ORIGINAL PAPER

Low force chiropractic adjustment and post- isometric muscle relaxation for the ageing cervical spine: a case study and literature

review

Introduction Elderly patients often present with a complicated medical history. Conditions or symptoms are often noted which prima fascia could contraindicate chiropractic treatment. These potential contraindications are usually considered in the light of what might reasonably be expected of the ageing patient, and a decision to treat made by balancing the benefits to the patient of treatment against the consequences of clinical misjudgement [I]. This case report describes an elderly gentleman who presented with chronic neck pain and several potential contraindications to chiropractic treatment. After careful exclusion of these contraindications, the patient was treated for one month using a combination of post- isometric muscle relaxation techniques prior to low force chiropractic adjustment of the spine. Improvements, which were quantified, were maintained for up to six months.

Neck pain and stiffness are common complaints. Over half the adult population can recall an episode of neck pain or stiffness in their lifetime, and it has been estimated that approximately 9% of men and 12% of women will have neck complaints at any given time [2-41. This high prevalence is reflected by approximately 15% of hospital-based tertiary care physiotherapy services and 30% of chiropractic practices being made up of patients with primary complaints of neck pain [5,6]. Despite chiropractic treatment being sought often for the treatment of neck pain, it is not clear if such treatment is effective, since high-quality randomised controlled trials dealing specifically with this topic appear to be absent [7]. This lack of data often leads reviewers to combine all manual therapy approaches for neck pain when trying to assess effectiveness with confusing results. Thus, a recent review concluded that there was little information to support the use of physical medicine modalities for mechanical neck pain, yet the authors of this study did not appear to have included chiropractic in their analysis (table 1) [8]. In addition, a recent meta-analysis of 25 review articles on the effectiveness of conservative treatment for neck pain concluded that concordance amongst the reviews was either varied or absent, further highlighting the need for well- controlled studies 191.

Cervical manipulation also carries with it a risk. A report by the RAND insurance company estimated that the rates of vertebrobasilar accidents or other serious complications, such as spinal cord compression, haematoma or vertebral fracture were 1.46 per one million cervical manipulations [I 01. A more recent study, based on data from 24,000 USA chiropractors, has placed this risk lower, at 0.5 per one million adjustments [II]. It has been estimated that approximately 286 million chiropractic adjustments are

carried out each year in the USA and, of these, four might statistically be expected to result in adverse effects [12]. These studies indicate that the risk of serious complications after chiropractic treatment of the cervical spine is very low. Nevertheless, a responsible attitude by chiropractors should be to minimise this risk wherever possible. One situation where such steps might be taken is in the treatment of the ageing cervical spine.

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Fig. la. Vertebral angiogram showing a well-defined posteior deviation in the course of the vertebral artery between the axis and atlas (arrow), in addition to the bend as the artery winds round the lateral mass of the atlas (arrow head).

Fig. 1 b. Corrosion cast of the cervical arteries and veins showing the vertebral artery (arrow) deep to the external vertebral venous plexus just before the artery winds round the lateral mass of the

atlas. Related lateral to the vertebral artery are the internal carotid artery (a) followed by the internal jugular vein (v). Reprinted with

permission from the Royal College of Surgeons of England.

Here, age-related changes in the shape and conformation of the cervical vertebrae may be expected [13]. Also, the vertebral arteries may run a tortuous path in the neck. This is commonly seen on dissection of the aged cervical spine and in vertebral angiograms (Fig. ‘la), in addition to the well-documented lateral bend in these arteries as they wind round the atlas to enter the foramen magnum (Fig. lb). Against this background, therefore, there will be occasions in general practice when chiropractors treating elderly patients for neck problems will want to use minimal force to reduce the possibility of damage to the vertebral arteries or other cervical structures. Here, a case is presented of an elderly patient complaining of neck pain and stiffness who was treated using a combination of low force chiropractic reflex recoil adjustments of the spine preceded by post-isometric muscle relaxation.

