Extracorporeal shockwave therapy for treatment of delayed tendon-bone insertion healing in a rabbit model: A dose-response study

Background: Tendonbone insertion (TBI) consists of both hard and soft tissues. TBI injury with delayed repair is not uncommon. High-dose extracorporeal shockwave (ESW) is effective for treating nonunion fracture, whereas low-dose ESW is used for tendinopathy therapy. The dosing effect of ESW on delayed TBI healing is lacking. Hypothesis: Low-dose ESW might have a healing enhancement effect comparable to that of high-dose ESW in treating delayed TBI healing. Study Design: Controlled laboratory study. Methods: Partial patellectomy was adopted to create a delayed TBI healing model by shielding the healing interface between tendon and bone. Ninety-six female New Zealand White rabbits with unilateral delayed TBI healing at the knee joint were divided into 3 groups: controls, low-dose ESW (LD-ESW; 0.06 mJ/mm2, 4 Hz, 1500 impulses), and high-dose ESW (HD-ESW; 0.43 mJ/mm2, 4 Hz, 1500 impulses). The TBI shielding was removed at week 4 after partial patellectomy, followed by treatment with control or ESW at week 6. The rabbits were euthanized at week 8 and week 12 for radiological, microarchitectural, histological, and mechanical assessments of healing tissues. Results: Radiologically, both the LD-ESW group and the HD-ESW group showed larger new bone area than the controls at week 8 and week 12. Microarchitectural measurements showed that the LD-ESW and HD-ESW groups had larger new bone volume than the controls at week 12. Histological assessments confirmed osteogenesis enhancement. Both the LD-ESW and HDESW groups showed significantly higher failure load at the TBI healing complex than the control group at week 12. No significant difference was detected between the 2 ESW treatment groups at week 8 or week 12. Conclusion: Extracorporeal shockwave, a unique noninvasive physical modality, had similar effects between the low and high dose for treating delayed TBI healing. Clinical Relevance: Low-dose ESW for TBI delayed healing might be more desirable and have better compliance in clinical applications.