Knee Ligament Injuries

Definition

Instability

• Abnormal ↑ range of motion due to ligamentous, capsular, meniscal, cartilage or bone injury / abnormality

Strain

• Stretching injury to a musculo-tendinous attachment to bone

Sprain

• Injury limited to ligaments (connective tissue attaching bone to bone)
• stretch or tear ligament fibres but does not completely disrupt the ligament (as apposed to ligament rupture)

Degree	Description
1st	Tearing of minimal fibres resulting in local tenderness & no instability
2nd	Partial tear of the ligament with ↑ loss of function & joint reaction again with no instability
3rd	Complete tear or disruption resulting in instability

Grading	Amount
+	0 – 5mm
++	5 – 10mm
+++	> 10mm

Examination

• characteristic signs
  • Effusion
  • contusion
  • swelling,
  • tenderness over ligament insertions
• Haemarthrosis
  • Causes
    • ACL rupture (accounts for 70% of haemarthrosies)
    • Acute patella dislocation
    • Osteochondral fracture
    • Peripheral meniscal tear

Knee Instability

• Committee on Research & Education of the American Orthopaedic Society of Sports Medicine Research & Education Committee, 1976
  • Classification
    • straight ( nonrotatory)
    • rotatory ( simple or combined)

Straight instability

• Medial Opens
  • with valgus stress test in full extension
    • indicates
      • tear MCL,
      • medial capsular ligament,
      • ACL,
      • posterior oblique ligament
      • medial portion of the posterior capsule
      • PCL may be also torn but not necessarily so
  • Opens with valgus stress test in 30° flexion
    • indicates
      • tear to MCL only
• Lateral
  • Opens with varus stress test in full extension
    • indicates tear of lateral capsular ligament,
    • LCL , & commonly PCL
  • Opens with varus stress test in 30° flexion
    • may be present in minor lateral complex tears or may be normal
• Posterior
  • Demonstrated by posterior drop back of the tibia with no rotation
    • indicates
      • tear of PCL,
      • arcuate ligament complex,
      • posterior oblique ligament complex
• Anterior
  • Demonstrated by the anterior drawer test in neutral rotation with both tibial condyles subluxing anteriorly with no rotation. In this type of instability the test becomes negative as the tibia is internally rotated as in this position the PCL becomes taut
  • indicates
    • tears of ACL,
    • lateral capsular ligament,
    • medial capsular ligament

Rotatory instability

• Anteromedial
  • indicates
    • tear of medial capsular ligament,
    • MCL,
    • posterior oblique ligament,
    • ACL
  • the medial tibial plateau subluxes forward on the femur
  • The medial meniscus is an important adjunct to anteromedial stability
    • thus should be conserved if at all possible
  • Repair of the posterior oblique ligament is essential for stability
• Anterolateral
  • indicates
    • tear of lateral capsular ligament,
    • arcuate complex,
    • ACL
  • results in excess internal rotation of the tibia on the femur at 90° flexion
  • With an internal rotation /varus stress injury, an avulsion fracture of the attachment of the lateral capsule from the tibia may occur
    • Segond fracture
    • high associated with torn ACL
• Posterolateral
  • the lateral tibial plateau rotates posteriorly with respect to the femur with lateral opening of the joint
  • implies tear of
    • popliteus tendon,
    • arcuate complex,
    • lateral capsular ligament,
    • occasionally the PCL,
    • and the biceps from its insertion
  • results in an ER subluxation where the tibia rotates about an axis of the intact PCL
• Posteromedial
  • the medial tibial plateau rotates posteriorly with respect to the femur with medial opening of the joint
  • implies tear of
    • MCL,
    • posterior oblique ligament,
    • ACL,
    • medial portion of posterior capsule. May be stretching / injury to semimembranosus tendon
• Combined
  • Anterolat- anteromedial combined:
    • results from tears of ACL & both medial & lateral capsular ligs in their middle third.
    • PCL is intact
    • the anterior drawer test
      • is markedly positive in neutral,
      • exaggerated in ER,
      • but negative in IR ( PCL tightens in IR)
  • Anterolat- posterolateral combined:
    • results from tear of all of the lateral comp capsular ligs & ACL, with or without tear of the iliotibial band , PCL remains intact
      • varus instability marked,
      • Anterior + posterior drawer tests in neutral show lateral tibial plateau rotation anterior + post
  • Anteromed- posteromedial combined
    • medial & posteromedial structures are torn with ACL & often PCL
    • valgus instability marked, anterior + posterior drawer tests in neutral show medial tibial plateau rotation anterior & posterior

Investigations

• Arteriography
  • should be performedial if injury suspicious of vascular injury
  • If both cruciates & either collaterals disrupted probably dislocated knee & high incidence of vascular damage

Pathology

• Single collagen fibres are not extensible & begin to fail at elongations of 7% to 8%
• The number of fibres disrupted determines if the ligament is functionally or morphologically disrupted
• Complete disruption requires extreme joint displacement
• Ligament Healing

Phase	Time	Description
1	first 24 hours	* Acute inflammation ~ haematoma formation
2	48 – 72 hours post injury continuing for ~ 6/52	* Repair & regeneration ~ subsidence of inflammation ~ commencement of healing
3	requires 6 – 9 months	* Remodelling & maturation ~ Contraction of ligament ~ change collagen predominance with ↑ cross linking & ↑ tensile strength ~ original strength is not reached (probably 50 – 70%)

• Isolated Grade III ACL & PCL injuries do not heal as they are not contained in a vascularised bed
  • not all however have functional disability

Treatment

Goal of treatment

• restore the anatomy & stability to as near pre injury status as possible