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1.  Low Wear of a Second-generation Highly Crosslinked Polyethylene Liner: A 5-year Radiostereometric Analysis Study 
A sequentially irradiated and annealed, second-generation highly crosslinked polyethylene (XLPE) liner was introduced clinically in 2005 to reduce in vivo oxidation. This liner design has also been shown to reduce wear in vitro when compared with conventional and first-generation crosslinked liners. To date, there is only one study reporting an in vivo wear rate of this liner at 5 years’ followup. However, that study used measurements made from plain radiographs, which have limited sensitivity, particularly when monitoring very low amounts of wear.
What is the amount and direction of wear at 5 years using radiostereometric analysis (RSA) in patients who had THAs that included second-generation XLPE?
We prospectively reviewed 21 patients who underwent primary cementless THA with the same design of XLPE acetabular liner and 32-mm articulation. Tantalum markers were inserted during surgery and all patients had RSA radiographs at 1 week, 6 months, and 1, 2, and 5 years postoperatively. Femoral head penetration within the acetabular component was measured with UmRSA® software. One patient died and two had incomplete radiographs leaving 18 radiographic series for analysis.
The mean amounts of proximal, two-dimensional, and three-dimensional head penetration between 1 week and 5 years were 0.018, 0.071, and 0.149 mm, respectively. The mean proximal, two-dimensional, and three-dimensional wear rates calculated between 1 year and 5 years were all less than 0.001 mm/year with no patient recording a wear rate of more than 0.040 mm/year.
The head penetration of a second-generation XLPE liner remained low at 5 years and the wear rate calculated after the first year was low in all directions. This low level of wear remains encouraging for the future clinical performance of this material.
Level of Evidence
Level IV, therapeutic study. See Instructions for Authors for a complete description of levels of evidence.
PMCID: PMC3792282  PMID: 23893361
2.  Wear of a 5 Megarad Cross-linked Polyethylene Liner: A 6-year RSA Study 
One cross-linked polyethylene (XLPE) liner is manufactured using a lower dose of radiation, 5 Mrad, which may result in less cross-linking. The reported in vivo wear rate of this XLPE liner in patients undergoing THA has varied, and has included some patients in each reported cohort who had greater than 0.1 mm/year of wear, which is an historical threshold for osteolysis. Previous studies have measured wear on plain radiographs, an approach that has limited sensitivity.
We therefore measured the amount and direction of wear at 6 years using Radiostereometric analysis (RSA) in patients who had THAs that included a cross-linked polyethylene liner manufactured using 5 Mrad radiation.
We prospectively reviewed wear in 30 patients who underwent primary THAs with the same design of cross-linked acetabular liner and a 28-mm articulation. Tantalum markers were inserted during surgery and all patients had RSA radiographic examinations at 1 week, 6 months, 1, 2, and 6 years postoperatively.
The mean proximal, two-dimensional (2-D) and three-dimensional (3-D) wear rates calculated between 1 year and 6 years were 0.014, 0.014, and 0.018 mm/per year, respectively. The direction of the head penetration recorded between 1 week and 6 years was in a proximal direction for all patients, proximolateral for 16 of 24 patients, and proximomedial for eight of 24 patients.
The proximal, 2-D and 3-D wear of a XLPE liner produced using 5 Mrad of radiation was low but measurable by RSA after 6 years. No patients had proximal 2-D or 3-D wear rates exceeding 0.1 mm/year. Further followup is needed to evaluate the effect of XLPE wear particles on the development of long-term osteolysis.
PMCID: PMC3676600  PMID: 23334705
3.  Early migration characteristics of a hydroxyapatite-coated femoral stem: an RSA study 
International Orthopaedics  2009;35(4):483-488.
Measurement of early stem subsidence can be used to predict the likelihood of long-term femoral component loosening and clinical failure. Data that examines the early migration pattern of clinically proven stems will provide clinicians with useful baseline data with which to compare new stem designs. This study was performed to evaluate the early migration pattern of a hydroxyapatite-coated press-fit femoral component that has been in use for over ten years. We enrolled 30 patients who underwent THA for osteoarthritis. The median age was 70 years (range, 55–80 years). Patients were clinically assessed using the Harris hip score. Radiostereometric analysis was used to evaluate stem migration at three to four days, six months, one year and two years. We observed a mean subsidence of 0.73 mm at six months, 0.62 mm at one year and 0.58 mm at two years and a mean retroversion of 1.82° at six months, 1.90° at one year and 1.59° at two years. This data suggests that subsidence is confined to the first six months after which there was no further subsidence. The results from this study can be compared with those from novel cementless stem designs to help predict the long-term outcome one may expect from new cementless stem designs.
PMCID: PMC3066322  PMID: 20012862
4.  Second-generation Highly Cross-linked X3™ Polyethylene Wear: A Preliminary Radiostereometric Analysis Study 
First-generation highly cross-linked polyethylene liners have reduced the incidence of wear particle-induced osteolysis. However, failed acetabular liners have shown evidence of surface cracking, mechanical failure, and oxidative damage. This has led to the development of second-generation highly cross-linked polyethylene, which has improved wear and mechanical properties and resistance to oxidation in vitro. Owing to its recent introduction, there are no publications describing its clinical performance.
We assessed early clinical wear of a second-generation highly cross-linked polyethylene liner and compared its clinical performance with the published results of hip simulator tests and with first-generation highly cross-linked polyethylene annealed liners.
Patients and Methods
Twenty-one patients were enrolled in a prospective cohort study. Clinical outcome and femoral head penetration were measured for 19 patients at 6 months and 1 and 2 years postoperatively.
The median proximal head penetration was 0.009 mm and 0.024 mm at 1 and 2 years, respectively. The median two-dimensional (2-D) head penetration was 0.083 mm and 0.060 mm at 1 and 2 years, respectively. The median proximal wear rate between 1 and 2 years was 0.015 mm/year.
The wear rate calculated was similar to the in vitro wear rate reported for this material; however, it was less than the detection threshold for this technique. Although longer followup is required for wear to reach a clinically quantifiable level, this low level of wear is encouraging for the future clinical performance of this material.
Level of Evidence
Level IV, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.
PMCID: PMC3049610  PMID: 20151231
5.  Case Report: Cementless Stem Stabilization after Intraoperative Fracture: A Radiostereometric Analysis 
We present the case of a patient with intraoperative femoral fracture during THA, which was repaired using cerclage fixation and insertion of an hydroxyapatite-coated cementless stem. The patient was evaluated postoperatively using radiostereometry during a 2-year course, and despite a large amount of subsidence and rotation, stabilization occurred and was maintained by 6 months. By evaluating the pattern of stem migration after intraoperative fracture, this case shows, even in the presence of instability, a successful clinical outcome can be achieved using an hydroxyapatite-coated cementless stem.
PMCID: PMC2816748  PMID: 19760467

Results 1-5 (5)