Traumatic Knee Arthrotomy - A Comprehensive Review

1. Definition

Campbell's Operative Orthopaedics 15th Ed, p. 2772

2. Anatomy Relevant to the Injury

• Medial and lateral collateral ligaments
• Quadriceps/patellar tendon anteriorly
• Posterior capsule with oblique popliteal ligament
• Synovial membrane lining the inner capsule (produces synovial fluid)

3. Etiology and Mechanisms

Important: Occupational knee injuries often occur with the knee flexed. The position of the knee at the time of injury alters the trajectory - a wound that appears remote from the joint in extension may have communicated with it when flexed. Always reconstruct the injury position. Tintinalli's Emergency Medicine, p. 1899

4. Pathophysiology

External wound breaches skin + capsule
            ↓
Environmental bacteria enter sterile joint space
            ↓
Synovial fluid provides excellent bacterial growth medium
            ↓
Inflammatory response → synovitis → effusion
            ↓
Untreated: Septic arthritis → cartilage destruction → joint failure

5. Classification (Patzakis et al.)

1. Open joint injury with associated fracture - most complex, highest infection risk
2. Open joint injury without fracture - isolated capsular breach
3. Gunshot wounds - unique contamination profile, may have bullet fragments, lead toxicity risk

6. Signs and Symptoms

History

• Penetrating trauma or high-energy injury near the knee
• Wound over the anterior, medial, or lateral aspect of the knee
• Patients often present with a laceration and may not realize the joint is involved

Symptoms

• Knee pain - often disproportionate to wound size
• Swelling - rapid hemarthrosis/effusion if joint violated
• Restricted range of motion due to pain and effusion
• Wound discharge - straw-colored, oily fluid (synovial fluid) exuding from wound is pathognomonic
• Bubbles/crepitus at the wound base

Physical Examination Signs

The absence of synovial fluid or bubbles does NOT rule out arthrotomy - the wound must be formally tested.

7. Investigations and Evaluation

Step 1 - Initial Assessment

• Distal pulses (popliteal, dorsalis pedis, posterior tibial)
• Capillary refill
• Motor and sensory function (common peroneal nerve is at risk)
• Ankle-brachial index if vascular injury suspected

Step 2 - Wound Exploration

• Anesthetize the wound locally for comfort
• Irrigate with sterile saline
• Visualize the base of the wound thoroughly
• Use a hemostat or probe to detect tunneling
• Look for: synovial fluid, bubbles, visible bone/tendon/cartilage

Step 3 - Radiographic Investigations

• AP and lateral views of the knee
• Look for: intra-articular air (pneumarthrosis - highly specific), fractures, bullet fragments, osteochondral fragments, foreign bodies
• Radiopaque foreign bodies (metal, glass) are visible
• Pneumarthrosis on plain film is diagnostic of joint violation

AP view of right knee after high-velocity rifle wound. Note "lead snowstorm" bullet fragment pattern and severe comminution. (Campbell's Operative Orthopaedics 15th Ed, Fig 50.161)

• Now the preferred imaging modality for traumatic arthrotomy
• Look for pneumarthrosis (intra-articular gas/air on CT)
• A 2013 study by Konda et al. found CT to be 100% sensitive and specific for diagnosing traumatic knee arthrotomy (using arthroscopy or septic arthritis as gold standard)
• Also helps assess fracture complexity and surgical planning
• CT scan can identify periarticular wounds that do NOT require surgical intervention - avoiding unnecessary OR trips
• Sensitivity reported at 60-100% across studies; CT is superior to clinical exam alone

AP (A) and lateral (B) X-rays showing intra-articular bullet fragments in a 30-year-old man 14 years post-GSW, presenting with microcytic anemia and elevated blood lead. (Campbell's Operative Orthopaedics 15th Ed, Fig 50.162)

• Not routinely used for acute assessment
• Useful for associated ligament/meniscus/osteochondral injuries in subacute/chronic settings

Step 4 - The Saline Load Test (SLT)

1. Prepare a distant injection site (away from the wound) using sterile technique
2. Inject sterile normal saline into the joint space using a needle inserted through clean skin
3. Observe the wound for extravasation of saline (positive = joint violated)
4. Methylene blue dye may be added (some evidence of modest sensitivity improvement)

The traditional 60 mL volume is insufficient - higher volumes (155-194 mL) are needed for adequate sensitivity. Failure to use adequate volume leads to false negatives. Tintinalli's Emergency Medicine, p. 1899; Core EM

• Volume-dependent sensitivity
• Does not identify the extent or complexity of the injury
• Negative SLT does not definitively rule out arthrotomy
• CT scan is now preferred over SLT at many centers

