Background

Hip resurfacing arthoplasty (HRA) showed promising early and mid-terms results at the beginning of the new millennium. Adverse local tissue reactions associated with metal debris considerably slowed down the implantation of HRA which use is now limited to a few specialized centers. The long term success of this procedure, however, is still largely unknown. This study aimed to provide the clinical results of a series of 400 consecutive HRA with a minimum follow-up of 20 years.

Introduction

Hip resurfacing arthroplasty (HRA) lost its popularity because of excessive wear of the ASR M/M design. Now that causes of wear have been identified, it remains an attractive treatment option for young patients because of its bone-conserving nature, the preservation of bone mineral density, a low dislocation rate, and its biomechanical precision.

It has been suggested that metal ion levels are indicative of in vivo bearing performance of metal-on-metal hip replacements. A cobalt or Chromium level of 7μg/L or higher is proposed to be indicative of a bearing malfunction and the need for clinical intervention. Component design, size, acetabular orientation, patient gender and activity level have been suggested as factors leading to accelerated wear and elevated metal ions. The contact patch to rim (CPR) distance is a calculation that describes the distance from the point where a theoretical joint reaction force intersects the cup to the acetabular rim for a patient in standing position, dependent on the coverage, size, and orientation of the acetabular component. It has been suggested that CPR distance determines the hip joint susceptibility to edge loading, and the risk for increased wear and high ion levels (Langton et al JBJS Br 91: 2009). This study examined the effects of patient activity, gender, and CPR distance on serum metal ion concentrations in a series of patients treated with one type of metal on metal hip resurfacing arthroplasty (MMHRA) performed by one surgeon.

182 patients (73 females and 109 males)with a unilateral Conserve Plus (WMT, TN USA) MMHRA and had who had provided blood for metal ion analysis data from December 2000 to June 2011 were retrospectively studied. Only measurements made more than 12 months after surgery were included in order to exclude hips that had yet to reach steady-state wear. For patients with multiple draws, the most recent qualifying draw was used. Activity level was assessed by the UCLA activity score. The mean age was 51.5 years (20.0 to 77.5 years). The mean follow-up time for the last blood draw was 70 months (range, 12 to 165). Serum cobalt (CoS) and chromium (CrS) levels were analyzed using inductively coupled plasma mass spectrometry in a specialized trace element lab. Using acetabular abduction and anteversion measured by EBRA, component size, and reported coverage angle of the acetabular component, the CPR distance was calculated as previously described. Multiple logistic regression was performed to identify significant relationships between high metal ion levels (7 μg/L or greater) and gender, activity and CPR distance.

The median CoS level for the entire cohort was 1.13 μg/L (range, 0.15 to 175.30), and the median CrS level was 1.49 μg/L (range, 0.06 to 88.70). The average CPR distance was 13.8 mm (range, 3.2 to 22.1). There was a significant association between low CPR values and CoS and CrS. There was a 37-fold increase in the risk of CoS >7μg/L (p=0.005) and 11-fold increase in the risk of CrS > 7μg/L (p=0.003) when CPR distance was 10 mm or less. No associations were shown for gender and UCLA activity scores.

CPR distance was found to be a reliable predictor of ion levels > 7μg/L and appears to be a useful indicator to evaluate the multi-factorial process of edge-loading and wear. Patients with a low CPR distance should be monitored for increased metal ion levels.

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.

Obtaining fixation in DDH with Surface arthroplasty (SA) with a two part polyethylene (PE ) socket was technically challenging. Although dislocation was rare there was a high loosening rate secondary to polyethylene wear. The purpose of this study was to evaluate the results of Conserve Plus metal-on-metal SA in Crowe class I and II Developmental Dysplasia of the Hip patients.

54 patients (59 hips), 72% females, average age43.7 years (15 to 63.8) met these inclusion creteria with 2 years of follow-up minimum. Seven hips were Crowe type II and fifty-two were type I.

