10 The wrist and hand

Michelle A. Wessely, Julie-Marthe Grenier, Martin Young

Introduction

The clinical evaluation of the wrist and hand regularly results in the use of diagnostic imaging to determine the origin of the patient’s pain or complaint. Commonly, radiographs are taken to assess the osseous structures in particular; however, due to the complexity of the wrist and hand, coupled with the importance of this region in the ability to perform activities of daily living (ADLs), it is often vital that the soft tissue components can be scrutinized to achieve an accurate diagnosis.

In the past, further imaging has consisted of computed tomography (CT) and, in more recent times, ultrasound; however, the detail afforded by magnetic resonance (MR) imaging in determining the anatomical relationships of structures such as the fibrocartilage complex and the ligaments and tendons, which confer the function and stability to the wrist, and hand, has increasingly resulted in MR imaging being adopted to evaluate the detail of this region of the body.

History and examination

Much of what has already been written about the history-taking for the shoulder and elbow also holds true for the wrist and hand: it is part of a kinematic chain and clinical thinking must be directed to the other components of that chain, which may be responsible both for disrupting distal biomechanics and perpetuating symptoms and for referring proximal pathology.¹ It is also necessary to be alert for ‘double crush’ mechanisms of neural entrapment: the nerves that pass through the wrist are also subject to entrapment in the elbow, arm and thoracic outlet, which can refer pain or be comorbid with local entrapment.²

More than any other area, it is essential to enquire about the patient’s side of handedness, occupation and activities of daily living. Even in the face of an obvious precipitating cause, factors such as repetitive activity, computer use, writing and ergonomics can profoundly affect both management and prognosis.

Examination of the wrist and hand, perhaps unsurprisingly, reflects that of the ankle and foot, with emphasis on observation; active and passive ranges of motion; neurological assessment; digital palpation; and muscle testing. There is, again, a paucity of meaningful special orthopaedic tests; the one exception to this is Finkelstein’s test for stenosing tenosynovitis of the tendons of extensor pollicis brevis and abductor pollicis longus.³ This test involves the patient opposing their thumb so that it lies across the palm, then grasping it with the fingers so that it lies within a clenched fist. The examiner then forcibly adducts the thumb to recreate the patient’s symptoms. The examination should also include evaluation of the elbow, shoulder, thoracic outlet and cervical spine.⁴

The presence of obvious and persistent neurological signs and symptoms would, in the first instance, be likely to precipitate referral for nerve conduction studies; otherwise, diagnostic imaging is the next step for the inconclusive examination or unresponsive patient.^5,⁶

Clinical indications

MR imaging of the wrist and hand is performed in a variety of clinical scenarios. For example, in the case of trauma-induced wrist pain, MR imaging of the wrist is useful to determine damage to the soft tissues, such as the scapholunate ligament and triangular fibrocartilage complex, both crucial in maintaining the stability and, therefore, function of the wrist. The same is true of the hand, which is often comorbid with the wrist, and where lesions commonly affect the extensor and flexor mechanisms, both in cases of trauma and non-traumatic deformities.

MR imaging allows visualization of the anatomical structures that enables assessment of the anatomical and functional relationships of the area. In addition to the tissues that may be affected directly by trauma, complications may be also evaluated – such as the development of avascular necrosis, which commonly affects the scaphoid as a complication of fractures. This condition may be studied with great sensitivity using MR imaging and at an earlier stage than with radiography and this may, in some circumstances, alter the clinical prognosis and management of the patient. MR imaging is also useful in assessing the status of the median nerve, and for evaluating the presence of fibrosis, or scar tissue, that may be impeding full recovery for the patient with carpal tunnel syndrome.

Protocols

MR imaging of the wrist and hand may be performed with the patient supine or prone. The prone position is usually reserved for larger patients, where the wrist and hand are placed over the head of the patient, in the ‘Superman’ position. A surface coil will invariably be applied to the patient’s wrist or hand to improve the signal-to-noise ratio and maximize the quality of the image.

