Medacta GMK Sphere® vs. Medacta GMK PS Post-Market Outcomes Study

Medacta GMK Sphere® Medial-Pivot, Cruciate Substituting vs. Medacta GMK PS Posterior Stabilized Kne vs. OMNI Apex Knee Ultracongruent vs. Triathlon® Posterior Stabilized & Cruciate Substituting Outcomes Study

The study is a prospective, randomized comparison of total knee arthroplasty with the Medacta GMK Sphere® knee compared to the Medacta GMK PS knee, with comparison to data from previous trials of similar study design.

Study Overview

• Status: Completed
• Conditions: Osteoarthritis; Osteoarthritis, Knee; Joint Disease
• Intervention / Treatment: Device: Medacta GMK Sphere® Medial-Pivot Knee Prosthesis; Device: Medacta GMK PS Posterior Stabilized Knee Prosthesis

Detailed Description

There is no consensus within the Arthroplasty community as to whether a traditional post and cam-style PS total knee device is superior to a medial-pivot, more congruent device. However, the majority of surgeons seem to prefer the former, though there is a minority that uses the latter device with great success.

To date, there have been few prospective trials directly comparing these devices, and none with the latest generation of TKA implants. Almost all such studies have been retrospective, and/or non-randomized, and/or utilizing older generation devices.

The primary objective of this study is to compare the average Forgotten Knee Score (FJS) of those patients receiving the Medacta GMK Sphere knee with the average FJS of those receiving the Medacta GMK PS knee at the two and five year time points. It is expected that those subjects implanted with the Medacta GMK Sphere knee will show significantly better Forgotten Joint Scores at two and five year follow-up when compared with those receiving the Medacta GMK PS knee. The FJS was not collected in the prior comparison studies, and so cannot be evaluated across the knee systems.

• Study Type: Interventional
• Enrollment (Actual): 218
• Phase: Not Applicable

Contacts and Locations

Study Locations

• United States
  • Washington
    • Spokane, Washington, United States, 99218
      • Spokane Joint Replacement Center

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: 17 years to 76 years (Adult, Older Adult)
• Accepts Healthy Volunteers: Yes

Description

Inclusion Criteria:

• Patients willing to sign the Informed Consent.
• Patients able to comply with follow-up requirements including postoperative weight bearing restrictions and self-evaluations.
• Male and non-pregnant female patients ages 21 - 80 years of age at the time of surgery.
• Patients requiring a primary total knee replacement.
• Patients with a diagnosis of osteoarthritis (OA), traumatic arthritis (TA), or avascular necrosis (AVN).
• Patients with intact collateral ligaments.

Exclusion Criteria:

• Patients with inflammatory arthritis.
• Patients that are morbidly obese, body mass index (BMI) > 40.
• Patients with a history of total or unicompartmental reconstruction of the affected joint.
• Patients with neuromuscular or neurosensory deficiency, which would limit the ability to assess the performance of the device.
• Patients with a systemic or metabolic disorder leading to progressive bone deterioration.
• Patients that are immunologically compromised, or receiving chronic steroids (>30 days), excluding inhalers.
• Patients bone stock is compromised by disease or infection, which cannot provide adequate support and/or fixation to the prosthesis.
• Patients with knee fusion to the affected joint.
• Patients with an active or suspected latent infection in or about the knee joint.
• Patients whose surgery will utilize computer-assisted surgical navigation (CAOS) techniques.
• Patients whose surgery will utilize minimally invasive surgical techniques.
• Patients that are prisoners.

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Other
• Allocation: Randomized
• Interventional Model: Parallel Assignment
• Masking: Single

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Other: Medacta GMK Sphere® Medial-Pivot Knee Prosthesis; Research subjects in this arm received GMK Sphere.	Device: Medacta GMK Sphere® Medial-Pivot Knee Prosthesis
Other: Medacta GMK PS Posterior Stabilized Knee Prosthesis; Research subjects in this arm received GMK PS.	Device: Medacta GMK PS Posterior Stabilized Knee Prosthesis

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Forgotten Joint Score (FJS)	The average Forgotten Joint Score (FJS) of those patients receiving the Medacta GMK Sphere® knee prosthesis will be compared with the average FJS of those receiving the Medacta GMK PS knee prosthesis. The FJS total score range is 0-100, with higher scores indicating a higher degree of "forgetting" the artificial joint, that is, a lower degree of awareness.	Change from baseline at 2 years and 5 years post-operative

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Total Knee Society Score (KSS)	Clinical outcomes will be evaluated via the Knee Society Score (KSS). The KSS is subdivided into a Knee Assessment score which rates only the knee joint itself, and a Functional Assessment score which rates the subject's ability to walk and climb stairs. Both scores range from 0-100, with a higher score indicating a better outcome.	Pre-operative, 6 weeks, 6 months, 1, 2, 3, 4, and 5 years post-operative
Lower Extremity Activity Scale (LEAS)	Clinical outcomes will be evaluated via the Lower Extremity Activity Scale (LEAS). The LEAS scale range is 1-18, with a higher value indicating a higher level of activity.	Pre-operative, 6 weeks, 6 months, 1, 2, 3, 4, and 5 years post-operative
Radiographic Analysis	Radiographs will be assessed for radiolucency, migration and subsidence. An AP Longstanding view will be obtained pre-operatively, and at 6 weeks and 1 year post-operatively to determine degree of Varus or Valgus.	Pre-operative, 6 weeks, 6 months, 1, 2, 3, 4, and 5 years post-operative

Collaborators and Investigators

• Sponsor: David F. Scott, MD
• Collaborators: Medacta USA
• Investigators: Principal Investigator: David Scott, MD, Spokane Joint Replacement Center

Study record dates

Study Major Dates

• Study Start (Actual): April 1, 2015
• Primary Completion (Actual): November 27, 2023
• Study Completion (Actual): November 27, 2023

Study Registration Dates

• First Submitted: December 11, 2017
• First Submitted That Met QC Criteria: December 29, 2017
• First Posted (Actual): January 5, 2018

Study Record Updates

• Last Update Posted (Actual): April 29, 2026
• Last Update Submitted That Met QC Criteria: April 23, 2026
• Last Verified: April 1, 2026

More Information

Terms related to this study

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

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: Yes