Metal ion release after hip resurfacing arthroplasty and knee arthroplasty: a retrospective study of one hundred ninety-five cases.

PURPOSE: Hip arthroplasty with metal-on-metal bearings like hip resurfacing results in the release of metallic ions. In parallel, like every metallic implant, knee arthroplasty implants undergo passive corrosion. We analyzed blood levels of cobalt and chromium ions in patients who have a hip resurfacing arthroplasty and compared them to patients who have undergone knee arthroplasty at a minimum follow-up of one year. The hypothesis was that there is no difference in the ion release between hip resurfacing and knee arthroplasty. METHODS: Sixty-three patients who underwent knee arthroplasty were compared to a cohort of 132 patients who underwent hip resurfacing. The blood levels of cobalt and chromium ions were determined preoperatively and at six and 12 months postoperatively and then compared between groups. We analyzed the relationship between ion release and the change in clinical outcome scores (Harris Hip score, Oxford Hip score, Merle D'Aubigné Postel score, Oxford Knee score, International Knee Society score), the BMI, sex, physical activity, implant size and inclination of the acetabular implant (hip resurfacing patients only). Mixed linear models were used to assess the changes in ion blood levels over time. RESULTS: The cobalt blood levels were higher in the first 6 months in the resurfacing group (0.87 ug/L vs 0.67 ug/L; p = 0.011), while it was higher in the knee arthroplasty group at 12 months (1.20 ug/L vs 1.41 ug/L; p = 0.0008). There were no significant differences in chromium levels during the follow-up period. CONCLUSION: The increase in metal ion release after knee arthroplasty is as high as after hip resurfacing at the one year follow-up. The monitoring of this parameter probably should not be recommended in case of good clinicals outcomes.

Subchondral involvement in osteonecrosis of the femoral head: insight on local composition, microstructure and vascularization.

OBJECTIVE: To determine changes of subchondral bone composition, micro-structure, bone marrow adiposity and micro-vascular perfusion in end-stage osteonecrosis of the femoral head (ONFH) compared to osteoarthritis (OA) using a combined in vivo and ex vivo approach. DESIGN: Male patients up to 70 years old referred for total hip replacement surgery for end-stage ONFH were included (n = 14). Fifteen patients with OA were controls. Pre-operative MRI was used to assess bone perfusion (dynamic contrast-enhanced (DCE) sequences) and marrow fat content (chemical shift imaging). Three distinct zones of femoral head subchondral bone - necrotic, sclerotic, distant - were compared between groups. After surgery, plugs were sampled in these zones and Raman spectroscopy was applied to characterize bone mineral and organic components (old and newly-formed), and contrast-enhanced micro-computed tomography (CE-µCT) to determine bone micro-structural parameters and volume of bone marrow adipocytes, using conventional 2D histology as a reference. RESULTS: In the necrotic zone of ONFH patients compared to OA patients: 1) the subchondral plate did not exhibit significant changes in composition nor structure; 2) the volume fraction of subchondral trabecular bone was significantly lower; 3) type-B carbonate substitution was less pronounced, 4) collagen maturity was more pronounced; and 5) bone marrow adipocytes were significantly depleted. The sclerotic zone from the ONFH group showed greater trabecular thickness, and higher DCE-MRI AUC and Ktrans. Volume fraction of subchondral bone, trabecular number, and Kep were significantly lower in the distant zone of the ONFH group. CONCLUSIONS: This study demonstrated alterations of subchondral bone microstructure, composition, perfusion and/or adipose content in all zones of the femoral head.

Hip survival after plain core decompression alone versus bone morphogenetic protein and/or bone marrow reinjection with core decompression for avascular osteonecrosis of the femoral head: a retrospective case control study in ninety two patients.

INTRODUCTION: Injecting bone marrow or bone morphogenetic protein 7 (BMP) during core decompression for avascular osteonecrosis (AVN) may improve survival. We hypothesized that adding a complementary technique (injection of BMP and/or non-concentrated bone marrow) to core decompression would reduce the number of patients requiring a subsequent total hip arthroplasty (THA). METHODS: We retrospectively reviewed 92 cases from 2003 to 2018 with a minimum of 2 years of follow-up and an average follow-up of 64 months (24-204). Twenty-four patients had a core decompression (CD) (26.1% (24/92)), 25 had a CD associated with reinjection of bone marrow and BMP (rhBMP7) (27.2% (25/92)), and 43 patients had a CD with bone marrow reinjection (46.7% (43/92)). RESULTS: Hip survival after CD was 66.3% (61/92) at two years and 59.8% (55/92) at 10 years. CD with bone marrow and BMP reinjection had a better hip survival at ten years (HR: 0.492 (CI95%: 0.254-0.952) p = 0.035). A volume of necrosis greater than 30% (HR = 12.97 (CI95 [3.88-43.3] (p < 0.001))) and a Kerboul angle greater than 60° (HR: 12.5 (CI95 [2.84-54.6] (p < 0.001))) were risk factors for a subsequent THA. CONCLUSIONS: CD is an interesting non-invasive technique to preserve the native hip after AVN of the femoral head. Reinjection of bone marrow and/or BMP improved CD hip survival.

