What's available in Short Stem Hip Replacements
Published date : 30 April 2011
Article date : 30 April 2011
The quest for bone preservation in hip arthroplasty has lead to the development of femoral implants with relatively short stems. The thinking behind these includes not only the preservation of proximal bone stock but possibly also less stress shielding of the proximal femur, ease of revision, reduction of the risk of thigh pain and facilitating minimally invasive surgery, particularly when using an anterior approach. As hip resurfacing declines in popularity, it is likely that there will be a corresponding increase in the number of short stem femoral components in use. We’ve had a look at what’s available.
Short stem hips come in a number of designs and design philosophies, although most are titanium and have hydroxyapatite coatings. At the outset, it might be helpful to mention the Birmingham Mid-Head Resection Prosthesis (BMHR). This device involves resection through the base of the femoral head, has a short conical stem and is designed to be inserted into a reamed cone in the femoral head and neck. It is argued that preserving some of the base of the femoral head results in a shape which is better suited to loading the proximal femur. The stem has a 12/14 taper, and the head and acetabular components are identical to that of the Birmingham Hip Resurfacing, which has avoided some of the problems seen in other metal on metal bearings. Although there are early good results from the originator, long-term results are awaited.
Other short stem devices can be categorized as those with a collar, those without, straight or curved stems, or those which are shortened versions of stems already on the market. The device with the longest track record (98.2% survival at ten years) is the Mayo stem. This is a neck-retaining device which has a proximal wedge-shape for fixation, and the tip touches the lateral cortex, which is at risk of perforation during insertion. The original grit blasted finish has been superseded by a hydroxyapatite coating.
One of the few short stem devices with a collar is the CFP stem from Link, which is an evolution of the Pipino stem. This device has good medium term results (99% survival at 74 months), and the manufacturers report 25,000 implantations since 2000.
Of the remaining collarless devices, the Corin MiniHip and the Collo-MIS stem both have a similar, tapered, curved geometry without a shoulder, but neither have published results. The Aida Short Stem from Implantcast has a more tapered and angled tip to the stem, but again has no published results. Those considering using a new device should review the experience of the CUT Femoral neck prosthesis from Orthodynamics. Although one series demonstrates good results, others have struggled with alignment and offset.
The Metha short hip stem from Braun has a similar geometry to the Aida short stem, but is one of the few of these devices to have an ODEP 3A rating. The Proxima Short Stem Hip from Depuy has a proximal fit and fill geometry, with a larger lateral profile than other stems, but is shorter than some, so care needs to be taken with varus/valgus positioning. It is rated pre-entry by ODEP.
The Silent hip from Depuy is a short, straight stem device, which remains in clinical trials.
The remaining devices, the Fitmore from Zimmer, the SMF from Smith and Nephew and the Taperloc and Balance Microplasty stems from Biomet more closely resemble short versions of established devices, and in the case of the Taperloc and Balance Microplasty stems are overtly so. Once more, there are no or few published results.
To summarise, although there are potential benefits to these shorter stems, particularly for enthusiasts of the anterior approach, the majority of these devices do not have long term results, and there is a need for careful collection of data and clinical trials. In the rush to replace some hip resurfacing devices as an option for younger patients, care should be taken when considering other unproven implants.
