There is ongoing debate on the benefits of fixed versus mobile bearing Unicompartmental Knee Replacement (UKR). We report the results from a randomised controlled trial comparing fixed and mobile bearing of the same UKR prosthesis. Forty patients were randomized to receive identical femoral components and either a fixed or mobile bearing tibial component. At 6.5 years follow-up 37% of the mobile bearing design had been revised and 14% for the fixed bearing design. The main reasons for revision were pain and loosening. These results were compared with data from The Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR) that show a cumulative percent revision of 24.2% for the mobile bearing Preservation UKR at 6.5 years. All locally explanted mobile bearings were examined microscopically, and 83% demonstrated significant backside wear. Constraint on the undersurface of the bearing coupled with a congruent upper surface may have contributed to the excessive revision rate. This is the first randomised controlled trial examining mobile and fixed variations of the same UKR prosthesis and shows this design of UKR with the mobile bearing has an unacceptably high revision rate and patients with this knee design should be closely monitored.

Aim

The aim of this study was to compare a single-incision minimally invasive (MI) posterior approach with a standard posterior approach in a double-blind prospective randomised controlled trial.

Introduction: Increased wear is associated with aseptic loosening and late dislocations. Hard on hard bearings may reduce wear but still have topics of concern such as free metal ions in metal on metal bearings and the risk for fracture in ceramic articulations. Ceramic heads against conventional polyethylene is also used with the intention to reduce wear. But this effect has not been conclusively documented in the literature and is still discussed. 87 patients were operated consecutively by the same surgeon with the same surgical technique. All patients received a cemented all poly cup sterilized with irradiation in inert atmosphere and a cemented stem. Head size was 28 mm in all patients. 40 patients received cobalt-chrome heads and 47 patients aluminiumoxid heads. The patients were followed with RSA for 10 years and analysed for wear.

Results: Mean (SEM) wear for the group with cobalt chrome heads was 0.93 mm (0.13) and for the group with aluminiumoxide was 0.43 mm (0.08) (p = 0.001).

Discussion: We found significantly less wear with aluminumoxide heads compared to cobalt-chrome heads. The wear results in the cobalt-chrome group correlate well to wear values in the literature for conventional polyethylene. Although the polyethylene in this study is partly cross-linked (3Mrad) it is not clear whether these results can be extrapolated directly to the use of highly cross-linked PE. If longer follow-ups confirm the mechanical stability of highly cross-linked PE, ceramic heads might contribute additionally to the reduction of wear.

In conclusion we found significantly reduced wear for aluminumoxide heads compared to cobalt chrome heads which could be beneficial for young and active patients.

Introduction: Treatment of dual compartment osteoarthritis remains controversial, with conjecture over whether Uni-Compartmental (‘UKA’) or Total Knee Arthroplasty (‘TKA’) is more appropriate for patients with patello-femoral disease. The ‘Journey Deuce’ 2/3 Knee Arthroplasty (‘2/3 Knee’) (Smith & Nephew) is a bi-cruciate retaining prosthesis designed to treat this subgroup of patients with both antero-medial and patello-femoral disease.

We have conducted a prospective, observational clinical trial of 34 patients with dual compartment osteoarthritis of the knee treated with a 2/3 Knee.

Aims: To assess the safety and clinical efficacy outcomes of the 2/3 Knee.

Method: All patients pre-op leg alignment films, as well as MRI or arthroscopy to confirm the inclusion criteria of dual compartment osteoarthritis with a preserved lateral compartment and intact cruciate ligaments. All operations were performed by a single surgeon (DW) using computer assisted surgery (CAS) and a minimally invasive technique (MIS) at a local university affiliated private hospital (HPH).

Exclusion criteria included obesity, inflammatory arthritis and a fixed flexion deformity > 10 degrees.

Subjective outcome measures included Oxford Knee Scores (OKS) and EQ-5D Scores. RSA beads were implanted at surgery to detect loosening, micro-motion and prosthesis wear. Gait analysis was conducted at 1 year post op in a subgroup of patients.

