The great debate: Hybrid vs. fusion for two-level lumbar degenerative disc disease


Jack E Zigler, Texas Back Institute, Plano, USA, and Louis G Jenis, Massachusetts General Hospital, Boston, USA, debate the benefits and pitfalls of hybrid and fusion approaches to two-level lumbar degenerative disc disease.

Jack Zigler: Lumbar hybrids for two-level lumbar degenerative disc disease

Jack E Zigler
Jack E Zigler

A small number of patients develop two-level functionally disabling mechanical low back pain in their productive years, fail to improve with at least six months of conservative therapy, and are candidates for surgery. They have traditionally been offered two-level fusion.

In the two-level ProDisc-L vs. 360 fusion study, reported in J Bone Joint Surg Am as a level one prospective multicentre randomised trial, 237 patients at average age 41.8 years were enrolled and surgically treated.¹ At 24 months after surgery, 89.9% of total disc and 90.5% of fusion patients reported Oswestry Disability Index improvement from baseline. The mean score in the ProDisc-L group was an improvement of 34.5 points (53%); the fusion group showed an average improvement of 26 points (41.2%) (p=0.0424). In that study, Oswestry Disability Index success criteria of ≥15 point improvement was met by 73% of ProDisc-L and by 60.3% of fusion patients (p=0.0497). Secondary surgical procedures at the index level occurred in 2.4% of ProDisc-L and 8.2% of fusion patients (p=0.0497). Finally, narcotics usage was significantly lower in ProDisc-L (36.4%) compared to fusion patients (61%; (p=0.0017).

This represents the strongest scientific data we have regarding the clinical and radiographic outcomes of these two surgical treatments in patients who have failed at least six months of conservative treatment. Uniform patient selection was a key strong point of the study, because historic multiple-level fusion studies have included patients with disparate pathologies, ages, and levels, making interpretation difficult. This study offered us excellent treatment guidelines for those 42-year-old patients with disabling two-level lumbar degenerative disc disease. Unfortunately, two-level arthroplasty never completed US Food and Drug Administration approval, and two-level fusions are often denied in the USA by insurance carriers as “experimental.”

Hybrid constructs for two-level lumbar degenerative disc diseases were borne out of insurance necessity, not out of science. Surgeons recognised the altered mechanics of a two-level fusion in a 40-year-old, and patients wanted to maintain some motion and help protect the rest of their lumbar spine. Several analyses of hybrid constructs, both prospective and retrospective, demonstrated similar clinical outcomes with measurable motion at the arthroplasty level.

A post-hoc analysis of a consecutive series of two-level hybrids from the Texas Back Institute studied 135 patients with at least 12 months’ follow-up. Eighty-three of these patients had a stand-alone anterior lumbar interbody fusion (ALIF) at the fusion level, while 52 had a 360 fusion done at the arthrodesis level. Both groups improved in Oswestry Disability Index significantly from baseline. The hybrid ALIF patients trended better, although the difference was not significant. Both groups’ pain scores also improved significantly from the preoperative scores, but the difference between cohorts was not significant. Reoperation rates were significantly lower in the ALIF group (3.6% vs. 23.1%; p<0.01).

There is no long-term data yet available on adjacent level degeneration or adjacent level disease. We do have strong radiographic data published on radiographic changes above single-level 360 fusion vs. artificial disc replacement (showing a 3:1 difference).² There are also published in vitro studies showing increased adjacent level intradiscal pressures above a fusion as compared to levels above an artificial disc replacement.³

It is felt by many surgeons that a two-level fusion in a young person is less than optimal, given its association with future surgery. Hybrid constructs offer shorter operating room time, less blood loss and quicker recovery than a two-level fusion, as well as better motion with a mobile arthroplasty device at the transition level. Most importantly, they offer the potential for a lower incidence of anatomic adjacent level disease, which should translate to a lowered incidence of adjacent level surgeries occurring while the individual is still in their economically productive years.

Although there are clearly instances when fusion is necessary, such as the presence of posterior instability, if the indication for the second level is discogenic pain due to internal derangement, a hybrid construct using a stand-alone ALIF at the fusion level is clearly a reasonable option.


