The human body is a biological movement machine designed to maintain a centralized center of gravity inside its base of support (hereinafter "BOS"). Skeletal bones of the body form the framework, while skeletal muscles move the framework. Tendons found at the ends of skeletal muscles attach the skeletal muscles to the skeletal bones and help maintain the postural alignment of the body. Ligaments attach bone to bone, and have a limited amount of flexibility in order to maintain the attachment of the skeletal bones in the framework.
The articulating bones of the body that form joints stay aligned and positioned properly using skeletal muscles, ligaments, tendons, and fascia. Locomotion that keeps the joints aligned as designed and inside the body's natural BOS also keeps the skeletal muscles and fascia strong and flexible, and helps the body produce synovial fluid. Synovial fluid lubricates, shock absorbs and reduces friction on joints. It also brings nutrients to joints and removes carbon dioxide and metabolic waste.
Over time, repetitive movement that doesn't maintain the body's COG over its base can result in physical and functional disability.
When the joints of the human body are in postural alignment during locomotion, the body stays within its BOS and maintains a low center of gravity (hereinafter "COG"). The upward support force from the BOS aligns with the downward force of gravity. The stability of the body during locomotion depends on the gravitational balance and stability of the arms and legs. Injury or movement of a joint outside of the body's natural BOS creates overloading or under loading to all other joints due to the redistribution of forces. Under loading or over loading of a joint or movement that causes hyper-extension of a joint or its supporting tissue can result in a loss of physical stability and postural alignment. Over time, repetitive movement that doesn't maintain the body's COG over its base can result in physical and functional disability. The Specific Adaptation to Imposed Demands ("SAID") principle states that the body will gradually adapt to stresses and overloads that it is subjected to. Wolff's Law states that bone function changes cause bone structure modification. Davis's Law states that soft tissue's tendency is to shorten and contract unless subject to frequent stretching; in other words, and to quote Dr. Davis, "[u]se it or lose it." Hook's Law states that tissue strain is directly proportional to applied compressive or stretching stress so long as tissue elasticity is not exceeded.
Balance and Stability Principles
The general principles of balance and stability include the following:
- Gravity intersects the BOS of the subject;
- Anything that decreases the BOS decreases stability of the subject;
- The lower the COG above the BOS, the more stability of the subject;
- Objects that have more mass over or near the COG tend to be more stable;
- The farther the COG intersection line is from the edge of the BOS, the more stable the subject;
- Stability is directly proportional to the area of the BOS on which a body rests;
- Stability in a given direction is directly proportional to the horizontal distance of the COG from the edge of the BOS;
- When two objects have a different shape, but an equal mass, the one with the wider base will be more stable;
- The further the COG is from the direction of movement, the more likely it is to maintain stability;
- When a body has balance and physical stability, it has equilibrium, and the COG is inside the BOS;
- When the BOS is widened in the direction of the line of force (hereinafter "LOF"), the body has greater stability. When the BOS is widened laterally on one side of the body, the COG move closer to the edge and the body has less stability; and
- Postural stability occurs when the COG and the LOF are over the center of pressure (COP).
Now, relating these principles to walking, during the normal gait cycle the arms as well as the rest of the body stay within the body's natural BOS to maintain the body's balance. The heel makes contact with the ground before the rest of the foot. The body's COG is over and inside its BOS. The shoulder and hip joints maintain vertical orientation and alignment with the pectoral and pelvic girdles. After the heel contacts the ground, the rest of the foot rolls onto an over the ground. The body's weight then passes over its COG as the heel lifts off the ground and the body moves forward. When the gait cycle has reciprocal movement, the shoulder, hip, knee and ankle joints work together to load the weight of the body over and on the foot within the body's BOS. The head stays positioned over the body and the line of sight is in the direction the person is moving.
During locomotion, the human foot has two functions. First, during the stance phase of the gait cycle the foot acts as a mobile adaptor and shock absorber to maintain the body's balance and physical stability on uneven surfaces or terrain. Second, during the swing phase of gait the foot lifts off the ground completely and acts as a lever to propel the body forward. A lever is a rigid bar resting on a pivot, used to help move a heavy or fixed load with one end when pressure is applied to the other.
Limitations of traditional canes
Canes extend the BOS on one side of the body and act as a substitute for the hip flexors on that side by transmitting part of the body's weight to the ground. In order to have a mechanical advantage when using a traditional cane, the distance between the axis of the hip joint and the contralateral hand must be extended away from the body. The mean position of the COP shifts laterally toward the cane side to maintain the body's balance. However, when the COP moves laterally on one side only, the COG of the body moves higher and closer to the edge of the BOS. Due to the size, shape, and orientation of the traditional cane foot and its orientation with the cane shaft, the person's arm, wrist and head shift forward and downward during locomotion.
When the head is positioned downward during locomotion, the line of sight is towards the ground. This causes a reduction to both sensory and proprioceptor input which results in a loss of afferent messages traveling from the body to the brain, as well as motor responses traveling from the brain back to the body. In order to maintain vertical orientation of the body during locomotion when the head and line of sight are positioned towards the ground, the length of the step as well as the stride must be shortened.
As a result of the shortened strides, the heel of the foot nearest the cane stops striking the ground from heel to toe and the foot loses its ability to quickly transform from a mobile adaptor to a ridged lever during the gait cycle. Instead, the downward position of the head and line of sight along with the shortened step and stride force the heels to rotate medially towards each other, while the toes rotate laterally away from the direction the person is moving to maintain the body's vertical orientation.
... when the head and line of sight are positioned towards the ground, the length of the step as well as the stride must be shortened.
