A common complication following total knee replacement (TKR) is arthrofibrosis, a severe stiffening of the knee caused by scar tissue.

The aims of this mixed methods feasibility study are to (1) record the effect of use of the STAK Tool on knee flexion active range of movement (KROM) immediately following 8 weeks use and 6 months following use, (2) explore patients' experiences of arthrofibrosis and use of the STAK Tool, (3) Consider appropriate outcome measures (e.g. KROM, patient experience/acceptability, The Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), Oxford Knee Score (OKS) and other clinical measures and (4) design a protocol to evaluate the effectiveness of the STAK Tool.

Arthrofibrosis most commonly occurs after total knee replacement (TKR), extensive intra-articular injury or surgical procedures, for example fracture of the proximal tibia or distal femur or multiple ligament reconstructions (Creighton and Bach 2012). Arthrofibrosis involves a severe stiffening of the knee caused by scar tissue. This often results in a lack of crucial range of knee flexion movement. Traditional physiotherapy treatment includes a home exercise programme involving regular intense stretches and mobilisations delivered by the physiotherapist at the hospital aiming to enable the patient to regain optimal, functional knee bend. The inflammatory process and remodeling of soft tissues following trauma can lead to production of scar tissue and subsequent stiffness. This results in increased pain and difficulty in performing exercises. This often limits progress requiring high numbers of physiotherapy sessions and potentially further surgery (manipulation under anaesthetic) to restore range of movement.

The STAK Tool enables the patient to perform intense self-stretching of the knee more easily and effectively. Intense stretching is essential to increase KROM (Bonutti et al 2008, Bonutti 2010, Papotto et al 2012, Stephenson et al 2010). Patients who fall into the category of having restricted KROM (less than 70 degrees flexion) and those whose Clinicians identify them as requiring further intensive physiotherapy to address their stiffness would be approached to take part in this study. 36 participants would be recruited. Participants would be over 18 years old, between 44kg and 159kg. This mixed methods feasibility study would investigate patients' progress and outcomes in overcoming arthrofibrosis using the STAK Tool a medical stretching device at home plus standard physiotherapy treatment (intervention group), compared to patients receiving physiotherapy treatment only (comparative group). Participants would be allocated into either the intervention or comparative group. Participants would be instructed to use the STAK Tool for 5-10 minute periods for a minimum total of 20 minutes and maximum of 60 minutes a day.

Participants would receive their standard physiotherapy treatment including KROM, full weight bearing exercises including sit to stands, squats, body weight assisted passive stretches, strengthening exercises and mobilisations. Angle of knee flexion would be measured (standardised method) by the Principal Investigator and the WOMAC and OKS are administered on the day the participant consents to the study (Visit 1), the day the intervention starts. This will be within approximately 2 weeks of the patient being identified by their clinician. (The Principal investigator will visit the participant within 10 days to ensure there are no problems using the STAK Tool (Visit 2 - only intervention group). During Visit 1 an interview (interview 1), would be conducted to explore the patients' initial thoughts on the STAK Tool after being introduced to it. Both the intervention and comparative groups will have their KROM recorded using two different measuring instruments, the universal goniometer and the Hudl Ubersense App. Outcome measures including KROM, WOMAC and OKS will be recorded again following approximately 8 weeks treatment (dependent on time available before manipulation as per normal clinical care), at either the patient's final follow-up with their Clinician or at their home (Visit 3) (end of intervention). The WOMAC and OKS would help to ascertain the patient's perceptions of pain, stiffness and functional improvements. At Visit 3 participants would also complete a questionnaire regarding the frequency of knee stretching exercise completed and how easy/difficult it had been to achieve. On completing 8 weeks standard treatment patients in the comparative group who were deemed eligibility by their Clinician would be offered the STAK Tool 8 week treatment.

Visits would then be completed as per the intervention group minus the interviews.

An in-depth semi-structured interview (interview 2) will be conducted with participants in the intervention group exploring their thoughts and experiences of using the STAK Tool to increase their knee flexion, their perceived progress and acceptability of the device.

A follow up meeting (Visit 4) would take place at 6 months after Visit 3, this would take place at the participant's home patients KROM, WOMAC and OKS would be recorded to provide data relating to participants long term outcomes.

Inclusion Criteria:

• male or female,
• 18 to 95 year olds,
• having received a primary total knee replacement within the last 12 months.
• Following their TKR have less than 70 degrees knee flexion or have been prescribed intensive physiotherapy for their knee stiffness by their Consultant.
• Between 44kg and 159kg.

Exclusion Criteria:

• post malignancy or knee trauma
• have leaking wounds or infected joints,
• have rheumatoid arthritis or osteoporosis,
• have undergone long term steroid treatment or the clinician felt the patient was at risk of post-operative fracture.
• Fell outside weight limits (44kg to 159kg),
• Unable to give consent themselves (confusion, non-English speaking patients).