In Part 1 of this three-part series, we talked about alignment changes viewed from front-to-back (sagittal plane). In this installment, we'll focus on side-to-side alignment and how it changes affect your walking and joints.
The purpose of the “Prosthetic Foot Alignment” series is to help you become more familiar with the importance of proper prosthetic foot alignment, how it affects your walking, and how it can cause discomfort in the joints above.
Changes in the side-to-side movement of a prosthetic foot along the frontal plane can negatively impact your knee. When foot placement remains uncorrected for a long time, you can expect issues that can lead to a long-term deterioration of the knee joint. This holds true regardless whether you wear an above- or below-the-knee prosthesis.
Alignment reference point
To align a prosthetic foot correctly, prosthetists begin at a reference point. In this case, when looking at the prosthetic foot from the front, the reference point is located directly along the center of the foot.
When using a plumb bob, the vertical alignment should fall through this point and any deviation—whether inset or outset—can dramatically affect a smooth gait pattern.
Alignment line too far inset
When the alignment line falls to the inside of the aforementioned reference point, you will notice more weight distribution on the inside heel of your prosthetic foot. Viewing from behind, your heel will not contact the ground level, but rather the inside of your prosthetic heel will hit the ground first. This creates a few issues, one of which is the inability to experience full energy return from the prosthetic heel of your foot because it hits the ground uneven.
Another issue—one with long-term adverse effects—with this malalignment is it throws your knee to the inside, creating deteriorating stress on the knee joint. This is true whether you wear a prosthetic knee or not.
Simply stated, an alignment line that is too far inset will make you feel as if you’re walking on the inside edge of your prosthetic foot. And in extreme cases, your walking will present as if you have "knock-knees."
Alignment line too far outset
Walking around with a prosthetic foot that is aligned too far to the inside (or the alignment line is too far to the outside), will make you feel unstable. Walking with one foot set too far to the inside can throw your balance off. In this situation, you will feel as if you’re falling to the outside. And standing on your prosthesis will give the appearance of your leg tilting or angling to the outside.
In other words, you’ll know your foot alignment is too far inset when you feel as if you’re walking on the outside edge of your prosthetic foot.
Attaining a proper prosthetic alignment is both an art and a science. A poorly aligned prosthetic foot, whether to the inside or outside, can leave you feeling unbalanced. We strongly suggest visiting your prosthetist to ensure proper placement of your foot to prevent any long-term deterioration of your knee that can lead to arthritis or premature wear of your prosthetic mechanical knee.
There are prosthetic feet on the market, such as the Össur Proflex, that help mitigate long-term stresses placed on your knee joint. If you wear a prosthetic knee, an adequately aligned foot will assist in its smooth functioning.If you have any questions or comments, please let us know in the comments section below.