Injuries to the Patella and Extensor Mechanism

Charles G. Haddad, Jr., MDLisa K. Cannada, MD

Emory University

Robert Cantu, MD

Anatomy

• Largest sesamoid bone• Thick articular

cartilage proximally• Articular surface

divided into medial and lateral facets by longitudinal ridge

• Distal pole nonarticular

Anatomy

• Patellar Retinaculum– Longitudinal tendinous

fibers– Patellofemoral

ligaments• Blood Supply

– Primarily derived from geniculate arteries

Biomechanics

• The patella undergoes approximately 7 cm of translation from full flexion to extension

• Only 13-38% of the patellar surface is in contact with the femur throughout its range of motion

Biomechanics

• The patella increases the moment arm about the knee– Contributes up to 30%

increase in force with extension

• Patella withstands compressive forces greater than 7X body weight with squatting

Biomechanics

• Twice as much torque is needed to extend the knee the final 15 degrees than to extend from a fully flexed position to 15 degrees of flexion

History

• Fall from height• Direct blow to the

anterior knee (dashboard injury)

• Rapid knee flexion with quadriceps resistance

Physical Examination

• Pain, swelling, contusions, lacerations and/or abrasions at the site of injury

• Palpable defect• Assessment of ability to extend the knee

against gravity or maintain the knee in full extension against gravity

Radiographic Evaluation

• AP, Lateral, and Tangential – Note fracture pattern

• Articular step-off, diastasis

– Patella alta or baja• CT Scan

– Occult fractures

Radiographic Evaluation

• Bipartite Patella– Obtain bilateral views– Often involves

superolateral corner– Accessory ossification

center

Etiology• Allows prediction of outcome• Direct trauma

– Dashboard injury– Increasing cases with penetrating

trauma– Often with comminution and

articular damage• Indirect trauma

– Violent flexion directed through the extensor mechanism against a contracted quadriceps

– Results in simple, transverse fractures

Classification

• Allows prediction of treatment

• Types – Transverse– Marginal – Vertical– Comminuted– Osteochondral

Transverse Fractures

• 35% are nondisplaced*

• If nondisplaced then medial and lateral retinaculum usually intact

*Bostrom Acta Orthop Scand Suppl 1972

Vertical Fractures

• Account for 22% of patella fractures*

• Typically results from compression of patella with flexed knee

• Sometimes only seen on sunrise view

*Browner et al. Skeletal Trauma 2nd Ed

Stellate Fractures

• Result from direct blow

• 65% of stellate fractures are displaced

• May have associated articular damage to femoral condyles

Nonoperative Treatment

• Indicated for nondisplaced fractures– <2mm of articular stepoff and <3mm of

diastasis with an intact extensor mechanism• May also be considered for minimally

displaced fractures in the elderly • Patients with a extensive medical

comorbidities

Nonoperative Treatment

• Long leg cylinder cast for 4-6 weeks– May consider a knee immobilizer for the

elderly• Immediate weightbearing as tolerated• Rehabilitation includes range of motion

exercises with gradual quadriceps strengthening

Operative Treatment• Goals

– Preserve extensor function– Restore articular congruency

• Preoperative Setup– Tourniquet

• Prior to inflation, gently flex the knee

• Approach– Longitudinal midline incision

recommended– Transverse approach

alternative– Consider future surgeries!

Techniques

• Modified tension band wiring• Lag-screw fixation• Cerclage• Cannulated lag-screw with tension band• Partial patellectomy• Patellectomy

Modified Tension Band Wiring

• Transverse, noncomminuted fractures

• After reduction, fracture is fixed with two parallel, 2mm Kirschner wires placed perpendicular to the fracture

• 18 gauge wire passed behind proximally and distally

Modified Tension Band Wiring

• Wire converts anterior distractive forces to compressive forces at the articular surface

• Two twists are placed on opposite sides of the wire– Tighten simultaneously to

achieve symmetric tension

• Repair any retinacular tears

Lag-Screw Fixation

• Indicated for stabilization of comminuted fragments in conjunction with tension band wiring

• May also be used as an alternative to tension band wiring for transverse or vertical fractures

Lag-Screw Fixation

• Contraindicated for extensive comminution and osteopenic bone

• Small secondary fractures may be stabilized with 2.7mm or 3.5mm cortical screws

• Transverse or vertical fractures require 3.5mm or 4.5mm cortical screws– Retrograde insertion of screws may be

technically easier

Operative Treatment of Patella Fractures

• Stellate pattern may be fixed with cerclage wiring

Cannulated Lag-Screw with Tension Band

• Fully threaded screws placed with a lag technique

• Wire through screws and across anterior patella in figure of eight tension band

