The occipital knob skull deformity appears as a prominent bump on the back of the head. It is an enlarged inion bone which all of us have but some more so than others. It is clearly more likely to become prominent in men than women. What makes the inion become enlarged to the point of sticking out beyond the profile of the occipital bone is unknown.
Reduction of the prominent occipital knob is done by a bone burring technique through a small overlying scalp incision. With the patient in the prone position direct access is available to it. When burring down the enlarged inion aggressive reduction can be done as this is an abnormal thickening of this midline bone structure and there is no risk of going completely through the thickness of the skull. It is also interesting how incredibly thick the scalp can be to get down to the occipital knob. In many male patients it can be well over an inch or more of soft tissue to get to the bone.
When reducing the occipital knob it is important to remember that the back of the head is a curved surface. If the knob is just burred down to make it flat (white line), a residual prominence will still exist. It is important to continue the reduction on the lower end more inward, reducing it to a curved shape. (green line) This will allow for assurance that the bony prominence will be completely eliminated particularly when the patient bends their head down.
In getting a complete occipital knob reduction this does not require any additional scalp incisional length. It does necessitate that the fascia be released from the lower edge of the bony knob as well as some fibers of the splenius capitus muscle. It is this fasciomuscular release that creates some mild discomfort after surgery with neck flexion.
Dr. Barry Eppley