Patellar Fractures

Original Editor - Rachael Lowe Top Contributors - Marie Avau, Leana Louw, Lise De Wael, Rachael Lowe and Debby Decock


Patella fractures are caused by directly by trauma or a compressive force, or indirectly as the result of quadriceps contractions or excessive stress to the extensor mechanism.[1][2][3] Indirect injuries are commonly associated with tears of the retinaculum and vastus muscles.[1] Patella fractures make up about 1% of all skeletal injuries.[4][5]

Clinically relevant anatomy

The patella is a triangular bone situated on the anterior surface of the knee at the distal end of the femur. It is the largest sesamoïd bone in the body and makes part of the knee joint.[6][7][8] Vastus medialis and lateralis, as part of the quadriceps group, control movement at the patella.[9] The extensor mechanism as a whole plays a major role in patella fractures. This consists of the quadriceps, quadriceps tendon, retinaculum, patella tendon, tibial tubercle and patellofemoral and patellotibial ligaments.[10] See the page on the patella for more details on the anatomy.

658px-Knee diagram.svg.png
Knee joint.png


In a recent study, the average mortality rate at one year after patella fractures was 2.8%, increasing to 6.2% in the geriatric population. Patella fractures are not associated with an increased mortality rate, as the relative risk of death was 0.9.[11]


  • Injuries (sprain/rupture) to ligaments and tendons attached to the patella
  • Avascular necrosis[12]
  • Post-traumatic arthritis
  • Osteochondral damage to patellofemoral joint
  • Stiffness
  • Non-union
  • Malunion
  • Concomitant injuries (e.g. injuries to the acetabulum, femur and tibia)
  • Long term complications:[13]
    • Stiffness
    • Extension weakness
    • Patellofemoral arthritis.


Characteristics/Clinical Presentation

Types of fractures

Patella fractures are classified as either displaced or non-displaced. Displaced fractures are unstable and can be further classified as:[14]

  • Comminuted: As a result of direct trauma (mostly due to blows or falls on flexed knee)
    • Can cause damage to the articular cartilage of patella and femoral condyles.
  • Tansverse/stellate: As a result of muscle contraction/extensive stress on the extensor mechanism, e.g. explosive quadriceps contraction after jumping from height.
    • Most common type
    • Proximal blood supply may be compromised
    • Usually as a result of hyper-flexion of the knee
  • Marginal: As a result of a fall on the knee
  • Vertical/longitudinal
  • Lower/upper pole
  • Osteochondral
  • Sleeve (only in paediatric patients)


The prognosis of the injury depends on the amount of chondral damage at the time of injury. Functional outcome depends on the ability to achieve pain-free and stable range of motion in an early stage. [17]

Differential diagnosis



  • Details regarding accident
  • Mechanism of injury
  • Pain at knee
  • Complaints of difficulty standing or snapping sensation at knee


Physical examination

  • Observation:
    • Whole extremity
    • Swollen, bruised knee
    • Deformity around knee
    • Possible wounds (open fracture)
  • Palpation (often done after local anesthetics to eliminate pain):
    • Tenderness around patella
    • Palpable gap (for displaced fractures)
  • Rule out concomitant injuries:
    • e.g. fractures of the acetabulum, femur and tibia
  • Haemarthrosis
  • Range of motion:
    • Acute:
      • Limited knee and painful knee flexion and extension
      • Often unable to do straight leg raise
    • Chronic:
      • Full knee flexion with extension lag
  • Distal pulses
  • Assess compartment of the leg
  • Neurological assessment


Special investigations


  • AP view:
    • May be difficult to see patella
  • Lateral view:
    • Undisplaced - < 2mm separation
    • Displaced - > 2mm separation, step deformity noted
  • Sky view
  • Used for regular monitoring of healing process and any possible complications
AP view
Lateral view
  • CT scan: Usually not needed
  • MRI: Diagnosis of associated injuries to nearby tendons and ligaments
  • Bone scans: To identify stress fractures


Outcome measures

Medical management

  • In acute cases, local anesthetics can be given to eliminate pain.[18] This helps to aid in the assessment and diagnosis of the patella fracture.

