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Disc degeneration after disc herniation: are we accelerating the process?

Study design: Systematic review. Study rationale: Disc degeneration is a common process starting early in life. Often disc herniation is an early step in disc degeneration, which may cause pain or stenosis. How quickly this subsequent disc degeneration occurs following a disc herniation and subsequent surgical treatment and whether certain spinal procedures increase the rate of degeneration remain unclear. Objectives: To investigate the risk of subsequent radiographic disc degeneration following discectomy, discography, and conservative care in patients with a first-time diagnosed herniated nucleus pulpous (HNP) and to ascertain whether this risk in these defined groups changes over time. Methods: A systematic review of pertinent articles published up to June 2012. Key articles were searched to identify studies evaluating the risk of subsequent radiographic disc degeneration following treatment for HNP. Studies that included patients undergoing secondary surgery for disc herniation or that did not use a validated classification system to measure the severity of disc degeneration were excluded. Two independent reviewers assessed the strength of evidence using the GRADE criteria and disagreements were resolved by consensus. Results: From a total of 147 possible citations, three cohort studies (class of evidence III) met our inclusion criteria and form the basis for this report. The risk of subsequent lumbar disc degeneration following standard discectomy was significantly greater compared with both microdiscectomy (48.7% vs 9.1%) and asymptomatic controls (90% vs 68%) in two studies with mean follow-ups of 5.5 and 25.3 years, respectively. Following conservative care for first-time HNP in the third study, the risk of progression of lumbar disc degeneration was 47.6% over the first 2 years of follow-up and 95.2% over the next 6 years of follow-up. In the same study, the risk of lumbar disc degeneration was shown to increase incrementally over the course of the 8-year follow-up, with all patients showing signs of degeneration at final examination. Conclusion: Standard discectomy in first-time lumbar HNP may increase the risk of subsequent same-level lumbar disc degeneration compared with microdiscectomy as seen in one low-quality study. However, disc degeneration is likely a natural, temporal consequence following HNP, as demonstrated in a second low-quality study. The overall strength of evidence for the conclusions is very low.


STUDY RATIONALE AND CONTEXT
Disc degeneration is a common process starting in the second decade of life [1,2]. We commonly use imaging tests to quantify its severity [3]. In many cases, disc herniation is an early step in disc degeneration [4]. As the disc progressively degenerates, it may clinically manifest itself with pain or stenosis. How quickly this subsequent disc degeneration occurs following treatment for disc herniation and whether certain spinal procedures increase the rate of degeneration remain unclear. Of particular concern is if nonoperative care may be associated with a slower rate of progression than invasive diagnostic or surgical interventions, and if certain less invasive procedures offer advantages over more conventional extensile procedures.

OBJECTIVES
To investigate the risk of subsequent radiographic disc degeneration following discectomy, discography, or conservative care in patients with a first-time diagnosed herniated nucleus pulpous (HNP) and to ascertain whether this risk in these defined groups changes over time.

Study design: Systematic review.
Search: PubMed; Cochrane collaboration database; National Guideline Clearinghouse database; bibliographies of key articles.
Outcomes: Severity classification system of disc degeneration (Kambin severity scale or Pfirrmann classification).
Analysis: Descriptive statistics of the cumulative incidence or prevalence.

Cumulative incidence:
The proportion of people who had been degeneration-free at the time of the initial evaluation that had subsequent development of new degeneration at final follow-up.

Prevalence:
The proportion of people with disc degeneration at any follow-up point.
Data were summarized in tables and figures but were not pooled due to the limited number of studies available and the heterogeneity of patient populations, outcome measures, and follow-up periods.
Overall strength of evidence: Risk of bias determined using CoE rating scheme developed by the Oxford Centre for Evidence-based Medicine by The Journal of Bone and Joint Surgery American Volume [Wright] (see Web Appendix at www.aospine.org/ebsj). The overall body of evidence with respect to each key question was determined based on modified precepts outlined by the Grades of Recommendation Assessment, Development and Evaluation (GRADE) system.

Volume 3/Issue 4 -2012
Evidence-Based Spine-Care Journal Systematic review-Disc degeneration after disc herniation: are we accelerating the process?

