Scaphoid Fractures: Advanced Clinical Guide to Anatomy, Biomechanics, & Management
Key Takeaway
Scaphoid fractures are problematic due to their unique anatomy and precarious retrograde blood supply, making them prone to nonunion and avascular necrosis (AVN). Their critical role in carpal biomechanics means delayed or inadequate treatment can lead to progressive wrist arthritis (SNAC wrist) and chronic dysfunction.
A 24-year-old male presents with persistent wrist pain 4 months after a FOOSH injury. He was initially managed with a wrist brace by his GP for a "sprain." He now has pain at the anatomical snuffbox and loss of grip strength. You order radiographs and a CT scan. What is your diagnosis, how do you classify it, and what are the clinical implications of the findings shown?
Candidate: This patient has a scaphoid nonunion. It likely involves the waist or proximal pole. The implication is that he is at risk of SNAC wrist (Scaphoid Nonunion Advanced Collapse). I would classify it based on the location (waist/proximal) and whether there is evidence of avascular necrosis or humpback deformity on the CT.
Candidates often fail to describe the pattern of progression. A weak answer mentions "arthritis" without specifically defining the SNAC sequence (radial styloid to scaphocapitate to lunocapitate joints) or fails to address the "humpback" deformity, which is the mechanical driver of the secondary carpal instability (DISI).
A high-scoring response identifies the clinical diagnosis as established scaphoid nonunion. The candidate should systematically evaluate the CT for: 1) Humpback deformity (loss of length/sagittal plane angulation), 2) Proximal pole viability (sclerosis/fragmentation suggesting AVN), and 3) SNAC staging (I: radial styloid, II: scaphocapitate joint). The answer must conclude with the biomechanical consequence: loss of scaphoid stability leading to lunate extension (DISI) and the inevitable progression to midcarpal arthrosis.
You decide to take the patient to theatre for an open reduction and internal fixation. Which surgical approach would you choose if there is a significant humpback deformity, and why?
Candidate: I would use a volar (Henry) approach. This allows me to expose the palmar aspect of the scaphoid, which is necessary to perform a corrective osteotomy and insert a bone graft to restore the length and correct the humpback deformity.
Failing to mention the vascular anatomy or the reason for the approach choice. A poor candidate simply says "volar is better" without explaining that the humpback deformity is a ventral collapse, making the volar approach the only one that allows for anatomic reconstruction of the scaphoid length using a wedge graft.
The candidate explicitly states the Volar (Henry) approach is the approach of choice for reconstructing "humpback" malunions because it provides the best visualization for restoring the scaphoid's longitudinal length via a palmar wedge bone graft. They should mention protecting the radial artery and FCR tendon, and clarify that the volar approach is biomechanically advantageous for distal-to-proximal screw insertion in the context of restoring alignment.
Following fixation of a proximal pole fracture, you are concerned about the risk of Avascular Necrosis (AVN). How would you technically adjust your procedure to mitigate this risk?
Candidate: For proximal pole fractures, I would consider a dorsal approach to allow for proximal-to-distal screw insertion, which is less disruptive to the remaining distal blood supply. If AVN is already suspected, I would add a vascularized bone graft, such as a 2,3-ICSRA pedicled graft.
Ignoring the vascular anatomy. Failing to recognize that the proximal pole is entirely dependent on retrograde flow, and therefore, any surgical approach that requires excessive capsular stripping of the dorsal ridge will further jeopardize the viability of the bone.
The gold standard answer demonstrates an understanding of the retrograde blood supply. 1) Utilize the dorsal approach, which is the standard for proximal pole access. 2) Minimize capsular stripping at the dorsal ridge, as this is where the main arterial supply enters. 3) For recalcitrant nonunion with AVN, advocate for a vascularized bone graft (e.g., 2,3-ICSRA) to actively revascularize the proximal fragment, explaining the clinical rationale of "biological" versus "mechanical" fixation.
