Anterior cervical discectomy and fusion represents the gold standard surgical intervention for cervical myelopathy and radiculopathy. However, bone nonunion remains a major clinical challenge that compromises long-term clinical recovery. Identifying early anatomical predictors of pseudarthrosis after ACDF empowers spine surgeons to personalize patient care and refine risk stratification. Recent evidence highlights dynamic cervical muscle degeneration as an essential prognostic marker for fusion success. In particular, structural deterioration within the sternocleidomastoid muscle reflects biological healing potential.

Understanding Pseudarthrosis After ACDF and Muscle Quality

Solid bony fusion provides structural stability and relieves neurological compression across affected cervical levels. Unfortunately, pseudarthrosis develops in up to one-third of multilevel reconstructive procedures. When nonunion occurs, patients frequently suffer from persistent axial neck pain, hardware failure, or progressive deformity. Traditionally, spine surgeons attribute nonunion to patient comorbidities, including chronic tobacco use, poorly controlled diabetes mellitus, and osteopenia. Furthermore, multilevel constructs create elevated biomechanical shear stresses that challenge graft integration. However, systemic frailty and paraspinal musculature also dictate regional biological healing capacity. Researchers previously demonstrated that lumbar muscular sarcopenia predicts implant loosening and inferior patient recovery. In contrast, clinicians historically overlooked the role of anterior cervical musculature in arthrodesis. The sternocleidomastoid muscle acts as a major dynamic stabilizer for the anterior cervical spine. Consequently, loss of muscular integrity permits micro-motion across bone-graft interfaces during early osteogenesis. Therefore, evaluating cervical muscle quality offers valuable predictive insight into structural union rates before surgical intervention.

Evaluating Sternocleidomastoid Morphology and Degeneration

The sternocleidomastoid muscle serves as a critical surgical landmark and biomechanical stabilizer during cervical spine motion. Clinicians assess both cross-sectional area and myosteatosis to measure muscular degeneration. Axial T2-weighted magnetic resonance imaging at the C5-C6 disc level provides clear visualization of muscle borders. Radiologists apply the Goutallier classification system to grade fatty infiltration within paraspinal muscle bellies. Grade 0 describes normal muscle tissue without visible fat streaks. Grade 1 reflects minimal fatty infiltration scattered within the muscle parenchyma. In contrast, Grade 2 demonstrates pronounced fatty deposits, although viable muscle tissue still exceeds fat content. Grades 3 and 4 signify severe fatty degeneration where adipose tissue equals or exceeds muscle volume. Importantly, muscle cross-sectional area measures gross muscular size, while Goutallier grading assesses physiological tissue quality. Progressive fatty infiltration reflects chronic muscular senescence, systemic inflammation, and localized denervation. As a result, qualitative assessments capture metabolic deficits that bulk muscle volume cannot detect. Incorporating routine MRI muscle grading requires no extra imaging costs or specialized hospital equipment.

Clinical Evidence Linking Muscle Quality to Arthrodesis Failure

A pivotal retrospective cohort study conducted by Dalton and colleagues evaluated 205 adult patients undergoing elective ACDF. The investigators reviewed preoperative magnetic resonance scans to determine sternocleidomastoid cross-sectional area and Goutallier grades at C5-C6. They assessed fusion status at one year using dynamic flexion-extension cervical radiographs. Overall, pseudarthrosis developed in 33.7% of the total cohort. Nonunion occurred significantly more often in multilevel constructs than in single-level fusions. For example, pseudarthrosis developed in over 30% of three-level procedures and in over 7% of four-level cases. Remarkably, total muscle cross-sectional area normalized to body mass index showed no association with nonunion rates. In contrast, fatty infiltration independently predicted arthrodesis failure. After controlling for patient age, sex, body mass index, and fusion levels, elevated Goutallier grades tripled nonunion odds. Specifically, patients with mild fatty infiltration experienced a 3.46-fold increased risk of developing pseudarthrosis. Interestingly, patient-reported outcome measures did not correlate negatively with muscle degeneration. Nevertheless, biological bone union depended strictly on qualitative muscle health rather than gross muscular dimensions.

