High Yield Overview

PATELLA FRACTURES - EXTENSOR MECHANISM

Largest Sesamoid | Tension Band Principle | Extension is Key

1%Of all fractures

3mmStep-off threshold

2mmGap threshold

50%Transverse pattern

FRACTURE PATTERNS

Transverse

Pattern50% - most common, central

TreatmentORIF if displaced over 2mm

Comminuted

Pattern30% - multiple fragments

TreatmentAttempt reconstruction or partial patellectomy

Polar

PatternSuperior or inferior pole

TreatmentORIF or excision + repair

Vertical

PatternSagittal, less common

TreatmentOften stable, may be conservative

Critical Must-Knows

Extensor mechanism function is key - can patient actively extend knee against gravity?
Operative indications: displacement over 2-3mm, articular step over 2-3mm, loss of active extension
Tension band principle: converts tensile force to compression at articular surface
Tension band wiring (TBW) is classic, but screw fixation increasingly preferred for transverse
Hardware removal common (50%) due to prominence - counsel patients preoperatively

Examiner's Pearls

"
50% of patients need hardware removal - wire prominence is main reason
"
Check active extension BEFORE giving analgesia - critical exam finding
"
Vertical fractures often stable (patella wide in sagittal plane)
"
Inferior pole excision + tendon repair = satisfactory if under 30% pole

Clinical Imaging

Imaging Gallery

A-B: Open reduction and internal fixation of the patella fracture and tibial tubercle pseudarthrosis and 36 months follow-up radiographs, showing healing of the tibial tubercle and incomplete patella — A-B: Open reduction and internal fixation of the patella fracture and tibial tubercle pseudarthrosis and 36 months follow-up radiographs, showing healCredit: Manzotti A et al. via BMC Musculoskelet Disord via Open-i (NIH) (Open Access (CC BY))

Spontaneous patella fracture 9 months following the revision procedure.Credit: Manzotti A et al. via BMC Musculoskelet Disord via Open-i (NIH) (Open Access (CC BY))

Anteroposterior and lateral radiographs of left knee 3 months after patellar fracture and cerclage wiring (K-wires and wiring perpendicular to fracture line). — Anteroposterior and lateral radiographs of left knee 3 months after patellar fracture and cerclage wiring (K-wires and wiring perpendicular to fracturCredit: Hirschmann MT et al. via Cases J via Open-i (NIH) (Open Access (CC BY))

Lateral radiograph of a patient with a left patellar fracture three months after total knee arthroplastyCredit: Vaishya R et al. via Cureus via Open-i (NIH) (Open Access (CC BY))

Patella fracture with tension band wiring AP and lateral views — AP and lateral knee radiographs demonstrating patella fracture treated with tension band wiring technique. The figure-of-eight wire configuration provides dynamic compression during knee flexion, converting tensile forces to compressive forces at the articular surface.Credit: PMC - CC BY 4.0

Critical Patella Fracture Exam Points

Test Active Extension!

Active straight leg raise is the key exam finding. Failed SLR = disrupted extensor mechanism = needs surgery. Test BEFORE giving analgesia - cannot assess after.

Operative Indications

Surgery indicated for: Displacement over 2-3mm, articular step over 2mm, loss of active extension. Any doubt about extension = operative management.

Tension Band Principle

Converts tensile forces to compressive forces at articular surface during knee flexion. This allows early motion and compression with loading.

Hardware Problems

50% require hardware removal - mainly K-wires/TBW prominence. Counsel patients preoperatively. Screw fixation may have lower removal rates.

Quick Decision Guide

Fracture Pattern	Key Assessment	Treatment	Pearl
Non-displaced (under 2mm), intact extension	Can actively extend	Cylinder cast/brace 4-6 weeks	Weekly X-rays first 2 weeks
Displaced transverse (over 2mm)	Gap or step-off visible	ORIF - TBW or cannulated screws	Tension band principle applies
Comminuted reconstructable	Major fragments identifiable	ORIF with multiple techniques	Cerclage + TBW or basket plate
Comminuted non-reconstructable	Multiple small fragments	Partial patellectomy + repair	Preserve as much as possible
Inferior pole fracture	Small pole, intact mechanism	Excision + tendon repair	Under 30% pole excised OK

Mnemonic

GAPSOperative Indications

Gap over 2-3mm

Fracture displacement

Active extension lost

Failed straight leg raise

Patellofemoral step over 2mm

Articular incongruity

Surgery needed

All are operative indications

Memory Hook:If there are GAPS, you need surgery!

