Varus-Valgus Constraint in Primary Total Knee Arthroplasty: A Short-Term Solution but Will It Last?

BACKGROUND: Prostheses with varus-valgus constraint (VVC) are increasingly utilized in primary total knee arthroplasty (TKA) to address coronal malalignment and instability though little is known regarding the association between added constraint and aseptic loosening. We sought to systematically review the literature for reports of VVC in primary TKA and meta-analyze clinical results and implant survival. METHODS: PubMed was searched using broad terms to identify articles reporting VVC in primary TKA. Any article reporting clinical or survival outcomes was included. Clinical scores, close to 2 years postoperatively were converted to standardized mean differences, and the latest survival estimates were weighted using the inverse of their variance and meta-analyzed. RESULTS: Three hundred ninety-two search results were reviewed identifying 30 relevant articles reporting on 3620 knees in total. The estimate for the improvement in clinical scores postoperatively was 3.1 standard deviations (95% confidence interval 2.6-3.6). The estimate for implant revision slowly increased from 1% at 2 years to 2% at 6 years and then began to increase more rapidly beyond this point. The estimated revision rate was 9% by 12 years and 28% by 20 years. This revision rate estimate was stable with and without the inclusion of outlying studies. CONCLUSION: VVC in primary TKA is associated with significant clinical improvement without significant risk of early failure. Meta-regression estimates raise concerns for significant revision risk with extended follow-up, especially beyond 5 years. In the absence of new data, VVC should continue to be used cautiously in the primary TKA.

Fifteen-Year Results of Total Hip Arthroplasty With Cobalt-Chromium Femoral Heads on Highly Cross-Linked Polyethylene in Patients 50 Years and Less.

BACKGROUND: Highly cross-linked polyethylene (HXLPE) is the most commonly used bearing surface in total hip arthroplasty (THA) because of its superior wear properties, but long-term results in young patients are limited. Mid-term survivorship has been promising; however, polyethylene wear rates and need for revision surgeries remain a concern in this population. The purpose of our study is to investigate polyethylene wear rates, implant survivorship, wear-related revisions, and patient-reported outcomes in a young patient cohort at 15-year follow-up. METHODS: We performed a retrospective study of a prospective longitudinal cohort of 82 consecutive patients (89 hips) who underwent primary THA with an HXLPE acetabular liner and a cobalt-chromium femoral head. The mean age at the time of surgery for the cohort was 38.8 years (range 12-50). All patients received HXLPE liners with a cementless acetabular component coupled with a cobalt-chrome femoral head through a posterior approach with a cementless femoral component. All components were from a single manufacturer. We recorded University of California, Los Angeles Activity, and modified Harris Hip Scores. Wear calculations were made using the Martell Hip Analysis Suite (Version 8.0.4.3). RESULTS: At average 15 years (range 13.1-18.5), there was a revision-free survivorship of 97.8% in our HXLPE group with no wear-related revisions. We observed a linear wear rate of 0.0185 mm/y (standard deviation 0.05) after accounting for a 1-year bedding-in period. The volumetric wear rate was found to be 12.80 mm3/y (standard deviation 22.69). These numbers are registered as clinically undetectable and are comparable to steady state wear rates in the same cohort of patients at earlier time points. We found no radiographic changes concerning osteolysis. We observed excellent patient-reported outcomes at this time point with improvements in modified Harris Hip Scores (35.3 [22.5], P < .0001) and University of California, Los Angeles Activity Scores (median 6.0, P < .0001). CONCLUSION: At 15-year follow-up, we demonstrated that HXLPE bearings in this young cohort had excellent wear properties, maintained superior clinical improvements, and underwent no wear-related revision operations. The HXLPE and cobalt-chrome bearing couple continues to be extremely effective 15 years after primary THA in patients less than 50 years. LEVEL OF EVIDENCE: IV.

Time to Dislocation Analysis of Lumbar Spine Fusion Following Total Hip Arthroplasty: Breaking Up a Happy Home.

