Purpose: Better clinical outcome is generally reported after hip resurfacing when compared to conventional 28mmTHA. This may simply be the consequences of biased patient selection, patient perception or the advantageous use of larger diameter femoral heads in HR. The true clinical benefits of HR can only be assessed by comparison with LDH-THA in a blinded randomized study to eliminate/reduce those biases. This was the aim of the study.

Method: Charnley class A patients were randomized between HR or LDH-THA and kept blinded for one year. Clinical data, gait analysis, postural balance evaluations and functional tests were performed pre-operatively at 3, 6, 12 and 24 months postoperatively. Fourteen normal patients served as controls.

Results: Twenty-four patients were assigned to each group. There was no significant difference in WOMAC, SF-36, activity scores, and patient satisfaction. A slight advantage was observed for HR during the functional reach test (postural balance) and for LDH-THA during the step test (speed, strength and balance), all other tests showing no differences. Both groups quickly reached controls value for all tests by 3 months.

Conclusion: We have failed to demonstrate a clear difference in outcome between HR and LDH-THA. Both groups fully recovered quickly. The postulated clinical advantages of HR over 28mmTHA most likely result from using a larger head in highly motivated patients. The only clear advantage of HR over LDH-THA remains proximal femoral bone conservation, although with the excellent durability of currently used femoral stems, HR has to demonstrate comparable survivorship before bone conservation is considered a true benefit.

Purpose: The goal of this study is to compare patients’ perception of their hip or knee joint following joint replacement surgery.

Method: A total of 357 patients who underwent hip or knee joint surgery were included in the study. Of the patients who had knee replacement surgery, 46 had unicompartmental knee replacement (UKR) and 119 had total knee replacement (TKR). In the group of patients who had hip replacement surgery, 98 underwent hip resurfacing (SRA) and 97 had total hip replacements (THR). The perception patients had of their replaced articulation as well as functional outcome scores such as the WOMAC and SF-36 were measured at one year post-surgery and compared between the four groups.

Results: Although global satisfaction and clinical outcome scores were excellent in all four groups, WOMAC scores at 1–2 year follow-up were significantly different between hip or knee replacement surgery (p< 0.0001). Also, the perception that patients had of their reconstructed joint was significantly different between the hip and knee groups (p< 0.001). Half of patients from the hip group considered their replaced hip “as a natural joint” and 76% considered their joint as having no functional limitations compared to only 19% and 39% respectively for the knee group. Of patients with knee joint surgery, 14% (20/165) considered their joint as “artificial with important limitations” as opposed to only 1% (2/195) of those who had hip joint surgery. There were no significant differences in Womac scores or perception when comparing TKR and UKR or THR and SRA patients. Perception was strongly correlated to Womac scores for all four groups (R²=0.951).

Conclusion: Hip and knee joint replacement surgery are recognized as highly effective medical interventions in terms of cost/benefit ratio in current medical practice. It is remarkable to see that replacement of each of these articulations can yield vastly different results in terms of patient function, perception and satisfaction. From this study, it is clear that research in prosthetic development and surgical techniques should be focused on the interventions such as knee joint replacement, which are not yet capable of offering both a high level of function and satisfaction to patients.

Introduction: Metal on metal hip replacement using large diameter bearings can be used as part of a hip resurfacing (HR) system or with a large diameter head total hip arthroplasty (LDH-THA). Both types of implant release metal ion, but the amount of ion released after LDH-THA has not been studied. The aim of the present study was to assess whole blood metal ion release at one year following LDH-THA.

Material and Method: Pre and post operative Cr, Co and Ti concentrations in whole blood were measured using a high resolution mass spectrometer (HR-ICP-MS) in 29 patients with LDH-THA (Durom LDH, Zimmer). The results were compared to published ion levels on a HR system (Durom, Zimmer) possessing the same tribological characteristics, the only differences being the presence of a modular sleeve and opened femoral head design in LDH-THA.

Summary of results: Post operative Cr, Co and Ti mean levels of LDH-THA were 1.3, 2.0 and 2.8 μg/L at 6 months and 1.3, 2.2 and 2.7 μg/L at 12 months. In the LDH-THA, the opened femoral head design showed significantly higher Co ion concentrations than the closed femoral head design (3.0 vs 1.8 ug/L, p=0.037). Compared to previously published results after HR, Co levels were significantly higher at one year in the LDH THA (2.2 ug/L vs. 0.7 ug/L, p< 0.001).

