Over the past 10 years, the orthopedic community has witnessed an increased interest in more conservative surgical techniques for hip arthroplasty. During this time, second-generation hip resurfacing and minimally invasive surgery enjoyed extensive marketing attention. After a decade of this renewed interest, both of these methods have met with serious concerns. As hip resurfacing numbers decline, both patients and surgeons are looking for other potentially successful conservative treatments to THA. This search has focused surgeon interest toward short-stem designs.

Today, a variety of short-stem implants are available with very little clarification of design rationale, fixation features, surgical technique, and clinical outcomes. Virtually every major implant company now offers a “short stem,” and now there are a plethora of different designs. It is important to note, however, that not all short stems achieve initial fixation at the same bone interface region. Furthermore, surgical techniques vary greatly, and postoperative radiographic interpretation of short-stem position and fixation need to be carefully scrutinized.

The purpose of this paper is to review past, present, and potential future developments of short femoral stems and to present a classification system that can offer guidance when reporting on the many different stem variations.

Short Curved neck-sparing stem (JISRF classification 2a). Recently, new designs are following Pipino's Biodynamic stem style of saving the femoral neck. These designs feature a short curved stem that finds its stabilization contact region in the femoral neck and saves considerable bone in the medial calcar region. In addition, the curvature of the stem prevents violation of the lateral trochanteric region. The shorter stem also reduces blood loss by not reaming the femoral canal distally. These style stems generally have a variable stem length between 90 and 135 mm. This might not appear much shorter than conventional cementless stems (110 to 150 mm). However, the shorter curved neck sparing stems penetrate on average 1 to 2 cm less distally in the femoral canal.

Short stems have a definite role in modern THA, as greater emphasis is being placed on soft tissue and bone sparing techniques and as refinements continue in the understanding of proximal femoral fixation.

Metaphyseal short stems have significantly less surface contact area compared with conventional length stems and as a result, they might have less torsional and axial resistance.

Neck-retaining short stems provide additional axial and torsional stability and reduced stress at the implant– bone interface and may be a consideration in the more active patient profile. Bone quality and the patient's physical activity should be considered prior to the selection of short-stem devices. Many short-stem designs have considerably different style features that may alter bone remodeling. Knowing the design and the required technique is vital to fit the device properly to the patient. The variations of short stems available call for caution in their overall use until there is better understanding of how dependent these stems are on individual stem features, bone quality, and surgical techniques. Overall, the authors are cautiously optimistic and continue advocating their selective use.

Wear debris associated with CoCr bearings has been implicated in the development of adverse soft tissue reactions and pseudotumors following THA with large metal heads and following hip resurfacing. Additional concerns have been raised regarding trunion fretting and corrosion. Most recently, the neck-stem junction of some modular femoral stem designs have come under additional scrutiny. We undertook a review of patients who had undergone THA with a proximal modular junction stem design in order to ascertain the state of the junction in early follow up.

We examined the records of all patients in our practice who had undergone uncomplicated, unilateral THA with the ARC stem (OmniLife Science, East Taunton, MA, USA) between April 2010 and April 2012. Office records, radiographs and laboratory data were included. Serum or blood cobalt and chromium ion levels were obtained at the one-year post-op visit or later or if the patient had unexpected pain. The test obtained (serum or blood) was dependent on the lab performing the study.

In the study period 100 patients met the inclusion criteria and had metal ion levels available for review. No patient required revision for adverse soft tissue reaction or elevated metal ion levels. Cobalt levels fell with the normal lab ranges in the majority of patients with a very small percentage demonstrating levels slightly above the normal range. Chromium levels all fell within the expected normal range. One patient had a neck exchange for mechanical reasons at 8 weeks following primary THA. This patient went on to develop elevated serum cobalt levels and a large hip effusion. The hip was revised at one year to a non-modular stem.