BACKGROUND: Although a history of lumbar spine fusion (LSF) is associated with increased dislocation risk following total hip arthroplasty (THA), the effect of LSF following THA is not well described. This study sought to describe the dislocation-free survival experience of patients with THA undergoing LSF, compare this to similar patients not undergoing LSF, and assess factors associated with dislocation risk following LSF. METHODS: Center for Medicare Service billing data from 2005 to 2014 was analyzed utilizing the PearlDiver platform. Patients without evidence of hip instability, defined as no dislocation event within at least 6 months following THA, were identified and stratified by having subsequent LSF. Kaplan-Meier curves were used to describe dislocation-free survival of these groups and assess factors associated with dislocation. RESULTS: Among 17,223 patients without history of hip instability following THA, there was no spike in dislocations following LSF with patients having a persistent and stable rate of dislocation of 0.7% per year. This experience was of similar shape but increased hazard when compared to that of 863,182 patients not undergoing LSF who had a dislocation rate of 0.4% per year (P < .001). Dislocations were not strongly associated with gender, age, comorbidities, or fusion length. CONCLUSION: Patients without evidence of hip instability following THA subsequently undergoing LSF do not have a spike in dislocations in the perioperative period but do assume a persistently elevated risk of dislocation. Future research should identify factors responsible for this increased risk to determine whether they may be modifiable.

Conventional Polyethylene in Total Hip Arthroplasty in Young Patients: Survivorship, Wear Analysis, and Clinical Outcomes Between 15 and 20 Years.

BACKGROUND: Total hip arthroplasty (THA) remains a successful procedure for most patients. However, there is a paucity of information regarding the long-term performance of conventional polyethylene (CPE) bearings in young patients undergoing THA. METHODS: After accounting for incomplete follow-up of a prospective cohort of 123 THAs in patients ≤50 years, we performed a retrospective review of 101 hips in 84 patients (82.1%) with an average 17.1-year follow-up (14.7-19.6 years). Outcomes of interest included linear and volumetric wear, clinical outcome scores, implant survivorship, and patient mortality. Wear rates were calculated using Martell Software. RESULTS: Wear analysis revealed median linear and volumetric wear rates of 0.106 mm/y (confidence interval, 0.079-0.133) and 43.58 mm3/y (confidence interval, 33.4-53.75). The modified Harris hip scores improved by 36 points while University of California, Los Angeles activity scores improved by 2.0 points at 15-year follow-up (P < .0001). Twenty-two hips (21.8%) were revised, 13 of which (12.8%) were for wear-related causes at an average of 14.9 years (range, 9.2-21 years) from index arthroplasty. There was significantly higher mortality in patients with a preoperative diagnosis of inflammatory avascular necrosis (P = .015). CONCLUSION: Because CPE was commonly used in THA over the last 25 years, it is important to understand its implications on the growing revision burden. Significant concerns exist with regard to the long-term durability of CPE bearings in young, moderately active patients 15 years after THA. These patients should be followed closely for wear-related problems. Our results should be used as a comparison when evaluating the outcomes of more modern bearing surface combinations.

Large Metal Heads and Highly Cross-Linked Polyethylene Provide Low Wear and Complications at 5-13 Years.

BACKGROUND: Highly cross-linked polyethylene (XLPE) is reported to have low rates of linear and volumetric wear at 10-14 years. In a prior study, larger (36 and 40 mm) femoral heads were associated with more volumetric wear, but there were only 12 hips with these heads. METHODS: We evaluated 107 hips (93 patients, with a mean age of 76 years) with one design of uncemented acetabular component, a 36 (90 hips) or 40 mm (17 hips) metal femoral head, and one electron beam 100 kGy irradiated and remelted XLPE at a mean follow-up of 8 years (range 5-13 years). Selection of these femoral heads was based on several factors, including the perceived risk of dislocation, the outer diameter size of the acetabular component, and liner availability. Measurements of linear and volumetric wear were performed in one experienced laboratory by the Martell method and analyzed using the first-to-last method. Standard radiographs, with additional Judet views, were used to detect periprosthetic osteolysis. Clinical records were used to determine the complications of dislocation, liner fracture, and painful trunnion corrosion. RESULTS: For the entire cohort, the median linear wear rate was 0.041 mm/y (95% confidence interval, 0.031-0.057) and the median volumetric wear rate was 34.6 mm3/y (95% confidence interval, 31.4-53.5). With the numbers available, there was no difference in linear or volumetric wear between the 36 and 40 mm head sizes. Small, asymptomatic osteolytic lesions were noted in 3 hips (2%). There were 3 patients (3%) with dislocation (2 early and 1 late), but these have not had a revision. There were no revisions for loosening, no liner fracture, and no patient with symptomatic trunnion corrosion. CONCLUSION: This acetabular component and XLPE with large metal heads had low rates of linear and volumetric wear. Large metal femoral heads did not lead to liner fracture, loosening, or symptomatic trunnion corrosion in this patient population. However, we recommend longer clinical follow-up studies and caution in the routine use of larger metal femoral heads in other, younger patient populations.