Mnemonic

COMPRESSTension Band Principle

Converts

Changes force direction

Opposite

Tensile becomes compressive

Motion

Allows early knee motion

Principle

AO/Pauwels principle

Reduces

Fracture gap

Eccentric

Wire on tension side

Surface

Articular surface benefits

Stabilizes

Dynamic compression

Memory Hook:The wire on the front COMPRESSES the joint as you bend the knee!

Mnemonic

LEVERPatella Function

Lever arm

Increases extensor moment arm

Extension power

Increases by 30-50%

Variable contact

Area changes with flexion

Eccentric loading

Descending stairs/slopes

Retinacular tension

Medial and lateral support

Memory Hook:The patella is a LEVER that increases extension power!

Mnemonic

WIREDTBW Construct

Wire figure-8

Anterior to K-wires

Intraosseous K-wires

Two parallel pins

Reduce gap

With knee extended

Eight configuration

Classic figure-8 pattern

Dynamic compression

With flexion

Memory Hook:WIRED correctly means the patella will heal!

Overview and Epidemiology

Why This Topic Matters

Patella fractures test your understanding of the extensor mechanism, the tension band principle, and decision-making around fixation vs partial patellectomy. The examiner wants to hear you discuss biomechanics and early motion.

Demographics

Bimodal: Young (high-energy) and elderly (falls)
Male:Female 2:1
Peak age: 20-50 years
Often isolated injury in direct blow

Mechanism

Direct blow: Dashboard injury, fall on knee
Indirect: Forceful eccentric contraction (landing)
Combined: Most common - direct + muscle contraction

Anatomy and Biomechanics

Key Anatomical Concept

The patella is the largest sesamoid bone in the body. It increases the lever arm of the extensor mechanism by up to 50%, improving quadriceps efficiency. Patellofemoral contact forces reach 3-7x body weight during stair descent.

Patella Anatomy

Bony Structure

Largest sesamoid in body
Triangular with apex inferior
Articular surface has lateral facet (larger) and medial facet
Odd facet on far medial edge
3-7cm long, 2-3cm thick

Soft Tissue

Quadriceps tendon inserts on superior pole
Patellar tendon originates from inferior pole
Medial retinaculum: VMO, MPFL
Lateral retinaculum: VL, ITB fibers
Expansions allow some extension even with fracture

Blood Supply

Blood supply from superior and inferior genicular arteries forming an extraosseous anastomotic ring. Vessels enter mainly on the anterior surface and inferior pole. This is why anterior surgical approach is safe.

Classification Systems

Fracture Pattern Classification

Pattern	Frequency	Characteristics	Treatment
Transverse	50%	Central fracture, usually 2 fragments	TBW or screws if displaced
Comminuted	30%	Multiple fragments, high-energy	Reconstruct if possible, partial patellectomy if not
Inferior pole	10%	Avulsion by patellar tendon	Excision + repair if small, ORIF if large
Superior pole	Rare	Avulsion by quads tendon	ORIF or excision + repair
Vertical/Sagittal	5%	Sagittal plane, often undisplaced	Usually stable, conservative
Osteochondral	Rare	With patellar dislocation	Fragment removal or fixation

Clinical Assessment

History

Mechanism: Direct blow, fall, dashboard
Ability to walk after injury
Knee swelling - hemarthrosis if intra-articular
Previous knee surgery or patella problems
Occupation/sport - return to activity considerations

Key Examination

Palpable gap at patella (indicates displacement)
Hemarthrosis - tense effusion
ACTIVE EXTENSION - straight leg raise (critical!)
Retinacular integrity (can extend despite fracture?)
Skin condition - may be open fracture

Test Active Extension FIRST!

Active straight leg raise is the KEY clinical test. Perform BEFORE giving analgesia - pain inhibits accurate assessment. Failed SLR = disrupted extensor mechanism = operative indication regardless of displacement.

False Negative SLR

Some patients with patella fractures can still extend the knee via intact retinaculae (medial and lateral expansions). This doesn't mean the fracture is stable - X-ray and examination of gap still determine treatment.

