Understanding Hip Joint Pain in the Young Adult
I’m going to write a really quick overview of my understanding of the young adult hip joint (the joint itself, not the region). Why? Well I’m kind of considered an expert on it for some weird reason and you may find some value in it. I was the founder of the Hip Special Interest Group of the Sports Section of the American Physical Therapy Association. I’ve written a ton of articles/textbook chapters on the subject and am currently involved in several research projects trying to answer more questions regarding the hip, specifically in athletes. I also teach a weekend course around the United States on evaluation and treatment of hip pathology. All this makes me an “authority”. Of course, if history has taught us anything, all of this makes me the LAST person you should listen to…
In this article, I’m going to give a bulleted list of my thought process. I’m not going to give you a bunch of citations for a few reasons:
1. This is a blog post which makes it cursory, unreviewed, and illegitimate.
2. I could say whatever the hell I want and find at least one citation to support it – means nothing.
3. None of these statements are controversial and I don’t feel like stringing out the 20 possible citations on each.
4. Here’s a reference list. Providing it means nothing since I could be misrepresenting it all.
5. Think critically about what I say no matter what. There is no way in hell that I’m 100% right.
If I feel that something might be a bit controversial, I’ll throw you a bone. Again, this is going to be pretty simple. Like a lot of things in in physical therapy, it doesn’t need to be that complicated.
Femoroacetabular Impingement (FAI) is a thing
FAI has to do with bony morphology. The femoral head and the acetabulum have a…uhhhh…let’s call it “an imperfect fit”. “Pincer” is when the acetabulum covers too much of the femoral head. In isolation, I really don’t care about a pincer since its ability to cause any real damage is limited. When we talk about a cam, it gets more complicated.
What is a cam?
A “normal” (whatever that means) femoral head is spherical in nature. Round peg (femoral head) and round hole (acetabulum) work really well together. When there is a cam, you no longer have a spherical head, it is more egg or cam shaped. This offset can be measured via the “alpha angle” on frog-leg radiograph.
The term “cam” refers to a mechanical concept of an offset shape used for work. Mechanical cams can be useful. Due to its shape, a cam interfaces one way in one position, but another way in another position. For example, when rock climbing, a climber will put a cam-shaped device with a cable or webbing attached into a crack in the rock. When she pulls on the cable or webbing, the cam turns in the crack. The offset shape causes the cam to exert more force on the walls of the crack as it turns and “spreads”. The harder you pull, the more it binds inside creating a fixed anchor point for her rope. How do you remove it? Just turn the cam the other way and it slides right out.
Cams can be a “bad thing”
A cam shaped femoral head acts in the same way as the rock climbing example above. As the hip goes into flexion and/or internal rotation, the aspherical portion of the head slides into the joint. Just like in the crack of rock, that creates an increasing “spreading” force in the acetabulum. The greater the spread, the greater the shear force to the articular cartilage of the acetabulum. As we all know, articular cartilage handles compressive forces very well. Shear forces? Not so much. The damage associated with the presence of a cam is a delamination injury to the articular cartilage of the acetabulum right where the cam engages. There is a correlation between cam and OA but that doesn’t mean cams always cause OA. Definitely plausible, but, in general, lots of things are plausible.
The cam tends to present on the anterior femoral head-neck junction. They will not have a hard, bony stop during range of motion. When you take them into terminal flexion and/or internal rotation, they will have a progressive seizing sensation that will be described as “tight”. What do you think happens when you stretch this “tightness”? You ruin their day.
I don’t care so much about an acetabular labral tear
As in the shoulder, degenerative labral tears happen. FAI can cause them. Sure, when you go into a symptomatic hip arthroscopically, you will find FAI (most likely cam) and a labral tear. So what? In isolation, those two things do not correlate with joint pain. You heard me (or read me). What correlates most with hip joint pain is damage to the articular cartilage. Read this. Also, that pain will ALWAYS present in the front of the hip. Not the side or back (although they may ALSO have pain in those other areas from something else). Front. Got it? Good.
Let me summarize hip pain from cams in an oversimplified way
The cam articulates with the acetabulum creating an increasing shear force to the articular cartilage of the acetabulum resulting in hip joint pain (perceived in the anterior hip region). Over time, a secondary labral tear can evolve. The bigger the cam, the earlier this can happen during the range of motion of the hip – the “good fit” happens in a smaller arc. More cam does correlate with more pain.
