The Risk of Adjacent Segment Disease After Anterior Cervical Discectomy With Fusion for Cervical Degenerative Disc Disease

1. SUMMARY Radiculopathy and/or myelopathy due to cervical degenerative disc disease are increasingly common pathologies in our ageing population. Both can be treated non-surgically or surgically. The most commonly used neurosurgical treatment is anterior cervical discectomy with or without fusion. The goal is to achieve neural decompression of the operated segment in both procedures. However, due to this fusion and reduced mobility of the cervical spine at the level of the intervention, adjacent segment disease may occur. This can lead to new symptoms like radiculopathy and/or myelopathy at an adjacent level which requires reoperation in about 2/3 of patients. Reoperations are burdensome for patients and have a socio-economic impact due to the costs of hospital admissions, operations, and secondary costs such as work-absenteeism. The primary objective of this retrospective study is to determine the occurrence of adjacent segment disease after a single- or multi-level anterior cervical discectomy with fusion procedure for radiculopathy and/or myelopathy in the investigators' centre and to compare this to the incidence in literature. The investigators also look at the risk of adjacent segment disease after different anterior surgical techniques, such as anterior cervical discectomy, anterior cervical discectomy with fusion and plating, and corpectomy. As a secondary outcome they aim to determine risk factors predicting the occurrence of adjacent segment disease.
2. INTRODUCTION AND RATIONALE Radiculopathy and myelopathy are pathologies which, amongst others, occur due to cervical disc herniation or spondylosis, also known as cervical degenerative disc disease (CDDD). Radiculopathy has been estimated to affect around 100 per 100.000 males and 60 per 100.000 females in the general population. The incidence of myelopathy is estimated to be 4 per 100.000 in the general population. The consequences of CDDD can be severe and can disable patients to an extent that it impairs working ability. Therefore, it leads to a significant socio-economic burden of disease.

Cervical radiculopathy is caused by compression of the cervical nerve roots as they exit the vertebral column through the neuroforamina. Patients present with radiating pain in the arm in the corresponding dermatome, weakness and/or sensory loss, with or without associated neck pain. Cervical myelopathy is caused by a central canal stenosis, which causes compression of the spinal cord itself. Damage to the central nervous system at this level can cause loss of coordination, motor, and sensory function of both arms and legs. Treatment for radiculopathy and/or myelopathy due to CDDD can be non-surgical or surgical. The majority of patients with radiculopathy respond well to non-surgical treatment options, such as physical therapy, a neck collar, analgesic or anti-inflammatory medication. Surgery can be considered in cases of insufficient relief with these non-surgical treatment options. The reported surgery rates range from 8% to 35%. When patients have mild myelopathy, which does not progress clinically, non-surgical treatment with frequent follow-up is an option, however, controversy exists. Others suggest surgical treatment with mild myelopathy, to prevent deterioration of symptoms. Surgery is recommended in patients with moderate and severe degenerative cervical myelopathy (DCM) or with rapid clinical deterioration.

Both anterior and posterior surgical techniques are used to treat radiculopathy and/or myelopathy. No clear consensus exists on which anterior technique is superior. Depending on country, centre and surgeon, different approaches are used, mostly based on experience. Anterior cervical discectomy with (ACDF) or without fusion (ACD) are the most commonly used interventions for CDDD since the compression is often located on the anterior side. Alternatives are corpectomy or ACDF with plating. In the investigators' centre ACDF is the procedure of choice in most patients with single- or multilevel CDDD and radiculopathy and/or myelopathy. ACD and ACDF both have good short-term clinical results. However, in the long-term patient satisfaction drops, which is probably for a large part due to adjacent segment disease (ASD). This occurs in approximately 25% of patients during 10 years follow-up and over 2/3 of these patients need additional surgery. ASD is thought to be a consequence of fusion of two or more vertebra which eliminates mobility at the level of the intervention. Adjacent levels compensate for this reduced mobility by increasing their mobility and thus increasing their risk at disc degeneration. This risk is not only determined by the biomechanical stress on the adjacent level caused by fusion. Changes in the anatomy at the adjacent level with the initial surgery and the natural course of the adjacent disc also plays a role.

Anterior cervical discectomy with arthroplasty (ACDA) was developed in an effort to reduce the incidence of ASD by preserving physiological motion in the operated segment. ACDA has been confirmed to ACDF for treatment of two-level CDDD, a significantly lower re-operation rate in the ACDA group compared to the ACDF group was found after two years (3.1% versus 11.4%, respectively). Re-operation rates for ACDA and ACDF after 7 years were compared. They reported reoperation rates of 3.7% for ACDA versus 13.6% for ACDF in single-level CDDD patients. The rate of reoperation was also significantly lower in the two-level ACDA group compared to ACDF, with rates of subsequent surgery at the index level of 4.4% versus 16.2% and rates of adjacent level surgery of 4.4% versus 11.3%, respectively. In a systematic review from 2017 multilevel ACDA was proven at least as safe and effective as ACDF, with preservation of cervical motion and potentially with fewer reoperations expected.

The goal of this study is to determine the risk of ASD after ACD(F) for radiculopathy and/or myelopathy in the study population, and to compare this to the rates reported in literature. The expectation is that the occurrence in the study population is similar to the occurrence in the general population.