Osteoarthritis (OA) is a progressive disease of the synovial joints that causes joint pain and limitation of function resulting in considerable morbidity and impairment of quality of life. Knee OA is the most common type of OA, and symptomatic knee OA is highly prevalent among people aged over 50 years. With the increasing aging population, worldwide prevalence of knee OA is expected to be rising. The goals of treatment are to reduce pain, maintain or improve joint mobility, minimize functional impairment and improve quality of life. When conservative management, which includes structured land-based exercise programs, aquatic exercise, education and appropriate analgesic medications, fails, surgical approach can be considered. Unicompartmental knee arthroplasty (UKA) has become an alternative to TKA in cases of end-stage OA that are limited to a single compartment. Patients who underwent UKA have a quicker recovery, lower risk of complications, and improved range of motion. Physiotherapy rehabilitation is an integral part of good knee arthroplasty outcome. Conventional post-operative physiotherapy rehabilitation, which includes range of motion exercises, muscle strengthening exercises, balance and gait training, have been shown to have improvement in range of motion, muscle strength and functional outcome measures of patients. Recently, hydrotherapy is gaining its popularity as being incorporated into one of the components in the rehabilitation after knee arthroplasty. Studies reported that hydrotherapy could decrease pain, and improved physical function, strength and quality of life for patients after total hip or knee arthroplasty. However, there are no studies to investigate the effect of hydrotherapy on patients after UKA. With the increasing popularity of UKA as a surgical alternative in patients with end-stage single-compartmental OA, it is worth investigating the effects of hydrotherapy on the clinical outcomes of patients following UKA.

Osteoarthritis (OA) of the knee is one of the most common chronic degenerative joint diseases, primarily affecting the ageing population, limiting joint movement and causing disability because of pain and stiffness. Prevalence of radiologic knee OA increased in proportion to age, reaching 64.1% for those who were aged 60 and over, and had a higher prevalence in females than males. OA is a progressive joint disorder, characterized by progressive softening and disintegration of articular cartilage, growth of osteophytes and fibrosis of joint capsule. Clinical presentations vary from asymptomatic despite the presence of radiological evidence, to progressively evolving symptoms and eventually severely disabling joints. Knee OA is the most common type of OA, affecting patello-femoral joint and/or medial tibio- femoral joint. Symptoms of knee OA include joint pain, knee effusion, quadriceps muscle weakness and wasting, giving way, and knee deformities such as fixed flexion contractures and varus knees. These can lead to functional limitations, resulting in substantial morbidity and impaired quality of life. The Global Burden of Diseases studies reported that OA was the leading cause of lower extremity disability in elderly, with hip and knee OA accounting for 1.12% of years lived with disability. OA has been reported to be ranked the seventh leading cause of global years lived with disability. Moreover, knee OA leads to substantial medical expenses and economic burden. Patients suffering from knee OA flock to general practitioners and orthopaedic specialists for analgesic medications and injections, or physiotherapists for exercise consultations, or orthopaedic surgeons for surgery. These reactions subsequently become burden to healthcare systems and expenses leading to healthcare dilemmas.

The ever-aging population proved to be one of the strongest predictors of OA, particularly in patients with age 50 years and higher. Studies reported that there was a high prevalence of symptomatic knee OA among people aged over 50 years, affecting more than 250 million people worldwide. With the growing aging population, worldwide prevalence of knee OA is expected to be rising. Therefore, knee OA is gaining attention from our society, policy makers and medical professionals on its management, aiming at holistic, cost-effective and evidence-based care approach. Management of knee OA can be classified into conservative and surgical approaches, aiming at reducing pain, maintaining or improving joint mobility, minimizing functional impairment and improving quality of life. For conservative approach, a combination of non-pharmacological and pharmacological modalities, which include structured land-based exercise programs, aquatic exercise, education and appropriate analgesic medications, are recommended and supported by evidence.

Surgery is the subsequent approach after failure in conservative management. Total knee arthroplasty (TKA) has been the dominating surgery for patients who suffer from severe end- stage symptomatic OA but fail to respond to conservative management and have significantly impaired function and quality of life. Recently, unicompartmental knee arthroplasty (UKA) has become an alternative to TKA for patients with end-stage knee OA.

Patients after UKA reported quicker recovery period, lower risk of complications and better range of motion if the knee. Our group investigated the correlation between femoral and tibial component axial rotational alignment and functional outcomes in 83 Oxford UKA from in 67 patients with isolated medial or lateral compartment knee osteoarthritis. We found that femoral component axial rotation between 2° and 6° external rotation, and tibial component axial rotation between 1° and 8° external rotation correlated with significantly better functional scores, with the highest functional scores observed at 3°-4° external rotation for femoral component, and 4°-5° external rotation for tibial component.

After knee arthroplasty, physiotherapy rehabilitation is a part of non-invasive treatments leading to a successful outcome after surgery. Conventional post-operative physiotherapy, including exercises aiming at improving range of motion, muscle strengthening, body balance and gait training, showed to have improvement in range of motion and muscle strength of knee. An European review on exercises after knee arthroplasty reported improvements in various functional outcome measures such as Western Ontario and McMaster Universities Arthritis Index (WOMAC), Medical Outcome Study Short Form-36 (SF-36), Oxford Knee Score, American Knee Society Score, Lower Extremity Functional Scale and Iowa Lower Extremity Scale.

Recently, hydrotherapy is gaining popularity on its use being an important component in rehabilitation programme after knee arthroplasty. Hydrotherapy is the external or internal use of water in any of its forms (water (liquid), ice (solid), steam (gas)) for health promotion or treatment of various diseases with various temperatures, pressure, duration, and site. In clinical settings, patients exercise in a temperature-controlled water pool led by a physiotherapist. Exercising in water has a long history of beneficial therapeutic effect to promote healing in certain medical conditions. Hydrotherapy has been widely used in various musculoskeletal and neurologic conditions, from paediatric to geriatric population. Patients exercising in a hydrotherapy pool could perform better than on land and let patients who could not perform the same exercise on land work out under water. Benefits of warm-bathing hydrotherapy include relieving pain and muscle spasm through warmth, reducing loading of joints through buoyancy, decreasing oedema through pressure from immersion, and producing resistance to movement through turbulence and hydrostatic pressure. Studies proved that hydrotherapy could decrease pain, and improve physical functions, muscle strength and quality of life in patients after total hip or knee arthroplasty.

Given the benefits of hydrotherapy on patients who underwent joint replacement, there is no study investigating the effect of hydrotherapy on patients after UKA. With the increasing popularity of UKA as a surgical alternative to TKA for patients with end stage single-compartmental knee OA, it is worth investigating the effects of hydrotherapy on the clinical outcomes of patients following UKA. Results can guide further discussions on whether hydrotherapy should be incorporated into the post-joint replacement surgery physiotherapy rehabilitation in clinical practice.

Inclusion Criteria:

• Patients who aged 18 or above, and underwent primary unilateral UKA , with the Oxford model, at the Department of Orthopaedics and Traumatology of the Alice Ho Miu Ling Nethersole Hospital (AHNH) in year 2018 and 2019 were included.

Exclusion Criteria:

• Patients who had post operative complications, underwent revision or robotic assisted surgery or bilateral knee arthro plasty, defaulted follow up, received post operative physiotherapy rehabilitation which was not at the Physiotherapy Department of AHNH, had cognitive impairment, or were unsuitable for exercise training, were excluded in this study.

Share among Study PI and research assistants within the facility only.