Diagnosing Knee Pain: What Every Healthcare Professional Should Know

Knee pain is a common complaint among patients and can be caused by various factors, ranging from acute injuries to chronic conditions. Proper assessment of knee pain is crucial in diagnosing the underlying cause and developing an effective treatment plan. This comprehensive guide will delve into the essential aspects of knee pain assessment, providing medical students and healthcare professionals with the knowledge and tools necessary for accurate evaluation.

1. Understanding the Anatomy of the Knee

Before assessing knee pain, it's vital to have a thorough understanding of the knee's anatomy. The knee is a complex joint that involves the interaction of bones, cartilage, ligaments, tendons, and muscles.

• Bones: The knee joint is formed by the femur (thighbone), tibia (shinbone), and patella (kneecap).
• Cartilage: Articular cartilage covers the ends of the femur, tibia, and back of the patella, allowing for smooth movement. The menisci are two crescent-shaped cartilage pieces that act as shock absorbers between the femur and tibia.
• Ligaments: The knee has four main ligaments: the anterior cruciate ligament (ACL), posterior cruciate ligament (PCL), medial collateral ligament (MCL), and lateral collateral ligament (LCL). These ligaments provide stability to the knee.
• Tendons: The quadriceps tendon connects the quadriceps muscle to the patella, and the patellar tendon connects the patella to the tibia.
• Muscles: The quadriceps and hamstrings play crucial roles in knee movement and stability.

Understanding this anatomy is essential for identifying the structures involved in knee pain.

2. Patient History

A detailed patient history is the first step in assessing knee pain. It provides valuable information that can guide the physical examination and diagnostic tests.

• Onset of Pain: Determine whether the pain is acute or chronic. Acute pain usually results from trauma or injury, while chronic pain may indicate degenerative conditions.
• Location of Pain: Ask the patient to describe the specific location of the pain (e.g., anterior, posterior, medial, or lateral knee).
• Nature of Pain: Understand the characteristics of the pain (e.g., sharp, dull, throbbing, or burning).
• Associated Symptoms: Inquire about symptoms such as swelling, locking, clicking, or instability.
• Aggravating and Relieving Factors: Identify activities that worsen or alleviate the pain (e.g., walking, climbing stairs, or resting).
• History of Trauma: Ask about any recent falls, twists, or direct blows to the knee.
• Previous Injuries or Surgeries: Determine if the patient has a history of knee injuries or surgeries.
• Occupation and Hobbies: Consider the patient's occupation and physical activities, as these can contribute to knee pain.
• Systemic Symptoms: Check for symptoms such as fever, weight loss, or night sweats, which could indicate systemic conditions like infection or malignancy.

3. Physical Examination

The physical examination is crucial in assessing knee pain. It involves inspection, palpation, range of motion (ROM) testing, and specific maneuvers to identify the source of the pain.

3.1. Inspection

• Swelling: Look for swelling, which may indicate effusion, inflammation, or injury.
• Deformity: Check for deformities such as valgus (knock-knee) or varus (bow-leg) alignment.
• Skin Changes: Observe any skin changes, including redness, warmth, or bruising.
• Muscle Atrophy: Look for muscle atrophy, particularly in the quadriceps.

3.2. Palpation

• Joint Line Tenderness: Palpate along the medial and lateral joint lines to identify tenderness, which may suggest meniscal injury.
• Patella: Palpate the patella for tenderness, particularly at the superior, inferior, and medial aspects.
• Ligaments: Palpate the MCL and LCL for tenderness or thickening.
• Bursa: Palpate the prepatellar and infrapatellar bursa for signs of bursitis.
• Popliteal Fossa: Palpate the popliteal fossa for masses or tenderness, which may indicate a Baker’s cyst.

3.3. Range of Motion Testing

• Flexion and Extension: Test the knee's ability to flex and extend fully. Limited ROM may indicate joint effusion, arthritis, or a mechanical block.
• Hyperextension: Check for hyperextension, which may suggest ligamentous laxity.

3.4. Specific Tests and Maneuvers

• Lachman Test: Assess ACL integrity by performing the Lachman test, which involves stabilizing the femur and pulling the tibia anteriorly. A positive test suggests an ACL tear.
• Anterior Drawer Test: Similar to the Lachman test, the anterior drawer test assesses ACL integrity by pulling the tibia anteriorly with the knee flexed at 90 degrees.
• Posterior Drawer Test: Test for PCL injuries by pushing the tibia posteriorly while the knee is flexed at 90 degrees.
• McMurray Test: Evaluate meniscal tears by flexing the knee, then rotating the tibia internally and externally while extending the knee. A click or pain may indicate a meniscal tear.
• Apley’s Grind Test: With the patient prone and knee flexed, apply downward pressure on the heel while rotating the tibia. Pain suggests meniscal injury.
• Varus and Valgus Stress Tests: Apply varus and valgus stress to assess the integrity of the LCL and MCL, respectively.
• Patellar Apprehension Test: Assess patellar stability by gently pushing the patella laterally. The patient’s apprehension or pain suggests patellar instability.

4. Imaging Studies

Imaging studies are often necessary to confirm the diagnosis and assess the extent of knee injuries or conditions.