Daptomycin versus Vancomycin as Post-Operative Empirical Antibiotic Treatment for Prosthetic Joint Infections: A Case-Control Study.

Purpose: To compare safety and efficacy of Vancomycin (Van) versus Daptomycin (Dap) as post-operative empirical antibiotic treatment (PEAT) in patients with periprosthetic joint infections (PJIs). Methods: Medical charts of patients treated empirically with Van or Dap in the post-operative period of total hip/knee prosthesis septic revision until the results of intra-operative culture were reviewed. Cefotaxime, cefepime or aztreonam were used in combination with Dap or Van. Results: Twenty Dap patients were matched with 20 other Van patients according to the age and type of prosthesis. The ASA score and the distribution of the pathogens was similar in the two groups especially regarding the number of methicillin-resistant staphylococci. The mean duration of the PEAT was 6.07 ± 0.85 days. A total of 17 episodes of adverse events (AE) in 10 patients (25%) were recorded during the PEAT which led to discontinue the treatment in 5 patients, all of them treated with Van (P=0.02). At the end of a mean post-treatment follow-up of 618 +/- 219 days, 36 patients remained in remission of infection; 2 patients failed in each group. Conclusions: Our observations suggest that PEAT with Van for septic revision of PJIs is associated with a higher discontinuation rate due to AE but with a similar outcome than it is with Dap.

Diagnostic accuracy of the alpha defensin lateral flow device (Synovasure) for periprosthetic infections in microbiologically complex situations: A study of 42 cases in a French referral centre.

BACKGROUND: Joint aspiration is currently the reference standard test for diagnosing periprosthetic joint infection (PJI) despite the high rate of false-negative results, of which a major cause is the fastidious nature of some microorganisms. A rapid diagnostic test that detects alpha defensin (Synovasure™, Zimmer, Warsaw, IN, USA) in joint fluid can provide the diagnosis of PJI within a few minutes across the full spectrum of causative organisms (including mycobacteria and yeasts). Its performance in detecting bacterial infections is unaltered by concomitant antibiotic therapy. Few studies of Synovasure™ have been conducted by groups that were involved in designing the test, which has not been validated in France. Assessments in referral centres where complex microbiological situations are common hold considerable interest. The objective of this prospective study was to determine the sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and causes of error of Synovasure™ used to diagnose periprosthetic infection in complex microbiological situations. HYPOTHESIS: The rapid diagnostic test Synovasure™ has greater than 90% NPV for detecting periprosthetic infections in complex microbiological infections. MATERIAL AND METHODS: Synovasure™ was used 42 times in 39 patients between October 2015 and October 2017 in challenging microbiological situations [discordant joint aspiration results (n=20), negative cultures with clinical or laboratory evidence of infection, (n=21), and concomitant antibiotic therapy (n=1)]. Of the 39 patients, 23 had total knee prostheses, 13 total hip prostheses, and 3 total femoral prostheses. The reference standard to which the Synovasure™ results were compared was the PJI criteria set developed by the Musculoskeletal Infection Society (MSIS). RESULTS: Synovasure™ was negative in 30 cases with negative joint fluid cultures (30/42, 71.4%). Of the 12 (28.6%) cases with positive Synovasure™ results, only 7 (7/12, 58.3%) had positive joint fluid cultures. According to the MSIS criteria 9 cases were infected, including 8 with positive and 1 with negative Synovasure™ results. Of the 33 cases that were not infected according to MSIS criteria, 29 had negative and 3 positive Synovasure™ results; the remaining case had a positive Synovasure™ result but was excluded when metallosis was found intra-operatively. NPV was 96.7%, PPV 72.7%, sensitivity 88.9%, and specificity 90.6%. DISCUSSION: The high NPV of Synovasure™ suggests a role for this test in microbiologically complex situations as a new tool for ruling in and, most importantly, ruling out infection in doubtful cases. LEVEL OF EVIDENCE: III, prospective study of diagnostic accuracy.

Opening-wedge high tibial osteotomy performed with locking plate fixation (TomoFix) and early weight-bearing but without filling the defect. A concise follow-up note of 48 cases at 10 years' follow-up.

