This document provides detailed information about the anatomy of the anterior cruciate ligament (ACL). It describes the ACL's embryology, histology, blood supply, nerve supply, measurements, biomechanics, and variations. It discusses ACL injuries and reconstruction procedures. Key points include that the ACL attaches to oval footprints on the femur and tibia, has a spiral arrangement that allows it to tuck under the intercondylar notch, and is most commonly reconstructed using a bone-patellar tendon-bone autograft.

1. Anterior cruciate
ligament injury
Dr.PONNILAVAN

2. ANATOMY

3. ANATOMY
• ACL is a band of dense connective tissue that connects the femur and
the tibia.
• Enveloped by the synovial membrane
• Intraarticular but extra-synovial

4. EMBRYOLOGY

5. HISTOLOGY
• Made of multiple collagen fiber
bundles
• Major cell type – fibroblast
• 65–75% of lig. Wt. composed of
water
• Type 1 collagen (80%)
• Type 3 collagen(<20%)

6. • The Chondral apophyseal enthesis is present in femoral & tibial
insertions
 Mostly elongated fibroblasts except in distal third of ACL
 Due to “physiological Impingement”– presence of Chondrocytes like cells is a
functional adaptation to the compressive stress
4 Layers:
1. Ligament fibres
2. Non-mineralised cartilage zone
3. Mineralised cartilage zone
4. Subchondral bone plate

7. BLOOD SUPPLY
• PROXIMALLY - middle
geniculate artery.
• DISTALLY - lat. and med. branch
of inferior geniculate artery
• Proximal and distal vessels
support a synovial plexus from
which small vessels runs parallel
into the collagen bundles.

8. ACL (measurements)
• Length 32mm (22-41mm)
• Width 10mm (7-12mm)
• Midsubstance cross- section “irregular,”
“oval,” “corded,” or “bundled”
• Midsubstance - diameter 36mm²(f) & 44mm²(m).
• Tibial and femoral insertion was > 3.5 times
larger than midsubstance

9. NERVE SUPPLY
Subsynovial layer and near ACL insertions
2 types of receptors- RUFFINI: STRETCH receptor.
• FREE NERVE ENDING : NOCICEPTOR
Electromyographic studies show receptors respond to knee extension
Nociceptor  Vasoactive neuropeptide– enhances graft healing
Positive correlation between the number of mechanoceptors and the accuracy of
joint position sense in the remaining ACL stump

10. • The axis of the long diameter of the ACL is tilted 26°+/- 6° forward from the
vertical
• lateral spiral arrangement. This external rotation is app. 90°
• Orientiation of attachments:
Femur- longitudinal axis
Tibia - Transverse axis
PHYSIOLOGICAL IMPINGEMENT:
The ACL tibial attachment fans out and forms a “foot” region.
This allows the ACL to tuck under the roof of the
intercondylar notch.
In full extension the anterior fibers of the ACL turn around the
anterior edge of the intercondylar notch
ACL graft (BPTB/Hamstring) do not posses
such “foot” region and orientiation
Notch impingement

11. • Intercondylar Notch
• Wide –posterior ; narrow – anterior
• Narrow in females
• Notch Width Index (NWI) – ratio of
epicondylar width to notch width
• “Gothic shape”-intercondylar fossa and
the roof is called Blumensaat line.
• Notch roof angle = 23 to 60 degrees
• Small roof angled knees called “Non
Forgiving Knees”- Tibial tunnel placement
is critical .

12. BUNDLE THEORIES OF ACL
• Differentiation into bundles is controversial.
• Odensten et al: histologically found no evidence of
separation
• Girgis et al: 2 bundles, (AM and PL)
• Amis et al: 3 bundles, (AM, intermediate and PL
bundle.
Amis AA, et al: Functional anatomy of the ACL.JBJS Br73:260-267, 1991
Odensten M,et al: Functional anatomy of the ACL and a rationale for reconstruction. JBJS 67A:257-262, 1985
Girgis FG, et al: The cruciate ligaments of the knee joint. Anatomical, functional and experimental analysis. Clin Orthop 106:216-231, 1975

13. R.Siebold et al., Anterior Cruciate Ligament
Reconstruction, ESSKA 2014
“double-bundle effect” was created by the twisted flat ribbonlike structure of the ACL from
femoral to tibial, which leads to the impression of two or three separate bundles when the knee was flexed.

