椎骨關節間部應變量測：椎弓解離危險因子之探討

Abstract

目的：探討脊椎運動元接受大小相同的彎曲力矩時，受力姿勢對關節間部的影響，並推測造成椎弓解離的危險因子。 背景簡介：椎弓解離是一種好發於年輕運動員以及青少年脊椎的壓迫性骨折，病灶位於在同節椎骨的上、下小面關節之間，又稱為關節間部，以L5的發生機率最高。目前，對於形成椎弓解離的生物力學機制尚未明朗，但推測反覆式後仰、扭轉，以及前後向剪力會帶給關節間部極大的壓力，是造成此病的主要機械因子，然而支持此看法的力學證據仍十分缺乏，相關的力學研究並不多。 方法：從八個月大的幼豬頸椎，截取C3-C5, C6-T1等兩段雙脊椎運動單元為試樣，分別對每副試樣施加1.2J的前屈、後仰、側彎(左、右)、前屈合併側彎(左、右)，以及後仰合併側彎(左、右)等六種彎曲力矩。利用黏貼在中間椎骨左、右關節間部的單軸應變規，量測關節間部的應變量。將實驗數據以變異數分析（ANOVA）檢驗對關節間部影響最大的受力姿勢，歸納可能造成椎弓解離的危險因子。 結果：關節間部的應變量以後仰合併側彎時最高，其次為側彎、後仰、前屈、前屈合併側彎，以及正中姿勢。前三者之中的任何一個姿勢對關節間部造成的應變量，皆明顯大於後三者中的任一種。就異側關節間部而言，仍以後仰合併側彎時最大。當試樣側彎以及後仰合併側彎時，同側關節部的應變量與異側關節間部的差距，具有顯著意義。 結論：容易形成椎弓解離的受力姿勢有後仰、側彎以及後仰合併側彎。後仰合併側彎與側彎是之前較少被提出來探討的受力姿勢，當脊椎處於這兩種姿勢時，同側關節間部的應變量明顯大於異側，證明了這兩種姿勢是預防椎弓解離或阻止脊椎進一步滑脫時，需要列入參考的因素。在本實驗中，前屈、前屈合併側彎對脊椎關節間部造成的應變量不大，與文獻所述有所出入，需要再作進一步的探討。

Objectives：The purpose of the present study was to evaluate the effects of postures on the pars interarticularis when the specimens were applied with constant bending moment. The evaluation will be helpful in estimating the risk factors of spondylolysis. Summery of Background Data： Spondylolysis is defined as the stress fracture occurred on the pars interarticularis, commonly on L5. The exclusive prevalence is seen in adolescence and young athletes. It is mostly believed that the cyclic extension, rotation and unbalanced shear force are the main mechanical factors leading to the disease. However, the related biomechanical studies and supportive evidence are still sparse. Methods：Two motion segments (C3-C5, C6-T1) were dissected from the porcine cervical spines. Each specimen was loaded with bending moment of 1.2J under the postures of flexion, extension, neutral position, left /right lateral bending, and extension/ flexion combined with left/ right lateral bending, respectively. The strain gages attached to the bilateral pars interarticularis of middle vertebrae were used to measure the strain response in situ. ANOVA was used to exam the significantly effective postures and estimate the risk factors of spondylolysis. Results：The interarticular strain was greatest when specimens were under extension combined with lateral bending, followed by lateral bending, extension, flexion combined with lateral bending, flexion, and neutral position. Any one of the former three postures led to much greater interarticular strain than any one of the latter three postures. As for contralateral side, the greatest strain occurred when the specimens were under extension combined with lateral bending. The difference of ipsilateral and contralateral interarticular strain was significant when the specimens were under lateral bending and extension combined with lateral bending. Conclusion：Extension, lateral bending and extension combined with lateral bending appear to endanger the pars interarticularis. The latter two postures are less highlighted before; however, the present study proves they should be taken into considerations when it comes to the prevention and treatment of the spondylolysis. However, the present study is not sufficient enough to portrait the role of flexion and flexion combined with lateral bending in the etiology of the spondylolysis, so the further researches are necessary in the future.