The Unipolar Endoprosthesis for Hip Fractures: is it the Best Solution?

Pierre Guy, MDCM, MBA, FRCSC
Assistant Professor, University of British Columbia
Vancouver, BC

Few procedures in orthopaedics have endured the test of time longer than ORIF1,2 or hemiarthroplasty3,4 for femur neck fractures. This injury so commonly presents to the orthopaedic surgeon that one would think there be little variation in treatment. In contrast, many published surveys5,6 still demonstrate a wide spectrum of practise in caring for femur neck fractures.

The present and future volume of cases7 require orthopaedic surgeons to make clinically and economically sound decisions in the treatment choices offered to these patients. The optimal choices seven key attributes would be to: minimize mortality, pain, bleeding, length of stay, revision rates and costs, while maximizing function. The ability to change the habits of practitioners to evidence-based ones is impeded not only by the limited good science available on the topic, but also by the fact that most surgeons have likely already treated many of these patients and have preset ideas on the topic.

The following text will answer four clinically relevant questions based on the highest level of scientific evidence (randomized control trials or meta-analyses) when available, otherwise relying on well designed studies.

1) Should I Fix the Fracture (ORIF) or Replace the Head (Arthroplasty)?

Recent meta-analyses systematic reviews of Randomized Controlled Trials (RCTs)8,9 have demonstrated how arthroplasties have performed versus ORIF according to the seven attributes listed above. Grouping arthroplasties together (unipolar, bipolar, total hip replacement), these authors showed lower revision rates with this operation, while ORIF showed decreased OR time, estimated blood loss, and potentially decreased mortality.

Mortality: On this last point of mortality, one of the reviews8 demonstrated an increased four-month mortality rate with arthroplasty versus ORIF (RR=1.27), while this risk equalized at one year (RR=1.04). In further support of this finding, reviews of large state-based clinical data pools10 showed an increased odds ratio for in-hospital mortality for Hemiarthroplasty (OR=1.42) in favour of ORIF.

Revision rate: The same meta-analysis8 showed a 77% decreased risk of requiring a revision if an arthroplasty is used instead of ORIF. Stratifying for the type of fixation, arthroplasties decreased the risk of revision by 89% when compared to simple screw fixation, and by 41% when compared to using a sliding hip screw for a femur neck fracture.

Proponents of ORIF denounce the definition of revision surgery in some studies11, which treat the removal of prominent screws as significant revision procedures. They also point to the timing of failure, which occurs early (<1 year) in ORIF while later (>1 year) for arthroplasties. Attrition from death of patients could allow for under-reporting of the need for revision surgery in arthroplasty cases. Additionally the perceived extent of revision surgery of an arthroplasty compared to revision of a fixation in an older individual could influence the surgeon in not offering arthroplasty revision surgery. Finally, it appears that stratifying for poor mental function and low demand shows lower revision rates for ORIF and higher specific complications (hip dislocations) rates for arthroplasties.

Other outcomes: Pain and function showed similar results (RR= 1.12 & 0.99, respectively), up to the three-year mark in one study12. In contrast, infection rates (RR=1.81), blood loss (+176ml) and OR time (+29min) were worse outcomes for arthroplasties, the clinical significance of the last two being debatable.

2) Which Arthroplasty Should I Use?

While many systematic reviews have grouped arthroplasties (Moore, Thompson, other unipolar prostheses, bipolars, total hip replacements) under a single heading, one meta-analysis13 has reviewed the limited number of RCTs comparing implants.

Uni vs Bipolar: This systematic review of the six RCTs (n=742) showed no significant difference between uni and bipolar arthroplasties. In further support of this are the many non-randomized studies14,15,16 , which failed to demonstrate a difference in such aspects as mortality, length of stay, blood loss and function. Finally, fluoroscopic examination of 15 cases17 in one study failed to show movement between the bipolar components in 11/15 implants.

Unipolar vs THR: Here the systematic review concluded that too few trials with too small a sample (n=269) had been done to comment conclusively. It appears that the level of cognition/level of activity will influence the success rate. A non-randomized trial18 of 74 active patients showed more Good-Excellent Harris Hip Scores 86% with THR than 12% with unipolars. Additionally, the 3.7-year revision rate was 3% for THR and 38% for unipolars at 3.9 years.

Another Non-RCT of 166pts of all activity-level patients, at average 56 months follow-up, showed a revision rate of: 2% for THR, 7.9% for cemented unipolars and 13% for non-cemented unipolars. These data must however be interpreted cautiously.

Bipolar to THR: RCT related to this topic compared too many types of prostheses to allow for comparison. A review of long-term survival analyses of separate implants shows high survivorship for all, however guarded conclusions can be made from these types of observational studies and this type of analysis.