Harlan C. Amstutz, John Antoniades, Michel J. Le Duff, Paul E. Beaulé

The results of MMSA are much improved over those of prior generations of SA and socket fixation is stable even in Crowe type II with the porous coated acetabular components without adjuvant fixation despite incomplete acetabular coverage of the socket. The hips have-been stable even with important range of motion. Recent short term failure and radiolucencies have been eliminated by improved technique despite a high incidence of femoral cysts and reduced area of fixation.

The purpose of the present study was to identify risk factors for femoral loosening and neck fracture for Conserve+ metal-on-metal hybrid surface atrhroplasty.

The first 500 hips (of over 700 implanted by the senior author) in 436 patients were reviewed. Mean age was 48.6 with 74% of males patients.

16 hips were converted to THR secondary to aseptic failure on the femoral side (11 femoral component loosenings and 5 femoral neck fractures). 14 hips showed radiolucencies around the short metaphyseal stem at last follow-up. A retrieval analysis was performed and analyzed specimens compared with the intra operative photos of the prepared femoral head and the post-op X-rays. The cause of neck fractures is multifactorial. Risk factors include: uncovered reamed bone, leaving the component proud, notching the neck, impingement, osteopenia and cysts, and trauma. Avoidance of technical deficiencies and proper patient selection can eliminate neck fractures. Loosening is also multifactorial. Risk factors for loosening 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.

Meticulous initial preparation of the femoral bone surfaces, drying with suctioning, and maximizing the fixation area are critical when the fixation area is small, especially with osteopenia and cystic degeneration. These techniques have dramatically diminished the incidence of loosening and radiolucencies. Cementing the femoral metaphyseal stem is a meaningful technical improvement towards the prevention of early femoral failure in patients with risk factors.

The purpose of this study was to review our entire primary THR experience using large diameter femoral heads in order to prevent dislocation.

83 hips in 77 patients (average age 61years) had a total hip replacement using femoral heads at least 36 mm in diameter. Average follow-up was 4.4 years (range 1 to 17). 22% of the bearings used were conventional UHMWPE, 25% Metal on Metal (two thirds of which were one-piece sockets), and 53% cross-linked polyethylene.

UCLA hip scores improved significantly (p< 0.001) to 9.4, 8.4, 7.5, and 5.2, for pain, walking, function and activity respectively. All of the hips were stable at last follow-up although 3 hips had to be revised: 2 for instability in the early post-op period for poorly positioned socket and one for acetabular component aseptic loosening, which was rectified by revision surgery. Two out of these 3 hips had an etiology of DDH. The dislocations occurred in hips reconstructed with a head size less of 36mm only and none of the hips that dislocated had to be revised with a constrained acetabular liner.

As the safety of new wear-resistant joint bearings has improved, an increase of femoral head size leads to a lower prevalence of dislocation in THR potentially without adverse wear consequences. However, adequate positioning of the acetabular component remains a key factor in the success of this type of hip arthroplasty. Metal-on-metal, which provides the largest ball size for a given socket diameter, especially with a one-piece socket, best addresses component-to-component impingement by increasing the range of motion. Bone-to-bone impingement risks are also minimized as the travel distance to dislocation is increased by maximizing the head diameter and minimizing the socket shell thickness.

Aims: Review short to medium term results of a metal-on-metal (M/M) hybrid surface arthroplasty (SA) for a young and active patient population. Methods: The þrst 400 hips (of 533) in 355 patients underwent M/M hybrid surface arthroplasty. Mean age 48.2; 73% males, 27% females; 198 Charnley Class A; 139 Class B and 18 Class C. Diagnosis at surgery: OA 64%, DDH 11%, ON 9%, Post-traumatic 8%, Inßammatory arthritis 3%, SCFE and LCP 4%, Melorheostosis 0.3%. Results: Mean follow-up 3.9 years (2.6–6.5). Average UCLA hip scores post-op: pain 9.4, walking 9.5, function 9.4, and activity 7.7. The SF-12 physical and mental components were respectively, 31.2 and 46.8 pre-op and 50.1 and 53.0 post-op. 12 hips were converted to THA (8 in the þrst 102): 2 neck fractures, 7 femoral loosenings, 1 socket protrusio due to over-reaming, 1 subluxation due to impingement and 1 sepsis. Conclusions: Clinical results are excellent despite very high activity levels. The experience with SA of all cemented metal/UHMWPE bearing demonstrated failure rates of 15%–33% at 3 years. At longer follow-up, the preliminary experience is encouraging (3% failure rate). Dislocation is rare, and acetab-ular þxation secure. Initial femoral þxation is critical as the þxation area is small, especially with osteopenia and cystic degeneration. The percent of complications and potentially adverse radiographic changes was much greater in the þrst 100 cases, during the time of development of instrumentation, technique, and bearing optimization.

