Correct Answer: A. Proximal scaphoid
Proximal scaphoid fractures have the highest non-union rate (up to 12–15%) among all carpal and tarsal bones due to a critical anatomical feature: the scaphoid has a retrograde blood supply—the proximal pole receives blood only from distal-to-proximal vessels entering through the fracture site itself. When the fracture line is at the proximal pole, this tenuous blood supply is completely disrupted, leaving the proximal fragment avascular. Combined with the scaphoid's small surface area, high mobility within the wrist, and the difficulty in achieving rigid immobilization in a cast (the wrist must be held in extension and radial deviation), healing is severely compromised. Non-union is further promoted by the scaphoid's intracapsular location, which limits periosteal callus formation. In Indian orthopedic practice, delayed diagnosis (common in rural settings where scaphoid fractures are initially missed on plain radiographs) and non-compliance with prolonged immobilization (12–16 weeks) significantly increase non-union risk. The waist and proximal pole fractures carry the worst prognosis; distal pole fractures unite reliably because they retain a robust blood supply.
Why the other options are wrong
B. Talar neck — Talar neck fractures do carry a significant non-union risk (~10%) due to the talus's precarious blood supply and intracapsular location. However, the scaphoid's retrograde supply and smaller surface area make it more prone to non-union overall. Talar neck fractures are serious but less frequently non-unite than proximal scaphoid fractures in clinical series. C. Inter-trochanteric — Inter-trochanteric femur fractures have excellent blood supply from the medial and lateral femoral circumflex arteries and large cancellous bone surfaces at the fracture site. Non-union is rare (<1%) in this region. This option exploits the misconception that hip fractures are inherently high-risk; in fact, intracapsular (femoral neck) fractures are the concern, not inter-trochanteric. D. Distal radius — Distal radius fractures (Colles' fractures) have excellent healing potential due to rich vascular supply, large cancellous bone area, and good immobilization with casts. Non-union is rare (<1%). This option is a distractor; distal radius fractures are among the most reliably healing fractures in orthopedics.
High-Yield Facts
- Proximal scaphoid non-union rate: 12–15%—highest among all carpal bones due to retrograde blood supply.
- Scaphoid blood supply is retrograde (distal-to-proximal)—proximal pole fractures render the proximal fragment avascular.
- Scaphoid fractures require 12–16 weeks immobilization—non-compliance is a major cause of non-union in Indian practice.
- Talar neck non-union rate: ~10%—second highest; talus is also intracapsular with precarious supply.
- Inter-trochanteric fractures have <1% non-union rate—excellent blood supply and large cancellous surfaces.
- Distal radius fractures have <1% non-union rate—rich vascular supply and good immobilization potential.
Mnemonics
SCAPHOID RISK = Retrograde + Retrograde + Retrograde Remember: Scaphoid = Retrograde supply, Retrograde healing, Retrograde diagnosis (often missed initially). Three Rs = three reasons for non-union. HIGH NON-UNION BONES: SCAPHOID & TALUS Scaphoid (12–15%) and Talus (10%) are the two carpal/tarsal bones most prone to non-union. Both are intracapsular with tenuous blood supply. Remember: Small bones, Small supply, Small chance of union.
NBE Trap
NBE pairs "inter-trochanteric" with "hip fracture non-union" to exploit the common misconception that all hip fractures are high-risk; students confuse inter-trochanteric (excellent prognosis) with femoral neck (poor prognosis). The scaphoid's retrograde blood supply is the discriminating fact that separates it from all other options.
Clinical Pearl
In Indian emergency departments, scaphoid fractures are frequently missed on initial plain radiographs, especially in rural trauma centers. By the time the diagnosis is made (often weeks later), the fracture is already in the "delayed union" phase. Combined with poor compliance to prolonged immobilization due to economic pressures (loss of work), non-union becomes inevitable. High index of suspicion and early CT/MRI imaging are critical.
_Reference: Bailey & Love Ch. 34 (Fractures and Dislocations); Rockwood & Green's Fractures in Adults (Scaphoid Fractures)_