Clinical Implications of Spinal Cord Levels

• Innervated Muscles: Upper trapezius, diaphragm, and cervical paraspinal muscles.
• Possible Movements: Neck flexion, extension, and rotation; scapular elevation; and inspiration.

Clinical Note: Even though C4 patients have diaphragm function, the lack of intercostal muscle control means they may still require assistance to clear secretions from the airway to prevent pneumonia.

C5 Injury: Elbow Flexion and Functional Independence

As we move down to the C5 level, the patient gains significant upper extremity function, specifically regarding the ability to move the arms, though hand and wrist function remain absent.

Neurological Deficits and Capabilities

A C5 injury results in total paralysis of the trunk and lower extremities, but provides the patient with the ability to perform elbow flexion and shoulder movements.

• Innervated Muscles: Deltoid, biceps, brachialis, brachioradialis, rhomboids, and partial innervation of the serratus anterior.
• Possible Movements: Shoulder flexion, abduction, and extension; elbow flexion and supination; and scapular adduction and abduction.
• Patterns of Weakness: There is a complete absence of elbow extension, pronation, and all wrist and hand movements.

Impact on Activities of Daily Living (ADLs)

The functional independence of a C5 patient is highly dependent on assistive technology and caregiver support.

C6 and Beyond: The Tenodesis Grasp

The C6 level is a major milestone in spinal cord injury rehabilitation because it introduces wrist extension, which enables a unique functional mechanism known as the tenodesis grasp.

The Tenodesis Mechanism

At C6, the patient innervates the extensor carpi radialis longus and brevis, as well as the clavicular pectoralis supinator. This allows for radial wrist extension. When the patient extends their wrist, the long finger flexors (which are stretched) create a passive tension that allows the fingers to curl toward the palm. This allows the patient to "grasp" objects without having active finger flexion.

• Possible Movements: Scapular protraction, some horizontal adduction, forearm supination, and radial wrist extension.
• Weakness Patterns: Absence of wrist flexion, elbow extension, and all hand movement.

Exam Tip: When assessing a C6 patient, look for the ability to use wrist extension to compensate for the lack of intrinsic hand muscle function. This is the hallmark of the tenodesis grasp.

Thoracic and Lumbar Injuries (T1–S5)

As the injury level moves into the thoracic and lumbar regions, the primary clinical focus shifts from respiratory survival to trunk stability and lower limb mobility.

Thoracic Injuries (T1–T9)

Patients with injuries in the T1–T9 range typically have intact upper extremity function. However, they face:

• Complete paralysis of the lower limbs.
• Limited stability of the upper trunk.

Lumbar and Sacral Injuries (L2–S5)

Injuries at the lower levels of the spine allow for much greater functional independence:

• L2–S5: These patients have intact upper body function and significantly improved trunk stability. While they may still experience complete paralysis of certain lower limb segments depending on the exact level, their ability to manage their core and balance is much higher than those with cervical injuries.

In summary, the clinical implications of spinal cord levels follow a predictable pattern: higher injuries necessitate life-sustaining respiratory interventions, while lower injuries focus on maximizing mobility and independence through trunk control and limb function.