Cannulated Lag-Screw with Tension Band

• Most stable construct – Screws and tension band wire combination

eliminates both possible separation seen at the fracture site with modified tension band and screw failure due to excessive three point bending

Partial Patellectomy

• Indicated for fractures involving extensive comminution not amenable to fixation

• Larger fragments repaired with screws to preserve maximum cartilage

• Smaller fragments excised– Usually involving the distal

pole

Partial Patellectomy

• Tendon is attached to fragment with nonabsorbable suture passed through drill holes in the fragment– Drill holes should be near the articular surface to

prevent tilting of the tendon and minimize articular step-off

• Load sharing wire passed through drill holes in the tibial tubercle and patella may be used to protect the repair and facilitate early range of motion

• Watch for patellar tilt!

Total Patellectomy

• Indicated for displaced, comminuted fractures not amenable to reconstruction

• Bone fragments sharply dissected• Defect may be repaired through a variety of

techniques• Usually results in extensor lag and loss of

strength

Postoperative Management

• Immobilization with knee brace• Immediate WBAT• Early range of motion

– Based on intraoperative assessment of repair– Active flexion with passive extension

• Quadriceps strengthening– Begun when there is radiographic evidence of

healing, usually around 6 weeks

Complications

• Knee Stiffness– Most common

complication • Infection

– Rare, depends on soft tissue compromise

• Loss of Fixation– Hardware failure in up

to 20% of cases

• Osteoarthritis– May result from

articular damage or incongruity

• Nonunion < 1% with surgical repair

• Painful hardware– Removal required in

approximately 15%

Quadriceps Tendon Rupture

• Typically occurs in patients > 40 years old• Usually 0-2 cm above the superior pole• Level often associated with age

– Rupture occurs at the bone-tendon junction in majority of patients > 40 years old

– Rupture occurs at midsubstance in majority of patients < 40 years old

Quadriceps Tendon Rupture

• Risk Factors– Chronic tendonitis – Anabolic steroid use– Local steroid injection– Diabetes mellitus– Inflammatory

arthropathy– Chronic renal failure

History

• Sensation of a sudden pop while stressing the extensor mechanism

• Pain at the site of injury• Inability/difficulty weightbearing

Physical Exam

• Effusion • Tenderness at the

upper pole• Palpable defect above

superior pole• Loss of extension• With partial tears,

extension will be intact

Physical Exam Quadriceps Tendon Rupture

• Palpable defect proximal to superior pole of patella

• If defect present but patient able to extend the knee then the extensor retinaculum is intact

• If no active extension, then both tendon and retinaculum completely torn

Quadriceps Tendon Rupture

Radiographic Evaluation

• X-ray- AP, Lateral, and Tangential (Sunrise, Merchant)– Distal displacement of

the patella• MRI

– Useful when diagnosis is unclear

Treatment• Nonoperative

– Partial tears and strains• Operative

– For complete ruptures

Blumensaat’s Line• Based on lateral x-ray with

knee in 30 degrees of flexion

• Lower pole of patella should be at level of line projected anteriorly from intercondylar notch (Blumensaat’s line)

• Patella alta may be seen with patellar tendon rupture and patella baja with quadriceps tendon rupture

Nonoperative Treatment Quadriceps Tendon Rupture

• Reserved for incomplete tears in which active, full knee extension is preserved

• Immobilize leg in extension for approximately 4-6 weeks

• Progressive physical therapy required to regain strength and motion

Operative Treatment

• Reapproximation of tendon to bone using nonabsorbable sutures– Locking stitch (Bunnel, Krakow) with No. 5

ethibond passed through transverse bone tunnels

– Repair tendon close to articular surface to avoid patellar tilting

Operative Treatment

• Midsubstance tears may undergo end-to-end repair after edges are freshened and slightly overlapped– May benefit from

reinforcement from distally based partial thickness quadriceps tendon turned down across the repair site (Scuderi Technique)

Treatment

• Chronic tears may require a V-Y advancement of a retracted quadriceps tendon (Codivilla V-Y-plasty Technique)

Postoperative Management

• Knee immobilizer or cylinder cast for 5-6 weeks

• Immediate vs. delayed (3 weeks) weightbearing as tolerated

• At 2-3 weeks, hinged knee brace starting with 45 degrees active range of motion with 10-15 degrees of progression each week