Investigations

Imaging Protocol

First LineAP and Lateral X-rays

Lateral view is most important - shows displacement, gap, step-off. AP shows transverse vs vertical pattern. Get knee fully extended for accurate assessment.

AdditionalSkyline/Merchant View

Shows patellofemoral joint articular surface. Helps assess vertical fractures and chondral injury. May be difficult acutely due to pain.

If UncertainCT Scan

For comminuted fractures to plan reconstruction. Assess posterior cortex integrity. 3D reconstructions helpful for operative planning.

Key X-ray Findings

Lateral View

Measure displacement (gap between fragments)
Articular step-off at patellofemoral joint
Over 2-3mm separation = surgical indication
May see hemarthrosis (joint effusion)

AP View

Fracture pattern (transverse, vertical, comminuted)
Width of patella
Bipartite patella (DDx - typically superolateral)
Osteochondral fragments if dislocated

Bipartite Patella

Bipartite patella is present in 1-2% of population, usually superolateral fragment. Differentiate from fracture by: rounded margins, no hemarthrosis, bilateral comparison (often bilateral). Occasionally symptomatic without trauma.

Radiographic Examples

Management Algorithm

Operative vs Non-Operative Decision

Operative indications: (1) Displacement over 2-3mm, (2) Articular step over 2mm, (3) Lost active extension. Non-operative only if: non-displaced (under 2mm), intact active extension, and patient compliant.

Conservative Management

Non-Operative Protocol

ImmobilizationWeek 0-2

Cylinder cast or hinged knee brace locked in extension. Weight bearing as tolerated with brace.

X-ray CheckWeek 2

Repeat X-ray to confirm no displacement. If displaced now, conversion to surgery.

Progressive MotionWeek 2-6

If stable at 2 weeks, begin ROM exercises. Unlock brace gradually. Continue cylinder for walking.

StrengtheningWeek 6+

Discard brace if X-ray shows healing. Quadriceps strengthening. Return to activity by 3 months.

Non-Operative Criteria

Non-operative management requires: Displacement under 2mm, articular step under 2mm, intact active extension, and reliable patient for weekly X-rays initially (secondary displacement occurs).

Surgical Technique

Modified Tension Band Wiring

Lateral knee radiograph showing patella fracture tension band wiring — Lateral radiograph demonstrating patella fracture fixation with modified tension band wiring technique. Note the two parallel K-wires with cerclage wire in figure-of-eight configuration anterior to the fracture, providing dynamic compression during knee flexion.Credit: PMC - CC BY 4.0

AP knee radiograph showing patella fracture tension band wiring — AP radiograph demonstrating patella fracture fixation with tension band wiring. The parallel K-wires traverse from inferior to superior pole, with the cerclage wire passed through bone tunnels creating the figure-of-eight tension band construct.Credit: PMC - CC BY 4.0

Patient Positioning:

Supine on radiolucent table
Knee flexed over bolster or triangle
Ensure full fluoroscopy access

Approach:

Longitudinal midline incision
Preserve prepatellar bursa if possible
Evacuate hematoma and debris
Inspect articular surface

Reduction:

Reduce fracture with pointed reduction clamps
Assess articular congruity with palpation and fluoro
Accept no more than 2mm step-off

K-Wire Placement:

Two parallel 1.6-2.0mm K-wires
Enter through superior pole, exit inferior pole
Avoid articular penetration
Wires parallel and medial-lateral to avoid impingement

Figure-of-Eight Wire:

18-gauge cerclage wire
Pass through anterior cortex (not intramedullary)
Figure-of-eight configuration around K-wire ends
Twist anteriorly to compress fracture
Bend K-wires and bury into bone

Proper technique ensures compression during knee flexion.

Complications

Complication	Incidence	Risk Factors	Management
Hardware irritation/removal	Up to 50%	TBW, thin soft tissue	Planned second surgery counseling
Stiffness	10-20%	Prolonged immobilization, poor rehab	Early ROM, aggressive physio
Patellofemoral OA	40-50% long-term	Articular damage, malreduction	Activity modification, ?later arthroplasty
Non-union	2-5%	Poor fixation, comminution, infection	Revision fixation or partial patellectomy
Loss of reduction	5-10%	Poor fixation technique, early loading	Revision ORIF
Extensor lag	5-10%	Lengthening of mechanism	Quadriceps strengthening, rarely requires revision
Infection	1-2%	Open fracture, multiple surgeries	Washout, antibiotics, hardware removal if needed

Hardware Removal Rate

50% of patients undergoing TBW require hardware removal (mainly K-wire prominence). Counsel patients preoperatively about likely second surgery. Screw fixation may have lower removal rate.

