Bone mineral density of the femoral neck in resurfacing hip arthroplasty

Dual-Energy X-Ray Absorptiometry Does Not Confirm Validity of the Craig's Test

The Craig's test is a clinical assessment used to quantify femoral version. The validity of the Craig's test has been called into question due to instances where the test exhibits relatively poor correlation with three-dimensional imaging. Our study purpose was to use dual-energy X-ray absorptiometry (DXA) to indirectly assess the validity of the Craig's test. Twenty-three volunteers (n = 46; each hip analyzed separately) received two hip DXA scans using two different methods of positioning. During the first scan, a standard-sized wedge, the conventional tool of hip positioning for DXA scans, was used to fixate the legs without regard for individual levels of femoral version. For the second scan, the participants' hips were manually positioned according to their degree of femoral version determined by the Craig's test. We hypothesized that the bone mineral density (BMD) values from the customized positions would be lower due to the X-ray beams hitting the femoral neck perpendicularly. A paired t-test revealed weak evidence of a difference between BMD readings of the conventional and customized positions (p-value = 0.065); moreover, contrary to our hypothesis, the BMD readings obtained in the standard position were lower than those obtained in the customized position, albeit not significantly. Our findings suggest that the Craig's test is not a valid clinical assessment of true femoral version. A secondary conclusion is that the widespread use of the standard wedge for hip positioning during DXA scans is a better option than trying to find a customized position that is based on findings of the Craig's test.

Assessing Periprosthetic Bone in Total Wrist Arthroplasty: The Validity of DXA

INTRODUCTION

Dual-energy X-ray absorptiometry (DXA) can measure bone mineral density (BMD) around joint arthroplasties. DXA has never been used in total wrist arthroplasties (TWA). We investigated (1) whether BMD differs between 2 TWAs implanted in the same cadaver forearm, (2) the effect of forearm rotation and wrist extension on measured BMD around TWA in a cadaver, and (3) the precision of DXA in a cadaver and patients.

METHODOLOGY

One ROI around the distal and 1 and 3 ROIs (ROI1-3) around the proximal component were used. Ten DXA scans were performed on forearm and femur mode convertible to orthopedic knee mode without arthroplasty, with ReMotion, and with Motec TWA in one cadaver forearm. Ten scans with 5° increments from 90°-70° pronation and 0°-20° extension, were performed with Motec. Precision was calculated as coefficient of variation (CV%) and least significant change (LSC%) from cadaver scans and double examinations with femur mode converted to orthopedic knee mode in 40 patients (20 ReMotion, 20 Motec).

RESULTS

BMD was higher in all Motec than corresponding ReMotion ROIs (p < 0.05). BMD changed with 10° supination in the distal ROI and ROI1, and with 5° extension in the distal ROI (p < 0.05). In the cadaver the orthopedic knee mode was more precise than the forearm mode in 3 Motec ROIs (p < 0.05). In patients CV was 2.21%-3.08% in the distal ROI, 1.66%-2.01% in the proximal ROI, and 1.98%-2.87% with 3 ROIs.

CONCLUSIONS

DXA is feasible for BMD measurement around the proximal component using the orthopedic knee mode, but not the distal component of TWA.

Bone Mineral Density Measurements Around Osseointegrated Implants: A Precision Study and Validation of Scan Protocol for Transfemoral Amputees

Visual evaluation of bone changes around an osseointegration (OI) implant in femoral amputees examined on plain radiographs shows that periprosthetic bone resorption takes place during the first years after OI surgery, but the bone mineral density (BMD) change has not been previously quantified by dual-energy X-ray absorptiometry (DXA). Precision is vital when monitoring BMD changes around implants, and thus the aim of this study was to evaluate the precision and feasibility of a scan protocol for BMD measurements in proximity of OI implants. The proximal part of 2 human cadaveric femoral bones (specimens A and B) with OI implants were mounted in a positioning jig and DXA scans were repeated 5 times in increments of 5° from neutral (0°) to 20° flexion and rotation. BMD changes as a result of change in leg position were evaluated. Repeated patient examinations (n = 20) were conducted in a clinical setting and the precision error was calculated for each of 7 periprosthetic custom-made regions of interest (ROIs). The precision of cadaveric BMD measurements in neutral position was <3.3%. Even 5° flexion or rotation in femur position caused significant changes in average BMD (p <0.04). Depending on ROI, the percentage of coefficient of variation (%CV) and average BMD was <6% at 10° flexion and rotation. At 20° flexion, %CV increased up to 12.7% and average BMD increased up to 9.9%. The clinical short-term precision root mean square standard deviation ranged from 0.031 g/cm² to 0.047 g/cm² and %CV ranged from 3.12% to 6.57% depending on ROI. Simulated hip flexion or rotation of the femur affected periprosthetic BMD measurements around OI implants in cadaveric femoral bones, which stresses the importance of a reproducible set-up during DXA scans to reduce measurement errors caused by variation in leg position. Adherence to the scan protocol with a relaxed position of the residual limb resulted in an acceptable short-term precision below 6.6%.