Complications

• Rerupture• Persistent quadriceps

atrophy/weakness• Loss of motion• Infection

Patellar Tendon Rupture

• Less common than quadriceps tendon rupture

• Most often occurs in patients < 40 years old• Associated with degenerative changes of

the tendon• Rupture often occurs at inferior pole

insertion site

Patellar Tendon Rupture

• Risk Factors– Rheumatoid– Systemic Lupus

Erythematosus– Diabetes– Chronic Renal Failure– Systemic Corticosteroid

Therapy– Local Steroid Injection – Chronic patellar tendonitis

Anatomy

• Patellar tendon– Averages 4 mm thick but widens to 5-6 mm at

the tibial tubercle insertion– Merges with the medial and lateral retinaculum– 90% type I collagen

Blood Supply

• Fat pad vessels supply posterior aspect of tendon via inferior medial and lateral geniculate arteries

• Retinacular vessels supply anterior portion of tendon via the inferior medial geniculate and recurrent tibial arteries

• Proximal and distal insertion areas are relatively avascular and subsequently are a common site of rupture

Biomechanics

• Greatest forces are at 60 degrees of flexion

• 3-4 times greater strain are at the insertions compared to the midsubstance prior to failure

• Forces through the patellar tendon are 3.2 times body weight while climbing stairs

History

• Often a report of forceful quadriceps contraction against a flexed knee

• May experience and audible “pop”

• Inability to weightbear or extend the knee

Physical Examination

• Palpable defect• Hemarthrosis • Painful passive knee flexion• Partial or complete loss of active extension• Quadriceps atrophy with chronic injury

Radiographic Evaluation

• AP and Lateral X-ray– Patella alta seen on lateral view

• Patella superior to Blumensaat’s line

• Ultrasonagraphy– Effective means to determine continuity of tendon– Operator and reader dependant

• MRI– Effective means to assess patellar tendon, especially if

other intraarticular or soft tissue injuries are suspected– Relatively high cost

Classification

• No widely accepted means of classification• Can be categorized by:

– Location of tear• Proximal insertion most common

– Timing between injury and surgery• Most important factor for prognosis• Acute- within two weeks • Chronic- greater than two weeks

Treatment

• Surgical treatment is required for restoration of the extensor mechanism

• Repairs categorized as early or delayed

Nonoperative Treatment of Patellar Tedon Rupture

• Nonoperative treatment reserved for partial tears in which patient able to fully extend knee

• Treatment is immobilization in full extension for 3-6 weeks

Early Repair

• Better overall outcome• Primary repair of the tendon• Surgical approach is through a midline incision

– Incise just lateral to tibial tubercle as skin thicker with better blood supply to decrease wound complications

• Patellar tendon rupture and retinacular tears are exposed

Early Repair• Frayed edges and

hematoma are debrided• With a Bunnell or Krakow

stitch, two ethibond sutures or their equivalent are used to repair the tendon to the patella

• Sutures passed through three parallel, longitudinal bone tunnels and tied proximally

• Repair retinacular tears

• May reinforce with wire, cable or umbilical tape

• Assess repair intraoperatively with flexion

Operative Treatment of Patellar Tendon Rupture

• For rupture at osteotendinous junction, tendon reattached to patella with heavy, nonabsorbable sutures passed through drill holes in patella

• Medial and lateral retinacula repaired with heavy absorbable suture

• Knee immobilized in extension for 6 weeks

Operative Treatment of Patellar Tendon Ruptures

• 18 gauge wire can be used to reinforce repair

• Repair should be tested with flexion of knee in OR and any loose sutures replaced

Postoperative Management

• Hinged knee brace locked at 20 degrees• Immediate isometric quadriceps exercises• Active flexion with passive extension at two

weeks; start with 0-45 degrees and advance 30 degrees each week

• Active extension at three weeks

Postoperative Management

• Initial toe-touch weightbearing is gradually advanced to full weightbearing by six weeks

• Maintain hinged knee brace which is gradually increased as motion increases

• All restrictions are lifted after full range of motion and 90% of the contralateral quadriceps strength are obtained; usually at 4-6 months

Delayed Repair

• > 6 weeks from initial injury• Often results in poorer outcome• Quadriceps contraction and patellar migration are

encountered• Adhesions between the patella and femur may be

present • Options include hamstring and fascia lata

autograft augmentation of primary repair or Achilles tendon allograft

Postoperative Management

• More conservative when compared to early repair

• Bivalved cylinder cast for 6 weeks; may start passive range of motion

• Active range of motion is started at 6 weeks

Complications

• Knee stiffness• Persistent quadriceps weakness• Rerupture• Infection • Patella baja

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