In humans, fractures of the distal radius are prevalent. Most of these fractures, if they do not require surgical intervention, are managed by splinting the forearm in a cast for a period of weeks. While the cast helps stabilise and support the fracture it also denies the healing fracture exposure to mechanical stimuli, which play a fundamental role in the fracture repair process.
The device incorporating a compression pump and cuff, which has formed the basis of this thesis, was developed in an attempt to devise a method by which a regime of loading could be imposed upon a healing fracture without interfering with the traditional splinting mechanism which has become a constant in the orthopaedic treatment of most fractures. It was proposed that sharp circumferential pressure applied to the muscle tissue proximal to a fracture would simulate a flexor and extensor muscle co-contraction. A transversely orientated fracture in the distal portion of a long bone (in particular the radius) would subsequently experience an increase in load. The aim of this thesis was therefore to develop, construct and test the efficacy of such an apparatus to apply cyclic loads to healing fractures of the distal radius.
A cadaveric study initially verified that the pneumatic pressure on the forearm musculature was able to alter the load within the radiocarpal joint. It was then argued that the same effect would occur at a transverse fracture of the distal radius since this fracture shared a common orientation to the radiocarpal joint.
In the first instance, a randomized, controlled clinical trial was conducted to investigate whether the application of the pneumatic soft-tissue pressure or purported cyclic loading could influence the rate of healing of fractures of the distal radius while patients were being treated conservatively in plaster casts. The progress of the healing fractures was assessed using functional outcome measures. These measures showed a significantly faster rate of return of hand and forearm strength in the group that received the cyclic loading when compared with a control group. This was despite there being a trend towards more severe fractures in the treatment group.
An effect was shown in the clinical trial and this opened questions about the true mechanism of action application of the pneumatic soft-tissue pressure and purported cyclic loading. An ovine model was adopted for further testing of the compression pump device and inflatable cuff. This ovine model was chosen primarily because the sheep forelimb musculature and size of the radius are similar to humans. An invitro study was designed to investigate whether the pneumatic pressure applied to the proximal forearm musculature resulted in an increase in load at a transverse fracture of the distal radius and whether there was a correlation between the amount of pneumatic pressure and the load generated at the fracture site. The relationship between the cuff pressure and the resulting load at the osteotomy site proved to be strongly correlated (r = 0.99). Once it was clearly established that pneumatic pressure over the musculature proximal to a distal radial fracture could effect a change in load at the fracture site, an in vivo study was designed using the ovine model.
A pilot study was conducted before the commencement of the in vivo sheep study to answer methodological issues prior to the main study. In the main sheep study, 37 sheep underwent surgical osteotomy of the right radius and were subsequently managed postoperatively in a non weight-bearing splint. Half of the sample received the cyclic pneumatic soft-tissue compression treatment via the inflatable cuff and compression pump apparatus; the other half who acted as controls did not receive the treatment. Sheep were sacrificed at either four or six weeks after their osteotomy. X-rays, biomechanical testing and histomorphometry were used to determine differences between the fractures in the treated group and the control group.
The results of the in vivo sheep study showed that at four weeks there was a significant difference (p < 0.05) over all outcome measures in the amount of healing between the fractures treated with the cyclic loading and the control fractures. At six weeks there was no significant difference between the two groups although there was a trend towards a difference. Importantly though, and in agreement with the earlier clinical trial, there was no difference between treated fractures at four weeks and control fractures at six weeks implying that the cyclical loading treatment administered by the compression pump and cuff was able to enhance the rate of fracture healing by approximately one third. These results suggest that external splintage may be able to be removed at four weeks post fracture to allow earlier functional use following a fracture to the distal forearm.
The inflatable cuff and compression pump apparatus described in this thesis provides a simple, non-invasive and inexpensive method of cyclically loading fractures of long bones, in particular those of the distal radius. With its efficacy proven in this and future research, it is hoped that it will find its way into the everyday orthopaedic management of fractures.