Avascular Necrosis of the Lunate.

Incidence and risk factors

Incidence

The condition tends to affect males in their third or fourth decades. It is usually limited to one wrist.  Certain individuals may be predisposed due to anatomic variations in blood supply, ulnar length, and lunate shape:

1. Vascular

There are various patterns of blood supply to the lunate including “X”, “I”, and “Y” patterns.  Between 7 and 26 percent of lunates have only one artery supplying them (“I” pattern), with 31 percent having no arterial branching within the lunate (Gelberman, Bauman et al. 1980; Panagis, Gelberman et al. 1983). This pattern may render the lunate more susceptible to avascular necrosis, as injury to the single vessel cannot be compensated by collateral flow.

2. Load distribution

a. Ulnar Variance
The length of the distal ulna with respect to the distal radius in the AP plane is called ulnar variance. A shorter ulna, or negative ulnar variance, may lead to increased load across the radiolunate articulation, with increased risk of lunate avascular necrosis. This relationship has been shown in some studies; others have found no such correlation, and since Kienböck’s disease occurs in individuals with neutral and even positive ulnar variance, other factors must be involved as well.(Gelberman, Salamon et al. 1975; Chen and Shih 1990; Coe and Trumble 1993; Weiss 1994)

b. Lunate Shape
The geometry of the lunate itself and of surrounding bones may also be significant.

One investigator noted a tendency toward a smaller lunate in his patients with the disorder.(Tsuge and Nakamura 1993) Three different patterns of lunate morphology at the articulation with the scaphoid, radius, and triquetrum have been described along with findings that the vascular foramina tended to occur in proximal triangular areas of the bone, such that some lunate specimens are less well vascularized than others.

Acquisition

Kienbock’s is idiopathic meaning there is no known etiology.  However, as previously discussed, it likely results from both being predisposed (triangular lunate, negative ulnar variance, “I” pattern artery) as well as being exposed to environmental influences (repetitive trauma). 

Genetics

Communicability

Lifestyle risk factors

Exposure to repetitive trauma is a risk factor. Activities that involve compression loading of the wrist particularly in extension (eg jackhammers) have been postulated to cause vascular injury.

Other generic risk factors for avascular necrosis include history of steroid use, sickle cell anemia, exposure to increased barometric pressure (eg diving), and smoking.  These risk factors are not particular to Kienbock’s and have been documented more commonly in the hip, knee, and shoulder.

Injury & trauma risk factors

Prevention

There is no prophylaxis against Kienbock’s since you cannot identify individuals at risk.

Manual jackhammers have largely been replaced with hydraulic ones.  Other than this intervention in the workplace, there are no guidelines for primary prophylaxis against Kienbock’s.

Surgery for Kienbock's Disease at the University of Washington, Department of Orthopaedics and Sports Medicine, Seattle, Washington

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