Background/Aim: A preliminary biomechanical study conducted on cadaver fibulae, was observed to have a significant (p< 0.001) difference between two different methods of interfragmentary screw fixation for oblique fractures.

A further study was undertaken to verify the results on composite material with biomechanical properties similar to human bone.

Material and Methods: Forty, custom designed composite fibular specimens were used for the biomechanical testing. The specimens were divided into two groups of 20 each. Group I comprised of specimens with biomechanical properties similar to young healthy bone and group II comprised of osteoporotic bone quality. The fibular specimens were osteotomised to resemble a short oblique fracture of the lateral malleolus. The fractures were fixed with interfragmentary cortical lag screws placed in antero-posterior and postero anterior directions, 10 samples in each group.

Results: In both groups, the mean force required to disrupt the fracture fixation was observed to be 0.45 kN higher in samples fixed with screws placed in postero anterior direction.

Conclusion: This study further confirms the screw placement in postero- anterior direction provides a stronger biomechanical construct for short oblique fracture of the lateral malleolus.

A study on cadaver ankles was performed; two methods of ‘Danis-Weber type B’ lateral malleolar fracture fixation were compared.

Materials and Method: Ten ankles from five female cadavers were used. The distal fibulae were osteotomised at the level of the syndesmosis with a saw and the fracture fixations were divided into two groups. In Group I, the fractures were fixed with traditional anteroposterior cortical screws and in Group II, the contra lateral fractures from the same cadaver were fixed with postero-anterior cortical screws. The distal fibulae in both groups were subjected to biomechanical compression and torsion forces and the force at which the fixation gave way was recorded.

Results: In the former group the breaking force was significantly lower than that required in the latter group by a mean of 0.4 kN.

In conclusion, the fixation done in Group II was found to be better.

Abstract: A study on cadaver ankles was performed; two methods of ‘Danis-Weber type B’ lateral malleolar fracture fixation were compared.

Materials and Method: Ten ankles from five female cadavers were used. The distal fibulae were osteotomised at the level of the syndesmosis with a saw and the fracture fixations were divided into two groups. In Group I, the fractures were fixed with traditional antero-posterior cortical screws and in Group II, the contra lateral fractures from the same cadaver were fixed with postero-anterior cortical screws. The distal fibulae in both groups were subjected to biomechanical compression and torsion forces and the force at which the fixation gave way was recorded.

Results: In the former group the breaking force was significantly lower than that required in the latter group by a mean of 0.4 kN.

In conclusion, the fixation done in Group II was found to be biomechanically more stable.

Over the past four decades, internal fixation has continued to gain popularity as a method for treating fractures because of significant improvements in both implant design and materials. This biomechanical study compares the compressive forces generated by a conventional 4.5 AO/ASIF cortical screw lag screw with a differential pitch cortical compression screw in a simulated fracture model using whole bone composite femur. The differential pitch screw investigated in this study generates 82% of the compression generated by a conventional 4.5mm AO/ASIF cortical screw. Proving compression in diaphyseal fractures is achievable using a differential pitch screw. Sufficient compression is generated to allow osteosynthesis using a plate to be preformed independent of the lag screw positioning. It is thus advantageous over the traditional compromise that arises when exposure to the fracture site is limited, of either incorporating the lag screw into the plate of choosing a non-optimal plate or screw position. It is proposed as an adjunct to the internal fixation of long bone fractures and not a single fixation device.

Injuries to the sciatic nerve are an occasional complication of surgery to the hip and acetabulum, and traction is frequently the causative mechanism. In vitro and animal experiments have shown that increased tensile strain on peripheral nerves, when applied for prolonged periods, impairs nerve function.

We have used video-extensometry to measure strain on the human sciatic nerve during total hip replacement (THR). Ten consecutive patients with a mean age of 72 years undergoing primary THR by the posterior approach were recruited, and strains in the sciatic nerve were measured in different combinations of flexion and extension of the hip and knee, before dislocation of the hip. Significant increases (p = 0.02) in strain in the sciatic nerve were observed in flexion of the hip and extension of the knee. The mean increase was 26% (19% to 30%). In animal studies increases of this magnitude have been shown to impair electrophysiological function in peripheral nerves. Our results suggest that excessive flexion of the hip and extension of the knee should be avoided during THR.

A technique of examining the infant hip joint with real-time ultrasound is described. Since the cartilaginous femoral head is clearly imaged by ultrasound, anatomical structures and their relationships can be accurately determined. Dislocated hips are easily detected and subluxations also can be visualized. We report our experience with 131 examinations in 104 patients, comprising 259 single hip studies. Of 83 patients who were previously untreated, there were 178 hip studies with three false-negative and four false-positive ultrasound results. No dislocations were missed. Twenty-seven patients who were already being treated were examined to assess hip location, comprising a total of 81 hip studies. In some cases the patients were examined while in an abduction device, cast, or Pavlik harness. In one case a dislocation was not detected. The method of examination using real-time ultrasound is considered to be reliable, accurate, and a useful adjunct to radiography. The advantages are that it is non-invasive, portable, and involves no exposure to radiation.