EFFECT OF COUNTERFACE ON CARTILAGE BOUNDARY LUBRICATING ABILITY BY HYALURONAN AND PROTEOGLYCAN 4: CARTILAGE-CARTILAGE VS CARTILAGE-GLASS

INTRODUCTION Proteoglycan 4 (PRG4), also known as lubricin, is a mucin-like glycoprotein found in synovial fluid (SF) [1]. Hyaluronan (HA) is another constituent of SF that works synergistically with PRG4 to promote joint lubrication required for joint health [2]. Current in vitro friction tests used to analyze these lubricants have found similar trends but varying friction coefficient (m) magnitudes. These effects may be attributed to different testing protocols, and in particular the various interfaces [3,4,5,6,7,8]. Previous studies have used cartilage-cartilage [7,8] and cartilage-glass [6] friction tests to assess SF lubricants. However, few studies have examined the friction reducing ability of SF lubricants at various velocities and different interfaces. The objective of this study was to determine HA and PRG4’s lubricating ability at cartilage-glass and cartilage-cartilage biointerfaces at various velocities.   METHODS HA (1.5 MDa, Lifecore Biomedical) was prepared at 3.3 mg/mL with phosphate buffered saline (PBS) [9]. PRG4 was purified from media conditioned bovine cartilage explants, and prepared at 450 μg/mL in PBS [9]. Two sets of tests were conducted using a modified boundary lubrication test protocol [7]. For cartilage-glass, a 6mm radius glass piece, with a root mean square surface roughness of 6.061±0.7554 nm, acted as the base core with a cartilage annuli [7]. Three lubricants were tested over three days, PBS (n=8), HA or PRG4 (n=4), and SF (n=8). Cartilage-cartilage underwent the same test sequence. Both sets of samples underwent the same testing protocol; samples were compressed to 18% of the total cartilage thickness with a 40 minute stress relaxation [9]. Samples were then rotated at effective sliding velocities of 10, 3, 1, 0.3, 0.1, and 0.01 mm/s with a 120s pre-sliding duration. Kinetic μ was calculated with instantaneous (<μkinetic>) load values. A two-factor ANOVA was used to determine effects of lubricant and velocity, with Tukey post-hoc testing. RESULTS At the cartilage-glass interface (Fig. 1A), <μkinetic> varied with test lubricant and velocity (p<0.001), with no interaction (p=0.78). All lubricants were significantly different from each other (p<0.001), except for PBS/HA (p=0.65) and PRG4/SF (p=0.72). Velocities were significantly different from each other when comparing 0.01 mm/s to all other speeds (p<0.02). At the cartilage-cartilage interface (Fig. 1B), <μkinetic> varied with test lubricant and velocity (p<0.01), with no interaction (p=0.82). All lubricants were significantly different from each other (p<0.01), except for HA/SF (p=0.07) and HA/PRG4 (p=0.35). Velocity was only significantly different at 0.01mm/s when compared to 3 and 10 mm/s (p<0.028). DISCUSSION AND CONCLUSIONS These results indicate that different articulating interfaces can result in different trends of <μkinetic>, and also affect the magnitude of the value. This agrees with previous research; showing that stiff and impermeable surfaces versus hydrated and permeable surfaces results in different <μkinetic> [3]. This data illustrates that HA is indeed a cartilage boundary lubricant and reduces friction at the cartilage-cartilage interface, but not at a cartilage-glass set up. Overall, different test systems are suitable for characterizing lubrication properties, but direct <μkinetic> values should not be compared

Pain catastrophizing and pain health-related quality-of-life in endometriosis

OBJECTIVES: To determine if pain catastrophizing is independently associated with pain health-related quality-of-life in women with endometriosis, independent of potential confounders. METHODS: Analysis of cross-sectional baseline data from a prospective database at a tertiary referral center for endometriosis/pelvic pain. Referrals to the center were recruited between December 2013 to April 2015, with data collected from online patient questionnaires, physical examination, and review of medical records. The primary outcome was health-related quality-of-life as measured by the 11-item pain subscale of the Endometriosis Health Profile-30 questionnaire. The Pain Catastrophizing Scale was the independent variable of interest. Other independent variables (potential confounders) included other psychological measures, pain severity, comorbid pain conditions, and social-behavioral and demographic variables. Multivariable linear regression was used to control for these potential confounders and assess independent associations with the primary outcome. RESULTS: 236 women were included (87% consent rate). The mean age was 35.0±7.3 years, and 98 (42%) had Stage I-II endometriosis, 110 (47%) had Stage III-IV endometriosis, and 28 (11%) were of unknown stage after review of operative records. Regression analysis demonstrated that higher pain catastrophizing (p<0.001), more severe chronic pelvic pain (p<0.001), more severe dysmenorrhea (p<0.001), and abdominal wall pain (positive Carnett test) (p=0.033) were independently associated with worse pain health-related quality-of-life. DISCUSSION: Higher pain catastrophizing was associated with a reduced pain health-related quality-of-life in women with endometriosis at a tertiary referral center, independent of pain severity and other potential confounders.Medicine, Faculty ofNon UBCObstetrics and Gynaecology, Department ofPopulation and Public Health (SPPH), School ofReviewedFacultyResearcherGraduat