4.1. X-Rays

• Plain Radiographs: X-rays are the first-line imaging modality for assessing bony structures, joint alignment, and degenerative changes. Obtain weight-bearing views to assess joint space narrowing in osteoarthritis.
• Sunrise and Merchant Views: Special views like the sunrise or Merchant view can evaluate patellar alignment and subluxation.

4.2. Magnetic Resonance Imaging (MRI)

• Soft Tissue Evaluation: MRI is the gold standard for assessing soft tissue structures such as ligaments, menisci, tendons, and cartilage. It is particularly useful for diagnosing ACL, PCL, and meniscal injuries.
• Bone Marrow Edema: MRI can detect bone marrow edema, which may indicate occult fractures or bone contusions.
• Synovitis and Effusion: MRI can identify synovitis, joint effusion, and intra-articular bodies.

4.3. Ultrasound

• Dynamic Evaluation: Ultrasound is useful for dynamic evaluation of the knee, particularly for detecting effusions, synovitis, and superficial soft tissue structures.
• Guided Injections: Ultrasound can also be used to guide intra-articular injections or aspirations.

4.4. Computed Tomography (CT)

• Fracture Assessment: CT is helpful in assessing complex fractures, particularly in the tibial plateau or distal femur.
• Preoperative Planning: CT scans can be used for preoperative planning, especially in cases involving bone deformities or malalignment.

5. Common Knee Conditions

5.1. Osteoarthritis

• Presentation: Patients typically present with chronic, gradual onset of pain, stiffness, and reduced ROM. Pain is often worse with activity and relieved by rest.
• Assessment: Look for joint line tenderness, crepitus, and reduced ROM. X-rays typically show joint space narrowing, osteophytes, and subchondral sclerosis.

5.2. Meniscal Tears

• Presentation: Acute meniscal tears often occur during twisting injuries and present with localized pain, swelling, and locking or clicking of the knee.
• Assessment: Positive McMurray and Apley’s grind tests suggest a meniscal tear. MRI is the imaging modality of choice for diagnosis.

5.3. Anterior Cruciate Ligament (ACL) Injuries

• Presentation: ACL injuries typically result from non-contact pivoting injuries and present with a popping sensation, immediate swelling, and instability.
• Assessment: Positive Lachman and anterior drawer tests indicate ACL injury. MRI confirms the diagnosis.

5.4. Patellofemoral Pain Syndrome

• Presentation: Commonly seen in young athletes, patellofemoral pain syndrome presents with anterior knee pain, particularly during activities like squatting, running, or climbing stairs.
• Assessment: Assess for patellar maltracking and perform the patellar apprehension test. X-rays may show patellar subluxation or malalignment.

5.5. Bursitis

• Presentation: Bursitis, particularly prepatellar or infrapatellar, presents with localized swelling, pain, and warmth over the affected bursa.
• Assessment: Palpate the bursa for tenderness and swelling. Ultrasound can confirm the diagnosis.

5.6. Gout

• Presentation: Acute gout attacks in the knee present with sudden onset of severe pain, redness, and swelling, often affecting a single joint.
• Assessment: Aspirate the joint for synovial fluid analysis to confirm the presence of urate crystals. X-rays may show tophi or joint erosions in chronic cases.

5.7. Rheumatoid Arthritis

• Presentation: Rheumatoid arthritis typically presents with symmetrical joint pain, stiffness, and swelling. The knee is commonly involved in advanced stages.
• Assessment: Look for signs of synovitis, joint deformities, and reduced ROM. Blood tests for rheumatoid factor (RF) and anti-cyclic citrullinated peptide (anti-CCP) antibodies are useful for diagnosis.

6. Management and Treatment

The management of knee pain depends on the underlying cause, severity, and patient factors.

6.1. Conservative Management

• Rest and Activity Modification: Recommend rest and activity modification to reduce strain on the knee.
• Physical Therapy: Physical therapy is crucial for strengthening muscles, improving flexibility, and restoring function.
• Medications: Nonsteroidal anti-inflammatory drugs (NSAIDs) are commonly used for pain relief. In cases of gout or rheumatoid arthritis, disease-specific medications are required.
• Bracing and Support: Knee braces or orthotics may be used for support and stabilization.

6.2. Interventional Procedures

• Intra-Articular Injections: Corticosteroid or hyaluronic acid injections can be administered for pain relief and inflammation control.
• Aspiration: Joint aspiration is performed to relieve effusion or confirm a diagnosis (e.g., septic arthritis, gout).

6.3. Surgical Interventions

• Arthroscopy: Arthroscopic surgery may be required for meniscal tears, loose bodies, or ligament repairs.
• Ligament Reconstruction: ACL or PCL injuries often require surgical reconstruction, particularly in active patients.
• Knee Replacement: Total or partial knee replacement may be indicated in severe osteoarthritis or rheumatoid arthritis.

7. Preventive Measures

Preventing knee injuries and conditions involves education, lifestyle modifications, and early intervention.

• Education: Educate patients on the importance of proper body mechanics, especially during physical activities.
• Weight Management: Encourage weight management to reduce stress on the knee joints.
• Strengthening Exercises: Promote regular strengthening exercises for the quadriceps, hamstrings, and hip muscles to support knee stability.
• Early Intervention: Early intervention and treatment of knee pain can prevent progression to more severe conditions.