In an adult presenting with acute pain, swelling, and loss of function after a sudden stretch or impact, how can I differentiate a tendon injury from a ligament injury and what is the initial management?

Differentiating Tendon from Ligament Injuries

In acute soft-tissue injuries, distinguish tendon from ligament injuries by anatomical location and mechanism: tendons connect muscle to bone and fail with eccentric loading or forced stretch during active contraction, while ligaments connect bone to bone and fail with joint distraction or abnormal rotational forces.

Clinical Differentiation

Anatomical and Functional Distinctions

• Tendons transmit forces from muscle contraction to bone, enabling joint movement, while ligaments stabilize joints by connecting bone to bone 1, 2
• Tendon injuries typically occur at the musculotendinous junction or insertion site during active muscle contraction under load (e.g., Achilles rupture during push-off, flexor digitorum profundus avulsion during gripping) 3
• Ligament injuries occur at joint lines during passive joint stress, typically from sudden deceleration, cutting movements, or direct impact causing abnormal joint translation or rotation 3

Key Clinical Features

Tendon Injuries:

• Pain with active movement against resistance in the direction of the affected muscle
• Palpable defect or gap along the tendon course in complete ruptures
• Loss of active range of motion with preserved passive motion
• Examples: inability to plantarflex ankle (Achilles), inability to flex distal phalanx (jersey finger) 3

Ligament Injuries:

• Pain with passive joint stress or instability maneuvers
• Joint line tenderness and effusion
• Abnormal joint laxity or instability on stress testing
• Preserved active motion (unless severe pain or associated injuries) 3

Initial Management Algorithm

Immediate Assessment (First 24-48 Hours)

1. Obtain plain radiographs first to exclude fracture or avulsion injury before advanced imaging 3
2. Apply RICE protocol: Rest, Ice (20-30 minutes, 3-4 times daily), Compression, Elevation above heart level 4
3. Immobilize in functional position: Semi-rigid or lace-up brace for ligament injuries; splint in neutral for tendon injuries 4

Imaging Strategy

When radiographs are negative but clinical suspicion persists:

• MRI without contrast is the reference standard for both tendon and ligament injuries, with superior sensitivity for detecting soft-tissue pathology 3, 4
• For tendon injuries: MRI demonstrates 92-100% sensitivity for flexor tendon tears, shows level of retraction, and identifies associated pulley injuries 3
• For ligament injuries: MRI shows 96-98% sensitivity and specificity for deltoid ligament tears, 97% accuracy for anterior talofibular ligament injuries 3, 5
• Ultrasound is an acceptable alternative for focused evaluation when expertise available: 96% sensitivity for plantar plate tears, allows dynamic assessment of tendon subluxation 3

Conservative Management (Weeks 0-8)

For partial tears and low-grade injuries:

• Supervised physical therapy is mandatory - reduces recurrence by 62% and shortens recovery by 4 days compared to immobilization alone 4
• Include proprioceptive training (balance board), graded eccentric loading, and coordination exercises 4
• Functional bracing during weight-bearing activities while allowing controlled motion 4
• Re-evaluate at 6-8 weeks to assess response 4

Red Flags Requiring Urgent Surgical Consultation

• Complete tendon rupture with significant retraction (>2cm gap)
• Stener lesion (displaced ulnar collateral ligament of thumb) - requires surgical repair as interposed adductor aponeurosis prevents healing 3
• Complete deltoid ligament rupture with instability - augmented repair prevents chronic instability 5
• Inability to bear weight after 48 hours despite appropriate immobilization
• Mechanical symptoms (locking, catching, giving way) suggesting osteochondral injury 4

Common Pitfalls to Avoid

• Do not rely on radiographs alone - 15% of significant ligamentous injuries show no fracture on plain films 3
• Do not immobilize indefinitely - prolonged immobilization increases stiffness and delays return to function; supervised PT is superior 4
• Do not assume all tendon pathology is symptomatic - up to 34% of asymptomatic patients have peroneus brevis tears on MRI 3
• Do not order repeat MRI prematurely - only indicated if new trauma, marked worsening despite therapy, or no improvement after 6-8 weeks of supervised PT 4

Prognosis

• Ligament injuries (MCL, lateral ankle ligaments) can heal spontaneously but remodeling takes years and biomechanical properties remain inferior to normal tissue 2
• Tendon injuries vary widely: tendinopathies may take 12 months for pain resolution, while complete ruptures require surgical repair 2
• With appropriate supervised PT and functional bracing, mild injuries return to normal activity within 6-8 weeks 4