Orthopedics · Part Four · Seeing and Ruling Out

43PART IV

Lesson 43 / 44

When Conservative Care Stops: The Thresholds That Move a Case Onward

The complete portal-of-entry clinician is defined by the care they deliver and equally by the moment they choose to hand it on. Knowing when conservative care stops is the discipline that lets it begin with confidence.

Conservative care stops when the clinical picture stops matching it. Four signals move a case onward: a lack of expected progress over a reasonable trial, a red flag, a progressive neurological deficit, or a presentation that belongs with another specialist. Spine surgeons publish overlapping thresholds, naming pain refractory to at least six weeks of care and any bowel or bladder symptom. The Unified Model of Tone reads escalation as correct dosing.

Sciatica carried past 12 months before discectomy

less favorable functional outcome at one year

Leg pain carried past eight months before surgery

lower clinical overall score at one year

Referred patients whose family physician received information back

26.5 percent

Reactions after manipulation that had gone within 24 hours

74 percent

A referral threshold

A referral threshold is the point at which a clinical picture stops matching conservative care and management moves to another discipline. Crossing one is an event with a name and a time, recorded in the notes. The clinician who acts on it promptly is doing what a first portal of entry exists to do, which is to rule in, rule out, and direct.

The magnitude axis

Every intervention in medicine sits on one continuous axis of magnitude, running from the lightest sustained touch to the most invasive surgery. How deep in the body a distortion sits decides which magnitude can reach it. A surface input reaches a surface problem, and a problem that has descended below that reach answers only to a larger one.

01When to refer

A clinician refers the moment the picture stops matching conservative care

A clinician sends someone onward the moment the clinical picture stops matching the conservative-care lane. Knowing that moment is what makes the profession an intelligent first portal of entry rather than a dead end. The question patients quietly carry into a spine consultation is simple. If this is not something you can help, will you know, and will you say so.

The complete clinician answers yes on both counts before treatment ever begins. Leading the conservative-care lane means owning its edges. The same judgment that selects a person for a gentle trial of manual care also recognizes the presentation that belongs in a surgeon’s clinic, an oncologist’s differential, or an emergency department. It moves that presentation there without hesitation.

This is not deference to a higher authority. It is the mature reasoning of a diagnostician who has already ruled the dangerous possibilities in and out, and who refers from a position of clarity. Referral is a clinical act, not a retreat.

Triage built on that reasoning has been measured. A mixed methods review of 34 studies found that musculoskeletal triage improved diagnostic agreement, appropriateness of referral and waiting list time (Joseph 2014). It worked whether physiotherapists, general practitioners, nurses or multidisciplinary teams performed it, which places the value in the reasoning rather than in the letters after a name.

The four signals that move a case onward

Four signals move a case out of conservative care, and a skilled clinician watches for all of them at once. The first is a lack of expected progress over a reasonable trial of treatment. When a condition with a favorable natural history refuses to follow it, the working diagnosis deserves fresh scrutiny. Why Disc Pain Resolves carries the natural history that makes a trial reasonable in the first place.

The second is a red flag surfacing in history or examination, the kind of feature that shifts probability toward something manual care cannot touch. The Red Flags Clinicians Screen For carries the diagnostic accuracy of each one. The third is a progressive neurological deficit: a deepening weakness, a spreading sensory loss, or the constellation that suggests cauda equina compromise. Any of those converts a routine visit into an urgent one, and Cauda Equina and the Spinal Emergencies sets out the timeline.

Surgeons write the same list. A review of microdiscectomy for a paracentral lumbar herniated disk names three indications. They are significant pain refractory to at least six weeks of conservative care, a severe or progressive motor deficit, and any symptom of bowel or bladder dysfunction (Millhouse 2016). Two professions describing the same thresholds is what a shared threshold looks like.

The trigger that is easiest to miss

The fourth trigger is quieter. A presentation simply belongs with another specialist. Not every spinal complaint is a spinal problem, and part of expertise is recognizing the case that maps onto rheumatology, vascular medicine, or oncology rather than mechanics.

Inflammatory Back Pain and Vascular Mimics and Claudication carry the two patterns that most often hide inside a mechanical story. Each trigger is a threshold, not a failure. The clinician who acts on them promptly is doing exactly what a portal of entry exists to do.

