Wrist

The elaborate saddle joint of the wrist, alongside its partner the thumb, was our gateway to consciousness by opening for us the path of tool use. It is also among the first places to develop arthritis. The knees take first place. The knees that, along with our spines, must support a lifetime of upright, bipedal walking that they were never designed for. Walking being among the latest evolutionary gambles that led to us. This uniquely human form of locomotion is far younger than our wrists and far, far younger than our back and legs which struggle to accommodate the change. These new, untested features are still prone to bugs, and are greatest points of failure. But, they will not be fixed as these are the changes that brought us to the intelligence that sets us apart from all other life on Earth. And with that intelligence came ways to compensate for our failures, to remove their narrowing effects upon the gene pool. We have freed ourselves from the harrowing processes of natural selection. It is our greatest victory, but it means we have to accept what we have as the final version. There are no more patches coming from the manufacturer. If there's something that needs to be fixed, we have to hack the source code and fix it ourselves. It's a risky move, especially considering we only learned the language not so long ago. But, when a potential bug fix could save thousands of lives, it's a risk we must accept.