Biomedical subjects

Michael D Ries

Publications and source records attributed to Michael D Ries.

At least 19 recordsLinked to original sources

PubMed2006

Revision total hip arthroplasty for large medial (protrusio) defects with a rim-fit cementless acetabular component.

Seventeen patients (19 hips) with protrusio acetabuli resulting from a failed total hip arthroplasty, large medial bone defect, and an intact bony rim were treated with an oversized cementless acetabular component and medial morcelized allograft. An average of 55% of the revision component was not supported by host bone. At an average follow-up of 2.8 (range 2-6) years, none of the acetabular components required revision for loosening. The average cup position preoperatively was 10.5 mm medial to Köhler's line and postoperatively was 6.8 mm lateral to Köhler's line. Despite very large medial defects, reconstructions with this technique remained stable.

Acetabulum↗

PubMed2006

In vivo behavior of acrylic bone cement in total hip arthroplasty.

Polymethylmethacrylate (PMMA) bone cement serves as the primary fixation material between bone and the prosthetic component in cemented total hip arthroplasty. In vivo degradation of bone cement may lead to a decrease in mechanical properties of PMMA and result in aseptic loosening. However, other factors such as porosity and location of the cement relative to the bone implant interface may also contribute to mechanical behavior in vivo. This study investigated the mechanical properties of Simplex cement retrieved from 43 patients undergoing revision total hip arthroplasty. The time in vivo was between 1 month and 27 years. The variables studied included fracture toughness (KIC), porosity, molecular weight, time in vivo of the cement, and relative in vivo location of the cement with respect to the implant and bone. KIC did not correlate with time in vivo of the samples or with molecular weight. This suggests that time in vivo may not be the limiting factor in the mechanical integrity of the bone cement, A significant and inverse relationship was found between porosity and KIC. This implies that porosity is the most important factor in the mechanical behavior of bone cement during in vivo use.

Arthroplasty, Replacement, Hip↗

PubMed2006

Osteolysis caused by tibial component debonding in total knee arthroplasty.

Late failure of total knee arthroplasties usually results from ultrahigh molecular weight polyethylene wear or implant loosening. Early failure from osteolysis is uncommon. However, we treated a patient with a failed total knee arthroplasty from osteolysis that developed 2 years postoperatively. The failure was associated with tibial component debonding from the cement mantle with abundant cement and metal debris. Although there was some third-body debris in the ultrahigh molecular weight polyethylene insert surface, the insert wear was not extensive. Although abundant cement and metal debris were found in the periarticular soft tissues, no ultrahigh molecular weight polyethylene was seen in histologic specimens under polarized light. The osteolysis seems to have been caused primarily by debris generated from debonding and torsional motion at the tibial baseplate-cement interface rather than the bearing surface. Although this failure mechanism has been well recognized in cemented total hip arthroplasties, it has not been reported to be a substantial cause of failure in total knee arthroplasties.

Aged↗

PubMed2006

Medial gastrocnemius flap coverage for treatment of skin necrosis after total knee arthroplasty.

UNLABELLED: Skin necrosis after total knee arthroplasty is a rare complication that can rapidly lead to deep infection of the prosthetic components. The medial gastrocnemius transposition flap usually provides adequate soft tissue coverage to salvage the total knee arthroplasty. However, variations in defect location and excursion of the muscle flap can affect results. Twelve patients were treated with a medial gastrocnemius transposition flap after total knee arthroplasty. The skin defect that required flap coverage was located over the tibial tubercle or patellar tendon in eight patients (Group 1). The defect extended proximally to the patella or quadriceps tendon in four patients (Group 2). A functioning total knee arthroplasty was salvaged in 11 patients (92%). The medial gastrocnemius flap healed primarily in all patients in Group 1. Three patients in Group 2 required additional fasciocutaneous, lateral gastrocnemius, or free flap coverage, and one patient underwent above knee amputation. The medial gastrocnemius flap is most effective for coverage of distal defects over the tibial tubercle or patellar tendon. Defects that extend more proximally over the patella or quadriceps tendon are more likely to require additional procedures to achieve adequate soft tissue coverage. LEVEL OF EVIDENCE: Therapeutic study, level IV (case series). See Author Guidelines for a complete description of levels of evidence.

