The Ankle Reflex Trap — When Experience Becomes the Enemy

A hospitalist checks ankle reflexes on a patient with severe back pain. They're intact. The brain says cauda equina syndrome is unlikely. But intact reflexes have no validated role in ruling it out — and that single reassuring finding becomes the cognitive failure point in one of medicine's most litigated missed diagnoses. This episode reconstructs the decision chain behind delayed CES diagnosis, the exam findings that falsely reassure, and the one bedside test that can change your clinical calculus in two minutes.

Transcript

SPEAKER_03 1:13

It is two in the morning. You are covering the hospital floor, and the ED calls with an admission. Forty-six-year-old man, a back pain. He has a history of disc disease, L4 to L5 herniation, documented on MRI two years ago. He works in a factory, and his pain got worse lifting something at work three days ago. Now he cannot get comfortable. His pain is a nine out of ten. You pull up his chart, prior ED visits for back pain, prior MRI showing the disc, outpatient pain management notes. You already have a picture forming in your head, and the picture looks like chronic back pain exacerbation. You go see the patient. He is in obvious pain. You do your exam. Strength looks intact. He has sensation in his feet. His ankle reflexes are present and symmetric. You document your findings, order pain management, and plan to get him comfortable overnight. Here is what you did not do. You did not ask about his bladder. You did not ask about numbness in his groin. You did not check saddle sensation. And you did not do those things because nothing in his presentation, as you understood it, told you to.

SPEAKER_04 3:02

Today we are reconstructing the cognitive failure behind one of medicine's most litigated missed diagnoses, Cauta Aquina Syndrome. Paul set the stage for us. How common is this diagnosis?

SPEAKER_03 3:16

So here is the math that matters. Low back pain makes up roughly 2-5% of all emergency department visits. In a busy ED, that is multiple patients per shift. Every shift, every day. Across a career, an emergency physician or hospitalist will see thousands of back pain patients. One to three cases per 100,000 people per year. A hospitalist might encounter one genuine CES case across an entire career. So you are looking for a 1 in 300 needle. In a haystack, you sift through every single shift. And every time you sift through that haystack and find nothing, your brain gets a little more confident that there is nothing to find. And the clinical challenge goes deeper than just rarity. It does, and this is the part that should give every clinician listening a moment of pause. We tend to think of CES as having a classic triad back pain, saddle anesthesia, urinary retention, the textbook picture. But only 19% of CES patients present with that full combination. That means more than 80% of people with Cauta Equina syndrome do not look like the textbook when they walk through your door. And the individual red flags, the symptoms we are supposed to catch, perform far worse than most of us assume. A systematic review by Dion and colleagues in 2019 looked at pooled sensitivity data for each red flag symptom. The results are sobering. Bilateral leg pain, the most sensitive finding, catches only 43% of CES cases. Saddle anesthesia, about 35%, urinary retention, about 30%, urinary incontinence, 19%, reduced anal tone, 25%. No single symptom reaches even 50% sensitivity. You cannot rule out CES based on the absence of any one of these findings. The British Association of Spine Surgeons states this explicitly, and I want to quote them because this is important. No symptom or sign allows us to diagnose or exclude CES unless and until the lesion is severe and often irreversible.

SPEAKER_00 6:15

And that clinical reality has direct legal consequences. When plaintiff attorneys establish that no individual exam finding can exclude CES, the defense argument that the presentation was not classic becomes very difficult to sustain. The standard is not whether the patient had the full triad. The standard is whether the physician asked the right questions and pursued appropriate workup when any red flag was present.

SPEAKER_03 6:39

Right. And this is where one bedside test actually can change the calculus. Post-void residual bladder volume, a bladder scan. Katsuraki and colleagues published a prospective study of 260 patients in the Bone and Joint Journal. A PVR of 200 milliliters or more had 94.1% sensitivity, and a negative predictive value of 98.7% for CES. It was a small study, but it gives us another tool to use. That is a non-invasive bedside test you can do in two minutes. That dramatically changes your pretest probability. It is not perfect. About 33% of confirmed CES patients had PVR below 100 milliliters in one series, and the UK National Pathway notes that 60% of patients needing emergency surgery had PVR under 200, so it does not replace clinical judgment. But it can be a useful screening tool.

