July 2002

Anterior Head Translation:

Biomechanics Measurement and Treatment

by Deed E. Harrison, DC

 After his undergraduate pre-chiropractic courses at the University of Utah, Dr. Deed Harrison graduated from Life-West in 1996. He is co-author of more than 50 peer-reviewed, indexed, research articles. These include 32 in JMPT, tjree in Chiropractic Technique, and 15 at major Index Medicus journals. He is a Reviewer for an Index Medicus Orthopaedic journal. He is a certified instructor for CBP® Seminars, has written three new CBP® text books, and is Vice-President of CBP® Nonprofit, Inc. He has a private practice in Elko, Nevada.

In previous issues of the AJCC, I have been discussing the known reliability, validity, consequences, and treatment of different types of postural/spinal subluxations. Here, I will stay with the same agenda. In this issue, the postural subluxation of anterior head translation will be discussed. While many authors have discussed this cervical subluxation, I believe the reader will find the current approach both informative and unique.

Literature Review

            Clinically, anterior head translation (AHT) has been shown to be a common postural displacement, with a conservative estimate being 66 percent of the patient population.1

            In a study of 252 asymptomatic subjects, Harrison et al.2 found that the average amount of AHT was 15.0mm (standard deviation of 10.0mm). The measurement of AHT was taken off of standing lateral cervical radiographs where the horizontal displacement of the posterior superior body corner of C2 was compared to a vertical line drawn superiorly from the posterior inferior body C7 (Figure 1). Of importance, this method of measurement for AHT has been shown to be highly reliable with a standard error of measurement of < 2.0mm.3,4

            According to the data from Harrison et al.,2 a statistical normal magnitude for AHT in asymptomatic subjects would be 15.0mm (10mm or up to 1.0 inch would be considered normal. However, mechanically, 1.0 inch of AHT would cause large compressive, bending, and shear stresses to the cervico-thoracic spine.

            In cadaveric sections, Clauser et al.5 found that the head is approximately 7.55 percent of body mass. Therefore, a 200 lb individual with one inch of AHT would have a minimum of 15 inch lbs. of increased load acting on the upper dorsal spine due to this forward shift in load (Note: a two-inch displacement would be 30 inch lbs). However, due to the increased muscle effort required to stabilize this displacement, the actual increase in load on the spine will likely be much higher.

            Recently, Harrison et al.6,7 have calculated that a mere 30 mm of AHT will increase the compressive and bending loads acting on the lower cervical spine by a factor of 1.25-4.25. Their calculations showed that the stresses acting on the lower cervical spine (C5-T1) changed from tension to compression at the anterior bodies and from compression to tension at the posterior bodies when AHT is present. This information indicates that posterior body osteophytes would form from increased tension (traction spurs) and anterior osteophytes would form from increased compressive loading in the lower cervical spine as a result of AHT.

Cervical coupling patterns and range of motion

            Range of motion for sagittal plane head translation has been studied.8-11 Unfortunately, some investigators describe the motion in terms of angular displacement of C7 relative to the tragus of the ear (this is dependent upon the height of the subject) instead of the more appropriate and valid linear measurement methods.8,9 In a comparison of 42 pain free subjects matched by age and gender with neck pain subjects, Hanten et al.10 found the total range of motion (ROM) for sagittal head translation to be 7.5 cm in neck pain subjects and 10.9 cm in normal subjects. This finding suggests that sagittal head translation ROM may be able to discriminate between normal and neck pain subjects.  Although this is an important range of motion to test for the cervical spine, it is seldom performed in either clinical or impairment rating settings. Interestingly, at least two separate studies have found that men demonstrated a larger ROM in sagittal head translation than women.10,11         

         The main motion displacement of AHT is one of the most widely studied postural abnormalities of the cervical spine. However, only three studies detailing the kinematic coupling patterns of this movement could be found.12-14 Importantly, the studies have found the same coupling patterns. Namely, that the lower cervical vertebra (C5-C7) will flex and the cervical segments C0-C4 will extend during AHT.12-14

            In Figure 2A-B, the coupling patterns for AHT are depicted. In Figure 2B, the neutral ideal alignment of the cervical spine is shown.

            In Figure 2A, a large amount of AHT is present. Here, the lower cervical spine (C5-C7) has flexed relative to the ideal in 2B, while the segments from C0-C4 are in slight extension. Generally with primary AHT subluxations less than 50mm, the cervical lordosis (C2-C7) will be between 25 and 40.   In contrast, with large AHT subluxations (usually above 50 mm), the lower cervical spine will appear kyphotic and the upper cervical spine slightly lordotic. Thus, large head translations give the appearance of an S-curve with a lower cervical spine reversed. Many times the S-curve depicted in Figure 2A is mistaken for a true cervical kyphotic S-curve between C4/C5-T1, when in fact it is normal cervical coupling patterns for a large anterior head translation. To illustrate the discussed effect that large AHT has on the cervical spine, Harrison, Harrison, and Haas15 presented a case study in their new Cervical Spine Rehabilitation text (the interested reader is referred to this text in Figure 2-28 A and B page 29).