INTRODUCTION: Use of a locking plate during medial opening high tibial osteotomy (HTO) eliminates the need to fill the defect and its associated complications. It also allows early weight-bearing. Since long-term data with this type of construct are rare, we wanted to report the outcomes of a 51-patient cohort evaluated after a mean follow-up of 10.2years. The goals were to determine (1) the HTO survival and whether the correction was maintained between 2 and 10years later, (2) the stability of the functional outcomes, (3) the complication rate related to use of locking plates. HYPOTHESIS: The correction following medial opening HTO with a Tomofix™ plate without void filling is maintained after 10years' follow-up. MATERIAL AND METHODS: Fifty-one patients ranging from 37 to 72years of age at the time of surgery between 2003 and 2005 underwent a medial opening HTO that was stabilized with a Tomofix™ locking plate (Synthes, Oberdorf, Switzerland) without void filling. Forty-eight patients were reviewed between March and September 2014; 1 patient had died and 2 were lost to follow-up. RESULTS: The mean HKA angle went from 172±3.18° (165-178°) preoperatively to 181±1.18° (176-185°) postoperatively, to 181±1.60° (176-185°) at 2years, and 180.8±2.4° (175-184°) at 10years' follow-up. This equates to a loss of correction of 0.71±1.9° (0-6°) (p=0.02) between 2 and 10years after the surgery. Five patients underwent total knee arthroplasty (TKA), thus the 10-year survival of the HTO procedure was 88% (95% CI: 81-98%). If the five TKA procedures are excluded, the mean IKS knee score went from 90±7.4 (66-98) at 2years' follow-up to 77±15.3 (43-97) at 10years (p>0.05). There were four complications in all (8%), of which three occurred within 2years (2 cases of nonunion and 1 surgical site infection) and one occurred later (infection after 118months that resolved once the hardware was removed and the patient given appropriate antibiotics). There were no complications related to the five subsequent TKA procedure and no bone grafting was required. DISCUSSION: There was a small (less than 1 degree) but statistically significant loss of correction and non-significant deterioration in the functional outcomes. Conversely, the complication rate did not increase over time, despite the lack of void filling, particularly in patients who subsequently underwent TKA. The 10-year survival was similar to other HTO procedures. This locking plate construct without void filling is reliable after 10years. LEVEL OF EVIDENCE: Level IV, prospective study without control group.

Ten-year survival and complications of total knee arthroplasty for osteoarthritis secondary to trauma or surgery: A French multicentre study of 263 patients.

BACKGROUND: Previous surgical procedures raise technical challenges in performing total knee arthroplasty (TKA) and may affect TKA outcomes. Survival rates of TKA done after trauma or surgery to the knee have not been accurately determined in large populations. The objectives of this retrospective study in 263 patients with TKA after knee trauma or surgery and a follow-up of 10 years were to assess survival, functional outcomes, and the nature and frequency of complications. HYPOTHESIS: Knee trauma or surgery before TKA increases the risk of complications and decreases implant survival. MATERIAL AND METHODS: Two hundred and sixty-three patients (122 [47%] females and 141 [53%] males) underwent TKA between 2005 and 2009 at nine centres in France. Mean age at surgery was 61 years. The patients had knee osteoarthritis secondary to a fracture (n=66), osteotomy (n=131), or ligament injury (n=66). Mean time from trauma or surgery to TKA was 145 months (range, 72-219 months). RESULTS: Major complications were infection (n=12, 4.5%), skin problems (n=8, 3%), and stiffness (n=8, 3%). Ten-year survival to implant exchange for any reason was 89%±2.8%. Flexion range increased by 2.5°±17° (p=0.02) to a mean of 110° (range, 30° to 140°); extension range increased by 4°±7° (p<0.001) to a mean of -1.19 (range, -20° to 0°). Of the 263 patients, 157 (60%) reported little or no pain at last follow-up. Mean postoperative hip-knee-ankle angle was 179°±3.2° (range, 171°-188°). CONCLUSION: TKA performed after knee injury or surgery carries a risk of specific complications (infection, skin problems, and stiffness) and may have a lower survival rate compared to primary TKA. LEVEL OF EVIDENCE: IV, retrospective cohort study.

The benefit of the systematic revision of the acetabular implant in favor of a dual mobility articulation during the treatment of periprosthetic fractures of the femur: a 49 cases prospective comparative study.

