The Journal of Bone & Joint Surgery

The Journal of Bone & Joint Surgery, Volume 95, Issue 1

Scientific Articles | January 02, 2013

Effect of Sliding-Taper Compared with Composite-Beam Cemented Femoral Prosthesis Loading Regime on Proximal Femoral Bone Remodeling: A Randomized Clinical Trial

Raveen L. Jayasuriya, BMedSci, MBChB¹; Simon C. Buckley, MBChB, FRCS(Orth)²; Andrew J. Hamer, MBChB, MD, FRCS(Orth)²; Robert M. Kerry, MBChB, FRCS(Orth)²; Ian Stockley, MBChB, MD, FRCS(Orth)²; Mohamed W. Tomouk, MBChB²; Jeremy Mark Wilkinson, MBChB, PhD, FRCS(Orth)¹

¹ Academic Unit of Bone Metabolism, University of Sheffield Medical School, Beech Hill Road, Sheffield S10 2RX, United Kingdom. E-mail address for J.M. Wilkinson: j.m.wilkinson@sheffield.ac.uk
² Department of Orthopaedics, Northern General Hospital, Herries Road, Sheffield S5 7AU, United Kingdom

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Investigation performed at Northern General Hospital, Sheffield, United Kingdom

J Bone Joint Surg Am, 2013 Jan 02;95(1):19-27. doi: 10.2106/JBJS.K.00657

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Abstract

Background:

This two-year randomized clinical trial was performed to examine whether the geometry of the cemented femoral prosthesis affects the pattern of strain-adaptive bone remodeling in the proximal aspect of the femur after primary total hip arthroplasty.

Methods:

One hundred and twenty patients were randomized to receive a Charnley (composite-beam), Exeter (double-tapered), or C-Stem (triple-tapered) prosthesis. The change in proximal femoral bone mineral density over two years was measured by dual x-ray absorptiometry (DXA). Bone turnover markers were measured in urine and serum samples collected at the preoperative baseline and during the first postoperative year. N-telopeptide of type-I collagen was measured in urine as a marker of osteoclast activity, and osteocalcin was measured in serum as a marker of osteoblast activity. Clinical outcome was measured with use of the Harris and Oxford hip scores and prosthesis migration was measured with use of digitized radiographs during the first two postoperative years.

Results:

The baseline characteristics of the subjects in each group were similar (p > 0.05). Decreases in femoral bone mineral density were observed over the first year for all prosthesis designs, with no further loss during the second year. The decreases were similar in regional distribution and magnitude between the composite-beam and sliding-taper designs (p > 0.05). Bone loss was greatest (14%) in the proximal medial aspect of the femur (Gruen zone 7). Transient increases in both N-telopeptide of type-I collagen and osteocalcin activity also occurred over the first year, and these increases were similar in pattern among the three prosthesis groups (p > 0.05). All prostheses showed migration patterns that were consistent with their design type, and similar improvements in clinical hip scores were observed over the two-year course of the study.

Conclusions:

Differences in the mechanism of load transfer between the prosthesis and host bone in composite-beam or sliding-taper cemented femoral prosthesis designs were not a major determinant of proximal femoral bone loss after total hip arthroplasty, and the design that included a third taper exhibited a remodeling profile that was similar to those of the double-tapered design.

Level of Evidence:

Therapeutic Level I. See Instructions for Authors for a complete description of levels of evidence.

Figures in this Article

Introduction

Introduction | Materials and Methods | Results | Discussion | Appendix

Total hip arthroplasty causes an alteration of the local mechanical environment, resulting in bone loss through strain-adaptive remodeling¹. Bone loss is confined primarily to the first two years after surgery, but it may result in the loss of >30% of periprosthetic bone mass^2-4. Current designs of cemented femoral prostheses may be classified according to their pattern of load transfer to the femur^5,6. “Shape-closed” designs, such as the Charnley prosthesis (DePuy International, Leeds, United Kingdom), are nontapered or have a mild taper, have a bonded prosthesis-cement interface, and exhibit minimal postoperative subsidence (Fig. 1)^5,6. The prosthesis-cement-bone construct functions mechanically as a “composite beam,” and it transfers load principally at the level of the femoral diaphysis⁷.