Inter-Rater and Intra-Rater Repeatability and Reliability of EOS 3-Dimensional Imaging Analysis Software.

BACKGROUND: Quantifying ideal component position for the acetabulum and stem during total hip arthroplasty (THA) has been described by many methods. A new imaging method using low-dose digital stereoradiography, the EOS imaging system, is a biplanar low-dose X-ray system that allows for 3-dimensional modeling of lower limbs and semiautomated measurement of pelvic parameters and implant alignment. METHODS: Twenty-five patients who underwent primary THA by a single surgeon between October 2014 and December 2014 were retrospectively selected. Only patients with unilateral THA without associated spine pathologies were included, totaling 16 right hips and 9 left hips. There were 8 men and 17 women in the cohort, with a mean age of 67 years (range, 53-82). Three individuals performed measurements of pelvic parameters and implant alignment on 3 separate occasions. An interclass correlation of >0.75 was accepted as evidence of excellent agreement and a confirmation of measurement reliability. RESULTS: Before reviewing patient radiographs, 4 pelvic phantom models were analyzed using the EOS 3-dimensional software to verify accuracy. All anatomic and implant measurements performed by the 3 independent reviewers showed interobserver and intraobserver agreement with interclass correlation >0.75. CONCLUSION: Three-dimensional modeling of hip implants with the EOS imaging system is a reasonable option for the evaluation of component position after THA.

Gender Differences in Wear Rates for 28- vs 32-mm Ceramic Femoral Heads on Modern Highly Cross-linked Polyethylene at Midterm Follow-Up in Young Patients Undergoing Total Hip Arthroplasty.

BACKGROUND: We report on the midterm linear and volumetric wear of highly cross-linked polyethylene (HXLPE) and survivorship of 2 prospective young total hip arthroplasty (THA) cohorts that differed by the size of ceramic femoral head used: 28 vs 32 mm. METHODS: We prospectively analyzed 220 consecutive primary THAs in patients aged ≤50 years who received a cementless THA with a ceramic femoral head on HXLPE liner (C-HXLPE). There were 101 patients (46%) with 28-mm heads and 119 patients (54%) who received 32-mm heads at a mean follow-up of 5.5 years (range, 60-109 months). Wear was calculated using Martell Software. RESULTS: The 28-mm C-HXLPE cohort demonstrated average linear and volumetric wear of 0.020 mm/y (standard deviation [SD], 0.074; 95% CI, 0.003-0.037) and 18.775 mm(3)/y (SD, 21.743; 95% CI, 13.773-23.778) compared with 0.032 mm/y (SD, 0.087; 95% CI, 0.013-0.050]) and 29.847 mm(3)/y (SD, 35.441; 95% CI, 22.294-37.401) in the 32-mm C-HXLPE group. Subgroup analysis by gender and head size discovered significantly greater wear in females with 32-mm heads compared with 28-mm heads in both linear (0.01, 95% CI = -0.014 to 0.033 vs 0.048, 95% CI = 0.022-0.074 mm/y, P = .004) and volumetric wear (14.11, 95% CI = 8.957-19.271] vs 29.71, 95% CI = 17.584-41.840] mm(3)/y, P = .009). We found a 96% (95% CI = 92.30%-97.94%]) survivorship by Kaplan-Meier analysis at minimum 5 years with no failures because of osteolysis. CONCLUSIONS: Ceramic on HXLPE demonstrates extremely low wear properties in young patients at midterm follow-up. We identified a gender-dependent difference in wear based on head size, with 32-mm heads being associated with increased wear in females.

Long-Term Results of Total Hip Arthroplasty with 28-Millimeter Cobalt-Chromium Femoral Heads on Highly Cross-Linked Polyethylene in Patients 50 Years and Less.

Highly cross-linked polyethylene (HXLPE) is the most commonly used bearing surface in total hip arthroplasty (THA) because of its superior wear properties, but long-term results in young patients are limited. We report on the clinical outcome, radiographic wear patterns and survivorship of 72 patients ≤50 years old who had a 28-millimeter cobalt-chromium femoral head on HXLPE acetabular liner. Mean and median true linear wear rates at average ten-year follow-up were 0.0104 and 0.01 mm per year ± 0.07 mm. Mean and median two-dimensional volumetric wear rates were 12.79 mm(3) and 5.834 mm(3) per year ± 26.1mm(3) as determined by Martell analysis. As a result of the minimal wear profile, there was no evidence of radiographic osteolysis and no wear-related revisions.

