Introduction

Locking nail have considerably improved the treatment of long weight bearing bones. However, distal locking needs experience and may expose to radiations. Many methods have been proposed to facilitate distal locking and improve safety. Recently, an external distal targeting device adapted to the ancillary of the Long Gamma Nail has been proposed. We report our experience with this device through a comparative series of distal lockings. Aim of this work was to assess feasibility and advantages brought about with this targeting device when considering time or dose of irradiation.

Purpose of the study: Computed tomography is recommended for the preoperative work-up of joint fractures as it allows an optimisation of the access as a function of the injury. During the operation, 2D radiographic or fluoroscopic controls are still widely used. After one year’s experience, we evaluated the potential pertinence of using 3D reconstructions intraoperatively with a mobile isocentric fluoroscope (iso-C-3D).

Material and methods: All operations for which the amplifier was used were collected prospectively. The type of fixation as well as the details of the installation and measures taken intraoperatively were noted.

Results: At one year, intraoperative 3D reconstructions were made during 48 operations in 47 patients: fracture of the calcaneum (n=13), thoracolumbar spin (n=12), acetabulum (n=11), tibial condyles (n=9), odontoid (n=2), pelvis (n=1). The installation was habitual for the calcaneum and odontoid fractures. For the other localizations, use of a carbon plateau table facilitated good quality imaging for spinal and tibial condyle fractures; a carbon orthopaedic table was useful for acetabulum and pelvis fractures. With the intraoperative 3D reconstruction the surgeon was able to check the freedom of the canal after reduction and fixation. For the calcaneum fractures, reduction of the thalamic fragment was revised in one patient; in another, an intra-articular screw was replaced. One intra-articular screw stabilizing the posterior wall was also changed during an acetabulum fixation.

Discussion: During our first year of use, 3D reconstruction intraoperatively has allowed us to avoid three early reoperations (for two calcaneums and one acetabulum). Classical 2D imaging of these two localizations is difficult to interpret because of the spherical form of the hip joint and, for the calcaneum, the difficulty in obtaining quality retrotibial images. Quality images requires specific installation, limiting interference with metallic supports.

Conclusion: The results we have obtained in our first year of use of the ISO-C-3D amplifier has led us to generalise its use for percutaneous fixation procedures involving the acetabulum and the calcaneum.

Purpose of the study: We report a prospective consecutive series of femoral fractures on prosthesis. The goal was to evaluate mid-term outcome of treatment with a locking plate.

Material and methods: From June 2002 to December 2007, we treated 35 patients (1 bilateral), 28 female and 7 male, with a fracture around their total hip arthroplasty (n=21), total knee arthroplasty n=7), unicompartmental knee prosthesis (n=1), between a THA and a TKA (n=2), or between a trochanteric osteosynthesis and a TKA (n=5). Mean age was 76 years (39–93). For the majority, osteosynthesis was achieved via a mini-invasive incision, using a locking plat (Synthes^®) bridging the implant in situ. The rehabilitation protocol consisted in immediate weight-bearing for most of the cases.

Results: At revision, one patient was lost to follow-up, one was an early failure, and seven patients had died, including four which were retained for the analysis because data was available for 24, 40, 43 and 67 months respectively. The analysis thus included 30 patients with 31 fractures and mean 26 months follow-up (range 6 – 67 months). The following results were obtained for the initial series: mini-invasive surgery (n=26), access to fracture focus (n=10), total postoperative weight bearing (n=20), partial weight bearing at 20 kg (n=3), no weight-bearing for six weeks (n=13). Complications were: infection (n=2), general (n=2), disassembly (n=3, one femoral stem replacement and two revision ostheosynthesis). Bone healing was obtained in all cases except one. There was a misalignment > 5 in five cases. At review, there was no implant loosening.

Discussion: This work shows that locking compression plates inserted via a mini-invasive approach followed by weight-bearing is a feasible option. This technique combines the principles of closed osteosynthesis with preservation of the haematoma and stability of osteosynthesis material. The rehabilitation protocol was developed in consideration of the nature of the material. The locked plate acts like an internal fixator, allowing increased implant stability. Screw hold appeared to be sufficient to allow early weight-bearing.

Conclusion: Use of locking compression plates for femoral fractures on osteosynthesis implants is effective. The stability of the assembly allow, despite the age of the patients, early weight-bearing and walking, with a stable outcome over time.