INTRODUCTION: The SOFCOT symposium (2005) on periprosthetic fractures of the femur (PFFs) highlighted a high rate of dislocation (15.6% at 6 months) after change of prosthesis. So far, no study has ever proved the benefit of dual-mobility articulation during PFFs revisions. We conducted a comparative study on two prospective cohorts in order to (1) assess the influence of systematic acetabular revision in favor of a double mobility on dislocation rate (2) and in order to evaluate the rate of morbidity associated with this extra surgical procedure. HYPOTHESIS: A systematic replacement of the cup in favor of a dual-mobility articulation enables to reduce the dislocation rate in PFFs revisions without increasing morbidity. METHODOLOGY: We compared two prospective multicenter cohorts over a year (2005 and 2015) using the same methodology. Any fracture around hip prosthesis which occurred 3 months at least after surgery was included. Data collection was clinical and radiological on preoperative, intraoperative and 6 months after surgery. The 2015 "bipolar" group (n = 24) included patients who had a bipolar revision (both femoral and dual-mobility articulation). The 2005 "unipolar" group (n = 25) included patients who had only a femoral implant revision. Patients were comparable by age (p = 0.36), sex (p = 0.91), ASA score (p = 0.36), history of prosthetic revision (p = 1.00), Katz score (p = 0.50) and the type of fracture according to the Vancouver classification (p = 0.55). RESULTS: There was a 4% rate of dislocation in the "bipolar group" while there was 21% rate of dislocation in the "unipolar group" (8% of recurrent dislocation) (p = 0.19). The rate of all-cause complications 6 months after surgery was not significantly different (p = 0.07): 12.5% in the 2015 "bipolar" cohort (one dislocation, one non-symptomatic cup migration and one pseudarthrosis of the major trochanter) versus 35% in the "unipolar" cohort (5 dislocations, 1 major trochanter fracture and 1 femur pseudarthrosis, 1 secondary displacement associated with a superficial infection). The surgical revision after 6 months was not significantly different (1/23 or 4% vs. 4/25 or 16%, p = 0.35). CONCLUSION: We confirm the low rate of dislocations after fitting a dual-mobility cup in case of revision of the femoral side in case of periprosthetic femoral fracture, as well as the need for additional cases to be carried out upon further studies to significantly confirm the interest of preventing instability after femoral revision.

Hip resurfacing before 50years of age: A prospective study of 979 hips with a mean follow-up of 5.1years.

BACKGROUND: Hip resurfacing arthroplasty (HRA) is an alternative to total hip arthroplasty (THA) for the treatment of hip osteoarthritis in patients younger than 50 years. Data on revision rates after HRA are conflicting. The National Institute for Health and Care Excellence (NICE) recommends performing only those hip arthroplasty procedures associated with 10-year revision rates no greater than 5% (0.5% per year). Follow-up studies can rapidly determine whether this criterion is met. The uncertainties surrounding revision rates after HRA prompted us to design a study of prospectively enrolled patients aiming (1) to determine the revision rate after HRA performed before 50years of age and (2) to assess the functional, radiological, and biological outcomes of HRA. HYPOTHESIS: The revision rate after HRA performed before 50years of age meets the NICE criterion. MATERIAL AND METHODS: Consecutive patients undergoing HRA before 50years of age were enrolled prospectively. The same implant was used in all patients. Functional outcomes were assessed based on the Harris Hip Score (HHS), Postel-Merle d'Aubigné (PMA) score, 12-item Oxford Hip Score (OHS), and UCLA activity score. Radiographic outcomes were assessed, and blood levels of chromium and cobalt were assayed. RESULTS: The study included 936 patients (979 HRAs) with a mean age of 42.7years (16.4-50.0years) at surgery and a mean follow-up of 5.1years (range: 3.1-9.0 years). All four mean functional scores were significantly improved at last follow-up vs. baseline: HHS, 95.9 (39.0-100) vs. 44.3 (18.0-83.0); PMA score, 17.6 (6.0-18.0) vs. 11.7 (3.0-16.0); OHS, 14.3 (12.0-37.0) vs. 40.6 (25.0-60.0); and UCLA activity score, 7.8 (2.0-10.0) vs. 5.6 (1.0-10.0) (p<0.0001). Mean cup inclination in the coronal plane was 42.1° (25.0°-68.0°). Mean blood cobalt level was significantly higher at last follow-up than at baseline (1.36µg/L [0.05-8.2µg/L] vs. 0.61µg/L [0.01-3.6]) (p<0.001). No patient experienced dislocation. Revision was required for 17 hips and involved changing the implant in 12 (1.2%). The 10-year survival rate with implant change, as the endpoint was 98.7% (95%CI, 97.6%-99.3%), indicating that the NICE criterion was easily met. DISCUSSION: The NICE criterion allows the rapid identification of prostheses with insufficient survival. HRA is theoretically associated with a high risk of aseptic mechanical loosening, as it is performed in young patients who have a high level of physical activity. Nevertheless, our study showed that implant survival after HRA was better than required by the NICE criterion. Thus, HRA is a valid alterative to THA in patients younger than 50years. LEVEL OF EVIDENCE: IV, prospective study with no control group.

Course of dislocated posterior hip arthroplasty: A continuous 232-patient series at a mean 10 years' follow up (range, 1-22 years).

