Abstract
Background
Previous research on spinal alignment and postoperative outcomes after cervical and upper thoracic fixation has suggested that clinical and patient-reported outcomes are improved when certain anatomical parameters are maintained. These parameters include the cervical sagittal vertical axis (cSVA), C2 and T1 slopes, and cervical lordosis (CL). For patients with primary and metastatic tumors involving the subaxial cervical and/or upper thoracic spine, there is minimal guidance on how to apply these parameters. Surgeons must make critical decisions when designing the optimal construct, considering patient life expectancy, bone quality, oncology goals and deformity. This study aims to evaluate the impact of cervical spine alignment parameters on postoperative hardware failure in spine tumor patients and highlight instances of complications in patients with instrumentation crossing the cervicothoracic junction (CTJ).
Methods
A retrospective review of a single institutional spine tumor database identified seventeen patients who underwent spinal fusion crossing the CTJ from 2015 to 2023. All patients had postoperative neutral standing radiographs with measurable cSVA, C2 and T1 slopes, and/or CL. The primary endpoint was instrumentation failure, defined as hardware pull out or breakage, and secondary endpoints included other complications including wound infection and spinal fluid leak.
Results
The number of instrumented levels ranged from 3 to 15 segments with a mean of 7.47. Surgical approaches included anterior (n=3), posterior (n=12), and simultaneous anterior and posterior (n=2). The mean cSVA was 3.39±1.02 cm (range 1.59–4.9 cm). Fourteen patients had measurable C2 slopes with a mean of 25.03±9.16° (range 8.7 - 38.6°). Ten patients had measurable T1 slopes with a mean of 31.5±11.54° (range 18.4–59.6°). Thirteen patients had a measurable CL with a mean of 9.13±9.93° (range 0–37.5°). No cases of instrumentation failure were noted. Four patients experienced other postoperative complications (24%), but rates did not vary with increasing deviation from ideal parameters for cSVA, C2 and T1 slope, or CL.
Conclusions
Although there was wide variability in alignment parameters in this cohort, there were no instances of hardware failure with crossing the CTJ at a mean follow-up of 41 months. The overall complication rate was high at 24%. Despite common concerns about the impact of exaggerated slope and SVA on instrumentation failure these results suggest that cervical and upper thoracic tumor patients may still have a satisfactory result following CTJ fixation, even with unfavorable alignment parameters. Larger prospective studies are needed.
Keywords: Cervical sagittal vertical axis, Cervical lordosis, Alignment, Spine tumor, Cervicothoracic junction, T1 slope
Background
The need for cervical spine surgery is projected to increase drastically over the next 15 years [1], and the frequency with which cervical spine surgeries are performed has led to increasing research on improving postoperative patient outcomes. Moreover, maintaining cervical sagittal alignment and balanced curvature has historically been more of an art than a science, with many spine surgeons using personal experience, patient characteristics and historical outcomes to guide surgical decision-making [2]. These factors have led to the exploration of ideal cervical spine parameters, such as the cervical sagittal vertical axis (cSVA), C2 and T1 slopes, and cervical lordosis (CL), and their impacts on postoperative results.
Research on obtaining and interpreting cervical spine parameters is still ongoing, and there does not yet seem to be a consensus on what these parameters truly signify. For example, no standardized method exists for measuring cervical sagittal balance, and retrospective research into this topic is complicated as neutral standing radiographs are needed to measure true alignment [3]. Patient compliance during radiograph acquisition as well as neck pain limiting range of motion can limit the utility of these images. However, some evidence from cervical spine alignment research has been integrated into clinical decision-making to optimize patient outcomes. In general, it seems that the quality of postoperative outcomes decreases with increasing deviation of cervical spine alignment parameters from an ideal value, though ideal values vary based on study design and population [2,3]. This is further complicated by the fact that the cervical spine has the greatest variation in physiological curvature of the entire spine [4]. A 2021 meta-analysis of cervical spine alignment parameters suggested the following physiologic parameters for a healthy, asymptomatic cohort: cSVA 1.87±0.176 cm and T1 slope 24.5±0.98° [2]. In a 2020 study developing a predictive formula of cervical spine parameters in an asymptomatic cohort, the following physiological parameters were obtained: C2-C7 SVA 1.46±0.82 cm; T1 slope 25.84±5.36°; CL 17.11±6.31° [5].
