Elbow Muscle Weakness in Lateral Epicondylalgia
Elbow Muscle Weakness in Lateral Epicondylalgia
Characteristics of the study participants ( Table 1 ) were comparable between groups and with previous studies of LE. Only BMI differed significantly between groups, the LE group being more obese. The LE group comprised middle-aged males and females, predominantly right-handed individuals, with the condition predominantly affecting their dominant arm. They reported a mean 6-month duration of symptoms with 23.3% reporting previous LE. Most commonly, the onset was reported as insidious (26.7%), or related to sport (25.3%), unusual activities (24%) and work (20%). The mean resting and worst pain levels (VAS) were 9.5 and 60.6 mm, respectively. Thirty-four per cent were engaged in sports involving gripping of a club or racquet while 24% were employed in manual occupations.
Fifteen LE participants were unable to complete elbow strength testing due to pain levels before or during testing. These participants reported significantly greater resting pain (VAS) (MD −14.7 mm, 95% CI −27.8 to −1.6, p=0.03), greater total pain and disability (PRTEE) (MD −17.7, 95% CI −24.7 to −10.6, p=0.000) and weaker PFG in their affected arm (MD 27.4 N, 95% CI 1.2 to 53.5, p=0.04) than the LE participants who completed testing.
The results of ANCOVA analyses demonstrated significant side by group interaction effects for both maximal elbow extensor (p=0.008) and flexor (p=0.009) muscle strength. Interaction plots (figure 1) revealed that elbow strength of the affected arm of LE was weaker than that of the matched arm of controls, while the unaffected arm was comparable with controls. Group by side data are presented in Table 2. Follow-up testing of the interaction effects identified significant differences between LE and controls for their between-side differences (elbow extension (−6.54 N, 95% CI −11.43 to −1.65, p=0.008); flexion (−11.26 N, 95% CI −19.59 to −2.94, p=0.009)). These differences exceeded the minimum differences required to be 95% confident of a true change (2.09 N for extension and 3.14 N for flexion). These values represent small-sized effects (SMD: extension −0.45; flexion −0.46).
(Enlarge Image)
Figure 1.
Group (lateral epicondylalgia (LE), control (C)) by side (affected, unaffected) interaction plot for maximal elbow flexion and extension strength. Data are adjusted for age, gender and body mass index.
ANCOVA analysis of PFG demonstrated a significant interaction between group and side (p=0.000), with interaction plots highlighting the large deficit in the affected side of LE (figure 2). Table 2 presents group by side data. Follow-up testing of the differences between sides confirmed the observation from the interaction plot, with the magnitude of the difference between LE and control groups (MD: −230.94 N, 95% CI −254.2 to −207.8) representing a very large SMD of −3.15.
(Enlarge Image)
Figure 2.
Group (lateral epicondylalgia (LE), control (C)) by side (affected, unaffected) interaction plot for grip strength. Data are adjusted for age, gender and body mass index.
All analyses were repeated using independently randomised allocations of matched arms to the control group. This did not change study results.
The mean level of elbow pain (VAS) experienced by LE participants during testing of elbow flexion and extension was 8.1 and 7.6 mm, respectively. No correlation was found between pain levels experienced during testing and maximal elbow strength. Pain intensity (VAS) over the preceding week and injury duration did not correlate significantly with any strength measures. There was a weak correlation for PRTEE (pain and disability) ratings with PFG (Srho: −0.356, p=0.000), elbow flexion (Srho: −0.217, p=0.008) and extension (Srho: −0.224, p=0.006).
Results
Characteristics of the study participants ( Table 1 ) were comparable between groups and with previous studies of LE. Only BMI differed significantly between groups, the LE group being more obese. The LE group comprised middle-aged males and females, predominantly right-handed individuals, with the condition predominantly affecting their dominant arm. They reported a mean 6-month duration of symptoms with 23.3% reporting previous LE. Most commonly, the onset was reported as insidious (26.7%), or related to sport (25.3%), unusual activities (24%) and work (20%). The mean resting and worst pain levels (VAS) were 9.5 and 60.6 mm, respectively. Thirty-four per cent were engaged in sports involving gripping of a club or racquet while 24% were employed in manual occupations.
Elbow Strength
Fifteen LE participants were unable to complete elbow strength testing due to pain levels before or during testing. These participants reported significantly greater resting pain (VAS) (MD −14.7 mm, 95% CI −27.8 to −1.6, p=0.03), greater total pain and disability (PRTEE) (MD −17.7, 95% CI −24.7 to −10.6, p=0.000) and weaker PFG in their affected arm (MD 27.4 N, 95% CI 1.2 to 53.5, p=0.04) than the LE participants who completed testing.
The results of ANCOVA analyses demonstrated significant side by group interaction effects for both maximal elbow extensor (p=0.008) and flexor (p=0.009) muscle strength. Interaction plots (figure 1) revealed that elbow strength of the affected arm of LE was weaker than that of the matched arm of controls, while the unaffected arm was comparable with controls. Group by side data are presented in Table 2. Follow-up testing of the interaction effects identified significant differences between LE and controls for their between-side differences (elbow extension (−6.54 N, 95% CI −11.43 to −1.65, p=0.008); flexion (−11.26 N, 95% CI −19.59 to −2.94, p=0.009)). These differences exceeded the minimum differences required to be 95% confident of a true change (2.09 N for extension and 3.14 N for flexion). These values represent small-sized effects (SMD: extension −0.45; flexion −0.46).
(Enlarge Image)
Figure 1.
Group (lateral epicondylalgia (LE), control (C)) by side (affected, unaffected) interaction plot for maximal elbow flexion and extension strength. Data are adjusted for age, gender and body mass index.
Pain-free Grip
ANCOVA analysis of PFG demonstrated a significant interaction between group and side (p=0.000), with interaction plots highlighting the large deficit in the affected side of LE (figure 2). Table 2 presents group by side data. Follow-up testing of the differences between sides confirmed the observation from the interaction plot, with the magnitude of the difference between LE and control groups (MD: −230.94 N, 95% CI −254.2 to −207.8) representing a very large SMD of −3.15.
(Enlarge Image)
Figure 2.
Group (lateral epicondylalgia (LE), control (C)) by side (affected, unaffected) interaction plot for grip strength. Data are adjusted for age, gender and body mass index.
Sensitivity Analysis
All analyses were repeated using independently randomised allocations of matched arms to the control group. This did not change study results.
Pain and Disability
The mean level of elbow pain (VAS) experienced by LE participants during testing of elbow flexion and extension was 8.1 and 7.6 mm, respectively. No correlation was found between pain levels experienced during testing and maximal elbow strength. Pain intensity (VAS) over the preceding week and injury duration did not correlate significantly with any strength measures. There was a weak correlation for PRTEE (pain and disability) ratings with PFG (Srho: −0.356, p=0.000), elbow flexion (Srho: −0.217, p=0.008) and extension (Srho: −0.224, p=0.006).
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