Reliability and Validity of Measurement Methods

            In the literature, there are a variety of different methods for the measurement of AHT. These methods include:                       1) the linear excursion measurement device (LEMD) which measures the displacement of C7 spinous relative to the tragus or helix of the ear or to the posterior aspect of the eye,

            2) body postural photographs where either the C7 or AC-joint of the shoulder is measured relative to the EAM or similar location,

            3) the CROM device,

            4) a simple plumb line measurement of the ear to the shoulder,5 a horizontal angular measurement of the C2 spinous relative to T1 or C7,6 and lateral cervical x-ray analysis where the horizontal displacement of either C1 or C2 is compared to a vertical line originating at T1 or C7 respectively.1-4,8-11,15-19 

            Without exception, these methods have been found to have high intra and inter-examiner reliability. Further, even on different day, week, and month measurements of the same subjects, provided the subject had no treatment nor trauma, the measurements have been found to be repeatable and stable on repeat measures.9,18-22 This information proves that posture measurement is stable over time.

            A serious concern with AHT measurements is the validity of the measurement method. One of the primary validity problems is the use of angular measurement methods to quantify a linear displacement. With an understanding of basic trigonometry, it becomes apparent that angular measurements are largely dependent upon the height of the subject. Using C7 spinous relative to the tragus of the ear compared to horizontal, for the same magnitude of translation, a taller subject would have a greater angle than a shorter individual.

            A second validity concern is the fact that more than one posture of the head relative to the thorax can cause the ear to be displaced in front of the shoulder (head flexion).

            A third validity concern is that postural displacements below the head can mimic AHT. For example, if the thorax is in extension relative to the pelvis and the head is flexed relative to the thorax, then it will appear in 3-D space that the skull is anteriorly translated when in fact it is flexed.

            Figure 3A depicts the double combination of thoracic extension and head flexion. Finally, the last validity issue is that some combinations of shoulder and head postures can hide the true magnitude of AHT.

            Figure 3B depicts a subject with a large amount of AHT.                       

  Figure 3C depicts the same large amount of AHT but this time with the added posture of rounded shoulders. Notice that the large amount of AHT is hidden by the added shoulder posture.

            According to the above information, we at CBP® see it as paramount that the lateral cervical x-ray is taken in each case. In this manner, the lateral cervical coupling patterns can be compared to the subjects lateral spine posture.

AHT Correlated to Pain and Health

            Several authors have found a relationship between AHT and various pain syndromes, including: neck pain,1,23 headaches,1,24,25 thoracic outlet syndrome,26 radicular pain,27 TMJ and other dental dysfunctions,28,29 and obstructive sleep apnoea.30,31 In contrast, some studies have found no relationship between AHT and neck pain.10,18,22

            The discrepancy between studies is dependent on several factors. These include:

            1) the measurement method use to assess AHT,

            2) the use of the standing versus seated measurement position,

            3) the use of control groups that were not appropriately matched to the treatment group, and

            4) the lack of appropriate pain or disability questionnaires for quantification of pain and dysfunction.

Causes of AHT

            In the literature, there are several purported factors linked to the cause of AHT. Most of the causes of AHT can be considered to be repetitive micro-traumatic events. Willford et al.32 found that the continued use of multifocal lenses was linked to AHT. Ordway et al.12 state that AHT commonly occurs in activities such as “...driving, reading, TV watching, and desk/keyboard activities.” Recent studies have found that backpack carrying in children is a definitive cause of AHT.33,34 It should be obvious that macro-traumatic events (motor vehicle accidents, falls, sport collisions, etc...) will also cause AHT.

Treatment

            Harrison35-38 has developed unique postural adjustments, exercises, and traction for the correction/reduction of AHT. These procedures are termed Mirror Image®.

            Figure 4A shows the Mirror Image® Adjustment using the Omni Drop Table for the correction of AHT.

            Figure 4B depicts the Mirror Image® Adjustment using the CBP® hand held instrument to correct the postural displacement of AHT.

Figure 5A and 5B depict the pain free range of motion and resistance Mirror Image® Exercise for the correction of AHT.

Lastly, Figure 6 depicts one type of Mirror Image® Traction in order to correct AHT.

            According to CBP® protocol,14,35 a patient will be progressed depending upon tolerance (over a 10 +/- 2 week program) into all three Mirror Image® Postural procedures, adjustment, exercise, and traction.

            The patient is required to treat at a frequency of 3-5 times per week for the duration of the program. After completion, a re-evaluation with appropriate spinal x-rays and posture analysis are performed and the progress/percentage improvement of the patient’s displacement is noted.

