Biomedical subjects

C Anderson Engh

Publications and source records attributed to C Anderson Engh.

At least 19 recordsLinked to original sources

PubMed2006

Relationship between product demand, tibial polyethylene insert shelf age, and total knee arthroplasty survival: retrospective review of total knees of one design.

Shelf aging of gamma-irradiated-in-air polyethylene tibial components has been associated with increased articular surface wear and an elevated risk for revision. Nine hundred fifty cruciate-retaining inserts of one design were implanted between 1987 and 1996 (shelf age, 1.0 +/- 1.2 years). Less frequently used inserts (smallest/largest sizes, thicker thicknesses, supplemental articular constraint) had longer shelf ages (means ranged from 1.2 to 2.6 years). Survival analysis showed that shelf age (P < .01) and gamma-sterilization in air (P = .01) elevated the risk for revision. Surgeons must remain attentive to identify the shelf-aged gamma-irradiated-in-air polyethylene tibial component while following designs from the era when this sterilization method was used. Recognition is expedited by understanding how shelf life is related to product demand and can be of aid when diagnosing the painful knee.

Arthroplasty, Replacement, Knee↗

PubMed2006

A randomized prospective evaluation of outcomes after total hip arthroplasty using cross-linked marathon and non-cross-linked Enduron polyethylene liners.

Cross-linked liners were introduced with the promise that they would substantially reduce polyethylene wear. In 1999, our institution initiated a prospective study to compare the outcome of total hip arthroplasty patients who were randomized to non-cross-linked Enduron liners with that of total hip arthroplasty patients who were randomized to Marathon polyethylene liners that had been cross-linked with 5 Mrad (50 kGy) of gamma-irradiation and heat-treated to eliminate free radicals. At a mean follow-up of 5.7 years, the clinical outcomes among the Marathon and Enduron liners were similar. However, the mean wear rate was 0.01 +/- 0.07 mm/y for the Marathon group, which represents a 95% reduction compared with the mean wear rate of 0.19 +/- 0.12 mm/y for the Enduron group. In addition, the incidence of osteolysis was lower in the Marathon group.

Adult↗

PubMed2006

Incidence and reasons for reoperation after minimally invasive unicompartmental knee arthroplasty.

The goal of this report is to review reoperations undertaken on the initial 221 unicompartmental arthroplasties performed using a minimally invasive technique. A comparison was then performed between these cases and the previous 514 open medial unicompartmental arthroplasties performed at our institution. In the minimally invasive group, 9 (4.1%) of 221 knees were revised (8 for component loosening, 1 for deep infection). Of 212 unrevised knees, 16 have required a total of 18 nonrevision reoperations. Overall, 25 of 221 knees required at least 1 reoperation (total reoperation rate, 11.3%). Despite an accelerated recovery and decreased hospital stay in our minimally invasive unicompartmental arthroplasties, the rate of revision due to aseptic loosening (3.7% vs 1.0%) and the overall reoperation rate (11.3% vs 8.6%) compare unfavorably with those performed with an open technique.

Adult↗

PubMed2005

The effect of total hip arthroplasty cup design on polyethylene wear rate.

Using 743 total hip arthroplasties that included 6 hemispheric porous-coated cup designs, this study used a multiple linear regression to identify those factors that influenced polyethylene wear rates. Wear rates for each hip were based on serial head penetration measurement made with computer-assisted techniques. Implant factors associated with an increased wear rate included terminal sterilization with a non-cross-linking chemical surface treatment, a 4-mm lateralized liner, a cobalt-chrome femoral head, and a longer shelf life for liners gamma-irradiated in air. After accounting for these implant characteristics and patient factors, wear rates among the 6 cup designs were not significantly different (P = .89). Although polyethylene wear is frequently characterized for specific implant designs, this study demonstrated that there are several common factors that influence polyethylene wear rates.

Acetabulum↗

PubMed2005

Comparison of CT, MRI, and radiographs in assessing pelvic osteolysis: a cadaveric study.

