Imaging modalities of the painful wrist: the role of bone scintigraphy

M. Al-Janabi

Department of Nuclear Medicine, King's College Hospital, London SE5 9RS, UK

The wrist is perhaps the most complicated joint in the body and the most important joint for today's human being in this computer and internet age. Evolutionary in concept where so many bones are constrained to work together, it is not surprising that where there is strain there is conflict. Pain is often the presenting symptom. It is not surprising, then, that the painful wrist presents the physician with a diagnostic challenge. The differential diagnosis is extensive and a definite diagnosis is only achieved in about 70% of cases [1].

Injuries to the wrist account for 14% of all attendances at the accident and emergency department [2]. The time from injury to diagnosis and treatment is a relevant prognostic factor. Patients may present with acute (<1 week), subacute (<1–6 weeks) or chronic (>6 weeks) wrist pain or instability [3].

Physicians are encountering more active patients with illnesses and injuries as a result of the growing numbers who participate in sport and exercise activities. Many conditions can be diagnosed with a good history and physical and radiological examinations. However, evaluation may require other imaging modalities when clinicians are uncertain or want to confirm or exclude a disorder. In some cases, the presumably appropriate therapy fails and the clinician or the patient requires another imaging modality to determine an alternative diagnosis. In addition, active individuals are often reluctant to tolerate inactivity or a delay in diagnosis and hence put pressure on their clinicians to expedite the diagnosis and treatment.

Here I present to the practising physician an approach to the imaging modalities for the painful wrist when the history and examination require further investigation to elucidate a clinical diagnosis.

Standard radiographs are the first line of investigation of the painful wrist. A postero-anterior view of the wrist and good lateral radiographs are essential. They should be examined for bone alignment and abnormalities, joint space width and symmetry and soft tissue injuries [4].

Bone scanning is a valuable diagnostic tool because of its sensitive and non-invasive nature. It is used increasingly in the assessment of the painful wrist as it is successful in the early detection of infectious, inflammatory, traumatic and ischaemic problems of the wrist components. It is often used when patients present with wrist pain despite treatment or when the physical examination and/or radiograph is inconclusive or unremarkable.

The technique's strength lies in its ability to provide early physiological information, such as the blood perfusion pattern and bone metabolic activity, in ambiguous clinical situations such as undetected fractures. The scan can help detect occult fractures, particularly those of the scaphoid. Fracture of the scaphoid can be detected by scintigraphy as early as 7–24 h and its sensitivity approaches 100% within 2 days [5]. Negative bone scans (no active uptake) will reliably rule out acute fractures in questionable cases [5].

The procedure involves the injection of a radioisotope tracer, usually technetium 99m diphosphonate, which is subsequently taken up by the bony tissue. Areas of greater uptake indicate increased osteoblastic activity at the affected site. Decreased tracer localization is seen in areas of reduced or absent blood flow, as in bone infarction, and in areas where the bone has been completely destroyed, as in some cases of cancer.

In some patients, MRI or CT studies of a symptomatic site yield indeterminate findings or suggest only a probably unrelated old lesion [6]. Because bone scans are physiological studies, they can differentiate abnormalities that are metabolically active and may be causing symptoms from those that are inactive. Patient exposure to radioactivity during the bone scintigraphy procedure is low; moreover, a bone scan typically costs about one-third to half the cost of CT or MRI [6].

Bone scans are extremely sensitive for evaluating skeletal pathology but they can be non-specific in some instances. Technical refinements and the elucidation of characteristic scintigraphic patterns of some entities have contributed to increased diagnostic specificity. Well-established scintigraphic patterns include those for stress fractures, osteonecrosis, reflex sympathetic dystrophy, non-union, arthritis and Charcot.

Three-phase/two-phase bone scanning is particularly useful for orthopaedic/rheumatological imaging. In the perfusion phase images are acquired immediately, whereas in the blood pool phase images are acquired 2–10 min after injection. The perfusion and blood pool images, together with the delayed bone images, are particularly useful in diagnosing occult fractures when the history, examination and standard radiographs may not readily identify them, for example fracture of the hamate and scaphoid bones. Careful assessment of bone scan images allows assessment of how long ago the injury took place [7]. A positive finding in all three phases is consistent with an acute lesion up to 4 weeks old, whereas a scan that reveals an abnormality only in the blood pool and delayed images suggests a subacute injury that is 4–12 weeks old. A scan that shows the lesion only in the delayed images usually indicates a chronic process.

