Aims

Pin-site infection remains a significant problem for patients treated by external fixation. A randomized trial was undertaken to compare the weekly use of alcoholic chlorhexidine (CHX) for pin-site care with an emollient skin preparation in patients with a tibial fracture treated with a circular frame.

Aims

This study reports the mid-term results of total hip arthroplasty (THA) performed using a monoblock acetabular component with a large-diameter head (LDH) ceramic-on-ceramic (CoC) bearing.

Large bearing surfaces are appealing in total hip arthroplasty (THA) as they may help create a greater range of impingement free motion and reduce the risk of dislocation. However, attempts to achieve this with a metal bearing surface have been blighted by adverse reactions to metal debris. Ceramic bearings have a good long-term track record in more conventional head sizes, and manufacturing techniques now permit the use of larger ceramic bearing surfaces using monoblock uncemented acetabular components. In this study, we are reviewing the early results of the Maxera® acetabular component (Zimmer, Indiana) at our institution.

All data was collected prospectively. Maxera® acetabular component is a Titanium (Ti) shell with plasma sprayed Ti for the osteointegrative surface. Delta ceramic liner is inserted & locked into the cup shell by the manufacturer (non-modular). With the Maxera cup system, the bearing diameter is dictated by the acetabular component size. Acetabular components (AC) of 46 and 48 mm have a bearing diameter (BD) of 36 mm, AC of 50 and 52 mm: have a 40 mm BD, AC of 54 and 56 mm: have a BD of 44 mm and AC of 58–64: have a 48mm BD. Delta ceramic femoral head size of 44 and 48 mm have a modular Ti sleeve between the head and femoral stem trunnion. Femoral head sizes of 36 and 40 mm have no Ti sleeve. All THA had an uncemented femoral stem. Implants were inserted with a posterior approach. Patients were reviewed at 6 weeks, 6 months and then annually with radiographs. Clinical function was evaluated using WOMAC and UCLA scores along with joint perception questionnaires.

Five hundred components have been implanted in 442 patients (250 women, 192 men) with a mean age of 55, (min 17, max 80) and a mean BMI of 26.9 (min 17.8, max 51). The mean acetabular size was 54 (min 46, max 64), leading to a mean femoral head size of 44. At a minimum of two years follow-up (mean 3.8 years): 5 patients have been revised, 4 secondary to undetected intraoperative fracture of the femur and only one due to early displacement of a Maxera® cup (0.2%). Five patients reported a mild squeaking; two reported clicking and one patient presented with a symptomatic heterotopic ossification. The WOMAC score improved significantly post-operatively, (57.4 compared to 4.4 post-operatively, p<0.001). The mean post-operative UCLA score was 6.9. Sixty percent (60.6%) of patients rated their joint perception as either “natural” or “artificial without limitation”. two patients (0.4%) suffered a dislocation after high velocity trauma without recurrence after closed reduction. No ceramic component fracture was recorded.

This prospective study shows that this monoblock acetabular component provides an easy implantation with minimal complications. The ceramic bearing surface provides good clinical function and joint perception. Bearing surfaces of this design may provide an alternative to large head metal on metal (MoM) implants without the side effects of metal debris/ions.

Purpose: Massive cavitary and segmental bone defects of the medial wall in revision arthroplasty are usually managed with large auto and/or allograft in association with a cemented or a cementless cup. To obtain a satisfactory hip center reconstruction with such a procedure can be sometimes challenging and the complications rate can be high. One other option is the use of a cup with a medial expansion (“protrusio cup”) to treat the medial bone defect.

Method: We carried out a retrospective study including 21 consecutive acetabular revisions arthroplasties using a cementless Converge Protrusio™ cup (Zimmer, Warsaw, IN, USA). Clinical outcomes were assessed by Harris Hip Score (HHS), WOMAC index and SF-12. Hip centre was assessed on anteroposterior (AP) view and the reconstruction 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 > 4mm and to > 4° in comparison with the immediate postoperative AP view.

Results: At the last follow up [radiological data: 71.6 months (24–128.3) and clinical data: 72.1 months (24–129.5)], two patients were died and there were no lost of follow up. The mean HHS was 79.4% (52–100), WOMAC 82% (46–100), SF-12 52 (23–71) and 44 (18–65). Bone defect were filled with cancellous bone chips allograft in 16 cases and bulk bone allograft was used in only two cases to manage a large segmental defect of the roof. Bone graft integration was completed in all cases. The mean abduction cup angle was 43.6° (32–60). A satisfying hip centre positioning was obtained in 19 cases on x axis and in 10 cases on y axis, in all the remaining cases, we noted an improved implant positioning. The complications were: recurrent dislocation in one case (successfully revised with a constrained liner), infection in two cases (1 treated conservatively and the other one revised in two times procedure) and Brooker’s type III and IV ectopic ossifications in three cases. A significant cup migration occurred in only one case at nine years but was not revised because of painless. No case required revision for aseptic loosening.

