In that picture it mentions how triangle wounds are impossible to stitch up. If that is true how would one treat a triangle puncture wound on the human body?
A triangular wound can possibly be sutured, depending on many considerations regarding the wound including its type, condition, location, size, shape, depth, cleanliness vs presence of debris, mechanism of injury, the force of the injury, the age of the wound, tension on the wound, the patient’s medical history, species if the wound is a bite, etc...
In “stellate” wounds, tissue viability is a major consideration before proceeding. (Wound preparation is an extensive topic not covered here.) The triangular bits at the center of the wound are at risk of not being viable (or savable) tissue if there is inadequate circulation to that specific area. If the triangular tips are pink and the subcutaneous tissue appears to be intact and adequately supportive, then a “purse-string” suture can be considered for bringing those points together, followed by placement of ordinary straight suturing of the “arms” of the stellate wound. (The above image is from this wound care slideshow at slideshare.net)
If the triangular tips are pale, grey or purple, or have no obvious subcutaneous support, they would be deemed non-viable and would therefore be removed from the wound, thus requiring a larger excisional solution. One possibility would be to cut an elliptical excision around the entire wound, which would then be closed by pulling the edges together with simple interrupted sutures. (This is similar to the excisional method used for biopsies or removal of cancerous cutaneal lesions.) (My drawing of an elliptical excision and suturing.)
Of course this entire explanation is a gross oversimplification of a process which actually requires extensive professional training. My reference for the above material is this excellent slide show summarizing the entire suturing process, paraphrased through the lens of my own experience.
Triangular blades were created for pretty much one reason, and one reason only. The triangular cross section made a stronger blade, ensuring more damage was done in a charge/stab versus a flat blade.
The triangular blade was introduced in the early 1700's, mostly due to strength reasons. A triangular blade is less likely to bend/break when stabbing in a charge, especially if you hit a piece of armor, another weapon or bone. The cross section is much stronger in a triangle versus a flat blade.
There is anecdotal evidence galore about the wound, and the wiki states that it is harder to heal, as the scar tissue filling in the wound tends to pull apart the rest of the wound as it heals. I can find several anecdotal references, but nothing concrete to confirm this. There is also anecdotal evidence that the Geneva Convention bans triangular blades, however the language only states "weapons that cause unneeded suffering" (paraphrased).
Pretty much the only reason for them was strength, and as other weapons became better, the bayonet went back to a single/double blade, as they are much more useful in that shape in non combat situations (Cutting ropes, food, straps, etc).