Capitate Fractures

The carpus has a family of bones that die the same way, and the capitate belongs to it. Retrograde intraosseous supply entering distally means the PROXIMAL pole is the fragment at risk - the identical arrangement that makes a scaphoid proximal-pole fracture the one that goes on to nonunion, and that produces idiopathic necrosis of the scaphoid in Preiser disease and of the lunate in Kienböck disease. Reading them together is more useful than reading any of them alone.

And an isolated capitate fracture should make you doubt the word "isolated". The capitate sits in the middle of the carpus and is shielded by everything around it, so the energy needed to break it usually breaks something else too: the scaphoid, in scaphocapitate syndrome, or the whole greater arc, in a perilunate injury. The neighbouring carpal fractures with the same high-energy company are the hamate and the lunate.

What it is, and how often. A capitate fracture is a fracture of the largest carpal bone, lying centrally in the distal carpal row. It accounts for 1-2% of all carpal fractures, which places it among the least common carpal injuries, and the mechanism is high-energy axial loading with hyperextension. The patients are predominantly young adults, with a male predominance.

The company it keeps. Over 50% of capitate fractures occur with another carpal injury, so the assessment is of the whole carpus. The scaphoid waist is the most common association, giving scaphocapitate syndrome; beyond it come perilunate injury as part of the greater arc, fracture of the hamate, lunate or triquetrum, and ligamentous injury of the scapholunate and lunotriquetral ligaments.

When it really is isolated. Fewer than half are, and those tend to be body or avulsion fractures, with a better prognosis and often no need for surgery. At the other end, a capitate broken alongside several other carpal bones may need complex reconstruction.

The shape, and the part that breaks. The capitate is the largest carpal bone and occupies the central position. Its head is proximal and rounded, carrying the smooth convexity that sits in the concavity of the lunate; the neck is the constricted waist and the usual fracture site; and the body is the larger distal portion, with a flat distal surface for the metacarpal bases.

What it articulates with. Its articular surfaces, with its size and central position, are what make the capitate critical to wrist function:

• Proximal, the head, with the lunate
• Radial, with the scaphoid
• Ulnar, with the hamate
• Distal, with the bases of the 2nd, 3rd and 4th metacarpals

Load and motion. As the keystone of the distal carpal row the capitate takes axial load from the 2nd and 3rd metacarpals and distributes it to the proximal row through the lunate, which is what makes it essential to wrist stability and motion. It moves as part of the distal row rather than independently, following the scaphoid and the lunate.

Why it is so rarely broken. It is recessed in the carpal concavity and surrounded by the other carpal bones, so significant force is required to fracture it.

The blood supply, and the trap inside it. The capitate has a retrograde blood supply similar to the scaphoid. Palmar (volar) vessels contribute the majority of its supply (Vander Grend, PMID 6386955) - a common exam trap, because the dorsal supply is often mis-remembered as the dominant one. Dorsal vessels enter through the dorsal non-articular surface and make a real but smaller contribution, and Vander Grend described three patterns of intraosseous supply, so the surface of dominance varies and a single arrangement should not be over-specified.

The point that actually causes necrosis. Whichever surface predominates, the proximal pole (head) receives its supply exclusively in a retrograde direction across the capitate waist, exactly analogous to the proximal scaphoid. No vessel enters the head independently, so a fracture at the neck or waist can devascularise the proximal pole regardless of which surface the parent vessel came from, and a displaced or rotated proximal fragment is more vulnerable still.

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Capitate fractures are described by where the line runs and by what else is broken. Location determines the prognosis and the treatment; the company it keeps determines how much of the carpus the operation has to address.

AnatomicalScaphocapitate

Neck fractures are the most common, running through the waisted region, and are prone to displacement.

Body fractures run through the distal capitate and may be undisplaced.

Head (proximal pole) fractures are the least common pattern, isolated or alongside other injuries; the fragment involved is the one living on retrograde flow, so it is the fragment at risk of avascular necrosis, and it is fixed to preserve what supply it has.

Avulsion fractures are small fragments pulled from ligament insertions, usually of minimal clinical significance and treated conservatively unless large or symptomatic.

The injury. Scaphocapitate syndrome, Fenton's syndrome, is a combined fracture of the scaphoid waist and the capitate neck with characteristic rotation of the proximal capitate fragment.

The mechanism, in sequence:

1. Wrist hyperextension with axial load
2. The dorsum of the capitate head impacts the dorsal radius
3. The capitate neck fractures
4. The scaphoid waist fractures from bending
5. As the wrist returns to neutral, the proximal capitate rotates 180 degrees

What the rotation means. The articular surface of the proximal fragment ends up facing the fracture site instead of the lunate. It is often not recognised on the initial radiographs, and the fragment has to be derotated and both bones fixed, so recognising the rotation is the step everything else depends on.

