Overview & Anatomy
The pisiform is the smallest of the eight carpal bones and is unique in being a true sesamoid bone — it develops within the substance of the flexor carpi ulnaris (FCU) tendon rather than as a primary carpal ossification centre. It articulates with the triquetrum at the pisiotriquetral joint (a small synovial joint) and has no direct articulation with any other carpal bone. It forms the medial border of Guyon`s canal (the ulnar canal), through which the ulnar nerve and artery pass immediately adjacent to its medial and anterior surfaces. It serves as the origin of the abductor digiti minimi (ADM) and flexor digiti minimi (FDM), and as the insertion point of the flexor retinaculum and the pisohamate and pisometacarpal ligaments.
- Guyon`s canal anatomy: the pisiform forms the medial wall of Guyon`s canal; the ulnar nerve divides into its superficial (sensory) and deep (motor) branches within or just distal to the canal; a pisiform fracture or post-traumatic haematoma can compress either or both branches; compression of the deep motor branch → intrinsic hand weakness (ulnar nerve motor palsy — `bishop`s hand` deformity — interosseous weakness, hypothenar weakness) without sensory loss; compression of the superficial sensory branch → little finger and ulnar ring finger numbness; combined compression → both deficits; always examine the ulnar nerve distribution in all pisiform injuries
- Functional role: the pisiform acts as a pulley for the FCU (increasing its mechanical advantage by moving the tendon further from the wrist joint axis), as a bony lever for the hypothenar muscles (ADM/FDM originate from it), and as part of the `pisiform-triquetrum complex` that helps stabilise the medial wrist; pisiform excision has minimal long-term impact on grip strength because the FCU reattaches directly to the hamate and fifth metacarpal via the pisohamate and pisometacarpal ligaments
Epidemiology & Mechanism
- Epidemiology: pisiform fractures account for approximately 0.2–1.2% of all carpal fractures; they are the least common of the common carpal fractures (behind scaphoid, triquetrum, and trapezium); they occur most commonly in young to middle-aged adults; male predominance; frequently missed (up to 40–50% are not identified on initial radiography); they are particularly common in sports involving direct contact with a ball, handle, or racquet (hockey, baseball, cycling, gymnastics — the hypothenar eminence is directly impacted); occupational injuries from pneumatic tools and direct blows to the palm also account for a significant proportion
- Mechanisms: (1) direct impact — the most common mechanism; a direct blow to the hypothenar eminence (the prominent fleshy pad overlying the pisiform on the medial palm) drives the pisiform against the triquetrum; the pisiform is compressed between the impacting object and the hard triquetrum, resulting in a comminuted or transverse fracture; examples: a fall onto a clenched fist, a cricket ball or hockey puck impacting the palm, handlebar injury in cycling; (2) avulsion — forced dorsiflexion or strong FCU contraction may avulse a fragment from the pisiform at the FCU-pisiform junction; this mechanism is similar to the avulsion that causes pisiform stress fractures in gymnasts and rowers; (3) stress fracture — repetitive loading from tool use or sport produces a stress fracture, typically transverse through the mid-pisiform; the `cane fracture` in elderly patients using walking canes is a classic example
Classification
There is no universally adopted numerical classification for pisiform fractures. The fractures are most commonly described by their morphological pattern, which guides management and prognosis.
| Pattern | Description | Stability | Clinical Significance |
|---|---|---|---|
| Transverse | The most common pattern; a horizontal fracture line divides the pisiform into proximal and distal halves; occurs from direct impact; the fracture plane is perpendicular to the long axis of the pisiform | Relatively stable if undisplaced; the FCU tendon holds the fragments together in most cases | Most respond to non-operative management; the fracture heals reliably with cast immobilisation in wrist flexion + ulnar deviation (relaxing the FCU) |
| Comminuted | Multiple fragments; the pisiform is shattered; typically from high-energy direct impact (dense bone compressing between the impacting object and the triquetrum); the articular surface of the pisiotriquetral joint is invariably disrupted | Unstable; the fragments have no inherent stability | A higher proportion of comminuted fractures ultimately require pisiform excision (either acutely or for post-traumatic pisiotriquetral arthritis); primary excision can be considered at the outset for severely comminuted fractures in high-demand patients |
| Articular (pisiotriquetral) | The fracture involves or extends into the articular surface between the pisiform and triquetrum; may be part of a transverse or comminuted pattern; the articular disruption is the key feature affecting long-term prognosis | Variable | Articular involvement directly predicts post-traumatic pisiotriquetral arthritis; even anatomically healed articular fractures may develop symptomatic arthritis, particularly in high-demand workers and athletes; CT is essential to identify articular involvement |
