Abstract
Introduction
Proximal junctional kyphosis (PJK) has traditionally been defined by a 10 degree or greater increase in kyphosis at the proximal junction as measured according to Cobb method. Especially patients who have advanced spine deformity are prone to PJK and it is related with aggressive treatment protocols. In this biomechanical study, we aimed to evaluate interspinous ligament complex disruption and facet joint degeneration on PJK development.
Material and Methods
Randomly selected 21 sheeps were operated via posterior approach and pedicle screws were instrumented from T2 to T7. Three groups with seven samples were established to create junctional disruption. First group selected as control group (CG), of which posterior soft tissue and facet joints were preserved intact. In the second group (spinous group, SG), interspinous ligament complex which one segment cranial to UIV has been transected, and third group (facet group FG) where facet joint excision was performed. 25 N, 50 N, 100 N, 150 N, and 200 N forces applied at frequency of 5 Hz as 100 cycles axial to the samples. To determine strength of proximal junctional area in static loading 250 N, 275 N, and 300 N forces was applied. Changes in the proximal junctional region were defined radiologically. Lateral X-ray views were taken to measure interspinous distances, kyphosis angles, and discus heights. Abnormal PJK was defined by a proximal junctional angle greater than 10 degree and at least 10 degree greater than the corresponding preoperative measurement.
Results
In CG group, average interspinous distance was 6.6 ± 1.54 mm and kyphosis angle was 2.2 ± 0.46 degree before biomechanical testing, and they were measured as 9.4 ± 1.21 mm and 3.3 ± 0.44 degree respectively after forces applied to samples. In SG group, average interspinous distance was 6.2 ± 1.71 mm and kyphosis angle was 2.7 ± 1.09 degree before the experiment, and they were measured as 20.8 ± 5.66 mm and 15.1 ± 2.33 degrees, respectively, after biomechanical testing. In FG group, average interspinous distance was 4.8 ± 1.15 mm and kyphosis angle was −1 ± 4.14 degree before experiment, and they were measured as 11.1 ± 1.96 mm and 11 ± 2.87 degree, respectively, after forces applied to samples. Statistically significantly junctional kyphosis development was detected on both FG and SG group than group control group (p < 0.05). PJK was seen significantly more frequently on SG group than FG group (p < 0.05). Disc distances were similar in all groups (p > 0.05).
Conclusion
Protecting interspinous ligament complex and facet joint on surgical treatment of spine deformity is mandatory to prevent PJK. To our knowledge, this is the first biomechanical study that reveals that the interspinous ligament complex is more effective in preventing PJK development than facet joints.