C5 Palsy after Cervical Disc Arthroplasty: Two Case Reports and Literature Review

Abstract

Cervical disc arthroplasty (CDA), also known as cervical artificial disc replacement, has become an alternative for the treatment of cervical spondylosis with radicular or myelopathic symptoms. However, there is limited literature regarding its complications and outcomes. We present two cases that developed C5 nerve palsy (C5P) following two-level CDA. Both patients presented with C5P in a delayed fashion with 2/5 and 1/5 deltoid weakness on MMT, respectively. Postoperative imaging did not demonstrate any spinal cord compression and symptoms resolved (5/5 on MMT) with conservative management in both cases. To our knowledge, these represent the first cases of delayed C5P after cervical arthroplasty reported in the literature. We performed a literature review to further enhance our knowledge regarding CDA. By understanding its pathophysiology and response to treatment, these cases can serve as a guide for spine surgeons and improve their future outcomes.

1. Introduction

Postoperative C5 palsy (C5P) is a known complication after cervical spine surgery using both the anterior and posterior approaches. There has been significant literature published regarding C5P following cervical spine surgery with an overall incidence of 5.3–6% [1,2,3]. C5P presents as new unilateral weakness of the deltoid and biceps muscles immediately or several days after surgery [4,5,6,7]. The diagnosis of C5P is one of exclusion; other etiologies for shoulder abduction weakness must be ruled out, including disc herniation, residual stenosis, and hematoma [5]. A temporal aspect is also suggestive of this diagnosis, as C5P is usually transient. The literature reports C5P after posterior cervical laminectomy, foraminotomy, laminoplasty, anterior corpectomy, and anterior cervical fusion, but has limited data available after cervical disc arthroplasty (CDA). To our knowledge, there have been no reports of C5P after CDA published to date. CDA is an artificial cervical disc replacement technique that is ideal for maintaining normal neck motion and reducing the degeneration of adjacent segments [8]. It is especially fitting for patients that have a soft disc herniation causing neurological symptoms, physiologic motion without instability, hypermobility, kyphosis, osteoporosis, infection, inflammatory disease, or facet arthritis [8]. We present two independent cases of C5P after CDA and situate their cases within the broader literature.

2. Case Presentation

2.1. Case 1

A 47-year-old female presented with progressive bilateral upper extremity radicular pain. This pain was consistent with a bilateral C5 and right C7 dermatomal distribution. She had a past surgical history of C5–C6 anterior cervical discectomy and fusion (ACDF). On her physical exam, she demonstrated hyperreflexia (3+) of the biceps, patella, and brachioradialis. On her manual muscle testing (MMT), she was (5/5) in all muscle groups.

Cervical spine MRI demonstrated severe spinal cord compression at the C6–C7 level along with moderate stenosis at C4–C5, consistent with adjacent level disease (Figure 1). The patient underwent CDA with bilateral anterior foraminotomies at C4–C5 and C6–C7. The intervention was performed using standard techniques with the use of intraoperative neuromonitoring with a combination of motor and somatosensory evoked potentials and electromyography. A 6mm ProDisc implant was placed at both levels (Figure 2). Neuromonitoring remained stable throughout the procedure. The patient was discharged home on postoperative day (POD) 1 with the resolution of her bilateral upper extremity pain; she was also (5/5) on MMT on all muscle groups.

On POD 3, the patient complained of a sudden left-sided arm and neck pain with progression of severity until POD 8, when she had a sudden onset of left arm weakness, prompting emergency medical attention. On physical examination, she had left deltoid weakness (2/5) on MMT with the inability to raise her arm above 30° at shoulder level; the remainder of her neurologic exam was normal. A CT myelogram was performed, which showed no cervical cord compression or foraminal stenosis with no evidence of hardware failure (Figure 3). The patient was diagnosed with C5P and was discharged home with oral dexamethasone 2 mg two times daily, ibuprofen 400 mg every 6 h, and gabapentin 300 mg every 8 h. She was encouraged to use a shoulder sling to prevent secondary traction injury and started on physical therapy to assist with shoulder mobilization. The patient experienced a full return of strength in the deltoid (5/5) on MMT 6 weeks after surgery and has remained well more than a year after the event.