02Findings

What the research shows

From two surgical cohorts, a therapy cohort, a side-effect survey and three clinician surveys.

Surgeons name six weeks and a progressive deficit
A surgical review of microdiscectomy names three indications. They are pain refractory to at least six weeks of conservative care, a severe or progressive motor deficit, or any symptom of bowel or bladder dysfunction (Millhouse 2016). Two disciplines share that threshold.
Twelve months of sciatica changed the result
Among 113 patients followed for a year after lumbar discectomy, duration of radiculopathy tracked the change in Oswestry Disability Index score (p = 0.005). Sciatica lasting more than 12 months predicted a less favorable outcome (Ng 2004). Waiting is not a neutral act.
Eight months of leg pain did the same
Among 132 patients operated on for lumbar disc herniation, only duration of leg pain and sick leave predicted the one-year clinical overall score. Leg pain past eight months correlated with an unfavorable result (Nygaard 2000). Delay carries a measurable cost.
Early response predicted the endpoint
Pain recorded before the second, third and fourth physical therapy visits correlated with the change at discharge, most strongly at the fourth (r = 0.615). A discriminant analysis on those early responses classified 80.4 percent of discharge outcomes correctly (Tong 2006). A course of care reports its trajectory early.
Reactions after manipulation are common, mild and brief
Across 4,712 treatments on 1,058 new patients, 55 percent reported at least one unpleasant reaction. Reactions were mild or moderate in 85 percent of patients, and 74 percent had gone within 24 hours (Senstad 1997). Soreness alone is not a trigger to escalate.
Thirty surgeons, five cases, five different answers
Twenty-two orthopedic surgeons and eight neurosurgeons reviewed five simulated lumbar cases. Recommendations varied significantly on every case except the lytic spondylolisthesis (Irwin 2005). The surgical answer depends partly on which surgeon is asked.
Sixfold variation between cities
Medicare data for 2001 showed sixfold variation in spine surgery rates among United States cities and tenfold variation in fusion rates (Deyo 2006). Rates varying that widely report local practice as much as disease.
A quarter of shared patients generate a letter
In a national random sample survey, family physicians received information from chiropractors on 26.5 percent of referred patients, and chiropractors on 25.0 percent (Mainous 2000). The handoff fails at the paperwork.

03Judging the response

Response is judged through function and durability, not through the immediate reaction

Response to a trial of conservative care is judged through function, durability, physiological stability, adverse effects, and whether a person’s capacity is expanding or narrowing. The drama of what happens in the hour after treatment is a poor guide. Those five criteria are better decision rules than any visit count, because they measure the thing the trial was meant to change.

A trial declares itself early enough to act on. Tong and colleagues recorded pain on a 100 mm visual analog scale before each physical therapy visit in chronic low back pain. Change at the second, third and fourth visits all correlated with change at discharge, most strongly at the fourth (r = 0.615, P < 0.001). A discriminant analysis on those early responses classified 80.4 percent of discharge outcomes correctly (Tong 2006).

So a clinician sets an expectation at the start and reviews it against the record rather than against a feeling. A trial that has produced nothing measurable by its fourth session is reporting something real. That is not proof of a dangerous diagnosis. It is a reason to re-examine the working diagnosis and to consider the next magnitude.

A flare after treatment is not a verdict

Soreness after manual care is common, mild and short. Structured interviews covered 4,712 treatments on 1,058 new patients by 102 Norwegian chiropractors. At least one unpleasant reaction was reported by 55 percent of patients over a course of up to six treatments (Senstad 1997). Local discomfort accounted for 53 percent of reactions, headache 12 percent, tiredness 11 percent and radiating discomfort 10 percent.

The time course is the useful part. Reactions were mild or moderate in 85 percent of patients, 64 percent appeared within four hours, and 74 percent had gone within 24 hours. No serious complications were reported in the series. A reaction that follows that shape belongs to the ordinary business of loading a sore body.

A reaction that breaks that shape is a different signal. Discomfort that arrives late, deepens across days, or takes function with it does not match the published profile. Neither does new or advancing weakness. Separating those two patterns is the practical content of judging response through durability rather than through immediate reaction.

