1. Knee Anatomy Reza Omid, M.D. Assistant Professor Orthopaedic Surgery
Shoulder & Elbow Reconstruction
Sports Medicine
Keck School of Medicine of USC

2. Bony Anatomy
Tibiofemoral joint
Patellofemoral joint

3. Femoral Condyles Smaller radius of curvature Smaller in all dimensions
A – Lateral Condyle
Smaller radius of curvature
Smaller in all dimensions
Extends more anteriorly
B – Medial Condyle
Larger radius of curvature
Extends more distally
C – Intercondylar notch

4. Tibial Plateau D – Medial Plateau Greater surface area Concave
Circular shape
E – Intercondylar Eminence
F – Lateral Plateau
Smaller surface area
Convex
Oval shape

5. Patella Sesamoid bone in quadriceps Dividing central ridge
Comprised of seven facets
Medial and Lateral facets divided into 3rds
7th facet is most medial (odd facet)
Medial half usually smaller
Thick hyaline cartilage (5.5mm)

6. Femoral Sulcus
Lateral wider and higher
Both with sagittal convexity

7. Screw Home Mechanism
Knee achieves terminal extension via the “screw home mechanism
The tibia externally rotates in relation to the femur.
When the knee needs to flex, the popliteus contracts which causes internal rotation of the tibia and in essence unlocking the knee and allowing it to bend

8. Bony Alignment

9. Popliteal Artery
Originates at the adductor hiatus and passes through the popliteal fossa, then deep to the fibrous arch over the soleus muscle
Divides into the anterior and posterior tibial arteries at the distal aspect of the popliteus muscle

10. Popliteal Artery
The popliteal artery is 9mm posterior to the posterior cortex of the tibia at 90° of flexion and even closer in extension.
Place retractors biased to the medial side when possible.

11. Skin Blood Flow
If two longitudinal incisions are present, the more lateral incision should be used (if allows adequate exposure) because most of blood supply comes in medially.
The lateral skin edge is more hypoxic than the medial skin edge so keep this in mind when placing sutures.

12. Tibial Nerve Initially lateral to the popliteal artery
Crosses at midpoint to end medial to the artery at soleus arch

13. Common Peroneal Nerve Lateral aspect of the popliteal space
Medial and posterior to the biceps femoris tendon

14. Infrapatellar Branch of Saphenous

15. Patellofemoral Biomechanics
Joint Reactive Force
In flexion, patella compressed onto femur creating joint reactive force
Stair climbing – 3.5 X BW
Deep bends – 7-8 X BW

16. Menisci
Primarily type I collagen with fibers arranged obliquely, radially, and vertically
Outer 10% to 30% has blood supplied from the perimeniscal capillary plexus off the superior and inferior medial and lateral genicular arteries

17. Secondary Stabilization
Meniscus Function
Load Transmission
50% load transmitted in extension
85% load transmitted at 90 degrees flexion
Resection of 15-34% increases pressure 350%
Secondary Stabilization
Medial meniscus provides anterior restraint
Especially in ACL deficient knee

18. Lateral Meniscus
Loose peripheral attachment allows greater translation during motion
Average excursions of the menisci with knee flexion
5.2 mm for the medial
11 mm for the lateral
Bare area anterior to popliteus tendon
Two highly variable meniscofemoral ligaments attach it to medial femoral condyle:
Anterior – Humphrey
Posterior – Wrisberg’s

19. Ligaments Tensile strengths of various knee ligaments:
MCL ~ N
PCL ~ N
ACL ~ N
LCL ~750N

20. Anterior Cruciate Ligament
26-38 (33) mm in length
ACL graft selection you aim for at least mm graft length because it needs about ~33mm for the tibial tunnel, ~33mm for the femoral tunnel and ~33 for the graft itself
11 mm in width
Primary restraint
Anterior translation of tibia (74-85%)
Normal 3-5mm of translation
Secondary restraint
Internal rotation
Varus/Valgus
Hyperextension

21. Anterior Cruciate Ligament
Two bands
Anteromedial band taut in flexion
Posterolateral band taut in extension

22. Anterior Cruciate Ligament
Femoral Attachment
Posterior portion of medial surface of LFC
Oriented in line of axis of femur in extension
Footprint in shape of circular segment
Posterior convexity 4 mm anterior to articular surface
Surface area measures x 11 mm
Lateral to midline on AP view
Posterosuperior on lateral view

23. Anterior Cruciate Ligament
Tibial Attachment
Anterolateral to medial spine
Insertion has oval shape
Sections attach to bone, AHLM, PHLM
15 mm posterior to anterior tibia
17-30 x 11 mm surface area
Just lateral to midline on AP
40% back on lateral view

24. Lateral Bifurcate Ridge
Running perpendicular to the lateral intercondylar ridge) seperates the origins of the anteromedial and posterolaterla bundles.

25. Lateral Intercondylear Ridge
Resident’s ridge on the lateral femoral condylar wall denotes the lateral intercondylear ridge and marks the most anterior and superior extent of the femoral origins of the ACL.