BACKGROUND: Dislocation rates in posterior total hip arthroplasty (THA) range between 2% and 5%, but long-term course (recurrence of dislocation or revision surgery) is not known, most series having short follow-up or small populations. We therefore conducted a retrospective study on a large series, to determine long-term rates of recurrence and surgical revision and recurrence risk factors. HYPOTHESIS: Long-term follow-up of a large cohort of THA dislocations enables recurrence rate and factors to be determined. MATERIAL AND METHOD: Five hundred and nine cases of THA dislocation were admitted to our center between 1994 and 2008. A hundred and twenty seven incomplete files and 150 patients who had received their THA elsewhere were excluded, leaving 232 patients: 150 female, 82 male. Mean age at THA (163 primary, 69 revision) was 63 years (range, 15-90 years), and 65 years (range 20-90 years) at first dislocation, with a mean interval to dislocation of 25 months. Minimum follow-up was 8 years up to 2016, or 1 year taking account of deaths (111 deaths). There were 46 anterior, 185 posterior and 1 multidirectional dislocations. The following potential recurrence factors were assessed: gander, age, body-mass index (BMI), etiology, surgical history, bearing diameter and type, component fixation means, dislocation direction, and time to dislocation. RESULTS: A hundred and thirty three of the 232 patients (57%) showed at least 1 recurrence, at a mean 38 months (range, 0.5-252 months); 78 experienced a second and 32 a third recurrence. Ninety-nine (43%) had only 1 dislocation, without recurrence, but 17 of these (17%) underwent reoperation for other causes. The reoperation rate was 17/232 (7%) excluding recurrent instability, and 84/232 (36%) for instability. Fourty-eight months after the first dislocation, 84/133 cases of recurrence (63%) had been reoperated on: 16 complete replacements, 18 bearing replacements, 42 dual mobility cups, one large diameter cup, seven Lefèvre retentive cups. The rate of revision surgery for instability was high, at 84/232 (36%), and higher again in relation to recurrence (84/133: 63%). Only posterior dislocation emerged as a factor for recurrence (HR=1.774, 95% CI [1.020-3.083]), the other tested factors showing no correlation.14 of the 84 revision surgeries for instability (16.6%) were followed by recurrence, without identifiable risk factors. CONCLUSION/DISCUSSION: The recurrence rate was 57%, with posterior dislocation as the only risk factor. The rate of revision surgery for recurrence was 84/232 (36%), with 14/84 revision procedures (16.6%) followed by further recurrence. LEVEL OF EVIDENCE: IV, retrospective, without control group.

Litigation in orthopedic surgery: What can we do to prevent it? Systematic analysis of 126 legal actions involving four university hospitals in France.

INTRODUCTION: Orthopedic surgery produces 20% of medical malpractice claims. However only a few studies have examined the reasons for and consequences of these disputes, and they have usually been limited to a single hospital. This led us to perform a retrospective analysis of the claims at four teaching hospitals in northwestern France. The goals were (1) to describe the circumstances that led to these claims and recommend ways to prevent them, and (2) to describe the conduct of the proceedings and their financial and social outcomes. HYPOTHESIS: A systematic analysis of litigation cases will provide accurate information on the circumstances leading to these claims. METHODS: The study included 126 disputes settled between 2000 and 2010 and related to orthopedic or trauma care given at one of four teaching hospitals in northwestern France. The method of recourse, grounds of the complaint, type of surgical procedure, expert findings and amount of the award were systematically analyzed. RESULTS: Of these 126 cases, 54 (43%) of them were submitted to the French CRCI (regional conciliation and compensation commission), 48 (39%) to the French administrative courts and 51 (41%) were settled amicably. Multiple methods of recourse were used in 21% of cases (n=27/126). The average length of administrative court proceedings was 36.7±27 months [4-102], which was significantly longer than the CRCI proceedings (22.7±17.9 months [3-80]) or out-of-court settlement (23.7±21.5 months [0-52]) (p<0.0001). Damages were sought for medical error or treatment-related risk in 67.5% of the complaints (n=85/126), and for failure to inform in 15.8% of cases (n=20/126). There was a suspected surgical site infection in 79.3% of cases (n=100/126). There were multiple grounds for complaint in 68.3% of cases (n=86/126). Poor communication between the physician and patient was identified in 26.2% of cases (n=33/126). Damages were awarded in 25% of cases (n=31/126), with an average award of €58,303±€91,601 [0-357,970]. CONCLUSION: The primary grounds for legal action are infection-related complications combined with a deterioration in the doctor-patient relationship. Disputes could be prevented by continuing efforts to combat hospital-acquired infections and providing better communications training. LEVEL OF PROOF: IV (retrospective study).

Can a target zone safer than Lewinnek's safe zone be defined to prevent instability of total hip arthroplasties? Case-control study of 56 dislocated THA and 93 matched controls.

