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

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

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

Introduction. Dual Mobility (DM) implants have gained popularity for the treatment and prevention of hip dislocation, with increased stability provided by a large diameter mobile liner. However, distal regions of the liner can impinge on soft-tissues like hip capsule and iliopsoas, leading to anterior hip pain. Additionally, soft-tissue impingement may trap the mobile liner, leading to excessive loading of the liner rim, from engagement with the femoral stem, and subsequent intra-prosthetic dislocation. The hypothesis of this study was that reducing the liner profile below the equator (contoured design) can mitigate soft-tissue impingement without compromising inner-head pull-out resistance and overall hip joint stability (Fig. 1). Methods. The interaction of conventional and contoured liners with anterior soft-tissues was evaluated in 10 cadaveric hips (5 specimens; 2 male, 3 female; age 65 ± 10 yrs; liner diameter 42–48mm) via visual observation and fluoroscopic imaging. A metal wire was sutured to the deep fibers of the iliopsoas tendon/muscle, and metal wires were embedded in the mobile liners for fluoroscopic visualization (Fig. 2). All soft-tissue except the anterior hip capsule and iliopsoas was removed, and a rope was attached to the iliopsoas to apply tension along its natural orientation. Resistance to inner-head pull-out was evaluated via Finite Element Analysis (FEA) by simulating a full cycle of insertion of the inner head into the mobile liner and subsequent pullout. The femoral head, acetabular shell, and stem were modeled as rigid, while the mobile liner was modeled as plastically deformable. Hip joint stability was evaluated by dynamic simulations in for two dislocation modes: (A) Posterior dislocation (at 90° hip flexion) with internal hip rotation; (B) Posterior dislocation (starting at 90° flexion) with combined hip flexion and adduction. A 44 mm diameter conventional and a 44 mm contoured liner were evaluated during these tests. Results. The cadaver experiments showed that distal portion of conventional liners impinge on anterior hip capsule and iliopsoas at low flexion angles (<30°). Additionally, when the hip moved from flexion into extension, the liner motion was blocked between posterior neck engagement, and anterior soft-tissue impingement. In all hips, the soft-tissue impingement / tenting was significantly reduced with contoured liners (Fig. 7). The change in tenting could be visualized as change in distance between the iliopsoas wire, and the contoured/conventional liners on sequential fluoroscopic images. The maximum reduction in iliopsoas tenting for a given specimen ranged from 1.8 mm to 5.5 mm. Additionally, the contoured and conventional liners had identical inner-head pull-out resistance (901N vs. 909N), jump distance (9.4 mm mode-A, 11.7 mm mode-B) and impingement-free range of motion (47° mode-A, 29° mode-B). Conclusion. This study showed that distal portions of conventional DM liners can impinge against iliopsoas and hip capsule in low flexion leading to functional impediment of liner motion. Additionally, reducing the liner profile below the equator led to significant reduction in soft-tissue impingement/tenting without affecting mechanical performance. Thus, a contoured dual mobility liner design may reduce the risk of anterior hip pain and intra-prosthetic dislocation resulting from soft-tissue impingement and liner entrapment. To view tables/figures, please contact authors directly