14. MECHANICAL PROPERTIES OF ACL
• Tensile load : 2,160 N
• Stiffness : 242 N/mm
Forces in the intact ACL:
• 100 N during passive knee extension
• 400 N on walking
• ̰ 1,700 N with cutting and acceleration-
deceleration activities.

15. BIOMECHANICS
• Length and orientation changes throughout flexion and extension as well as tibial
internal and external rotation.

16. Variations in the length of ACL
Distances between origin and attachment of the ACL fibers vary with motion
Takai et al. - 3.3 mm
Hollis et al. - 3.9 mm
AM PL
1.5 mm
7.1 mm
On 90 deg flexiom
Hefzy and Grood et al.
 Fiber length is affected more by varying the femoral attachment.
 Moving the tibial location had only a small effect;

17. Functional rationale
• 1° restraint for ant.
Tibial translation
• 2° restraint to tibial
rotation on
wt.bearing knee or
valgus/varus stress

18. FEMORAL FOOTPRINT
• original studies: ACL attachment in narrow oval area in LFC
• Recent studies: described ACL attachment in wide area on
the LFC

19. FEMORAL FOOTPRINT
In the lower third of inner wall of LFC, Inferior to the lateral
intercondylar ridge.

20. SHAPES OF FEMORAL FOOT PRINT
A. CIRCULAR
B. ELLIPTICAL
C. KIDNEY- SHAPE
D. SEGMENT OF CIRCLE
E. SEGMENT OF
ELLIPSE
F. TRAPEZOIDAL
G. OVAL
H. TRIANGULAR
I. OTHER: (fits none)
MAX KONSTANTIN ZAULECK et al: Origin of the ACL and the Surrounding Osseous
Landmarks of the Femur Clinical Anatomy 27:1103–1110 (2014)

21. Sebastian Kopf Size Variability of the HumanAnterior Cruciate Ligament
Insertion Sites Am J Sports Med 2011 39
• There is large variation in size of the ACL insertion sites
and the AM and PL bundles
• There is no correlation between the size of the
insertions and height, weight, and body mass index of the
individual patient.

22. ACL femoral tunnel can be located intraop by:
1. Native ACL footprint
2. Lateral intercondylar and bifurcate ridges
3. ACL ruler method
4. Intraoperative fluoroscopy (grid method).

23. REASONS FOR PRESERVING ACL STUMP
1. Guide for the tunnel placement.
2. Increased mechanical strength in the early
postoperative period
3. Preservation of the blood supply, which may aid in the
healing process of the graft
4. Maintenance of proprioception

24. Femoral ridge method
• 1.7 mm deep to the bifurcate ridge
• 7.3–8.5 mm high or anterior to the posterior articular cartilage of LFC

25. ACL RULER METHOD
• knee is flexed to 110°
• length of the ACL femoral
attachment site is measured
along its long axis
• The ACL ruler is inserted
• angled microfracture awl
inserted at 50 % mark

26. Bernard-Hertel grid method
- measurement along
Blumensaat’s line
- the height of the intercondylar
notch

27. Bernard-Hertel grid
ACL attachment site is located
at:
• 27 % along Blumensaat’s line
• 34 % of the height from the
intercondylar notch

28. Bernard-Hertel grid (Intraoperative fluoroscopic image)

29. Bernard-hertel grid method
• (ACUFEX Smith & Nephew, Director Application
Anatomic Guide software) can be used to plot the Bernard
and Hertel grid from the intraoperative c-arm image

30. Femoral tunnel
• Steiner et al recommended that “the femoral tunnel be
placed at the centre of the femoral footprint, although he
recommended that the tibial tunnel be placed at the AM
footprint”.

31. POST OP TUNNEL POSITION ASSESMENT
(AP Xray)
• Femoral tunnel angle relative
to the long axis of the femur
• Angle > 32° is suggestive of
anatomic tunnel placement

32. C, J, CC INSERTIONS IN TIBIA
Śmigielski R (2012) The ribbon concept of the ACL. ACL Study Group Meeting.

33. Landmarks for Tibial footprint
• Anterior border of the PCL
• Posterior border of the anterior
horn of the lateral meniscus.
• Interspinous area of the tibial
plateau
• Retro–eminence ridge
• Transverse ligament