| Avulsion / stress | A small cortical fragment avulsed from the proximal pole of the pisiform by the FCU tendon; or a stress fracture (typically transverse) from repetitive loading; occurs in gymnasts, rowers, and users of hand tools | Often minimally displaced; the FCU maintains position | Rest and activity modification are the cornerstone of management; most stress fractures heal with 6–8 weeks of immobilisation and activity cessation; return to sport is permitted once pain-free; chronic symptomatic cases → pisiform excision |
Clinical Assessment
- History: acute injury or overuse (in stress fractures); hypothenar pain; pain with grip and pinch; pain on wrist flexion and ulnar deviation (FCU activation loads the pisiotriquetral joint); weakness of grip; paraesthesia in the little finger and/or ring finger (ulnar nerve involvement) — if present, document carefully including whether it is sensory only (superficial branch) or both motor and sensory (both branches)
- Examination: point tenderness directly over the pisiform (on the medial volar wrist, just distal to the wrist flexion crease at the proximal hypothenar eminence); the pisiform is the most easily palpable carpal bone — it is subcutaneous and mobile when the wrist is relaxed; the `Pisiform ballottement test` (pressing the pisiform against the triquetrum and applying shear stress) reproduces pain in pisiotriquetral joint pathology; Finkelstein`s sign is NOT positive (the FCU is not involved in the de Quervain`s mechanism); ulnar nerve assessment: test intrinsic function (Froment`s sign — compensatory IP flexion with pinch from adductor pollicis weakness), two-point discrimination in the little finger and ulnar ring finger, and grip/pinch dynamometry
Investigations
- Plain radiographs: the standard PA and lateral wrist views frequently MISS pisiform fractures because the pisiform is superimposed on other structures in these projections; specialised views are required: (1) the carpal tunnel view (the wrist is maximally dorsiflexed and the X-ray beam is directed along the palm axis) — this projects the pisiform free of overlying structures and demonstrates transverse and comminuted fractures clearly; (2) the supinated oblique (30–45° supination oblique) view — another option that profiles the pisiform; (3) the lateral wrist view with the forearm in 30° supination — may also demonstrate the pisiform profile; sensitivity of standard two-view wrist X-ray for pisiform fractures is approximately 60–65%; sensitivity of the carpal tunnel view is approximately 85–90%
- CT scan: the gold standard investigation for pisiform fractures; CT clearly demonstrates: the fracture pattern (transverse, comminuted, articular); the degree of displacement; the extent of pisiotriquetral articular surface involvement; associated triquetral fractures; the position of free fragments; CT should be obtained for all suspected pisiform fractures where plain radiographs are inconclusive or where surgical planning is required; sagittal and coronal CT reconstructions are the most useful planes for pisiform assessment
- MRI: useful for: (1) detecting stress fractures before they are radiologically apparent (bone marrow oedema — STIR high signal); (2) assessing soft tissue injuries (FCU, Guyon`s canal structures, ulnar nerve); (3) assessing the pisiotriquetral articular cartilage; (4) distinguishing pisiform non-union from bisected pisiform (a normal anatomical variant in which the pisiform fails to fuse from two ossification centres — a bipartite pisiform has smooth corticated margins and no associated marrow oedema, distinguishing it from a fracture non-union)
- Nerve conduction studies (NCS) / electromyography (EMG): indicated if ulnar nerve injury is suspected; confirms the level of compression (at Guyon`s canal vs more proximal); identifies which branch is affected (superficial sensory, deep motor, or both); guides surgical planning if nerve decompression is required
Management
| Indication | Treatment | Detail |
|---|---|---|
| Undisplaced acute fracture | Non-operative — short-arm cast | Short-arm cast in slight wrist FLEXION (30°) and ULNAR DEVIATION (20°) — this position relaxes the FCU, reducing the deforming tensile force on the pisiform; 4–6 weeks immobilisation; repeat CT at 4–6 weeks to confirm healing; graduated physiotherapy and return to activity after union; avoidance of hypothenar loading for 3 months post-cast removal |
| Displaced fracture (>2 mm) | Non-operative trial first; ORIF or excision | An initial trial of cast immobilisation (as above) is appropriate for most displaced fractures; if the fracture remains displaced at 4–6 weeks or if symptoms persist despite adequate immobilisation → surgical intervention; ORIF (mini-fragment or headless compression screw) for large two-part fragments with adequate bone stock; pisiform excision for comminuted fractures or failed ORIF |
| Comminuted fracture | Primary pisiform excision (selected cases) or non-operative followed by delayed excision | In high-demand manual workers or athletes with severely comminuted fractures where ORIF is not technically feasible → primary pisiform excision provides the most reliable and predictable outcome; alternatively, a period of non-operative management (4–6 weeks cast) followed by excision if symptomatic; post-traumatic pisiotriquetral arthritis from comminuted articular fractures is the primary long-term concern |
| Failed conservative management / post-traumatic arthritis | Pisiform excision | The definitive surgical option for symptomatic pisiform fracture non-union, chronic pisiotriquetral arthritis, or persistent pain after healed fracture; performed through a palmar approach (longitudinal incision over the FCU tendon); the pisiform is excised within the FCU tendon sheath while carefully protecting the ulnar nerve and artery in Guyon`s canal; the FCU tendon end is sutured closed; outcomes are consistently good — most patients return to full activity within 3 months; grip strength and range of motion are well maintained |