An area of locally increased uptake on the perfusion and blood pool images with normal uptake on the corresponding delayed bony images suggests soft tissue inflammation and rules out skeletal pathology, and hence bone scintigraphy is useful in assessing soft tissue injuries around the wrist.

The bone scan is invaluable in the evaluation and early detection of stress injuries of the wrist. This is particularly important in young gymnasts, in whom the wrist may be subjected to repetitive injury [7]. Early detection may prompt therapy, thereby allowing early return to the daily routine. The development of single photon emission computed tomography (SPECT) has enhanced the resolution of bone scans by separating overlying or underlying tissue. This results in improved detection and localization of small abnormalities, especially in areas such as the spine, pelvis and knees. This modality of bone scintigraphy may reveal better anatomical bone detail, but this requires further study.

The white cell scan is also a useful radionucleotide modality in inflammatory and infective arthritis [8]. It assesses accurately the inflammatory or infective process and its response to treatment and does not suffer the problem of a lag period, as in the case of bone scintigraphy.

Ultrasound examination of the wrist is a quick and accessible method of excluding soft tissue abnormalities, particularly tendon damage [9]. Ultrasound is also valuable for identifying ganglia and synovial cysts, which may cause persistent wrist pain. Some physicians would advocate the use of ultrasound scanning as an extension of the physical examination. However, ultrasound findings and the quality of their interpretation is operator-dependent. Furthermore, given the complexity of the wrist joint, ultrasound findings may be limited. Because of this, it is recommend that bone scanning be used first and that, where necessary, ultrasound examination is performed and interpreted by a radiologist experienced in wrist imaging [1].

The above imaging modalities, together with the history and physical examination, should allow the physician to reach a diagnosis in the great majority of patients [1].

CT used with or without a contrast medium is particularly helpful in identifying joint irregularities and soft tissue injuries [10]. Fractures that are difficult to detect, such as those of the hook of hamate and subluxation of the distal radioulnar joint, may be evaluated by CT imaging.

MRI is valuable in the assessment of the painful wrist. It helps to depict soft tissue injuries, such as those of muscle, ligament and cartilage, as well as bone lesions. Avascular necrosis of the lunate (Kienböck's disease) is accurately evaluated on MR images, as are injuries of the scapholunate ligament [11, 12]. Assessment of the growth plate in adolescent patients may reveal physeal cartilage extension into the metaphysis, representing a healing sign in chronically stressed wrists, as is the case in young athletes. However, several studies cast doubt over the accuracy of MRI in identifying triangular fibrocartilage complex tears [13].

Cineradiology is perhaps the only real dynamic investigation in which the wrist is moved through a full range of movement, with specific attempts to reproduce the stresses and positions known by the patient to cause the pain or instability. It is possible to assess for instability of the scapholunate and other interosseous ligaments by this dynamic method [14].

Arthrography is an investigation that serves to determine the integrity of the capsular and intracapsular structures, such as ligaments. The radiocarpal, radioulnar and midcarpal joints are commonly examined in ‘three-phase arthrography’ [15]. The findings of arthrography must be interpreted in the context of the patient's age, the site of pain and the clinical suspicion. Arthrography may be combined with other imaging modalities for more specific and accurate diagnosis. This imaging modality, although still practised in some centres, has been superseded by other techniques.

Arthroscopy is not an imaging technique, but it is discussed here because of its usefulness in diagnosing the chronic wrist pain. Direct visualization of the different components of the wrist remains by far the most reliable means of identifying a cause of the painful wrist and including biopsy [16, 17]. Compared with arthrography, arthroscopy is superior in diagnosing wrist pain [1820]. It also allows potential therapeutic intervention.

Arteriography may be indicated in cases of suspected peripheral vascular disease or thrombosis.

In conclusion, the painful wrist presents clinicians with a diagnostic challenge. A detailed history and careful clinical assessment are of paramount importance. Imaging plays an important role in arriving at the diagnosis and bone scintigraphy plays a central part in this after the plain X-ray. Other imaging modalities mentioned above have a useful secondary role in diagnosing some specific conditions.

References

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Submitted ; Accepted





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