Surgical correction includes removing the cam via a femoroplasty (duh) and repairing or performing a debridement of the torn labrum (why the hell not?) but the reduction in hip joint pain most likely comes from decompressing that irritated acetabulum. Now, if you stop reading here, you are missing half the story about cams.
Cams can be normal and perfectly fine
It is a well-known fact that elite soccer players have cams. So well-known that some are suggesting that playing soccer causes the cam. Maybe. People with cams really like to be externally rotated which may give them an advantage in soccer – the game may naturally select those with developing cams. Also, the older you are, the more likely you are to have a cam whether or not you play soccer. Let’s just say, keep playing soccer for now.
HAVING a cam is not a problem. ENGAGING a cam can be. As long as you don’t shove that cam deep into the acetabulum, everything is hunky-dory. If you discover a cam (even a labral tear) without pain in the front of the hip, then carry on. Just don’t push their range of motion…obvious right?
I have a cam. My favorite hip surgeon has a cam. Neither one of us is rushing to the operating room. It is a finding that correlates with pathology, but is not pathology itself. Cams are a spectrum from “more cam” to “less cam”. The cut-off point is very debatable.
A simple look at the hip that anyone can do
Here you go internet. Here is the most basic of hip joint assessments from a worldwide leader in hip pain™!
Do they complain of pain in the front of their hip as their chief complaint or during impingement tests?
If no, do not send to a hip surgeon at this point no matter what else you find. It is a waste of everyone’s time. It is unlikely that they have any hip joint problem. Look outside the joint (I’m not going open THAT can of worms in this post – there are some crazy ideas out there). If the answer to that question is yes, carry on with your evaluation.
Do they have less than 40 degrees of internal rotation?
If they have MORE than 40 degrees of internal rotation AND anterior hip pain with impingement tests, they likely have a symptomatic pincer at worst. Conservative management should take care of it (strengthen and coordinate glutes, keep them out of terminal/painful ranges as it calms down).
If they have LESS than 40 degrees and NO anterior hip pain, take note that they MAY have an asymptomatic cam (only frog-leg radiograph will tell for sure). Read this. A little education on not engaging that thing is probably all that they need. The less the IR range, the more education I provide. In my experience, I don’t start getting concerned at all until the range presents below at least 20 degrees. Even then, I’m concerned that some education is warranted, not treatment.
If they have LESS than 40 degrees AND anterior hip pain, take a step back. The likelihood of it being a symptomatic cam is increasing. The less the internal rotation, the higher the likelihood. Again, I use 20 degrees as my concern point but that’s anecdotal. Remember what is most likely causing that pain? Not the cam itself. Not a labral tear. The articular cartilage – most likely in a delaminating fashion. Not good. If they have been dealing with this for more than 6 months, I’ll work with them, but I will also recommend a surgical consult for a full workup of that joint. Diagnostic pain injection is the best tool to rule out the joint. It is the only way you can have confidence that the pain is coming from the hip joint. Never do surgery without one.
How do you treat a cam conservatively?
Look, I’m not going to tell you how to do your job but what is really the big problem here? An engaging cam creating shear forces across the joint right? So what should we try to do? Ok – stay with me here ‘cause it gets complicated.
Teach them not to engage the cam to hopefully reduce the shear forces likely occurring.
Modify their squats and other activities to fit the cam. What motion is most likely to engage that cam? Hip flexion with internal rotation, right? Hey! That’s dynamic valgus – the boogeyman of the lower extremity! Teach them to activate their external rotators as they squat, land, jump, cut, etc. A “normal” movement for one person may not be “normal” for another. Again, “normal” hips come in all sorts of shapes and sizes. Find the position that works best for your patient. Could there be more going on here? Sure, but start here.
Should you try to gain hip mobility? Uh, how? If you reduce the irritation (unloading, rest, anti-inflammatories, time, or any voodoo you and the patient might think helps) you may gain some mobility secondarily, but otherwise there is a bone causing the limitation. You are saying that they NEED that hip mobility? Then you are saying that they NEED surgery because otherwise that cam will continue to engage in those positions. You can’t have it both ways.
The goal of any treatment, whether conservative or surgical, is to restore desired function within tolerable/manageable pain. The joint doesn’t have to be “normal” nor does its mobility.