If the scar forms around the outside (from a bruise), why do the nerves and axons have to grow throught it? I could see if the bruise went across the cord, but what about in a bruise?

Adhesion of the spinal cord to the surrounding dura and tethering of the cord has several potential deleterious effects on the spinal cord. First, cerebrospinal fluid normally flow in the space between the spinal cord and dura. Adhesions between the spinal cord and dura may obstruct the fluid flow. The fluid then may be forced to flow in the central canal or through any channel that it can find.

Over time, this abnormal flow causes an enlarged cyst in the spinal cord called a syringomyelia or syrinx. Second, the spinal cord normally slide smoothly within its dural enclosure. When it does not, every movement of the spinal cord imposes additional tension on the spinal cord, stretching or pulling the cord.

This may cause progressive damage and loss of function over time. Removal of such adhesions or untethering the spinal cord may be useful.