The solvent extraction step applied in conventional oxidation measurement protocols for UHMWPE retrievals resulted in an elevated oxidation index (OI) in remelted highly cross-linked UHMWPE (RM-HXLPE). The present study seeks to confirm the effect of solvent extraction on OI measurement and to understand the relationships among soak-aging, fluid uptake, and resulting OI from various test protocols. Two materials were tested, representing legacy gamma-in-air sterilized (GammaAir-PE, GUR4150, 30 kGy) and remelted highly cross-linked (RM-HXLPE, GUR1050, 100 kGy, 147°C/5h) UHMWPE. Concave discs approximately 19 millimeters (mm) in diameter and 3 mm in dome thickness were machined from both materials prior to soak-aging. Soak-aging consisted of a combination of: (1) ASTM F2003 accelerated aging (5 atm O2, 70 °C for 14 days), and (2) either static soaking (SS, for 11.57 days) or dynamic load-soaking (LS, 2280 N at 1 Hz for 1 million cycles) in bovine synovial fluid at 37 °C to simulate the combination of shelf and in-vivo aging, respectively. Unsoaked samples were used as control (C) group. Thin films (150 μm) were harvested from cross-sections of all groups and were subjected to two solvent extraction protocols using Sohxlet (Heptane for 6 h (HEP6) or Hexane for 16 h (HEX16)) prior to be analyzed by two OI analyses using Fourier transform infrared spectroscopy (FTIR). FTIR analyses (128 scans/spectra, 4 cm−1 resolution) were carried out using both peak height at and peak area centering 1714 cm−1 for OI and 1734 for fluid uptake index (FI); carbon-carbon vibration at 1368 cm−1 was used for normalization. All GammaAir-PE data was further normalized using prewash control while RM-HXLPE data used computed results. The paired t-test was used with a significance level of p < 0.05.Introduction:
Materials and Methods:
For cementless TKA, highly crosslinked UHWMPE is traditionally used with modular components because of manufacturing and sterilization complexities of monoblock metal-backed components. However, it would be very useful to have a highly crosslinked UHMWPE monoblock metal-backed cementless component to address historical clinical issues. The purpose of this study was to evaluate the wear properties of a unique process for achieving a monoblock metal-backed cementless component featuring highly crosslinked polyethylene to standard highly crosslinked UHWMPE. The knee system used for testing consisted of cobalt chrome femoral components and tibial trays (Triathlon®, Stryker Orthopaedics, Mahwah, NJ). Modular tibial inserts were machined from GUR 1020 polyethylene that was irradiated to 30 kGy and annealed three times (Modular, n=5) (X3, Stryker Orthopaedics, Mahwah, NJ). Monoblock tibias were direct compression molded to a metal substrate and then irradiated to 30 kGy and annealed three times. For the purposes of this test, the polyethylene was removed from the monoblock component and machined into a standard tibial insert (Monoblock, n=5). A 6-station knee simulator was utilized for testing (MTS, Eden Prairie, MN). All motion and loading was computer controlled and waveforms followed ISO 14243-3 [1]. Testing was conducted at a frequency of 1 Hz for 3 million cycles. The lubricant used was Alpha Calf Fraction serum (Hyclone Labs, Logan, UT) diluted to 50% with a pH-balanced 20-mMole solution of deionized water and EDTA [2]. The serum solution was replaced and inserts were weighed for gravimetric wear at least every 0.5 million cycles. Standard test protocols were used for cleaning, weighing and assessing the wear loss of the tibial inserts [3]. Soak control specimens were used to correct for fluid absorption with weight loss data converted to volumetric data (by material density). Statistical analysis was performed using the Student's t-test with significance determined at the 95% confidence level (p < 0.05).INTRODUCTION
MATERIALS AND METHODS
Scarf osteotomy for correction of painful hallux valgus is an effective technique, giving a predictable correction of the deformity. However, some patients remain less than fully satisfied, despite normalisation of the usual radiographic parameters. This study examines whether lateral soft tissue release can cause late splaying of the forefoot. A series of 32 feet in 29 consecutive patients in a single centre, operated on by a single surgeon, over a 12 month period were studied. After pre-operative weight-bearing x-rays and consenting, a standardised ‘Barouk-technique’ Scarf procedure was undertaken with on-table assessment for lateral soft tissue release and phalangeal varisation. Post-operatively, patients were kept heel weight-bearing without cast for 6 weeks, with use of a fabric splint after removal of bandages at 2 weeks. HVA and IMA were measured pre-operatively, at 6 weeks, and at 6-12 month follow-up. Distance from the mid-points of the 1st to the 5th metatarsal heads and distance from lateral sesamoid to 2nd metatarsal shaft were also recorded by blinded observers. AOFAS Foot Scores were collected prospectively. Student's t-test for single-tailed paired data was applied and p-values calculated. There were 22 female and 10 male feet; in patients aged 27 to 74 (mean 58). Average HVA improved from 34° to 17° and was maintained at 16°. IMA improved from 14° to 7°, but then increased significantly to 10°. Overall inter-metatarsal width reduced from 76mm to 65mm but then significantly increased to 71mm. Sesamoid distance was also reduced and later increased, but not significantly. Mean foot scores improved from 52 to 85 at late follow-up. Complication rate was low. Late widening occurred more in those feet with bigger original HVA, which were likely to have had more extensive soft tissue release (deep inter-metatarsal ligament). We recommend cautious release; and pre-operatively counselling specifically regarding eventual overall foot-width.
