1. Shane Cass, DO UNM Sports Medicine
Acute knee pain
Shane Cass, DO
UNM Sports Medicine

2. Objectives Provide a comprehensive case based review of knee pathology
Review clinically relevant anatomy
Synthesize a diagnosis and differential
Appropriately use relevant radiological studies
Provide a rational and useful treatment plan

3. References
To get the most out of this module go to the link below. Here you’ll find great MSK articles by the AAFP.
AAFP MSK Modules
Also please click the link below to review a complete knee exam
Knee exam video

4. High yield articles for this module
Evaluation for acute internal knee derangement
Evaluating the patient with a knee injury. Point of care guideline
Evaluation of patients presenting with knee pain

5. Internal knee anatomy

6. Etiology
Primary care physicians see about 4 million cases of knee pain a year. It is the 10th most common reason for primary care visits.
True or False: The most common cause of knee pain in outpatient visits is internal derangement/ligamentous injury.
False. The majority of knee pain seen in primary care clinics is for knee osteoarthritis. 10% of all acute knee visits are for meniscal tears, 4% are for cruciate ligaments and 7% are for collateral ligament injuries.

7. Tibial Plateau Fracture
Case: a 52 year old female is involved in a head on MVA, her knee hit the dash board. She was unable to bear weight afterwards, has a large effusion and is unable to flex knee to 90 degrees.
Should you get an x-ray or an MRI?
X-ray!!!
Tibial Plateau Fracture

8. Clinical decision rules: Choose the right answer
1. Clinical Decision rules are neither sensitive or specific
2. Pittsburg Knee rule is specific but not sensitive
3. Both Knee rules are sensitive but not specific
A prospective study in the ED comparing Ottawa to Pittsburg showed both sensitive % but Pittsburg was more specific at 60% compared to Ottawa at 27%
Only 1% chance of fracture in the ED if no Ottawa findings present
Sort Level A at AFP

9. This meets Ottawa criteria
An 18 year old football player from la cueva comes in after a player hit him directly in the knee cap with his helmet. He felt a pop and had severe pain and a large effusion. Lachman and anterior drawer test are positive. He is unable to bear weight and won’t tolerate a pivot shift test. Choose the best answer.
1. Likely diagnosis is a meniscal tear.
2. It is unnecessary to get an x-ray in this patient.
3. Lachman’s test has a high negative predictive value
4. Pivot shift is rarely useful
This meets Ottawa criteria
Pivot shift has a higher positive predictive value than Lachman’s, but most patient’s don’t tolerate it.

10. ACL evaluation Lachman’s
Click below to see an example of the Anterior Drawer, Lachman and Pivot Shift test
ACL testing
Keep in mind, the anterior drawer test is the least specific or sensitive test for the ACL, although widely used.
Lachman’s

11. Imaging for ACL tears? Should MRI be done to rule in an ACL tear?
The American Academy of Orthopaedic Surgeons states that it is usually not required to diagnose an ACL tear and should be considered to rule out internal derangement.
With a negative exam, the ACL is unlikely to be injured (less than 2% likelihood)

12. Practice guidelines from Aaos
Key Points for Practice
• The presence of a popping sensation in combination with swelling is a significant predictor of an ACL injury.
• Magnetic resonance imaging has a high sensitivity and specificity for confirming an ACL injury.
• If reconstructive surgery is indicated, it should be performed within the five months following injury.
• Early accelerated (19 weeks) and non-accelerated (32 weeks) rehabilitation programs may be beneficial after ACL reconstruction.
Read the article here

13. 1. Joint line pain is very specific for meniscal injury
A 23 year old intramural soccer player from UNM comes in after injuring her right knee in a twisting motion with a planted foot. She reported pain, swelling and a clicking sensation accompanied by locking. Examination shows positive joint line pain, effusion and positive thessaly test. Choose the best answer.
1. Joint line pain is very specific for meniscal injury
2. McMurray test is very sensitive for meniscal injury
3. The Thessaly test is the best examination test for meniscal injury
4. A composite of historical data and examination findings give the best clinical picture of a meniscal tear.

14. Joint line pain is fairly sensitive (76%) but only 29% specific
McMurrays test is 97% specific, but it’s sensitivity is only 52%
Thessaly test is highly validated with an 81% positive predictive value and a 1% negative predictive value.
See a video of Thessaly Test here
Thessaly Test

15. True or false
An effusion is big predictor of internal derangement of the knee.
True!
74 to 91 percent of patients with traumatic injury and effusion have internal derangement of the knee
Detect swelling with a positive ballotment test

16. What if our patient presented much the same way but is 67 and was playing soccer with her grandchildren? The x-ray is below and her right knee is the “injured knee.”
Treat the osteoarthritis and don’t order an MRI. Her meniscus is already destroyed!

17. For suggestions on improving this educational Module contact me below by e-mail…