (Fabrication Enterprises Inc., White Plains, NY) dynamometer for 5 seconds avoiding discomfort. Three replications with a 60 s interval between trials were performed. The average of the 3 replications was used as the pain free grip strength.

Rate of force development

The Multi-Axial Profile (MAP) dynamometer was used for measurement of rate of force development.24 The MAP dynamometer has demonstrated excellent test-retest reliability (ICC=0.99) and excellent concurrent validity when compared to the BASELINE® dynamometer (r=0.88–0.90).24

The participants were seated in a chair with the elbow in an extended position. Upon receipt of a randomly timed visual stimulus, participants were instructed to squeeze the handle as quickly and as hard as possible without pain for 5 seconds.7 The rate of force development was calculated by taking the time derivative of the force signal (FIGURE 1).1 Rate of force development was measured at 30, 50, and 100 ms from onset of contraction. The onset of contraction was defined as a rise of 1 N from baseline level.29 Peak rate of force development was also measured. This method is consistent with that of others for evaluating force development.1, 2 Three replications with intervals of 60 s were performed, and the average of the 3 replications was used for data analysis. The signals from the MAP dynamometer were sampled at the rate of 1000 samples/s using a National Instruments (National Instruments Corporation, Austin, TX) USB 6009 card.

FIGURE 1
RFD and EMD measurements. (Note: figure is not to scale). Abbreviations: EMD, electromechanical delay; EMG, electromyogram; RFD, rate of force development

The MAP also provides a measure of the pain free grip strength but due to a different handle geometry compared to the Baseline dynamometer, the grip strength values are different.24 We report both the grip strength values here using the following variable names: pain free grip strength – Baseline and pain free grip strength – MAP.

Electromechanical delay

Electromechanical delay was measured using the MAP dynamometer force output and the raw electromyographic (EMG) signal from the extensor carpi radialis (ECR) muscle. EMG signal was measured using a Noraxon Telemyo 2400 EMG system (Noraxon USA Inc., Scottsdale, AZ). Electrodes were placed on the ECR at one third of the distance from the proximal end of a line from the lateral epicondyle to the distal end of the radius.38 Electrodes were placed on the ECR with the forearm in neutral position. The reference EMG electrode was attached to the lateral epicondyle of the right elbow. Prior to electrode placement, skin preparation was performed according to SENIAM (Surface ElectroMyoGraphy for the Non-Invasive Assessment of Muscles) 22 guidelines. Disposable, self-adhesive Ag/AgCl snap dual electrodes with individual electrode diameter of 1 cm and inter electrode distance of 2 cm manufactured by Noraxon were used. Preamplified EMG leads with a differential gain of 500 connected the electrodes to the 16 channel Noraxon Telemyo 2400 wireless transmitter with 16-bit A/D converter and bandwidth 10–500 Hz. The EMG amplifier characteristics were: gain of 1000, input impedance much greater than (>>) 100 MOhm, and CMRR greater than 100 dB. The signals were sampled at the rate of 1500 samples/second. The onset of muscle activation was defined as a deviation of ±15 µVolts in the EMG signal from resting baseline level.29 The time between the onset of muscle activation based on the change in EMG signal intensity and the onset of force as measured with the MAP dynamometer is considered the electromechanical delay (FIGURE 1). Sufficient practice was provided to all participants to become comfortable with the testing procedures prior to completing 3 repetitions. The average of the 3 repetitions was used for data analysis.

Tendon Pathology Measures

Tendon pathology was assessed using MRI and ultrasound. For those with unilateral LE, imaging was conducted on the affected arm. For individuals with bilateral LE, ultrasound was conducted on the most affected arm (as determined by the VAS scores) and MRI was conducted bilaterally. For the correlational analyses used in this paper, we used the results from the more affected arm. When both arms were equally affected, the results from the dominant arm were used. Three participants did not complete the ultrasound assessment and 1 participant declined the MRI scan. Therefore, both MRI and ultrasound parameters were available for 22 individuals (elbows).

