How does bilateral knee flexion contractures (of about 30 degrees) and a forward trunk lean during gait affect a patient’s line of gravity? (question modified).

A line of gravity (LOG) is an imaginary line that extends from the center of gravity (COG) to the base of support. [1] The direction of the force of gravity through the body is downward, towards the center of the earth and through the COG. The LOG is important in determining a person’s ability to successfully maintain Balance. When the line of gravity falls outside the base of support, then a reaction is needed in order to stay balanced. [2]

A contracture is a deformity which prevents the movement of a joint through its normal range. Structurally, contractures are the result of shortening of the soft tissues of a limb, and/or tightening of the ligaments of a joint. This can happen as the result of disuse, soft tissue or bony injuries (especially burns and fractures) and muscle imbalance due to weakness of the nerves supplying a group of muscles. [3]

The position of the LOG is determined by the distribution of body weight and is important in determining muscular activity involved in maintaining posture. The LOG extends superiorly through the junctions of the curves of the vertebral column and inferiorly in a line posterior to the hip joints but anterior to the knee and ankle joints. When a subject is in the easy standing position, the hip and knee joints are extended and are in their most stable positions. [4]

Knee flexion contracture will cause a limping type gait pattern. The knee is restricted in extension, meaning heel strike is limited and step length reduced. ‘Toe walking’ is a likely compensation during stance phase. [5]

The LOG is not static and tends to move depending on the patient’s body weight distribution, position, posture and gait. Generally, in an upright position, a patient with knee flexion contracture will have the LOG pass posterior to the hips and knee joints and anterior to the ankle joint. In the case of a forward lean, the LOG passes anterior to the hip joint (the hip moves in flexion) and passes posteriorly to the knee and ankle joints.

Reference 1, Reference 2, Reference 3, Reference 4, Reference 5