U2 Total Knee System – PF+ Patella; USTAR II System– PF+ Patella

The U2 Total Knee System – PF+ Patella and USTAR II System – PF+ Patella are metal-backed patellae (kneecap replacements) indicated for knee arthroplasty to reduce pain and improve function in patients with severe knee arthritis, trauma, or failed prior surgery. The devices come in two variations—symmetric (Onset) and asymmetric (Asymmetric Onset)—and are approved for both cemented and cementless implantation.

The patella body is manufactured from Vitamin E-blended, highly cross-linked UHMWPE (per ASTM F2695, ASTM F648/ISO5834-1). The metal back and three pegs are produced via additive manufacturing from Ti-6Al-4V alloy (ASTM 2924) with porous titanium coating on the bone, peg, and polymer sides. The symmetric option differs from its predicate in sterilization method and size ranges; the asymmetric option uses different metal base and UHMWPE materials compared to its secondary predicate.

ASTM F2695, ASTM F648/ISO5834-1 (UHMWPE specification), ASTM 2924 (Ti-6Al-4V alloy). FDA guidance documents cited: 'Technical Considerations for Additive Manufactured Medical Devices,' 'Guidance Document for Testing Orthopedic Implants with Modified Metallic Surfaces Apposing Bone or Bone Cement,' and 'Testing of Metallic Plasma Sprayed Coatings on Orthopedic Implants.'

Both the subject device and primary predicate (K212941, Porous Patella e+™) are indicated for knee arthroplasty to reduce pain and improve function in similar patient populations, using both cemented and cementless fixation. The materials, fixation methods, and intended use are substantially identical, with only differences in sterilization method and size ranges for the symmetric option and different metal/polymer materials for the asymmetric option—variations that do not affect the fundamental safety and effectiveness profile. Non-clinical testing (pull-out, Ti coating characterization, durability, usability, and endotoxin testing) confirms performance equivalence.