The emergence of modularity in total hip arthroplasty (THA) in the 1980s and 1990s was based on the fact that the benefit of these design features outweighed the risk. The use of metallic modular junctions presents a unique set of advantages and problems for use in THA. The advantages include improvement in fit and fill of the implant to bone, restoration of joint mechanics, reduced complications in revision surgery and reduction of costly inventory. However, the risks or concerns are a little harder to identify and deal with. Certainly corrosion, and fatigue failure are the two most prevalent concerns but now the specifics of fretting wear and corrosive wear increasing particulate debris and the potential biological response is having an impact on the design and potential longevity of the reconstructed hip. Material and designs are facing a shorter life expectancy than what was previously thought, mostly due to an increasing level of physical activity by the patient. Because there are no accurate laboratory test whereby the service life and performance of these implants can be predicted, early controlled clinical evaluations are necessary. Early publication of testing and clinical impressions should be encouraged in an attempt to reduce exposure to potential at risk patients, implants and material. The reduction and possible elimination of risks will require a balancing of all the variables requiring a multidisciplinary endeavor.This paper is designed to review the risk factors, and benefits of modular junctions in total hip arthroplasty (THA). Also some basic engineering principals that can reduce risk factors and improve functionality of modular junctions.

We describe four patients who were treated with primary total hip arthroplasty (THA) at two tertiary academic Australian teaching hospitals that experienced premature failure of head-neck trunnions through dissociation of the head-neck taper junction. This retrospective case series has similar clinical presentations and macroscopic pathology with severe head-neck taper junction loss of material, corrosion and early catastrophic failure. It is proposed that the accelerated wear is related to use of varus offset neck in a proprietary beta titanium alloy (Ti-12Mo-6Zr-2Fe or TMZF� Stryker Osteonics, Mahwah NJ, USA) TMZF femoral stem, longer head-neck combination in a relatively active, older, male patient population. In this limited case series presentation was on average 80 months (range 53-92) following index procedure. In three of the four patients, a prodromal period of groin or buttock pain was reported for between 1 week and 2 months prior to acute presentation. Significant metallosis and local tissue damage including gluteal muscle insufficiency was evident. Each stem revised was well fixed. An extended trochanteric osteotomy was required in two of the four cases for stem extraction. We recommend caution and further evaluation on the relationship between TMZF metal alloy and its longevity in higher demand patients with high neck offset, varus stem geometry and large CoCr bearing heads.

In recent years, specialized, non-sterile, traction table systems have facilitated Direct Anterior Approach (DAA) hip arthroplasty. To combat the potential downsides of these traction systems, a sterile, intra-operative retractor option has emerged as a means to access the surgical site more easily, minimize soft-tissue trauma, and reduce the degree of required human assistance. This chapter describes the setup, surgical approach, and early results of a retractor system (the Phantom MIS Anterior Hip Retractor system [TeDan Surgical Innovations, Inc. {TSI}, Houston, Texas, US Patent # 8,808,176 B2]), which uses a standard operating table, allows preparation of both lower extremities free in the surgical field, is compatible with fluoroscopy, and aids in both acetabular and femoral exposure, preparation, and implantation. Early outcome data indicates that this system significantly minimizes the need for surgical assistance, while allowing for safe and effective DAA performance, facilitating the procedure for high-volume surgeons and shortening the learning curve for surgeons new to the procedure.

Background: The complexity of hip reconstruction has been and continues to be a perplexing problem with restoring leg length, femoral offset, joint stability and overall hip implant fixation. These were contributing factors that lead to the development of a novel proximal femoral component design "Apex Modular Stem" (Omni, Raynham, MA). The basic stem geometry features a straight stem with a metaphyseal fit and fill cone, a medial triangle and a modular neck junction that allows for version and offset adjustment.

Purpose. To evaluate early and mid-term risk factors and dislocation rates in the posterior surgical approach in three separate community private practices using a short curved neck-sparing total hip stem design.Material and Methods.The three senior authors performed 338 short curved neck-sparing stem designs since April 2010 to June 2014.  Various cementless acetabular components were used for all three surgical centers based on preoperative and intraoperative risk factors. All cases were reviewed retrospectively for incidence of dislocation after surgery.Version and inclination of the acetabular component and version of the femoral component were assed intra-operatively prior to final implantation. Various risk factors were reviewed including surgical approach, cup position, combined cup and stem positioning, and femoral head size.There have been significant papers in the past ten years that have recommended large head diameters to reduce the chances of head/neck mechanical impingement. Since the neck-sparing designs have a potentially increased risk of mechanical impingement head diameters were restricted to 32 mm or larger. In the smaller patient profile if a 32 mm head size could not be reached a dual-mobility style implant was chosen or stem choice was changed to a conventional style design.Results.Historically the posterior approach has had higher reports of dislocations as compared to direct anterior, anterolateral or straight lateral approach in conventional cemented and cementless implant designs. Older neck-sparing designs of conventional stem length by Freeman, Townley and Whiteside have not reported any increased dislocation problems but these stems have been associated with modified acetabular component designs, including the short curved neck sparing design of Pipino back in the 1980s.Incidence of dislocation in our series utilizing a short curved neck-sparing stem with more traditional hemispherical cementless acetabular components was 3 or 0.88%.Conclusion.Neck sparing stem designs do save significantly more bone and require less soft tissue dissection as compared to conventional cementless stem designs. Mechanical risk factors are increased with the use of short curved neck-sparing stem designs. Careful pre-operative and intra-operative evaluation does reduce the risk factors resulting in low and in some cases lower than previous published rates with conventional style stems.Short curved neck sparing stems do provide safe and reliable reproduction of the joint mechanics in routine primary total hip arthroplasty in both short and mid term results.Key Words: hip, arthroplasty, posterior approach, dislocation, neck sparing, and risk factors