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ORIGINAL ARTICLE
Year : 2022  |  Volume : 9  |  Issue : 2  |  Page : 94-100

Does harvesting cancellous bone destabilize cervical spine in cervical interbody fusion? A prospective clinicoradiological analysis


Department of Neurosurgery, Kovai Medical Center Hospital, Coimbatore, Tamil Nadu, India

Date of Submission19-Mar-2022
Date of Acceptance29-Mar-2022
Date of Web Publication31-May-2022

Correspondence Address:
J K B C Parthiban
Department of Neurosurgery, Kovai Medical Center Hospital, Coimbatore, Tamil Nadu
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/joss.joss_14_22

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  Abstract 


Background: To analyse the effect of graft harvesting from adjacent vertebral bodies in Anterior Cervical Discectomy and Fusion.
Objective: The objective of this study is to analyze the effect of harvesting bone graft from adjacent vertebral bodies on cervical spine stability, vertebral segment height, and cervical lordosis in single-level anterior cervical discectomy and fusion (ACDF).
Material and Methods: Thirty patients suffering from cervical radiculopathy and myelopathy were operated on using adjacent corticocancellous bone graft (ACBG) technique. In this technique, autologous cancellous bone is harvested from adjacent vertebral bodies and packed in the intervertebral body cage and the cavities in vertebral bodies are filled with tricalcium phosphate granules. Radiological studies with X-rays of the cervical spine were taken in lateral views preoperatively, immediate postoperatively, and during follow-up periods at intervals of 3-month duration, namely 3, 6, 9, 12 months, and at the end of 2 years postoperatively. Studies undertaken were – degree of fusion using modified Bridewell's formula, disc space settlement using Indigenous method, and vertebral segment height and lordotic angle using Cobb's angle.
Results: Satisfactory bony fusion was seen achieved in all patients at the end of 1 year. Although the settlement of disc space was appreciated, vertebral segment height remained increased at the end of 1 year. Cervical lordosis increased over a period of time during fusion process. The average preoperative Cobb's angle of 15.61° ± 1.81° improved to 20° ± 1.37°degrees at the end of 2 years postoperatively.
Conclusion: Harvesting bone from adjacent cervical vertebrae does not weaken spinal segment and the fear and skepticism that prevailed over the years are false. ACBG technique is a potential alternative to other existing techniques in ACDF.

Keywords: Adjacent bone graft, anterior cervical discectomy fusion, cervical lordosis, corticocancellous bone, disc space settlement


How to cite this article:
Parthiban J K, Ali S. Does harvesting cancellous bone destabilize cervical spine in cervical interbody fusion? A prospective clinicoradiological analysis. J Spinal Surg 2022;9:94-100

How to cite this URL:
Parthiban J K, Ali S. Does harvesting cancellous bone destabilize cervical spine in cervical interbody fusion? A prospective clinicoradiological analysis. J Spinal Surg [serial online] 2022 [cited 2022 Jul 7];9:94-100. Available from: http://www.jossworld.org/text.asp?2022/9/2/94/346354


  Introduction Top


Anterior cervical interbody fusion following discectomy is an accepted and standard technique in spinal surgery.[1] To augment fusion and prevent disc space settlement, titanium cages packed with bone grafts and bone substitutes in combination or in isolation are inserted using modified Smith-Robinson technique.[2],[3],[4] Autologous cancellous bone that has all three important properties, namely osteogenesis, osteoinduction, and osteoconduction are best available at iliac crest and this needs a separate incision which prolongs operative time and produces significant morbidity in the postoperative period.[5],[6],[7] To prevent donor site morbidity, bone chips obtained from osteophytes and synthetic bone substitutes such as tricalcium phosphate (TCP) granules are used for packing interbody cages.[8],[9] Poly Ethylene Ethylene Ketone cages filled with bone substitutes are other alternatives available. Ironically, abundant quantity of cancellous bone is available in adjacent vertebral bodies and if used for grafting can potentially avoid distant donor site morbidity. In this technique called adjacent corticocancellous bone graft (ACBG), the interbody cage is filled with cancellous bones harvested from adjacent vertebral bodies, along with chips of osteophytes and later, the cavities created are packed with TCP granules [Figure 1]a and [Figure 1]b.
Figure 1: (a) Illustration showing Cancellous bone harvesting from the vertebral body and packed in interbody titanium cage. (b) Illustration showing Tricalcium phosphate granules packed in the harvested cavity in the vertebral body completing the adjacent corticocancellous bone graft technique

