Kienbock Disease

Etiology

No consensus exists regarding the primary cause of Kienböck disease. The disorder is multifactorial and is associated with the following variables:

Negative ulnar variance: Negative ulnar variance, also known as ulna minus, refers to an ulna that is disproportionately shorter than the radius. A shortened ulna increases mechanical stress and repetitive microtrauma to the lunate from the relatively longer radius. Results from some studies showed that up to 78% of patients with Kienböck disease have this finding.[4]

Vascular supply to the lunate: The lunate receives blood from a variable number of dorsal and volar penetrating arteries that arise from the dorsal and palmar radiocarpal and intercarpal arches. Intraosseous collateral vessels are sparse. A lower number of penetrating arteries, particularly volar branches from the palmar radiocarpal arch, is associated with a greater likelihood of developing Kienböck disease.[5][6]

Lunate morphology: The risk of Kienböck disease increases as lunate size decreases, causing the bone to bear a greater axial load. The lunate may have a square or rectangular shape, classified as type 2 or type 3, or a more triangular shape without a medial articular facet, classified as type 1. The type 1 lunate has a weaker trabecular pattern and is associated with disease development and progression.[7]

Radial inclination angle: The radial inclination angle is formed by a horizontal line and a line extending from the ulnar edge of the radial articular surface to the tip of the radial styloid. The risk of Kienböck disease increases as the radial inclination angle decreases.[8]

Epidemiology

Kienböck disease is the second most common type of avascular necrosis affecting the carpal bones, after avascular necrosis of the scaphoid. The disorder most commonly affects men aged 20 to 40 years.[5]

History and Physical

Patients usually present with unilateral dorsal wrist pain, restricted wrist motion, weakness, or a combination of these findings. Wrist extension and axial loading typically worsen the pain. Symptoms range from mild to debilitating. Bilateral involvement is rare, and a history of trauma is often absent.[9] Physical examination commonly reveals wrist swelling, tenderness over the lunate, synovitis, and reduced grip strength.[9]

Evaluation

Kienböck disease is diagnosed through clinical assessment and imaging. Radiography, CT, and MRI are highly specific; however, MRI is the most sensitive modality and can detect radiographically occult disease.

Magnetic resonance imaging: A diffuse decrease in lunate bone marrow signal intensity on T1-weighted images is a hallmark of the disease. Signal changes on T2-weighted images or short tau inversion recovery images, which suppress fat signal, vary with disease progression and the extent of osteonecrosis. MRI also evaluates the integrity of the articular cartilage.[6][9]

Radiography: Radiographic findings may be normal early in the disease. When present, findings depend on the morphologic stage and may include diffuse lunate sclerosis, cystic changes, articular surface collapse, carpal collapse, and secondary midcarpal or radiocarpal arthrosis. Coronal fractures may occur in lunates with type 1 morphology.[6][9]

Computed tomography: CT is useful for surgical planning and is more sensitive than radiography for detecting subtle subchondral fractures, coronal lunate fractures, fragmentation, carpal instability, and the degree of trabecular disruption. Patients are frequently restaged after CT imaging.[10]

Nuclear scintigraphy: Findings are nonspecific. Nuclear scintigraphy was previously used as an adjunct for diagnosing early-stage disease but has largely been replaced by MRI.[6]

Treatment / Management

The goals of treating Kienböck disease are to relieve pain, preserve wrist motion, and maintain grip strength.[11] Treatment depends on the disease stage and contributing factors. Stage I disease is treated with splinting or cast immobilization. Stage II disease may also be treated with immobilization when necrosis is incomplete. Stage II disease with complete necrosis and stages III and IV generally require joint-leveling surgical procedures, sometimes combined with vascularized bone grafting or transfer of branches from adjacent arteries. Later-stage disease with lunate collapse and secondary degenerative wrist arthrosis may require proximal row carpectomy or intercarpal arthrodesis. Radial shortening osteotomy is the most common procedure used to unload the lunate in patients with coexisting negative ulnar variance. Treatment may improve symptoms and function without altering imaging findings in advanced disease.[6][9][11](B2)

