Use of high resolution dual‐energy x‐ray absorptiometry‐region free analysis (DXA‐RFA) to detect local periprosthetic bone remodeling events

Dual‐energy x‐ray absorptiometry (DXA) is the gold standard method for measuring periprosthetic bone remodeling, but relies on a region of interest (ROI) analysis approach. While this addresses issues of anatomic variability, it is insensitive to bone remodeling events at the sub‐ROI level. We have validated a high‐spatial resolution tool, termed DXA‐region free analysis (DXA‐RFA) that uses advanced image processing approaches to allow quantitation of bone mineral density (BMD) at the individual pixel (data‐point) level. Here we compared the resolution of bone remodeling measurements made around a stemless femoral prosthesis in 18 subjects over 24 months using ROI‐based analysis versus that made using DXA‐RFA. Using the ROI approach the regional pattern of BMD change varied by region, with greatest loss in ROI5 (20%, p < 0.001), and largest gain in ROI4 (6%, p < 0.05). Analysis using DXA‐RFA showed a focal zone of increased BMD localized to the prosthesis–bone interface (30–40%, p < 0.001) that was not resolved using conventional DXA analysis. The 20% bone loss observed in ROI5 with conventional DXA was resolved to a focal area adjacent to the cut surface of the infero‐medial femoral neck (up to 40%, p < 0.0001). DXA‐RFA enables high resolution analysis of DXA datasets without the limitations incurred using ROI‐based approaches. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 33:712–716, 2015.     

Pelvic Periprosthetic Bone Mineral Density Measurement Around Cemented vs Cementless Acetabular Prostheses

We compared the short-term precision of pelvic periprosthetic bone mineral density (BMD) measurement around a cementless acetabular prosthesis (n = 29) vs a cemented all-polyethylene acetabular prosthesis (n = 19) in patients after total hip arthroplasty. Two dual-energy x-ray absorptiometry scans of the pelvis were made on the same day in each subject with subject repositioning between scans and analyzed independently with a 4-region of interest model. Precision was expressed as coefficient of variation (CV%). The measured BMD around the cemented prostheses was greater than the cementless prostheses p < 0.004, all analyses). The net CV for pelvic BMD measurements around the cementless prosthesis was 1.9% vs 3.6% around the cemented prosthesis (F-test p < 0.001). The CVs of individual regions of interest was between 2.8% and 4.8% for the cementless prosthesis vs 4.4% to 8.4% for the cemented prosthesis (F-test; p < 0.05, all comparisons). Prospective studies would require 57 subjects to detect a 10% change in net pelvic BMD around a cementless prosthesis and 122 to detect a similar change around a cemented prosthesis with 90% power and with an alpha error of 0.05. In conclusion, the precision of pelvic BMD measurements made around cementless prostheses are better vs those for cemented prostheses. Dual-energy x-ray absorptiometry studies of cemented prosthesis require approximately double the number of subjects vs cementless prostheses to achieve a similar level of power.     

Effect of cavity preparation and bone mineral density on bone‐interface densification and bone‐implant contact during press‐fit implantation of hip stems

Implant loosening and periprosthetic fracture are two major revision causes for uncemented hip stems. The chosen method of cavity preparation could play a key role for both failure mechanisms. The aim of this study was to determine the dependence of the broach type as well as patient bone mineral density (BMD) on densification and contact conditions at the bone‐implant interface. Hip stems were implanted into cadaveric femora using compaction, blunt extraction or sharp extraction broaches with computed tomography scans performed prior to broaching, after broaching and after stem implantation. Proximal periprosthetic bone densification as well as press‐fit, contact area and stem seating relative to the last broach were determined. Median bone densification was higher with the compaction and blunt extraction broaches compared to sharp extraction broaches (181% and 177%, respectively, p = 0.002). The bone densification of femora prepared with compaction broaching increased with higher BMD (R² = 0.183, p = 0.037), while stem seating decreased with higher BMD for all broach types (R² = 0.259, p = 0.001). Incomplete seated prostheses were associated with smaller press‐fit and bone‐implant contact area (R² = 0.249, p = 0.001; R² = 0.287, p < 0.001). Clinical Significance: The results suggest that compaction broaching maximizes bone densification in patients with higher bone density. However, there appears to be an increased risk of insufficient stem seating in high‐density bone that could limit the benefits for primary stability. For lower quality bone, the broach type appears to play a lesser role, but care must be taken to limit extensive stem seating which might increase periprosthetic fracture risk. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1580–1589, 2019.     

