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The U2 Total Knee system is indicated in knee arthroplasty for reduction or relief of pain and/or improved knee function in skeletally mature patients with severe knee pain and disability due to rheumatoid arthritis, osteoarthritis, primary and secondary traumatic arthritis, polyarthritis, collagen disorders, avascular necrosis of the femoral condyle or pseudogout, posttraumatic loss of joint configuration, particularly when there is patellofemoral erosion, dysfunction or prior patellectomy, moderate valgus, varus, or flexion deformities. This device may also be indicated in the salvage of previously failed surgical attempts if the knee can be satisfactorily balanced and stabilized at the time of surgery. This device is a single use implant and intended for cemented use only.

This subjected device includes femoral component, tibial insert, XPE tibial insert and ultracongruent insert. It is a size extension to the cleared "UNITED" U2 Total Knee System (K051640, K120507, K131864, K103733, K132752, and K140073). The indications, materials, design of this subject device are identical to the cleared "UNITED" U2 Total Knee System except for its dimension.

The provided text is a 510(k) summary for the U2 Total Knee System-Additional Sizes. This document outlines the regulatory filing for a medical device and typically focuses on demonstrating substantial equivalence to a predicate device, rather than presenting a detailed study proving the device meets specific performance acceptance criteria in terms of AI/software performance.

Therefore, many of the requested categories related to AI/software performance, such as sample size for test sets, expert ground truth, adjudication methods, MRMC studies, standalone performance, and training set details, are not applicable to this type of regulatory submission for a physical knee implant.

However, I can extract information related to the device's non-clinical performance and its comparison to a predicate device, as that is the focus of this document.

Here's the breakdown of the information that can be extracted, and where applicable, a note on why certain information is not present:

1. A table of acceptance criteria and the reported device performance

The document does not explicitly state quantitative "acceptance criteria" for the non-clinical tests in the usual sense of a specific pass/fail threshold with reported numerical performance values against those thresholds. Instead, it states that the tests "demonstrated that this device is safe and effective." The demonstration of safety and effectiveness relies on the device having the "same basic design, intended use, materials and the same manufacturing method" as predicate devices, with the only difference being "dimension." The non-clinical tests listed below were performed to confirm performance characteristics.

Note: The document confirms these tests were conducted "in accordance with the Agency's, 'Class II Special Controls Guidance Document: Knee Joint Patellofemorotibial and Femorotibial Metal/Polymer Porous-Coated Uncemented Prostheses; Guidance for Industry and FDA'." This implies that the tests were designed and evaluated against established industry and regulatory standards, which serve as the implicit "acceptance criteria." However, the exact numerical criteria and specific results are not detailed in this summary.

2. Sample sizes used for the test set and the data provenance: Not applicable. This document describes physical device testing, not AI/software performance evaluation with a "test set" in the computational sense. The "tests" refer to laboratory-based mechanical and materials evaluations.

3. Number of experts used to establish the ground truth for the test set and the qualifications of those experts: Not applicable. No "ground truth" establishment by experts in the context of image analysis or diagnostic AI is mentioned. Evaluations are based on engineering principles and test results.

4. Adjudication method (e.g. 2+1, 3+1, none) for the test set: Not applicable.

5. 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: Not applicable. This is a physical prosthetic device, not an AI software.

6. If a standalone (i.e. algorithm only without human-in-the-loop performance) was done: Not applicable.

7. The type of ground truth used (expert consensus, pathology, outcomes data, etc): Not applicable in the context of conventional AI/software ground truth. The "truth" for this device lies in its compliance with engineering standards, material properties, and mechanical performance under simulated physiological conditions, benchmarked against predicate devices.

8. The sample size for the training set: Not applicable. This is not an AI/machine learning device.

9. How the ground truth for the training set was established: Not applicable.

Summary of the Study that Proves the Device Meets Acceptance Criteria (as described in the document):

The "study" refers to a series of non-clinical performance tests conducted on the U2 Total Knee System-Additional Sizes. The summary states these tests were performed "in accordance with the Agency's, 'Class II Special Controls Guidance Document: Knee Joint Patellofemorotibial and Femorotibial Metal/Polymer Porous-Coated Uncemented Prostheses; Guidance for Industry and FDA'".

The key premise for demonstrating safety and effectiveness and meeting acceptance criteria, as per this 510(k) summary, is substantial equivalence to several predicate devices (e.g., "UNITED" U2 Total Knee System K051640). The document explicitly states:

• "U2 Total Knee System, Additional Sizes has the same basic design, intended use, materials and the same manufacturing method as device of the 'United' U2 Total Knee System..."
• "The only difference between the cleared and subjected device is dimension."

The non-clinical tests listed above (Range of Motion, Contact Area and Pressure, Constraint, Fatigue Compression, Locking Strength, Fatigue Performance of Insert Spine, Material Properties) were performed to confirm that, despite the dimensional differences, the additional sizes maintain the same performance characteristics as the predicate devices, thereby ensuring safety and effectiveness. The conclusion provided is that "the test results demonstrated that this device is safe and effective."

Clinical Performance Data:
The document explicitly states: "None provided as a basis for substantial equivalence." This reinforces that the substantial equivalence determination for this submission relies entirely on non-clinical data and comparison to predicate devices, rather than new clinical trials for the specific additional sizes.

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