Orthopaedic Surgery - Knee Pain

Basics

Knee pain has a broad differential diagnosis and may arise from pathology within the knee itself or from disorders elsewhere that refer pain to the knee.

Pain may be diffuse or localized to a particular region.

In many patients, a careful history combined with a focused physical examination substantially narrows the diagnosis.

Knee pain can be broadly classified as:

Traumatic or acquired/nontraumatic.

Risk Factors

Factors that increase the likelihood of knee pain include:

Athletic activity, lower-extremity malalignment, ligamentous instability, obesity, and physical deconditioning or sedentary behavior.

Etiology

Major causes include:

Acute traumatic injury, repetitive overuse, degenerative disease, inflammatory disease, infection, and abnormalities involving structures around the knee.

Associated Conditions

Systemic disorders that may produce knee symptoms include:

Rheumatoid arthritis, gout, pseudogout, and other inflammatory arthropathies.

Increasing physical activity may also uncover previously asymptomatic structural abnormalities or overuse conditions.

Diagnosis

History

The history should clarify:

Onset, mechanism, pain location, swelling, locking, popping, instability, activity relationship, night pain, and functional limitations.

Symptoms such as difficulty climbing stairs or rising from a chair may point toward specific patterns of knee pathology.

General Symptoms

Common complaints include:

Swelling, locking, popping, giving way, difficulty using stairs, difficulty rising from a chair, and chronic pain that worsens with activity.

Patellofemoral Disorders

Patellofemoral Pain Syndrome

Patellofemoral pain commonly occurs in adolescents and young adults.

Pain is usually located at the anterior knee and is worsened by activities that increase patellofemoral joint loading, such as:

Climbing or descending stairs, squatting, prolonged sitting, and rising from a chair.

Crepitus may occur during knee motion.

Compression of the patella against the femoral trochlea may reproduce symptoms.

Patellofemoral pain is not synonymous with cartilage softening, although chondral abnormalities may coexist.

Patellar Subluxation and Dislocation

Patellar instability may be traumatic or related to underlying anatomy.

Predisposing factors can include:

Increased femoral anteversion, genu valgum, trochlear dysplasia, patella alta, abnormal rotational alignment, and increased lateralizing forces on the patella.

A positive J sign, in which the patella shifts laterally near terminal extension, may indicate abnormal tracking.

Articular Cartilage Injury

Articular cartilage injuries frequently follow trauma but may also result from chronic degenerative disease.

Pain is usually worsened by:

Weight bearing, impact activity, or repetitive loading.

Associated symptoms may include swelling, catching, or mechanical discomfort.

Meniscal Injury

Meniscal pathology may be:

Acute and traumatic or degenerative and related to chronic tissue deterioration.

Symptoms

Patients commonly report:

Joint-line pain, intermittent swelling, catching, locking, or giving way.

Effusion often develops gradually rather than immediately and may fluctuate with activity.

Location

Medial meniscal pathology causes medial joint-line pain, whereas lateral meniscal disease produces lateral joint-line symptoms.

Knee Arthritis

Arthritic symptoms typically have a gradual and progressive onset, although an acute osteochondral event may suddenly worsen a previously chronic condition.

Pain generally:

Increases with activity and improves with rest.

Patients may also develop pain:

At night after an active day or after prolonged periods of inactivity, such as a long car ride or bed rest.

Stiffness, swelling, crepitus, and loss of motion are common as arthritis progresses.

Anterior Cruciate Ligament Injury

The ACL primarily prevents anterior translation of the tibia relative to the femur and contributes importantly to rotational stability.

Mechanism

ACL injuries commonly occur through noncontact mechanisms such as:

Sudden deceleration, pivoting, cutting, or landing from a jump.

An audible or palpable pop and rapid swelling are common.

Reinjury Risk

A previous ACL tear increases the risk of:

Recurrent ACL injury in the reconstructed or previously injured knee and ACL injury in the contralateral knee.