Introduction. Impingement of total hip arthroplasties (THAs) has been reported to cause rim damage of polyethylene liners, and in some instances has led to dislocation and/or mechanical failure of liner locking mechanisms in modular designs. Elevated rim liners are used to improve stability and reduce the risk of dislocation, however they restrict the possible range of motion of the joint, and retrieval studies have found impingement related damage on lipped liners. The aim of this study was to develop a tool for assessing the occurrence of impingement under different activities, and use it to evaluate the effects a lipped liner and position of the lip has on the impingement-free range of motion. MATERIALS & METHOD. A geometrical model incorporated a hemi-pelvis and femur geometries of one individual with a THA (DePuy Pinnacle® acetabular cup with neutral and lipped liners; size 12 Corail® stem with 32mm diameter head) was created in SOLIDWORKS (Dassault Systèmes). Joint motions were taken from kinematic data of activities of daily living that were associated with dislocation of THA, such as stooping to pick an object off the floor and rolling over. The femoral component was positioned to conform within the geometry of the femur, and the acetabular component was orientated in a clinically acceptable position (45° inclination and 20° anteversion). Variation in orientation of the apex of the lip was investigated by rotating about the acetabular axes from the superior (0°) in increments of 45° (0°−315°), and compared to a neutral liner. Results. When a lipped liner was used, implant (neck on acetabular rim) impingement was found to occur when performing sit-to-stand from a normal seat, leg cross and pivot, whereas no impingement occurred with a neutral liner. The presence and position of the lip reduced the impingement-free range of motion, compared to the neutral liner. Impingement occurred when the lip was positioned superiorly and anteriorly, when performing most of the activities that were prone to posterior dislocation, and posteriorly, posterior-superiorly and posterior-inferiorly when performing activities prone to anterior dislocation. During sit-to-stand from a normal seat no impingement occurred when a lipped or neutral liner was used. Bone impingement was observed when the performing the roll activity with both lipped and neutral liners. DISCUSSION. Impingement was observed more with lipped liners compared to neutral liners, this agrees with the findings of some clinical studies. The results indicate that the positioning of the lip influences the possible range of impingement-free motion. Considering this and the improved joint stability of using a lipped liner, a balance is required to achieve an optimal range of motion without increasing the risk of dislocation. This tool could potentially to be used to optimise lipped liner design and position, and could assist with the liner selection for patients based on their activities

INTRODUCTION. Femoral head diameter has a major influence on stability and dislocation resistance of the hip joint after Total Hip Arthroplasty (THA). Dual Mobility (DM) implants can also reduce the risk of dislocation due the large diameter mobile liner which forms the femoroacetbular articulation. However, recent studies have shown that large head prostheses can directly impinge against native soft tissues, particularly the iliopsoas, leading to anterior hip pain. Dual mobility systems have emerged as a revision option in the treatment of failed metal on metal devices because of the high incidence of post revision instability secondary to abductor loss and need for capsulectomy. We hypothesized that an Anatomically Contoured Dual Mobility (ACDM) liner could provide joint stability while better accommodating the soft tissues surrounding the hip joint. METHODS. The dislocation resistance of a 44 mm ACDM implant was compared to that of a 44 mm conventional DM liner. Both implants consisted of a 28 mm inner small diameter head and the liner was abducted to be in the worst case position for dislocation (Fig. 1). The ACDM liner was based on a 44 mm sphere with smaller radii used to contour the peripheral region below the equator of the liner. MSC Adams was used for dynamic simulations based on two previously described dislocation modes: (A) Posterior dislocation (at 90° hip flexion) with internal rotation of the hip and a posterosuperior directed joint force; (B) Posterior dislocation (starting at 90° flexion) with combined hip flexion and adduction and a posteromedial force direction (Fig. 2). Impingement-free motion (motion without neck impingement against the acetabular cup) and jump distance (head separation from acetabulum at dislocation) were measured for each implant. The acetabular cup was placed at 42.5° abduction and 19.7° anteversion, while the femoral component was anteverted by 9.75° based on published data. RESULTS. The results showed no differences between the novel anatomically contoured 44 mm liner (ACDM) and a conventional 44 mm DM implant for both dislocation modes. The 44 mm ACDM and conventional DM liner showed impingement-free motion of 47° for mode A and 29° for mode B which are much higher compared to the contemporary small heads. The jump distance between the 44 mm ACDM and the conventional liner was also identical (Fig. 3). CONCLUSION. The novel Anatomically Contoured Dual Mobility (ACDM) liner matched the dislocation resistance of a conventional DM liner of the same size. This confirmed the hypothesis that dual mobility liners can be anatomically shaped to alleviate the risk of soft tissue impingement, without jeopardizing stability

