A Functional Comparison of Two TKR Designs

Total knee replacement (TKR) is an established treatment for knee osteoarthritis and leads to a satisfactory outcome in over 75% of patients. However, up to 25% of patients are not entirely satisfied with their TKR. Patient dissatisfaction has been associated with inadequate functional outcome, especially during negotiation of stairs and slopes. This phenomenon, known as mid-flexion instability, is believed to be caused by excessive anterior-posterior motion of the implant during activities of daily living. This is characterised as a perception that the replaced knee is unsteady during certain tasks.

This study will compare the functional outcome of two implants that have been designed to provide patients with a functionally stable knee throughout its range of motion. The different design roles in preventing implant-related mid-flexion instability remain unknown. The functional outcome and stability of these implants will be tested non-invasively with 3D motion capture technology.

This study will compare the functional outcome of two implants that have been designed to provide patients with a functionally stable knee throughout its range of motion. The different design roles in preventing implant-related mid-flexion instability remain unknown.

The Medacta GMK-Sphere implant consists of a fully congruent medial compartment which allows freedom of movement in the lateral compartment. Both femoral and tibial components are also available in a range of 13 sizes, allowing the surgeon to find a 'best fit' for each patient. These design features are aimed to mimic the movement of a natural healthy knee, potentially preventing implant-related mid-flexion instability.

The DePuy Synthes Attune implant design aims to provide patients with optimal functional outcome. The femoral component of this implant has a gradually reducing radius, and the tibial component an S-shaped post-cam mechanism. These features are designed to facilitate smooth movement and stability during flexion.

The comparative functional outcomes and stability in gait, and other activities of daily living has not been established for the two different TKR design concepts. Functional assessments will be carried out on TKR patients pre- and post-operatively. These assessments will non-invasively quantify the knee's stability, range of motion, strength as well as walking kinematics using 3D motion capture technology. As mid-flexion instability is most notable during downhill walking, patients will be required to walk downhill on a treadmill as part of this study, to better investigate the phenomenon of mid-flexion knee instability.

This study will not involve any invasive procedure in addition to the standard of care. As such, the research burden is minimal. The main ethical issue may be that patients will not be randomised into one of the two proposed groups.

Patients will receive either the GMK-Sphere implant or the Attune implant according to their surgeon's usual practice. Surgeons who specialise in the GMK-Sphere implant will only implant the GMK-Sphere for this study, and surgeons who specialise in the Attune implant will only implant the Attune. This allows surgeons to undertake the prosthesis with which they are expert, and also limit potential surgical error in the case of surgeons having to randomise patients to different designs on the same list.

Patients will be seen by the trial team on 3 separate occasions:

1. Routine pre-admission clinic: Recruitment, collection of patient information and questionnaire data and completion of pre-operative physical tests (including gait analysis with 3D motion capture technology)
2. Routine post-operation clinic: Six-weeks post-operative physical tests (including gait analysis with 3D motion capture technology) and questionnaire data
3. Annual post-operation clinic: 1-year post-operative physical tests (including gait analysis with 3D motion capture technology) and questionnaire data

   Collection of baseline data during pre-admission clinic (standard care except physical tests):
   * Descriptive: Patient demographics (sex, age, height, mass, BMI), diagnosis, pattern of OA, medical co-morbidity
   * Questionnaire Data

     * Oxford Knee Score - A joint specific questionnaire which asks patients on the level of pain and function they believe to have in their affected knee.
     * EQ5D - A questionnaire on patients' perception of their overall health. It contains a visual analogue scale where patients have to choose on a scale of 0-100 how well they believe their general health to be.
     * SF12 - A general Quality of Life score. It has mental and physical components.
     * Forgotten Joint Score - This asks questions not covered in the OKS on patient perception of their knee that are important to know following TKA. It focuses on other aspects of outcome other than joint pain and function.
     * Expectation questionnaire - This asks what the patients expect from the surgery. The investigators use this to gauge whether patients are expecting to achieve too much or too little post-op. This is important for understanding post-operative patient satisfaction.

   All questionnaires ask different questions (although there is some overlap). Together, they give an overall view of the patients' perception of their general health and knee specific problems. As such, they are all deemed necessary for this investigation.

   There are separate scoring sheets for these subjective quantitative scores. The results are typically presented as a Mean ± SD score for each questionnaire (provided the data is normally distributed). All are valid in the English language.

   • Non-invasive Physical Tests: Range of knee movement, knee muscular strength, lower limb kinematics during level (0°)- and downhill (7.5°)-walking

   Collection of follow-up measures by trial team between operation and post-operative visit (standard care):

   • Surgical complications

   Collection of data during routine follow-up clinics:

6 weeks post-operation (standard care except physical tests):

* Questionnaire Data: Oxford Knee Score, SF12, EQ5D, Forgotten Joint Score
* Non-invasive Physical Tests: Range of knee movement, knee muscular strength, lower limb kinematics during level (0°)- and downhill (7.5°)-walking

  12 weeks post-operation (standard care):
* Descriptive: Radiographic measurement of alignment (Non-invasive)

  1 year post-operation (standard care except physical tests):
* Questionnaire Data: Oxford Knee Score, SF12, EQ5D, Forgotten Joint Score, Satisfaction questionnaire
* Descriptive: Late complications
* Non-invasive Physical Tests: Range of knee movement, knee muscular strength, lower limb kinematics during level (0°)- and downhill (7.5°)-walking

Eligibility Criteria:
Inclusion Criteria:

* Clinical diagnosis of osteoarthritis of the knee which is sufficiently symptomatic to require knee arthroplasty as assessed by their consultant orthopaedic surgeon

Exclusion Criteria:

* Inflammatory arthropathy
* Patients requiring bone augmentation
* Patients with collateral ligament incompetence
* Valgus deformity \>5 degrees.