orthopaedics and trauma

1. Injuries to the Patella and
Extensor Mechanism
Charles G. Haddad, Jr., MD
Lisa K. Cannada, MD
Emory University
Robert Cantu, MD

2. Anatomy
• Largest sesamoid bone
• Thick articular
cartilage proximally
• Articular surface
divided into medial
and lateral facets by
longitudinal ridge
• Distal pole
nonarticular

3. Anatomy
• Patellar Retinaculum
– Longitudinal tendinous
fibers
– Patellofemoral
ligaments
• Blood Supply
– Primarily derived from
geniculate arteries

4. 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

5. 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

6. 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

7. History
• Fall from height
• Direct blow to the
anterior knee
(dashboard injury)
• Rapid knee flexion
with quadriceps
resistance

8. 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

9. Radiographic Evaluation
• AP, Lateral, and
Tangential
– Note fracture pattern
• Articular step-off,
diastasis
– Patella alta or baja
• CT Scan
– Occult fractures

10. Radiographic Evaluation
• Bipartite Patella
– Obtain bilateral views
– Often involves
superolateral corner
– Accessory ossification
center

11. 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

12. Classification
• Allows prediction of
treatment
• Types
– Transverse
– Marginal
– Vertical
– Comminuted
– Osteochondral

13. Transverse Fractures
• 35% are
nondisplaced*
• If nondisplaced then
medial and lateral
retinaculum usually
intact
*Bostrom Acta Orthop Scand Suppl 1972

14. 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

15. Stellate Fractures
• Result from direct
blow
• 65% of stellate
fractures are displaced
• May have associated
articular damage to
femoral condyles

16. 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

17. 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

18. 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!

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

20. 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

21. 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

22. 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

23. 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

24. Operative Treatment of Patella
Fractures
• Stellate pattern may be
fixed with cerclage
wiring

25. 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

26. 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

27. 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

28. 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!

29. 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

30. 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

31. 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%

32. 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

33. Quadriceps Tendon Rupture
• Risk Factors
– Chronic tendonitis
– Anabolic steroid use
– Local steroid injection
– Diabetes mellitus
– Inflammatory
arthropathy
– Chronic renal failure

34. History
• Sensation of a sudden pop while stressing
the extensor mechanism
• Pain at the site of injury
• Inability/difficulty weightbearing

35. Physical Exam
• Effusion
• Tenderness at the
upper pole
• Palpable defect above
superior pole
• Loss of extension
• With partial tears,
extension will be
intact

36. 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

37. 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

38. 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

39. 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

40. 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

41. 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)

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

43. 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

44. Complications
• Rerupture
• Persistent quadriceps
atrophy/weakness
• Loss of motion
• Infection

45. 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

46. Patellar Tendon Rupture
• Risk Factors
– Rheumatoid
– Systemic Lupus
Erythematosus
– Diabetes
– Chronic Renal Failure
– Systemic Corticosteroid
Therapy
– Local Steroid Injection
– Chronic patellar tendonitis

47. 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

48. 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

49. 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

50. History
• Often a report of
forceful quadriceps
contraction against a
flexed knee
• May experience and
audible “pop”
• Inability to weightbear
or extend the knee

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

52. 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

53. 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

54. Treatment
• Surgical treatment is
required for
restoration of the
extensor mechanism
• Repairs categorized as
early or delayed

55. 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

56. 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

57. 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

58. 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

59. 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

60. 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

61. 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

62. 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

63. 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

64. Complications
• Knee stiffness
• Persistent quadriceps weakness
• Rerupture
• Infection
• Patella baja
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