Hip simulator studies on MOM bearings have historically involved ‘custom’ cetabular cups. I.e. having neither beaded layers nor biological coatings.

The aim of this study was to investigate wear using such MOM bearings and evaluate the potential wear and evaluate the potential for error in the gravimetric assessment.

Six x 38 mm HC Co-Cr bearings were supplied (Global and IO International Orthopaedics). The cups were received in ‘off-the-shelf’ condition with a cast Co-Cr beaded/HA-coated backing. To remove the HA-coating, the cups were pre-soaked in lemon juice for 4 days (articular surfaces shielded). Custom plastic fixtures were machined to fit the beaded contours of the cups. Test duration was 5Mc inorbital hip simulator (Shore-Western). MOM wear was estimated from serum ion contamination. Serum samples were digested and assessed using ICP/MS (Weck Labs Inc, CA).

The majority of the HA-coating was removed from the cups after four days of soaking inlemon juice after 21 days of soaking all cup weights appeared atable (within 1 mg). Reflected-light microscopy (RLM) showed no descernible signs of HA and the total weight loss due to HA remval averaged∼400mg.

During hip simulator there was no visual evidence of lost or broken beads, 3rd body abrasion etc (Sa<30nm). Both gravimetric and metal ion analysis showed consistent wear trends for all MOM cups. The MOM with the highest wear (predicted by ion analysis) demonstrated 1.2 mm (3)/Mc)OWR) at 5Mc. In comparsion, gravimetric analysis predicted an OWR of 1.3 mm (3)Mc for the same MOM, a difference of only 8%. Soaking beaded-HA cups in lemon juice and BCS proved effective in removing the coating.

The beaded cups remained stable in weight during the wear study and caused little discrepancy in gravimetric analysis (8%).

The method described did not lead to breaking of beads, elevated 3rd-body abrasion, cup damage or distorted wear scars.

Ceramic-on-ceramic alumina bearings (ALX) have demonstrated low wear with minimal biological consequences for almost four decades. An alumina-zirconia composite (BIOLOX-DELTATM) was introduced in 2000 as an alternative ceramic. This contains well-distributed zirconia grains that can undergo some surface phase transformations from tetragonal to monoclinic. We analyzed 5 cases revised at 1–7 years to compare to our simulator wear studies. For the retrieved DELTA bearings, two important questions were

how much tetragonal to monoclinic transformation was there in the zirconia phase and

The retrieval cases were photographed and logged with respect to clinical and revision details. The DELTA balls varied from 22mm to 36mm diameters. These had been mated with liner inserts varying by UHMWPE, BIOLOX-FORTE and BIOLOX-DELTA materials. Bearing features were analyzed for roughness by white-light interferometry, for wear by SEM, for dimensions by CMM and for transfer layers by EDS technique. Surface transformations on DELTA retrievals were mapped by XRD. The four combinations of 36mm diameter BIOLOX-FORTE and BIOLOX-DELTA were studied in a hip simulator, which was run in ‘severe’ micro-separation test mode to 5 million cycles. Wear rates, wear stripes, bearing roughness and wear debris were compared to the retrieval data.

In two DELTA ball cases, there were conspicuous impingement signs, stripe wear and black metallic smears. It is to be noted that the metal transfer sites (EDS) appeared to be from the revision procedures. The retrieved balls run with alumina liners showed monoclinic phase peaking at 32% on the particular surface and internal bore. On the fracture surface of case 1, the monoclinic content had increased to 40%. Various surface roughness indices were assessed on the bearings. The polished articular surfaces averaged roughness (Sa) of the order 3 nm, representing extremely smooth surfaces. The main wear zone was only marginally rougher (5 nm). In contrast the stripe wear zones had roughness of the order 55–140 nm.

In the laboratory, the DELTA bearings provided a 3–6 fold wear reduction compared to FORTE controls. Roughness of stripes increased to maximum 113nm on controls. Roughness of wear stripes showed FORTE with the highest and DELTA with the lowest values. DELTA bearings also revealed much milder wear by SEM imaging. Phase transformations showed peaks at < 30% for both main wear zone and stripe wear sites. It is hypothesized that the concentration of monoclinic phase reached a certain level due to compression contraint imposed by the alumina matrix. With implant wear, additional tetragonal grains of zirconia are exposed and these will also transform to tetragonal. This consistency between laboratory and retrieval studies confirmed the stable nature of the bearings. The BIOLOX-DELTA combination provides optimal potential for a clinically relevant reduction in stripe wear.

