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.

Introduction: Polyethylene and metal has been the material of choice since the 1960’s.

We are now seeing the third generation of cross-linked polyethylene along with work on alternative hard on hard bearings trying to reduce the generation of wear debris.

Issues have been raised from squeaking to high trace elements and strength characteristics of current materials.

Ideally, the surfaces for articulating bearing surfaces will be made from materials having high strength, high wear, and corrosion resistance, a high resistance to creep, and low frictional moments. This paper will review characteristics of a novel new approach for a bearing material.

Methods: A review of past and current materials along with mechanical testing in creating a new approach to the development of a hydrophilic material replacing the polyethylene side of the bearing surface.

Studies have demonstrated the advantages of the fullfluid film layer of lubrication in-terms of enhanced wear performance.

An acetabular “buffer” bearing was developed that features a pliable bearing surface formulated, biocompatible polycarbonate urethane (PCU). A review of design objectives and testing will be highlighted in this paper.

Results: Wear studies have demonstrated performance up to twelve times better compared to polyethylene.

34 components have been implanted reaching two years post-op. Two devices have been removed both for non-related implant issues. Retrieval analysis did not show any appreciable wear or damage to the bearing material.

Conclusions: To date we are encouraged by the early basic and clinical science, however, only additional research and time will demonstrate the long-term viability of this material.

Introduction: Architectural changes in the proximal femur after THA continue to be a problem. In an attempted, to reduce these changes some surgeon designers have advocated the concept of neck sparing stem designs.

To-date neck-sparing stems have been disappointing in their ability to maintain the calcar. A new approach was undertaken to improve load transfer and to create a tissue-sparing stem that would be simple in design, reproducible in technique and provide for fine-tuning joint mechanics while maintaining compressive loads to the calcar.

Methods: Review of previous published work was evaluated along with FEA modeling in creating a new approach to neck sparing stems for THA. The MSA^™ Stem is a simple curved stem with a unique lateral T-back designed for torsional stability, ease of preparation and insertion. The proximal design has a novel proximal conical shape designed to transfer compressive forces to the calcar.

A modular neck provides for fine-tuning joint mechanics.

Results: FEA modeling will be reviewed. Strain patterns for the MSA^™ stem demonstrated better patterns vs. long stems or the short Biodynamic stem.

Discussion: In theory neck retaining devices provide or:

Bone and Tissue sparring

We are encouraged and believe there are advantages in the concept of neck sparing stems. Clinical/surgical evaluation is now underway and will be reported on in the future.

Introduction: Cemented stems are still widely used in THA; however, there remain concerns with hip dislocation and wear debris. Restoring joint mechanics is essential for soft tissue balance and reduction of mechanical impingement. These concerns have lead to the development of a modular neck for cemented THA.

Material and methods: 200 R-120™ cemented stems were implanted in 190 patients since 2001. The shape of the stem is trapezoidal with a large collar that provides for impaction and compression of the cement. The stem collar is made with a cavity where a self-locking taper and a positive indexing mechanism provide 12 different positions to ensure proper restoration of joint mechanics.

One to five years follow up with a mean of 2.8 years. Two-thirds were female and one- third male. Age ranged from 39 to 87 with a mean of 73. Majority was treated for OA. A c.c. head (28mm or 32mm) and poly bearing in a cementless cup were used for all patients. Selection of neck position was recorded for all patients.

Results: 635 of all head-neck positions were other than neutral. There were 0 dislocations, no significant leg length discrepancies (+/− 5mm), and 0 infections. There was one stem removed due to a post-op peri-prosthetic fracture at 3 years that was treated with a long cement-less stem. 1 death due to a PE ten days post-op. 1 intra-operative calcar fracture wired and healed uneventfully. 1 intra-op greater trochanter fracture that was treated with screws. 2 neck fractures revised to cementless stems.

Conclusions: Modular neck design aids in fine tuning joint mechanics after stem insertion, and allows for ease and access in case of revisions. This modular neck design has eliminated (to date) hip dislocations and we remain optimistic about its long-term potential to improve outcomes. Fatigue properties have been significantly improved and no additional neck fractures have occurred.

Cemented total knee arthroplasty has excellent long term survivorship however deficiencies of the cement mantle can compromise results. Minimising mantle deficiencies and increasing mantle size, may improve implant fixation and survivorship. The aim of this study was to evaluate the effectiveness of pressurized carbon dioxide lavage in an attempt to increase cement penetration into bone.

