Aims. The aim of this study was to identify the optimal lip position for total hip arthroplasties (THAs) using a lipped liner. There is a lack of consensus on the optimal position, with substantial variability in surgeon practice. Methods. A model of a THA was developed using a 20° lipped liner. Kinematic analyses included a physiological range of motion (ROM) analysis and a provocative dislocation manoeuvre analysis. ROM prior to impingement was calculated and, in impingement scenarios, the travel distance prior to dislocation was assessed. The combinations analyzed included nine cup positions (inclination 30-40-50°, anteversion 5-15-25°), three stem positions (anteversion 0-15-30°), and five lip orientations (right hip 7 to 11 o’clock). Results. The position of the lip changes the ROM prior to impingement, with certain combinations leading to impingement within the physiological ROM. Inferior lip positions (7 to 8 o’clock) performed best with cup inclinations of 30° and 40°. Superior lip positions performed best with cup inclination of 50°. When impingement occurs in the plane of the lip, the lip increases the travel distance prior to dislocation. Inferior lip positions led to the largest increase in jump distance in a posterior dislocation provocation manoeuvre. Conclusion. The lip orientation that provides optimal physiological ROM depends on the orientation of the cup and stem. For a THA with stem anteversion 15°, cup inclination 40°, and cup anteversion 15°, the optimal lip position was posterior-inferior (8 o’clock). Maximizing jump distance prior to dislocation while preventing impingement in the opposite direction is possible with appropriate lip positioning. Cite this article: Bone Joint Res 2023;12(9):571–579

To evaluate the results of open reduction in unreduced posterior dislocation of the elbow, done irrespective of the time since injury or age of the patient. Ten such cases in which the dislocation had been unreduced for more than 3 weeks since injury were included. Stiffness of the elbow was the main indication for the operation. Average age of the patient was 34.3 years (range 13 years to 65 years). Average time since injury was 3.9 months (range 2 month to 6 months). 3 patients had associated fractures around the elbow joint. All the patients had non functional elbow motion to perform any activity of daily living. We used speed’s procedure in all cases. At an average follow up of 18.5 months (range from 11 to 28 months), 8 patients achieved functional range of motion for activities of daily living and maintained an average arc of flexion(median) of 100 degrees and an average supination – pronation arc of 139.5 degrees. According to the Mayo Elbow Performance Index 5 patients achieved excellent results, 3 achieved good results and 2 achieved poor results. Complications included 2 cases of pin site infection, 1 case of ulnar neuritis and 1 case of delayed wound healing. We conclude that open reduction can provide painless, stable and functional elbow even in cases which are unreduced up to 6 months after the original injury

Recurrent posterior dislocation is a recognised complication following primary total hip arthroplasty. Incidences of between 0.11% and 4.5% have been reported in the literature. Component revision is regarded as standard management of recurrent posterior dislocation. However, revision surgery is a major surgical procedure and is often unsuitable for elderly, frail patients. A congruent, ultra-high molecular weight polyethylene acetabular augment with a stainless steel backing plate has been developed. This can be inserted providing there is no malalignment, wear or loosening of the primary components. In this study we compared twenty patients who underwent conventional revision surgery to twenty patients who had a PLAD inserted for recurrent posterior dislocation following primary Charnley total hip arthroplasty. Both groups were age and sex-matched and the average number of dislocations prior to surgery was three for each group. For the PLAD group, the mean operative time, the mean intraoperative blood loss, the time spent in HDU, the transfusion requirements and the duration of hospital stay was significantly less than that for the revision group. Furthermore, there was no significant difference in the Oxford Hip Score recorded preoperatively and at 6 weeks, 6 months, one year and two years following surgery. None of the patients had sustained a further dislocation at latest review. We conclude that the Posterior Lip Augmentation Device is a safe and effective option in the management of patients with recurrent posterior hip dislocation when there is no evidence of component failure or gross malposition

