Anterior cruciate ligament (ACL) tear is common. It accounts for over 50% of all knee injuries. Anterior cruciate ligament reconstruction (ACLR) with hamstring tendon (HT) autograft is the common graft choice for ACLR. However, the outcomes of donor site healing and recovery of muscle strength of HT are not satisfactory, resulting in hamstring muscle weakness and hamstring strength deficit during deep knee flexion, which may lead to hamstring strain after ACLR. Moreover, activation of the hamstring muscle is vital for maintaining dynamic knee joint stability and preventing excessive ACL shear forces. The presence of hamstring muscle deficits after surgery therefore affects the function of the reconstruction ACL. A previous study has reported that the hamstring muscle showed nearly 20% strength deficit at 4 months after ACLR with hamstring autograft

Pulsed electromagnetic field (PEMF) treatment is a non-invasive therapy that has been shown to enhance muscle cell activity and accelerate tissue repair. In clinic, PEMF treatment has been reported to be safe.

This study aims to conduct a double-blinded, placebo-controlled randomised clinical trial to investigate the effects of PEMF therapy for improving the tissue regeneration and strength of the HT donor site in ACLR patients with HT autograft.

Inclusion Criteria:

1. Male and female with age ≥ 18 years at the time of surgery
2. First ACLR with HT autograft
3. Both knees without a history of injury/prior surgery
4. LSI for hamstring strength <85% of contralateral leg at 4-month isokinetic assessment (70)
5. Voluntarily agreed to participate and signed the informed consent form

Exclusion Criteria:

1. Any concomitant bone fracture, major meniscus injury or full-thickness chondral injuries requiring altered rehabilitation program post-op
2. Preoperative radiographic signs of arthritis
3. Other associated injuries (fractures and other ligament involvement such as neurovascular bundles injury)
4. Patient with a pacemaker, an implantable defibrillator, neurosurgical clips, a neurostimulator, cochlear implant, a stent, an insulin pump
5. Pregnant or breastfeeding
6. Inability to give informed consent