Introduction: Architectural changes in the proximal femur after THA continue to be a problem. In an attempted, to reduce these changes some surgeon designers have advocated the concept of neck sparing stem designs.

To-date neck-sparing stems have been disappointing in their ability to maintain the calcar. A new approach was undertaken to improve load transfer and to create a tissue-sparing stem that would be simple in design, reproducible in technique and provide for fine-tuning joint mechanics while maintaining compressive loads to the calcar.

Methods: Review of previous published work was evaluated along with FEA modeling in creating a new approach to neck sparing stems for THA. The MSA^™ Stem is a simple curved stem with a unique lateral T-back designed for torsional stability, ease of preparation and insertion. The proximal design has a novel proximal conical shape designed to transfer compressive forces to the calcar.

A modular neck provides for fine-tuning joint mechanics.

Results: FEA modeling will be reviewed. Strain patterns for the MSA^™ stem demonstrated better patterns vs. long stems or the short Biodynamic stem.

Discussion: In theory neck retaining devices provide or:

Bone and Tissue sparring

We are encouraged and believe there are advantages in the concept of neck sparing stems. Clinical/surgical evaluation is now underway and will be reported on in the future.

From 1985 metal-on-metal (MOM) designs of resurfacing (RSA) and total hip arthroplasties (THR) have been available over a large diameter range (28–60mm). In-vitro studies indicated satisfactory low wear performance for all designs and diameters tested (wear = 0.1 to 7 mm3). While reports from many centers have been encouraging, some have reported adverse effects. We reviewed clinical and metal ion studies in large diameter retrievals and compared these to 28mm MOM cases. Patients with the latter THR ranged 36–76 years of age and were followed 9–11 years. Main finding in our revisions was osteolysis and pain. The 28mm ball was represented 86% of cases; 71% balls had stripe wear. For liners, 25% had circumferential stripe wear and impingement was evident in 64% cases. Seven cemented stems were recovered with impingement marks; 26 stems were undamaged and therefore not revised. Using the concept of ‘damage modes’ from McKellop, normal wear mode #1 was evident in only 14% of 28mm retrievals whereas incidence of ‘abnormal’ modes #2-4 approached 30% each. Thus the 28mm MOM appeared susceptible to impingement risks with CoCr liners. Summarizing MOM retrievals, damage modes 2–4 were most likely implicated in revisions. The performance of such ‘small diameter’ THRs will be contrasted to our large diameter THR and RSA experience. The questions to be reviewed include, how much of the reported MOM adversity was predictable and how much risk was due to

wear of small diameter MOM,

Ceramic-on-ceramic bearings (ALX: pure alumina) have been used for human hip joints for almost 40 years. However an alumina matrix composite with zirconia (AMC) was introduced in year 2000 as a high-strength ceramic with almost double the fatigue resistance (AMC = 80.5%ALZ and 18vol% ZrO2). However we have not found any retrieval studies reported for this new ceramic bearing.

Wear maps were generated on three retrieved AMC femoral heads (28 and 36mm diameters) using x-ray diffraction, roughness and SEM imaging techniques. The wear study ran a physiologically appropriate, micro-separation test on 36mm ceramic balls and liners (AMC/ALZ). Wear rates were determined for the four combinations of balls and cups (ALX:AMC) with mapping of main-wear and stripe-wear zones, surface-roughness and analysis of debris morphology. In addition, the zirconia transformation to monoclinic phase was studied in AMC bearings

The retrieval study showed for the first time the wear phenomena occurring on three retrieved AMC femoral heads (at 1, 3, 6 years). Two had been paired with alumina liners and one with a polyethylene liner. Case-1 featured a 36mm ball in an UHMWPE socket, case-2 was an intact 28mm AMC ball and case-3 had a fractured ball from an IDE study. Laser interferometry and SEM were used to image ceramic wear and x-ray diffraction for analysis of transformation in the zirconia phase. Main-wear zones, stripe-wear zones, metal contamination and sites of implant impingement were also characterized. Surface roughness and in-vivo aging were quantified for both non-worn and worn areas. The SEM studies showed well-preserved articular surfaces, some with faint parallel scratches still evident. The latter likely represented the manufacturer’s original polishing marks. Multiple stripe-wear sites were identified with roughness 25–65nm (Sa) whereas polished main-wear zones averaged very low at 2–3nm. Metal impingements sites stained black with transfer of titanium increased roughness up to 140nm. Mildly worn areas of case-2 AMC ball averaged 10% transformation in the zirconia phase (tetragonal to monoclinic). In the stripe-wear zones, the monoclinic phase increased to 30%. The taper-bore and fracture surfaces in case-3 averaged 30% to 40% monoclinic, respectively. The stripe-wear zones and black metal contamination on these retrieved 28mm balls were correlated to multiple impingement sites on the rim of the alumina liners and titanium shells.