Discussion: In order to reduce wear and ion release from metal-metal bearing, most manufacturers focus research on improvements at the bearing surfaces. This study has demonstrated that the addition of a sleeve with modular junctions and an open femoral head design of LDH-THA causes more Co release than bearing surface wear (157% and 67% respectively). Even if no pathological metal ion threshold level has been determined, efforts should be made to minimize their release. We recommend modification or abandonment of the modular junction and femoral head closed design for this specific LDH-THA system. The total amount of ion released from a metal-metal implant should be considered globally and newer implant design should be scientifically evaluated before their widespread clinical use.

Background: Acetabular implant revision with large bone defects, can be challenging. One of the reconstruction options is a “jumbo cup” (outer diameter ≥62mm in women and ≥66mm in men). We hypothesized that cementless jumbo cups is a reliable technique to reconstruct hip joint with satisfying radiological and clinical outcomes.

Material and Methods: Fifty-two consecutive acetabular revisions arthroplasty where a cementless jumbo cup was used were assessed. Clinical outcomes were assessed by Harris Hip Score (HHS), WOMAC index and SF-12. Hip centre was assessed on anteroposterior (AP) view according to Pierchon’s criteria. The reconstructed hip center was considered as satisfying when its location was located from −10 to + 10 mm proximally (y axis) and/or medially (x axis) in comparison with ideal theoretical hip center location. Cup migration and modification of abduction angle were considered as significant when there were respectively ≥5mm and to ≥5° in comparison with the immediate postoperative AP view.

Results: Mean component size was 67.6 mm (min 62, max 81). According to Paprosky classification, there were 5 cases of type 1, 11 type 2A, 12 type 2B, 11 type 2C, 11 type 3A and 2 type 3B. Cancelous bone chips allograft were used in 34 cases and bulk bone allograft in 14. Immediate postoperative AP view showed a mean abduction cup angle of 41.3° (26–53), a satisfying hip centre positioning in 78% on x axis and in 70 % on y axis. In the remaining cases, we noted an improved implant positioning. For the patients with intact contra-lateral hip (n=29), we noted, in comparison with normal side, a mean lateralisation of the hip center of 3 mm (−10 – +16) and a mean ascension of 7 mm (−10 – +33) associated with an average limb length discrepancy of – 4 mm (−19 – +9). At the last follow up [radiological data: 79 months (24–236) and clinical data: 88 months (27–241)], 6 patients were died and 3 were lost of follow up. The mean HHS was 82% (15–100), WOMAC 86% (27–100), SF-12 46 (14–61) and 53 (15–63). Bone graft integration was completed in all but 3 cases. Significant cup migration (≥5mm) occurred in only one case. The complications were: dislocation in 5 cases (4 revisions with constrained liner), infection in 4 cases (2 treated conservatively and 2 revised in 2 times procedure) and Brooker’s type III or IV ectopic ossifications in 11 cases. No case required revision for aseptic loosening.

Discussion: Jumbo cups appear as a reliable procedure to manage bone loss in acetabular revision. The complication rate is comparable with other reconstruction procedures (massive allograft, reinforcement rings, high hip center…). Cementless fixation and satisfying hip center restoration promote respectively the bone integration and allow an optimal biomechanical joint functioning. These are the main conditions for high long term survival rate.

Introduction: Better clinical outcome is generally reported after hip resurfacing when compared to conventional 28mmTHA. This may simply be the consequences of biased patient selection, patient perception or the advantageous use of larger diameter femoral heads in HR. The true clinical benefits of HR can only be assessed by comparison with LDH-THA in a blinded randomized study to eliminate/reduce those biases. This was the aim of the study.

Materials and Methods: Charnley class A patients were randomized between HR or LDH-THA and kept blinded for one year. Clinical data, gait analysis, postural balance evaluations and functional tests were performed preoperatively, at 3, 6, 12 and 24 months postoperatively. 14 normal patients served as controls.

Results: 24 patients were assigned to each group. There was no significant difference in WOMAC, SF-36, activity scores, and patient satisfaction. A slight advantage was observed for HR during the functional reach test (postural balance) and for LDH-THA during the step test (speed, strength and balance), all other tests showing no differences. Both groups quickly reached controls value for all tests by 3 months.

Discussion: We have failed to demonstrate a clear difference in outcome between HR and LDH-THA. Both groups fully recovered quickly. The postulated clinical advantages of HR over 28mmTHA most likely result from using a larger head in highly motivated patients. The only clear advantage of HR over LDH-THA remains proximal femoral bone conservation, although with the excellent durability of currently used femoral stems, HR has to demonstrate comparable survivorship before bone conservation is considered a true benefit.

