SDL 2 Knee Pain and ACL Injury

• These notes cover knee pain, injury, and related conditions, focusing on diagnosis, clinical presentation, and treatment.

Knee Pain Workflow

• Use history, physical exam, and diagnostic studies to determine the cause of knee pain.
• Assess if the pain is trauma-related.
• Rule out dangerous medical conditions.
• Determine if osteoarthritis or other arthritis types are the cause.
• Check for nerve pathology, like radiculopathy.
• Identify if the pain is localized and which structure is the pain generator.

Anterior Cruciate Ligament (ACL) Injury

• ACL injuries are typically acute, occurring during sports or trauma.
• They most commonly happen in non-contact movements involving abrupt direction changes.
• The ACL connects the femur to the tibia inside the knee joint.
• It is composed of two bundles, anteromedial which is tight in flexion and posterolateral which is tight in extension.
• The ACL is the most commonly injured ligament in the knee.
• Classic presentation involves a "pop" sound, followed by pain, swelling, and instability.
• Approximately 100,000–200,000 cases occur annually in the U.S., with an incidence of about 1 in 3,500 in the general population.
• Female athletes are at higher risk due to anatomic, hormonal, and neuromuscular factors.
• High-risk sports include soccer, basketball, wrestling, and gymnastics.
• The ACL prevents anterior translation of the tibia relative to the femur and controls rotational stability.
• Injuries often result from sudden deceleration, cutting/pivoting, or rotation with valgus force.
• Examination reveals a "Pop" sound at injury, immediate pain, rapid swelling, and instability and difficulty with weight bearing.
• A physical exam may show a positive anterior drawer test, Lachman test (most sensitive), and pivot shift test.
• X-rays are used to rule out fractures and detect Segond fractures.
• MRI is the best modality to confirm ACL tears and assess other knee structures.
• ACL injuries are often associated with meniscus tears (lateral more common), MCL injuries, and articular cartilage damage.
• "Unhappy triad" refers to ACL, MCL, and medial meniscus injury, although lateral meniscus involvement is more common.
• Initial treatment involves protecting the joint with rest, ice, compression, and elevation.
• Prehabilitation includes physical therapy to reduce inflammation and restore ROM.
• Surgical reconstruction is often recommended for young, active patients.
• Older, less active patients might benefit from non-operative management.
• Post-operative physical therapy restores strength and knee stability.

Posterior Cruciate Ligament (PCL) Injury

• PCL injury involves the strongest ligament in the knee, which prevents posterior tibial translation relative to the femur.
• PCL injuries are less common than ACL injuries occurring during contact sports or motor vehicle accidents.
• Injury usually stems from falling onto a flexed knee, forced hyperflexion knee during trauma or sports.
• Examination reveals posterolateral knee pain, mild swelling, and worsening pain with knee flexion, sensation of looseness.
• Exam includes the posterior drawer test (most sensitive), posterior sag sign, and quadriceps active test.
• Grading of the posterior drawer test: Grade 1 (0–5 mm translation), Grade 2 (5–10 mm translation), Grade 3 (greater than 10 mm).
• X-rays rule out fractures, while MRI confirms PCL tears and evaluates for associated injuries.
• Non-operative management is standard for isolated PCL injuries, using RICE and physical therapy focusing on quadriceps strengthening.
• Surgical intervention is considered in cases of bony avulsion, multiligamentous injuries, or chronic instability in athletes.

Medial Collateral Ligament (MCL) Injury

• MCL injury is the most common ligament injury in the knee, especially during contact sports.
• It accounts for approximately 7.9% of all knee injuries and 40% of all knee ligament injuries.
• Common in football, rugby, wrestling, and hockey.
• Caused by a lateral force applied to the knee, leading to valgus stress (medial collapse of the knee).
• Can be caused Atraumatic due to abduction or external rotation of the leg which occurs in sudden directional changes or twisting motions.
• The MCL provides resistance against valgus stress and stabilizes the medial knee.
• Examination reveals pain and swelling localized over the medial knee, and pain at end range of motion may be present.
• The valgus stress test is key, performed at 30 degrees flexion (superficial MCL) and 0 degrees (deep MCL and joint capsule).
• Grading of MCL Tears: Grade 1: 10 mm laxity, no endpoint, indicates a complete tear. Grade 2: 5–10 mm laxity, indistinct endpoint, partial tear. Grade 3: Laxity of 10 mm, no endpoint, complete tear
• X-rays are used to rule out fractures and the arcuate sign.
• MRI is best for evaluating tear severity and associated ligament injuries.
• Most cases are managed conservatively, with knee bracing and physical therapy.
• Surgical referral is needed for unstable injuries, mid-substance LCL tears, complete Grade 3 tears, or multiligamentous injuries.

