Biomechanical study on the load-bearing characteristics of the fibula and the effects of fibular resection.

The objective of this research was to investigate the load-bearing function of the fibula in relation to donor leg morbidity in patients who have had fibular resections. Biomechanical loading experiments were performed on ten anatomic specimens. Force transducers were mounted in place of resected tibial and fibular segments to allow load transmission to be measured. Load transmission through the fibula varied with ankle position. With the ankle at neutral position, the load distribution to the fibula averaged 7.12% of the total force transmitted through the tibia and fibula. Maximum loads occurred at full dorsiflexion and eversion. Resection of the proximal fibula results in a significant reduction of load through the distal fibular remnant. The values varied between 0.62% and 0.81% of the total force transmitted. When a cortex screw was introduced to anchor the distal fibula remnant to the tibia, the load distribution to the distal fibula remnant was partially restored with values ranging from 1.71% to 5.14% of the total force transmitted depending on the different ankle positions. These observations suggest that more consideration of the loading characteristics of the fibula should be taken into account in planning resection operations.

Effect of preservation medium on the mechanical properties of cat bones.

Mechanical properties of long cat bones after freezing at -20 degrees C and after storage in 10 percent buffered formalin were investigated. The right humeri and femora from 48 adult cats were divided into four groups: Groups 1 and 2 were stored in a freezer at -20 degrees C for 3 and 21 days, respectively, while Groups 3 and 4 were stored in 10 percent buffered formalin for 3 and 21 days, respectively. The control left bones were tested fresh. The humeri were subjected to a torsion test and the femora to a four-point bending test. Freezing had no effect on the mechanical properties evaluated, while formalin storage caused a 50 percent reduction in energy absorption and increased the brittleness of the bones.

Biofeedback device for patients on axillary crutches.

The axillary crutch is commonly prescribed as an ambulatory aid to patients with temporal or permanent disability in the lower extremity. When fitting the axillary crutch, it is important that the user be instructed not to bear excessive weight on the axillary bar. Excessive weight bearing on the axillary bar can result in a sevenfold increase in the reaction force under the armpit. This force may be a contributory factor to crutch paralysis or thrombosis of the axillobrachial artery. In order to prevent this occurrence an electronic biofeedback device was designed and developed for use in the training of 3-point swing-through axillary crutch ambulation. It detects excessive weight bearing on the axillary bar during crutch ambulation and produces an audible signal which prompts the patient to make necessary adjustment to relieve load bearing on the axillary bar. The design and development of the biofeedback device is discussed in this paper.