Fracture Screening: Neck, Knee, Foot, and Ankle

We're back after a busy break to review everyone's favorite fracture rules from the Great White North: the Canadian Cervical Spine Rules, Ottawa Knee Rules, and Ottawa Foot and Ankle Rules. We're giving special attention to common misunderstandings and misapplications of the rules. 

Some sources mentioned in the podcast:
Canadian C Spine derivation: https://pubmed.ncbi.nlm.nih.gov/11597285/
Ottawa Knee derivation: https://pubmed.ncbi.nlm.nih.gov/7574120/
Ottawa Knee in pediatrics: https://pubmed.ncbi.nlm.nih.gov/19307383/
Ottawa Ankle original refinement and validation: https://pubmed.ncbi.nlm.nih.gov/8433468/
Ottawa Ankle in pediatrics: https://pubmed.ncbi.nlm.nih.gov/19187397/
Awareness among clinicians: https://pubmed.ncbi.nlm.nih.gov/37957570/

Chapters

• 1:27 Cervical Fracture Rules
• 14:27 Knee Fracture Rules
• 21:18 Foot and Ankle Fracture Rules
• 23:03 Discussion

Transcript

Introduction

Hello, everyone! We are back after quite a hiatus, and we appreciate you sticking with us. You might have noticed we had to put the podcast on the backburner for the last cycle, but we have not been idle. Last year we focused on adding more resources to our Patreon page for those of you currently preparing for the OCS. We also partnered with Medbridge and now have 8 of our podcast episodes available for continuing education credit in most jurisdictions. To find those episodes and get your credit, just head to Medbridge’s OCS prep course and look for our content there. If you’re not a Medbridge user, you can sign up with promo code FIELDGUIDE—that’s all one word—for a discount. Links to our Patreon and our Medbridge discount will be in the show notes.

But we don’t want to waste time reviewing the last year—we want to jump back into refining your clinical skills. Today we want to focus on fracture screening—particularly in the cervical spine, knee, foot, and ankle. You probably remember the NEXUS and Canadian and Ottawa rules from school, but we have found that there are a lot of common mistakes clinicians make when applying them, so we are going to try to clarify the rules and help you avoid those mistakes.

Cervical Rules

We’re going to talk about cervical spine fracture screening first. Before we talk about the rules themselves, we need to make very clear that these rules only apply if there has been trauma to the head and neck. They do not apply to people with nontraumatic pain. So you’re only applying these following a head or neck trauma. Second, these rules are meant to decide if the patient needs initial imaging. If they have already had adequate imaging done that ruled out a fracture, then we don’t need to apply the rules.

There are two commonly used rules: the NEXUS criteria and the Canadian C Spine rules. The NEXUS criteria were created first, and they indicated the need for imaging if ANY of the following are present: focal neurological deficit, midline spinal tenderness, altered level of consciousness, intoxication, or a cervical distraction injury. This rule was better than nothing, but there are a couple of problems: specificity is low, so too many people without fractures were getting referred to imaging. Also, sensitivity declined as patients got older, so it was missing fractures in patients older than 65. The Canadian C Spine rules were introduced to address these problems, and it’s the algorithm that is generally recommended today, so we are going to spend a lot more time on it.

First things first: the inclusion criteria for Canadian C Spine rules are: 

·      acute trauma to the head or neck

·      have neck pain or visible injury above the clavicles or had a dangerous MOI

·      age at least 16

·      stable vitals

·      alert with a Glasgow Coma Scale of 15

Since you are probably an ortho PT, you might not recall the Glasgow Coma Scale very well. In this scale, you’re looking for whether the patient’s eyes are open, whether they are alert and oriented, and whether they can follow commands. A 15 is a perfect score, so if a patient is not alert and oriented or is confused or can’t follow commands, the Canadian C Spine rules don’t apply—this person needs to go straight to imaging. And you will notice that “altered level of consciousness” was an indication for imaging in the NEXUS criteria, so the two rules work together here.