Periprosthetic bone remodelling of two types of uncemented femoral implant with proximal hydroxyapatite coating: a 3-year follow-up study addressing the influence of prosthesis design and preoperative bone density on periprosthetic bone loss

Periprosthetic bone loss is a major cause of concern in patients undergoing total hip arthroplasty (THA). Further studies are required to identify the factors determining the pattern of bone remodelling following THA and obtain improvements in the design and durability of prostheses. In this study, we monitored periprosthetic bone loss around two different types of hydroxyapatite coated femoral implant over a 3-year period to evaluate their design and investigate the relationship with the preoperative bone mineral density (BMD) at the spine, hip and forearm. Sixty patients (35 F, 25 M, mean age 63 years, range 46–75 years) undergoing THA were randomised to either the Anatomic Benoist Girard (ABG) or Mallory-Head (MH) femoral stem. Preoperative dual-energy X-ray absorptiometry (DXA) scans were acquired of the posteroanterior (PA) and lateral lumbar spine, the contralateral hip and the non-dominant forearm. Postoperative DXA scans were performed to measure periprosthetic BMD at 10 days (treated as baseline), 6 weeks, and 3, 6, 12, 24 and 36 months after THA using a standard Gruen zone analysis. Results were expressed as the percentage change from baseline and the data examined for the differences in bone loss between the different Gruen zones, between the ABG and MH stems, and the relationship with preoperative BMD. A total of 50 patients (24 ABG, 26 MH) completed the study. Three months after THA there was a statistically significant BMD decrease in every Gruen zone that varied between 5.6% and 13.8% for the ABG prosthesis and between 3.8% and 8.7% for the MH prosthesis. Subsequently, in most zones BMD reached a plateau or showed a small recovery. However, BMD continued to fall in Gruen zones 1 and 7 in ABG patients and Gruen zone 1 in MH patients. Bone loss was less in every Gruen zone in MH patients compared with ABG with the largest difference (10%, P=0.018) in Gruen zone 7. Highly significant relationships were found between periprosthetic bone loss and preoperative BMD measured at the PA spine (P<0.001), total hip (P=0.004) and total distal radius (P<0.001). This study showed differences between two different designs of hydroxyapatite-coated implant that confirmed that prosthesis design influences periprosthetic bone loss. The study also showed that patients bone density measured at the spine, hip or forearm at the time of operation was a major factor influencing bone loss around the femoral stem.     

Impact of trochanteric heterotopic ossification on measurement of femoral bone density following cemented total hip replacement

During a study of bone mineral density changes around cemented femoral implants, we recognized heterotopic ossification occurring regularly in a position anterior to the greater trochanter and proximal femur. The aim of this study was to describe the incidence, distribution, and effect of this ossification on periprosthetic DXA scans following primary cemented total hip replacement. One hundre eleven patients underwent postoperative DXA examinations measuring changes in bone mineral density with heterotopic ossification identified and localized on standard radiographs with confirmation using DXA subtraction imaging. Male gender and age within the male group were significantly associated with occurrence of heterotopic ossification (p = 0.003 and 0.046, respectively). Femoral stem type, weight, and body mass index had no significant effect (p = 0.525, 0.372, and 0.243, respectively). Examining the Gruen zones in all patients suggested a median (plus interquartile range) zone 1 density drop of 4% (?12% to +7%). When separated and analyzed for the effect of heterotopic ossification, the 45 patients with heterotopic ossification showed a 2‐year density gain of +6% (?5% to +15%), whereas those without heterotopic ossification showed a loss of 8% (?14% to 0%), a significant difference (p < 0.001). Zone 2 also showed a significant difference (p = 0.048). We therefore recommend that affected zones should be identified and excluded from analysis at all time points. Without this precaution, researchers risk underestimating periprosthetic bone loss in their studies and reporting misleading conclusions. © 2008 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 26:1334–1339, 2008     

