This is a study to evaluate the Clinical Performance and Safety of a single intra-articular (i.a.) injection of hyaluronic acid product (as HL-01) in the treatment of pain due to osteoarthritis (OA) of the knee.

Inclusion Criteria:

• Female and male subjects ≥40 to 80 years of age.
• Subjects with primary knee OA of the medial or lateral femoro-tibial compartment, documented according to ACR criteria with symptoms, at screening, from at least 3 months.
• Subjects with Kellgren & Lawrence (K-L) radiological grade 2-3.
• Subjects with at least one antero-posterior view X-Ray image of the target knee taken within 12 months prior to the screening.
• Subjects with OA pain intensity meeting the criteria below:

If unilateral knee OA: Subjects demonstrating at screening pain intensity in the target knee measured by Visual Analogue Scale (VAS) ≥40 mm VAS, and ≤ 20 mm in the contralateral knee and confirmed at randomization after wash-out from analgesics/NSAIDs.

If bilateral knee OA: definition of the most symptomatic joint at screening based on subject's evaluation and Investigator's clinical judgment with subjects demonstrating pain intensity in the target knee measured by Visual Analogue Scale (VAS) ≥40 mm VAS, and ≤ 20mm in the contralateral knee and confirmed at randomization after wash-out from analgesics/NSAIDs.

• Subjects are able to understand and are willing and able to comply with study procedures including usage of acetaminophen as the only analgesic.
• Subjects are able to provide informed consent.
• Any female subject of childbearing potential must agree to use adequate methods of contraception throughout the course of the study.

Exclusion Criteria:

• Subjects with secondary (post-traumatic) knee OA of the target and non-target joints.

• Subjects with K-L radiological grade 4 knee OA.

• Subjects with a history of knee joint replacement/arthroplasty of the target knee.

• Subjects with a history of arthroscopy, osteotomy, or surgery of the target knee in the past 12 months.

• Subjects with any significant injury to the target knee in the last 6 months (as per Investigator judgment).

• Subjects with Body Mass Index (BMI) ≥32 kg/m2.

• Subjects with any musculoskeletal condition affecting the target knee that would impair proper assessment of the Investigational Medicinal Device (IMD) performance in the target knee as assessed by the Investigator and such as:

  1. severe varus/valgus deformity (>15°)
  2. predominantly patello-femoral pain/syndrome.

• Subjects with a history of symptomatic hip OA or other health condition i.e. associated with pain and interfering with adequate study endpoints evaluation.

• Subjects with a known history or present evidence of conditions which may affect the target knee assessments, like rheumatic disease and inflammatory, infective or metabolic joint diseases; recurrent clinical chondrocalcinosis; crystal arthropathies; osteo-articular pathologies differing from arthrosis; articular fracture; ochronosis; acromegaly; haemochromatosis; Wilson's disease; primary osteochondromatosis; heritable disorders; collagen gene mutations.

• Subjects with venous or lymphatic stasis in the relevant limb.

• Subjects with a history of the following treatments for knee OA:

  a) I. a. knee corticosteroids: i. target knee - in the past 3 months ii. non-target knee/other joints - in the past 4 weeks b) Systemic (both oral and parenteral) and topical corticosteroids at the target knee in the past 3 months.

  c) Topical anti-inflammatories and analgesics applied at the target knee in the past 48 hrs.

  d) Viscosupplementation with hyaluronic acid or joint-lavage in the target knee in the past year.

  e) Physical therapy started in the last 3 months in the target knee. f) Symptomatic Slow-Acting Drugs for OA (SYSADOA) such as glucosamine, chondroitin sulfate, diacerhein, or other medications like avocado/soya extracts, etc. in the past 3 months.

  g) Chronic or recurrent use of narcotic analgesics. h) Use of analgesic (other than acetaminophen) and NSAIDs for a time of 5-half-lives before the screening.

• Subjects with a history of chronic or recurrent use of NSAIDs/analgesics/narcotics because of diseases different from OA of the target knee.

• Subjects treated with drugs having an influence on pain: hypnotics, muscle relaxants, anxiolytics if the intake has started less than 8 days before the screening.

• Subjects who currently use heparin or anti-vitamin K (e. g. crystalline warfarin) anticoagulant therapy.

• Subjects with the presence of infection, skin diseases, other disease or trauma in the area of the injection site or joint.

• Subjects with a known history or suspected allergy or hypersensitivity to hyaluronic acid or to hyaluronate preparations.

• Subjects with a known history or suspected allergy or hypersensitivity to acetaminophen.

• Subjects with any major surgery scheduled in the next 6 months.

• Subjects who have participated in a clinical study / investigation in the last 3 months.

• Pregnant or lactating women and women of childbearing potential not willing to use adequate contraception.

During the course of the study only the physicians who will perform the intra-articular injection (injectors) will be unblinded. All the other physicians (assessors) and study participants will be blinded