Objectives
The aim of the proposed study is to examine whether ACDA is preferred over ACDF in terms of cost-effectiveness from a healthcare and societal perspective, in patients with single- or multi-level symptomatic CDDD. Secondary objectives include differences in clinical and radiological outcomes between the two techniques, as well as the qualitative process surrounding anterior decompression surgery.
Study design
This is a prospective, single-blinded, randomized controlled trial. Patients will be randomized in a computer-generated 1:1 ratio to ensure equal division among both groups. One study arm receives ACDA (intervention group), and the other receives ACDF (control group). Group allocation will be performed per patient, not per level, meaning that no hybrid constructs will be used in this study. Figure 1 depicts the flowchart of the study process. Data will be collected at baseline, and at six-month intervals until four years post-surgery. A follow-up period of four years was chosen to encompass the expected incidence of 1.6–4.2% of additional CASP-related surgeries of per year, with a peak incidence in the first 2.5 years16. It is reasonable to expect that most CASP events will occur within this follow-up period, and that we will be able to gather reliable cost-data of patients and informal caregivers (ICGs). The patients will be blinded to their received treatment for the first year after surgery to obtain more reliable patient-reported outcome measures (PROMs).
Ethical principles and funding
This research will be conducted according to principles enshrined in the Declaration of Helsinki (3th edition 2013) and in accordance with the Medical Research Involving Human Subjects Act (WMO). The study protocol has been approved by the Medical Ethical Committee of the Zuyderland Medical Center, Heerlen (document nr: METCZ20200025, NL72534.096.20). Written informed consent will be obtained from all patients included in the study. To protect the privacy of all participants, all collected data will be encoded. Data collection will be carried out using the data management module from the research manager at Zuyderland. This application for detailed custom-made electronic data collection meets all guidelines of Good Clinical Practice (GCP). Trial auditing is incorporated in this system. Handling of personal data will comply with the General Data Protection Regulation (GDPR) (in Dutch: Algemene Verorderning Gegevensbescherming (AVG)). All patients are insured for participation in this trial and the possible consequences.
Monitoring will be performed by trained and qualified monitors from an external party, remotely and on site (Clinical Trial Centre Maastricht). All (serious) adverse events will be recorded.
In-kind support is provided by B. Braun Aesculap in the form of reduced cost for the implants. They have no influence on any aspect of conception/writing of the protocol, selection of subjects, data acquisition or data analysis, or any step in the writing or publication process of articles concerning this study.
Participants and Recruitment
Patients will be enrolled in the Department of Neurosurgery, Zuyderland Medical Center, Heerlen, the Netherlands. All adult patients indicated for single- or multi-level surgery for radiculopathy and/or myelopathy due to CDDD are eligible to be included in the study.
If patients choose not to participate in the study, the standard treatment will be offered. If patients agree to be included in the study, they will fill in the informed consent form. ICGs will also be asked to participate, to enable a broad societal evaluation of costs. Patients can leave the study at any time for any reason without consequences. The investigator can decide to withdraw a patient from the study for urgent medical reasons. Since the sample size accounts for a 10% loss over follow-up, patients will not be replaced after withdrawal.
Inclusion criteria
In order to be eligible to participate in this study, a patient must meet all of the following criteria:
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- Indication for anterior cervical decompression surgery.
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- Single- or multi-level CDDD between C3 and C7.
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- Symptoms of myelopathy, radiculopathy, or myeloradiculopathy.
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- In the case of pure radiculopathy: refractory to at least 6 weeks of conservative therapy.
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- In the case of myelopathy, it must be symptomatic.
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- Patients ≥ 18 years of age.
Exclusion criteria
Patients who meet any of the following criteria will be excluded from participation in this study:
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- Indication for (additional) posterior surgical approach.
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- Indication for additional stabilization of the pathological segment by a plate.
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- Previous ventral surgery of the cervical spine.
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- Traumatic origin of the compression.
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- Previous radiotherapy of the cervical spine.
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- Metabolic bone disease.
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- Inflammatory spinal disease: e.g., Bechterew’s disease, Forestier’s disease.
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- Infection of the cervical spine.
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- Unable to fill out Dutch questionnaires.
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- Informed consent not possible.
