Michael D. Ries

The Impact of Infection After Total Hip Arthroplasty on Hospital and Surgeon Resource Utilization

BACKGROUND Deep infection following total hip arthroplasty is a devastating complication for the patient and a costly one for patients, surgeons, hospitals, and payers. The purpose of this study was to compare revision total hip arthroplasty for infection, revision total hip arthroplasty for aseptic loosening, and primary total hip arthroplasty with respect to their impact on hospital and surgeon resource utilization and referral patterns to a tertiary-care hospital. METHODS Clinical, demographic, and economic data were obtained for twenty-five consecutive patients with an infection after a total hip replacement who underwent a two-stage revision arthroplasty (Group 1) performed by one of two surgeons, between March 2001 and December 2002, at a single institution. Similar data were collected during the same time-period for a cohort of twenty-five consecutive patients who underwent revision of both components because of aseptic loosening (Group 2) and twenty-five consecutive patients who underwent a primary hip arthroplasty (Group 3). Quantitative and categorical variables were compared among the groups. Referral patterns were examined by reviewing the primary diagnosis for all patients referred to our institution for a revision total hip arthroplasty during a five-year period. RESULTS Revision procedures for infection were associated with longer operative time, more blood loss, and a higher number of complications compared with revisions for aseptic loosening or primary total hip arthroplasty (p < 0.02 for all). Revisions for infection were also associated with a higher total number of hospitalizations, total number of days in the hospital, total number of operations, total hospital costs, total outpatient visits, and total outpatient charges during the twelve-month period following the index procedure (p < 0.001 for all). The incidence of referrals to our institution for a diagnosis of infection following total hip arthroplasty increased significantly over a five-year period (Spearman rank correlation, 1.0; p = 0.0083), while referral rates for revision for causes other than infection remained relatively constant (Spearman rank correlation, 0.500; p = 0.3910). CONCLUSIONS The treatment of patients with an infection after a total hip arthroplasty is associated with significantly greater hospital and physician resource utilization compared with the treatment of patients who have a revision because of aseptic loosening or who have a primary total hip arthroplasty. We believe that the lack of incremental reimbursement associated with these procedures results in strong financial disincentives for physicians and hospitals to provide treatment for patients with an infection after a total hip arthroplasty.

Antibiotic-impregnated Cement Spacers for the Treatment of Infection Associated with Total Hip or Knee Arthroplasty

![Graphic][1] Infection at the site of a total joint arthroplasty can be classified into four basic categories: Type I (early postoperative), Type II (late chronic), Type III (acute hematogenous), and Type IV (positive intraoperative cultures with clinically unapparent infection). ![Graphic][2] The current standard of care for late chronic infection is considered to be two-stage revision arthroplasty including removal of the prosthesis and cement, thorough debridement, placement of an antibiotic-impregnated cement spacer, a course of intravenous antibiotics, and a delayed second-stage revision arthroplasty. ![Graphic][3] The choice of the spacer, either articulating or nonarticulating, is based on many factors, including the amount of bone loss, the condition of the soft tissues, the need for joint motion, the availability of prefabricated spacers or molding methods, and antibiotic selection. ![Graphic][4] Current data have demonstrated that the use of antibiotic-impregnated cement spacers has improved the outcomes of the treatment of infection associated with total joint arthroplasty. Total joint replacement is one of the most frequent and successful types of operations in orthopaedics. Infection is a rare yet devastating complication of the procedure, with a reported prevalence of 0.5% to 3% and with a higher reported prevalence after total knee arthroplasty than after total hip arthroplasty1-4. There is also a higher rate of infection after revision hip and knee arthroplasties than after primary hip and knee arthroplasties1-8. Two-stage revision surgery was first described in 1983 by Insall et al., who demonstrated the necessity of removing the implants as well as the cement and of introducing antibiotic therapy for definitive treatment9. This procedure has emerged as the standard of care for a late chronic infection at the site of a total joint replacement4,5,10-17. Garvin and Hanssen reviewed twenty-nine studies and found that two-stage … [1]: /embed/inline-graphic-1.gif [2]: /embed/inline-graphic-2.gif [3]: /embed/inline-graphic-3.gif [4]: /embed/inline-graphic-4.gif

Hospital resource utilization for primary and revision total hip arthroplasty

BACKGROUND Previous reports have suggested that hospital resource utilization for revision total hip arthroplasty is substantially higher than that for primary total hip arthroplasty. However, current United States Medicare hospital-reimbursement policy does not distinguish between the two procedures. The purpose of this study was to compare primary and revision total hip arthroplasties with regard to actual hospital resource utilization and to identify clinical and demographic factors that are predictive of higher resource utilization associated with these procedures. METHODS We evaluated the clinical, demographic, and economic data associated with 491 consecutive unilateral primary or revision total hip arthroplasties performed by two surgeons at a single institution between January 2000 and December 2002. The distributions of various demographic, clinical, and utilization characteristics were compared between the two types of arthroplasty procedures, and multivariable linear regression techniques were used to determine independent patient characteristics that were predictive of higher costs for both the primary and the revision procedures. RESULTS The mean total hospital cost was

