Tethered Spinal Cord

A tethered spinal cord is a condition in which the lower end of the spinal cord is abnormally fixed to surrounding structures, restricting its normal movement and placing it under mechanical traction. Most often arising from a developmental anomaly such as a thickened filum terminale, lipoma, or dysraphic lesion, the abnormal tethering is thought to impair cord metabolism and produce a progressive neurological, urological, and orthopaedic syndrome.

Definition

A tethered spinal cord is an abnormal fixation of the caudal spinal cord to adjacent tissue that limits its normal mobility and subjects it to chronic traction, giving rise to tethered cord syndrome when it produces progressive neurological dysfunction.

Scope

The topic covers the concept of pathological cord fixation, the developmental anomalies that cause it, the proposed mechanism by which traction impairs the cord, and the characteristic multi-system presentation. It treats tethered cord as a reference orientation within spinal cord pathology and does not specify surgical indications or techniques for untethering.

Core questions

• What anatomical anomalies cause the cord to become abnormally fixed?
• How is mechanical traction thought to impair spinal cord function?
• Why does the syndrome involve neurological, urological, and orthopaedic features together?
• How does tethered cord relate to the spectrum of spinal dysraphism?

Key concepts

• Abnormal cord fixation
• Filum terminale
• Conus medullaris position
• Spinal dysraphism
• Traction and impaired metabolism
• Neuro-urological dysfunction
• Untethering principle

Key theories

Traction-ischaemia mechanism

Abnormal caudal fixation places the cord under longitudinal stretch that is proposed to impair oxidative metabolism and blood flow in the lower cord, providing a mechanistic account of the progressive, traction-related deficits of tethered cord syndrome.

Mechanisms

In the tethered cord the caudal spinal cord is anchored by an abnormal structure, such as a thickened or fatty filum terminale, a lipoma, or a dysraphic band, preventing the normal cephalad ascent and free movement of the cord. The resulting chronic longitudinal traction is proposed to impair oxidative metabolism and microcirculation in the lower cord, a mechanism advanced to explain the progressive and traction-related nature of the deficits (Yamada, 1981). Because the affected segments serve lower-limb, bladder, and bowel function, the clinical syndrome characteristically combines neurological, urological, and orthopaedic features (Hoffman, 1976). The underlying anomalies frequently fall within the spectrum of spinal dysraphism arising from disordered neurulation (Pang, 2013).

Clinical relevance

Tethered cord is a recognised cause of progressive, potentially preventable neurological and urological decline, particularly relevant in the context of spinal dysraphism, and its mechanism explains the rationale for surgical untethering as a concept. This entry is a reference description and does not provide diagnostic criteria, indications for surgery, or treatment guidance, which rest with treating clinicians.

Epidemiology

Tethered cord most often presents in the context of spinal dysraphism and may become symptomatic in childhood or adulthood; occult forms can accompany cutaneous or radiological markers of dysraphism (Pang, 2013; Hoffman, 1976). Precise incidence figures depend on the underlying anomaly and are not summarised here.

History

The tethered spinal cord was characterised through the latter twentieth century as surgeons recognised that a low-lying, fixed cord could produce a progressive and partly reversible syndrome. Hoffman and colleagues described its protean manifestations and surgical correction, Yamada and colleagues proposed a traction-based metabolic mechanism, and later work by Pang and others clarified the developmental dysraphic anomalies that underlie tethering (Hoffman, 1976; Yamada, 1981; Pang, 2013).

Debates

How should occult or 'tight filum' tethering with a normally positioned conus be approached?

The diagnosis and significance of tethering in patients with a normally positioned conus but suggestive symptoms is debated, since the mechanism and selection criteria for intervention are less clear-cut than in overt low-lying lesions.

Key figures

• Dachling Pang
• Shokei Yamada
• Harold Hoffman

Seminal works

• yamada-1981
• hoffman-1976
• pang-2013

Frequently asked questions

What does it mean for the spinal cord to be 'tethered'?

It means the lower end of the cord is abnormally fixed to surrounding tissue, such as a thickened filum terminale or a lipoma, so it cannot move freely and is held under chronic traction.

Why does tethered cord affect the bladder and legs together?

The traction predominantly affects the lower segments of the cord, which supply lower-limb, bladder, and bowel function, so the syndrome characteristically combines neurological, urological, and orthopaedic features.