Introduction: Preoperative use of tomodensitometry is a common practice when assessing fractures with intraarticular involvement, helping to determine the most appropriate surgical approach according to the lesions observed. To date, during the surgical procedure itself, radiographical or fluoroscopic controls still largely rely on two dimensions X rays. We assessed the possible benefits of intraoperative tridimensional reconstructions using mobile isocentric fluoroscopy (iso-C-3D) after one year of use.

Material and Methods: All the procedures where intra-operative tridimensional fluoroscopy was used were assessed prospectively for one year. The type of osteosynthesis as well as specific modalities of installation and therapeutic measures driven from analysis of the images were analyzed.

Results: During the first year of use, intraoperative tridimensional reconstruction had been carried out in 48 procedures in 47 patients. The region involved was calcaneus 13 times, thoracolumbar spine 12 times, acetabulum 11 times, tibial condyles 9 times, axis 2 times and pelvis one time. Installation was the same than usually performed in the cases of calcaneus and axis osteosynthesis. For the other localisations, obtention of good quality images was facilitated through the use of a carbon table for spine and osteosynthesis of the tibial condyles, and through the use of a carbon traction table for acetabular or pelvic fractures. Intraoperative tridimensional reconstruction allowed to check for freedom of the vertebral canal after reduction and osteosynthesis of the spine. in the cases of fracture of the calcaneus, reduction of one thalamic fragment was improved in one case and one intraarticular screw could be changed in another case. In the case of acetabular surgery, one screw stabilizing the posterior wall was found intraarticular on tridimensional reconstruction and could be changed before closure.

Discussion: Intraoperative tridimensional reconstruction, during its first year of use, allowed to avoid 3 early reinterventions (for 2 calcaneus and one acetabulum). Accurate interpretation of standard plain X ray in these two localizations is difficult because of the spherical shape of the hip joint and because good quality imaging, especially the retrotibial view, is hardly obtained intraoperatively in fractures of the cacaneus. When using tridemensional reconstructions, acquisition of good quality images has to be anticipated during the installation of the patient, limiting any interfereces with metallic supports to a minimum.

Conclusion: the results obtained over the first year of use of intraoperative tridimensional reconstructions with the ISO-C-3D encouraged the authors to generalize its use when performing osteosynthesis of the acetabulum or calcaneus as well as percutaneus osteosynthesis of articular fractures.

Purpose of the study: The double-mobility concept was introduced for clinical applications for total hip arthroplasty in 1976. The concept preserves joint range of motion while increasing stability. In this study we evaluated the consequences of these advantages in terms of polyethylene wear, measuring wear both on the concave and convex surfaces and volumetrically.

Material and methods: Forty polyethylene inserts were explanted and analyzed. Explantation had been performed for mechanical or septic failure after eight years implantation on average. Mean age of patients at implantation was 46 years. After examining the gross aspect of the insert, surface analysis was performed with direct measurement of changes in the curvature using a BHN 706 position sensor for the inner concave surface and lateral projection for the outer convex surface. Estimated measurement error was ±5μm for each method; the manufacturer's tolerance for production of the inserts was 50μm. Volumetric wear was determined by reference to the manufacturer’s data. Student’s t test for paired series was applied.

Results: At gross inspection, all inserts had lost the strips originally present on the convex surface; 40% presented visible wear of the retaining ring. Mean annual wear (± standard deviation, SD) obtained with the measuring system was 9±9 μm/yr) for the convex surface and 73 ± 69 μm/yr for the concave surface. Total annual wear, the sum of inner and outer surface wear, was 82±72 μm/yr. The mean volumetric wear was 28±28 mm3/year for the convex surface and 25±23 mm3/year for the concave surface and 53.4±40 mm3/year for total wear.

Discussion: Total wear for these 40 double-mobility inserts which had functioned in vivo was not greater than the values reported for the metal-polyethylene bearing with 22.2 mm femoral heads. The double mobility is not associated with greater wear. While there was no significant difference between the wear volume of the convex versus the concave surfaces, the differentials wear were widespread, which can be considered to result from functional differences.

Purpose of the study: The reversed total shoulder prosthesis is one of the treatments currently proposed for excentered glenoid osteoarthritic degeneration with massive rotator cuff tears. In light of the mediocre or at best highly variable results obtained with osteosynthesis or humeral arthroplasty for four-fragment fractures of the proximal humerus, indications for the reversed total shoulder prosthesis have been widened to include this category of traumatology patients. The purpose of this prospective study was to report outcome with the reversed prosthesis used for complex fracture of the proximal humerus in subjects aged over 70 years.