Results: Follow up ranged from 6 months to 2 years. There have been no early failures requiring complete revision. The first 23 knees (18 patients) did not have primary resurfacing of the patella. Some of these patients suffered palpable and audible patello-femoral crepitus, with a subgroup (17%, 4 knees-3 patients) having associated anterior knee pain. This subgroup had revision procedures to resurface their patellae with resolution of their symptoms. All subsequent patients have had primary patella resurfacing with no incidence of Significant crepitus or anterior knee pain.

The patients have recorded Significant improvement in their Oxford Knee Scores at 6 months (mean reduction all patients: 17.3, resurfaced 20).

Early RSA results have not detected Significant migration to indicate early loosening. Gait analysis has shown that patients return to approximate normal rather than pre-operative gait.

Conclusions: Although longer follow up is required the 2/3 Knee appears a safe and effective treatment option for patients with dual-compartment osteoarthritis; with rehabilitation, function and gait tending towards that seen in UKA rather than TKA.

It is essential that patients undergo primary patella resurfacing to prevent crepitus and associated anterior knee pain.

A study comparing clinical outcomes of 2/3 Knee vs TKA is underway at our institution.

We treated 34 patients with recurrent dislocation of the hip with a constrained acetabular component. Roentgen stereophotogrammetric analysis was performed to assess migration of the prosthesis.

The mean clinical follow-up was 3.0 years (2.2 to 4.8) and the radiological follow-up was 2.7 years (2.0 to 4.8). At the latest review six patients had died and none was lost to follow-up. There were four acetabular revisions, three for aseptic loosening and one for deep infection. Another acetabular component was radiologically loose with progressive radiolucent lines in all Gruen zones and was awaiting revision. The overall rate of aseptic loosening was 11.8% (4 of 34). Roentgen stereophotogrammetric analysis in the non-revised components confirmed migration of up to 1.06 mm of translation and 2.32° of rotation at 24 months. There was one case of dislocation and dissociation of the component in the same patient. Of the 34 patients, 33 (97.1%) had no further episodes of dislocation.

The constrained acetabular component reported in our study was effective in all but one patient with instability of the hip, but the rate of aseptic loosening was higher than has been reported previously and requires further investigation.

Introduction Primary and revision total hip surgery in the face of poor neuromuscular function, cognitive impairment or recurrent dislocation are fraught with complications. A useful option for such cases is the constrained acetabular component, or “captive cup”. We present the largest series reported to date, and use radiostereometric analysis (RSA) to assess cup migration.

Method Between February 1999 and September 2003 133 patients (141 hips) were identified as high risk of dislocation and were treated with a constrained acetabular component. One hundred and twenty cases were revision arthroplasties and 21 were primary replacements. Patients were assessed pre-operatively (WOMAC, Harris Hip Scores and SF-36). Defects were reconstructed with allograft (massive, morsellised or strut) where required. Most components were inserted into uncemented metal cups. Radiostereometric beads were inserted. Post-operatively patients were followed up regularly and clinical scores repeated. Radiostereometric analysis (RSA) was performed at 6 months, and then annually to assess prosthesis migration.

Results Mean follow-up was 3.1 years (range 1 – 5.6 years). At last review 26 patients had died, and 7 were lost to follow-up. There were 8 revisions for cup loosening. There were 5 dislocations and 2 dissociations in 6 patients. There was a statistically significant improvement in WOMAC and Harris Hip scores. RSA confirmed cup migration was greater than for non-captive cups, but was nevertheless minimal. Interestingly there was no statistically significant difference at 6, 12 and 24 months suggesting most migration occurs early on.

Conclusion Our results suggest the “captive cup” is an effective and safe option for the treatment of primary and revision arthroplasty in those at high risk of dislocation.