Case Report A 71-year-old gentleman presented with progressive left sided dull neck pain radiating into the upper trapezius region of approximately six months duration. No specific event was associated with the onset of neck pain. The pain was provoked by active neck movement, but not by exercise. He had a history of hypertension that was being managed by his GP with beta- blockers and had undergone a radical prostatectomy for prostatic carcinoma one year previously. Subsequent regular assays of

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FIGURE 2: Lateral radiograph of the patients neck showing mild osteopaeniaa, loss of disc height at C6i7 and C7TT1, zygoapophyseal joint degenerative changes at C415 and C6/7 and osteophytes at

the anterior aspects of the bodies of C5-7.

serum prostate specific antigen had been negative. A surgical reduction of Dupuytren’s contracture on the right had been carried out one year previously and there were signs of this condition developing on the left. No other clinical signs of rheumatoid arthritis were detected. The patient was generally in good health, ate a mixed diet and engaged in regular gentle exercise.

On examination, an age-related increase in thoracic kyphosis was seen. This was accompanied by loss of cervical lordosis and a slight anterior flexion at the cervico-thoracic junction, so that the whole of the head was carried anterior to the normal line of weight. Slight displacements in various planes of the dorsal spines or transverse processes of several cervical and upper thoracic vertebrae were noted on static palpation. This was associated with increased tonus of the

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posterior nuchal muscles and upper trapezius bilaterally. Goniometer-assessed ranges of motion for the thoracolumbar and cervical spine were generally reduced to 80% of normal values for the elderly [14]. However, left and right active lateral flexion and active rotation of the cervical spine were reduced to 28% of normal, and associated with bilateral pain and occasional crepitus. George’s test for vertebrobasilar artery insufficiency was negative and no provocation of neck or arm pain was found on axial distraction or compression of the cervical spine. No abnormal neurological signs were detected. Passive movements of the lumbosacral and cervical spine were generally pain-free and reduced to approximately 80% of normal. Passive lateral flexion and rotation of the neck however, was reduced to 20-30% of normal and was limited by pain, causing muscle

tightness and a soft joint end-feel. Motion palpation revealed reduced zygapophyseal joint movement at several cervical levels bilaterally. Palpation of the entire spine and pelvis also revealed minor displacements of the dorsal spines of the vertebrae. A right anterior pelvic torsion was found which was associated with a functional loss of approximately 1 cm to the length of right lower limb as measured by comparing the positions of the left and right malleolli with the patient supine. Blood pressure was 18985 and body mass index 22.8 (normal range for men 20.7- 26.4). Plain x-rays of the cervical spine (Fig. 2) were taken, which showed some degenerative changes that could be expected with a patient aged 71. A working diagnosis of mechanical neck pain was made.

The patient consented to a four-week course of joint mobilisation and chiropractic adjustment, with three-monthly reassessments thereafter. He was given advice on avoidance of a head-forward posture, on choice of pillow for sleeping, and some simple home exercises involving lateral flexion of the neck with gentle overpressure. He was informed that chiropractic would not reverse the age-related changes detected, but that some increase in neck movement and a decrease in pain could be expected. Treatment included specific adjustments of the lumbosacral spine and thorax designed to restore pelvic balance and to increase thoracic mobility. Particular attention was paid to the neck region. Here, post-isometric relaxation procedures were used to reduce tension and lengthen muscles and this was then followed by low force ‘reflex-recoil’ adjustments delivered by hand (vide infra) to specific cervical vertebrae without cervical extension or rotation.

Post-isometric relaxation (PIR) procedure: The general PIR procedure adopted has been described in detail elsewhere [I 51. In brief, the neck or shoulders were taken passively and gently to a point where previously nominated muscles just started to limit movement by their increased tension, or occasionally by their reflex contraction, as a ‘pain limit’ was reached. The neck or shoulders were then taken back to a point just before this ‘pain limit’. The patient was then asked to breathe in and hold the breath, to resist the chiropractor’s pressure with about one quarter to one third of their strength, and at the same time to turn their eyes to ‘look in the direction of their intended head or shoulder movement, Resistive force was maintained for five seconds and the patient kept informed of their progress by the chiropractor counting down from five to zero. The patient was then asked

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FIGURE 3: Chiropractor and patient positions for post-isometric relaxation of muscles. A) left sternocleidomastoid muscle; B) left scalene and upper trapez- ius muscle; C) initial treatment approach adopted for the upper and middle portions of the trapezius muscle; D) later treatment approach adopted for the

upper and middle portions of the trapezius muscle; E) later treatment approach to stretch neck muscles generally. Solid arrows indicate the direction of force exerted by the muscles generally, dashed arrows the counter-force exerted by the patient. No counterforce was exerted in E. See text for details.

