Stability of the Medial Pivot Total Knee Prosthesis

The purpose of this study is to compare objective and subjective measures of knee stability following total knee arthroplasty with a medial pivot design vs. a posterior stabilized design.

Study Overview

• Status: Completed
• Conditions: Osteoarthritis of Knee
• Intervention / Treatment: Device: Medacta GMK Sphere prosthesis; Device: Medacta GMK posterior stabilized prosthesis

Detailed Description

Several different prostheses are available for use in total knee arthroplasty (TKA). These designs aim to replicate the normal kinematics of the knee joint while maintaining stability throughout a full range of motion. The posterior cruciate ligament (PCL) contributes to these functions in the native knee, and if preserved it can function similarly in the prosthetic knee. Prostheses in which the PCL is sacrificed, and its function not replaced by other means, have poorer outcomes. However, various problems with preserving the PCL, including PCL deterioration in arthritic knees and difficulties with proper tensioning, have led to the development of alternative ways to emulate normal femoral rollback and sagittal plane stability. These posterior-substituted (PS) designs substitute for the PCL with either a cam and post mechanism or a symmetrical ultra-congruent tibial insert.

The cruciate-retaining (CR) and PS designs, together with advances in surgical techniques and component materials, have achieved excellent implant survivorship with rates of > 90% at 20 years. Reports of functional outcomes, however, have been variable. One potential area for improvement in TKA is optimization of implant design to better approximate native knee kinematics. In the normal knee, the medial condyle remains stable in the sagittal plane, functioning like a ball-and-socket, whereas the lateral condyle translates anterior to posterior during flexion. The designs of the CR and PS knees do not allow for this medial-centered rotation. Analysis has revealed paradoxical anterior sliding of the femur during flexion, abnormal axial rotation, and condylar lift-off. Edge loading and increased sagittal plane motion may predispose to accelerated polyethylene wear. The posterior stabilized design uses a cam-and-post mechanism in which one piece of the prosthesis has a plastic post that fits into a slot in the other piece of the prosthesis.

A newer design that attempts to address these issues is the medial pivot knee (MP). This design is characterized by an asymmetrical tibial insert in which the medial compartment is ultra-congruent, providing antero-posterior stability and the lateral compartment allows for rollback around a medial axis of rotation i.e uses a ball-and-socket mechanism. This design more accurately recreates normal knee kinematics, reduces anteroposterior instability, and avoids condylar lift-off. Early studies indicate improved polyethylene wear characteristics. Midterm studies report excellent implant survivorship and clinical outcomes.

Several randomized trials have compared the MP knee favorably with other designs. Patients with bilateral TKAs with a different prosthesis on each side preferred their medial pivot knee to a PS, CR, or mobile-bearing (MB) design. A trial comparing the MP and PS designs found greater range of motion (ROM) and better patient-reported outcomes in the MP group at 2 years. There also exists literature reporting poorer outcomes with the MP design. A trial involving 96 patients who had received both an MP knee and an MB knee on contralateral sides found lower ROM, higher complication rates, and worse patient reported outcomes in the MP knee.

Given the lack of consensus in the literature, further investigation is warranted to determine the impact of the MP design on outcomes following TKA.

• Study Type: Interventional
• Enrollment (Actual): 61
• Phase: Not Applicable

Contacts and Locations

Study Locations

• United States
  • Illinois
    • Chicago, Illinois, United States, 60611
      • Northwestern Medicine Department of Orthopaedic Surgery

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: 14 years to 81 years (Adult, Older Adult)
• Accepts Healthy Volunteers: No

Description

Inclusion Criteria:

• Age 18-85, regardless of gender, ethnicity, or pathology
• Must require a total knee arthroplasty
• All subjects must have given signed, informed consent prior to registration in study.

