MR Imaging of Muscle Trauma: Anatomy, Biomechanics, Pathophysiology, and Imaging Appearance

MR Imaging of Muscle Trauma: Anatomy, Biomechanics, Pathophysiology, and Imaging Appearance


Jeffery S. Klein, MD Hi. I’m Jeff Klein, Editor of RadioGraphics
and today I’m pleased to have with us Dr. Mini Pathria from the University of California,
San Diego Medical Center Department of Radiology who is the senior author of a featured paper
in the current January 2018 issue of RadioGraphics entitled “MR Imaging of Muscle Trauma: Anatomy,
Biomechanics, Pathophysiology, and Imaging Appearance.” Welcome Dr. Pathria. Mini N. Pathria, MD Thank you. Good morning. J.S.K. Good morning. Mini your paper in the current issue begins
with and introduction that reviews the spectrum of acute, sub-acute, and chronic muscle injuries
and these are listed in Table 1. Can you review the table with us and give
us an indication as to which of these injuries a radiologist is most likely to encounter
in clinical practice? M.N.P. Sure. You know the reason I decided to break this
down is I think that we emphasize acute trauma and obviously I think that’s what most of
us deal with in our practices when a patient is injured. But I think radiologists also really need
to be familiar that there are functional abnormalities and symptoms related to old injuries that
may not be as obvious on MR or more subtle abnormalities like delayed onset muscle soreness
that may not be as flagrant and you might not have that history of acute injury and
that we’re responsible for those as well. So obviously having a history of a timeline
of symptoms is useful, but that’s the way I try to break it down in my head is acutely
injured patient, somebody in the first 2 to 6 weeks after trauma, or somebody that had
a remote trauma and is still having some sequelae from it. J.S.K. Sure. Well thank you. So you know after you go through the classification
and the spectrum of injuries based on time line, the next part of the paper reviews normal
muscle structure and function which is obviously important, and then you delve into the main
forms of muscle injury which begin with indirect injuries which include muscle strain and delayed
onset muscle soreness. Let’s discuss the most common form of strain
or tear which occurs at the myotendinous junction and we’ll review Figure 6 as an example
of this. M.N.P. So you know strain is something that all of
us that deal with sports either in professional athletes or in weekend warriors see quite
frequently and I think the spectrum of what you’re going to encounter varies on your
practice because most of these are actually injuries we see in younger adults and if your
practice is very heavy with geriatrics, they’re more tendon pathology than muscle pathology
that we’re going to see. But in terms of you know what we encounter
most commonly in our practice, it’s often under conditioned athletes rather than professional
athletes that experience these types of traumas because they’re not doing the exercise correctly,
their form may not be correct, or they overdo it and they wind up getting either delayed
onset muscle soreness because of too much exercise that they’re not ready to do or
wind up getting a frank strain because they slip, fall, twist, or something during the
activity itself. So in terms or Figure 6 it’s actually a
little bit more of an unusual type of injury to see a complete tear like this at the myotendinous
junction. At least in our practice the injuries tend
to be lower grade. Usually the clinicians are very astute at
picking up a complete tear as we have in this example where the rectus femoris muscle belly
was completely separated from the quadriceps tendon with a large fluid gap distally. This was actually a radiologist, not the most
conditioned, participating in soccer. J.S.K. Thank you for that. In discussing muscle strains you focus on
the variation in muscle architecture and how this impacts the location and the configuration
of the myotendinous junction and its effects on the associated MR and ultrasound findings
in patients who are affected by this. Can we review this concept by looking at Figure
7 which I think nicely illustrates the differences between parallel and pennate muscles and then
we can look at Figure 10 which illustrates a commonly strained pennate muscle? M.N.P. I think this is actually the most important
concept in this paper and something that I personally wasn’t aware of, and I’ve been
interested in muscle injury for a long time, until several years ago how important the
architecture is in terms of what the imaging findings are going to look like after a muscle
injury. I had a Popeye muscle picture in my head from
medical school that the tendon was always in the middle with muscle fibers converging
to it and never understood why so many muscle injuries showed so much fluid on the surface
of the muscle. And in fact the powerful muscles in our body
in our hamstrings in particular that are commonly injured all have this pennate architecture
where there’s no true tendon inside the muscle belly but it rides on the surface as
an area of collagen thickening and so all the injuries tend to be on the surface of
