Approach to the patient with chronic/gradual knee buckling

[cbrsmurf]

So I get this typically older patients >50 y/o who c/o of a knee "giving out" or sudden weakness occurring more frequently over months or years, but deny pain or hx of trauma. Exam of the joint is usually negative (full ROM, strength 5/5, neg McMurray) What is the pathology and diagnosis/management of these kind of patients? Please edumacate me

[polarbebe]

So I get this typically older patients >50 y/o who c/o of a knee "giving out" or sudden weakness occurring more frequently over months or years, but deny pain or hx of trauma. Exam of the joint is usually negative (full ROM, strength 5/5, neg McMurray) What is the pathology and diagnosis/management of these kind of patients? Please edumacate me

 

I am sure there is a wide differential in such symptoms. Besides obvious cardiac causes such as arrhthymias... from my previous neuro experience, I would consider "drop attacks" given the age and likely possible risk factors for CVA. "Drop attacks" are due to vertebro-basilar insufficiency. If you believe given hx, exam and have ruled out other more likely causes... Imaging by CTA head and neck with contrast or MRA head and neck which can be done with or without gadolinium (quality obviously better with gad).

[Guest JMPA]

So I get this typically older patients >50 y/o who c/o of a knee "giving out" or sudden weakness occurring more frequently over months or years, but deny pain or hx of trauma. Exam of the joint is usually negative (full ROM, strength 5/5, neg McMurray) What is the pathology and diagnosis/management of these kind of patients? Please edumacate me

 

start with weight bearing xray of bilat knees for comparison. consider nsaids/tylenol for mild pain relief. if no draw signs or laxity then wait until you have the xray results

[Acebecker]

The medial/oblique portion of vastus medialis (the "VMO" or vastus medialis - oblique) is a crucial muscle in maintaining knee extension - in fact it is the pirmary muscle responsible for knee extension from 20 degrees of flexion to 0 or locked. It produces internal rotation of the leg as well to a small extent that keep the knee stable. I'd look at the VMO for atrophy first. Atrophy can occur for a variety of reasons, chief in this age group would be chondromalacia patella resulting in mild knee effusion, which decreased VMOs ability to activate (even as little as 10cc of extra fluid in the knee capsule can produce inability of VMO to sustain contraction, which leads to atrophy within a matter of days). On exam you'll feel crepitus under the patella with seated knee ext to zero and flexion to 90 degrees, on xray you'll see spurring of the patella and probably lateral deviation of the patellae on the sunrise. VMO atrophy will be fairly notable and with sustained attempt at full knee extension there will be fasciculations in the VMO as well. The problem can be fixed with simple knee exercises, generally, but in a noncompliant patient he will need PT ordered to keep him on the ball.

 

If your exam is totally benign, no spurring on imaging, normal neuro, I'd consider going down the chronic degenerative pathway - something like muscular dystrophy, ALS, etc. EMG may be a good diagnostic tool to aide in diagnosis. The "drops" would also enter my differential at that point.

 

Andrew

[bradtPA]

Knee stable to varus/valgus stress? Negative anterior/posterior drawers? Seen a lot of chronic unstable knees that were 40 year old injuries with an unrepaired ACL tear.....

[cbrsmurf]

I am sure there is a wide differential in such symptoms. Besides obvious cardiac causes such as arrhthymias... from my previous neuro experience, I would consider "drop attacks" given the age and likely possible risk factors for CVA. "Drop attacks" are due to vertebro-basilar insufficiency. If you believe given hx, exam and have ruled out other more likely causes... Imaging by CTA head and neck with contrast or MRA head and neck which can be done with or without gadolinium (quality obviously better with gad).

 

I will consider that under my differential, but I figure cardiac/vascular causes would be associated with syncope, CP, sob, or dizziness.