“Force-closed designs,” such as the polished, double-tapered Exeter prosthesis (Stryker, Newbury, United Kingdom) and the polished, triple-tapered C-Stem prosthesis (DePuy International), have a nonbonded prosthesis-cement interface and act mechanically as a taper-slip; they migrate distally within the cement mantle postoperatively^6,8. It is proposed that taper-slip loading arising from this subsidence sets up hoop stresses in the proximal cement mantle, resulting in femoral loading that is more proximal than that occurring with a prosthesis that acts as a composite beam⁹. The inclusion of a third taper has been proposed to further enhance load transfer to the proximal medial femoral cortex, which is the site of most periprosthetic bone loss¹⁰. However, we are aware of no randomized clinical trial data to confirm that this predicted benefit results in preservation of proximal femoral bone mass in patients.

The aims of this study were to determine (1) whether changes in regional bone mineral density and biochemical markers of bone turnover differ after total hip arthroplasty using composite-beam compared with sliding-taper femoral prosthesis designs, and (2) whether the number of tapers (double compared with triple) in a sliding-taper design affects the change in regional bone mineral density or bone turnover markers.

Fig. 1

Drawing showing the principal design characteristics of the three femoral prostheses studied.

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Materials and Methods

Introduction | Materials and Methods | Results | Discussion | Appendix

Study Design, Recruitment, and Randomization

We conducted a single-center, randomized controlled trial of 120 patients undergoing primary total hip arthroplasty. The study was approved by a National Research Ethics Committee and all subjects provided written, informed consent prior to inclusion. This clinical trial was registered at http://clinicaltrials.gov (NCT00293605).

Patients were recruited from the waiting lists of the Department of Orthopaedics, Northern General Hospital, Sheffield, United Kingdom. Patients who were at least sixty years of age and were undergoing unilateral total hip arthroplasty for primary or secondary osteoarthritis of the hip were eligible for the trial if they were deemed suitable to receive a cemented prosthesis. Patients were excluded if they had any history of a disorder known to affect bone or bone mineral metabolism, or if they had inflammatory arthropathy. Patients were also excluded if they had taken pharmacological doses of estrogen, progestin, androgen, calcitonin, glucocorticoid therapy, or dietary calcium or vitamin D supplements within the preceding twelve months, or if they had ever taken a bisphosphonate or fluoride (excluding dental prophylaxis). Subjects were randomized on the day of surgery to receive a Charnley, Exeter, or C-Stem cemented stem component. The randomization was performed by means of a sealed envelope that was opened prior to the start of surgery.

Surgical Protocol

All surgical procedures were carried out via an anterolateral surgical approach. All subjects received a monoblock acetabular prosthesis composed of conventional ultra-high molecular weight polyethylene (Charnley LPW; DePuy International) that was cemented with use of Palacos R bone cement with gentamicin (Schering Plough, Welwyn Garden City, United Kingdom). Insertion of the femoral prosthesis was performed according to the manufacturer’s instructions for each prosthesis design. For the Exeter and C-Stem prostheses, this involved broaching the femoral canal to the required size. For the Charnley stem, this involved reaming the stem to the required size with use of Charnley reamers. The bone cement was introduced in a retrograde fashion with use of a cement gun following pulse lavage of the femoral canal, occlusion of the canal distally with use of a cement restrictor, and cement pressurization. All modular prostheses were fitted with a metal femoral head 22 mm in diameter. Postoperative mobilization consisted of full weight-bearing as tolerated using two crutches for support, beginning on the first or second postoperative day, followed by independent mobilization as soon as the patient was able.