Introduction: Locked posterior dislocations of the shoulder, with humeral head defects are rare injuries. It constitutes less than 2% of all posterior dislocations of the shoulder and 60% are misdiagnosed. There have only been a few articles describing the treatment of such injuries either by bone graft or Mc Laughlin’s procedure. Patients: The first patient is a 23 year-old who presented as a missed diagnosis three weeks after a seizure. The second is a 35 year-old male referred four weeks after a traumatic dislocation. The third is a 55 year-old, known epileptic, who was diagnosed on admission. CT scan revealed a locked humeral head against the posterior glenoid rim, with defects of 30%, 20% and 30% respectively. Treatment: All underwent reconstruction of the defect. The first using freeze-dried allograft, the second and third using iliac autograft. Results: Each patient was assessed using the Constant and Murley score. The first patient scored 76 points at 30 months, the second patient scored 95 at 12 months and the third scored 97 after 12 months post-operatively. Conclusion: Early diagnosis is important in management and prognosis of such injuries. Using bone graft in the reconstruction of the humeral head defect restores the normal anatomy, rather than distorting it by using McLaughlin’s procedure

Traumatic dislocation of the hip in children is rare. Large series have shown this injury to be 25 times less common in children than in adults. Only 70 cases of Neglected traumatic dislocation of hip in children has been reported in the English literatures and most of those studies are too small to draw a significant conclusions. We report our experience of treating 20 such cases of neglected traumatic dislocation of hip in children (< 12 years). All had posterior dislocations without any associated fracture. They attended the hospital between 1–52 weeks after injury.Closed reduction under G.A was performed in 12 cases which were less than 3 weeks old while 8 hips(> 3 weeks old) had open reductions following failed reductions with skeletal traction. At 2 years follow-up, a complete range of motion was found in 18 children while the remaining two had 80% of normal hip movement with no significant deformity. All the hips showed varying degree of avascular necrosis, with preservation of joint space on radiographs. We suggest that attempted closed reduction of under 3 weeks old and open reductions for older dislocations gives satisfactory results. Also an anatomically placed femoral head maintains the stimulus for growth of pelvis and the femur

AIM: The diagnosis of the posterior dislocation can be missed. Chronic missed locked posterior fracture dislocations of the shoulder raise a difficult problem for treatment especially in young patients. The options for the treatment depend on the size of the humeral defect, the age of the patients and the time from injury to diagnosis. METHOD: Eleven patients with missed locked posterior fracture dislocation of the glenohumeral joint, 25 to 52 years of age were treated with open reduction and transfer of the subscapularis tendon to the defect (modified Mc Laughlin technique). The interval from the injury to diagnosis ranged from 6 weeks to 6 months. Significant pain, prominence of the acromion, posterior bulging and complete loss of external rotation of the shoulder led to the diagnosis that was confirmed by an axillary radiograph and C.T. scan. The humeral head defect was from 20 to 40 per cent of the articular surface. Four patients also had a minimally displaced fracture of the upper humerus. RESULTS: The average length of follow up was 3,5 years. Stability was restored and maintained in all cases. Six patients reported little or no pain. They had almost full range of motion and no functional restriction in the ADL. The remaining five patients had mild pain and slight restriction of movements mainly in external rotation in abduction (elevation 150°, external rotation 25°, internal rotation to L5). These patients had mild functional dysfunction in the ADL. All patients had normal muscle strength and constant score from 60–82. CONCLUSION: Once the diagnosis is established, open reduction and subscapularis tendon transfer reliably decreased patients pain level and significally improved the range of motion and the level of function, restoring stability of the joint. The alternative for older patients or patients with humeral head defect greater than 40% is the use of shoulder prosthesis