Posterior Cruciate Ligament Injury

The PCL is the primary restraint to posterior translation of the tibia.

Mechanism

A classic mechanism is a direct blow to the anterior proximal tibia when the knee is flexed, such as a dashboard injury.

Symptoms

Pain and swelling occur acutely after injury and often improve over several weeks.

Chronic PCL deficiency may later contribute to:

Medial-compartment and patellofemoral degenerative symptoms.

Medial Collateral Ligament Injury

The MCL is the primary restraint to valgus stress.

Pain is typically located along the medial knee and may extend proximally or distally along the course of the ligament.

Mechanism

An isolated MCL injury commonly follows a direct blow to the lateral side of the knee, creating valgus stress.

MCL injury may also occur together with:

ACL tears, meniscal injury, or other multiligament trauma.

Lateral Collateral Ligament Injury

The LCL extends from the lateral femoral epicondyle to the fibular head and resists varus stress.

Isolated LCL injury is relatively uncommon.

It is often associated with:

Cruciate ligament or posterolateral corner injury.

Because of the proximity of the common peroneal nerve to the fibular head, motor and sensory function should be assessed carefully.

Quadriceps and Patellar Tendon Rupture

Disruption of either the quadriceps tendon or patellar tendon impairs the extensor mechanism.

Symptoms

Patients may have:

Anterior knee pain, effusion, inability to actively extend the knee, and inability to perform a straight-leg raise.

Examination

A palpable defect may be present.

Patellar position may also be abnormal:

Patella baja may occur with quadriceps tendon rupture, whereas patella alta may occur with patellar tendon rupture.

Mechanism

These injuries may follow:

Direct trauma or sudden forced knee flexion against a maximally contracting quadriceps muscle.

Bursitis and Tendinopathy

Inflammation or irritation may develop at bursae or tendon insertions around the knee.

The diagnosis is commonly suggested by localized tenderness directly over the involved structure.

Common Bursae

Common symptomatic locations include:

Prepatellar and pes anserine bursae.

Common Tendons

Tendinopathy frequently involves the:

Patellar tendon or distal quadriceps tendon.

Osteochondritis Dissecans

Osteochondritis dissecans commonly affects active children, adolescents, and young adults.

It involves a localized abnormality of the subchondral bone and overlying articular cartilage.

Symptoms

Patients may develop:

Activity-related pain, effusion, localized tenderness, catching, or locking.

Mechanical symptoms become more likely if an unstable fragment separates and becomes a loose body.

Osgood–Schlatter Disease

Osgood–Schlatter disease is a traction apophysitis of the tibial tubercle.

It is common in active growing children and adolescents.

Repetitive traction from the patellar tendon produces:

Pain, swelling, and tenderness over the tibial tubercle.

Symptoms are aggravated by running, jumping, kneeling, and resisted extension.

Baker Cyst

A Baker or popliteal cyst is a distension of the posterior knee capsule or bursa that often communicates with the knee joint.

It is frequently associated with intra-articular pathology, including:

Meniscal tears, arthritis, and chronic synovitis.

Presentation

Patients may complain of:

A posterior knee mass, fullness, or pressure.

The underlying intra-articular disease may itself produce few symptoms.

Fracture

A fracture around the knee must be considered after significant trauma.

Potential sites include:

Distal femur, proximal tibia, tibial plateau, and patella.

Plain radiographs are usually the initial diagnostic study.

Bone Tumor

Bone tumors are uncommon but should remain in the differential diagnosis, especially when pain is:

Persistent, progressive, present at night, unrelated to activity, or associated with constitutional symptoms.

Symptoms

Patients may describe:

Deep, dull, aching pain that gradually becomes constant.

Additional findings may include:

Swelling, reduced function, fatigue, low-grade fever, weight loss, or a pathologic fracture.