Exclusion Criteria:

• Minors
• Any patients that are unable to consent
• Patients with active infection or osseous tumor of the operative extremity
• Patients undergoing revision surgery

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Treatment
• Allocation: Randomized
• Interventional Model: Single Group Assignment
• Masking: Single

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Other: Medacta Sphere; Ball-and-socket	Device: Medacta GMK Sphere prosthesis
Other: Medacta PS; Cam-and-post	Device: Medacta GMK posterior stabilized prosthesis

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Oxford Knee Score (OKS) Pre-operative Through 2 Years Post-operative	Patient completed Oxford Knee Score questionnaire used to assess the patient's perspective of outcome following Total Knee Arthroplasty (TKA); score range is reported between 0-48 with improvement in outcomes reflected as a higher numerical value (e.g. a 'complete' return to pre-disease functionality would be reported as a score of 48)	Pre-operatively on day of surgery, 6 weeks, 3 months, 6 months, 12 months and 24 months post-operatively
Veteran's RAND 12 (VR-12) Mental Composite Score (MCS) Through 2 Years Post Operative	Veteran's RAND 12 Item Health Survey used to assess health-related quality of life, to estimate disease burden, and to evaluate disease-specific benchmarks. Scores for the Mental Composite Score (MCS) range from 5.2 to 76.3 and are evaluated as a summative T-score with population mean of 50 (Standard Deviation = 10);higher scores indicate improved mental wellness/function as reported by patients.	Pre-operatively, 6 weeks post-operatively, 3 months post-operatively, 6 months post-operatively, 12 months post-operatively, and 2 years post-operatively.
Veteran's RAND 12 (VR-12) Physical Composite Score (PCS) Through 2 Years Post Operative	Veteran's RAND 12 Item Health Survey used to assess health-related quality of life, to estimate disease burden, and to evaluate disease-specific benchmarks. Scores for the Physical Composite Score (MCS) range from 6.3 to 71.8 and are evaluated as a summative T-score with population mean of 50 (Standard Deviation = 10);higher scores indicate improved physical wellness/function as reported by patients.	Pre-operatively, 6 weeks post-operatively, 3 months post-operatively, 6 months post-operatively, 12 months post-operatively, and 2 years post-operatively.
PROMIS Computerized Adaptive Tests (CATs) for Physical Function Through 2 Years Post-operative	Patient-reported outcome (PRO) measures use answers that patients provide to questions to produce numeric values which indicate patients' state of wellbeing or suffering as well as their ability or lack of ability to function. Values are reported as T-scores with a reference population mean of 50 (SD=10); for the Physical Function domain higher scores indicated improved physical function as reported by the patient	Pre-operatively, 6 weeks post-operatively, 3 months post-operatively, 6 months post-operatively, 12 months post-operatively, and 2 years post-operatively.
PROMIS Computerized Adaptive Tests (CATs) for Pain Interference Through 2 Years Post-operative	Patient-reported outcome (PRO) measures use answers that patients provide to questions to produce numeric values which indicate patients' state of wellbeing or suffering as well as their ability or lack of ability to function. Values are reported as T-scores with a reference population mean of 50 (SD=10); for the Pain Interference domain an increased value indicates greater severity/frequency of pain reported by the patient.	Pre-operatively, 6 weeks post-operatively, 3 months post-operatively, 6 months post-operatively, 12 months post-operatively, and 2 years post-operatively.
PROMIS Computerized Adaptive Tests (CATs) for Pain Behavior Through 2 Years Post-operative	Patient-reported outcome (PRO) measures use answers that patients provide to questions to produce numeric values which indicate patients' state of wellbeing or suffering as well as their ability or lack of ability to function. Values are reported as T-scores with a reference population mean of 50 (SD=10); for the Pain Behavior domain an increased value indicates greater severity/frequency of pain reported by the patient	Pre-operatively, 6 weeks post-operatively, 3 months post-operatively, 6 months post-operatively, 12 months post-operatively, and 2 years post-operatively.
Total Score Calculated Using the Forgotten Joint Score in Order to Assess the Subject's Ability to Forget the Artificial Joint in Everyday Life	Patient completed questionnaire used to assess the patients' ability to forget about a joint as a result of successful treatment. Every question is scored 1 (never) to 5 (mostly) according to the selected response categories. Thus, the raw score ranges from 12 to 60 where a high score indicates an improved outcome. The raw score is linearly transformed to a 0-100 scale and then reversed to obtain the final score with higher scores indicating improved physical function/reduced impact of symptoms on activity: Final score = 100 - ((sum(item01 to item12) - 12)/48*100)	12 months post-operatively
International Knee Documentation Committee (IKDC) Questionnaire Assessed Through 2 Years Post-op	The International Knee Documentation Committe (IKDC) Questionnaire is a subjective scale that provides patients with an overall function score based on a summative score for 3 sub categories (knee function, sports activities, pain/symptoms). A score between 0-100 is obtained as the sum of scores for each individual question, with increasing composite scores correlating positively with patient functional status/quality of life.	Pre-operatively, 6 weeks post-operatively, 3 months post-operatively, 6 months post-operatively, 12 months post-operatively, and 2 years post-operatively.
Score for the Knee Society Score (KSS) Knee Component at 1 Year Post-operatively	Physician completed Knee Society Score questionnaire used to measure a patient's functional ability before and after total knee arthroplasty (TKA); score range is reported between 0-100 with improvement in outcomes reflected as a higher numerical value (e.g. a 'complete' return to pre-disease functionality would be reported as a score of 100)	12 months post-operatively
Score for the Knee Society Score (KSS) Function Component at 1 Year Post-operatively	Physician completed Knee Society Score questionnaire used to measure a patient's functional ability before and after total knee arthroplasty (TKA); score range is reported between 0-100 with improvement in outcomes reflected as a higher numerical value (e.g. a 'complete' return to pre-disease functionality would be reported as a score of 100)	12 months post-operatively