Conservative management

Indication: Undisplaced fracture (mostly vertical, horizontal and comminuted fractures) with extensor mechanism in place [1][17]


  • Fracture immobilized with POP cylinder cast or range of motion brace locked in extension (4-6 weeks):
    • As healing takes place, knee flexion can gradually be increased
    • Range of motion brace must be worn until union (on X-rays) and clinical signs of healing (not tender on palpation) are present
  • Crutch walking 6-8 weeks
  • Rehabilitation

Surgical intervention

Indication: Significant displacement with extensor mechanism not intact.[1]

Aim: Restore extensor function, align articular incongruities, and allow early motion[17][20][23][24]


  • Transverse/simple, comminuted mid-patella fracture: Open reduction and internal fixation using tension band wire technique using pins and wires and 'a figure of eight' to press the pieces together
    • POP cast in extension for 6 weeks
Tension band wire ORIF
  • Proximal/distal <1/3 - simple or comminuted: Excision of small piece & tendon repair
    • POP cast for 6 weeks
  • Longitudinal (uncommon): Interfragmentary screw fixation
  • Comminuted fracture/irreducible or irreparable fracture or when cartilage too badly damaged: Partial vs complete patellectomy:[18]
    • Quadriceps muscles is is attached to the patellar ligament to ensure function of the extensor apparatus during a complete patellectomy[18]
    • Patellectomy: Relatively old procedure, last treatment of choice
  • Repair of bilateral vastus muscles
  • Rehabilitation same as with conservative management

Later stages:

Manipulation under anesthesia or the arthroscopic releasing of adhesions is required when athrofibrosis occurs.[17]

Physiotherapy management

As clinical healing phases do not always correlate with theoretical healing, the surgeon will guide rehabilitation taking X-ray findings into consideration. The following is a guide to be used in the rehabilitation of a patient after a patella fracture, but it is always good to discuss treatment plans with your orthopaedic surgeons.

Conservative management

Conservative management are used when the extensor mechanism is still intact.[1]

Phase 1: 0-6 weeks

  • Range of motion (as per surgeon):
    • Range of motion brace locked in extension 2-3 weeks
    • Controlled motion brace at 2-3 weeks
    • Exercises:
      • Open kinetic chain strengthening and knee range of motion at 3-4 weeks - focus on active flexion & extension in inner ranges
      • Quadriceps
      • Hamstring
      • Gluts sets
      • SLR
      • Open and closed kinetic chains hip strengthening exercises
      • Circulatory drills
  • Weight-bearing:
    • Partial weight-bearing in brace
    • May stand tandem
    • Weight-bearing restrictions normally apply for 6-8 weeks[10][22]
    • Duration of crutches/weight-bearing restrictions as per surgeon
  • Patella mobilization
  • Pain & oedema management using cryotherapy


Phase II: 6-12 weeks

  • Range of motion knee brace as per surgeon
  • Range of motion:
    • Progress to full knee flexion & extension
  • Exercises:
    • Stationary bike with seat elevated and no resistance
    • Progress closed kinetic chain exercises: Mini squats, step up, retro step, etc
    • Progress resistance on hip exercises
    • Proprioception
    • Lunges from weeks 8-10


Post-operative rehabilitation

Surgical intervention are done in cases where there are significant displacement and the extensor mechanism is not intact. Open reduction and internal fixation using the tension band wire technique is normally the treatment of choice.[1]

Phase I: 0-2 weeks

  • Range of motion brace:
    • Locked in extension (if POP cast not used)
    • Only to be taken off for physiotherapy sessions, 0-30° knee flexion range of motion allowed at first.
  • Mobilization:
    • Knee locked in extension with range of motion brace
  • Exercises:
    • Isometric quadriceps/hamstring/adductor/abductor strengthening
    • Resisted ankle exercises (e.g. with theraband)

Phase II: 2-6 weeks

  • Range of motion brace (if applicable):
    • To be worn for weight-bearing activities, locked in extension
    • May be removed at night
  • Range of motion:
    • 5° of flexion can be added each week to achieve 90° by week 6
  • Exercises:
    • Isometric quadriceps/hamstring/adductor/abductor strengthening
    • Resisted ankle exercises (e.g. with theraband)
    • Initiate SLR

Phase III: 6-10 weeks

  • Range of motion brace:
    • Unlocked; to be worn for weight-bearing activities
  • Range of motion:
    • Progress to full range of motion by week 10
  • Exercises: As previous phase

Phase IV: 10-12 weeks

  • Range of motion brace: Discontinue
  • Range of motion: Full
  • Exercises: As previous phase
    • Start with stationary cycling

Phase V: Up to 3-6 months

Return to normal activities as tolerated.



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