Introduction: Primary and revision total hip surgery in the face of poor neuromuscular function, cognitive impairment or recurrent dislocation are fraught with complications. A useful option for such cases is the constrained acetabular component, or “captive cup”. We present the largest series reported to date, and use radiostereometric analysis (RSA) to assess cup migration.

Method: Between February 1999 and September 2003 126 patients were identified as high risk of dislocation and were treated with a constrained acetabular component. One hundred and sixteen cases were revision arthroplasties and 10 were primary replacements. Patients were assessed pre-operatively (WOMAC, Harris Hip Scores and SF-36). Defects were reconstructed with allograft (massive, morsellised or strut) where required. All components were inserted into uncemented metal cups. Radiostereometric beads were inserted. Post-operatively patients were followed up regularly and clinical scores repeated. Radiostereometric analysis (RSA) was performed at 6 months, and then annually to assess prosthesis migration.

Results: Mean follow-up was 3.1 years (range 1 – 5.6 years). At last review 8 patients had died, and 2 were lost to follow-up. There were 7 revisions: 3 for infection, 2 for periprosthetic fractures, and 2 for aseptic loosening. There was one case of cup disassociation successfully treated with open reduction. There have been no further dislocations. There was a statistically significant improvement in WOMAC and Harris Hip scores. RSA confirmed cup migration was greater than for non-captive cups, but was nevertheless acceptable: 0.16mm medially, 0.47mm proximally, 0.16mm posteriorly. Interestingly there was no statistically significant difference at 6, 12 and 24 months suggesting most migration occurs early on.

Conclusion: Our results suggest the “captive cup” is an effective and safe option for the treatment of primary and revision arthroplasty in those at high risk of dislocation. RSA analysis confirms minimal prosthesis migration.

Introduction We believe minimally invasive surgery should be defined by the extent of soft tissue dissection rather than incision length. We describe a new technique that is truly soft-tissue sparing and report our early results.

The surgical approach The landmarks for the incision are identified and a 6–8cm oblique incision is made over the posterior aspect of the greater trochanter. Longer incisions are required in more difficult cases. Piriformis and the proximal insertion of gluteus maximus are preserved. After implant insertion, meticulous capsular repair is performed through drill holes into bone to reconstruct the posterior envelope. There are no restrictions to mobility. No specialised instruments are required.

Method The standard posterior approach (group 1) was compared with the PSMI approach (group 2) in a prospective cohort study of 200 consecutive patients over 60 years of age. In the standard approach the external rrotators were dettached. The capsule was repaired to bone, and the piriformis tendon reattached to the Gluteus Medius tendon. Routine restrictions to mobility were imposed. Patients were scored pre-operatively and followed up prospectively, by a blinded observer.

Results Demographics and functional scores were similar. Mean operation time was about 1 hour in both groups. Mean incision length was 21.5 cm (range 15 – 25) in group 1 and 8.4 cm (range 6 – 16) in group 2. Mean blood loss in group 1 was significantly higher than group 2 (P< 0.0001, 95%CI 191–547). Mean inpatient stay was 8.0 days in group 1, and 4.8 days in group 2 (P< 0.0001, 95%CI 3.4–6.0).

Minimum follow-up was 3 years in group 1 and 1.5 years in group 2. There were 3 dislocations in group 1, and none in group 2. There were 2 re-operations in both groups. The relative improvement in WOMAC scores was significantly greater in group 2 at 3 months and 1 year (P< 0.05).

Conclusion The PSMI approach to the hip is truly soft-tissue sparing. It is safe and relatively easy to perform. The stability and minimal morbidity allow early mobilisation. This is the first study to suggest the benefits of minimally invasive surgery may be prolonged. Cosmesis is a by-product rather than primary objective.

We carried out a blinded prospective randomised controlled trial comparing 2-octylcyanoacrylate (OCA), subcuticular suture (monocryl) and skin staples for skin closure following total hip and total knee arthroplasty. We included 102 hip replacements and 85 of the knee.