Describing it. There is no formally validated sub-classification of scaphocapitate syndrome; injuries are described pragmatically by whether the proximal capitate fragment is rotated:

• Non-rotated - capitate neck and scaphoid waist fractures with the proximal fragment aligned
• Rotated - capitate neck and scaphoid waist fractures with the proximal fragment rotated up to 180 degrees, its articular surface facing the fracture site

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The mechanism is the first clue. The energy required is the point of the history:

• High-energy trauma - motor vehicle accident, motorcycle crash, fall from height
• Sports injury - contact sports, gymnastics with axial load
• FOOSH - fall onto the outstretched hand with hyperextension
• Direct trauma - rare, given the protected position

What else to ask. The energy of the injury, since significant force is required; the position of the wrist at impact; symptoms suggesting other injuries; the immediate disability and swelling pattern; and hand dominance and occupation.

Inspection and palpation. Swelling sits over the central wrist and may be diffuse, less localised than with a scaphoid or triquetral injury, so compare with the other side. Capitate tenderness is difficult to isolate because the bone is deep: palpate through the axis of the 3rd metacarpal and over the dorsal central wrist, then palpate every other carpal bone in turn.

Movement and nerves. Range of motion is limited by pain; test flexion, extension and deviation against the contralateral side. Neurovascular function is usually preserved, and a baseline is documented.

The tests worth doing.

• Axial compression - load through the 3rd metacarpal; pain suggests capitate pathology
• Watson test - for associated scapholunate injury, which matters given how often the scaphoid is involved
• Systematic carpal examination - the rate of associated injury is high enough that every carpal bone is examined
• Finger cascade - to be sure there is no metacarpal malrotation; grip strength is limited by pain

Clinical examination is often non-specific, so a high index of suspicion after high-energy wrist trauma is what carries the diagnosis.

Differential diagnosis. Central dorsal wrist pain after trauma has several mimics. Because the capitate is hard to isolate clinically and is frequently missed on plain films, the differential drives the imaging strategy.

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Radiographs first, and expect them to under-report. They are quick and available, so they are the screening test, but the overlapping carpal bones obscure the capitate, the fracture is often not visible on the initial films, and scaphocapitate syndrome is frequently missed altogether. Carpal alignment has to be assessed alongside the fracture line:

• PA - may show the fracture line through the capitate
• Lateral - carpal alignment and displacement
• Oblique - an additional perspective on the bone

What to look for when nothing is obvious. A fracture line through the capitate, which is often subtle; disruption of the carpal arcs (Gilula's lines); an associated scaphoid fracture; and a DISI or VISI pattern on the lateral.

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CT is the study that makes the diagnosis. Obtain it for any suspected capitate injury, after high-energy wrist trauma, for surgical planning and to assess fragment rotation. It shows the orientation of the fracture line, the displacement and rotation of the fragments, associated carpal fractures and articular involvement. In scaphocapitate syndrome both fractures are visible and the 180-degree rotation of the proximal capitate is seen directly, its articular surface facing the fracture site.

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MRI answers the questions CT cannot. Use it to assess vascularity, to detect an occult fracture, to evaluate ligamentous injury and to monitor for AVN. It shows bone marrow oedema in an acute fracture, signal change suggesting necrosis, and associated soft-tissue injury. Cost and availability are what limit it.

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Bone scintigraphy is sensitive and non-specific, and is rarely needed where CT and MRI are available, though it may detect occult injuries.

The decision. It turns on the displacement, the level of the fracture and what else is broken, and the threshold differs by level: displacement of a body fracture over 2mm is a relative indication, whereas any displacement of the neck, and any rotation, is an absolute one.

Algorithm

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On the table. The capitate is small and may fragment during manipulation, so the technique is gentle and a comminuted bone takes additional fixation. A screw can penetrate the joint or fail to gain purchase: measure carefully, check on fluoroscopy, and revise it if it is intra-articular.

In the first weeks. Infection is rare; dehiscence may expose hardware and is managed with antibiotics, and debridement if needed. A prominent screw or a migrating K-wire comes out once the fracture has healed. Stiffness is common after prolonged immobilisation, which is the argument for early finger motion, then hand therapy and patience.

Later. Avascular necrosis is the most significant complication of a capitate fracture. Nonunion follows from AVN, from inadequate fixation or from the biology, and may require bone grafting, with a vascularised graft where the pole is avascular. Post-traumatic arthritis is the consequence of AVN or malreduction and declares itself as progressive wrist pain, managed from activity modification upwards. Carpal instability may develop where the ligaments were injured, as a DISI or VISI pattern, and may require carpal fusion.

