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Sport Orthopaedic Biomechanics > ACL Injury > Flashcards

ACL Injury Flashcards

Daniel Fong Lecture 2 of 6

1
Q

Describe the bone anatomy of the knee

A
  • Femur
  • Patella
  • Tibia (Medial)
  • Fibula (Lateral)
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2
Q

What are the 4 muscle groups that make up the:
Knee extender
Knee flexor
Dorsal Flexor
Calf Muscle

A

Quadricep
Hamstring
Tibialis anterior
Gastrocnemius

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3
Q

Describe the 3 planes of movement of the knee

A
  • Flexion =/ Extension
  • Internal =/ External rotation
  • Valgus (Abduction) =/ Varus (Adduction)
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4
Q

Simply put, How does a muscle output force?

A

Contractile filaments change the size of the muscle, producing a muscular force

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5
Q

What is the difference between tendons and ligaments

A

Tendons: connect muscle to bone (withstands forces of tension applied when muscle contracts, transferring the force to bone)
Ligaments: connect bone to bone (maintain join stability)

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6
Q

Draw or explain the anatomy of the knee

A

4 bone, 4 ligaments, 2 meniscus, 2 cartilage

ACL - Closer to the front (hence anterior)
PCL - More posterior

(to remember, touch finger tips, point to feet, that is the ACL direction)

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7
Q

What is the job of the ACL

A
  • Stabilising ligament for the knee
  • Strong internal brace
  • resists internal rotation
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8
Q

How is the ACL usually injured

A
  • Usually due to violent pivoting
    1) knee in toe out (Valgus Knee and externally rotated)
    2) Knee out toe in (Varus knee and internally rotated)
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9
Q

What are the symptoms of an ACL injury?

A
  • ‘Pop’ sound when ruptured
  • Intensive pain
  • Joint becomes locked
  • Reduced ROM
  • Immediate swelling in an hour or so (Ligaments have good blood supply), hemarthrosis (swelling of the joint cavity)
  • Anterior tibial translation
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10
Q

What is the purpose of the meniscus?

A
  • Acts as a shock absorber for the knee and reduces the stress applied to the articular cartilage on the femur condyles
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11
Q

Why does the meniscus often not heal quickly or fully?

A
  • Very limited blood supply
  • Blood is only supplied to the peripheries of the cartilage
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12
Q

What are common symptoms of a meniscus tear?

A
  • gradual Swelling over a longer period (24 hours)
  • Locking sensation as torn meniscus can jam into the joint
  • the loss of joint motion calls for immediate surgical treatment, while ACL ruptures do not tend to do this
  • Long recovery time
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13
Q

What is the general trend in injured tissues found from knee in & toe out mechanism

A
  1. Torn ACL
  2. Crushed lateral meniscus
  3. Over-stretched/torn Medial collateral ligament
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14
Q

How has the toe in knee out mechanism been analysed in Oslo?

A
  • Using model based image matching (MBIM) motion analysis
  • The software creates a skeletal model to fit the patients anthropometric data
  • Analysis on the image based skeleton is conducted during the injury
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15
Q

These graphs are taken from MBIM analysis of 10 ACL rupture, what do they show?
At time zero the foot strike occurs

A
  • Upon foot strike, knee abduction/adduction was neutral with a slight external rotation
  • after 40ms, momentum had forced the knee to become valgus (13 degrees) and internally rotated to 7 degrees
  • after 200ms the knee externally rotated to 17 degrees creating the knee in to out mechanism
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16
Q

Explain what is going on in this sequence of diagrams

A

A. Healthy joint
B. Valgus Knee: Stresses on the MCL and compression on the Lateral Meniscus
C. Ruptured ACL: Posterior translation (the lower leg moves forward) of the tibia, and slight internal rotation of the knee
D. ACL Fully gone: With no stability posterior tibial translation progresses, and nod external rotation occurs resulting in the knee in toe out

17
Q

Describe the Lachman physical examination for an ACL injury?