Differential Diagnosis

Ulnar impaction syndrome: Ulnar impaction syndrome is more common in patients with positive ulnar variance and results from repetitive microtrauma to the lunate from a relatively long ulna. Similar to Kienböck disease, ulnar impaction syndrome causes decreased signal intensity on T1-weighted images and increased signal intensity on T2-weighted images when hyperemia is present or decreased T2-weighted signal intensity after progression to lunate sclerosis. However, signal abnormalities in Kienböck disease are more diffuse or more pronounced along the radial aspect of the lunate. Additionally, ulnar impaction syndrome affects the ulnar head and triquetrum, which remain intact in patients with Kienböck disease.[6][12]

Lunate intraosseous ganglion: Intraosseous ganglia are true cysts that demonstrate low signal intensity on T1-weighted images and high signal intensity on T2-weighted images. Sharp, smooth margins on MRI and radiography help distinguish these lesions from Kienböck disease.[6]

Bone contusion: A bone contusion may be difficult to distinguish from early-stage Kienböck disease on MRI. A history of recent trauma and associated wrist or hand injuries may help establish the diagnosis.[6] 

Arthritis: Bone marrow signal changes in inflammatory or degenerative arthritides may mimic those seen in Kienböck disease. Distinguishing features include demographics, clinical presentation, and absence of ulna minus in arthritis.[6]

Osteoid osteoma: Osteoid osteoma of the carpal bones is rare, with only a few reported cases in the literature. The clinical presentation and identification of a lucent nidus surrounded by a sclerotic rim on CT help distinguish osteoid osteoma from Kienböck disease.[13]

Enostosis or bone island: An enostosis demonstrates low signal intensity on all imaging sequences while preserving normal bone morphology. The sclerotic area is typically stellate and interdigitates with the normal trabeculae.[6]

Staging

Staging of Kienböck disease is essential for treatment planning and includes morphologic and functional classification systems.

Morphologic Staging

Morphologic staging follows the Lichtman Classification, which is based on radiographic and MRI findings and has low interobserver variability.[6][9][14]

Stage 1: Normal radiograph, lunate signal intensity changes on MRI.

Stage 2: Radiography shows lunate sclerosis with or without fracture lines. The lunate maintains its normal shape.

Stage 3: The lunate articular surface has collapsed.

• 3A: Carpal alignment and height are preserved.
• 3B: Scaphoid flexion and loss of carpal height are present.
• 3C: A coronal lunate fracture is present.

Stage 4: Stage 3B findings are accompanied by radiocarpal or midcarpal arthrosis.

Functional Staging

Functional staging uses contrast-enhanced MRI to assess osseous perfusion and the extent of necrosis. This system helps guide revascularization procedures for morphologic stages 2 and 3A. Precontrast and postcontrast images are acquired using a T2-weighted fat-suppressed sequence.[6][15]

Stage 1: Intense homogeneous contrast enhancement reflects bone marrow ischemia and edema and a viable lunate (corresponds to morphologic stage 1).

Stage 2: Patchy, inhomogeneous enhancement reflects partial necrosis. The remaining viable portion is usually distal.

Stage 3: Absent contrast enhancement reflects complete necrosis.

Prognosis

Kienböck disease is invariably progressive, with joint destruction typically occurring within 3 to 5 years after onset.[6]

Prognosis depends on the following factors:

Functional staging: A greater proportion of viable bone is associated with a better prognosis.[6]

Negative ulnar variance: Greater negative variance is associated with more severe disease and a higher likelihood of progression.[16]

Age at diagnosis: Patients diagnosed at an older age are more likely to have advanced-stage disease and subsequent progression.[16]

Notably, symptom severity does not always correlate with the morphologic stage.

Complications

Kienböck disease can lead to scapholunate dissociation, secondary radiocarpal and midcarpal degenerative arthrosis, and triquetral malalignment.[5]