There is destruction of the joint surfaces, with or without significant bone deformity.
The cruciate and/or collateral ligaments do not stabilize the knee joint.
The ligaments are inadequate and/or the musculature is weak. And/or
Revision is required of a failed prosthesis where there has been gross instability, with or without bone loss or inadequate soft tissue.

When used with MRH femur and/or MRH tibial baseplate replacement indicated in revision of an existing prosthesis:

Revision is required of a failed prosthesis where there has been gross instability, with or without bone loss or inadequate soft tissue.

When used with compatible GMRS components:

Where segmental resection and/or replacement of femur and/or proximal tibia is required

Device Description

The subject THK components are a line extension of the previously cleared Triathlon® Hinge Knee System (K223528, K230416). The THK System (K223528, K230416) is a tricompartmental knee system consisting of a stemmed femoral component and a stemmed tibial bearing component connected by a set of previously cleared MRH or THK Bushings and an MRH or THK Axle (K994207, K002552, K223528, K230416). A bumper locks this assembly. This assembly provides motion through the MRH or THK Axle/Bushings combination in the flexion/extension plane. The articulation between the bearing surfaces on the underside of a tibial bearing component and a tibial insert provides motion in the rotating plane. A hinge tibial insert is assembled to a Triathlon® Hinge Revision Tibial Baseplate that incorporates a longitudinal bore to accept a previously cleared MRH Tibial Sleeve (K994207, K002552) or Triathlon Tibial Sleeve (K223528, K230416). Optional distal femoral and tibial augments are available to fill bone defects.

The subject Triathlon® Hinge Small Proximal Tibial Bearing Component and Triathlon® End Cap are sterile, single use devices intended for cemented use only and are being added to the previously cleared THK system (K223528, K230416) as an extension. They can be used with previously cleared MRH Knee components (K994207, K002552), GMRS (K023087, K222056), and Triathlon® Knee System components (K172634, K172326, K190991, K143393, K141056, K132624, K070095, K061521, K053514, K052917, K051948, K051146, K040267).

AI/ML Overview

This FDA 510(k) clearance letter is for a mechanical medical device (a knee implant system), not an AI/software as a medical device. Therefore, the request for "acceptance criteria and the study that proves the device meets the acceptance criteria" using metrics relevant to AI/software (like sensitivity, specificity, MRMC studies, ground truth for training/test sets, etc.) is not applicable here.

The document provided details about the substantial equivalence of the "Triathlon® Hinge Knee System" to previously cleared predicate devices. The "study" proving the device meets acceptance criteria for a mechanical implant typically involves non-clinical (benchtop) testing and engineering analyses to demonstrate performance, material compatibility, and safety, rather than clinical trials or AI performance evaluations with ground truth.

Here's how the provided information relates to the typical evaluation of such a device, addressing the closest analogues to your requested points:

Acceptance Criteria and Device Performance for a Mechanical Implant:

For mechanical implants like the Triathlon® Hinge Knee System, "acceptance criteria" are generally tied to the successful completion of various non-clinical (benchtop) tests and analyses. These tests simulate the physical stresses and conditions the implant will experience in the human body. The "study" proving the device meets these criteria is the execution and successful outcome of these non-clinical tests.

No direct table of "acceptance criteria" vs. "reported device performance" in the AI sense is provided in this 510(k) summary. Instead, the summary lists the types of non-clinical tests performed to demonstrate performance and substantial equivalence to predicate devices. The implied acceptance is that the device passed these tests, meaning its performance in these simulated scenarios was deemed acceptable and comparable to existing, legally marketed devices.

Table of Non-Clinical Tests (Analogous to Performance Metrics):

