By Dr Ng Eng Seng, Consultant Hand & Microsurgeon

Amongst other uses, the 3T MRI scanner is a great diagnostic tool for hand and wrist injury.

31 May 2009 - Innovations in the field of medical imaging have seen the devlopment of many a “wonder” machine. One such ionnovation is 3T MRI (MRI stands for Magnetic Resonance Imaging). The 3T MRI scan is an effective way to detect wrist ligament tears in greater detail, thus avoiding unnecessary surgery such as invasive arthroscopy.

Conventionally, arthroscopy was used to investigate and treat symptoms of fractures or torn ligaments in the hand and wrist. However, with 3T MRI, the resolution is comparatively sharper and small ligaments can be better seen; bone bruises, cysts, and other tears which are painful can be seen and this will be a map for the doctor to use to outline a treatment plan or eliminate unnecessary surgery. The 3T MRI should be used to determine the origin of the pain before arthroscopy.

The hand and wrist is one of the most complex structures in the human body. There are many bones, joints, and internal structures (ligaments, tendons, nerves, and vessels) that allow us to perform a great variety of movement, from gross grasping to fine hand work. These structures are tiny compared to their lower limb counterparts.

Ligament tears normally occur in people who are into extreme or competitive sports and also in people over the age of 40 (due to ageing). Degeneration can cause the tearing of ligaments too. Problems of the hand and wrist can be very debilitating and may interfere with daily activity or work.

Treating the hand and wrist is a great challenge. The problems that can occur are varied, ranging from congenital, injury, and degeneration to inflammation, metabolic, vascular, and tumour. Injury can involve bones, joints, tendons, blood vessels, and nerves.

Due to its complex structure, with tiny nerves and blood vessels, diagnosing a problematic hand can be rather difficult. Even a proper history and physical examination may not be able to help pinpoint the actual location of the problem. Investigative methods such as X-rays and CT scans only allow the scanning of bony structures (while the patient is being exposed to radiation).

Arthroscopy with the injection of a dye into the joint with X-ray and ultrasound scan have its limitations too because it can be invasive, although this may be minimal. Therefore, 3T MRI is the ideal choice of scanning and is becoming increasingly important in evaluating the pathology of the hand and wrist.

The use of 3T MRI enables greater accuracy and excellent resolution of muscle, ligament, tendon, tendon sheath, vessel, nerve, and marrow images. Therefore, 3T MRI has great potential to replace conventional methods of diagnosis and detection of such problems

The MRI is currently used in the evaluation of ligament injury of the wrist, triangular fibro cartilage complex (TFCC) injury, vascularity of scaphoid or lunate bone (Kienbock Disease), fracture, and assessment of hand swelling.

Carpal (wrist) ligament injury

The human wrist is strong and it forms a stable link between the forearm and the hand in order to allow the hand to function. It consists of eight carpal bones joined together by many strong, short ligaments.

In a normal hand, the bones and ligaments work together to provide smooth movement of the hand and wrist. These ligaments are prone to injury after a fall. A break in the ligament will change the smooth mechanics of the wrist. The commonest ligament that gets injured is the scapholunate ligament that links the scaphoid and lunate bone. Other ligaments can be injured less frequently.

A lot of wrist injuries that are treated as wrist sprains by general practitioners may actually involve torn ligaments. Depending on the severity of injury, a torn ligament is best repaired or stabilised as early as three to six weeks after injury to ensure a stable wrist. If diagnosis is delayed, the ligament will shrink and this will make subsequent repair difficult. If left untreated, it will invariably lead to an osteoarthritic, painful wrist in the future.

An MRI scan allows early detection of partial or complete ligament tear. Such an injury can be treated early with better predictable outcome. It is now the standard investigation method in patients with suspected wrist ligament tears. 3T MRI of the wrist is an effective way to detect wrist ligament tear and can avoid unnecessary arthroscopy surgery, according to a study published in the American Journal of Roentgenography.

Triangular fibrocartilage complex (TFCC) injury

Pain over the ulnar side (the side of the little finger) of the wrist is common and the causes are difficult to elicit. Most of them are treated empirically and wrongly, which commonly result in poor outcomes.

The most common cause of ulnar side wrist pain is triangular fibrocartilage complex (TFCC) injury. The TFCC is formed by cartilage and ligament that ties the lower end of the forearm (radius and ulnar) bone together. Its main role is to stabilise the distal radio-ulnar joint (DRUJ – this lies between the lower end of the radius and ulnar bones) and also provide a cushion to the ulnar side of wrist joint.

Tear of the TFCC can be due to injury, degeneration, or overuse. It can lead to instability of the DRUJ, persistent ulnar side pain on forearm rotation and finally osteoarthritis of the DRUJ. A plain x-ray is unable to detect early TFCC tear. Diagnosis classically depends on invasive arthrography and there is high false positive due to normal degeneration with ageing.

Most cases of mild TFCC tear can be treated with simple cast to allow the ligament to heal. Early complete tear can be treated with surgical repair.

A high quality MRI scan allows an accurate early diagnosis of TFCC tear and proper treatment can ensure a congruent and stable DRUJ.

Scaphoid fracture

A scaphoid fracture is the most common fracture seen in the wrist bones and it is usually caused by falling on an outstretched hand. It is the most important wrist bone and acts as the keystone that links all the wrist bones together.

The diagnosis of a scaphoid fracture can be made with an X-ray but 10-15% of such fractures cannot be seen in early X-rays. Those fractures not seen on X-ray are clearly and easily identified by an MRI scan.

Diagnosing a scaphoid fracture is important because if it is missed, complications such as non-union (failure to heal) or avascular necrosis (bone death due to the shutdown of blood supply) can result. This will lead to long-term problems such as pain, osteoarthritis of the wrist, and impairment of wrist function. CT scans or radioactive isotope scans are used to confirm an occult fracture. However, a CT scan can miss an occult fracture (this has been shown to occur in about 21% of such fractures) while a radioisotope scan shows less specificity.

Many studies have shown that an MRI has a 100% reliability in detecting an occult fracture and picking up other carpal or distal radius fractures.

Besides detection of a fracture, assessment of the vascularity and viability of scaphoid fracture fragments through MRI scans can help us to determine whether re-vascularised bone grafting surgery is required.

Kienbock disease

Kienbock disease is due to the loss of blood supply to the lunate bone of the wrist. It presents as wrist pain, stiffness, and loss of motion. The loss of blood supply can cause bone death (avascular necrosis). It is difficult to diagnose in the early stages as the appearance of the lunate bone is unchanged on x-ray. Early detection is important as it can help to stop the disease from getting worse (this is done by putting the arm in a cast or shortening the radius bone). This gives the bone a chance to regain its blood supply and heal. It can also eliminate pain and keep the normal hand and wrist function. MRI scans allow us to detect early changes in Kienbock disease.

In the later stages, or if it is not treated, bone death will eventually cause lunate collapse and osteoarthritis of the wrist. A patient can lose function and risk permanent damage. Hence early detection of Kienbock disease is essential to avoid long term wrist dysfunction.

Hand and wrist tumours

Tumours of the hand and wrist are quite common and most of them are benign ganglions (a gel-filled cyst arising from the joint). The most common aggressive lesion is giant cell tumour of the tendon sheath that arises from the tendon sheath of the finger.

An MRI scan is essential for diagnosis and assessment of the extent and origin of the tumour before surgery. As the structures of the hand are small, high resolution images are important in order to view the different structures of the hand clearly.

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