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Knee and Patella Injuries

Knee Dislocation

Epidemiology

  • More common in males
  • Morbid obesity is a risk factor

Etiology/pathophysiology

  • High energy trauma – e.g. motor vehicle accident, crush injury, fall from height
    • Results in axial load to a flexed knee
  • Low energy trauma – e.g. routine activity in a morbidly obese patient
  • Anterior dislocations – caused by hyperextension injuries
  • Posterior dislocations – caused by posteriorly directed force across the proximal tibia
  • Associated injuries – vascular injury; nerve injury (common peroneal nerve); fractures; soft tissue injuries (patellar tendon rupture, displaced menisci)

Anatomy

  • Articulations of the knee – tibiofemoral, patellofemoral, tibiofibular
  • Ligaments – main stabilisers of the knee
    • Anterior cruciate (ACL) – controls rotation and forward movement of the tibia
    • Posterior cruciate (PCL) – controls backward movement of the tibia
    • Medial collateral (MCL) – gives stability to the inner knee
    • Lateral collateral (LCL) – gives stability to the outer knee
  • Blood supply – from the anastomses of the 6 genicular arteries
    • Descending genicular artery (GA) – branch of femoral artery
    • 2 superior GA, 1 middle GA, and 2 inferior GA – branches of the popliteal artery

Classification – Kennedy Classification (based on direction of displacement of the tibia)

  • Anterior (most common) – due to hyperextension injury
    • Involves tear of PCL
    • Highest incidence of peroneal nerve injury
  • Posterior – due to axial load on flexed knee (dashboard injury)
    • Highest incidence of vascular injury – complete tear of popliteal artery
  • Lateral – due to valgus force
    • Involves tear of collaterals and cruciates
  • Medial – due to varus force
    • Involves tear of collaterals and cruciates
  • Rotational – usually reducible

Clinical features

  • Knee pain and instability
  • Absence of deformity – 50% spontaneously reduce
  • Deformity – ‘dimple sign’ indicates irreducible posterolateral dislocation
  • Absent/diminished pulses – indicates arterial injury

Diagnosis

  • Anterior drawer test – to detect injury in ACL
    • Patient is supine, hips flexed 45o, knees flexed 90o, examiner tries to shift the tibia anteriorly at the joint line
    • Positive test – a higher degree of anterior displacement when compared to contralateral knee
  • Posterior drawer test – to detect injury in PCL (similar method, but tibia is displaced posteriorly)
  • X-ray
  • CT/MRI

Treatment

  • Emergent closed reduction followed by vascular assessment (orthopaedic emergency)
    • If pulses are absent following reduction
  • Immobilisation – if there is successful closed reduction without vascular compromise
    • Persistent loss in ROM in the long term
  • Open reduction – for irreducible knee; posterolateral dislocation; vascular injury
  • External fixation
  • Delayed ligamentous reconstruction – for knee instability after immobilisation

Patella Fracture

Epidemiology

  • More common in males
  • 20-50 year olds

Etiology/pathophysiology

  • Direct trauma – from fall or dashboard injury
    • Usually results in a comminuted fracture
  • Indirect eccentric contraction – due to rapid knee flexion against a contracted quadriceps muscle
    • Usually results in a transverse fracture, splitting the patella into two (two-part fracture)

Anatomy

  • Osteology
    • Largest Sesamoid bone in the body
    • The posterior articular surface is comprised of medial and lateral facets (lateral facet is larger)
    • Superior 3/4 of the posterior surface is covered by articular cartilage
  • Soft tissue attachments
    • Quadriceps tendon and fascia lata is attached to the antero-superior margin
      • Quadriceps tendon is composed of three layers – superior, middle, deep
    • Patellar tendon is attached to the inferior margin
  • Blood supply – from the anastomses of the 6 genicular arteries (see above)

Classification – based on fracture pattern

  • Nondisplaced
  • Displaced
  • Transverse
  • Pole/sleeve – can be upper or lower
  • Vertical
  • Marginal
  • Osteochondral
  • Comminuted

Clinical features

  • Pain and swelling over the knee
  • Ecchymosis
  • Haemarthrosis
  • Patient cannot lift the leg in full extension
  • Crepitus – in a comminuted fracture

Diagnosis

  • X-ray
    •    Patella alta – high riding patella; indicates disruption of the patellar tendon
    •    Patella baja – low riding patella; indicates disruption of the quadriceps tendon
  • CT/MRI

Treatment

  • Knee immobilised in extension – if extensor mechanism is intact; fracture is non/minimally displaced; vertical fracture
  • ORIF – if there is extensor mechanism failure; open fractures; sleeve fracture
  • Partial patellectomy – for comminuted superior/inferior pole fracture
  • Total patellectomy – only for severely comminuted fractures where the patella is unable to be salvaged

Tibial Plateau Fractures

Epidemiology

  • Bimodal age distribution – males in their 40s; females in their 70s
  • Common locations – lateral condyle > bicondylar > medial condyle

Etiology/pathophysiology

  • Mechanisms
    • Varus or valgus load with or without axial load
    • High energy trauma – motor vehicle accidents, sports injuries (younger patients)
    • Low energy trauma – falls (older patients)
  • Most common fracture patterns
    • Younger patients – splitting fractures
    • Older/osteoporotic patients – depression fractures
  • Fractures of the lateral plateau are more common than the medial plateau
  • Associated conditions
    • Damage to cruciate and collateral ligaments
    • Meniscal tears
    • Compartment syndrome
    • Vascular injury

Anatomy

  • Lateral tibial plateau – convex in shape
  • Medial tibial plateau – concave in shape

Classification –  Schatzker Classification

  • I – lateral plateau split fracture without depression
  • II – lateral plateau split fracture with depression
  • III – lateral pure depression fracture
  • IV – medial plateau fracture
  • V – bicondylar plateau fracture
  • VI –  bicondylar fracture with a dislocation of the metaphysis from the diaphysis

Clinical feature

  • Pain and swelling
  • Inability to bear weight
  • Bruising, haemarthrosis
  • Reduced knee range of movement

Diagnosis

  • X-ray – depressed articular surface, sclerotic band of bone (indicates compression), abnormal joint alignment
  • CT/MRI

Treatment

  • Hinged knee brace – for minimally displaced fractures
  • ORIF – for all medial plateau fractures; fractures with condylar widening; bicondylar fractures
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