We report on an innovative surface grafting to highly crosslinked (HXLPE) bearing for THA using a biocompatible-phospholipid-polymer poly (2-methacryloyloxyethyl phosphorylcholine) (PMPC). Such hydrophilic surfaces mimic articular cartilage and are hypothesized to improve lubrication and thereby reduce friction and wear.

We performed in vitro testing of wear and friction of ceramic-on-polyethylene THRs with the PMPC treatment, and compared them with untreated controls. Highly cross-linked UHMWPE bearings, gamma-ray-irradiated at different levels with and without vitamin E (HXL Vit. E: 125 kGy, HXL: 75 kGy, respectively) were divided so half were PMPC treated (n=3 for all four groups). All were paired with identical 40 mm diameter zirconia-toughened-alumina ceramic heads. Testing was carried-out on an AMTI hip simulator for 10 million simulated walking cycles with standard lubricant and conditions (ISO-14242-1). Wear was measured gravimetrically at 21 intervals, and so was frictional torque with a previously described and tested methodology.

PMPC treatment produced a statistically significant 71% in wear reduction of HXL poly (1.70±1.36 mg/Mc for PMPC vs. 5.86±0.402 mg/Mc for controls, p=0.013). A similar significant wear reduction was found for PMPC treated HXL with Vit. E liners (0.736±0.750 mg/Mc, vs. 2.14±0.269 mg/Mc, p=0.035). The improvements were associated with 12% and 5% reductions in friction of the HXL and Vit. E HXL respectively (statistically significant p=0.003, and marginal p=0.116, one tailed).

These results were an important step in the quest for lower wearing, thin and strong UHMWPE liners for larger diameter femoral heads with the potential benefit of longevity and less risk of dislocation after surgery.

The burden of hospital length of stay (LOS) and readmissions for total hip arthroplasty (THA) patients has resulted in great scrutiny. The purpose of this study was to determine our patients' LOS and hospital readmissions over the past 7 years. The second purpose was to determine what comorbidities affected the LOS and readmissions of 1440 THA patients.

1440 THA patients were retrospectively reviewed. The group included 622 males, 818 females. The average age of the cohort was 60 years (12 to 94 years). Ninety-day hospital readmissions were measured for the patients. Fisher's exact test, independent Sample t-test and Spearman correlation coefficients were used to determine associations of patient characteristics and comorbidities with readmission status and LOS with comorbidity status.

The LOS decreased over the time of the study (p=0.02), however; readmissions remained constant at approximately 6% (p=0.73). The mean LOS for patients not readmitted was significantly shorter than for those readmitted (3.2 vs. 4.4 days; p=0.0003). Comorbidities associated with a longer hospital stay included diabetes (p=0.0052), hypertension (p=0.04), coronary artery disease (p=0.0034), congestive heart failure (p=0.0012), peripheral vascular disease (p=0.015), chronic obstructive pulmonary disease (p=0.016), renal disease (p=0.009), and mental illness (p=0.03). Increased body mass index (BMI) was not associated with a significant increase in LOS (r=0.01, p=0.83). Increased readmission rates were associated with comorbidities including hypertension (p=<0.0001), coronary artery disease (p=<0.0001), congestive heart failure (p=0.0007), peripheral vascular disease (p=<0.0001), chronic obstructive pulmonary disease (p=0.003), asthma (p=0.0128), renal disease (p=0.0001), and mental illness (p=0.0147). Obesity was not associated with increased readmission rates until the patients were morbidly obese (>40 BMI; p=0.03).

Although the LOS decreased over the time of the study, this did not result in an adverse increase in readmission rates. Several comorbidities including hypertension, coronary artery disease, congestive heart failure, peripheral vascular disease, chronic obstructive pulmonary disease, and mental illness were all associated with both a longer LOS and an increase in readmission rates. Asthma was associated with increased readmission rates only and diabetes was associated with an increased LOS only. BMI was not associated with readmission rates unless the BMI exceeded 40 and had no significant effect on LOS at any BMI level.