Adult↗

PubMed2006

Whole patellar allograft for total knee arthroplasty after previous patellectomy.

UNLABELLED: We treated seven consecutive patients (nine knees) with previous total knee arthroplasties and patellectomies with whole patellar allograft reconstructions of the extensor mechanism. The patients' extensor mechanism soft tissue sleeve was intact, but the patella was not present. Deficient patellae were reconstructed using patellar ligament (whole patella) quadriceps tendon allograft. Six knees had previous patellectomies and underwent primary total knee arthroplasties. Three knees had previous patellectomies and underwent revision total knee arthroplasties. Two patients who had primary total knee arthroplasties had failed results; one from infection and one from aseptic allograft resorption and fragmentation. One patient in the revision total knee arthroplasty group had failed results from infection. After an average followup of 44 months (range, 39-48 months), the six intact knees had an increase in quadriceps strength of one grade. The average Knee Society knee and function scores increased from 59 and 63 points, respectively, to 85 and 67 points, respectfully. The average patellar thickness was 24 mm 6 weeks postoperatively, and 15 mm (38% decrease) at the most recent followup. Patellar allografting improved quadriceps function by restoring patellar height. However, a high risk of allograft complications can occur with this procedure. LEVEL OF EVIDENCE: Therapeutic study, Level IV (case series).

Arthroplasty, Replacement, Knee↗

PubMed2006

Porous tantalum patellar augmentation: the importance of residual bone stock.

Trabecular metal augmentation of bone defects has been associated with favorable bone ingrowth. Animal studies also suggest fibrous tissue attachment to trabecular metal can be achieved. We treated 16 patients with total knee arthroplasty (18 knees) with severe patellar bone loss using trabecular metal patellar reconstruction. The patients were divided into two groups based on the amount of residual patellar bone stock present at the time of surgery: Group 1 (six patients, seven knees) with no patellar bone stock and Group 2 (10 patients, 11 knees) in whom at least 50% of the patellar component surface was covered by host bone. All seven patellar components in Group 1 loosened within 1 year. Two of these developed necrosis of the extensor mechanism leading to extensor mechanism discontinuity. One component in Group 2 became infected and loosened, whereas the remaining 10 components remained stable at minimum 12-month followup. Our results suggest stable fixation of a trabecular metal patellar component can be achieved when residual bone is present for implant fixation, but early loosening is likely to occur when soft tissue is used for fixation to the implant.

Aged↗

PubMed2006

Clinical impact of obesity on stability following revision total hip arthroplasty.

Similar outcomes have been reported for obese and nonobese patients after primary total hip arthroplasty (THA), indicating obesity is not a contraindication to total hip arthroplasty. However, obese patients may develop implant failure and require revision THA. We compared the outcomes of revision THA in a matched cohort of obese and nonobese patients. Patients were stratified into two groups according to BMI (body mass index, kg/m2): Group 1 included 31 obese patients (BMI > 35), and Group 2 included 62 nonobese patients (BMI < 30) matched on age, gender, and type of revision procedure. Obese patients had increased total operating room time, a higher rate of discharge to a skilled nursing facility, and a higher dislocation rate (p < 0.05). Seven patients in the obese group underwent revision surgery, six of whom underwent additional reoperations to treat recurrent postoperative dislocation. Obese patients should be counseled about the increased risk of dislocation that can occur after revision THA.

Arthroplasty, Replacement, Hip↗

PubMed2005

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

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.

Adult↗

PubMed2005

Magnetic resonance imaging of in vivo kinematics after total knee arthroplasty.

