Understanding Stability

Author: Philip A. Croatan

Knee Instability

The knee, or the femoro-patellar joint articulation, is a synovial-plane joint that serves as stable region in the kinetic chain. It is functionally diarthrotic allowing gliding of patella. The knee is the largest and most complex joint in the body. Collectively, the intermediate articulation between the patella and the lower end of the femur, and the lateral and medial joints (tibiofemoral) between the femoral condyles above and the C-shaped menisci of the tibia make up the entire knee joint (Anatomy, Physiology, 2012). 

When stability is sacrificed at the knee, vertical compensation occurs at the hip and or ankle. Instability of the knee is most commonly manifested as medial valgus collapse stimulating from the lack of mobility at one or both of its adjacent mobile structure (ankle and hip). The quadriceps femoris muscles insert at the patella and are primarily responsible for knee extension. The hamstrings muscles posteriorly cross the knee and are primarily responsible for flexion of the knee. The knee joint is functionally limited to flexion and extension (Anatomy, Physiology, 2012).

Limitation within the hip joint is a common causality of knee instability. The loss of functional abilities such as squatting, bending, and hinging due to the lack of hip mobility are compensated for with knee valgus and places excess stress on medial and lateral structures. Valgus collapse can prevent proper rebounding during landing and jumping movements (Davis, 2015).

Post-faciliatation is a treatment method to address issues commonly affecting knee instability such as tightness of hip flexors and internal hip rotation. The technique affects both contractile and non-contractile structures of which play a significant role in the kinetic chain between the ankle, knee, and hip. However, the technique requires the patient’s ability relax immediately and on demand. This stretch is usually performed over the most stable joint available, in this case is the knee (Page, Lardner, & Frank 2015).

The complexity of the knee joint allows for multiple assessment tools. A close observation of spinal-hip-knee-ankle alignment throughout squatting motion, as well as dynamic gait analysis will allow for clinical reference of the pathomechanics displayed. Compliant and whole-body vibrational surfaces stress the sensorimotor cortex to store memory of the most efficient movement solutions (McKeon, 2012). However, more practical treatment solutions of knee instability target the improvement of neuromuscular control by means of stretching, full ROM exercises, quadricep strengthening exercises. There is no current consensus regarding the utility of nonoperative management of patellofemoral instability. Treatment is recommended to remain relative to the dysfunctions experienced by patients.

Cervical Instability

The cervical vertebrae refer to vertebral bodies C1-C7 and are the smallest and lightest vertebral structures. This region is anatomical region of stability. Cervical vertebrae C1 and C2 have distinguishing anatomical features specific to rotational function, while C3-C7 are similar in structure. Cervical vertebral structures C3-C7 have oval shaped bodies that are wider from side-to-side compared to the anterior-posterior dimensions. Excluding C7, the vertebral bodies have a short bifid spinous process that projects posteriorly. The foramen is large and triangular in shape. Additionally, the bodies possess two transverse foramens in which the vertebral arteries pass to service the brain (Anatomy, Physiology, 2012).

The cervical spine is a part of most recognized postural chain which occurs throughout the entirety of the spine to the pelvis. The regions of the spine are interconnected through the vertebral system and postural changes in any region has direct effect on adjacent structures. An example of this phenomena is well-described in Brügger’s sitting posture (Page, Lardner, & Frank, 2010).

Literature surrounding the assessment and treatment of cervical instability has grown significantly in the last decade. Subjective features of clinical instability of the cervical spine include but are not limited to: intolerance to prolonged static posture, fatigue and instability to support weight of head, decreased symptoms with external support, frequent self-manipulation, and shaking or lack of control. Objective features of clinical cervical instability include poor coordination and neuromuscular control, segmental hinging/fulcrumming, aberrant movement, and hypomobility of the upper thoracic spine (Physiotutors, 2017).

The cervical spine is characteristically a first-class lever in which the effort is applied posteriorly and the load anteriorly. The alanto-occipital joint acts as the fulcrum (Anatomy, Physiliology, 2012). The cervical vertebral column is highly dependent on the active support of muscles for physical support and instability dysfunction is therefore usually attributed to the imbalance of forces between anterior (sternocleidomastoid and scalenes) and posterior (Splenius capitis and Splenius cervicis) muscles. Patients with Mechanical Neck Pain Disorders (MNPD) consistent display changes in muscle behavior. Hyperactivity in the anterior-scalene and sternocleidomastoid during cranio-cervical flexion and upper-limb movement, as well as coactivation of superficial cervical flexors and or extensor muscles during isometric contraction (O’Leary, Falla, Elliott, & Jull, 2009). Common MNPD is accompanied by perturbation within the phasic system that runs posteriorly, allowing for hypomobility of the upper thoracic spine and hyperkyphotic posture. Scalenes and upper-extremity extensors and supinators are prone to muscle lengthening and subsequent weakness. Clinical imaging devices such as Digital Motion X-ray (DMX) are ideal for observing faulty movement of vertebral bodies. However, these machines are not commonly available to clinicians and require a specific skill set to operate. More practical options for clinicians include observational analysis. The observation of dynamic postural control is considered cornerstone in clinical assessment. Functional-oriented approaches encourage patient compliance. Functional activities should progress from coordination between deep-and-superficial cervical flexors, to low-load supine endurance training of deep cervical flexors, to prone concentric contraction and eccentric contraction of cervical flexors utilizing weight of head, to functional upright tension (O’Leray et al., 2009).


Anatomy, Physiology. (2012). Reference & Research Book News, 27(3), 187–190. Retrieved from http://p.atsu.edu/login url=http://search.ebscohost.com/login.aspx?direct=true&db=lih& AN=77480523&site=eds-live

Davis, K. (2015). Flexibility, mobility, and stability: What’s the difference and why are they important. Retrieved from https://www.fix.com/blog/flexibility-mobility-stability/ 

O’Leary, S., Falla, D., Elliott, J. M., & Jull, G. (2009). Muscle dysfunction in cervical spine pain: implications for assessment and management. The Journal Of Orthopaedic And Sports Physical Therapy, 39(5), 324–333. https://doi- org.p.atsu.edu/10.2519/jospt.2009.2872

McKeon, P. O. (2012). Dynamic Systems Theory as a Guide to Balance Training Development for Chronic Ankle Instability. Athletic Training & Sports Health Care: The Journal for the Practicing Clinician, 4(5), 230–236. Retrieved from http://p.atsu.edu/login?url=http://search.ebscohost.com/login.aspx?direct=true&db=s3h& AN=83407294&site=eds-live

Page, P., Lardner, R., & Frank, C. (2010). Assessment and Treatment of Muscle Imbalance : The Janda Approach. Champaign, IL: Human Kinetics, Inc. Retrieved from http://p.atsu.edu/login?url=http://search.ebscohost.com/login.aspx?direct=true&db=nlebk &AN=698372&site=ehost-live&scope=site

Physiotutors [Screen Name], (2017, July 17). Signs and Symptoms of Clinical Cervical Spine  Instability. Retrieved from https://www.youtube.com/watch?v=WZABj0Ajwdw