INTRODUCTION. Femoral head diameter has a major influence on stability and dislocation resistance after Total Hip Arthroplasty (THA). Although routine use of large heads is common, several recent studies have shown that contemporary large head prostheses can directly impinge against native soft tissues, particularly the iliopsoas which wraps around the femoral head, leading to refractory anterior hip pain. To address this, we developed a novel Anatomically Contoured large diameter femoral Head (ACH). We hypothesized that anatomical contouring of the ACH implant for soft tissue relief would not compromise dislocation resistance, and the ACH implant would provide increased stability compared to small heads. METHODS. In this study the dislocation resistance of a 36 mm ACH was compared to that of 28 mm and 36 mm contemporary heads. The ACH implant was based on a 36 mm sphere with smaller radii used to contour the peripheral region below the equator of the head. MSC Adams was used for dynamic simulations based on two previously described dislocation modes: (A) Posterior dislocation (at 90° hip flexion) with internal rotation of the hip and a posterosuperior directed joint force; (B) posterior dislocation (starting at 90° flexion) with combined hip flexion and adduction and a posteromedial force direction (Fig. 1). Impingement-free motion (motion without neck impingement against the acetabular liner) and jump distance (head separation from acetabulum prior to dislocation) were measured to evaluate the dislocation risk of each implant. The acetabular cup was placed at 42.5° abduction and 19.7° anteversion, while the femoral component was anteverted by 9.75° based on published data. RESULTS. The results showed no differences between the novel anatomically contoured 36 mm head and a conventional 36 mm head for both dislocation modes. The 36 mm ACH and conventional head showed greater impingement-free motion compared to the 28 mm conventional head, with an increase of 7° for dislocation mode A, and 4° for mode B. Relative to the 28 mm head, the jump distance for the 36 mm ACH and the 36 mm conventional head increased by 1.5 mm for dislocation mode A, and 2 mm for mode B (Fig. 2 and Fig. 3). CONCLUSION. The novel Anatomically Contoured large diameter femoral Head (ACH) showed increased dislocation resistance compared to a conventional small diameter head and matched the stability of a conventional large head of the same size. This confirmed the hypothesis that large femoral heads can be anatomically shaped to alleviate the risk of soft-tissue impingement, as in the ACH implant, without jeopardizing the desired stability

Objective. To define the common pathology of the hips with irreducible posterior dislocation combined with femoral head fracture and the outcome of surgical treatment using surgical hip dislocation technique. Design: retrospective observational clinical study. Setting: Level III referral trauma center. Patients/Participants: from January 2011till February 2014 five patients with irreducible posterior hip dislocation and femoral head fracture who underwent operation were included and they followed for at least 18 months. Intervention. Open reduction and internal fixation of fractured femoral head and labral repair by suture anchors using surgical hip dislocation through trochanteric flip osteotomy approach. Main Outcome Measures: Clinical and radiographical findings of the irreducible posterior hip dislocation, intraoperative findings, clinical outcomes using Merle d'Aubigné & Postel and Thompson & Epstein scores, and radiological outcome. Results. All patients presented clinically with a shortened lower limb in neutral or external rotation of the hip (not in Internal rotation). All were Pipkin type II fracture of femoral head with the intact part of the head buttonholed on the posterior wall of the acetabulum through a capsule-labral flap. Postoperative computed tomography revealed perfect reduction except one case with severe comminution with good reduction. Only one patient with delayed operative management developed avascular necrosis and underwent total hip arthroplasty. Conclusion. Irreducible femoral head fracture-dislocation is rare injury with different clinical presentation that shows neutral or externally rotated limb and optimal surgical management is not clear. Surgical hip dislocation gives full access to the femoral head for reconstruction and opportunity to direct repair of the labral tears