04Choosing the candidate

Selection decides who gets a trial of manual care

Not everyone qualifies for manipulation, and saying so out loud is the mark of a clinician who selects patients rather than treats reflexively. Consider the lumbar disc lesion, the presentation medical colleagues watch most warily. A moderate central protrusion that remains contained by the posterior longitudinal ligament, with an intact annular wall and a benign neurological status, is a reasonable candidate for a short trial of gentle care.

The mirror image disqualifies. A breached annulus, a frank radiculopathy that is deepening, or a deficit that advances between visits removes a person from the conservative candidate pool and into onward referral. The decision lives in the whole clinical picture, and the picture is what a good portal-of-entry clinician reads.

What imaging can and cannot settle

Imaging informs this judgment without settling it. A disc bulge is common in adults with no pain at all, and its prevalence climbs steeply with age rather than resting at any single figure. Findings in People Without Pain carries the age-stratified table. Structural abnormality alone is not a contraindication to conservative care, and Why MRI Misleads follows what happens when a scan is read as a verdict.

The contained and uncontained distinction behaves less simply than intuition suggests. In the prospective cohort of 113 discectomy patients, those with an uncontained herniated disc had a shorter duration of symptoms and a better functional outcome than those with a contained herniation (Ng 2004). Containment describes the anatomy. It does not rank the prognosis on its own, and selection rests on the neurological status and the direction of travel.

05Who decides on surgery

The choice between conservative care and surgery belongs to an informed patient

For most degenerative spine presentations no single correct answer waits to be discovered, and the decision belongs to the person living in the body. The evidence for that starts with how much the surgical recommendation itself varies. Twenty-two orthopedic surgeons and eight neurosurgeons were given five simulated lumbar cases. Their recommendations differed significantly on every case except the lytic spondylolisthesis, where all thirty recommended fusion (Irwin 2005).

The population data show the same variation at scale. Medicare figures for 2001 showed sixfold variation in spine surgery rates among United States cities and tenfold variation in fusion rates, with fusion rates tripling during the 1990s (Deyo 2006). Conservative Care vs Surgery carries the trials that ran the two paths side by side.

What a decision aid changes

Decision aids change what patients know and what they choose. The Cochrane review now covers 209 randomized trials and 107,698 participants across 71 different decisions. Decision aids probably increase the congruence between a person’s informed values and the care they choose, with a risk ratio of 1.75 and a confidence interval from 1.44 to 2.13 (Stacey 2024).

Elective surgery is where that matters most. A systematic review of shared decision making in elective surgical care screened 10,929 articles and included 24 studies, of which spine was the largest group at seven (Boss 2016). Decision quality improved in all three studies that measured it, and decisional conflict fell in four of six. The effect on whether people chose surgery was mixed, falling in nine studies, unchanged in eight and rising in one.

A spine-specific trial makes the mechanism concrete. One hundred potential surgical candidates were randomized to an interactive video with a booklet or to the booklet alone. Knowledge improved in both arms and improved more with the video, most of all among those who began with the lowest scores. Of the video group, 93 percent rated the materials easy to understand against 72 percent of the booklet group (Phelan 2001).

Preference for surgery was 23 percent in the video group and 42 percent with the booklet alone. With 100 patients the trial could not settle that difference (P = 0.4). What it did show is that information delivered well moves what a person understands, and understanding is the input a shared decision runs on.

06The handoff letter

The referral report that travels decides whether coordination becomes routine

How a clinician communicates a diagnosis to a medical colleague determines whether coordination becomes routine or friction. The default is friction. A national random sample survey of 400 chiropractors and 400 family physicians drew 360 responses. Family physicians received information from chiropractors on 26.5 percent of referred patients, and chiropractors received it back on 25.0 percent (Mainous 2000).

Both groups reported that they did not receive enough information about adverse outcomes or treatment plans for shared patients. The authors named the result fragmentation. A referral threshold is worth nothing if the case crosses it into silence.

The vehicle is a Working Diagnosis and Management report written in the shared language of anatomy and physiology, because that is the language of inter-professional understanding. It names what was ruled out before it names the conclusion, so a reader sees the reasoning rather than a bare label. It raises the very concern a general practitioner would raise, then answers it. A well-built letter about a disc lesion states plainly that the protrusion is contained and the annular wall intact before proposing any hands-on approach.

Precision in the wording

Language does quiet work here. The word gentle signals that manipulation can be graded and tailored. Writing that a nerve root is somewhat compromised rather than compressed calibrates the intensity of the message without distorting it. This care with wording is precision, and it reflects how the nervous system reads spinal input as either safe or threatening, a distinction Central Sensitization sets out.

