Residency · Residency · Family Medicine

Knee Pain: Evaluation, Imaging, and Non-Operative Management

Overview

Knee pain is one of the most common musculoskeletal complaints in primary care, with causes ranging from degenerative osteoarthritis to acute ligamentous injuries. A systematic physical examination, judicious imaging, and evidence-based non-operative management are core competencies for the family physician.

Anatomy Review

The knee contains three compartments: medial tibiofemoral, lateral tibiofemoral, and patellofemoral. Four major ligaments provide stability: the ACL (anterior cruciate), PCL (posterior cruciate), MCL (medial collateral), and LCL (lateral collateral). The menisci include the medial meniscus (C-shaped, attached to the MCL, and less mobile) and the lateral meniscus (O-shaped and more mobile). The extensor mechanism comprises the quadriceps tendon, patella, and patellar tendon. Important bursae include the prepatellar, infrapatellar, pes anserine, and suprapatellar bursae.

History

The history should establish the mechanism of injury (twisting, hyperextension, direct blow, overuse, or atraumatic onset), pain location (anterior, medial, lateral, posterior, or diffuse), and onset pattern (acute versus gradual). Mechanical symptoms are particularly important: locking suggests a meniscal tear or loose body, giving way suggests ligamentous instability, and clicking or popping may indicate various pathologies. The timing of swelling provides diagnostic clues: immediate effusion within 2 hours suggests hemarthrosis from an ACL tear or fracture, while delayed effusion suggests meniscal tear or reactive causes. Aggravating factors help narrow the differential, as stairs suggest patellofemoral pathology, running suggests IT band or patellofemoral issues, and squatting suggests meniscal involvement. Prior knee injuries or surgeries should be documented. Red flags including significant trauma, inability to bear weight, fever, and erythema should raise concern for fracture or septic joint.

Physical Examination

Inspection

Inspection includes gait observation, assessment of alignment (varus or valgus), and evaluation for swelling, erythema, ecchymosis, and muscle atrophy, particularly VMO wasting.

Palpation

Palpation targets the joint lines (medial or lateral tenderness suggesting meniscal pathology), patellar facets, patellar tendon, tibial tubercle, collateral ligaments, bursae (prepatellar and pes anserine), and the popliteal fossa (for Baker cyst).

Range of Motion

Normal range extends from 0 degrees of extension to 135 degrees of flexion. Loss of terminal extension suggests a mechanical block from a meniscal tear or loose body.

Special Tests

Meniscal Tests

The McMurray test is performed by flexing the knee, externally rotating the tibia and extending (for the medial meniscus) or internally rotating and extending (for the lateral meniscus), with a click, pop, or pain constituting a positive result. The Thessaly test has the patient stand on the affected leg at 20 degrees of flexion and rotate, with pain at the joint line being positive. The Apley compression test is performed with the patient prone and the knee flexed to 90 degrees, compressing and rotating, with pain being positive.

Ligament Tests

The Lachman test is the most sensitive examination for ACL tear. It is performed with the knee at 20 to 30 degrees of flexion, stabilizing the femur and translating the tibia anteriorly; increased laxity with a soft endpoint is positive. The anterior drawer test assesses the ACL at 90 degrees of flexion by pulling the tibia forward. The posterior drawer test assesses the PCL at 90 degrees by pushing the tibia posteriorly. The posterior sag sign is observed from the lateral side with the knee flexed 90 degrees, where posterior sag of the tibial plateau indicates a PCL tear. Valgus stress testing (for the MCL) applies valgus force at 0 and 30 degrees, with laxity at 30 degrees indicating MCL injury. Varus stress testing (for the LCL) applies varus force at 0 and 30 degrees.

Patellofemoral Tests

The patellar grind or Clarke test compresses the patella into the trochlea while the patient contracts the quadriceps, with pain being positive. The patellar apprehension test laterally translates the patella, with patient apprehension suggesting a history of subluxation or dislocation. The J-sign observes patellar tracking during extension, where lateral deviation at terminal extension suggests patellar maltracking.

Effusion Assessment

The ballottement test detects large effusions by compressing the suprapatellar pouch and pushing the patella down; the patella bouncing indicates a positive test. The bulge or wipe test detects small effusions by sweeping fluid from medial to lateral and observing a medial bulge when tapping laterally.