Aims: To review the medium term clinical and X-Ray results of DDH in SA, using the Conserve Plusª. Methods: 28 hips (26 patients, avg. age 43.2 years) with DDH were treated with hybrid MMSA. 81% were female. 42% had prior osteotomies. 25% had acetabular cysts that were grafted and 64% had femoral cysts (> 1cm in size) & 1 was grafted. A posterior approach was used in all but one case. Results: Mean F/U was 4.1 years (3.3– 6.5). UCLA hip scores were 3.3, 6.0, 5.7 and 4.5 pre-op and 9.2, 9.3, 9.3 and 7.1 at last F/U for pain, walking, function and activity. SF-12 scores normalized. Range of motion was 121.3û, 73.7û and 83.7û at last F/U for Flexion, abductionadduction, and rotation arcs. 2 hips were converted to THA: 1 for femoral neck fracture at 2 months (neck osteopenia and cystic degeneration) and 1 for recurrent subluxations due to poor offset and impingement due to prior multiple osteotomies. 4 technical complications successfully resolved: 1 trochanteric non-union, 1 post-op dislocation (closed reduction), 1 component mismatch (acetabular component exchange) and 1 femoral nerve palsy. X-ray analysis: 2 pts. presented complete radiolucencies around the metaphyseal stem and 1 patient was symptomatic and will require revision). Conclusions: SA is stable, except for 1 subluxation due to impingement with poor off-set compared to 7–10% with THA. The socket þxation is secure with grafts incorporating whereas prior SA with PE were poor due primarily to socket loosening. Femoral bone preparation is critical to avoid fractures and loosening.

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.

Aims: To review the results and clinical performance of the Anthropometric Total Hip (ATH) with line to line broaching. Methods: 70 press þt titaniumalloy double-wedge taper (136 to 213 mm [mean, 187 mm]) extensively coated grit-blasted (RA=12.0μ) stem prostheses were implanted in 67 patients. There were 29 primary THA, 33 conversions of surface replacements, 6 revision THA and 2 conversions of Hemi-Surface Replacements. The mean age was 55.8 years (range, 20 to 77 years). There were 34 males and 33 females (3 bilateral). The initial etiology was OA (50%), ON (11%), DDH (23%), Post- Trauma (4%), SCFE (2%), Rheumatoid (2%), and Ç other È (8%).Results: The mean follow-up time was 4.7 years (Range: 2–8). UCLA hip scores improved for Pain, Walking, Function, and Activity from 4.8, 6.0, 5.5, and 4.5 pre-operatively to 9.2, 8.3, 7.9, and 5.9 post-operatively. ROM was also comparable to cemented THA results. There were no intra operative fractures. One patient had a bicycling accident, fractured his femoral shaft which healed without surgery. Solid biologic þxation (Ç osseointegration È) was achieved in 100% with the grit-blasted stem. Conclusions: This early investigation shows excellent clinical results, and none of the patients reported any thigh pain. Intra-operative fractures were eliminated with line to line broaching. Our results demonstrate that thigh pain with cementless THA can be essentially eliminated with a titanium-alloy stem and a gentle double-wedge taper geometry. Extensive Ç osseointegration È suggests potential for long term durability.