Triage research points the same way. Across 34 studies, what made musculoskeletal triage work was the interdisciplinary support around the clinician, and patients expressed a preference for experienced clinicians to perform it (Joseph 2014). A report built this way earns trust, and trust is what turns a single letter into ongoing co-management.

07Claims removed from this page

Two claims from the earlier version were removed

An imaging figure came off. The earlier text put a disc bulge in roughly 52 percent of pain-free adults, with no citation and no mention of age. Published prevalence is age-stratified and climbs steeply across the decades, so a single pooled number hides the finding.

A treatment claim came off with it. The earlier text said the literature demonstrates the safety and efficacy of graded manual methods in the presence of a contained lesion. It attributed the benefit to reflex analgesia and improved vascular turnover in the Batson venous plexus. No study cited on this page tested that mechanism, and neither claim is needed to make the case for a trial of conservative care. The Nerve Root carries what is established about the Batson plexus and root vascular supply.

08An intelligent first portal

The portal is defined by the traffic it sends outward

An intelligent first portal of entry is defined by the traffic it sends outward as much as by the care it keeps. As trust develops with a local medical community, autonomy follows, and the chiropractor becomes a resource other professionals reach for when faced with spinal uncertainty. That standing is earned through diagnostic skill first.

General practitioners value the clinician who can distinguish a discogenic complaint from a sacroiliac one, a cervicogenic headache from a migraine, and a mechanical presentation from a sinister one. The Sacroiliac Joint and Three Headaches, One Neck carry two of those distinctions in full.

The traffic runs both ways only when the information does. In the national survey of shared patients, family physicians were significantly less comfortable than chiropractors about sharing care (P < .001). Both groups reported receiving too little detail on adverse outcomes (Mainous 2000). A portal that closes that gap becomes the place other clinicians send their uncertain spines.

Conservative care stops at a clear boundary, and the clinician who names that boundary is proving the lane is well run. Some people arrive, receive a confident trial of care, and recover. Others arrive, receive an equally confident referral, and reach the right place faster than they would have alone. Both outcomes are the portal working.

Referring someone onward is not the moment conservative care fails. It is the moment it proves it was intelligent all along, because a clinician who knows the edges of the lane is the safest guide within it. The mark of the complete clinician is that patients leave the office having been read accurately, whether the next step is an adjustment or an ambulance, a rehabilitation plan or a neurosurgical opinion.

That is what it means to lead the conservative-care lane and to know, without flinching, where it ends. Conservative First states the case for beginning inside that lane at all, with the guideline recommendations and the cost comparisons that close this section.

09The model on escalation

What the Unified Model of Tone claims about escalation

Everything above is established science, including the video trial whose difference in surgical preference did not reach significance. What follows is this model’s reading, stated as ours rather than drawn from the papers cited.

Our model places every intervention in medicine on a single continuous axis of magnitude, running from the lightest sustained touch to the most invasive surgery. Specificity settles which signal matches the pattern a body is holding. Magnitude is a second and independent variable, and it answers how much.

From that axis follows the rule this page rests on. Begin with the least invasive input that can carry the message. When a distortion has descended past what any surface input can reach, the larger magnitude is the correct one, and delay becomes its own kind of harm.

The delay data fits that rule. Sciatica carried past 12 months before discectomy produced a less favorable change in Oswestry score at one year (Ng 2004). Leg pain carried past eight months produced a lower clinical overall score in a separate cohort of 132 patients (Nygaard 2000). Neither cohort tested magnitude directly, and both recorded the cost of holding a small input against a problem that had outgrown it.

Surgery keeps its standing in this reading. A successful surgery is one whose magnitude was matched to the system, invasive enough to deliver the message and restrained enough that the surrounding tissue can still integrate it. That is the same sentence our model applies to a light contact, with the numbers changed.

The same axis is why the future of care lies in many professions working the same system together, each fluent in its own access point, rather than in one prevailing over the others. A referral changes the access point and the magnitude. It does not change the subject.

How the model judges a trial

Our model judges response through function, durability, physiological stability, adverse effects, and whether a person’s capacity is expanding or narrowing. The immediate reaction carries almost no weight in that judgment. The Norwegian side-effect series is why the distinction is practical, since 55 percent of patients reported a reaction and 74 percent of those reactions had gone within a day (Senstad 1997).

