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Peri-implant debris certainly lead to osteolysis, necrosis, pseudotumor formation, tissue granulation, fibrous capsule contractions, and even implant failure. For the three-dimensional (3D) printed cage, impaction during cage insertion is one of the most potential sources of fracture debris. A finite-element study was carried out to reduce the impact-induced debris of the 3D-printed cage. This study focused on the design strategy of solid and cellular structures along the load-transferring path. Using the finite-element method, the cellular structure of the transforaminal lumbar interbody fusion (TLIF) cage was systematically modified in the following four variations: a noncellular cage (NC), a fully cellular (FC) cage, a solid cage with a cellular structure in the middle concave (MC) zone, and a strengthened cage (SC) in the MC zone. Three comparison indices were considered: the stresses at the cage-instrument interfaces, in the MC zone, and along the specific load-transferring path. The NC and FC were the least and most highly stressed variations at the cage-instrument interfaces and in the MC zone, respectively. Along the entirely load-transferring path, the FC was still the most highly stressed variation. It showed a higher risk of stress fracture for the FC cage. For the MC and SC, the MC zone was consistently more stressed than the directly impacted zone. The further strengthened design of the SC had a lower peak stress (approximately 29.2%) in the MC zone compared with the MC. Prior to 3D printing, the load-transferring path from the cage-instrument interfaces to the cage-tissue interfaces should be determined. The cage-instrument interfaces should be printed as a solid structure to avoid impact-induced fracture. The other stress-concentrated zones should be cautiously designed to optimize the coexistence strategy of the solid and cellular structures.

Background: Wrist arthroplasty is increasingly offered to patients with symptomatic wrist arthritis as an alternative to wrist arthrodesis. The purpose of this study was to present our outcomes with the ReMotion™ wrist arthroplasty in a consecutive series of patients with wrist arthritis from non-inflammatory conditions.

Methods: Thirteen (eight women, nine dominant wrists) patients, 68 (44–85) years of age with advanced radiocarpal arthritis due to SLAC/SNAC (11) and Kienbock disease (2) had a ReMotion™ (Stryker, Michigan, USA) wrist arthroplasty implanted, and were prospectively followed for 7 (4–9) years. The outcome measures included patient-rated wrist and hand evaluation (PRWHE) score, disabilities of the arm, shoulder and hand questionnaire (QuickDASH) score, visual analogue pain score (0–10) on the radial and ulnar aspect of the wrist at rest (VASrR/VASuR) and activity (VASrA/VASuA), active wrist range of motion (AROM) including flexion, extension, ulnar and radial deviation, pronation and supination and grip and key-pinch strength measured preoperatively and at yearly follow-ups by independent hand therapists.

Results: Six patients had ten re-operations during the follow-up including four revisions to a new arthroplasty. Four were considered loose at follow-up. A significant reduction in PRWHE (63 to 12), radial pain at activity (6 to 1) and increased pronation (85° v 90°) was observed.

Conclusions: We found a high complication and reoperation rate, two out of 13 had no complications or reoperations. The ReMotion™ arthroplasty should be used with caution in non-inflammatory wrist patients and the patients followed closely. A high reoperation and revision rate can be expected, and surgeons familiar with revision arthroplasty procedures should perform the surgery.

Level of Evidence: Level II (Therapeutic)

Wear debris–induced periprosthetic disease is a major concern after total joint replacement. The wear debris stimulates a cascade of inflammation, resulting in peri-implant osteoclastogenesis and osteolysis. Although in vitro studies have contributed considerably to our understanding of wear debris-induced adverse biological reactions, animal experiments are necessary to understand the more complex mechanisms in vivo. In this chapter, we describe a mouse model that allows the quantification of osteoclastogenesis and osteolysis. Ultrahigh molecular weight polyethylene (UHMWPE) particles are implanted onto calvariae in C57BL/J6 mice, which then develop greater levels of active inflammatory osteolysis than do the control species. The particles are washed in ethanol to remove surface-adherent endotoxin, thus reducing endotoxin interference. Osteolysis can be found in the middle sagittal suture and the adjacent region in mouse calvaria 1 week after implantation. Decalcified hematoxylin and eosin (H&E)-stained sections are used to quantify the osteolysis area. Osteoclastogenesis regions are identified and quantified in tartrate-resistant acid phosphatase (TRAP)-stained sections. Larger areas of osteolysis and TRAP-stained osteoclastic activity are found to be induced by UHMWPE particles than developed by the sham group.

Fifteen patients (20 hip joints) with rheumatoid arthritis, who underwent hip arthroplasties using alumina-made bipolar endoprosthesis with or without bone graft, were evaluated clinically and roentgenographically. They were followed at least for five years (range; 5-9 ys). Average hip scores improved from 32 to 72 postoperatively. According to the roentgenographic analysis, osteolysis as well as aseptic loosening of femoral components was not observed in all of the hip joints. Although proximal migration of the outer head was seen in all of the hip joint, that was not progressive in seven out of the 20 hips. In addition, the proximal migration did not affect hip scores as well as patients’ daily function. One hip joint was revised due to the breakage of alumina inner head. Average linear wear rate of polyethylene insert was 0.07 mm/year according to the computer digital analysis. The results of the present study suggests that alumina-made bipolar endoprosthesis may be an alternative to total hip arthroplasty for rheumatoid patients because of low wear performance and less invasive surgery.