SPEAKER_04 7:53

So the clinical picture is this a rare emergency hiding in the most common complaint, presenting a typically the majority of the time, with individual symptoms that miss more cases than they catch. And this is the environment where the cognitive failure happens. Let me walk you through what this looks like when it goes wrong. Not one case, a pattern. Because what the malpractice data shows is that CES diagnostic failures follow a remarkably consistent sequence across cases, across years, across different practice settings. In a case from a regional medical center in New England, a hospitalist was managing a patient with back pain and worsening neurological symptoms. The hospitalist examined the patient and found that ankle reflexes were intact. Based on that finding, the hospitalist concluded that cauda equina syndrome was unlikely. The patient went on to surgery, where a disc fragment was found compressing the cauda equina. The case settled for one million dollars.

SPEAKER_03 9:06

Paul, talk to us about this decision. This is the case I keep coming back to, because I understand exactly how it happened. And I think most hospitalists listening will understand it too. You have a patient with back pain, you do your neurological exam, you check ankle reflexes, and they are intact and symmetric. In your mental model, CES involves nerve root compression, and nerve root compression should produce reflex changes. The reflexes are normal, so your brain says a CES is unlikely. The problem is that intact ankle reflexes have no validated role in excluding cata equina syndrome. The cata equina is a bundle of nerve roots, not a single root. Compression can be partial, affecting some roots and sparing others. You can have a disc fragment sitting on the cata equina, causing early bladder dysfunction and saddle numbness, while the ankle reflex arc, which runs through S1, remains completely intact. But here is what makes this so insidious. The hospitalist did not make a lazy decision. They examined the patient, they checked reflexes, they performed a clinical assessment and reached a clinical conclusion. The problem was not effort, it was the weight given to a single reassuring finding.

SPEAKER_00 10:45

And in litigation, that distinction matters enormously. A physician who documents a thorough exam and reaches the wrong conclusion faces a different legal landscape than a physician who barely examined the patient. But in CES cases, the result is often the same because the standard of care requires pursuing imaging when red flags are present, regardless of other exam findings. In this case, the plaintiff's experts establish that intact ankle reflexes do not exclude CES. The defense could not overcome that.

SPEAKER_04 11:21

Now let me layer in a second case that shows what happens when the system fails even after the cognitive failure is overcome. At another regional hospital, a middle-aged factory worker was admitted with severe back pain. The attending physician recognized the concern and ordered an MRI marked ASAP. The MRI machine was available, no other patients were scheduled, yet the MRI was not performed for almost two days. During that delay, the patient's condition deteriorated. Cauda Aquinas syndrome was ultimately diagnosed, but the window for optimal intervention had closed. That case settled for two and a half million dollars.

SPEAKER_03 12:08

That is a case where the physician did everything right and still lost because the system behind the order did not execute. The physician recognized the urgency and ordered the right test, but the system did not execute. And the attending ordered it, but the system delayed it is not a defense that protects either the physician or the hospital. This is why I tell residents, if you are ordering an emergent MRI for a suspected CES, you personally follow up. You call the MRI tech, you confirm it is scheduled, you check back. Because a CES patient is losing function at a rate of roughly 1% per hour. And here is something that catches people off guard. ASAP is not the same as stat, neither is urgent. I have seen EMR systems, and many of you have too, where the order priority dropdown includes routine, ASAP, urgent, and stat as separate options. You would assume ASAP and urgent carry real weight in the radiology queue, but in some systems both ASAP and urgent default to routine priority on the radiology side. So you select ASAP for your suspected CES patient, thinking you have communicated urgency, and the order sits in the same queue as an outpatient knee MRI. If you mean emergent, select STAT and then pick up the phone and confirm with radiology that the order is being treated as emergent. Do not let the EMR's priority labels give you false reassurance. Explain that number. Todd published data in the British Journal of Neurosurgery, showing that in medical-legal cases, 10% of patients deteriorated from incomplete CES to CES with retention, meaning complete loss of bladder function. Within 12 hours of their first contact with a healthcare provider. That works out to approximately 1% per hour. 26% progressed within 24 hours. So when you are managing a patient with possible CES and the MRI is delayed, every hour that passes is not neutral. It is the clock running on a conversion from a potentially recoverable state to a potentially permanent one.

