Knee Injuries

The knee joint is the largest, most complicated and most commonly injured joint in the human body. It is also the leading cause of long-term disability in athletes. Fortunately many advances have been made in understanding the mechanisms of injury, biomechanics diagnosis and treatment of knee injuries. Unfortunately however, little progress has been made in the prevention of knee injuries. As such, most athletes should have a basic understanding of knee anatomy, function and injury management.


The knee includes the following structures:

1) Bones
– femur (thigh bone)
– tibia (shin bone)
– patella (knee-cap)

2) Ligament
– medial collateral ligament (MCL)
– lateral collateral ligament (LCL)
– anterior cruciate ligament (ACL)
– posterior cruciate ligament (PCL)

3) Menisci (cartilages)
– medial meniscus
– lateral meniscus

4) Joint capsule

The glossary at the end of the article explains the medical terms that are used.

These structures are illustrated below:

Knee joint and Anterior knee musculature

Knee joint and Anterior knee musculature.

Tibial attachments

Tibial attachments of the anterior and posterior cruciate ligaments (ACL, PCL) in relationship to the synovial cavity

Bone Fractures


Large forces are required to fracture the knee joint. These may be the result of a direct force e.g. being hit by the bumper bar of a car (or getting a stop kick to the knee) or an indirect force e.g. a sudden contraction of the thigh muscle can fracture the patella.

knee injury bone fractures


– severe pain
– weight-bearing and walking difficult or impossible
– moving the knee difficult or impossible (due to pain)


– swelling around the knee
– very limited range of movement
– difficulty weight-bearing and walking
– generalised tenderness


Depends on the severity of the break.


The fully extended knee is stable chiefly because the joint capsule and ligaments are taut. Most ligament injuries occur while the knee is bent, relaxing the capsule and ligaments and permitting rotation.

1. Medial Collateral Ligament

Anatomy – see previous illustration

Mechanism – Most commonly due to a combination of a direct force applied to the lateral side of the knee and a twisting force to the tibia.

medial collateral ligament injury

e.g. a side kick to the lateral of the knee, a rugby player tackled from the lateral side or a skier catching an inside edge.

Classification of Ligament Injuries

tears of the medial collateral ligament

Tears of the medial collateral ligament are classified into first degree, second degree, third degree and third degree plus associated anterior cruciate ligament rupture

Definition Pain Swelling Tenderness Laxity ** Ability to work
1st degree small number of fibres torn slight slight slight nil normal
2nd degree moderate number of fibres torn moderate moderate moderate moderate with difficulty
3rd degree all fibres torn (i.e. complete rupture) variable * variable * severe severe unable

* Paradoxically severe injuries can be relatively free of pain and swelling.
** See section on "Assessing knee injuries"


1st degree – physiotherapy

2nd degree – brace followed by physiotherapy

3rd degree – brace or surgical repair followed by physiotherapy

Healing Time

1st degree: 1-3 weeks
2nd degree: 4-6 weeks
3rd degree: 6+ weeks

Return to Sport

Only when the following have been achieved:

i) full range of movement
ii) full strength
iii) minimal ligament tenderness
iv) minimal symptoms

2. Lateral Collateral Ligament

Tearing of the LCL is rare and is usually caused by a direct force to the medial side of the knee. They are managed along similar lined to MCL injuries.

3. Anterior Cruciate Ligament


The ACL and PCL run between the femur and tibia crossing over like "X". They prevent the tibia from sliding backwards and forwards when the knee bends.


The majority of people with torn ACL's will state that they turned, pivoted or landed from a jump with a subsequent "giving way" of the knee.

Many will note an audible "crack" or "pop" at the time, followed by immediate pain and swelling.


No area of sport medicine is debated more vigorously than the management of ruptured ACL's. In New Zealand surgical reconstruction of the ACL is reserved for elite athletic and people who have chronic symptoms (usually of instability). The majority of people are managed conservatively with aggressive physiotherapy aimed at setting the swelling, restoring full painless range of movement and restoring full muscle power.


1/3 of people are able to return to sport at their previous level.
1/3 of people are able to return to sport at a lower level.
1/3 of people have chronic symptoms and are unable to return to sport at all.

partial and complete tears of ACL

Partial and Complete ruptures of ACL

4. Posterior Cruciate Ligament


Twice as strong as the ACL and is therefore less frequently injured.


A direct blow to the anterior knee.


Minimal and difficult to detect.

Treatment – physiotherapy (surgery if chronic symptoms).

posterior cruciate ligament tear

Posterior cruciate ligament tear



The menisci are "C" – shaped structures made out of cartilage. They are loosely attached to the end of the tibia and function as shock absorbers.

