Introduction: Minimally-invasive techniques are being advocated increasingly for spine surgery, on the grounds that they are less traumatic and reduce postoperative recovery time. A minimally-invasive technique for posterior lumbar interbody fusion (MPLIF) has become available. In order to compare its efficiency and effectiveness with the open technique (OPLIF), a prospective audit was undertaken.
Methods: Forty-seven adult patients with radicular pain resulting from isthmic or degenerative spondylolisthesis, with a slip less than 50%, and no previous surgery, elected to undergo either MPLIF (n = 23) or OPLIF (n = 24). The MPLIF procedure was performed through two, 2.5cm paramedian incisions using a tubular retractor system and dilators (METRx-MD, Medtronic Sofamor Danek, Memphis). OPLIF was performed thorugh a 10 cm midline incision. In both procedures, the listhesis was reduced using polyaxial pedicle screws, and reduction tabs or bolts (Expedium, Depuy); the disc space was distracted using interbody spacers (R-90, Metronic Sofamor Danek) and packed with iliac crest graft. Intra-operative and postoperative variables were recorded. Clinical outcomes were assessed, before and 12 months after surgery, using a visual analog scale for pain and the SF36 for function.
Results: The two groups were comparable, demographically and with rspect to clinical features at inception, save that the MPLIF group had signficantly greater disc heights. Listhesis (median; interquartile range) was reduced from 25% (20–32) to 8% (1–13) after OPLIF, and from 20% (15–25) to 5% (0–10) after MPLIF. Disc height was increased from 12% (6–17) of vertebral body height to 24% (20–26) after OPLIF, from 17% (10–23) to 30% (26–36) after MPLIF. Fusion was achieved in all patients except one in the PLIF group. After OPLIF, median scores (interquartile ranges) for leg pain reduced from 8 (7–9) to 1 (0–4); scores for back pain reduced from 8 (6–8) to 2 (1–4); social functioning improved from 38 (13–57) to 82 (47–100), and in physical functioning improved from 20 (5–48) to 68 (44–86). After MPLIF, leg pain reduced from 8 (7–9) to 1 (0–3); back pain reduced from 8 (8–10) to 2 (1–4); social functioning improved from 38 (25–66) to 75 (50–91), and physical functioning improved from 20 (10–48) to 65 (34–82). All improvements within groups were significant (p = 0.000), but no statistically significant differences occurred between the groups for any outcome measure. Improvements in leg pain amounted to an 88% reduction for both groups, Back pain improved by 64% after OPLIF and by 78% after MPLIF. Duration of surgery and need for transfusion were not different between groups (5 patients required transfusion during OPLIF, and 1 during MPLIF (p = 0.09)); but the MPLIF patients had significantly shorter delays before commencing and achieving mobilization post-operatively, and had a shorter length of stay (4 days v 7 days).
Discussion: Clinical outcomes after MPLIF and OPLIF were not statistically different. Both procedures reduced back pain as well as leg pain, and restored function. Although there was no detectable correlation between pain and function before treatment, relief of pain was strongly correlated with restoration of function, after treatment. The advantage of MPLIF is that promotes faster recovery and shortens hospital stay. Its only disadvantage is the need to adapt to the technology involved and becoming familiar and confident with its use.