Magnetic Resonance Imaging

MRI examination was performed using an Artoscan (GE Healthcare, Waukesha, WI) 0.17 T extremity scanner. Axial and coronal intermediate-weighted fast spin-echo (FSE) and short tau inversion recovery (STIR) sequences of the elbow were used for semi-quantitative assessment of disease severity (FIGURE 2). Intermediate-weighted FSE scan parameters were: TR = 2050 ms, TE = 18 ms, Slices = 7, Gap = 1.0 mm, Thickness = 3.5 mm, Readout FOV = 180, Encoding FOV = 180, Samples = 192, Encoding # = 192. STIR scan parameters were: TR = 2050 ms, TE = 34 ms, TI = 75 ms, Slices = 7 Gap = 1.0 mm, Thickness = 3.5 mm, Readout FOV = 180, Encoding FOV = 180, Samples = 192, Encoding # = 192. A semi-quantitative grading scale was used to estimate the severity of chronic degeneration and pathologic changes in the common extensor tendon origin.44 The grading scale is as follows:

  • Grade 0 = normal common extensor tendon which is of uniform low signal intensity on intermediate--weighted FSE and fat-suppressed T2-weighted STIR images.
  • Grade 1 = common extensor tendon with mild tendinopathy which is thickened and has intermediate signal intensity on intermediate-weighted FSE and STIR images
  • Grade 2 = common extensor tendon with moderate tendinopathy which is thinned and shows focal areas of intense fluid-like signal intensity on STIR images which comprise less than 50% of the total cross sectional diameter of the tendon.
  • Grade 3 = common extensor tendon with severe tendinopathy which is thinned and shows focal areas of intense fluid-like signal intensity on STIR images which comprise more than 50% of the total cross sectional diameter of the tendon.
FIGURE 2
Coronal short tau inversion recovery images of the common extensor tendon. For the left common extensor tendon, the MRI score is 0 and for the right common extensor tendon, the MRI score is 3. The image on the left is from a previous study that included ...

Ultrasound

All ultrasound exams were performed at the University of Wisconsin Sports Clinic using a Philips IU-22 (Philips Healthcare, Andover, MA). A fellowship trained musculoskeletal radiologist with 5 years of ultrasound experience performed all the diagnostic exams. Diagnostic ultrasound images were obtained with the patient in the seated position and elbow resting on a table at 90-degree of flexion. Ultrasound images were obtained of the common extensor tendon origin in orthogonal planes, long and short axis. All images were recorded in the Radiology Picture Archiving and Computer System (PACS). Ultrasound-based diagnostic features of LE included thickening of the common extensor tendon, focal hypoechogenic regions with tissue heterogeneity, neovascularity ("neovessels"), and intrasubstance clefts or calcification (FIGURES 3 and and4).4). We used 2 published scales of neovascularity and hypoechogenicity to grade the severity of LE specific structural changes of the elbow.36 Severity of neovascularity was graded as:

  • Grade 0 = none (no neovessels)
  • Grade 1 = mild (1–2 neovessels)
  • Grade 2 = moderate (3–4 neovessels)
  • Grade 3 = severe (more than 4 or diffuse neovessels).
FIGURE 3
Long axis ultrasound image comparing asymptomatic normal common extensor tendon (arrowheads) (left) to symptomatic common extensor tendon (right). Arrow indicates intrasubstance calcification. Abbreviations: LE, lateral epicondyle; RH, radial head
FIGURE 4
Long axis Doppler ultrasound image of the common extensor tendon. Red area indicates increased neovascularity

Severity of hypoechogenicity was graded as:

  • Grade 0 = normal;
  • Grade 1 = mild focal hypoechogenicity
  • Grade 2 = moderate focal hypoechogenicity
  • Grade 3 = severe diffuse hypoechogenicity.

These 2 scales allow a semi-quantitative severity grading of LE related structural elbow changes.

Statistical Analysis

Spearman correlation coefficients were calculated to detect possible monotonic relationships between the PRTEE scores (pain, function, and composite) and the biomechanical (grip strength, rate of force development, and electromechanical delay) and imaging (MRI and ultrasound) measures. Both full (usual) and partial correlations adjusting for baseline covariates (age, gender, weight, and height) were calculated. For secondary analyses, full and partial Spearman correlation coefficients were calculated among and between biomechanical and imaging measures. P-values were calculated without adjustment for multiplicity. Data analysis was conducted using the R language and environment for statistical computing (R Foundation for Statistical Computing, Vienna, Austria).