Equal Primary Fixation of Resurfacing Stem, but Inferior Cup Fixation With Anterolateral vs Posterior Surgical Approach. A 2-Year Blinded Randomized Radiostereometric and Dual-energy X-Ray Absorptiometry Study of Metal-on-Metal Hip Resurfacing Arthroplasty

BACKGROUND

The anterolateral (AntLat) surgical approach may spare the blood supply to the femoral head and improve the accuracy of cup positioning in metal-on-metal hip resurfacing arthroplasty. Thereby, potentially lessen complications such as avascular head necrosis, femoral neck narrowing and fracture, improve implant fixation, and lessen periprosthetic bone mineral density (BMD) loss.

METHODS

Between November 2008 and January 2012, a randomized clinical trial was performed at Aarhus University Hospital. A total of 49 patients (28 males) were allocated to metal-on-metal hip resurfacing arthroplasty by the AntLat (n = 25) or the posterior (Post; n = 24) surgical approach. Patients were followed with radiostereometric analysis, measurements of periprosthetic BMD, clinical outcome scores of Harris hip score and visual analogue scale, serum metal ions, and conventional radiographs.

RESULTS

At 3 months, cups in the AntLat group had higher total translations of mean 1.00 ± 0.70 mm vs mean 0.64 ± 0.45 mm in the post group (P = .04), and higher total rotations of mean 2.44° ± 1.36° vs mean 1.39° ± 1.17° in the Post group (P = .002). All migrations of cup and stem were similar at 1 and 2 years postoperative (P > .07). At 1 year, periprosthetic BMD since postoperative at the medial side of the stem was reduced to mean 98.45% ± 8.57% in the AntLat group, and increased to mean 105.57% ± 11.07% in the Post group (P = .02), but measurements were comparable at 2 years (P = .05).

CONCLUSION

Cups inserted by the AntLat approach migrated more until 3 months postoperative. This illustrates a less good primary cup fixation with the AntLat approach; however, all cups were well-fixed after 3 months' follow-up indicating a good secondary fixation.

Proximal Femur Bone Density Decreases up to 5 Years After Total Hip Arthroplasty in Young, Active Patients

BACKGROUND

The number of young, active patients undergoing hip arthroplasty continues to increase. The purpose of this study was to evaluate femoral bone density over a 5-year period after hip arthroplasty in young, active patients.

METHODS

A total of 96 patients (103 hips) with a presymptomatic University of California at Los Angeles (UCLA) score ≥6 who had a total hip arthroplasty (THA; 45 hips) or surface replacement arthroplasty (SRA; 58 hips) were prospectively enrolled. UCLA and Harris Hip Scores were collected preoperatively and postoperatively, and dual energy X-ray absorptiometry scans were performed at 6 weeks, 6 months, 1 year, 2 years, and 5 years postoperatively. Bone density was analyzed for 7 traditional Gruen zones in both groups and 6 femoral neck zones in the SRA group. Bone density ratios were calculated for change in bone density compared with baseline.

RESULTS

No differences were present in the preoperative or postoperative UCLA or Harris Hip Scores between the SRA and THA cohorts (P = .07-.7). In the THA group, bone density never returned to baseline during the 5-year period in Gruen zones 1 (91.2% of baseline), 2 (94.8%), 6 (97.3%), and 7 (89.2%). There were no decreases in bone mineral density ratio for the femoral Gruen zones in the SRA group at any interval. Femoral neck bone density after SRA increased on the lateral, tension side up to 5 years postoperatively (P < .0001).

CONCLUSION

Young, active patients undergoing THA with cementless femoral fixation demonstrate reductions in bone density in the proximal femur in Gruen zones 1, 2, and 7 over time.

Periprosthetic Bone Remodeling After Novel Short-Stem Neck-Sparing Total Hip Arthroplasty

BACKGROUND

Short femoral stems have been designed with the aims of reducing proximal bone loss, improving load transfer, and increasing compressive loads at the medial proximal femoral calcar. This study examines bone mineral density (BMD) changes associated with a novel neck sparing short femoral stem design.

METHODS

The study was a prospective, single-center, multi-investigator consecutive series, which assessed bone-remodeling changes after insertion of the MSA Stem (Global Orthopaedic Technology). Dual-energy X-ray absorptiometry scans were performed preoperatively and postoperatively at 6, 12, and 24 months assessing the BMD at the 7 Gruen zones. The secondary objectives assessed were the Harris Hip Score, 12-Item Short Form Health Survey preoperatively, and perioperative complications.