Simple posterior elbow dislocations are often being treated with strict immobilization after reduction. We performed a study in order to investigate if a functional protocol of rehabilitation, allowing early motion, would be more effective. We prospectively followed twenty five consecutive patients for simple posterior elbow dislocation in a non-randomized study. Patients were divided in two groups. Group A (twelve cases) was treated with immobilization using a cast in 90 degrees of flexion and neutral rotation for three weeks. Group B (thirteen cases) was treated according to a functional rehabilitation program that allowed early controlled mobilization starting on the 2nd post-traumatic day, consisting of immediate flexion from 90° and gradual extension after the 2nd week. Follow-up of the patients was recorded at six weeks and three months. The functional scores used were Mayo Clinic Performance Index, Liverpool Elbow score and Broberg and Morey. None of the patients had an incident of redislocation. Patients of group B had statistically significant better (p< 0.05) functional scores at six weeks and better no statistically significant in three months: group B/group A: Mayo: 91.6/65.5, Liverpool: 8.8/6.1, Broberg and Morey: 89.1/73.3. It seems that a functional rehabilitation program gives the same result in terms of stability offering at the same time patients a better range of motion and functional score at least at six weeks and three months

To devise an operative approach to the management of acute posterior fracture-dislocation of the shoulder which restores or retains normal proximal humeral anatomy and allows the early restoration of a complete, stable range of motion. Since 1996 we have treated four male patients (five shoulders) aged between 19 and 54 years at the time of first dislocation with autogenous iliac grafting of the anterior humeral head defect for acute and acuteon-chronic posterior dislocation of the shoulder. Two patients had epilepsy: one of these patients had bilateral dislocations. Two patients had motorbike RTAs. The deltopectoral approach with vertical division of the subscapularis tendon was used in all cases. The defects comprised 20– 25% of the volume of the humeral head at the equator after preparation for grafting. Grafts were fixed with compression screws. The subscapularis tendon was repaired anatomically. Active-assisted rehabilitation was started immediately, restricting external rotation to the neutral position for six weeks, thereafter allowing full rotation and elevation as comfort allowed. The patient with bilateral dislocations died of unrelated causes 18 months after surgery. He was reported to have had no further dislocations, complete pain free functional use of both shoulders and no complications of the procedure. The remaining three patients were reviewed at a minimum of 20 months after surgery (average 35 months). All grafts had incorporated. There was no graft collapse or boundary arthrosis. The absolute Constant scores were 85.1, 90.9, and 89.2; the subjective shoulder scores were 98%, 90%, and 99%; the Oxford rating scale for pain scores were 14 out of 60, 13 out of 60, and 14 out of 60; and the Oxford rating scale for instability scores were 14 out of 60, 15 out of 60 and 15 out of 60. There were no redislocations, or complications of the procedures. Posterior stability appears more dependant on surface arc of contact than on capsular integrity, in contrast to the anteriorly unstable shoulder. Restoration of the articular surface arc of contact by segmental autogenous grafting retains normal humeral anatomy, allows normal motion with excellent cuff function, and a return to normal daily activities. The procedure has been shown to be safe at a minimum of 20 months

Abstract. Background. The Oxford Domed Lateral (ODL) Unicompartmental Knee Replacement (UKR) has some advantages over other lateral UKRs, but the mobile bearing dislocation rate is high (1–6%). Medial dislocations, with the bearing lodged on the tibial component wall, are most common. Anterior/posterior dislocations are rare. For a dislocation to occur distraction of the joint is required. We have developed and validated a dislocation analysis tool based on a computer model of the ODL with a robotics path-planning algorithm to determine the Vertical Distraction required for a Dislocation (VDD), which is inversely related to the risk of dislocation. Objectives. To modify the ODL design so the risk of medial dislocation decreases to that of an anterior/posterior dislocation. Methods. The components were modified using Solidworks. For each modification the dislocation analysis tool was used to determine the VDD for medial dislocation (with bearing 0–6mm from the tibial wall). This was compared with the original implant to identify the modifications that were most effective at reducing the dislocation risk. These modifications were combined into a final design, which was assessed. Results. Modifying the tibial component plateau, changing the femoral component width and making the bearing wider medially had little effect on VDD. Shifting the femoral sphere centre medially decreased VDD. Shifting the femoral sphere laterally, increasing tibial wall height and increasing bearing width laterally increased VDD. A modified implant with a femoral sphere centre 3mm lateral, wall 2.8mm higher, and bearing 2mm wider laterally, implanted so the bearing is ≤4mm from the tibial wall with a bearing thickness ≥4mm had a minimum VDD for medial dislocation of 5.75mm, which is larger than the minimum VDD for anterior/posterior dislocation of 5.5mm. Conclusions. A modified ODL design should decrease the dislocation rate to an acceptable level, however, further testing in cadavers is required. Declaration of Interest. (a) fully declare any financial or other potential conflict of interest