SPEAKER_04 14:53

A third case adds another dimension. In a case from the Midwest, a worker presented to an urgent care center after a back injury. The urgent care physician gave the patient an injection for pain and told him to go back to work. When his condition worsened, he was sent back again with pain medication. By the time he reached an emergency department and was diagnosed with cauda quina syndrome, the damage was done. The patient was paralyzed from the waist down. The verdict was four and a quarter million dollars, plus an additional amount for loss of consortium.

SPEAKER_03 15:35

That case illustrates diagnostic momentum at its most dangerous. The first visit created a diagnostic label, work-related back strain. The second visit reinforced it. Each encounter made it harder for anyone to reconsider. And there is a finding that haunts me about this pattern. Shapiro published in Spine that physician-related factors accounted for 83% of diagnostic delays in CES. Not system factors, not patient factors, physician decisions. And the average time from symptom onset to correct diagnosis was 11 days.

SPEAKER_00 16:21

The Daniel study out of orthopedics analyzed CES malpractice cases from Lexus Nexus and found something that every physician should know. Time to surgery beyond 48 hours was positively associated with an adverse verdict. But, and this is critical, the actual degree of functional loss did not independently affect verdicts. What that means is this juries punish delay. The narrative of the patient was there, the symptoms were there, and nobody acted is more powerful in the courtroom than the severity of the final outcome. A two-day delay with moderate residual deficit can produce a larger verdict than immediate progression to severe deficit if the timeline shows the physician had every opportunity to act.

SPEAKER_04 17:09

One more case. In the United Kingdom, a patient presented to an emergency department with red flag symptoms. Numbness from the knees down, unable to walk. The physician ordered an X-ray. Not an MRI, an X-ray. The patient was told he did not have CES and was sent home. He returned five days later with confirmed cauda equina syndrome. That case settled for a seven-figure amount.

SPEAKER_01 17:40

An X-ray cannot visualize the cauda equina. It cannot show soft tissue compression. It is the wrong test for the question being asked. That is a different failure mode, not failing to test, but choosing the wrong test. And it tells you something about the physician's mental model. An X-ray is what you order for a fracture. Ordering an X-ray for a patient with neurological red flags means the physician was not thinking about neural compression at all. The mental model was still back pain. And within that model, X-ray makes sense.

SPEAKER_04 18:13

This is satisfaction of search in real time. You ordered a test, you got a result. The result was normal. And your brain marked the diagnostic question as answered. Even though the test could never have answered it. This is where we go deeper into the cognitive science. Paul, across all of these cases, where is the actual pivot point? The exact moment where the clinical path diverged.

