Extracorporeal Shock Wave Therapy in the Treatment of Periarticular Bone Marrow Edema in Patients With Knee Osteoarthritis

Bone marrow edema (BME) is a common magnetic resonance imaging (MRI) finding in patients with knee osteoarthritis (OA) and is associated with pain, functional impairment, and structural progression of the disease. MRI is considered the gold standard imaging method for the diagnosis of BME. In the early stages, BME typically appears as an area of low signal intensity on T1-weighted images and high signal intensity on fluid-sensitive sequences, particularly T2-weighted, fat-suppressed, and short tau inversion recovery (STIR) images. These findings reflect increased water content and inflammatory changes within the bone marrow. As the lesion progresses, a subchondral pattern with low signal intensity on both T1- and T2-weighted images may develop, reflecting more advanced structural changes in the subchondral bone. BME is thought to represent an active pathological process involving subchondral bone damage, bone remodeling, inflammation, vascular changes, and altered mechanical loading.

Conservative treatment is generally considered the first-line treatment for BME and includes reducing weight-bearing on the affected limb, activity modification, pain control, and physical therapy modalities. Extracorporeal shock wave therapy (ESWT) is a noninvasive treatment modality used in various musculoskeletal disorders. Its proposed effects include improving local blood flow, promoting angiogenesis and bone remodeling, stimulating osteogenic activity, and reducing pain. Previous studies have suggested that ESWT may reduce pain, improve functional outcomes, and improve MRI findings in patients with BME. However, evidence regarding the effectiveness of ESWT specifically in patients with periarticular BME associated with knee OA remains limited. Further investigation is needed to determine its effects on clinical outcomes and quantitative volumetric changes in BME.

This study is a prospective, randomized, double-blind, sham-controlled clinical trial designed to investigate the effects of radial ESWT in patients with knee OA accompanied by periarticular BME. A total of 24 patients aged 40-70 years who present to the Department of Physical Medicine and Rehabilitation at Dokuz Eylül University Faculty of Medicine with knee pain and meet the eligibility criteria will be included. Eligible patients will have knee OA based on clinical findings, Kellgren-Lawrence grade 2 or 3 disease on radiographs, and unilateral BME involving the bones around the knee joint on MRI. The BME lesion must be limited to one compartment of the knee, either the medial or lateral compartment. In the medial compartment, the lesion may involve the medial femoral condyle, medial tibial plateau, or both. In the lateral compartment, it may involve the lateral femoral condyle, lateral tibial plateau, or both. Patients who meet the eligibility criteria and provide written informed consent will be randomly assigned to either the active ESWT group or the sham ESWT group, with 12 patients in each group. Randomization will be performed using a sealed-envelope method. Group allocation will be concealed using sequentially numbered, opaque, sealed envelopes, which will be opened only after participant enrollment.

Both groups will receive the same standard conservative treatment for BME throughout the study. Patients will be instructed to reduce weight-bearing on the affected limb for five weeks and to use a cane or crutches to avoid full weight-bearing. They will be allowed to continue their usual daily and work-related activities while avoiding movements that aggravate their symptoms or place excessive stress on the affected knee. Paracetamol will be permitted as rescue medication when needed, while other analgesic medications will not be allowed. The total number of 500 mg paracetamol tablets consumed will be recorded during the study period. No additional physical therapy modalities, intra-articular injections, or surgical procedures will be permitted during the study period. Thus, ESWT will be evaluated as an additional treatment to standard conservative management rather than as a stand-alone treatment.

In the active ESWT group, radial shock wave therapy will be applied to the predetermined BME area identified on MRI. The ESWT probe will be placed directly on the skin over the treatment area. Each treatment session will consist of 2,000 shock waves delivered at a frequency of 6-8 hertz (Hz) and a pressure of 1.8-2.5 bar. Treatment will be administered once weekly for five consecutive weeks, for a total of five ESWT sessions. During each treatment session, both researchers will be present in the treatment room. The first researcher will administer ESWT, while the second researcher will remain in the room without performing any additional intervention.

In the sham ESWT group, treatment will be administered according to the same schedule. The ESWT device will be operated at a low setting to reproduce the characteristic treatment sound without delivering therapeutically effective shock waves. The ESWT probe will be held close to the treatment area without direct contact with the skin. At the same time, the second researcher will place the inactive probe of a switched-off ultrasound device, similar in size to the ESWT probe, directly on the skin over the BME area to reproduce the physical sensation of treatment.

To maintain participant blinding, patients in both groups will wear an eye mask throughout each treatment session and will not be able to observe the devices or procedures being performed. Both researchers will be present in the treatment room during all active and sham treatment sessions. The duration of the sessions, patient positioning, device sounds, and overall treatment environment will be kept as similar as possible between the two groups. These standardized procedures will be used to minimize differences between active and sham treatment sessions and to prevent participants from determining their treatment allocation.

Before treatment, demographic and clinical characteristics of the participants will be recorded. Pain intensity will be evaluated using the visual analog scale (VAS), and symptoms and functional status related to knee OA will be assessed using the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC). Both assessments will be performed at baseline, immediately after completion of the five-week treatment period (week 5), four weeks after treatment completion (week 9), and eight weeks after treatment completion (week 13).

BME volume will be evaluated using MRI at baseline and week 13. Volumetric changes in BME lesions will be measured to assess the radiological response to treatment. All MRI examinations will be evaluated by a single experienced radiologist who will be blinded to treatment allocation. Patient satisfaction will be assessed at weeks 5, 9, and 13. Paracetamol consumption will be documented as the number of 500 mg tablets used during three intervals: baseline to week 5, week 5 to week 9, and week 9 to week 13.

The primary outcomes of the study will be changes in pain intensity assessed by the VAS and changes in BME volume assessed by MRI. Secondary outcomes will include changes in WOMAC total scores and patient satisfaction. Paracetamol consumption will be recorded as an additional outcome measure. The study aims to determine whether adding radial ESWT to standard conservative treatment provides additional clinical and radiological benefits in patients with knee OA-associated periarticular BME.