Material and methods: Ten patients, mean age 76 years, underwent surgery performed by the same surgeon to insert a Delta (DePuy) reversed prosthesis for four-fragment complex displaced fracture of the proximal humerus. The deltopectoral approach was used for all patients. The rotator cuff status was assessed intraoperatively. Clinical (Constant score) and radiological assessment were noted at 24 months.

Results: During the operation, only three of the ten shoulders presented a full thickness rotator cuff tear. One patients developed a complication requiring revision: early dislocation revised with a retaining polyethylene insert without recurrent dislocation. There were no cases of glenoid loosening at last follow-up. The weighted Constant score was 65/100. A pain-free shoulder was achieved in all ten patients. Anterior elevation was 130° on average, internal rotation reached hand to buttocks and active external rotation 20°.

Discussion: In patients aged over 70 years presenting a complex four-fragment fracture of the proximal humerus, the reversed prosthesis enables improved function and restoration of satisfactory joint movement. Early postoperative recovery and the gain in pain relief are encouraging factors. There was however unsatisfactory restoration of active rotation. For the elderly subject, free of a massive rotator cuff tear, rapid recovery after insertion of an reversed prosthesis should be balanced against the possible preservation of active rotations with an anatomic prosthesis.

Purpose of the study: Double mobility prostheses are increasingly popular. Evidence in the literature demonstrates greater efficacy for the treatment and prevention of prosthesis instability. Ten-year survival is to the order of 95% (Aubriot, Philippot). One of the drawbacks is the risk of prosthetic head displacement outside the retaining polyethylene ring, i.e. intraprosthetic dislocation. We searched for factors causing this complication.

Material and methods: We reviewed retrospectively 67 files concerning intraprosthetic dislocation among a series of Novae cups (Serf) implanted from 1982. Head diameter was 22.2 mm for 59 cases, with a Pro stem (Serf) for 31 cases and a PF stem (Serf) for 36. Each type of stem has a specific neck design. All patients underwent revision surgery; the retaining function of the explanted pieces was analyzed.

Results: Mean time to the complication was 91 months; mean patient age at implantation was 54 years. Early cases exhibited macroscopically intact retaining capacity. Intermediary and late cases exhibited macroscopic wear with an oval shaped retaining ring. For three cases, intraprosthetic dislocation followed an episode of dislocation reduced under sedation. The cups measured 53 mm on average. The rate of calcification was high in this population (15 cases of Brooker grade 3 or 4). Mean survival was significantly different between the Pro and PF stems.

Discussion: Early dislocations were related to insufficient retaining capacity of the initially inserted ring. After a corrective measure by the manufacturer, this type of early complication has disappeared. Late dislocations resulted from impingement wear. Dislocation of a prosthesis with a double-mobility cup increases the risk of intraprosthetic dislocation after reduction; reduction procedures should thus be performed under general anesthesia with curare treatment. We analyzed the different parameters involved: head-neck relation, activity, periprosthetic calcification, cup diameter, resurfacing of the prosthetic neck. Observations were compared with data in the literature.

Purpose of the study: The iliopsoas bursa lies immediately anteriorly to the hip joint capsule and in certain cases there exists a natural communication between a hip prosthesis and the iliopsoas bursa, enabling formation of an inguinal mass by distension of the bursa.

Material and methods: We report six cases of a pseudo-tumoral mass which developed in the femoral scarpa triangle revealing a complication of total hip arthroplasty. These six patients, aged 66–79 years had their prosthesis for 11.5 years on average (range 4–20 years). Three had a history of acetabular dysplasia. All complained of pain. Five patients presented a palpable mass in the inguinal region. Two patients underwent emergency surgery, one for suspected strangulation of a crural herniation and the second for septic inguinal adenopathy. In two patients the clinical presentation was related to the local effect of the mass: lower limb edema with recurrent phlebitis due to venous and lymphatic compression, and femoralgia due to compression of the femoral nerve. The underlying prosthetic complications were: aseptic loosening (n=4), polyethylene wear (n=2), infection (n=1). All patients underwent revision surgery to change the prosthesis. The cystic formation was drained without resection. Symptoms resolved after replacement surgery in all patients.