3) Should I cement the stem?

Intraoperative hypotension related to arthroplasty has been described for both cemented and cementless19 implants. Literature on the topic is divided into publications which either track clinical outcomes or which measure the embolic phenomenon using trans-esophageal echocardiography (TEE) under various conditions.

Clinical: Two systematic reviews13, 20 have attempted to clarify the issues. Parker et al13 included 4 RCTs (n=391) to address this question. Cemented prostheses showed a lower risk of failure to regain mobility (RR=0.6) and a lower risk of postoperative pain at 1 year (RR=0.51). No other outcomes could be compared (e.g., mortality).

The second review20 generally found the studies to be of poor quality and limited itself to qualitative comparisons. On the topic of mortality, three of the studies it reviewed showed lower early mortality for the first five weeks with cementless arthroplasty. These values equalized at three months. The majority of studies showed lower revision rate, less thigh pain, and increased function with cemented implants. The following factors may be associated with the use of cement: increased OR time, increased blood loss.

Experimental: These studies observe embolisation of marrow material through the right heart at the time hemiarthroplasty of the hip. Cardiac hemodynamics measured at six stages of cemented implant placement21 have shown a decrease in cardiac output and stroke volume on cement insertion, without an effect on heart rate and mean arterial pressure or with clinical consequences. Another study22 linked the risk of clinical complications to the presence of a high (>30mmHg) preoperative pulmonary artery pressure. The risk is apparently further increased by not vacuum-mixing the cement. Venting the femur proximally and distally has also proven to be a useful strategy23 in preventing TEE identified emboli. The presence of pre-existing conditions appeared to increase the effect of clinically relevant emboli.

4) What About These New Unipolar Implants? Are They Worth the Cost and Effort? Is it Malpractise to Put in a Moores / Thompsons in the 21st Century?

There is no comparative study available that measures clinical or economical outcomes between the new unipolar implants and the classic single block prostheses. A systematic review13 showed no difference between bi- and unipolar implants in six trials (n=742). In the absence of specific information on unipolar prostheses, one could carefully infer information from reports on the mode of failure of hemiarthroplasties. Warwick et al.24 reviewed 56 THRs for revision post hemiarthroplasty (11 uncemented Moore, 45 cemented Thompsons) and found the mode of failure to be loosening of the stem in 21/56 (median time to loosening 7 months), and acetabular erosion 26/56 (median time to erosion 25.5 months). These suggest that improved fixation at the implant bone interface and decreased friction at the head-acetabulum interface could decrease revision rates.

Finally, in the absence of strong evidence, one could use the opinion of so called experts in the field. The practise in our unit reflects the previously mentioned wide variance in practise surveys5,6. Of the five dedicated trauma surgeons in our group, one always puts in Thompson arthroplasties without cement, except if the stem is grossly loose. Two will cement Thompsons as a routine in the frail elderly, except if the patient has cardio-vascular disease (Thompson cementless) or dehydration, or if the patient is physically active they will place a New stem unipolar endoprosthesis). One will put in cementless Thompsons in the frail elderly and a cementless new stem unipolar prosthesis in the active individual. Finally, the last member will put in cementless new stem unipolar prosthesis in everyone. This question evidently requires further study.

Summary

The proximal femur still remains the unsolved fracture25. It appears that certain parameters such as revision rates would guide surgeons toward an arthroplasty over ORIF for a displaced fracture. The arthroplasty decision would then accept an increased early mortality risk (at <3 months) particularly in the cognitively impaired patient; increased infection risk, while increases in blood loss and OR time appear to be in the range of limited clinical significance. The surgeon would then decide what is best for this patient as increasing support builds for ORIF in the severely cognitively impaired with limited ambulatory demands.

Once an arthroplasty is chosen, limited information is available to guide the surgeon to the best implant: THR, bipolar or unipolar. Stratification for cognitive function and level of activity appear to come into play, while the presence of arthropathy (OA, RA) would favour THR. There seems to be no short to medium term difference between bipolar and hemiarthroplasty. More trials that compare these options are already in progress and will hopefully clarify some of the issues related to bipolar implants26.

The safe use of cement is still debated. Specific techniques for cement preparation and implantation appear to reduce the incidence of embolisation. The clinical significance of the embolisation event appears to be related to pulmonary vascular hemodynamics. As use of precise intraoperative cardiac hemodynamic monitoring (Swan-Ganz) is not a routine, limiting the use of cement to patients who do not have a history or signs of severe cardio-respiratory disease and who are well hydrated is recommended.

References

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2. Smith-Petersen M.N., C.E., Van Gorder G.W. Intracapsular fractures of the neck of the femur. Arch Surg, 1931. 23: p. 715.

