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|Year : 2021 | Volume
| Issue : 3 | Page : 780-781
Biomechanical Factors Influencing Fixation Angle in Occipitocervical Fusion
Sachin Anil Borkar, Ravi Sharma
Additional Professor, Department of Neurosurgery, 720, CNC, All India Institute of Medical Sciences, New Delhi, India
|Date of Submission||21-Mar-2021|
|Date of Decision||21-Mar-2021|
|Date of Acceptance||21-Mar-2021|
|Date of Web Publication||24-Jun-2021|
Dr. Sachin Anil Borkar
Department of Neurosurgery, 720, CNC, All India Institute of Medical Sciences, New Delhi - 110029
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Borkar SA, Sharma R. Biomechanical Factors Influencing Fixation Angle in Occipitocervical Fusion. Neurol India 2021;69:780-1
There is a growing body of literature on OCF, which suggests that inadequate postoperative occipitocervical angles leading to restriction of neck movements, dysphagia and dyspnea severely affects the functional outcome following OCF.,,,, Matsunaga et al. reported the utility of occipitoaxial angle (O-C2A: the angle formed by the McGregor line and the inferior endplate of the C2 vertebra) after fusion. They suggested that a decrease from preoperative value causes stenosis of the oropharyngeal airway leading to dysphagia and dyspnea. Apart from the functional discomfort of the patients, various authors have proposed the impact of such improper postoperative occipitocervical angles on alignment of the subaxial cervical spine and subsequent degenerative changes that follow. Hence, to prevent all these complications it is important to perform OCF without causing any biomechanical malalignment. O2CA has been widely used by spine surgeons because of its simplicity but intraoperative adjustment of the O2CA curvature despite the advent of contoured rods still remains a challenge and is significantly influenced by the availability of quality fluoroscopy. Also, many centres in the world are still using conventional contouring templates which explains the need to popularise such preoperative biomechanical evaluation. ,,,
Nagashima et al. suggested using an alternative biomechanical measurement as assessment of conventional OC2A is difficult due to soft tissue shadows on fluoroscopy. They defined the angle (OC-Ax) between the line running to the inferior border of the occipital bone up to external occipital protuberance (Oc line), and the posterior longitudinal line of the C2 vertebra, (Ax line). They validated that this method allows equally precise evaluation of craniocervical angle compared to the conventional OC2A measurement described by Matsunaga et al.
Posterior occipito-cervical angle (POCA) was initially described by Riel et al. and was expected to aid in the designing and testing pre-contouring of fusion implants. They have also highlighted in their study that higher POCA is associated with higher revision rates and greater postoperative respiratory compromise. Apart from the conventional OC2A measurement, the authors have additionally utilised POCA for calculating the amount of bend needed for the rod for OCF.
Li et al., in the current study, have reported their experience using the composite operative strategy for achieving proper occipitocervical fixation angle in 22 patients undergoing posterior instrumented occipitocervical fusion (OCF). The authors have concluded from their retrospective analysis that the ABAC (Adjust/Bending/Adjust/Confirm) strategy is a replicable and simple way to maintain appropriate fixation angle in occipitocervical fusion. This is probably the first study that has used the combination of OC2A and POCA in the same study population for calculating occipitocervical neutral position. The correlation between OC2A and POCA is also important as Tang et al. have reported a negative correlation between OC2A and POCA and provided an evidence that interplay between these two helps to maintain biomechanical balance at occipitocervical junction. This correlation between OC2A and POCA could be the subject of another study.
The authors have provided useful data for a composite strategy to manage biomechanics in OCF which provides good neurological and functional outcome. This strategy will have to be validated at various spine centres across the world before its widespread acceptance. This study shall form the basis for larger multicenter prospective studies which will help to better understand biomechanics at the occipitocervical junction post -OCF.
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Matsunaga S, Onishi T, Sakou T. Significance of occipitoaxial angle in subaxial lesion after occipitocervical fusion. Spine 2001;26:161-5.
Nagashima S, Nagae M, Arai Y, Tonomura H, Takatori R et al
. A new method of measuring the occipitocervical angle that could be applied as an intraoperative indicator during occipitocervical fusion. Clin Spine Surg 2017;30:E981-7.
Riel RU, Lee MC, Kirkpatrick JS. Measurement of a posterior occipitocervical fusion angle. J Spinal Disord Tech 2010;23:27-9.
Tang C, Li GZ, Liao YH, et al
. Importance of the occipitoaxial angle and posterior occipitocervical angle in occipitocervical fusion. Orthop Surg 2019;11:1054–63.