Description of the condition

Cervical degenerative disc disease can cause axial pain, radicular pain, sensory loss or motor weakness due to neural compression, and headache (Grob 1998; Persson 1997; Polston 2007). Possible causes are a bulging or herniated intervertebral disc, foraminal narrowing due to loss of disc space height or osteophyte formation, or a combination of these. The majority of patients respond well to conservative treatment options, such as physical therapy, traction, use of a collar, analgesic or anti‐inflammatory medication (Kuijper 2009). With such a treatment regimen, up to 60% of patients are satisfied or very satisfied at six weeks (Kuijper 2009a); up to 83% of the patients who undergo conservative treatment report good or excellent results at a mean follow‐up of two years (Saal 1996). Surgical treatment can be considered in cases of insufficient relief of symptoms with these conservative treatment options (Gore 1984; Gore 1998; Klein 2000; White 1973). While surgery is a common option in cases of radiculopathy or myelopathy, controversy exists regarding the operative treatment of axial neck pain, headache, or both (Wieser 2007). Therefore, we will focus on surgical intervention in the case of radiculopathy, myelopathy, or a combination. Primary goals of surgical intervention are to relieve radiating arm pain in the case of radiculopathy, and to prevent progression of neurologic deficit in the case of myelopathy. A systematic review of the trials comparing conservative treatment with surgical intervention for cervical degenerative disc disease is the subject of a separate review (Nikolaidis 2010).

The mean annual incidence of cervical radiculopathy is reported to be about 83 per 100,000 people, with a peak incidence of 202 per 100,000 for people aged 50 to 54 years. The male to female ratio is about 1.7 to 1. The prevalence is about 3.5 per 100,000 people, also with a peak in the sixth decade. In contrast, with the higher incidence reported in males, a consistently higher age‐specific prevalence is reported in females. After the age of 60 years, a rapid decline in incidence is described, more dramatic in females than in males (Radhakrishnan 1994; Salemi 1996).

The reported proportion of patients who are eventually treated surgically ranges from 8% to 35% (Radhakrishnan 1994; Saal 1996; Wolff 2002). The reason for surgical treatment varies from patient to patient but generally falls within one of two groups; a group where surgery is elective, and a group where there is an absolute indication. Surgery on patients presenting with intractable pain despite maximum conservative treatment, or patients with complaints persisting longer than an arbitrary period of conservative treatment of two to eight weeks is generally considered elective. Significant or progressive (or both) neurological deficits are considered an absolute indication for surgical treatment (Saal 1996; Wolff 2002).

Description of the intervention

The most commonly performed procedure is discectomy, either with or without fusion (for the rest of the document, these will be referred to as fusion and simple discectomy, respectively). In fusion, a bony fusion between the two vertebrae is promoted by interposition of a cage, autograft, or allograft material in the disc space, plate and screw fixation, or a combination of these. In simple discectomy, all or part of an intervertebral disc is removed (Jacobs 2011). Posterior laminoforaminotomy is less common, and falls outside the scope of this review (Henderson 1983). Fusion and simple discectomy have good clinical results, with short term (up to six to eight weeks) satisfactory or good results in 90% to 100% of the patients (Dowd 1999; Nandoe 2007; Wirth 2000). In the long term, patient satisfaction slowly decreases. This decrease is the result of a substantial portion of the patients who develop recurrent symptoms in the years after surgery, usually at a level adjacent to the previously operated segment. Numbers for recurrent pain vary between studies. In one study, around 68% of the patients reported no recurrent pain at 20‐year follow‐up, while another study reported satisfactory results in 68% after a mean follow‐up of seven years (Gore 1998; Nandoe 2007). Yet another study reported satisfactory to excellent outcomes in 96% of treated patients after a mean follow‐up of 11 years; this included five patients (4%) who were operated on at an adjacent level due to recurrent symptoms (Palma 2010). For both types of surgery, a high rate of fusion, up to 80% in simple discectomy and over 95% in fusion, has been reported (Dowd 1999; Fountas 2007; Gore 1998; Grob 1998; Persson 1997).

The first part of the surgical procedure for simple discectomy, fusion, and arthroplasty is almost identical: the discectomy. An incision is made on the left or right side of the front of the neck, after which the subcutis and platysma are opened. This is followed by blunt dissection of muscles, oesophagus, trachea, and arteries to reach the anterior aspect of the vertebral column. The longus colli muscles are dissected, and a retractor is placed to ensure good visualisation. The correct level is identified, usually by means of fluoroscopy. The anterior longitudinal ligament and intervertebral disc are incised, after which the contents of the disc space are removed. If necessary, additional decompression of nerve roots and spinal cord is accomplished by removing disc material, osteophytes, or both, usually with microscopy. In simple discectomy, the wound is then closed. In fusion, some form of interposition material is then placed inside the disc space to promote fusion of the adjacent vertebrae. The procedures most commonly performed are variations on the techniques described by Smith and Robinson (Smith 1958), and by Cloward (Cloward 1958; Emery 1994). These variations are primarily based on the amount and type of bony resection, the origin, shape and material of the interposition graft, and the use of additional anterior plating.

In arthroplasty, moveable disc prostheses are inserted instead of a rigid interposition material. Since their introduction in the 1980s (Cummins 1998), several types of artificial cervical discs have been developed, with different materials and movement characteristics (Galbusera 2008; Seo 2008).

