Constrained liners, dual mobility or large diameter heads to avoid dislocation in THA.

Dislocation remains a common cause of failure after total hip arthroplasty. The limitations of existing approaches to address instability have led to the development of powerfull options: constrained liners, dual mobility and large heads. These implant-related options have proven to be very efficient, but have raised concerns.With constrained liners, restricted range of motion (ROM) is responsible for impingement leading to high likelihood of failure, depending on the design, with various failure modes.Improvements of the bearing materials have addressed some of the concerns about increased volumetric wear of conventional polyethylene and offer an option to reduce instability: large diameter heads have the advantage of increased ROM before impingement, increased head-neck ratio, and jump distance. Highly cross-linked polyethylene helps address the risk for increased wear, and also large heads provide improved stability without the risk of mechanical failures observed with constrained liners. However, the increase of the head size remains limited as reducing the thickness of the liner may lead to fractures. In addition, the jump distance decreases as the cup abduction increases.The dual mobility concept simultaneously attempts to address head-neck ratio, constraint, and jump distance. Despite the need for longer follow-up, concerns raised about potential increased wear and intra-prosthetic dislocation with first generation implants have been addressed with modern designs.With a dramatic increase of the head-neck ratio whilst reducing the risk of mechanical failure or excessive wear, dual mobility THA outperforms large diameter heads and constrained liners at 10 years follow-up. For these reasons, dual mobility continues to gain interest worldwide and is becoming the most popular option to manage instability. Cite this article: Guyen O. Constrained liners, dual mobility or large diameter heads to avoid dislocation in THA. EFORT Open Rev 2016;1:197-204. DOI: 10.1302/2058-5241.1.000054

High failure rate of the Duraloc Constrained Inlay

Background and purpose After total hip arthroplasty, dislocations are a frequent complication and are difficult to treat in some patients. A great variety of implants and antiluxation mechanisms are used in surgical therapy

Effect of friction and clearance on kinematics and contact mechanics of dual mobility hip implant.

The dual mobility hip implant has been introduced recently and increasingly used in total hip replacement to maintain the stability and reduce the risk of post-surgery dislocation. However, the kinematics and contact mechanisms of dual mobility hip implants have not been investigated in detail in the literature. Therefore, finite element method was adopted in this study to investigate dynamics and contact mechanics of a typical metal-on-polymer dual mobility hip implant under different friction coefficient ratios between the inner and the outer articulations and clearances/interferences between the ultra-high-molecular-weight polyethylene liner and the metal back shell. A critical ratio of friction coefficients between the two pairs of contact interfaces was found to mainly determine the rotating surfaces. Furthermore, an initial clearance between the liner and the back shell facilitated the rotation of the liner while an initial interference prevented such a motion at the outer articulating interface. In addition, the contact area and the sliding distance at the outer articulating surface were markedly greater than those at the inner cup-head interface, potentially leading to extensive wear at the outer surface of the liner

Hemiarthroplasty or total hip arthroplasty in recent femoral neck fractures?

The optimal treatment of recent femoral neck fractures remains debated. The available options are internal fixation, hemiarthroplasty (HA) and total hip arthroplasty (THA). There is a consensus in favour of internal fixation in younger patients. In elderly individuals who are institutionalised and have limited physical activity, HA is usually performed when the joint line is intact. Whether HA or THA deserves preference in patients aged 60 years or over is unclear. In addition, there are two types of HA, unipolar and bipolar, and two types of THA, conventional and dual-mobility. Both HA types provide similar outcomes with satisfactory stability but a risk of acetabular wear that may eventually require conversion to THA. THA is associated with better functional outcomes and a lower risk of revision surgery in self-sufficient, physically active patients. Instability is the leading complication of conventional THA and occurs with a higher incidence compared to HA. With all implant types, preoperative factors associated with mortality and complications include walking ability and level of self-sufficiency, nutritional status, and haematocrit. An evaluation of these factors before surgery is of paramount importance. Factors amenable to treatment should be corrected by working jointly with geriatricians to develop a preoperative management strategy. In patients who are self-sufficient, physically active, and free of risk factors, THA remains the option of choice, as it provides better functional outcomes. A dual-mobility implant deserves preference to prevent instability. HA is indicated in patients whose self-sufficiency and physical activity are limited. A unipolar implant should be used, as no evidence exists that bipolar implants provide additional benefits. When performing HA, the posterior approach should be avoided given the risk of instability. For THA, in contrast, the posterior approach is a reliable option in the hands of an experienced surgeon using a dual-mobility cup. Cement fixation of the stem is recommended to minimise the risk of peri-prosthetic fracture

Suivi des patients avec arthroplastie de hanche métal-métal et stratégie de prise en charge des complications [Patients with metal-on-metal hip arthroplasty: evaluation and management of complications]

The potentially severe complications related to metal-on-metal (MoM) hip replacements have led to a dramatic decrease of their use. Large diameter heads are more likely to fail than smaller diameters, but complications have been described even with « small » diameters. Therefore, monitoring of MoM arthroplasties is mandatory. This includes physical examination, X-Rays, metal ion levels, and potentially cross-sectional imaging. Despite pathophysiology of adverse reactions to metal debris (ARMD) is better understood, their evolution and the potential systemic complications remain unclear. Symptomatic hip arthroplasties, elevated ions levels, and ARMD may lead to revision of the components. In such a situation, an adaquate stategy must be achieved given the high potential for complications

Reconstructed hip joint architecture with a standard hip arthroplasty with a unique declined offset

Abstract: Possible advantages of the architectural restoration of the hip joint after total hip arthroplasty (THA) are numerous. The relationship between the femoral offset (FO) and the abductor moment arm and the polyethylene wear, loosening, instability, persistent limp due to gluteus medius insufficiency, even dislocation, leg length discrepancy have been reporte

Intra-prosthetic dislocation of dual mobility hip prosthesis: an original and unusual complication.

A 78-year-old female presented with dislocation of a dual mobility hip prosthesis. On standard radiographs after closed reduction, the hip prosthesis appeared to be properly reduced, but clinically the hip was unstable. A Computed Tomography showed a round foreign body, that was in fact a dislocation of the intra-prosthetic implant. This was confirmed intra-operatively during revision surgery. Intra-prosthetic dislocation is a specific complication of dual mobility system. Classically, it's a late complication, linked to the wear of retention area of the polyethylene insert. In this case report we describe an unusual reason of intra-prosthetic dislocation caused by a reduction maneuver of a dislocated dual mobility total hip prosthesis, which to our knowledge has never been documented with Computed Tomography imagery and intra operative pictures. The aim of this article is to analyse the advantages and complications of this implant and to establish recommendations. Dealing with an intra-prosthetic dislocation of a dual mobility hip prosthesis, we recommend attempting a reduction under general anesthesia to avoid mechanical complications. In case of persistent instability after reduction, we recommend performing a Computed Tomography scan