Kienböck’s disease, medically known as avascular necrosis of the lunate, is a debilitating condition affecting the wrist. This progressive disorder involves the deterioration and eventual collapse of the lunate, one of the small carpal bones. The condition causes significant pain and functional impairment, presenting a complex challenge in orthopedic medicine.
Defining the Condition
Kienböck’s disease is the medical term for avascular necrosis, or osteonecrosis, of the lunate bone in the wrist. The lunate is one of eight small carpal bones that form the wrist joint, situated centrally in the proximal row. It plays a significant role in wrist movement and stability, linking the forearm bones (radius and ulna) and the hand’s central column.
Avascular necrosis refers to the death of bone tissue resulting from an interruption of its blood supply. When the lunate’s delicate vascular network fails, the bone cells die. This necrotic tissue cannot withstand normal mechanical stresses, leading to structural weakening. Over time, the lunate fragments, collapses, and changes shape, disrupting the carpal structure and often resulting in arthritis.
Understanding the Rarity and Incidence
Kienböck’s disease is classified as a rare disorder, making precise incidence rates difficult to determine. Reported prevalence is estimated around 7 per 100,000 individuals, though figures vary based on the population studied. One nationwide study found a mean annual incidence rate of 9.60 per million person-years.
Challenges in accurate tracking arise because early-stage cases may be misdiagnosed as a simple wrist sprain or go entirely unreported. This underreporting, along with documented asymptomatic cases, complicates the measurement of true prevalence and large-scale epidemiological studies.
The condition typically affects males between the ages of 20 and 40 years, who have a higher incidence rate than women. Women who are affected tend to be older at diagnosis. The disease is overwhelmingly unilateral, meaning it affects only one wrist, and often occurs in the dominant hand.
Known Causes and Contributing Factors
Kienböck’s disease has a multifactorial origin involving mechanical, anatomical, and vascular elements. A primary anatomical risk factor is negative ulnar variance, where the ulna is shorter than the radius. This length difference between the forearm bones is frequently observed in patients.
This discrepancy transmits greater and uneven compressive forces through the radius directly onto the lunate bone. This increased mechanical stress can lead to microtrauma or a stress fracture, compromising the bone’s blood supply. Studies indicate that up to 78% of people with the disease may exhibit a shorter ulna.
Vascular factors are equally important, as the lunate bone often has a unique and limited blood supply pattern. Sparse intraosseous arterial connections make the lunate vulnerable to ischemia if a vessel is damaged. Acute trauma or repetitive microtrauma from occupational activities can injure these delicate vessels, initiating avascular necrosis.
Diagnosis and Treatment Approaches
The clinical pathway for Kienböck’s disease begins with imaging to confirm the diagnosis and determine the stage of the disease. While plain X-rays are the first step, they may appear normal in the earliest stage. Magnetic Resonance Imaging (MRI) is considered the most reliable test for early diagnosis, as it visualizes reduced blood flow and cellular changes before structural collapse occurs.
Treatment selection depends heavily on the disease stage, which is commonly classified using the Lichtman system. For early-stage disease, treatment is often nonoperative, focusing on conservative management such as wrist immobilization and anti-inflammatory medications. This approach aims to protect the bone and allow for potential revascularization. When the disease progresses, surgical intervention becomes necessary, with procedures categorized based on the goal of treatment.
Leveling Procedures
Leveling procedures, like radial shortening osteotomy, are performed if negative ulnar variance is present to reduce the mechanical load on the lunate.
Revascularization Procedures
Revascularization procedures involve transferring a vascularized bone graft to the lunate to directly restore blood flow.
Salvage Operations
In advanced stages where the lunate has fully collapsed and arthritis has set in, salvage operations are required, such as a proximal row carpectomy or wrist fusion, to relieve pain and stabilize the joint.