RESULTS
• From 147 citations, 24 articles underwent full-text review; three cohort studies, all graded CoE III, met our inclusion criteria and form the basis for this report (Fig 1). Characteristics of each study are outlined in Table 1. See Web Appendix at www.aospine.org/ebsj for critical appraisal and a list of excluded articles. • We found no studies reporting the risk of radiographic disc degeneration following discography for HNP. • Two studies investigated the risk of disc degeneration following standard discectomy; one compared with posterolateral microdiscectomy [5] and one compared with asymptomatic controls [6]. The third study was conducted in patients who had undergone conservative care [7].
Key question 1: What is the risk of subsequent radiographic disc degeneration following discectomy, discography, and conservative care in patients with a first-time diagnosed HNP?

Conservative treatment
• Of 21 patients treated conservatively, 38.1% were men with a mean age of 49 years. • The prevalence of progression of disc degeneration, defined as an increase of 1-2 grades, was 47.6% from initial presentation to 2 years, and 95.2% from 2 years to final follow-up. When defined as an increase of two grades, the prevalence of progression was 4.8% and 47.6%, respectively.    Conservative treatment (Fig 4, Table 2) • The prevalence of moderate to severe (grade ≥ III, Pfirrmann classification) lumbar disc degeneration increased incrementally over the study period from 28.6% at initial presentation to 66.6% at 2 years, and finally to 100% at the 8-year follow-up.

CLINICAL GUIDELINES
No clinical guidelines were found addressing this topic.
Systematic review-Disc degeneration after disc herniation: are we accelerating the process? Table 3 Strength of evidence summary.

Strength of evidence Conclusions/comments
Key question 1: What is the risk of subsequent radiographic disc degeneration following discectomy, discography, and conservative care in patients with a first-time diagnosed herniated nucleus pulpous?

Discectomy vs microdiscectomy
Very low Low M oderate H igh Subsequent lumbar disc degeneration occurred five times more often following standard discectomy compared with microdiscectomy (48.7% vs 9.1%; mean follow-up, 5.5 years) in one low-quality study

ILLUSTRATIVE CASE
A 53-year-old healthy woman suffered from extreme radicular pain in her right leg in the S1 distribution. On magnetic resonance imaging (MRI), a central disc herniation was noted (Fig 5). She was treated with oral analgesics and physical therapy; however, the pain did not remit. Six months later she was referred for a discectomy. On surgery, a standard discectomy was performed and a large disc fragment was removed from the canal (Fig 6). Her pain resolved and she went back to her daily life. Nine months later, she returned to the clinic with a new onset of lower back pain and pain radiating down the left leg. A new MRI was performed showing loss of disc height, severe degeneration, and recurrent herniation of the disc (Fig 7).

EVIDENCE SUMMARY
The overall strength of evidence evaluating the risk of subsequent radiographic degeneration in the lumbar spine following standard discectomy compared with microdiscectomy, standard discectomy compared with asymptomatic controls, and conservative treatment for first-time HNP is very low, that is, any effect estimate is uncertain ( Table 3). The overall strength of evidence evaluating whether this risk of subsequent radiographic disc degeneration changes over time is also very low, as addressed by only one study in patients undergoing conservative care.  Modic end plate changes and reherniation of the L5-S1 disc.

DISCUSSION
• Strengths: -We included only studies that used a severity classification system to measure disc degeneration.
• Limitations: -Few studies were available to address the issue, all with small sample sizes (n = 83, n = 100, n = 21). -All studies were class of evidence III.
-Heterogeneity of patient populations, outcome measures, and follow-up periods made comparisons across studies difficult. -No studies were found that met our criteria in patients treated with discography.
• Not all cases of HNP will lead to advanced disc degeneration in 5 to 10 years; however, close to two-thirds will show some signs of degeneration. • Surgical intervention may increase the risk of disc degeneration. • Standard discectomy may cause more degeneration than microdiscectomy. • The biologics behind disc nutrition and degeneration and the effects of interventions on these processes need to be better understood. • As discectomy is the most common spine procedure in the world, better data needs to be gathered on the long-term effects of surgical procedures.