The occipital knob is a well known aesthetic skull deformity which falls into the category of more minor aesthetic skull reshaping surgery. It is easily recognizable as a midline protrusion on the back of the head at the lower end of the visible occipital bone. While it presents with varying degrees of severity it always appears as a knob-like protrusion.
The name knob implies that it is a circular structure and that is largely how it appears when exposed through the scalp. A circular outcropping of bone is seen in which the lower half is hanging below the occipital bone edge onto which there are numerous soft tissue musculoligamentous attachments. Interestingly and surgically relevant is that on 3D CT scans the knob at its base is more triangular in shape and not round. In essence it can have a sharp-like or spike inferior edge to it. This in some patients may explain why there can be discomfort associated with the knob in neck extension.
Surgical reduction of the occipital knob is conceptually straightforward by high speed burring bone removal. While the knob is flattened down to its base (red line) it is important to remember that the base is not flat. Rather there is a curvature to the occipital bone so a complete reduction require the tail or v-shaped end of the bone to be reduced lower than its superior end which further up on actual occipital bone. (green line) Failure to do so may leave a residual bump albeit smaller than the original one.
Reduction of the tail of the occipital knob must be reduced so it has an inward curvature. This will require some release of soft tissue attachments to do so and this is why some patients may have some mild initial neck discomfort immediately after the surgery.
Occipital knob reduction is the most limited aesthetic bone reduction procedure of the skull. And while the surface area of the bone reduction is small the thickness of the bone removed can be up to 1 cm or more. Thus it is easy to think that a complete reduction has occurred by burring it down flat and the prominent residual tail overlooked.
Dr. Barry Eppley
World-Renowned Plastic Surgeon