Congenital Partial C5-C6 Fusion: Clinical Significance
A congenital partial C5-C6 fusion is generally not significant in isolation and typically remains asymptomatic throughout life, but becomes clinically relevant when it predisposes adjacent segments to accelerated degenerative changes or when associated with other congenital anomalies. 1
Natural History and Baseline Risk
Congenital cervical fusions involving 2-3 segments are common and show no clinical signs of abnormality in most patients, nor are they typically associated with other malformations. 1
The C2-3 level is most frequently involved in congenital cervical fusions, followed by C3-4, with C5-C6 being less common but following similar clinical patterns. 1
Single-level congenital fusions do not typically produce symptoms until later in life when degenerative changes develop in the unfused (mobile) vertebrae adjacent to the fusion, or occasionally following trauma. 1
When Congenital Fusion Becomes Clinically Significant
Adjacent Segment Degeneration
The primary clinical concern with congenital C5-C6 fusion is accelerated degenerative disease at adjacent mobile segments (C4-C5 and C6-C7), which occurs because these levels must compensate for the lost motion at the fused segment. 2
Hypermobility at adjacent segments develops as a compensatory mechanism, leading to earlier disc degeneration, facet arthropathy, and potential stenosis at these levels. 2
Associated Anomalies That Increase Risk
Fusion of multiple cervical segments, though rare, is often associated with other anomalies including short neck, lowered posterior hairline, webbed neck, and malformations of internal organs and other bones—these patients require more careful monitoring. 1
Congenital absence of pedicles can occur in conjunction with cervical fusions and represents a more serious condition requiring surgical intervention when myelopathy develops. 3
Fusion at C2-3 with occipitalization of the atlas predisposes nerves to damage and represents a higher-risk pattern than isolated lower cervical fusions. 1
Clinical Presentation Requiring Intervention
Radiculopathy Pattern
Symptoms from congenital cervical fusion typically manifest as radiculopathy caused by degenerative changes at adjacent unfused levels, presenting with arm pain, numbness, or weakness in specific dermatomal distributions. 1
Conservative treatment is appropriate for radiculopathy symptoms, including physical therapy and pain management. 1
Myelopathy Pattern
Operation is necessary for patients who develop myelopathy symptoms, which include bilateral hand weakness, gait disturbance, hyperreflexia, and sensory level changes. 1, 4
Myelopathy from adjacent segment disease in the setting of congenital fusion presents with bilateral hand clumsiness affecting both fine motor control and grip strength, often with lower extremity involvement. 4
Cord compression at levels adjacent to congenital fusion (such as C4-C5 or C6-C7) manifests with involvement of multiple muscle groups including biceps, triceps, wrist extensors, and finger flexors bilaterally. 4
Surgical Considerations When Intervention Required
Staged anterior and posterior cervical decompression and fusion is the appropriate surgical approach for patients with congenital cervical anomalies who develop myelopathy or instability. 3
Cervical arthroplasty may be considered at adjacent degenerated levels in selected patients with congenital fusion to restore motion and prevent further adjacent segment degeneration by reducing hypermobility. 2
Postoperative spondylolisthesis is a potential complication following cervical fusion procedures, particularly in patients with underlying congenital stenosis, requiring vigilant follow-up even after "successful" surgery. 5
Practical Management Algorithm
Asymptomatic Patients
No intervention is required for incidentally discovered congenital C5-C6 fusion in asymptomatic patients. 1
Counsel patients about potential for future adjacent segment degeneration and symptoms to monitor (arm pain, hand weakness, gait changes). 1
Symptomatic Radiculopathy
Initiate conservative management with physical therapy, NSAIDs, and activity modification for at least 6 weeks. 6
Consider epidural steroid injections if conservative measures fail. 6
Surgical decompression is reserved for failed conservative treatment with persistent radicular symptoms. 1
Myelopathy Presentation
Urgent surgical evaluation is warranted for any patient with congenital cervical fusion who develops myelopathy signs (bilateral hand dysfunction, gait disturbance, hyperreflexia, sensory level). 1, 4
MRI is essential to identify the level of cord compression, which typically occurs at segments adjacent to the congenital fusion. 4
Surgical decompression and fusion should not be delayed in the presence of progressive myelopathy. 3
Common Pitfalls to Avoid
Do not attribute isolated unilateral symptoms (such as single finger drop) to cord compression at levels showing incidental cord edema on MRI—this represents a mismatch requiring evaluation for alternative diagnoses like peripheral nerve pathology or radiculopathy from a different level. 4
Avoid assuming that congenital fusion alone requires treatment; intervention is only necessary when symptoms develop from adjacent segment degeneration or associated instability. 1
Do not overlook the possibility of multiple congenital anomalies when fusion involves multiple segments, as these patients may have associated organ or skeletal malformations requiring additional evaluation. 1