Acceptance Criteria (Test Type)	Reported Device Performance (Implied "Pass")	Notes
Triathlon Hinge Bearing Component Varus/Valgus Fatigue	Met performance standards	Tests the component's ability to withstand repeated bending stresses in side-to-side directions, simulating loading during gait.
Triathlon Hinge Bearing Component Chair Rise Testing	Met performance standards	Simulates stresses experienced during a common activity (standing up from a chair).
Triathlon Hinge Full Construct Fatigue	Met performance standards	Evaluates the fatigue life of the entire assembled knee system under cyclic loading.
Wear Test Rationale for New Constructs	Acceptable wear characteristics demonstrated	Rationale provided to show that wear performance is acceptable, likely through comparison to predicate devices or established standards. Direct wear testing is implied by "wear test rationale".
Analysis of Contact Area/Contact Stress & Constraint Analysis	Acceptable contact mechanics & constraint	Computer modeling and/or benchtop tests to evaluate how the components interact under load, ensuring appropriate stress distribution and constrained movement.
Range of Motion and Rotational Freedom Analysis (ASTM F1223-20)	Met specified ranges and freedoms	Tested for flexion/extension, internal/external rotation, varus/valgus, and translation (medial/lateral, proximal/distal, anterior/posterior) to ensure physiological movement.
Total Femur Construct Compatibility & Triathlon Hinge Bushing/Axle Compatibility	Compatible with legacy components	Ensured new components integrate properly with existing cleared femoral and tibial components.
Triathlon Revision Baseplate-End Cap Locking Strength Analysis	Adequate locking strength	Evaluated the mechanical strength of the connection points.
Triathlon End Cap Tightening Analysis	Optimal tightening confirmed	Ensured secure fixation of the end cap.
Triathlon End Cap Load Carrying Capacity Rationale	Acceptable load capacity	Analysis provided to demonstrate the end cap can withstand expected loads.
Triathlon End Cap Stability Analysis	Stable under normal use	Evaluated the end cap's ability to remain in place and function without loosening.
MRI Testing (Safety for imaging) - Displacement, Torque, Artifacts, RF Heating	All MRI safety criteria met	Performed to confirm the device is safe for patients undergoing MRI procedures (e.g., no excessive magnetic pull, acceptable image distortion, no dangerous heating). Standards: ASTM F2052-15, ASTM F2213-17, ASTM F2119-07 (reapproved 2013), ASTM F2182-191ae.
Biocompatibility (ISO 10993-1:2020)	Biocompatible with human tissue	Testing to ensure the materials used in the implant do not cause adverse biological reactions in the body.
Shelf-life Validation (ISO 11607-1:2019, ISO 11607-2:2019, ASTM F1980-21)	Validated shelf-life	Ensures the sterility and integrity of the packaging system and the device itself are maintained over the specified shelf-life. Methods: ASTM F1886/F1886M-16, ASTM F88/88M-21, ASTM F2096-11(2019).
Bacterial Endotoxin Testing (ANSI/AAMI ST72:2019)	Endotoxin limit < 20EU/Device	Confirms the device is free from pyrogens (substances that can cause fever).

Since this is for a mechanical knee implant system (not an AI/software device), most of the requested points related to AI are not applicable. Here's a breakdown based on the provided document:

A table of acceptance criteria and the reported device performance:
- As shown above, the acceptance criteria are implicitly defined by the successful completion of the listed non-clinical tests and analyses. The performance is "Met performance standards" or "Acceptable," as detailed in the Notes column. The document doesn't provide specific numerical results of these tests (e.g., how many cycles endured, specific force resistance values) but states they were performed to determine substantial equivalence.
Sample sized used for the test set and the data provenance:
- This concept (test set, data provenance) is typically for AI/software. For mechanical device testing, the "sample size" refers to the number of physical units tested according to each standard. These details are generally found in the full test reports, which are not part of the public 510(k) summary. The "data provenance" would refer to the lab where tests were conducted (e.g., an accredited testing lab).
- Not explicitly stated in the 510(k) summary.
Number of experts used to establish the ground truth for the test set and the qualifications of those experts:
- This is an AI/software concept. For mechanical device testing, "ground truth" is defined by established engineering and medical device standards (e.g., ASTM, ISO guidelines) and the physical properties and performance characteristics of the materials and design. Expert engineers and quality assurance specialists verify the test results against these standards.
- Not applicable for a mechanical device.
Adjudication method (e.g. 2+1, 3+1, none) for the test set:
- This is an AI/software concept for resolving discordant expert opinions. For mechanical testing, test results are typically objective and quantitative, allowing for direct comparison against predefined acceptance criteria from standards.
- Not applicable for a mechanical device.
If a multi reader multi case (MRMC) comparative effectiveness study was done, If so, what was the effect size of how much human readers improve with AI vs without AI assistance:
- This is an AI/software concept measuring clinical impact with human-AI interaction. For this mechanical device, the comparison is to legally marketed predicate devices through substantial equivalence, primarily based on design, materials, and non-clinical performance, rather than an MRMC study.
- No MRMC study was done, as it's not applicable to a mechanical implant.
If a standalone (i.e. algorithm only without human-in-the-loop performance) was done:
- This refers to AI performance. For a mechanical device, its "standalone" performance is assessed through the non-clinical benchtop tests listed.
- The non-clinical tests listed in the summary represent the "standalone" performance assessment of the device.
The type of ground truth used (expert consensus, pathology, outcomes data, etc.):
- For a mechanical implant, "ground truth" for performance is established by engineering principles, material science, and performance standards (e.g., ASTM, ISO). For biocompatibility, the ground truth is established per ISO 10993-1. For MRI safety, it's established by ASTM standards.
- Ground truth established by relevant engineering and medical device standards.
The sample size for the training set:
- This refers to AI algorithm development. For a mechanical device, there isn't a "training set" in this sense. The training for the design of the device comes from established engineering principles, prior device designs, and material science research.
- Not applicable for a mechanical device.
How the ground truth for the training set was established:
- Again, this is an AI concept.
- Not applicable for a mechanical device.

