Pain thresholds and tenderness in neck and head following acute whiplash injury: a prospective study

Pain thresholds and tenderness in neck and head following acute whiplash injury: a prospective study H Kasch1,2, K Stengaard-Pedersen2,3, L Arendt-Nie...
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Pain thresholds and tenderness in neck and head following acute whiplash injury: a prospective study H Kasch1,2, K Stengaard-Pedersen2,3, L Arendt-Nielsen4 & T Staehelin Jensen1,2 1 Department of Neurology, Aarhus University Hospital, 2 Danish Pain Research Centre, Aarhus University, 3Department of Rheumatology, Aarhus University Hospital, Aarhus, Denmark, 4Centre for Sensory±Motor Interaction, Aalborg University, Aalborg, Denmark

Kasch H, Stengaard-Pedersen K, Arendt-Nielsen L & Staehelin Jensen T. Pain thresholds and tenderness in neck and head following acute whiplash injury: a prospective study. Cephalalgia 2001; 21:189±197. London. ISSN 0333-1024 Objective of the investigation: In a 6-month prospective study of 141 consecutive acute whiplash-injured participants, and 40 acute, ankle-injured controls, pain and tenderness in the neck/head, and at a distant control site, were measured. Basic procedures: Muscle palpation and pressure algometry in ®ve head/neck musclepairs were performed after 1 week and 1, 3 and 6 months after injury. Algometry was performed at a distant control site. Main ®ndings: Whiplash-injured patients had lowered pressure-pain-detection thresholds and higher palpation-score initially in the neck/head, but the groups were similar after 6 months, and the control site was not sensitized. Principal conclusion: Focal, but not generalized, sensitization to musculoskeletal structure is present until 3 months, but not 6 months, after whiplash injury, and probably does not play a major role in the development of late whiplash syndrome. Pressure algometry and palpation are useful clinical tools in the evaluation of neck and jaw pain in acute whiplash injury. u Whiplash injuries, pressure algometry, palpation, muscle pain, injuries, ankle Helge Kasch, Danish Pain Research Centre and Department of Neurology, Aarhus University Hospital, Noerrebrogade 44, Building 1C, DK-8000 Aarhus, Denmark. Tel.+45 89493455, fax+45 89493269, e-mail [email protected] Received 7 July 2000, accepted 31 January 2001

Introduction Subjects exposed to a whiplash injury of the neck may develop a chronic pain condition (a so-called late whiplash syndrome) without detectable, pathological lesions at physical examination or using imaging techniques, such as X-ray, CT or MRI scan (1±4). The incidence rates of whiplash injury differ considerably amongst various countries, and even amongst regions in countries. In Canada, for example, Quebec had 70 compensated whiplash insurance claims per 100 000 inhabitants in 1987 (no-fault system: person receives immediately after injury an amount of money for pain and suffering), whereas Saskatchewan (tort system: person can sue for pain and suffering) had 700 compensated claims in the same time-span (5). The no-fault system seems superior to the tort system as shown in a large study from Saskatchewan, changing from tort system to no-fault system in 1995 with # Blackwell Science Ltd Cephalalgia, 2001, 21, 189±197

subsequent decline in whiplash incidence rate and reduced pain and other symptoms after injury (6). A Dutch study ®nds a 10-fold increase during a 25-year period of neck sprain following car collision (7) from 3.4 in 1970 to 40.2/100 000 in 1994. An unknown proportion of whiplash-injured people will develop late whiplash syndrome. The proportion with chronic symptoms is reported differently in various prospective studies. In a questionnaire-based study from Lithuania, none of 201 whiplash-injured subjects became chronic whiplash patients, and all recovered from symptoms, including neck pain and headache, within the ®rst 20 days (8). In contrast, a UK study reported that 76% of 50 whiplash-injured patients took legal action after 2 years (9), and 70% of 40 available from the cohort complained of symptoms related to whiplash injury 15 years later (10). Neck pain and headache are more consistently reported symptoms in both early and late whiplash 189


