[Our Experience with ICON Hip Resurfacing System]

PURPOSE OF THE STUDY Our study aimed to assess the mid-term outcomes and complications with the ICON hip resurfacing system and to carry out a detailed analysis of pitfalls and risks associated with pairing the bearing surfaces of metal-on-metal hip implants. MATERIAL AND METHODS A total of 52 hip joints were assessed in 43 patients who received the ICON hip resurfacing system at our department between 2009 and 2013. The cohort included 34 men and 9 women. Their age at the time of primary surgery ranged from 34 to 67 years, with the mean age of 51.8 years. The mean follow-up was 7.6 years. The evaluation focused on the position and osseointegration of both components, bone remodelling around the implant, and signs of potential aseptic loosening. The functional status of the hip was assessed by Harris Hip Score. RESULTS The primary stability of both components was always good, there were no femoral neck fractures reported in our cohort. All the acetabular components were stable, showing appropriate osseointegration, with no radiolucent zones or signs of osteolysis around them. There was not a single case of the femoral component stem being in a biomechanically disadvantageous varus position. In zone I and III according to Beaulé, cancellous bone osteolysis developed in two patients. The narrowing of the femoral neck below the end of the femoral component, compared to postoperative X-rays, achieved the mean value of 1.3% according to Grammatopolouse. The HHS increased from 64 to 95.5 points. An excellent outcome was observed in 48 joints, whereas the outcome of the remaining 4 joints was very good. The mean survival rate of the resurfacing hip implant calculated using the Kaplan-Meier analysis achieved 100%. The cobalt and chromium levels in the blood of patients did not exceed the reference physiological value. DISCUSSION The resurfacing system enables to preserve the bone tissue of the metaphysis and a part of the femoral head. The reduced mechanical endurance of the peripheral part of femoral components smaller in size caused by implant malposition resulted in fatal consequences in the ASR system. Greater range of motion conditioned by the design of the resurfacing system led to a mechanical wear, with a significant increase in the concentration of metal particles in the effective joint space. The elevated levels of cobalt and chromium ions in some patients induced delayed-type hypersensitivity with subsequent development of aseptic lymphocyte-dominated vasculitis associated lesions presented as peri-acetabular changes (pseudotumors to osteolysis) with subsequent failure of implant fixation. We have not observed this complication in the ICON system as yet. In patients suffering from hip pain after the resurfacing hip arthroplasty and simultaneous high chromium and cobalt blood levels, pelvic CT/MRI is indicated with reduction of artefacts around the metal material. Surgical treatment of soft tissue affections, bone defects and reimplantation using conventional or revisioncementless components is a possible treatment option. CONCLUSIONS The ideal patient indicated for hip resurfacing is a physically active man under 60 years of age (with a femoral head size of 54-60 mm), with primary or secondary osteoarthritis, no joint deformity, with a good quality bone tissue in the femoral neck and head region. As for the functional performance, the resurfacing system allows the patients a large range of motion with very good joint stability immediately after surgery. Despite that, the metal-on-metal tribological pairing must be approached with caution. The risk of developing lesions associated with ALVAL is unpredictable. In our cohort of patients with ICON hip resurfacing system, mostly excellent outcomes with minimum complications were reported provided the indication criteria and the correct surgical procedure had been complied with. Key words: hip resurfacing system, metal articulating surfaces, adverse reaction to metal particles, aseptic lymphocytedominated vasculitis associated lesions, pseudotumor.