In vivo implant fixation of carbon fiber‐reinforced PEEK hip prostheses in an ovine model

Carbon fiber‐reinforced polyetheretherketone (CFR/PEEK) is theoretically suitable as a material for use in hip prostheses, offering excellent biocompatibility, mechanical properties, and the absence of metal ions. To evaluate in vivo fixation methods of CFR/PEEK hip prostheses in bone, we examined radiographic and histological results for cementless or cemented CFR/PEEK hip prostheses in an ovine model with implantation up to 52 weeks. CFR/PEEK cups and stems with rough‐textured surfaces plus hydroxyapatite (HA) coatings for cementless fixation and CFR/PEEK cups and stems without HA coating for cement fixation were manufactured based on ovine computed tomography (CT) data. Unilateral total hip arthroplasty was performed using cementless or cemented CFR/PEEK hip prostheses. Five cementless cups and stems and six cemented cups and stems were evaluated. On the femoral side, all cementless stems demonstrated bony ongrowth fixation and all cemented stems demonstrated stable fixation without any gaps at both the bone‐cement and cement‐stem interfaces. All cementless cases and four of the six cemented cases showed minimal stress shielding. On the acetabular side, two of the five cementless cups demonstrated bony ongrowth fixation. Our results suggest that both cementless and cemented CFR/PEEK stems work well for fixation. Cup fixation may be difficult for both cementless and cemented types in this ovine model, but bone ongrowth fixation on the cup was first seen in two cementless cases. Cementless fixation can be achieved using HA‐coated CFR/PEEK implants, even under load‐bearing conditions. © 2012 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 31: 485–492, 2013     

Periprosthetic cortical bone remodeling in patients with an osseointegrated leg prosthesis

Qualitative studies have shown that the periprosthetic cortical bone may decrease in the first years after the implantation of an osseointegrated leg prosthesis (OILP) in patients with a transfemoral amputation. The resorption of periprosthetic cortical bone may endanger implant survival because of outbreak fractures and aseptic loosening. A decrease in periprosthetic bone quality may also lead to insufficient bone stock for potential revision surgery. This study quantified the periprosthetic bone changes and skeletal remineralization in 27 patients with an ILP (Integrated Leg Prosthesis)‐type transfemoral OILP. Periprosthetic cortical thickness was analyzed from standard anteroposterior (AP) radiographs that were taken immediately postoperatively and at both 12 and 24 months post‐implantation. The bone mineral density of the femoral hip neck on both sides was measured pre‐operatively with Dual X‐ray absorptiometry (DXA) and at 12 and 24 months post‐implantation. Compared to that immediately post‐operative, the periprosthetic cortical thickness increased significantly by 9.6% (p = 0.020) and 8.9% (p < 0.001) at 12 and 24 months, respectively. The change in bone mineral density of the hip neck on both sides was not significant. In contrast to previous observations, this study reports increased periprosthetic cortical thickness around the OILP implant in the first 2 years after implantation. These data indicate good prospects for implant survival and possibilities for revision surgery. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1237–1241, 2017.