In this study, we compared the accuracy of radiography, computed tomography, and magnetic resonance imaging in assessing periacetabular osteolytic lesions. Using a previously published cadaver model, we created 87 lesions in pelves implanted with total hip replacement components. The sensitivity for detecting lesions was 51.7% for radiography, 74.7% for computed tomography, and 95.4% for magnetic resonance imaging. For all three techniques, sensitivity increased as lesion size increased. Magnetic resonance imaging emerged as the most effective tool for detecting small periacetabular osteolytic lesions (< or = 3 cm). For lesions larger than 3 cm, which are of more concern clinically, computed tomography and magnetic resonance imaging were effective in identifying lesions with detection rates greater than 80%. For radiography and computed tomography, lesion detection was dependent on lesion location, whereas magnetic resonance imaging had consistently good sensitivity in all lesion locations. Although the mean volumetric errors for computed tomography and magnetic resonance imaging (0.3 cm and 0.8 cm) were small compared with mean lesion volume (6.1 cm), computed tomography was more accurate than magnetic resonance imaging at measuring lesion volume, with a lower mean absolute error. This study verifies the problems associated with radiographic detection of osteolysis while showing the effectiveness of computed tomography and magnetic resonance imaging in determining the presence of lesions and assessing their three-dimensional volume.

Arthrography↗

PubMed2005

Osteolysis after total knee arthroplasty: influence of tibial baseplate surface finish and sterilization of polyethylene insert. Findings at five to ten years postoperatively.

BACKGROUND: Debris displaced from the articular and backside surfaces of the polyethylene inserts of modular tibial components is considered a chief cause of osteolysis at the sites of total knee arthroplasties. One design of total knee replacement featured changes, over time, in the proximal surface roughness of the tibial baseplate and the method of sterilization of the polyethylene insert. We hypothesized that polishing the baseplate surface and sterilizing the insert with means other than gamma radiation in air had reduced the prevalence of osteolysis. METHODS: Three hundred and sixty-five posterior cruciate ligament-retaining Anatomic Modular Knee primary total knee arthroplasties were performed in 300 patients from 1987 to 1998. Anteroposterior and lateral radiographs of the knees were made within a five to ten-year postoperative interval. Two arthroplasty specialists independently examined the radiographs for evidence of osteolysis (defined as any nonlinear region of cancellous bone loss with delineable margins). RESULTS: Osteolysis was identified in 34% (eighty-two) of 242 knees treated with an insert that had been gamma-irradiated in air and affixed to a rough baseplate surface, and it was identified in 9% (nine) of ninety-eight knees treated with an insert that had been gamma-irradiated in an inert gas, or had not been irradiated, and joined to a polished surface. Osteolysis was associated with six factors, including one related to the patient (male gender), one related to the tibial baseplate (the proximal surface finish), three related to the polyethylene insert (the material from which it was machined, the sterilization method, and the shelf age), and one related to the technique (hyperextension of the femoral component relative to the tibial component). CONCLUSIONS: In this design of a total knee prosthesis, polishing the tibial baseplate counterface and implementing a more contemporary sterilization practice (as opposed to gamma radiation in air) noticeably diminished but did not eliminate osteolysis.

Aged↗

PubMed2005

Conventional ultra-high molecular weight polyethylene: a gold standard of sorts.

Data from a series of four recent studies showed that conventional polyethylene liners sterilized by gamma irradiation in air and coupled with second-generation acetabular components outperformed first-generation components with consistent average wear behavior below 0.1 mm/yr. It was found that liners sterilized by gamma irradiation in air outperformed liners sterilized by gas plasma, indicating that cross-linking induced by gamma irradiation sterilization, even if the component is radiated in an oxygen environment, is essential for keeping wear rates low. No negative clinical effects were found on wear for conventional polyethylene sterilized by gamma irradiation in air with a shelf life up to 3 years (r2 = 0.04, P = 0.60). Finally, 16-year temporal wear patterns for gamma irradiation in air sterilized components demonstrated no significant changes in wear rates over time, indicating that gamma irradiation sterilized liners with short shelf lives will not likely experience late increases in wear because of continued in vivo oxidation of the polyethylene. From these studies it was determined that standardized radiographic methods, optimal radiographs, serial measurements, and minimum 4-year follow-up are essential for reliable wear data. More specifically, it was concluded that a conventional ultra-high molecular weight polyethylene liner gamma irradiation sterilized in air with a shelf life less than 3 years, coupled with a second-generation cup, performs well in vivo and is unlikely to experience late increases in wear. Because no comparable in vivo data will be available for new cross-linked polyethylene materials for several years, conventional gamma irradiated polyethylene can be considered the industry's current gold standard for wear performance comparisons.