Physical Examination

Palpation

Palpate the knee for:

Effusion, localized swelling, warmth, and focal tenderness.

Joint-Line Tenderness

Medial or lateral joint-line tenderness may suggest:

Meniscal pathology or compartmental arthritis.

Other Tender Areas

Palpate the:

Pes anserine bursa, patellar tendon, quadriceps tendon, patella, collateral ligaments, and other symptomatic structures.

Range of Motion

Compare the affected knee with the contralateral side.

Assess:

Flexion, extension, presence of contracture, pain, crepitus, and extension lag.

Patellar Tracking

Observe the patella as the knee moves from flexion into extension.

Abnormal lateral translation or a J sign may indicate patellar maltracking or instability.

Ligament Stability

Assess the major ligament groups systematically.

MCL

Use valgus stress testing.

LCL

Use varus stress testing.

ACL

Use the:

Lachman test and anterior drawer test.

The Lachman test is generally the more sensitive examination maneuver.

PCL

Assess with:

Posterior drawer, posterior sag, and quadriceps active testing.

Laboratory Tests

Laboratory testing should be guided by the suspected diagnosis rather than ordered routinely for all patients with knee pain.

Suspected Septic Arthritis

Appropriate studies may include:

Complete blood count with differential, ESR, CRP, blood cultures when indicated, and urgent synovial fluid analysis.

Suspected Inflammatory Arthritis

Targeted evaluation may include:

Rheumatoid factor, anti-CCP antibodies, ANA, ESR, CRP, and other tests depending on the clinical context.

Suspected Gout

Serum uric acid may be obtained, although a normal value does not exclude an acute gout attack.

Definitive diagnosis is made by synovial crystal analysis.

Imaging

Plain Radiographs

Radiographs are usually the first imaging study when structural pathology is suspected.

Useful views include:

Weight-bearing AP or PA, lateral, and tangential patellofemoral views such as Merchant or sunrise views.

Depending on the clinical question, additional views may be obtained.

MRI

MRI is useful for evaluating:

Meniscal tears, ligament injuries, articular cartilage lesions, osteochondral abnormalities, synovial proliferative disorders, tumors, and osteonecrosis.

MRI should be obtained when the result is expected to alter diagnosis or management.

Arthrocentesis

Joint aspiration can provide critical diagnostic information in a patient with an unexplained effusion.

Septic Arthritis

Synovial findings may include:

High white blood cell count with neutrophil predominance and positive bacterial culture.

A count above approximately 50,000 cells/mm³ strongly raises suspicion, although infection may occur at lower values and inflammatory arthritis may occasionally produce similarly high counts.

Gout

Gout is characterized by:

Monosodium urate crystals that are needle-shaped and strongly negatively birefringent under polarized light.

Synovial leukocytosis is common and may occasionally be substantial.

Pseudogout

Calcium pyrophosphate deposition disease demonstrates:

Rhomboid-shaped, weakly positively birefringent crystals.

Fat Droplets

Fat droplets within aspirated joint fluid may suggest an intra-articular fracture with marrow communication.

Pathological Findings

Pathologic findings vary entirely according to the underlying disorder.

Differential Diagnosis

Common diagnostic categories include:

Patellofemoral disorders

Articular cartilage and osteochondral injuries

Meniscal disease

Osteoarthritis and inflammatory arthritis

Ligament tears

Tendinopathy and tendon rupture

Osteochondritis dissecans

Osgood–Schlatter disease

Baker cyst

Gout and pseudogout

Fracture

Tumor

The diagnosis is established by integrating the history, pain location, physical examination, laboratory studies when appropriate, and imaging.

Clinical Clues From History and Pain Location

Certain patterns are particularly useful.

Locking with medial or lateral joint-line pain suggests a meniscal tear.

A pop during a sudden pivot followed by swelling suggests ACL injury.

Anterior knee pain with stairs or rising from a chair suggests patellofemoral pathology.