3. Thompson F.R. Vitallium intramedullary hip prosthesis: preliminary report. New York State J Med, 1952. 52: p. 3011.

4. Moore A.T. The self-locking metal hip prosthesis. J Bone Joint Surg Am, 1957. 39: p. 811.

5. Chua D., J.S., Schatzker J. An orthopedic surgeon survey on the treatment of displaced femoral neck fracture: opposing views. Can J Surg., 1997. 40((4)): p. 271-7.

6. Crossman P.T., K.R., MacDowell A., Gardner A.C., Reddy N.S. Keene G.S. A survey of the treatment of displaced intracapsular femoral neck fractures in the UK. Injury, 2002. 33((5)): p. 383-6.

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8. Bhandari M., D.P., Swiontkowski M.F, Tornetta P. 3rd, Obremskey W., Koval K.J., Nork S., Sprague S., Schemitsch E.H., Guyatt G.H. Internal fixation compared with arthroplasty for displaced fractures of the femoral neck. A meta-analysis. JBJS-Am, 2003. 85-A(9): p. 1673-81.

9. Masson M., P.M., Fleischer S. Internal fixation versus arthroplasty for intracapsular proximal femoral fractures in adults. Cochrane Database Syst Rev., 2003((2):CD001708).

10. Su H., A.G., Hiebert R., Zuckerman J.D., Koval K.J. In-hospital mortality after femoral neck fracture: do internal fixation and hemiarthroplasty differ? Am J Orthop., 2003. 32((3)): p. 151-5.

11. Tidermark J., P.S., Svensson O., Soderqvist A., Tornkvist H. Internal fixation compared with total hip replacement for displaced femoral neck fractures in the elderly. A randomised, controlled trial. J Bone Joint Surg Br, 2003. 85((3)): p. 380-8.

12. Parker M.J., K.R., Crawford J., Pryor G.A. 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)): p. 1150-5.

13. Parker M.J., R.D. Arthroplasties (with and without bone cement) for proximal femoral fractures in adults. Cochrane Database Syst Rev., 2001((3)): p. CD001706.

14. Raia F.J., C.C., Herrera M.F., Schweppe M.W., Michelsen C.B., Rosenwasser M.P. Unipolar or bipolar hemiarthroplasty for femoral neck fractures in the elderly? Clin Orthop., 2003. (414): p. 259-65.

15. Ong B.C., M.S., Aharonoff G.B., Zuckerman J.D., Koval K.J. 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)): p. 317-22.

16. Wolfel R., W.W., Walther M., Beck H. [Hemiprosthesis in femoral neck fracture], [Article in German]. Zentralbl Chir, 1995. 120((9)): p. 721-4.

17. Eiskjaer S., O.S. Survivorship analysis of hemiarthroplasties. Clin Orthop., 1993. 286: p. 206-11.

18. Squires B, B.G. Displaced intracapsular neck of femur fractures in mobile independent patients: total hip replacement or hemiarthroplasty? Injury, 1999. 30((5)): p. 345-8.

19. Gierer P., L.J., Grubwinkler M., Gradl G., Lob G., Andress H.J. [The femoral neck fracture in the elderly patient - cemented or cementless hip arthroplasty?], [Article in German]. Zentralbl Chir., 2002. 127((6)): p. 514-8.

20. Khan R.J., M.A., Crossman P., Keene G.S. Cemented or uncemented hemiarthroplasty for displaced intracapsular fractures of the hip--a systematic review. Injury, 2002. 33((1)): p. 13-7.

21. Clark D.I., A.A., Baxendale B.R., Moran C.G. Cardiac output during hemiarthroplasty of the hip. A prospective, controlled trial of cemented and uncemented prostheses. J Bone Joint Surg Br., 2001. 83((3)): p. 414-8.

22. Leidinger W., H.G., Meierhofer J.N., Wolfel R. [Reduction of severe cardiac complications during implantation of cemented total hip endoprostheses in femoral neck fractures], [Article in German]. Unfallchirurg, 2002. 105((8)): p. 675-9.

23. Pitto R.P., B.J., Kossler M. Transesophageal echocardiography and clinical features of fat embolism during cemented total hip arthroplasty. A randomized study in patients with a femoral neck fracture. Arch Orthop Trauma Surg., 2000. 120((1-2)): p. 53-8.

24. Warwick D., H.M., Sarris I., Strange J. Revision of failed hemiarthroplasty for fractures at the hip. Int Orthop., 1998. 22((3)): p. 165-8.

25. Dickson J.A. The "unsolved" fracture: a protest against defeatism. J Bone Joint Surg Am, 1953. 35: p. 805-22.

26. Kreder H. (personal communication). 2001.

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