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The viscoelastic nature of cancellous bone is vital for weight-bearing and the architecture of vertebral bodies is essential for maintaining cervical lordotic curve. Skepticism prevailed over the integrity of vertebral bodies following harvesting of bone plugs in the cervical spine. Even today surgeons are reluctant to use them fearing collapse, instability, and long-term unsatisfactory results. While the presence of good quality cancellous bones in neighborhood was not even ever thought of, few research works were undertaken in history about the impact of removal of bone plugs from cervical vertebral bodies. In 2012, Pitzen et al.[10] concluded from their laboratory studies that removal of a bone plug measuring 5 mm diameter and 5 mm length from the center of anterior vertebral bodies on either side of the fusion site with a cage did not weaken the mechanical strength of a functional spinal unit in the cervical spine. In 2017, Walterscheid et al.,[11] in another laboratory study performed using biomechanical grade polyurethane foam blocks as vertebral bodies concluded that harvesting bone from adjacent vertebral bodies did not produce significant clinical effects, hence claimed the technique as novel and was recommended in settings of osteopenia. During the same period, we presented the preliminary observational clinical case studies of adjacent bone grafts on the same subject at the Asia Pacific Cervical Spine Society meet in Seoul 2016 and the World Federation of Neurosurgical Societies Congress in Istanbul 2017. The present study provides a detailed analysis of vertebral body integrity, changes in cervical lordosis, and fusion and disc space settlement in 30 patients with 2-year postoperative follow-up.


  Materials and Methods Top


Thirty patients suffering from cervical radiculopathy and myelopathy operated using ACBG technique at the Department of Neurosurgery, Kovai Medical Center and Hospital, Coimbatore, India, with 2-year follow-up (till November 2020) at the time of the study were analyzed. Patients belonged to both sex, 22 males and eight females, and were between the age group of 20 and 75 years. Pregnant women, osteoporosis, previous cervical spine surgery, traumatic spine, bleeding diathesis, and small vertebrae were excluded from the study. Radiological studies with X-rays of the cervical spine in lateral views in flexion, extension, and neutral were taken at preoperative, immediate postoperative, and during follow-up periods at intervals of 3 months, namely 3, 6, 9, 12 months, and at the end of 2 years postoperatively. Lateral views of the cervical spine in neutral position were used for the assessment of the disc space height, degree of fusion (using modified Bridewell's formula), disc space settlement (with indigenous methodology), vertebral segment height (measurement between anterosuperior corner of the upper vertebral body and anteroinferior corner of the lower vertebral body), and lordotic angle (using Cobb's angle measurement). Using dynamic X-rays, stability and motion were analyzed at the fusion site and adjacent segments. Since the senior author had done earlier research with Allo-and Autografts in anterior cervical discectomy and fusion, the same parameters were used in the study on disc space settlement[12] [Figure 2]. Statistical analysis was done using Student paired t-test and analysis of variants study. Radiological fusion in X-rays and the absence of instability were taken as satisfactory bony fusion. All these patients were either clinically stable or improving at follow-up and there were no complications recorded in any one of these patients.
Figure 2: Line diagram showing methodology of measurement of disc space settlement and arbitrary settlement

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Adjacent corticocancellous bone graft surgical technique

Through conventional anterior approach following cervical discectomy, the end plates are prepared and an interbody cage is inserted in the disc space. Chips of anterior osteophytes and scraped end plates are preserved. A small corticectomy is done at the center of the anterior wall of neighboring vertebral bodies (around the distraction pin site) and cancellous bones is curated and packed in the titanium cage instantly [Figure 3]a and [Figure 3]b. Sufficient amount of cancellous bone is harvested from the adjacent vertebrae. Curettage is done sequentially, directed away from the fusion site cartilage on both vertebrae as required. Chips of osteophytes in addition if available are mixed and packed along with the cancellous bones in the cage. Finally, the cavities in the adjacent vertebrae are packed with TCP granules [Figure 3]c and [Figure 3]d. This technique is named ACBG. The anterior cervical wound is closed in layers. The patient is mobilized with a Philadelphia collar for 6 weeks and followed up regularly with lateral and Antero Posterior (AP) view X-rays at regular intervals of 3, 6, 9, 12 months, and 2 years postoperatively.
Figure 3: Intraoperative pictures showing the surgical steps of adjacent corticocancellous bone graft. (a) Cancellous bone curated from the adjacent vertebral body. (b) Cancellous bone is packed in the interbody titanium cage. (c) Harvested cavity seen on both adjacent vertebral bodies. The cage is seen packed with cancellous bone. (d) Tricalcium phosphate granules packed in harvest cavities completing adjacent corticocancellous bone graft technique