Discussion: Palpation of an inguinal mass with signs of local compression in a patient with a painful total hip arthroplasty is a sign of a prosthetic complication (infection, loosening, wear). The diagnostic work-up should include bacteriology and plain x-rays of the hip joint. Bone scintigraphy may be contributive. Arthrography can demonstrate presence of a communication. Computed tomography provides the best visualization of the mass and its relations with neighboring organs. A duplex-Doppler is needed in all cases to search for thromboembolic complications prior to surgery. We chose not to resect the cystic formation in our patients, preferring treatment of the intra-articular cause. The fact that the mass and local its effects resolved in all cases with no recurrence at last follow-up leads us to recommend this attitude for typical presentations.

Introduction: Infection after hip or knee replacement occurs with low frequency but shares high morbidity. Aim of this study was an evaluation of incidence and risk factors related to post operative infection after joint lower limb joint replacement in an orthopaedics unit.

Material and methods: This is a monocentric, retrospective, case control study over the years 2000 to 2002. All first intention Total Hip and Knee Replacement and revision cases for mechanical reasons that became infected were identified. Demographic, surgical and medical variables, potentially associated to prosthetic infection were compared for these patients to a control group of non ifected patients over the same time, matched for sex, age and surgery type.

Results: Ten patients, all male, contracted post operative joint infection, out of 630 Total Hip or Knee Arthroplasties. This represented 1.2% after hip replacement and 3.1% after knee replacement. Bacteriological datas showed a majority of Staphylococal infection (5 aureus, 1 epidermidis), 2 among these being resistant to meticillin, but also evidence of ENT commensals (2 Streptococci milleri, 1 Actinomyces) and one epidermal commensal (Propionobacterium acnes). Univariate analysis: datas associated with increased risk of infection were diabetes melitus (OR 9.3; CI 95% 1.4–63), operating time exceeding 120 minutes (OR15.5 ; CI 95% 1,73–139,66), superficial wound infection (odds ratio 29; CI95% 2,77–303,32), coinfection outside the operation site (urinary tract , dental infection) (OR: 9,3 ; CI 95% 1,33–63,2). In our study an MNIS score higher than 1, autologous transfusion, locore-gional anaesthesia with or without the use of a catheter, antibioprophylaxis that did not comply with national recommendations could not be drawn as a risk factor.

Discussion: Incidence of infection and risk factors related to infection in our study were found similar tothe results of published datas. The small number of events (10 cases) did not allow us to realize multivariate analysis and could explain that some known risk factors such as non recommended antibioprophylaxis, could not be elicitated. However these results suggested the need to reevaluate the system of prevention of infection in our centre such as protocolization of antibioprophylaxis and screening for and treatement of perioperative coinfection.

Purpose: Partial epiphysiodesis of the growth plate due to physeal aggression is a common problem in paediatric patients. Surgical management requires precise imaging. We recall other imaging techniques currently employed and describe a novel method for studying the characteristic features of epiphysiodesis bridges of the growth plate: 3D-magnetic resonance imaging (3D-MRI).

Material and methods: We analysed retrospectively MRI series of 27 epiphysiodesis bridges in 23 children (ten boys and thirteen girls) aged 11.3 years (range 2.5 – 15). We recorded information concerning the cause of the physeal aggression, the joint involved, the type of bony bridge (Ogden classification), the clinical deformation, and the proposed treatment. The 27 bridges were studied on coronal MRI acquired with echo-gradient and fat suppression sequences. Data were processed with a manual 3D reconstruction program in 15 minutes to precisely define the localisation, the volume, and the morphology of the bony bridge and the active physis.

Results: The epiphysiodeses were caused by trauma (65%), iatrogenic aggression (17%), ischemia-infection (purpura fulminans) (9%), juxta-physeal essential cyst (4.5%), and unknown causes (4.5%). Eighty-seven percent involved a lower limb joint, 75% of which involved the tibia. The surface of the epiphysiodesis bridge covered 20% of the physis. The bridges were peripheral (46.5%), central (46.5%), and linear (7%).

Discussion: It is difficult to determine the position and the 3D relations of an epiphysiodesis bridge in a healthy active physis with imaging techniques such as plain x-rays, scintigraphy, tomography and computed tomography. The 3D-MRI method described here provides a sure way to distinguish the active growth plate which gives a high intensity signal and the epiphyseal bridge which gives a low intensity signal. Morphological (size, form) and topographic characteristics of the bony bridge and the physis can be described with precision facilitating therapeutic decision making and guiding surgery. The lack of radiation risk is also an advantage of MRI.

