Orthopaedics 360
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.
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
Soft Tissue Issues
Generalised Ligamentous Laxity – Extreme Joint mobility | Flexibility
Tight Lateral (Outer) soft tissues
Quadriceps (VMO) Weakness
Recurrent Patella Dislocations can lead to Arthritis
SHARE THIS:
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.
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.
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.
How not to rupture your ACL – Emily Peut
Our trusted partners in Physiotherapy - we have the pleasure of our continued collaboration with Physio Fit's Emily Peut. Emily has a passion and knowledge base for ACL (Anterior Cruciate Ligament) injuries in Adelaide. She has extensively studied and applied her...
ACL injuries – Rupture Repair and Rehabilitation
This week I have the pleasure of introducing Patrick Carbone from Inertia Health Group. He has been working with us for over 5 years with a focus on rehabilitation of our patients with their unique rehab protocols for total hip replacement, total knee replacement...
Mindfulness in Hip and Knee Surgery
Being aware of how you feel, and putting yourself into a good state of mind before, during and after surgery can have an impact on the outcomes of surgery, especially surgery as large as hip and knee replacement surgery. In this weeks article, we join Dr Sharon...
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.
Orthopaedics 360
Orthopaedics 360
P: (08) 7099 0188
F: (08) 7099 0171
Southern Specialist Centre
Orthopaedics 360
P: (08) 7099 0188
F: (08) 7099 0171
Health @ Hindmarsh
Orthopaedics 360
P: (08) 7099 0188
F: (08) 7099 0171