Patients with neuromuscular disease and imbalance present a particularly challenging clinical situation for the orthopaedic hip surgeon. The cause of the neuromuscular imbalance may be intrinsic or extrinsic. Intrinsic disorders include those in which the hip is in development, such as cerebral palsy, polio, CVA, and other spinal cord injuries and disease. This can result in subluxation and dislocation of the hip in growing children, and subsequent pain, and difficulty in sitting and perineal care. Extrinsic factors involve previously stable hips and play a secondary role in the development of osteoarthritis and contractures in later life. Examples of extrinsic factors are Parkinson's disease, dyskinesis, athetosis, and multiple sclerosis. Goals of treatment in adults with pain and dysfunction in the setting of neuromuscular imbalance are to treat contractures and to perform salvage procedures to improve function and eliminate pain. Treatment of patients with neuromuscular imbalance may include resection arthroplasty (Girdlestone), arthrodesis, or total hip arthroplasty. Resection arthroplasty is typically reserved for patients that are non-ambulatory, or hips that are felt to be so unstable that arthroplasty would definitely fail due to instability. In modern times arthrodesis has limited use as it negatively impacts function and self-care in patients with neuromuscular disorders. Total hip arthroplasty has the ability to treat pain, relieve contractures, and provide improved function. Due to the increased risk of instability, special considerations must be made during primary total hip arthroplasty in this patient cohort. Risk of instability may be addressed by surgical approach, head size, or use of alternative bearing constructs. Posterior approach may have increased risk of posterior dislocation in this patient group, particularly if a posterior capsular repair is not possible due to the flexion contractures and sitting position in many patients. Surgeons familiar with the approaches may utilise the anterolateral or direct anterior approach judicially. Release of the adductors may be performed in conjunction with primary total hip arthroplasty to help with post-operative range of motion and to decrease risk of instability. In a standard bearing, the selected head size should be the largest that can be utilised for the particular cup size. Rigorous testing of intra-operative impingement, component rotation, and instability is required. If instability cannot be adequately addressed by a standard bearing, the next option is a dual mobility bearing. Multiple studies have shown improved stability with the use of these bearings, but they are also at risk for instability, intraprosthetic dislocation, and fretting and corrosion of the modular connections. Another option is a constrained liner. However, this results in reduced range of motion, and an increased risk for mechanical complications of the construct. The use of a constrained liner in a primary situation should be limited to the most severe instability cases, and the patient should be counseled with the associated risks. If total hip arthroplasty results in repeated instability, revision surgery or Girdlestone arthroplasty may be considered

The shoulder is the least constrained of all joints of the body and is more susceptible to injury including dislocation. The rate of recurrent instability following primary stabilization procedure at 10 years of follow-up ranged from 3.4 to 35 %. We describe the outcomes of 74 patients who underwent knotless arthroscopic anterior stabilisation using 1.5 mm Labral Tape with 2.9mm Pushlock anchors for primary anterior instability. We performed a retrospective analysis of patients who underwent surgery for post-traumatic recurrent anterior instability for 2 years by a single surgeon. Patients with glenoid bone loss, >25% Hill Sachs lesion, posterior dislocation, paediatric age group and multidirectional instability were excluded from this study. Over 90% of our case mix underwent the procedure under regional block anaesthesia and was discharged on the same day. The surgical technique and post-operative physiotherapy was as per standard protocol. Outcomes were measured at 6 months and 12 months. Of the 74 patients in our study, we lost 5 patients to follow up. Outcomes were measured using the Oxford Shoulder Score apart from clinical assessment including the range of motion. We noted good to excellent outcomes in 66 cases using the Oxford Instability Scores. All patients achieved almost full range of motion at the end of one year. Our cumulative Oxford Instability Score (OIS) preoperatively was 24.72 and postoperatively was 43.09. The Pearson correlation was .28. The t Critical two-tail was 2.07 observing the difference between the means of the OIS. Complications included recurrent dislocation in 2 patients following re-injury and failure of procedure due to recurrent instability requiring an open bone block procedure in one case. We had no reported failures due to knot slippage or anchor pull-out. We publish the largest case series using this implant with distinct advantages of combining a small bio absorbable implant with flat braided, and high-strength polyethylene tape to diminish the concern for knot migration and abrasive chondral injury with the potential for earlier rehabilitation and a wider footprint of labral compression with comparative outcomes using standard techniques. Our results demonstrate comparable and superior results to conventional suture knot techniques for labral stabilization