Ottawa Knee Rules (Imaging Decision)

X-ray is indicated if any of the following are present: age 55 or above, isolated tenderness of the patella, tenderness at the fibular head, inability to flex to 90 degrees, or inability to bear weight for 4 steps both immediately after injury and in the office. These rules have approximately 99% sensitivity for fractures and safely reduce unnecessary X-rays by approximately 30%.

Imaging

X-Ray

Standard views include AP standing, lateral, Merchant or sunrise (for the patellofemoral joint), and tunnel view (if a loose body is suspected). Weight-bearing views are essential for osteoarthritis assessment because non-weight-bearing films underestimate joint space narrowing. Osteoarthritis findings include joint space narrowing, osteophytes, subchondral sclerosis, and subchondral cysts.

MRI

MRI is indicated when mechanical symptoms are present (locking or giving way), when there is clinical suspicion for meniscal or ligamentous injury that would change management, or when symptoms persist despite conservative treatment. It is the gold standard for soft tissue evaluation of menisci, ligaments, cartilage, and bone marrow edema. MRI is not indicated for straightforward osteoarthritis, acute minor injuries without red flags, or as a first-line test.

Common Conditions and Management

Osteoarthritis

Osteoarthritis is the most common cause of knee pain in adults over 50. Risk factors include age, obesity, prior injury, female sex, and occupational stress. It is a clinical diagnosis characterized by insidious onset of pain worsened by activity and improved with rest, morning stiffness lasting less than 30 minutes, and crepitus. Non-pharmacologic management is the cornerstone: exercise (strengthening of the quadriceps and hamstrings, aerobic, and flexibility exercises) is the most evidence-based intervention. Weight loss of 5 to 10% of body weight significantly reduces pain. Physical therapy with supervised exercise and manual therapy, unloader bracing for unicompartmental disease, and use of a cane in the contralateral hand all provide benefit. Pharmacologically, topical diclofenac gel is first-line with fewer systemic side effects. Oral NSAIDs are effective but carry gastrointestinal, renal, and cardiovascular risks. Acetaminophen provides minimal benefit for knee OA per meta-analyses. Duloxetine is FDA-approved for chronic musculoskeletal pain and is helpful when central sensitization is present. Topical capsaicin serves as an adjunctive therapy. Corticosteroid injection (triamcinolone 40 mg with lidocaine) provides short-term relief lasting weeks to months but should be limited to 3 to 4 per year per joint, as long-term repeated injections may accelerate cartilage loss. Hyaluronic acid viscosupplementation has debated efficacy, with AAOS not recommending it though some guidelines offer conditional support. PRP has emerging evidence but is not consistently recommended and is often not covered by insurance. Total knee arthroplasty should be considered through shared decision-making when conservative measures fail and functional impairment is significant, with surgery delayed if possible in younger patients.

Meniscal Tears

Acute traumatic tears are common in young athletes with twisting injuries, while degenerative tears are common in those over 40 and are often incidental findings on MRI. Symptoms include joint line pain, swelling, and mechanical locking or catching. Management is conservative first, with physical therapy, NSAIDs, and activity modification. Surgical repair is indicated for traumatic tears in young patients with locking or failed conservative treatment. Arthroscopic partial meniscectomy for degenerative tears shows no benefit over physical therapy, as demonstrated by the ESCAPE and FIDELITY trials.

ACL Tears

ACL tears typically occur through non-contact pivoting or sudden deceleration mechanisms. Acute hemarthrosis (effusion within 2 hours) is present in 70% of cases. The Lachman test is the most sensitive physical examination finding. Initial management includes RICE and physical therapy for stability training. Surgical reconstruction is recommended for young active patients, those with combined ligament injuries, and those with functional instability despite rehabilitation. Non-operative management focused on rehabilitation is reasonable for lower-demand patients and older adults.

MCL Sprains

MCL injury is the most common knee ligament injury, caused by valgus stress (a blow to the lateral knee). It is graded as I (pain without laxity), II (partial tear with increased laxity but a present endpoint), or III (complete tear with no endpoint). Treatment is almost always non-operative. Grade I and II sprains are managed with a hinged knee brace, weight-bearing as tolerated, and physical therapy. Grade III sprains require a hinged brace initially locked in extension with progressive range of motion; surgery is rarely necessary unless combined injuries are present.

Patellofemoral Pain Syndrome

Patellofemoral pain syndrome is the most common cause of anterior knee pain, especially in young active women. Often called "runner's knee," it presents with pain on stairs, prolonged sitting (the theater sign), and squatting. There is no single diagnostic test, and it is a diagnosis of exclusion. Treatment focuses on physical therapy emphasizing quadriceps strengthening (especially the VMO), hip abductor and external rotator strengthening, patellar taping, activity modification, and orthotics if overpronation is present.