The laboratory model produced stripe wear on the ceramic balls and liners. The AlX/AlX controls produced the highest run-in and steady-state wear rates at 6.3 and 2mm3/Mc respectively). In contrast, the AMC/AMC combination produced the lowest wear rates at 0.5 and 0.1 mm3/Mc, respectively). With hybrid ball:cup combinations (AlX:AMC; AMC:AlX) the wear rates were similar and showed a 3-fold reduction compared to controls. In hybrid pairings, the AMC ceramic wore preferentially more than its AlX counterpart, regardless if present as a ball or cup implant. Thus the AMC ball contributed 66% to AMC/AlX total wear whereas the ALZ ball contributed only 33% of the total AlZ/AMC wear.

This study appears to be the first documentation of wear in retrieved AMC bearing surfaces. In general, the AMC surfaces worn in-vivo corresponded well to our in-vitro wear model. The stripe-wear zones in AMC femoral heads had rougher surfaces and higher monoclinic transformation than the main-wear zone. Overall the AMC ceramic appeared more resistant to stripe-wear effects created by the micro-separation and impingement phenomena.

Introduction and Aims: There is good preliminary evidence that Bone Morphogenic Protein 7 (BMP-7) plays an integral role in fracture healing and metabolism of bone. It is not known, however, whether the implantation of an OP-1 device will enhance the rate of fracture healing in the presence of osteoporosis. The object of this study was to determine the effects of OP-1 on osteoporotic fracture healing in rats.

Method: An open fracture of the mid-shaft of the femur was created in 60, three months post-surgical ovarectomised female Sprague Dawley rats. Thirty rats had OP-1 device with CMC putty implanted into the fracture site and 30 rats had CMC putty implanted without OP-1. The fracture was stabilised with a 1.4mm K-wire. Muscle and skin closed. Ten rats from each group were sacrificed at three time points – 12, 20 and 31 days post-surgery, and bilateral femurs harvested. The fractured femurs were analysed by DEXA scanning, high-resolution radiography, cross-sectional area, biomechanical assessment and histology.

Results: There was a statistically significant acceleration of fracture healing with the use of OP-1 in DEXA, radiological, cross-sectional area and biomechanical analysis and a qualitative enhancement by histological analysis.

Conclusion: The results show that an OP-1 device can enhance fracture healing in the presence of osteoporosis in a rat.

Introduction Minimally invasive surgery (MIS) for THR may accelerate rehabilitation. The objectives of this study were to determine the effect of three surgical approaches (standard, mini [< 10 cm], Stryker two incision approach [MIS]) on length of stay, rehabilitation rates, clinical outcome, quality of life, patient safety, complications and implant position.

Methods Each surgeon completed six to eight documented cases using the MIS technique before commencing enrolment to eliminate any learning curve effect. Prior to enrolment patients were assessed for eligibility and provided signed informed consent. Patient demographics, medical histories and surgical details were collected. Post-operative rehabilitation was independently documented by a physiotherapist. Clinical evaluations (HHS) were collected pre-operatively, 10 days, six weeks, three months and one year. Patient outcomes (SF12/WOMAC) were collected pre-operatively and at one year. Radiological evaluations were completed at six weeks. CTs/x rays were subject to an independent review.