Subject Monitoring and Assessments

Patients were assessed preoperatively and postoperatively and monitored over a two-year follow-up period (see Appendix). Patients underwent dual x-ray absorptiometry (DXA) scans of the proximal aspect of the femur one week postoperatively (baseline) and at twelve, twenty-six, fifty-two, and 104 weeks postoperatively according to a previously described acquisition and analysis protocol¹¹. Scans were acquired with use of a fan-beam densitometer (Discovery; Hologic, Bedford, Massachusetts). All scans were analyzed by the same trained operator with use of the seven Gruen regions of interest¹¹ and Hologic metal-removal software (version 12.4). Bone mineral density in the ipsilateral femoral neck was also measured preoperatively with use of standard Hologic acquisition and analysis protocols for measurement of femoral neck bone mineral density (Hologic software version 8) and expressed as a femoral neck Z-score. This was done to establish whether there were systematic preoperative differences in hip bone mineral density among groups that might confound interpretation of the study findings. The Z-score is a measure of the bone mineral density at a given anatomic site relative to that in a reference population matched according to age and sex, and it is a routine output of clinical diagnostic DXA scanners.

Serum samples and urine samples from the second morning void were obtained for measurement of biochemical markers of bone turnover at the preoperative baseline and at six, twelve, twenty-six, and fifty-two weeks postoperatively. All samples were collected between 8 and 10 a.m. following an overnight fast. Samples for bone turnover markers were not collected at the 104-week time point, as a previous study suggested that biochemical markers return to baseline by one year following surgery¹². Serum samples were stored at −70°C and urine samples were stored at −20°C; all samples were analyzed in a single batch following study completion. N-telopeptide of type-I collagen (NTX-I, a marker of osteoclast activity) was measured in urine by electrochemiluminescent immunoassay with use of a VITROS 250 ECi analyzer (Ortho Clinical Diagnostics, High Wycombe, United Kingdom). The NTX-I level was expressed as a ratio to urinary creatinine, which was also measured with use of the VITROS 250 ECi analyzer. The N-terminal-mid fragment of osteocalcin (a marker of osteoblast activity) was measured in serum by electrochemiluminescent immunoassay with use of a cobas e 411 analyzer (Roche Diagnostics, Burges Hill, United Kingdom).

Subsidence of the femoral prosthesis was measured on digitized standardized anteroposterior radiographs of the hip and proximal aspect of the femur obtained one week postoperatively (baseline) and at twelve, twenty-six, fifty-two, and 104 weeks postoperatively according to a previously described protocol¹³. All radiographs were digitized with use of a Lumiscan 200 laser digitizer (Lumisys, Sunnyvale, California) and analyzed with use of EBRA-FCA migration measurement software (2003 version; University of Innsbruck, Innsbruck, Austria) according to a previously described protocol¹³.

The clinical outcome was assessed with use of both clinician-administered and patient-reported outcome measures. The Harris hip score (clinician-administered) and the modified Oxford hip score (patient-reported) were evaluated preoperatively (baseline) and at twelve, fifty-two, and 104 weeks postoperatively^14,15. All Harris hip score assessments were performed by the same research nurse.

Primary Outcome Measure and Power

The primary outcome measure of the study was the change in proximal femoral bone mineral density over the first two postoperative years in composite-beam compared with sliding-taper prosthesis designs. The sample size necessary to demonstrate a change in this primary outcome was calculated prior to trial recruitment, using data from control group subjects participating in a randomized trial of the effect of pamidronate on prevention of periprosthetic bone loss after total hip arthroplasty with a cemented sliding-taper femoral prosthesis¹⁶. The power calculation for the present study was performed with use of the method described by Altman¹⁷.

Data for the change in bone mineral density in Gruen zone 7 of the femur at two years in the placebo group (initial bone mineral density, 1.47 g/cm²; change [and standard deviation] at two years, –0.16 ± 0.13 g/cm²) were used to calculate the standardized difference, based on an estimated mean therapeutic effect of 5% for a tapered prosthesis (standardized difference, [0.16/2]/0.13 = 0.62). The effective sample size (N) for eighty tapered (n₁) compared with forty composite-beam (n₂) prostheses was calculated to be 107 with use of the equation N = 4N′k/(1 + k)², where k = n₁/n₂ and N′ = n₁ + n₂. A p value of <0.05 was considered significant. The study was expected to have a final power of 90% to detect a 5.5% difference in bone mineral density between the tapered and composite-beam groups at two years. All data were analyzed on an intent-to-treat basis in the 120 randomized subjects.