            Figure 7A depicts a patient suffering from neck and upper thoracic pain with an initial subluxation of 72 mm of AHT on the pre-treatment x-ray. After 12 weeks of CBP® care (approximately 36 visits), the pain levels were improved and the translation has been reduced to 43 mm on second lateral cervical x-ray in Figure 7B. Notice the improvement in the cervical lordosis due to the correction of the AHT subluxation.

            Currently, there are five papers in the indexed medicus literature showing that the magnitude of AHT can be reduced by both exercise39,40 and CBP® traction methods.41-43 However, no study to date has specifically shown that reducing the AHT is effective at reducing a patient’s pain syndrome and disability.

            Currently, we are collecting data on the ability of CBP® Mirror Image® procedures to correct/reduce AHT in chronic neck pain patients. 

References

            1. Griegel-Morris P, Larson K, Mueller-Klaus K, Oatis CA. Incidence of common postural abnormalities in the cervical, shoulder, and thoracic regions and their association with pain in two age groups of healthy subjects. Phys Ther 1992;72:425-431.

            2. Harrison DD, Janik TJ, Troyanovich SJ, Holland B. Comparisons of lordotic cervical spine curvatures to a theoretical ideal model of the static sagittal cervical spine. Spine 1996;21:667-675.

            3. Harrison DE, Harrison DD, Cailliet R, Troyanovich SJ, Janik TJ, Holland B. Cobb Method or Harrison Posterior Tangent Method: Which is Better for Lateral Cervical Analysis? Spine 2000; 25:2072-78.

            4. Harrison DE, Holland B, Harrison DD, Janik TJ.  Further Reliability Analysis of the Harrison Radiographic Line Drawing Methods: Crossed ICCs for Lateral Posterior Tangents and AP Modified Risser-Ferguson. J Manipulative Physiol Ther 2002; 25(2):93-98.

            5. Clauser, C.E., McConville, J.T., and Young, J.W. Weight, Volume, and Center of Mass of Segments of the Human Body.  pp. 3, AMRL-TR-69-70, Aerospace Medical Research Library, Aerospace Medical Division, Air Force Systems Command, Wright-Patterson Air Force Base, Ohio, 1969.

            6. Harrison DE, Jones WE, Janik TJ, Harrison DE. Evaluation of axial and flexural stresses in the vertebral body cortex and trabecular bone in lordosis and two sagittal cervical translation configurations with an elliptical shell model. J of Chiropractic Education 2002;16(1):76.

            7. Harrison DE, Jones WE, Janik TJ, Harrison DE. Evaluation of axial and flexural stresses in the vertebral body cortex and trabecular bone in lordosis and two sagittal cervical translation configurations with an elliptical shell model. J Manipulative Physiol Ther 2002;25: In Press.

            8. Grimmer K. Measurement of cervical excursion angles in a treatment setting. A pilot study. Physiotherapy 1993;79:451-456.

            9. Braun BL, Amundson LR. Quantitative assessment of head and shoulder posture. Arch Phys Med Rehabil 1989;70:322-329.

            10. Hanten WP, Olson SL, Russell JL, Lucio RM, Campbell AH. Total head excursion and resting head posture: Normal and patient comparisons. Arch Phys Med Rehabil 2000;81:62-66.

            11. Hanten WP, Lucio RM, Russel JL, Brunt D.  Assessment of total head excursion and resting head posture. Arch Phys Med Rehabil 1991;72:877-880.

            12. Ordway NR, et al. Cervical flexion, extension, protrusion, and retraction. A radiographic segmental analysis. Spine 1999;24:240-247.

            13. Penning L. Normal movements of the cervical spine. Am J Roentgenol 1978;130:317-326.

            14. Penning L. Kinematics of cervical spine injury. A functional radiological hypothesis. Eur Spine J 1995;4:126-132.

            15. Harrison DE, Harrison DD, Haas JW. CBP® Structural Rehabilitation of the Cervical Spine. Harrison CBP® Seminars, Inc., 2002, page 29.

            16. Zonnenberg AJJ, Van Maanen CJ, Elvers JWH, Oostendorp RAB. Intra/Interrater reliability of measurements on body posture photographs. J Craniomandibular Practice 1996;14:326-331.

            17. Garrett TR, Youdas JW, Madson TJ. Reliability of measuring forward head posture in a clinical setting. JOSPT 1993;17:155-160.

            18. Harrison AL, Barry-Greb T, Wojtowicz G. Clinical measurement of head and shoulder posture variables. JOSPT 1996;23:353-361.

19. Refshauge K, Goodsell M, Lee M. Consistency of cervical and cervicothoracic posture in standing. Australian J Physiotherapy 1994;40:235-240.