Okay, so you have a patient with a traumatic head or neck injury who is at least 16, is stable, and is alert and oriented. Now we want to start checking to see if they have any high-risk factor that tells us they need imaging immediately. The high-risk factors are 1) age 65 or older, 2) a dangerous mechanism of injury, or 3) paresthesias in the extremities. A dangerous MOI is:

·      A fall from at least 3 feet or 5 stairs

·      An axial load to the head (like diving in a swimming pool)

·      A high speed motor vehicle accident (>100 kmph or >62 mph) or rollover or ejection

·      A bicycle collision, or

·      A motorized recreational vehicle collision

If any of these are positive, the patient goes straight to imaging. Again, the high-risk factors are 1) age 65 or older, 2) dangerous MOI, or 3) paresthesias in the extremities.

Let’s take a second to highlight some common misunderstandings here. First, it’s easy to forget the age cutoff, and I always get pushback from students asking whether I would really refer a patient out for imaging after head or neck trauma with neck pain just because the patient was 65 years old. The answer is yes, I would, and so should you. Remember that the NEXUS criteria missed a lot of fractures in people older than 65, so the Canadian C Spine rules fixes that by referring them all for imaging. Additionally, the C Spine Rule derivation study found that age of at least 65 was more predictive of the presence of a fracture than paresthesias in the upper extremity. In fact, while a dangerous mechanism of injury had an odds ratio for a fracture of 5.2, age of at least 65 was not far behind with an odds ratio of 3.7. So don’t forget to check the age of the patient.

Another area of confusion is the dangerous mechanism of injury. Once more, a dangerous mechanism is f fall from at least 3 feet or 5 stairs, an axial load to the head (like diving in a swimming pool), a high speed motor vehicle accident (>100 kmph or >62 mph) or rollover or ejection, a bicycle collision, or a motorized recreational vehicle collision. Where I see confusion here is the fall height. I have heard clinicians say that if a patient is more than 3 feet tall and falls on their head, then it’s a fall from more than 3 feet. I can understand where those clinicians are coming from, but that’s not what the rule is saying. It’s clear from the statement “3 feet or 5 stairs” that we’re talking about the patient’s feet being at a height of at least 3 feet above the ground. A fall from less than that height still needs the rest of the C Spine Rules to be applied, but it does not automatically qualify as a “dangerous mechanism” indicating immediate referral.

The last mistake people make when looking at a case or a patient is that they catch a high-risk factor, but they proceed to assess cervical rotation ROM anyway. However, because there is already a high risk for fracture and possible instability, we do not want to assess ROM in patients who have a high-risk factor. We send them straight to imaging.

Let’s return to our head and neck trauma patient. Let’s say our patient is less than 65 years old, did not have a dangerous mechanism of injury, and has no paresthesias in the extremities. Now we’re looking for any low-risk factor that tells is it’s probably safe to ask the patient to rotate their head side to side so we can measure cervical rotation. To be clear: we only need one of these factors to be true. The low-risk factors are:

·      a simple rear-end MVC

·      patient in a sitting position in the ED

·      patient has been ambulatory at any time since the injury

·      delayed onset of neck pain, or

·      absence of midline c-spine tenderness

This is where it becomes really obvious that these rules were created for use in the emergency department. Since we only need one of these to be true, a patient in an outpatient clinic is almost never going to be excluded at this step. Since ambulation is one of the low-risk factors, then if the patient walked into your clinic, it’s safe to assess ROM at this stage. Even if you did not see them walk in, if they are in a sitting position, then they have a low-risk factor and we can assess ROM. Don’t get thrown off if some of these are negative, like in a case where the onset of neck pain was immediate. We only need one low-risk factor to proceed, and that’s usually going to be that the patient was ambulatory at some point between the injury and presentation at your facility.