Source of Funding

This study was an investigator-initiated study funded by a grant from DePuy International, Leeds, United Kingdom. The funding source played no role in the investigation, analysis, interpretation, or manuscript preparation. R.L.J’s studentship was funded by Arthritis Research UK.

Results

Introduction | Materials and Methods | Results | Discussion | Appendix

Subject Characteristics

Five hundred and sixty-two patients were approached to participate in the study, 120 subjects were randomized, and 108 completed the study (Fig. 2). Four of the twelve subjects who did not complete the study died from unrelated conditions, three withdrew by choice, one was lost to follow-up, and four were excluded because of protocol violations. The four protocol violations included commencement of bisphosphonate therapy for vertebral fracture in one subject, chemotherapy for cancer in one subject, glucocorticoid therapy for temporal arteritis in one subject, and glucocorticoid therapy for chronic obstructive pulmonary disease in one s ubject.

Fig. 2

Flow of patients through the study.

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The baseline demographic characteristics, femoral neck bone mineral density, and bone turnover markers were similar among the treatment groups (p > 0.05 for all comparisons as determined by analysis of variance [ANOVA], Table I). The preoperative diagnosis was primary osteoarthritis in all subjects except one (in the Exeter group) in whom the diagnosis was secondary osteoarthritis due to hip dysplasia.

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TABLE I Baseline Characteristics of Study Subjects

Subject Baseline Characteristics*	Composite-Beam (N = 38)	Double-Tapered (N = 40)	Triple-Tapered (N = 42)	P Value†
Age‡(yr)	72 ± 6	72 ± 6	71 ± 7	>0.05
Sex, F:M§	24:14	21:19	20:22	>0.05
Side, L:R§	19:19	16:24	12:30	>0.05
Height‡(m)	1.64 ± 0.08	1.67 ± 0.08	1.66 ± 0.10	>0.05
Weight‡(kg)	77.2 ± 15.7	81.5 ± 15.0	80.0 ± 13.5	>0.05
Body mass index‡(kg/m2)	28.6 ± 4.6	29.2 ± 3.9	29.1 ± 5.1	>0.05
Femoral neck BMD‡(g/cm2)	0.91 ± 0.17	0.91 ± 0.14	0.88 ± 0.16	>0.05
Femoral neck Z-score‡	0.46 ± 1.12	0.73 ± 1.15	0.46 ± 0.96	>0.05
NTX-I‡(nM BCE/mM creatinine)	59.7 ± 37.9	67.6 ± 31.6	68.1 ± 36.3	>0.05
Osteocalcin‡(ng/mL)	23.6 ± 7.4	25.3 ± 9.4	24.5 ± 9.3	>0.05
Harris hip score‡	44 ± 9	40 ± 9	43 ± 11	>0.05
Oxford hip score‡	17 ± 6	19 ± 7	17 ± 8	>0.05

*BMD = bone mineral density, NTX-I = N-terminal telopeptide of type-I collagen, and BCE = bone collagen equivalent.
†For the comparison among all three groups.
‡Values are given as the mean and the standard deviation; p values are calculated with use of one-way analysis of variance.
§P values are calculated with use of the chi-square test.

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TABLE I Baseline Characteristics of Study Subjects

Subject Baseline Characteristics*	Composite-Beam (N = 38)	Double-Tapered (N = 40)	Triple-Tapered (N = 42)	P Value†
Age‡(yr)	72 ± 6	72 ± 6	71 ± 7	>0.05
Sex, F:M§	24:14	21:19	20:22	>0.05
Side, L:R§	19:19	16:24	12:30	>0.05
Height‡(m)	1.64 ± 0.08	1.67 ± 0.08	1.66 ± 0.10	>0.05
Weight‡(kg)	77.2 ± 15.7	81.5 ± 15.0	80.0 ± 13.5	>0.05
Body mass index‡(kg/m2)	28.6 ± 4.6	29.2 ± 3.9	29.1 ± 5.1	>0.05
Femoral neck BMD‡(g/cm2)	0.91 ± 0.17	0.91 ± 0.14	0.88 ± 0.16	>0.05
Femoral neck Z-score‡	0.46 ± 1.12	0.73 ± 1.15	0.46 ± 0.96	>0.05
NTX-I‡(nM BCE/mM creatinine)	59.7 ± 37.9	67.6 ± 31.6	68.1 ± 36.3	>0.05
Osteocalcin‡(ng/mL)	23.6 ± 7.4	25.3 ± 9.4	24.5 ± 9.3	>0.05
Harris hip score‡	44 ± 9	40 ± 9	43 ± 11	>0.05
Oxford hip score‡	17 ± 6	19 ± 7	17 ± 8	>0.05