Postoperative Care and Rehabilitation

Post-ORIF Rehabilitation

Early MotionWeek 0-2

Hinged knee brace. Immediate ROM exercises (tension band allows motion). Brace locked for walking. Heel slides, SLR with brace.

Progressive MotionWeek 2-6

Increase ROM goal to 90° by week 4. Weight bearing as tolerated in brace. Pool therapy if available.

StrengtheningWeek 6-12

Discard brace as strength improves. Quadriceps strengthening progresses. Stationary biking.

Return to ActivityMonth 3-6

Return to normal activity if X-ray shows union. Running at 3-4 months. Sport-specific by 4-6 months.

Why Early Motion?

Tension band fixation is designed for early active motion. Knee flexion creates compression at articular surface, promoting healing. Prolonged immobilization leads to stiffness and poor outcomes.

Outcomes and Prognosis

Functional Outcomes

Outcomes by Pattern and Treatment

Pattern/Treatment	Union Rate	Good Function	Key Issues
Transverse + TBW	95-98%	85-90%	Hardware removal common (50%)
Transverse + screws	95-98%	85-90%	Lower removal rate (10%)
Comminuted + ORIF	85-95%	70-80%	Depends on articular restoration
Partial patellectomy	N/A	70-80%	Up to 30% excision well tolerated
Non-operative (stable)	95%+	85-90%	For undisplaced, intact mechanism

Prognostic Factors

Favorable Factors

Simple transverse pattern, Minimal articular comminution, Anatomic reduction achieved, Early ROM rehabilitation, Compliant patient

Unfavorable Factors

Comminuted pattern, Significant articular damage, Malreduction (over 2mm step-off), Prolonged immobilization, Open fracture or infection

Long-term Outcomes

Most patients achieve satisfactory outcomes with proper treatment. The main long-term issue is patellofemoral osteoarthritis, which develops in 40-50% of patients by 10-20 years. Hardware irritation requiring removal is the most common early complication with TBW. Extensor mechanism function is generally well preserved with modern fixation techniques. Total knee arthroplasty may eventually be required for severe post-traumatic arthritis.

Evidence Base and Key Trials

TBW vs Cannulated Screws - Meta-Analysis

Dy CJ et al. • J Knee Surg (2012)

Key Findings:

Meta-analysis comparing TBW and screw fixation
Similar union rates and functional outcomes
TBW higher hardware removal rate (50% vs 10%)
Screws lower profile preferred by patients

Clinical Implication: Cannulated screws have lower hardware complications. Consider for simple transverse fractures with good bone quality.

Limitation: Heterogeneous studies, variable techniques.

Partial Patellectomy Outcomes

Marder RA et al. • Clin Orthop Relat Res (1993)

Key Findings:

Retrospective review of partial patellectomy
Excision up to 30% gives good functional results
Quadriceps strength preserved if under 50%
Total patellectomy has poor outcomes

Clinical Implication: Partial patellectomy with tendon repair is preferable to total excision for non-reconstructable polar fractures.

Limitation: Older study, retrospective.

Locking Plates for Patella

Thelen S et al. • J Orthop Trauma (2013)

Key Findings:

Prospective study of mesh/basket locking plates
Useful for comminuted fractures
Lower hardware removal than TBW in comminuted
Maintains fragments in position

Clinical Implication: Consider locking mesh plates for comminuted fractures where TBW alone is insufficient.

Limitation: Small numbers, newer technique.

Operative vs Non-Operative Thresholds

Carpenter JE et al. • J Orthop Trauma (1997)

Key Findings:

2-3mm displacement used as threshold
Articular step over 2mm affects outcomes
Intact active extension alone not sufficient criterion
Serial X-rays needed for non-operative

Clinical Implication: Use 2-3mm displacement and 2mm step as operative thresholds. Monitor non-operative closely for secondary displacement.