A
  • Bend knee to 30 degrees, apply anterior stress to the tibia to see for translation/subluxation
18
Q

Describe the Anterior Drawer Test examination for an ACL injury

A
  • Bend the knee to 90 degrees, apply anterior stress to the tibia to find signs of subluxation
  • (Same as lachman test but more flexed knee)
19
Q

What is the pivot shift test?

A

A test to examine ACL injury
- Put patient into supine (on their back)
- lift their leg to 30 degrees holding the ankle and lower leg
- apply 20 degrees of tibial internal rotation
- Apply a valgus force to see if there’s any subluxation

20
Q

What do these images tell us about ACL injury

A

X-ray: Can look for displacement (not super useful)
MRI: Solid black line shows an intact ACL, whereas that is not seen in the second image

21
Q

What is arthroscopy?

A

Using a tiny camera in keyhole surgery to assess damage and perform surgery

22
Q

What is in these images?

A

A partial and fully ruptured ACL

23
Q

Name and describe the physical examination used for assess meniscus injury

A
  • McMurray Test
  • Have patient on their back in supine
  • lift their knee to 90 degrees and internally/externally rotate the tibia
  • feel for clicking (trapped meniscus) and tenderness
23
Q

What is the surgery required to repair the meniscus? And how does it work?

A
  • A partial menisectomy
  • Cut and remove fragments/debris or torn parts of the meniscus to make it smooth again
24
Q

Describe the operative procedures taken to reconstruct the ACL

A

1) Remove the torn ACL
2) Drill a tunnel at the femur and tibia
3) Pass the graft through the tunnels
4) Fix the graft in place with screws

25
Q

What different types of grafts are there?

A

Autograft: Transplanted from another site of the same patient
Allograft: Transplanted from another patient
Xenograft: Transplanted from another species

26
Q

In an autograft surgery to fix the ACL, sometimes hamstring tendon or patella tendon is used. What are the benefits of either

A

Patellar tendon: Significantly stronger than the ACL (140%), but cannot regenerate

Hamstring tendon: Less strong than ACL tissue (70%), but can regenerate

27
Q

Describe how a tendon to bone graft heals

A

1) The bone-tendon interface begins to mineralise and this progresses into the tendon
2) This fixes the tendon into the bone, removing cells and replacing them with a remodelled matrix structure

28
Q

What methods have been employed by scientists to promote bone-tendon healing?

A

1) Injecting cell growth factors, proteins and stem cells
2) Using biomaterials such as demineralised bone matrix and injecting bone cement
3) Stimulating bone growth via Ultrasound, and shockwave therapy

29
Q

What modern methods have arised in literature to promote bone-tendon growth?

A
  • Extracting multipotent mesodermal cells which have the capacity to differentiate into bone or cartilage progenitor cells and culturing these onto the graft material
  • Using hydrogel films to culture these stem cells and wrapping the graft in the hydrogel film
30
Q

Anatomically describe the ACL and what it does

A
  • About 32mm in length and 10mm wide
  • Comprised of 2 bundles (the AMB, anteromedial bundle and PLB, posterolateral bundle)
  • These bundles provide rotational and translational stability
31
Q

How can the translational stability of the tibia be measure?

A
  • Using an arthrometer
  • A specific quantity of force can be applied (pull or push) and the device measures displacement, aka joint laxity
32
Q

How can the rotational stability of the tibia be measured?

A
  • Using a torque sensor linked to a boot (aka, clamp)
  • Use the sensors to track the internal/external rotation of the lower limb in comparison to the upper limb when applying a constant force (eg 5nm)
33
Q

What methods have biomechanists developed to analyse the rehabilitation of patients with ACL injuries?

A
  • Performing dynamic functional tests, measuring force outputs pre and post op
  • Biplanar X-ray motion analysis with C-arm (basically can recreate your joint to measure your range of motion in static positions)
  • Biplanar x-ray motion analysis, for dynamic analysis
  • Computational modelling and FEA of specific patient anatomy trying different surgical techniques

Sport Orthopaedic Biomechanics (6 decks)

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