Lower-Extremity Trauma: Patella & Tibia to Ankle – Comprehensive Exam Notes

Extensor Mechanism ("Links of the Chain")

  • Components (proximal ➜ distal)
    • Quadriceps muscle belly
    • Quadriceps tendon (blends with retinaculum / superior joint capsule)
    • Patella (largest sesamoid bone)
    • Patellar tendon
    • Tibial tubercle
  • Function
    • Converts quadriceps contraction into knee extension
    • ANY disruption = loss of active extension / failed straight-leg-raise (SLR)
  • Common pathologies compromising the chain
    • Patella fracture (bony link)
    • Quadriceps-tendon rupture (superior tendinous link)
    • Patellar-tendon rupture (inferior tendinous link)

Patella Fractures

  • Mechanisms
    • Direct impact (fall on knee, dashboard in MVC, sports collisions)
  • Clinical findings
    • Visible/palpable defect across patella
    • Hemarthrosis (effusion + blood)
    • Abrasions / lacerations possible
    • Inability to perform SLR ➜ pathognomonic for disrupted extensor mechanism
  • Imaging
    • Mandatory AP\text{AP} + lateral\text{lateral} knee
    • Look for subtle cortical step-offs & joint effusion
    • CT if fracture pattern unclear or surgical planning needed (esp. comminution)
  • Management
    • Minimally or non-displaced: straight-leg immobilizer (full extension) for 6–8 wk
      • Brace must NOT hinge; passive dangling or active quad firing creates distraction forces
    • Displaced/comminuted: ORIF
      • Typical construct = figure-8 tension-band wiring ± screws; post-op immobilizer

Tibial Plateau Fractures

  • Etiology = axial load into extended knee (falls from height, skiing, dashboard)
  • Classification
    • Schatzker I → VI (higher number = greater energy & comminution)
  • Structures at risk
    • Articular cartilage
    • Menisci (medial & lateral sit on plateau)
    • Cruciate ligaments (ACL anterior, PCL posterior insertions)
    • MCL (inserts on proximal medial tibia). LCL less often due to fibular insertion.
  • Key complication: Compartment Syndrome (CS)
    • Tibia fractures bleed into closed fascial compartments ➜ escalating pressure
    • 4 compartments: anterior, lateral, superficial posterior, deep posterior
    • 5 P’s: pain (out of proportion), paresthesia, pallor, paralysis/weakness, pulselessness
    • Normal compartment pressure <10 mmHg<10\,\text{mmHg}; concern >30 mmHg>30\,\text{mmHg} ➜ emergent fasciotomy
  • Work-up
    • Neurovascular check FIRST (pulses, sensation, motor)
    • AP & lateral X-ray ± CT 3-D mapping for surgical planning
  • Treatment
    • Restore articular surface (plate/screws, raft screws, bone graft) + address soft-tissue injuries
    • Always monitor & decompress CS before definitive fixation

Tibial Shaft ("Calf") Fractures

  • High-energy (young) vs low-energy (elderly) bimodal distribution
  • Always obtain 2 orthogonal views; AP may reveal displacement invisible on lateral
  • Frequently associated fibular fracture (second fracture not to miss)
  • Acceptable alignment = common-sense rule
    • If you would accept the alignment in yourself/family, likely acceptable (formal numbers exist: <5^{\circ} angulation, <1\,\text{cm} shortening, etc.)
  • Complications identical to plateau: CS is #1 immediate threat
  • Management options
    • Long-leg casting / functional brace for minimally displaced
    • Intramedullary nailing or plate fixation for displaced/unstable patterns

Compartment Syndrome Summary

  • Pathophysiology: bleeding/edema raises intracompartmental pressure ➜ capillary collapse
  • Measurement
    • Needle manometer technique (zeroed syringe into compartment)
    • Emergent fasciotomy if P<em>c≥30 mmHgP<em>c \ge 30\,\text{mmHg} or ΔP=P</em>d−Pc≤30\Delta P = P</em>d - P_c \le 30 (diastolic minus compartment)
  • Surgical release = long skin & fascial incisions over affected compartments; fracture addressed later