Limitation: Consensus-based thresholds, limited RCT evidence.

Cable Pin System

Yang KH et al. • Clin Orthop Relat Res (2003)

Key Findings:

Alternative to TBW with lower profile
Cable through bone tunnels and around pins
Lower irritation rate than K-wires
Biomechanically similar

Clinical Implication: Cable systems may reduce hardware irritation compared to traditional TBW with K-wires.

Limitation: Equipment availability varies.

Exam Viva Scenarios

Practice these scenarios to excel in your viva examination

VIVA SCENARIOStandard

Scenario 1: Displaced Transverse Patella Fracture

EXAMINER

"A 35-year-old man falls off a ladder onto his knee. He cannot straighten his leg. X-ray shows a transverse patella fracture with 5mm of displacement. He is otherwise healthy. What is your management?"

EXCEPTIONAL ANSWER

This is a displaced transverse patella fracture in a young healthy man - a clear operative indication. My assessment confirms: First, he cannot actively extend the knee, indicating **extensor mechanism disruption**. Second, 5mm displacement exceeds the 2-3mm threshold for surgery. Third, he is young with good bone quality and high functional demands. For surgical management, I would perform **ORIF within 1-2 weeks**. My preferred technique for this simple transverse pattern would be either **cannulated screw fixation** or **tension band wiring**. For cannulated screws: two 4.0mm parallel lag screws from inferior to superior pole, which provides good compression and has lower hardware prominence. I may add a cerclage wire through the screw heads if I want additional tension band effect. Alternatively, classic TBW with two parallel K-wires and figure-8 cerclage wire remains reliable. The key principle is the **tension band** - the wire/construct must be anterior to the fracture axis so that knee flexion compresses the articular surface. Post-operatively, I would allow **early ROM** from day one as the tension band construct allows motion. He would be in a hinged brace, weight bearing as tolerated, and progress to full motion by 6 weeks.

KEY POINTS TO SCORE

5mm displacement + lost extension = clear surgical indication

Tension band principle: anterior wire converts tension to compression

Options: cannulated screws (lower profile) or TBW (reliable, versatile)

Early ROM is key - tension band construct allows motion

Counsel about 50% hardware removal rate if using TBW

COMMON TRAPS

✗Attempting non-operative with 5mm displacement - will fail

✗Not explaining tension band principle

✗Forgetting to counsel about hardware removal

✗Prolonged immobilization post-op - leads to stiffness

LIKELY FOLLOW-UPS

"How would you modify your technique if this were a 75-year-old with osteoporosis?"

"What if the fracture was comminuted?"

"Describe the steps of TBW technique"

VIVA SCENARIOChallenging

Scenario 2: Comminuted Inferior Pole Fracture

EXAMINER

"A 50-year-old woman trips and falls onto her knee. X-ray shows a comminuted inferior pole patella fracture with multiple small fragments (largest 1cm). She cannot actively extend. CT confirms 4 small fragments making up the inferior 25% of the patella. How would you manage this?"

EXCEPTIONAL ANSWER

This is a comminuted inferior pole patella fracture involving approximately 25% of the patella - the fragments are too small to reconstruct with standard techniques. My management would be: First, confirm the clinical assessment - she cannot actively extend, confirming extensor mechanism disruption requiring surgery. Second, review the CT carefully - are any fragments large enough to fix? With 4 small fragments and the largest being 1cm, reconstruction would be challenging and unlikely to hold. Third, my recommended treatment is **partial inferior patellectomy with patellar tendon repair**. The technique involves: excising the comminuted fragments, creating a flat bone surface on the remaining patella, drilling two or three transosseous tunnels, and passing heavy non-absorbable sutures (e.g., FiberWire or Ethibond) through the patellar tendon and through the tunnels. I would tension the repair with the knee at 30 degrees flexion and match patellar height to the contralateral side using intraoperative fluoroscopy. Evidence shows that excision of up to **30% of the patella** gives satisfactory functional outcomes, and since she has 25% involvement, this is within acceptable limits. Post-operatively, she would be protected in a hinged brace, with ROM beginning at 2-3 weeks, but avoiding resisted extension for 6 weeks to protect the repair.