OCA was associated with less wound discharge in the first 24 hours for both the hip and the knee. However, with total knee replacement there was a trend for a more prolonged wound discharge with OCA. With total hip replacement there was no significant difference between the groups for either early or late complications. Closure of the wound with skin staples was significantly faster than with OCA or suture. There was no significant difference in the length of stay in hospital, Hollander wound evaluation score (cosmesis) or patient satisfaction between the groups at six weeks for either hips or knees.

We consider that skin staples are the skin closure of choice for both hip and knee replacements.

Introduction and Aims: A number of ‘minimally invasive’ approaches have been described which are essentially a standard approach through a smaller incision: the term ‘mini-incision’ is more appropriate. We describe a new technique that is truly soft-tissue sparing and report our early results.

Method: Following Malchau’s principles we performed cadaver studies to familiarise ourselves with the approach before conducting a pilot study. The approach involves a 6–8cm oblique incision over the posterior aspect of the greater trochanter. Care is taken to preserve piriformis and gluteus maximus. Meticulous capsular repair is performed through drill holes into bone at the end of the procedure to reconstruct the posterior envelope. There are no restrictions to mobility post-op.

Patients were scored pre-operatively and followed up prospectively. The only special instruments required are two large curved Hohmann retractors and an angled cup introducer.

Results: One hundred and one consecutive routine primary total hip replacements were performed via the ‘piriformis-sparing minimally invasive approach’ by a single surgeon. Marked on-table stability was noted in all hips prior to capsular repair.

Forty-two percent of patients were male. Mean age was 68.9 years (42–90) and BMI 26 (14–39). Average operation time was 64.1 minutes and anaesthetic time 92.5 minutes. Mean fall in haemoglobin in the first 24 hours was 2.3g/dl. Mean incision length was 7.4cm.

Follow-up was a minimum of one year (range 12–29 months). There was a highly statistically significant improvement in WOMAC and SF-36 scores at three and 12 months post-operatively (p< 0.0001). Early medical complications occurred in 12 patients, including two superficial infections, all of which resolved. There were no peri-prosthetic fractures and importantly, no dislocations. There were two re-operations: one revision for cup displacement and one washout for deep infection.

Conclusion: We believe that the marked stability that we achieve on-table is only possible by sparing piriformis and careful capsular repair. As with all new procedures however, there is a learning curve for both surgeon and assistant. Preliminary results from our pilot study may be interpreted with guarded optimism.

Introduction: Uncemented press fit cups function well in the medium term, but often seem to develop backside osteolysis in the long term. This study was done to compare migration and osteolysis for cups with different fixation to find out if augmentation is needed or more a risk factor.

Method: Eighty seven hips in 81 patients planned for a THA due to OA were randomised and operated with a Reflection cup inserted with under reaming and press fit. Group 1 had a porous coated cup without holes; group 2 had the same cup with additional HA coating. Group 3 had a porous coated cup with six holes and fixed with three screws; and group 4 an identical cup fixed with three pegs. Early cup stability, migration, osteolysis and function were followed over five years with RSA, x- rays and Harris hip score and the groups compared statistically.

Results: At five years the mean (SD) translation for all cups was 0.13 (0.28) mm proximally, 0.002 (0.41) mm medially, and 0.13 (0.42) mm anteriorly. The inclination increased 0.13 degrees (0.84 degrees), anteversion 0.13 degrees (0.84 degrees), and anterior tilt 0.15 degrees (0.92 degrees). There were no differences in migration between the four modes of fixation (p=0.053–0.9). An inducible displacement test of stability one week after operation showed only minor movements, below the detection limit for RSA and without group differences. Thirty-five cups had a central gap post-operatively, all disappeared within two years and did not imply either inferior fixation or radiolucencies. The HA-coated cups displayed less radiolucent lines (p=0.003) than the other groups when measured as percentage of the total interface. Most lucent lines were seen in zones 2 and 3 and developed during the initial two years. At five years, minor focal osteolytic lesions were found in 13 hips, most in cups with screws and all progressing slowly. The proximal wear was 1.02mm and the 3D wear 1.05 mm after five years, equal for the four modes of fixation and higher for young and male patients. Harris hip score was 96 at 5 and 93 at five years and equal for the groups.