Background: Moore et al. recently described five radiological signs (absence of radiolucent line, zone 2 osteo-penia, superolateral buttress, inferomedial buttress and radial trabeculae) for predicting osseointegration of porous coated uncemented acetabular components in the long term. The positive predictive value for a stable fixation was 96.9% when three or more signs were present. 83% of the cups with one or no signs were unstable.

Aim: To evaluate the prevalence of these signs in clinically well functioning uncemented acetabular components in the short term and to evaluate whether there is a difference acetabular components with different modulus of elasticity.

Materials and methods: The preoperative, immediate postoperative and the latest (minimum 2 years) radiographs of 196 hip replacements with 2 different acetabular components: a 2.9 mm, thin, flexible, macro textured titanium component (Allofit, Zimmer) and a 4 mm thick, stiff, titanium plasma sprayed chrome-cobalt component (Durom, Zimmer) were reviewed by two independent observers searching for the five osseointegration signs. The observers also looked for conventional signs of loosening including: continuous radiolucency of more than 2 mm, component migration of more than 3 mm, component rotation, or the presence of broken screws.

Results: 95 Allofit components and 101 Durom components were available for evaluation. None of the hips were considered loose according to conventional criteria and were well functioning. Out of the new osseointegration signs, at least one sign was present in 100 % of the cases, two signs or more in 30%, three signs or more in 5% and four signs in 1%. There was no difference between the two types of cups. In addition, superolateral buttress and zone 2 osteopenia were also present in preoperative/immediate postoperative radiographs in 8% and 4% of respectively.

Conclusion: Apart from absence of radiolucency, very few of the five osseointegration signs were present at short term follow-up of two very different well functioning uncemented acetabular components designs. We conclude they are not useful in evaluation of unce-mented acetabular components at a follow up of 2–5 years. Further study at mid-term follow-up might reveal whether the bony adaptive changes occur with time.

Purpose: The aim of our study was to compare the precision and effectiveness of a CT-free computer navigation system against conventional technique (using a standard mechanical jig) in a cohort of unselected consecutive series of hip resurfacings.

Method: 139 consecutive Durom hip resurfacing procedures (51 navigated and 88 non-navigated) performed in 125 patients were analysed. All the procedures were done through a posterior approach by two surgeons and the study cohort include the hip resurfacings done during the transition phase of the surgeons’ adoption of navigation.

Results: There were no significant differences in the patients caracteristics, native neck-shaft angles, component sizes and blood loss between the two groups. There was a significant difference in the operative time between the two groups (111 minutes for the navigated group versus 105 minutes for the non-navigated group; p=0.048). There were 4 cases of notching in the non-navigated group. There was no other intra-operative technical problem in either of the groups nor were there any femoral neck fractures. No significant difference was found between the mean post-operative stem-shaft angles (138.5° for the navigated group versus 139.0° for the non navigated group, p=0.740). However there was a significant difference in the difference between the planned stem-shaft angle versus the post-operative stem-shaft angle (0.4° for the navigated group versus 2.1° for the non-navigated group; p=0.005). While, none of the cases in the navigated group had a post-operative stem-shaft angle with more than 5° deviation from the planned neck-shaft angle when compared to 33 cases (38%) in the non-navigated group (p≤0.001). For a given patient with a target angle set, it is estimated that positioning precision using the navigation is 1.3° +/− 0.9°, compared to 4.4° +/− 3.6° without navigation (p< 0.0001).

Conclusion: Hip resurfacing is a technically demanding procedure with a steep learning curve. Varus placement of the femoral component and notching have been recognised as important factors associated with early failures following hip resurfacing. While conventional instruments allowed reasonable alignment of the femoral component, our study has shown that use of computer navigation allows more accurate placement of the femoral component even when the surgeons had a significant experience with conventional technique.

Purpose: Surface replacement arthroplasty is being increasingly offered as the treatment of choice to young and active patients with hip arthritis with proposed advantages including bone conservation and better functional outcome. Excellent outcome has been reported in the few recent short-term clinical series of surface replacement arthroplasty. However they have an inbuilt patient selection bias. There are no direct prospective randomized studies comparing the newer generation of surface replacement arthroplasty with conventional total hip arthroplasty. Our study addresses this issue.

