, Paul D. Siney1 and Patricia A. Fleming1
(1)
The John Charnley Research Institute Wrightington Hospital, Wigan, Lancashire, UK
Total hip replacement offers a very important field for studying this complication (pulmonary embolism) because it is performed in relatively large numbers on a small range of closely related hip conditions.
Embolism following total hip replacement presents a special problem because to achieve full anticoagulant levels quickly brings risks of wound haematoma… and invites infection
Fatal pulmonary embolism is rightly considered the most serious event, more so when it occurs after elective surgery for a condition that, by itself, is not life threatening. The advent of total hip arthroplasty, as a method of choice of treatment for the arthritic hip, has uncovered the demand, extended the indications and increased the expectations of an ever more favourable outcome. The emphasis has changed from pain relief to activity levels demanded or promised.
It is, therefore, not unexpected that under such circumstances single adverse events attract wide publicity and focus the attention on the all encompassing term: thromboprophylaxis.
The literature on the ever changing subject of thromboprophylaxis is so vast that any attempt to offer even a summary would not do justice.
Increasingly more sophisticated methods of the diagnosis, prevention and treatment, demand ever greater numbers in any study to establish a level of statistically acceptable significance.
Whether the results in such studies make an individual clinician’s decision any easier is debatable: “We think in generalities but we live in detail” (Alfred North Whitehead 1861–1947).
It is probably correct to suggest that the general perception is that prevention of clot formation is not only possible but mandatory. The pressure on clinicians is to apply the currently applicable “thromboprophylactic measures” for to do otherwise might imply negligence. Under such circumstances complications of the “prophylaxis” are, at times, more readily acceptable.
In clinical practice three aspects remain of importance:
Circumstances leading to clot formation.
Events resulting in clot migration.
The consequences.
Clot Formation
In this context the Virchows’s triad is usually quoted [1]. The three factors predisposing to intravascular thrombosis are:
Alterations of patterns of blood flow
Damage to the vascular endothelium.
Changes in blood constituents – hypercoagulability.
Prevention of clot formation would obviate the need for any more complex measures to be applied. The assumption is not only simple but may appear very logical: Unfortunately – by definition – what does not clot – bleeds.
Clot Migration
The clot, once formed, must be the subject of Newton’s First law of motion “it must be acted upon by an external force” in order to move from its position of rest.
The clot at risk for migration would be the one that is not firmly adherent to the vessel wall. Therefore more likely formed in larger veins, with larger calibre vessels downstream from the clot. Compressive stockings may encourage venous return or help to prevent clot migration, once the clot has formed. Early mobilisation may help to prevent clot formation, but may encourage clot migration once the clot has formed.
The Consequences
The consequences of clot migration? A spectrum from the asymptomatic to fatal. This is related to the mass of the clot. This is the most urgent and clinically significant event.
The long-term effects on the pulmonary circulation have not received detailed attention. This is either because the mild episodes do not carry significant long-term problems, or conversely they make take years to present clinically. Even if, or when they do, such patients are unlikely to find themselves under the care of an orthopaedic surgeon. Pulmonary hypertension has not been a subject of investigations. From long-term follow-up studies, it would appear that some 18–22 years must elapse before a previously well documented deep vein thrombosis presented as a local venous insufficiency [2].
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