Conclusion: In this study, screws and pegs did not add any stability to the already excellent fixation of cups but lead to less satisfactory interfaces. Since osteolysis is the main clinical problem and not stability, both facts suggest more cups should be used without holes, to minimise particle penetration and osteolysis.

Introduction and Aims: The Lateral Femoral Cutaneous Nerve is placed at risk of iatrogenic injury in the dual incision minimally invasive approach THA. A number of trials have indicated rates of injury up to 30%. This clinical and cadaver study examined the morphology of the nerve in 101 cadaver specimens and in 78 dual incision THA patients.

Method: One hundred and one lateral femoral cutaneous nerves of the thigh were dissected in fresh and formalin embalmed specimens. Dissection was limited to the anterior thigh and the branch pattern of the LFCN recorded. Dual incision patients were followed prospectively and examined with regard to LFCN paraesthesia.

Results: Despite the variability of the nerve, three basic morphologic patterns emerged. Approximately 55% had a major medial trunk and smaller lateral branch, 30% involved two distinct large branches and 15% had a trifurcation or other pattern.

In our clinical series, over 30% of patients experienced paraesthesia and some experienced a burning dysaesthesia in the distribution of the LFCN.

Conclusion: Iatrogenic injury to the LFCN is relatively common in the dual incision minimally invasive THA and patients must be informed of such a risk. Based on this study we have slightly modified our incision and approach.

Introduction and Aims: The use of ‘superglue’ (2-Octylcyanoacrylate) in wound closure is well established in other surgical specialties, but not described in orthopaedics. The aim was to compare superglue with staples and subcuticular suture in a prospective randomised trial.

Method: One hundred and fifty patients admitted for a primary total knee or hip replacement were randomised to receive either clips, continuous subcuticular suture (3.0 Monocryl) or ‘superglue’ for wound closure. All knee replacements were mobilised on the day of surgery with CPM and hip replacements on the first post-operative day. Patients’ wounds were assessed on day one and at six weeks by a blinded observer.

Results: There were 80 hips and 70 total knee replacements performed; 51 wounds were closed with clips, 50 with suture and 49 with superglue. Mean duration of skin closure was significantly shorter with staples, and superglue was significantly faster than suture. There was no significant difference in the complication rates between the groups, including infection, dehiscence or allergic reaction. There was significantly more ooze by day one from the wounds closed with clips than the other two groups. Significantly more of the wounds closed with glue had no strike-through on to the dressing, and were therefore deemed to be ‘sealed’. Patient satisfaction at six weeks was significantly higher with superglue and suture than staples. The suture and super-glue groups had higher median scores on the Hollander wound evaluation scale than staples, however the difference was not statistically significant. Surgeon satisfaction with technique was highest with superglue and staples (no significant difference between the groups), and significantly higher than with subcuticular suture.

Conclusion: Superglue is safe to use for skin closure in primary knee and hip arthroplasty. Although closure with staples is faster, superglue is associated with less wound ooze and better patient satisfaction. The cosmetic result with superglue is comparable to that of subcuticular sutures but has a better surgeon satisfaction score.

Introduction An approximation of normal knee kinematics after knee replacement may improve knee function and implant fixation and reduce wear of the prosthesis. This study describes the knee joint kinematics after unicondylar knee arthroplasty (UKA) in general, and compares the Miller-Glante (MG, fixed bearing) and Oxford (mobile bearing) implants in particular.