Chronic pelvic discontinuity (CPD) during revision hip arthroplasty is a challenging entity to address. The aim of this study was to evaluate the clinical and radiologic outcomes, and complications of the “acetabular distraction technique” for the management of CPD during revision hip arthroplasty. Patients with CPD, who underwent acetabular revision between 2014 and 2022 at two tertiary care centres, using an identical distraction technique, were evaluated. Demographic parameters, pre-operative acetabular bone loss, duration of follow-up, clinical and radiologic outcomes, and survivorship were evaluated. In all, 46 patients with a mean follow-up of 34.4 (SD=19.6, range: 24–120) months were available for evaluation. There were 25 (54.3%) male, and 21 (45.7%) female patients, with a mean age of 58.1 (SD=10.5, range: 40–81) years at the time of revision surgery. Based on the Paprosky classification of acetabular bone loss, 19 (41.3%), 12 (26.1%), and 15 (32.6%) patients had type 3b, 3a, and 2c defects. All patients were managed using the Trabecular Metal™ Acetabular Revision System; 16 patients required additional Trabecular Metal™ augments. The mean HHS improved from 50.1 (SD=7.6, range: 34.3 – 59.8) pre-operatively, to 86.6 (SD=4.2, range: 74.8 -91.8) at the last follow-up. Two patients (4.3 %) developed partial sciatic nerve palsy, two (4.3%) had posterior dislocation, and one (2.2%) required re-revision for aseptic loosening. Radiologically, 36 (78.3%) patients showed healing of the pelvic discontinuity. The Kaplan-Meier construct survivorship was 97.78% when using re-revision for aseptic acetabular loosening as an endpoint. The acetabular distraction technique has good clinical and radiologic outcomes in the management of CPD during revision hip arthroplasty

Aims. In the native hip, the hip capsular ligaments tighten at the limits of range of hip motion and may provide a passive stabilizing force to protect the hip against edge loading. In this study we quantified the stabilizing force vectors generated by capsular ligaments at extreme range of motion (ROM), and examined their ability to prevent edge loading. Methods. Torque-rotation curves were obtained from nine cadaveric hips to define the rotational restraint contributions of the capsular ligaments in 36 positions. A ligament model was developed to determine the line-of-action and effective moment arms of the medial/lateral iliofemoral, ischiofemoral, and pubofemoral ligaments in all positions. The functioning ligament forces and stiffness were determined at 5 Nm rotational restraint. In each position, the contribution of engaged capsular ligaments to the joint reaction force was used to evaluate the net force vector generated by the capsule. Results. The medial and lateral arms of the iliofemoral ligament generated the highest inbound force vector in positions combining extension and adduction providing anterior stability. The ischiofemoral ligament generated the highest inbound force in flexion with adduction and internal rotation (FADIR), reducing the risk of posterior dislocation. In this position the hip joint reaction force moved 0.8° inbound per Nm of internal capsular restraint, preventing edge loading. Conclusion. The capsular ligaments contribute to keep the joint force vector inbound from the edge of the acetabulum at extreme ROM. Preservation and appropriate tensioning of these structures following any type of hip surgery may be crucial to minimizing complications related to joint instability. Cite this article: Bone Joint Res 2021;10(9):594–601