Conclusion: Protusio cups appear as a reliable procedure to manage bone loss in acetabular revision. The revision procedure is widely simplified by reducing the use of the massive allograft and by promoting a satisfying hip center reconstruction to allow an optimal biomechanical joint functioning. Moreover, the cementless fixation in contact with patient acetabular bone makes more easy bone integration.

Purpose of the study: Tribology studies of total hip arthroplasty (THA) have demonstrated that large diameter head in metal-on-metal bearings produce fewer wear particles than small diameter heads. The other advantages of this option are better stability, less dislocation, and optimal joint range of motion. The purpose of this work was to compare blood levels of chromium, cobalt and titanium six months and one year after implantation of different models of large diameter metal-on-metal THA.

Material and methods: We conducted a retrospective comparative and randomised study including 110 patients who had been implanted with a larger diameter head THA/Zimmer? Smith and Nephez, Biomet or Depuy. The metal ion concentrations (Cr, Co, Ti) were measured in whole blood by an independent laboratory using high-resolution mass spectrometry (HR-ICP-MS). Blood samples were drawn preoperatively and postoperatively at six months and one year.

Results: At six months, the concentrations of metal ions in whole blood expressed as mean (range) for Cr (μg/L) Co (μg/L) and Ti (μg/L) were, respectively: Zimmer 1.3 (0.4/2.8) 1.7 (0.9/6.8) 2.5 (0.6/6.7); Smith and Nephew 2.0 (0.7/4.2) 2.1 (0.5/6.6) 1.1 (0.5/4.1); Biomet 1.2 (0.4/2.2) 0.9 (0.3/3.4) 1.4 (0.8/2.4); Depuy 1.7 (0.5/3.2) 1.9 (0.3/4.2) 1.3 (0.5/3.9). There was a significant difference between groups for Cr (p=0.006), Co (p=0.047) and Ti (p< 0.001). The Biomet implants presented the lowest concentrations for Cr and Co; the Zimmer implants gave the highest levels of Ti.

Discussion and Conclusion: Several implant-related factors affect blood concentrations of metal ions: contact surfaces leading to “active” abrasion but also wear in other parts of the implant giving rise to “passive” corrosion. Bearing wear is related to the diameter of the head, its roughness, its spherical shape, joint clearance, the manufacturing technique (forging, casting) and its carbon content. The Biomet head corresponds to a better compromise for these different factors. Passive corrosion can result from an exposed metal surface or from metal to metal contact. This explains the high level of Ti ions found for all implants tested since titanium is not present in the bearings.

Purpose: Tribological studies of hip arthroplasty suggest that larger diameter metal-on-metal (MOM) articulations would produce less wear than smaller diameter articulations. Other advantages of these large femoral head implants include better stability with lower dislocation rates and improved range of motion. The aim of the present study was to compare chromium (Cr), cobalt (Co) and titanium (Ti) ion concentrations up to one year after different large diameter MOM total hip arthroplasties (THAs).

Method: One hundred and twelve patients were randomized to receive large (femoral head > 36 mm diameter) metal-on-metal articulation THA (LDH) from one of the following companies: Zimmer, Smith & Nephew, Biomet or Depuy. Samples of whole blood were collected pre-operatively and post-operatively at six months and one year. Cr, Co and Ti concentrations were measured by high-resolution mass spectrometry in an independent laboratory. All LDH implants have a modular Cr-Co tapered sleeve for leg length adjustment, except for Biomet with its sleeve made of Ti. All groups had Ti stems, and Zimmer and Biomet had, in addition, a Ti acetabular porous surface for secondary fixation. We undertook statistical analysis (SPSS 14.0) with p< 0.05 as significant.

Results: The groups were comparable in respect to pre-operative parameters (age, gender ratio, body mass index, etc.) as well as post-operative functional scores at six months and one year. We found that Biomet, Depuy and Smith & Nephew LDH had similar Co ion levels at 12 months post-op with 1.5, 1.4 and 1.6 ug/L, respectively. Durom LDH had the highest Co level with 2.3 ug/L (p< 0.01 versus the three other groups). The highest Ti ion levels were observed in the Zimmer group with 3.2 ug/L (p< 0.01 versus the three other groups) and the Biomet group with 2.0 ug/L (p=0.01 versus Zimmer and NS versus the other 2). Ti levels tripled versus pre-op for BHR and ASR (0.5 versus 1.5 and 0.5 versus 1.4 ug/L).

Conclusion: Different implant factors may influence metal ion levels measured in whole blood: articular surface wear and implant passive corrosion. Zimmer’s Durom LDH presents higher Co levels than the other groups. Since previously-published Durom hip resurfacing (same bearing characteristics as Durom LDH) showed much lower Co ion results, the modular sleeve may be incriminated. The plasma-sprayed acetabular surface of Zimmer’s and Biomet’s components seems to be responsible for the significant difference in Ti versus the other implants. Biomet’s plasma-sprayed Ti appears to be less prone to corrosion than Durom’s plasma spray coating. When evaluating metal ion release from MOM THA, total metal load from the implants should be considered, and newer implant designs should be evaluated scientifically before their widespread clinical use. LDH-THA should be seen as an improvement and should not be blamed as the source of metal ion release when a specific implant produces unsatisfactory results.

