As stated in this thread, any given Spiral Knight is not in the possession of feet with which to place socks. This presents a very obvious crisis, as the absence of feet is apt to ultimately mean the absence of one's material self from the overall ultimate material universe.
The concept of feet is one that has evolved alongside us as something taken "for granted", that we would always keep close to our physical vessels, especially considering that Spiral Knights, even when adorned with wings, possess no capacity for sustained flight outside of the workings of artificial vessels. Thus, there is no other option for bipedal creatures such as the Isorans. Feet must be a concept that exists alongside the secondary concept of socks, as if there are no feet to place socks on, that means feet do not occupy a space present in a spacetime that connects to ours--essentially a blind spot from reality. It would be absurd that a single essential portion of a physical vessel would ascend in this manner, unhindered by its anchoring in the material universe. Given the state of this sudden transcendence of feet and socks alike, there is virtually no limit to the percentage of one's physical form that is able to vanish from this plane of existence at the whim of an Administrator.
This limitless "disappearance" presents the fundamental question: Do we, the Spiral Knights, exist on this plane in a physical form at all? Are we content with this? To let our physical vessels be spun out of spacetime at the whim of another? The reality bending that is occurring right in front of us is one on a grand scale of cosmic power. The most basic science dictates to us that matter cannot be created nor destroyed, and the physical matter we once inhabited with the feet-shaped nothingness that may possibly be present beneath us has been thus destroyed by powers beyond reason, without warning or notification before such a massive event. The destabilization of everything we automatically assume to be true is unfolding beneath our possibly not-feet, and it is us alone, the masses affected by this, who must demand an answer for this occurrence.
I put the question to the Administrator Hera, for what will not be the final time so long as it goes answered, for so long as shards of the physical form are ripped away from us by forces unseen and unknowable to the most essential of sciences: By your judgment, is it so that an Isoran foot has no place on this material plane? What other fundamental mechanisms have been taken from us by yourself or others? What is the ultimate fate of us who inhabit Cradle in the strictest terms of being? What, I ask you, is behind the armor of those sworn to serve the Core until their dying breath, assuming such functions as breathing and dying have not been taken from us?
It is your duty and your duty alone to clarify the grand enigma put forth concerning such things as a bipedal organic entity is to assume a path of motion on top of. For otherwise, this grand mystery will devour us more wholly, more completely than the darkest Swarm of material corruption could ever accomplish.
ʇı ƃuıʌɐɥ ɟo ʇuıod ǝɥʇ uǝʌǝ s,ʇɐɥʍ 2/ uı ʇsodɥsɐɹʇ ʇuɐɔ ɐʎ ɟı
Alright, so I'm gonna pull something out of thin air, but it has a fair amount of backing to it.
Knights are beings made of energy and soul, rather than flesh and blood, according to the old lead artist. This is their headcanon specifically, but it's one I've been following since I saw it.
This can explain why knights utilize condensed forms of energy to revive (sparks of life), why they can have fully functioning wings on one armor piece but not another, and retain full mobility despite having costumes and armors directly squish or mutilate their figure (mecha knight armor). Their body is not limited by physical constraints, however they have limited amounts of energy (and must have a soul bound to them).
Spiral Knights aren't without flesh and blood, but simply are composed of energy and soul. Much like how a human will die if they suffer severe bloodloss, a knight without soul is dead or dying. This doesn't mean humans don't have souls, or knights don't have flesh, but rather they are less important to the being for survival.
With this train of thought, Spiral Knights could very well have no "feet", but still have stubs, hooves, peglegs, etc. If it makes you happier, we can call them "energy appendages".