As the longest bone in the body, when it breaks a fractured shaft of femur is a very painful and potentially life threatening injury. One of the main initial treatments for this injury is application of some sort of traction splint, designed to apply distracting force between the lower leg and the relatively “fixed” base of the pelvis, which pulls the displaced and shortened femur back into a more anatomical position.
The Fare-Tec CT-6 splint. Image source
There are two main reasons for use of traction splinting for fractured shaft of femur.
Movement is the main cause of fracture related pain, hence why splinting is part of the routine care of almost all fractures. However the anatomy of the femur makes application of the flexible aluminium/foam-padded splints, inflatable splints or plaster backslabs impractical and ineffective. Whilst none of the available traction splints support the thigh fully, application of traction will allow less movement than would occur with an unsupported leg. It also prevents the inevitable thigh muscle spasm from further displacing or moving the fracture (sometimes jamming the injured bone ends together) which can be very painful.
2) Haemorrhage control
There are many misconceptions and incorrect descriptions in online articles/blog posts about how and why traction splinting reduces blood loss from a fractured shaft of femur, however it is commonly accepted that fractured femurs can bleed a lot. How much? It seems no-one really knows and we’ve all been quoting a guesstimate.
I was unable to find any useful references that provide an accurate evidence base for the oft-quoted figure of 1500ml (or “4units… producing class III shock” – from the ATLS manual 8th edition which has no obvious reference for this figure) for the potential amount of blood that can be lost from a fractured femur. Searching on PubMed there is a paucity of studies that provide any accurate calculations or estimates for this number.
A small, retrospective chart review that relied on changes in hematrocrit and several estimates/assumptions (for example: estimated total blood volume based on weight, assumed ml of blood loss per percent drop in hematocrit, requirement for transfusion based on symptomatology) showed an average estimated blood loss of 1,276 ml, with a wide range of 740ml-2,620 ml. Reference. Interestingly the authors did not find an association between open, comminuted or segmental fractures (fracture types that have traditionally been assumed to result in higher blood loss) and estimated blood loss.
A paediatric study showed no significant haematocrit or haemodynamic change in children with isolated femur fractures, prompting the comment that even in cases of diagnosed femur fracture in children, dropping haematocrit or haemodynamic instability should prompt a search for bleeding elsewhere. Reference.
Perhaps the most useful demonstration of blood loss from a femoral fracture comes from Gunther’s ER:
NB: NSFW if you go past the 42:16 mark!
Suffice to say that yes, the medullary cavity of the femur is a highly vascular space that can bleed when fractured.
One can lose a moderate to large amount of blood which may potentially contribute to haemodynamic instability in adults, but probably not in children.
How does traction splinting reduce blood loss?
It’s a simple matter of geometry. The thigh is generally in the shape of an inverted conical frustum (a cone with the pointy end cut off).
When the femur fractures and the thigh begins to fill with blood, it becomes more spherical in shape.
As it fills even more, it becomes cylindrical.
For geometric shapes of equivalent upper radius dimensions, a sphere has 2/3 the volume of cylinder and a cone (or frustum) has 1/3 the volume of a cylinder. This increase in volume is still apparent even if some relative shortening of the broken bone is taken into account (although obviously the exact 1/3:2/3:1 proportions may be slightly different).
So traction splinting endeavours to draw the thigh back into its more anatomical, frustum (or inverted cone) shape, which minimises the potential space for blood loss.
X-ray source: Radiopaedia
Obviously this is a theoretical assumption and given we don’t have an accurate way to measure blood loss from fractured femurs, we’ll never be able to tell how much traction splinting reduces blood loss. But it’s a nice theory and given the other main benefit of stabilisation and analgesia and the lack of apparent serious harm (i.e. traction splints have not been shown to worsen blood loss), it is probably OK to continue using them for the purpose of haemorrhage control whilst remaining nascent of the limitations of the science behind the technique.
We haven’t touched on the best method or device for applying traction, complications of traction splinting, other methods of analgesia for femoral shaft fractures or other related issues but hopefully we can cover these in future posts.
Are there other benefits of traction splinting?
Do you have a reference that more accurately describes blood loss from femoral shaft fractures?
Feel free to leave a comment below.