KEY POINTS TO SCORE

Small comminuted fragments cannot be reconstructed reliably

Partial patellectomy with tendon repair indicated

Up to 30% inferior pole excision has good outcomes

Transosseous suture technique for tendon to bone

Protect repair from resisted extension for 6 weeks

COMMON TRAPS

✗Attempting to fix tiny fragments with multiple screws - will fail

✗Total patellectomy - unnecessary and poor functional outcome

✗Not tensioning repair appropriately - leads to patella alta

✗Early resisted extension - risks re-rupture

LIKELY FOLLOW-UPS

"What if the comminution involved 50% of the patella?"

"How do you prevent patella alta after this procedure?"

"What is the long-term prognosis after partial patellectomy?"

VIVA SCENARIOCritical

Scenario 3: Non-Displaced Patella Fracture

EXAMINER

"A 65-year-old diabetic woman presents after tripping on a rug. She has painful knee swelling but can actively extend her knee (demonstrated straight leg raise in ED before analgesia was given). X-ray shows a transverse patella fracture with approximately 1-2mm of displacement. How would you manage this?"

EXCEPTIONAL ANSWER

This is a minimally displaced transverse patella fracture with intact active extension - a patient who may be suitable for non-operative management, but requires careful consideration. Key factors in my decision: First, she demonstrated active straight leg raise before analgesia, confirming the **retinaculae are intact** and she has functional extension. Second, the displacement is borderline (1-2mm) - at the threshold. Third, she is 65 with diabetes, which increases surgical and healing risks. My management would lean toward **non-operative treatment** given: borderline displacement, intact extension, comorbidities. The protocol would be: (1) Cylinder cast or hinged brace locked in extension for 4-6 weeks. (2) **Serial X-rays weekly for first 2 weeks** - critical to detect secondary displacement which occurs in up to 10-20%. (3) Weight bearing as tolerated in brace. (4) If any increased displacement or loss of extension, convert to surgery. If she remains stable at 2 weeks, begin ROM exercises in the brace. I would emphasize patient education - she must understand that secondary displacement means surgery. I would also monitor her diabetes closely as it affects wound healing if surgery becomes necessary.

KEY POINTS TO SCORE

1-2mm displacement with intact extension = consider non-operative

Intact SLR indicates functional retinaculae

Serial X-rays essential - secondary displacement occurs

Low threshold to convert to surgery if displacement increases

Patient selection: compliant patient, able to follow protocol

COMMON TRAPS

✗Automatic surgery for all patella fractures

✗Non-operative without close monitoring (missing displacement)

✗Not checking X-rays at 1-2 weeks

✗Not discussing surgical backup if displacement occurs

LIKELY FOLLOW-UPS

"At 1 week follow-up, X-ray shows the gap has increased to 4mm. What now?"

"What are the risks of non-operative treatment?"

"How long does patella fracture take to heal?"

MCQ Practice Points

Anatomy Question

Q: By how much does the patella increase the extensor mechanism moment arm? A: 30-50%. The patella acts as a lever (sesamoid) that increases the quadriceps moment arm, improving efficiency. Patellectomy significantly weakens extension.

Operative Threshold Question

Q: What displacement threshold indicates need for surgical fixation of patella fractures? A: Greater than 2-3mm fracture displacement or greater than 2mm articular step. Loss of active extension is also an absolute indication regardless of displacement.

Fixation Question

Q: What is the principle behind tension band wiring? A: The wire is placed on the tension side (anterior) of the patella. During knee flexion, the tensile forces are converted to compressive forces at the articular surface, promoting healing.

Complication Question

Q: What percentage of patients require hardware removal after TBW? A: Up to 50%. This is mainly due to K-wire prominence causing anterior knee pain. Cannulated screw fixation has lower removal rates due to lower profile.

Partial Patellectomy Question

Q: What percentage of the patella can be safely excised without significant functional loss? A: Up to 30% of the inferior pole. Beyond 50% excision, extensor strength is significantly compromised. Total patellectomy results in 30% strength loss.

Pattern Question

Q: What is the most common patella fracture pattern? A: Transverse fracture (50%). This is followed by comminuted (30%), polar fractures (10-15%), and vertical (5%). Transverse fractures are typically fixed with TBW or screws.

