DOS BULLETIN - Dansk Ortopædisk Selskab

2010-378_DOS nr. 3 2010 29/09/10 10:08 Side 77
Increased migration of cemented Bi-Metric® stem in
hybrid THA might explain poor survival rates of this
stem observed by Danish National Hip Registry.
A radiostereometric study
Juozas Petruskevicius, Mogens Berg Laursen,
Mogens Brouw Jørgensen, Kjeld Søballe, Poul Torben Nielsen
Orthopedic Division, Northern Denmark Region, Aalborg Hospital,
University of Aarhus; Department of Orthopaedics,
University Hospital of Aarhus
Background: Contradictory outcomes for cemented Bi- Metric® stem in
hybrid total hip arthroplasty (THA) are reported by the Danish National Hip
Registry in 2007. The survivorship rates of this stem after 11 years were 88.6%,
when revisions related to femoral component in hybrid THA were analyzed. In
a randomized study investigating the preheating effects on stem stability in vivo,
we evaluated migration rates of 80 cemented femoral components using radiosteometric
analysis (RSA).
Purpose: The detail analysis of significant migration of some cemented
femoral components observed in previous study is presented in this abstract.
Methods: Eighty patients undergoing hybrid hip THA with cemented matt-surfaced
Ti stem (Bi-Metric®, Biomet) were enrolled into prospective RSA study.
Prostheses were equipped with three tantalum beads to enable RSA. Tantalum
markers were also inserted both into the bone and cement, which allowed evaluation
of prosthesis-cement and prosthesis- bone micromotions as well as
cement- mantle migration relative to bone (CBI). The RSA examinations were
performed at the second or third postoperative day and again after 3, 12 and 24
months. RSA images were analyzed using UmRSA software (Umeå, Sweden).
Migration of femoral head centre, the tip of the prosthesis and cement mantle’s
translations were analyzed.
Findings: Seventy one patients reached at least 2 RSA examinations and 65
patients accomplished the study. The main stem migration occurred inside the
cement mantle where subsidence, medial and posterior translations of femoral
head centre were observed. The cement mantle migrated proximally i.e. opposite
to stem. At 2 years we observed femoral head subsidence more than 1mm
in 9 hips. This subsidence was always related with increased posterior translation
of femoral head, which ranged from 0.84 to 14.3 mm. Additional 20 components
subsided between 0.4 and 1mm. Increased femoral head migration was
correlated with male sex and increasing BMI. Proximal cement mantle’s migration
observed at 3 months remained unchanged during the next 2 years.
Conclusion: One third of all stems had considerable migrations after 2 years,
indicating debonding of this particular stem with a risk of development of wear
debris and secondary osteolysis.
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