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Approach to the Critical Patient
Immediate priorities
Threats and triggers
If hemodynamic instability, trauma resuscitation pathway
If open injury, open injury pathway
If knee dislocation concern, vascular injury pathway
If severe uncontrolled pain, escalation analgesia and sedation readiness
Limb threat screen
Distal pulses
Capillary refill
Foot temperature and color
If absent pulses or cool pale foot, immediate reduction if dislocated and vascular consult
Extensor mechanism failure screen
If inability to straight leg raise, complete extensor mechanism disruption until proven otherwise
If palpable gap at patellar tendon, high likelihood complete rupture
If high riding patella on exam or imaging, patellar tendon rupture pattern
Immediate immobilization decisions
Knee immobilizer in full extension
Non weight bearing until definitive plan
If skin tenting or threatened soft tissue, urgent orthopedics
Monitoring and analgesia readiness
Monitoring needs
Continuous pulse oximetry when parenteral opioids or sedation
Cardiac monitoring when significant comorbidity or deep sedation
Capnography when procedural sedation planned
Consultation triggers
Immediate orthopedics for complete rupture suspicion
Immediate vascular surgery for hard signs of vascular injury
Immediate transfer if no timely operative capability and complete rupture
PITFALLS
High risk misses
Mislabel as knee sprain when straight leg raise not tested
Miss associated knee dislocation and popliteal artery injury
Miss open rupture with small anterior wound
Miss quadriceps tendon rupture mimic
Imaging traps
Normal radiographs do not exclude rupture
Patella alta absent in partial tears
History
Mechanism and timeline
Injury context
Sudden deceleration with planted foot
Landing from jump
Forced knee flexion against quadriceps contraction
Direct blow to anterior knee
Time course
Time since injury
Immediate pop sensation
Immediate swelling or hemarthrosis
Immediate inability to extend knee
Functional baseline
Baseline mobility and assistive device use
Baseline knee pain or tendon symptoms
Risk factors and contributors
Tendon vulnerability
Prior tendinopathy
Prior knee surgery
Previous tendon rupture
Recent fluoroquinolone exposure
Recent systemic corticosteroid exposure
Systemic disease associations
Chronic kidney disease and dialysis
Diabetes mellitus
Inflammatory arthritis
Hyperparathyroidism
Connective tissue disorders
Associated injury screen
Knee injury patterns
Twisting injury and ligament concern
Mechanical instability sensation
Locking or catching concern
Neurovascular symptoms
Foot numbness or weakness
Cold foot
Severe calf pain
Skin integrity
Laceration over anterior knee
Contamination or foreign material
Physical Exam
Inspection and palpation
Local findings
Knee effusion
Ecchymosis over anterior knee
Patella position
Patella alta appearance
Tendon palpation
Tenderness at inferior pole of patella
Palpable gap in patellar tendon
Tenderness at tibial tubercle insertion
Extensor mechanism function
Functional tests
Straight leg raise ability
Active knee extension against gravity
Active knee extension against resistance if tolerated
Interpretation
If unable straight leg raise, complete extensor mechanism disruption likely
If painful but able straight leg raise, partial tear or pain inhibition possible
Neurovascular and compartment
Distal perfusion
Dorsalis pedis pulse
Posterior tibial pulse
Capillary refill
Neurologic
Dorsiflexion strength
Plantarflexion strength
Sensation dorsal foot
Sensation plantar foot
Compartment concern
Disproportionate pain
Pain with passive toe motion
Tense compartments
Joint above and below
Regional checks
Hip pain and ROM
Ankle pain and ROM
Tibia and fibula tenderness
Differential Diagnosis
Extensor mechanism and anterior knee causes
Key alternatives
Quadriceps tendon rupture
Patellar fracture
Tibial tubercle avulsion fracture
Sleeve fracture of patella in pediatrics
Mimics
Severe patellar tendinopathy flare
Prepatellar bursitis
Acute hemarthrosis from ACL rupture
Ligament and dislocation emergencies
Limb threatening conditions
Knee dislocation with popliteal artery injury
Compartment syndrome of leg
Open knee injury with traumatic arthrotomy
Coding aligned labels
Traumatic rupture of patellar tendon
SNOMED CT 415748002
ICD-10-CM category S86.8 injury of other muscles and tendons at lower leg level
Quadriceps tendon rupture
ICD-10-CM category S76.1 injury of quadriceps muscle and tendon
Patellar fracture
ICD-10-CM category S82.0 patella fracture
Laboratory Tests