PURPOSE: To improve the quality of magnetic resonance imaging (MRI) on knees after total knee arthroplasty (TKA) by minimizing image artifacts caused by metallic implants, and to establish a method determining in vivo kinematics of TKA knees using MRI. MATERIALS AND METHODS: Two knee implants made of cobalt-chrome and oxidized zirconium were tested with different pulse sequences and imaging parameters. Then, in vivo kinematic MRI was performed on five well-functioning TKAs under simulated weight-bearing conditions. Kinematic measurements were made and a linear correlation test was run between the tibio- and patellofemoral measurements. RESULTS: The best images with minimum metallic artifacts were observed using oxidized zirconium implants, a fast spin echo sequence (FSE), thin slice thickness, and high readout gradient. TKA kinematics exhibited a large deviation from the normal kinematics and considerable patient-to-patient variability. However, significant linear correlations between tibiofemoral and patellofemoral kinematics were observed (R = -0.96, 0.92, 0.88). CONCLUSION: Metallic artifacts due to orthopedic implants can be reduced in MR images for some materials, appropriate pulse sequence, and imaging parameters selection, enabling MR quantification of knee kinematics. Tibiofemoral kinematics appears to affect patellofemoral position after total knee arthroplasty.

Aged↗

PubMed2005

Cemented hip arthroplasty with a novel cerclage cable technique for unstable intertrochanteric hip fractures.

Thirty-nine consecutive patients with unstable three and four part intertrochanteric hip fractures were treated with cemented bipolar hip arthroplasty. A standard length primary femoral component was used with a novel technique of cerclage fixation of the trochanteric bone fragments allowing retention of the femoral calcar. At one year minimum follow up, there was no loosening or subsidence of the femoral components. All trochanters healed. One dislocation and one deep infection occurred. Unstable three and four part hip fractures can be treated with a standard femoral stem and cerclage cabling of the trochanters. The technique allows safe early weight bearing on the injured hip and had a relatively low rate of complications in our series.

Aged↗

PubMed2005

Extended trochanteric osteotomy for 2-stage revision of infected total hip arthroplasty.

We evaluate the rate of osteotomy healing, implant stability, and eradication of infection when an extended trochanteric osteotomy, with interval placement of an antibiotic-impregnated cement spacer and delayed osteotomy fixation, is used to treat the chronically infected total hip arthroplasty. Thirteen cases were followed for a minimum of 2 years. All patients had complete healing of the extended trochanteric osteotomy within 6 months. At an average follow-up of 39 months, recurrent infection occurred in 3 (23%) patients. Femoral component subsidence of 5 mm occurred in 2 patients, both of which had recurrent infection. Extended trochanteric osteotomy with interval placement of an articulating antibiotic-impregnated cement spacer and delayed osteotomy fixation permits reliable healing of the osteotomy.

Adult↗

PubMed2005

The ball and socket articulating spacer for infected total knee arthroplasty.

Articulated antibiotic impregnated cement spacers permit knee motion and may facilitate patient mobilization during 2-stage treatment of infected total knee arthroplasty (TKA). However, molds for articulating knee spacers are not always readily available. We have treated 13 infected total knee arthroplasties with large bone defects or collateral ligament loss using the rubber bulb portion of an irrigation syringe and a bipolar trial to create a ball and socket articulating spacer. This technique was successful in controlling infection in 9 of 13 knees. All patients were able to ambulate independently with the spacer in place using a walker or crutches, including one patient with bilateral spacers. At an average follow-up of 28 months after reimplantation, average knee flexion was 98 degrees .

Adult↗

PubMed2005

Highly cross-linked polyethylene: the debate is over--in opposition.

Highly cross-linked polyethylene compared to conventional ultra high molecular weight polyethylene (UHMWPE) results in significantly decreased wear in hip simulators and early prospective randomized clinical studies. However, the contact stresses in a total knee bearing surface are much higher than in a total hip. As a result, fatigue wear mechanisms occur more typically in total knee compared with total hip arthroplasty. Cross-linking reduces the mechanical properties of UHMWPE including fatigue crack propagation resistance, which may limit its role in total knee arthroplasty. Although the in vitro and in vivo studies provide compelling evidence that highly cross-linked polyethylene may improve the longevity of total hip arthroplasty, it does not appear to offer similar benefits for total knee arthroplasty.

Arthroplasty, Replacement↗

PubMed2005

Effect of cross-linking on the microstructure and mechanical properties of ultra-high molecular weight polyethylene.