BACKGROUND: Various factors contribute to instability of total hip arthroplasty (THA), with implant orientation being a major contributor. We performed a case-control study with computed tomography (CT) data to determine whether: 1) orientation contributes to THA instability and 2) a safer target zone for stability than Lewinnek's classic safe zone can be defined. MATERIAL AND METHODS: We included prospectively 363 cases of THA dislocation that occurred during the calendar 2013 year in 24 participating hospitals. Of the 128 dislocations that occurred in patients who underwent THA at these centers, 56 (24 anterior, 32 posterior) had CT scans, thus were included in the analysis. The control group was matched 4:1 based on implant type, year of implantation, age, sex, bearing types and THA indication. Of the 428 matched control THA cases, 93 had CT scans. In all, the CT scans from 149 cases (56 unstable, 93 stable) were analyzed to determine the acetabular cup's inclination and anteversion, and the femoral stem's anteversion. RESULTS: In the unstable THA group, cup inclination was 46.9°±7.4°, cup anteversion was 20.4°±10.8° and stem anteversion was 14.2°±9.9°. In the stable THA group, cup inclination was 44.9°±5.3° (P=0.057), cup anteversion was 22.1°±5.1° (P=0.009) and stem anteversion was 13.4°±4.4° (P=0.362). The optimal total anteversion (cup+stem) of 40-60° was achieved in 16.5% of unstable THA cases and 13.9% of stable THA cases, thus this parameter does not predict stability (odds ratio [OR] of 0.40, P=0.144). The cup was positioned in Lewinnek's safe zone in 44.6% of patients in the unstable group and 68.2% of those in the stable group (OR 3.74, P=0.003). A target zone defined as 40-50° inclination and 15-30° anteversion was better able to distinguish between unstable cases (23.2%) and stable cases (71.6%) resulting in an OR of 13.91 (P<0.001). DISCUSSION: Implant positioning was the only risk factor for instability found in this study. Moreover, our findings reinforce the theory put forward by other authors that Lewinnek's safe zone is not specific enough to differentiate between stable and unstable THA implantations. The target zone for acetabular cups proposed here (40-50° inclination and 15°-30° anteversion) is related to a lower risk of instability. This orientation can be used as a guide, but must be combined with other technical elements to optimize stability. By balancing stability and biomechanics, the 40-50° inclination and 15°-30° anteversion target zone redefines the optimal positioning window. LEVEL OF EVIDENCE: III case-control study.

What are the risk factors for dislocation in primary total hip arthroplasty? A multicenter case-control study of 128 unstable and 438 stable hips.

INTRODUCTION: Dislocation after total hip arthroplasty (THA) is a leading reason for surgical revision. The risk factors for dislocation are controversial, particularly those related to the patient and to the surgical procedure itself. The differences in opinion on the impact of these factors stem from the fact they are often evaluated using retrospective studies or in limited patient populations. This led us to carry out a prospective case-control study on a large population to determine: 1) the risk factors for dislocation after THA, 2) the features of these dislocations, and 3) the contribution of patient-related factors and surgery-related factors. HYPOTHESIS: Risk factors for dislocation related to the patient and procedure can be identified using a large case-control study. PATIENTS AND METHODS: A multicenter, prospective case-control study was performed between January 1 and December 31, 2013. Four patients with stable THAs were matched to each patient with a dislocated THA. This led to 566 primary THA cases being included: 128 unstable, 438 stable. The primary matching factors were sex, age, initial diagnosis, surgical approach, implantation date and type of implants (bearing size, standard or dual-mobility cup). RESULTS: The patients with unstable THAs were 67±12 [37-73]years old on average; there were 61 women (48%) and 67 men (52%). Hip osteoarthritis (OA) was the main reason for the THA procedure in 71% (91/128) of the unstable group. The dislocation was posterior in 84 cases and anterior in 44 cases. The dislocation occurred within 3 months of the primary surgery in 48 cases (38%), 3 to 12 months after in 23 cases (18%), 1 to 5years after in 20 cases (16%), 5 to 10years after in 17 cases (13%) and more than 10years later in 20 cases. The dislocation recurred within 6 months of the initial dislocation in 23 of the 128 cases (18%). The risk factors for instability were a high ASA score with an odds ratio (OR) of 1.93 (95% CI: 1.4-2.6), neurological disability (cognitive, motor or psychiatric disorders) with an OR of 3.9 (95% CI: 2.15-7.1), history of spinal disease (lumbar stenosis, spinal fusion, discectomy, scoliosis and injury sequelae) with an OR of 1.89 (95% CI: 1.0-3.6), unrepaired joint capsule (all approaches) with an OR of 4.1 (95% CI: 2.3-7.37), unrepaired joint capsule (posterior approach) with an OR of 6.0 (95% CI: 2.2-15.9), and cup inclination outside Lewinnek's safe zone (30°-50°) with OR of 2.4 (95% CI: 1.4-4.0). DISCUSSION: This large comparative study isolated important patient-related factors for dislocation that surgeons must be aware of. We also found evidence that implanting the cup in 30° to 50° inclination has a major impact on preventing dislocation. LEVEL OF EVIDENCE: Level III; case-control study.

