: This observational case-control study aims to evaluate the efficacy of a single-dose intra-articular injection of a hybrid purified hyaluronic acid with high molecular weight and sodium chondroitin of biotechnological origin, combined with rehabilitation treatment, in sports adults with moderate to severe knee osteoarthritis. Additionally, the study incorporates isokinetic testing to assess muscle strength and functional capacity.

The primary objective is to determine whether this combined treatment improves pain relief, functional capacity, and overall quality of life compared to rehabilitation treatment alone. Participants aged 18 to 50 years, diagnosed with knee osteoarthritis, will be recruited from clinics at the U.O.C. of Recovery and Functional Rehabilitation at A.O.U.P. P. Giaccone in Palermo. Participants will be divided into two groups: one receiving the hybrid hyaluronic acid and sodium chondroitin injection along with rehabilitation, and the other receiving only rehabilitation. The study will also utilize isokinetic testing to provide objective measurements of muscle strength and endurance.

Inclusion Criteria:

• Adults aged between 18 and 50 years.
• Radiologically confirmed diagnosis of knee osteoarthritis (Kellgren-Lawrence grade ≤3), present for at least 6 months.
• Persistent moderate to severe pain due to osteoarthritis, interfering with physical performance.
• Documented reduction in sports performance (use appropriate scales or tests to validate this).
• Lack of response to pharmacological or other conservative treatments.
• Willingness to provide written informed consent for participation.

Exclusion Criteria:

• Coexisting rheumatic diseases.
• History of intra-articular viscosupplementation in the target knee within the previous 6 months.
• Presence of significant venous or lymphatic stasis.
• Body Mass Index (BMI) ≥ 30 kg/m².
• Use of systemic or intra-articular corticosteroids in the target knee within the last 3 months.
• Chronic use of topical/systemic analgesics, NSAIDs, or narcotics.
• History of alcohol or drug abuse.
• Allergy or hypersensitivity to hyaluronic acid or any of its components.
• Pregnant or breastfeeding women, or those not using adequate contraception.

Participants will be recruited from the outpatient clinics of the Unit of Recovery and Functional Rehabilitation at the A.O.U.P. P. Giaccone Hospital in Palermo. The study focuses on sports-active adults aged 18 to 50 years with clinically and radiologically confirmed knee osteoarthritis, seeking treatment for moderate to severe pain affecting physical performance.