Study Design. Experimental study.
Objective. To compare the effects of fusionless instrumentation (FI) and instrumented fusion (IF) on the adjacent segment in an immature pig model.
Summary of Background Data. Observations reveal proximal junctional kyphosis after FI. Possible reasons are stress concentration, repeated distractive forces, and/or soft tissue damage done in the index surgery. It was speculated that FI can decrease stressors to the junctional area by preserving the spinal mobility in some manner; however, this has not been proven to date.
Methods. Thirteen piglets of 10- to 14-week age were used. FI and IF were performed on 7 and 3 piglets, respectively, and 3 piglets formed the control group. Control piglets did not undergo any surgical procedures. T11–L4 instrumentation, decortication, and grafting were applied to IF piglets. In FI groups, however, L1–L2 was left uninstrumented and unfused using T11–T12 and L3–L4 levels as anchors to the growing construct. A total of 4 lengthening procedures were performed: 1 in the index operation and 3 more, once in each lengthening procedure monthly, for 3 months. Four months after the index operations, all piglets were killed and the adjacent segment motion capabilities, disc, and facets were evaluated with radiographical, magnetic resonance imaging, biomechanical, and histological analyses.
Results. Comparison of proximal junctional Cobb angles of the postindex (mean: 21, range: 17–27) and presacrification (mean: 21, range: 11–31) radiographs in the FI group revealed no difference (P> 0.05). In magnetic resonance imaging, both surgical group proximal adjacent discs showed degeneration to some degree that was statistically indifferent (P = 0.903). Biomechanical evaluation revealed restriction of adjacent segment motion in all directions for both groups; however, this negative effect was significantly less in FI group (P < 0.01). Degeneration observed in histological evaluation in adjacent discs and facets of FI group was significantly lower (P = 0.00).
Conclusion. In this quadruped straight spine model, in comparison with IF applications, FI is closer to normal physiology even after several lengthening procedures regarding the adjacent segment discs, facet joints, and motion, when interpreting the radiological, biomechanical, and histological results altogether.
Level of Evidence: N/A