One indication to undergo spinal surgery is the presence of a primary or metastatic neoplasm. Tumor resection in the cervical spine is challenging due to the high risk of neurological injury with manipulation of the cervical cord and nerve roots as well as the proximity of local structures such as the vertebral and carotid arteries [1]. For these reasons, facet and pedicle resection is often required to obtain an adequate surgical corridor, which increases the risk of deformity and instability that is best corrected via fusion.
A major consideration in cervical spine fusion is extending the instrumented construct across the cervicothoracic junction (CTJ). The physiological progression from cervical spine lordosis to thoracic spine kyphosis creates increased biomechanical stress at the CTJ in a normal spine, and the mobility of the cervical spine makes it especially prone to deformity [6]. A construct ending just before the CTJ, at C7, is thought to be biomechanically unfavorable due to increased motion, which can result in degeneration of adjacent spinal levels and increased risk of construct failure and subsequent revision surgery [7]. Crossing the CTJ, thus ending a fusion at T1, has been associated with lower revision rates, which are thought to be due to avoidance of adjacent segment disease by improving distribution of force across the C7-T1 disk [8]. Although constructs crossing the CTJ are associated with lower rates of revision than constructs terminating at C7, it should be noted that there is little research to suggest that constructs terminating below T1 are superior to those terminating below T1 in regard to revision rates [9]. This suggests that crossing the CTJ but ending the construct at T1 is likely sufficient to mitigate biomechanical strain.
The risk of cervical spine deformity is increased when dealing with structurally compromised vertebrae, which is often the case in patients with spinal tumors. Bone quality in these patients is often suboptimal due to the lesion itself or the administration of neoadjuvant radiation and chemotherapy [10]. For these reasons, surgeons must think through the likelihood of future deformity when designing their surgical construct. Further, as patients survive longer with metastatic cancers, their cumulative risk of developing adjacent segment disease and other degenerative conditions increases.
Therefore, patient selection is critical to determine who will benefit from instrumentation crossing the CTJ. In a single institutional cohort, we examined the cSVA, C2 and T1 slopes, and CL for cervical spine tumor patients who received instrumentation spanning the C7-T1 levels. We also evaluated cases of common complications within this cohort to better determine how to optimize patient outcomes and avoid complications following cervical spine surgery.
Methods
We performed a narrative review of pertinent literature regarding tumors of the cervical spine, particularly those that cross the CTJ and their operative techniques and outcomes. Articles were identified in Pubmed using search terms including “cervicothoracic junction” or “cervical tumors” or “cervical spine sagittal alignment”.
Cases of primary and metastatic tumors resected at the authors’ institution between 2015 and 2022 were retrospectively identified using our local database. Patients with primary or metastatic spine tumor, undergoing surgery with instrumentation involving C7-T1, over the age of 18, with at least 6 months of follow up were included. Retrospective review of electronic medical records with waiver of informed consent was approved by the local Institutional Review Board.
Cervical alignment parameters were measured from standing neutral radiographs. Preoperative radiographs were not available for most patients due to variability in provider preference. Postoperative radiographs were available for all but 4 patients otherwise meeting inclusion criteria, yielding a final patient cohort of n=17. The C2 slope was defined as the angle between the inferior C2 endplate and the horizontal plane. The T1 slope was defined as the angle subtended from the superior endplate of T1 and a horizontal reference line. The cSVA was measured as the horizontal distance between the posterosuperior corner of the C7 vertebral body and a plumb line drawn from the centroid of C2, as previously described by Martini et al. [11] CL was measured by drawing tangent lines for the superior aspect of C2 and the inferior aspect of C7, and then drawing orthogonal lines through each tangent line. CL was defined as the angle of intersection of the orthogonal lines. These measurements are shown on a sample patient in Fig. 1.
