The Conserve® Plus (Wright Medical Technology Inc., Arlington, TN) was introduced clinically in the United States in 1996. A study of the serum cobalt and chromium ion levels was started in 2000 in our center to monitor the metal ion levels over time as part of an FDA clinical trial.

Thirteen male and five female patients received this resurfacing for idiopathic osteoarthritis (14), post-traumatic degenerative changes (3) or developmental dysplasia (1). Fourteen received a unilateral implant but four subsequently received a contralateral device from 52 to 86 months post-op. Four patients had bilateral resurfacings done in a one-stage procedure. All surgeries were performed by the senior author. None of these patients had known exposure to cobalt or chromium, kidney disease or other metal implants elsewhere in their bodies. Each prospectively provided blood samples and then yearly thereafter to measure cobalt and chromium levels for up to 11 years. Metal levels were measured using atomic absorption spectrophotometry and inductively coupled plasma mass spectrometry by a specialized trace element analysis laboratory. Acetabular component position was evaluated using Einzel-Bild-Röentgen-Analysis (EBRA) software. Contact patch to rim (CPR) distance was computed as described by Langton et al JBJS Br 91: 2009. A mixed model linear regression analysis was performed to evaluate long term trends, and multivariate analysis was performed to examine effects of implant and patient covariates on the metal ion levels.

One bilateral patient underwent revision for femoral loosening, all other patients were clinically well-functioning at the time of last follow-up (ave 89 mos). The median pre-operative Co was below the detection limit (d.l) of 0.3μg/L and the median pre-operative Cr was 0.069μg/L (d.l. 03μg/L). Metal levels increased within the first year then decreased and stabilized (fig 1). For unilaterals over all time intervals, the median Co was 1.06 μg/L, while the median Cr was 1.58 μg/L. For bilaterals, the mean post-operative Co was 2.80 μg/L, while the mean Cr was 5.80 μg/L. Generally, Cr levels were higher at all time points than Co. Bilateral patients had Co values 1.96 times greater on average than the unilateral patients (p<0.001). None of the possible covariates studied (femoral size, cup abduction angle, cup anteversion, CPR distance, activity, BMI and testing method) were related to the assay values.

The results of this study have shown that serum metal levels in well functioning implants can be low and do not increase over time. These are among the lowest levels reported for resurfacing devices and comparable to levels reported for well functioning small diameter metal-on-metal total hips. The study is limited due to the relatively small sample size and limited range of values for the covariates studied. However, it included patients who were active, female or bilateral and we collected ion levels up to 11 years. We now recommend that patients who have well-oriented Conserve Plus components with stable radiographic interfaces and no incidences of unexplained pain or hip noises be scheduled for follow-up every 2–3 years, rather than annually.

The purpose of the present study was to analyze the-clinical and radiographic factors which determine the enduring fixation of metal on metal hybrid surface arthroplasty.

The first 500 hips (in 436 patients) of a consecutive series of over 700 Conserve® plus were reviewed clinically and radiographically. The patients were 48.6 years-old in average, 74% were male and the dominant etiology was idiopathic osteoarthritis (64.6%). All femoral components were cemented but the femoral metaphyseal stem was cemented in 112 hips and press-fit in the remaining 388.

Average follow-up was 4.8 years (range, 2.7 to 7.8 years). Eighteen hips were converted to a THR, 11 of them for aseptic loosening of the femoral component at an average follow-up of 40.5 months. Put in positives mention fx and loose incidence, survor ship details of loose and fx for other At last review, 14 hips presented metaphyseal stem radiolucencies and 16 hips (3.2%) showed a narrowing of the neck of 10% or more at the interface with the femoral component. None of the components with cemented stems showed femoral radiolucencies, neck narrowing, or were revised for aseptic loosening. Cementing the femoral stem significantly (p = 0.013) reduces the chances of early femoral failure or appearance of a metaphyseal stem radiolucency.

Risk factors for loosening or radioluciences included cysts > 1 cm, small femoral head size, female gender, early cases (before improved acrylic fixation including femoral suctioning measures were instituted) and reduced stem shaft angle. Metal-on-metal surface arthroplasty provides a stable, bone conserving, low morbidity and wear resistant prosthetic solution well suited for young and highly active patients.

Because the femoral head/neck junction is preserved in hip resurfacing, patients may be at greater risk of impingement, leading to abnormal wear patterns and pain. We assessed femoral head/neck offset in 63 hips undergoing metal-on-metal hip resurfacing and in 56 hips presenting with non-arthritic pain secondary to femoroacetabular impingement. Most hips undergoing resurfacing (57%; 36) had an offset ratio ≤ 0.15 pre-operatively and required greater correction of offset at operation than the rest of the group. In the non-arthritic hips the mean offset ratio was 0.137 (0.04 to 0.23), with the offset ratio correlating negatively to an increasing α angle. An offset ratio ≤ 0.15 had a 9.5-fold increased relative risk of having an α angle ≥ 50.5°. Most hips undergoing resurfacing have an abnormal femoral head/neck offset, which is best assessed in the sagittal plane.

Aims: The purpose of this study was to determine the success of retaining a well-þxed acetabular component at the time of isolated femoral revision and identify variables that may inßuence clinical decision making and outcome. Methods: 83 consecutive patients (90 hips) with a retained cementless socket during revision of a femoral component were reviewed. Eighty-þve percent of the hips were initially reconstructed as metal on polyethylene surface arthroplasty (SA) and 15% as a standard stem type total hip replacement (THR). Average age at the time of revision was 54. 33% of the patients had acetabular osteolysis of which 52% were grafted. Results: Mean follow up 9.6 years (5.5 to 15.9). Average time in situ of socket 14.8 years (7.1 to 20.2). 5 sockets were revised at a mean of 6.8 (2.5–10.4) years post revision and 13.1 years in situ. Reasons for socket revision were: 1 socket loosening, 1 dissociation of the liner cemented into the original socket, 1 instability, 1 conversion to a Metal/Metal bearing and 1 because it was the surgeonñs preference to remove the well-þxed socket. Dislocation rate was 15% with 50% occurring in the þrst 6 months post revision. Nine had more than one episode of dislocation. No recurrence or expansion of pelvic osteolysis was observed at last follow-up. Discussion: Revision of a cementless socket on the basis of the duration in vivo and/or presence of osteolysis does not appear to be warranted. Because of the high risk of dislocation off set liners/stems and larger femoral head sizes should be considered, especially in revision of SA.