Australian Context

Epidemiology

Common in falls (elderly) and MVA (young)
Work-related injuries - WorkCover implications
Sports injuries (AFL, rugby) in athletes
Increasing cycling-related injuries

Healthcare Funding

Public waiting lists for hardware removal
Private insurance covers most procedures

Medicolegal Considerations

Key documentation: (1) Active extension tested BEFORE analgesia given, (2) Displacement measurements from good-quality lateral X-ray, (3) Informed consent including hardware removal discussion (particularly for TBW), (4) Serial X-ray protocol for non-operative management. Missed secondary displacement in non-operative cases is a potential litigation risk.

PATELLA FRACTURES

High-Yield Exam Summary

Key Anatomy

•Largest sesamoid bone
•Increases extensor moment arm by 30-50%
•Blood supply: genicular arteries, anterior
•Thickest articular cartilage (5-7mm)

Operative Indications (GAPS)

•Gap over 2-3mm displacement
•Active extension lost (failed SLR)
•Patellofemoral step over 2mm
•Surgery for any of the above

Tension Band Principle

•Wire placed ANTERIOR to fracture
•Converts tensile to compressive force
•Allows early ROM (motion = compression)
•Only works if posterior cortex intact

Fixation Options

•TBW: K-wires + figure-8 wire (classic)
•Cannulated screws: lower profile, less removal
•Basket plates: for comminuted fractures
•Partial patellectomy: non-reconstructable poles

Complications

•Hardware removal: 50% for TBW
•Patellofemoral OA: 40-50% long-term
•Stiffness: if immobilized too long
•Extensor lag: if lengthened mechanism

Important Numbers

•2-3mm: displacement threshold for surgery
•2mm: step-off threshold for surgery
•30%: pole excision acceptable
•50%: hardware removal rate TBW

Fracture Pattern

Key Assessment

Treatment

Pearl

Non-displaced (under 2mm), intact extension

Can actively extend

Cylinder cast/brace 4-6 weeks

Weekly X-rays first 2 weeks

Displaced transverse (over 2mm)

Gap or step-off visible

ORIF - TBW or cannulated screws

Tension band principle applies

Comminuted reconstructable

Major fragments identifiable

ORIF with multiple techniques

Cerclage + TBW or basket plate

Comminuted non-reconstructable

Multiple small fragments

Partial patellectomy + repair

Preserve as much as possible

Inferior pole fracture

Small pole, intact mechanism

Excision + tendon repair

Under 30% pole excised OK

Pattern

Frequency

Characteristics

Treatment

Transverse

50%

Central fracture, usually 2 fragments

TBW or screws if displaced

Comminuted

30%

Multiple fragments, high-energy

Reconstruct if possible, partial patellectomy if not

Inferior pole

10%

Avulsion by patellar tendon

Excision + repair if small, ORIF if large

Superior pole

Rare

Avulsion by quads tendon

ORIF or excision + repair

Vertical/Sagittal

Sagittal plane, often undisplaced

Usually stable, conservative

Osteochondral

Rare

With patellar dislocation

Fragment removal or fixation

Operative vs Non-Operative Decision

Conservative Management

Non-Operative Protocol

ImmobilizationWeek 0-2

Cylinder cast or hinged knee brace locked in extension. Weight bearing as tolerated with brace.

X-ray CheckWeek 2

Repeat X-ray to confirm no displacement. If displaced now, conversion to surgery.

Progressive MotionWeek 2-6

If stable at 2 weeks, begin ROM exercises. Unlock brace gradually. Continue cylinder for walking.

StrengtheningWeek 6+

Discard brace if X-ray shows healing. Quadriceps strengthening. Return to activity by 3 months.

Non-Operative Criteria

Complication

Incidence

Risk Factors

Management

Hardware irritation/removal

Up to 50%

TBW, thin soft tissue

Planned second surgery counseling

Stiffness

10-20%

Prolonged immobilization, poor rehab

Early ROM, aggressive physio

Patellofemoral OA

40-50% long-term

Articular damage, malreduction

Activity modification, ?later arthroplasty

Non-union

2-5%

Poor fixation, comminution, infection

Revision fixation or partial patellectomy

Loss of reduction

5-10%

Poor fixation technique, early loading

Revision ORIF

Extensor lag

5-10%

Lengthening of mechanism

Quadriceps strengthening, rarely requires revision

Infection

1-2%

Open fracture, multiple surgeries

Washout, antibiotics, hardware removal if needed

Pattern/Treatment

Union Rate

Good Function

Key Issues

Transverse + TBW

95-98%

85-90%

Hardware removal common (50%)