     

Bone loss around 2 different types of hip prostheses

Dual energy x-ray absorptiometry (DXA) allows the measurement of bone mineral density (BMD) around an uncemented hip prosthesis. The aims of this study were: 1) to determine the reproducibility of periprosthetic BMD measurements; 2) to delineate the time course of bone loss that occurs after insertion of a hip prosthesis; and 3) to compare the bone loss around two different types of hip prosthesis. We studied 20 patients: 11 had Bateman and 9 had porous-coated anatomic prostheses inserted. The mean bone loss in 20 patients between 6 and 52 weeks after surgery was 6%. The greatest loss during this period was 18% and occurred from the proximal medial cortex. We conclude that measurement of periprosthetic bone mass by DXA is a precise technique. Bone loss was rapid in the first 6 months following total hip replacement. There was no difference in the bone loss occurring around the two prostheses studied.     

Measurement of periprosthetic bone mineral density after cementless hip arthroplasty by dual energy X-ray absorptiometry: Longitudinal and cross-sectional evaluation

To clarify changes in bone mass around a femoral prosthesis, periprosthetic bone mineral density (BMD) was measured by dual energy X-ray absorptiometry (DXA) in 60 patients after unilateral cementless hip arthroplasty. Changes in BMD were evaluated by cross-sectional analysis in all patients and by longitudinal analysis in 26 patients who were available for measurement from 1 month to 2 years after surgery. The mean reproducibility of BMD measurements was within 1.74% in vivo. Periprosthetic BMD began to decrease early after surgery, and although it recovered temporarily within 1 year, it did not return to the level of the 1st month even after 2 years. BMD was reduced by 30.4% in the whole periprosthetic region compared with the contralateral untreated femora 4–7 years after surgery. The reduction in BMD was remarkable around the proximal part of the stem, especially in zone 7 (44.7% reduction 4–7 years after surgery). Significant positive correlations were observed between the low level of the preoperative cortical remodelling index and the reduction in BMD and between the preoperative femoral BMD and the reduction in BMD, indicating that the postoperative bone loss was greater in patients who preoperatively showed quantitative and qualitative deterioration of the femur. Abstracts of this paper were presented at the 66th and 67th Annual Meeting of the Japanese Orthopaedic Association, the 19th Conference of Société Internationale de Chirurgie Orthopédique et de Traumatologie (SICOT), and the 20th Conference of the Japanese Hip Society     

Female patients with low systemic BMD are prone to bone loss in Gruen zone 7 after cementless total hip arthroplasty: A 2-year DXA follow-up of 39 patients

Background and purpose Factors that lead to periprosthetic bone loss following total hip arthroplasty (THA) may not only depend on biomechanical implant-related factors, but also on various patient-related factors. We investigated the association between early changes in periprosthetic bone mineral density (BMD) and patient-related factors.Patients and methods 39 female patients underwent cementless THA (ABG II) with ceramic-ceramic bearing surfaces. Periprosthetic BMD in the proximal femur was determined with DXA after surgery and at 3, 6, 12, and 24 months. 27 patient-related factors were analyzed for their value in prediction of periprosthetic bone loss.Results Total periprosthetic BMD was temporarily reduced by 3.7% at 3 months (p < 0.001), by 3.8% at 6 months (p < 0.01), and by 2.6% at 12 months (p < 0.01), but recovered thereafter up to 24 months. Preoperative systemic osteopenia and osteoporosis, but not the local BMD of the operated hip, was predictive of bone loss in Gruen zone 7 (p = 0.04), which was the only region with a statistically significant decrease in BMD (23%, p < 0.001) at 24 months. Preoperative serum markers of bone turnover predicted the early temporary changes of periprosthetic BMD. The other patient-related factors failed to show any association with the periprosthetic BMD changes.Interpretation Female patients with low systemic BMD show greater bone loss in Gruen zone 7 after cementless THA than patients with normal BMD. Systemic DXA screening for osteoporosis in postmenopausal patients before THA could be used to identify patients in need of prophylactic anti-resorptive therapy.     