High-impact sport after hip resurfacing: The Ironman triathlon.

BACKGROUND: Returning to high-impact sport is an increasingly frequent functional demand following hip replacement. The literature, however, is sparse on the subject and nonexistent regarding triathlon. We therefore conducted a retrospective study of hip resurfacing in triathlon players, to determine: (1) whether it is possible to return to this kind of sport; (2) if so, whether it is possible to return to the same level; and (3) how a resurfaced hip behaves under these conditions. HYPOTHESIS: Hip resurfacing allows return to competition level in long-distance triathlon. MATERIAL AND METHODS: A single-center single-operator retrospective study included patients undergoing hip resurfacing with the Conserve Plus implant inserted through a posterolateral approach, who had ceased long-distance triathlon practice due to osteoarthritis of the hip. Fifty-one of the 1688 patients undergoing resurfacing during the inclusion period were long-distance triathlon players. RESULTS: The series comprised 48 patients: 51 implants; 43 male, 5 female; mean age, 44.8 years (range, 28.2-58.9 years). At a mean 4.7 years' follow-up (range, 2.2-7.6 years), all clinical scores showed significant improvement; Merle d'Aubigné and Harris scores rose respectively from 12.3 (5-16) and 42 (37-56) preoperatively to 17.5 (13-18) and 93.2 (73-100) (P<0.001). There were no cases of dislocation or implant revision. Forty-five patients returned to sport (94%). Rates of return to swimming, cycling and running were respectively 38/48 (79%), 41/48 (85%) and 33/48 (69%). Preoperatively, all patients had taken part in at least 1 competition: 29 with distance=70.3km and 19 with distance=140.6km. At follow-up, 28 patients had taken part in an Ironman competition: 21 with distance=70.3km and 7 with distance=140.6km. Mean competition performance did not differ between pre and postoperative periods. DISCUSSION: Return-to-sport rates were good following hip resurfacing. Non-impact sports (swimming, cycling) predominated postoperatively, whereas the rate of impact sport (running) diminished. Return to competition-level sport (extreme triathlon) was possible for 28/48 patients (58%). Implant survival seemed unaffected by this high-impact sports activity at a mean 4.7 years' follow-up. LEVEL OF EVIDENCE: IV, retrospective, non-controlled.

Validation of a French patient-reported outcome measure for patello-femoral disorders: The Lille Patello-Femoral Score.

BACKGROUND: The diagnosis of patello-femoral instability (PFI) relies chiefly on the patient's clinical findings. Nevertheless, few clinical scores specifically designed to evaluate the patello-femoral joint are available. The Lille scoring system is a 12-item self-questionnaire yielding a score from 0 to 100 that is used in France but has not been validated. We therefore conducted a validation study in a population of younger patients with PFI. HYPOTHESIS: The Lille scoring system meets validation criteria for patient-reported outcome measures (PROMs). MATERIAL AND METHOD: A retrospective study done in two centres identified 136 patients with objective (n=109) or potential (n=27) PFI. Before and after surgery, the Lille score was determined by all patients and the Kujala score in 61 patients. The Lille score was also determined by 30 controls free of patello-femoral disorders to allow an evaluation of discrimination between PFI and other knee disorders in individuals of similar age. RESULTS: The response rate was 100%, indicating that the Lille questionnaire was easy to complete. Consistency was established: (a) the global score showed no floor or ceiling effect (in no questionnaires were over 85% of items given the highest or lowest possible score), and saturation occurred neither for the global score nor for the item sub-scores (fewer than 85% of patients had the lowest or highest possible score); (b) a single redundancy was found, between the items 'pain' and 'locking', for which the correlation coefficient was≥0.7 (P<0.0001). Discriminating performance was assessed by comparing the mean Lille score values in the controls (67.8±9.2) and patients (38.1±10.4); the difference was significant (P<0.05) and the estimated effect size was>0.8, indicating strong discrimination by the Lille scoring system. Item uniformity, with all items measuring the same phenomenon, was established by the Cronbach alpha coefficient value>0.7. External consistency between the Lille and Kujala scoring systems was confirmed in the 61 patients for whom both scores were available (Pearson correlation coefficient, 0.5). Sensitivity to change was established by the>0.8 effect size of surgical treatment. DISCUSSION: The Lille scoring system deserves to be used routinely in clinical practice as a patient-reported outcome measure. A prospective study will assess intra-observer reproducibility and sensitivity to change in patients treated non-operatively. Although confined to retrospective data, this study based on methods designed to assess PROMs establishes the validity of the Lille scoring system and supports its use in PFI. LEVEL OF EVIDENCE: III, case-control design.

