Ulnar variance describes the relative lengths of the forearm bones, the radius and the ulna, where they meet the small bones of the wrist. Variations in this measurement can influence wrist joint biomechanics. Negative ulnar variance occurs when the ulna bone is shorter than the radius at the wrist. This anatomical difference is a common variation that can sometimes contribute to wrist problems.
Understanding Ulnar Variance
The wrist is formed by the radius and ulna, which articulate with the carpal bones in the hand. The radius is the larger of the two forearm bones at the wrist end, located on the thumb side, while the ulna is on the pinky finger side. Ulnar variance refers to the length difference between the distal ends of these bones. This measurement is typically performed using an X-ray of the wrist, usually taken with the arm in a neutral position.
Ulnar variance can be classified into three types. Neutral ulnar variance means the ulna and radius are approximately the same length, with a difference generally between 0 and 1 millimeter. Positive ulnar variance indicates the ulna is longer than the radius, extending further towards the hand. Negative ulnar variance signifies the ulna is shorter than the radius at the wrist joint.
Primary Causes of Negative Ulnar Variance
Negative ulnar variance can arise from several factors, including developmental issues, traumatic injuries, and, less commonly, certain systemic conditions. These factors alter the growth or structure of the forearm bones, leading to a shorter ulna relative to the radius. Understanding these origins helps in comprehending the potential impact on wrist mechanics.
Developmental factors include congenital conditions like Madelung deformity, which can cause an abnormal curvature and shortening of the radius, making the ulna appear relatively shorter. Uneven growth plate closure during childhood can also contribute, where the radius growth plate might grow more than the ulna, leading to a length discrepancy.
Traumatic injuries are a common cause of acquired negative ulnar variance. Fractures of the distal radius, particularly those that heal with shortening or angulation, can make the ulna relatively longer. Growth plate injuries in children, such as Salter-Harris fractures affecting the distal radius, can prematurely stop or slow its growth, leading to a greater relative length of the ulna over time. Injuries to the distal radioulnar joint ligaments, such as those seen in Galeazzi or Essex-Lopresti fracture-dislocations, can also contribute to changes in ulnar variance.
While less common, some systemic conditions can influence bone growth and contribute to negative ulnar variance. Certain skeletal dysplasias or metabolic bone disorders might affect the proportional growth of the forearm bones. These conditions can disrupt the normal developmental processes that dictate bone length, resulting in a shorter ulna relative to the radius.
Associated Conditions and Symptoms
Negative ulnar variance can alter wrist biomechanics, leading to increased stress on certain structures and potentially causing various symptoms. One recognized association is with Kienböck’s disease, a condition involving the death of bone tissue in the lunate, a small carpal bone. The shortened ulna can cause increased load on the lunate, which may contribute to Kienböck’s disease, though many with negative ulnar variance do not develop it.
Individuals may experience wrist pain, particularly during gripping or weight-bearing activities. This pain often arises from altered force distribution across the wrist joint. Changes in load transfer can also lead to reduced range of motion, making certain movements difficult or uncomfortable. Some people might also notice clicking sounds or a sensation of instability in their wrist, reflecting altered joint mechanics.
Diagnosis and Management Approaches
Diagnosing negative ulnar variance typically begins with a physical examination and a review of the patient’s medical history. Imaging studies are crucial for confirming the diagnosis and assessing its severity. X-rays of the wrist, specifically a posteroanterior (PA) view, are the initial and most common method for measuring the relative lengths of the radius and ulna.
Magnetic Resonance Imaging (MRI) may evaluate associated soft tissue damage or detect early signs of conditions like Kienböck’s disease, especially when X-ray findings are inconclusive. In some cases, Computed Tomography (CT) scans can provide more detailed three-dimensional images of the bones, which is helpful for complex cases or surgical planning. The choice of imaging depends on the specific clinical presentation and suspected complications.
Management approaches for negative ulnar variance vary depending on the presence and severity of symptoms and associated conditions. Conservative treatments are often the first line of approach, especially for mild symptoms. These can include rest, immobilization with a splint, and physical therapy to strengthen wrist muscles and improve range of motion. Nonsteroidal anti-inflammatory drugs (NSAIDs) may also be used to manage pain and reduce inflammation.
If conservative measures do not alleviate symptoms, surgical options may be considered to correct the bone length discrepancy or address associated pathologies. Procedures like ulnar lengthening or radial shortening osteotomy aim to equalize the length of the ulna and radius, thereby reducing abnormal stresses on the wrist joint. The specific surgical technique chosen depends on the individual’s condition and the surgeon’s assessment.