RESULTS

The descriptive statistics for the self-report, biomechanical, and tendon pathology measures are presented in TABLE 2.

TABLE 2
Descriptive statistics for self-report, biomechanical and imaging measures (n = 26)

PRTEE

The mean +/− SD for the PRTEE composite, pain, and function scores were 44.3 +/− 18.8, 23.9 +/− 8.3, and 20.4 +/− 11.4, respectively. FIGURE 5 shows the relationship between the PRTEE function and pain component scores with a correlation coefficient of 0.76 (P<.01) and partial correlation coefficient of 0.73 (P<.01).

FIGURE 5
Relationship between PRTEE function and pain scores (partial correlation coefficient, r=0.73, P< .01). Abbreviation: PRTEE, Patient-rated Tennis Elbow Evaluation

PRTEE and Biomechanical Measures

TABLE 3 shows full and partial Spearman correlation coefficients of PRTEE components and composite scores with biomechanical measures. Partial Spearman correlation coefficients, adjusted for covariates, are reported in the text.

TABLE 3
Full and partial Spearman correlation coefficients between biomechanical measures and PRTEE

All partial correlation coefficients were in the expected directions with negative correlation coefficients indicating that higher PRTEE scores were associated with lower grip strength and rate of force development. Positive partial correlation coefficients between PRTEE scores and electromechanical delay indicate that higher PRTEE scores were associated with higher electromechanical delay. Nineteen of 21 partial correlation coefficients were found to be nominally statistically significant (P<.05). Statistically significant partial correlation coefficients between biomechanical and PRTEE measures ranged in magnitude from 0.44 to 0.68 (P<.05) with the greatest partial correlation coefficient observed between rate of force development at 100ms and PRTEE composite score (r = −0.68, P<.01). FIGURE 6 shows the relationship between the PRTEE composite score and peak rate of force development.

FIGURE 6
Relationship between PRTEE questionnaire composite score and peak RFD (partial correlation coefficient, r = −0.66, P<.01). Abbreviations: PRTEE, Patient-rated Tennis Elbow Evaluation; RFD, rate of force development

PRTEE and Imaging Parameters

Correlation coefficients between the imaging parameters and PRTEE components and composite scores are shown in TABLE 4. None of the 12 partial correlation coefficients was found to be statistically significant. FIGURE 7 shows the distribution of PRTEE pain and function scores by MRI score.

FIGURE 7
Boxplots of PRTEE pain (left) and function scores (right) versus MRI scores. The median is the dark band in the box. The bottom and top of the box represent the 25th and 75th percentile respectively. The whiskers extend to the most extreme data point ...
TABLE 4
Full and partial Spearman correlation coefficients between imaging parameters and PRTEE

Secondary Associations

Biomechanical Measures

Higher grip strength was found to be associated with higher rate of force development (TABLE 5). All 3 partial correlation coefficients among biomechanical measures were found to be statistically significant (P<.01). The greatest correlation occurred between pain free grip strength-MAP and pain free grip strength-BASELINE® (r = 0.74, P<.01). Relationships of pain free grip strength measures with rate of force development at 30, 50, and 100ms (not shown) were similar to the relationships observed with peak rate of force development.

TABLE 5
Full and partial Spearman correlation coefficients between biomechanical measures

Imaging Measures

Only 2 out of 6 partial correlation coefficients were found to be nominally significant (P<. 05; TABLE 6). The strongest correlation was that observed between neovascularity and MRI score (r=0.55, P<.01).

TABLE 6
Full and partial Spearman correlation coefficients between imaging measures

Biomechanical and Imaging Measures

There was no statistically significant association between the biomechanical and the ultrasound imaging measures with none of the 9 partial correlation coefficients being nominally statistically significant (TABLE 7). MRI score was found to be consistently negatively associated with biomechanical measures, and all 3 partial correlation coefficients were nominally statistically significant (P<.05), including a strong observed negative partial correlation coefficient (r = −0.72, P<.01) between MRI score and MAP grip strength.