Method: 210 hips in 194 patients were randomized to receive either an uncemented total hip arthroplasty or a hybrid metal-on-metal surface replacement arthroplasty. Complications, functional outcomes, along with patient satisfaction and radiographic evaluation were compared at a minimum of two years follow up.

Results: Patients in both groups demonstrated a very high satisfaction rate and achieved similar functional scores. Four dislocations occurred in the THA group (one needing acetabular cup revision) and none in the SRA group. There were no femoral neck fractures in the surface replacement arthroplasty group. However, two surface replacement arthroplasty cases underwent revision for late head collapse and one needed a femoral neck osteoplasty for persisting femoro-acetabular impingement. Better biomechanical restoration was attained with surface replacement arthroplasty. All the components were considered to be stable after an average follow up of 45 months.

Conclusion: Although surface replacement arthroplasty of the hip offer similar patient satisfaction, functional outcome and complication rate as an uncemented total hip arthroplasty in a young and active group of patients, different complications were associated to each procedure. Better patient selection could avoid some of the complications in the surface replacement arthroplasty group. One main advantage that remains for the surface arthroplasty technique it is the proximal femoral bone stock preservation. However, long term survival analysis is necessary to determine the true advantage of these implants over total hip arthroplasty.

We have updated our previous randomised controlled trial comparing release of chromium (Cr) and cobalt (Co) ions and included levels of titanium (Ti) ions. We have compared the findings from 28 mm metal-on-metal total hip replacement, performed using titanium CLS/Spotorno femoral components and titanium AlloFit acetabular components with Metasul bearings, with Durom hip resurfacing using a Metasul articulation or bearing and a titanium plasma-sprayed coating for fixation of the acetabular component.

Although significantly higher blood ion levels of Cr and Co were observed at three months in the resurfaced group than in total hip replacement, no significant difference was found at two years post-operatively for Cr, 1.58 μg/L and 1.62 μg/L respectively (p = 0.819) and for Co, 0.67 μg/L and 0.94 μg/L respectively (p = 0.207). A steady state was reached at one year in the resurfaced group and after three months in the total hip replacement group. Interestingly, Ti, which is not part of the bearing surfaces with its release resulting from metal corrosion, had significantly elevated ion levels after implantation in both groups. The hip resurfacing group had significantly higher Ti levels than the total hip replacement group for all periods of follow-up. At two years the mean blood levels of Ti ions were 1.87 μg/L in hip resurfacing and and 1.30 μg/L in total hip replacement (p = 0.001).

The study confirms even with different bearing diameters and clearances, hip replacement and 28 mm metal-on-metal total hip replacement produced similar Cr and Co metal ion levels in this randomised controlled trial study design, but apart from wear on bearing surfaces, passive corrosion of exposed metallic surfaces is a factor which influences ion concentrations. Ti plasma spray coating the acetabular components for hip resurfacing produces significantly higher release of Ti than Ti grit-blasted surfaces in total hip replacement.

Background: Leg length equality and femoral offset restoration are important parameters related to success of total hip arthroplasty (THA). However, it is not uncommon for errors to occur during surgery which can lead to less optimal functional result and potential source for litigation. Several techniques that are commonly used to assess leg length and femoral offset during THA include pre-operative templating, intra-operative measurements with a ruler using bony landmarks, assessing soft tissue tension and using measurement device with a reference pin in the iliac crest. We have previously reported on our precision to reconstruct the diseased hip with THA done without navigation. Post-operative radiographic analysis demonstrated that leg length was restored to within +/− 4mm of the contralateral side in only 60% of the patients with 4 patients needing a shoe lift. With regards to femoral offset reconstruction, it was increased by a mean of 5.1 mm and restored to within +/− 4mm of the normal contralateral side in only 25% of patients.

Computer navigation has proven to be a more precise tool to achieve optimal positioning of THA implants and precise biomechanical reconstruction of the hip joint. However, performing complete THA using navigation is complex including the requirement to change the position of the patient during registration. A recent stand-alone CT-free hip navigation software from Orthosoft Inc allows navigation to be used for limb length and offset measurements during THA. We report our results from a preliminary study using this technique in 14 hips undergoing THA.

In this technique, a tracker is placed over the iliac crest. There is no need to fix a tracker on the femur. Registration of the following are done: greater trochanter (using a screw), patella (using an ECG lead) and the plane of the operating table (using three points on the surface of the operating table in a triangular configuration). The centre of rotation of the hip is determined by either mapping the acetabulum or by using the appropriate sized calibrated reamer. With the definitive acetabular component in place, the new center of rotation is registered and the hip is reduced with trial femoral component. Re-registration of the new position of the greater trochanter and patella allows the computer to calculate the relative change in the limb length and offset compared to the pre-operative status. The differences in the pre-operative and post-operative limb length and offset were calculated using Imagika software and compared with the navigated values recorded by the computer.

