Sigma CR150 Versus Sigma CR Knee RCT

This study will compare two very similar designs of knee replacement device. One device (Sigma CR150) is a slightly modified version of the original (Sigma CR) and has been modified to enhance/accommodate higher flexion. The original device has been in widespread clinical use with excellent results since 1996 and this study will determine whether the design modifications of the newer device add further value. The newer device has been in clinical use with good short-term(unpublished) outcomes since becoming commercially available in January 2009.

Achieving higher knee flexion may be required for cultural reasons or by the increasingly younger, more active patient population undergoing knee replacement today. In addition to promoting flexion, it is also possible that this design change may help the knee replacement to last longer than traditional implants in patients who achieve higher flexion. Therefore, the study will compare the two devices in terms of survivorship, flexion and other measures of the success of a total knee replacement (range of motion, knee-related quality of life, activity and generic quality of life) over the short-term.

A minimum of one hundred and forty subjects (minimum 70 per group) with osteoarthritis and aged 50-75 years will be included at UK/international hospitals.

Study duration is 2 years and patients will complete standard knee outcome scores plus radiological evaluation.

Subjects would receive one of the study devices regardless of their involvement in the study, and apart from (possible)additional visits, x-rays and/or questionnaires, treatment and follow-up care will be as per the care they would receive outside of the study.


Eligibility Criteria:
Inclusion Criteria:

i)Male or female subjects, aged between 50 and 75 years inclusive.

ii)Subjects who are able to give voluntary, written informed consent to participate in this clinical investigation and from whom consent has been obtained.

iii) Subjects who, in the opinion of the Clinical Investigator, are able to understand this clinical investigation, co-operate with the investigational procedures and are willing to return to the hospital for all the required post-operative follow-ups.

iv) Subjects defined by the Investigator as ASA Grade I or II.

v) Subjects with a primary diagnosis of osteoarthritis.

vi) Subjects who require a primary total knee arthroplasty.

vii) Subjects who can achieve active flexion of 90 degrees.

Exclusion Criteria:

i) Subjects who, in the opinion of the Clinical Investigator, have an existing condition that would compromise their participation and follow-up in this clinical investigation.

ii) Subjects who are known drug or alcohol abusers or with psychological disorders that could affect follow-up care or treatment outcomes.

iii) Subjects who have participated in a clinical investigation with an investigational product in the last month.

iv) Subjects who are currently involved in any injury litigation claims.

v) Subjects with an anatomical limb alignment of above 20 degrees varus or valgus.

vi) Subjects with a fixed flexion deformity of over 20 degrees.

vii) Subjects with recurvatum (definition: hyperextension ≥ 5 degrees).

viii) Subjects who cannot flex their hip to 90 degrees.

ix) Subjects with a BMI of 35 or above.

x) Subjects defined by the Investigator as ASA Grade III-V.

xi) Subjects who are identified pre-operatively as having bone defects which require augmentation.

xii) Subjects who have previously undergone total or unicondylar knee arthroplasty, high tibial osteotomy, ligament reconstruction, ORIF or with previous fracture in the knee joint.

xiii) Subjects with primary or secondary diagnosis of inflammatory or traumatic arthritis.

xiv) Subjects who have undergone contralateral total knee arthroplasty during the previous 6 months.

xv) Subjects who in the opinion of the Investigator require patellar resurfacing.

Intra-operative exclusion criteria:

i) Subjects who have uncontained bone defects or defects bigger than 8 mm3 and/or require augmentation.

ii) Subjects who are not suitable to receive both the study and comparator devices.

iii) Subjects who require patellar resurfacing