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to simultaneously breathe out, to relax the muscles and to turn their eyes to ‘look’ in the direction that their head or shoulders were being gently moved by the chiropractor. In most cases, this resulted in reduced muscle tension that allowed a small degree of extra pain-free movement. When this new range to the limit of movement was reached, the head or shoulders were held for a further five seconds with the muscle in a stretched state. The procedure was then repeated two more times, each time starting with the muscles in their new stretched position. Post-isometric relaxation was used for an unknown number of muscles nominally termed ‘sternocleido- mastoid’ (Fig. 3a), ‘upper portion of trapezius and scalene muscles’ (Fig. 3b) and ‘upper and middle portions of trapezius muscle’ (Fig. 3c) based on their presumed role as prime movers. By the end of the second week, neck stiffness and pain had decreased markedly and a more forceful method of applying resistive pressure to the ‘trapezius’ was adopted (Fig. 3d). In addition, gentle stretch of the neck was also introduced (Fig. 3e). Although vertigo did not occur in this study, the patient was observed continuously during post-isometric relaxation so that the procedure could be halted if any dizziness developed. Reduced muscle tension was confirmed by direct palpation of the aforementioned muscles, although it is likely that other deeper and smaller nuchal muscles will also have been affected by the procedure. Qualitative assessment of active neck movement and the patients perception of any change in pain-free movement were used to monitor the efficacy of these procedures.

Chiropractic adjustment of cervical vertebrae: After the post-isometric relaxation procedures, malaligned cervical vertebrae were adjusted using the manual reflex-recoil method developed by Hugh Corley which is practised as McTimoney-Corley Technique. Here, the pad of the middle finger made

contact with either the dorsal spines of the vertebrae or the transverse process of the atlas depending on the adjustment required. A low force, high velocity adjustment was then made by applying a preload to the contact point followed by the rapid withdrawal of the adjusting hand normal to the intended direction of adjustment, using the fingers of the other hand as a pivot. Small painless erythemae on the skin at the site of finger pad contacts were usually visible shortly after the adjustments. The patients perception of the adjustments was that it caused their head or neck to ‘wobble’ or ‘shake’ slightly and transiently.

To obtain an estimate of the force and time characteristics of the reflex recoil adjustment, a series of ten adjustments were made blind to a 1 Omm* area of a 1 mm thick steel force transducer connected via a preamplifier to a digital storage oscilloscope (Nicolet 420, Texas Intruments, Madison, WI). This gave a value of 111.8 + 17.7 N (mean &standard deviation) for the force of the adjustment. This characteristically showed the development of the preload over approximately 200m.s followed by a plateau in force development of about IOOms and then finally a rapid release of the force over a period of 30ms. Time from onset of the force plateau to release of the force in ten trials was 123 f 33 mSec (mean f standard deviation). Additional measurements with material of different compliance were also obtained by performing reflex recoil adjustments to the central lmm* area of a 5 x 5 x 25mm piece of expanded polystyrene placed centrally on the weighing pan of electronic scales (Sartorius Basic, Gottingen) accurate to 100 milligrams. Expanded polystyrene was chosen at it approximated more closely the consistency and deformability of tissue found over the dorsal spines of the vertebrae than other substitutes (e.g. the latex of anatomical models or skin substitute pads used by medical students to practise suturing). The preload was held for

approximately 2-3 seconds (normally this would be less than one second) and a verbal warning given to an assistant just before the adjustment. This was necessary, as the change in the electronic display of the balance during the adjustment was rapid, and it was found that records to the nearest 1 OOg or 1 Og were the most accurate that could be obtained for the preload and adjustment, respectively. These measurements using expanded polystyrene indicated that a preload of 3.0 to 3.8 Kg (3.45 f 0.26) was exerted and that a very slight additional load of 0.339 f 0.14Kg was exerted just before release. The estimated force delivered under these very different conditions of compliance was 37.13 f 259N. An estimate of 535 ms-* for fingertip acceleration during the adjustment was kindly provided by Mr. S Hollar, Berkely Sensor and Actuator Center, University of California.