  1. Delamarter R etal.JBoneJointSurgAm 2011; 93: 705-715
  2. Zigler JE, Glenn J, Delamarter RB. JNeurosurgSpine2012; 17: 504-511
  3. Dmetriev AE, Gill NW, Kuklo TR, Rosner MK. TheSpineJournal 2008; 8: 918-925

Jack E Zigler is medical director of the Texas Back Institute, Plano, USA

Louis G Jenis: Lumbar fusion for two-level degenerative disc disease


Louis G Jenis
Louis G Jenis

The patient who describes chronic low back pain in the presence of two-level disc degeneration (L4L5/L5S1) presents a challenging clinical scenario. There is great controversy about which surgical treatment option is best, or whether surgery is even an alternative at all. When surgery is considered, options include fusion vs. total disc replacement or a hybrid construct. However, numerous issues must be weighed. Are these interchangeable treatments, or are they competitive for same patient? Are they complementary strategies for a heterogeneous population of degenerative disc disease? Does total disc replacement provide better clinical outcomes and the proposed downsides of fusion? 

To answer these questions we need to assess the literature for evidence-based data for guidance. The literature is replete with studies reporting clinical and radiographic outcomes after lumbar fusion but vary based on study design, surgical indications and techniques. There have been at least 18 randomised controlled trials published depicting surgical outcomes for degenerative disc disease, with numerous level one data studies confirming some beneficial effect of surgery vs. conservative treatment. When the total disc replacement literature is analysed the data is less consistent, although, there is some evidence of effectiveness.
In terms of pain relief and functional outcomes, there are numerous level three and a few level one studies confirming that total disc replacement accomplishes at least comparable improvement in both the short and longer term, as shown in the Charité five-year follow-up study, among others.1-3

At the index level of surgery, a primary goal of total disc replacement is to restore or maintain range of motion. Literature and clinical experience confirm that these are challenging procedures, and must be performed technically well with appropriate indications to achieve these results. Early follow-up studies suggest that range of motion is maintained with a trend to better outcomes with optimal placement of the device, while longer term data report conflicting results of index level degeneration and the impact on range of motion may actually decrease with time.4-6 Variable results have been published regarding the progression of facet joint degeneration at the index level, and the effects remain unclear at this time.

Is progressive facet arthrosis part of the natural history and degenerative cascade, or is it a failure of total disc replacement to prevent this occurrence in the long term?

One of the major proposed goals of total disc replacement—and often cited as a primary indication in clinical practice—is to maintain or ‘normalise’ motion at the adjacent level and at least slow down or prevent the development of adjacent segment degenerative changes or symptoms. While this is a theoretical goal, it remains very controversial as numerous causes of adjacent segment degenerative changes and symptoms have been described. While the literature lacks any level one supportive data, systematic reviews consisting of retrospective data and case reports and longer term level II and III publications suggest a higher incidence of adjacent segment degenerative changes after fusion.7-8 A potential higher risk of requiring additional adjacent segment surgeries after fusion or total disc repleacement is not established at this time.

So what can we make of this data and the controversial decision on how to treat the patient with two-level lumbar degenerative disc disease? The literature suggests equivalence in clinical outcomes and possible loss of range of motion at the index level with time, while the adjacent segment issues are controversial and remain multifactorial. I would argue that two-level fusion remains the standard of care at this time.


  1. Blumenthal et
 al, Spine 2007; 30:1565-1575
  2. Guyer et
 al, Spine 2009; 374-386
  3. Lu et
 al, ESJ 2015; 24:2056-2064
  4. McAfee et
 al, Spine J 2005; 30:1576-1583
  5. Zigler et
 al, Spine
 2007; 32:1155-1162
  6. Patel et
 al, Spine
 J 2006; 31:948-953
  7. Harrop et al, Spine 2008; 33: 1701-1707
  8. Wang et
 al, Spine J 2012; 37:s135-s143

Louis G Jenis is chief of Spine Surgery at Massachusetts General Hospital and Newton Wellesley Hospital, Boston, USA