Fig. 1.
Demonstration of cervical alignment parameters C2 slope (purple, 21.8°), T1 slope (green, 47.4°), cSVA (yellow, 3.31 cm, white line represents plumb line), and CL (blue, 17.3°).
Results
Seventeen cases of CTJ instrumentation after tumor resection were identified at the authors institution between the 2015 and 2022. Demographic and construct data is provided in Table 1. Ten patients presented with metastatic disease, and 7 with primary tumors. The average age of the cohort was 60.6 years (range: 31–70 years) at time of operation. Despite the variation of size of construct, approach, materials, devices, and instrumentation, (Table 2) no construct failure was seen in any patient for an average follow up of 45 months (range: 9–98 months). The average Eastern Cooperative Oncology Group (ECOG) score, which measures a patient's functioning in terms of their daily living abilities, with 0 being fully active and 5 being deceased, was 0.65 (range: 0–2).
Table 1.
Patient demographics.
| Case No. | Age (yrs), Sex | Tumor Type | Tumor Levels |
|---|---|---|---|
| 1 | 53, F | Breast (metastasis) | C7–T1 |
| 2 | 63, M | Schwannoma (primary) | C6–7 |
| 3 | 72, F | Schwannoma (primary) | C5–7 |
| 4 | 31, M | Schwannoma (primary) | C4–6 |
| 5 | 63, M | Oropharyngeal (metastasis) | C5–7 |
| 6 | 75, F | Schwannoma (primary) | C6–7 |
| 7 | 57, F | Myeloma (metastasis) | C5–7 |
| 8 | 56, F | Cholangiocarcinoma (metastasis) | T1 |
| 9 | 67, M | Chondrosarcoma (primary) | C6–7 |
| 10 | 67, M | Lung (metastasis) | T1–2 |
| 11 | 77, M | Thyroid (metastasis) | C6–7 |
| 12 | 69, F | Lung (metastasis) | C7 |
| 13 | 70, F | Myeloma (metastasis) | T1–2 |
| 14 | 31, M | Ependymoma (primary) | C4–7 |
| 15 | 69, F | Endometrial carcinoma (metastasis) | C1–3 |
| 16 | 64, M | Kidney (metastasis) | C7 |
| 17 | 47, F | Schwannoma (primary) | C6–T2 |
Table 2.
Surgical, reconstruction, and instrumentation details.
| Case no. | Levels instrumented | Surgical approach | Reconstruction devices/Materials | Instrumentation for fusion/fixation |
|---|---|---|---|---|
| 1 | C5-T3 | A/P | Morselized allograft, demineralized bone matrix, titanium expandable cage | Pedicle screws, vertebral body screws, bilateral single rods, plates, lateral mass screws |
| 2 | C3-T2 | Posterior | Morselized autograft, demineralized bone matrix | Pedicle screws, bilateral single rods, lateral mass screws |
| 3 | C3-T1 | Posterior | Morselized autograft, demineralized bone matrix | Pedicle screws, bilateral single rods, lateral mass screws |
| 4 | C2-T2 | Posterior | Morselized autograft, demineralized bone matrix | Pedicle screws, bilateral single rods, lateral mass screws, laminar screws |
| 5 | C2-T3 | A/P | Demineralized bone matrix | Pedicle screws, bilateral single rods |
| 6 | C3-T2 | Posterior | Demineralized bone matrix | Pedicle screws, bilateral single rods, lateral mass screws |
| 7 | C5-7 | Anterior | Demineralized bone matrix, expandable cage (unspecified material) | Plates, vertebral body screws |
| 8 | C7-T2 | Anterior | Morcelized allograft, demineralized bone matrix, titanium expandable cage | Vertebral body screws, plate |
| 9 | C3-T3 | A/P | Morselized autograft, autograft strut, demineralized bone matrix | Pedicle screws, unilateral rod, cross connectors, lateral mass screws |
| 10 | C2-T7 | Posterior | Demineralized bone matrix, chest tube (in corpectomy defect), polymethyl methacrylate | Pedicle screws, lateral mass screws, bilateral single rods, cross connectors |
| 11 | C2-T3 | Posterior | Morselized allograft, demineralized bone matrix, chest tube with polymethyl methacrylate | Bilateral single rods, lateral offset connectors, lateral mass screws |