A modular proximal stem offers the advantages of addressing variable anatomy and allowing less soft tissue dissection. Some designs have enjoyed success while others have been withdrawn from the market due to fatigue failure, dissociation or metal-associated adverse reactions. Modular junction designs vary greatly which can impact their inherent stability and their ability to resist micro-motion. In this patient group the junction has shown good stability in early follow up as judged by clinical and laboratory data. Cobalt levels were all normal or well below the range considered suspicious for adverse reaction. Chromium levels all fell within the normal range. A case of an exchanged neck with retention of the stem was associated with high cobalt levels. We discuss several junction designs and their characteristics.

Introduction

Architectural changes occurring in the proximal femur after THA continues to be a problem. Stress shielding occurs regardless of fixation method. The resultant bone loss can lead to implant loosening and breakage of the implant. A new novel tissue sparing neck-stabilised stem has been designed to address these concerns.

Introduction

The use of short stems has been growing in THA for the past five years. As a result, a large number of short stem designs are available in the market place. However, fixation points differ for many of the designs resulting in different radiographic modeling creating confusion when trying to collate to clinical findings. We have created a classification system in an attempted to provide clarity in analyzing radiographic and clinical findings.

THA continues to improve but complications still occur. Improper restoration of hip mechanics can lead to a number of clinical problems: increase in leg length, soft tissue laxity, weakness of the abductors, mechanical impingement, increase of wear and improper implant sizing can lead to thigh pain, subsidence and hip dislocation.

Six-hundred-and-fifty-five primary cementless THA were performed over the past twenty-four years by the senior author at two hospitals. Three different stems were used, two being modular and one being monoblock. A variety of cups head sizes and bearing material were used. All cups were implanted cementless. All surgeries were performed with the posterior approach. Sixty percent of patients were female forty percent males. Majority of cases were for OA.

Cup revisions have been the biggest problem to-date with excessive wear of the poly material. This is more than likely due to the first and second generation designs that had poor locking mechanics. Over the last four years since going to MOM technology cup revisions have not been seen. On the femoral side there have been no femoral lysis, five dislocations two treated closed and three open reductions treated with constrained sockets. Four stem revisions, all for late sepsis. There has been two recent aseptic loosening, and only one traumatic dislocation since going to large MOM heads.

One was one post-op with an ASR MOM cup that had spun out of position of function and the second a week later that was only six weeks post-op and came in for her first post-operative visit.

Routine use of intra-operative x-rays has resulted in +80% decision on fine-tuning of implant sizing by either increasing stem size and or femoral offset. Intra- operative x-rays provide valuable assistance and allow full advantage of the features and benefits of stem modularity reducing post-operative complications.

Total hip arthroplasty has a very high success rate, as measured by pain relief, improved function and patient satisfaction. However, on occasion, complications do happen. This paper will review three cases that required surgical intervention and design features of a modular stem making revision surgery considerably easier. Three patients received cementless THA within the past two years. All three had a ‘Dual Pressâ’ proximal modular stem design. Two patients had metal-on-metal (MOM) bearings that shifted position and one had a cementless porous cup with a 36 mm poly bearing with metal head that dislocated. All were performed at the same hospital by the senior author using a small posterior surgical approach.

All three required revision surgery that was made considerably easier by the design feature of proximal Dual Pressâ modularity.

The Dual Pressâ modular junction has a novel design that allows for retrievability in just these types of cases. A proximal setscrew is removed allowing access of a slap hammer, making the proximal neck disengage from the stem body. This greatly improves exposure for removal and implantation of the acetabular component. In both cup revisions, the explant cup removal system was used without difficulty, as a result of increased exposure achieved by removal of the neck portion of the stem. Then a new proximal neck segment with head was attached with no disruption of the stem/bone interface.

The dislocation case was addressed by removal of the proximal modular neck body, then increased femoral offset and 13° angle added to the new neck position. The cup, liner and stem body were not changed at all. Patient was stable (hip closed) and discharged the next day.

Modern day designs in implants and instrumentation have made THA more reproducible and in cases of revision surgery provide design features and benefits that reduce operative time, complications and as a result offer significant cost savings as compared to traditional monoblock stem designs.

Modular hip designs offer potential for customising the implant to the patient. However, the more features a device has to offer, the potential for misuse increases. This paper will review one modular stem and the pearls learned over the years to make this a simple and reproducible surgical technique.