There are small but definite risks associated with surgical therapy (Anderson 2008; Daniels 2008; Fountas 2007; Pickett 2006). The most common complication of anterior cervical spine surgery is dysphagia. A recent systematic review reported postoperative incidence of dysphagia ranges from 1% to 79% (Riley 2010). The authors attributed this large range to the fact that there is no universally accepted method to determine the presence of dysphagia. Six months after surgery, the incidence had dropped to 8% to 22%, while at 12 months and 24 months, incidences of 13% to 21% and 13.6%, respectively, were reported(Lee 2007; Riley 2010). Female gender and multilevel surgery were identified as risk factors (Riley 2010). One study reported a significantly lower incidence for dysphagia in arthroplasty when compared to fusion; resolution of symptoms was significantly higher as well (McAfee 2010). Serious and potentially life‐threatening complications are relatively rare. Spinal cord injury or increased myelopathy has been reported in 0.2% to 0.4% and oesophageal perforation in 0.3% of surgeries. A prevertebral or epidural hematoma was reported in 0.2% to 5.6% of cases; a portion of which required surgical exploration. No vertebral artery lesions were reported in this type of surgery. Reported mortality was very low, at 0 to 0.1%. A lesion of the recurrent laryngeal nerve was reported in 0.05% to 8.3% of cases (Anderson 2008; Fountas 2007; Pickett 2006). The true incidence of recurrent laryngeal nerve palsy is probably much higher, since only 35% of the people diagnosed with it through laryngoscopy were found to exhibit symptoms (Jung 2005). Wound infections are rare, with superficial infections being reported in 0.1% to 1.8% of cases. Leakage of cerebrospinal fluid was reported in 0 to 1% of cases. Hardware failure (screw back‐out, migration) has been reported in 0.1% to 1% of cases. No deep infections have been reported, although one fatality was reported due to mediastinitis following a oesophageal tear. Patients generally have a good chance of recovery in the case of a complication (Fountas 2007).

How the intervention might work

Depending on the symptoms of a patient, the primary goal of surgery is to relieve radicular pain, prevent progression of neurologic deficit due to spinal cord compression, or both. Theoretically, since a discectomy is performed to achieve both goals, the direct effect on preoperative symptoms should be equal.

In addition to the surgical decompression, interposition material is added to retain or restore normal cervical lordosis, increase foraminal height, and improve the effects of decompression (Bartels 2001). Lastly, the interposition material leads to a higher fusion rate with subsequent segmental stability and alignment (Dowd 1999). There are reports in the literature that suggest that fusion of a segment would result in reabsorption or blunting of osteophytes (Bailey 1960; Martel 1962). However, this has been contradicted in another publication (Stevens 1993).

In addition to the advantages of fusion, arthroplasty has the supposed advantage of motion sparing in the operated segment (Goffin 2003). This is thought to reduce aforementioned stress on adjacent motion segments, which in turn should lead to less adjacent segment degeneration.

Why it is important to do this review

Currently, there is much debate about whether fusion is a contributing factor to clinical outcomes, and whether it causes accelerated degeneration of adjacent segments, so‐called adjacent segment degeneration. If this adjacent segment degeneration causes symptoms, it is referred to as adjacent segment disease. This may be the result of increased intradiscal pressure and increased mobility at the segments adjacent to a fused segment (Eck 2002). However, it may simply be the result of natural progression of degeneration in an aging spine. Therefore, it remains unclear whether fusion should be regarded as a goal of treatment, or should be prevented (Seo 2008). The yearly risk of adjacent segment disease is calculated to be around 2.9%. Up to 75% of these cases end up undergoing additional surgery (Gore 1984; Gore 1998; Hilibrand 1999; Wirth 2000; Van Eck 2014).

In order to reduce chances of adjacent segment disease as a presumed long‐term effect of fusion, arthroplasty has become increasingly popular. The value of arthroplasty in reducing adjacent segment disease remains a matter of discussion (Seo 2008). In one systematic review, the authors concluded that there was no evidence of a reduction of adjacent level degeneration in arthroplasty compared to fusion (Botelho 2010). The maximum duration of follow‐up in this review was 24 months. Another meta‐analysis found 5.1% of adjacent segment disease after arthroplasty in studies reporting data at a follow up of 12 to 24 months (Shriver 2016). No comparison to fusion was made in that study.

Trials with long‐term follow‐up, and a direct comparison to fusion, are required to evaluate the effectiveness of arthroplasty in preventing adjacent segment disease (Goffin 2003; Seo 2008).

It is important to realize that the possible benefits of preserving motion in the long term will only be useful if arthroplasty is at least as successful in resolving pain and disability as simple discectomy or fusion in the short term. In the original Cochrane review on this subject, we concluded that there were no clinically relevant differences at a maximum of 12 to 24 months follow‐up, although several outcomes were statistically in favour of arthroplasty (Boselie 2012; Boselie 2013).

Although the intended long‐term benefits of arthroplasty compared to fusion should lead to less recurrent disability, pain, and concomitant surgery, it is important to realize that these benefits are not proven. The maximum follow‐up in the previous review was one to two years. This cannot be seen as long‐term follow‐up, and will be referred to as mid‐term in this updated review. Studies reporting longer term results (longer than four years) are becoming available, which should enable better conclusions about the long‐term comparative effects of these treatments, as well as the occurrence of adverse events.

As was the case in the original review, a preliminary search only identified randomised controlled trials that compared fusion and arthroplasty; there were none that compared all of the aforementioned treatment arms combined, or simple discectomy compared to arthroplasty alone. A systematic review of the trials comparing simple discectomy and several methods of fusion in cervical degenerative disc disease has been the subject of a separate review (Jacobs 2011). Studies comparing simple discectomy, fusion, and arthroplasty are being planned or conducted at the moment (Arts 2010). Therefore, adding simple discectomy to the comparison should be possible in future updates of this review, in which case it would be interesting to investigate the possibility of combining data with the previously mentioned review (Jacobs 2011).

This protocol replaces the previous version of the review (Boselie 2012 ; Boselie 2013).