Okay, so let’s say our patient has no high-risk factors, and we saw the patient walk into the clinic, so we know the patient has at least one low risk factor. Now we ask the patient to perform active cervical rotation ROM. If there is at least 45° rotation to both sides, then it is very unlikely the patient has a fracture. If the patient cannotrotate 45° to either side, we refer for imaging.

At this point, you might have noticed that I have been saying “refer to imaging” instead of specifying what time of imaging you should refer to. There has been some debate that has erupted in the last few years around whether you should refer for radiographs or CT. We have a longer discussion of this on our Patreon page, but here is the short version:

The Canadian C Spine rules were created for plain film radiographs and repeatedly validated with radiographs. They are very, very sensitive when used with radiographs, with studies typically finding sensitivity values between 97 and 100%. That being said, CT is slightly better that radiographs at catching cervical fractures, and the C Spine Rules have also been validated with CT. Last year the American College of Radiology updated their appropriateness criteria so that they now recommend CT instead of radiographs when the Canadian C Spine Rules are positive. So both plain film radiographs and CT have been validated and recommended at different times, and CT is currently recommended over radiographs by the ACR appropriateness criteria.

The most recent Cochrane review of the C Spine Rules notes, “In practice, the choice of using CT versus plain radiography for the diagnosis of cervical spine injury is subjective and depends on many factors, such as hospital policies and protocol, the availability of imaging equipment (e.g. CT), the severity of the trauma, and age of the patient.” In other words, although CT is most sensitive, other factors like the availability of equipment may cause a clinician to choose radiographs. If you are a PT working in an emergency department and CT is easily available to you, then CT is probably the best choice. If you are in a private outpatient clinic and there’s no CT nearby, but there is an urgent care that can do radiographs next door, radiographs still have decent sensitivity for ruling out fracture. So we don’t think the OCS will give you a case and make you pick between CT and radiographs. If they do, CT is going to be the most sensitive for catching fractures. But if CT is not an option and radiographs are, then radiographs are a fine choice.

Let’s summarize. If you’re following the NEXUS criteria, you are referring to imaging if the patient has focal neurological deficit, midline spinal tenderness, altered level of consciousness, intoxication, or a cervical distraction injury. The Canadian C Spine Rules are better at catching fractures than the NEXUS criteria, but they only apply to patients who are alert and oriented, so if you see that altered level of consciousness or confusion, you should follow the NEXUS criteria and refer. For the C Spine Rules, we refer immediately if there are any of the following high-risk factors: age 65 or older, dangerous MOI (meaning fall from 3 feet, axial load to the head, motor vehicle collision >62 mph, rollover, ejection, bicycle collision, or motorized recreational vehicle collision), or paresthesias in the extremities. If all of those are negative, we look for low-risk factors, like a simple rear-end collision, the patient is in a sitting position, the patient has been ambulatory at any time since the injury, neck pain onset was delayed, or there is absence of midline c-spine tenderness. Since we only need one of these, if the patient walked into your clinic or is sitting upright in front of you, we can check rotation AROM. We’re looking for 45° of rotation to both sides. If the patient does not have 45° rotation to one or both sides, we refer for imaging. CT is best, but radiographs are typically more accessible.

Knee Rules

Let’s move on to the knee. A 2023 systematic review by Kharel et al. found that between the NEXUS, Canadian C Spine, Ottawa ankle, and Ottawa knee rules, awareness and implementation of the Ottawa knee rule was lowest, with two studies finding only 18% of clinicians reporting awareness of the rule. This is shocking, and we’re on a mission to change that today.

The Ottawa knee rule was derived 30 years ago, and, like the C Spine Rules, are meant to be applied to acute knee trauma in adults. It has been repeatedly validated, and a 2023 meta-analysis of 18 studies found it has a pooled sensitivity of 98% and specificity of 43%, so it is pretty good at catching fractures. There have also been a small number of studies attempting to apply the rule to children, and they have found similar sensitivity and specificity in children over 5. This is low-certainty evidence, but it does provide some support that the rule can be cautiously applied to anyone over 5-years-old.