Wear and Osteolysis of Highly Crosslinked Polyethylene at 10 to 14 Years: The Effect of Femoral Head Size.

BACKGROUND: Highly crosslinked polyethylene (XLPE) was introduced to decrease periprosthetic osteolysis related to polyethylene wear, a major reason for revision of total hip arthroplasty. However, there are few reports of wear and osteolysis at 10 years postoperatively. QUESTIONS/PURPOSES: (1) What are the linear and volumetric wear rates of XLPE at 10 to 14 years? (2) What is the relationship among linear wear, volumetric wear, and femoral head size? (3) What proportion of hips developed osteolysis and was there a relationship between osteolysis and femoral head size or polyethylene wear? METHODS: We evaluated a previously reported cohort of 84 hips (72 patients) with one design of an uncemented acetabular component and one electron beam 10-kGy irradiated and remelted XLPE at a mean followup of 11 years (range, 10-14 years). The choice of femoral head size was based on several factors, including the outer diameter size of the acetabular component implanted, the perceived risk of dislocation (including the history of alcohol abuse and patient age), and liner availability from the manufacturer. The femoral head sizes used were 26 mm in 10 hips (12%), 28 mm in 31 hips (37%), 32 mm in 31 hips (37%), 36 mm in eight hips (10%), and 40 mm in four hips (5%). Measurements of linear and volumetric wear were performed in one experienced laboratory by the Martell method and analyzed using the first-to-last method. Standard radiographs, with additional Judet views, were used to detect periprosthetic osteolysis. Statistical analysis of wear and osteolysis compared with head size was performed. RESULTS: For the entire cohort, the median linear wear rate as 0.024 mm/year (95% confidence interval [CI], 0.016-0.030) and the median volumetric wear rate was 12.19 mm(3)/year (95% CI, 6.6-15.7). With the numbers available, we found no association between femoral head size and linear wear rate. However, larger femoral heads were associated with more volumetric wear; 36/40-mm femoral heads had higher volumetric wear (median 26.1; 95% CI, 11.3-47.1) than did 26-mm heads (median 3.1; 95% CI, 0.7-12.3), 28-mm heads (median 12.3; 95% CI, 3.0-19.3), and 32-mm heads (median 12.9; 95% CI, 6.6-16.8; p = 0.02). Small osteolytic lesions were noted in 12 hips (14%), but with the numbers available, there was no association with head size or volumetric wear rates. CONCLUSIONS: This uncemented acetabular component and this particular XLPE had low rates of linear and volumetric wear. Small osteolytic lesions were noted at 10 to 14 years but were not related to femoral head size or linear or volumetric wear rates. We recommend additional longer-term clinical followup studies and perhaps alternative imaging studies of patients with XLPE and osteolysis. LEVEL OF EVIDENCE: Level III, therapeutic study.

Highly cross-linked polyethylene improves wear and mid-term failure rates for young total hip arthroplasty patients.

We compared clinical outcomes and polyethylene wear for 2 young primary THA patient cohorts (<50 years of age) at mid-term follow-up. In total, 72 patients (84 hips) received a coventional polyethylene liner (CPE) and 84 patients (89 hips) received a highly cross-linked polyethylene liner (HXLPE). Mean Harris Hip Score improved to 81 points for both groups. UCLA activity scores were higher for HXLPE patients (6.0 vs 5.3, p = 0.03), with lower mean linear wear (0.02 vs 0.13 mm/year, p<0.001) and lower mean volumetric wear (75.1 vs 229.8 mm3, p<0.001) at an average of 70 months follow-up. No HXLPE patient required revision for wear related concerns, compared to 5 CPE patients with revision for aseptic loosening or impending radiographic failure (0% vs 5.9%, p = 0.02). HXLPE is associated with reduced wear among young, active THA patients without increased risk of early mechanical failure.

Interobserver and intraobserver reliability of the radiographic analysis of femoroacetabular impingement and dysplasia using computer-assisted measurements.

