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Three Part Question

In [patients with lower extremity injury requiring temporary immobilisation with above knee plaster of paris] does [prophylactic anticoagulation with LMWH] reduce the risk of [venous thromboembolic disease within the next three months]

Clinical Scenario

You see a 27 year old male who has ruptured his achilles tendon whilst playing football and you decide to treat him in an equinus cast. You are aware of a recent case in which a patient died from a pulmonary embolism after receiving similar treatment, as well as recent evidence noting a high (39%) proportion of venous thromboembolism in this particular ambulatory cohort [Nilsson-Helander].

You wonder if the evidence supports treatment with prophylactic LMWH.

Search Strategy

MEDLINE and EMBASE databases were searched, using the Ovid interface, the week ending the 25th February 2012. The Cochrane Database of Systematic Reviews was also search using direct terminology.


MEDLINE: (exp venous thrombosis OR exp thromboembolism OR exp pulmonary embolism OR DVT.mp OR deep vein thrombosis.mp OR PE .mp OR pulmonary embolism.mp OR venous thromb$.mp) AND (exp casts surgical OR plaster cast$.mp OR exp immobilization OR immobilisation.mp)

EMBASE: (exp vein thrombosis OR exp thromboembolism OR exp lung embolism OR exp venous thromboembolism OR exp deep vein thrombosis OR DVT.mp OR deep vein thrombosis.mp OR PE.mp OR pulmonary embolism.mp OR venous thromb$.mp) AND (exp plaster cast OR exp immobilization OR plaster cast$.mp OR immobilisation.mp)

All searches were limited to human studies only.

Search Outcome

491 and 1700 records were found in the MEDLINE and EMBASE searches respectively. Following an initial abstract review 14 of these were deemed to be relevant to the 3 part question. However, 13 of these were subsequently rejected. Nine because they duplicated data presented elsewhere or dealt with surgical patients and a further 4 as they did not include patients treated in above knee casts. One RCT is presented below which addressed the three part question, and is proposed as the highest level of evidence available.

Relevant Paper(s)

Author, date and country	Patient group	Study type (level of evidence)	Outcomes	Key results	Study Weaknesses
Kock H-J et al 1995 Germany	Ambulatory patients between 18-65 years with leg injuries requiring conservative out-patient management in below-knee or cylinder casts.	Open randomised controlled trial including completed data on 339 patients. 48 were managed in above knee cylinder casts. Patients randomised to receive either no thromboprophylaxis or 32mg of Mono-Embolex. Trial was stopped early due to meeting efficacy criteria. (level of evidence 2b)	Overall DVT rate	LMWH group: 0%, Control group: 4.3% p<0.007	Open study with no use of placebo. Some high risk groups (previous DVT and pregnancy) excluded. High post recruitment exclusion (52 patients) although intention to treat analysis performed. Only small numbers of patients with above knee casts included and no statistical analysis performed.
			DVT rate in above knee casts	LMWH group: 0/24 = 0%, Control group: 2/24 = 8.3% (no statistical analysis)

Comment(s)

The evidence available with regards to the use of thromboprophylaxis in patients with above-knee casts is limited, with only one paper providing data in this subgroup. Unfortunately, as this was not a pre-determined subgroup the numbers included are small and no statistical analysis has been performed. However, the data suggests an ARR in the order of 8% which would give an NNT of 12. These results are comparable with the effect of thromboprophylaxis in patients treated in below knee casts [3] and given that an above-knee cast provides a greater degree of immobility than a below-knee one it would be logical to assume that the risk of venous thromboembolism is at best the same with the two different types. It should be noted that a large proportion of above-knee casts are also non-weight bearing, which is an independent risk factor within this non surgical ambulatory cohort for development of VTE during the period of immobilisation [4].

Clinical Bottom Line

The use of LMWH thromboprophylaxis appears to be effective at reducing the incidence of VTE in ambulatory patients with above-knee plaster casts. The incidence in this cohort when untreated, is deemed to be higher and more severe than in patients with below knee immobilisation.

References

1. Nilsson-Helander K, Thurin A, Karlsson J, et al. High incidence of deep vein thrombosis after Achilles tendon rupture: a prospective study. Knee surgery, Sports traumatology, Arthroscopy 2009;17(10):1234-1238
2. Kock H-J, Schmit-Neuerburg KP, Hanke J, Hirche H Thromboprophylaxs with Low-Molecular-Weight Heparin in Outpatients with Plaster-Cast Immobilisation of the Leg The Lancet 1995; 346: 459 - 461
3. Testroote M, Stigter WAH, de Visser DC, et al. Low Molecular Weight Heparin for revention of Venous Thromboembolism in Patients with Lower-leg Immobilization. The Cochrane Database of Systematic Reviews 2009; (4): CD006681
4. Riou B, Rothmann C, Lecoules N, et al. Incidence and risk factors for venous thromboembolism in patients with nonsurgical isolated lower limb injuries. American Journal of Emergency Medicine 2007; 25: 502- 508