Hip Prosthesis↗

PubMed2004

Long-term porous-coated cup survivorship using spikes, screws, and press-fitting for initial fixation.

This study examined the long-term outcome of a single institution's experience with 4,289 primary total hip arthroplasties using hemispheric porous-coated cups. Initial fixation was achieved with spikes (255 AML TriSpike cups), by press-fitting with rim screws (427 Arthropor cups) or by press-fitting the component (83 Harris-Galante, 391 ACS Triloc+, 2,537 Duraloc, and 596 Pinnacle cups). Among 203 revised hips, only 18 cups were found to be loose at the time of revision. Using revision for any reason as an end point, 15-year survivorship was 82.9% +/- 5.6% (95% confidence interval) for spiked components, 71.6% +/- 8.5% for press-fit cups with adjunctive rim screws, and 72.0% +/- 12.6% for press-fit components (P<.001, log rank). Using revision for aseptic loosening as an end point, 15-year survivorship was 94.7% +/- 3.4% for spiked cups, 98.4% +/- 1.9% for press-fit cups with screws and 100% +/- 0.1% for press-fit cups. Despite an increasing incidence of polyethylene wear-related revisions, porous-coated acetabular components have demonstrated excellent long-term fixation.

Acetabulum↗

PubMed2004

Assessing the pattern of femoral head penetration after total hip arthroplasty.

We evaluated temporal changes in wear rates among 205 primary cementless total hip arthroplasties that had minimum 10-year follow-up and at least 6 follow-up x-rays. Using the pelvic anteroposterior x-rays from each hip, two-dimensional head penetration was measured and wear rates were calculated using several techniques. The average wear rate for the study population did not demonstrate evidence of accelerated wear at 10- to 18-year follow-up. As an increasing number of follow-up x-rays were included in the least-squares linear regression used to calculate the wear rate, the 95% confidence interval associated with the wear rate for an individual hip tended to progressively decrease. These results indicate that a constant wear rate is a reasonable assumption for modeling clinical wear data. Although we cannot quantify the effects of polyethylene oxidation, femoral head roughening, debris accumulation, or activity level changes, the combination of these factors is not leading to clinically perceptible accelerated wear at intermediate to long-term follow-up in this heterogeneous population of cups representing our institutional experience.

Adult↗

PubMed2004

Distal ingrowth components.

The literature documents that distal ingrowth fixation provides a reproducible, durable option that can be used in many femoral revision situations. In this review, we describe our use of cylindrical, extensively porous-coated stems to achieve distal fixation. The procedure involves choosing 5 cm to 7 cm of diaphyseal bone and reaming it cylindrically for a porous-coated femoral stem. Surgical implantation is uncomplicated because the femoral diaphysis aligns the component and imparts a reproducible press-fit sensation during impaction. The complications are well documented and can be avoided with adequate exposure, intraoperative radiographs, and surgical experience. Survivorship data based on femoral revisions done at our institution with extensively porous-coated stems show overall excellent results although a relatively poorer outcome is associated with patients whose prerevision cortical damage involves bone more than 10 cm below the lesser trochanter.

Arthroplasty, Replacement, Hip↗

PubMed2004

Database production and maintenance.

The advent of computers and electronic databases have revolutionized the way that clinical research is done. If study inclusion criteria are saved in the database, creating a study population can be accomplished by constructing an electronic query. Prospectively-entered outcome data related to a particular patient population then can be accessed and exported to a statistical software application for analysis. The senior author has more than 2 decades of experience with computer-based clinical outcome databases. In the context of his personal experience, this review offers some insights related to database design and maintenance.

Arthroplasty, Replacement, Hip↗

PubMed2004

The pros and cons of polyethylene sterilization with gamma irradiation.

