Characteristics of wear particles and wear behavior of retrieved PEEK-on-HXLPE total knee implants: a preliminary study

Abstract

Polyether-ether-ketone (PEEK) has been used clinically for intervertebral fusion and internal fixators in spine and trauma surgery because of its mechanical properties and bioinertness. The present study aimed to assess the suitability of PEEK as an alternative material to cobalt-chromium-molybdenum alloy in total knee arthroplasty (TKA) and evaluate the in vivo wear property on the contact surface of the PEEK-on-highly cross-linked polyethylene (HXLPE). PEEK prosthesis was designed and manufactured using injection molding based on the computed tomography data of a standard goat right hind limb. Fifteen goats underwent TKA using PEEK-on-HXLPE prosthesis on the right hind limb. The goats were sacrificed at 12, 24, and 48 weeks postoperatively. The mean surface roughness (R _a) of the retrieved components, proinflammatory cytokines in the synovial fluid, and characteristics of wear particles in the synovial membrane were investigated using laser confocal microscopy, ELISA and polarized light microscopy. The R _a of the femoral component was about 0.08, 0.1, 0.2, and 0.26 μm at pre-study, 12-, 24-, and 48 weeks in the retrievals, respectively. The R _a of the HXLPE bearing samples was approximately 0.38, 0.4, 0.1, and 0.42 μm at pre-study, 12-, 24-, and 48 weeks in the retrievals, respectively. The median size of the particles was 2.63 μm, 1.98 μm, and 3.00 μm at 12, 24, and 48 weeks, respectively. The particles ranged in size from 0.4 μm to 15 μm, and particles <1 μm accounted for 7-13%, those of size 2-5 μm accounted for 67-76%, and those >5 μm accounted for 11-22%. Levels of interleukin (IL)-6, IL-10, and tumor necrosis factor-α (TNF-α) were significantly increased in synovial fluids at 24- and 48 weeks after surgery. Wear occurred on the surfaces of the PEEK and HXLPE material and the size of most wear particles was 1-5 μm. This induced an inflammatory response in the synovial membrane and release of proinflammatory cytokines. A high polishing process may be necessary to lengthen the life of the PEEK prosthesis by reducing the wear and the generation of debris. The PEEK prosthesis as a new generation of artificial joints is promising to be used clinically in the future.

Fig. 1. Design, manufacture, implementation, and retrieval of the PEEK prosthesis. The right hind limb was obtained from a standardized goat (A and B). The three-dimensional model of the knee joint was based on the computed tomography data (C and D). The prosthesis model was designed by a computer and manufactured by injection molding using polyether-ether-ketone (PEEK) material. The goat prosthesis consists of a PEEK material femoral component and a PEEK material tibial tray with a highly cross-linked polyethylene (HXLPE) material insert (E, F and K). The tray and insert were embedded tightly together and locked using 1 mm metal wires (G). The total knee arthroplasty operation for goats (H and I). Retrievals of PEEK prosthesis at different intervals (J).

Fig. 2. Laser confocal profile of the initially manufactured polyether-ether-ketone (PEEK) (a–d) and highly cross-linked polyethylene (HXLPE) components in retrieved prosthesis (e–h). The mean surface roughness (R_a) change in PEEK (i) and HXLPE (j) material in vivo. Magnification ×400; N = 5.

Fig. 3. Morphological observation of wear particles in the synovial membrane and characterization of polymer particles. Measurement of the size and area of particles based on the particle which show a strong birefringence under polarized light (A, i–iii), scale bars = 20 μm. The number and frequency distribution of different size particles (B, i–v) and sizes of the particles in the three groups (B, vi), the red horizontal lines indicate median values. The area and frequency distribution of different sized particles (C, i–v).

Fig. 4. Morphological observation of wear particles in the synovial membrane. Wear particles in the synovial membrane in 48 week samples (a–c). A number of eosinophilic stained cells near the particles and gather along the site of the particles (d–f). The inflammatory response, such as infiltration of inflammatory cells and fibrous tissue hyperplasia, was observed in the surrounding tissues (g–i). The white arrow indicates inflammatory cells, the yellow arrow indicates particles; black scale bars = 100 μm.

Fig. 5. Detection of tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6, and IL-10 in the synovial fluid. IL-1β shows an increasing trend at 24 and 48 weeks after surgery, but no statistical significance compared with the values at pre-study (A). IL-6 and TNF-α levels were lower in the normal synovial fluid, but significantly increased at 24 and 48 weeks after surgery (B and C). IL-10 significantly increased in the postoperative period over time (D).