• 1. American Orthopaedic Foot and Ankle Society (AOFAS) 2. Short Musculoskeletal Function Assessment (SMFA) 3. Foot and Ankle Ability Measure (FAAM) 4. Work Productivity and Activity Impairment Questionnaire-Specific Health Problem (WPAI-SHP) 5. X-ray [ Time Frame: Pre-operative, 6 weeks, 3, 6, 12 , 24 and 36 month intervals. ]
  

The study is designed as a prospective, randomized, controlled, single-blind study to address the safety and efficacy of the investigational Mobility™ Total Ankle System, a three-component, cementless, unconstrained, mobile-bearing prosthesis with a dedicated instrumentation system. The study is designed to compare the investigational device with a control device comprised of the Agility™ LP Total Ankle Prosthesis, a cemented, semi-constrained prosthesis with a dedicated instrumentation system. The Agility™ LP was selected as the control device because it is one of the few approved ankle prostheses in the United States, and is a modification of the most widely used ankle arthroplasty system in the United States (Agility™ Total Ankle Prosthesis K920802). Arthroplasty was chosen over arthrodesis because although both techniques reduce pain and restore alignment, arthroplasty also replaces motion of the ankle joint, which has a substantial effect on clinical outcomes. The success of the ankle prostheses will be based on a combination of clinical, radiographic, and survivorship assessments at 24 months after surgery.

The Mobility™ investigational device consists of three components, tibial, bearing, and talar. The Agility™ LP Total Ankle Prosthesis is a modular ankle prosthesis that is comprised of a tibial tray, a polyethylene tibial insert and a talar component as described in 510(k) K053569. It is available for cemented use only.

Inclusion Criteria:

• Willing or capable of providing consent to participate in the clinical investigation.
• Has medical insurance to cover costs associated with ankle arthroplasty, or is willing to assume personal responsibility for costs.
• Subject is ≥ 50 years of age and ≤ 80 years of age at the time of surgery.
• Body mass index (BMI) ≤ 35 kg/m².
• Subject does not participate in repetitive impact loading activities (e.g. jogging, running, mountain biking , heavy lower body weight lifting and competitive sports).
• Undergoing primary ankle replacement surgery for end-stage tibiotalar arthritis, including: Osteoarthritis, rheumatoid arthritis, post-traumatic arthritis.
• Sufficient soft tissue to support stable, anatomic positioning and motion of arthroplasty components.
• Meets the following selected radiographic parameters: X-ray evaluation confirms the presence of tibiotalar arthritis. Bone stock, including talus, distal tibia, and malleoli, is sufficient regarding strength and shape, and considered suitable to receive and support the implants. No structural bone grafts are required to support the prosthetic component(s) or to shape the bone to receive the implant(s).
• Stable subtalar joints and functioning ankle dorsiflexors and plantarflexors.
• Pre-operative AOFAS score of <60 including a Pain rating of 'Moderate, daily' or 'Severe, almost always present'.
• Willing to have knowledge of treatment withheld until study closure unless disclosure is deemed legally and/or medically necessary.

Exclusion Criteria:

• Subject currently has, or has had active local or systemic infection within the past twelve months.
• Neuropathy of the foot or ankle, determined using a 10 g Semmes-Weinstein monofilament.
• Impaired vascular circulation in the affected limb, evidenced by non-palpable pedal pulse or ankle-brachial pressure index < 1.0 if pulse not palpable.
• A skin condition, such as infection, medications that impede proliferation of fibroblasts or collagen synthesis (steroids and anti-metabolites), nutritional problems (protein, calorie, or vitamin/mineral deficiency that may impair wound healing mechanisms), tissue necrosis, hypoxia, other wounds present on foot/ankle, or low temperature (reduction more than 1.5 degrees C/ 3 degrees F from normal core body temp), that may impair wound healing.
• Subject is taking > 10 mg/day corticosteroids (e.g. prednisone) excluding inhalers, or selected immunosuppressants prior to defined washout period.
• Any type of diabetes.
• Uncorrectable coronal plane deformity of the ankle, 15 degrees valgus or varus.
• Uncorrected idiopathic or post-traumatic tibia deformity, 10 degrees in coronal or sagittal planes.
• Avascular necrosis of the talus.
• Subject's total ankle replacement (TAR) is required for the revision of a previously failed TAR or arthrodesis.
• A contralateral TAR.
• Subject is expected to need contralateral TAR in the subsequent two years.
• Amputation of the contralateral leg.
• Known allergy to cobalt, chromium, molybdenum, titanium, aluminum, vanadium, or nickel.
• Significant neurological or musculoskeletal deformity, paralysis, or other disorder or disease that may adversely affect gait or weight bearing, (e.g., muscular dystrophy, multiple sclerosis).
• Unwilling or unable to comply with a rehabilitation program for TAR or is known to have difficulty or inability to return for follow-up visits prescribed by the study protocol.
• Subject is known to be pregnant, a prisoner, mentally incompetent, and/or alcohol or drug abuser.