Today, I review, link to, and excerpt from The Curbsiders‘ “#406 Kneedful Things: Knee Pain 201 with Dr. Ted Parks”.*

*Parks EH, Williams PN, Watto MF. “#406 Kneedful Things”. The Curbsiders Internal Medicine Podcast. thecurbsiders.com/category/curbsiders-podcast July 31, 2023.

All that follows is from the above resource.

Download the Transcript

Ready for more knee pain?  You’ve already memorized episode #98, so join us as Ted Parks to returns to teach us even more about common causes of knee pain (anterior knee pain, patellofemoral pain, knee bursitis, pain after knee replacement) and what to do about them!

Knee Pain Pearls

1. Anterior knee pain is an umbrella term that includes patellofemoral pain
2. The management of patellofemoral pain consists primarily of physical therapy–surgery should be avoided
3. Prepatellar bursitis and pes anserine bursitis are common causes of knee pain, and characterized by local tenderness
4. Management of aseptic bursitis includes NSAIDs and stretches, and a cortisone injection can be considered
5. Pain after knee replacement can be divided into pain that persists after surgery and pain that recurs years after surgery
6. Loosening of hardware can be evaluated by plain film, but a bone scan is more sensitive and should be performed if suspicion is high enough
7. Loosening of hardware warrants surgical revision, and diagnosis of septic loosening can be made intra-operatively
8. Diagnostic evaluation for suspected periprosthetic infection often begins with serologic markers of inflammation, with subsequent arthrocentesis for confirmation

Kneedful Things – Show Notes 

Anterior Knee Pain

Relevant anatomy

• Extensor mechanism: Chain of structures that include the quadriceps
  • Hamstrings work to flex the knee, but gravity plays a large role too
  • Quadriceps extend, and counteract gravity during standing or squatting
• The patella can undergo chondromalacia, which is a softening or degradation of articular cartilage
  • Anterior knee pain can be caused by patellar or quadriceps tendonitis
• The Q angle represents the angle between the long axes of the femur and tibia (Gaitonde et al. 2019)
  • This angle impacts patellar tracking
  • Females have a wider pelvis, which leads to a greater Q angle
    • This leads to more lateral patellar tracking, which can lead to patellofemoral pain, and is why this is more common in women

Patient presentation

• Anterior knee pain or patellofemoral pain are broad and imprecise terms that encompass various conditions affecting the extensor mechanisms
  • Activities like squatting, descending stairs, and standing from sitting without using hands typically worsen symptoms
  • Patients may report stiffness that is worse after sitting, or crepitus with movement
• Pain localized below the patella suggests patellar tendon involvement
• Pain above the patella may suggest quadriceps tendonitis

Physical examination

• Patellar crepitus is not terribly helpful unless the symptomatic side has more pronounced crepitus, which may suggest pathology of patellofemoral articulation
• The patellar tilt test is performed by placing your thumb under the lateral patella and attempting to raise the edge above the horizontal plane
  • Inability to do so suggests tightening of the lateral retinaculum, which may indicate patellar maltracking
• The patellofemoral apprehension sign occurs when patients have apprehension when the patella is pushed laterally, which is a test for patellofemoral instability
• The compression test or Clark’s test is done by compressing the patella against the femur and having the patient contract their quadriceps to elicit pain
  • This test is neither sensitive nor specific (Nunes et al. 2014)

Imaging

• If there is uncertainty about the diagnosis, imaging may be helpful, and should include the Merchant’s view* to evaluate for patellofemoral arthritis and maltracking

*Link to Google search of Merchant’s view knee xray.

Management

• The mainstay of treatment for patellofemoral syndrome is stretching to increase the elasticity of the extensor mechanism
• Preferential strengthening of the medial quadriceps can also correct maltracking
  • Exercise on the stationary bike can be helpful for this
• NSAIDs can be a helpful adjunct for analgesia
• Surgery can be done, but is often considered a last resort (Gaitonde et al. 2019)

Bursitis of the knee

Relevant anatomy

• Bursae are closed, fluid-filled sacs that reduce friction between tissues of the body
• The two main knee bursae that undergo bursitis are the prepatellar bursa and the pes anserine bursa
  • The prepatellar bursa overlies the patella
  • The pes anserine bursa is medial and about three inches below the joint line, where the pes anserine tendons (the sartorius, gracilis, and semitendinosus) attach to the medial tibia

Patient presentation

• Prepatellar bursitis is often the result of repetitive, blunt trauma, like kneeling on the floor
  • Septic patellar bursitis can occur in the setting of penetrating trauma (i.e., a splinter that penetrates the skin and innoculates the bursa)
• Pes anserine bursitis can be precipitated by squatting and lunges
• Local tenderness the hallmark of pes anserine bursitis
• A palpable fluid collection just beneath the skin over the patella is the hallmark of prepatellar bursitis

Physical examination

• The diagnosis of bursitis of the knee can generally be made by history and pain with palpation over the relevant bursa
• Aspiration is typically not necessary to make a diagnosis

Management

• The mainstays of management for aseptic bursitis are rest, NSAIDs, and compression (Aaron et al. 2011)
• Hamstring stretches can be helpful, particularly if there is associated tendinitis of the pes tendons
• Cortisone injections can be helpful, but it’s important to avoid the creation of a sinus tract when injecting the prepatellar bursa

Knee pain after knee replacement

Relevant anatomy and pathophysiology

• In the immediate postoperative period, causes of pain after replacement can include poorly implanted replacement technique or infection
• With recurrence of pain long after a knee replacement, consider the three articular surfaces: the femur, tibia, and patella
• The polyethylene cap over the tibia can begin to wear down over time
  • This can be accelerated if there is a scratch on the metal surface of the femur component
• There are instances when the patella is not resurfaced during knee replacements
  • This patellar cartilage can wear down over time as it rubs against the metal of the femur covering
• Loosening of the bond of the hardware components from the bone can also lead to knee pain and instability
• Infection of the joint replacement via hematogenous spread can occur at any point during the patient’s lifetime
  • A knee replacement is essentially a large foreign body in the joint space, which can predispose this site to infection
  • These infections can be indolent, and may not necessarily present with marked swelling and erythema

Patient presentation

• In a patient who has continued pain following knee replacement, consider infection or possible implantation or sizing abnormalities
• In patients who have recurrence of pain after a significant period of relief, Dr. Parks thinks about aseptic loosening of the hardware, periprosthetic infection, and referred pain from other joints, especially the hip
• Prosthetic wear can manifest as instability
  • As the plastic piece wears down, the points of origin of the ligaments move closer together, which leads to ligamentous laxity

Physical examination

• Palpation around the joint can help identify bursitis, tendinitis, and even scar neuroma as a cause of pain (Momoli et al. 2017)
• Ligamentous laxity with valgus and varus stress on examination can suggest polyethylene wear
• Evaluate the hip for referred pain by doing the “windshield wiper” test
  • With the patient sitting and the hip flexed at 90°, internally and externally rotate the hip by moving the leg back and forth below the knee
  • This elicits discomfort in patients with intra-articular hip pathology