By Dr Chan Kin Yuen, Consultant Orthopaedic Surgeon

MRI is also very useful in orthopaedic trauma surgery. Acute muscle haematomas (collection of blood), tears and avulsions are clearly demonstrated.

24 May 2009 - MRI is a safe non-invasive imaging method that does not involve x-ray radiation.

It is now increasingly used in orthopaedic surgery and its sub-specialties that include orthopaedic sports medicine, shoulder and elbow surgery, spine surgery, hip and knee replacement surgery, hand and microsurgery, orthopaedic trauma surgery, foot and ankle surgery, paediatric orthopaedic surgery, and orthopaedic tumour surgery.

It is a modality that specialises in the diagnosis and treatment of diseases involving the musculoskeletal system. The advent of MRI as an imaging method with enhanced tissue contrast, spatial resolution and the possibility of tissue characterisation continue to have tremendous impact on musculoskeletal imaging and improving the basic understanding and treatment of diseases involving the musculoskeletal system.

The newer MRIs with higher resolution images enable more accurate diagnoses and therefore help in surgical planning too.

Some of the common clinical applications of MRIs in orthopaedic surgery include imaging of bones that are affected by avascular necrosis.

What causes this condition is poorly understood but the end result is that bone death occurs. MRI is the imaging modality of choice as it is very sensitive and can detect early bone changes before x-ray changes can be seen. This allows early preventative surgery, which is less extensive.

When bone death occurs at a joint, the joint congruency is lost. When the bone collapses, it requires a more extensive joint replacement surgery as the bones at the joints have undergone permanent osteoarthritis changes.

MRI is particularly sensitive at detecting the early presence and extent of infection. Some studies have suggested that it is even better than bone scans that require injecting radioactive substance intravenously and taking sequential x-rays at timed intervals, which is time-consuming and invasive. Conditions like osteomyelitis, soft tissue abscess, pyoarthritis, infected tendon sheath, cellulites and oedema can be detected early.

MRI is also very useful in orthopaedic trauma surgery. Acute muscle haematomas, tears and avulsions are clearly demonstrated in MRI. MRI is commonly used to detect spinal cord or nerve root damage from spinal fractures with fragments impinging and compressing these structures.

It also helps to determine prognosis for patients with spinal cord oedema rather than haematoma.

For injuries around the knee, MRI has been shown to be an excellent imaging modality for intra- and extra-capsular injuries. It is a valuable adjunct to confirming an anterior cruciate ligament tear that commonly occurs in sports like futsal, football, basketball and badminton that may require anterior cruciate ligament reconstructive surgery.

In more severe injuries, posterior cruciate ligament tears can also be clearly detected. The MRI is also better at differentiating between sprains from a complete tear of collateral knee ligaments. For complete ligament tears, a repair or reconstructive ligament surgery may be necessary depending on the site of the tear.

For meniscal tears from sports-related trauma or degenerative changes, MRI helps in determining if these can be repaired. Those that have degenerative signal changes may suggest that a repair may not be viable.

MRI is also useful to determine if loose bodies in the knee causing locking and pain symptoms may be bone fragments or more importantly from osteochondral fragments.

Those that involve articular surfaces require surgical procedures to fix these large loose fragments, especially if these are cartilaginous in origin and will not show up clearly in plain knee x-rays.

More recently, the MRI has been used extensively in assessing stiff shoulders.

It helps to differentiate stiff shoulders from capsular contractures and impingement from the acromion and those that have an associated rotator cuff tear as an underlying cause for the stiffness. It is also helpful as a prognostic tool, especially when there is wasting of the rotator cuff muscles where the outcome from surgical repair would be poorer. Early detection and surgical intervention would improve the long-term results in terms of better pain control and strength.

In the younger, more active population, MRI is useful for demonstrating the extent of damage to the glenoid labrum when dislocation of the shoulder occurs. This will determine if arthroscopic labral repair is feasible or a more extensive open surgical procedure may be appropriate.

Newer MRIs with high resolution images greatly help in clearly defining the pathologies affecting the shoulder joint.

MRI is superior at detecting foot and ankle instabilities from torn ligaments around the ankle. The site and thickness of these residual torn ligaments will determine the type and extent of the surgery needed to stabilise the ankle. Additionally, any loose bodies or anterior distal osteophytes that cause anterior ankle impingement, especially in very active footballers, can be clearly demonstrated and will assist in the surgical planning and treatment to the problem.

Other areas of importance is the early detection of primary and metastatic bone tumours.

MRI is particularly sensitive and essential for the treating surgeon in staging primary malignant bone tumours by demonstrating medullary or soft tissue extension. The ability to image the tumour in any plane assists greatly in surgical planning.

Bone metastasis, especially involving the spine with spinal canal invasion and compression, can easily be detected and MRI has now replaced myelography as an investigation of choice in most institutions.

For soft tissue primary tumours, MRI is the best available tool that can assess the size and extent of the tumour as well as any neurovascular involvement. However it is not always possible to differentiate between benign and malignant soft tissue tumours. With Gadolinium (Gd-TPA) contrast medium injected intravenously, this helps to differentiate the benign tumour that does not have an increased uptake or increased signal changes on the MR images.

MRI is also useful in assessing synovial disease in rheumatoid arthritis where there is spinal cord impingement and compression of the brain stem and bone destruction from the pannus in any synovial joint involved with the disease.

In the spine, MR is excellent for assessing if there are any nerve root or cord compression from a prolapsed intevertebral disc or degenerate disc, or the degenerate disc causing mechanical instability and pain that may require spinal stabilisation procedures.

Future advancement will allow dynamic MR images that are particularly useful in orthopaedic surgery. This especially applies to conditions that involve the patello femoral joint (around the knee).

Additionally, with future developments, not only structural disorders can be detected but also the physiological function of specific soft tissues can be assessed. This is especially useful in muscle disorders.

It should be remembered that although these high-tech imaging systems are helpful in clarifying the diagnosis and treatment of diseases, it is the patient that health professionals treat and not the images. All these information should be taken in totality, together with a thorough history and examination by the treating attending physician in formulating appropriate treatment.

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