Interventions
One of two surgical procedures will be performed on patients participating in this study; ACDA (intervention group) and ACDF (control group). In both techniques, the disc space contents are resected through a right- or left-sided anterior surgical approach. The endplates are prepared with curettes and the disc space contents are removed. The posterior longitudinal ligament is opened, and the dura is visualized to ensure adequate decompression. In the ACDF group, a cage is implanted; in the ACDA group, a disc prosthesis is implanted after the discectomy. This is done in accordance with the manufacturer’s protocol for implantation and endplate preparation. In both groups, the wound is closed in layers, after a prevertebral wound drain is placed. Potential surgical risks are similar between the cage (ACDF) and the arthroplasty group (ACDA)38,61.
Post-surgical care is the same for both groups. Patients receive 24 hours of antibiotic prophylaxis, and after 24 hours the prevertebral wound drain is removed. Patients can use analgesics post-operatively, and they are allowed to mobilize immediately. The day after surgery, a physical therapist provides patients with standardized exercises. Patients are not routinely referred to a physical therapist, and no neck collar is used. Most patients are discharged home one or two days after the surgery.
Outcome measures
All outcomes will be measured at baseline, and at six-month intervals until four years post-surgery.
Primary Outcome
The primary outcome is cost-effectiveness and cost-utility of ACDA compared to ACDF from a societal perspective, in patients with single- or multi-level CDDD and symptoms of radiculopathy and/or myelopathy. The economic evaluation will involve a combination of a cost-effectiveness analysis (CEA) and cost-utility analysis (CUA) from a societal perspective. In the CUA, the effects are presented as quality-adjusted life years (QALYs), based on the EuroQol 5 dimensions 5 levels (EQ-5D-5L)62 utility scores63. The Incremental Cost-Effectiveness Ratio (ICER) will be expressed as the incremental costs per QALY. This economic evaluation will be conducted according to the Dutch Guidelines of the National Health Care Institute64–66. The following validated cost questionnaires will be used: Productivity Cost Questionnaire (iPCQ)67and the Medical Consumption Questionnaire (iMCQ)67. These questionnaires allow a broad measurement of societal costs, including medical consumption, and both paid and unpaid loss of productivity for patients. ICG’s will be asked to fill out the Limited Valuation of Informal Care Questionnaire (iVICQ)68, which consists of the Care-related Quality of Life instrument (CarerQol-7D) and the Self-Rated Burden scale (SRB). This measures the (subjective) burden for ICG and the assessment of caregiving in terms of wellbeing.
Secondary outcomes
Secondary outcomes will consist of both clinical and radiological outcome measurements. Per-operative parameters such as intraoperative complications, operative time, size of the implant and blood loss will be evaluated.
Clinical outcomes will be assessed according to the rate of CASP and associated additional surgeries, combined with patient reported outcome measures (PROMs). The included PROMs are; the Neck Disability Index (NDI)69, Visual Analogue Scale (VAS)70 for neck and arm pain, Hospital Anxiety Depression Scale (HADS)71, and the modified Japanese Orthopedic Association score (mJOA)72 for myelopathy patients.
Radiological outcomes will be assessed at three time points; pre-operatively, directly post-operative and one-year post-operative. Pre-operative imaging will assess baseline degeneration according to the Kellgren-Lawrence Score (KS)73, cervical sagittal alignment and baseline disc height. Moreover, a full sagittal spine X-ray will be taken to assess pre-operative global balance according to the odontoid-hip axis (OD-HA)74. A standard cervical spine X-ray will be taken at the immediate post-operative period (before discharge) to assess the position of the implant, subsidence and cervical sagittal alignment. Cervical spine X-rays will be taken again one-year post-surgery. A standard cervical spine X-ray will be taken to assess fusion, cage subsidence, adjacent segment degeneration (KS), adjacent segment disc height and alignment. A flexion and extension X-ray will be taken to assess movement. Radiological cage subsidence will be defined as > 3mm decrease of interbody height compared to the direct post-operative X-ray75,76.
Moreover, a process evaluation will be performed to determine the underlying values, needs, impacts and preferences of people with CDDD. The focus will be on the experiences and opinions of patients, caregivers, and professionals concerning the process surrounding ACDA and ACDF. A process evaluation might also identify gaps or limitations in the published research with regards to important outcomes to those with lived experience. A qualitative analysis will be performed according to the framework provided by Saunders et al77.