Acromial morphology has been implicated as a risk factor for unidirectional posterior shoulder instability. Studies utilising plain film radiographic landmarks have identified an increased risk of posterior shoulder dislocation in patients with higher acromion positioning. The aims of this study were to develop a reproducible method of measuring this relationship on cross sectional imaging and to evaluate acromial morphology in patients with and without unidirectional posterior shoulder instability. We analysed 24 patients with unidirectional posterior instability. These were sex and age matched with 61 patients with unidirectional anterior instability, as well as a control group of 76 patients with no instability. Sagittal T1 weighted MRI sequences were used to measure posterior acromial height relative to the scapular body axis (SBA) and long head of triceps insertion axis (LTI). Two observers measured each method for inter-observer reliability, and the intraclass correlation coefficient (ICC) calculated. LTI method showed good inter-observer reliability with an ICC of 0.79. The SBA method was not reproducible due suboptimal MRI sequences. Mean posterior acromial height was significantly greater in the posterior instability group (14.2mm) compared to the anterior instability group (7.7mm, p=0.0002) as well when compared with the control group (7.0mm, p<0.0001). A threshold of 7.5mm demonstrated a significant increase in the incidence of posterior shoulder instability (RR = 9.4). We conclude that increased posterior acromial height is significantly associated with posterior shoulder instability. This suggests that the acromion has a role as an osseous restraint to posterior shoulder instability

Purpose of the study: Posterior shoulder instability is a rare condition. Several surgical treatments have been proposed. Material and methods: This was a retrospective series of 21 posterior bone block procedures performed between 1984 and 2001 and analyzed with mean follow-up of six years. Fifteen patients (n=16) had experienced one or more episodes of posterior dislocation. Thirteen patients were athletes and five had traumatic subluxation with chronic posterior instability. Voluntary recurrent dislocations were not observed in these patients. Male gender predominated (n=19 men, 1 woman). Mean age at surgery was 24.8 years (range 17–40). The dominant side was involved in 12 patients (57%). The Constant and Duplay scores were noted as were the pre- and postoperative x-ray findings. There were ten glenoid fractures, two glenoid impactions, ten anterior humeral notches. Mean retroversion, measured on the scans (n=17) was 9.6° (range 0–21°). Results: All patients (n=20) were satisfied or very satisfied. At last follow-up, the mean Constant score was 93.3 (range 80–103) and the mean Duplay score (n=21) 85.6 (40–100); 68.2% of patients (n=15) resumed sports activities at the same level. Failure was noted in three patients, one with recurrent posterior dislocation and two with major apprehension. For two patients, glenohumeral osteoarthritis developed postoperatively. Discussion: Most of the series in the literature have reported results for patients with recurrent posterior subluxations and not for traumatic posterior dislocation, the much more uncommon entity presented here. The rate of bony lesions was high in our series compared with former series in the literature. These results can be explained by two facts. The first that this was a group of recurrent posterior dislocations and second that the analysis of the osteoarticular lesions was made on plain x-rays and/or CT scans. For the two cases of glenohumeral osteoarthritis which developed postoperatively, the position of the bone block does not appear to be involved. Conclusion: The posterior bone block remains the treatment of choice for recurrent posterior dislocation. The risk of developing osteoarthritis appears to be low but a longer follow-up would be necessary for confirmation