Effect of Total Hip Bone Area on Osteoporosis Diagnosis and Fractures

DXA is affected by skeletal size, with smaller bones giving lower areal BMD despite equal material density. Whether this size effect confounds the use of BMD as a diagnostic and fracture risk assessment tool is unclear. We identified 16,205 women of white ethnicity ≥50 yr of age undergoing baseline hip assessment with DXA (1998–2002) from a population‐based database that contains all clinical DXA test results for the Province of Manitoba, Canada. Total hip measurements were categorized according to quartile in total hip bone area (Q1 = smallest, Q4 = largest). Longitudinal health service records were assessed for the presence of nontraumatic osteoporotic fracture codes during a mean of 3.2 yr of follow‐up after BMD testing (757 osteoporotic fractures, 186 hip fractures). Total hip bone area strongly affected osteoporosis diagnosis with much higher rates in Q1 (14.4%) than Q4 (8.9%). However, incident fracture rates were constant across all area quartiles, and prevalent fractures were paradoxically fewer in smaller area quartiles (p < 0.001 for trend). Age was a potential confounder that correlated positively with area (r = 0.12, p < 0.0001). When age was not included in a Cox regression model, Q1 seemed to have a lower rate of incident osteoporotic fractures (HR = 0.80, 95% CI = 0.66–0.98, reference Q4) and hip fractures (HR = 0.63, 95% CI = 0.43–0.94) for a given level of BMD. In age‐adjusted regression models, total hip BMD was strongly predictive of incident osteoporotic fractures (HR per SD = 1.83, 95% CI = 1.68–1.99) and hip fractures (HR per SD = 2.80, 95% CI = 2.33–3.35), but there was no independent effect of bone area (categorical or continuous). Nested matched subgroup analysis and ROC analysis confirmed that bone area had no appreciable effect on incident fractures. We conclude that total hip areal BMD categorizes a substantially higher fraction of women with smaller bone area as being osteoporotic despite younger age. Incident fracture rates correlate equally well with BMD across all bone area quartiles when adjusted for age.     

DXA and pQCT predict pertrochanteric and not femoral neck fracture load in a human side‐impact fracture model

The validity of dual energy X‐ray absorptiometry (DXA) and peripheral quantitative computed tomography (pQCT) measurements as predictors of pertrochanteric and femoral neck fracture loads was compared in an experimental simulation of a fall on the greater trochanter. 65 proximal femora were harvested from patients at autopsy. All specimens were scanned with use of DXA for areal bone mineral density and pQCT for volumetric densities at selected sites of the proximal femur. A three‐point bending test simulating a side‐impact was performed to determine fracture load and resulted in 16 femoral neck and 49 pertrochanteric fractures. Regression analysis revealed that DXA BMD trochanter was the best variable at predicting fracture load of pertrochanteric fractures with an adjusted R² of 0.824 (p < 0.0001). There was no correlation between densitometric parameters and the fracture load of femoral neck fractures. A significant correlation further was found between body weight, height, femoral head diameter, and neck length on the one side and fracture load on the other side, irrespective of the fracture type. Clinically, the DXA BMD trochanter should be favored and integrated routinely as well as biometric and geometric parameters, particularly in elderly people with known osteoporosis at risk for falls. © 2013 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 32:31–38, 2014.     

Alendronate reduces periprosthetic bone loss after uncemented primary total hip arthroplasty: a prospective randomized study.

Periprosthetic bone loss, especially in the proximal part of the femur, is common after cemented and uncemented total hip arthroplasty (THA). Bone loss can be progressive and, in the extreme, may threaten survival of the prosthesis. To study whether alendronate therapy can reduce bone loss adjacent to prostheses, 13 uncemented primary THA patients were randomized to the study. They received 10 mg alendronate + 500 mg calcium (n = 8) or 500 mg calcium only (n = 5) daily for 6 months follow-up after THA. Periprosthetic bone mineral density (BMD) was measured with dual energy X-ray absorptiometry (DXA). Decreases in periprosthetic BMD in the alendronate-treated group were lower compared with the changes in the calcium-only group in the same regions of interest at the same follow-up time. In the proximal femur, the mean BMD decrease was 17.1% in the calcium-only group, whereas in the alendronate-treated group the decrease was only 0.9% (p = 0.019). The mean periprosthetic BMD change was also significantly different in the total periprosthetic area between the study groups at the end of the follow-up (calcium-only group -9.9% vs. alendronate-treated group -2.6%; p = 0.019). Alendronate therapy led to a significant reduction in periprosthetic bone loss after primary uncemented THA compared with the changes found in patients without therapy. This kind of bone response may improve the support of the prosthesis and may result in better survival of the prosthesis. However, in this study the follow-up time was too short and the study population was too small to make any long-term conclusions as to the prognosis for THA patients treated with alendronate.     