Outcome measures: A neck disability score of 36% (moderate disability) was obtained prior to treatment [16]. This fell to 24.4% (mild disability) at the end of the four-week course of treatment and remained at the mild disability level at three and six-month follow- up visits (Table 2). This change amounted to 5.8 neck disability index points, which is considered to be the minimum change that can be detected clinically [16]. Goniometer- assessed cervical lateral flexion and rotation increased bilaterally by 2.5- to 3-fold, four weeks after the onset of treatment (Table 2) and were largely retained by six months. Static and motion palpation were used to confirm skeletal re-alignment after chiropractic adjustment of the thorax, lumbosacral spine or pelvis. The medical outcomes short form 36 (SF-36) questionnaire was used with permission (QualityMetric Inc., Rhode Island, USA; http://www.qmetric.com) to assess general health status before treatment and six months after the end of treatment [I 71. This

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questionnaire indicated that role limitations due to physical functioning (role physical; 4 items) and interference with normal social activities due to physical or emotional problems (social functioning; 2 items) had improved between the first visit and six months after the end of treatment (Table 3). Using SF-36 data for 128 males in non- manual professions reported in the Oxford Healthy Life Survey 1991-1992 [17], Z-scores before treatment of -1.4 and -1.8 for role physical and social functioning, respectively, were obtained using the formula (X- Y)/SD(y), where X = patient score, Y = population mean and SD(y) = population standard deviation. Neither of these scores before or after treatment were statistically significant at the 5% level from the ageing population norm values (z-score of 2 needed). Both z-scores, nevertheless rose to 0.6 six months after the end of treatment.

Discussion The present study shows that a medium-term

increase in range of motion and decrease in disability and pain can be achieved in an elderly patient by combining post-isometric muscle relaxation with specific low force chiropractic adjustments of the spine. This approach was tolerated well by the patient and may provide an alternative to rotary break methods for the treatment of neck pain.

Safety: It is not possible from this single case to make any comments about the safety of this treatment regime per se or to compare it meaningfully with others where much larger

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sample sizes have been used. It is interesting, however, that a review of 367 case reports of vertebrobasilar artery dissection after cervical trauma and neck manipulation concluded that it was not possible to identify any particular neck movement or patient type that would increase the risk of vertebrobasilar damage [I 81. Similarly, a recent review of the safety of spinal manipulation concluded that no reliable data existed about the incidence of serious adverse events, but that they probably occurred only rarely and could therefore only be estimated [I 91. Another recent review studied the incidence of vertebrobasilar stroke in 582 patients between 1993 and 1998 in Ontario, which has a population of approximately 10 million [20]. The authors found that over a period of six years, six patients in a sub-group aged less than 45years-old had apparently suffered a stroke within one week of receiving chiropractic treatment. Those aged more than 45 did not show any significant associations. While this data indicates that approximately 1% of people suffering a vertebrobasilar stroke had

previously sought chiropractic treatment, it does not establish a causal relationship between such strokes and recent chiropractic visits. Also, it is likely that some of the strokes will have been preceded by neck pain, a symptom that is likely to prompt a visit to a chiropractor. Loss of intervertebral disc height due to its desiccation is a well-known feature of ageing, and this was noted in the cervical spine of the present patient [I 31. While this may provide some protection against intervertebral disc prolapse, it has been reported that sudden twisting or flexion/extension movements can cause

sequestration of the ageing disc and lead to spinal root and/or spinal cord compression [21]. The extent to which these observations apply to the ageing population generally, however, is unknown. In addition, catastrophic vascular accidents can follow minor neck movements in the absence of any chiropractic intervention [I I]. Given the very low incidence of serious complications and the difficulty of proving a causal relationship between chiropractic treatment and vascular accidents, therefore, it is almost impossible to quantify the risk of provoking a serious adverse event as a result of cervical chiropractic adjustment [II ,12,18]. But this should not be taken as an invitation to ignore this risk. Indeed, a recent report on the orientation of the cervical zygapophyseal joints indicates the need to exercise care during chiropractic adjustments of the cervical spine, especially in the elderly where the biomechanical integrity of the neck may be compromised [22]. In a study of 33 dry macerated male vertebral columns Pal and colleagues found that the superior articular facets at C314 face posteromedially, whereas those at C7fTl face posterolaterally, and that the transition zone for facet orientation was found at C4/5 [22]. The authors conclude that some common assumptions about the orientation of the zygapophyseal joints are incorrect and that the pooled data used in some biomechanical studies is frankly misleading [23]. Until the significance of these new findings in relation to the choice of direction of thrust during cervical adjustments is determined, a conservative approach might be considered, especially in the elderly.