In conclusion, the Triathlon® Hinge Knee System is a physical implant, and its clearance is based on demonstrating substantial equivalence to existing legally marketed devices through a series of rigorous non-clinical (benchtop) tests and engineering analyses that confirm its material properties, mechanical performance, biocompatibility, and safety (e.g., MRI compatibility, sterility). Clinical testing was explicitly stated as not required for this 510(k) submission, a common occurrence for devices demonstrating substantial equivalence through non-clinical data.

Summary

FDA 510(k) Clearance Letter - Triathlon® Hinge Knee System

Page 1

U.S. Food & Drug Administration
10903 New Hampshire Avenue
Silver Spring, MD 20993
www.fda.gov

Doc ID # 04017.08.00

July 25, 2025

Howmedica Osteonics Corp. dba Stryker Orthopaedics
Niyati Dave
Staff Regulatory Affairs Specialist
325 Corporate Drive
Mahwah, New Jersey 07430

Re: K251665
Trade/Device Name: Triathlon® Hinge Knee System
Regulation Number: 21 CFR 888.3510
Regulation Name: Knee Joint Femorotibial Metal/Polymer Constrained Cemented Prosthesis
Regulatory Class: Class II
Product Code: KRO
Dated: May 25, 2025
Received: May 30, 2025

Dear Niyati Dave:

We have reviewed your section 510(k) premarket notification of intent to market the device referenced above and have determined the device is substantially equivalent (for the indications for use stated in the enclosure) to legally marketed predicate devices marketed in interstate commerce prior to May 28, 1976, the enactment date of the Medical Device Amendments, or to devices that have been reclassified in accordance with the provisions of the Federal Food, Drug, and Cosmetic Act (the Act) that do not require approval of a premarket approval application (PMA). You may, therefore, market the device, subject to the general controls provisions of the Act. Although this letter refers to your product as a device, please be aware that some cleared products may instead be combination products. The 510(k) Premarket Notification Database available at https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfpmn/pmn.cfm identifies combination product submissions. The general controls provisions of the Act include requirements for annual registration, listing of devices, good manufacturing practice, labeling, and prohibitions against misbranding and adulteration. Please note: CDRH does not evaluate information related to contract liability warranties. We remind you, however, that device labeling must be truthful and not misleading.

If your device is classified (see above) into either class II (Special Controls) or class III (PMA), it may be subject to additional controls. Existing major regulations affecting your device can be found in the Code of Federal Regulations, Title 21, Parts 800 to 898. In addition, FDA may publish further announcements concerning your device in the Federal Register.

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K251665 - Niyati Dave
Page 2

Additional information about changes that may require a new premarket notification are provided in the FDA guidance documents entitled "Deciding When to Submit a 510(k) for a Change to an Existing Device" (https://www.fda.gov/media/99812/download) and "Deciding When to Submit a 510(k) for a Software Change to an Existing Device" (https://www.fda.gov/media/99785/download).

Your device is also subject to, among other requirements, the Quality System (QS) regulation (21 CFR Part 820), which includes, but is not limited to, 21 CFR 820.30, Design controls; 21 CFR 820.90, Nonconforming product; and 21 CFR 820.100, Corrective and preventive action. Please note that regardless of whether a change requires premarket review, the QS regulation requires device manufacturers to review and approve changes to device design and production (21 CFR 820.30 and 21 CFR 820.70) and document changes and approvals in the device master record (21 CFR 820.181).

