Humby's Knife
BAPRAS/768
1936
What is this instrument?
This knife, was perhaps the first in common use which allowed safer, more predictable split thickness skin graft harvest.
It was the invention of Graham Humby in about 1934. Humby’s original concept was a long- bladed knife secured and sliding horizontally within a rectangular frame applied with varying tension to the donor site by skin anchoring needles. In the ”Preparations and Appliances” section of the British Medical Journal that year, he claimed that “Human skill is almost completely eliminated, and so the need for practice is reduced to a minimum. The machine should prove of particular value to the general surgeon who is called upon to perform a skin grafting operation on only rare occasions, enabling him to cut large grafts with comparative ease”.
He rapidly evolved the concept within two years, removing the frame, but adding an adjustable rolling, sliding guard directly in front of the blade. This now permitted sheets of graft to be taken at the set depth. This example, was the personal property of Graham Humby. He referred to it irreverently as his “bacon slicer”. It was donated to the Collection by his son.
What does it Do?
There is no better description than from Graham Humby himself, in his second article describing his modification, published in the British Medical Journal of 1936. “May I bring to your notice a singular modification of the graft cutting razor that I described two years ago. It is used in the ordinary way, a piece of wood in the left hand keeping the skin taught and the assistant retracting the skin distally. Two screws on the upper surface control the thickness of the graft and the roller smooths out the skin in front of the cutting edge. The width of the graft is determined by the pressure of the knife. In order to sharpen the knife the roller is removed and the blade wiped over with an Arkansas stone slip which gives it the necessary amount of saw edge for cutting skin. If kept sharp the knife will cut any thickness or width of graft in the hands of an inexperienced operator.”
Note that this knife in its original form still had a fixed blade, which required to be regularly sharpened, usually before each case.
Significance to Plastic Surgery
Prior to the development of knives with depth adjustment, split thickness skin graft harvest with plain and unguarded blade Thiersch and Blair knives required considerable skill and judgement. The aim was to harvest a sheet of epidermis without shaving too deep into the underlying dermis. Too thin a graft would not heal (or “take”). More often too thick a graft would be taken, delaying or preventing rapid healing of the donor site.
Both Hoffman and Ricardo Finochietto had previously devised knives permitting predictable thickness skin graft harvest using screw-adjusted guards in front of the blade. The Humby design with an adjustable depth setting, significantly improved the reliability and predictability of skin graft harvest. It thus became widely used.
Contributors: MC, Ruth Neave and Roger Green