This study was to examine the effect of rESWT on muscle strength, physical function, knee pain and range of motion during an ACLR rehabilitation program. The results of this randomized, controlled trial involving ACL reconstruction indicate that a strategy of rESWT plus standard rehabilitation was superior to a strategy of standard rehabilitation.
After ACL reconstruction, there may be changes in knee joint control and motor perception, decreased spinal reflex and excitability of corticospinal pathway, and persistent defects in quadriceps function[18, 19].Therefore, early intervention in rehabilitation therapy is very important to improve the postoperative effect. The traditional initial treatment of choice is standard rehabilitation, comprehending modalities such as cryotherapy, continuous passive motion(CPM)[20], high-intensity neuromuscular electrical stimulation (NMES)[21], neuromuscular training and muscle strength training[14]. However, this method has not produced encouraging results over the past years.
To our knowledge, there is limited evidence on functional outcomes of the ACLR by using rESWT. This is a study to compare the rESWT program and standard rehabilitation program for patients with ACLR. rESWT acts at the tendon-bone interface by physical impact, triggering cell regeneration and stimulating the release of growth factors[22–24]. The effect of physical energy on biological tissues is similar to a cascade process, in which the energy of shock wave sequentially activates the cytoskeletal system and organelles, releasing proteins for the healing process[25]. Among these, the growth factor stimulates cell surface to express the protein, activating the intercellular interactions. In addition, rESWT promoted extracellular matrix metabolism, neovascularization[26], bone mineralization, and formation. Reductions in adhesions and improvements in joint mobility allow patients to recover better, including reductions in pain and improvements in function and microcirculation.
In the present study, we sought to preliminarily determine the efficacy of rESWT in reducing pain and improving function and mobility in ACL reconstruction patients. Additionally, VAS, IKDC, LKS and ROM were assessed. In the course of rehabilitation, pain, inflammatory irritation and limited mobility[27]all have an adverse impact on patients' mood and training, as well as the overall rehabilitation outcome. Pain mainly originates from inflammation, swelling and muscle adhesions in rehabilitation[28]. The VAS score is mainly used to score the patients' pain and quantify subjective perception. In our study, there was a more pronounced improvement in VAS of experimental group at 3 and 6 weeks (P < 0.05). The reasons for the outcome were that standard rehabilitation stimulates knee mechanoreceptors by joint mobilization and traction, which achieve the effect of assisted movement, only in a movable range. In contrast, rESWT can modulate local inflammatory factors and nociceptive transmission, exert anti-inflammatory, anti-swelling, and analgesic effects, and make the pain-relieving effects more pronounced[29].
The IKDC primarily assesses activities of daily living following knee injury, and provides a comprehensive assessment of stability and pain[30]. The higher the score, the lower the subjective discomfort and the stronger the function. The improvement in IKDC of experimental group (P < 0.05) at 3 and 6 weeks might be attributed to a decrease of postoperative discomfort. Even though rESWT point had the highest mean IKDC score improvement after 24 weeks the differences between the groups were statistically insignificant.However, due to the considerable disparity in the patients' tolerance, the questionnaire ratings may be influenced.
Lysholm score emphasizes patients' subjective feelings about symptoms, and combined with digital score and patients' daily activity level, the degree of patients' dysfunction can be graded. The research shows that the scale is the most reliable for patients with anterior cruciate ligament reconstruction, and the score difference is more significant when evaluating patients with self-limiting activities. Wang et al[31]reported an rESWT treatment to ACL reconstruction patients in the bone tunnel area, and the rESWT group showed higher LKS and superior knee stability at a follow-up of 2 years after surgery, similar to our results of LKS in the experimental group, all dramatically higher than the control group (P < 0.05). In addition, ROM can determine the degree of joint limitation as an evaluation method for treatment and training. Notably, the results of ROM were significantly higher in the experimental group at 3 and 6 weeks (P < 0.05), indicating a pronounced improvement in knee function. After ACL reconstruction, the injured site secretes growth factors and cytokines, which guide cells to migrate from the periphery of the graft to the injured site, further proliferate and produce extracellular matrix, and tendinous differentiation is performed under growth factor stimulation to promote ligament healing. In this study, rESWT combined with standard rehabilitation methods had better recovery effect, which was consistent with Lu et al. [32] who found that rESWT could enhance the residual cell activity of anterior cruciate ligament and the activity and differentiation of surrounding cells, induce ACL cells to secrete transforming growth factor TGF-βand vascular endothelial growth factor VEGF, and promote vascular and tissue regeneration. Experimental group had a larger range of ROM, and the LKS was higher than that of the control group. The reason may be that standard rehabilitation methods can release adhesion, improve physiological axial movement, whereas rESWT enhances ACL residual cell activity, strengthen tendon-bone connection, significantly improve ligament recovery, stimulate muscles around the knee joint, improve local lymphatic circulation, and promote inflammatory absorption[33].
In the present research, we have demonstrated that all participants showed significant improvement in knee function after 24 weeks of treatment. Experimental design in this study focused on the effects of rESWT on pain relief, knee function and mobility in the short-term postoperative period, with follow-up and data recorded at 3, 6 and 24 weeks. Some measures about subjective perception and knee joint function have been improved in different degrees, which is consistent with the research results of Aldajah et al.[34]. This study found that rESWT can significantly relieve the pain, upper limb function and grip strength in volunteers with humeral epicondylitis. According to Lie et al[35], the application of rESWT triggered nerve tissue regeneration, stimulated cell differentiation, and reduced neuronal loss, all of these might aid to repair acute traumatic spinal cord damage. Because early postoperative rehabilitation training is particularly important for the recovery of knee joint function after ACL reconstruction, it is more vital to study the improvement of knee joint function and rehabilitation effect by rESWT in the short term after surgery for early rehabilitation training.
Strengths and Limitations
rESWT, as a positive factor affecting the rapid recovery of patients, has the advantages of non-invasive, low cost and energy regulation, and can strengthen the training and auxiliary effect in the postoperative rehabilitation stage. The results of this study suggest that rESWT is promising in the rehabilitation of ACL reconstruction and musculoskeletal system diseases, therefore, it is worthy of further study in this direction. However, this study is not without its limitations. Our study did not provide a more objective evaluation of healing, such as MRI, X-ray, KT1000, etc. Furthermore, it remains unclear whether patients with higher pain levels and severe knee impairment would benefit from rESWT and whether multiple applications of rESWT would lead to different outcomes. Due to the limitations of this study, it is necessary to include more comprehensive evaluation criteria in subsequent studies. For patients after ACL reconstruction, the optimal treatment protocol has not yet been established, and a higher level of evidence is needed to demonstrate and determine the efficacy of rESWT in future clinical trials.