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.

Aim: The aim of the current study is to investigate if viscosupplemetation therapy will increase the effect of microfracture technique by acting the quality and quantity of the new cartilage after microfracture.

Material and Method: Full thickness chondral defects were created to intercondylar notch as a nonweightbearing area by using a handle drill bit. Microfracture holes between bridges were performed with a 1mm K wire.

The present study was performed on 30 mature white rabbits (male range, 2800–3500 gr). The right knees were accepted as study and left knees as control group. Group 1 was received intraarticular 0.1ml sodium hyaluronate treatment, rabbits in group 2 were received 0.1 ml Serum Physiologique once a week for three weeks. Biopsy was taken from both knees at the 3rd and 6th week. Histopathological evaluation was performed by a pathologist who is blind to study according to modified Mankin score.

Results: Although the difference of the scores between study and control group was not statistically different at the third week, it was seen different at the sixth week histologically.

Conclusion: Hyaluronic acid may be benefecial in the treatment of chondral lesion addition to arthroscopic microfracture technique.

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.

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.

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.

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.

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: 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

Purpose: To determine if some subsets of healthy subjects displayed other than a typical gait pattern and to identify which subsets have similar kinematic pattern to patients with knee osteoarthritis.

Methods: The healthy subject dataset consisted of 106 asymptomatic volunteers. These subjects were over 17 years of age, pain-free, had no record of surgery to the lower limb and no evidence or history of arthritic disease at the time of testing. The patient population consisted of 12 patients diagnosed with knee OA, evaluated within 6 months prior to the tests. The 3D movements of right knee joint were recorded using a functional knee analyzer with magnetic sensors while subjects walked on a treadmill at their own preferred speed. The magnetic sensors are non-invasive electromagnetic devices, which track the 3D positions and orientations of sensors relative to a source. The system has been shown to be accurate, especially in the frontal and transversal planes. K-means clustering analysis was chosen to identify the gait patterns among healthy subjects based on three components of the knee joint angles, and analyses of variance were performed to determine which parameters were different between subsets.

Results: Three gait groups or patterns were identified in the healthy subjects. The first group (G1) was characterized by a kinematic profile similar to the OA group. The second group (G2) had the highest external rotation angle, which was significantly different from OA group. The abduction angles were always greater in the G2 and G3 than in the OA group. This might be attributed to a valgus static alignment in G2 and G3 comparing to a varus alignment in the patient with OA.

Conclusions: The newly developed functional knee analyzer provided a non-invasive way to accurately measure 3D kinematic data which enabled cluster analysis to distinguish three gait patterns from 106 healthy subjects. The results suggested a strong correlation between static alignment and dynamic ad-abduction angles during the gait, which need to be investigated. Funding: Other Education Grant Funding Parties: NSERC, CIHR and FCAR

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

Purpose: Femoral offset restoration is recognised as an important part of THA procedure to reduce the joint reactive force and improve stability. In SRA, femoral offset is often reduced due to the femoral component valgus position. The main objective of this study was to correlate the clinical function of SRA and THA patients with their different biomechanical hip reconstruction (femoral offset).

Methods: 156 patients aged 23 to 65 years old and suffering from advanced hip joint degeneration were randomly assigned to two treatment groups: the THA or SRA group. All surgeries were performed through a posterior approach. Standardized pre and post operative antero-posterior radiographs of the pelvis were made and clinical scores were assessed.

Results: Compared to the normal contra lateral side, the femoral offset increased on average 4.85mm (range -2.77 to 11.59mm, SD 3.31) for THA and decreased an average of 3.42mm (range −7.78 to 1.96, SD 2.12) for SRA (p=0.0001). In addition, offset restoration was within lees than 4 mm in 60.0% of the SRA group and 21.8% in the THA group (p=0.0001). There were no differences between the both groups in terms of clinical and subjective scores: the PMA and SF-36 scores were, respectively, in average 17.1 (SD 0.4) and 101 (SD 1.25) for THA and 17.0 (SD 0.4) and 101 (SD 1.14) for SRA. No relation was found between offset restoration and clinical scores for both groups.

Conclusions: In this study, surgeons were less precise reconstructing the femoral offset in the THA group compared to the SRA group. However, femoral offset was lower (reduced) in the SRA in comparison to THA. This significant decreased femoral offset in SRA, seems inherent to the preferential valgus positioning of the femoral component in that technique. The excellent clinical outcome reported with SRA does not suggest that restoring normal offset is as crucial for the success of SRA because no correlation was found between femoral offset and the clinical scores used.