| 12 | C3-T3 | Posterior | Morselized allograft | Pedicle screws, lateral mass screws, bilateral single rods |
| 13 | C2-T9 | Posterior | Demineralized bone matrix, allograft strut | Pedicle screws, laminar screws, lateral mass screws, bilateral single rods, cross connectors |
| 14 | C6-T1 | Posterior | None documented | Pedicle screws, lateral mass screws, plates |
| 15 | C1-T4 | Posterior | Demineralized bone matrix, allograft strut | Pedicle screws, lateral mass screws, bilateral single rods |
| 16 | C6-T1 | Anterior | Demineralized bone matrix, morselized allograft, expandable cage (unspecified material) | Plates, interbody cages/spacers, vertebral body screws |
| 17 | C3-T5 | Posterior | Morselized autograft, allograft strut, demineralized bone matrix | Pedicle screws, lateral mass screws, bilateral single rods |
The number of instrumented spinal levels ranged from 3 to 15 with a mean of 7.47. Surgical approaches included anterior (n=3), posterior (n=12), and simultaneous anterior and posterior (n=2). Postoperative sagittal parameters were measured for each patient. The mean cSVA was 3.39±1.02 cm (range 1.59–4.9 cm). Fourteen patients had measurable C2 slope with a mean of 25.03±9.16° (range 8.7–38.6°). Ten patients had measurable T1 slope with a mean of 31.5±11.54° (range 18.4–59.6°). Thirteen patients had a measurable CL with a mean of 9.13±9.93° (range 0–37.5°). Four patients experienced postoperative complications: 3 were wound infections, and one was a cerebral spinal fluid (CSF) leak, as shown in Table 3. All complications occurred within 1 month postoperatively, with all requiring a reoperation. There were no other reoperations.
Table 3.
Complications and outcomes.
| Case no. | Follow up (Mo) | Complication | Reoperation | ECOG score |
|---|---|---|---|---|
| 1 | 98 | None | No | 0 |
| 2 | 55 | None | No | 0 |
| 3 | 64 | None | No | 0 |
| 4 | 44 | None | No | 0 |
| 5 | 19 | None | No | 1 |
| 6 | 62 | None | No | 1 |
| 7 | 65 | None | No | 0 |
| 8 | 19 | None | No | 1 |
| 9 | 24 | None | No | 1 |
| 10 | 9 | Wound Infection | Yes | 1 |
| 11 | 75 | None | No | 1 |
| 12 | 15 | Wound Infection | Yes | 1 |
| 13 | 47 | None | No | 1 |
| 14 | 12 | Wound Infection | Yes | 2 |
| 15 | 46 | None | No | 0 |
| 16 | 32 | None | No | 0 |
| 17 | 22 | CSF Leak | No | 1 |
Cases
Patient 1. The patient was a 66-year-old female who presented with a T1 burst fracture secondary to an undiagnosed multiple myeloma. At the initial presentation she had bilateral hand pain with numbness and paresthesia. Nonsurgical intervention was initially recommended involving radiation, systemic chemotherapy, and a brace. Five months later she had improved pain and numbness but had persistent paresthesia as well as a T2 fracture and worsening kyphosis at the CTJ.
The patient underwent kyphosis correction with post position MEP and SSEP stability. Laminar screws were placed at C2, with bilateral lateral mass fixation at C3–6. T3-T9 pedicle screws were then placed. Bilateral tapered rods were used to complete the fixation from C2-T9, with an additional rod placed bilaterally with rod connectors. Post fusion the patient had decompressive laminectomies of C7, T1, and T2 bilaterally, the rostral aspect of T3, and the caudal aspect of C6 (Fig. 2). A fibular strut graft was then placed from C6-T3 to further reinforce the construct. Demineralized bone matrix was placed from C2-T9 bilaterally, completing the fusion. Plastic surgery performed wound closure involving musculocutaneous flap mobilization. Standing lateral radiographs taken 20 days postoperatively demonstrated a C2 slope of 31.8° (Fig. 2). Additional alignment parameters were not able to be measured due to the quality of the radiographs.