Please be advised that FDA's issuance of a substantial equivalence determination does not mean that FDA has made a determination that your device complies with other requirements of the Act or any Federal statutes and regulations administered by other Federal agencies. You must comply with all the Act's requirements, including, but not limited to: registration and listing (21 CFR Part 807); labeling (21 CFR Part 801); medical device reporting (reporting of medical device-related adverse events) (21 CFR Part 803) for devices or postmarketing safety reporting (21 CFR Part 4, Subpart B) for combination products (see https://www.fda.gov/combination-products/guidance-regulatory-information/postmarketing-safety-reporting-combination-products); good manufacturing practice requirements as set forth in the quality systems (QS) regulation (21 CFR Part 820) for devices or current good manufacturing practices (21 CFR Part 4, Subpart A) for combination products; and, if applicable, the electronic product radiation control provisions (Sections 531-542 of the Act); 21 CFR Parts 1000-1050.

All medical devices, including Class I and unclassified devices and combination product device constituent parts are required to be in compliance with the final Unique Device Identification System rule ("UDI Rule"). The UDI Rule requires, among other things, that a device bear a unique device identifier (UDI) on its label and package (21 CFR 801.20(a)) unless an exception or alternative applies (21 CFR 801.20(b)) and that the dates on the device label be formatted in accordance with 21 CFR 801.18. The UDI Rule (21 CFR 830.300(a) and 830.320(b)) also requires that certain information be submitted to the Global Unique Device Identification Database (GUDID) (21 CFR Part 830 Subpart E). For additional information on these requirements, please see the UDI System webpage at https://www.fda.gov/medical-devices/device-advice-comprehensive-regulatory-assistance/unique-device-identification-system-udi-system.

Also, please note the regulation entitled, "Misbranding by reference to premarket notification" (21 CFR 807.97). For questions regarding the reporting of adverse events under the MDR regulation (21 CFR Part 803), please go to https://www.fda.gov/medical-devices/medical-device-safety/medical-device-reporting-mdr-how-report-medical-device-problems.

For comprehensive regulatory information about medical devices and radiation-emitting products, including information about labeling regulations, please see Device Advice (https://www.fda.gov/medical-devices/device-advice-comprehensive-regulatory-assistance) and CDRH Learn (https://www.fda.gov/training-and-continuing-education/cdrh-learn). Additionally, you may contact the Division of Industry and Consumer Education (DICE) to ask a question about a specific regulatory topic. See the DICE website (https://www.fda.gov/medical-devices/device-advice-comprehensive-regulatory-

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K251665 - Niyati Dave
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assistance/contact-us-division-industry-and-consumer-education-dice) for more information or contact DICE by email (DICE@fda.hhs.gov) or phone (1-800-638-2041 or 301-796-7100).

Sincerely,

Lixin Liu -S

Lixin Liu, PhD
Assistant Director
DHT6A: Division of Joint Arthroplasty Devices
OHT6: Office of Orthopedic Devices
Office of Product Evaluation and Quality
Center for Devices and Radiological Health

Enclosure

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FORM FDA 3881 (8/23)
Page 1 of 1
PSC Publishing Services (301) 443-6740 EF

DEPARTMENT OF HEALTH AND HUMAN SERVICES
Food and Drug Administration

Indications for Use

Form Approved: OMB No. 0910-0120
Expiration Date: 07/31/2026
See PRA Statement below.

510(k) Number (if known): K251665

Device Name: Triathlon® Hinge Knee System

Indications for Use (Describe)

Triathlon® Hinge Knee System is intended to be implanted with bone cement for the following condition(s):

There is destruction of the joint surfaces, with or without significant bone deformity.
The cruciate and/or collateral ligaments do not stabilize the knee joint.
The ligaments are inadequate and/or the musculature is weak. And/or
Revision is required of a failed prosthesis where there has been gross instability, with or without bone loss or inadequate soft tissue.

When used with MRH femur and/or MRH tibial baseplate replacement indicated in revision of an existing prosthesis:

Revision is required of a failed prosthesis where there has been gross instability, with or without bone loss or inadequate soft tissue.

When used with compatible GMRS components:

Where segmental resection and/or replacement of femur and/or proximal tibia is required

Type of Use (Select one or both, as applicable)

☒ Prescription Use (Part 21 CFR 801 Subpart D)
☐ Over-The-Counter Use (21 CFR 801 Subpart C)

CONTINUE ON A SEPARATE PAGE IF NEEDED.

This section applies only to requirements of the Paperwork Reduction Act of 1995.

DO NOT SEND YOUR COMPLETED FORM TO THE PRA STAFF EMAIL ADDRESS BELOW.