Two consecutive series of TKAs where performed by the senior surgeon. During the first series standard cementing techniques where utilised prior to prosthesis implantation. The bone surfaces were cleaned with pulsatile lavage and then dried prior to cementation (n=69). During the second series a jet of high pressure carbon dioxide was also delivered to the bone surfaces via a hand held device (CarboJet, Kinamed Inc, Global Orthopaedic Technology)(n=50). A single investigator reviewed standardised post operative radiographs with respect to, depth of cement mantle around the prosthesis, and the presence of mantle defects.

The cement mantle around the tibial and femoral prosthesis was divided into multiple zones, similar to that applied by the Knee Society. The depth of cement penetration was then measured for each zone in 0.5 mm increments using a 115% rule. Depths were averaged and then analysed using students’ T test. Cement penetration was greater with the use of pressurized carbon dioxide lavage. The greatest difference was seen in zones 1 and 4 beneath the Tibial prosthesis. A Significant difference was noted between groups.

The size of the cement mantle can be increased with the use of pressurized carbon dioxide lavage. It is postulated that the bone interstices are cleared of fat and fluid more effectively than with fluid lavage alone. This may lead to an improved outcome for cemented total knee arthroplasty.

Dislocation continues to be a significant problem in THA. Instability due to improper reconstruction of the abductors can be a contributing factor.

Eight hundred primary THA’s were performed over the past four years utilizing a proximal “Dual Press™” cementless porous coated modular stem. This design allows for a large selection of proximal bodies that enable the restoration of proper soft tissue tension and joint biomechanics after the stem is inserted.

Data on stem, neck and head centers were available for 600 of these cases. Head center locations were tabulated and compared to data from the literature.

The head center location data clearly showed that a wide variety of offsets and lengths are required to properly balance the soft tissues. Further, when the data were sorted by distal stem diameter, there is little correlation between head center location and stem size. All were performed utilizing the posterior approach and used without bone cement. 3 fractured stems, 2 dislocations, 14 intra-op fractures, no significant leg length inequalities (+/− 5mm), and 10% indexed to a position other than neutral.

Restoration of joint mechanics was possible using this proximal modular “Dual Press” stem due to the intra-operative versatility offered in regards to head center location when compared to monoblock stems. The data suggest that hip reconstruction benefits from the availability of many head centers for every stem size. The authors conclude that this proximal modular design provides for a more intra-operative accurate approach for reconstructing the biomechanics of the hip.

Traditionally the most commonly used femoral implants in revision hip arthroplasty are distally fixed monoblock designs. Ability to adjust length version and offset is limited once the stem is inserted. Revision using this type of stem has been associated with high incidence of complications including dislocation. Modular distally fixed femoral implants have been developed in order to decrease the complication rate by restoring normal hip mechanics. The goal of this study is to evaluate the performance of these type stems as it relates to fixation and instability.

Seventy three revisions were done using three modular stem designs. All stems were common in design featuring a proximal cone shape body attached by a taper to a fluted distal stem. Revisions were performed for loosening, periprosthetic fractures and infections. Most revisions were in patients with severe bone loss. Follow-up range from 6 to 72 months with an average of 30 months. Parameters evaluated included fixation and instability.

In this series we obtained excellent bony fixation as well as an acceptable dislocation rate in revision of severely compromised femurs. There were no stem fractures at the modular junction at early follow-up. Dislocation was readily managed by revision of the proximal portion of the stem without compromising distal fixation. This study demonstrates that modular approaches can be used successfully.

Concern was expressed that the use of a modular stem might produce fretting leading to osteolysis, and component failure. The goal of this study was to document the variability of this design by looking at the long-term i.e. 5–17 year follow-up of the use of a Proximal Modular Stem in primary cases.

A cohort of 955 (S-Rom) primary cases have been followed prospectively and rated clinically using the Harris Hip Score and radiologically after the fashion of Gruen. The mean age was 53. Follow-up was 5–17 years (mean 8.5).

Aseptic loosening requiring revision occurred in three cases (0.3%). One a non-union of a subtrochanteric osteotomy. Two others, one for fracture at the stem tip and one for fracture of the proximal part of a subtrochanteric osteotomy. Harris rating was 78.2% excellent, 16.4% good, 2.3% fair and 3.1% poor. Gruen rating, no lucency in 98.8%, low grade in 1.1% and high grade in 0.1%. Distal osteolysis occurred in two cases. Six patients had persistent thigh pain (type C bone) that was treated by onlay-strut graphs.

There have been no cases of device failures. Other than in the two loose cases distal osteolysis has not been seen. It would appear therefore that the sleeve does act as an adequate seal. There have been no cases of late aseptic loosening and limited thigh pain in type C bone. The authors concluded that this modular device is safe, effective and continue to recommend its use in primary THA.