This retrospective study evaluated the implant, patient and surgical factors associated with polyethylene wear for one type of porous-coated hemispheric total hip arthroplasty cup. Radiographic wear measurements among 567 Duraloc cups (512 patients) revealed that liners sterilized by gamma-irradiation wore 0.085 mm/year less than those that were sterilized by gas-plasma, a noncross-linking chemical surface treatment. The substantially decreased wear rate associated with gamma-irradiation was attributed to sterilization-induced polyethylene cross-linking. Shelf-aging adversely affected liners that were gamma irradiated in air. On average, highly crystalline Hylamer liners showed a 0.064 mm/year increase in wear rates for each year of shelf storage after terminal sterilization with gamma-irradiation in air. Among conventional Enduron liners, the effect of shelf aging after gamma-irradiation in air was more modest, increasing wear rates by 0.014 mm/year for each year of shelf storage. Because Hylamer's wear performance degraded at about five times the rate of Enduron's, the improved wear resistance associated with gamma-irradiation in air would be lost after 1.3 years of shelf aging for Hylamer compared with 6.1 years for Enduron. For every additional year of age at the time of surgery, the wear rate decreased by 0.003 mm/year. Increased body mass index, a preoperative diagnosis of inflammatory arthritis, and a ceramic femoral head also were associated with decreased wear rates.

Aged↗

PubMed2004

Femoral fixation in the face of considerable bone loss: cylindrical and extensively coated femoral components.

One option for dealing with considerable femoral bone deficiency at revision surgery is the use of extensively porous coated cobalt-chrome cylindrical stems. This technique has been shown to be a reliable, technically straightforward method that can be applied to all but the most severe femoral structural defects. Very high rates of osseointegration and durability of fixation are obtained when simple principles are followed. The key to success is obtaining initial endosteal diaphyseal fixation over 5 cm-7 cm. To achieve this, adequate exposure and accurate bone preparation are essential. The limitations of this technique relate directly to the severity of bone loss, which can be easily predicted on plain preoperative radiographs. For Paprosky 3B and 4 defects, other options such as allograft prosthetic composites, impaction grafting, or alternate modes of distal fixation should be considered.

Aged↗

PubMed2004

Shelf age of the polyethylene tibial component and outcome of unicondylar knee arthroplasty.

BACKGROUND: A recent report linked shelf-aging of unicondylar polyethylene tibial components with accelerated fatigue wear and rapid failure. We retrospectively reviewed our experiences with another unicondylar knee system to investigate the relationship between the shelf age of the polyethylene components and clinical outcome. METHODS: One hundred Single Compartment Replacement unicompartmental knee arthroplasties were performed with cement between 1990 and 1996. The median shelf age for the polyethylene inserts was 1.7 years. At the time of the review, four knees had been lost to follow-up, sixteen were in patients who had died, and nineteen had been revised. Sixty-one knee replacements remained in situ at a mean and standard deviation of 8 +/- 2 years postoperatively. RESULTS: With revision as the end point, Kaplan-Meier survivorship analysis demonstrated a six-year rate of survival of 96% when the shelf age of the insert was less than the median shelf age but only 71% when the median shelf age was exceeded. Fatigue wear was identified on all retrieved components except for two that had shelf ages under one year and had been revised within three years. At four to six years of clinical follow-up, the group of knees in which the median shelf age had been exceeded also had poorer Knee Society knee scores and function scores. CONCLUSIONS: Aging on the shelf accelerated fatigue failure of polyethylene inserts sterilized with gamma irradiation in air and compromised our intermediate-term clinical outcomes with this unicondylar knee replacement system. Attention to the relationship between the shelf age and the clinical performance of the polyethylene component continues to be warranted with unicondylar knee arthroplasty implants.

Aged↗

PubMed2004

Advancement and separation of apex hole eliminators with cementless Duraloc 100 cups. A report of nineteen cases.