The mean absolute error for the relative change in the limb length as measured by the computer when compared to the radiographic measurement was 1.25 mm with a standard deviation of 1.77 mm. The mean absolute error for the relative change in the offset as measured by the computer when compared with the radiographic measurement was 2.96 mm with a standard deviation of 2.56 mm. The process of navigation was quick and on average adds 10 minutes to the operative time.

Our preliminary study shows that the accuracy of the navigation software is very good in estimating the change in the limb length intra-operatively with a maximum error of 3 mm. The accuracy was also good in estimating the offset (3 mm or less except in one case where the error was 5 mm and this may be due to technical error in registration). This compares favorably with our own data on THA done without navigation. This easy to use navigation technique has the potential to decrease the magnitude of error in restoration of limb length and offset during THA.

We thank Francois Paradois and Michael Lanigan from Orthosoft Inc. for their technical advice.

Hip Resurfacing (HR) is nowadays widely used as an alternative to Total Hip Replacement (THR), especially for the young and active patients. Because of the more physiological distribution of the load in the femur, this technique is particularly known to reduce bone loss due to stress shielding behaviour, a major problem encountered with THA. Different computational studies have analysed the performance of HR prostheses. Therefore, the purpose of this study is to apply a computational approach, in fact a bone remodelling analysis, in order to investigate its application to evaluate the bone structure changes postoperatively.

A Finite Element model was developed of a femur with HR prosthesis. The model was reconstructed starting with the femur medical images, and then the prosthesis was positioned in the clinical implantation angle (5° valgus). A cement mantle thickness of 1mm was included. Then a Finite Element Analysis in combination with a bone remodelling model (bone material properties) was performed. The results obtained predict as there is a certain bone loss in the superolateral and inferior medial zone. Additional bone material apposition is locally found with the aim of fixing the implant stem on the medial side, but also a remarkable distal ingrowth around the stem tip. All these findings are in good qualitative agreement with clinical observations.

We conclude that the numerical simulation used in this study is a useful tool in predicting bone remodelling inside a cemented HR prosthesis. This kind of methodologies will help on the design of devices, surgical techniques, etc.

The aim of our study was to compare the precision and effectiveness of a CT-free computer navigation system against conventional technique (using a standard mechanical jig) in a cohort of unselected consecutive series of hip resurfacings.

One hundred and thirty nine consecutive Durom hip resurfacing procedures (51 navigated and 88 non-navigated) performed in 125 patients were analysed. All the procedures were done through a posterior approach by two surgeons and the study cohort include the hip resurfacings done during the transition phase of the surgeons’ adoption of navigation.

There were no significant differences in the gender, age, height, weight, BMI, native neck-shaft angles, component sizes and blood loss between the two groups. There was a significant difference in the operative time between the two groups (111 minutes for the navigated group versus 105 minutes for the non-navigated group; p=0.048). There were 4 cases of notching in the non-navigated group and none in the navigated group. There were no other intra-operative technical problems in either of the groups nor were there any femoral neck fractures.

No significant difference was found between the mean post-operative stem-shaft angles (138.5° for the navigated group versus 139.0° for the non navigated group, p=0.740). However there was a significant difference in the difference between the planned stem-shaft angle versus the post-operative stem-shaft angle (0.4° for the navigated group versus 2.1° for the non-navigated group; p=0.005). There was significantly more scatter in the difference between the post-operative stem-shaft angle and the planned stem-shaft angle in the non-navigated group (standard deviation = 3.6°) when compared with the navigated group (standard deviation = 0.9°; Levene’s test for equality of variances = p≤0.01). No case in the navigated group showed a post-operative stem-shaft angle of more than 5° deviation from the planned neck-shaft angle when compared to 33 cases (38%) in the non-navigated group (p≤0.001). While only 4 cases (8%) in the navigated group had a postoperative stem-shaft angle deviating more than 3° from the planned stem-shaft angle, this occurred in 50 cases (57%) in the non-navigated group (p≤0.001).

Hip resurfacing is a technically demanding procedure with a steep learning curve. Varus placement of the femoral component and notching have been recognised as important factors associated with early failures following hip resurfacing. While conventional instruments allowed reasonable alignment of the femoral component, our study has shown that use of computer navigation allows more accurate placement of the femoral component even when the surgeons had a significant experience with conventional technique.