The burden time for this collection of information is estimated to average 79 hours per response, including the time to review instructions, search existing data sources, gather and maintain the data needed and complete and review the collection of information. Send comments regarding this burden estimate or any other aspect of this information collection, including suggestions for reducing this burden, to:

Department of Health and Human Services
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PRAStaff@fda.hhs.gov

"An agency may not conduct or sponsor, and a person is not required to respond to, a collection of information unless it displays a currently valid OMB number."

Page 5

510(k) Summary

Sponsor: Howmedica Osteonics Corp. dba Stryker Orthopaedics
325 Corporate Drive
Mahwah, NJ 07430

Contact Person: Niyati Dave
Staff Regulatory Affairs Specialist
Howmedica Osteonics Corp
325 Corporate Drive
Mahwah, NJ 07430
Phone: (201) 972-3477
Email: Niyati.dave@stryker.com

Alternate Contact: Margaret Klippel
Chief Specialist, Regulatory Affairs
Howmedica Osteonics Corp
325 Corporate Drive
Mahwah, NJ 07430
Phone: (201) 831-5559
Email: margaret.klippel@stryker.com

Date Prepared: July 25, 2025

Proprietary Name: Triathlon® Hinge Knee System

Common Name: Rotating Hinge Knee System
Artificial Knee System
Total Knee Joint Prosthesis

K251665 Page 1 of 6

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K251665 Page 2 of 6

Classification Name: Knee joint femorotibial metal/polymer constrained cemented prosthesis. (21 CFR Part 888.3510)

Product Codes: KRO

Legally Marketed Primary Predicate Device to which Substantial Equivalence is Claimed:

Triathlon® Hinge Knee System; Triathlon® Revision Insert X3® - K230416

Legally Marketed Additional Predicate Devices Used to Support Substantial Equivalence:

Triathlon® Total Knee System - K053514, K141056, K172326
GMRS Tibial Rotating Component - K023087, K222056
MRH Tibial Rotating Component- K994207, K002552

Reason for 510(k) Submission:

The purpose of this Traditional 510(k) Premarket Notification is to support the marketing clearance of the new Triathlon® Small Proximal Tibial Bearing Component and Triathlon® End Cap as part of the Triathlon® Hinge Knee (THK) System. Additionally, this submission expands the compatibility of the THK system for use with components of the existing Modular Rotating Hinge (MRH) Knee System and Global Modular Replacement System (GMRS).

Device Description:

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K251665 Page 3 of 6

incorporates a longitudinal bore to accept a previously cleared MRH Tibial Sleeve (K994207, K002552) or Triathlon Tibial Sleeve (K223528, K230416). Optional distal femoral and tibial augments are available to fill bone defects.

Intended Use:

The subject components of THK System have the same general intended use as those specified in the 510(k) submissions for the predicate devices listed. The intended use statement has been updated to add reference to the proximal tibial replacement and to clarify that the use with GMRS/MRH is for knee replacement procedures as well as bone tumors.

The THK System components are sterile, single-use devices intended for cemented use in primary and revision total knee arthroplasty. The THK System is intended to be used for the treatment of a severely unstable knee, particularly with the loss of collateral support in both primary and revision cases. The THK System is also compatible with the GMRS and MRH systems for distal femoral and total femoral replacements and/or proximal tibia replacements performed for the treatment of bone tumors. It is a partially constrained prosthesis with limited rotational capability, which allows more natural motion and reduces torque on the fixation.

The Indications for Use have been updated to reflect the additional compatibilities, and for clarity.

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K251665 Page 4 of 6

Indications:

Triathlon® Hinge Knee System:

Triathlon® Hinge Knee System is intended to be implanted with bone cement for the following condition(s):

There is destruction of the joint surfaces, with or without significant bone deformity.
The cruciate and/or collateral ligaments do not stabilize the knee joint.
The ligaments are inadequate and/or the musculature is weak. And/or
Revision is required of a failed prosthesis where there has been gross instability, with or without bone loss or inadequate soft tissue.

When used with MRH femur and/or MRH tibial baseplate replacement indicated in revision of an existing prosthesis:

Revision is required of a failed prosthesis where there has been gross instability, with or without bone loss or inadequate soft tissue.