Conclusion: The quality of the images obtained, the safety of MRI and the easy interpretation of 3D reconstructions makes this imaging technique an excellent method for pre-therapeutic analysis of epiphysiodesis bridges.

Purpose: Treatment of femoral epiphysiolysis with major displacement remains a controversial subject. Open repositioning of the epiphysis via a lateral approach as proposed by Dunn allows nearly anatomic restitution but with a high rate of complications. We report our experience with open repositions via an anterior approach which has been more reliable in our hands.

Material and methods: During the last decade, we operated nine hips for epiphysiolysis with major displacement, using the anterior approach to spare the medial circumflex artery. External reduction was not attempted. Preoperative and residual displacement were evaluated using the Southwick technique and according to the position of the femoral head in relation to the Klein line. Early after surgery, a bone scintigram was obtained for all hips. We followed these patients to bone maturity, with a mean follow-up of four years.

Results: The early postoperative scintigrams did not reveal any case of insufficient uptake in the femoral head. Mean correction was 43° on the lateral view, with a mean preoperative displacement of 72°. Mean residual displacement after surgery was 23°. After repositioning, position of the epiphysis in relation to the Klein line was not significantly different from the position observed on the healthy side. Postoperatively, leg length discrepancy was 1 cm. At last follow-up, there have been no signs of osteonecrosis, chondrolysis or osteoarthritic degeneration. At mean 44 months follow-up, all of the patients have unlimited activities, including sports. Only one patient complained of mild climate-related pain.

Discussion: Compared with the lateral approach with trochanterotomy as proposed by Dunn, we have found the anterior approach technically easier and more reliable in terms of protecting the epiphyseal blood supply. The correction obtained, voluntarily preserving a certain degree of under-correction, associated with resection of a portion of the neck enables repositioning without risking vessel stress. Use of a stable internal fixation which allows early mobilisation would be an explanation of the absence of postoperative chondrolysis.

Conclusion: These results appear to be sufficiently encouraging to advocate this technique previously described by PH Martin in 1948.

Purpose: Amstuz introduced the notion of a lever arm ratio to describe the relationship between the abductors and weight in arthroplasty. He demonstrated that patients may limp if defective lateralisation produces a low lever arm ratio. We analysed a continuous series of arthroplasty patients with excellent outcome at one year to compare restoration of lateralisation with the preoperative status. We also performed the same analysis in a series of patients who limped after arthroplasty, excluding cases with classical causes of failure. We then compared these two series.

Material and methods: We had a series of 100 arthroplasties with excellent results at one year. These patients had undergone unilateral arthroplasty and had a healthy contralateral hip. The centre of the arthroplasty head was identified on preoperative and one-year AP x-rays of the pelvis (same magnification). We measured the lateralisation in relation to the femoral axis. The position of the cup was measured with a U ratio. Results were expressed in percent restitution of the preoperative status. Amstutz’s lever arm ratio was also measured. Finally, we measured the distance between the pubic symphysis and the outermost point of the femur on the prosthetic and healthy side.

We also had a second population of twelve patients presenting persistent limping at one year with no objective cause. The same parameters were measured for this population.

Results: We found that we had achieved only partial restitution of the initial lateralisation and had a tendency to medialise the acetabulum. The restitution of lateralisation was significantly different between the series with excellent outcome and the series with limping.

Discussion: Deficient lateralisation appears to be a factor involved in persistent limping. There is a threshold for restitution of lateralisation; limping is always observed under this threshold. Data in the literature reveal a very wide variability in lateralisation. It would thus appear important to restore the initial lateralisation to avoid limping; this has led us, like others, to use lateralised implants for certain patients.

Purpose: A new locked nail is proposed for the treatment of proximal fractures of the humerus. This simple system with self-locking screws was designed for all types of proximal fractures. The purpose of this prospective study was to determine indications and identify limitations.

Material and methods: We used the proposed fixation method sparing the cuff muscles and using a cup-and-ball technique for complex three or four-fragment fractures with major displacement. All nails were locked proximally, with at least two screws, and distally. Early joint mobilisation recommended for this type of osteo-synthesis was applied diversely. This series included 50 fractures of the upper humerus which were all treated with a Telegraph nail between January 2000 and January 2002. We identified 18 fractures of the surgical neck and 32 cephalotuberosity fractures. Mean age was 67 years, range 23–94 years.