Ankle Fractures (Malleolar)

  • Mechanism: inversion / twisting ➜ lateral malleolus ≈70%\approx70\%, medial ± posterior malleolus (bi- / tri- malleolar)
  • Always inspect syndesmosis width on AP mortise; widened = injury/dislocation
  • Risk factors: alcohol (risky behaviour), falls, sports
  • Evaluation priorities: distal pulses, cap refill, sensory/motor (peroneal, tibial)
  • Imaging: AP, mortise, lateral ankle ± full-length tibia
  • Treatment
    • Stable avulsion below joint line: cast/boot
    • Any fracture at or above joint line, bimalleolar, trimalleolar, or syndesmotic widening: ORIF (plate on fibula, screws across syndesmosis, screws in medial/posterior fragments)

Quadriceps & Patellar Tendon Ruptures

  • Mechanism = forceful sudden knee flexion (eccentric overload) in middle-aged/elderly (e.g., slip on ice while moving trash can)
  • Findings
    • Large hemarthrosis, palpable gap above (quad) or below (patellar) patella
    • Patella alta (tendon rupture) vs baja (quad rupture) compared with contralateral side
    • Failed SLR / active extension lag
  • Imaging: AP & lateral knee show high-riding or low-riding patella; MRI rarely needed acutely
  • Management
    • Partial tears: immobilizer + PT
    • Complete: surgical re-attachment (trans-osseous sutures, anchors) + immobilizer 6–12 wk

Salter–Harris (Physeal) Classification – Pediatrics

  • Physis = growth plate (radiolucent line in skeletally immature)
  • Types ("SALTR": Same, Above, Lower, Through, Rammed)
    • I = Straight across (distraction) – physis only; looks normal
    • II = Above (metaphysis + physis)
    • III = Lower (epiphysis + physis)
    • IV = Through (metaphysis + physis + epiphysis)
    • V = Rammed/compression – crush of physis; also looks near-normal acutely
  • Test trick: II goes up (metaphysis), III goes down (joint), IV through both, I & V appear "normal" but history reveals injury (I = separation, V = compression)

Greenstick / Torus (Buckle) Fractures – Children

  • Pediatric bones bend before they break (elastic)
  • Greenstick = cortical break on convex side with intact concave cortex (like bending fresh tree limb)
  • Torus/Buckle = compressive failure; cortical bulge without full cortical break
  • Imaging clues: subtle angulation, cortical buckle; compare ulna & radius, both views
  • Treatment: short arm cast/splint for comfort & protection; heals rapidly (≈4 wk) as bone remodels

Imaging Pearls (Global)

  • Always obtain TWO orthogonal views (AP & lateral) of the involved bone/joint; single view can miss displacement
  • CT (especially 3-D recon) valuable for:
    • Tibial plateau comminution
    • Intra-articular orientation
    • Pre-op templating

Practical / Ethical Implications

  • First priority in trauma = neurovascular status; fracture fixation deferred until limb perfusion & nerve function secured
  • Compartment syndrome is a time-critical emergency; delays ➜ irreversible nerve & muscle ischemia, limb loss
  • Immobilization decisions balance fracture stability with risk of joint stiffness
  • Patient education about compliance with straight-leg immobilizer crucial to avoid re-displacement
  • In high-altitude or remote settings (ski areas) transport delays mandate early CS surveillance via phone/telemedicine with receiving surgeon

Key Numeric & Formula Recap

  • Normal compartment pressure: <10\,\text{mmHg}
  • Critical CS threshold: >30\,\text{mmHg} OR ΔP=P<em>diastolic−P</em>compartment≤30 mmHg\Delta P = P<em>{diastolic} - P</em>{compartment} \le 30\,\text{mmHg}
  • Acceptable alignment (generic long-bone): <5^{\circ} angulation, <10^{\circ} rotational, <1\,\text{cm} shortening (institution-specific)
  • Schatzker tibial-plateau: I – VI (increasing energy/comminution)
  • 4 leg compartments; 5 P’s of CS
  • Straight-leg immobilizer duration: ≈6–12 wk for fractures & tendon repairs