Study design: A biomechanical analysis of lifting through flexed and extended elbows in C5 and C6 quadriplegics.
Objective: To determine the mechanisms used by C5 and C6 quadriplegics to prevent elbow collapse when bearing weight through flexed upper limbs.
Setting: A biomechanics laboratory.
Methods: Six motor complete C5 and C6 quadriplegic subjects with paralysis of their triceps brachii muscles were recruited. A three dimensional kinematic and kinetic analysis of the upper limbs was performed whilst subjects attempted to lift their body weight through their upper limbs under four different conditions. In one condition subjects lifted with their hands placed at the same height as the seat upon which they were sitting, whilst in the other three conditions subjects lifted with their hands placed on blocks of various heights. The four different conditions required subjects to bear weight through their upper limbs with their elbows initially flexed between 15 and 40 degrees.
Main outcome measures: Angular displacements and corresponding moments about the shoulder, elbow and wrist joints. In addition, EMG data were collected from the upper pectoralis, anterior deltoid and biceps brachii muscles during all lifts and expressed as a percentage of maximal isometric voluntary contractions.
Results: As block height and initial elbow flexion increased, subjects lifted progressively less weight. However, even under the high block conditions when subjects' elbows were initially flexed up to 40 degrees, subjects lifted a mean+/-SD of 43%+/-20.4 of their seated body weight with one subject lifting 76% of his seated body weight. Subjects lifted by generating shoulder and wrist flexor moments.
Conclusion: Quadriplegics with paralyzed triceps brachii muscles can bear moderate and sometimes substantial weight through flexed elbows. This is largely achieved by the generation of shoulder flexor moments.