Background. The acetabular labrum is an essential stabilizer of the hip joint, imparting its greatest effect in extreme joint positions where the femoral head is disposed to subluxation and dislocation. However, its stabilizing value has proved difficult to quantify. The objective of the present study was to assess the contribution of the entire acetabular labrum to mechanical joint stability. We introduce a novel “dislocation potential test” that utilizes a dynamic, cadaveric, robotic model that functions in real-time under load-control parameters to map the joint space for low-displacement determination of stability, and quantify using the “stability index”. Methods. Five fresh-frozen human cadaveric hips without labral tears were mounted to a six-degree-of-freedom robotic manipulator and studied in 2 distinct joint positions provocative for either anterior or posterior dislocation. Dislocation potential tests were run in 15° intervals, or sweep planes, about the face of the acetabulum. For each interval, a 100 N force vector was applied medially and swept laterally until dislocation occurred. Three-dimensional kinematic data from conditions with and without labrum were quantified using the stability index, which is the percentage of all directions a constant force can be applied within a given sweep plane while maintaining a stable joint. Results. Global stability indices, considering all sweep planes, were significantly greater with labrum intact than after total labrectomy for both anterior (Figure 1A) (p = 0.02) and posterior (Figure 1B) (p<0.001) provocative positions. Regional stability indices, based upon the expected range of dislocation for each provocative position, were also significantly greater and of slightly larger magnitude for the intact condition than after total labrectomy (p<0.001). Conclusions. This is the first known application of a six-degree-of-freedom robot to recreate mechanical hip impingement and dislocation to elucidate the role of the labrum in hip stability. Our results suggest that at least in extreme positions, the labrum imparts significant overall mechanical resistance to hip dislocation compared to the condition without the labrum. Regional contributions of the labrum are greatest in the direction of dislocation as foretold by joint position as indicated by region-based stability indices. Future studies involving more clinically relevant injury patterns with greater soft tissue preservation in a younger cadaveric population would better reflect the in vivo effects of labral injury so that treatment strategies can be developed accordingly

A trochanteric osteotomy offers extensile exposure of the hip on both the acetabular and femoral sides. The classical trochanteric osteotomy which is transverse and involves a release of the vastus lateralis muscles is complicated by a significant incidence of trochanteric nonunion and more importantly, trochanteric migration. The trochanteric slide was designed to avoid trochanteric migration by keeping the trochanteric fragment in continuity with the abductors and the vastus lateralis. Even if there was a trochanteric nonunion, a trochanteric migration was prevented by continuity of muscles enclosing the greater trochanter in a sling of muscle. When we first started doing the trochanteric slide, we used the technique originally described which involved starting with the posterior approach to take down the external rotators and the posterior capsule, and then proceeding with the trochanteric osteotomy. We found that our incidence of posterior dislocation increased to 15%. We therefore decided that we would attempt to do this operation but try to preserve the external rotators and the posterior capsule so they remained in situ attached to the main body of the femur, so that the trochanteric osteotomy was carried out just anterior to these muscles and posterior capsule. As a result of this our dislocation rate went from 15% to 3%. This exposure provides an extensile exposure of the pelvis and femur. If femoral component removal is anticipated to be difficult, then we use exactly the same approach but we extend the trochanteric fragment down as in an extended trochanteric osteotomy

Introduction. Pelvic flexion and extension in different body positions can affect acetabular orientation after total hip arthroplasty, and this may predispose patients to dislocation. The purpose of this study was to evaluate functional acetabular component position in total hip replacement patients during standing and sitting. We hypothesize that patients with degenerative lumbar disease will have less pelvic extension from standing to sitting, compared to patients with a normal lumbar spine or single level spine disease. Methods. A prospective cohort of 20 patients with primary unilateral THR underwent spine-to-ankle standing and sitting lateral radiographs that included the lumbar spine and pelvis using EOS imaging. Patients were an average age of 58 ± 12 years and 6 patients were female. Patients had (1) normal lumbar spines or single level degeneration, (2) multilevel degenerative disc disease or (3) scoliosis. We measured acetabular anteversion (cup relative to the horizontal), sacral slope angle (superior endplate of S1 relative to the horizontal), and lumbar lordosis angles (superior endplates of L1 and S1). We calculated the absolute difference in acetabular anteversion and the absolute difference in lumbar lordosis during standing and sitting (Figure 1). Results. Nine patients had normal lumbar spines or scoliosis, and 11 patients had multilevel disc disease. The median change in cup anteversion for normal and scoliosis patients was 29° degrees (range 11° to 41°) compared to 21° degrees (range 1° to 34°) for multilevel disc disease patients (p=0.03). There was a positive correlation between the change in cup anteversion and the change in lumbar lordosis (p=0.01; Figure 2). From standing to sitting, cup anteversion always increased and lumbar lordosis always decreased. Conclusions. The change in cup anteversion from standing to sitting was variable in patients with normal, degenerative, and scoliosis lumbar spines. Patients with degenerative disc disease have less pelvic extension, and thus less acetabular anteversion in the sitting position compared to normal spines. This may increase their risk of posterior dislocation