To compare the volume of acetabular bone resection after primary hip arthroplasty with different cup designs and technique of implantation using a computer model.

The factors influencing acetabular bone resection during acetabular cup implantation in THA or hip resurfacing (SRA) include the design of the component and technique of implantation. The impact of these variables on bone resection was simulated with a computer model. A 3-D pelvis was reconstructed from CT scan images. The bony acetabulum circumference was 52.5mm. Implantation of pressfit acetabular component sustaining angles of 165°, 170° and 180° with different wall thicknesses (3.5, 4.0, 5.0mm) at various depths was simulated.

Bone loss of 2742mm3 was calculated for the 165°, 4mm thick, 54mm cup, and deepening of reaming by 1 and 2mm would result in bone loss of 3780mm3 (+38%) and 5076mm3 (+85%), respectively. When oversizing to a 56mm 165° component, 4998mm3 (+82%) of bone was removed. For a 54mm, 5 mm thick component sustaining an angle of 180°, the bone loss would reach 12 410mm3 (+450%).

Acetabular component design has a significant influence on the amount of acetabular bone resection. The surgical technique (avoiding over deepening and oversised components) should minimise bone loss. This knowledge is of particular importance in hip resurfacing since the acetabular component size depends on the selected femoral component size. The knowledge is is also important in THA to minimise bone loss at primary implantation.

The purpose of this study was to compare the post operative ROM of patients randomised between SRA and 28mm THA.

Restoration of normal ROM has been proposed as an advantage of hip resurfacing (SRA) over THA and is due to the use of larger diameter femoral heads. However, the head-neck diameter ratio, which is an important factor governing ROM, would in theory allow more ROM with THA (28mm head/14mm neck = ratio 2:1) versus SRA (approximate ratio 1.3–2.0:1).

Patients were randomised between SRA and THA. Osseous landmarks were identified with a marker pen. Both ASIS served as the reference line for the pelvis position. Digital photographs of hip motion were taken and a blinded rater (with respect to the side and type of surgery) performed range of motion testing on the operated and normal side. Pre-study validation of ROM measurement method with a software program revealed high intra and inter observer reliability.

Sixty SRA and sixty-two THA were evaluated at minimum follow-up of twelve months. Preoperative ROM and demographic data were similar for both groups. No significant differences (p> 0.05) were found in the total arc of motion (SRA=204.2°, THA=196.5°), arc of rotation (SRA=47.7°, THA=44.3°), flexion-extension arc (SRA=118.1, THA=120.1), abduction-adduction arc (SRA=43.1°, THA=42.9°).

In theory, ROM should have been greater in THA. Fear of instability may have limited ROM recovery potential in THA. Since pre operative soft tissue contracture is an important factor influencing post operative ROM, the complete capsular release performed during SRA may have been an advantage of this technique.

Heterotopic ossification (HO) occurs commonly after total hip arthroplasty (THA). Its severe form can result in impaired range of motion with reduced functional outcome. The rate and severity of HO after hip surface replacement arthroplasty (SRA) have never been well studied.

Two hundred and ten hips were randomised to receive uncemented metal-on-metal THA or metal-on-metal SRA. Standard radiographs of the pelvis were assessed for HO by two reviewers at the latest follow-up (minimum of six months), using Brooker severity grading and Kjaersgaard-Andersen regional classification.

The incidence of HO was 38.5% in the SRA group compared to 32.6% in the THA group (p=0.5). However, there was a significant difference in severity grades for the two groups (chi square, p=0.02). According to Brooker’s classification, nearly half of HO was of grade two in SRA and of grade one in THA. SRA was associated with significantly higher rates of severe HO (grades three and four) than THA (12.5% vs. 2.2%; p=0.009). Inter-rater agreement for Brooker grading was excellent (Cohen’s kappa, 0.88; p< 0.01).

The incidence of HO after hip arthroplasty seems to be determined by patient-related factors. However, HO severity appears to be associated with local surgical factors and thereby SRA may result in more severe HO than THA. An extensive surgical approach, additional soft tissue release and the blunt damage occurring in gluteal muscles with SRA may signal the induction of more severe HO. Peri-operative deposition of bone debris derived from femoral head preparation may also play a role by transplanting osteoprogenitor cells. Surgeons must be aware of this risk of severe HO when offering SRA as an alternative treatment to younger patients. Routine prophylaxis with NSAIDs needs to be considered in these patients. A meticulous surgical technique to reduce muscle damage, pulsed lavage to clear bone debris, and debridement of necrotic tissue, may help to decrease the risk of severe HO in SRA.

