In vitro biomechanical evaluation of fibular movement in below knee amputations

In below knee amputations, the remaining fibula may be subjected to abnormal forces resulting in problematic tibia-fibular movement. The purpose of the current work was to examine the effect of amputation length and interosseous membrane integrity on fibular movement when subjected to unopposed biceps femoris muscle tension.

Forty embalmed cadaveric specimens were subjected to a below knee amputation with fibular lengths of 5cm and 10cm. A subset of specimens (n=20) was further modified by sectioning the interosseous membrane. The tibias were mounted in a material testing machine and the biceps femoris was sutured to the actuator. Position-controlled tensile cyclic loading was applied (initial displacement of 4mm for 100 cycles at 0.5Hz with increments of 2mm up to 20mm) to the biceps femoris. The kinematics of the fibula with respect to the tibia was analyzed for three degrees of freedom: abduction, flexion and rotation.

There was no interaction between below knee amputation length and interosseous membrane integrity on the degree of abduction, flexion, and rotation. However, below knee amputations with a sectioned interosseous membrane are abducted to a significantly greater degree than intact interosseous membrane below knee amputations. Furthermore, although embalmed specimens were tested here, embalming was consistent across specimens and it is unlikely that this confounded the findings.

Understanding the cause of fibular abduction in below knee amputation will lead to recommendations for preventive surgical and rehabilitative measures.