Introduction. Dislocation is one of severe complications after total hip arthroplasty (THA). Direct anterior approach (DAA) is useful for muscle preservation. Therefore, it might be also effective to reduce dislocation. The purpose of this study is to investigate the ratio and factors of dislocations after THA with DAA. Materials & methods. Nine hundred fifity two primary THAs with DAA are examined. Mean age at operation was 64.9 yrs. 838 joints are in women and 114 (joints) in men. All THAs were performed under general anesthesia in supine position. We reviewed the ratio, onset and frequency of dislocations, build of the patients, preoperative Japanese Orthopaedic Association (JOA) Hip scores, implant setting angles, pelvic tilt angles and diameter of inner heads. Results. The ratio of dislocation was 14 joints (1.47%). All patients were women and mean age was 67.1 yrs. Anterior dislocation was in 9 joints and posterior was in 5 joints. Primary diagnosis for THA was the following: osteoarthritis in 9 hips and rheumatoid arthritis in 5 (hips). About primary onset, 7 joints were within 3 weeks, 5 joints from 3 weeks to 3 months and 2 joints after 3 months. About frequency, 9 joins were simple and 5 joints were multiple. Revision surgery was done in 2 joints due to ceramic fracture and cup migration. About build of the patients, mean body height was 153.1cm, mean body weight (was) 55.6 kg and mean BMI (was) 23.6. Mean preoperative JOA score was 40.0 points. Implant setting angles were the following: mean cup inclination was 42.4 degree, mean cup anteversion (was) 24.8 degree and mean stem anteversion (was) 18.7 degree. Cup inclination and anteversion in the anterior dislocation group were bigger than that in no dislocation group. Stem anteversion in the posterior dislocation group was smaller than that in no dislocation group. The difference of pelvic tilt angle between supine and standing position was 6.4 degree. It was significant bigger in the posterior dislocation group. The most of used Inner head was 28mm in 375 joints. There was no significant difference of the dislocation rate among inner head size. Discussion and conclusion. DAA-THA can expect the reduction of dislocation rate due to intermusclar approach; however there are some reports of high dislocation rate because of difficult technique. In our study, dislocation ratio was 1.47%. Risk factors of dislocation after THA was rheumatoid arthritis, large cup inclination and anteversion for anterior dislocation, small stem anteversion and large difference of pelvic tilt angle between supine and standing position for posterior dislocation

The posterior-stabilized knee prosthesis is designed specifically to provide the posterior stability to a knee arthroplasty when PCL is deficient or has to be sacrificed. Posterior dislocation of such prosthesis is rare but dreaded complication. There are several causes of postoperative dislocation such as malposition of the prosthesis, preoperative valgus deformity, a defect of the extensor mechanism and overwidening of the flexion gap. Posterior-stabilized rotating-platform mobile-bearing knee implants have been widely used to further improve the postoperative range of motion by incorporation of the post and cam mechanism to improve the posterior roll back during flexion and to overcome the wear and osteolysis problems due to significant undersurface micromotion of posterior-stabilized fixed-bearing knees. But, spin-out or rotatory dislocation of the polyethylene insert can occurs as result of excessive rotation of the rotating platform accompanied by translation of the femur on the tibia after mobile-bearing total knee arthroplasty, but that is very rare. Here, authors describe an unusual case of acute 180° rotatory dislocation of the rotating platform after posterior dislocation of a posterior-stabilized mobile-bearing total knee arthroplasty. A 71-year-old male with knee osteoarthritis underwent a TKRA using posterior-stabilized mobile-bearing prosthesis. The posterior dislocation of the total knee arthroplasty occurred 5 weeks postoperatively(Fig. 1). We underwent closed reduction of posterior dislocated total knee arthroplasty resulting in a complete 180° rotatory dislocation of the rotating platform (Fig. 2). He was treated with open exploration and polyethylene exchange with a larger component. This case illustrates that dislocation of a posterior-stabilized mobile-bearing total knee arthroplasty can occur with valgus laxity, cause 90° spin-out of the polyethylene insert and closed reduction attempts may contribute to complete 180° rotatory dislocation of the rotating platform. Special attention needs to be paid to both AP and lateral view to ensure that the platform is truly reduced and not just rotated 180° as was in this case