Patellar Tendinopathy (Jumper's Knee)

Patellar tendinopathy is an overuse injury common in jumping sports such as basketball and volleyball. It presents with pain at the inferior patellar pole worsened by jumping, squatting, and stairs. The eccentric decline squat program is the gold standard treatment, complemented by activity modification and physical therapy. PRP may be considered for refractory cases.

IT Band Syndrome

IT band syndrome causes lateral knee pain in runners and cyclists, with pain localized to the lateral femoral epicondyle and a positive Noble compression test. Treatment includes IT band stretching and rolling, hip strengthening (particularly the abductors), activity modification, and gradual return to training.

Pes Anserine Bursitis

Pes anserine bursitis presents with medial knee pain 2 to 3 cm below the joint line at the tibial attachment of the sartorius, gracilis, and semitendinosus tendons. It is common in obese women with osteoarthritis. Treatment includes ice, NSAIDs, and physical therapy, with corticosteroid injection for refractory cases.

Baker Cyst (Popliteal Cyst)

A Baker cyst presents with posterior knee swelling and fullness and is usually secondary to intra-articular pathology such as osteoarthritis or meniscal tear. Treatment addresses the underlying cause, with aspiration providing temporary relief and surgical excision rarely needed. Cyst rupture can mimic DVT, producing pseudothrombophlebitis.

<image>A systematic physical examination guide for the knee showing key inspection points, palpation landmarks (joint lines, patellar facets, bursae), and the proper technique for special tests (Lachman, McMurray, valgus/varus stress, patellar apprehension) with illustrations of positive findings and their clinical significance.</image>

<image>The Ottawa Knee Rules displayed as a decision algorithm with the five criteria (age >= 55, patellar tenderness, fibular head tenderness, inability to flex 90 degrees, inability to bear weight for 4 steps), showing the pathway to imaging versus clinical observation, with sensitivity and specificity data.</image>

<image>A differential diagnosis map of knee pain organized by anatomical location (anterior, medial, lateral, posterior) showing the most common conditions in each region: anterior (patellofemoral pain, patellar tendinopathy, prepatellar bursitis), medial (medial meniscal tear, MCL sprain, pes anserine bursitis, medial OA), lateral (lateral meniscal tear, IT band syndrome, LCL sprain), and posterior (Baker cyst, PCL injury, hamstring tendinopathy).</image>

Clinical Pearls

The Lachman test is the most sensitive physical examination maneuver for ACL tear and should always be performed with the knee at 20 to 30 degrees of flexion, not at 90 degrees. The Ottawa Knee Rules have approximately 99% sensitivity for fracture and should be applied to all acute knee injuries to determine whether X-ray is needed, safely reducing unnecessary imaging. Weight-bearing X-rays should always be obtained when evaluating for knee osteoarthritis because non-weight-bearing films underestimate the degree of joint space narrowing. Arthroscopic surgery for degenerative meniscal tears provides no benefit over physical therapy in multiple randomized controlled trials, and patients with a clinical picture consistent with degenerative disease should not be referred for arthroscopy. Exercise and weight loss are the most effective interventions for knee OA and should be prescribed before considering injections or surgery. Immediate knee effusion within 2 hours of injury suggests hemarthrosis and is ACL tear until proven otherwise, while delayed effusion at 6 to 24 hours is more suggestive of meniscal injury. Repeated corticosteroid injections may accelerate cartilage loss and should be limited to 3 to 4 per year, used as a bridge to definitive management. Patellofemoral pain syndrome is best treated with proximal hip strengthening of the gluteus medius and external rotators in addition to quadriceps rehabilitation, not quadriceps exercises alone.

References

• Jevsevar DS et al. AAOS Clinical Practice Guideline: Treatment of OA of the Knee. J Am Acad Orthop Surg. 2013
• Sihvonen R et al. Arthroscopic Partial Meniscectomy vs. Sham Surgery (FIDELITY). N Engl J Med. 2013
• Stiell IG et al. Validation of the Ottawa Knee Rules. Ann Emerg Med. 1996
• Kolasinski SL et al. ACR/AF 2019 Guideline for Management of OA of the Hand, Hip, and Knee. Arthritis Care Res. 2020
• Bunt CW et al. Knee Pain in Adults and Adolescents: Evaluation and Diagnosis. Am Fam Physician. 2018

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