Prevention of strain‐related osteopenia in aseptic loosening of hip prostheses using perioperative bisphosphonate

The hypothesis tested in this study was that perioperative administration of the bisphosphonate zoledronate will reduce strain protection‐related calcar osteopenia and maintain functional integration of the femoral component in an ovine hemiarthroplasty model. Twelve sheep received a unilateral cemented hemiarthroplasty where six animals were given nine intravenous infusions of zoledronate (10 µg/kg) pre‐, peri‐, and postsurgery over 8 months. Control animals received physiological saline only. Implants remained in vivo for 9 months. Ground reaction force (GRF) was used to assess functional loading of the implanted limb, bone mineral density (BMD) was quantified using dual energy X‐ray absorptiometry (DEXA). Cortical bone area, thickness, and viable osteocytes were assessed histologically. No significant differences in GRF data between groups was identified. Results demonstrated a significant drop in BMD values in the control group (9.7%) when compared with the bisphosphonate‐treated group (3.2%) (p = 0.0159). Histological results showed that cortical area, thickness, and the percentage of lacunae with viable osteocytes was significantly greater in the bisphosphonate‐treated group when compared with control (p = 0.002, p = 0.001, p = 0.003, respectively). The administration of zoledronate reduced cortical osteopenia in the calcar region of the proximal femur and this therapy could be used as a preventive measure to combat strain protection osteopenia and its contribution to associated aseptic loosening in total hip replacement surgery. © 2007 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 26:693–703, 2008     

Correlates of Subchondral BMD: A Cross‐Sectional Study

Subchondral bone is hypothesized to be important in the development and progression of osteoarthritis (OA); however, little is known about the determinants of subchondral bone. This study describes the relationship between tibial subchondral BMD (sBMD) and anthropometric, lifestyle, and structural measures in 740 randomly selected subjects (mean age, 62 yr; range, 50–80 yr; 52% women). We measured medial tibial sBMD by DXA at two regions of interest (ROIs). We also assessed anthropometrics, vitamin D, steps per day by pedometer, joint space narrowing (JSN) and osteophytes (by X‐ray), cartilage defects, cartilage volume, and bone marrow lesions (BML; by MRI), and hip and spine BMD (by DXA). sBMD using ROI 1 was negatively associated with age and female sex and positively associated with BMI. In multivariable analysis, sBMD was positively correlated with steps per day (r = 0.08, p = 0.025), tibial osteophytes (r = 0.08, p = 0.028), JSN (r = 0.11, p < 0.01), cartilage defects (r = 0.16, p < 0.01), cartilage volume (r = 0.12, p = 0.01), BMLs (r = 0.17, p = 0.013 [tibial]; r = 0.16, p = 0.018 [femoral]), and hip and spine BMD (r = 0.36, p < 0.01 and r = 0.38, p < 0.01, respectively). Similar associations were observed using ROI 2, with vitamin D also associated with sBMD (r = 0.10, p < 0.01). In conclusion, this study identified a large number of factors associated with sBMD, of which the most novel is cartilage defects. Longitudinal studies are required to address causality.     