Meniscal Injury

• Menisci are C-shaped fibrocartilage pads in the knee joint.
• The medial meniscus is more commonly injured than the lateral meniscus.
• Menisci function in shock absorption, joint stabilization, and lubrication.
• Affects 61 per 100,000 in the general population
• More common in men
• Increased risk after age 40 due to degeneration
• Degenerative tears are seen in older adults, related to osteoarthritis, and can occur without trauma.
• Traumatic tears are common in younger, active individuals from twisting injuries and are often associated with ACL injuries.
• Examination reveals localized joint line pain, swelling hours after injury, locking/clicking/catching, instability, and limited motion.
• Diagnostic exam test include joint line tenderness, McMurray test, Apley compression test, Steinman test, and Thessaly test.
• X-rays cannot visualize menisci but may show degenerative changes.
• MRI is the best test to diagnose tears, their patterns/location, and associated injuries.
• Initial management includes PRICE along with avoiding squats and twisting.
• Physical therapy strengthens supporting muscles.
• Surgical referral is indicated for mechanical symptoms, failure of conservative treatment, multiligamentous injuries, and large or repairable tears in young patients.

Unhappy Triad (Terrible Triad of the Knee)

• The unhappy triad is a combination of ACL, MCL, and medial meniscus injuries.
• It is caused by a valgus force with rotation, often in contact sports.
• Clinical presentation: Acute pain, swelling, instability, and a "pop" sound.
• Positive Lachman test, valgus stress test, and joint line tenderness.
• Initial treatment includes immobilization and PRICE.
• Surgical repair is common in young, active patients.

Patellofemoral Syndrome (PFS)

• PFS is pain around or behind the patella due to abnormal tracking or overuse.
• Also known as chondromalacia patella or runner’s knee.
• Common in runners, cyclists, and young active females.
• Results from overuse, trauma, or biomechanical issues like weak quadriceps or tight hamstrings.
• Presents as anterior knee pain, worsened by stairs, squatting, or prolonged sitting.
• May have crepitus and pain with patellar compression.
• X-rays are usually normal, while MRI is used for persistent symptoms.
• Conservative management leads with physical therapy, and injections are considered in chronic cases.

Prepattellar Bursitis

• Prepattellar bursitis is inflammation of the bursa in front of the patella.
• The bursa reduces friction between the skin and patella.
• Common in individuals with frequent kneeling.
• Presents as swelling over the kneecap and pain with kneeling or bending.
• Infectious bursitis presents with fever, chills, erythema, and warmth over the bursa.
• Diagnosis is usually clinical, but ultrasound can confirm fluid presence.
• Lab tests on aspirated fluid rule out infection or gout.
• Initial treatment includes PRICE and avoiding kneeling.
• Aspiration is indicated for suspected infection or gout.
• Medications include antibiotics for infection and NSAIDs for gout.

Patellar Subluxation

• Patellar subluxation is when the patella partially slips out of the trochlear groove.
• it does not fully dislocate, but becomes misaligned and unstable
• Accounts for 2–3% of all knee injuries
• Most common in adolescents, adolescent females and athletes are at higher risk
• Caused by weak quadriceps, ligamentous laxity, or trauma.
• Presents as anterior knee pain, buckling sensation, catching/locking, and swelling.
• Worsened by stairs, squatting, jumping, and prolonged sitting.
• X-rays evaluate patellar alignment, and MRI assesses soft tissue damage.
• Initial management involves PRICE, bracing, and physical therapy.
• Surgical intervention is considered for recurrent subluxation, MPFL tears, cartilage damage, or structural abnormalities.

Popliteal Cyst (“Baker’s Cyst”)

• A popliteal cyst is a fluid-filled swelling behind the knee due to synovial fluid buildup in the gastrocnemius-semimembranosus bursa.
• More noticeable when standing with knee extended, may disappear when the knee is flexed
• Common in children (4–7 years) as isolated bursitis and adults (35–70 years) secondary to joint disorders.
• Presents as popliteal swelling, tightness, and difficulty with knee flexion
• If ruptured, it causes pain and swelling in the calf, mimicking DVT.
• Ultrasound confirms the cyst, and MRI identifies underlying pathology in adults.
• In children, watchful waiting is appropriate.
• In adults, management addresses the underlying joint disorder, with physical therapy, NSAIDs, and aspiration.

Osteoarthritis (OA)

• Osteoarthritis is a degenerative joint disease characterized by loss of articular cartilage, joint space narrowing, and subchondral bone changes.
• It is the most common form of arthritis, with variable clinical presentation.
• History, Physical exam, and Imaging can assess for OA on the knee.
• Diagnosis includes assessing location, severity, and triggers of the pain, determine difficulty walking, squatting and stairs.
• Common findings on the physical examine include decreased range of motion due to joint degeneration, Bony enlargement ,Tenderness, and Crepitus.
• X-rays identify joint space narrowing, osteophytes, and subchondral sclerosis.
• Diagnosis requires persistent, use-related knee pain, age ≥ 45 years, and morning stiffness ≤ 30 minutes.
• Progression is monitored using pain scores, functional assessments, and radiographic grading.

OA Treatment

• Core treatment includes arthritis education and structured land-based exercise programs.
• First line pharmacologic includes topical NSAIDs
• Non-pharmacologic consists of Aquatic Exercise, Gait Aids, Self-Management Programs
• Pharmacologic management includes NSAIDs, COX-2 inhibitors, IACS, and IAHA
• Oarsi clinical guidelines recommend intra-articular treatment and NSAID risk mitigation.