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  Results Top


The mean age of the study group was 49.76 years with 83.3% of patients above 40 years old. There was a male predominance with 66.6% over females with 33.4%. Clinically, most of these patients improved neurologically with satisfactory improvement in range of movement over a period of time. The average preoperative Cobb's angle was 15.61° ± 1.81° and that improved to 20° ± 1.37° at 2 years postoperatively. The graph shows significant increase in lordosis at immediate postoperative period, followed by a plateau and again increases subsequently after 3 months indicating improvement in functionality [Figure 4] The P of 0.189 was significant and implies that there was an attempt to maintain and improve biomechanical cervical lordosis [Figure 5]a, [Figure 5]b, [Figure 5]c, [Figure 5]d, [Figure 5]e, [Figure 5]f. The analysis of vertebral segment height done with paired t-test showed increase in segmental height in comparison to the preoperative state due to distraction that was maintained during the early period and subsequently reduced marginally without vertebral body collapse [Figure 6] and [Figure 7]a, [Figure 7]b, [Figure 7]c, [Figure 7]d. Marginal reduction (1 mm) in height of the anterior vertebral wall was observed in few cases but they were not significant enough to cause collapse. Close analysis of the dynamic lateral X-ray views did not elicit instability or subluxation at the operated segment during fusion process at the end of 3 months and later on during fusion process. The analysis of disc space settlement (P value 0.00) at 1 year and arbitrary settlement (P value 0.396) showed initial increase in disc space due to distraction of disc space by the placement of cages and subsequent settling with remodeling over 2 years [Figure 8]a and [Figure 8]b.
Figure 4: Graph showing progression of Cobb's angle of the cervical spine. Cobb's angle increase over a period of time during fusion process

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Figure 5: (a-f) Serial lateral view X-rays of the cervical spine showing the evolution of Cobb's angle. The Cobb's angle was seen improving during fusion process following adjacent corticocancellous bone graft and improved lordosis. (a - preoperative, b - immediate Postoperative, c - 3 months, d - 6 months, e - 1 year, and f - 2 years.). Furthermore, note the fusion process within the cage and between the vertebral bodies posteriorly. The tricalcium phosphate filled cavities can be appreciated

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Figure 6: Graph showing vertebral segment height increase due to distraction technique

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Figure 7: (a-d) Serial X-rays lateral view of C6/7 adjacent corticocancellous bone graft fusion technique showing vertebral segment heights at different periods. (a - preoperative, b - immediate postoperative, c - 1 year, and d - 2 years)

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Figure 8: (a) Graph showing the degree of settlement at fusion site at different periods. (b) Graph showing the progression of arbitrary settlement at the fused segment

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  Discussion Top


Tricortical corticocancellous bone harvested from the iliac crest is considered a gold standard in the anterior cervical interbody fusions. However, the major concern in iliac crest harvesting is postoperative morbidity and the need for another incision altogether. Hence, it is wiser to seek and harvest cancellous bone close to the operating site. Cervical vertebral bodies have abundance of cancellous bone within the thick cortical walls. This cancellous bone has all properties, namely osteoblastic, osteoinductive, and osteoconductive needed for good fusion. However, cervical vertebral bodies were not considered harvesting sites for fear of possible collapse of vertebral bodies and biomechanical instability that may follow through. Hence, even today surgeons are reluctant to attempt harvesting at the neighboring cervical bone. Literature does not yield any clinical studies on this subject except for few laboratory studies done by Pitzen et al.[10] and Walterscheid et al.[11] that mentioned harvesting limited bone from cervical vertebral bodies did not produce weakening of spinal segments. In spite of these valuable lab studies, no clinical studies were undertaken and reported so far.

While Pitzen et al. conducted their study by harvesting a bone plug measuring 5 mm long and 5 mm diameter at the center of the vertebral body; we instead performed corticectomy at the center and curetted sufficient cancellous bone from the center of the vertebral body. The aim of curettage away from the fusion site was to preserve cancellous bones near fusion cartilage and preserve cortical ring that holds the cage and prevents subsidence. Although both techniques were similar, we presume the quantity of cancellous bone removed was more in our technique. We did not measure the quantity of cancellous bones harvested. The cancellous stock varied from patient to patient and sufficient amount was obtained from one or both adjacent bones. We usually harvested bone from a good vertebral body first and avoided extensive curettage from a single body. Preoperative radiological assessment of the cervical spine was very useful in making decisions.

In our earlier cases, we left the vertebral body cavity vacant[13] and we noticed reduction of height of the anterior vertebral wall by few millimeters in follow-up X-rays. We also observed radiolucency at the harvested site and insignificant pincer collapse at the anterior wall in these clinically normal patients. Although this radiological finding was not associated with any clinical changes, we subsequently modified our technique and filled the harvesting site (cavity) with TCP granules in all cases. Subsequent to that even the marginal height reduction was not observed thus concluding that the packed TCP granules act like a scaffold and prevented height reduction.

