Anterior Lumbar Interbody Fusion (ALIF) - Sam Church 7/1/2002
The main indication for lumbar fusion is instability. American Medical Association definition of spinal instability is 'an anterior slip of >5mm or a difference of >11 degrees (15 degrees for L5/S1) angular motion between two adjacent segments.' Symptoms of instability include giving way, 'catching' and lower back pain but these do not correlate well with the xray findings described above and are often complicated by concomitant spinal stenosis, disc herniation and psychiatric problems.
Lumbar fusions are also commonly performed for 'discogenic' back pain or in combination with discectomies/decompressions. This is controversial and the spinal community is split over whether there is satisfactory evidence to support this.
Other indications for lumbar fusion include the treatment of other failed spinal procedures, certain spinal deformities, infections, fractures and tumours.
Methods of fusion include interbody, posterior, posterolateral and intertransverse (or various combinations of the above). The interbody fusion is theoretically biomechanically superior to the others as the graft is placed in the centre of segmental motion thus minimising the lever arm effect. Interbody fusions can be approached anteriorly or posteriorly. Although the anterior approach has the disadvantage of requiring a surgeon practised in laparotomies, once in there the dissection is easier, you can completely excise the disc and the (posterior approach) complications of posterior element pain and scarring within the spinal canal are avoided. Laparoscopic ALIF and retroperitoneal endoscopically assisted minilaparotomy (REAM) for ALIF are very trendy now although there are no long-term results available yet.
Interbody fusions can be performed using tricortical iliac crest graft, fibular strut grafts, femoral ring grafts or cages (with bone graft packed inside). Most surgeons seem to be steering towards using cages (metal or carbon fibre) these days as they're quicker and easier (although more expensive) and they are more reliable at restoring disc space height thereby reducing subluxed facet joints and enlarging nerve root foramina. Autograft and/or allograft can be used and, not surprisingly, this is the subject of much debate.
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