Use of traditional canes can also cause continuous repetitive movement that hyper-extends the wrist joint outside the body's natural BOS. The head of the humerus on the side of the body using the cane loses vertical alignment and postural equilibrium with the shoulder girdle during locomotion, as does the scapula. Over time, movement that moves the COP laterally on one side of the body only, and hyper-extends the wrist joint forward away from the body's natural BOS may result in physical and functional disability and pain.
When the wrist joint hyper-extends, the distance between the axis of the hip joint and the contralateral hand becomes greater. A body is in equilibrium when the downward directed linear force is equal to the upward force and the vector sum of all forces equals zero. When the COP on one side of the body is located laterally and at the edge of the BOS and not centrally orientated during locomotion, the body loses postural equilibrium and the COG becomes higher and less stable. Low stability of a person or object is associated with a high COG and a gravity projection at the edge or outside of the BOS.
To put this in perspective, there are twenty-six bones, thirty-three joints, and over a hundred muscles, ligaments, and tendons in each foot. Thirty of the thirty-three joints found in each foot are synovial joints. Synovial joints have no blood supply of their own, and therefore rely on movement in and around the joint to maintain adequate levels of synovial fluid inside the joint. The size, shape, alignment, and positioning of the traditional cane foot with the cane shaft and handle keeps the body's weight from rolling over the foot nearest the cane from heel to toe. When the body weight does not roll over and onto the foot from heel to toe, the synovial joints of the foot stop producing adequate amounts of synovial fluid, and the muscles and fascia around the synovial joints of the feet contract and the feet can become painful.
There remains a need for an ambulatory aid or cane having a cane foot that more closely functions to mirror the normal gait cycle of the musculoskeletal system.
The Aggiornamento® Cane gives the user mechanical advantage without extending the distance between the axis of the hip and the contralateral hand. The shaft of this cane is aligned at an angle with the handle and the foot, with the top of the cane shaft more posteriorly aligned than the bottom. This is done to reduce the distance between the axis of the hip joint and the contralateral hand and to help the foot nearest the cane strike the ground from heel to toe. When the foot strikes the ground from heel to toe it is able to act as a mobile adaptor during the stance phase of the gait cycle, and to act as a lever to help propel the body forward during the swing phase of the gait cycle.
The top of the cane shaft is aligned at a more posterior angle than the bottom of the shaft. The handle of the cane is elongated and extends posterior and anterior to the shaft. The posterior portion of the handle is longer, and optionally larger in surface area than an anterior portion of the handle such that the handle is configured so that when the person's hand is gripping the handle, the handle will be offset over the shaft.
The anterior portion of the foot and the posterior portion of the cane handle extend a substantially similar or the same length in relation to the center of the cane's shaft, while the posterior portion of the foot portion and the anterior portion of the cane handle also extend a substantially similar or the same length in relation to the center of the cane's shaft. With this configuration, a substantially vertical imaginary line extends from an end of the anterior portion is cane handle and the end of the posterior portion of the foot portion, creating two right triangles, one inverted to the other, the cane shaft forming the hypotenuse of each.
Large Foot Area
The stability of a person or object is directly proportional to the alignment of the COG over the area of the BOS on which a body rests. During the swing phase of the gait cycle, the traditional cane shaft becomes more horizontal than vertical and only the small anterior edge of the cane's foot maintains the body's stability. The larger size, shape, and surface area of cane's foot or foot portion of The Aggiornamento® Cane, as well as its orientation in relation to the cane's shaft and handle, keeps the cane's shaft more vertical to give the user more vertical stability during locomotion. As opposed to traditional canes, an entire front or anterior portion of the cane's foot, and not just the front edge, maintains contact with the ground during the swing phase of the gait cycle such that the body maintains a shorter distance between the hip joint's line of axis and the contralateral hand when standing and during locomotion when using this cane. Furthermore, the positioning of the cane's handle, relative to the foot portion and the shaft, keeps the wrist, arm, and shoulder joints from hyper-extending in the direction of locomotion, and the orientation of the cane handle to the cane foot maintains the alignment of the bottom of the scapula with the shoulder girdle and the rest of the body during locomotion.
The foot portion of the cane is elongated and extends anterior and posterior to the cane shaft. The anterior portion of the foot portion is longer than the posterior portion. The bottom and sides of the foot portion are tubular or arcuate in shape. In other words, a surface contacting portion of the foot portion is non-planar, but is instead curved or arcuate, allowing the foot portion to roll onto and over a surface during the gait cycle, thereby mimicking the heel to toe motion of the normal gait cycle. The cane foot is formed of an interior and a tubular rubber exterior, optionally with one or more ridges to provide friction and additional stability.
Keep Your Head Up!
The head preferably maintains vertical orientation during locomotion in order to maintain postural alignment and stability with the rest of the body. The relationship between the cane's foot portion and handle keeps the LOG and the COP more centralized over the BOS during locomotion. Unlike traditional canes, The Aggiornamento® Cane allows the user to keep their head in postural alignment with the rest of their body and line of sight, and toes and heels moving in the direction that the subject is moving. This is preferred because when the line of sight is in the direction the person is moving, and not down at the ground, during locomotion the body experiences more sensory and proprioceptor input, and therefore balance and physical stability.
The cane shaft is adjustable at a top end, middle, a bottom end, or any combination thereof. In a particular embodiment, in which the cane shaft is adjustable at both the top and bottom ends of the shaft, this configuration allows the user to maintain postural stability and vertical alignment while adjusting the cane's height before sitting or standing, and before ascending or after descending a flight of stairs.
In contrast to presently existing canes, The Aggiornamento® Cane’s features serve an unmet need because they better maintain the user's vertical orientation and postural stability during locomotion, when making transitions from sitting to standing, and when ascending or descending a flight of stairs.