Mini-incision total hip arthroplasty seeks to eliminate some complications of traditional extensile exposure and also facilitates more rapid post-operative rehabilitation. Posterior approach has been associated with increased risk of posterior dislocation. Thus, a modified mini-incision lateral approach of Hardinge was described not only to overcome this problem by preserving the posterior capsule, but also allows adequate access for orientation of the implant. The author has modified the Hardinge approach by a V-shaped incision where the apex is centered over the tip of the greater trochanter with the one limb extending proximally along the fibers of the gluteus medius muscle and the distal limb extending across the proximal part of vastus lateralis. This innovative surgical approach is described in this article. Conclusion. Larger incisions and surgical approaches have been associated with larger blood loss, greater need for perioperative transfusion, use of more postoperative analgesics, a longer hospital stay, and a slower recovery. In this modified approach, the gluteus medius is left intact. The postoperative strength of the abductors of the operated side was the same as that on the non-operated side and functionally, the direct lateral approach was a safe alternative to other approaches in decreasing the trendelenburg gait and incidence of heterotrophic ossification

A trochanteric osteotomy offers extensile exposure of the hip on both the acetabular and femoral sides. The classical trochanteric osteotomy which is transverse and involved a release of the vastus lateralis muscles is complicated by a significant incidence of trochanteric nonunion and more importantly, trochanteric migration. The trochanteric slide was designed to avoid trochanteric migration by keeping the trochanteric fragment in continuity with the abductors and the vastus lateralis. Even if there was a trochanteric nonunion, a trochanteric migration was prevented by continuity of muscles enclosing the greater trochanter in a sling of muscle. When we first started doing the trochanteric slide, we used the technique originally described which involved starting with the posterior approach to take down the external rotators and the posterior capsule, and then proceeding with the trochanteric osteotomy. We found that our incidence of posterior dislocation increased to 15%. We therefore decided that we would attempt to do this operation but try to preserve the external rotators and the posterior capsule so they remained in situ attached to the main body of the femur, so that the trochanteric osteotomy was carried out just anterior to these muscles and posterior capsule. As a result of this our dislocation rate went from 15% to 3%. This exposure provides an extensile exposure of the pelvis and femur. If femoral component removal is anticipated to be difficult, then we use exactly the same approach but we extend the trochanteric fragment down as in an extended trochanteric osteotomy

Neglected traumatic dislocation of hip in children is very rare and most of the studies are too small to draw a conclusion. There is no consensus on timing for closed VS open reductions and post reduction care. The aim of our prospective study was to analyse and characterise the short term treatment outcome of treating 20 such cases in children (<12 years). All had posterior dislocation without any associated fractures (Thompson & Epstein type 1) sustained during typical childhood play activities and/or a fall from a height less than 10 feet. All attended the hospital between 1-52 weeks of injury. Closed reductions under GA were performed in 12 cases which were less than 3 weeks old, followed by hip immobilisation for 3 weeks and PWB mobilisation for 3 weeks. 8 hips (> 3 weeks old) had open reductions as none of them could be reduced by skeletal tractions and were allowed for FWB mobilisation after 9 weeks. Functional result (Garrett et al) at 2 years follow-up showed a complete range of motion in 18 children while the remaining two had 80% of normal hip movements with no deformity. All the hips showed varying degrees of avascular necrosis, with preservation of joint space on radiographs (Ficat & Arlet stage 1-3). There were no redislocations. We suggest that closed (for <3 weeks old dislocation) and open (for >3 weeks old dislocations) reductions are satisfactory treatment for traumatic neglected hip dislocations in children