SPEAKER_03 18:44

It is always the same moment, and it happens earlier than you think. The pivot point is not the decision about MRI. It is not the discharge. It is not even the physical exam. The pivot point is the moment the physician categorizes the patient. When a patient presents with back pain and you mentally file them as back pain, that categorization determines everything that follows. Which questions you ask, which exam maneuvers you perform, which tests you consider, and crucially which red flags you are even looking for. In the Bristol case, the hospitalist with the ankle reflexes. The pivot was not when the reflexes came back normal. The pivot was upstream of that. It was the moment the hospitalist decided this was a routine back pain evaluation. Within that frame, checking ankle reflexes is thoroughness. Within the frame of possible CES, checking ankle reflexes is irrelevant because they cannot exclude it. This is what CrossCarey describes in his dual process model. System one, fast pattern-based thinking, recognizes back pain and activates the back pain script. That script does not include bladder questions, saddle sensation testing, or emergent MRI. System two, slow analytical thinking, is needed to override System one and say, wait, what is the worst thing this could be? But System two has to be triggered, and CES is uniquely positioned to avoid triggering it. Why? Three reasons working together. First, anchoring. Back pain is one of the highest frequency chief complaints in medicine. Your brain has a deeply worn groove for it. Known disc disease, prior imaging, pain management history. Every one of those data points reinforces the benign interpretation. Second, base rate neglect. You have seen hundreds, maybe thousands, of back pain patients. Essentially none of them had CES. Your experiential base rate for CES and back pain is effectively zero. And here's the paradox. A 2025 multi-center study of 274 physicians found an inverse correlation between experience and CES knowledge. More experienced physicians scored lower. The correlation coefficient was negative 0.34. Almost a quarter of consultants chose inappropriate management even when red flags were present. Experience, the thing we rely on to keep patients safe, becomes the trap for the specific diagnosis. Because experience teaches you that back pain is benign and it is until it is not. Third, premature closure. Once you have categorized the patient as back pain, and your exam is consistent with that, which it usually will be because CES exam findings are unreliable, you close the diagnostic loop, sciatica, disc disease, musculoskeletal strain. Done. The diagnosis feels complete. There is no cognitive dissonance pushing you to keep looking.

SPEAKER_00 22:40

From the legal perspective, this cognitive pattern creates a specific vulnerability. Plaintiff experts will testify about these biases by name. They will explain anchoring to the jury. They will walk through the decision chain and identify the exact moment the physician stopped thinking about CES. And they will contrast that with the standard of care, which requires per A CEP affiliated guidance, per the ACR appropriateness criteria, per the BASS standards, emergent MRI when any red flag is present. The defense that the presentation was not classic is weakened by the evidence that 81% of CES presentations are not classic. The defense that the exam was reassuring is weakened by the evidence that no exam finding can exclude CES.

SPEAKER_03 23:30

And this brings us to the 48-hour rule, because it is central to how these cases are litigated. In 2000, Ahn and colleagues published a meta-analysis in spine. 42 studies of 322 patients that established the principle. Patients who had surgery within 48 hours had significantly better outcomes in sensory, motor, and bladder function than those who had surgery after 48 hours. That paper is the third most cited CES publication. It is the foundation of plaintiff expert testimony in nearly every CES case. But in 2022, Woodfield and colleagues published a prospective study in the Lancet Regional Health. 621 patients across multiple UK centers that found something different. On multivariable regression, bladder outcomes and disability were associated with severity at presentation, but not with time to surgery.

SPEAKER_00 24:43

That finding matters in the courtroom in two directions. Defense experts cite Woodfield to argue that earlier surgery would not have changed the outcome. But plaintiff experts counter, correctly in my view, that the Woodfield data actually strengthens the case for early detection. If outcomes are driven by severity at presentation rather than surgical timing, then preventing progression from incomplete to complete CES is even more important. And preventing progression requires early diagnosis, which requires asking the right questions, getting the right imaging, and not dismissing red flags.

SPEAKER_04 25:18

Exactly. The Woodfield study does not give anyone permission to delay. It reframes the urgency from get to the OR within 48 hours to do not let this patient deteriorate while you are standing there. Let us look at the full legal landscape. Sarah, how does CES litigation compare to other malpractice claims?

SPEAKER_00 25:41

CES is disproportionately litigated relative to its clinical incidence. An estimated 10% of all CES patients pursue malpractice claims, far higher than most other diagnoses. And the success rate for plaintiffs is extraordinary. Hamdan and colleagues analyzing NHS data found that 87.5% of closed CES claims resulted in payment to the plaintiff. That is second only to wrong site surgery at 100%. In the United States, verdicts range from roughly $550,000 to $5.2 million, and settlements from $1 million to $4.9 million. Garcia and colleagues wrote in clinical practice and cases in emergency medicine that CES is a favorite litigating diagnosis for malpractice attorneys because it leads to both higher and more frequent awards.