INTRODUCTION: Improved factors influencing component wear with regards to bearing surfaces, metallurgy, tribology, and manufacturing technology allowed reintroduction of metal-on-metal (MOM) articulation in total hip arthroplasty (THA) and surface replacement arthroplasty (SRA).

MATERIALS AND METHODS: Sixty three patients were implanted with a forged, high carbon content, chrome-cobalt, MOM SRA component (Durom, Zimmer, USA). Samples of whole blood and serum were collected pre-operatively and, post-operatively at three months, six months one year and two years. Chromium and cobalt concentrations were measured using a a high-resolution, sector-field, inductively-coupled plasma mass spectrophotometer (HR-SF-ICP-MS).

RESULTS: At two years, whole blood levels were Cr 1.25 umol/L (SD 0.55), Co 0.62 umol/L (SD 0.26). In comparison to the pre-operative levels, the levels increased significantly for both elements Cr 1.3X, Co 5.0 X. Component size was inversely proportional to the chromium and cobalt ion levels at one year post operatively (ANOVA regression analysis, p = 0.0404, for Co and p = 0.0156 for Cr). Other factors such as age and activity level did not correlate with the metal ions levels.

DISCUSSION AND CONCLUSION: Chromium and cobalt metal ions measured in patients following implantation of the high carbon content, forged, metal on metal SRA implants used in this study are very low in comparison to other published results with different SRA implants. We believe that these encouraging results found with the SRA components used are resultant of favourable manufacturing and tribologic factors such as low surface roughness, high carbon content, forged chromium and cobalt material, component clearance, and optimum component sphericity. The results of this study are also in accordance with the concepts of reduced wear with larger diameter MOM articulations.

PURPOSE: The purpose of this study was to compare the level of post operative sport activity in a randomized study of SRA and THA.

INTRODUCTION: Return to high activity level has been proposed has an advantage of hip resurfacing (SRA) compared to THA. However, patient selection for SRA favours higher demand individuals, thus leading to a biased comparison of both techniques.

MATERIALS AND METHODS: Patients were randomized to THA or SRA. At minimum one year follow-up, the patients were asked about the activities they have resumed, the level of satisfaction regarding return to sports and the factors limiting full return to intense activities. 80 THA and 85 SRA with a mean follow-up of 16 months were analyzed.

RESULTS: The postoperative UCLA activity score was significantly higher in the SRA group (6.3 versus 7.1, p< 0.05). 77% of the SRA patients returned to high or moderate activity level vs 39% in the THA group (p=0.007). In the THA group, the activity level was mostly restricted due to concern about instability. However, some THA patients were still able to perform high demand activities.

DISCUSSION AND CONCLUSION: This study suggests that SRA allows return to higher activity level when compared to THA. This may be due in part to the larger diameter head of SRA which improves stability and suction-fit (reducing micro separation of the bearing during activities). Enhanced proprioception due to the retained femoral neck may also be involved in the bias towards SRA. Further follow-up is will determine if higher activity level is detrimental to implant survivorship

Introduction: Heterotopic ossification (HO) occurs commonly after total hip arthroplasty (THA). Its severe form can result in impaired range of motion with reduced functional outcome. The rate and severity of HO after hip surface replacement arthroplasty (SRA) have never been well studied.

Methods: Two hundred and ten hips (194 patients) were randomized to receive uncemented metal-on-metal THA (103) or metal-on-metal SRA (107). Standard antero-posterior radiographs of the pelvis were assessed for HO by 2 reviewers at the latest follow-up (minimum of 6 months), using Brooker severity grading and Kjaersgaard-Andersen regional classification.

Results: Pre-operative and post-operative data were similar for both groups. The incidence of HO was 38.5% in the SRA group compared to 32.6% in the THA group (p=0.5). However, there was a significant difference in severity grades for the 2 groups (chi square, p=0.02). According to Brooker_s classification, nearly half of HO was of grade 2 in SRA and of grade 1 in THA. SRA was associated with significantly higher rates of severe HO (grades 3 and 4) than THA (12.5% vs. 2.2%; p=0.009). Inter-rater agreement for Brooker grading was excellent (Cohen_s kappa, 0.88; p< 0.01). HO in SRA involved both the central and lateral regions in 26% of cases, whereas only 3% of HO in THA showed such a pattern (p=0.025). Risk factors, such as male gender, osteoarthritis, bilateral predilection, and previous history of HO, were observed in both groups. Patients with HO had reduced internal hip rotation (16.4° vs. 22.2°; p=0.02) and a higher incidence of postoperative hip pain (52% vs. 30%; p=0.04), but comparable functional outcome scores.

