Mechanics of Breathing

Mechanics of quiet respiration

The Diaphragm is primary respiratory muscle.  The Diaphragm contracts, pulling the central tendon down until the abdominal wall prevents the abdominal viscera from moving any further.  This increases the vertical diameter.  The 12th rib is fixed by quadratus lumborum.

Central tendon is fixed so the diaphragm now elevates the lower 6 ribs, which increases the infrasternal angle with a bucket handle movement.  This increases the transverse diameter of the thorax.

Lower 6 ribs push upward thereby elevating the sternum and the upper 6 ribs thrust their anterior ends upward and forward until all motion at the manubriosternal symphysis taken up.  This increases the antero-posterior diameter.

The elevation force then produces a bucket handle movement at ribs 3-6 while ribs 1 and 2 are fixed by scalenes.  This increases the transverse diameter.  The intercostals contract to prevent tissues from being drawn in.  The scalenes maintain vertical diameter by preventing 1st and 2nd ribs from being drawn in while fascia suspends the thorax to the axial skeleton

Canadian Cervical Spine Rule

Canadian Cervical spine Rule [i] [ii]


The Canadian “C” spine rule is a tool used to determine the necessity of radiology after cervical trauma.  It is used on patients who are alert and in stable condition following a trauma and when cervical spine injury is a concern.  It does not apply to non-traumatic cases, if the patient has unstable vital signs, acute paralysis, has known vertebral disease or has a previous history of cervical spine surgery and if they are less than 16 years old.


Rule: High- Risk Factors


  1. Age> 65
  2. Trauma such as fall > 1 meter or 5 stairs, axial loadingto head and neck (diving), high-  speed MVA, or recreational vehicle injury, bicycle collision.
  3. Paresthesiain extremities.


Rule: Low-Risk Factors that allow safe assessment of ROM


  1. Simple rear end MVA
  • excluding being hit by a bus, large truck, being pushed into oncoming traffic, roll over or being hit by high-speed
  1. Normal sitting posture
  2. Ambulatory
  3. Delayed onset of pain
  4. No midline tenderness of C-spine


Can the patient rotate neck greater than 45 degrees in each direction?

If there is 1 high-risk factor or 2 low-risk factors and the inability to rotate the neck 45 degrees warrants an x-ray.

The evidence shows a sensitivity of 99.4 and a specificity of 45.1.  The negative likelihood ratio associated with this highly sensitive test is less than 5% which means there is only a 5% chance that if you get a negative finding, the patient would still have the condition.

[i] Belot, M et al. Candian C-Spine Rule. n.d. web. Jan 16 2016.

[ii] Stiell, IG et al.  The Canadian C-Spine Rule versus the NEXUS Low- Risk Critieria in Patients with Trauma.  N Engl J Med. 2003 Dec. 25;349 (26):2510-8.

Differential Diagnosis of the Spine

Differential Diagnosis of the Spine is available on in kindle and soft cover formats

Cervical Myelopathy Quiz

Cervical Myelopathy is a reduction of the sagittal diameter of the cervical spinal canal.  The canal is normally 17-18mm wide in adults.  It  can be caused by a mechanical reason such as a disc lesion or degenerative stenosis (most common level C5/6, C6/7), bone spurs, traumatic dislocation or fracture or medical issues such as transverse myelitis, MS, neuromyelitis optica (immune disorder that affects the optic nerve and the spinal cord), viral and autoimmune disorders, neoplasms, epidural or subdural hemorrhage.  It is the most common cause of spinal cord dysfunction in adults over the age of 55.

Signs and symptoms are neck pain and stiffness with or without shoulder pain and stiffness. Progressive disability is a typical history. Wide based ataxic gait or gait disturbances, loss of hand dexterity, paresthesia in one or both arms or hands, changes in handwriting, loss of fine motor ability of the hands, hyperreflexia, positive plantar response, positive Hoffman’s, Lhermitte’s sign during slump testing especially neck flexion/extension, urinary retention which can progress to overflow incontinence and low back pain can be present.  Plantar response is the most reliable screening test.

Clinical Prediction Rule for Cervical Myelopathy

Clinical tests for cervical myelopathy include a plantar response (Babinski, clonus), Hoffman’s sign, deep tendon reflexes, hand withdrawal reflex, suprapatellar quadriceps test and the inverted supinator sign.

Cluster test for cervical myelopathy

  • gait deviation/ataxiaor unsteadiness
  • (+) Hoffman’s sign
  • (+) Inverted supinator sign
  • (+) Babinski
  • over the age of 45

If three of five or four of five of these signs are present, the probability of the diagnosis is 94-99%. [i]

[i] Chad Cook, Christopher Brown, Robert Isaacs, Matthew Roman, Samuel Davis, and William Richardson. Clustered clinical findings for diagnosis of cervical spine myelopathy. J Man Manip Ther. 2010 December; 18(4): 175–180.



Differential Diagnosis of the Spine


Now available on in kindle and soft cover format