Anterior Disectomy and Fusion Using Simmons Keystone Technique: Discussion

There are some interesting points to be gleaned from these two cases. The first and utmost is that surgery should only be considered for severe and disabling pain syndromes which have failed an intensive course of conservative treatment. If a patient has struggled with severe pain for an extended period and either chiropractic or physical therapy has not improved the situation it is unlikely that continuation of the same treatment will be helpful, and surgery may be a consideration. If the pain is less severe, and can be controlled with conservative modalities then surgery is not required.

Both patients had severe pain from pathological conditions of the intervertebral disc, however the cause of the pain was different for each patient. S.O. was an active ballet dancer who started getting referred pain to her shoulder 5 years ago which she attributed to muscle soreness. It is likely that this occurred as a result of C5-6 disc degeneration. In January of 1991 she experienced an acute extrusion of the C6-7 disc which characteristically affects the C-7 root producing numbness in the middle finger, weakness in the triceps muscle, and loss of the triceps reflex. The fragment was so large that it displaced the spinal cord and was in danger of producing permanent damage to that structure (fig. 5, fig. 6). She experienced pain from C-7 root inflammation and compression. Her symptoms were severe, and unresponsive to physical therapy, and chiropractic treatment. They prevented sleep and necessitated the use of narcotic medication. The clinical symptoms of aching in the back of the arm and numbness in the middle finger were consistent with the physical exam showing weakness in the triceps muscle and loss of the triceps reflex. Extension of the neck characteristically produced further narrowing of the nerve root canal reproducing the numb sensation in her hand. Removal of the extruded fragment in this situation can be expected to produce a 95% good to excellent result and indeed S.O. returned to rehearsal 3 weeks post op and continues to dance professionally two years later (fig. 7).

P.M. also had disabling pain as a result of disc pathology , but of a different type. She developed pain in her shoulder which was initially misconstrued as a rotator cuff injury and subsequently almost resulted in an unnecessary shoulder arthroscopy. To compound matters , she had a work related injury and underwent a workers compensation evaluation which concluded that due to the normal shoulder arthrogram she was not a qualified injured worker. P.M. has pain characteristic of a degenerative spinal joint (fig. 8, fig. 9)

The symptoms do not follow a specific root pattern because the root is not severely compressed. Certain positions or activities may produce root irritation but the symptoms are transient and in a compensation setting often lead to issues with regard to patient credibility. The pain is characteristically felt in the neck, and is referred to the trapezius and medial border of the scapula, much like low back pain is referred to the sacro-iliac joint. It can produce severe headache due to spasm of the muscles inserting on the base of the skull. It not infrequently produces numbness in the ulnar two digits of the upper extremity which can be mistaken for cubital tunnel syndrome, and is due to spasm of the scalene muscles compressing the lower trunk of the brachial plexus. The pain is aggravated by flexing and rotating the neck, and is usually relieved by a collar or cervical traction. Strenuous overhead activity, prolonged sitting, or driving , makes the condition worse, rest makes the symptoms better. The shoulder symptoms were obviously a red herring since abduction and external rotation of the shoulder joint provoked no pain. P.M. had successful Keystone anterior discectomy and fusion and has returned to normal activity now 1 year post op even though she had an on-going workman's compensation claim(fig. 10).

Two common questions always come up in discussing cervical fusion. One is couldn't you have taken the disc out without doing the fusion? The answer is intuitively obvious when you consider that the intervertebral disc forms part of a joint, and removing cartilage from any joint leads to further degeneration of that joint. In the cervical spine this commonly leads to further disabling neck pain. The cascade of further narrowing of the intervertebral disc, scar tissue formation, root tethering, osteophyte formation, recurrent disc herniation, root entrapment from narrowing of the foramen and painful motion of the disrupted spinal joint can be arrested by simply inserting the Keystone graft. The answer is that anterior cervical discectomy should always be done with fusion.

The second question that is commonly asked is doesn't fusion put excessive pressure on the adjacent discs and cause them to "wear out"? This is a somewhat more difficult question to answer. Fusion of the cervical spine does not produce a perfectly physiologic situation. There is stiffening of usually 1 or 2 spinal segments which could each be expected to move 5 degrees under perfectly normal conditions. Taking into account the fact that only severely abnormal discs are fused, and that these discs themselves do not move more than a degree or two, and themselves produce spasm and stiffness from associated pain, it is not likely that when fused, they would produce excessive pressure on the adjacent levels. A long term multicenter study shows that only 7% of patients required surgery at an adjacent level an average of 10 years following the procedure. In each case there was a significant new trauma responsible for the injury. If the adjacent disc is affected it is usually the next higher segment. Cervical fusion is not perfect. The results are superior to discectomy done without fusion. The benefit of the procedure in most cases outweighs the small risk of possibly needing something done in the future.

References

1. Hult L: The Munkfors investigation. Acta Orthop Scand (Suppl) 16:1, 1954.
2. Taylor R, Collier J: The occurrence of optic neuritis in lesions of the spinal cord: Injury, tumour, myelitis. Brain 24:532, 1901.
3. Kahn EA: The role of the dentate ligaments in spinal cord compression and the syndrome of lateral sclerosis. J Neurosurg 4:191-199, 1947.
4. Scoville WB: Types of cervical disc lesions and their surgical approaches. JAMA 196:479, 1966.
5. Bailey RW, Badgley CE: Stabilization of the cervical spine by anterior fusion. J Bone Joint Surg 42A:607, 1958.
6. Robinson RA, Smith GW: The treatment of certain cervical spine disorders by the anterior removal of the intervertebral disc and interbody fusion. J Bone Joint Surg 40A:607, 1958.
7. Cloward RB: The anterior approach for removal of ruptured cervical discs. J Neurosurg 15:602, l958.
8. Simmons EH, Bhalla SK: Anterior cervical discectomy and fusion: A clinical and biomechanical study with a year follow-up. J Bone Joint Surg 51B:225, 1969.

Suggested Reading

1. Mayfield FH: Cervical spondylosis: A comparison of the anterior and posterior approaches. Clin Neurosurg 13:181, 1965.
2. Odem GL, Finney W, Woodhall B: Cervical disc lesions. JAMA 166:23, 1958.
3. Rob Martinns AN: Anterior cervical discectomy with and without interbody bone graft. J Neurosurg 44:290, 1976.
4. Robinson RA, Smith GW: Anterolateral cervical disc removal and interbody fusion for cervical disc syndrome. Bull Johns Hopkins Hosp 96:223, 1955.
5. Stuke G: Compression of the spinal cord due to ventral extradural cervical chondromas: Diagnosis and surgical treatment. Arch Neurol Psychiatry 20:275, 1928.
6. White AA III, Southwick WO: Relief of pain by anterior cervical spine fusion for spondylosis . A report of 65 cases. J Bone Joint Surg 55A:525, 1973.

Material courtesty of Kenneth I. Light, M.D.
at The San Francisco Spine Center