2.2. Case 2

A 52-year-old female presented with intermittent neck pain radiating to the right shoulder and arm (consistent with a C5–C6 dermatomal distribution) for a period of approximately 2 months. On a physical exam, she was (5/5) on MMT in all muscle groups. She showed marked spasticity, with bilateral patellar hyperreflexia, as well as bilateral Hoffman’s sign and 1–2 beats of ankle clonus, consistent with cervical myelopathy. A non-contrast cervical spine MRI (Figure 4) demonstrated severe stenosis at C3–C4 and moderate stenosis at the C4–C5 level. The patient underwent CDA using the Mobi-C implant at both levels. The patient was subsequently discharged home on POD 1 without any new neurologic deficits and with (5/5) MMT in all muscle groups and significant improvement in her neck and right arm pain. However, on POD 4, the patient developed progressively worsening severe bilateral neck and right shoulder pain, described as being more severe than her preoperative pain. She was evaluated in the outpatient setting with an MMT of 5/5 in all muscle groups and no evidence of neurological deficits; she was started on gabapentin. This led to symptomatic improvement. However, on POD 14, she was unable to abduct her right arm past 10 degrees with (1/5) on MMT; the remainder of her muscle groups were 5/5 on MMT. Postoperative lateral and anterior–posterior cervical X-rays showed stable hardware with no evidence of hardware failure (Figure 5). At this time, the diagnosis of C5P was established and she was managed on oral dexamethasone 2 mg every 12 h and physical therapy for 10 days. She demonstrated resolution of her pain and full restoration of her deltoid weakness approximately four weeks after surgery. Her physical exam was (5/5) on MMT in all muscle groups. She remains well one year after surgery with all bilateral upper extremity muscle groups (5/5) on MMT.

3. Discussion

Although C5P is a well-noted complication after cervical spine surgery, no reports to date describe C5P after CDA. Traditional theories of C5P pathophysiology describe the posterior translation of the spinal cord with resulting nerve root traction as the cause of delayed paresis [9,10]. While compelling, these explanations fail to account for the small but substantial rate of C5P following anterior cervical surgery [11], prompting other etiological hypotheses, such as ischemia–reperfusion injury and residual foraminal stenosis [12]. However, a single unifying theory remains elusive, and C5P is better understood as a clinical phenomenon, rather than a single pathophysiological entity [13]. Therefore, we will focus on several pertinent details of these cases, rather than attempt to posit a single causative theory of C5P after CDA.

First, motion through the cervical spine represents a complex mixture of rotation and translation, described kinematically through the instantaneous axis of rotation (IAR). Although disc replacement devices attempt to reproduce this motion, they do so imperfectly. This discord between the native cervical spine’s IAR and that of the disc replacement device may potentially lead to dynamic foraminal encroachment [14]. This phenomenon may be relevant to both cases, where the use of a centrally placed device (Case 1) or anterior placement of the device’s IAR to the disc’s natural IAR (Case 2) could lead to abnormal disc kinematics with dynamic encroachment and compression of the C5 nerve root. This mechanical disturbance could be a potential cause of our patients’ C5P.

Second, both patients demonstrated a classic presentation of C5P with delayed-onset weakness followed by the relatively rapid return of arm function. Although multiple factors predict recovery after C5P, spontaneous full recovery is the general natural history of the phenomenon, especially in patients without bicep involvement and partially preserved deltoid strength [15]. Our cases of CDA demonstrate a similar recovery trajectory to those following other forms of cervical spine surgery. Although posterior foraminotomy represents a biomechanically sound way to salvage postoperative radiculopathy following cervical arthroplasty, our experience suggests against its routine usage in the management of C5P after CDA [16]. Although standard protocols for C5P do not exist, non-operative management consisting of physical therapy and steroids provided the rapid resolution of symptoms in both patients. Our cases differ from the case reports previously described by Akshay et al., who described two cases of delayed C5P after the use of FloSeal (Baxter, Inc., Deerfield, IL, USA) hemostatic matrix. Both of their patients displayed evidence of a small identifiable lesion in their postoperative MRI with evidence of neural foraminal compression, which was described as a “flosealoma” [17]. Our study also describes two cases of delayed C5P, but both of our cases had no evidence of compression at the foramen on postoperative images. We were also extremely cautious by irrigating any residual or extra hemostatic agents at the foramen. Another difference from their case reports is that our patients exhibited symptom resolution with conservative management; both of their cases required posterior decompression [17].

Our study has some limitations, starting with the fact that we only present two cases. CDA is a rare surgical procedure and is only indicated in some patients with cervical spine pathology; this reduces our power. Also, C5P is rare after anterior cervical spine surgery; thus, the number of cases reported in the literature are limited. It is imperative that future cases be published to discover a cause and decrease its incidence.

In summary, we present a novel presentation of a well-characterized complication of cervical spine surgery. Although increasingly well established, CDA represents a relatively novel surgical technique with different complication profiles compared to other forms of surgical decompression. Our experience illustrates that CDA is not exempt from the possibility of C5P and that expectant management remains an appropriate management strategy with the potential for excellent outcomes.

4. Conclusions

We present two independent cases of C5P after CDA performed by independent surgeons using independent device classes. Both cases resolved with expectant management, suggesting that C5P after CDA may be managed in a similar fashion to C5P following other cervical procedures. We favor conservative management with physical therapy and oral dexamethasone once all other causes of neural compression have been ruled out.