Three cases of posterior dislocation of the Kinemax Posterior- Stabilized total knee replacement are reported, and predisposing factors, including operative technique and prosthesis design, are discussed. All three patients underwent posterior-stabilised knee replacement surgery at the Avon Orthopaedic Centre for osteoarthritis, between 1984 and 2000. In all cases the patient represented to the Emergency Department of a local hospital with posterior dislocation, at between 9 months and 6 years postoperatively. The mechanism for dislocation was hyperflexion of the knee. The dislocations could not be reduced under sedation because of obstruction by the protruding tibial insert, and required general anaesthesia to disengage the components. In all cases posterior dislocation became recurrent problem, and further surgery was required to address the instability. Two of the three patients underwent exchange of their stabilised tibial inserts for thicker versions of the same design, in order to reduce the excessive laxity present in flexion. The third patient underwent exploratory surgery and it was found that his patellar button had separated from the underlying bone. The patella was therefore resurfaced, restoring the integrity of his extensor mechanism. No further dislocations have occurred in any of the three patients. The causes of posterior dislocation of posterior-stabilized total knee replacements are multifactorial. They include malrotation of the tibial component, although this was not found to be the case in the three patients reported here. The design of the prosthesis may also contribute, and the upsloping and relatively shallow tibial spine of the Kinemax prosthesis (Howmedica) appears to be less forgiving than others. This is particularly the case if soft tissue lateral release or excessive resection of the posterior condyles has produced an increased flexiongap and therefore excessive flexion laxity. Our cases demonstrate the pitfalls that can produce this uncommon but serious complication, some of which can be predicted preoperatively, particularly in the patient with a valgus knee or deficiency of the extensor mechanism

Management of recurrent instability of the hip requires careful assessment to determine any identifiable causative factors. While plain radiographs can give a general impression, CT is the best methodology for objective measurement. Variables that can be measured include: prosthetic femoral anteversion, comparison to contralateral native femoral anteversion, total offset from the medial wall of the pelvis to the lateral side of the greater trochanter, comparison to total offset on the contralateral side, acetabular inclination, & acetabular anteversion. Wera et al describe potential causes of instability. These are typed into I. Acetabular Component Malposition; II. Femoral Component Malposition; III. Abductor Deficiency; IV. Impingement; V. Late Wear; and VI. Unknown. Acetabular component malposition is the most common cause of instability and so measurement of cup orientation is essential. It is well known that excessive or inadequate anteversion can lead to anterior and posterior dislocation respectively but horizontal components are also associated with posterior dislocation due to deficient posterior/inferior acetabular surface. Similarly, excessive or inadequate femoral anteversion can be easily identified on CT as can insufficient total offset of the reconstructed joint compared to the contralateral side. This can be caused by medialization of the acetabular component. Abductor deficiency can be a soft-tissue cause of instability, but it certainly isn't the only one. Knowledge of the prior surgical exposure can be instructive. Anterior exposures can be prone to deficient anterior capsule just as posterior exposures can be prone to deficient posterior capsule and short rotators, while anterolateral and lateral exposures can be associated with gluteus minimus and gluteus medius compromise. Impingement, whether involving implants, bone, or soft tissue are primarily secondary to the above factors, if osteophytes were properly trimmed at the index procedure. Correction of the incorrect variables is the primary goal of revision for instability and greatly preferable to using salvage options such as dual-mobility or constrained articulations which invoke additional concerns. Ultimately though, such salvage options are necessary if the cause of the instability cannot be determined or can be determined but not corrected. Bracing, while highly inconvenient and sometimes impractical for certain patients, still has a role in specific circumstances. Formal analysis of the unstable prosthetic reconstruction is the key to successful treatment