34. Tibial acl anatomy 1. In line with ant. horn of lat. meniscus
2. Anterior to insertion of PCL

35. ACL tibial footprint
Ziegler et al
• 7.5 mm medial to the anterior horn of the lateral meniscus
• 13.0 mm anterior to the retro-eminence ridge
• 15.7 mm anterior to the PCL
Kong charoensombat et al
• transverse ligament coincides with the anterior edge of
the ACL tibial footprint in the sagittal plane

36. ACL Tibial footprint
Ferretti
• 9.1 ± 1.5 mm posterior to the intermeniscal ligament
• 5.7 ± 1.1 mm anterior to apex of the medial tibial eminence
Morgan (MRI study)
• 7 mm anterior to the anterior margin of the PCL with the knee
flexed at 90°
Hutchinson
• Center of ACL is 10.4 ± 2.4 mm anterior to the PCL
• Posterior border of the ACL tibial footprint is 6.7 ± 1.2 mm
anterior to PCL

37. Intra op Tunnel position assesment
• In AP view, the pin should emerge on the down slope of the medial tibial spine
• In lateral view, the pin should be at the junction of anterior and middle third of the tibial
plateau
• In extension (lateral view),the pin should be posterior to extension of the Blumensaat line

38. How ACL is torn???
Primary
• Non- Contact Pivot Mechanism
Primary
• Quadriceps active Mechanism
Primary
• Contact Mechanism
2 ̊
• HyperValgus
2 ̊
• HyperExtension/flexion

39. Direct contact or collision, such as a football tackle

41. • Higher incidence of ACL injury
than men because of
Differences in
Anatomical disparities
Muscular strength
Neuromuscular control
pelvis and lower extremity
alignment
the effects of estrogen on ligament
properties(?)

42. Changing direction rapidly
Stopping suddenly
Slowing down while running
Landing from a jump incorrectly

43. ACL RECONSTRUCTION
• EXTRA-ARTICULAR-(iliotibial band tenodesis and bicepsplasty).
MacIntosh
 Losee
 Andrews
• INTRA-ARTICULAR.[ARTHROSCOPY]

44. • ACL Tear-
• No repair
• Only Recontruction
• Graft - Autograft - common
• Allograft

45. Graft Options
• Autograft
 BPTB-Bone-Patellar TendonGraft
 Hamstring
 Quadriceps
• Allograft

46. Bone-Patellar Tendon Graft
 ConsideredGOLDstandard
 CLANCY, MODIFIED

47. Bone-Patellar Tendon Graft:STEPS
A rear-entry commercial drill guide system (Acufex, Smith & Nephew,
Memphis, TN) is used for the femoral tunnel, and the bone plugs of the bone-
tendon-bone composite free patellar tendon graft are secured in the tunnels
with interference screws.
 Any intraarticular pathological condition is corrected with chondroplasty,
meniscal repair, or partial meniscectomy, and the contents of the intercondylar
notch are examined.

48.  Harvest of the graft and the reconstruction can be done through two incisions
or a single incision. The necessity of posteromedial or posterolateral incisions
(as for meniscal repair), previous incisional scars, or surgical preference
influences the choice of incision placement.
The single skin incision begins 8 cm superolateral to the patella and courses
distally to cross the tibial tuberosity to the anteromedial tibia

49. • Expose the patella and patellar tendon through the plane of the prepatellar
bursa.
• Measure the width of the patellar tendon.
• Make two parallel incisions through the full thickness of the tendon, 10 mm
apart, from the inferior pole of the patella to the attachment of the tibial
tuberosity if the patellar tendon is at least 30 mm wide. If the patellar tendon is
not this wide, use only the central third.

50. Continue the parallel incisions through the aponeurosis, over the anterior surface of the
patella from its inferior pole to the quadriceps tendon insertion, and distally through the
periosteum over the tibial tuberosity, extending 2 to 3 cm inferior to the tendon insertion.
The incisions mark the line for releasing the graft with its patellar and tibial tuberosity
bony attachments

51. Take the central slip of10 mm

56. BPTB Graft
• Advantages-
• Ease of harvest
• Consistent size & shape
• Strong bone-tendon interface
• Strong Bone to Bone fixaton
• Good healing

57. BPTB
• Dis-advantages- Risk of patellar # Patellar tendonitis
• Patello-femoral pain
• Donor site tenderness on kneeling
• Bigger incision scar
• Loss of sensation lat.to scar

58.  Quadrupled Semi-T / Doubled STGgraft
 4 strands of Hamstrings = 250% strength of nativeACL
• Advantages ‒
 Stronger graft
 Smaller Incision-Cosmesis
 Can be used in skeletally immature
Hamstring Grafts

