What type of knee injury typically presents with hemarthrosis in a patient, possibly an athlete, who has experienced a traumatic injury?

Knee Hemarthrosis: Typical Injury Patterns

Anterior cruciate ligament (ACL) tear is the most common knee injury presenting with traumatic hemarthrosis, accounting for approximately 65-72% of cases, with the highest incidence in younger patients and athletes.

Primary Injury Causing Hemarthrosis

• ACL disruption is the predominant cause of acute traumatic knee hemarthrosis, identified in 72% of cases with some degree of ligament disruption (28% partial tears, 44% complete tears) 1
• ACL injuries represent 64.8% of all intra-articular pathology causing hemarthrosis, particularly when diagnosed within the first week following trauma 2
• The presence of hemarthrosis itself indicates significant intra-articular injury requiring thorough evaluation 1

Associated Injuries Commonly Present

Isolated ACL tears are uncommon—most hemarthrosis cases involve multiple structures:

• Meniscal tears occur in 62% of hemarthrosis cases (30% partial, 70% complete tears), frequently accompanying ACL injuries 1
• Chondral injuries affect 20% of patients, typically presenting as femoral chondral fractures or surface defects 1
• Collateral ligament sprains without laxity occur in 41% of cases, while major associated ligament injuries occur in 21% 1
• Isolated meniscus pathology accounts for only 12.48% of hemarthrosis cases 2

Age-Related Patterns

• Patients under 30 years predominantly have ACL damage as the cause of hemarthrosis 3
• Patients over 30 years more commonly present with crack fractures (29% overall incidence) rather than isolated ligamentous injuries 3
• Younger athletes with sports-related hemarthrosis warrant specialist referral due to high ACL injury rates 3

Clinical Examination Limitations

Physical examination alone is unreliable for diagnosing ACL tears in acute hemarthrosis:

• The anterior drawer test without anesthesia is positive in only 24% of knees with confirmed ACL tears 1
• One-third of patients with significant injuries report minimal to no pain at the time of injury 1
• A "popping sensation" occurs in only 33-36% of cases and is not discriminatory between intact and torn ACL 1
• Examination under anesthesia plus arthroscopy or MRI is required for accurate diagnosis 1, 2

Diagnostic Approach

• MRI is the gold standard imaging modality for evaluating suspected internal derangement after traumatic hemarthrosis with negative radiographs 4
• MRI demonstrates high sensitivity (96%) and specificity (97%) for detecting meniscal tears and ACL injuries 4
• Knee effusion >10 mm on lateral radiograph in patients <40 years with acute injury should prompt MRI consideration 4
• Arthroscopy combined with examination under anesthesia allows definitive diagnosis when MRI is unavailable or inconclusive 1, 2

Other Causes of Hemarthrosis

• Patellar dislocation accounts for traumatic hemarthrosis in select cases, with 45% having associated chondral or osteochondral fractures requiring surgery 2
• Tibial plateau fractures can present with hemarthrosis and lipohemarthrosis on imaging 4
• Intercondylar eminence fractures are less common causes, particularly in younger patients 2
• Only 7.84% of hemarthrosis cases involve minor lesions not requiring surgical intervention 2

Clinical Significance

• 89.4% of intra-articular lesions causing hemarthrosis require surgical intervention 2
• Conservative treatment with aspiration and casting alone results in poor outcomes: 37% require subsequent surgery, 43% have significant disability, and only 20% return to sports without symptoms 5
• 70% of patients initially treated conservatively have undiagnosed ACL injury at follow-up 5
• The presence of blood products in the joint accelerates degenerative changes and early-onset osteoarthritis through heme-mediated cartilage damage 6