The Exeter Trauma Stem (ETS) - Rationale
Indication for Hemiarthroplasty
Most Western countries have recently seen a rapid rise in the rate of intracapsular hip fractures and this trend is set to become a worldwide problem due to demographic changes. These fractures are the cause of considerable morbidity and mortality and the orthopaedic community must address how they should be best managed both for the individual and for society. The basic tenet of hip fracture management is to relieve pain and thus to restore the patient to the best possible function, taking into account their previous health and function. When selecting a particular treatment for a patient, several factors will need to be considered including the effectiveness of pain relief of the treatment method, the cost of the treatment and the failure rate and complication rates.
The ideal surgical treatment of intracapsular fractures remains a topic of controversy, and there are a wide range of options that include internal fixation of the fracture and prosthetic replacement of the femoral head1. The potential advantages of internal fixation include shorter operating times and lower blood loss and transfusion requirements2 3 but these come at the expense of a significantly higher failure rate and the need for revision in up to 30% of patients4. A recent review of 14 randomised trials3 has demonstrated that the relative risk of revision surgery after hemiarthroplasty when compared to the risk after internal fixation was 0.23 (p=0.0003).
The Exeter Trauma Stem (ETS) has been developed to provide the orthopaedic surgeon with a cost-effective cemented unipolar hemiarthroplasty using a stem based on the geometry of the Exeter Total Hip Replacement.
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Why a Cemented Hemiarthroplasty?
Prosthetic replacement of the femoral head following intracapsular neck fracture is performed to relieve pain and to facilitate early mobilisation, with the aim of preventing the complications that may occur in an elderly, recumbent patient. Hemiarthroplasties may be inserted with or without the use of acrylic bone cement to achieve fixation. In the past, uncemented hemiarthroplasties have been used in the hope that they will avoid some of the anaesthetic complications of using cement and thus reduce mortality. However, a recent study that compared cemented and uncemented versions of the same prosthesis5 found no difference in the mortality rates between the two groups. In contrast there was highly statistically significant deterioration of pain, walking ability, use of walking aids and activities of daily living among the uncemented group compared to the cemented. In addition, significantly fewer of the cemented group had been revised or were awaiting revision. Two recent systematic reviews of the literature, including one published in the Cochrane Library,6 7 have confirmed these results, with cemented prostheses demonstrating lower relative risks of persistent pain, failure to regain mobility and revision surgery. These studies did not show any difference in mortality between cemented and uncemented hemiarthroplasties. Recent data from the Australian National Joint Replacement Registry8 have shown that the uncemented Austin Moore hemiarthroplasty is associated with a relative risk of revision of 3.94 compared to the cemented Thompson hemiarthroplasty, with no difference in the risk of mortality.
Therefore in order to fulfil the aims of the procedure, namely to relieve pain and restore function with a low rate of revision surgery the use of a cemented hemiarthroplasty is advised.
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Why a Unipolar Hemiarthroplasty?
A unipolar prosthesis is one in which the prosthetic femoral head articulates directly with the acetabulum of the patient, and it may be of monoblock or modular design. Bipolar hemiarthroplasties are designed with an additional articulation in the prosthesis between a small inner femoral head and an outer shell, which in turn articulates with the cartilage of the acetabulum. The rationale behind their design is that a proportion of the movement at the hip will occur between the inner head and outer shell, and this will improve range of movement and walking function and reduce rates of acetabular erosion and dislocation. The main drawback of bipolar hemiarthroplasties is that they are more complex to produce, and therefore they are more expensive, which has implications for health care providers and society as a whole.
Several comparative studies now exist4 6 9 10 that show that the theoretical advantages of bipolar hemiarthroplasties have not been realised in the clinical setting. These studies have shown no differences in blood loss, length of hospital stay, dislocation rates, post-operative pain, recovery of ambulatory status and activities of daily living or post-operative functional outcome scores.
Therefore there is little evidence to suggest that bipolar hemiarthroplasties confer any benefit over unipolar devices, and it is difficult to justify their considerable additional expense.
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Why a Hemiarthroplasty with the Exeter Geometry and Surface Finish
There are two main reasons why the geometery and surface finish of the ETS helps the surgeon to achieve the optimal result following intracapsular fractures of the femoral neck: Survivorship; And ease of conversion to total hip replacement if required.
The geometry and surface finish of the ETS is based upon the Exeter Total Hip Replacement stem, being a polished collarless double tapered stem. The polished Exeter Total Hip Replacement has been demonstrated to have excellent long-term survivorship with no femoral lysis11 and no revisions for aseptic loosening of the femoral stem12 13 at up to 12 years follow-up. The ETS is designed to load the femur in exactly the same way as the primary hip replacement stem, to achieve the same excellent long-term results.