Reflex recoil adjustment: An estimated recoil force of the reflex recoil adjustment of 111 f 17.7 N (mean f standard deviation) was obtained from studies using a small area steel force transducer, yet only 37.1 f 2.59 N was obtained using a much larger area of expanded polystyrene placed on an electronic balance. This indicates that the compliance of the tissue at and around the site of the reflex recoil adjustment will make a marked difference to the force delivered. These are only crude measures, however, unlike the more accurate ones that can be obtained, for example, using an AMTI force platform and strain gauge, and the extent to which these data are applicable to the clinical situation is unknown. It would, however, appear to be the first time any attempt has been made to quantify the force of a reflex recoil adjustment. Factors that may affect this force are shown in Table 4. By correlating the forces of manipulation with a physiological marker of effect (changes in leukocyte function), it has been suggested that a threshold of approximately 500N

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distinguishes potentially effective from “non- effective” procedures [24,25]. Assuming that up to 112N is delivered during the reflex recoil adjustment, it is difficult to imagine how such a small force, which does not result in joint cavitation, would be sufficient to move vertebrae anything more than a small distance within neutral zones. Paradoxically, this seemingly ineffectual adjustment is associated with many anecdotal reports from patients and chiropractors of increased range of movement and reduced pain. In the present study, the results reported for this single patient may be unrelated to the reflex recoil adjustments made; they could be due to the post-isometric relaxation regime employed; or due to a placebo effect, or some combination of these. It will be important in the future, therefore, to test for these variables using larger sample sizes in well-controlled trials. Some insight into possible underlying chiropractic mechanisms may be obtained, however, by drawing analogy between reflex recoil adjustments and adjustments delivered using hand-held mechanical devices, such as the Activator II device. The latter mechanical device can deliver a force of up to 140N rapidly which appears to cause periodic vertebral displacements of a few hundred microns in a range of resonant frequencies from 4.5 to 13Hz and to produce afferent and efferent volleys in mixed spinal nerve roots [26-281. Preliminary studies here using a steel force transducer found that the Activator Adjusting Instrument (AAI), set at its maximum 4 rings, delivered its force in approximately IOms, while the manual reflex recoil adjustment took approximately 30ms from the end of the preload plateau, The reflex recoil adjustment therefore appears to be more variable than the AAI, delivering 2580% of the force of the mechanical device and taking 3-5 times longer. There are also important differences between these two methods of adjustment. The AAI relies on an additional force being delivered after developing a mild preload; the recoil component of this is

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unknown and is likely to vary between practitioners. In contrast, the reflex recoil adjustment relies on the recoil produced when the preload is rapidly removed; the amount of preload, speed of adjustment and the adjusting vector selected are very likely to vary considerably between practitioners. More studies where variables due to practitioner and patient are controlled for are clearly needed. Surprisingly, a recent study on fresh cadavers found that high velocity postero-anterior thrusts to the thoracic spine produce oscillatory movements within the very same range as those produced by a mechanical adjusting instrument [29]. This raises the possibility that the reflex recoil adjustment may also be operating via resonance of the vertebrae. If so, such vibrations are likely to be detected by proprioceptors in spinal joints and deep muscles, and this may in turn influence muscle tone via proprioceptive reflexes. Interestingly, abnormal thresholds for vibration sensitivity are commonly found in idiopathic scoliosis, which is

characterised by postural muscle imbalance, and altered stretch reflexes are recurring themes in hypotheses of the mechanisms underlying chiropractic adjustments [30-331.