SPEAKER_04 26:42

What makes these cases so hard to defend?

SPEAKER_00 26:46

Several factors converge. First, the injuries are devastating and visible. Permanent incontinence, sexual dysfunction, altered gait, catheterization for life. Juries see these outcomes and they are moved by them. Second, the timeline is usually provable. Electronic health records show exactly when the patient presented, what was documented, what was not documented, and how much time elapsed before the correct diagnosis. There is no ambiguity about the sequence of events. Third, and most important, the documentation gaps are usually glaring. In case after case, the medical record shows no documentation of bladder function questions, no saddle sensation exam, no PVR measurement. The absence of documentation is interpreted reasonably as absence of evaluation.

SPEAKER_03 27:36

And the electronic health record cuts both ways. The plaintiff's attorney will establish that you could not possibly have performed a complete neurological exam in three minutes, and the templated normal documentation becomes evidence of a perfunctory evaluation rather than a thorough one.

SPEAKER_00 28:14

One case worth discussing is a matter from Georgia where the emergency physician recognized the severity of the patient's presentation, prescribed pain medication, and ordered an outpatient MRI. The patient did not follow through with the MRI. She presented to another hospital about a week later with confirmed CES and massive disc herniation. Permanent incontinence, chronic catheterization, recurrent sepsis. The verdict was $5.2 million, but the jury assigned 40% comparative negligence for the patient's failure to obtain the ordered MRI. So the effective award was reduced accordingly.

SPEAKER_03 29:09

Outpatient MRI is a pain management workup tool, not an emergency diagnostic tool. Second, even though the patient did not follow through, the jury still found the physician 60% liable. The safety netting obligation, making sure the patient understands why the test is urgent, what symptoms to watch for, when to come back. That obligation is real. I ordered the test, and the patient did not get it is not a complete defense.

SPEAKER_00 29:46

And in the United Kingdom, the amounts are comparable. In one case, a young mother was assessed by multiple providers who dismissed bilateral sciatica, saddle numbness, and urinary difficulties. A spine surgeon advised against surgery, despite MRI confirmation. Over a week of delay, irreversible bladder and bowel paralysis. That case settled for the equivalent of over $5 million. In another UK case, a patient presented to the emergency department with numbness from the knees down and inability to walk. An X-ray was ordered instead of MRI, sent home, returned five days later with confirmed CES seven-figure settlement. CES accounts for 23% of all spinal surgery litigation claims in the UK. The NHS paid out approximately 186 million pounds across 340 CES claims in a single decade. Defense verdicts are documented in Oregon, Arizona, New York, and California, among others. The common threads in successful defenses are thorough documentation, a genuinely ambiguous clinical presentation, and a reasonable care timeline. When the record shows the physician asked about red flags, documented the answers, performed a detailed neurological exam, provided specific return precautions, and the patient's presentation was truly atypical. Juries may find for the defense. The lesson is not that CES cases are indefensible. It is that they are indefensible when the record shows you did not look.

SPEAKER_04 31:30

Paul, we close every cognitive autopsy with the one thing. The single change a physician can make after hearing this episode.

SPEAKER_03 31:40

What is it for CES? It is simpler than you think, and it is not order more MR is. The one thing is this for every back pain patient with any neurological symptom, leg weakness, numbness, tingling, pain radiating below the knee, ask four questions and do one test. The four questions one, has your bladder been working normally? That covers retention, incontinence, urgency changes, anything. Two, have you noticed any numbness or unusual sensations in your buttocks, groin, or inner thighs? That is your saddle anesthesia screen. Three, have you had any problems controlling your bowels, fecal incontinence? Four, has your sexual function changed? Patients will not volunteer this. You have to ask. And the one test, if any of those answers gives you pause, do a bedside bladder scan. PVR of 200 or more has a 94% sensitivity and a nearly 99% negative predictive value in that one study we quoted. It takes two minutes. Those are the tools I would add to my arsenal now.

