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- The importance of press-fit and three-point fixation in treating large acetabular defects with porous tantalum components
Stuart Callary1,2; John Abrahams1,2; Yi Zeng3; Robyn Clothier1,2; Kerry Costi1,2; Donald Howie1,2; Lucian Solomon1,2
1Department of Orthopaedics and Trauma, Royal Adelaide Hospital, Adelaide, South Australia
2Centre for Orthopaedic and Trauma Research, The University of Adelaide, Adelaide, South Australia
3Department of Orthopaedic Surgery, West China Hospital of Sichuan University, Chengdu, China
Introduction: First-time revision acetabular components have a 36% re-revision rate at 10 years in Australia, with subsequent revisions known to have even worse results. The most common cause of re-revision is loosening. Acetabular component migration >1mm at two years following revision THA is a surrogate for long term loosening. This study aimed to investigate the effect of implant fixation, bone density, implant-to-bone contact and defect grade on the migration of porous tantalum components used at revision surgery.
Material and Methods: Between May 2011 and March 2018, 55 patients (56 hips; 30 female, 25 male) underwent acetabular revision THR with a porous tantalum component and Radiostereometric Analysis (RSA) examinations. A porous tantalum component was used because the defects treated (Paprosky IIa:IIb:IIc:IIIa:IIIb; 2:6:8:22:18; 13 with pelvic discontinuity) were either deemed too large or in a position preventing screw fixation of an implant with low coefficient of friction. Press-fit and three-point fixation was assessed intra-operatively and on postoperative imaging. A post-operative CT scan was used to assess implant-to-bone contact achieved and bone density.
Results: Three-point acetabular fixation was achieved in 51 hips, 34 of which were press-fit. The mean implant-to-bone contact achieved was 36% (range 9-71%). Poor bone density did not influence implant stability. The majority (52/56, 93%) of components demonstrated acceptable early stability. Four components migrated >1mm proximally at two years (1.1, 3.2, 3.6 and 16.4mm). Three of these were in hips with Paprosky IIIB defects, including 2 with pelvic discontinuity. Neither press-fit nor three-point fixation was achieved for these three components and the implant-to-bone contact achieved was low (30, 32 and 59%).
Interpretation and Conclusion: The majority of porous tantalum components had acceptable stability at two years following revision surgery despite treating large acetabular defects and poor bone density. Components without press-fit or three-point fixation were associated with unacceptable amounts of early migration.
Keywords: Revision THA; Acetabular defects, Discontinuity, Three-point fixation; Cup Migration
55
- Long-term micromotion of fully cemented versus hybrid fixation in revision total knee arthroplasty: a 10-year radiostereometric analysis RCT
Kelly Mills, Nienke Kosse, Ate Wymenga, Gijs van Hellemondt, Petra Heesterbeek
Sint Maartenskliniek Nijmegen, the Netherlands
Introduction: Stable implant fixation of revision total knee arthroplasty (rTKA) can be challenging because of the reduced bone stock left for implantation. Generally, both femur and tibia components are cemented, while stems can be placed either cemented or press-fit (hybrid construct). This randomized controlled trial (RCT) focused on assessing the stability of rTKA with cemented or hybrid-constructs, using radiostereometric analysis (RSA). The mid-term results up until 6.5 years postoperatively showed no differences between the two groups. However, there were some implants showing micromotion >1 mm translation or 1° rotation. Therefore, this study investigated micromotion of cemented versus hybrid-placed rTKA 10 years postoperatively.
Material and method: Of the 32 original RCT patients, 19 (9 cemented, 10 hybrid-constructs) were available for long-term follow-up. New RSA images were taken at 10 years postoperatively. Micromotion of the femoral and tibial implants was assessed using model-based RSA software (RSAcore, Leiden, The Netherlands). Clinical results were evaluated using the Knee Society Score (KSS), VAS-pain and -satisfaction. Group differences for all outcomes were compared using Wilcoxon-Mann-Whitney tests.
Results: Preliminary results showed a median (IQR) total femoral translation and rotation at 10 years of 0.39 (0.44) mm and 0.59 (0.31)° for the cemented stems versus 0.72 (0.61) mm and 0.78 (0.71)° for the hybrid-construct. For the tibial components this was 0.38 (0.71) mm and 0.98 (1.12)° versus 0.44 (0.20) mm and 0.74 (0.32)°, respectively. None of these values were significantly different between the two groups. The clinical scores for the cemented and hybrid constructs showed no differences between the groups as well.
Interpretation and conclusion: These preliminary results suggest no difference in micromotion and clinical outcome between fully-cemented and hybrid-placed rTKAs and demonstrate good fixation at 10 years post-operatively, which builds on earlier short to mid-term results.
Keywords: Revision total knee arthroplasty, stem fixation, long-term follow-up, RCT
56
- Micromotion of a cemented hinged-type knee revision system – 1 year results with model-based RSA
Simon Nurettin van Laarhoven, M.E.M te Molder, A.B. Wymenga, G.G. van Hellemondt, P.J.C. Heesterbeek
Department of Orthopaedics, Sint Maartenskliniek, Nijmegen, The Netherlands
Introduction: Hinge knee implants are highly constrained prostheses used in cases in which adequate stability is mandatory. Due to the high constraint nature of the implant, multidirectional stresses are directed through the bone-cement-implant interface. This might be one of the reasons for the high rates of aseptic loosening. The goal of this study was to assess the micromotion of a fully cemented hinged implant by the use of radiostereometric analysis (RSA).
Materials and Methods: Twenty patients requiring a fully cemented Legion Hinge Knee System (Smith+Nephew, Memphis, USA) were included.RSA images were taken at baseline, 6 weeks, 3, 6, 12, and 24 months postoperatively. Micromotion of the femoral and tibial components referenced to the markers in the bone was assessed with model-based RSA software, using implant CAD-models (RSAcore, Leiden, The Netherlands). Maximal total point motion (MTPM), total translation (TT) and total rotation (TR) were calculated (median; interquartile range [IQR]).
Results: MTPM of the femoral component at 6 and 12 months was 0.80 [0.57]mm and 0.83 [0.55]mm and of the tibial component 0.33 [0.25]mm and 0.45 [0.66]mm. TT for the femoral component was 0.31 [0.45]mm and TR was 0.64 [0.48]° at 12 months. For the tibia component the TT was 0.22 [0.42]mm and the TR was 0.41 [0.51]°. So far, none of the implants have been revised. At the time of the conference, results of the 2 year follow-up will be available.
Interpretation and conclusion: World-wide this is the first RSA study on a (fully cemented) hinged-type revision TKA. It is important to know early and continuous migration of the components to predict later aseptic loosening and implant survival. So far, micromotion of both femur and tibia components seems to be stable between 6 and 12 months.
Keywords: Hinged-type Knee Revision System; revision total knee arthroplasty, cemented implant