Pathophysiology and Management of Degenerative Disk Disease

Note: This is the abstract which I gave a lecture last November in Annual Congress of Philippines Orthopaedic Association.  Some viewpoints are according to my personal clinical experiences.

Pathophysiologyn and Management of Degenerative Disk Disease

 The spectrum of degenerative disc disease (DDD) ranges from premature disc degeneration in adolescence (juvenile discogenic disease, Fig. 1)

Fig. 1: 18 y, male. Chronic LBP 2 years

to the elderly with or without degenerative scoliosis (Fig. 2. A), 

Fig. 2: 65 y, male with degenerative scoliosis and claudication LBP 1 year . A. Reformatted CT shows vacuum at L3-4 disc. B. LBP was relieved by analgesic discography (2 ml bupivacaine) for 4 hours and underwent lateral fusion.

with one or more disc levels affected. The etiology of DDD seems to have a genetic predisposition according to identical twins studies, and environmental factor is considered playing a lesser role. The once hydrated disc becomes gradually desiccated and alters the normal biomechanics of the functional spine unit. Abnormal ingrowth of nerve endings in the endplates, annulus, and nucleus is thought to be the origin of pain. There is a known wide discrepancy between imaging and symptomatology that in patients with similar image findings, the pain intensity varies from minor to excruciating, and it is further complicated by spinal stenosis and renders the diagnosis of DDD difficult.

 We classified DDD into two categories: without and with vacuum sign based on clinical presentations and images. 1. Painful DDD without vacuum sign (type 1) usually occurs below 50 years old and rarely above that age. Clinical presentation is chronic fluctuating low back pain (LBP), the pain intensity is increasing in stepwise fashion over time. At the peaks of pain attack, the pain is persistent and the patient cannot tolerate any fixed posture for a few minutes, and even sleep is disturbed; at the lows of pain, the pain decreases to an extent of tolerable or negligible, but is not completely gone. The durations of the peaks and lows vary from hours, days, or weeks. 2. In painful DDD with vacuum sign (type 2, detected by reformatted CT, Fig. 2A), the mean age of the patients is generally older: above 50 years old. Clinically, they present with chronic LBP (+/- thigh pain) with claudication in feature that backache or thigh pain is aggravated by prolonged standing and walking and relieved by sitting and lying. The clinical pictures are similar to neurogenic claudication of spinal stenosis. In contrast, in type 2 DDD the pain is rarely referred below the knee joints. We postulate it is due to anterior column insufficiency. There is lack of correlation between type 1 and 2 DDD, because no longitudinal study has been done.

 Diagnosis of type 1 DDD is based on typical clinical presentation and compatible to a standard pain graph. The role of pain provocation discography is controversial; furthermore, literature do not mention its role in type 2 DDD and we had only one instance of provoked pain in type 2 DDD. In type 2 DDD, spinal stenosis has to be ruled out firstly by using selective nerve root block when in doubt. We use functional analgesic discography in diagnosing type 2 DDD by injecting anesthetic agent to relieve pain (Fig. 2 B); it is ineffective in type 1 DDD and renders the patient more painful. The pitfall is possible false-positive outcomes due to epidural leakage of the anesthetic agent from the torn annulus resulting in minor degree of epidural spinal block that root and disc pain are both masked. Its estimated sensitivity (95.8%) is high but specificity (28.6%.) is low.

 In surgical treatment, canal stenosis should be addressed primarily. Interbody fusion is used in intractable, carefully selected cases.  We prefer to use lateral retroperitoneal access to minimize tissue trauma; and use of standalone cage supplemented with an intravertebral plate (Fig. 3 B, C) 

Fig. 3. 32 Y, F, LBP 5 years. A: 3-level degenerated discs. B,C: underwent lateral fusion, using lateral cage-intravertebral plate device. Preop VAS 10 improved to 2.

to stabilize the segment without additional screw-based instrumentation to reduce device-related issues.

 In conclusion, the diagnostic protocol for DDD needs to be standardized; the choice of surgical procedure should be least traumatic.