Step 5 - Laboratory Tests

• CBC, ESR, CRP (baseline; elevated in established infection)
• Blood cultures if septic arthritis suspected
• Synovial fluid analysis if joint is aspirated (WBC >2500/mm³ with >60% PMNs suggests infection)
• If GSW: blood lead level if intra-articular fragments present
• Tetanus immune status

8. Treatment

FIGURE: Treatment algorithm for traumatic arthrotomy (Brubacher JW, Grote CW, Tilley MB. J Am Acad Orthop Surg. 2020;28:102 - reproduced in Campbell's Operative Orthopaedics 15th Ed, Fig 50.160)

Initial/Emergency Management (All patients)

1. Antibiotics - Start empirical IV antibiotics immediately
   • First-generation cephalosporin (e.g., cefazolin) covers Staph and Strep - adequate for most wounds
   • Broader coverage needed for: human/animal bites (add amoxicillin-clavulanate or piperacillin-tazobactam), underwater injuries, fecal contamination
2. Tetanus prophylaxis - Update as indicated by immunization status
3. Wound coverage - Moist sterile dressing; do not close before formal OR washout
4. Splint/immobilize the joint
5. Orthopaedic surgery consultation - Emergent for confirmed arthrotomy

Decision Pathway

• Emergent surgical exploration in OR
• Consider CT for surgical planning and fracture assessment

• Obtain CT scan
• If CT shows positive intra-articular air → surgical exploration
• If CT is negative (no intra-articular air) + no contamination/nerve/vessel injury → oral antibiotics + local wound care + close follow-up

Definitive Surgical Treatment

• Formal arthrotomy incision (existing wound may be incorporated if alignment allows)
• Thorough joint irrigation with copious sterile saline (minimum 9-10 L recommended)
• Debridement of devitalized tissue, foreign material, bone fragments
• Repair of injured structures (ligaments, tendons) as anatomically feasible
• Primary closure of joint capsule and wound in most cases
• Suction drainage may be placed for severely contaminated wounds

• Preferred when open fracture reduction is NOT required
• Advantages: shorter hospital stay, less postoperative pain, better cosmetic result, can identify intra-articular injuries (meniscus, ligament, cartilage)
• Same debridement and irrigation principles apply

• NOT routinely recommended after arthrotomy
• Reserved only for severe contamination or when soft-tissue closure is desired
• These drainage tubes themselves may become a source of contamination (Patzakis et al.)

Fracture Management (if present)

• Casting or bracing (stable, non-displaced)
• Open reduction and internal fixation (displaced intra-articular fractures)
• External fixation (highly comminuted, soft tissue compromise)
• Arthroscopic fixation for osteochondral fragments

Soft-Tissue Coverage

• Skin grafts or flaps (rotational, free) for large defects
• Wound VAC (negative pressure wound therapy) for contaminated wounds requiring staged closure

Gunshot Wound Specifics

• Bullet fragments in the joint must be removed (cartilage damage, risk of lead toxicity)
• Arthroscopic removal preferred for small fragments
• Monitor blood lead levels for intra-articular fragments
• Lead poisoning signs: microcytic anemia, nausea, abdominal pain, weakness; treat with chelation + fragment removal

Postoperative Care

• Brace locked in extension initially
• Range-of-motion exercises started early
• Continuous passive motion (CPM) machine may be used
• Close monitoring for signs of infection (fever, wound breakdown, joint effusion)
• Repeat debridement if signs of infection develop
• Rehabilitation: progressive weight bearing and physiotherapy

9. Antibiotic Protocol Summary

10. Complications

11. Prognosis

12. Key Take-Home Points

• Traumatic knee arthrotomy = any wound that breaches the joint capsule - requires emergent orthopedic consultation
• The knee is the most commonly involved joint (53-91% of open joint wounds)
• A seemingly small wound can communicate with the joint - never dismiss periarticular lacerations
• Visible synovial fluid is pathognomonic; its absence does not rule out arthrotomy
• CT scan is the current investigation of choice (100% sensitivity/specificity in key studies)
• Saline load test requires 194 mL for adequate (95%) sensitivity - traditional 60 mL is insufficient
• Definitive treatment is OR washout + debridement with IV antibiotics
• Arthroscopic washout is preferred when no fracture requires open reduction
• Intra-articular bullets must be removed to prevent cartilage damage and lead toxicity

• Campbell's Operative Orthopaedics 15th Ed 2026, Chapter 50, pp. 2772-2774
• Tintinalli's Emergency Medicine - A Comprehensive Study Guide, Chapter 274, pp. 1899-1900
• Brubacher JW, Grote CW, Tilley MB. Traumatic arthrotomy. J Am Acad Orthop Surg. 2020;28:102
• Konda SR et al. CT scan to detect traumatic arthrotomies. J Orthop Trauma. 2013;27:498-504 (PMID: 23287770)
• Nord RM et al. Detection of traumatic arthrotomy of the knee using the saline solution load test. JBJS. 2009;91(1):65-70