the muscle. It’s just not the way that I think we think
about muscle normally. In fact the bi-pennate architecture where
the tendon rides centrally in the muscle in more commonly seen in the upper extremity,
in the hands, in the supraspinatus for example. Those types of strains look very different. They don’t have much edema. I think we tend to under grade injuries in
that kind of muscle and over grade injuries in the muscles that have a superficial tendon. So I think this is really something that really
change how I read because you need to titrate the amount of fluid is going to be very different
than the two types. And I’m sorry you wanted to refer to a figure. J.S.K. Yeah Figure 10 I think shows you know a nice
example of a common strain. M.N.P. Yes. So this is an injury here in the biceps femoris
which is the most commonly strained with a very powerful, with a very strong superficial
tendon, just illustrating that the pathology doesn’t necessarily look muscular. You might interpret this as fascial disease
or even subcutaneous edema all riding on the surface. And another concept that’s important with
these architecture when you have superficial tendons, is that a lot of muscles have a tendon
on one side proximally and on a different side distally. And if you go back to the diagram you can
see this relationship and that’s true for all of the hamstrings is that the tendon starts,
for example, medially proximally, and then winds up being lateral distally. So the actual side that’s injured can reverse
relationships as you move from proximal to distal. And I think just looking at a lot of normal
cases you can appreciate that. It’s just one of those subtleties that you
know when you’re busy reading a stack you may not really focus on. J.S.K. Sure. Thanks. So let’s move on to the issue of delayed
onset muscle soreness which is another indirect injury that you describe. Can you describe for us what this injury actually
entails and we’ll look at Figure 17 which is an example I think of this type of injury. M.N.P. Well delayed onset muscle soreness has been
known about for a long time clinically in patients who perform some activity usually
one that they’re not doing regularly, a new activity or an increased level of activity,
and they don’t have symptoms at the time but develop soreness two to three days later. So we all know about this you know. I know to start taking Motrin the day I go
skiing because it’s gonna hurt like hell by two days in. But until MR the only way to really assess
this was by biopsy which nobody really wants to have to do and they know there are changes
in free water concentration and it’s been shown that there’s microscopic sarcomere
damage and that was shown in the 70’s. But really MR has allowed us to see this effectively
I think for the first time. I think ultrasound is now very sensitive to
this. And it’s a bizarre look on MR because it’s
often just one muscle and if you don’t get the accurate history that they did something
unusual like weightlift for three hours or go swim training, or in this particular case
this was a child given a twist board at Christmas who twisted the next day for hours, you may
not really know what you’re looking at. I think the thing that’s hardest to distinguish
from sometime is a denervated muscle which can also have this uniform pattern of edema,
but the swelling is not a feature that you’d see with denervation. That’s the best clue that you’re dealing
with DOMS, but you’ve got to ask the patient did you do something. I mean it could have been weeks ago. They may not recall because this can last
for a long time. J.S.K. Right. Terrific. So Dr. Pathria contusions are a common direct
traumatic injury and you mention in this, the paper, these are the second most common
reason for professional athletes to miss playing time second only to strains. Figure 19 is an example of the most common
of these injuries. Can you describe these contusions and we’ll
look at Figure 19 as an example. M.N.P. Yes so contusion injuries are quite different
than a strain because the history is usually quite obvious. There’s a direct blow and there may be you
know good clues to it like a bone bruise underneath it or a skin hematoma overlying the area. So we tend to see these for example in our
soccer and professional football players who wind up having a direct impact. It’s not that common an injury that we see
in our general practice. We tend to be more in a knife and gun club
hospital so we see a lot of penetrating trauma. But the history is usually quite evident and
what I think is interesting about these is they look much worse than strain and they
do much better than strain. They heal more quickly. So I think the important take home is that
the myotendinous junction and tendon are a bigger problem in terms of healing than muscle
tissue itself. But really they don’t have anything to do
with the tendon localization that strained us. They have a different appearance. I used to write in the old days that they
looked the same. They really don’t look the same. J.S.K. Great. So speaking about penetrating injuries, muscle
lacerations are the result of penetrating injury obviously, and in your paper Figure