Strategic Surgical Decision-Making for At-Risk Patients

These findings offer spine surgeons actionable guidance for pre-surgical planning and implant selection. Traditionally, surgeons relied upon dual-energy X-ray absorptiometry and clinical comorbidities to identify poor fusion candidates. However, standard bone density scans frequently fail to reveal localized cervical mechanical instability. Because clinicians already obtain cervical magnetic resonance imaging, surgeons can readily check C5-C6 muscle quality. When surgeons recognize elevated Goutallier grades preoperatively, they can modify surgical tactics proactively. For instance, surgical teams can utilize rigid plate fixation and supplemental posterior instrumentation for multilevel reconstructions. Alternatively, clinicians can employ osteoinductive bone graft enhancers or cellular allografts instead of simple local bone chips. Furthermore, surgeons might extend postoperative cervical immobilization periods with rigid cervical orthoses to limit interfacial shear stress. Addressing dynamic muscle weakness also encourages closer radiographic monitoring during the first postoperative year. Consequently, surgeons can detect delayed union early and initiate noninvasive bone stimulation before hardware failure occurs. Proactive management thus protects patients from the substantial morbidity associated with revision anterior cervical surgery.

Preoperative Rehabilitation and Muscle Optimization Strategies

Muscular steatosis represents a modifiable metabolic state rather than an irreversible degenerative condition. Therefore, surgical teams should view myosteatosis as an opportunity for therapeutic prehabilitation before elective spinal surgery. Targeted cervical physiotherapy strengthens the deep anterior flexors and superficial sternocleidomastoid muscles. Supervised isometric exercises enhance muscle recruitment, improve postural balance, and reinforce dynamic cervical stabilization. In addition, healthcare providers should address underlying metabolic derangements that accelerate intramuscular fat accumulation. For example, unmanaged diabetes, chronic systemic inflammation, and sedentary lifestyles directly promote muscle fat infiltration. Nutritional counseling emphasizing adequate dietary protein intake and optimal vitamin D supplementation supports skeletal muscle protein synthesis. Moreover, structured smoking cessation programs restore microvascular perfusion to both muscle bellies and healing bone interfaces. Implementing these conservative interventions during the preoperative waiting period enhances overall physiological reserve. Consequently, multidisciplinary collaboration between spine surgeons, physiotherapists, and primary care physicians optimizes surgical candidacy. Prehabilitation transforms passive surgical patients into proactive participants, improving long-term biomechanical outcomes after cervical reconstruction.

Frequently Asked Questions

How does sternocleidomastoid fatty infiltration increase pseudarthrosis risk?

Fatty infiltration compromises muscle contractility and dynamic mechanical support across the cervical spine. When paraspinal muscles weaken, pathological micro-motion persists across operative disc spaces. This subtle instability disrupts early capillary ingrowth and cellular matrix deposition, preventing rigid osteointegration and directly promoting radiographic pseudarthrosis after anterior cervical fusion.

Why does muscle quality predict nonunion better than muscle size?

Muscle cross-sectional area reflects gross volume but overlooks internal tissue health. Sarcopenic obesity often conceals true muscular atrophy beneath voluminous adipose deposition. Fatty infiltration indicates chronic cellular senescence, metabolic dysfunction, and loss of functional contractile fibers. Consequently, muscle quality provides a much more accurate physiological marker of biomechanical resilience than anatomical dimensions alone.

Can surgeons evaluate muscle quality without ordering specialized radiological tests?

Yes, surgeons can reliably grade muscle degeneration using routine preoperative T2-weighted cervical magnetic resonance imaging. Clinicians visually assess the sternocleidomastoid muscle at the C5-C6 disc space using the established Goutallier classification system. This rapid qualitative assessment requires no specialized software, eliminates unnecessary ionizing radiation, and avoids adding healthcare expenses to patient workups.

Disclaimer: This content is for informational and educational purposes only. It does not constitute medical advice, diagnosis, or treatment. Healthcare professionals must exercise independent clinical judgement. Verify all clinical guidelines, procedures, and medication dosages independently. The author and publisher are not liable for actions taken based on this content. Refer to the latest local and national guidelines for clinical practice.

References

1. Dalton J et al. Mild Changes in Sternocleidomastoid Muscle Quality Predict Pseudarthrosis After Anterior Cervical Discectomy and Fusion. Spine (Phila Pa 1976). 2026 Mar 15. doi: 10.1097/BRS.0000000000005360. PMID: 40237123.
2. Goutallier D, Postel JM, Bernageau J, Lavau L, Voisin MC. Fatty muscle degeneration in cuff ruptures: pre- and postoperative evaluation by CT scan. Clin Orthop Relat Res. 1994 Jul;(304):78-83. PMID: 8020238.
3. Kim CW, Lee SH, Lee DH, et al. Impact of Cervical Sarcopenia on Postoperative Alignment and Clinical Outcomes Following Multilevel Anterior Cervical Discectomy and Fusion. Neurospine. 2023 Sep;20(3):912-921. doi: 10.14245/ns.2346420.210.