Metastatic tumor (i.e. osteosarcoma, chondrosarcoma, giant cell tumor or osteoma) where massive resection and transplantation are needed.
Severe knee joint damage resulting from trauma where massive resection and transplantation are needed.
Non-inflammatory degenerative joint disease such as avascular necrosis, osteoarthritis, or traumatic arthritis.
Revision of previously failed total joint arthroplasty, osteotomy, or arthrodesis.
Joint instability resulting from excessive bone resection

For Femoral component, Hinged/ Tibial baseplate, Hinged/ Cemented tibial stem/ Cemented Straight stem, RHS, non coated/ Cemented Curved stem, RHS, non coated/ Cemented Straight stem, RHS/ Cemented Curved stem, RHS/ Tibial Augment: These devices are single use implant and intended for cemented use only.

For Distal Femoral Component, RHS/ Proximal Tibial Component, RHS/ Tibial stem/ Segment Part, RHS/ Segment Part, RHS, Bridge: These devices are single use implant and PSC and intended for cementless use only.

Device Description

"United" USTAR II System is used for patients who present large quantity of bone loss and deformity associated with previous failed arthroplasty, ligament deficiencies, tumor resection, or trauma and may require a further operation or reconstruction. The USTAR II System includes implanted arthroplasty components of both the USTAR II Knee System and USTAR II Hip System.

For the subject device, it's an extension line of 510(K) cleared device USTAR II System (K190100), which introduces two new variations:

Cemented curved stem, RHS, non-coated: diameter 17×200 mm
Tibial stem: stem length from 30mm to 150 mm by stem diameter from diameter 9 to diameter 24

The compatibility of cemented curved stem, RHS, non-coated and tibial stem is same as that of the 510(k) cleared USTAR II system (K190100).

Cemented Curved Stem, RHS, non-coated is an extension in terms of sizes to 510 (k) cleared device USTAR II system (K190100). Its design, materials, geometrical characteristic, locking mechanism, and manufacturing process are identical to that of the 510(k) cleared Cemented Curved Stem, RHS, non-coated.

Tibial stem's design, materials, geometrical characteristic, locking mechanism, and manufacturing process are identical to that of the 510(k) cleared Tibial Stem while the only difference lies in its specification

AI/ML Overview

Please note: The provided FDA 510(k) clearance letter and summary describe a medical device (Stem Extension Line for the USTAR II System), which is an orthopedic implant. This document does not describe an AI/Software as a Medical Device (SaMD).

Therefore, the requested information about "acceptance criteria and the study that proves the device meets the acceptance criteria" in the context of an AI/SaMD, including details like "number of experts used to establish ground truth," "adjudication method," "MRMC study," "standalone performance," "training set size," and "ground truth establishment for training set," are not applicable to this type of device submission.

The provided text focuses on the mechanical and design equivalence of the new implant variations to a previously cleared predicate device. The "study" mentioned refers to non-clinical mechanical analyses.

Below is an interpretation of the requested points adapted to the context of this orthopedic implant:

Acceptance Criteria and Study for the Stem Extension Line (USTAR II System)

1. Table of Acceptance Criteria and Reported Device Performance

For this orthopedic implant, the acceptance criteria are based on established international standards for the mechanical performance of prosthetic components and demonstrate equivalence to the predicate device.

Acceptance Criteria Category	Specific Test Standard / Requirement	Device Performance (Reported Outcome)
Stem Fatigue Analysis	ISO 7206-4 (Implants for surgery — Partial and total hip joint prostheses — Part 4: Determination of endurance properties and performance of stemmed femoral components)	Met required acceptance criteria. (Implied to be comparable to or better than the predicate device under the specified test conditions).
Mechanical Strength of Tibial Baseplate	ASTM F1800 (Standard Practice for Testing of the Cement-Stem Interface for Femoral Hip Prosthesis) and ISO 21536:2023 (Implants for surgery — Joint replacement prostheses — Specific requirements for knee joint prostheses)	Met required acceptance criteria. (Implied to be comparable to or better than the predicate device under the specified test conditions).
Design, Materials, Geometrical Characteristics, Locking Mechanism, Manufacturing Process	Identical to 510(k) cleared USTAR II system (K190100).	Confirmed identical.
Safety and Effectiveness	Equivalent to predicate devices based on the same analysis method applied in previous submission; no new risks identified.	Established equivalent safety and effectiveness.