The placement of titanium cages in the disc space not only increases the disc space but also increases the segmental height. That apart by distraction at anterior intervertebral space, the lordotic angle improves from its preoperative status. Interbody cages act like scaffolds by holding the vertebral bodies distracted during fusion process, maintain the segmental height, and biomechanically acceptable lordosis of the cervical spine. Although settlement during fusion process is natural and quicker during the first 3 months, it does continue to 1 year during remodeling of the fusion segment. In spite of settlement and remodeling, the vertebral segment height was seen higher than its preoperative status at the end of 1 year in our series. Interbody cages also improve fusion rate while preventing settlement. The combination of corticocancellous bone in the cage and TCP in the vertebral cavity in ACBG technique has shown enhanced fusion rate in our series.

In recent years, anterior cervical plates are recommended along with cages to prevent collapse of grafts, spinal segments, and to maintain cervical lordosis citing biomechanical principles. In this present study with ACBG technique at single level, cervical lordosis has in fact increased over a period of time during fusion, signifying maintenance of biomechanics, and improved range of movement [Figure 9]a and [Figure 9]b. Anterior plates for multilevel fusions certainly hold the cervical spine in good lordotic position during fusion and score over stand-alone cage fusions. However, the clinical utility of anterior plates for single-level fusions over stand-alone cage fusion is debatable.
Figure 9: (a and b) Dynamic X-rays showing a good fusion with improved lordosis and range of movement in a patient with C4-C5 adjacent corticocancellous bone graft after 1 year

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Resection of bone from vertebral bodies is always considered serious. This was more specific in the lumbar spine when compared to the cervical spine. However, laboratory studies disproved those concerns particularly when small quantity of bones was harvested from the cervical spine. Many surgical procedures without instrumentations such as anterior cervical discectomy without fusion,[14],[15] transcorporeal cervical foraminotomy,[16] anterolateral functional discectomy,[17] and oblique corpectomy[18] are reported without much disturbance to the biomechanics of the spine. This further substantiates the fact that minimal resection of the bone does not produce notable clinical worsening. When compared to the abovesaid techniques, ACBG technique stands far superior in terms of biomechanical sense by reconstructing the excavated vertebral body with TCP.

There are few limitations in this technique worth discussing. Harvesting in weak and thin cancellous matrix from osteoporotic bones may lead to collapse. Moreover, subsidence has been noted when titanium cages were used in osteoporotic patients in our earlier cases. Hence, we do not recommend ACBG technique in a setting of osteoporosis at present although subsidence and collapse may be of radiological interest in many asymptomatic patients. This study is also limited with noninclusion of computed tomography scan for assessing bony fusion as an additional parameter. However, X-rays were sufficient to assess vertebral heights, Cobb's angle, and instability required for the study.

Our experience with two-level fusions is limited and yet to be analyzed. Harvesting and sharing of cancellous bone from three vertebrae for two-level fusion are satisfactory although it may need additional cortical chips from neighboring osteophytes or TCP granules. Mixing the osteoblast-rich cancellous bone and TCP is a great combination altogether. More than two-level fusions need to be considered carefully and hence at present, we recommend ACBG for one-level stand-alone fusion.


  Conclusion Top


Our clinical study has eliminated the fear and skepticism that prevailed over the years that harvesting bone plugs from cervical vertebrae may lead to weakening and biomechanical instability in spinal segments in clinical practice.

ACBG in anterior cervical interbody fusion is a potential alternative to the existing surgical techniques in practice for single-level stand-alone fusion. This technique obviates the need for a second site for harvesting grafts and its side effects. It is safe, less time-consuming, straightforward, easily learned, and does not require special instruments. The abundant cancellous bone from vertebral bodies adjacent to the fusion site can be effectively used without compromising cervical spine stability.

Acknowledgment

We profoundly thank Dr. Woralux Phusoongnern MD., FRCNST, Neurosurgery division, Chiangmai Neurological hospital, Chiangmai, Thailand, for having provided the illustrations depicting the ACBG technique with precision and class.

We also thank Prof. Harmendra Kumar Dangi, Ph.D., Associate professor, the Department of Commerce, Delhi School of Economics, Delhi, for having done the statistical analysis meticulously and providing valuable results.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

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Bosacco DN, Berman AT, Levenberg RJ, Bosacco SJ. Surgical results in anterior cervical discectomy and fusion using a countersunk interlocking autogenous iliac bone graft. Orthopedics 1992;15:923-5.  Back to cited text no. 4
    
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Parthiban JK, Singhania BK, Ramani PS. A radiological evaluation of allografts (ethylene oxide sterilized cadaver bone) and autografts in anterior cervical fusion. Neurol India 2002;50:17-22.  Back to cited text no. 12
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Noordhoek I, Koning MT, Vleggeert-Lankamp CL. Evaluation of bony fusion after anterior cervical discectomy: A systematic literature review. Eur Spine J 2019;28:386-99.  Back to cited text no. 15
    
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  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9]



 

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