Knee osteoarthritis (OA) is one of the most common joint disorders worldwide and is a leading cause of pain, limited mobility, and functional disability, particularly in the elderly population. According to 2020 data, approximately 654 million individuals aged 40 years and older are affected by knee OA worldwide, with a global prevalence of 22.9% in this age group. In our country as well, OA is reported as the second most common rheumatologic disease. The disease not only negatively affects individuals' quality of life but also creates a significant socioeconomic burden through work loss, hospital admissions, and the need for surgical interventions.

The pathogenesis of knee OA is a complex process involving articular cartilage degeneration, subchondral bone sclerosis, synovial tissue proliferation, and osteophyte formation. Once cartilage damage begins, its capacity for spontaneous healing is extremely limited; therefore, early interventions aimed at slowing or halting disease progression are of critical importance. In this context, non-pharmacological interventions, particularly exercise programs that may contribute to maintaining cartilage integrity, are strongly recommended as first-line treatment options in current clinical guidelines.

The beneficial effects of exercise therapy on pain and function in patients with knee OA are well documented. However, the structural effects of exercise on femoral cartilage thickness have been relatively less investigated. Tuna et al. evaluated femoral cartilage thickness using ultrasonography in 40 patients with knee OA following a 12-week quadriceps strengthening program and reported statistically significant increases in cartilage thickness in the medial condyle, lateral condyle, and intercondylar region at 3 months. This pioneering study suggests that muscle strengthening programs may have not only symptomatic but also structural benefits. Similarly, Bozan et al. reported a strong positive correlation between quadriceps muscle thickness (rectus femoris + vastus intermedius) and femoral cartilage thickness, supporting the idea that muscle loss parallels cartilage degeneration. However, these studies focused exclusively on the quadriceps muscle, and the effects of hip musculature on femoral cartilage thickness have not been investigated. Recent biomechanical studies indicate that hip abductor and adductor muscles play a critical role in knee joint loading patterns.

Hip abductor muscles provide pelvic stability during gait and directly influence knee adduction moments. Weakness of the gluteus medius leads to contralateral pelvic drop, increasing medial compartment loading on the ipsilateral knee and accelerating medial tibiofemoral cartilage wear. Indeed, Segal et al., using data from the Multicenter Osteoarthritis Study (MOST), demonstrated via MRI that greater hip abductor strength significantly reduces the risk of progression of medial patellofemoral and lateral tibiofemoral cartilage damage. On the other hand, hip adductor muscles are also thought to contribute to knee adduction moments by eccentrically controlling femoral varus motion; however, this relationship has been studied far less compared to quadriceps and abductors.

Systematic reviews and meta-analyses have shown that individuals with knee OA have up to 24% lower isometric hip abductor strength compared to healthy controls. Randomized controlled trials investigating combined hip and quadriceps strengthening programs have reported significant improvements in pain and function. However, none of these studies have used femoral cartilage thickness measured by ultrasonography as a primary outcome.

A review of the current literature reveals that although studies exist examining the effects of quadriceps strengthening on femoral cartilage thickness, no randomized controlled trial has compared hip abductor and adductor strengthening exercises with a quadriceps strengthening program, using ultrasonographic femoral cartilage thickness as the primary outcome measure. This study aims to address this gap. All interventions will be applied as non-invasive home exercise programs, and all measurements will be performed using ultrasonography. Baseline, 1-month, and 3-month assessments will also allow evaluation of the temporal effects of exercise on cartilage structure. The findings are expected to provide scientific evidence regarding the structural protective effects of hip exercises in knee OA rehabilitation and serve as pilot data for future large-scale multicenter studies.

The aim of this study is to compare patients with knee OA receiving quadriceps strengthening exercises alone with those receiving additional hip abductor/adductor strengthening exercises in terms of changes in femoral cartilage thickness, and to evaluate whether there is a correlation between femoral cartilage thickness and the thickness of the rectus femoris, gluteus medius,

Inclusion Criteria:

1. Age ≥18 years
2. Diagnosis of knee osteoarthritis according to ACR criteria, Kellgren-Lawrence grade 2-3
3. Knee pain for at least 3 months
4. Having the physical capacity to perform a home exercise program
5. Willingness to provide written informed consent

Exclusion Criteria:

1. History of knee, hip, or spine surgery
2. Active inflammatory arthritis (e.g., rheumatoid arthritis, gout, psoriatic arthritis)
3. Intra-articular injection within the last 3 months
4. Neurological or neuromuscular disorders
5. Body mass index (BMI) > 40 kg/m²
6. Pregnancy
7. Cardiovascular or orthopedic contraindications preventing participation in a regular exercise program
8. Cognitive impairment