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Patella Fracture

Fracture of the kneecap accounting for 1 percent of all skeletal fractures, typically from direct blow (dashboard injury) or indirect quadriceps contraction; classified by displacement, comminution, and articular surface integrity; surgical fixation indicated for displacement > 2-3 mm or articular incongruity > 2 mm.

Written by: Saygı Hospital Health Guide Editorial Board
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This content has been compiled by the Saygı Hospital Health Guide Editorial Board and is periodically reviewed by a specialist physician.

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What is Patella Fracture?

Patella fracture is the breakage of the patella (kneecap), the largest sesamoid bone in the human body, embedded within the quadriceps tendon and continuous with the patellar ligament. Annual incidence is 13.1 per 100,000 population, accounting for approximately 1 percent of all skeletal fractures and 8 percent of fractures around the knee. Bimodal distribution: peak in adults age 20-50 (high-energy trauma — motor vehicle accidents, falls from height, sports injuries) and secondary peak in elderly (low-energy falls in osteoporotic patients, simple falls onto flexed knee). Male-to-female ratio 2:1 in young adults, more equal in elderly.

Anatomy and biomechanics: Patella is a triangular sesamoid bone embedded in the quadriceps tendon, articulating with the trochlear groove of the femur posteriorly. Functions include increasing the moment arm of the quadriceps tendon (improving extension efficiency 30-50 percent), protecting the femoral condyles, and contributing to knee flexion-extension biomechanics. Blood supply primarily from inferior pole and through quadriceps tendon (genicular arteries); avulsion of inferior pole or comminution can devascularize patella. Articular surface has the thickest cartilage in the human body (5-7 mm) accommodating high contact stresses (up to 7 times body weight during stair climbing).

Mechanisms of injury: 1) Direct trauma (most common, 60-70 percent) — fall onto flexed knee, dashboard injury in motor vehicle accidents, blow to anterior knee (sports — soccer, basketball, hockey), industrial accidents; produces transverse, comminuted, or stellate fracture pattern; 2) Indirect mechanism (forceful quadriceps contraction with knee flexion) — sudden eccentric loading during fall to prevent collapse, jumping injury, lifting heavy load with knees flexed; produces transverse fracture (often through middle third); 3) Combination — common in high-energy trauma. Classification: 1) AO/OTA — 34-A extra-articular (avulsion of poles), 34-B partial articular (vertical), 34-C complete articular (transverse, comminuted, stellate); 2) Rockwood — based on displacement and pattern; 3) Open vs closed (per Gustilo for open).

Pathophysiology: Disruption of extensor mechanism (quadriceps-patella-patellar tendon-tibial tubercle complex) leads to inability to actively extend knee against gravity; intact retinaculum (lateral and medial patellar retinacula from vastus lateralis and medialis) may allow some extension despite displaced fracture (false sense of preserved function); articular incongruity > 2 mm leads to abnormal patellofemoral biomechanics, post-traumatic arthritis, chronic anterior knee pain. Healing complicated by relatively poor blood supply (avascular necrosis of fragments), synovial fluid environment limiting callus formation, high tension forces from quadriceps.

Symptoms

Severe anterior knee pain immediately after injury
Visible deformity, palpable gap or step-off in patella
Inability to actively extend the knee or perform straight leg raise
Hemarthrosis (joint effusion with blood) — knee swelling
Local tenderness over patella
Bruising over knee anterior surface
Limp or inability to bear weight
Crepitus on palpation of patella
Visible open wound (open fracture, especially direct trauma)
Decreased knee range of motion (especially extension)

Risk Factors

Direct trauma (motor vehicle accident with dashboard injury, falls onto flexed knee, sports — soccer, basketball, football, hockey)
Forceful quadriceps contraction (jumping, sudden change of direction, weightlifting)
Osteoporosis (postmenopausal women, elderly with vitamin D deficiency)
Athletic activities (basketball, soccer, hockey, football, gymnastics, ski)
Occupational hazards (construction worker, military, police)
Prior knee surgery (TKA, ACL reconstruction with bone-patellar tendon-bone graft)
Stress fractures in athletes (basketball, gymnastics, military recruits — overuse)
Pathologic fracture (rare, metastatic disease, primary bone tumor)
Diabetes (impaired healing)
Smoking (impairs bone healing)
Long-term steroid use (skin and bone fragility)

When to See a Doctor?

If you experience any of the following symptoms, seek medical attention promptly:

  • Severe knee pain after fall on knee or trauma to anterior knee
  • Inability to walk or bear weight on injured knee
  • Inability to lift leg straight when sitting (loss of extensor mechanism)
  • Visible bruise, swelling, or deformity over front of knee
  • Open wound over knee (CALL EMERGENCY 112 for open fracture)
  • Severe knee swelling (hemarthrosis) within hours of injury
  • Knee instability or giving way after recent injury
  • Persistent severe pain after knee injury 24-48 hours despite ice and elevation
  • Suspicion of dislocation (palpable defect over patella, inability to extend)
  • Stress fracture symptoms in athletes — anterior knee pain worsening with activity over weeks