Routine labs when needed
Indications for labs
Planned operative pathway
Significant comorbidity
Anticoagulant use
Polytrauma
Baseline labs for OR or sedation pathway
Complete blood count for anemia or bleeding concern
Electrolytes and creatinine for comorbidity or contrast planning
INR and aPTT for anticoagulant concern
Point of care testing
Glucose when diabetes or altered status concern
Hypoglycemia exclusion before sedation
Hyperglycemia context for wound healing risk
PITFALLS
Limitations
Normal labs do not exclude rupture
CK not routine unless crush or prolonged ischemia concern
Diagnostic Tests
Scoring Systems
Decision frameworks
Complete tear suspicion
Inability to straight leg raise
Palpable tendon defect
Patella alta on imaging
Knee dislocation vascular screen
Hard signs
Absent distal pulses
Expanding hematoma
Active hemorrhage
Bruit or thrill
If hard signs, emergent vascular imaging or OR per local pathway
Radiographs
Plain films
Knee radiographs 2 to 3 views
Patella position assessment
Fracture exclusion
Radiographic patterns
Patella alta supports patellar tendon rupture
Avulsion fragments at inferior pole possible
Tibial tubercle avulsion fracture consideration
MRI
Indications
Partial tear suspected with preserved straight leg raise
Equivocal exam due to pain or swelling
Surgical planning for tissue quality and gap
Key outputs
Tear location proximal midsubstance distal
Retraction distance
Associated cartilage or ligament injury
CT
Indications
Complex fracture concern on radiographs
Tibial plateau fracture concern
Surgical planning for bony injury
Disposition
ED disposition pathways
Discharge with urgent ortho follow up
Suspected partial tear
Intact extensor mechanism on exam
Pain controlled on oral regimen
Safe mobility with crutches or walker
Admission or transfer
Suspected complete patellar tendon rupture
Inability to ambulate safely
Open injury
Neurovascular compromise
Knee dislocation concern
Follow up timing
Complete rupture suspicion
Orthopedics evaluation within 24 to 48 hours
Earlier if rapidly worsening swelling or skin compromise
Partial tear suspicion
Orthopedics or sports medicine within 3 to 7 days
Activity restrictions
Mobility plan
Knee locked in extension
Non weight bearing or weight bearing as tolerated only if explicitly cleared and brace locked
No active knee extension against resistance
Treatment
Immediate life-saving interventions
Critical injury exclusions
If knee dislocation concern, reduction and vascular assessment pathway
If open injury, antibiotics and tetanus pathway
If compartment syndrome concern, emergent surgical consult
Pain control escalation
If severe pain, parenteral opioid titration with monitoring
If sedation required for reduction of dislocation, procedural sedation pathway
Immobilization and Splinting
Immobilization choice
Knee immobilizer in full extension
Hinged knee brace locked in extension if available
Immobilization principles
Extension to approximate tendon ends
Avoid flexion positioning
Neurovascular recheck after immobilization
Adjuncts
Elevation
Ice
Compression wrap if tolerated and no vascular compromise
Reduction
Reduction indications
If concurrent patellar dislocation, reduction when safe
If knee dislocation, emergent reduction with vascular precautions
Analgesia and anesthesia options
Non opioid analgesia
Acetaminophen PO 1000 mg once
Ibuprofen PO 400 mg once if no contraindication
Naproxen PO 500 mg once if no contraindication
Opioid titration
Fentanyl IV 0.5 to 1 microgram per kg
Repeat 0.25 to 0.5 microgram per kg every 5 minutes to effect
Hydromorphone IV 0.2 to 0.5 mg
Repeat 0.2 mg every 10 to 15 minutes to effect
Regional anesthesia
Femoral nerve block ultrasound guided
Ropivacaine 0.5% 15 to 20 mL
Maximum total ropivacaine 3 mg per kg
Adductor canal block ultrasound guided
Ropivacaine 0.5% 15 to 20 mL
Sensory predominant option for anterior knee
Procedural sedation if required
Sedation setup
Airway equipment at bedside
Suction ready
Continuous monitoring including capnography
Ketamine IV
Initial 1 mg per kg IV
If inadequate, additional 0.5 mg per kg IV
Repeat every 5 to 10 minutes to effect
Propofol IV
Initial 0.5 to 1 mg per kg IV
If inadequate, 0.25 to 0.5 mg per kg IV boluses
Repeat every 1 to 3 minutes to effect
Post reduction requirements
Neurovascular recheck
Post reduction radiographs when dislocation reduced
Immobilization in extension
Open fracture medications and timing
Open injury antibiotics
Cefazolin IV 2 g once
If severe beta lactam allergy, clindamycin IV 900 mg once