One of the potential complications of hemiarthroplasty is acetabular erosion, which may lead to pain for which revision surgery may be required. The revision of a hemiarthroplasty may be a difficult operation and the documented rates of major intra-operative and post-operative complications are as high as 50%14. Intra-operative complications include femoral perforation and fracture, which are particular problems during the revision of curved cemented stems because the cement mantle must be removed before the revision stem can be inserted. The curved direction of the cement mantle tends to push instruments towards the weak cortices of the femur risking fracture and perforation. These difficulties can be avoided with the ETS because it has the same geometry as the Exeter Total Hip. To convert the ETS to an Exeter Total Hip replacement the surgeon merely needs to clear the cement over the shoulder of the ETS and then the prosthesis may be tapped out easily. This allows insertion of an acetabular component and then a new Exeter Total Hip replacement stem may be cemented directly into the old cement mantle without any need for further removal of cement. This makes the revision procedure fast and safe. The Exeter group of surgeons have carried out 175 femoral stem revisions of Exeter prostheses with this “in cement” technique and at a minimum 5years follow-up there have been no revisions for aseptic stem loosening15.
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Summary
The ETS has been developed to provide the orthopaedic surgeon with an affordable and effective hemiarthroplasty to treat intracapsular fractures of the hip. The stem design is built upon the results of cemented unipolar hemiarthroplasties, and the clinical results of the Exeter Total Hip system, to relieve pain, restore function, and to be durable in the long-term. If conversion to a total hip replacement is required for acetabular erosion then the ETS can be easily changed to the Exeter Total Hip replacement femoral stem without the need for cement mantle removal, making the revision procedure fast and safe.
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Reference List
1. Crossman PT, Khan RJ, MacDowell A, Gardner AC, Reddy NS, Keene GS. A survey of the treatment of displaced intracapsular femoral neck fractures in the UK. Injury 2002; 33(5):383-6.
2. Parker MJ, Khan RJ, Crawford J, Pryor GA. Hemiarthroplasty versus internal fixation for displaced intracapsular hip fractures in the elderly. A randomised trial of 455 patients. J Bone Joint Surg Br 2002; 84(8):1150-5.
3. Bhandari M, Devereaux PJ, Swiontkowski MF et al. Internal fixation compared with arthroplasty for displaced fractures of the femoral neck. A meta-analysis. J Bone Joint Surg Am 2003; 85-A(9):1673-81.
4. Davison JN, Calder SJ, Anderson GH et al. Treatment for displaced intracapsular fracture of the proximal femur. A prospective, randomised trial in patients aged 65 to 79 years. J Bone Joint Surg Br 2001; 83(2):206-12.
5. Khan RJ, MacDowell A, Crossman P et al. Cemented or uncemented hemiarthroplasty for displaced intracapsular femoral neck fractures. Int Orthop 2002; 26(4):229-32.
6. Parker MJ, Rajan D. Arthroplasties (with and without bone cement) for proximal femoral fractures in adults. Cochrane Database Syst Rev 2001; (3):CD001706.
7. Khan RJ, MacDowell A, Crossman P, Keene GS. Cemented or uncemented hemiarthroplasty for displaced intracapsular fractures of the hip--a systematic review. Injury 2002; 33(1):13-7.
8. Australian Orthopaedic Association National Joint Replacement Registry. Annual Report. Adelaide:AOA, 2003.
9. Ong BC, Maurer SG, Aharonoff GB, Zuckerman JD, Koval KJ. Unipolar versus bipolar hemiarthroplasty: functional outcome after femoral neck fracture at a minimum of thirty-six months of follow-up. J Orthop Trauma 2002; 16(5):317-22.
10. Raia FJ, Chapman CB, Herrera MF, Schweppe MW, Michelsen CB, Rosenwasser MP. Unipolar or bipolar hemiarthroplasty for femoral neck fractures in the elderly? Clin Orthop 2003; (414):259-65.
11. Crawford RW, Gie GA, Ling RSM. An 8-10 year clinical review comparing matt and polished Exeter stems. Orthopaedic Transactions 1998; 22(1):40.
12. Howie DW, Middleton RG, Costi K. Loosening of matt and polished cemented femoral stems. J Bone Joint Surg 1998; 80-B:573-6.
13. Williams HD, Browne G, Gie GA, Ling RS, Timperley AJ, Wendover NA. The Exeter universal cemented femoral component at 8 to 12 years. A study of the first 325 hips. J Bone Joint Surg Br 2002; 84(3):324-34.
14. Warwick D, Hubble M, Sarris I, Strange J. Revision of failed hemiarthroplasty for fractures at the hip. Int Orthop 1998; 22(3):165-8.
15. Hubble MJW. In cement revisision of the Exeter stem. Personal Communication 2004.
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