When used with compatible GMRS components:

Where segmental resection and/or replacement of femur and/or proximal tibia is required

Summary of Technological Characteristics:

The subject Triathlon Hinge Small Proximal Tibial Bearing Component is a sterile, single-use device and manufactured from the same material ASTM F1537, as that of the legally marketed predicate Triathlon Hinge Tibial Bearing Components (K223528, K230416). The subject component design is also based on the predicate device, and the only differences are smaller AP and ML widths to prevent the overhanging on the tibial insert during internal/external rotation of the tibia. The subject component utilizes the same basic principles of operation as the cited predicate devices.

The subject Triathlon End Cap is a sterile, single-use device that has the same material (ASTM F1537) and similar design as that of the predicate Triathlon 50mm Cemented Stems (K053514, K141056, K172326). The subject device is identical to the existing subcomponent Triathlon Universal Baseplate End Cap (5560-S-016) cleared in K053514; the subject End Cap will now

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K251665 Page 5 of 6

be packaged as a standalone saleable part. The subject component utilizes the same basic principles of operation as those of the cited predicate devices.

Non-Clinical Testing:

The following non-clinical laboratory testing and/or engineering analysis were performed to determine substantial equivalence:

Triathlon Hinge Bearing Component varus/valgus fatigue
Triathlon Hinge Bearing Component chair rise testing
Triathlon Hinge full construct fatigue
Wear test rationale for new constructs
Analysis of contact area/contact stress and constraint analysis
Range of motion and rotational freedom analysis – tibia/femoral (all modes of rotation – flexion/extension, internal/external, varus/valgus, and translation – medial/lateral, proximal/distal, anterior/posterior) (ASTM F1223-20)
Total Femur construct compatibility and Triathlon Hinge Bushing/Axle compatibility analysis with legacy bearing components
Triathlon Revision Baseplate-End Cap locking strength analysis
Triathlon End Cap tightening analysis
Triathlon End Cap load carrying capacity rationale
Triathlon End Cap stability analysis
MRI Testing
- Magnetically induced displacement force test (ASTM F2052-15)
- Magnetically induced torque test (ASTM F2213-17)
- Image artifact tests (ASTM F2119-07, reapproved 2013)
- RF Heating evaluation (ASTM F2182-191ae)
Biocompatibility evaluated per ISO 10993-1:2020
Shelf-life validated per the following standards:
- ISO 11607-1:2019
- ISO 11607-2:2019
- ASTM F1980-21

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K251665 Page 6 of 6

Testing performed per the following methods:
- ASTM F1886/F1886M-16
- ASTM F88/88M-21
- ASTM F2096-11(2019)
Bacterial endotoxin testing (BET) as specified in ANSI/AAMI ST72:2019 was used for pyrogenicity testing to achieve an endotoxin limit of < 20EU/Device.

Clinical Testing:

Clinical testing was not required as a basis for substantial equivalence.

Conclusion:

Based upon a comparison of the intended use, indications for use, design, materials and sterilization method, technical and performance characteristics, and operational principles, the subject THK System components are substantially equivalent to the respective predicate devices identified in this premarket notification.

Regulation Number and Section

§ 888.3510 Knee joint femorotibial metal/polymer constrained cemented prosthesis.

(a)
Identification. A knee joint femorotibial metal/polymer constrained cemented prosthesis is a device intended to be implanted to replace part of a knee joint. The device limits translation or rotation in one or more planes and has components that are linked together or affined. This generic type of device includes prostheses composed of a ball-and-socket joint located between a stemmed femoral and a stemmed tibial component and a runner and track joint between each pair of femoral and tibial condyles. The ball-and-socket joint is composed of a ball at the head of a column rising from the stemmed tibial component. The ball, the column, the tibial plateau, and the stem for fixation of the tibial component are made of an alloy, such as cobalt-chromium-molybdenum. The ball of the tibial component is held within the socket of the femoral component by the femoral component's flat outer surface. The flat outer surface of the tibial component abuts both a reciprocal flat surface within the cavity of the femoral component and flanges on the femoral component designed to prevent distal displacement. The stem of the femoral component is made of an alloy, such as cobalt-chromium-molybdenum, but the socket of the component is made of ultra-high molecular weight polyethylene. The femoral component has metallic runners which align with the ultra-high molecular weight polyethylene tracks that press-fit into the metallic tibial component. The generic class also includes devices whose upper and lower components are linked with a solid bolt passing through a journal bearing of greater radius, permitting some rotation in the transverse plane, a minimal arc of abduction/adduction. This generic type of device is limited to those prostheses intended for use with bone cement (§ 888.3027).(b)
Classification. Class II.