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.
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.
A modular neck provides for fine-tuning joint mechanics.
Bone and Tissue sparring Restoration of joint mechanics Minimal blood loss Potential reduction in rehabilitation Ease of revision Simple surgical technique Options for bearing surface Selection of femoral head diameter Standard surgical approach to the hip 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.
It is well established in the literature that the tribological properties of sliding metallic and ultra-high molecular weight polyethylene (UHMWPE) counterfaces are a major contributor to accelerate wear rates that contribute to osteolysis. The majority of the research over the years has been on improving the UHMWPE properties through manufacture and secondary processing of the polymer. Little attention has been directed towards the optimisation of the Chromium Cobalt Molybdenum (CrCoMo) surface finish. The focus of this research has been on the highly polished CrCoMo metallic surface. A new surface finishing technique was applied to CrCoMo femoral knee prosthetic implants. The surface finish of our finished implants was compared to that finished by traditional mechanical polishing techniques. A representative number of polished CrCoMo knee femoral components were compared under the following topics; tribological, topographical and the extent of processing containments present. It was found that traditional mechanically polished parts contained a significant amount of embedded polishing compounds (Al2O3), coarse interdendritic (M7C3) and fine (M23C6) carbide elements. Both the polishing containments and carbide elements stand proud of the articulating surface and thus act as micro cutting tools to accelerate UHMWPE wear. The new polishing technique completely eliminated hard carbide particles and embedded polishing compound media. Consequently, the samples prepared using the new polishing technique produced lower UHMWPE wear debris and improved wear patterns to that of the traditionally polished samples. Additionally, all sub-micron scratching was removed from the surface of the samples. This polishing technique for CrCoMo prosthesis represents a milestone in CrCoMo surface finishing and will significantly reduce the UHMWPE wear debris generated and consequently increasing prosthesis longetivity.