Fig. 2.
Preoperative MRI postoperative AP and lateral radiographs with and without alignment measurements demonstrating reconstruction for Patient 1. The postoperative C2 slope was measured as 31.8°. Tapered cervicothoracic rods can be seen with varying diameter along the rod length.
Patient 2. The patient was a 45-year-old female with breast carcinoma skeletal metastasis presenting with a complete collapse of the C7 vertebral body, pathological fracture spinous process fracture of C7, and complete involvement of the T1 vertebra. This was associated with interscapular pain and bilateral upper extremity numbness and paresthesia. Imaging also demonstrated spinal cord compression and instability as well as a lesion at T5. Positioning was optimized for an anterior left cervical approach, and the disk spaces at C6-C7, C7-C8, and T1-T2 were identified. The PLL was dissected to define normal anatomic markers and the tumor was resected. A cage filled with demineralized bone matrix was placed extending from C6-T2.
For the second stage, pedicle screws were placed at T2 and T3 bilaterally, and cervical lateral mass screws were placed at C6 and C7. A C7-T2 laminectomy was performed as well as medial facetectomy of C6-C7 and C7-T1 bilaterally. For instrumentation, rods were placed from C7-T2 and demineralized bone was packed from C5-T3 (Fig. 3). Standing lateral radiographs taken 5 days postoperatively demonstrated a C2 slope of 16.7° and an estimated T1 slope of 26.6° (Fig. 3). The C2 slope was estimated as the angle of the inferior aspect of the expandable cage from the horizontal. Additional alignment parameters were not able to be measured due to the quality of the radiographs.
Fig. 3.
Preoperative MRI and postoperative AP and lateral radiographs with and without alignment measurements demonstrating reconstruction for patient 2. Postoperative C2 slope was measured as 16.7°, and postoperative T1 slope was measured as 26.6°.
Discussion
Oncological resection and fixation across the CTJ pose significant challenges due to the mechanics of the subaxial cervical spine, the patient's baseline health characteristics, and the concern for progressive or worsening deformity in the setting of ongoing cancer. The increased likelihood of cervical spine stabilization and fusion after tumor resection coupled with oncological treatment related considerations, such as bone health and overall prognosis, make designing constructs for this patient population challenging.
In this cohort, the postoperative cSVA was 3.39 cm ± 1.02, greater than the recommended physiological range of less than 2 cm. Further, the T1 slope for the cohort was 31.5° ± 11.54°, greater than the physiological range of 25–30°. Despite the final postoperative alignment parameters being outside of recommended neutral or normal ranges, and the increased physiological stresses of adjuvant cancer treatments in many cases, there were no instances of hardware failure at a mean follow-up of 41 months. Although this cohort is small, this data suggests that selecting the proper construct can compensate for the physiological stress of cervical deformity when executed correctly. When faced with a patient with a tumor involving the lower cervical and/or upper thoracic spine, considerations for quality of life and extent of surgery must be weighed against the reality of likely future deformity. Specifically, a complex cervicothoracic deformity case may require prolonged anesthesia time, which may be associated with greater operative risk for a patient with advanced metastatic disease. However, stabilizing the CTJ limits the risk of catastrophic hardware failure and deformity, preventing neurological decline. The results of this cohort study suggest that patients with cervical or thoracic tumors are unlikely to experience hardware failure if the CTJ is incorporated into the construct, regardless of the postoperative alignment parameter measurements.
