Introduction
Platelet-rich plasma (PRP) injection has been proved to significantly improve pain associated with lateral epicondylitis (LE), commonly scaled with patient-reported outcome questionnaires. However, little is known about force precision control for the patients with LE who receive PRP injections. The aim of this study was to investigate the effect of PRP injections on precision control for force generation at the three-month follow-up.
Methods
In addition to 15 age-matched healthy participants (male: female= 9:6, 26-52 yrs), a total of 15 patient participants (male: female= 9:6, 27-51 yrs) with LE who received a single PRP injection (ACP, Arthrex Inc., Naples, FL) enrolled in this study. In the pre-test and post-test when the PRP group received injection for 3 months, they completed 3 maximal voluntary contraction (MVC) trials of the wrist extension followed by a visually-guided trapezoidal force task of wrist extension (8-sec ramp-up phase up to 75 % MVC followed by 2-sec holding phase and 8-sec ramp-down phase) with the injured hand. The same force tasks, separated by 3 months, were repeated for the control group with the matched hands. Task errors and force fluctuation dynamics during force increase of the isometric trapezoidal contraction were characterized. The differences force fluctuation characteristics during the ramp-up phase was contrasted between the pre-test and post-test for the PRP and control groups.
Results
For the PRP group, root mean square (RMS) of task errors and force fluctuations were smaller in the post-test than those in the pre-test (task errors: 5.11±2.12 % MVC to 3.54±1.91 %MVC, p=0.025, force fluctuations :2.29±0.31 % MVC to 1.51±0.36 % MVC, p < 0.001). In terms of sample entropy (SampEn) and mean frequency (MF), complexity (0.13±0.04 to 0.18±0.08 p=0.014) and spectral level (0.43±0.16 to 0.59±0.22, p = 0.053) showed increasing trend after PRP injections. Compare with control group, pre-test extremities showed higher task errors and fluctuations in all aspect(task error RMS: p=0.025; force fluctuation RMS p=0.002; MF of force fluctuations: p=0.007; SampEn of force fluctuations: p=0.006). In contrast, there were no differences in all aspects of force fluctuations between the post-test for the and group (task error RMS: p=0.405; force fluctuation RMS p=0.149; MF of force fluctuations: p=0.476; SampEn of force fluctuations: p=0.853). MVC of injured extremity is significantly higher in post-test at 3 months follow up (154.15±120.18 NT to 196.77±110.89 NT, p =0.002).
Conclusions
PRP injection significantly improves precision control of wrist extension during force increase. In addition to force precision, PRP injections add to richness of force regulation and error correction attempts for the patient group. Our study clearly demonstrates that PRP injections are able to satisfactorily restore all aspects of force generation capacity at the 3 months follow-up.