2. Sample size used for the test set and the data provenance

Sample Size for Test Set: Not explicitly stated as a number of physical implants or test articles in the provided summary. For mechanical testing, typically a defined number of test samples are used per standard, but the specific quantity is not given here.
Data Provenance: The studies are non-clinical mechanical analyses performed to international standards (ISO, ASTM). The origin of the "data" itself would be the laboratory where these mechanical tests were conducted. It's a prospective design verification process, not a retrospective or prospective clinical study with human data.

3. Number of experts used to establish the ground truth for the test set and the qualifications of those experts

Not Applicable. This is a non-clinical, mechanical device clearance. "Ground truth" in the context of clinical interpretation or diagnosis by experts (e.g., radiologists) is not relevant here. Ground truth is established by standardized material properties, engineering specifications, and mechanical test results per the referenced ISO and ASTM standards. Experts involved would be engineers and material scientists responsible for the design, testing, and analysis, ensuring compliance with manufacturing and performance standards.

4. Adjudication method (e.g. 2+1, 3+1, none) for the test set

Not Applicable. Adjudication methods like 2+1 or 3+1 typically refer to consensus readings or evaluations by multiple human experts in studies involving subjective interpretation (e.g., imaging, clinical outcomes). For mechanical testing, the results are quantitative and objective, measured against predefined acceptance criteria from engineering standards.

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. MRMC studies are specific to evaluating the clinical performance of diagnostic aids, particularly those involving human interpretation, and are commonly used for AI/ML in medical imaging. This submission concerns the mechanical safety and functionality of an orthopedic implant. No human reader involvement or AI assistance is relevant.

6. If a standalone (i.e. algorithm only without human-in-the-loop performance) was done

Not Applicable. "Standalone performance" refers to the performance of an AI algorithm independent of human input. This device is a physical orthopedic implant, not an algorithm or software.

7. The type of ground truth used (expert consensus, pathology, outcomes data, etc)

The "ground truth" for this type of device is based on engineering standards and specifications. This includes:
- Material properties: Verifying components meet specified material strengths and compositions.
- Geometric tolerances: Ensuring dimensions align with design specifications.
- Mechanical performance: Demonstrating the implant can withstand anticipated loads and stresses as defined by the ISO and ASTM test standards (e.g., fatigue life, static strength).
- Equivalence to Predicate Device: The primary "ground truth" is that the new variations perform equivalently to or better than the already cleared predicate device under the same test conditions.

8. The sample size for the training set

Not Applicable. This is not an AI/ML device where a "training set" of data is used to develop an algorithm. The "design" and "manufacturing process" are based on established engineering principles and prior validated designs (the predicate device).

9. How the ground truth for the training set was established

Not Applicable. As there is no "training set" in the context of an AI/ML algorithm for this physical device, there is no method for establishing its "ground truth." The design and manufacturing processes are validated through engineering analyses and quality control processes to meet the required specifications and standards.

Summary

FDA 510(k) Clearance Letter - Stem Extension Line (USTAR II System)

Page 1

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

Doc ID # 04017.08.00

August 22, 2025

United Orthopedic Corporation
Lois Ho
Regulatory Affairs Manager
No 16. Luke 1st Rd., Luzhu Dist.
Kaohsiung City, 82151
Taiwan

Re: K252303
Trade/Device Name: Stem Extension Line (USTAR II System)
Regulation Number: 21 CFR 888.3510
Regulation Name: Knee Joint Femorotibial Metal/Polymer Constrained Cemented Prosthesis
Regulatory Class: Class II
Product Code: KRO, KWL, LPH, LWJ, LZO, OQI
Dated: July 22, 2025
Received: July 24, 2025

Dear Lois Ho:

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.

Page 2

K252303 - Lois Ho 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-

Page 3

K252303 - Lois Ho Page 3

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, Ph.D
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

Page 4

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.