INTRODUCTION. Component impingement in total hip arthroplasty (THA) can cause implant damage or dislocation. Dual mobility (DM) implants are thought to reduce dislocation risk, but impingement on metal acetabular bearings may cause femoral component notching. We studied the prevalence of (and risk factors for) femoral notching with DM across two institutions. METHODS. We identified 37 patients with minimum 1-year radiographic follow-up after primary (19), revision (16), or conversion (2) THA with 3 distinct DM devices between 2012 and 2017. Indications for DM included osteonecrosis, femoral neck fracture, concomitant spinal or neurologic pathology, revision or conversion surgery, and history of prosthetic hip dislocation. Most recent radiographs were reviewed and assessed for notching. Acetabular anteversion and abduction were calculated as per Widmer (2004). Records were reviewed for dislocations and reoperations. RESULTS. 2/37 of cases demonstrated femoral component notching, best seen on Dunn views (available in 7/37 cases). Notching was associated with increased mean acetabular anteversion (32.5° with notch, 19.6° without; p=.03). 2/5 patients with anteversion greater than 30° had notching, while no patients with less anteversion had notching (p=.01). Recurrent posterior instability was the indication for 6 revision THAs studied. Both cases of notching were in this group. Although not statistically associated with implant design, notching occurred in 2/18 MDM, 0/10 ADM and 0/9 G7 constructs. Dislocation occurred in 0/18 MDM, 0/10 ADM and 2/9 G7 constructs (p=.04), resulting in one revision to a constrained liner. We observed no significant differences in rate of notching or dislocation with respect to age, cup or head size, or component abduction. DISCUSSION AND CONCLUSION. Femoral notching was identified in 5% of DM cases, equal to the rate of dislocation. Dunn views are not routine after THA, so the incidence may be underestimated. Increasing acetabular anteversion to minimize posterior dislocation is a risk factor. Dislocation and notching incidence may vary between DM components based on design features. Further study is warranted to determine clinical significance. For any figures or tables, please contact authors directly

Aims

Post-traumatic periprosthetic acetabular fractures are rare but serious. Few studies carried out on small cohorts have reported them in the literature. The aim of this work is to describe the specific characteristics of post-traumatic periprosthetic acetabular fractures, and the outcome of their surgical treatment in terms of function and complications.

Purpose: Fracture of the neck of the femur in elderly subjects is generally treated by arthroplasty, either using a total or intermediary hip prosthesis, but with a high risk of dislocation, estimated at about 10% in the literature. We investigated the contribution of a double mobile cup to lower this risk. Material and methods: This prospective study was conducted by several operators in the same university unit between 1998 and 2001. A total of 177 mobile prostheses were implanted in patients with fracture of the anatomic neck of the femur (n=145), the neck and trochanter (n=22), or pathologic fracture (n=4). For six patients, the prosthesis was implanted after failed osteosynthesis of a trochanteric fracture. The postero-lateral approach was used for 136 women and 41 men (age range 61 – 92 years) living at home (n=124), or in an institution with a high degree of independence (n=53). The femoral stem was cemented (n=115) or impacted (n=62). A double mobile cup was used in all cases. A chromium-cobalt/ polyethylene couple was used and head diameters were 28 mm (n=150) or 22.2 mm (n=27). We studied outcome and risk of dislocation one year after implantation. Results: There were six deaths during the postoperative period. Among the 171 patients, 134 were seen at two months, 108 at six months and 89 at one year: 39 were questioned to ascertain outcome. During the first postoperative year, there were 37 deaths; these patients were followed. Six patients were lost to follow-up. We had two cases of intraprosthetic dislocation related to a defect in the chromium-cobalt head retention of the polyethylene insert. These two cases required revision and were reported to material surveillance with corrective measures for the manufacturer. There were three true dislocations (2%): 1) a posterior dislocation on day 24 in a female patient presenting a fracture with impaction of the femoral stem; 2) a posterior dislocation on day 22 in a female patient in very poor general condition (severe cardiorespiratory failure, death at 48 hr); 3) one recurrent posterior dislocation related to major acetabular retroversion, revised at four months. Discussion and conclusion: The double-mobile cup appears to be a simple reproducible method for preventing dislocation of prostheses implanted for fracture of the neck of the femur