Effectiveness of posterior structures in the development of proximal junctional kyphosis following posterior instrumentation: A biomechanical study in a sheep spine model

Abstract

IntroductionProximal junctional kyphosis – PJK has been defined by a 10 or greater increase in kyphosis at the proximal junction as measured by the Cobb angle from the caudal endplate of the uppermost instrumented vertebrae (UIV) to the cephalad endplate of the vertebrae 1 segments cranial to the UIV. In this biomechanical study, it is aimed to evaluate effects of interspinosus ligament complex distruption and facet joint degeneration on PJK development.Materials and methodsPosterior instrumentation applied between T2 – T7 vertebrae using pedicle screws to randomly selected 21 sheeps, divided into 3 groups. First group selected as control group (CG), of which posterior soft tissue and facet joints are protected. In second group (spinosus group, SG) interspinosus ligament complex which 1 segment cranial to UIV has been transected, and third group (faset group-FG) was applied facet joint excision. 25 N, 50 N, 100 N, 150 N and 200 N forces applied at frequency of 5 Hertz as 100 cycles axial to the samples. Then, 250 N, 275 N and 300 N forces applied static axially. Interspinosus distance, kyphosis angle and discus heights was measured in radiological evaluation. Abnormal PJK was defined by a proximal junctional angle greater than 100 and at least 100 greater than the corresponding preoperative measurement.ResultsIn CG group, average interspinosus distance was 6,6 ± 1.54 mm and kyphosis angle was 2,2 ± 0.46° before biomechanical testing, and they were measured as 9,4 ± 1.21 mm and 3,3 ±0.44° respectively after forces applied to samples. In SG group, average interspinosus distance was 6,2 ± 1.72 mm and kyphosis angle was 2,7 ± 1.01° before experiment, and they were measured as 20,8 ± 5.66 mm and 15,1 ± 2.34° respectively after forces applied to samples. In FG group, average interspinosus distance was 4,8 ± 1.15 mm and kyphosis angle was −1 ± 4.14° before experiment, and they were measured as 11,1 ±1.96mm and 11 ± 2.87° respectively after forces applied to samples. In comparison to group CG, statistically significant junctional kyphosis was seen on both FG and SG group after statistical analysis. (p < 0.05). PJK was seen statistically significant more on SG group than FG group. (p < 0.05). Not any statistically significant difference was seen on measurement of disk distances among three groups. (p > 0.05)ConclusionsProtecting interspinosus ligament complex and facet joint unity during posterior surgical treatment for spine deformation is vital to prevent PJK development. Based on our literature review, this is the first biomechanical study that reveals interspinosus ligament complex are more effective on preventing PJK development than facet joints.

Conditions for Achieving Postoperative Pelvic Incidence-Lumbar Lordosis < 10° in Circumferential Minimally Invasive Surgery for Adult Spinal Deformity

“…In this study, the incidence of PJK was approximately 13% and the re-surgery rate was 8%, which is lower than that in previous reports [32][33][34]. The first reason for the low incidence of PJK is due to the effect of a reduction in the posterior soft tissue damage by using PPS, which is similar to those of past reports [13,34,37]. The second reason is ensuring sufficient kyphosis of terminal rod contour, suitable for postoperative reciprocal change, as in our previous report [35].…”

“…Rhee et al reported that PJK is seen less frequently in anterior spinal fusion than in posterior spinal fusion [ 36 ]. Some studies report that the reduction in posterior soft tissue damage using PPS is useful in the prevention of PJK [ 13 , 34 , 37 ]. In this study, the incidence of PJK was approximately 13% and the re-surgery rate was 8%, which is lower than that in previous reports [ 32 , 33 , 34 ].…”

The influence of ligament biomechanics on proximal junctional kyphosis and failure in patients with adult spinal deformity

“…Current surgical recommendations have been based off computer simulations of cadaveric data, with no in vivo validation. 17 With the growing incorporation of ligament augmentation techniques in surgical management of ASD, the importance of validating the underlying biomechanical and biological assumptions of ligamentous mechanical properties is paramount. The goal of our study was to determine if certain ligamentous biomechanical properties could be associated with the in vivo development of PJK/PJF.…”

“…Prior studies investigating tissue‐specific risk factors for PJK/PJF report muscle atrophy 15 and poor bone mineral density 16 as independently associated with failure; however, to our knowledge no prior studies investigated the mechanical properties of the ligamentous complex as an independent risk factor. Current surgical recommendations have been based off computer simulations of cadaveric data, with no in vivo validation 17 …”

“…Korkmaz et al concluded that the PLC dysfunction played a more significant role in the development of PJK than facet joint incompetency 17. …”