Rigid fixation of the lumbar spine alters the motion and mechanical stability at the adjacent segment level

Abstract

Amaç: Bu çalışmada lomber omurganın rijit tespitinden sonra komşu segmentin hareket genişliği ve stabilitesi araş-tırıldı. Gereç ve yöntemler: Bu çalışmada 17 taze donmuş kuzu lomber omurgası (sakrum T 12 'yi içeren) kullanıl-dı. Biyomekanik test aksiyel kompresyon test cihazı ile yapıldı. Aksiyel kompresyon tüm numunelere 5 mm/dk. yükleme hızı ile uygulandı. Özel dizayn edilmiş fikstür ile 8400 Nmm tork oluşturuldu. Fikstür aksiyel yönde fleksiyon, ekstansiyon, sağ ve sola eğilme pozisyonlarında yüklenme uygulanacak şekilde numuneler ayarlandı. Tüm numuneler sağlam omurga, pedikül vida ve rod fiksasyonu sonrasında teste tabi tutuldu. Test esnasında komşu seviye L5-S1 arasındaki ayrılma değerleri süreğen bir şekilde ekstansometre ile kaydedildi. Bulgular: Komşu segmentte (L5-S1), aksiyel yüklenme ve üst-alt ayrılma değerleri, ön-arka ayrılma değerlerinden düşük bulundu. İstatistiksel analizde sağlam omurga ile komşu segment arasında aksiyel kompresyon ve ekstansiyon pozisyonunda sayısal anlamlı değişiklikler tespit edildi (p<0.027). Bunun yanında ekstansiyon pozisyonunda komşu segmentte sağlam omurgaya göre daha yüksek çıktı (p<0.015). Sonuç: Lomber omurganın rijit fiksasyonu komşu segment seviyesinde hareket genişliğini değiştirmektedir. Bundan dolayı, komşu segmentte anormal stres ve spinal instabiliteye neden olur; bu durum, faset eklem dejenerasyonuna ve bel ağrılarına yol açabilir.Anahtar sözcükler: Komşu segment instabilitesi; faset eklem; omurlar arası disk; lomber omurga.Objectives: This study aims to examine the motion and stability of the adjacent segment following rigid fixation of the lumbar spine. Materials and methods:The study included 17 fresh-frozen lamb lumbar spines (including the sacrum to T 12 ). Biomechanical testing was performed using an axial compression testing machine. Axial compression was applied to all the specimens using a loading speed of 5 mm min-1. A specifically designed fixture was used to generate torque ≤8400 Nmm. The fixture was used with each specimen to achieve flexion and extension, axial neutral compression, and right and left bending. All specimens were tested intact, and again after implantation using posterior pedicle screws and rod fixation. During testing intervertebral displacement at the adjacent level (L5-S1) was recorded continuously via extensometry. Results: Axial compression and superior-inferior displacement were lower in the adjacent segment (L5-S1) than anterior-posterior displacement following rigid fixation. Statistical analysis showed that there was a numerical difference and a significant change between the intact spine and the adjacent segment in the axial compression and extension positions (p<0.027). The intact spines demonstrated the maximum displacement and the difference in extension positions were significant (p<0.015). Conclusion: Rigid fixation of the lumbar spine altered the range of motion at the adjacent segment level. As such, abnormal stress on the adjacent segment causes spinal instability, which may subsequently cause facet joint degen...

Experimental Study on Spine Segment Fixation Technique

“…The results of this study differ from the results of other scientists [12], [18] in extension testing. Karakaşlı study obtained maximum displacement results for a healthy sheep spine comparing with a reinforced rigid decreased 1.4 mm during extension trials; ≤0,5 mm in flexion tests.…”

“…For fixing the spine segment in testing machine the holders were specially designed and manufactured. Bending simulation methodology has been drawn up in accordance with Karakasli study description [18]. Research metrics present flexion moments exerted on the spine range between 3 Nm and 12 Nm [12,18].…”

“…Bending simulation methodology has been drawn up in accordance with Karakasli study description [18]. Research metrics present flexion moments exerted on the spine range between 3 Nm and 12 Nm [12,18]. Since current study aims to keep the spine intact during the test, the upper holder was adapted to create a bending moment of 2.4 Nm close to the minimal limit of mentioned range of 3 Nm.…”

“…Research works of Büsscher [11] and Sheng [10] have confirmed that the porcine lumbar spinal sample compared with other animal samples are superior as an analogue for PMHS spines. The studies used to test objects are cadaveric [12][13][14][15][16] or animal [17,18].…”

Are pedicular screws and lateral hook screws more resistant against pullout than conventional spinal hooks and screws in terminal vertebral segment fixation?

“…[1][2][3][4][5][6] The incidence of distal construct failure ranges from 3% to 50%, based on previous clinical studies. [7,8] The mechanical and material properties of implants are important factors in determining the strength of the fixation and the biomechanical properties of bone-instrumentation interface.…”