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Assessing Knee Stability Using the KT-1000 Arthrometer (at 30 Degrees)	Used for grading the stability of the knee in various degrees of flexion according to section 4 of the International Knee Documentation Committee's Knee Ligament Standard Evaluation Form where normal (-1 to 2 mm); nearly normal (3 to 5 mm); abnormal (6 to 10 mm); severely abnormal (>10 mm)	1 year post-operatively
Assessing Knee Stability Using the KT-1000 Arthrometer (at 90 Degrees)	Used for grading the stability of the knee in various degrees of flexion according to section 4 of the International Knee Documentation Committee's Knee Ligament Standard Evaluation Form where normal (-1 to 2 mm); nearly normal (3 to 5 mm); abnormal (6 to 10 mm); severely abnormal (>10 mm)	1 year post-operatively
Get-up-and-Go Test	Used to assess a person's mobility and requires both static and dynamic balance. It uses the time that a person takes to rise from a chair, walk three metres, turn around, walk back to the chair, and sit down.	Between 6 months and 1 year post-operatively

Collaborators and Investigators

• Sponsor: Northwestern University

Study record dates

Study Major Dates

• Study Start (Actual): April 1, 2014
• Primary Completion (Actual): April 1, 2017
• Study Completion (Actual): June 1, 2017

Study Registration Dates

• First Submitted: October 13, 2015
• First Submitted That Met QC Criteria: October 15, 2015
• First Posted (Estimate): October 16, 2015

Study Record Updates

• Last Update Posted (Actual): May 19, 2023
• Last Update Submitted That Met QC Criteria: May 17, 2023
• Last Verified: May 1, 2023

More Information

Terms related to this study

• Additional Relevant MeSH Terms: Joint Diseases; Musculoskeletal Diseases; Rheumatic Diseases; Arthritis; Osteoarthritis; Osteoarthritis, Knee
• Other Study ID Numbers: STU00090745