RESULTS

Thirty-nine total hip arthroplasties were performed on 37 patients, with 27 patients completing the 24-month dual-energy X-ray absorptiometry scan. The overall preoperative baseline BMD was 0.2. At 6 months, the Gruen zone BMD had increased significantly in all zones in comparison to the preoperative mean BMD. Between 6 months and 24 months, there were only slight changes in the Gruen zones, with small gains in zones 1-2 and zones 4-6, with no zone showing a significant decrease. The Harris Hip Score improved from a preoperative mean of 39.7-75.3, whereas the 12-Item Short Form Health Survey score also improved from 32.6 to 49 at 24 months. However, 5 patients had aseptic loosening requiring revision surgery (4 femoral and 1 acetabular component).

CONCLUSION

Short-stem neck-sparing femoral stem prosthesis has the capacity to address the stress-shielding problem identified in femoral stems. However, the high early revision rate is a significant issue.

A randomised controlled trial of cemented and cementless femoral components for metal-on-metal hip resurfacing: a bone mineral density study

The primary purpose of this study of metal-on-metal (MoM) hip resurfacing was to compare the effect of using a cementless or cemented femoral component on the subsequent bone mineral density (BMD) of the femoral neck. This was a single-centre, prospective, double-blinded control trial which randomised 120 patients (105 men and 15 women) with a mean age of 49.4 years (21 to 68) to receive either a cemented or cementless femoral component. Follow-up was to two years. Outcome measures included total and six-point region-of-interest BMD of the femoral neck, radiological measurements of acetabular inclination, neck-shaft and stem-shaft angles, and functional outcome scores including the Harris hip score, the Western Ontario and McMaster Universities Osteoarthritis Index and the University of California at Los Angeles activity scale. In total, 17 patients were lost to follow-up leaving 103 patients at two years. There were no revisions in the cementless group and three revisions (5%) in the cemented group (two because of hip pain and one for pseudotumour). The total BMD was significantly higher in the cementless group at six months (p < 0.001) and one year (p = 0.01) than in the cemented group, although there was a loss of statistical significance in the difference at two years (p = 0.155). All patient outcomes improved significantly: there were no significant differences between the two groups. The results show better preservation of femoral neck BMD with a cementless femoral component after two years of follow-up. Further investigation is needed to establish whether this translates into improved survivorship.

Patterns of changes in femoral bone mineral density up to five years after hip resurfacing

This is a prospective study of 26 patients (29 hips) on the patterns of change in the Bone Mineral Density (BMD) in various zones of the femoral neck and proximal femur five years after hip resurfacing. We have found that BMD continues to positively change up to five years after hip resurfacing. This was observed primarily in the trochanteric and superior neck regions. In both these regions BMD had decreased by up to 10% at six-weeks and three-months after surgery and then had recovered to preoperative level by one year. A regression analysis to assess the influence of age, gender, BMI, preoperative BMD, component size and orientation revealed that the best predictor of change in BMD at five years in the trochanteric area was acetabular component inclination.

Dose optimisation for intraoperative cone-beam flat-detector CT in paediatric spinal surgery

BACKGROUND

During surgery for spinal deformities, accurate placement of pedicle screws may be guided by intraoperative cone-beam flat-detector CT.

OBJECTIVE

The purpose of this study was to identify appropriate paediatric imaging protocols aiming to reduce the radiation dose in line with the ALARA principle.

MATERIALS AND METHODS

Using O-arm® (Medtronic, Inc.), three paediatric phantoms were employed to measure CTDI(w) doses with default and lowered exposure settings. Images from 126 scans were evaluated by two spinal surgeons and scores were compared (Kappa statistics). Effective doses were calculated. The recommended new low-dose 3-D spine protocols were then used in 15 children.

RESULTS

The lowest acceptable exposure as judged by image quality for intraoperative use was 70 kVp/40 mAs, 70 kVp/80 mAs and 80 kVp/40 mAs for the 1-, 5- and 12-year-old-equivalent phantoms respectively (kappa = 0,70). Optimised dose settings reduced CTDI(w) doses 89-93%. The effective dose was 0.5 mSv (91-94,5% reduction). The optimised protocols were used clinically without problems.

CONCLUSIONS

Radiation doses for intraoperative 3-D CT using a cone-beam flat-detector scanner could be reduced at least 89% compared to manufacturer settings and still be used to safely navigate pedicle screws.

Changes in bone mineral density of the acetabulum, femoral neck and femoral shaft, after hip resurfacing and total hip replacement

It is accepted that resurfacing hip replacement preserves the bone mineral density (BMD) of the femur better than total hip replacement (THR). However, no studies have investigated any possible difference on the acetabular side.