Change in Proximal Femoral Bone Mineral Density

Decreases in overall and regional periprosthetic bone mineral density in the femur over the 104-week study period were found for all prosthesis designs (Fig. 3). In all Gruen zones, the bone mineral density loss was most rapid over the first twelve postoperative weeks for all prosthesis designs. Thereafter, a return toward baseline was observed in zones 1 through 6; this return varied according to region. The greatest bone loss was observed in zone 7; this loss was most rapid over the first twelve weeks, reached a nadir (a 14% decrease) at fifty-two weeks, and persisted to the end of the study at 104 weeks.

Fig. 3

Mean percentage change in proximal femoral bone mineral density (BMD) for the three prosthesis designs over 104 weeks, as measured with use of dual x-ray absorptiometry in the seven Gruen zones (labeled as R1 through R7 on the graphs and the accompanying radiograph). The error bars indicate the 95% confidence interval. Composite-beam compared with sliding-taper, p > 0.05 by repeated-measures analysis of variance (ANOVA) in all Gruen zones. Double compared with triple taper within the sliding-taper group, p = 0.007 by ANOVA for Gruen zone 1 and p > 0.05 for all other Gruen zones.

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The pattern of bone mineral density change in all femoral zones was similar between composite-beam and sliding-taper designs (p > 0.05 [ANOVA], Fig. 3). The change in proximal femoral bone mineral density in zones 2 through 7 was also similar between the double and triple-tapered designs (p > 0.05 [ANOVA], Fig. 3). However, the bone mineral density values in zone 1 indicated less bone loss for the triple-tapered compared with the double-tapered design (p = 0.007 [ANOVA]).

Bone Turnover Markers

Transient rises in both NTX-I and osteocalcin occurred for all prosthesis designs during the first postoperative year (Fig. 4). NTX-I increased immediately postoperatively, peaked at six weeks, and thereafter declined to baseline by fifty-two weeks. No differences in the change in NTX-I were found between composite-beam and sliding-taper designs or between double and triple-tapered designs (p > 0.05 [ANOVA] for both comparisons). Serum osteocalcin peaked later than NTX-I did, at twelve weeks postoperatively for all prosthesis designs. Thereafter, osteocalcin declined back toward baseline between twelve and fifty-two weeks. No differences in the change in osteocalcin were found between composite-beam and sliding-taper designs or between the double and triple-tapered prostheses (p > 0.05 [ANOVA] for both comparisons).

Fig. 4

Mean percentage change in bone turnover markers for the three prosthesis designs measured over fifty-two weeks. NTX-I = N-telopeptide of type-I collagen, and OC = osteocalcin (N-terminal-mid fragment). The error bars indicate the 95% confidence interval. Composite-beam compared with sliding-taper, p > 0.05 by repeated-measures analysis of variance (ANOVA) for both markers. Double compared with triple taper within the sliding-taper group, p > 0.05 by ANOVA for both markers.

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Prosthesis Migration

The prostheses in all three study groups displayed an initial rapid subsidence over the first twelve weeks (Fig. 5). Thereafter, the rate of subsidence of the composite-beam prosthesis slowed abruptly, whereas the sliding-taper prostheses continued to subside at a slightly slower rate up to week 104. The sliding-taper designs subsided by a greater amount compared with the composite-beam design at all follow-up time points (p < 0.001 [ANOVA]). The mean subsidence (and standard deviation) of the composite-beam design at 104 weeks was 0.68 ± 1.43 mm compared with 1.92 ± 1.11 mm for the sliding-taper designs (p < 0.001). The amount of subsidence was similar between the double-tapered and triple-tapered designs at all time points (p > 0.05 [ANOVA]).