A direct blow to the proximal tibia with the knee flexed suggests PCL injury.

Side impact with medial or lateral pain suggests collateral ligament injury.

Chronic activity-related pain with stiffness suggests arthritis or another degenerative process.

Treatment

Treatment depends on the underlying diagnosis.

Patellofemoral Pain

Initial treatment commonly includes:

Activity modification, NSAIDs or other simple analgesia when appropriate, and exercise-based physical therapy.

Therapy should focus on:

Quadriceps strength, hip and core strength, flexibility, and correction of movement patterns.

Patellar Instability

Many first-time or mild cases can be managed with:

Physical therapy, activity modification, and selected patellar-stabilizing braces.

Recurrent instability or major structural abnormalities may require surgical evaluation.

Arthritis

Initial nonoperative management may include:

Analgesics, NSAIDs, activity modification, weight reduction when appropriate, physical therapy, assistive devices, unloader bracing for selected unicompartmental disease, and intra-articular injections.

Bursitis and Tendinopathy

Treatment generally consists of:

Activity modification, ice, topical or oral analgesic therapy, and correction of contributing mechanical factors.

Routine aspiration of uncomplicated bursitis is usually avoided unless infection or another specific indication is suspected.

Osgood–Schlatter Disease

Treatment includes:

Relative rest, activity modification, stretching, and anti-inflammatory medication when appropriate.

Most cases resolve as skeletal maturity is reached.

Ligament and Meniscal Injuries

Initial management may include:

Protected weight bearing, controlled range of motion, ice, analgesia, and orthopaedic or sports-medicine referral when indicated.

Treatment depends on:

Patient age, instability, tear pattern, activity level, associated injuries, and chronicity.

Physical Therapy

Physical therapy is highly useful for many causes of knee pain.

Common goals include:

Restoring range of motion, strengthening the quadriceps and hamstrings, improving hip and core strength, increasing flexibility, correcting gait and movement mechanics, and restoring proprioception.

Adjunctive modalities may include:

Cryotherapy and selected electrical stimulation.

Exercise-based rehabilitation is generally the core of treatment.

Medication

Common medication options include:

NSAIDs and acetaminophen.

Long-term opioid therapy generally should be avoided for routine musculoskeletal knee pain.

Intra-Articular Therapy

For selected patients with arthritis, intra-articular treatment may include:

Corticosteroid injections and, in some settings, hyaluronic acid products.

Expected benefit varies according to the underlying diagnosis and patient factors.

Surgery

Knee surgery can broadly be grouped into three categories.

Arthritis Surgery

Potential procedures include:

Osteotomy, unicompartmental knee arthroplasty, and total knee arthroplasty.

Arthroscopic debridement has a limited role in routine degenerative osteoarthritis and is generally reserved for selected mechanical pathology rather than arthritis alone.

Sports Medicine Procedures

These include:

Arthroscopic meniscal treatment, ligament reconstruction, cartilage procedures, and patellar stabilization or realignment surgery.

Trauma Surgery

Trauma procedures include:

Internal fixation of fractures and repair of quadriceps or patellar tendon rupture.

Follow-Up

Prognosis

The prognosis is generally excellent when:

The underlying diagnosis is accurately identified and appropriate operative or nonoperative treatment is provided.

Outcome depends on the severity and chronicity of the underlying disorder.

Complications

Potential consequences of inadequately treated knee pathology include:

Loss of motion, loss of function, impaired weight bearing, persistent instability, progressive arthritis, and chronic pain.

Patient Monitoring

Patients should be reassessed according to the severity of the underlying diagnosis.

For many musculoskeletal conditions, follow-up at approximately 4–6 week intervals is appropriate until:

Range of motion, strength, stability, and function have substantially recovered.

Persistent swelling, mechanical locking, night pain, fever, progressive weakness, or failure to improve should prompt reconsideration of the diagnosis and further investigation.