| Ulnar nerve compression | Guyon`s canal decompression ± pisiform excision | If ulnar nerve compression is confirmed by NCS/EMG → surgical decompression of Guyon`s canal at the time of pisiform surgery (or as a standalone procedure if the fracture has already united); the deep branch of the ulnar nerve is particularly at risk in pisiform fractures and haematoma; decompression is combined with pisiform excision when both are present |
Pisiform Excision — Surgical Technique
- Approach: longitudinal incision over the FCU tendon at the wrist; the FCU sheath is opened; the pisiform is identified within the tendon; the FCU fibres are carefully separated from the pisiform (the FCU inserts proximally onto the pisiform surface and continues distally as the pisohamate and pisometacarpal ligaments); the pisiotriquetral joint capsule is incised; the pisiform is excised in its entirety (total excision is preferred — subtotal excision leaves a potentially symptomatic fragment); the ulnar nerve and artery must be identified and protected throughout — the deep motor branch of the ulnar nerve passes immediately adjacent to the pisiform-hamate junction; the FCU tendon end is sutured after excision; the pisohamate and pisometacarpal ligaments are preserved where possible
- Post-operative care: a padded compression bandage is applied for 1–2 weeks; early active finger and thumb motion is encouraged; wrist range of motion exercises begin at 2 weeks; return to full activity at 8–12 weeks; most patients return to manual work and sport without significant functional restriction
Complications
- Post-traumatic pisiotriquetral arthritis: the most important late complication; develops from articular surface damage at the pisiotriquetral joint; presents with persistent ulnar-sided palmar wrist pain, exacerbated by resisted wrist flexion and ulnar deviation; pain on pisiform ballottement (pressing the pisiform against the triquetrum creates pain and a grating sensation); radiographs show joint space narrowing, subchondral sclerosis, and osteophytes; CT confirms the articular changes; management: intra-articular corticosteroid injection (diagnosis + short-term treatment); pisiform excision (definitive — consistently reliable treatment for post-traumatic pisiotriquetral arthritis)
- Non-union: uncommon with adequate immobilisation; more common after comminuted fractures or inadequate cast position; presents with persistent hypothenar pain; CT confirms the non-union; management — pisiform excision (ORIF of a non-union is rarely indicated given the excellent results of excision)
- Ulnar nerve injury / Guyon`s canal syndrome: either from the initial injury (haematoma or fracture fragment compression) or from post-traumatic fibrosis within Guyon`s canal; the deep motor branch is most vulnerable; treatment — surgical decompression of Guyon`s canal; most neuropraxia injuries resolve after decompression
- Bipartite pisiform confusion: a bipartite pisiform (failure of two ossification centres to fuse — a normal variant in approximately 1–2% of the population) may be mistaken for a fracture non-union; key distinctions — bipartite pisiform: smooth, corticated, rounded fragments; no associated marrow oedema on MRI; bilateral in ~50%; frequently asymptomatic; no history of acute trauma; fracture non-union: irregular, non-corticated fracture line; marrow oedema on MRI; history of trauma
Exam Pearls
- Pisiform: true sesamoid bone within the FCU tendon; articulates with the triquetrum (pisiotriquetral joint); forms medial wall of Guyon`s canal; ulnar nerve and artery pass adjacent to it; fractures account for <2% of carpal fractures; frequently missed on standard PA/lateral X-ray — request carpal tunnel view or CT
- Mechanism: direct blow to hypothenar eminence (most common); avulsion by FCU; stress fracture from repetitive loading (gymnasts, rowers, tool users)
- Radiological diagnosis: standard views miss up to 40%; carpal tunnel view and supinated oblique view profile the pisiform; CT is gold standard for fracture pattern, articular involvement, and displacement; MRI for stress fractures (bone marrow oedema before fracture visible on X-ray)
- Cast position: wrist flexion (30°) + ulnar deviation (20°) — relaxes the FCU, reduces deforming tension on the pisiform; 4–6 weeks immobilisation
- Pisiform excision: the most reliable surgical treatment for displaced, comminuted, and non-union fractures as well as post-traumatic pisiotriquetral arthritis; good outcomes; grip strength well maintained; FCU function preserved via pisohamate and pisometacarpal ligaments; the ulnar nerve (especially the deep motor branch) must be protected during excision
- Post-traumatic pisiotriquetral arthritis: the primary long-term complication; pisiform ballottement test positive; CT shows articular changes; definitive treatment = pisiform excision
- Bipartite pisiform vs non-union: bipartite = smooth corticated margins, bilateral in 50%, no marrow oedema, asymptomatic or incidental; non-union = irregular margins, marrow oedema on MRI, history of trauma, symptomatic; MRI is the key differentiator
- Ulnar nerve assessment is mandatory in all pisiform injuries: test both sensory (little finger and ulnar ring finger) and motor (intrinsics — Froment`s sign, grip/pinch dynamometry); deep motor branch compression = intrinsic weakness without sensory loss