BACKGROUND: A comprehensive evaluation of hip radiographs in the young adult with hip pain has become increasingly complex and time consuming. The interobserver reliability of manually performed measurements of femoroacetabular impingement, including the alpha angle, has been questioned. Methods to improve the reliability of a radiographic evaluation may increase the clinical utility of these parameters. PURPOSE: To determine the interobserver and intraobserver reliability of a computer-assisted radiographic analysis of the young adult hip in a clinically relevant setting. STUDY DESIGN: Cohort study (diagnosis); Level of evidence, 3. METHODS: A reliability study of a comprehensive computer-assisted radiographic evaluation was performed, which included 25 radiographic parameters of proximal femoral morphology, acetabular morphology, hip osteoarthritis, and pelvic tilt/rotation. Anteroposterior pelvis and 45° Dunn lateral radiographs of 70 consecutive patients undergoing hip preservation surgery were included. Each radiograph was analyzed by 4 experienced hip surgeons. The reliability of continuous measurements was analyzed using intraclass correlation coefficients (ICCs), while categorical parameters were analyzed using κ values and percentages of agreement. RESULTS: The interobserver reliability of the parameters of proximal femoral morphology, acetabular morphology, and osteoarthritis was generally substantial to excellent. Parameters with lesser interobserver reliability included the alpha angle (ICC, 0.43), Tönnis osteoarthritis classification (κ = 0.22), and classification of pelvic tilt (using the coccyx or sacrococcygeal joint) (κ = 0.43 and 0.61, respectively). CONCLUSION: A computer-assisted analysis of young adult hip radiographs generally demonstrates substantial to excellent levels of interobserver reliability for most parameters. However, alpha angle measurements demonstrated only moderate interobserver reliability, despite excellent intraobserver reliability. Measurements of the joint space width appear to be significantly more reliable than the use of the Tönnis osteoarthritis classification in this population. The classification of pelvic tilt utilizing the coccyx or sacrococcygeal joint is only moderately reliable.

Reassessment of computerized wear measurement for total hip arthroplasty with correction for projectional image distortion: a brief follow-up report.

BACKGROUND: Wear of the ultra-high molecular weight polyethylene articular surface has been recognized as a major factor threatening the long-term success of total hip arthroplasty. Manual techniques that have been used to measure femoral head penetration into the polyethylene have been plagued with poor reproducibility and limited accuracy. Using a previously described phantom model simulating an unworn total hip arthroplasty, we previously demonstrated significant limitations in the accuracy of several widely used computerized wear measurement programs. A major component of these inaccuracies is projectional distortion of the femoral head and acetabular shell on the radiograph. These inaccuracies can be "corrected for" mathematically. METHODS: In the present follow-up study, we evaluated a widely used hip wear measurement software program (Hip Analysis Suite version 8.0.3.0) that corrects for these projectional errors with use of our previously described "zero wear" phantom model. A cementless metal-backed acetabular component was evaluated radiographically at three different cephalocaudad locations with respect to a radiopaque centering target. At all three positions, the cup was aligned in three different angles of planar abduction (35 degrees , 45 degrees , 55 degrees ) and four angles of planar anteversion (10 degrees , 20 degrees , 30 degrees , 40 degrees ). The accuracy and reproducibility of Hip Analysis Suite version 8.0.3.0 were determined and compared with the results obtained with the earlier version, Hip Analysis Suite version 4.0. RESULTS: Hip Analysis Suite version 8.0.3.0 was significantly more accurate than Hip Analysis Suite version 4.0 for determining linear wear and volumetric wear. Hip Analysis Suite version 8.0.3.0 was significantly more accurate for determining femoral head penetration at the different cephalocaudad acetabular positions and over the range of acetabular component anteversion and abduction angles in comparison with Hip Analysis Suite version 4.0. CONCLUSIONS: With use of the same methodology that was used to evaluate earlier versions of Hip Analysis Suite, the present study showed improvement in the accuracy of wear measurement with Hip Analysis Suite version 8.0.3.0 as compared with Hip Analysis Suite version 4.0. CLINICAL RELEVANCE: On the basis of the results of the present study, Hip Analysis Suite version 8.0.3.0 appears to fulfill the needs for a user-friendly, efficient, and accurate method of assessment of polyethylene wear following total hip arthroplasty.

The Daily Activity Questionnaire: a novel questionnaire to assess patient activity after total hip arthroplasty.

