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Rigid spinal fusion with instrumentation has been widely applied in treating degenerative spinal disorders and has shown excellent and stable surgical results. However, adjacent segment pathology or implants' loosening could be problematic due to the spine's segmental fusion. Therefore, this study verified a novel concept for posterior stabilization with polyethylene inserts inside a pedicle screw assembly using bone models. We observed that although the gripping capacity of the dynamic pedicle screw system using a tensile and compression tester was less than half that of the rigid pedicle screw system, the flexion‐extension moment of the dynamic pedicle screws was significantly lower than that of the rigid pedicle screws. Furthermore, while the bending force of the rigid pedicle screw assembly increased linearly with an increase in the bending angle throughout the test, that of the dynamic pedicle screw assembly also increased linearly until a bending angle of 2.5° was reached. However, this angle decreased at a bending angle of more than 2.5°. Additionally, the fatigue test of 1.0 × 106 cycles showed that the pull‐out force of the dynamic pedicle screws from two different polyurethane foam blocks was significantly higher than that of the rigid pedicle screws. Therefore, based on our results, we propose that the device can be applied in clinical cases to reduce screw loosening and adjacent segment pathology. [ABSTRACT FROM AUTHOR]

Measurements of wear resistance and metal ion release are important for designing bearing couples or interfaces in total hip arthroplasty (THA). In this study, we investigated wear resistance and metal ion release of surface‐modified metal‐free all‐polymer hip bearings, such as poly(ether‐ether‐ketone), (PEEK) on cross‐linked polyethylene (PEEK‐on‐CLPE), with a hydrated gel‐like surface layer, to propose an improved alternative to the conventional materials used to design THA bearings. The PEEK surface resulted in less metal ion release than the cobalt–chromium–molybdenum (Co–Cr–Mo) alloy surface owing to the lack of metal. The PEEK‐on‐CLPE bearing (6.33 mg/106 cycles) had lower wear (rate) than the bearing with Co–Cr–Mo alloy‐on‐CLPE (10.47 mg/106 cycles) under controlled laboratory conditions; the wear performance of the all‐polymer hip bearings was further improved with hemi‐ or both‐surface modified with a hydrated poly(2‐methacryloyloxyethyl phosphorylcholine) (PMPC) layer (3.74 and 3.06 mg/106 cycles, respectively). The PMPC‐grafted interface of PEEK‐on‐CLPE will be especially suitable for THA candidates. This study is of key importance for the design of lifelong THA and a better understanding of the limitations resulting from using PEEK. Further studies are necessary to evaluate the possibility of using this material in artificial hips. [ABSTRACT FROM AUTHOR]

Taper fretting corrosion is considered a potentially limiting factor for total hip arthroplasty longevity. Recently, attention has been focused on new materials for ceramic femoral heads, for example, zirconia‐toughened alumina (ZTA), since they have an alternative bearing surface that can improve the wear resistance. Moreover, ceramics have high chemical stability and corrosion resistance. In this study, we evaluated the effects of ZTA and Co–Cr–Mo alloy femoral heads on their taper fretting and/or corrosion characteristics under a controlled hip simulator test. After the test, less fretting and corrosion were observed in the taper surface of the trunnion against the ZTA femoral head than for that against the Co–Cr–Mo alloy femoral head. In addition, corrosion damages were only observed in the lateral‐distal taper surface (noncontact area) of the trunnion in the Co–Cr–Mo alloy femoral head group. The ZTA femoral head group also eliminated the potential for Co ion release into the lubricants from taper corrosion, reducing the possibility of adverse local tissue inflammatory responses. In conclusion, ZTA femoral heads showed markedly less fretting corrosion compared to Co–Cr–Mo alloy femoral heads and have a lower potential for metal ion release. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 2815–2826, 2018. [ABSTRACT FROM AUTHOR]

Abstract: Younger, active patients who undergo total hip arthroplasty (THA) have increasing needs for wider range of motion and improved stability of the joint. Therefore, bearing materials having not only higher wear resistance but also mechanical strength are required. Carbon fiber‐reinforced poly(ether ether ketone) (CFR‐PEEK) is known as a super engineering plastic that has great mechanical strength. In this study, we focused on poly(2‐methacryloyloxyethyl phosphorylcholine) (PMPC)‐grafted CFR‐PEEK and investigated the effects of PMPC grafting and the femoral heads materials on the wear properties of CFR‐PEEK liners. Compared with untreated CFR‐PEEK, the PMPC‐grafted CFR‐PEEK surface revealed higher wettability and lower friction properties under aqueous circumstances. In the hip simulator wear test, wear particles generated from the PMPC‐grafted CFR‐PEEK liners were fewer than those of the untreated CFR‐PEEK liners. There were no significant differences in the size and the morphology of the wear particles between the differences of PMPC‐grafting and the counter femoral heads. Zirconia‐toughened alumina (ZTA) femoral heads had significantly smoother surfaces compared to cobalt–chromium–molybdenum alloy femoral heads after the hip simulator test. Thus, we conclude that the bearing combination of the PMPC‐grafted CFR‐PEEK liner and ZTA head is expected to be a lifelong bearing interface in THA. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1028–1037, 2018. [ABSTRACT FROM AUTHOR]

One of the important factors in determining the success of joint replacement is the wear performance of polyethylene. Although highly crosslinked polyethylene (CLPE) is presently used, it is still not adequate. We have developed a surface modification technology using poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) in an attempt to improve wear performance. In this study, we evaluated the wear and creep deformation resistances of 3-mm and 6-mm thick PMPC-grafted CLPE disks, set on a metal back-plate, with and without a sham screw hole. The gravimetric wear and volumetric change of the disks were examined using a multidirectional pin-on-disk tester. PMPC grafting decreased the gravimetric wear of CLPE regardless of the presence of a screw hole, and did not affect the volumetric change. The volumetric change in the bearing and backside surfaces of the 3-mm thick disk with a screw hole was much larger than that of those without a screw hole or those of the 6-mm thick disk, which was caused by creep deformation. PMPC grafting on the bearing surface can be a material engineering approach to reduce the wear without changing the creep deformation resistance, and is a promising surface modification technology that can be used to increase the longevity of various artificial joints. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 610-618, 2018. [ABSTRACT FROM AUTHOR]