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Orthopaedics 360

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Patella (‘Knee-cap’) instability is a complex condition. The term ‘Instability’ refers to a spectrum of conditions ranging from subtle mal-alignment of the patella, to a chronic patella dislocation. The most common form of ‘Instability’ is recurrent subluxations/ dislocations of the patella.

What Causes Patella Dislocations

The patella is a large bone over the front of the knee that has connections to both the quadriceps tendon and the patella tendon. This arrangement forms the ‘Extensor mechanism’ that is responsible for bein

g able to extend your knee out straight. As the knee bends, the patella is designed to glide smoothly in a ‘V’ shaped groove in the femur (‘Thigh bone’) called the ‘Trochlea’.  Any disruption to this smooth gliding design can result in ‘patella instability’

 

Traumatic Dislocation

The patella can be acutely displaced as the result of a specific acute injury.

patella dislocations treatment mike smith chien wen liew knee specialist adelaide
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Atraumatic Dislocation 

In this situation, the patella loses contact with the trochlea without an acute injury. This can be seen in patients that have experiences multiple traumatic dislocations in the past, or in patients with bony abnormalities (see below) that predispose to this ‘Instability’. While there are many factors that can lead to this condition (See Below) , it is often a combination of several of these that result in the patella losing its normal contact with the thigh bone.

 

Bony Issues 

 

Abnormal Leg alignment / Rotation

High Riding Patella (Patella ‘Alta’)

Shallow Trochlea (Groove) = Trochlea Dysplasia

patella dislocation treatment mike smith knee surgeon patella alta
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Soft Tissue Issues 

 

Generalised Ligamentous Laxity – Extreme Joint mobility | Flexibility

Tight Lateral (Outer) soft tissues

Quadriceps (VMO) Weakness

adelaide orthopaedic knee surgeon patella dislocation mpfl tear
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Recurrent Patella Dislocations can lead to Arthritis

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What happens when you dislocate your patella

You may already know

Patients who experience a frank dislocation will notice that the knee cap sits on abnormally on the outer (‘lateral’) side of the knee. An ambulance or medical officer may be required to reposition the knee cap by straightening the leg. In patients who experience multiple dislocations, the patella can often be repositioned by the patient themselves. Fluid often accumulates inside the knee joint and pain is experienced on the inner (‘medial’) side of the knee owing to a ruptured ligament (‘Medial patellofemoral Ligament’)

Making the Diagnosis

Patella Instability is a complex spectrum that certainly warrants a very thorough evaluation. A detailed history is taken to determine the patients symptoms and frequency of dislocations. A detailed examination is performed to assess for underlying bony and soft tissue factors that may be contributing. Plain xrays are routinely ordered. Frequently a CT scan and a MRI scan are required in the setting of patient that is experiencing multiple episodes or ongoing pain.

 

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Surgical intervention is considered in the following situations

Acute Dislocation with a loose body inside the knee joint

Occasionally the patella will ‘knock off’ a fragment of bone from either the patella itself, or the end of the thigh bone during a dislocation episode. This requires an arthroscopy to remove or repair the loose fragment depending on its size.

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Recurrent Dislocations | Chronic Instability 

Patients who have ongoing episodes, despite initial conservative treatment, are candidates for patella realignment surgery. This involves restoring the normal gliding of the patella in its groove of the thigh bone.

 

Arthritis

Patients who have had ‘Instability’ for many years, often have cartilage damage underneath the knee cap. Surgical treatment is aimed at reducing pain.

 

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Disclaimer: Please note that this is general advice only - for more information, please consult your regular doctor, or obtain a referral to see a specialist orthopaedic surgeon. 

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Orthopaedics 360 are proud to be partnered with Rugby Union SA. With one of the most active sporting clubs in South Australia, we have acknowledged the growing need for customised care for the growing and established athletes.

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