If gross contamination, add gentamicin IV 5 mg per kg once per local protocol
Tetanus prophylaxis
If unknown or incomplete immunization, tetanus toxoid vaccine
If dirty wound and immunization incomplete or unknown, tetanus immune globulin per local protocol
Wound care
Sterile saline soaked dressing
Avoid probing in ED
Urgent orthopedics
DVT prophylaxis when relevant
Risk assessment
Lower limb immobilization
Prior VTE
Active malignancy
Significant mobility limitation
Prophylaxis decisions
If high risk and prolonged immobilization anticipated, align with local protocol and orthopedics plan
If imminent surgery planned, coordinate timing with orthopedics
Special Populations
Pregnancy
Pregnancy considerations
Fall mechanism and fetal monitoring needs by gestational age
Imaging shielding and justification
Analgesia selection
Medication safety
Avoid NSAIDs in later pregnancy per obstetric guidance
Opioid short course risk benefit discussion
Geriatric
Older adult considerations
Higher spontaneous or low energy rupture risk with systemic disease
Higher fall risk and mobility support needs
Delirium risk with opioids and sedatives
Disposition bias
Lower threshold for admission if unsafe ambulation
Early physiotherapy and gait aid planning
Pediatrics
Pediatric considerations
Tibial tubercle avulsion fracture mimic
Patellar sleeve fracture consideration
Growth plate injury patterns
Management differences
Early pediatric orthopedics involvement
Weight based analgesia dosing per local pathway
Background
Epidemiology
Occurrence patterns
Rare injury
More common in physically active adults
Male predominance reported in many series
Risk context
Systemic disease increases susceptibility
Tendinopathy and prior surgery increase risk
Pathophysiology
Mechanism
Failure of patellar tendon as part of extensor mechanism
Eccentric quadriceps contraction against flexing knee as common pathway
Tear locations
Inferior pole of patella
Midsubstance
Tibial tubercle insertion
Functional consequence
Loss of active knee extension
Patella alta due to unopposed quadriceps tension
Therapeutic Considerations
Treatment rationale
Complete rupture typically requires operative repair for restoration of extensor mechanism
Early repair generally associated with easier mobilization and less retraction
Partial tear with intact extensor mechanism may be managed nonoperatively in selected cases
Immobilization rationale
Extension reduces gap and protects healing or limits pain
Flexion increases tension and separation at rupture site
Recommendation style framing
Class I recommendation based on expert consensus for urgent orthopedic evaluation in suspected complete rupture
Class IIa recommendation based on expert consensus for MRI when exam equivocal or partial tear suspected
ACEP Level B recommendation for capnography as adjunct monitoring during ED procedural sedation
Patient Discharge Instructions
Copy discharge instructions
Discharge packet
Knee immobilizer locked in full extension at all times unless told otherwise
Non weight bearing with crutches or walker unless told otherwise
Elevation above heart level when resting
Ice 15 to 20 minutes up to every 2 to 3 hours for 48 hours
Keep brace dry and intact
Pain plan
Acetaminophen 1000 mg every 6 to 8 hours as needed
Ibuprofen 400 mg every 6 to 8 hours as needed if safe for you
Opioid only if prescribed and smallest amount needed
Follow up timing
Orthopedics within 24 to 48 hours if complete rupture suspected
Orthopedics or sports medicine within 3 to 7 days if partial tear suspected
Return to ED now
New numbness or weakness in foot
Foot becomes cold pale or blue
Severe increasing pain not controlled with meds
Rapidly increasing swelling
New inability to move toes
Fever or wound drainage
Brace too tight or worsening tingling after brace placement
References
Clinical guidelines and evidence sources
Core references
ACEP Clinical Policy Procedural Sedation and Analgesia in the Emergency Department
AAOS OrthoInfo patient and clinician education on extensor mechanism injuries
Review articles on acute patellar tendon rupture management and outcomes
Evidence statements
Capnography adjunct monitoring during ED procedural sedation ACEP Level B recommendation
Timely surgical repair for complete patellar tendon rupture commonly recommended in orthopedic consensus guidance
MRI utility for partial tears and equivocal exams supported in orthopedic diagnostic pathways
SymptomDx is an educational tool for medical professionals. It does not replace clinical judgment. Verify all clinical data and drug dosages with authoritative sources.