Introduction: Fragility of the bone is widely regarded as a cause of Colles’ Fracture particularly in middle aged or elderly women[1]. However not every fall results in fracture of the wrist. The normal volar angle of the distal radius is said to be about 10 degrees although in one study the mean volar angulation was found to be 12 degrees with a range from 4 to 23 degrees[2]. We hypothesised that the volar angle of the distal radius or the position of the wrist at impact could affect where the peak stresses occurred during a fall onto the outstretched arm. We investigated the effect of these two variables on the location and magnitude of the peak stresses using finite element analysis.

Materials and Method: A finite element model of the distal radius was constructed in MARC (MSC software, USA). The model was developed from CT data of the right wrist of a 46 year old male. The data was examined by edge detection software (Materialise, Belgium). The inner and outer boundaries of the cortex were imported as curves into MARC. A surface mesh of the distal radius was constructed, from which a 3D solid mesh of the distal radius was generated automatically. The volar angle was modified to represent between 5 to 25 degrees in 5 degree increments. The wrist position was also changed for each volar angle. This varied in 5 degree increments from 0 to 35 degrees, and then at 45, 75 and 90 degrees. Material properties assigned to cortical and cancellous bone were 20GPa and 6GPa respectively with a Poisson’s Ratio of 0.3. The model consisted of 17660 8 noded hexahedral elements and was fully fixed at the cut end of the proximal radius. For each volar angle a load of 500N and 400N was applied perpendicularly to the articular surface across the scaphoid and lunate fossa respectively. The magnitude and location of peak stresses in the proximal and distal radius were recorded.

Results: Results show that the location and magnitude of peak stresses vary as a result of wrist position. Distally the stress rises with increasing dorsiflexion and at 35 degrees exceeds the load to failure. The volar angle does not influence the stresses unless it is 20 degrees or more. Proximally the volar angle had no effect, but if the wrist is in more than 75 degrees of dorsiflexion then the peak stresses exceeded the load to failure.

Conclusion: Results show that a fall onto the outstretched arm will produce differential stresses in the radius depending on the position of the wrist at impact. The volar angle affected the stresses in the distal radius at greater than 20 degrees but proximally it did not. Proximally stresses above 130MPa (when the wrist is in more than 75 degrees of dorsiflexion) will subject the wrist to fracture[3]. Distally (when the wrist is in more than 35 degrees of dorsiflexion) with high volar angles (greater than 20 degrees) is likely to produce the conditions for a fracture (cancellous bone has been reported to fail as a result of fracture at 50 MPa [4] and for osteoporotic bone at 0.44MPa [4].

We describe a rare form of congenital snapping knee. In six knees in four children, the tibia subluxed anteriorly on the femur when the knee was extended and reduced spontaneously on flexion. The abnormal movements were seen and felt as sudden snaps or clunks at about 30 degrees of flexion. All six knees showed similar dysplastic features, although the patients had different clinical syndromes. The mechanism of the subluxation and its management are discussed.

We studied the morphology of the contralateral femur in 10 patients with subcapital fractures, 10 with trochanteric fractures and 10 with unilateral osteoarthritis. We found that the patients with trochanteric fractures had a significantly shorter femoral neck (4.5 +/- 0.5 cm) than patients with subcapital fractures or osteoarthritis (5.4 +/- 0.4 cm). It may be that this difference in femoral neck length is related to the site at which a proximal femoral fracture occurs.

Quantitative polarised light microscopy was applied to sections of unfixed, undecalcified bone taken at operation from patients with two types of proximal femoral fracture, subcapital and trochanteric. Specimens were also taken from the equivalent sites in otherwise normal subjects at autopsy, and from various other sites of traumatic fractures; these two latter groups acted as controls. Analysis of the 57 specimens disclosed changes in the nature of the bone at the site of subcapital fractures, namely the presence of relatively large crystals of hydroxyapatite and a change in the molecular orientation, but not total content, of the acidic proteoglycans of the bone matrix. Our results have confirmed and extended the findings of others on subcapital fractures, and have also shown very similar changes in the trochanteric fractures. It thus appears that the bony changes in the two types of proximal femoral fracture are not as different as has been suggested.

Aspergillus infection of the spine is rare; for it to lead to paraplegia is still more rare. When this does occur it is usually treated by decompression and antifungal agents, but the results have usually been poor. We report two cases of successful conservative treatment of Aspergillus paraplegia in patients with chronic granulomatous disease.