BACKGROUND: From 1992 to 1996, we performed 541 cementless total hip arthroplasties using a Duraloc 100 acetabular component with an apex hole eliminator that did not have a positive stop design. During routine follow-up radiographic evaluation, we noted several hips with advanced or separated hole eliminators. This study presents the clinical consequences of this occurrence and its relationship to polyethylene wear and osteolysis. METHODS: A total of 541 hips (358 with a minimum duration of follow-up of five years) were evaluated clinically with use of the method of Merle D'Aubigné and Postel. Anteroposterior pelvic and iliac oblique radiographs were used to evaluate polyethylene wear, osteolysis, hole eliminator position, and component stability. RESULTS: Nineteen hips that had been followed for an average of eighty-nine months showed advancement or complete separation of the hole eliminator on radiographic evaluation. In most hips, advancement of the hole eliminator was visible on only the iliac oblique radiograph. In all but one hip with separation of the hole eliminator, complete plug separation was detectable on both the iliac oblique and anteroposterior pelvic radiographs. No association was found between polyethylene wear and either advancement or separation of the hole eliminator. No osteolysis was visible radiographically in the hips with hole eliminator advancement, but osteolysis was always visible in the hips that had complete separation of the hole eliminator. CONCLUSIONS: The hole eliminator has been redesigned since November 1995 to prevent possible advancement. However, patients with earlier designs should be followed carefully because advancement or separation can be expected in about 5% of the patients who have been followed for a minimum of five years. Despite this complication, which is seen radiographically, all patients were satisfied with the function of the hip. We do not recommend surgery solely to remove or replace the hole eliminator.

Adult↗

PubMed2003

Dislocation after polyethylene liner exchange in total hip arthroplasty.

Little has been published on the outcomes of polyethylene liner exchanges for wear or osteolysis. We assessed 24 patients from our clinic who had an isolated polyethylene liner exchange for wear or osteolysis with retention of the acetabular shell and femoral stem. At a mean 56-month follow-up time, 6 hips (25%) had dislocated. Of these, 2 underwent repeat surgery for recurrent dislocation; 1 had 3 dislocations; 1 had 2 dislocations; and 2 had single dislocations. Seventeen of the remaining patients answered our questionnaire: 13 recovered faster from the polyethylene liner exchange than from the primary arthroplasty; 4 believed that their hips were not as stable, 4 believed the hip did not function as well; and 1 underwent revision for cup loosening. We conclude that polyethylene liner exchanges, with or without femoral head exchange for wear or osteolysis, are associated with a high risk of dislocation and possible decrease in function.

Arthroplasty, Replacement, Hip↗

PubMed2003

Clinical assessment of tibial polyethylene thickness: comparison of radiographic measurements with as-implanted and as-retrieved thicknesses.

Sixty-six posterior cruciate-retaining inserts of one fixed-bearing design were revised because of wear or osteolysis. Tibial polyethylene thickness was estimated from standard anteroposterior radiographs and compared with the original or final minimum thicknesses. The most accurate method involved measuring the shortest distance from each femoral condyle to a transverse line through the middle of the baseplate's superior surface. On radiographs acquired 6 weeks after arthroplasty, the mean error was -0.1 mm (underestimate) +/- 0.6 mm (standard deviation), with 72% of the measurements within 0.5 mm of the original minimum thickness and 87% within 1.0 mm. The method was less accurate for radiographs made before revision, for which the mean error was 0.6 mm (overestimate) +/- 1.0 mm. In this study, 41% and 70% of the prerevision measurements were accurate to within 0.5 and 1.0 mm, respectively.

Arthrography↗

PubMed2003

Clinical consequences of stress shielding after porous-coated total hip arthroplasty.

From a series of 223 extensively porous-coated total hip arthroplasties, 208 hips had radiographic followup at a minimum of 2 years, which could be evaluated for radiographic evidence of stress-shielding. These patients had a mean 13.9-year followup (range, 2-18 years). We compared the outcome of 48 total hip arthroplasties that had radiographically evident stress-shielding with 160 total hip arthroplasties that did not have radiographically visible stress-shielding or that had less severe stress-shielding. Stress-shielding was more likely in females, patients with a low cortical index, and patients with larger stems. At the most recent followup, patients with stress-shielding had a lower mean walking score than patients without stress-shielding and less osteolysis. No patients with stress-shielding had femoral loosening, implant fractures, or loss of porous coating. The revision rate was 13% (six hips) among hips with stress-shielding and 21% (33 hips) among hips without stress-shielding. Fifteen-year survivorship was 93% among hips with stress-shielding and 77% among hips without stress-shielding. Stress-shielding did not produce adverse consequences in these extensively porous-coated total hip arthroplasties.

Arthroplasty, Replacement, Hip↗