Vitamin D Supplementation After Parathyroidectomy: Effect on Bone Mineral Density—A Randomized Double‐Blind Study

Patients with primary hyperparathyroidism (PHPT) have higher bone turnover, lower bone mineral density (BMD), and an increased risk of fractures. They also have a high incidence of low vitamin D levels (25‐OH‐vitamin D <50 nmol/L) that could worsen the negative effect on the bone. In this double‐blinded clinical trial, 150 patients with PHPT were randomized, after successful parathyroidectomy (PTX), to 1‐year daily treatment with either cholecalciferol 1600 IU and calcium carbonate 1000 mg (D +) or calcium carbonate alone (D–). BMD was measured in the lumbar spine, femoral neck, total hip, distal and 33% radius using dual‐energy X‐ray absorptiometry (DXA) before surgery and after 1 year of study medication. Median age was 60 (range 30–80) years and there were 119 (79%) women and 31 (21%) men; 76% had 25‐OH‐D <50 nmol/L before PTX and 50% had persistent elevated parathyroid hormone (PTH) 6 weeks after PTX. A similar increase in BMD in the lumbar spine, femoral neck, and total hip was observed in both groups (D + : 3.6%, 3.2%, and 2.7%, p < 0.001, respectively; and D–: 3.0%, 2.3%, and 2.1%, respectively, p < 0.001). Patients with vitamin D supplementation also increased their BMD in distal radius (median 2.0%; interquartile range, ?1.7% to 5.4%; p = 0.013). The changes in BMD, especially in the hips, were correlated to the baseline concentrations of PTH, ionized calcium, and bone markers (p < 0.001). A benefit from vitamin D substitution was observed among patients with a persistent postoperative PTH elevation, who also improved their BMD at 33% radius and radius ultradistal (p < 0.05). In conclusion, except for a minor improvement of radius BMD, our data show no beneficial effect on BMD or bone turnover markers of vitamin D supplementation after PTX. Preoperative PTH seems to have the strongest association with improvement in BMD. © 2014 American Society for Bone and Mineral Research.     

Effects of chronic cobalt and chromium exposure after metal‐on‐metal hip resurfacing: An epigenome‐wide association pilot study

Metal‐on‐metal (MOM) hip resurfacing has recently been a popular prosthesis choice for the treatment of symptomatic arthritis, but results in the release of cobalt and chromium ions into the circulation that can be associated with adverse clinical effects. The mechanism underlying these effects remains unclear. While chromosomal aneuploidy and translocations are associated with this exposure, the presence of subtle structural epigenetic modifications in patients with MOM joint replacements remains unexplored. Consequently, we analyzed whole blood DNA methylation in 34 OA patients with MOM hip resurfacing (MOM HR) compared to 34 OA patients with non‐MOM total hip replacements (non‐MOM THR), using the genome‐wide Illumina HumanMethylation 450k BeadChip. No probes showed differential methylation significant at 5% false‐discovery rate (FDR). We also tested association of probe methylation levels with blood chromium and cobalt levels directly; there were no significant associations at 5% FDR. Finally, we used the “epigenetic clock” to compare estimated to actual age at sample for all individuals. We found no significant difference between MOM HR and non‐MOM THR, and no correlation of age acceleration with blood metal levels. Our results suggest the absence of large methylation differences systemically following metal exposure, however, larger sample sizes will be required to identify potential small effects. Any DNA methylation changes that may occur in the local periprosthetic tissues remain to be elucidated. © 2017 The Authors. Orthopaedic Research Society. Published by Wiley Periodicals, Inc. on behalf of Orthopaedic Research Society. J Orthop Res 35:2323–2328, 2017.

