The Standard Procedure: A Hand and Wrist X-Ray
To determine an individual's skeletal maturity, doctors most commonly order an X-ray of the left hand and wrist. This method is the gold standard for several reasons: it exposes the patient to a very low dose of radiation, is quick and painless, and the hand and wrist contain a high concentration of bones that show developmental changes over time. By focusing on one side of the body, the procedure is standardized and reproducible.
Why the Left Hand and Wrist Are Used
The hand and wrist serve as a window into the body's skeletal development. They contain numerous bones, including the small carpal bones and the growth plates, or physes, at the ends of the longer bones in the fingers, hand, and forearm. These growth plates are areas of new bone growth and are softer and less mineralized, appearing darker on an X-ray. As a person matures, these growth plates change in size, shape, and density until they eventually close, or fuse, when skeletal growth is complete. The left hand is chosen to standardize the process and avoid any potential bias from an individual's dominant, and potentially more developed, hand.
The Examination Process
The procedure is simple. The patient is asked to place their left hand, palm down and fingers spread, on a table. A heavy, protective apron may be placed over the patient's torso to minimize radiation exposure. The X-ray technician then captures an image of the hand and wrist, which takes only a few seconds. The resulting image is a black and white picture of the bones and soft tissues.
Interpreting the Results: The Comparison Methods
Once the X-ray is complete, a pediatric radiologist or endocrinologist interprets the results. They use standardized methods to compare the X-ray to a reference standard, which allows them to assign a bone age.
Greulich and Pyle (GP) Atlas Method
This is one of the most widely used methods, particularly in the United States. It involves comparing the patient's X-ray image to a series of standard images in an atlas. The atlas contains X-rays of the left hand and wrist from children at different ages and of different genders. The radiologist finds the image in the atlas that most closely matches the patient's skeletal development, and the chronological age of that reference image becomes the patient's bone age. While this is a quick method, it was developed based on data from a specific population in the 1930s and 1940s, which may not perfectly reflect modern, diverse populations.
Tanner-Whitehouse (TW) Scoring Method
The Tanner-Whitehouse method is a more complex scoring system. Instead of a visual comparison, a radiologist assigns a numerical score to individual bones in the hand and wrist based on their level of maturity. These scores are then totaled and correlated to a sex-specific bone age. The TW method has evolved, with TW3 being the latest update, and is often considered more precise and reproducible than the GP method, though it is more time-consuming.
Automated Assessment
For decades, the standard methods for determining bone age have relied on visual evaluation of skeletal development in the hand and wrist. New technology has made it possible to use automated systems, such as BoneXpert, that use artificial intelligence and machine learning to analyze the X-ray images. These systems can reduce inter-rater variability and increase efficiency, though they require validation across different populations.
What Bone Age Can Reveal
The assessment of bone age provides crucial information for pediatricians and endocrinologists, especially when there are concerns about a child's growth or development.
Predicting Final Height
Based on a child's bone age and current height, doctors can use specialized tables, like the Bayley-Pinneau method, to predict a child's final adult height. This can be especially useful for children with growth disorders or those with constitutional growth delay.
Diagnosing Growth Disorders
A significant difference between a child's bone age and their chronological age can be a marker for an underlying medical condition. A bone age that is significantly advanced for a child's chronological age can indicate precocious puberty, while a delayed bone age can point to constitutional delay of growth, hypothyroidism, or growth hormone deficiency.
Timing of Puberty
Since the maturation of bones is directly linked to the production of sex hormones, bone age can offer a reliable estimate of when a child will enter puberty. An advanced bone age suggests an earlier onset of puberty, while a delayed bone age points to a later one.
Factors Influencing Bone Maturation
Several factors can influence a child's skeletal maturity, leading to variations in bone age. These include:
- Genetics: A child's genetic makeup is the primary driver of their growth patterns and potential final height. A family history of late bloomers, for example, can result in a delayed bone age that is considered a variation of normal development.
- Hormones: The progression of skeletal development is controlled by a complex interplay of hormones, including growth hormone, thyroid hormones, and sex steroids like estrogen and testosterone. Imbalances in these hormones can cause bone age to be either advanced or delayed.
- Nutrition: Severe malnutrition or dietary deficiencies can impede normal growth and delay skeletal maturation.
- Chronic Illness: Certain chronic conditions, such as kidney, heart, or gastrointestinal diseases, can affect a child's growth velocity and bone age.
| Feature | Greulich and Pyle Method | Tanner-Whitehouse (TW3) Method |
|---|---|---|
| Assessment Style | Comparison against a visual atlas of standard X-ray images. | Numerical scoring system based on specific bone maturity stages. |
| Required Skill | Relatively quicker and simpler to perform; higher intra- and inter-observer variability. | More complex and time-consuming, but generally more precise and reproducible. |
| Reference Population | Primarily based on data from white children in the 1930s-1940s. | Based on radiographs from children in the UK during the 1950s-1960s, with later updates for broader populations. |
| Output | A single bone age based on the closest matching atlas image. | A cumulative score that is converted into a sex-specific bone age. |
| Considerations | May not be fully accurate for all ethnic groups due to its historical data source. | Requires more training but provides a potentially more objective and detailed assessment. |
Conclusion
Understanding how to find out your bone age is a vital part of pediatric health, providing a deeper look into a child's biological development beyond their chronological age. The process, which relies on a standard X-ray of the hand and wrist, allows medical professionals to accurately assess skeletal maturity using established comparison and scoring methods. The information gleaned from a bone age assessment is crucial for diagnosing potential growth disorders, predicting a child's final adult height, and timing the onset of puberty. While a difference between bone age and chronological age can be a normal variation, it warrants medical attention to rule out any underlying issues affecting healthy growth and maturation. Consult a healthcare provider for a proper assessment and interpretation of results.