            20. Grimmer K, An investigation of poor cervical resting posture. Australian J Physiotherapy 1997;43:7-16.

            21. Raine S, Twomey L. Posture of the head, shoulder and thoracic spine in comfortable erect standing. Australian J Physiotherapy 1994;40:25-32.

            22. Grimmer K. The relationship between cervical resting posture and neck pain. Physiotherapy 1996;82:45-51.

            23. Haughie LJ, Fiebert IM, Roach KE. Relationship of forward head posture and cervicala backward bending to neck pain. J Manipulative Physiol Ther 1995;3:91-97.

            24. Watson DH, Trott PH. Cervical headache: an investigation of natural head posture and upper cervical flexor muscle performance. Cehpalalgia 1993;13:272-284.

            25. Marcus DA, Scharff L, Mercer S, Turk DC. Musculoskeletal abnormalities in chronic headache: a controlled comparison of headache diagnostic groups. Headache 1999;39:21-27.

            26. Smith KF. The thoracic outlet syndrome: a protocol of treatment. JOSPT 1979;1:89-99.

            27. Abdulwahab SS, Sabbahi M. Neck retractions, cervical root decompression, and radicular pain. JOSPT 2000;30:4-9.

            28. Rocabado M, Johnston BE, Blakney MG. Physical therapy and dentistry. An overview. J Craniomand Pract 1983;1:47-49.

            29. Shiau YY, Chai HM. Body posture and hand strength of patients with temporomandibular disorder. J Craniomand Pract 1990;8:244-251.

            30. Ozbek MM, Miyamoto K, Lowe AA, Fleetham JA. Natural head posture, upper airway morphology and obstructive sleep apnoea severity in adults. Eur J Orthod 1998;20:133-143.

            31. Tangugsorn V, Skatvedt O, Krogstad O, Lyberg T. Obstructive sleep apnoea: a ceophalometric study, part I. cervico-craniofascial skeletal morphology. Eur J Orthod 1995;17:45-56.

            32. Willford CH, Kisner C, Glenn TM, Sachs L. The interaction of wearing multifocal lenses with head posture and pain. JOSPT 1996;23:194-199.

            33. Chansirinukor W, Wilson D, Grimmer K, Dansie B. Effects of backpacks on students: measurement of cervical and shoulder posture. Aust J Physiotherapy 2001;47:110-116.

            34. Pascoe DD, Pascoe DE, Wang YT, Shim DM, Kim CK. Influence of carrying book bags on gait cycle and posture of youths. Ergonomics 1997;40:631-641.

            35. Harrison DD, Janik TJ, Harrison GR, Troyanovich SJ, Harrison DE, Harrison SO.  Chiropractic Biophysics Technique: A Linear Algebra Approach to Posture in Chiropractic. J Manipulative Physiol Ther 1996;19(8): 525-535.

            36. Harrison DD. CBP® Technique: The Physics of Spinal Correction. National Library of Medicine #WE 725 4318C, 1982-97. Harrison DD. CBP® Technique: The Physiscs of Spinal Correction.

            37. Harrison DD. Spinal Biomechanics: A Chiropractic Perspective. National Library of Medicine #WE 725 4318C, 1982-97. Harrison DD. CBP® Technique: The Physiscs of Spinal Correction.

            38. Harrison DD. Abnormal postural permutations calculated as rotations and translations from an ideal normal upright static spine. In: JJ Sweere, editor, Chiropractic Family Practice. Gaithersburg: Aspen Publishers, pp.6-1:1-22, 1992.

            39. Pearson ND, Walmsley RP. Trial into the effects of repeated neck retractions in normal subjects. Spine 1995;20:1245-1251.

            40. Darlilng DW, Kraus S, Glasheen-Wray MB. Relationship of head posture and the rest position of the mandible. J Prosthetic Dentistry 1984;52:111-115.

            41. Harrison DE, Cailliet R, Harrison DD, Janik TJ, Holland B. New 3-Point Bending Traction Method of Restoring Cervical Lordosis Combined with Cervical Manipulation: Non-randomized Clinical Control Trial. Arch Phys Med Rehab 2002; 83(4):447-453.

            42. Harrison DE, Harrison DD, Betz J, Janik TJ, Holland B, Colloca C. Increasing the Cervical Lordosis with CBP® Seated Combined Extension-Compression and Transverse Load Cervical Traction with Cervical Manipulation: Non-randomized Clinical Control Trial. J Manipulative Physiol Ther 2002; in press.

            43. Harrison DD, Jackson BL, Troyanovich SJ, Robertson GA, DeGeorge D, Barker WF. The Efficacy of Cervical Extension-Compression Traction Combined with Diversified Manipulation and Drop Table Adjustments in the Rehabilitation of Cervical Lordosis. J Manipulative Physiol Ther 1994; 17(7): 454-464.