Power considerations
The primary outcome of the proposed study is cost-effectiveness. No difference in QALYs is expected between the intervention and control group based on previous literature41.
The only expected difference in clinical effectivity is the additional adjacent segment surgery rate, with an average of 1.0% versus 2.2% [Table 1]. Although small, a difference in additional surgery rates is evidently present in all trials, increasing exponentially over the years. We believe that the small inter-group difference may result in a cost-effective intervention, mainly because we expect most of the difference in costs to arise from episodes of secondary symptoms, which can lead to absenteeism, use of analgesic medication, use of (para)medical supplies and additional adjacent segment surgery.
Reported additional adjacent segment surgery rates for ACDA vary from 0–2.8% per year, with an average of 1.0% based on the largest FDA/IDE trials46,78. As for ACDF, yearly reported additional adjacent segment surgery rates range from 0–4.2%, with an average of 2.2%79,80.
The cost of a cervical disc prosthesis for ACDA is estimated to be around €2,000, while the cage for an ACDF costs €500, resulting in a difference of €1,500 per implant. On average, 1.2 implants are used per procedure.
Hospital admission costs and procedural costs are similar for both procedures, which is estimated to be €11,000 in our center. As reported by ArboNed for the year 2019, the average absenteeism for cervical disc pathology was 242 days, with a standard deviation of 225 [personal communication]81. The average cost for one day of absenteeism varies between €200–€400, depending on salary and company; for example, one day of absence from work is usually calculated to cost around €250 in the Netherlands [personal communication]81.
In the Netherlands, the willingness to pay (WTP) threshold for spinal pathologies – classified as a moderate disease – is set at €50,000/QALY65,66. However, in the sample size calculation we will not fix WTP at one value. The sample size calculation is based on both QALYs and costs, using Net Monetary Benefit (NMB) as outcome. The NMB for a treatment is defined as82:
$$NMB=WTP x Effect-Costs$$
The smallest relevant effect in terms of NMB will be quantified in terms of Cohen’s d, which is defined as:
$$d=\frac{average NMB \left(ACDF\right)- average NMB \left(\text{A}\text{C}\text{D}\text{A}\right)}{Standard deviation of NMB}$$
The standard classification of Cohen’s d consists of a small effect (d=0.2), a medium-sized effect (d=0.5) and a large effect (d=0.8)83.
A two-sided test will be used with a 5% level of significance (α = 0.05). A Cohen’s d of 0.4 which is often referred to as the hinge point, meaning a greater than average effect83. We expect a bit less than a medium sized effect, for which we choose a Cohen’s d in between 0.5 and 0.4, resulting in a Cohen’s d of 0.45. Inclusion of 79 patients per treatment group will then yield a power of 0.80. Taking into account a 20% loss-to follow-up in 4 years, the required sample size is 99 per group, with a total of 198 patients.
Statistical Analysis
All statistical procedures will be conducted based on both the intention-to-treat principle and on actual participation in treatment (i.e., effectiveness analyses), and will be performed using SPSS statistics 27.0 (SPSS, IBM, Corporation, Chicago, USA). A two-sided significance level of 0.05 will be used as a threshold to determine whether differences are statistically significant. Dichotomous outcome measures (e.g., reoperation rates, presence of fusion), and ordinal outcome measures (Odom’s outcome scale) will be analyzed using a χ2 analysis or Fisher's exact test. Continuous outcome measures (e.g., NDI, VAS, SF36) will be analyzed using an independent samples t-Test after testing for normality. If normality is not met, a Mann-Whitney U test will be used. Multi-level analyses will be performed with measurements within the subjects’ factor and group, and between subjects’ factors to account for the nested structure of the data. Post-hoc analyses will be performed if significant effects are identified.
Costs will be calculated by multiplying volumes (resource use) with unit costs. For the unit costs, we will use the Dutch costing guidelines. Productivity costs will be calculated by means of the friction cost method, based on a mean added value of the Dutch working population. Cost prices (2021) will be expressed in euros. If necessary, existing cost prices will be updated using the consumer price index.
Patient and public involvement
No patient involved.