title: Prospective two-year subsidence analysis of 100 cemented polished straight stems - a short-term clinical and radiological observation.
abstract: Cemented stems show good long-term results and the survival of new implants can be predicted by their early subsidence. With EBRA-FCA (Femoral Component Analysis using Einzel-Bild-Röntgen-Analyse) early subsidence as an early indicator for later aseptic loosening can be analysed. For the cemented TwinSys stem mid- and long-term data is only avalible from the New Zeeland Arthroplasty register, thus close monitoring of this implant system is still mandatory.
  
  
  
  We conducted a 2 year follow up of 100 consecutive hybrid THA (Total hip arthroplasty) of a series of 285 primary THA operated between Jan 2009 und Oct 2010. These 100 received a polished, cemented collarless straight stem (twinSys®, Mathys AG® Bettlach, Switzerland) with an uncemented monobloc pressfit cup (RM pressfit®, Mathys AG® Bettlach, Switzerland). The other patients were treated with the uncemented version of this stem and the same cup. Clinical (Harris Hip Score) and radiological (ap and axial x-rays, cementing quality according to Barrack, alignment) outcomes besides an EBRA-FCA subsidence analysis were performed.
  
  
  
  Median age at operation was 78 (68 to 93) years. 5 patients died in the course of follow-up unrelated to surgery. The KM (Kaplan-Meier) survival at 2 years for the endpoint reoperation for any reason was 94.9 (95 % confidence interval 90.6-100 %). Survival for the endpoint aseptic loosening at 2 years was 100 %. The HHS (Harris Hip Score) improved from 56 (14-86) preoperatively to 95 (60-100) 2 years after the operation. Cementing results were judged 47 % Grade A, 45 % Grade B and 7 % Grade C. Osteolysis was found in 2 stems without clinical symptoms or correlation to subsidence or cementing quality. The EBRA-FCA analysis showed an average subsidence of -0.30 mm (95 % CI -0.5 mm to -0.1 mm). 11 patients showed a subsidence of more than 1 mm. In this group one patient showed a subsidence of 1.5 mm and one of 3.1 mm without further radiological changes.
  
  
  
  The twinSys stem showed excellent clinical and radiologic short term results at 2 years follow-up and seems to be a reliable implant.
authors.affiliation: Department for Orthopaedics and Trauma Surgery, Kantonsspital Baselland, CH-4410, Liestal, Switzerland. wolf.siepen@ksbl.ch.
authors.forename: Wolf
authors.identifier: 0000-0002-3363-7177
authors.initials: W
authors.lastname: Siepen
authors.affiliation: Department for Orthopaedics and Trauma Surgery, Kantonsspital Baselland, CH-4410, Liestal, Switzerland.
authors.forename: Lukas
authors.initials: L
authors.lastname: Zwicky
authors.affiliation: Department for Orthopaedics and Trauma Surgery, Kantonsspital Baselland, CH-4410, Liestal, Switzerland.
authors.forename: Karl Kilian
authors.initials: KK
authors.lastname: Stoffel
authors.affiliation: LEONARDO, Hirslanden Klinik Birshof, Münchenstein, Switzerland.
authors.forename: Thomas
authors.initials: T
authors.lastname: Ilchmann
authors.affiliation: Department for Orthopaedics and Trauma Surgery, Kantonsspital Baselland, CH-4410, Liestal, Switzerland.
authors.forename: Martin
authors.initials: M
authors.lastname: Clauss
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019644:Arthroplasty, Replacement, Hip / Q000295:instrumentation*; D001843:Bone Cements; D005260:Female; D006621:Hip Joint / Q000000981:diagnostic imaging; D006622:Hip Prosthesis / Q000706:statistics & numerical data*; D006801:Humans; D008297:Male; D011446:Prospective Studies; D011474:Prosthesis Design; D016896:Treatment Outcome
chemical_list: D001843:Bone Cements
keywords: Cemented; EBRA-FCA; RM pressfit; Straight stem; Subsidence; twinSys