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injury. Recent prospective whiplash studies from Switzerland and Sweden have shown a high frequency of neck pain after acute whiplash injury. Immediately after injury, neck pain occurs in 90% of whiplash-injured patients (11±13), and 2 years after injury, neck pain is present in 20±25% of subjects. The Swiss study ®nds that initial high pain intensity predicts a bad outcome, and the prognosis is worsened when the subject has pretraumatic neck pain, tension type headache or migraine (13±15). While pain and strain of soft-tissue of the neck have been proposed as causative factors for the immediate pain, the mechanisms underlying the more prolonged pain complaints are less clear. An extensive literature has provided evidence for sensitization of the nervous system, and for the development and persistence of experimental and clinical musculoskeletal pains (16). One aspect of such hyperexcitability is a lowering of thresholds to pain following different stimuli. For example, subjects with chronic tension-type headache, ®bromyalgia and rheumatoid arthritis display a lowering of pressure-pain-detection thresholds (17±21), and one study has demonstrated hypersensitivity in chronic whiplash patients (22). Palpometry (23, 24) and pressure algometry are simple methods for assessing tenderness and pain from deep structures. To our knowledge, pressure algometry has not previously been used in assessment of muscle pain in a longitudinal study of acute whiplash-injured persons. In the present study, we tested the hypothesis that soft tissue injury due to a whiplash injury sensitizes nociceptors, and that this sensitization may involve peripheral as well as central mechanisms. The hypothesis of sensitization in deep structures in subjects exposed to whiplash injury was tested by means of pain assessment in the neck and jaw muscles, and at a distant control site in acute whiplash-injured patients compared with acute ankle-distortion subjects. Both groups were expected to have initial pain, but of different origin.

Methods Patient ¯ow, age- and sex-matching have been described previously (25). From January 1997 to January 1998, all whiplashexposed persons in the Aarhus area, covering 284 000 inhabitants, were invited to participate, if they met following criteria: ' ' ' '

had had had had

been exposed to a rear-end car collision; preserved full consciousness during collision; shown no sign of amnesia after the injury; contacted the local emergency unit within 48 h


after collision with whiplash-related complaints, such as neck pain, headache and neck stiffness at the unit; and were aged between 18 and 70 years. Exclusion criteria were the following:





previously known considerable neck or back disorder or head injury complaints; previously known severe headache, migraine or widespread pain; previously known record of severe, psychiatric disease; and previously known abuse of drugs or alcohol.

Approval from the local ethical committee was obtained, and the study was conducted in accordance with the Helsinki II declaration. Subjects and control subjects gave informed written consent at their ®rst visit. The control group consisted of persons sustaining acute non-sport, ankle distortion, where X-ray had ruled out fracture, and who otherwise ful®lled the same criteria as whiplash-injured subjects. One hundred and twenty-one consecutive ankle distortion subjects seen at the Emergency Unit of the Department of Orthopaedic Surgery, Aarhus University Hospital, constituted a possible control sample. From this group 40 age- and sex-matched subjects gave their consent to participate. Selecting a control group with another acute traumatic pain condition allowed us to balance the design of the study, regarding possible in¯uence of post-traumatic stress on pain. At all visits, participants underwent semistructured interviews, the McGill Pain Questionnaire, and data considering medical/physical/pharmacological treatment, as well as other treatment not subscribed by medical doctors, were obtained. Whiplash-injured patients and controls rated their pain in the neck, head, shoulder/arm and low back with a visual analogue scale (VAS0x100) with 0=no pain and 100=worst imaginable pain. All measurements were carried out by the same examiner (HK) in a quiet room at room temperature with the subject comfortably seated in a supine position. Deep pain was measured by means of a pressure algometer (SOMEDIC AB, Algometer Type 1). Subjects were instructed to push a button, when the sensation changed from one of pressure alone to a sensation of both pressure and pain. Pressure algometry was performed in triplicate at each of 10 neck- and jaw-muscle spots, and three times at a reference point. Brie¯y, the algometer was placed at a right-angle on the muscle. The probe area was 1 cm2, and the slope control was set to a desired rate of change, in a pressure of 20 kPa/s (Fig. 1a). A test of the algometer showed that the slope at this setting actually was 33.3 kPa/s (¡4.2%). # Blackwell Science Ltd Cephalalgia, 2001, 21, 189±197