Epidemiology of patients with MSSA versus MRSA infections of orthopedic implants: Retrospective study of 115 patients.

Factors that predict the occurrence of a surgical site infection due to methicillin-resistant Staphylococcus aureus (MRSA) are not well known; however this information could be used to modify the recommended antimicrobial prophylaxis. We carried out a retrospective study of S. aureus infections on orthopedic implants to determine: (1) whether epidemiological factors can be identified that predict a MRSA infection, (2) the impact of these factors as evidenced by the odds ratio (OR). HYPOTHESIS: Risk factors for a MRSA infection can be identified from a cohort of patients with S. aureus infections. MATERIALS AND METHODS: We identified 244 patients who experienced a S. aureus surgical site infection (SSI) in 2011-2012 documented by intraoperative sample collection. Of these 244 patients, those who had a previous SSI (n=44), those with a SSI but no orthopedic implant (n=80) or those who had the infection more than 1-year after the initial surgery (n=5) were excluded. This resulted in 115 patients (53 arthroplasty, 62 bone fixation) being analyzed for this study. There were 24 MRSA infections and 91 MSSA infections. The following factors were evaluated in bivariate and multifactorial analysis: age, sex, type of device (prosthesis/bone fixation), predisposition (diabetes, obesity, kidney failure), and environmental factors (hospitalization in intensive care unit within past 5 years, nursing home stay). RESULTS: Two factors were correlated with the occurrence of MRSA infections. (1) Nursing home patients had a higher rate of MRSA infections (67% vs. 18%, P=0.017) with an OR of 8.42 (95% CI: 1.06-66.43). (2) Patients who had undergone bone fixation had a lower rate of MRSA infections than patients who had undergone arthroplasty (13% vs. 30%, P=0.023), OR 0.11 (95% CI: 0.02-0.56). Although the sample size was too small to be statistically significant, all of the patients with kidney failure (n=4) had a MRSA infection. DISCUSSION: Since these MRSA infection risk factors are easy to identify, the antimicrobial prophylaxis could be adapted in these specific patient groups.

Is there any range-of-motion advantage to using bearings larger than 36mm in primary hip arthroplasty: A case-control study comparing 36-mm and large-diameter heads.

BACKGROUND: Large-diameter (>36mm) total hip arthroplasty (THA) has developed rapidly since the advent of ceramic-on-ceramic (CoC) bearings and highly cross-linked polyethylene. Theoretically, the increase in diameter reduces the risk of instability, although the advantage of calibers beyond 36mm has not been demonstrated in terms of range-of-motion recovery. We conducted a comparative study with a single prosthesis model to determine whether increasing the caliber beyond 36mm provides: (1) better recovery of range-of-motion, (2) a higher functional score, and (3) reduction of the dislocation rate. HYPOTHESIS: Increasing the range-of-motion by increasing the caliber beyond 36mm provides better range-of-motion. MATERIAL AND METHODS: We analyzed two consecutive, single-operator cementless THA series performed via the mini posterior approach, which differed only in the bearing system (51 metal-on-metal [MoM] with a mean caliber of 45mm±3.3 [range, 40-54] and 61 CoC with a 36-mm caliber). Both series were comparable preoperatively in terms of age, diagnosis, functional scores, preoperative range-of-motion, body mass index, UCLA activity level, and Charnley score. We compared the joint range of movement at follow-up and the gains in range of movement, onset of dislocation, and functional scores (Oxford, Postel-Merle d'Aubigné [PMA]). RESULTS: The mean overall joint range-of-motion was 254°±39° (range, 150-310°) for an 81°±44° (range, -50 to 180°) gain in the MoM group and 256°±23° (range, 200-280°) for an 84°±40° (range, 0-160°) gain in the CoC group (NS). The MoM group presented the following results: Oxford=13.71±3.66 (range, 12-33) for a gain of 24.82 points±7.9 (range, -1 to 40), PMA=17.75±1.06 (range, 11-18) for a gain of 7.78 points±4.01 (range, 2-15). The CoC group had: Oxford=14.98±4.42 (range, 12-36) for a gain of 24.75 points±6.55 (range, 12-40), PMA 17.66±0.7 (range, 14-18) for a gain of 8 points±3.77 (range, 1-15). None of the gains and scores at follow-up differed significantly between the two groups. No episode of dislocation was identified. DISCUSSION: The current trend of increasing femoral head diameters beyond 36mm to improve the gains in joint range-of-motion and function is not warranted. The potential side effects of increasing the caliber call for even greater caution in the use of large-diameter heads because our hypothesis has not been confirmed. LEVEL OF EVIDENCE: Case-control study, level III.