Surgical Treatment of Isthmic Spondylolisthesis
Other options for surgical reconstructive treatment include in-situ fusion or reduction with subsequent fusion. For decades, proponents of reduction have cited the advantages of improved clinical results, restoration of normal anatomy, improved fusion rates due to better apposition of the vertebral bodies, and superior loading of the chosen bone grafts, as well as improved appearance. Those surgeons who elect to avoid reduction typically agree with these advantages, but they are unwilling to accept the described neurologic risk associated with reduction of isthmic Spondylolisthesis.
The neurologic risk associated with reduction of isthmic Spondylolisthesis ranges in the literature from 0% to 20% [2,3,5,7,11]. Molinara et al. conducted a review of 33 patients treated surgically for grade 3–4 isthmic Spondylolisthesis and reported 4/26 (15 %) patients with neurologic deficits attributed to their reduction (average reduction of two Meyerding grades) . Two of these patients' neurologic deficits were temporary; one required re-operation and the other exhibited a permanent footdrop. Ani and Steffee reported a neurologic injury rate of 4/41 patients (10 %) who underwent Spondylolisthesis reduction (average reduction of 68 % preoperative slip to 6% postoperative slip), two of whom exhibited permanent footdrop . Bradford et al. described neurologic injury of 19 % in the reduction of grade 3–4 Spondylolisthesis; one deficit was permanent (average reduction of 89% preoperative slip to 29 % postoperative slip) . Recently, Bradford et al. published a different approach whereby minimal correction of the Spondylolisthesis was attempted but substantial correction of the slip angle was accomplished . The reported neurologic deficit rate was 15 % and all deficits were temporary. Boos et al. reported a neurologic deficit rate of 20 % at the time of Spondylolisthetic reduction, but all deficits were temporary (average of 78 % preoperative slip to 39 % postoperative slip) . Albrecht et al. reported a detailed analysis of attempted Spondylolisthesis reductions and found neurologic deficits in two of 54 grade 1–2 reductions (both temporary), in none of three grade 3 reductions, and in eight of 11 grade 4–5 reductions (three were permanent) . Interestingly, the neurologic deficits in Albrecht's series all developed more than 72 h postoperatively. The exact amount of reduction is not recorded in their article.
Lehmer et al. described the Gaines procedure, i.e., L5 vertebral body resection in an effort to reduce neurologic complications associated with grade 4–5 Spondylolisthesis . This procedure is a major undertaking and the reported complication rate is as high as 75 % . It has been said that the neurologic complication rate may be as high with this procedure as with traditional Spondylolisthesis reduction (J.P. Kostuik 2002, personal communication).
The literature provides interesting information regarding the role of an interbody graft in patients who undergo arthrodesis for treatment of Spondylolisthesis. In Molinari's paper, a 45 % rate of pseudarthrosis was seen in patients who underwent isolated posterior-lateral in situ arthrodesis . A non-union rate of 29 % and an instrumentation failure rate of 29 % were seen in patients who underwent reduction and posterior-lateral fusion. Finally, a pseudarthrosis rate of 11 % and an instrumentation failure rate of 16 % were seen in patients treated with reduction and circumferential fusion.
Hu and Bradford reported a 25 % instrumentation failure and pseudarthrosis rate in partially reduced patients with an isolated posterior-lateral arthrodesis .
Boos reported a pseudarthrosis rate of 91 % in patients with reduction followed by isolated posterior-lateral fusion, but they achieved a 0% pseudarthrosis rate when a circumferential fusion was chosen . John Kostuik has extensive experience with Spondylolisthesis reduction and concurs that an interbody graft is mandatory (J.P. Kostuik 2002, personal communication). Therefore, it would seem that a circumferential fusion is a reliable mechanism to minimize the chance of pseudarthrosis.
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