The core of the neck

Chronic neck pain

The human neck is a complex system of muscle, bone, joints and connective tissue. Chronic neck pain is increasingly becoming common in the modern society. The incidence of neck problem is reported to be greater in modernised, western society with the prevalence in the adult population being reported to be between 6-22%1. Another study in Canada indicates that 67% of individuals will suffer neck pain at some stage throughout life2. With an increasing reliance on the computer, neck pain has become a great challenge in bodywork. Effective management of this condition is essential not only for symptoms relief but more importantly, for the prevention of recurrent episodes of neck pain.

Neck muscles predominately provide head stabilisation demands, it is estimated that neck muscles contribute about 80% to the mechanical stability of the cervical spine3. The other 20% is provided by the osseo-ligamentous system, which occurs mainly at end of range postures. Muscles provide dynamic support in activities around the neutral and mid-range postures, which are common during functional daily tasks.

In a paper published in the European Spine Journal in 2007, Swiss researchers examined the correlation between the presence of neck pain and alterations of the normal cervical lordosis. They examined using x-rays two groups of people: 54 people with a history of neck pain and 53 without. They found no significant difference between the two groups. The authors concluded that the presence of such structural abnormalities in the patient with neck pain must be considered coincidental, i.e. not necessarily indicative of the cause of pain.

Muscle weakness

Muscle weakness and impairment is a key feature of chronic neck pain⁵. Janda’s theory suggests the cervical flexor muscles become dysfunctional in the presence of neck pain. Simple clinical mechanical measures also demonstrated a reduction in the strength and endurance capabilities of the cervical flexor muscles in neck pain.

New research from the University of Queensland by Deborah Falla & Paul Hodges in the detection, recording and analysis of myoelectric signals with surface electromyography (EMG) demonstrates new and sophisticated ways of determining abnormal muscle function.  Results from their research have demonstrated that people with chronic neck pain will show the following conditions:

• impairment in the deep cervical muscles, which are considered to be functionally important for joint support and control,
• deficits in muscle coordination which could result in poor support and potential overload on cervical structures,
• insufficiency in the pre-programmed activation of cervical muscles,
• inefficient neuromuscular activation,
• greater fatigability of superficial cervical muscles.

The core of the neck

Research from Australia identified deficits in the motor control of the deep and superficial cervical flexors in people with chronic neck pain, characterised by a delay in onset of neck muscle contraction associated with movement of the upper limb.

Studies also demonstrated a reduction in the strength and endurance capacity of the cervical flexor and extensor muscles in people with neck pain. Sternocleidomastoid (SCM) and anterior scalene (AS) muscles showed  greater fatigability at moderate loads, and also during low load sustained contractions.

It was also found that people with neck pain demonstrated an altered pattern of muscle activation characterised by reduced deep flexor muscle activity during a low load functional task and increased activity of the superficial cervical flexors.

Whilst direct evidence of deep cervical extensor muscle dysfunction has been identified in people with neck pain, there was no succinct evidence that described impairment in the deep cervical flexor (DCF) muscles until recently. The DCF muscles, including the longus colli, longus capitis, rectus capitis anterior and rectus capitis lateralis, are histologically and morphologically designed to provide support to the cervical lordosis and the cervical joints. Now research has demonstrated reduced activation of the DCF muscles or the neck pain patient.

People with chronic neck pain have a disturbance in the neck flexor synergy, where impairment in the deep muscles is compensated for by increased activity in the superficial muscles (SCM and AS).

Reduced neuromuscular efficiency indicates that the neck pain patients required greater muscular activity to produce an equivalent amount of force as compared to normal person.

Researcher Deborah Falla suggest parallels between the deep core neck flexors in neck pain with transverse abdominis and multifidus dysfunction in people with lower back pain.

Chronic neck pain is a complex nature of muscle impairment as opposed to simple weakness.

Implications for rehabilitation

Neck strengthening exercises have been shown to be beneficial in preventing and treating work-related musculoskeletal disorders of the neck. When developing exercises for treatment, it is necessary to have an understanding of abnormalities in the muscular system associated with painful dysfunctional joints. The results of recent research have significantly advanced our understanding of the impairment in the deep and superficial cervical flexor muscles in patients with neck pain syndromes. Based on the muscle deficits considered to occur in neck pain, two types of exercise programs have been proposed in the literature to address cervical flexor muscle impairment. These two types of exercise programs are focused on two different functional requirements.

The first exercise regime consists of general strengthening and endurance exercises for the neck flexor muscles. These exercises involve high load training and thus recruit all the muscle synergists that is, both the deep and superficial muscles. For example, strengthening the neck flexor muscles is achieved by performing a head lift manoeuvre which would recruit all muscles capable of contributing to this action including, SCM, AS, longus colli and longus capitis. A typical exercise program would train the cervical flexors with the controlled head lift exercise and focus on training endurance and increasing the number of repetitions.

The second exercise regime has been designed to focus on the muscle control aspects and aims at improving control of the muscles within the neck flexor synergy. In contrast to more traditional high load strength and endurance exercises, low load exercise is used to train the coordination between the layers of neck flexor muscles. With this protocol, patients perform and hold progressively inner ranges of cranio-cervical flexion (C-CF) while trying to minimize activation of the superficial flexors. General strengthening exercises are not recommended in the early stages in this exercise approach as it is considered that general exercise will not necessarily address the dysfunction between the deep and superficial muscles. Thus, specific emphasis is first placed on re-educating the deep and postural muscles and general strengthening exercises are only introduced once the imbalance between the deep and superficial neck synergists has been addressed.

References

¹ Fejer R, Kyvik KO, Hartvigsen J. The prevalence of neck pain in the world population: a systematic critical review of the literature. European Spine Journal 2006;15:834-48.

² Cote P, Cassidy JD, Carroll L. The Saskatchewan Health and Back Pain Survey: the prevalence of neck pain and related disability in Saskatchewan adults. Spine 1998; 23:1689–98.

³ D. Grob, H. Frauenfelder, and A. F. Mannion The association between cervical spine curvature and neck pain. Eur Spine J. 2007; 16:669–678.

⁴ Panjabi MM, Cholewicki J, Nibu K, Grauer J, Babat LB, Dvorak J. Critical load of the human cervical spine: an in vitro experimental study. Clinical Biomechanics 1998;13:11–7.

5 Falla D. Unravelling the complexity of muscle impairment in chronic neck pain. Manual Therapy 2004; 9:125–133