Introduction:. Large diameter femoral heads have been used successfully to prevent dislocation after Total Hip Arthroplasty (THA). However, recent studies show that the peripheral region of contemporary femoral heads can directly impinge against the native soft-tissues, particularly the iliopsoas, leading to activity limiting anterior hip pain. This is because the spherical articular surface of contemporary prosthesis overhangs beyond that of the native anatomy (Fig. 1). The goal of this research was to develop an anatomically shaped, soft-tissue friendly large diameter femoral head that retains the benefits of contemporary implants. Methods:. Various Anatomically Contoured femoral Head (ACH) designs were constructed, wherein the articular surface extending from the pole to a theta (θ) angle, matched that of contemporary implants (Fig. 2). However, the articular surface in the peripheral region was moved inward towards the femoral head center, thereby reducing material that could impinge on the soft-tissues (Fig. 1 and Fig. 2). Finite element analysis was used to determine the femoroacetabular contact area under peak in vivo loads during different activities. Dynamic simulations were used to determine jump distance prior to posterior dislocation under different dislocation modes. Published data was used to compare the implant articular geometry to native anatomy (Fig. 3). These analyses were used to optimize the soft-tissue relief, while retaining the load bearing contact area, and the dislocation resistance of conventional implants. Results:. The resulting ACH prosthesis retained the large diameter profile of contemporary implants over an approximately hemispherical portion (Fig. 2). Beyond this, the peripheral articular surface was composed of smaller convex radii. With this design, the jump distance under posterior and anterior dislocation modes, and the femoroacetabular contact area under loads corresponding to walking, deep knee bend and chair sit, remained identical to that of contemporary implants. Additionally, while contemporary prosthesis extended beyond the native articular surface in the distal-medial and proximal-lateral regions (shaded grey), the ACH implant remained within the margins of the native anatomy (Fig. 3). Conclusion:. A novel large diameter anatomically contoured femoral head prosthesis was developed, to mitigate the soft-tissue impingement with contemporary prosthesis. The ACH retained the large diameter profile of contemporary implants over a hemispherical portion. However, in the peripheral region, the ACH had a smaller profile to reduce soft-tissue impingement

BACKGROUD/PURPOSE. Recently, the use of a large diameter femoral head has been discussed as a means to reduce the risk of hip dislocation after total hip arthroplasty (THA). Although it has been clear that increasing the head size increases the oscillation angle and hip stability, a consensus on the usefulness of a larger head size has not been reached due to an increased propensity for bone impingement. We studied the effect of the range of motion (ROM) and bone impingement caused by increasing the femoral head size using a 3D simulation system. PATIENTS AND METHODS. All patients who had undergone a primary THA in our hospital from October 2010 were selected, and we excluded those with severe osteoarthritis, severe dysplasia (Crowe group), or excessive femoral neck anteversion (35°). This resulted in 60 patients (16 men and 44 women), with a mean age of 66.6 years (range, 47–83 years). The diagnoses were osteoarthritis in 42 hips, osteonecrosis in 11 hips, rheumatoid arthritis in four hips, and femoral neck fracture in three hips. A virtual hip model was generated from the preoperative CT scan and a component was virtually implanted via computer simulation software (Zed Hip, LEXI, Japan). The acetabular cup was implanted with an inclination of 45°, anteversion of 20°, and the femoral stem was implanted into the femur recreating the same head height with an anteversion of 25°. We defined three leg positions: (A) maximum flexion (B) internal rotation with hip in 90°of flexion and 20°of adduction as posterior dislocation, and (C) external rotation with hip in 0°of extension as anterior dislocation. In each leg position, range of motion up to the impingement and the type of impingement (implant or bone) was assessed with 22-, 26-, 28-, 32-, and 36 mm femoral head sizes. RESULTS. We found a significant increase in ROM between the 22 mm and 26-, 28-, 32-, and 36 mm femoral heads, and between the 26 mm and 36 mm femoral head in each leg position, but no significant difference was found in femoral heads more than 28 mm. Bone impingement preceding implant impingement was increased with larger head sizes more than 50% of the 28 mm head size in each leg position. The 36 mm head size corresponded to (A) 87%, (B) 85%, and (C) 70%, respectively. CONCLUSIONS. We concluded that increasing the head size increased bone impingement, which led to restricting improvement in ROM. There was no significant increase in ROM for femoral heads more than 28 mm; therefore, excessively large head sizes may result in restrictive ROM due to an increased oscillation angle