Between April 2007 and March 2009, 39 patients were randomised into two groups to receive either a resurfacing or a THR and were followed for two years. One patient’s resurfacing subsequently failed, leaving 19 patients in each group.

Resurfaced replacements maintained proximal femoral BMD and, compared with THR, had an increased bone mineral density in Gruen zones 2, 3, 6, and particularly zone 7, with a gain of 7.5% (95% confidence interval (CI) 2.6 to 12.5) compared with a loss of 14.6% (95% CI 7.6 to 21.6). Resurfacing replacements maintained the BMD of the medial femoral neck and increased that in the lateral zones between 12.8% (95% CI 4.3 to 21.4) and 25.9% (95% CI 7.1 to 44.6).

On the acetabular side, BMD was similar in every zone at each point in time. The mean BMD of all acetabular regions in the resurfaced group was reduced to 96.2% (95% CI 93.7 to 98.6) and for the total hip replacement group to 97.6% (95% CI 93.7 to 101.5) (p = 0.4863). A mean total loss of 3.7% (95% CI 1.0 to 6.5) and 4.9% (95% CI 0.8 to 9.0) of BMD was found above the acetabular component in W1 and 10.2% (95% CI 0.9 to 19.4) and 9.1% (95% CI 3.8 to 14.4) medial to the implant in W2 for resurfaced replacements and THRs respectively. Resurfacing resulted in a mean loss of BMD of 6.7% (95% CI 0.7 to 12.7) in W3 but the BMD inferior to the acetabular component was maintained in both groups.

These results suggest that the ability of a resurfacing hip replacement to preserve BMD only applies to the femoral side.

2011 Marshall Urist Young Investigator Award: when to release patients to high-impact activities after hip resurfacing

BACKGROUND

Surface replacement arthroplasties are commonly performed in young, active patients who desire return to high-impact activities including heavy manual labor and recreational sports. Femoral neck fracture is an arthroplasty-related complication unique to surface replacement arthroplasty. However, it is unclear regarding whether patients are at lower risk for fracture after a certain postoperative time.

QUESTIONS/PURPOSES

We therefore raised the following questions: (1) does stress shielding occur after surface replacement arthroplasty, and (2) when does bone mineral density return to normal so patients can return to high-impact activities without excessive risk of fracture?

PATIENTS AND METHODS

We prospectively enrolled 90 patients (96 hips) with either surface replacement arthroplasty or THA, and performed dual energy x-ray absorptiometry scans at 6 weeks, 6 months, 1 year, and 2 years. We analyzed bone density by Gruen zone in both groups, and six femoral neck zones in the patients who had surface replacement arthroplasties. We calculated 6-month, 1-year, and 2-year ratios for the change in bone density compared with baseline.

RESULTS

Bone density was greater in patients who had surface replacement arthroplasties than for patients who had THAs at 6 months and 1 year in Gruen Zones 1, 2, 6, and 7, with the largest increase in femoral neck bone density on the tension side at 6 months in Zone L1. We saw no decrease in bone density in patients who had surface replacement arthroplasties in any Gruen zone at any time, and observed no decrease in bone density in female patients.

CONCLUSIONS

Increased bone density at 6 months postoperatively in patients who had surface replacement arthroplasties provides evidence that clinically relevant stress shielding does not occur after surface replacement arthroplasty. Owing to the increased bone mineral density at 6 months, we believe patients who underwent surface replacement arthroplasties may to return to high-impact activities at that time without increased risk of fracture.

Influence of different DXA acquisition modes on monitoring the changes in bone mineral density after hip resurfacing arthroplasty

Dual-energy X-ray absorptiometry (DXA) is a technique enabling the measurement of bone mineral density (BMD) around prostheses after hip resurfacing arthroplasty (HRA). In this study, we evaluated the consistency of different DXA acquisition modes with 33 patients who had undergone HRA. Patients were scanned with DXA immediately after surgery and at 3-, 6-, and 12-mo time points. All the patients were scanned with dual femur and orthopedic hip acquisition modes and analyzed using 10-region ROI model. With both acquisition modes, a statistically significant decrease (p<0.05, Wilcoxon's test) in BMD at 3mo was revealed in 3 ROIs, located to upper and lateral upper femur. Both acquisition modes detected similarly (p<0.01) preservation of the femoral bone stock within 12mo in all but 1 ROI. The applied acquisition protocols involved the use of different footplates for hip fixation. Because the differences between acquisition modes ranged between +1.6% and -7.1% and the reproducibility of BMD values can vary by as much as 28% due to hip rotation, it is proposed that both dual femur and orthopedic hip acquisition modes can be used to monitor the changes in BMD after HRA. However, the same hip rotation is recommended for all DXA measurements.