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The effect of hydroxyapatite (HA) coating on the fixation of a cementless femoral stem is discussed, in particular in cases of primary fixation with geometrically stable components. Therefore, we performed a comparative retrospective study of a series of Alloclassic-SL™ stems to: 1) present the long-term results and 2) evaluate the contribution, if any, of proximal HA coating.
Long-term cementless press-fit (“flat wedge-shaped”) fixation is reliable and HA coating only improves the radiological results of the proximal bone-prosthesis interface.
Materials and Methods
One hundred and ninety-eight Alloclassic total hip arthroplasties were performed in 179 patients, mean age 66 years old (22–85), including 105 with proximal HA coating and 93 with the original grit-blast coating. One hundred and ninety-three hips were analyzed after a mean follow-up of 9.8 years (1–24 years).
Results were excellent or good in 184 hips (95%) with no significant difference between the 2 groups (Merle d’Aubigné≥16 for 89/92 (98%) without HA compared to 95/101 (94%) with HA P=0.59). Radiographic signs of stable osseointegration were observed in 173 hips (90% of the cases). HA coating significantly improved the radiographic results of the proximal bone-implant interface: (42/92 (46%) of the stems without HA had proximal radiolucencies in zones 1 and 7 compared to 4/101 (4%) with HA (P=0.0001)). Polyethylene wear>0.1 mm/year was observed in 6 hips (3%) including 1/101 (1%) in the group with HA versus 5/92 (5.4%) without HA (P=0.17). One intra-operative femoral fracture occurred and there were 9 dislocations in the first 3 postoperative months (4.5%). The main cause of revision surgery was recurrent dislocation (11/17 cases). The “revision per-100 observed-femoral component years” was 0.10 in both groups and survival for aseptic loosening of the stem was 100% (95% CI=73.2% to 100%) at 20 years.
This study shows that secondary fixation by osseointegration of a straight standard grit-blasted titanium alloy non-anatomical implant is reliable. Possible proximal fibrous encapsulation, which is reduced by HA coating, but especially conventional polyethylene wear, were the main limitations of this system.
Level of evidence
III retrospective case-control study.Le texte complet de cet article est disponible en PDF.
Keywords : Cementless stem, Alloclassic system, Total hip arthroplasty, Hydroxyapatite