Knee Pain

Welcome to Leg Day #3 of the SplintER Series! Performing a fast and focused history and physical examination of a patient with an acute knee injury is an important skill that has the potential to be overlooked in our busy Emergency Departments. Our hope is that after reviewing this post and with enough practice you will be able to complete your exam within 2 minutes! These are can’t-miss points and expert tips on the knee exam for your next shift in the ED.

Why the Knee Exam Matters

Imaging is required to diagnose a number of important ED presentations. However, a thorough history and and physical exam can diagnose most causes of acute knee pain.1 For ED providers, this means gaining mastery in the knee exam may help you spare patients unnecessary imaging, cost, and length of stay. In fact, for the majority of musculoskeletal conditions, advanced imaging such as magnetic resonance imaging (MRI) isn’t necessary.

Key Questions for your History

  1. What was the mechanism of your injury?
  2. What were your subsequent symptoms (e.g. swelling, catching, snaps, or clicking)?
  3. Where is the location of your pain?
  4. Have you had this pain before?
  5. Have you had an injury or surgery performed on this knee before?

Key Points for the Knee Exam

  1. Visually examine the knee and ask the patient to take at least 4 steps.
  2. Evaluate the shin, calf, and dorsal and plantar foot for sensation.
  3. Test ankle dorsiflexion and plantar flexion strength.
  4. Palpate a posterior tibial (PT) and dorsalis pedis (DP) pulse.
  5. Evaluate for reduced range of motion (ROM), especially with knee flexion (< 90°) or inability to fully extend the knee.
  6. Palpate for tenderness at the joint line and the isolated patellar head or fibular head.
  7. Test knee stability by performing the Lachman’s, posterior drawer, and valgus/varus stress.

We recommend performing these steps in the sequence described as it allows for quick triage and prioritizes the neurovascular exam. The 7 step exam can be broken down into 3 critical questions:

  1. Is the patient neurovascularly intact?
  2. Is the ankle stable?
  3. Is there a fracture?

We review these 3 components in more detail.

Neurovascular Exam

Your exam should test for:

  • Sensation at the shin, calf, and dorsal and plantar foot – this evaluates the L4, L5, and S1 distributions of the tibial and common peroneal nerves.
  • Strength with ankle dorsiflexion and plantar flexion.
  • PT and DP pulses.

If you are unable to palpate PT and DP pulses, palpate for a popliteal pulse and then use a bedside Doppler or ultrasound to evaluate PT/DP pulses.

Knee Stability

There are 2 knee joints: the tibiofemoral and patellofemoral joint.

Knee stability relies on intact ligaments at the tibiofemoral joint. Complete tear of 2 or more ligaments is is considered unstable and places the knee at risk for dislocation.2 This warrants further diagnosis and management with orthopedic surgery.

There are 4 important knee ligaments (Figure 1), which are evaluated with specific exam maneuvers:


Figure 1. Major ligaments of the knee.
By BruceBlaus via Wikimedia Commons.3
Knee Ligament Exam Maneuver
Anterior cruciate ligament (ACL) Lachman’s test
Posterior cruciate ligament (PCL) Posterior drawer
Medial collateral ligament (MCL) Valgus stress
Lateral collateral ligament (LCL) Varus stress

Patellofemoral joint stability relies on intact patellofemoral ligaments. The medial patellofemoral ligament (MPFL) is the most commonly injured of these and can be disrupted during a patellar dislocation or subluxation.4 Knee immobilization and early physical therapy rehabilitation is usually recommended.

Always test the contralateral side even if it is without injury. Keep in mind that the patient may have previous injuries to the contralateral (uninjured) side and have an abnormal baseline exam.

Fracture

The Ottawa Knee rules5 can help guide you in fracture assessment. Evaluate for:

  1. Isolated patellar tenderness
  2. Fibular head tenderness
  3. Reduced knee flexion (<90°)
  4. Inability to bear weight more than 4 steps

A knee XR series is recommended if you identify any of these on exam. Any focal tenderness or focal swelling should raise suspicion for a fracture.

