Deep Layer Spinal Musculature: Biomechanical Properties and Clinical Relevance

The deep layer musculature of the spine, particularly the multifidus and longissimus muscles, plays a critical role in spinal stability, load distribution, and functional outcomes. Alterations in their biomechanical properties—such as reduced force generation, increased stiffness, and fatty infiltration—are strongly linked to spinal disorders, pain, and poor surgical outcomes.

Biomechanical Properties and Qualities

• Force Generation and Stiffness: Deep paraspinal muscles in patients with spinal degeneration or deformity show impaired specific force generation and highly variable sarcomere-length properties, indicating intrinsic contractile dysfunction (Noonan et al., 2024; Malakoutian et al., 2022). Increased passive stiffness, especially after injury or surgery, is often due to elevated collagen content in the extracellular matrix (Yamamoto et al., 2021).

• Muscle Quality: Fatty infiltration and atrophy of the multifidus and other deep muscles are common in degenerative conditions, correlating with reduced muscle function and strength (Fortin et al., 2017; Han et al., 2023; Guven et al., 2025; Kim et al., 2023). Advanced imaging (e.g., DTI, MRI-based PMQ score) can quantify these changes and predict muscle strength and clinical status (Guven et al., 2025; Klupp et al., 2019).

• Role in Spinal Loads: Deep muscles are essential for maintaining posture and spinal stability, especially during low-load activities and static postures. Their dysfunction increases spinal loading, risk of instability, and susceptibility to vertebral fractures (Malakoutian et al., 2022; Ignasiak et al., 2018; Xiong et al., 2024; Cheng et al., 2016; Panjabi et al., 1989; Granata & Marras, 2000).

Biomechanical Properties, Muscle Quality, and Clinical Outcomes

Property/Quality	Clinical Relevance	Citations
Reduced force generation	Linked to spinal imbalance, weakness, and poor functional recovery	(Noonan et al., 2024; Malakoutian et al., 2022; Han et al., 2023)
Increased stiffness/collagen	Raises spinal compressive loads, especially post-surgery or in degeneration	(Malakoutian et al., 2022; Yamamoto et al., 2021)
Fatty infiltration/atrophy	Predicts pain, disability, poor surgical outcomes, and higher fracture risk	(Fortin et al., 2017; Han et al., 2023; Guven et al., 2025; Xiong et al., 2024; Kim et al., 2023)
Imaging-based muscle quality	Correlates with pain, function, and can guide prognosis and therapy	(Guven et al., 2025; Klupp et al., 2019; Han et al., 2023)

Figure 1: Table summarizing deep muscle properties and their clinical impact.

Clinical Implications

• Diagnosis and Prognosis: Quantitative assessment of deep muscle quality (e.g., fatty infiltration, cross-sectional area) is a strong predictor of pain, disability, and risk of poor outcomes after spinal surgery (Han et al., 2023; Guven et al., 2025; Xiong et al., 2024).

  
  

• Rehabilitation: Targeted exercise interventions that improve deep muscle morphology and function can reduce pain and disability in chronic low back pain (Fortin et al., 2023).

  
  

• Prevention: Preserving or restoring deep muscle quality may help prevent spinal instability, fractures, and progression of degenerative changes (Ignasiak et al., 2018; Xiong et al., 2024; Kim et al., 2023).

Conclusion

Deep spinal muscles’ biomechanical integrity is vital for spinal health. Their degeneration—manifested as reduced force, increased stiffness, and fatty infiltration—directly contributes to pain, instability, and poor clinical outcomes, highlighting the importance of early assessment and targeted rehabilitation.

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References

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