Surgical Strategies for the Treatment of Lumbar Pseudarthrosis in Degenerative Spine Surgery: A Literature Review and Case Study

Revising Failed Posterolateral Fusions

Pseudarthrosis of an isolated posterolateral fusion (in other words, no attempt at interbody fusion) leaves the surgeon with the largest number of revision options. One is a second attempt at posterolateral fusion, although persistent pseudarthrosis after revision posterolateral fusion has been reported at rates of 35 to 51% [6, 20]. In such an attempt, screws may be upsized, meticulous attention must be paid to decortication, and the use of iliac crest bone graft or bone morphogenetic protein 2 (BMP-2) should be considered. A screw system with a different thread pitch can help increase purchase, and cement augmentation can be used in cases of severely osteoporotic bone. It should be noted that the available studies were performed before the widespread adoption of modern pedicle screw and rod instrumentation, but the results are discouraging nonetheless.

The addition of an interbody device has been associated with higher rates of successful fusion in patients undergoing revision surgery for pseudarthrosis [1, 4, 17]. Retroperitoneal approaches, such as anterior lumbar interbody fusion (ALIF) and lateral lumbar interbody fusion (LLIF), as well as related antepsoas approaches, are attractive in that they allow for placement of interbody grafts with large surface areas, which is beneficial from a biomechanical perspective while also providing a broader region for fusion. Fusion rates of 90 to 100% have been observed with circumferential surgery (ALIF and revision posterolateral fusion) [1, 4, 17].

Given the availability of ALIF cages with built-in fixation capabilities, ALIF alone may be appealing because it avoids further disruption of the posterior musculature. A retrospective review comparing ALIF and ALIF with revision posterolateral fusion in 38 patients with pseudarthroses after failed TLIF found fusion rates of 81 and 88%, respectively, a difference that did not attain statistical significance [18]. Consistent with other studies reporting clinical outcomes after revision surgery for pseudarthrosis, functional improvement was minimal in both groups. ALIF followed by percutaneous pedicle screw instrumentation (rather than open revision posterolateral fusion) is another option that has been described in an effort to reduce surgical morbidity [7].

TLIF may also be considered but may be more technically challenging in the setting of a prior laminectomy. In a 2016 retrospective cohort study of 128 patients treated for lumbar pseudarthrosis, Owens et al. found no statistically significant difference in health-related quality-of-life scores between patients treated with revision posterolateral fusion, TLIF, ALIF, or ALIF with posterior fusion [11]. Radiographic fusion rates were not reported, but clinical outcomes overall were discouraging—depending on the treatment group, only 17 to 28% of patients reached a minimal clinically important difference on the Oswestry Disability Index. This underscores the importance of achieving robust fusion during the index procedure.

Because ALIF and LLIF do not allow for direct access to posteriorly based implants, a 540° fusion (back–front–back) may be necessary, especially if significant changes to sagittal or coronal parameters (or both) are desired despite reasonably well-fixed posterior implants. In the first stage, pedicle screws and rods are removed, any necessary releases are performed, screws are replaced, and the posterior wound is closed. This is followed by the ALIF or LLIF (the second stage). The third stage involves reopening the posterior incision and placing rods to maintain the correction. The prolonged surgical time and the logistical complexity involved in repositioning the patient multiple times intra-operatively are certainly drawbacks to this technique. If there is concern about infection or about an older patient's ability to tolerate a three-stage procedure under one anesthetic, posteriorly based implants can be removed, cultures can be sent, and the wound can be closed to allow the patient to recover. Patients with positive intra-operative cultures can then be treated to eradicate the infection. The anterior interbody fusion and posterior reinstrumentation can be performed at a later time, in one or more operating room sessions during the same hospitalization.

In an effort to reduce the surgical burden, Kadam et al. introduced the use of hyperlordotic ALIF cages to “overpower” intact posterior fixation [5]. The authors performed two-stage surgery—ALIF followed by posterior implant removal, release, reinstrumentation, and compression—and found improvement in segmental lordosis to be approximately half that with the inserted cage (6.1°, 12.5°, and 17.7° with 12°, 20°, and 30° cages, respectively; all p values < 0.05). Use of this technique is likely ill-advised in patients with deficient bone mineral density because endplate violations or post-operative subsidence was observed in 8.3% of cases despite the fact patients with osteoporosis were excluded from the study cohort.

Revising Failed Interbody Fusions

The presence of a previously placed interbody device has implications for the choice of revision strategy. The above considerations and techniques apply, but additional thought must be given to removal of the previously placed cage if another attempt at interbody fusion is desired. Previously placed TLIF cages are most easily extracted using an anterior or lateral approach and can be replaced with larger ALIF or LLIF cages [7, 10]. Revision of a TLIF through an oblique lateral approach has also been described [13]. Loose cages may come out easily after being freed up with an osteotome, but partial corpectomies may be necessary to explant cages that are more stably fixed or have subsided into the subchondral bone. A high-speed burr can be used to obliterate interbody spacers made of bone or polyether ether ketone (PEEK) but not metallic cages. Eom et al. described a technique for the removal of difficult-to-remove PEEK interbody cages: a tap hole is created into which a rod with a threaded tip is screwed to function as a joystick to control the cage for removal [3]. If the geometry and orientation of the original TLIF cage allow for insertion of a second, revision TLIF can be performed using a contralateral approach.

Revision retroperitoneal approaches, although possible, are associated with higher surgical complication rates if there is difficulty mobilizing scarred-down vessels and viscera [19]. Given the larger footprints of ALIF and LLIF cages, associated pseudarthroses that are relatively stable may simply require a revision posterolateral fusion. However, if removal of a previously placed LLIF cage is necessary, the level can be approached from the other side, as long as the initial cage does not have integral fixation. Failed ALIFs can be addressed using a lateral approach, but a revision anterior approach is necessary to extract ALIF cages with associated anterior fixation. If the level of interest is L5–S1, the second anterior approach might be easier when a course through the contralateral retroperitoneum is taken, but this is less feasible at more cranial interspaces [19]. The level of experience of the surgeon performing the approach, as well as patient factors such as obesity and vascular anatomy, also comes into the equation when weighing the risks and benefits of revision ALIF.