Quantitative MRI using T1ρ and T2 in human osteoarthritic cartilage specimens: Correlation with biochemical measurements and histology

31,341 for the revision procedures compared with

Comparison of cemented and uncemented fixation in total hip replacement: a meta-analysis

24,170 for the primary procedures (p < 0.0001). The mean operative time was 41% longer for the revisions than for the primary procedures (4.5 hours compared with 3.2 hours, p < 0.0001), the mean estimated blood loss was 160% higher (1348 mL compared with 518 mL, p < 0.0001), the mean complication rate was 32% higher (29% compared with 22%, p = 0.072), and the mean length of the hospital stay was 16% longer (6.5 days compared with 5.6 days, p = 0.0005). A higher severity-of-illness score (a measure of preoperative medical health) was predictive of higher resource utilization for both primary and revision arthroplasty even after adjustment for other factors. Preoperative femoral and ace-tabular bone loss and a diagnosis of periprosthetic fracture were predictive of higher resource utilization associated with revision procedures. CONCLUSIONS At one institution, hospital resource utilization for revision total hip arthroplasty was found to be significantly higher than that for primary arthroplasty. This information is not reflected by current United States Medicare hospital reimbursement, which is the same for all lower-extremity arthroplasty procedures, regardless of the diagnosis, the complexity of the procedure, or the patients baseline medical health. If these findings are generalizable to other institutions, appropriate reimbursement formulas should be developed to accurately reflect the true costs of caring for patients with a failed total hip arthroplasty.

MR imaging findings in the follow-up of patients with different stages of knee osteoarthritis and the correlation with clinical symptoms

PURPOSE A direct correlation between T(1ρ), T(2) and quantified proteoglycan and collagen contents in human osteoarthritic cartilage has yet to be documented. We aimed to investigate the orientation effect on T(1ρ) and T(2) values in human osteoarthritic cartilage and to quantify the correlation between T(1ρ), T(2) vs. biochemical composition and histology in human osteoarthritic cartilage. MATERIALS AND METHODS Thirty-three cartilage specimens were collected from patients who underwent total knee arthroplasty due to severe osteoarthritis and scanned with a 3T MR scanner for T(1ρ) and T(2) quantification. Nine specimens were scanned at three different orientations with respect to the B(0): 0°, 90° and 54.7°. Core punches were taken after MRI. Collagen and proteoglycan contents were quantified using biochemical assays. Histology sections were graded using Mankin scores. The correlation between imaging parameters, biochemical contents and histological scores were studied. RESULTS Both mean T(1ρ) and T(2) at 54.7° were significantly higher than those measured at 90° and 0°, with T(1ρ) showing less increase compared to T(2). R(1ρ) (1/T(1ρ)) values had a significant but moderate correlation with proteoglycan contents (R=.45, P=.002), while R(2) (1/T(2)) was not correlated with proteoglycan. No significant correlation was found between relaxation times (T(1ρ) or T(2)) and collagen contents. The T(1ρ) values of specimen sections with high Mankin scores were significantly higher than those with low Mankin scores (P<.05). CONCLUSIONS Quantitative MRI has a great potential to provide noninvasive imaging biomarkers for cartilage degeneration in osteoarthritis.

Wear and surface cracking in early retrieved highly cross-linked polyethylene acetabular liners

Background The choice of optimal implant fixation in total hip replacement (THR)—fixation with or without cement—has been the subject of much debate. Methods We performed a systematic review and meta-analysis of the published literature comparing cemented and uncemented fixation in THR. Results No advantage was found for either procedure when failure was defined as either: (A) revision of either or both components, or (B) revision of a specific component. No difference was seen between estimates from registry and single-center studies, or between randomized and non-randomized studies. Subgroup analysis of type A studies showed superior survival with cemented fixation in studies including patients of all ages as compared to those that only studied patients 55 years of age or younger. Among type B studies, cemented titanium stems and threaded cups were associated with poor survival. An association was found between difference in survival and year of publication, with uncemented fixation showing relative superiority over time. Interpretation While the recent literature suggests that the performance of uncemented implants is improving, cemented fixation continues to outperform uncemented fixation in large subsets of study populations. Our findings summarize the best available evidence qualitatively and quantitatively and provide important information for future research.