Fig. 5

Mean distal migration pattern for the three prosthesis designs over 104 weeks measured with EBRA software. The error bars indicate the 95% confidence interval. Composite-beam compared with sliding-taper, p < 0.001 by repeated-measures analysis of variance (ANOVA). *p < 0.05, **p < 0.01, and ***p < 0.001 for the individual time points.

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Clinical Outcome Measures

Improvement in clinical outcome, as measured with the modified Oxford hip score and the Harris hip score, was observed in all study groups over the first two postoperative years and was consistent with improved physical function (Fig. 6). This increase was most rapid over the first twelve weeks following surgery, with a slower rate of improvement continuing to week 104. Subjects receiving a composite-beam prosthesis experienced a similar magnitude and rate of improvement in the modified Oxford hip score and Harris hip score compared with those receiving the sliding-taper designs (p > 0.05 [ANOVA]). Subjects receiving the double-tapered design experienced a similar rate and magnitude of improvement in clinical outcome scores compared with those receiving the triple-tapered prosthesis (p > 0.05 [ANOVA]).

Fig. 6

Mean clinical outcomes for the three prosthesis designs measured with use of the Harris and Oxford hip scores over 104 weeks. The error bars indicate the 95% confidence interval. Composite-beam compared with sliding-taper, p > 0.05 by repeated-measures analysis of variance (ANOVA) for both outcome measures. Double compared with triple taper within the sliding-taper group, p > 0.05 by ANOVA for both outcome measures.

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Discussion

Introduction | Materials and Methods | Results | Discussion | Appendix

The magnitude and regional distribution of proximal femoral bone loss observed in this randomized clinical trial were similar between patients with sliding-taper and composite-beam prostheses, and patients with triple-tapered compared with double-tapered prostheses showed a similar bone remodeling pattern. Bone turnover, as measured with use of systemic biochemical markers, was also similar between the prosthesis groups. Each prosthesis design demonstrated a distal migration pattern that was in keeping with its design philosophy^8,18.

The regional pattern and severity of bone loss for the sliding-taper prostheses were similar to the change in proximal femoral bone mineral density that we reported previously for other sliding-taper designs over the first two postoperative years¹⁶. The observation that bone loss was most rapid over the first three months following surgery and reached a steady state by two years is consistent with the biomarker data, which showed a peak in bone resorption activity at six weeks followed by a peak in bone formation between twelve and twenty-six weeks, with a return toward baseline in both markers by one year. The similar timing and magnitude of the peaks in each group suggests that the remodeling response was similar among the three prosthesis designs^16,19.

Finite-element modeling data have suggested that cemented femoral prosthesis designs based on the sliding-taper principle exhibit a more favorable pattern of stress distribution in the proximal aspect of the femur compared with composite-beam designs, and this could theoretically result in less bone loss at the calcar due to strain-adaptive remodeling⁹. Furthermore, modification of the basic double-tapered design to include a third, medial taper has been proposed to improve this load transfer further¹⁰. The data from our study showed that improvements in load transfer associated with double or triple sliding-taper designs of cemented femoral prostheses did not translate into a clinically measurable effect on bone mineral density or on biochemical markers of bone turnover, with the exception of a small (3%) difference in the bone mineral density change in Gruen zone 1 at two years between double and triple-tapered prostheses. However, the bone mineral density change for zone 7, where bone loss was greatest, showed an identical pattern of bone loss for all three prosthesis designs, and this result is also similar to that recently reported by Buckland et al.²⁰ in a cohort of 103 triple-tapered polished stems measured over the first two postoperative years by DXA²⁰. One explanation for the observed lack of differential bone loss is that the magnitude of the difference between the elastic modulus of the prosthesis (approximately 200 GPa) and that of the host bone (1-10 GPa) is such that any difference in loading regime between prosthesis designs is relatively inconsequential in comparison with the strain-adaptive remodeling induced by the presence of a prosthesis within the femoral medullary canal.