Other Useful Tips

  • Athletes will often injure other structures simultaneously. For example, the MCL and the menisci are often injured at the same time as the ACL.
  • Evaluate for a full thickness tendon rupture by asking the patient to extend against gravity or resistance.
  • You may find a “locked” knee on exam – you cannot passively extend the knee. This suggests that an intra-articular process (e.g. ACL tear, meniscal injury) is causing the knee to “lock” in place. It may require closer follow-up and an outpatient MRI and/or arthroscopy.
  • Communicate your exam findings to your patient. You can use exam findings to explain your diagnosis and why advanced imaging (e.g. MRI) isn’t warranted on the day of injury.

An Example Case

A 22-year-old soccer player presents with acute knee pain after running into another player. She recalls twisting her knee and states that she heard a “pop.” She subsequently developed swelling and immediate pain.

Figure 2. An effusion can be visualized overlying the patient’s left knee. Photo from Becky Stern via Flickr.6

Expert Evaluation: Dr. Kori Hudson

Associate Professor, Emergency Medicine, Georgetown University
Team Physician for Georgetown University
Consulting Physician for the Washington Capitals

Our young soccer player describes a classic mechanism for an ACL tear. Field sport athletes often play in cleats and can “anchor” the foot. This allows greater translation and rotation of the tibia in relation to the femur resulting in an ACL tear.

We first observe well healed surgical scars and learn that she has had a bilateral ACL repair several years ago. We note an effusion – this is consistent with intra-articular injury.

The neurovascular exam takes priority – test sensation, strength, and pulses. With an ACL tear, sensation, strength (dorsiflexion and plantar flexion), and pulses are typically preserved.

Evaluate for a fracture. She has full range of motion including flexion and intact extension. There is medial joint line tenderness, but no isolated patella or fibular head tenderness.

Knee stability is the final question. We utilize our 4 ligamentous tests and the patient has a positive Lachman’s test and pain with valgus stress. This means the knee is stable – only one ligament is torn (ACL) and another ligament is strained (MCL).

A knee XR series is warranted given her inability to bear weight (Ottawa Knee Rules). This was negative for an acute fracture. Since she is neurovascularly intact with a stable knee, she is offered a hinged knee brace and crutches for support if needed. She should not be placed in a knee immobilizer. Treat pain and swelling with ice and multi-modal analgesia before following up with Sports Medicine/Orthopedics in 1-2 weeks.

Conclusion

  • The key components of the knee exam include an evaluation for neurovascular compromise, knee instability, and a fracture.
  • Always test the contralateral (unaffected) side even if it is without injury.
  • A multi-ligamentous injury defines knee instability and warrants an orthopedic evaluation.
  • Remind patients that adequate time (1-2 weeks) for pain and swelling to improve will allow their sports medicine or orthopedic physician to determine the next step at follow-up.
  • With practice you can complete this thorough exam of the knee in under 2 minutes!

References

  1. 1.
    Jackson J, O’Malley P, Kroenke K. Evaluation of acute knee pain in primary care. Ann Intern Med. 2003;139(7):575-588. https://www.ncbi.nlm.nih.gov/pubmed/14530229.
  2. 2.
    Henrichs A. A review of knee dislocations. J Athl Train. 2004;39(4):365-369. https://www.ncbi.nlm.nih.gov/pubmed/16410830.
  3. 3.
    Blaus B. ACL Tear. Wikimedia Commons. https://upload.wikimedia.org/wikipedia/commons/thumb/b/b8/ACL_Tear.png/800px-ACL_Tear.png. Accessed January 15, 2019.
  4. 4.
    Sallay P, Poggi J, Speer K, Garrett W. Acute dislocation of the patella. A correlative pathoanatomic study. Am J Sports Med. 1996;24(1):52-60. https://www.ncbi.nlm.nih.gov/pubmed/8638754.
  5. 5.
    Stiell I, Greenberg G, Wells G, et al. Prospective validation of a decision rule for the use of radiography in acute knee injuries. JAMA. 1996;275(8):611-615. https://www.ncbi.nlm.nih.gov/pubmed/8594242.
  6. 6.
    Stern B. Another knee accident | swollen knee. Flickr. https://www.flickr.com/photos/bekathwia/4731245474. Accessed February 24, 2019.
William Denq, MD

William Denq, MD

Sports Medicine Fellow
Department of Emergency Medicine
University of Utah
William Denq, MD

@willdenq

Sports Medicine Fellow Emergency Medicine University of Utah George Washington University '18 University of Pittsburgh '14 and '10