The prediction

From that follows a claim the referral literature does not make. Our model predicts that a short trial of conservative care separates two groups whose reported pain scores match at the moment of measurement. In one group, four measures move together. In the other, none of them moves.

The four are active straight leg raise in degrees, pressure pain threshold measured away from the painful region, resting heart rate variability, and time to return to baseline after a standardized load test. The group whose four measures move together is the group for whom the smaller magnitude is still the correct dose. The group whose measures stay locked is the group our model expects to need the larger one.

This is a claim about how response to care is organized rather than a claim about what any treatment does. If active straight leg raise, pressure pain threshold away from the painful region, resting heart rate variability and time to return to baseline after a load test move together, the unification claim is confirmed.

10The tone reading

How escalation expresses tone

Every topic in this library expresses all of tone. In escalation three aspects carry the signature, because the same case answers to a light input at one moment and to a large one at another.

Time course

Delay is a variable, not a neutral pause. Sciatica carried past 12 months before surgery produced a less favorable functional outcome at one year.

Load

Magnitude is the dose. Surgeons set six weeks of unresponsive conservative care as one threshold, and the axis runs from the lightest touch upward.

Constraint

A distortion that has descended below the reach of a surface input has narrowed what the body can do, and the larger magnitude is what fits it.

The remaining foundations run through escalation as well. Input quality: a report written in shared anatomical language is the input the next clinician receives, and only 26.5 percent of referred patients generate one. Coupling: function, autonomic stability and sleep move together when a trial is working, which makes any one of them a poor sole endpoint. Gain: a system running at high sensitivity reports a benign reaction as a catastrophe. Set point: the level a person returns to between visits is the durable measure, rather than the level ten minutes after treatment. Prediction: a patient told in advance what the fourth visit should look like can help judge the trial. Oscillation: pain that still swings with the day is reporting a regulator that still moves. These are readings of one organization rather than separate systems, which is the core claim of the Unified Model of Tone.

11Across the library

How this page relates to the rest of the library

Every threshold named here depends on a lesson elsewhere in the section.

The Red Flags Clinicians Screen For

The measured diagnostic accuracy of each red flag, and why most raise probability less than clinicians assume.

Cauda Equina and the Spinal Emergencies

The one presentation here whose threshold is measured in hours rather than in weeks.

Conservative Care vs Surgery

The trials that ran both paths side by side, including the crossover that makes them hard to read.

Why Disc Pain Resolves

The natural history that makes a trial of conservative care a reasonable first move rather than a delay.

Findings in People Without Pain

The age-stratified prevalence of disc findings in people with no symptoms, which is why a scan rarely settles a referral question.

Why MRI Misleads

What happens to management when a scan is ordered before history and examination have narrowed the question.

Conservative First

The keystone case for beginning with the least invasive input, with the guidelines and the cost comparisons.

12Frequently asked

Questions patients ask about referral and escalation

When should a chiropractor refer me to a specialist?

Four situations trigger it. A reasonable trial of care has not brought the expected progress. A red flag has appeared in the history or examination. A neurological deficit is deepening. Or the presentation belongs with another specialist rather than with mechanics. Spine surgeons publish overlapping thresholds for lumbar disc herniation, naming pain refractory to at least six weeks of conservative care, a severe or progressive motor deficit, and any bowel or bladder symptom. A deficit that advances between visits converts a routine appointment into an urgent one.

Does referring mean chiropractic failed?

No. Referral is a clinical act, not a retreat. Knowing where the conservative-care lane ends is the same skill that lets a clinician work confidently inside it. Escalation changes the size of the input rather than passing judgment on the smaller one. The published thresholds are shared with surgery, so a case that crosses one has stopped matching conservative care. The clinician who acts promptly is doing exactly what a first portal of entry exists to do.

How long should conservative care take to work?

No fixed number of visits settles it, and the useful rule is a measured response rather than a calendar. In chronic low back pain treated with physical therapy, the change in pain recorded before the second, third and fourth visits predicted the outcome at discharge, correctly classifying 80.4 percent of cases. A clinician sets an expectation at the start and reviews progress against the record. A trial that has moved nothing measurable by its fourth session is a reason to re-examine the working diagnosis.

