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RCT
ACE Report #8974

Muller vs. Virtec straight stem shape comparable for long-term radiological change in THR


Study Type:Therapy
OE Level Evidence:2
Journal Level of Evidence:N/A

Similar effect of stem geometry on radiological changes with 2 types of cemented straight stem

Acta Orthop. 2016 Apr;87(2):120-5.

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Synopsis

646 patients (711 hips) patients undergoing primary total hip replacement with straight femoral stem cement fixation were randomized to receive either a Muller straight stem (MSS) or the Virtec straight stem (VSS) for the purpose of comparing long-term radiographical and survival success ten years post-surgery. Results demonstrated that patients in both groups had comparable implant survival, osteolysis, subsidence, and debonding rates at 10 years.

Publication Funding Details +
Funding:
Not Reported
Conflicts:
None disclosed

Risk of Bias

4/10

Reporting Criteria

15/20

Fragility Index

N/A

Was the allocation sequence adequately generated?

Was allocation adequately concealed?

Blinding Treatment Providers: Was knowledge of the allocated interventions adequately prevented?

Blinding Outcome Assessors: Was knowledge of the allocated interventions adequately prevented?

Blinding Patients: Was knowledge of the allocated interventions adequately prevented?

Was loss to follow-up (missing outcome data) infrequent?

Are reports of the study free of suggestion of selective outcome reporting?

Were outcomes objective, patient-important and assessed in a manner to limit bias (ie. duplicate assessors, Independent assessors)?

Was the sample size sufficiently large to assure a balance of prognosis and sufficiently large number of outcome events?

Was investigator expertise/experience with both treatment and control techniques likely the same (ie.were criteria for surgeon participation/expertise provided)?

Yes = 1

Uncertain = 0.5

Not Relevant = 0

No = 0

The Reporting Criteria Assessment evaluates the transparency with which authors report the methodological and trial characteristics of the trial within the publication. The assessment is divided into five categories which are presented below.

2/4

Randomization

3/4

Outcome Measurements

4/4

Inclusion / Exclusion

4/4

Therapy Description

2/4

Statistics

Detsky AS, Naylor CD, O'Rourke K, McGeer AJ, L'Abbé KA. J Clin Epidemiol. 1992;45:255-65

The Fragility Index is a tool that aids in the interpretation of significant findings, providing a measure of strength for a result. The Fragility Index represents the number of consecutive events that need to be added to a dichotomous outcome to make the finding no longer significant. A small number represents a weaker finding and a large number represents a stronger finding.

Why was this study needed now?

There are two major femoral stem fixation methods that are regularly used in total hip replacement: shape-closed or force-closed stems. In shape-closed fixation, stems are surrounded by a thin cement mantle and are enhanced with an additional press-fit fixation against the cortical bone. Furthermore, shape-closed fixation can use varying stem shapes, including the Muller straight stem (which has a rectangular cross section) and the Virtec straight stem (which has a wider cross section with rounder edges). Due to the lack of conclusive evidence supporting a significant long-term benefit of one stem shape over the other, the current study was conducted.

What was the principal research question?

For patients undergoing cemented shape-closed fixation during total hip replacement, did either the Muller straight stem (MSS) or the Virtec straight stem (VSS) result in significant radiographical improvement in osteolysis, radiolucency, and distal migration when compared at least ten years post-surgery?

Study Characteristics -
Population:
646 patients (711 hips) patients undergoing primary total hip replacement with straight stem cement fixation were included in this study between July 1996 and July 2003. All surgeries were performed with a standardized lateral transgluteal approach while patients were in the supine position.
Intervention:
VSS group: patients received a Virtec straight stem, which is noted to have an oval cross-section and is wider in the sagittal plane, thereby allowing for a fuller filling of the femoral canal (n=355 hips; mean age=69+/-11, 217M/138F).
Comparison:
MSS group: patients received the Muller straight stem, which is noted to have a rectangular cross-section and longitudinal grooves running anteriorly and posteriorly and a small proximal collar (n=356 hips; mean age= 69+/-10, 202M/154F).
Outcomes:
Outcomes included radiographs assessing osteolysis, subsidence, and debonding. Osteolysis was defined as progressive, newly developed endosteal bone loss with a diameter > 3 mm with either a "scalloping" or a "bead-shaped" lucency at the cement-bone interface. Subsidence was assessed by measuring increases in radiolucency as a result of distal migration in the prosthetic shoulder from overlapping proximal cement in Gruen zone 1 (labelled as abnormal if the increase was greater than 2 mm). Stems were considered loose if circumferential osteolysis or radiolucencies were visible in any Gruen zone, or if subsidence exceeded 10 mm.
Methods:
RCT: prospective, single-centre
Time:
Outcomes of interest were evaluated at 4 months, 1 year, 2 years, 5 years, and every 5 years thereafter.

What were the important findings?

  • When compared at 10 years, Kaplan-Meier (KM) survival after "revision of component for any reason" was observed to be 92% (95% CI 88-95) in the MSS group and 95% (95% CI 92-97) in the VSS group; the difference was not significant (p=0.1)
  • KM survival after revision for "aseptic loosening of the stem", specifically was 96% (95% CK 94-99) in the MSS group and 98% (95% CI 97-100) in the VSS group; the difference was also not significant (p=0.2).
  • 399 hips (196 in the MSS group and 203 in the VSS group) were radiologically assessed at a mean follow-up of 11 (10 to 16) years for unrevised hips and 6.85 (1 to 16) years for revised hips.
  • In the stems that were revised for aseptic loosening (n=22), 17 of them displayed radiological osteolysis on the final radiograph before revision; osteolysis was found to be more common in the MSS groups in Gruen zones 2, 6, and 7 (p=0.06, p=0.07, and p=0.04 respectively).
  • Subsidence was found in 5 MSS stems and 4 VSS stems; debonding at the cement-prosthesis interface was found in 6 MSS stems and 4 VSS stems (all 10 cases of debonding were observed in Gruen zone 1).

What should I remember most?

For patients undergoing cemented shape-closed fixation during total hip replacement, both the Muller straight stem (MSS) and the Virtec straight stem (VSS) resulted in adequate long-term survival with minimal aseptic loosening, incidence of osteolysis, subsidence and debonding.

How will this affect the care of my patients?

The results of this study suggest that Muller and Virtec stems offer excellent survival over a 10 year period. Further randomized trials should be undertaken to evaluate the effect of stem geometry on radiographic changes and survival in different implants.

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