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RCT
ACE Report #10101

Does approach significantly affect cup positioning in total hip arthroplasty?


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

Radiographic cup position following posterior and lateral approach to total hip arthroplasty. An explorative randomized controlled trial

PLoS One. 2018 Jan 29;13(1):e0191401

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Synopsis

80 patients scheduled for primary total hip arthroplasty were randomized to surgery completed through either a lateral approach or a posterior approach. Primary outcomes were cup inclination and anteversion, as well as the number of cups placed outside of Lewinnek "target zone" (40+/-10deg inclination; 15+/-10deg anteversion). While results for mean cup inclination and anteversion demonstrated significant differences between groups, the rate of cups placed outside the Lewinnek safe zone was similar between groups.

Publication Funding Details +
Funding:
Non-Industry funded
Sponsor:
The Danish Rheumatism Association; Region of Zealand; Region of Southern Denmark; Bevica Foundation; Bjarne Jensen Foundation; Odense University Hospital
Conflicts:
None disclosed

Risk of Bias

5.5/10

Reporting Criteria

18/21

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.

4/4

Randomization

3/4

Outcome Measurements

4/4

Inclusion / Exclusion

4/4

Therapy Description

3/5

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?

The approach used in total hip arthroplasty may significantly influence acetabular cup positioning, though few randomized controlled trials have been completed with an emphasis on cup alignment when comparing different approaches. Two of the most common approaches used in THA are the posterior and lateral approaches, and this study sought to compare postoperative acetabular cup angles between the two approaches.

What was the principal research question?

In total hip arthroplasty, does the posterior approach lead to significantly greater cup anteversion and significantly lower cup inclination when compared to the lateral approach?

Study Characteristics -
Population:
80 patients, 45-70 years of age, scheduled for primary, unilateral total hip arthroplasty due to primary osteoarthritis. All cases were completed using a cementless acetabular cup (Exceed ABT Ringloc-x Shell; Biomet) and cementless femoral stem (Bi-metric; Biomet). The Lewinnek "target zone" of 40+/-10deg inclination and 15+/-10deg anteversion was used in all cases.
Intervention:
Posterior approach: An incision was made over the posterior part of the greater trochanter, with blunt dissection of the gluteus maximus muscle, detachment of the external rotator muscles, and incision through the posterior part of the capsule for access to the joint. (41; 29 assessed) (Mean age: 61.5 [47-69])
Comparison:
Lateral approach: A midline incision was made over the greater trochanter, with detachment of the anterior one-third of the gluteus medius insertion and gluteus minimus insertion on the greater trochanter and incision, and incision in the anterior part of the capsule for access to the joint. (n=39; 29 assessed) (Mean age: 60.2 [45-69])
Outcomes:
Primary outcomes were cup anteversion and inclination angles on postoperative radiographs. Secondary outcomes included femoral offset, cup offest, total offset, abductor moment arm and leg length discrepancy on postoperative radiographs.
Methods:
RCT; Two surgeon
Time:
All outcomes assessed from postoperative radiographs

What were the important findings?

  • Cup anteversion was significantly different between the posterior approach group (15+/-8.4deg) and the lateral approach group (10+/-5.9deg) (p=0.006). A total of 10 cups in the posterior approach group (six <5deg; four >25deg) and 6 cups in the lateral approach group (all <5deg) were outside of the target 15+/-10 deg anteversion.
  • Cup inclination was significantly different between the posterior approach group (42+/-5.9deg) and the lateral approach group (47+/-3.6deg). (p<0.001). A total of 4 cups in the posterior approach group and 5 cups (all >50deg) in the lateral approach group (all >50 deg) were outside the target 40+/-10 deg inclination.
  • A total of 11 cups in each group were placed outside the target zone.
  • Leg length discrepancy did not significantly differ between the posterior approach group (1.9+/-5.2mm) and the lateral approach group (3.4+/-5.0mm).

What should I remember most?

In total hip arthroplasty, the posterior approach led to significantly lower cup anteversion and lower cup inclination when compared to the lateral approach, but similar rates of cup placement within the Lewinnek target zone were observed between groups.

How will this affect the care of my patients?

The results of this study suggest that the two approaches do significantly differ in cup angles in total hip arthroplasty, though display similar incidence of cup placement within the Lewinnek safe zone. Longer term follow-up is necessary to determine the impact of the differences in anteversion and inclination between approaches on dislocation rates, as well as clinical and functional outcome measures.

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