What counts as a progressive neurological deficit?

Weakness that is deepening, sensory loss that is spreading, or a reflex change that advances between visits, rather than a stable finding present since the first examination. Loss of bladder or bowel control, or numbness in the saddle area, is handled as an emergency rather than as a threshold to watch. Surgical reviews list a severe or progressive motor deficit as an indication in its own right, independent of how much pain a person reports at the time.

Is it normal to feel sore after treatment?

Reactions are common, mild and short. Structured interviews covering 4,712 treatments on 1,058 patients found that 55 percent reported at least one unpleasant reaction over a course of up to six treatments. Local discomfort accounted for 53 percent of them. Reactions were mild or moderate in 85 percent of patients, and 74 percent had gone within 24 hours, with no serious complications recorded. Discomfort that arrives late, deepens across days, or takes function with it does not match that profile.

Who decides whether I have surgery?

The patient decides, informed. Thirty spine surgeons given five identical simulated lumbar cases recommended significantly different treatment on every case but one. Medicare data showed sixfold variation in spine surgery rates between United States cities. Where recommendations vary that much, the preference of the person living in the body carries real weight. Decision aids probably increase the match between informed values and the care chosen, with a risk ratio of 1.75 across 209 randomized trials.

What does the Unified Model of Tone say about escalation?

That every intervention sits on one continuous axis of magnitude, from the lightest sustained touch to the most invasive surgery, and the correct dose is the amount the system can actually use. When a distortion has descended past what a surface input can reach, the larger magnitude is the correct one and delay becomes its own kind of harm. From that our model predicts that straight leg raise, pressure pain threshold, heart rate variability and recovery time share one underlying factor.

13The sources

References

1
Millhouse PW, Schroeder GD, Kurd MF, Kepler CK, Vaccaro AR, et al. Microdiscectomy for a Paracentral Lumbar Herniated Disk. Clin Spine Surg. 2016. PMID 26710186
2
Ng LC, Sell P. Predictive value of the duration of sciatica for lumbar discectomy. A prospective cohort study. J Bone Joint Surg Br. 2004. PMID 15174551
3
Nygaard OP, Kloster R, Solberg T. Duration of leg pain as a predictor of outcome after surgery for lumbar disc herniation: a prospective cohort study with 1-year follow up. J Neurosurg. 2000. PMID 10763681
4
Tong HC, Geisser ME, Ignaczak AP. Ability of early response to predict discharge outcomes with physical therapy for chronic low back pain. Pain Pract. 2006. PMID 17147593
5
Senstad O, Leboeuf-Yde C, Borchgrevink C. Frequency and characteristics of side effects of spinal manipulative therapy. Spine (Phila Pa 1976). 1997. PMID 9055373
6
Irwin ZN, Hilibrand A, Gustavel M, McLain R, Shaffer W, et al. Variation in surgical decision making for degenerative spinal disorders. Part I: lumbar spine. Spine (Phila Pa 1976). 2005. PMID 16205348
7
Deyo RA, Mirza SK. Trends and variations in the use of spine surgery. Clin Orthop Relat Res. 2006. PMID 16462438
8
Stacey D, Lewis KB, Smith M, Carley M, Volk R, et al. Decision aids for people facing health treatment or screening decisions. Cochrane Database Syst Rev. 2024. PMID 38284415
9
Boss EF, Mehta N, Nagarajan N, Links A, Benke JR, et al. Shared Decision Making and Choice for Elective Surgical Care: A Systematic Review. Otolaryngol Head Neck Surg. 2016. PMID 26645531
10
Phelan EA, Deyo RA, Cherkin DC, Weinstein JN, Ciol MA, et al. Helping patients decide about back surgery: a randomized trial of an interactive video program. Spine (Phila Pa 1976). 2001. PMID 11154542
11
Mainous AG, Gill JM, Zoller JS, Wolman MG. Fragmentation of patient care between chiropractors and family physicians. Arch Fam Med. 2000. PMID 10810950
12
Joseph C, Morrissey D, Abdur-Rahman M, Hussenbux A, Barton C. Musculoskeletal triage: a mixed methods study, integrating systematic review with expert and patient perspectives. Physiotherapy. 2014. PMID 25242531

12 primary sources, each linked to its record. Figures quoted on this page were checked against the published abstract.

Related evidence

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