The rule says that for those with acute knee trauma, we need to refer for radiographs if any of the following is present: age 55 or older, tenderness at the head of the fibula, isolated patellar tenderness, inability to flex the knee to 90°, and inability to bear weight for four steps both immediately after injury and in the ED.

Let’s talk about common mistakes and misunderstandings. It can be difficult to remember that the cutoff for the C Spine is 65 years or older and the cutoff for the knee is 55 years or older. Just remember that the neck is higher than the knee, so the cutoff age is higher for the neck than for the knee. And yes, the validation studies have found that age of at least 55 is a strong predictor for knee fractures, so don’t ignore it.

Tenderness at the head of the fibula indicates need for referral regardless of anything else going on in the knee, but notice that the patellar tenderness needs to be “isolated.” The original derivation and validation studies clarify that isolated patellar tenderness means there is no tenderness on any other bony structures besides the patella. A tricky case might give you something like patellar tenderness and tibial tuberosity tenderness—but since that is not isolated patellar tenderness, the rule is still negative.

Inability to flex the knee to 90° is the feature that I see most people forget. Just think about your C Spine Rules: there was a rotation ROM component to the C Spine Rule, and so there is a flexion ROM component to the knee rule.

Lastly, we have an inability to bear weight for four steps both immediately after injury and in the ED. The original studies define four steps as shifting weight twice to each foot regardless of limping—meaning that it’s okay to limp as long as weight was shifted onto that foot. Don’t panic and refer for imaging just because someone is limping. Also, we only refer if they cannot take four steps both immediately after injury and when they present to the ED (or when they present to you if you are serving as the primary point of contact). That means if they could take four steps at either point, we don’t need to send for imaging. So maybe they could take four steps immediately but not by the time they see you. That’s negative. Or maybe they couldn’t take four steps immediately but now they can. That’s also negative. It’s only if they could not take four steps when the injury happened and still can’t take four steps when they show up for screening that we have a positive finding.

We only need one of these findings to be positive to send for radiographs. So, one more time, we refer for radiographs if there has been acute knee trauma and the patient is 55 or older, or if there is tenderness at the fibular head (regardless of tenderness anywhere else), or if there is tenderness on the patella but not any other bony structures, or if they cannot flex their knee to 90°, or if they could not take four steps immediately after injury and when they present for screening.

Foot and Ankle Rules

Okay, let’s look at our last rule for today: the Ottawa Foot and Ankle Rule, sometimes just called the Ottawa Ankle Rule. Like the other rules, inclusion criteria requires some kind of blunt trauma causing ankle or midfoot pain in adults. And like the Knee Rule, we have a 2009 meta-analysis that found a pooled sensitivity of 98.5% when applying the rules to children; however, the rules missed some Salter-Harris fractures, so we should be careful if we choose to apply them to pediatric patients. In adults, a 2022 meta-analysis by Gomes and colleagues found a pooled sensitivity from 15 studies of 91% for the foot and ankle rules, and a pooled specificity of 25%. This means the rules are pretty good, but you should recognize that they are going to miss more fractures than the C Spine and Knee rules.

Now let’s cover the rule itself. The initial derivation study included an age cutoff, but it was removed by the authors after the subsequent validation study. So unlike the C Spine and Knee, there is not an age cutoff for the ankle rule. Instead, we’re looking for bony tenderness along the posterior edge or tip of the distal 6 cm of the medial or lateral malleolus, bony tenderness at the base of the 5th metatarsal, bony tenderness at the navicular, or inability to bear weight for four steps both immediately after injury and in the ED. If we find any of these, we refer for radiographs.

