Disc disorders can be defined as a gradual process, growing by age, which will propagate through the vertebral column. This is done by the mean of dehydration of the nucleus pulposus, which change the pattern in load transfer and load distribution between vertebrae. It leads to a non-uniform contour of loading in annulus fibrosus, which acts to deteriorate structurally by time.
Pain due to the inability of the dehydrating nucleus pulpsus to absorb shock is called axial pain or disc space pain, and the process of growing dehydration is called degenerative disc disease.
As the structure of the annulus fibrosus is exacerbated through time, it may be torn and create an opening to the nucleus pulpsus to extrude. Tears are almost always postero-lateral in nature owing to the presence of the posterior longitudinal ligament in the spinal canal. This tear in the disc ring may result in the release of inflammatory chemical mediators which may directly cause severe pain, even in the absence of nerve root compression.
This rupture leads to two types of damage to the spinal cord, compression and concussion. Compression is the physical pressure exerted over time against the spinal cord which leads to slow degeneration and loss of neurons (nerve cells).
Concussion force is the physical damage caused by a rapidly extruded disc impacting the spinal cord causing profound swelling and degeneration and loss of neurons. Purely concussive forces are usually rapidly progressive and have an acute onset.
The arm pain from a cervical herniated disc results because the herniated disc material “pinches” or presses on a cervical nerve, causing pain to radiate along the nerve pathway down the arm. Along with the arm pain, numbness and tingling can be present down the arm and into the fingertips. Muscle weakness may also be present due to a cervical herniated disc.
A cervical herniated disc will typically cause pain patterns and neurological deficits as follows:
- C4 – C5 (C5 nerve root) – Can cause weakness in the deltoid muscle in the upper arm. Does not usually cause numbness or tingling. Can cause shoulder pain.
- C5 – C6 (C6 nerve root) – Can cause weakness in the biceps (muscles in the front of the upper arms) and wrist extensor muscles. Numbness and tingling along with pain can radiate to the thumb side of the hand. This is one of the most common levels for a cervical disc herniation to occur.
- C6 – C7 (C7 nerve root) – Can cause weakness in the triceps (muscles in the back of the upper arm and extending to the forearm) and the finger extensor muscles. Numbness and tingling along with pain can radiate down the triceps and into the middle finger. This is also one of the most common levels for a cervical disc herniation.
- C7 – T1 (C8 nerve root) – Can cause weakness with handgrip. Numbness and tingling and pain can radiate down the arm to the little finger side of hand.
Since there is not a lot of disc material between the vertebral bodies in the cervical spine, the discs are usually not very large. However, the space available for the nerves is also not that great, which means that even a small cervical disc herniation may impinge on the nerve and cause significant pain. The arm pain is usually most severe as the nerve first becomes pinched.
The majority of the time, the arm pain from a cervical herniated disc can be controlled with medication, and conservative (non-surgical) treatments alone are enough to resolve the condition. Once the arm pain does start to improve it is unlikely to return, although it may take longer for the weakness and numbness/tingling to improve. However, if the pain lasts longer than 6 to 12 weeks, or if the pain and disability is severe, spine surgery may be a reasonable option.
- Anterior cervical discectomy and spine fusion: This is by far the most commonly preferred method among spine surgeons for most cervical herniated discs. In this surgery, the disc is removed through a small one-inch incision in the front of the neck.
The neurosurgeon enters the space between two discs through a small incision in front of and at the right or left side of the neck. The disc is completely removed, as well as arthritic bone spurs. The intervertebral foramen, the bone channel through which the spinal nerve runs, is then enlarged with a drill giving the nerve more room to exit the spinal canal.
To prevent the vertebrae from collapsing and to increase stability, the open space is often filled with bone graft, taken from the pelvis or cadaveric bone. The slow process of the bone graft joining the vertebrae together is called “fusion”. Sometimes a titanium plate is screwed on the vertebrae or screws are used between the vertebrae to increase stability during fusion, especially when there is more than one disc involved.
- Anterior discectomy without spine fusion: This is basically the same procedure as above except after removing the disc the space is left open and no bone is added to get a fusion. The disc space will still often fuse even without a bone graft but the healing seems to be longer and when and if it does heal, it tends to heal in a deformed position.
- Posterior cervical discectomy: This is similar to a posterior (from the back) lumbar discectomy, and for discs that occur laterally out in the neural foramen (the “tunnel” that the nerve travels through to exit the spinal canal) it is often a reasonable approach. However, it is technically more difficult than an anterior approach because there are a lot of veins in this area that can result in a lot of bleeding, and the bleeding limits visualization during the surgery. This approach also necessitates more manipulation to the spinal cord. The principal advantage of the posterior approach is that a spine fusion does not need to be done after removing the disc.