Osteoarthritis (OA) is a chronic degenerative disease characterized by the destruction of articular cartilage, leading to functional impairment of surrounding bone and soft tissues. It is a major global public health problem, with the knee joint being the most commonly affected site. Treatment modalities include exercise, diet, oral non-steroidal anti-inflammatory drugs (NSAIDs), intra-articular injections, and total knee arthroplasty (TKA). TKA is indicated in cases of severe pain, functional loss, deformity, and limited range of motion when conservative methods are no longer effective. However, some patients may continue to experience deformity and functional deficits after surgery. Postoperative quadriceps weakness and decreased functional capacity can negatively affect patient prognosis.

Following TKA, bone mineral density (BMD) tends to decrease during the first three months. The reduction in BMD and the increase in bone resorption may elevate the risk of implant loosening or periprosthetic fracture. Bone turnover markers (BTMs), which are enzymes or degradation products released into circulation by bone cells, reflect bone remodeling processes and can help identify increased fracture risk.

A significant proportion of TKA candidates are osteopenic. Since osteopenic individuals make up a larger segment of the population, most fragility fractures actually occur in individuals with osteopenia rather than osteoporosis. Therefore, BMD levels and the presence of osteopenia or osteoporosis should be taken into account in patients undergoing TKA.

To preserve both bone quality and muscle mass, early rehabilitation and progressive weight-bearing on the operated limb are considered essential. These strategies may improve both BMD and BTMs. Whole-body vibration (WBV) therapy has been suggested as an effective and safe method to increase mechanical loading on the bones. WBV can be applied in a static standing position on a vibration platform or combined with simultaneous exercise.

Given the limited availability of targeted strategies to improve bone remodeling and BTMs after TKA, and the lack of clarity regarding the optimal WBV protocol, this study aims to investigate the effects of different vibration applications on bone turnover markers, functionality, muscle strength, pain intensity, pressure pain threshold, range of motion, proprioception, edema, and muscle biomechanical properties in osteopenic women following TKA.

Participants will be randomly assigned to one of three groups: WBV only, WBV combined with exercise (WBV-E), or control. All groups will receive traditional rehabilitation three times per week for four weeks after surgery. WBV interventions will begin at the end of the fourth postoperative week, once patients are deemed ready. While WBV groups will receive additional vibration therapy, the control group will continue traditional rehabilitation alone.

Outcomes will be evaluated using bone turnover markers, the Timed Up and Go (TUG) test, the 30-Second Chair Stand Test, the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), measurements of muscle biomechanical properties and strength, pain intensity and pressure pain threshold, joint range of motion, proprioception, and edema.

Inclusion Criteria:

• Scheduled to undergo unilateral, primary, cemented total knee arthroplasty (TKA) using a posterior cruciate ligament-sacrificing technique and medial parapatellar approach due to knee osteoarthritis
• Ability to speak and understand Turkish
• Ability to comprehend both verbal and written information
• A T-score between -2.5 and -1 (i.e., -2.5 < T-score < -1) measured by DXA in the lumbar spine, total hip, or femoral neck within the past year

Exclusion Criteria:

• Scheduled for revision TKA
• American Society of Anesthesiologists (ASA) physical status classification score higher than 3
• History of major surgery on the limb to be operated
• Presence of comorbid diseases such as rheumatoid arthritis or cancer
• Presence of a neurological condition causing functional impairment
• Diagnosed psychiatric disorder
• Dementia
• Disorders affecting the vestibular system
• Having undergone anesthesia for any reason within the last month
• Regular use of hypnotic or anxiolytic medications
• Hearing or vision impairment not correctable by hearing aids or glasses
• Presence of endocrine system disorders
• Secondary osteoporosis or history of osteoporotic fracture
• Metabolic bone diseases or chronic illnesses potentially affecting bone metabolism
• Use of medications known to affect bone metabolism (e.g., menopausal hormone therapy, bisphosphonates, raloxifene, calcitonin, growth hormone, parathyroid hormones, corticosteroids) within 6 months prior to the start of the study

The study will share de-identified, summary-level outcome data, including group-level means, standard deviations, effect sizes, and p-values derived from statistical analyses. These data will be provided to support transparency and allow for interpretation of the study findings.

Summary-level data and supporting documents (e.g., study protocol and statistical analysis plan) will be available within 12 months following the final publication of study results and will remain accessible for at least 5 years via institutional repository or upon reasonable request.

The study's outcome results, including group-level means, standard deviations, p-values, and effect sizes, as well as supporting materials such as the study protocol and statistical analysis plan, will be made available to qualified academic researchers upon reasonable request. Data will be provided for ethically approved, non-commercial research purposes. Interested investigators should contact the principal investigator through the affiliated institution and submit a written request describing the intended use and data handling procedures. Each request will be reviewed individually in accordance with institutional data-sharing guidelines.