59. GRAFT HARVEST

60. •

63. Hamstring disadvantage
 Soft tissue to bone healing
 Tunnel widening
 Technically difficult than BPTB
 Loss of Hamstring strength( apprx 10%)

64. Quadriceps Tendon Graft
 Bony end on one side and soft
tissue strip on other
 Cross-sectional area thicker
than BPTB
• Disadvantages-
 Donor site risks

65. Quadriceps tendon graft

66. Tendon exposure

69. Quadriceps tendon
 Advantage
 Comparatively less harvest site morbidity
 Larger cross sectional area of graft
 Disadvantage
 Bone block at only one end of graft

70. Allografts
Advantages-
 No graft site mobidity
 Available off the shelf
 Boon- Multiligamentous Injuries
Disadvantages-
 Risk of disease transmission
 Weak graft
 Delayed incorporation
 Not universally available,Expensive

71. SINGLE MOST COMMON CAUSE INCORRECT TUNNEL PLACEMENT

72. TUNNELS FOR ACL
• LENGTH
• DIAMETER
• POSITION

73. TIBIALTUNNEL
ENTRY POINT
• Tibial jig- set at an angle of 45-550 ,300 medial to mid
sagittal axis
• Approx.. 4 cmsbelow joint line

74. • LANDMARKS-
(A) ACL Footprint
•Center ofACL footprint
(B) LATERAL Meniscus
•Post. Border ofAnt. Horn
Anatomic TibialTunnel

75. FEMORALTUNNEL
• Access for tunnel placement
-Through theTibialTunnel
-Through medialinstrument portal
ANATOMICAL POSITION
Over the top position
- Right Knee-9 ‒10pm
- Left Knee- 2 - 3 am

77. Anatomic tibial tunnel

78. Graft Fixation

79. GRAFT FIXATION
 Secure graft fixation is paramount to a successful
reconstruction
 ACL rehab emphasizes on immediate movement and
weight bearing
 High demand on initial graft fixation
 Ultimate long term success of an ACL reconstruction
depends on healing of the graft fixation sites and
biological healing

80. Ideal fixation
 Strong enough to avoid failure
 Stiff enough to restore knee
stabilty
 Secure enough to avoid slippage

81. Ideal Graft fixation
 Anatomic
 Biocompatible
 Safe and reproducible
 MRI compatible
 Allow easy revision

82. Graft Fixation

83. ACL Graft fixation
• Major factor influencing graft’s
mechanical properties in the
immediate post-operative period
Fixation site is the weakest
link in ACL graft construct

84. GRAFT HEALING
BPTB – bone to bone healing by 6 weeks
Soft tissue grafts – incorporate by sharpey fibres by 12
weeks
Allografts take longer time
Till then, FIXATION DEVICES need to play a major role

85. Anatomic
Biocompatible
Safe & reproducible
MRI compatible
Allows easy revision
Ideal Graft Fixation

87.  Anatomical – Directly at
joint line, site of insertion
of native acl
 Semi Anatomical –
Transfixation devices,
Distal interference
fixation
 Non Anatomical –
Buttons, Staples

88. Methods of fixation
• Bone to bone fixation
• -ingrowth of bone block within bone tunnel
• Fixed with interference screws or press fit bone plugs
• Tendon to bone fixation
• Tendon tissue heal to bone to achieve bony integration

89. Based on Different mechanisms
Femoral fixation:
• Hardware-free method
• Hybrid technique
TIBIAL
FIXATION

90. Fixation concepts
• Direct extra-articular fixation
• Graft anchored outside the
joint directly to the bone
Indirect extra-articular fixation
Graft anchored outside the joint
using single or loped threads
Reduces effective graft length

91. Fixation concepts
• Direct peri-articular fixation
• Graft pressed against
wall of bone tunnel
Fixation at level of joint line
Graft fixed directly at the level
of joint space

92. Soft Tissue fixation –
interference compression
Compressive loads transversely to
the longitudinal axis of the graft
Load shared along 3 interfaces
Bone-screw
Screw-tendon
Tendon-bone

93. Expansion
One or more cross pins pass through Graft &
femoral tunnel
As pins inserted transversely into the tunnel ->
increase volume of graft -> pressure against
tunnel walls (pressure in centrifugal way with
respect to pin insertion points)
Fixation based on initial press fit of graft into
tunnel
Rigid-Fix