     

Bone microarchitecture assessed by TBS predicts osteoporotic fractures independent of bone density: the Manitoba study

The measurement of BMD by dual‐energy X‐ray absorptiometry (DXA) is the “gold standard” for diagnosing osteoporosis but does not directly reflect deterioration in bone microarchitecture. The trabecular bone score (TBS), a novel gray‐level texture measurement that can be extracted from DXA images, correlates with 3D parameters of bone microarchitecture. Our aim was to evaluate the ability of lumbar spine TBS to predict future clinical osteoporotic fractures. A total of 29,407 women 50 years of age or older at the time of baseline hip and spine DXA were identified from a database containing all clinical results for the Province of Manitoba, Canada. Health service records were assessed for the incidence of nontraumatic osteoporotic fracture codes subsequent to BMD testing (mean follow‐up 4.7 years). Lumbar spine TBS was derived for each spine DXA examination blinded to clinical parameters and outcomes. Osteoporotic fractures were identified in 1668 (5.7%) women, including 439 (1.5%) spine and 293 (1.0%) hip fractures. Significantly lower spine TBS and BMD were identified in women with major osteoporotic, spine, and hip fractures (all p < 0.0001). Spine TBS and BMD predicted fractures equally well, and the combination was superior to either measurement alone (p < 0.001). Spine TBS predicts osteoporotic fractures and provides information that is independent of spine and hip BMD. Combining the TBS trabecular texture index with BMD incrementally improves fracture prediction in postmenopausal women. © 2011 American Society for Bone and Mineral Research     

Factors Affecting Short‐Term Bone Density Precision Assessment and the Effect on Patient Monitoring

The most widely used procedure for performing a BMD reproducibility assessment (same‐technologist with simple repositioning on the same day) systematically underestimates precision error and will lead to over categorization of change in a large fraction of monitored patients. Introduction: The most common procedure for establishing the least significant change (LSC) to monitor bone mineral density (BMD) with DXA is for the same technologist to perform repeat subject scans on the same day with simple repositioning. The objective of the current report is to determine how the reproducibility scanning procedure impacts on the precision assessment and categorization of change in routine clinical practice. Materials and Methods: The study population was drawn from the database of the Manitoba Bone Density Program which includes all clinical DXA test results for the Province of Manitoba, Canada. All patients who had baseline and follow up total spine (L1–4) and the total hip BMD measurements on the same instrument up to March 31, 2007 were included as the ‘clinical monitoring population’ (N = 5048 scan‐pairs). BMD precision was assessed in a convenience sample of patients who were agreeable to undergoing a repeat assessment (50% performed on the same day with repositioning, 68% by different technologists) (N = 331 spine and 328 hip scan‐pairs). Results: Precision error was greater when the scan‐pairs were acquired on different days than on the same day for both the total spine (p < .001) and total hip (p < .01). No other factor was consistently associated with precision error. The reference LSC (different days and different technologists) categorized the smallest fraction of the monitored population with change, whereas other combinations gave a significant rate of over categorization (up to 19.3% for the lumbar spine and up to 18.3% for the total hip). Conclusions: The most widely procedure for performing a BMD reproducibility assessment (same‐technologist with simple repositioning on the same day) systematically underestimates precision error and will lead to over categorization of change in a large fraction of monitored patients.     

Dual energy X-ray absorptiometry analysis of peri-prosthetic stress shielding in the Birmingham resurfacing hip replacement

Introduction: Numerous reports in the literature refer to the femoral neck fracture rate in hip resurfacing. The aim of this study was to determine the bone mineral density and evidence of stress shielding around the femoral component of the Birmingham resurfacing prosthesis. Material and methods: Twenty-eight patients with primary unilateral osteoarthritis had a Birmingham resurfacing prosthesis. DEXA analysis of the proximal femur and femoral neck was performed and compared with the opposite unaffected side. Results: Total periprosthetic bone mineral density was 0.49% greater than the control, but this did not achieve statistical significance. Although the BMD of the femoral neck was slightly increased on the prosthetic side (1.002 g/cm²) as opposed to the control side, this difference did not reach statistical significance. Conclusion: The Birmingham resurfacing prosthesis does not appear to reduce femoral neck bone mineral density in comparison to the normal femoral neck bone density. We conclude that femoral neck fractures are unlikely to be due to stress shielding related to the prosthesis.