[Nakasoner]

Don't forget to check the hip. Many times I find pain with int rotation and ext rotation of the hip, causing the thigh/knee to give way when weight bearing. If the knee exam is benign to stress testing and the ROM is fairly normal without an effusion, check the hip. Get weight bearing xrays and check the joint space. If the knee and the hip are negative, check the lumbar spine and do a neuro exam for motor weakness esp in the L2-4 roots for radiculopathy.

[cbrsmurf]

start with weight bearing xray of bilat knees for comparison. consider nsaids/tylenol for mild pain relief. if no draw signs or laxity then wait until you have the xray results

 

What XR findings would you expect to see that would correlate with the symptoms I presented?

[cbrsmurf]

The medial/oblique portion of vastus medialis (the "VMO" or vastus medialis - oblique) is a crucial muscle in maintaining knee extension - in fact it is the pirmary muscle responsible for knee extension from 20 degrees of flexion to 0 or locked. It produces internal rotation of the leg as well to a small extent that keep the knee stable. I'd look at the VMO for atrophy first. Atrophy can occur for a variety of reasons, chief in this age group would be chondromalacia patella resulting in mild knee effusion, which decreased VMOs ability to activate (even as little as 10cc of extra fluid in the knee capsule can produce inability of VMO to sustain contraction, which leads to atrophy within a matter of days). On exam you'll feel crepitus under the patella with seated knee ext to zero and flexion to 90 degrees, on xray you'll see spurring of the patella and probably lateral deviation of the patellae on the sunrise. VMO atrophy will be fairly notable and with sustained attempt at full knee extension there will be fasciculations in the VMO as well. The problem can be fixed with simple knee exercises, generally, but in a noncompliant patient he will need PT ordered to keep him on the ball.

 

If your exam is totally benign, no spurring on imaging, normal neuro, I'd consider going down the chronic degenerative pathway - something like muscular dystrophy, ALS, etc. EMG may be a good diagnostic tool to aide in diagnosis. The "drops" would also enter my differential at that point.

 

Andrew

 

Thanks for the detailed post.

[cbrsmurf]

Knee stable to varus/valgus stress? Negative anterior/posterior drawers? Seen a lot of chronic unstable knees that were 40 year old injuries with an unrepaired ACL tear.....

 

Yes, those tests are typically negative in these patients.

 

Just to note, the anterior drawer test has low sensitivity. I think there is an increasing shift toward the Lachman Test for ACL testing.

[cbrsmurf]

Don't forget to check the hip. Many times I find pain with int rotation and ext rotation of the hip, causing the thigh/knee to give way when weight bearing. If the knee exam is benign to stress testing and the ROM is fairly normal without an effusion, check the hip. Get weight bearing xrays and check the joint space. If the knee and the hip are negative, check the lumbar spine and do a neuro exam for motor weakness esp in the L2-4 roots for radiculopathy.

 

Good suggestions, I think I will do a more detailed exam of the hip and LS. I haven't been doing the weight-bearing knee XR's, and will start implementing those.

[Acebecker]

Two notes from ortho (these were learned on my ortho rotation and have stuck with me):

 

1. on xrays: if there's a chance of referral to ortho, they will want a 4 view series on the knee: weight bearing AP and lateral, non-weigth bearing tunnel, and bilateral sunrise. Since I'm in UC, all my patients are potential referrals to ortho, so I always get this series on the knees. Not once have I regretted it.

 

2. Lachman's is the gold standard test for the ACL. I was dressed down by the orthopedic surgeon I was learning from when I performed an anterior drawer when I couldn't get the patient to relax enough for Lachman's (I was an ATC before PA school, so I should know better). He said, "Anterior drawer is a worthless test."

[myironlung]

MRI after x-rays

[ventana]

I would think a good physical exam 1st, then x-rays as detailed above, if the patient feels like it is truly her knee. I would step to MRI.

 

If the patient feels it may well be from something else consideration for a varying differential, however I would not step very quickly did be doing these other workups.

 

common things happen commonly

[Guest JMPA]

What XR findings would you expect to see that would correlate with the symptoms I presented?

 

i would expect to see djd, also it may help to take a detailed hx including work hx and hobby