TABLE 7
Full and partial Spearman correlation coefficients between biomechanical and imaging measures

DISCUSSION

We found that biomechanical measures (grip strength and rate of force development) were associated with measurements of self-report pain and function as assessed by the PRTEE. No statistically significant association was observed between imaging measures (ultrasound and MRI) and measurement of self-report pain and function as assessed by PRTEE.

The PRTEE was previously reported to have significant but low association with pain free grip strength (r = 0.35– 0.40, P<.01).32, 40 It was hypothesized that maximal grip strength may not be required for function.40 Instead, alternative biomechanical measures such as the rate of force development or submaximal strength may be more important for function and thus, may have a stronger correlation with PRTEE scores.40

Although we did not measure submaximal strength, our results suggest that the rate of force development may have a greater role in determining function in patients with LE than maximal grip strength. In the current study we found that rate of force development was highly correlated with PRTEE, and it had a higher correlation with PRTEE than pain free grip strength. This is consistent with other studies in which rate of force development was associated with higher functional performance for the upper extremity as well as the lower extremity.25,47 Andersen et al3 found that rate of force development had a stronger association with self-reported pain than maximal strength. In our prior research, we found that rate of force development was significantly reduced in those with LE compared to matched controls.7 To perform activities of daily living a threshold level of strength is required. Greater strength beyond the threshold alone may not necessarily improve function.40, 45 However, a faster rate of force development helps in reaching the threshold strength levels faster and may have a greater contribution towards function.

Electromechanical delay was also significantly correlated with the PRTEE function but not pain. Previously, Bisset et al5 reported longer reaction times in individuals with LE and suggested that pain may cause cortical reorganization, resulting in longer reaction times. Similarly, Chourasia et al7 found that electromechanical delay was also increased in individuals with LE. Reaction time is comprised of electromechanical delay (also referred to as motor time), as well as the pre-motor time. Pre-motor time is the time between the stimulus and beginning of muscle electrical activity and electromechanical delay represents duration of the excitation contraction coupling in the muscle and the time to take-up the slack in the elastic structures of the muscle tendon unit.30 Electromechanical delay represents the initial stages of force production and longer electromechanical delay may partially explain the increase in reaction time observed by Bisset et al.4, 5

These findings may be relevant for physical therapy interventions for LE. Resistance training activities for the forearm muscles as well as grip strengthening activities are commonly used physical therapy interventions, with improvements in grip strength often used as an outcome measure in clinical research.5, 41 While a strong association exists between grip strength and rate of force development, exercises that address deficits in grip strength may not necessarily address the deficits in rate of force development. Ability to rapidly produce force is most affected by exercises that incorporate a velocity dependent component and not solely resistive strengthening.6, 17, 31

While the effects of velocity dependent training in LE have not been specifically studied, a number of other studies have found improvements in rate of force development for other muscle tendon groups following interventions that include velocity dependent training. Bottaro et al6 reported significant increases in arm and leg muscular power and functional performance for older men following 10 weeks of high velocity power training compared to no increase in muscular power following resistance training. Fielding et al17 reported similar results for older women. Häkkinen et al21 also report significant increases in rate of force development but not in maximal strength for knee extension following explosive type strength training. Conversely, Häkkinen et al21 observed significant increases in knee extension strength but not in rate of force development following resistance training and suggest that specific training induced adaptations in the neuromuscular system may be responsible for these changes in performance. Neuromuscular training may also help in addressing the deficits in reaction time. Linford et al34 found that a neuromuscular training program consisting of sensorimotor, strength and power components for the lower extremity resulted in a significant decrease in reaction time with a trend towards an increase in electromechanical delay. Grosset et al20 found that for the lower extremity, 10 weeks of plyometric training caused an increase in electromechanical delay while endurance training lead to shorter electromechanical delay. While these studies investigated larger muscle groups such as biceps or quadriceps, research is needed to evaluate the effect of velocity dependent exercise on forearm muscles that are involved in gripping activities. Further investigation is needed to determine the effect of this type of exercise protocol on rate of force development and function in those with LE.