The potential for vertebral collapse and subsequent revision could be mitigated by percutaneous vertebroplasty, which provides stabilization for vertebral fractures and adjacent levels. However, this procedure is challenging in the cervical spine due to the small size of the vertebral bodies and the narrow canal diameter of the subaxial cervical spine, which increases the risk of neurological compromise in the event of cement extravasation [12]. As a result, percutaneous vertebroplasty is not frequently used in the cervical spine, and many surgeons resort to multilevel fixation crossing the CTJ to ensure construct stability and longevity. Crossing the CTJ offers the opportunity for thoracic spine instrumentation, which creates 2 potential mechanical advantages. First, the use of pedicle screws in the thoracic spine may offer greater construct rigidity and stability as compared to lateral mass screws, which is the most common technique in the cervical spine.[7] Although the use of cervical pedicle screw fixation is gaining popularity [13], this technique is less widely practiced, and some sources suggest that cervical pedicle screw fixation at the C7 level has the highest risk of pedicle breach [14,15]. The second potential mechanical advantage offered by CTJ crossing is that extension into the thoracic spine offers greater surface area for fusion, increasing the odds that solid fusion is achieved [7]. Multiple recent studies suggest that not only is crossing the CTJ associated with fewer instances of construct failure, adjacent segment degeneration, and revision, but patients with CTJ crossing had similar patient-reported outcome measures to patients without CTJ crossing [7,16,17]. Therefore, crossing the CTJ is currently considered best practice in patients with reduced bone quality, instability, or deformity at C7-T1 [7,18]. However, for patients at the end of life or with advanced cancer, minimizing surgical time and incision length may be preferred over building the most robust surgical construct. Risk of wound healing complications has been associated with more levels instrumented, invasiveness and longer surgical times.
Wound infections were the most common complication in this patient cohort. Previous studies have demonstrated T1 fusion in particular to be significantly associated with an increased risk of wound infection [19]. Multidisciplinary management is indicated for the oncology patient population to reduce this risk, with a focus on maximizing preoperative nutrition, postoperative prophylactic antibiotics, limiting or pausing chemo and immunotherapy infusions during the perioperative period, and the involvement of plastic surgery [[20], [21], [22], [23]]. The results of this study support ongoing research into reducing postoperative wound infections in the oncology population. The study also suggests that patients with lower cervical and/or thoracic tumors and longer constructs should be closely monitored for wound complications.
This study is limited by the small patient cohort size, as well as the limited follow-up. Results should be validated in larger prospective cohorts with standardized imaging. Further, the pathology– metastatic versus primary tumor – is heterogeneous within this sample, further complicating the generalizability of our results. The study was not powered to capture statistically significant differences, and rather can serve as the start of a discussion with patients about the projected risks and expectations or combined with other single-center cohort studies in future metanalyses. Alignment parameters are also generally applied to patients with longer life expectancy, so it is possible that the absence of instrumentation failure within this cohort is due to the shorter follow up time.
Conclusion
This retrospective cohort study reviews the outcomes for patients with cervical or thoracic tumors and instrumentation crossing the CTJ. No cases of hardware failure were noted in this cohort despite alignment parameters such as cSVA and T1 slope being outside of the recommended physiological ranges, and the rate of wound infection was 18% (3/17). This study was limited by heterogeneous patient population, as well as the limited follow-up time, but suggests that more research is needed into how to best apply cervical alignment parameters to patients with CTJ tumors.
Declaration of competing interest
One or more of the authors declare financial or professional relationships on ICMJE-NASSJ disclosure forms.
Footnotes
FDA device/drug status: Not applicable.
Author disclosures: CBS: Nothing to disclose. MJM: Nothing to disclose. RAS: Nothing to disclose. AAC: Nothing to disclose. OPL: Nothing to disclose. FS: Nothing to disclose. JQCQ: Nothing to disclose. AAO: Nothing to disclose. AET: Nothing to disclose. JSF: Nothing to disclose. ZLG: Stock Ownership: Lenoss Stock Options (Amount not disclosed), SmollTap Stock Option (Amount not disclosed); Trips/Travel: Proprio to attend Board Meetings (Amount not disclosed); Scientific Advisory Board/Other Office: Proprio-stock options belong to Lifespan (Amount not disclosed); Research Support (Investigator Salary, Staff/Materials)^: AO Spine North America (Amount not disclosed). PZS: Grants: NIH (D, Paid directly to institution/employer). TN: Nothing to disclose.
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