Polished cemented femoral prostheses based on the sliding-taper principle have had excellent long-term results in both institutional series and national joint registries, and these results may be superior to those of the composite-beam Charnley prosthesis^21-24. Our data indicate that differences in strain-adaptive remodeling due to differing patterns of stress transfer are unlikely to be a major contributory factor to this differential survival. Late osteolysis leading to prosthesis loosening after total hip arthroplasty is currently thought to arise because of an inflammatory response to wear particle debris²⁵. A more likely explanation of the differential survival between composite-beam and sliding-taper prostheses is the effect of surface roughness of the prosthesis-cement interface on local production of wear debris particles²⁶. Although composite-beam prostheses are thought to function with a bonded prosthesis-cement interface, radiostereometric analysis studies have shown that migration occurs at this interface in both sliding-taper and composite-beam designs⁸. A polished sliding-taper design produces fewer cement particles during prosthesis migration compared with the nonpolished surface of a composite-beam prosthesis²⁶. Furthermore, a distal cement mantle fracture in a composite-beam prosthesis typically results in migration, osteolysis, and early failure^27,28. In a sliding-taper design, this event is more benign as the resulting migration causes resettling of the prosthesis through a taper-lock process without the generation of a large excess of cement particulate debris²⁹.

Measurement of bone mineral density by DXA is currently the most accurate method for assessing periprosthetic bone loss after joint arthroplasty, and it has high precision³⁰. Our study sample size was calculated a priori with use of pilot data from our previously published measurements of longitudinal bone mineral density changes around cemented sliding-taper femoral prostheses¹⁶, and it was designed to yield 90% power to detect a 5.5% difference in bone mineral density change in the proximal aspect of the femur (Gruen zone 7) over two years between eighty sliding-taper and forty composite-beam prostheses. A post hoc analysis of the resulting data showed an actual power of 94% to detect a 5% difference in bone mineral density in this region, closely approximating the a priori calculation. Further, the subjects in each study group were matched for baseline characteristics, including baseline bone mineral density at the femoral neck and systemic markers of bone turnover. Thus, interpretation of our finding of similar bone mineral density changes was not limited by differences in patient baseline characteristics, instrument imprecision, or inadequate power.

We studied bone mineral density changes over a two-year period and bone turnover over a one-year period, as we aimed to examine periprosthetic bone mineral density changes due to strain-adaptive remodeling resulting from the modified strain environment introduced by the differing prosthesis designs. Although later differential changes in bone mineral density might occur among prosthesis designs, the bone mineral density and biomarker data indicated that the design of the study captured the relevant strain-adaptive remodeling changes that occurred with these prosthetic designs in the short term^20,31,32.

Appendix

Introduction | Materials and Methods | Results | Discussion | Appendix

A figure summarizing subject assessment and monitoring is available with the online version of this article as a data supplement at jbjs.org.

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Disclosure: One or more of the authors received payments or services, either directly or indirectly (i.e., via his or her institution), from a third party in support of an aspect of this work. In addition, one or more of the authors, or his or her institution, has had a financial relationship, in the thirty-six months prior to submission of this work, with an entity in the biomedical arena that could be perceived to influence or have the potential to influence what is written in this work. No author has had any other relationships, or has engaged in any other activities, that could be perceived to influence or have the potential to influence what is written in this work. The complete Disclosures of Potential Conflicts of Interest submitted by authors are always provided with the online version of the article.

Topics

bone mineral density ; bone remodeling ; femur ; prosthesis design ; prostheses

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Raveen L. Jayasuriya, Simon C. Buckley, Andrew J. Hamer, Robert M. Kerry, Ian Stockley, Mohamed W. Tomouk, Jeremy Mark Wilkinson; Effect of Sliding-Taper Compared with Composite-Beam Cemented Femoral Prosthesis Loading Regime on Proximal Femoral Bone RemodelingA Randomized Clinical Trial. The Journal of Bone & Joint Surgery. 2013 Jan;95(1):19-27.

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