Methods Twenty-two knees in 17 patients (11 males, six females, mean age of 69.7 yrars) were randomized into MG (11 knees) or Oxford (11 knees). No clinical complications or signs of loosening were observed. At the one year follow-up, RSA (Radiosterometry) x-rays were taken by using two x-ray tubes positioned at knee level and exposing the knee simultaneously from the side. Four pairs of weight bearing x-ray were obtained at zero degrees, 30°, 60°, 90° of knee flexion, with zero as reference position. Tibial rotation, rollback, translation of tibia-femur contact point, and the bearing movement were analyzed using UmRSA software.

Results With the MG implant, the tibia internally rotated 3.0°, 3.0°, and 4.2° respectively at 30°, 60°, and 90° of flexion, while with the Oxford implant, the tibia internally rotated 4.3°, 7.6°, and 9.5° respectively at 30°, 60°, and 90°. No significant difference was found between the two groups (P> 0.05, Repeated-measures ANOVA). The medial femoral condyle moved backward (1.8 and 1.5 mm respectively in MG and Oxford) from zero degrees to 30° of flexion. At 60°, it moved anteriorly in both knees, in MG to 0.9 mm anteriorly and in Oxford to 0.6 mm posteriorly to the reference position. At 90° the condyle moved 4.2 mm (MG) and 0.7 mm (Oxford) anteriorly to the reference position. No significant difference between the groups (P> 0.05). The femur-tibia contact point in MG moved anteriorly 2.8, 5.1, and 3.9 mm, respectively at 30°, 60°, and 90° of flexion, whereas the contact point in Oxford moved posteriorly 2.6, 1.8, 2.4 mm respectively at 30°, 60°, and 90°. A significant difference was found between the groups (P=0.003). The bearing in the Oxford implant moved backward of 2.2, 2.0, and 0.9 mm respectively at 30°, 60°, and 90° of knee flexion.

Conclusions The in-vivo weight bearing 3D knee kinematics after UKA with fixed or mobile bearing was described. In MG the medial femoral condyle moved forward with knee flexion, whereas in Oxford it moved backward together with the bearing, which is closer to normal knee kinematics.

Introduction THR is a successful procedure with excellent long term results. With many patients requiring the procedure there is some advantage in rapid recovery and early discharge. This may require a change in the surgical approach and peri-operative management. We report the first series of a new minimally invasive surgical approach for THR.

Methods A two incision approach for THR has been developed after extensive cadaver tests. This consists of an anterior muscle splitting incision to insert the cup and a posterior incision for the stem insertion. The authors have undergone cadaver training and clinical surgery before embarking on clinical trials. Patients included in this study are those people awaiting THR who were selected for a cementless prothesis and who would benefit from early rehabilitation. Patients with previous surgery, hip dysplasia and significant obesity were excluded. An initial study group are presented with an average age of 59, average height 168 cms and average weight 71 kg.

Results Average length of stay was 3.7 days with an average operative time of 90 minutes. Average blood loss 505 mls with an average blood usage of 1.1 units. Early complications include lateral cutaneous nerve of thigh palsy (50% resolution at three months), two stable trochanter fractures, one infection and one anterior dislocation at eight weeks with a ceramic implant.

Conclusions The approach is technically difficult and initially time consuming. It does enable quicker mobilisation and appears to result in less need for analgesia post-operatively. We believe it is important to present the early results so the technique can be discussed and potential problems avoided. A randomised, prospective trial with clinical and RSA follow-up is underway.

Introduction Impaction grafting in revision hip arthroplasty has now been used with a number of cemented stem designs. Follow-up has been short/intermediate with variable results due to pronounced stem subsidence and incomplete cement mantles. This study investigated the performance of a cementless, HA-coated stem used with the impaction grafting technique.

Methods We performed revision hip arthroplasty on a series of 16 stems for mechanical loosening (majority type II) in 14 patients (mean age 64 years). An uncemented Anatomic® stem was inserted into a neomedullary canal of impacted fresh frozen allograft bone. Stem migration was assessed with RSA. Graft and host cortical bone remodeling were evaluated radiographically as was the quality of the impaction grafting and amount of radiographic bone ingrowth. Bone mineral density (BMD) was assessed with DEXA at two and 10 years. Harris Hip Score was recorded for clinical assessment.