Results A sample size of 48 patients was determined based on the primary objective - length of stay. Enrolment commenced at the end of 2002 and these results are based on the first cohort of patients; based on current recruitment rates, the authors anticipate that the majority of patients will be enrolled by presentation time. Preliminary results show mean incision lengths (cm) of 3.5/5.8 for the two incision MIS compared to 8.8 and 13.5 for the mini and standard respectively. Mean duration of surgery (mins) was 79 (MIS), 62 (mini) and 42 (standard). The median time (hours:minutes) from end of surgery until the first episode of knee flexion > 45°, straight leg raise, active abduction, standing, out of/in to bed, stair climbing and walking > 20 metres was shortest for MIS compared to mini and standard surgical approaches. The maximum distance walked was greatest for the MIS group. The mean length of stay (days) was shortest for the MIS group, 2.5 compared to 4.7 (mini) and 3.7 (standard). Mean blood loss (cc) was greatest for the MIS group, 667 compared to 525 (mini) and 467 (standard). There were no intra/post-operative complications or blood transfusions.

Conclusion Results suggest accelerated rehabilitation, decreased hospital stay and increased surgery duration for the MIS group. There are no safety concerns, however the procedure is felt to be quite technically demanding requiring an appropriate level of training/experience. The authors believe this is the only controlled study of this nature currently being conducted internationally.

In relation to the conduct of this study, one or more of the authors has received, or is likely to receive direct material benefits.

Aim: To assess the clinical and radiological performance of metal-on-metal articulations in uncemented total hip arthroplasty.

Method: Between 1996 and 2000, 60 uncemented S-ROM (Johnson & Johnson) total hip arthroplasties were performed on 55 patients with arthritis. Fifty-one of the patients (56 hips) were available for follow-up. This involved clinical assessments including completion of a hip score for each patient, along with radiological examinations.

Results: Follow-up ranged from six months to four years, with an average of 18 months. The average hip score improved from an average of 32.3 to 75.3 (maximum 84, range 53 to 84) at the latest follow-up. The average pain score improved from an average of 9.9 to 41.7 (maximum 44). No patients required revision for loosening of either the femoral or acetabular components. Thus far, there has been no radiological evidence of acetabular loosening.

Conclusions: In the short-term, the clinical performance of metal-on-metal articulations is equivalent to metal-on-polyethylene. In this group of patients, there has been no radiological evidence of acetabular loosening thus far.

Introduction: Osteochondral mosaic plasty is gaining popularity as a treatment for isolated chondral defects in femoral condyles. Most systems use a metal punch to impact the osteochondral grafts in pre-drilled defects. Damage to the chondrocytes during impaction grafting is of concern and new methods are being sort to minimise this deleterious effect.

This study was designed to see if using a plastic punch instead of a metal punch reduces the extent of chondrocyte damage in osteochondral mosaic plasty.

Method: Ten fresh sheep knees were used to harvest thirty osteochondral plugs using the COR system. The opposite condyles were then prepared to receive the osteochondral grafts. Ten plugs were impacted using a metal punch and ten using a plastic punch. The ten remaining plugs were used as controls. The plugs were then recovered and incubated for 24 hours prior to being stained with MTT. The stained cartilage was then photographed using a digital macroscope.

Images were interpreted using a graphics analysis programme.

Results: There was no significant difference in the extent of chondrocyte damage between the two groups. However, the extent of chondrocyte damage in the impacted groups was significantly greater than the control group.

Conclusion: Impaction grafting clearly damages chondrocytes of the osteochondral plug. In our study using a plastic punch did not reduce the extent of chondrocyte damage during mosaic plasty.

Introduction: Osteochondral mosaicplasty is gaining popularity as a treatment for isolated chondral defects in femoral condyles. Most systems use a metal punch to impact the osteochondral grafts in pre-drilled defects. Damage to the chondrocytes during impaction grafting is of concern and new methods are being sort to minimise this deleterious effect. This study was designed to see if using a plastic punch instead of a metal punch reduces the extent of chondrocyte damage in osteochondral mosaic plasty.

Method: Ten fresh sheep knees were used to harvest 30 osteochondral plugs using the COR system. The opposite condyles were then prepared to receive the osteochondral grafts. Ten plugs were impacted using a metal punch and ten using a plastic punch. The ten remaining plugs were used as controls. The plugs were then recovered and incubated for 24 hours before being stained with MTT. The stained cartilage was then photographed using a digital macroscope. The images were interpreted using a graphics analysis programme.

Results: There was no significant difference in the extent of chondrocyte damage between the two groups. However the extent of chondrocyte damage in the impacted groups was significantly greater than the control group.

Conclusions: Impaction grafting clearly damaged the chondrocytes of the osteochondral plug. In our study using a plastic punch did not reduce the extent of chondrocyte damage during mosaicplasty.