Results: The Constant score at maximum follow-up of 24 months was used to assess clinical outcome. Bone healing was effective in all cases but there were several complications: secondary displacement (n=3), fracture of proximal screws (n=5), nail ascension (n=3), rupture of the long head of the biceps (n=1), and stiffness at flexion (n=12), which required removal of the implant in five patients and prosthetic replacement in one.

Discussion: The self-locking screws used with this nail provide excellent stability. Despite the rigid assembly, we observed displacements which led to screw failure and tilting heads. The distal locking screw appears to play a deleterious role in impaction of the fracture. The high rate of complications, 26% in this series, has led to reconsider using plate fixation for complex fractures in young patients and ascending pinning with the Apprill or Hackethal method to avoid aggression on the rotator cuff for fractures of the surgical neck. The Telegraph nail thus does not appear to be indicated only for complex fractures of osteoporotic bone; arthroplasty should be retained for this indication.

Purpose: The anatomy of the endosteal canal of the proximal femur varies greatly in the general population. This variability can compromise total hip arthroplasty when a femoral stem is inserted without cement. While the secondary fixation of the implant is dependent on several parameters, the predominant factor is the primary stability and the large contact between the bone and the treatment surface of the apposed prosthesis. These two conditions, necessary but insufficient to guarantee an excellent clinical result, are obtained if there is a correct bone-implant morphology match. We analysed the morphology of the endosteal canal of the proximal femur to determine whether there is a standard anatomic conformation justifying the use of line prostheses.

Material and methods: We examined 30 femurs harvested from 30 individuals in a consecutive series in our anatomy laboratory. We made 12 scanner slices parallel to the knee joint line starting 1 cm above the apex of the lesser trochanter going up to 11 cm above the lesser trochanter. For each slice, we assimilated the canal to an ellipsoid surface to characterise its barycentre, the angle of the greater axis relative to the reference plane of the posterior condyles, and its dimensions defined with length (greater axis), and width (perpendicular to the greater axis).

Results: For each femur, the AP projections of the barycentres fell on a straight line (anatomic axis) and the lateral projections on a parabole. Helitorsion, i.e. the difference in the torsion angles between the first slice and the last slice was constant (57±8.5°). The dimensions were recorded for each slice.

Discussion: This method can be criticised. We were able to confirm the tridimensional data reported by Noble and confirmed the notion of a somatotype. We defined the normal (statistical) equation of the endosteal canal for the proximal end of the femur (barycentre, dimensions).

Conclusion: The anatomy of the endosteal canal of the upper extremity of the femur is not variable but standardised. It is thus possible to adapt the bone to the prosthesis.

Purpose: Dislocation of total hip arthoplasties is a sad reality. The incidence of this complication is estimated from 0.6 to 8%. Dislocation can be a single event that never recurs, but half of all dislocations will reoccur again. We analysed outcome after treating chronically unstable total hip arthroplasties using a double-mobility cup.

Material and methods: Between 1990 and 2000, we treated 42 cases of recurrent dislocation of total hip arthroplasties. Five were immediate, 33 early, and four late; five dislocations on the average. The prosthesis was implanted via the posterolateral approach for 36 patients. Thirteen patients treated in our unit had already had surgical treatment for chronic instability: 1 trochanteoplasty, 8 bone blocks, 5 restraining cups. A standing AP view of the pelvis was obtained in all patients before surgery to analyse shortening (gluteus medius insufficiency), cup tilt and anteversion, and stem lateralisation. Likewise a CT scan was performed systematically to analyse stem and cup anteversion. No position anomaly was found in 17 patients; at least one anomaly was found in the others. All patients were reoperated via the posterolateral approach. A double-mobility cup was implanted systematically without changing the stem.

Results: Among the 42 patients, we had two with recurrent dislocation, one in a neurologic patient and one in a patient with major anomalies in the position of the femoral component that was not changed. The incidence of recurrent dislocation was thus 4.75%.

Discussion: The therapeutic method used here can be compared with other solutions (trochanteroplasty, anti-dislocation crescent, antidislocation bone block, bipolar replacement). The double-mobility cup is particularly interesting for high-risk patients: neck fracture, tumour surgery, neurological disease, antecedent non-prosthetic surgery (dearthrodesis prosthesis). We advocate revision surgery after three dislocations.

Conclusion: The double-mobility cup appears to be a valid therapeutic option, both for the treatment and prevention of chronic instability of total hip arthroplasty.