Results At six months the stems had subsided 0.78 mm (−7.78 – 0.22). Thereafter, the majority stabilized (6 months vs. 12 years: p=0.3). The graft had a homogenous distribution proximally, but to a lesser extent distally. Remodeling of graft was frequently seen at two years, especially proximally. There were no signs of graft resorption and no change in BMD in any Gruen zone between two and 10 years (P=0.15 – 0.54). About one third of patients had evidence of cortical restitution. In most cases there were no radiolucencies at all between the HA-fiber mesh and the bone. Slight cortical erosion at the stem tip was observed in nine cases but none progressed after two years. These parameters (remodeling, ingrowth and radiolucencies) changed minimally between the two and 12 years. At two years, the Harris Hip (50 to 85) and pain scores (20 to 40) had increased (p = 0.001). Thereafter the scores remained stationary. One hip dislocated during the first year. Heterotopic ossification occurred in three cases. One case underwent two stage revision at 30 months for late infection. One fracture was detected post-operatively. This stem subsided 16.2 mm at two years requiring revision. One patient died due to unrelated causes. Early migration was seen. Radiographs suggest much of the graft was substituted with living bone with no deterioration between two and 12 years.

Conclusions Our findings are sufficiently encouraging to initiate trials of uncemented stems with extended HA coatings.

In relation to the conduct of this study, one or more of the authors is in receipt of a research grant from a non-commercial source.

The reported revision rate of total hip arthroplasties (THAs) due to wear and osteolysis is around 10% at 10 years. However, the actual rate is probably higher: the incidence of osteolysis is reported to be 10% to 45%. Apart from design improvements, improved or new materials and/or and combinations are important in reducing particle-induced osteolysis, especially in young and active patients.

Wear reduction of up to 40% after inert gas sterilisation of polyethylene (PE) has been demonstrated, both in vitro and in vivo. An effective means of providing further increases in wear resistance is to cross-link PE extensively. Early clinical results of non-melt-annealed PE at three years showed wear reduction of up to 85% compared to inert gas radiation-sterilised PE.

In hip joint simulator investigations, bearings with a ceramic ball-head articulating against a composite cup demonstrated wear rates similar to those of ceramic-ceramic bearings. The wear particles are benign. Clinical data collected over two years suggest no disadvantages compared to the standard articulation controls.

The wear resistance of alumina-alumina articulation has been enhanced. In-vitro investigation demonstrated that even with a cup inclination of 60° the wear rate is not increased. The effect of micro-separation of the artificial joint is also minimised. Several prospective multi-centre alumina-alumina studies have shown no additional complications with this articulation. However, alumina is a brittle material with an inherent risk of fracture. The addition of 25% zirconia to alumina (ZTA) in the manufacturing process improves its fracture resistance, increasing its strength by more than 50%, while maintaining its other properties. The wear properties of ZTA are even better than that of alumina, especially in micro-separation articulation mode.

Highly cross-linked and optimised PE and composite technology are promising concepts in address wear particle-induced osteolysis.

Introduction Wear particle induced osteolysis is regarded as the main reason for aseptic loosening of hip replacements. Crosslinked polyethylene show extremely low wear in lab studies and is routinely used today, though with very little clinical testing. We report wear, migration and function for uncemented cups with a crosslinked poly.

Methods Twelve hips in 12 patients with mean age of 70 years were operated with uncemented cups (Reflection), cemented stems and metal heads. Five Mrad cross linked liners annealed below melt temperature were used in all hips (XLPE, Smith & Nephew). Tantalum markers were inserted in liners and acetabular bone for RSA measurements and migration and wear measured over two years. The result was compared to matched controls from a study of 80 cups with the same implant and non cross linked poly, operated by the same surgeon. X-rays, WOMAC and Sf-36 were performed pre-operatively and at two years.

