Anatomy and Classification: Understanding the Stages
At a Glance
Radial longitudinal deficiency (radial hemimelia) is staged using the Bayne and Klug scale for the forearm and the Blauth scale for the thumb. The thumb's classification, specifically if the base joint is stable, is the critical tipping point for determining your child's surgical options.
Understanding the anatomy of your child’s arm is the first step in understanding their treatment path. The forearm naturally contains two bones: the radius (on the thumb side) and the ulna (on the pinky side). In radial longitudinal deficiency (RLD), the radius is the primary bone affected, but the thumb and wrist bones are almost always involved as well [1][2].
Doctors use two main “grading scales” to describe the severity of these differences. These classifications help your care team decide which surgeries will be most effective.
The Forearm: Bayne and Klug Classification
This system describes how much of the radius bone is present. As the “Type” number increases, more of the bone is missing [2].
- Type I (Short Radius): The radius is present but slightly shorter than normal. The hand may tilt slightly toward the thumb side [3].
- Type II (Hypoplastic): The radius is much smaller and thinner than usual, providing very little support for the wrist [3].
- Type III (Partial Absence): A large portion of the radius (usually the part near the wrist) is missing entirely [4].
- Type IV (Total Absence): This is the most common form. The radius bone is completely missing. Without the radius for support, the hand is often turned significantly inward [4][3].
The Thumb: Blauth Classification
Because the radius and the thumb develop from the same “instructions” in the womb, the severity of the radius deficiency usually matches the severity of the thumb deficiency [4][2].
| Type | Description | Functional Status |
|---|---|---|
| Type I | Small thumb | Slightly smaller but works well [5]. |
| Type II | Narrow web space | Small muscles; the “V” between thumb and index is tight [6]. |
| Type IIIA | Unstable base | The bones are there, but the joint at the bottom is weak [6]. |
| Type IIIB | Very unstable | The joint at the base is missing; the thumb cannot be used for pinching [6]. |
| Type IV | “Floating Thumb” | A tiny thumb attached only by skin and a few vessels [7]. |
| Type V | Absent Thumb | The thumb is completely missing [4]. |
Why “IIIA vs. IIIB” is the Most Important Detail
In your child’s medical report, pay close attention to whether the thumb is called “IIIA” or “IIIB.” This is the “tipping point” for treatment [6].
- Type IIIA thumbs can often be reconstructed (fixed) through surgeries to deepen the web space and strengthen the muscles [6][8].
- Type IIIB and IV thumbs usually cannot be made functional. In these cases, surgeons often recommend pollicization—a remarkable procedure where the index finger is moved into the thumb position to create a strong, working grip [9][7].
Auditing Your Child’s Report
When you receive an X-ray or specialist report, look for these two specific stages. A complete diagnosis should look something like: “Bayne Type IV radius with Blauth Type IV thumb.” If your report only mentions the radius, ask your surgeon to specifically stage the thumb as well, as this will dictate much of your child’s future hand function.
Common questions in this guide
What does a Type IV radius mean in the Bayne and Klug classification?
What is the difference between a Blauth Type IIIA and Type IIIB thumb?
What is a "floating thumb"?
Why does my child's diagnosis involve both the forearm and the thumb?
Questions to Ask Your Doctor
Curated prompts to bring to your next appointment.
- 1.Based on the X-rays, which Bayne and Klug Type is my child's forearm?
- 2.Is the base of the thumb (the carpometacarpal joint) stable? Does this make it a Type IIIA or a Type IIIB thumb?
- 3.How does the shortness of the ulna affect the overall classification and future growth?
- 4.Can you show me on the X-ray if there are any carpal (wrist) bones missing?
- 5.How does the specific classification of the radius and the thumb change our surgical options?
Questions For You
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References
References (9)
- 1
An Algorithm for Management of Radial Longitudinal Deficiency.
Bhat AK, Pai G M
The journal of hand surgery Asian-Pacific volume 2024; (29(6)):508-518 doi:10.1142/S2424835524300093.
PMID: 39544041 - 2
Association of Radial Longitudinal Deficiency and Thumb Hypoplasia: An Update Using the CoULD Registry.
Forman M, Canizares MF, Bohn D, et al.
The Journal of bone and joint surgery. American volume 2020; (102(20)):1815-1822 doi:10.2106/JBJS.20.00281.
PMID: 33086350 - 3
Long-term follow-up for the atypical radial longitudinal deficiency: A case report.
Satake H, Takeuchi R, Naganuma Y, et al.
Congenital anomalies 2024; (64(4)):172-176 doi:10.1111/cga.12570.
PMID: 38663448 - 4
Radial Longitudinal Deficiency: Severity Differences Between U.S. and Japanese Cohorts.
Halverson SJ, Takayama S, Ochi K, et al.
The Journal of hand surgery 2020; (45(3)):196-202.e2 doi:10.1016/j.jhsa.2019.12.004.
PMID: 31959377 - 5
Tendon Transfers for the Hypoplastic Thumb.
Wall LB, Goldfarb CA
Hand clinics 2016; (32(3)):417-21.
PMID: 27387085 - 6
Congenital Disorders of the Pediatric Thumb.
Nguyen JL, Ho CA
JBJS reviews 2022; (10(3)) doi:10.2106/JBJS.RVW.21.00147.
PMID: 35230999 - 7
Improvement of thenar bulk appearance in index finger pollicization with adipofascial flap fashioned from pouce flottant/rudimentary thumb.
Bercu C, Rosner B, Korah H, et al.
Journal of hand and microsurgery 2025; (17(3)):100248 doi:10.1016/j.jham.2025.100248.
PMID: 40224953 - 8
Surgical techniques for reconstruction of the hypoplastic thumb.
Mende K, Suurmeijer JA, Tonkin MA
The Journal of hand surgery, European volume 2019; (44(1)):15-24 doi:10.1177/1753193418793579.
PMID: 30134746 - 9
Functional Evaluation of Pollicization in Young Children with Radial Longitudinal Deficiency: Beneficial Results Despite the Presence of Finger Anomalies.
Mehta R, Sripathy AK, Thatte MR
Indian journal of orthopaedics 2026; (60(4)):886-892 doi:10.1007/s43465-025-01639-4.
PMID: 42027321
This page explains radial hemimelia classifications for educational purposes only. Always consult your child's pediatric orthopedic surgeon or hand specialist to interpret specific X-rays and medical reports.
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