Previous studies have found differences in the sensitivity and specificity of ultrasound and MRI for diagnosing LE. Miller et al37 reported 64–82% sensitivity and 67–100% specificity for ultrasound and 90–100% sensitivity and 83–100% specificity for MRI to detect lateral epicondylosis and suggest that sonography is as specific but not as sensitive as MRI to diagnose LE. We observed similar results for sensitivity in our study, with positive finding on the MRI for all tested participants (100% sensitivity), while hypoechogenecity was not observed in the ultrasound scans of 7 out of 23 tested participants (73% sensitivity) and no neovascularity was observed in the ultrasound scans of 12 of 23 tested participants (47% sensitivity). Specificity results were not available for our study as we only tested participants with LE.

A possible explanation for the lack of statistically significant association between the MRI and ultrasound imaging measures and PRTEE pain and function is the nature of the scales used for assessment of the imaging measures. The severity of neovascularity and hypoechogenecity and the MRI image were graded on 4-point scales, in contrast to the continuous biomechanical measures. The lower resolution of these 4-point scales may contribute towards a lack of significant association.

The partial correlations of MRI score with biomechanical measures are noteworthy, particularly the correlation of MRI score to MAP grip strength. It should be noted, however, that none of the full correlation coefficients were nominally statistically significant, and our data suggest that the interrelationship between MRI score, biomechanical parameters, and our selected covariates may be complex. Study of these associations in a larger sample is needed.

Our research, along with that of others, found that severity of ultrasound and MRI findings for lateral epicondylosis does not correlate with clinical symptom severity and function. 33, 43 Overall, our results suggest that use of imaging measures with ordinal scales may be best suited for diagnosis of disease rather than assessment of subtle differences in disease severity.

Limitations

Participants in this study had chronic LE and it is possible that over time they may have developed adaptive motor patterns to adjust for functioning with LE. Individuals with acute lateral epicondylitis may not have developed adaptive motor patterns. Also the severity of LE observed on imaging measures may not be as extreme in individuals with acute lateral epicondylitis. Therefore these results may not be generalizable to patients with acute lateral epicondylitis. Future studies involving a larger number of participants with varied duration of symptoms may help in further elucidating the relationship between biomechanics, tendon pathology, and function in individuals with LE.

While assessors were not blinded to group status because all participants had LE, assessors were blinded to the results of the other outcome measures. A biostatistician not involved in data collection completed all data analysis. To minimize assessor bias during biomechanical measurement, a standard operating procedure was used. Interrater reliability for measurement of biomechanical variables (EMG and force onset) for 2 assessors was found to have an ICC of 0.99.

CONCLUSIONS

Biomechanical measures (pain free grip strength, rate of force development, electromechanical delay) have the potential to be used as outcome measures to monitor progress in lateral epicondylosis. In comparison, the imaging measures (MRI and ultrasound) were useful for visualizing the pathophysiology of lateral epicondylosis. However, the severity of the pathophysiology was not related to pain and function, indicating that imaging measures may not provide the best clinical assessment.

KEY POINTS

  • FINDINGS: Rate of force development has greater association with function than maximal strength. Imaging measures of tendon pathology were not significantly associated with self-report symptoms.
  • IMPLICATIONS: Physical therapy interventions that include velocity dependent training may result in improvements in rate of force development and function.
  • CAUTION: Study participants had chronic LE. Results of the study may not be generalizable for individuals with acute lateral epicondylitis.

Footnotes

Statement of institutional study board approval: The Health Sciences institutional review board of the University of Wisconsin – Madison approved the study protocol.

Statement of Financial Disclosure

Drs. Sesto, Chourasia, and Buhr received support from the University of Wisconsin Clinical and Translational Science Award (NIH/NCRR 1 UL1RR025011). Dr. Rabago was partially supported by the American Academy Family Practice Foundation’s Research Committee Joint Grant Awards Program (G0810).

The manuscript has been read and agreed to by all authors; no conflicts of interest are reported.

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