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Saturday, January 11, 2020

Knee replacement surgery: What you need to know

Joint replacement surgeries are among the 10 most common surgeries in the USA. Many conditions may cause joint damage, but the most common reason is related to obesity. In general, the lower extremity joints experience 30 lbs of force for every 10 lbs of weight gain. The correlate is true, losing 10 lbs, will off-load 30 lbs of impact force from the lower extremities joints. Apart from increased load-bearing damage, the knees may splay outwards to maintain balance, called a valgus deformity ("knock-kneed" appearance). As the balance is thrown off, the gait may shit to a "waddling gait" as characterized by the vertex of the skull listing side-to-side while one walks (the vertex of the skull should stay midline and true with a normal gait). This side-to-side rocking gait increases stress on hip joints setting them up for damage. The magnitude of the joint stress directly correlates with the degree of the list from the vertical (0 degrees is normal, 5 degrees from vertical is increased stress, 15 degrees from vertical is more stress yet). Remember, as weight increases the axial skeleton does not. The axial skeleton for an individual at 150 lbs is the same as that individual at 350 lbs. As one's weight increases, the center of gravity shifts higher and higher thus, one becomes top-heavy and prone to tipping over (analogous to rollover risk of a truck vs a car). The lower body tries to compensate by splaying out the joints seeking a wider base for stability.
from Rajesh Harrykissoon, MD

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