26. Anterior Cruciate Ligament
Blood Supply
ACL completely ensheathed in fold of synovial membrane
Although intraarticular, technically extrasynovial
Main supply is middle geniculate with smaller contribution from both inferior geniculates
Innervation
Branches of tibial nerve
Very few pain receptors in substance of ACL

27. Posterior Cruciate Ligament
38 mm in length
13 mm in width
Narrowest diameter at midsubstance
Anterolateral band
More robust, Taut in flexion
Posteromedial band
Thinner, Taut in extension

28. Posterior Cruciate Ligament
Femoral Attachment
Lateral surface MFC
Shape of circular segment
Distal margin 3 mm proximal to articular surface

29. Posterior Cruciate Ligament
Tibial Attachment
Depression between tibial plateaus
1 cm distal to tibial articular surface
Can have contributions to PHLM as well as meniscofemoral ligaments
Average width 13 mm

30. PCL Biomechanics Function Primary restraint
Posterior translation of tibia (90-95%)
Greatest translation occurs at 75 degrees flexion
Secondary restraint
Varus/valgus
External rotation

31. Medial Structures
Layer 1: Deep fascia and Sartorius Layer 2: Superficial MCL, MPFL Layer 3: Joint capsule, Deep MCL

32. Pes Anserinus

33. Medial Ligaments Superficial MCL (Medial Collateral Ligament)
Originates on medial epicondyle
avg: 3.2 mm proximal and 4.8 mm posterior to medial epicondyle
Tibial insertions (2) distal and proximal
Proximal: anterior arm of the semimembranosus tendon
Distal: broad-based, just anterior to the posteromedial crest of the tibia, most located within the pesanserine bursa
Posterior Oblique Ligament (POL)
superficial, central (main component), and capsular arms
Deep MCL
Divided into meniscofemoral and meniscotibial ligaments

35. MCL

36. Superficial MCL most important for stability (57-78%)
MCL Biomechanics
Stability – Most important in flexion when posterior structures relaxed
Valgus rotation
External rotation
Medial/Lateral translation
Superficial MCL most important for stability (57-78%)
Sectioning Deep MCL does not result in instability if Superficial MCL intact

37. Medial Patellofemoral Ligament
Runs transversely in Layer 2 Originates from adductor tubercle, femoral epicondyle, and superficial MCL Proximal fiber inserts on undersurface of VMO and vastus intermedius Distal fibers insert on superomedial patella Width averages 1.3 cm

38. MPFL

39. MPFL Biomechanics
Soft tissue restraint of extensor mechanism Patella subluxes most easily at 20° knee flexion MPFL resists patellar lateral subluxation greatest in extension Primary stabilizer followed by patellomeniscal, patellotibial, and medial retinaculum

40. Lateral Structures Layer 1 IT band biceps tendon Layer 2
Lateral retinaculum
patellofemoral ligaments
Layer 3
Joint capsule
LCL
arcuate ligament
fabellofibular ligament
popliteofibular ligament

41. Lateral Structures Layer 1 IT band biceps tendon Layer 2
Lateral retinaculum
patellofemoral ligaments
Layer 3
Joint capsule
LCL
arcuate ligament
fabellofibular ligament
popliteofibular ligament

42. IT band continues distally to form the:
Iliotibial Band
Coalescence at greater trochanter of tensor fascia lata, gluteus medius and gluteus maximus
IT band continues distally to form the:
IT tract
Inserts distally on Gerdy’s tubercle and on distal femur through intermuscular septum
Iliopatellar band
Inserts on lateral patella resisting medial directed forces

43. IT Band Biomechanics Functions Stabilizes against varus opening
Knee extensor in extension
Knee flexor in flexion
External rotator of tibia in >40 flexion

44. Lateral Collateral Ligament
Arises in fovea slightly proximal (1.4 mm) and posterior (3.1 mm) to lateral epicondyle Attaches to V-shaped plateau of fibular head (8.2mm distal to anterior edge) Surrounded by biceps femoris tendon distally Average length mm AP diameter 3.4 mm ML diameter 2.3 mm

45. LCL Origin
Posterior (4.6 mm) and proximal (1.3 mm) to the lateral femoral epicondyle
Posterior and superior to the insertion of the poplitieus (18mm away from each other)

46. LCL Biomechanics
Tightest in extension, 0-30 degrees Becomes looser in flexion >30 degrees Primary restraint to varus Secondary restraint to ER and posterior translation

47. Posterolateral Corner
FCL
Popliteus tendon
Popliteofibular lig

48. Posterolateral Corner
Static Stabilizers (highly variable)
LCL
Fabellofibular ligament
Short lateral ligament
Popliteofibular ligament
Arcuate ligament
Posterolateral capsule
Posterior horn lateral meniscus
Lateral coronary ligament

49. Posterolateral Corner
Dynamic Stabilizers
IT band
Lateral gastrocnemius
Biceps femoris
Popliteus

50. Popliteus Complex Dynamic Static Popliteus muscle
Popliteofibular ligament
Popliteotibial fascicle
Popliteomeniscal fascicle

51. Popliteus Muscle
Originates from posteromedial surface of proximal tibia
Tendon passes in hiatus of coronary ligament, crosses under LCL, inserts on lateral femoral condyle 3-5 mm proximal to articular surface

52. Popliteofibular ligament
Average length 42 mm Descends from popliteus muscle (at musculotendinous junction) to posterosuperior fibular head Composed of anterior and posterior fascicle Functions as pulley to the popliteus

53. Arcuate Ligament
Fibers oriented in various directions Y-shaped configuration over popliteus Medial limb terminates into oblique popliteal ligament Lateral limb invariable present, and is less distinct

54. Fabellofibular vs Short Lateral Ligament
Fabellofibular ligament
Present when fabella present (8-16%)
Courses from fabella to fibular head
Short lateral ligament
Present when fabella absent
Courses from lateral femur to fibular head
Represents a homologue of the fabellofibular ligament