Here is the design of a clinical trial:

Official Title: Effectiveness of a Community-based Post-operative Rehabilitation and Fall Prevention Program Following Total Knee Arthroplasty - a Randomized Controlled Trial

Included conditions:
- Knee Osteoarthritis
- Fall

Study Armgroups:
- {'label': 'Fall prevention group', 'type': 'EXPERIMENTAL', 'description': 'Fall prevention program', 'interventionNames': ['Other: Fall prevention program']}
- {'label': 'Usual care group', 'type': 'NO_INTERVENTION', 'description': 'Usual postoperative care'}
- {'label': 'Asymptomatic control', 'type': 'NO_INTERVENTION', 'description': 'No intervention'}

Interventions:
- {'type': 'OTHER', 'name': 'Fall prevention program', 'description': '12-week fall prevention program (including warm-up, cool-down, education, Tai Chi, and lower limb strengthening)', 'armGroupLabels': ['Fall prevention group']}

Primary Outcomes:
- {'measure': 'Chinese version of Knee Injury and Osteoarthritis Outcome Scale', 'description': 'A 42-item questionnaire with 5 subscales to assess pain, symptoms, activities of daily living, sports and recreation function, and knee-related quality of life', 'timeFrame': '1 year'}

Please estimate the sample size based on the assumption: 
No formal statistical assumptions were made. The study aims to evaluate feasibility, recruitment, retention rates, and acceptability.
Sample size
        No formal sample size calculation was performed for this feasibility study. However, a minimum sample size for a pilot study to evaluate the feasibility of conducting a full-scale trial is suggested to be 50 per study [18, 19]. A total of 78 patients (26 per arm) were deemed an appropriate sample size for this trial to estimate the recruitment and retention rates and explore the acceptability of the intervention.