Ultra-high molecular weight polyethylene is a semicrystalline polymer, which means that a portion of the molecules is in a solid crystalline phase and the remaining portion is in a rubbery amorphous phase. Varying the polymer chemistry in the two phases can alter the mechanical properties of the material. When highly cross-linked polyethylene is formed, the cross-links occur in the amorphous but not the crystalline region. Remelting after irradiation-induced cross-linking neutralizes the free radicals that are caused by irradiation but also decreases the amount of crystallinity. Decreased crystallinity can contribute to a decrease in mechanical properties. Annealing below the melt temperature after irradiation retains a higher level of crystallinity. However, heating below the melt temperature does not neutralize irradiation-induced free radicals that can then react with oxygen, causing oxidative degradation. Newer "second-generation" highly cross-linked polyethylenes have been developed that are annealed below the melt temperature, but use either a pharmacologic antioxidant, mechanical deformation, or sequential low-dose irradiation and annealing treatments rather than heating above the melt point to neutralize residual free radicals. High-pressure treatment at elevated temperatures also can increase crystallinity. However, increased crystallinity is associated with an increase in modulus and contact stress, which can increase wear. Although cross-linking ultra-high molecular weight polyethylene can reduce wear, currently available highly cross-linked polyethylenes also decrease mechanical properties when compared with conventional ultra-high molecular weight polyethylene, so that use of these materials in total knee arthroplasty may contribute to mechanical failure of the bearing surface.

Compressive Strength↗

PubMed2005

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 $31,341 for the revision procedures compared with $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 patient's 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.

Arthroplasty, Replacement, Hip↗

PubMed2005

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.

Adult↗

PubMed2005

Enhanced polyethylene implants: have we been there before?

Ultra-high molecular weight polyethylene (UHMWPE) has been used as a bearing surface in total hip arthroplasty for nearly 40 years. Early failures have been attributed to gamma irradiation in air sterilization, poor implant design, and high patient activity. Currently available implants address the problems of gamma irradiation in air by using sterilization methods that avoid oxidative degradation. Previous efforts to modify UHMWPE, including carbon reinforcement, hot isostatic pressure, and heat pressing, have not resulted in improved clinical performance. More recently, highly cross-linked UHMWPEs have been developed that markedly reduced wear in hip simulators. However, cross-linking also reduces the mechanical properties, including fatigue crack propagation resistance. Although early clinical results with highly cross-linked UHMWPE are favorable, longer follow-up will be necessary to determine whether the results of in vitro testing accurately reflect long-term in vivo behavior.

Hip Prosthesis↗

PubMed2004

T2 relaxation time of cartilage at MR imaging: comparison with severity of knee osteoarthritis.

PURPOSE: To evaluate differences in T2 values in femoral and tibial cartilage at magnetic resonance (MR) imaging in patients with varying degrees of osteoarthritis (OA) compared with healthy subjects and to develop a mapping and display method based on calculation of T2 z scores for visual grading and assessment of cartilage heterogeneity in patients with OA. MATERIALS AND METHODS: Knee cartilage was evaluated in 55 subjects who were categorized with radiography as healthy (n = 7) or as having mild OA (n = 20) or severe OA (n = 28). Cartilage regions were determined with manual segmentation of an MR image acquired with spoiled gradients and fat suppression. The segmentation was applied to a map of T2 relaxation time and was analyzed in four knee cartilage compartments (ie, the medial and lateral tibia and femur). Differences between cartilage compartment T2 values and subject groups were analyzed with analysis of covariance. Correlations of cartilage T2 values with clinically reported symptoms and cartilage thickness and volume were examined. Cartilage T2 values were converted to z scores per voxel on the basis of normal population values in the same cartilage compartment to better interpret cartilage heterogeneity and variation from normal. RESULTS: Healthy subjects had mean T2 values of 32.1-35.0 msec, while patients with mild and severe OA had mean T2 values of 34.4-41.0 msec. All cartilage compartments except the lateral tibia showed significant (P <.05) increases in T2 relaxation time between healthy and diseased knees; however, no significant difference was found between patients with mild and severe OA. Correlation of T2 values with clinical symptoms and cartilage morphology was found predominantly in medial compartments. CONCLUSION: Femoral and medial tibial cartilage T2 values increase with the severity of OA.

Adult↗