Expensive electronic accelerometers are the only validated method to determine patient activity levels. The aim of this study was to develop a clinical questionnaire to assess patient activity. The Daily Activity Questionnaire (DAQ) was developed and evaluated using 3 groups of patients with osteoarthritis of the hip. A total of 160 patients underwent 855 days of monitoring. Practicability, reliability, and validity of the new questionnaire were assessed. The test-retest reliability of the DAQ was comparable to the electronic accelerometer StepWatch (ICC = 0.77-0.89). A significant correlation between the DAQ and the StepWatch was found (r = 0.742). The DAQ is a reliable and valid instrument to measure patient activity.

Femoral head size and wear of highly cross-linked polyethylene at 5 to 8 years.

UNLABELLED: Wear of highly cross-linked polyethylene is reportedly independent of head size. To confirm that observation we asked in our population whether head size related to wear with one type of electron beam highly cross-linked polyethylene. Of 146 hips implanted, we evaluated complete clinical and radiographic data for 90 patients (102 hips or 70%). The minimum followup was 5 years (mean, 5.7 years; range, 5-8 years). The head size was selected intraoperatively based on the size of the acetabular component and presumed risk of dislocation. Polyethylene wear measurements were performed in one experienced laboratory using the method of Martell et al. There was no hip with pelvic or femoral osteolysis. The median linear wear rate was 0.028 mm/year (mean, 0.04 mm/year), and the median volumetric wear rate was 25.6 mm(3)/year (mean, 80.5 mm(3)/year). Median total volumetric wear was 41.0 mm(3) (mean, 98.5 mm(3)). We found no association between femoral head size and the linear wear rate, but observed an association between larger (36- and 40-mm) head size and volumetric wear rate and total volumetric wear. Although the linear wear rate of polyethylene was not related to femoral head diameter, there was greater volumetric wear (156.6 mm(3)/year) with the 36- and 40-mm heads. Pending long-term studies of large head sizes, we advise caution in using larger femoral heads in young or active patients and in those with a low risk of dislocation. LEVEL OF EVIDENCE: Level IV, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

THA with highly cross-linked polyethylene in patients 50 years or younger.

UNLABELLED: Highly cross-linked polyethylene has been associated with low in vitro wear, but also has decreased in vitro ultimate yield strength. We therefore asked whether highly cross-linked polyethylene would result in lower outcome scores, wear, or early failure in a young patient population. Seventy THAs in 64 patients were performed using a highly cross-linked (electron beam-irradiated to 9 Mrads) acetabular liner and a cobalt-chrome femoral head. The average age of the patients at surgery was 41 years (range, 19-50 years). The minimum followup was 2.4 years (average, 4 years; range, 2.4-6.5 years). We recorded demographic and clinical data, including Harris hip score. Polyethylene wear measurements were analyzed with a validated, computer-assisted, edge detection method. The average Harris hip score improved from 53 to 92 at last followup. There was no evidence of acetabular or femoral loss of fixation, subsidence, or loosening. Linear wear was undetectable at this followup interval. No patient experienced catastrophic failure or underwent revision surgery. These data show low polyethylene wear rates and no catastrophic failures at early followup in a young patient cohort. LEVEL OF EVIDENCE: Level IV, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

Wear analysis in THA utilizing oxidized zirconium and crosslinked polyethylene.

UNLABELLED: Oxidized zirconium, a material with a ceramic surface on a metal substrate, and highly cross-linked polyethylene are two materials developed to reduce wear. We measured in vivo femoral head penetration in patients with these advanced bearings. We hypothesized the linear wear rates would be lower than those published for cobalt-chrome and standard polyethylene. We retrospectively reviewed a select series of 56 THAs in a relatively young, active patient population utilizing oxidized zirconium femoral heads and highly cross-linked polyethylene acetabular liners. Femoral head penetration was determined using the Martell computerized edge-detection method. All patients were available for 2-year clinical and radiographic followup. True linear wear was 4 microm/year (95% confidence intervals, +/- 59 microm/year). The early wear rates in this cohort of relatively young, active patients were low and we believe justify the continued study of these alternative bearing surfaces. LEVEL OF EVIDENCE: Level IV, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

Temporal radiographic texture analysis in the detection of periprosthetic osteolysis.