Because the lateral menisci have greater mobility they are less likely to get trapped and torn. Only the outer 1/3rd of the menisci have a blood supply – hence tears of the outer 1/3 may heal on their own whereas tears of the inner 2/3 will not.


The menisci can be split by forces which grind them between the femur and the tibia.

This can only occur if:

1) Weight is being taken on the leg
2) The knee is flexed
3) There is a twisting strain

In the middle age the menisci are less mobile and more brittle and hence can be torn more easily e.g. after prolonged squatting.


The single most important symptom of a menisci tear is pain localised to one side of the joint which is made worse by activity especially squatting, twisting and exercise. Sometimes a tearing sensation may be felt at the time of injury. Often the knee will become slightly swollen. The torn portion of the cartilage may shift and become jammed between the femur and tibia preventing the knee from straightening fully ('locking"). The knee may also feel unstable (like "giving way").


The three most common signs are:

1) Tenderness along the joint line
2) Slight swelling
3) Loss of full extension


Variable – small peripheral tears can heal completely whereas large central tears are more likely to cause chronic problems.


Initially – restrict activities
– physiotherapy

If symptoms continue for longer than six weeks a referral to an orthopaedic specialist for arthroscopy allows an accurate diagnosis to be made and certain surgical procedures can also be carried out at the same time e.g. repairing a peripheral tear or trimming a central tear (partial meniscectomy). Arthroscopic surgery results in a rapid recovery and an early return to work and sport.

N.B. Ligament and meniscal injuries can occur in any combination depending on the forces involved at the time of the injury.

Four tyes of meniscal tears

Four Types of meniscal tears. A. Bucket handle. B. Longitudinal tear of lateral meniscus. C. Horizontal tear. D. Radial tear


The patella is responsible for a significant number of problems around the knee.

1) Patella Dislocation

This is a relatively common condition occurring predominantly in young teenagers. There are often predisposing factors such as lax ligaments, tight muscles, a small "high" patella, "knock knees", a large angle between the femur and tibia and knees which hyperextend.

A relatively mild blow to the medial side of the patella causes the capsule to be tom, the patella dislocates to the lateral side, the knee gets "stuck" in a flexed position and the person falls to the ground.

First aid treatment involves splinting the knee in the most comfortable position e.g. putting pillows/towels/blankets underneath and rapid transport to an accident and emergency facility.

After the patella has been reduced crutches and a brace may be used initially, followed by a course of physiotherapy. Surgery is reserved for people who have recurrent dislocations.

2) Patella Tendonitis

Muscles, ligaments and tendons can be damaged in two ways:

i) A sudden injury e.g. a sprain/strain/contusion.

ii) A slower chronic over-use type injury. Here there is no single event that causes damage. Instead over a period of time the cumulative stresses of training and competing exceed the ability of those tissues to cope with those forces and tissue damage ultimately results e.g. tendonitis or stress fractures.

Hence over-use type injuries are more common in repetitive activities like jumping and kicking. Patella tendonitis causes pain anteriorly which is made worse by exercise. Tenderness is generally felt over the patella tendon. Treatment consists of a reduction in spouting activities together with physiotherapy and anti-inflammatory medications.

3) "Patello-Femoral Syndrome"

This includes a variety of conditions which all have in common the fact that they cause anterior knee pain (which is made worse by kneeling, prolonged sitting and descending hills and stairs) and a feeling of instability. Often the underlying problem is biomechanical meaning that the shape of the bones, the strength of the muscles and the flexibility of the ligaments causes the patella to "mal-track" as the knee flexes and extends.

"PFS" can be a very difficult problem to cure but physiotherapy remains the mainstay of treatment. Occasionally arthroscopy is used to evaluate chronic severe cases.

dislocated patella - osteoarthritis

from left: normal knee, dislocated patella, normal knee (smooth fibro-cartilage), osteoarthritis (fibro-cartilage split and cracked)


The end result of a lot of knee injuries is a condition called osteoarthritis. This is a normal "ageing" process but can be accelerated after knee injuries such as meniscal tears and cruciate ligament ruptures. The fibro-cartilage lining the ends of the smooth shiny white femur and tibia (identical to the "gristle" on the ends of chicken bones) start to degenerate and develop small fissures (splits). Eventually larger cracks and holes develop causing the bone ends to rub directly against one another. This causes pain, stiffness and a sensation of grating called "crepitus". Taking a high-quality glucosamine supplement (e.g. 'Flex' tablets from Pharmanex – visit my website to order) will cause an improvement in symptoms in approximately 50% of osteoarthritis sufferers. The optimal dose appears to be around 1500mgs per day.