Discussion: The incidence of HO after hip arthroplasty seems to be determined by patient-related factors. However, HO severity appears to be associated with local surgical factors and thereby SRA may result in more severe HO than THA. An extensive surgical approach, additional soft tissue release and the blunt damage occurring in gluteal muscles with SRA may signal the induction of more severe HO. Peri-operative deposition of bone debris derived from femoral head preparation may also play a role by transplanting osteoprogenitor cells. Surgeons must be aware of this risk of severe HO when offering SRA as an alternative treatment to younger patients. Routine prophylaxis with NSAIDs needs to be considered in these patients. A meticulous surgical technique to reduce muscle damage, pulsed lavage to clear bone debris, and debridement of necrotic tissue, may help to decrease the risk of severe HO in SRA.

Purpose: Tribological studies suggest that larger metal-on-metal articulations would produce less wear than smaller diameter components. The aim of the present study is to describe whole blood Chrome and Cobalt ions concentration after metal-metal total hip arthroplasty (THA) and surface replacement arthroplasty (SRA).

Methods: 180 patients eligible for the study were randomized to receive uncemented 28 mm metal-metal THA or a hybrid metal-metal SRA. Whole blood samples were collected pre-operatively, at three, six months and one year post operatively. Chrome and Cobalt concentration were measured by mass spectrophotometry.

Results: At one year post op, whole blood levels of the were Cr 1.8 umol/L and Co 0.6 umol/L for the SRA and Cr 1.7 umol/L and Co 0.8 umol/L for the THA group (Cr, p=0.676 and Co, p=0.08). In comparison to pre-operative levels, the post operative levels significantly incresed for all elements Cr 1.9x and Co 3.8x for the SRA; Cr 1.3x and Co 3.4x. for the SRA group, Anova regression tests showed a significant relation between component size and Cr and Co metal ions levels; the larger the component, the lower the ions levels (Cr p=0.0285 and Co p=0.0442)

Conclusions: Using these specific implants, the increases whole blood metal ions were similar to the best results found in the literature for 28 mm metal-metal THA. Results of this study confirm the good tribologic performances of the Metasul large diameter metal-metal articulations. Funding: Commerical funding Funding Parties: Zimmer

The dramatic improvement in clinical function after total hip arthroplasty (THA) has been well-documented. Gait studies, however, demonstrate abnormal gait pattern after THA. THA patients may complain of thigh pain, leg length inequality, instability and reduced range of motion. Surface replacement arthroplasty (SRA) has the benefit of restoring a more normal hip anatomy and biomechanics, which could improve clinical function and patient satisfaction after surgery. We compared the clinical function and patient satisfaction in a group of young patients randomized to receive SRA or THA. The results are presented and discussed.

The dramatic improvement in clinical function after total hip arthroplasty (THA) has been well-documented. However gait studies demonstrate abnormal gait patterns after THA, and patients may complain of thigh pain, leg length inequality, instability and reduced range of motion. Surface replacement arthroplasty (SRA) has the benefit of restoring a more normal hip anatomy and biomechanics, which could improve clinical function and patient satisfaction after surgery.

All patients eligible for the study were randomised to receive uncemented metal-metal THA or a hybrid metal-metal SRA. Clinical data were prospectively collected pre-operatively and at three, six and twelve months post-operatively. WOMAC score, SF-36, Merle D’Aubigné, and other clinical data, along with patient satisfaction, were compared.

One hundred and fifty patients were randomized. Both groups demonstrated a very high satisfaction rate. Although there was a tendency for the SRA group to participate in more demanding activities at six months post-operatively, no difference was found in clinical function scores. Two isolated dislocations occurred in the THA group and none in the SRA group. There were no other significant complications in either group.

The few short-term clinical data reported in the literature for new generation SRA implants demonstrate an excellent outcome comparable to THA. Despite enthusiasm about total hip resurfacing, no direct prospective comparative study with THA has been published in the literature. This study confirms the safety and benefits of metal-metal SRA of the hip in the early post-operative period.

Funding: This research project was funded by Zimmer, Warsaw