Let’s highlight areas of confusion. Notice that we are looking for bony tenderness at the malleoli tips or at the podterior edge of the malleoli. A tricky item writer will give you tenderness on the anterior edge of the malleoli, but this is not a positive Ottawa Rule finding. Keep in mind that most patients who have an inversion sprain are going to have tenderness in the region of the anterior edge of the malleolus, so you can see how you would find a lot of false positives if you were looking for tenderness in the anterior area. So it's tenderness on the posterior edge or tip of the malleoli that indicates a need for imaging.

Also notice that we have the same weightbearing rule as the Knee Rule: inability to bear weight for four steps both immediately after injury and in the ED. So if the patient can take four steps—even if they are limping—at any point after the injury up to the point of their initial screening, then they do not need imaging.

Once more, just to help you commit it to memory. If there is acute foot or ankle trauma and pain, then we need to refer for radiographs if there is any of the following: bony tenderness along the posterior edge or tip of the distal 6 cm of the medial or lateral malleolus, bony tenderness at the base of the 5th metatarsal, bony tenderness at the navicular, or inability to bear weight for four steps both immediately after injury and in the ED.

Discussion

Before we wrap up, there are a few things we need to acknowledge about these rules. First, they were developed for use in the emergency department following acute injury. There have been validation studies that have used the rules outside of the emergency department, but they still typically look at injuries that have happened less than 1 or 2 weeks prior to screening. So when we are applying these rules, we need to recognize that we don’t know how great they are beyond that acute stage. That does not mean we cannot use them to inform our decision-making, and we expect that the OCS will want you to use them even into the subacute stage, but we need to recognize that we have a bit of a knowledge gap there. 

Second, even though the rules have very high sensitivities, none of them have consistently produced 100% sensitive results. This means that there is a very small number of fractures that can still get missed. So we want to use these rules to reduce unnecessary imaging, and you definitely want to follow them to the letter on the OCS exam, but there may be times clinically where something just doesn’t feel right and you might want to ask for imaging in spite of a negative rule. That’s okay—just recognize that this should be the exception, not your everyday practice with every patient. 

Third, we need to recognize that there are some situations and comorbidities that are going to make these rules difficult to apply. Validation studies typically exclude individuals who do not have intact sensation or have known bone or spinal disorders. This makes sense, but let’s just go ahead and say it out loud: if your patient does not have sensation in their feet, you cannot trust that lack of tenderness on the foot is a true negative finding. Similarly, if a patient has a spinal condition or surgery, like a spinal fusion, that prevented them from rotating their head 45° to either side even before the head and neck trauma, then we probably wouldn’t expect rotation of 45° bilaterally after trauma. So in situations like these, we need to think beyond the screening rules—and typically, that’s going to mean requesting imaging after acute trauma. 

Lastly, I just want to re-emphasize that these rules are to determine the need for initial imaging. If a patient has already received adequate imaging in the emergency department or urgent care or somewhere else before seeing you, then we do not need to apply these rules. The keyword here, however, is adequate. We do occasionally see patients who had cervical radiographs that did not include an open-mouth view for visualization of the odontoid process. If that’s the case, then we need to apply the Cervical Spine Rule and see if we need to send them back for an open-mouth view or CT.

Conclusion

Hopefully this clears up some common misunderstandings about these fracture rules. In a future episode, we plan to go through cases to help you apply what you have learned. 

I am going to link some of the early derivation and validation studies I mentioned in the show notes if you are interested. 

It has been good to spend time with you again, and we look forward to sharing more with you soon.

Sources
Canadian C Spine derivation: https://pubmed.ncbi.nlm.nih.gov/11597285/
Ottawa Knee derivation: https://pubmed.ncbi.nlm.nih.gov/7574120/
Ottawa Knee in pediatrics: https://pubmed.ncbi.nlm.nih.gov/19307383/
Ottawa Ankle original refinement and validation: https://pubmed.ncbi.nlm.nih.gov/8433468/
Ottawa Ankle in pediatrics: https://pubmed.ncbi.nlm.nih.gov/19187397/
Awareness among clinicians: https://pubmed.ncbi.nlm.nih.gov/37957570/