Tendinopathy manifests as activity-related tendon pain with related motor and sensory impairments. Tendon tissue changes in animals appear in injured as well as contralateral non-injured tendon. This review investigated evidence for bilateral sensory and motor system involvement in unilateral tendinopathy in humans. A comprehensive search of electronic databases, and reference lists using keywords relating to bilateral outcomes in unilateral tendinopathy was conducted. Study quality was rated with the Epidemiological Appraisal Instrument and meta-analyses carried out where appropriate. Analysis focused on comparison of measures in the non-symptomatic side of patients against pain-free controls. The search revealed 5791 studies, of which 20 were included (117 detailed reviews, 25 met criteria). There were 17 studies of lateral epicondylalgia (LE) and one each for patellar, Achilles and rotator cuff tendinopathy. Studies of LE were available for meta-analysis revealing the following weighted pooled mean deficits: pressure pain thresholds (-144.3 kPa; 95% CI -169.2 to -119.2 p<0.001), heat pain thresholds (-1.2°C; 95% CI -2.1 to -0.2, p<0.001), cold pain thresholds (3.1°C; 95% CI 1.8 to 4.4, p<0.001) and reaction time (37.8 ms; 95% CI 24.8 to 50.7, p<0.001).
The study found that deficits in sensory and motor systems occur bilaterally in unilateral tendinopathy. This suggests possible central nervous system involvement. This indicates that rehabilitation should consider the contralateral side of patients. The authors concluded that research of unilateral tendinopathy needs to consider comparison against pain-free controls as well as the contralateral side to gain a complete understanding of sensory and motor features.