Treatment Methods

01
Initial assessment: detailed history (mechanism of injury, timing, ability to actively extend knee, prior knee problems), physical examination (anterior knee swelling, tenderness, palpable gap or step-off, hemarthrosis, ability to perform straight leg raise — key test for extensor mechanism integrity), neurovascular examination, photograph open wound, immediate splinting of knee in extension with padded splint, application of ice, elevation, partial weight-bearing with crutches
02
Imaging: 1) AP and lateral knee X-rays — visualize fracture pattern, displacement, comminution, articular involvement, patella alta or baja; bipartite patella (variant in 2 percent population, smooth round borders, do not confuse with fracture); 2) Skyline (sunrise, axial) view — best visualizes articular surface, vertical fractures, and patellofemoral congruity; 3) CT scan — for complex fractures requiring surgical planning, comminuted patterns, articular step-off measurement; 4) MRI — for occult fractures, tendon avulsions (quadriceps or patellar tendon rupture), retinacular tears, intra-articular pathology, stress fractures
03
Conservative management: indications — non-displaced fracture (< 2 mm displacement, < 3 mm articular step-off, intact extensor mechanism with full active extension against gravity); technique — long-leg cast or hinged knee brace in extension for 4-6 weeks (older patients tolerate brace better with allowed gentle ROM in low-demand fractures), partial weight-bearing with crutches initially, progress to full weight-bearing with cast/brace at 2-4 weeks; isometric quadriceps exercises in cast, gentle passive ROM after cast removal; expected healing 6-8 weeks; follow-up X-rays at 2, 6, and 12 weeks to confirm maintenance of alignment and progress of healing
04
Surgical management indications: displacement > 2-3 mm, articular step-off > 2 mm, loss of active extension against gravity, open fractures, segmental or comminuted fractures, vertical fractures (typically require fixation due to instability); timing — ideally within 7-10 days of injury for optimal soft tissue handling and prevention of contracture, can be delayed in polytrauma until stable
05
Surgical techniques: 1) Tension band wiring (TBW) — gold standard for transverse and bipolar fractures; technique includes parallel longitudinal K-wires (1.6-2.0 mm) through patella, figure-of-8 stainless steel wire (18 gauge) anterior to wires acting as tension band that converts tensile forces from quadriceps into compressive forces across fracture during knee flexion; modified AO technique with cannulated screws + tension band wire over screws (improved fixation); 2) Cannulated screws alone — for vertical fractures, simple oblique fractures in young patients; 3) Plate and screw fixation — for severely comminuted, multifragmentary, osteoporotic patterns where TBW inadequate; pre-contoured patella plates (Synthes, Zimmer Biomet, Acumed) provide circumferential stability; 4) Partial patellectomy — for inferior pole comminution non-reconstructible (10-20 percent of fractures); excise comminuted distal pole, reattach patellar tendon to remaining patella with transosseous sutures or suture anchors; 5) Total patellectomy — last resort for severely comminuted unreconstructible fractures; results in significant extensor weakness (30-50 percent decrease in quadriceps strength), prolonged rehabilitation, anterior knee pain
06
Open fracture management: emergency IV antibiotic prophylaxis (cefazolin for I/II, add gentamicin for III), tetanus prophylaxis, surgical debridement and irrigation within 6-24 hours, internal or external fixation depending on severity and contamination, soft tissue coverage with primary closure, advancement flap, or rotational flap as needed
07
Postoperative rehabilitation: 1) Phase 1 (0-2 weeks) — knee immobilizer or hinged brace locked in extension, partial weight-bearing 50 percent with crutches, isometric quadriceps and hamstring exercises, ankle pumps, ice, elevation, pain control; 2) Phase 2 (2-6 weeks) — hinged brace allowing 0-30° flexion at 2 weeks, progressing to 0-90° by 4-6 weeks (depending on fracture stability and bone quality), gentle passive and active-assisted ROM, continued quadriceps strengthening (straight leg raises, short arc quads, terminal knee extension, isometric quads sets), full weight-bearing with brace at 4-6 weeks; 3) Phase 3 (6-12 weeks) — discontinue brace, progress active ROM to full knee flexion, resistance exercises (leg press, squats partial range, lunges), proprioception training (balance board), stationary bicycle; 4) Phase 4 (3-6 months) — return to running, sport-specific training, gradual return to high-impact sports at 4-6 months for athletes; full recovery 6-12 months
08
Hardware removal: typically considered at 6-12 months post-fixation if symptomatic (prominent K-wires causing skin irritation, painful hardware especially with kneeling); not routinely required if asymptomatic; potential complications of removal include re-fracture if early, persistent pain, infection
09
Long-term complications and management: 1) Hardware-related symptoms (50 percent of patients have palpable hardware, 20-30 percent require removal); 2) Wire breakage (10-20 percent — does not necessarily require revision if stable); 3) Loss of fixation/displacement (5-10 percent) — revision surgery; 4) Infection (1-5 percent for closed, higher for open); 5) Nonunion (rare, 1-5 percent — bone grafting and revision fixation); 6) Malunion (10-20 percent — corrective osteotomy if symptomatic); 7) Post-traumatic patellofemoral arthritis (20-50 percent at 10+ years, especially with articular step-off > 2 mm) — conservative management initially (NSAIDs, physical therapy, weight loss, intra-articular injections), eventual patellofemoral or total knee arthroplasty if severe; 8) Chronic anterior knee pain (20-30 percent), kneeling pain (40-60 percent — interferes with occupations requiring kneeling); 9) Decreased knee range of motion (5-15 percent loss of full flexion common); 10) Quadriceps atrophy and weakness (gradual recovery 1-2 years post-injury with rehabilitation)

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Health Disclaimer: The information on this page is prepared for general informational purposes only. It does not replace medical diagnosis and treatment. Please consult your physician for your complaints. Saygı Hospital does not accept responsibility for actions taken based on the information on this page.