Pain and tenderness after whiplash injury Since the same algometer was applied throughout the study, it was anticipated that the insecurity in slope setting of the algometer equally in¯uenced the measurements on whiplash-injured persons and controls. Calibration of the algometer was performed at regular intervals, and internal error in the machine was 0.0¡0.062%. On the left and right side of the neck and the head, ®ve homologous spots were examined in the following order (Fig. 1a): (i) the super®cial mid-belly of the masseter muscle (1.5 cm from the mandibular angle); (ii) the temporal muscle at the intermediate portion (TP2); (iii) the sternocleid muscle at the mastoid attachment site; (iv) the trapezius muscle, upper trapezius ®bres (TP1) at the insertion site of the clavicle; and (v) the infraspinatus muscle 1.5 cm below the medial part of the scapular crest (26). Firstly, measurements were done on the left, and secondly on the right side. The left, dorsal, proximal interphalangeal joint was chosen as a control site for determination of distant pressure pain detection threshold (distant PPDT). Eight pericranial muscles were examined by manual palpation (Fig. 1b). Muscles were palpated on both sides as described by Langemark & Olesen (27) with the second and third ®ngers performing small rotatory movements, while ®rmly pressing the ®ngers against the examined muscle. From each of 16 examined sites, a tenderness score was given. Points were scored as described by Langemark & Olesen (27): 0=no visible (a)

(b) 1



4 2






8 4


Figure 1 (a) Examined points using pressure algometry: (1) m. temporalis; (2) m. masseter; (3) m. sternocleidomastoideus; (4) m. trapezius, upper trapezius ®bres; (5) m. infraspinatus. (b) Examined points using palpation: (1) m. temporalis posterior; (2) m. temporalis anterior; (3) m. masseter; (4) m. pterygoideus lateralis; (5) m. sternocleidomastoideus, insertion at processus mastoideus; (6) m. sternocleidomastoideus pars medius*; (7) superior and inferior nuchal lines; (8) m. trapezius, upper trapezius ®bres*. *Dig. I opposed to dig. II and III, other muscles palpated using ®rm pressure with dig. II and III.

# Blackwell Science Ltd Cephalalgia, 2001, 21, 189±197


reaction, and denial of tenderness; 1=visible reaction, but no verbal report of discomfort or mild pain; 2=verbal report of painful tenderness with facial expression of discomfort; 3=marked grimacing or withdrawal, verbal report of marked, painful tenderness and pain. Total tenderness score (TTS) was calculated (maximum possible score=48). The following examination order was used (Fig. 1b): (i) posterior temporal muscle; (ii) anterior temporal muscle; (iii) masseter muscle; (iv) lateral pterygoid muscle (the subject slightly opens his mouth during this procedure); (v) sternocleid muscle at the mastoid process; (vi) sternocleid muscle at the medial part, muscles inserting on superior and inferior nuchal lines; and (vii) trapezius muscle.

Statistics Sample size was calculated with an estimated standard deviation in total pressure pain detection threshold at 500 kPa. We expected a difference in means between whiplash and ankle distortion subjects of 300 kPa (an average of 30 kPa lowered PPDT in all measured point), giving a power of 0.90 at a =0.05 with a sample size of 120 whiplash-injured persons and 40 controls. To achieve most information, we computed regression lines for each participant using the following data pairs: x=number of days after trauma, y=measured value on exact day of examination. A line was ®tted through obtained values after each examination day for every participant. Participants were represented by a point on their individual line, and the computed value on this line at day 90 was chosen to describe each participant. Individual regression lines were expected to have greatest variation at endpoints (0 days and 180 days after trauma), and least variation at the midpoint. We also used day 0 (alpha) as a parameter, supposing data density would be highest at the start of the observation time. Individual regression lines were computed with Excel for Windows software. To be included in these calculations, participants needed to attend at least twice during follow-up. One hundred and twenty-three whiplash-injured and 36 ankle-injured patients ful®lled these criteria. Total pressure pain detection threshold (total PPDT), distant pressure pain detection threshold (distant PPDT), Total tenderness score (TTS) and mean VAS pain at day 0 and day 90 were calculated according to the above notions. Data were transformed by means of either natural logarithm transformation (pressure pain detection threshold data) or square root transformation (total tenderness score and mean VAS day 90) in order to achieve normally distributed data sets. A general linear model (GLM) was applied post-hoc to analyse


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covariation due to gender, subject type and age. GLM was further applied to evaluate the relationship between reported pain and measured total tenderness score and pressure pain detection threshold.

Results The whiplash and ankle distortion groups were similar with respect to age, gender and body mass index. Symptom frequency is presented in Table 1. Eighty-seven per cent of participating whiplashinjured patients had returned to work or usual activity within 6 months, 10% had not recovered, 3% did not

respond to enquiries. Ankle-injured controls had all recovered within 6 months. Whiplash-injured patients had a signi®cantly lower total pressure pain detection threshold than ankle distortion subjects at day 0 (P