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The first fortnight. A volar resting splint including the thumb, wrist neutral and thumb in a functional position, with finger motion allowed immediately and the hand elevated above heart level. Analgesia is multimodal, ice and elevation control the swelling, and the monitoring is neurovascular checks, inspection for infection and assessment of swelling.

The wound. First dressing change at 48-72 hours, with attention to the K-wire sites if wires were used. Sutures out at 10-14 days, steri-strips applied, and the patient transitioned to a cast.

Phase 1, protection, 0-6 weeks. Thumb spica cast, active finger motion throughout, shoulder and elbow range of motion, and oedema control.

Phase 2, early motion, 6-8 weeks. If CT shows healing, begin wrist range of motion with a removable splint between exercises, gentle and progressive, and no loading. A scaphocapitate injury may need longer than an isolated fracture before this starts.

Phase 3, progressive loading, 8-12 weeks. Progressive strengthening and light grip activities, with splint protection as needed under hand-therapy guidance.

Phase 4, return to function, 12 weeks onwards. Full range of motion and strength, then sport-specific activity and work conditioning, watching for the late complications.

Rehabilitation is prolonged because union has to be confirmed and necrosis watched for.

Isolated body fractures. Generally good outcomes when appropriately treated, with range of motion recovering to 80-90% of the contralateral side, variable recovery of grip strength, and return to previous activities expected.

Neck fractures. A higher complication rate than body fractures, and a meaningful avascular necrosis risk given the retrograde proximal-pole supply, although rates are uncertain owing to rarity and small series. The outcome depends on whether AVN develops, and residual stiffness may remain.

Scaphocapitate syndrome. The outcome depends on recognition and treatment. Delayed or missed diagnosis worsens the prognosis, while reasonable outcomes are reported in small series when the injury is properly treated; nonunion and AVN risk are higher than for an isolated body fracture.

What favours a good result.

• A body fracture, undisplaced
• Early diagnosis
• Anatomic reduction achieved
• An isolated injury

What counts against it.

• A neck fracture, or a rotated fragment
• Delayed diagnosis
• The scaphocapitate pattern
• Associated carpal injuries and a high-energy mechanism

AVN by pattern. Precise AVN rates are not reliably established, because capitate fractures are rare and reported only in small series. The relative risk gradient, however, is consistent across the literature:

• Body fractures - lowest risk, the fracture lying distal to the watershed
• Neck fractures - higher, interrupting the retrograde supply to the proximal pole
• Scaphocapitate syndrome - highest, with a rotated, devascularised proximal fragment

The basis is anatomical: the proximal pole's exclusive retrograde intraosseous supply across the waist, analogous to the proximal scaphoid (PMID 6386955, 6886331).

Return to activity. After cast treatment, light activities at 8-12 weeks and full activities at 12-16 weeks if healed. After fixation, light activities at 8-12 weeks, full activities at 12-16 weeks and contact sports at 4-6 months.

What to tell the patient. That AVN can develop late and may need a salvage procedure, and that outcomes are generally good with appropriate treatment.

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Global Epidemiology

Capitate fractures are among the rarest carpal injuries worldwide, classically quoted at roughly 1-2% of carpal fractures, with the great majority occurring in young men after high-energy axial loading and hyperextension. Because the scaphoid alone accounts for the large majority of carpal fractures, robust population data for the capitate are scarce and most evidence comes from case series.

Guidance Across Major Bodies

No society publishes a capitate-specific guideline; management is extrapolated from carpal/perilunate injury principles and the historical case-series literature. The table summarises how the major bodies' frameworks apply.

Registry Evidence

Capitate fractures are not tracked by the national arthroplasty registries (NJR, AJRR, AOANJRR, SHAR, Norwegian, NZJR), which capture joint replacements rather than carpal trauma. The evidence base therefore rests on case series and cadaveric vascular studies rather than registry data. Registries become relevant only at the salvage end of the spectrum (for example total wrist arthroplasty for post-AVN arthritis), where implant survival data inform the choice between arthrodesis and arthroplasty.

Global Practice Variation

• Imaging access: In high-resource settings CT is the default for diagnosis and planning, and MRI is added for vascularity; where cross-sectional imaging is limited, diagnosis depends on a high index of suspicion, repeat radiographs and clinical follow-up, so missed scaphocapitate syndrome is more likely.
• Fixation hardware: Headless compression screws are standard where available; K-wire fixation remains a wholly acceptable and widely used alternative in resource-limited environments and for small fragments.
• Referral pathways: Complex perilunate and scaphocapitate patterns are concentrated in units with hand/wrist expertise globally; initial stabilisation and imaging are performed at the presenting hospital with onward referral for definitive reconstruction.

Understanding these key concepts will help with exam success.

The evidence supports early recognition and anatomic surgical treatment for most displaced capitate fractures, with the retrograde proximal-pole blood supply explaining the avascular necrosis risk.