Transverse + screws

95-98%

85-90%

Lower removal rate (10%)

Comminuted + ORIF

85-95%

70-80%

Depends on articular restoration

Partial patellectomy

N/A

70-80%

Up to 30% excision well tolerated

Non-operative (stable)

95%+

85-90%

For undisplaced, intact mechanism

Function	Mechanism	Clinical Relevance
Increase lever arm	Moves extensor axis anterior	30-50% increase in extensor moment
Distribute forces	Increases contact area	Reduces patellofemoral stress
Protect femoral condyles	Covers trochlea	Prevents direct trauma
Provide smooth gliding	Articular cartilage (thickest in body)	5-7mm cartilage at center

Principle Element	Mechanism	Clinical Application
Wire placement	Anterior to fracture axis	Figure-8 wire in front of K-wires
Force conversion	Tensile becomes compressive	Articular surface compressed with flexion
Dynamic compression	Motion increases compression	Early ROM encouraged
Prerequisites	Intact cortex on compression side	Only works if articular cortex intact

Type	Description	Subtype Examples
34-A	Extra-articular	A1: Avulsion, A2: Transverse extra-articular
34-B	Partial articular	B1: Vertical, B2: Transverse marginal
34-C	Complete articular	C1: Transverse, C2: Transverse + 2nd fragment, C3: Comminuted

Indication	Reason
Comminuted fracture	Plan reconstruction vs partial patellectomy
Articular depression	Assess step-off better than X-ray
Pre-op planning	Fragment size, number, position
Associated tibial plateau injury	High-energy mechanism

Factor	TBW	Cannulated Screws
Hardware prominence	High (50% removal)	Low (lower removal rate)
Construct strength	Strong in tension	Strong if good bone
Comminution	Better for multiple fragments	Less suitable for comminuted
Bone quality	Less dependent	Needs adequate bone for screw purchase
Technical ease	Familiar technique	Requires cannulated system

Patella Fractures

Patella Fractures

PATELLA FRACTURES - EXTENSOR MECHANISM

FRACTURE PATTERNS

Critical Must-Knows

Examiner's Pearls

Clinical Imaging

Imaging Gallery

Critical Patella Fracture Exam Points

Test Active Extension!

Operative Indications

Tension Band Principle

Hardware Problems

Quick Decision Guide

GAPSOperative Indications

COMPRESSTension Band Principle

LEVERPatella Function

WIREDTBW Construct

Overview and Epidemiology

Demographics

Mechanism

Anatomy and Biomechanics

Key Anatomical Concept

Patella Anatomy

Bony Structure

Soft Tissue

Biomechanical Function

Patellectomy Consequences

The Tension Band Principle

Classification Systems

Fracture Pattern Classification

AO/OTA Classification

Clinical Assessment

History

Key Examination

Test Active Extension FIRST!

Investigations

Imaging Protocol

Key X-ray Findings

Lateral View

AP View

When to Order CT

Radiographic Examples

Management Algorithm

Operative vs Non-Operative Decision

Conservative Management

Non-Operative Protocol

Tension Band Wiring (TBW)

TBW Technique

TBW Technical Pearls

TBW Pitfalls

Cannulated Screw Fixation

Screw Technique

Partial Patellectomy

Indications for Partial Patellectomy

Partial Patellectomy Technique

Surgical Technique

Modified Tension Band Wiring

Cannulated Screw Technique

Managing Comminuted Fractures

Complications

Hardware Removal Rate

Postoperative Care and Rehabilitation

Post-ORIF Rehabilitation

Outcomes and Prognosis

Functional Outcomes

Outcomes by Pattern and Treatment

Prognostic Factors

Favorable Factors

Unfavorable Factors

Long-term Outcomes

Evidence Base and Key Trials

TBW vs Cannulated Screws - Meta-Analysis

Partial Patellectomy Outcomes

Locking Plates for Patella

Operative vs Non-Operative Thresholds

Cable Pin System

Exam Viva Scenarios

Scenario 1: Displaced Transverse Patella Fracture

Scenario 2: Comminuted Inferior Pole Fracture