Spatial Distribution and Relationship of T1ρ and T2 Relaxation Times in Knee Cartilage With Osteoarthritis

Objective: To assess the rate of cartilage loss, the change in bone marrow edema pattern and internal joint derangement at 1.5-T MRI in patients with knee osteoarthritis and to correlate these findings with the clinical Western Ontario and McMaster University Osteoarthitis (WOMAC) score. Methods: Forty subjects (mean age 57.7±15 years; 16 females and 24 males) were recruited: 6 healthy volunteers (OA0), 17 patients with mild osteoarthritis (OA1) and 17 with severe osteoarthritis (OA2) based on the Kellgren-Lawrence scale. MR scans, radiographs and WOMAC scores were obtained at baseline, first follow-up (1.4±0.67 years; n=40) and second follow-up (2.4±0.4 years; n=26). Cartilage morphology, bone marrow edema (BME), meniscal and ligamentous pathology were assessed on MR images and quantified by two radiologists in consensus. Results:Full-thickness cartilage lesions were observed in 12/17 OA2 at baseline, in 13/17 at the first follow-up and in 7/10 at the second follow-up. Cartilage loss was found in eight patients at the first follow-up and five at the second follow-up. BME was observed in 23/40 patients at baseline, in 22/40 at the first follow-up and in 12/26 at the second follow-up. Changes in BME were visualized in 19/22 and 4/13 patients at the first and second follow-up, respectively. Changes in WOMAC scores over time did not correlate significantly with the amount of cartilage loss and the change in BME (P>0.05). Conclusion:MRI is well suited to monitor the progression of OA in the longitudinal follow-up since it shows cartilage defects, BME and internal joint derangement, pathologies that are not visualized by radiographs. The lack of significant correlation between MRI findings and clinical findings is not unexpected, has been previously described and may in part be due to the fact that patients get more accustomed to their pain as the knee progressively degenerates.

MicroCT evaluation of normal and osteoarthritic bone structure in human knee specimens

BACKGROUND A higher degree of cross-linking has been shown to improve the tribological properties of ultra-high molecular weight polyethylene in laboratory studies; however, its effect on in vivo behavior has not been well established. We investigated in vivo wear mechanisms in retrieved highly cross-linked polyethylene acetabular liners in order to determine if early in vivo wear behavior is accurately predicted by hip-simulator studies. METHODS A total of twenty-four liners (twenty-one explanted and one unimplanted highly cross-linked liners and two explanted ethylene-oxide-sterilized non-cross-linked liners) were examined for this study. The average age of the patients was 59.9 years, and the average time in vivo was 10.1 months. Articular surface damage on the front and back sides of the liners was assessed with an optical scoring system. Surface quadrants were assigned a grade from 0 to 3 according to the observed wear mechanisms and the percentage of surface affected. The micromechanisms of liner damage were evaluated with use of scanning electron microscopy. RESULTS The average front and back-side explant damage scores were 11 (range, 2 to 26.5) and 6.7 (range, 3.7 to 13.3), respectively. There was consistent evidence of early surface deformation and cracking. All explants exhibited some form of surface change, including surface cracking, abrasion, pitting, or scratching. The original machining marks on the liner surface were observed to be either unaltered, drastically distorted, or absent. CONCLUSIONS Highly cross-linked ultra-high molecular weight polyethylene acetabular liners that were retrieved at an average of ten months after implantation exhibited signs of surface damage that had not been predicted by in vitro hip-simulator studies. These devices had not failed clinically as a result of wear. The discrepancy between in vitro and in vivo wear surfaces may be due to variability in terms of in vivo lubrication and cyclic loading or may represent early surface damage mechanisms that are not well demonstrated by long-term simulator studies.

Reduced wear with oxidized zirconium femoral heads.

T1ρ and T2 relaxation time constants have been proposed to probe biochemical changes in osteoarthritic cartilage. This study aimed to evaluate the spatial correlation and distribution of T1ρ and T2 values in osteoarthritic cartilage. Ten patients with osteoarthritis (OA) and 10 controls were studied at 3T. The spatial correlation of T1ρ and T2 values was investigated using Z‐scores. The spatial variation of T1ρ and T2 values in patellar cartilage was studied in different cartilage layers. The distribution of these relaxation time constants was measured using texture analysis parameters based on gray‐level co‐occurrence matrices (GLCM). The mean Z‐scores for T1ρ and T2 values were significantly higher in OA patients vs. controls (P < 0.05). Regional correlation coefficients of T1ρ and T2 Z‐scores showed a large range in both controls and OA patients (0.2–0.7). OA patients had significantly greater GLCM contrast and entropy of T1ρ values than controls (P < 0.05). In summary, T1ρ and T2 values are not only increased but are also more heterogeneous in osteoarthritic cartilage. T1ρ and T2 values show different spatial distributions and may provide complementary information regarding cartilage degeneration in OA. Magn Reson Med, 2009.