Periprosthetic osteolysis is one of the most serious long-term problems in total hip arthroplasty. It has been primarily attributed to the body's inflammatory response to submicron polyethylene particles worn from the hip implant, and it leads to bone loss and structural deterioration in the surrounding bone. It was previously demonstrated that radiographic texture analysis (RTA) has the ability to distinguish between osteolysis and normal cases at the time of clinical detection of the disease; however, that analysis did not take into account the changes in texture over time. The goal of this preliminary analysis, however, is to assess the ability of temporal radiographic texture analysis (tRTA) to distinguish between patients who develop osteolysis and normal cases. Two tRTA methods were used in the study: the RTA feature change from baseline at various follow-up intervals and the slope of the best-fit line to the RTA data series. These tRTA methods included Fourier-based and fractal-based features calculated from digitized images of 202 total hip replacement cases, including 70 that developed osteolysis. Results show that separation between the osteolysis and normal groups increased over time for the feature difference method, as the disease progressed, with area under the curve (AUC) values from receiver operating characteristic analysis of 0.65 to 0.72 at 15 years postsurgery. Separation for the slope method was also evident, with AUC values ranging from 0.65 to 0.76 for the task of distinguishing between osteolysis and normal cases. The results suggest that tRTA methods have the ability to measure changes in trabecular structure, and may be useful in the early detection of periprosthetic osteolysis.

Radiographic texture analysis in the characterization of trabecular patterns in periprosthetic osteolysis.

RATIONALE AND OBJECTIVES: Periprosthetic osteolysis is a disease attributed to the body's reaction to fine polyethylene wear debris shed from total hip replacements. The purpose of this preliminary study was to investigate the ability of radiographic texture analysis (RTA) to characterize the trabecular texture patterns on pelvic images for osteolysis and normal total hip arthroplasty (THA) cases. MATERIALS AND METHODS: Fourier-based and fractal-based texture features were calculated for a database of digitized radiographs from 202 THA cases, 70 of which developed osteolysis. The features were calculated from regions of interest selected at two time points: less than 1 month after surgery, and at the first clinical indication of osteolysis (or randomly selected follow-up time for normal cases). Receiver operating characteristic (ROC) analysis was used to compare feature performance at baseline and follow-up for osteolysis and normal cases. RESULTS: Separation between the RTA features for osteolysis and normal cases was negligible at baseline and increased substantially for the follow-up images. The directional Fourier-based feature provided the best separation with an A(z) value from ROC analysis of 0.75 for the follow-up images, in the task of distinguishing between normal and osteolytic cases. CONCLUSIONS: The results from this preliminary analysis indicate that qualitative changes in trabecular patterns from immediately after surgery to the eventual detection of osteolysis correspond to quantitative changes in RTA features. It therefore appears that RTA provides information that could potentially be useful to aid in the detection of this disease.

Steady-state penetration rates of electron beam-irradiated, highly cross-linked polyethylene at an average 45-month follow-up.

Steady-state penetration rates were determined on 53 total hip arthroplasties with a minimum 3-year follow-up using electron beam highly cross-linked melted polyethylene by determining the femoral head penetration occurring after the first year in vivo. These data were compared with that of a matched control group. The average steady-state penetration rate of the control group was 144 +/- 191 mum/y, significantly higher than that of the highly cross-linked polyethylene group, 25 +/- 99 microm/y (P = .0001). Linear regression analysis indicated that the magnitude of femoral head penetration did not increase with time in the cross-linked groups. Also, no significant difference existed between the steady-state wear rates of the highly cross-linked groups with two head sizes (28 vs 32 mm, P = .39).

Comparison of femoral head penetration using RSA and the Martell method.

UNLABELLED: Radiostereometry has high precision and accuracy measuring polyethylene wear in total hip arthroplasty but requires a specialized setup. The Martell method is simpler and can be used on larger populations. The hypothesis that the radiostereometry analysis and the Martell analysis would yield comparable wear data from the same group of patients having total hip arthroplasty was tested. A group of twenty-five total hip arthroplasty patients who had both radiostereometry and standard anterior-posterior pelvic and cross-table lateral radiographs of sufficient quality for analysis were identified. The films were taken at postoperative periods of 6 weeks, 1 year, 2 years, and 5 years. Femoral head penetration was measured by both methods at each time point. The median penetration rates measured by each method decreased over time. Penetration results were affected by method of analysis, time, and dimension, with greater penetration for Martell compared with radiostereometry at each time point, greater penetration with increasing time for each method, and larger three-dimensional magnitude compared with two-dimensional analysis. LEVEL OF EVIDENCE: Case series Level IV. See Guidelines for Authors for a complete description of levels of evidence.