94. Suspension -
cortical
Metal plates with suture loops
Hardware over lateral cortex of
distal femur suspends graft into the
femoral tunnel
Resistance vectors are parallel &
opposite to the pullout forces

95. Suspension - cancellous
Graft suspended to screw/press fit
anchor which is fixed to cancellous
bone of femoral metaphysis
Resistance is due to transverse
compressive forces at cancellous bone-
hardware interface
Linx-HT (Depuy Mitek)

96. Suspension – cortico-cancellous
Transepicondylar fixation system based on transverse suspension bar that is
perpendicular to pull out forces
Bio-Transfix
(Arthrex)

97. Soft tissue fixation – tibial fixation
compression devices
Compressive loads transversely
to the longitudinal axis of the
graft
Load shared along 3 interfaces
Bone-screw
Screw-tendon
Tendon-bone

98. Expansion devices
Expandable four-channel, ridged sheath &
tapered expansion screw
Four channels grip 4 strands of graft into
separate compartments & compress graft
strands against cancellous bone in order to
maximize bony integration
GraftBolt (Arthrex)
Expandable ridged sheath
Tapered expansion screw

99. Cortical anchoring
devices
 Staples
 Sutures over post
 Screws
 Spiked washers

100. Interference compression
Transverse compression
Transverse suspension
Hybrid system
Press Fit
FIXATION CONCEPTS: BONE
TO BONE FIXATION

101. Interference compression
Generation of friction between bone block
& bone tunnel wall
Engagement of screw threads into bone
block & bone tunnel wall

102. Transverse compression
Blunt nosed transverse screw enters femoral tunnel from lateral cortex
Pushes bone plug against medial tunnel wall

103. Transverse suspension
One or more cross
pins that pass
transversely
through the bone
plug

104. Press fit fixation
Autologous bone plug/ Beta tricalcium phosphate plug
No fixation device

105. Fixation devices

106. Interference screw
Interference is defined as the
amount by which the diameter
of the screw exceeds the gap
between the graft & the tunnel
Interference screw for BPTB – Gold
Standard
• Minimizes graft tunnel motion
• Less femoral canal widening

107. Screw divergence
Difference between angle of tunnel &
screw direction
More with transtibial technique
>20 deg compromises stability

108. Metallic screws
Traditional fixation for many years
High initial fixation strength
Damage to bone-tendon junction
Violation of posterior cortex
Intra articular hardware
Hardware removal during
revision
Distortion of MRI images

109. Bio screws
Biodegradable
Polyglycolic acid (PGA), poly-p-
dioxanone and copolymers of
polyglycolic acid/polylactic acid
(PGA/PLA), poly-l-lactic acid (PLLA)
& poly-d-lactic acid (PDLA)
Degrade slowly
Biocomposite
Combination of polymers &
osteoconductive materials [Beta-
tricalcium phosphate (β-TCP) or
hydroxyapatite]
Ultrastructural properties for cell
adhesion
Degrade more quickly,
osteoconductive properties promote
faster graft incorporation & bone
formation
• Polyglycolide absorbs early, hence fixation can
become lose early
• Crystalline polylactides take years to get
absorbed

111. Advantages disadvantages
May break during insertion
Need special screw driver
Tissue reaction can occur
Fixation lost after partial
degradation
By 6 weeks, 80% loss of
strength, 60% loss of stiffness
Tunnel widening more
No need for implant
removal
Revision easier
Does not interfere with MRI

112. Endo button
Fixed Loop suspensory fixation
Insertion & Connection parts
Insertion part drilled to the diameter of the graft
Connection part is 4.5mm diameter
No wear/abrasion of the graft
Adv
Can be used in osteoporotic bones and
femoral tunnel blow out
Disadv
Fixation away from aperture – tunnel widening
& Bungee effect

113. Tight rope
Adjustable Loop suspensory fixation
Loop length reduced after flipping by
tightening the rope
Allows full length filling of the graft
part in the tunnel

114. FIXATION DEVICES
• Fixation site is the weakest link in ACL graft construct
• Clinical results of various methods are comparable
• Interference screw gold standard for Bone grafts
• Suspensory fixation for femur & compression fixation
for tibia commonly done for Soft tissue grafts

115. Sources
• Campbells 12 th edition
• Millers 7 th edition
• Rockwood

116. Thank you