Submission Number (if known)
K252303

Device Name
Stem Extension Line (USTAR II System)

Indications for Use (Describe)

Metastatic tumor (i.e. osteosarcoma, chondrosarcoma, giant cell tumor or osteoma) where massive resection and transplantation are needed.
Severe knee joint damage resulting from trauma where massive resection and transplantation are needed.
Non-inflammatory degenerative joint disease such as avascular necrosis, osteoarthritis, or traumatic arthritis.
Revision of previously failed total joint arthroplasty, osteotomy, or arthrodesis.
Joint instability resulting from excessive bone resection

For Distal Femoral Component, RHS/ Proximal Tibial Component, RHS/ Tibial stem/ Segment Part, RHS/ Segment Part, RHS, Bridge: These devices are single use implant and intended for cementless use only.

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.

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Page 5

510(k) SUMMARY

Special 510(k)

[as required by 21 CFR 807.92(c)]

K252303 page 1 of 3

Contact Details

Field	Value
Applicant Name	United Orthopedic Corporation
Applicant Address	No. 16, Luke 1st Rd., Luzhu Dist., Kaohsiung City 82151, Taiwan
Applicant Contact Telephone	+886-3-5773351
Applicant Contact	Ms. Lois Ho
Applicant Contact Email	lois.ho@unitedorthopedic.com

Device Name

Field	Value
Device Trade Name	Stem Extension Line (USTAR II System)
Common Name	Total Knee Prosthesis / Total Hip Prosthesis

Classification Name

Knee joint femorotibial metal/polymer constrained cemented prosthesis.
Hip joint metal/polymer/metal semi-constrained porous-coated uncemented prosthesis.
Hip joint femoral (hemi-hip) metallic cemented or uncemented prosthesis.
Hip joint metal/ceramic/polymer semi-constrained cemented or nonporous uncemented prosthesis.

Field	Value
Regulation Number	888.3510, 888.3358, 888.3360, 888.3353
Product Codes	KRO, KWL, LPH, LWJ, LZO, OQI

Legally Marketed Predicate Devices

Predicate	Predicate Trade Name	Product Code
K190100	USTAR II System	KRO, LPH, LWJ, KWL

Device Description Summary

For the subject device, it's an extension line of 510(K) cleared device USTAR II System (K190100), which introduces two new variations:

Cemented curved stem, RHS, non-coated: Ø17×200 mm
Tibial stem: stem length from 30mm to 150 mm by stem diameter from Ø9 to Ø24

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K252303 page 2 of 3

The compatibility of cemented curved stem, RHS, non-coated and tibial stem is same as that of the 510(k) cleared USTAR II system (K190100).

Intended Use/Indications for Use

Metastatic tumor (i.e. osteosarcoma, chondrosarcoma, giant cell tumor or osteoma) where massive resection and transplantation are needed.
Severe knee joint damage resulting from trauma where massive resection and transplantation are needed.
Non-inflammatory degenerative joint disease such as avascular necrosis, osteoarthritis, or traumatic arthritis.
Revision of previously failed total joint arthroplasty, osteotomy, or arthrodesis.
Joint instability resulting from excessive bone resection

Indications for Use Comparison

The subject device's intended use is the same as the predicate device with similar indications for use.

Technological Comparison

The technological characteristics of the subject device are substantially equivalent to that of the predicate device USTAR II System (K190100) as the comparison given below.

Their intended use is the same.
The design, material, principle of operation, regulation number, risk class, intended users, fixation method, surface coating, geometry design, locking mechanism of stem locking, and sterilization method of the subject device is the same as that of the predicate device.
The design control activities were conducted for the difference in the specification (stem diameter and stem length). They validated equivalent safety and effectiveness compared to the predicate devices based on the same analysis method the previous submission applied. It established that no new risks arise compared to those of the predicate devices.

Page 7

K252303 page 3 of 3

Non-Clinical and/or Clinical Tests Summary & Conclusions

Mechanical Analyses

Stem fatigue analysis per ISO 7206-4
Mechanical strength analysis of tibial baseplate collocated with tibial stem per ASTM F1800 and ISO 21536:2023

No clinical tests were performed to support the safety and effectiveness of the subject device.

The mechanical analyses were used as a basis for the determination of substantial equivalence. The results of each show that compared to the predicate device, the subject device has met the required acceptance criteria, and there are no additional risks arising. Thus, the Stem Extension Line (USTAR II System) is considered substantially equivalent to the predicate device (K190100).

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.