The bones that make up the knee are the:

• Femur (thigh bone) 
• Patella (knee cap) 
• Tibia (shin bone)

The patella (knee cap) functions as a pulley, to improve the mechanical advantage of the quadriceps muscles, which act to extend (straighten) the knee. The articulation between the patella and femur is called the patellofemoral joint.

The joint surfaces are lined by articular cartilage, which is a fine bearing surface. Lubrication is provided by the synovial fluid, which is secreted by the joint lining (synovium).

The two menisci help protect the articular cartilage, by distributing the forces acting across the knee. They are made up of strong fibrocartilage.

The knee joint is stabilised by the joint capsule, and the four main ligaments:

• Anterior cruciate ligament (ACL) 
• Posterior cruciate ligament (PCL)
• Medial collateral ligament (MCL) 
• Lateral collateral ligament (LCL) 

The conditions that affect the structural components in the knee, lead to symptoms, which often require treatment.

Ligament injuries

• The most common ligament injuries are to the medial collateral ligament (MCL) and anterior cruciate ligament (ACL)
  
• Most MCL injuries will heal without surgery
  
• A significant proportion of ACL injuries require ligament reconstruction, particularly if the person plans to live an active lifestyle
  
• Multiple ligaments can be injured at the same time, particularly with severe trauma
  
• Multi-ligament injuries often require reconstructive surgery 

Meniscal tears

• Can occur with a traumatic injury or be part of the degenerative process within the knee
  
• Loss of the meniscus, predisposes to damage of the articular cartilage (osteoarthritis)
  
• Meniscal tears may require arthroscopic surgery to:
  
  • Remove debris within the knee
    
  • Repair the meniscus 

Osteoarthritis

• Damage to the articular cartilage, lining the joint surfaces
  
• Severe disease may require joint replacement surgery, if pain is resistant to other treatments 

Osteonecrosis

• Loss of blood supply to some of the bone around the joint
  
• This can lead to bone collapse and articular cartilage damage 

Patellofemoral Problems

Patellofemoral instability

• Tendency to dislocate or sublux (partially dislocate) the patella
  


Patellofemoral osteoarthritis

• Damage to the articular cartilage of the joint surfaces
  
• It may be secondary to:
  - Underdevelopment of the joint (eg. Trochlear hypoplasia)
  - Malalignment of the lower limbs (eg. Knock knees)
  - Poor soft tissue balance (eg. Lateral patella pressure syndrome)
  - Previous fracture

Paediatric (childhood) problems

• Osgood-Schlatter disease
  
• Also see Limb Reconstruction/Deformity Correction

Other

• Baker’s cyst
  
• Bursitis
  
• Effusion
  

The types of knee surgery performed include:

• Arthroscopic knee surgery
  
• Meniscal debridement and repair
  
• Anterior cruciate ligament (ACL) reconstruction
  
• Multi-ligament reconstructions, including
  - Anterior cruciate ligament (ACL)
  - Posterior cruciate ligament (PCL)
  - Medial collateral ligament (MCL)
  - Lateral collateral ligament (LCL)
  - Posterolateral corner
• Patellofemoral joint surgery, including
  - Patellofemoral stabilisation
  - Tibial tubercle transfer
  - Medial patellofemoral ligament (MPFL) reconstruction
  - Femoral trochleoplasty
• Total knee replacement
  
• Revision total knee replacement
  
• Osteotomy
  - High tibial osteotomy
  - Distal femoral osteotomy

A lot of knee problems can be managed without the need for surgery. Some of the modalities used are:

• Medications
  - Simple pain relievers, such as paracetamol
  - Anti-inflammatory medications
• Injections
  - Corticosteroid
  - Hyaluronic acid (eg. Synvisc or Durolane)
  - Platelet rich plasma (PRP)
• Activity modification
• Walking aids, such as crutches, walking sticks or frames
• Bracing
• Physiotherapy
• Low impact exercise
• Weight loss