As Dr. Shoaib and colleagues correctly point out, our economic analysis suggested extended antithrombotic prophylaxis with low-molecular- weight heparin (LMWH) could meet a $50,000 per QALY gained threshold with home care rates of less than 10%. At the figure Shoaib et al quote (6.5%), our model estimates the cost-effectiveness of LMWH would be roughly $35,000 per QALY gained, relative to no further prophylaxis. However, while we accept that LMWH has the potential to be cost-effective at such rates, we still feel this is an optimistic result. First, in their own words, the cohort Shoaib et al refer to was pre-screened to exclude patients in whom, among other factors, “self administration was not possible.” Our analysis considered LMWH used as routine antithrombotic prophylaxis in all patients following total hip arthroplasty. Second, as warfarin appears to be an effective alternative, it is important to consider the incremental cost-effectiveness of LMWH relative to warfarin. Based on home care rates of 6.5% for both LMWH administration and warfarin monitoring, the incremental cost-effectiveness of LMWH relative to warfarin would be approximately $107,000 per QALY gained.

The discrepancy between our baseline estimates of home care rates and Shoaib et al’s highlights the uncertainty around the ability to self- administer in such a cohort. Further research is required to clarify this important parameter.

We read with interest the recent paper, by Skedgel et al(1) regarding economic decision making, with reference to extended thromboprophylaxis after total hip arthroplasty. The authors refer to Lapidus et al(2) who states 38.4% of low molecular heparin (LMWH) patients required a community nurse for administration. For cost effectiveness the number requiring a community nurse must be less than 10%.

We reviewed the last 100 major lower limb arthroplasties by a single surgeon in two centres over the last year. Our practice is that LMWH is given for five weeks by self administration or by a patient advocate. Advice is given at preassesment/ consenting with instruction in injection technique after surgery. Warfarin is used if the patient is already on the drug pre-operatively, poor compliance is suspected, or self administration not possible. 92% of cases had LMWH (6.5% of these ultimately needing external help, especially if housed in short-term respite care). Advanced age, over 80 years, did not appear to be a limiting factor. Intuitively a patient deemed competent for major elective surgery should be deemed likely to succeed with this regime.

The cost-effectiveness of LMWH is therefore achievable with appropriate information, teaching and ward knowledge. Indeed most companies offer these facilities to staff and patients free of charge, which must surely be included in the equation as an indirect saving.

1 Skedgel C, Goeree R, Pleasance S, Thompson K, O'Brien B, Anderson D. The cost-effectiveness of extended-duration antithrombotic prophylaxis after total hip arthroplasty.J Bone Joint Surg Am. 2007 Apr;89(4):819-28.

2 Lapidus L, Borretzen J, Fahlen M, Thomsen HG, Hasselblom S, Larson L, Nordstrom H, Stigendal L, Waller L. Home treatment of deep vein thrombosis. An out-patient treatment model with once-daily injection of low-molecular-weight heparin (tinzaparin) in 555 patients. Pathophysiol Haemost Thromb.2002; 32:59 -66

Mr Amer Shoaib BSc.(Hons), FRCS( Tr and Orth) (1) Mr Narlaka Jayesekera MRCS (2) Dr Monika Oktaba (2) Mr Richard T. Roach BSc.(Hons), FRCS(Tr and Orth) (1,2)

(1) Robert Jones and Agnes Hunt Hospital, Oswestry (2) Princess Royal Hospital, Telford, Shropshire, UK.

The authors did not receive any outside funding or grants in support of their research for or preparation of this work. Neither they nor a member of their immediate families received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, division, center, clinical practice, or other charitable or nonprofit organization with which the authors, or a member of their immediate families, are affiliated or associated.