SPEAKER_00 33:12

And from the legal side, that documentation is what separates a defensible chart from a multimillion dollar verdict. Write down each question you asked. Write down the answer. If the answer is negative, write it as negative. Patient specifically denies urinary retention, urinary incontinence, saddle numbness, bowel incontinence, and sexual dysfunction. Bilateral lower extremity, motor strength, five out of five in all myotomes L2 through S1. Sensation intact to light touch, including saddle distribution, S2 through S4. PVR 45 milliliters by bladder scan. That note takes 90 seconds to write, it documents clinical reasoning. And it is essentially bulletproof in litigation because it shows you considered the diagnosis, evaluated for it, and excluded it based on a thorough assessment. Compare that to back pain, neurointact, discharge with pain meds. That note takes 15 seconds, and it is indefensible.

SPEAKER_03 34:22

I want to be honest about the difficulty here. Asking these four questions for every back pain patient with neurological symptoms means adding time to encounters for a condition that will almost never be present. It means asking about bladder function and sexual function. Questions that can feel awkward. It means documenting answers that will be negative 99.7% of the time. But the alternative is being the physician in one of these cases. Standing in a deposition, trying to explain why you did not ask about the bladder, looking at a medical record that says neuro intact, with an EHR timestamp showing you were logged in for four minutes, facing a jury that has heard, correctly, that no exam finding can exclude CES, and that the physician who does not ask will not learn about the symptoms because patients do not volunteer them. This is a rare diagnosis, hidden in the most common complaint. You will not catch it by waiting for the textbook presentation. You will catch it by building the screen into your routine, so that on the one day it matters, and it will matter at least once in your career. You are already asking the right questions. Four questions, one test, write it down. That is the one thing.

SPEAKER_04 36:02

The cognitive autopsy, where the diagnosis went wrong, is a premium production of the charted defense. Paul, Sarah, thank you. Thank you.

SPEAKER_00 36:16

Thank you.

SPEAKER_04 36:17

The following evidence limitations should be noted. The 48-hour rule debate is active. On 2000 remains the most cited evidence supporting the 48-hour standard. Woodfield 2022 is the strongest evidence challenging it. Both positions are presented in the episode. Neither has been definitively resolved, and no RCT will ever be conducted. PVR is the best bedside adjunct, but is not a rule-out test. The episode presents both the Katsuraki data, 94.1% sensitivity at greater than or equal to 200 milliliters, and the UK pathway caveat. 60% of surgical patients had PVR less than 200 milliliters. Listeners should understand PVR supplements, but does not replace clinical judgment. DRE slash anal tone evidence is evolving. The episode references the UK pathway removing anal tone from routine assessment, Tabra 2022, but does not take a definitive position on whether DRE should be performed. Some plaintiff experts still cite absence of DRE as a breach. The experienced knowledge inverse correlation R equals minus 0.34 is cited from a 2025 multi-center study referenced in the COMPASS research brief. The full primary citation was not independently verified beyond the research brief. Case details are anonymized per production rules. Roles replace physician names. Locations are generalized. Time frames are relative. Public case names and verdict amounts are retained in the sources section per policy. The composite cold open vignette is a fictional clinical scenario constructed from common elements across multiple litigated cases. It doesn't represent any single real patient or physician. U.S. versus UK data. Much of the CES diagnostic delay and litigation data originates from UK studies and NHS data. The episode notes this where relevant. U.S. specific time from presentation to diagnosis data is limited. This episode is produced for educational purposes only. It does not constitute medical advice, legal advice, or a standard of care. Clinical decisions should be based on individual patient assessment, institutional protocols, and current evidence-based guidelines. Legal questions should be directed to qualified attorneys in the relevant jurisdiction. The cases discussed are anonymized per the Chartered Defense Production Policy. Physician names have been replaced with roles, locations have been generalized, and dates have been presented as relative time frames. Public case information, including case names, courts, and verdict amounts, is retained in the sources section.