Utility of radiographs: It would be reasonable to assume from the history and clinical examination of this elderly patient that degenerative joint disease and some osteoporosis would be present [13]. Moreover, the patient had undergone a prostatectomy a year previously for prostate cancer, a tumour that often metastasises to the spine [34]. Advancedageandanyoneofthe aforementioned conditions could, therefore, have been used to justify the use of plain radiographs to assess whether chiropractic treatment was justified and safe [35,36]. When plain x-rays of the neck were examined, mild osteopaenia and some degenerative changes to the intervertebral and zygapophyseal joints were indeed noted. These changes were largely anticipated and this additional information did not make any difference to the treatment plan, since most of the relevant information had been gathered while taking the history. Thus, the patient was active, still engaged in a gentle sport (bowls), had not suffered any fractures in recent years and gave no reason (e.g. vegetarian diet, chronic steroid medication etc.) to suspect anything other than mild age-related osteoporosis [37]. If the degree of osteoporosis was considered important, then perhaps calcaneal ultrasound might have been a more appropriate way to measure and monitor this rather than plain x- rays, with referral for dual-energy x-ray absorptiometry (DEXA) held as a reserve [38]. Degenerative joint disease is likely to result in painful, restricted neck movements. In the

present case, active and passive range of motion and palpation studies showed restricted, painful movement, but no neurological or vascular signs were present or provoked. Given that there were no symptoms or signs that would suggest an infectious, endocrine, autoimmune or traumatic aetiology, the utility of radiographs is diminished. Neoplasia, however, needed to be considered carefully, since prostate carcinoma readily seeds to the spine via the valveless communication between the prostatic venous plexus and the internal vertebral venous plexus. High levels of insulin- like growth factor-l are expressed in bone, and it has been suggested that this serves as a mitogen for prostate and other bone-seeking tumours [39,40]. It is possible, therefore, that neck pain in this patient may have been due to the growth of a secondary tumour and that plain radiographs may have shown osteoblastic deposits in cervical vertebrae suggestive of metastasis. However, all this has to be balanced against a history of pain that was provoked by movement, rather than the constant pain that often characterises neoplasia. The patient had a normal biomass index, no history of recent weight loss or altered bowel habits and described his general health as good. Also, the patient had entered a screening programme for serum prostate- specific antigen (PSA) that had been consistently negative. Metastases from prostate tumours are almost always PSA positive and raised serum PSA precedes detection of tumour by either rectal examination or bonescan [41,42]. Notwithstanding the possibility that radiographs may have revealed neoplasia other than that which was secondary to prostate carcinoma, a strong case could in fact be made here for embarking on a course of conservative treatment based on the history and physical examination alone.

Outcome measures: The neck disability questionnaire and the SF-36 questionnaire are both robust tools that have good indices of reliability [16,17]. In retrospect, however, a visual analogue record of neck pain would have been useful to corroborate the patients subjective expressions used to describe the range of pain-free movement. A desire for detailed outcome measures, however, needs to be tempered with an appreciation of the patient’s expectations for treatment and a need to avoid excessive form filling. Because of this, a decision was taken not to include SF- 36 at intermediate points in this study. Range of neck movement was measured crudely in this study with a goniometer. This approach led to measurements that appeared to be within IO“ of those estimated by simple observation. The extent of this error was not quantified, neither was it known if the

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goniometer was any more accurate compared to simple visual estimation of the range of motion. A gravity goniometer (cervical range of motion device) or dual inclinometer (neither available in the clinic) may have given more accurate values for range of motion. It would be interesting in a future study, therefore, to determine the correspondence between values obtained with the latter instruments, those obtained using a goniometer and those obtained by direct observation and estimation.

