The aim of this observational study is to assess whether patient reported pain levels correlate with a Pain Index derived from deviations in multivariate physiology biomarkers captured in real-world setting. This study will be conducted using a clinical-grade wearable sensor to continuously monitor patient's physiology (pain related biomarkers) and allow subject participant to actively report their pain score, symptoms and quality of life using a mobile-based application.

The designated clinical-grade wearable sensor used in this study is the Biovotion Everion MD (See Annex for product description), a Bluetooth-compatible device that will automatically sync with the mobile application used in this study.

This study will recruit 55 patients aged 21 to 80 years who will be undergoing knee replacement, Anterior Cruciate Ligament(ACL), Knee Arthroscopy and Foot & Ankle related surgery. All study participants will be followed for an estimated total of 30 days(+6/-2 days, if visit schedule is fall on weekend), beginning four days before surgery, the entire period as an in-patient (four to five days), and 20-days post-discharge.

The changes in multivariate physiological biomarkers will be used to generate a Pain Index, and the Pain Index will be assessed against patient reported Numerical Rating Scale (NRS) pain.

Inclusion Criteria:

• Men and women aged 21 to 80 years
• Patients undergoing knee replacement surgery ( Total Knee Replacement (TKR), Unicompartmental Knee arthroplasty (UKA), Bilateral knee replacemenent, Patello-Femoral-Joint (PFJ) Knee replacement), Anterior Cruciate Ligament(ACL), Knee Arthroscopy and Foot & Ankle related surgery such as bunions, hammer toes, metatarsal, ankle fusion, triple fusion, ankle replacement, achilles tendon & tibialis posterior disorder
• Ability to provide informed consent
• Able to commit to using the app and inputting data as needed during the study duration
• Has access to an iPhone (minimum requirement iPhone 5S)

Exclusion Criteria:

• Previous myocardial infarction (MI)
• Known coronary artery disease - prior coronary revascularization
• Previous stroke. Stroke is defined as new focal neurological deficit perspective more than 24 hours.
• More than ongoing use of 2 or more anti-hypertensive agents.
• Expected life expectancy less than 1 year.
• Asthma or chronic lung disease requiring long-term medications or oxygen
• Mental illness that in the clinical judgment of the investigator will affect participation in the study e.g. dementia
• Inability to comply with the study protocol
• Any other acute or chronic medical or physical condition deemed by the investigator to affect study outcomes

55 study participants, aged between 21 to 80 years, regardless of gender, who is undergoing total knee replacement surgery will be enrolled for the study upon receiving informed consent.