Over a 1,000 primary THA have been performed since the development of the proximal modular stem in 2000. The two senior surgeons developed the stem design and surgical techniques used and described here. Two additional surgeon co-authors have used the device as described confirming the design and techniques to be simple, reliable and reproducible.

Often the tricks of the trade go unpublished and each new surgeon is left to his own learning curve with new devices. As with any surgical instrumentation there are significant little techniques that often make surgery more reproducible and enjoyable.

Surgical technique should be simple and reproducible. We have found that even simple procedures—such as head resection—can, and do, impact the surgical process and can affect surgical outcome. Canal reaming, flute engagement, conical reaming, broaching, trochanter clearance, proper use of modular trials and implant assembly all play critical roles to a successful outcome.

We have found, and previously reported, that the use of this proximal modular stem design has reduced our leg length inequalities +/− 5 mm and has all but eliminated dislocations and aseptic loosening.

There were some mechanical failure problems (previously reported) on the first generation modular junction design that was identified and corrected (never exported outside the U.S.). There have been no reported failures since introduction of the improved modular junction six years ago.

Independent selection of femoral offset and vertical height is possible and we feel that restoration of joint mechanics is more reproducible with proximal modular devices as compared to monoblock stems. It is the responsibility of surgeons to communicate their understanding and experience with newer devices and not rely on industry to fill this function.

There has been considerable activity in the past year as a result of the Justice Department Investigation into the medical device industry. There has been an over reaction by many which may negatively impact future research, development and reporting of clinical outcomes. This paper will review some of these activities. A review of professional standards and guidelines has been conducted looking at health care compliance issues as they related to commercial relationships, professional medical societies, individual surgeons, and health care workers with specific focus on disclosure.

Within any important issue, there are always aspects no one wishes to discuss: conflict of interest. Perception of a conflict of interest is often enough to bring about a review of activity.

Overreaction has occurred as a result of government intervention into the medical device industry. Continuing medical education, professional societies by-laws, clinical/surgical publications, medical/legal exposure, product research, development and industry marketing activities have all been impacted.

When professionals fail to provide a proper review process on standards and guidelines on ethical behavior they set themselves up for government oversight and restrictions on their behavior. Be informed and disclose. Know what, when and how to disclose. Protect yourself, no one else will.

Hip simulator studies on MOM bearings have historically involved ‘custom’ cetabular cups. I.e. having neither beaded layers nor biological coatings.

The aim of this study was to investigate wear using such MOM bearings and evaluate the potential wear and evaluate the potential for error in the gravimetric assessment.

Six x 38 mm HC Co-Cr bearings were supplied (Global and IO International Orthopaedics). The cups were received in ‘off-the-shelf’ condition with a cast Co-Cr beaded/HA-coated backing. To remove the HA-coating, the cups were pre-soaked in lemon juice for 4 days (articular surfaces shielded). Custom plastic fixtures were machined to fit the beaded contours of the cups. Test duration was 5Mc inorbital hip simulator (Shore-Western). MOM wear was estimated from serum ion contamination. Serum samples were digested and assessed using ICP/MS (Weck Labs Inc, CA).

The majority of the HA-coating was removed from the cups after four days of soaking inlemon juice after 21 days of soaking all cup weights appeared atable (within 1 mg). Reflected-light microscopy (RLM) showed no descernible signs of HA and the total weight loss due to HA remval averaged∼400mg.

During hip simulator there was no visual evidence of lost or broken beads, 3rd body abrasion etc (Sa<30nm). Both gravimetric and metal ion analysis showed consistent wear trends for all MOM cups. The MOM with the highest wear (predicted by ion analysis) demonstrated 1.2 mm (3)/Mc)OWR) at 5Mc. In comparsion, gravimetric analysis predicted an OWR of 1.3 mm (3)Mc for the same MOM, a difference of only 8%. Soaking beaded-HA cups in lemon juice and BCS proved effective in removing the coating.

The beaded cups remained stable in weight during the wear study and caused little discrepancy in gravimetric analysis (8%).

The method described did not lead to breaking of beads, elevated 3rd-body abrasion, cup damage or distorted wear scars.