Results The mean proximal head penetration at two months was 0.09 mm. This was thought to be mainly due to the creep of the polyethylene and was equal to “normal” poly. At the one year follow-up the mean proximal wear had increased with 0.02 mm and at two years 0.03 mm. This compares with the 0.33 mm recorded for the old poly (p=0.001, Mann Whitney U test.). The cups migrated 0.2 mm proximally and showed a normal migration profile, comparable to the cups with non cross-linked poly. The accuracy of measuring proximal wear, in this study, was found to be 0.07 mm (95% CI). No differences in radiolucent lines or clinical scores were found.

Conclusions The first two years proximal wear was 0.03 mm compared to the 0.33 mm found for non crosslinked poly. This is a reduction with 90% which certainly looks promising.

Introduction Debonding at the cement-prosthesis interface leading to stem movement and abrasion, has been proposed as initiating events in aseptic loosening of cemented total hip arthroplasties. A polished tapered or an absolutely stable stem possibly minimises this risk. This study evaluated a cemented, precoated femoral stem for stable fixation.

Methods The study included 24 patients, mean age of 64 years (48 to 78) undergoing single total hip arthroplasty for osteoarthritis. All were treated with cemented Definition (Stryker) stems which are straight, chromium-cobalt, with an integrated proximal polymethylmethacrylate mantle. One surgeon using fourth generation cementation techniques performed all surgeries. UHMWPE cups and Zirconia heads were used. At the time of surgery, tantalum markers were inserted into the femur, cement and stem for Radiostereometric analysis (RSA) of migration. Measurements were performed at two, 12 and 24 months intervals. Standard radiographs and Harris Hip Scores were obtained post-operatively and at two years.

Results During the first two years post-operatively the stems were shown to be absolutely fixed within the cement mantle and the mantle itself stable with the femur. At two years the mean subsidence of the stem in relation to the femur was 0.00 mm (SD 0.1), while the cement mantle subsided 0.2 mm (SD 0.2) in relation to the femur. The femoral head mean rotation was 0.02 retroversion. Postoperative radiolucent lines of > 1 mm where present in a mean of 1.4% (0 to 5%) of the cement-bone interfaces. This remained unchanged at two years (0 to 3%). Stems were in average positioned 0.8 in varus (1.2 valgus to 4.0 varus). Harris Hip Scores improved from a mean of 46 (23 to 68) pre-operatively to 93 (57 to 100) at two years.

Conclusions This is the first stem where no migration could be detected during the first two years. These results so far indicate good long-term performance of this precoated stem.

Aims: To investigate the cup interface with different means of þxation. Methods: 83 patients (89 hips) (median age of 56 years) were operated with a uncemented hemispherical porous-coated cup made of titanium alloy (Reßection, Smith & Nephew¨) with pressþt technique. The patients were randomised to pressþt-only (PF), PF + Hydroxyapatite (PF+HA), PF + 3 screws (PF+S) and PF + 3 pegs (PF+P). The development of radiolucent lines in percentage of circumference was evaluated on x-ray þlms postoperative and at two years. Radiostereometry was used for migration and wear measurement. Results: All cups were stable after 2 years. The groups showed no signiþcant difference in migration. Radiolucencies were found in a mean of 20% of interface in PF+S, 14% in PF+P, 11% in PF and 0% in PF+HA (P = 0.005, Kruskall Wallis test). 5 focal osteolysis were found in PF+S, 1 in PF+HA and PF and none in PF+P (ns). 35 cups had a gap between the central part of the cup and acetabulum postoperatively (no differences between groups). After 2 years the gaps in the HA group had disappeared. Cup wear was highest for HA coated cups. Conclusions: Further studies are necessary to reveal whether the better implant bone interface will outweigh the risk for increased wear.