Post-isometric relaxation (PIR) of muscles: Methods under the general umbrella of muscle energy techniques, which includes PIR, are increasingly being used in chiropractic and other forms of manual therapy as a means of reducing muscle tension and pain and increasing the range of joint movement [15,43,44]. The functional mechanisms underlying PIR are poorly understood. In most accounts, some reference is made to increased reciprocal inhibition mediated indirectly via la fibres of antagonist muscles, or increased direct inhibition mediated indirectly via lb fibres of homonymous muscle [I 545,461. These mechanisms are based primarily on studies of anaesthetised or decerebrate animals, often after extensive dissection of the limbs and spine to facilitate neurophysiological recording. In contrast, PIR is used on conscious intact humans. There is therefore a clear need to corroborate the experimental animal data with human studies. In support of anecdotal reports of the usefulness of MET, a randomised controlled trial on 100 outpatients suffering from neck pain found that the range of motion was increased after PIR treatment in 65% of patients, together with a reduction in pain [47]. However, in the same study, it was reported that a single high-velocity, low-amplitude thrust resulted in increased mobility in 85% of patients and a qualitative reduction in neck pain which was 1.5 times that achieved by PIR. The authors conclude that the high-velocity thrusts are better than PIR in the short term, but do acknowledge that the assessment of the long-term benefits of PIR will need further studies. Closer examination of texts on PIR reveals a very superficial treatment of the possible underlying mechanisms and a distinct lack of supporting references to purported facts. Lewit, for example, gives a description of PIR in terms of evidence of known reflex pathways, but then goes on to use these proposed mechanisms as explanations [44]. Korr slides between observations made on cats in quite artificial circumstances and the proposed effects of manipulation on motor reflexes in (intact) humans [46]. More recent texts also do not make the distinction between supposition from animal experiments and fact when explaining the basis of PIR [I 5,481. There does seem, however, to be a consensus in these articles that MET has

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something to do with the stretch reflex and with reciprocal inhibition. Polysynaptic influences on the stretch reflex in cats via modulation of the rate of gamma motoneurone firing have been found to be mediated by group one muscle afferents, group II muscle afferents, group Ill muscle afferents, group IV muscle afferents, mesencephalic descending tracts (mainly rubrospinal), recurrent excitation from ventral root axons, and afferents involved in the stretch reflex ipsilaterally as well as contralaterally [49- 551. It would appear, therefore, that almost any afferent from anywhere will eventually affect the rate of gamma motoneurone firing. These observations, if confirmed for humans, could have some bearing on PIR, as they would provide a mechanism whereby afferent inputs from a variety of sources (muscle skin, joint etc.) could affect the stretch reflex. Recently, it has been reported that peripheral nerve stimulation in a sample of nine humans caused a positive EMG peak to be obtained prior to afferent firing between -30 and -10 ms in 15 afferents (39% of the total studied) [56]. The authors use a conventional model of the myotatic reflex to conclude that the results are best explained by skeletofusimotor innervation of wrist extensors. If this is confirmed and also found to apply to other muscle groups, it will force a re-thinking of current concepts of the reflex control of movement in humans. The corollary is that it will also introduce yet another possible explanation for the mechanisms underlying PIR.

Ageing of muscle and nerve: Age-related changes in muscle and nervous tissue appear to receive less attention in manual therapy texts than age-related changes in the skeleton. This is unfortunate, as the effects of ageing on the neuromuscular system needs to be taken into account during the physical assessment of the elderly and in devising realistic outcomes for rehabilitation. Sarcopesnia of muscle is a well- documented consequence of ageing. As a consequence, the ability of skeletal muscle to produce force decreases steadily after 60 years of age at an average of 1 ON per year, resulting in a decline in force of 39% between the ages of 65 and 80 years of age [57]. It would be reasonable to expect some postural changes to result from this age-related weakness. This may lead to musculoskeletal pain and may temper expectations for rehabilitative therapy, especially that aimed at increasing muscle strength. It is also likely that major age-related changes in numbers of skeletal muscle tibres and the functional properties of the remaining tibres will be reflected by a similar reorganisation of motoneurones and their connections. The response of neurones including motoneurones to ageing, however, is poorly understood. Indeed, with the development of unbiased stereological

methods for estimating total numbers of neurones, major doubts have been cast on the dogma that neurones are inevitably lost with ageing and that their responses to injury can be expected to differ substantially from those in the adult [58-621. Moreover, there is now compelling evidence for the continued production of new neurones into adulthood [63,64]. Against this background of shifting paradigms and gaps in our understanding, care clearly needs to be taken when adducing to the ageing neuromuscular system data on the myotatic and inverse myotatic reflex that has been obtained from studies of young adults.

Acknowledgments

This case is published courtesy of fhe College of Chiropractors Pre-Registration Training Scheme for which it formed a part requirement.

The author is grateful to Dr. Elizabeth Loney, Consultant Radiologist, Royal Free Hospital, London for radiological advice and to Prof. Roger Woledge, Director and Professor of Experimental Physiology, lnstifufe of Human Performance, Royal National Orfhopaedic Hospital, Stanmore, Middlesex, for the use of force transduction equipment.

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