The MR imaging study will normally consist of all three imaging planes: coronal, axial and sagittal, which are normally planned from the axial scout view. T1-weighted and T2-weighted sequences are usually performed in one or more imaging planes, with a slice thickness of 1 to 3 mm being adopted. However, depending on the clinical indication for MR imaging of the wrist and hand, particular sequences or even planes may be selected. In the wrist, the imaging study includes the distal radius and ulna up to the bases of the metacarpal bones. In the hand, the imaging study will normally include the distal carpal row to just beyond the distal aspects of the fingers.⁷

For either area, contrast may be added, depending on the nature of the clinical situation being investigated. The contrast may be added via the intravenous route, to attempt to differentiate a soft tissue mass or active inflammation ⁸ or, in some institutions, injected directly in to the joint to perform MR arthrography⁹; however, due to the inherent contrast from the fluid in the wrist, these procedures are not usually necessary. Some institutions have advocated imaging with varying positions of the wrist, placing the patient in pronation and supination in order to further study the ligamentous relationships in these positions¹⁰; however, this has not been adopted as standard protocol in most imaging institutions.

Normal and abnormal imaging appearances of the wrist and hand

Perhaps it is because of the wealth of structures contained in a very limited space that it is, unlike in all of the previous chapters, easier to consider normal and abnormal pathology together on a topic-by-topic basis: it is useful to develop a standard order in which to evaluate these structures so as to be methodical for each imaging study that is presented to the practitioner.

Osseous structures

The coronal imaging study will provide information regarding a number of areas, including the overall gross alignment (Figure 10.01, Box 10.01). On these images, the convex head of the ulna and the articular surface of the distal radius should be at the same level; any variance from this can indicate abnormal stresses being placed on the wrist, and is associated with a number of syndromes (Table 10.01).¹¹^–¹⁵

Figure 10.01 • Coronal T1-weighted MR imaging of the wrist demonstrating the proximal and distal carpal rows in detail. Note the alignment of the carpal bones in both carpal rows as well as the homogeneous signal intensity in this patient where the bony structures are normal. In addition, the triangular fibrocartilaginous complex is seen as a low signal region just proximal to the lunate and triquetrum (oval).

Box 10.01 Key to anatomical structures in annotated figures

# Triangular fibrocartilage complex

I, II, III, IV, V – metacarpals

1. Interosseous muscles

2. Dorsal intercarpal ligament

3. Extensor retinaculum

4. Abductor pollicis longus tendon

5. Extensor pollicis brevis tendon

6. Extensor carpi radialis brevis tendon

7. Extensor carpi radialis longus tendon

8. Extensor carpi ulnaris tendon

9. Extensor pollicis longus

10. Extensor digitorum & indicis tendons

11. Extensor digiti minimi

12. Flexor carpi ulnaris tendon

13. Flexor digitorum superficialis

14. Flexor digitorum profundus

15. Flexor pollicus longus

16. Flexor carpi radialis

17. Radial artery

18. Ulnar artery and nerve

19. Median nerve

20. Thenar muscles

21. Flexor & abductor digiti minimi

22. Flexor retinaculum

23. Extensor digitorum and tendon

24. Flexor tendons of the digits

25. Dorsal digital vein

26. Palmar digital artery

27. Radial collateral ligament

Table 10.01 Syndromes associated with distal radioulnar misalignment

Ulna proximal to radius > 2 mm	Radius proximal to ulna > 2 mm
Avascular necrosis of the lunate (Kienböck’s disease) or scaphoid Epiphyseal injury Rett syndrome Chondromalacia of the ulnar head Scapholunate disassociations	Impaction between ulna and lunate Triangular fibrocartilage complex tear Distal radial growth-plate injury (most commonly associated with child gymnasts)

It is also essential to determine that all the carpal bones are present in the proximal and distal carpal rows (Figure 10.01). Carpal coalition is a condition whereby incomplete segmentation has occurred, resulting in two or more of the carpal bones appearing fused; most commonly, the lunate and triquetrum or the capitate and hamate,¹⁶^–¹⁸ although any adjacent bones may seemingly be involved.¹⁹^–²⁵ The distal carpals may also be congenitally fused with the metacarpals, the most common coalition being between the second metacarpal and trapezoid.²⁶ Accessory ossicles may be present, which represent a normal variation, usually without clinical consequence to either the patient or physician; one exception to this is the presence of an os styloideum, a common bony protuberance located on the dorsal surface of the base of the second and third metacarpals, which may be associated with degenerative changes, bursitis or ganglia.^26,²⁷ In patients with a history of trauma, ossification may occur in and around tendons, resulting in the appearance of osseous lesions about the wrist and hand, a form of myositis ossificans (Figure 10.02).²⁸