26 illustrates a patient with a laceration within the neck muscle. Can we look at that case? M.N.P. You know I don’t actually have a large number
of cases of penetrating trauma on MR because we rarely image them. If it’s a presumed deep injury or if there’s
any type of neurovascular question at all, the patient will go straight to surgery. So I don’t think there’s much indication
for doing imaging and as I went through my cases, many of the lacerations that I had
were older cases where there was a concern for infection or an infected hematoma which
weren’t really suitable for this paper. So really imaging and acute laceration in
my opinion is rarely indicated. The only main questions are vascular and we
handle those really with CTA at our institution. So I have a lot of lacerations from stingray’s
barbs winding up in feet, but I didn’t think that quite qualified, but that’s the most
common laceration of muscle that I see in my practice. J.S.K. Sure. Next in your paper is a review of connective
tissue disorders and that’s followed by a section on muscle healing. Can we talk about the stages of muscle healing
from the injuries that you’ve detailed in the paper and in particular how MR factors
into the decision of when athletes can return to play after muscle injury? M.N.P. You know muscle healing is a really complicated
topic and I’m gonna give you a simplistic way of looking at it which is that it either
heals and become muscle again which is good, and in many cases doesn’t become muscle
again and it becomes something else. It becomes fat or it becomes collagen with
scar, or in a worst case scenario we have a myositis ossific cancer or some other abnormal
tissue that forms. That normal healing phase, it’s not linear. There are many stages and they overlap in
time. So you may have a lesion that’s undergoing
absorption in one portion and regeneration in another portion. So there’s a considerable heterogeneity
especially in large muscle injuries in how healing takes place. I don’t think that there is convincing literature
at this time that MR predicts the quality of the healing that takes place. A lot of things that look normal on delayed
MR don’t function normally. That doesn’t stretch as well. And compliance is a big issue in muscle. It needs to change length. That’s how it works. And we only look at it statically and we’re
not good at recognizing loss of compliance in tissue stiffness. So I think maybe with elastography or newer
techniques, we’ll do better. We’re only really looking at the amount
of fluid that’s there and the healing process happens faster clinically than it looks like
it’s happening on MR. There’s definitely a lag on MR. J.S.K. Great. So in the final section of your paper you
discuss the grading systems for muscle injury. Can we just discuss the relevance of these
systems to the imaging of muscle injuries? And we’ll take a look at Figure 2 as you
discuss this which I think lists some of the more commonly used muscle injury grading systems. How important is this to the practicing musculoskeletal
radiologist to be aware of these systems? M.N.P. You know I think it’s really important because
I hate to make people’s lives complicated because usually a good paper should simplify
people’s lives. But the old three grade grading system that
we’ve been using is deeply flawed. It doesn’t separate strain from contusion,
something very fundamental to how long it’s going to take an athlete to come back and
it correlates very poorly with return to activity. So while it’s simple to use, we don’t
really have good criteria, other than a grade 3 which is complete tear, for looking at those
and predicting anything very accurately. So I think you need to move on from that. My personal favorite out of all of these is
the British Athletic System. That seems to be the one that’s becoming
most widely used and it really pays emphasis to the size of the lesion in terms of its
length and cross section, but more importantly it really focuses on whether there is tendon
injury and where that’s located precisely. Is it inside the muscle or on the surface
of the muscle? And so I would suggest that if you’re gonna
learn one system to use British Athletics. It’s actually quite easy to use. It divides strain from contusion, you have
to give some dimensions of the lesion in terms of cross sectional involvement and length
described precisely where the area is abnormal, and pay a little bit of detailed attention
to whether there is tearing or swelling or some sort of derangement of the tendon itself. So I think the 3 isn’t gonna work or clinicians
don’t have any respect for the moderate grade report. It doesn’t really help them very much. J.S.K. Terrific. Well Dr. Pathria I want to thank you for taking
the time today to discuss your paper in the current January 2018 issue of RadioGraphics
which deals with the MR imaging of muscle trauma. It’s a really important topic. There’s not much out there in the literature
on this and really appreciate your contribution to the journal and sharing your expertise
with the audience today. Thanks so much. M.N.P. Thank you for having me. Thank you. J.S.K. Thanks.

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