Cervical Facet Capsular Injury and Biomechanics

Injury to the cervical facet capsular ligaments is a potential mechanism for chronic pain after an acute whiplash injury.

It is generally well known and accepted in the medical community that car crash victims whose heads are turned prior to impact have more severe and persistent whiplash symptoms than patients who were facing forward.[1]’[2] These findings have prompted biomechanical studies using necks from human cadavers to investigate why a head-turned posture increases injury potential.  Detailed measurements of the strain field in the facet capsule have also shown that a head-turned posture generates higher capsular strains than a neutral head posture,[3] but the quasi-static loads applied during those tests were limited to pure flexion/extension moments and did not include the axial compression or posterior shear present during whiplash loading. Until recently, no such biomechanical studies analyzed in detail how a head-turned posture, combined with multi-axial whiplash loads, affects facet capsular ligament strain, if at all.

In a 2008 Canadian-based study on the head-turned posture and its increased risk on cervical facet capsule injuries during a car crash, scientists used thirteen motion segments from 7 women donors (each around 50 years of age)[4]   Researchers applied axial pre-torques, axial compressive preloads and quasi-static shear loads to the superior vertebral body to simulate whiplash kinematics with the head turned. Three-dimensional displacements of markers placed on the right facet capsular ligament were used to estimate the strain field in the ligament during loading.  The effects of pre-torque direction, compression, and posterior shear on motion segment motion and maximum principal strain in the capsule were examined using repeated-measures analyses of variance.

The study revealed some of the following results:

• Maximum Principal Strain (MPS) in the facet capsule was affected more by axial pre-torque than either axial compression or posterior shear

• At all but the lowest shearloads, MPS was higher for the ipsilateral pre-torque than the contralateral pre-torque

• MPS in the facet capsule occurred most frequently in elements located in the superior and anterior quadrants of the capsule

• Axial pre-torque and the resulting axial rotation of the intervertebral joint have a large effect on the MPS in the cervical facet joint capsule when combined with compression, shear, and extension loads simulating a lowspeed rear-end automobile impact

• Peak strains in the capsule with an ipsilateral pre-torque were double the previously-reported peak strains without a pre-torque, but similar to the previously reported strains to cause partial failures in these specimens

• These findings potentially explain the increased severity and persistence of whiplash symptoms in patients who had their heads turned at impact[5]

The key takeaways from this study include:

• The likelihood of a severe injury is greater when uneven loads are applied to the spine. This can occur when a vehicle is struck in the left-rear corner, as it is turning, or when the occupant’s head is turned to the side while gazing out a window or talking to another occupant.  When the head is rotated 45 degrees, the neck’s ability to extend backwards is decreased by 50 percent.  This results in increased forces on the joints on one side and different forces on the other. The spaces in the spine through which the nerves pass are smaller when the head is turned, making the nerves more vulnerable to injury.
• Cervical injury can be more severe when the head is turned, so it is important to make sure to discuss with the patient the biomechanics of how the injury occurred and to make sure it is well documented in the chart notes.  This is especially important if you are treating a whiplash patient who is outside the typical “bell curve” in terms or response to treatment and length of recovery.  As noted above, if the patient’s head was turned to the left or right (e.g. looking in the side mirror, or talking with a passenger) at impact it can dramatically increase the severity of the injury.

Proper documentation of the bio-mechanism of injury goes a long way in supporting payment for treatment services and providing continued access to the treatment needs of your patient. Similarly, having the right attorney represent the patient with traumatic injuries can go a long way in helping the patient get the care they need so that they can get well.

For more information on personal injury claims, request a complimentary copy of Richard Adler’s highly acclaimed book, From Injury to Action: Navigating Your Personal Injury Claim for yourself or your patient.