Assessing Knee Injuries

Assessing a recently damaged knee is very difficult even for a doctor.

The full extent of a knee injury may not become apparent for several hours, days or even weeks. Assessing a knee injury (or any injury for that matter) involves four separate stages.

listen – look – feel – move

1) Listen:

Take a careful history from the patient including:

i) How did the accident happen (e.g. blow to the lateral side or jumped and landed awkwardly)?

ii) Is it painful? (Where? How much?)

iii) Have they been able to move the knee since the accident?

iv) Have they been able to walk on the leg since the accident?

v) Has the knee been injured previously?

2) Look for:

Deformity e.g. patella stuck laterally



3) Feel for:

Tenderness – start anteriorly working from top to bottom and repeat medially and laterally.

4) Move:

Get the patient to flex and extend the knee. Check for collateral ligament laxity and cruciate ligament laxity.

Any knee injury accompanied by moderate – severe pain, rapid swelling (within one hour of injury), widespread tenderness and difficulty in movement, weight-bearing and walking requires urgent medical attention.

Do Prophylactic Braces Work?

These are braces designed to prevent or reduce the seventy of knee injuries. Evidence to date suggests that they do not appear to be effective in reducing either the number or severity of knee injuries.

What about Functional Braces?

These are designed to provide stability for unstable (i.e. previously damaged) knees. They are constructed with hinges and posts and are held on with straps around the thigh and calf. They are of some value, but only when the forces applied to the knee are low.


Anterior – Situated at the front
Arthroscopy – Surgical technique where a small "telescope" is inserted into a joint
Crepitus – Crackling sound or sensation
Extension – Moving a limb so that the two posts are straightened
Flexion – Moving a limb so that the two parts are bent
Fracture – Broken or cracked bone
Hyperextended – Over extended
Lateral – A position away from the centre of the body (opposite to "medial")
Laxity – Looseness
Locking – Inability to fully straighten a joint
Medial – A position toward the centre of the body
Meniscectomy – Removal of a meniscus
Meniscus – Cartilage inside knee joint
Osteoarthritis – Degeneration of a joint causing pain and stiffness
Periphery – Towards the edge of a structure (opposite to "central")
Posterior – Situated at the back
Prognosis – Outlook
Prophylactic – Preventative
Rotation – Twisting
Signs – Something that is apparent on physical examination e.g. tenderness, swelling
Symptom – Something that the patient complains of e.g. pain

Mechanism Symptoms Signs Treatment
Bone Fracture Direct or indirect force Pain Swelling
Reduced movement
Difficulty weight-bearing
Difficulty walking
Urgent medical attention
MCL Lateral force Tearing sensation
Pain medially
Tender over ligament
LCL Medial force As above As above As above
ACL Turning
Landing from jump
"Giving way"
Surgery if not settling
PCL Direct blow to front of knee Pain Swelling Physio
Meniscal Tears Weight-bearing
Flexed knee
Twisting force
Tearing sensation
Pain medially or laterally
Giving way
Tender joint line
Loss of extension
Surgery if not settling
Patella Dislocation Blow to medial knee Patella going out of place
Pain anteriorly
Patella stuck laterally Doctor for reduction
Tendonitis Repetitive activity e.g. kicking Pain anteriorly Tender patella
Patella-femoral syndrome Biomechanical abnormalities Pain anteriorly Biomechanical abnormalities Physio
Osteoarthritis Previous injury Pain Swelling

Article written by Dr Tom Palfi

'Doctor Tom' is a sports medicine doctor and fitness specialist currently working at Les Mills, Hamilton. He has post-graduate qualifications in sports medicine, emergency medicine, diving medicine, nutrition and adult education. Dr Tom has participated in many sporting events including the DB Ironman, South Island Coast-to-Coast, Rotorua Marathon, Lake Taupo Cycle Challenge, Motu Challenge, Rotorua Toughman Challenge, Goat Alpine Adventure Classic and multiple triathlons; he has climbed Mt Cook and Mera Peak in Nepal (22,000'); other interests include weight-training, tramping, skydiving, hang-gliding, kayaking and skiing; he has dabbled in a variety of Martial Arts including Kempo, Muay Thai, Balintawak, Kickboxing, Close Quarter Combat and Multi-Style Martial Arts.

Dr Tom's philosophy on life is best summarized in this quote:
"When you think you've been burning the candle at both ends & partying too hard just remember this: Life is not a journey to the grave with the intention of arriving safely in a pretty and well-preserved body, but rather to skid in sideways, thoroughly used, totally worn out and loudly proclaiming... 'Sh*t, what a trip!'"