Pisiform Fractures

Pisiform fractures are rare, only 1-2% of all carpal fractures, but clinically significant. The pisiform is the only sesamoid bone in the carpus, lying entirely within the tendon of flexor carpi ulnaris (FCU), and that anatomy shapes how it breaks, how it presents and how it is treated.

Who. More common in males, with a peak incidence at 20-40 years. The fracture is often associated with other wrist injuries.

Mechanism. A direct blow to the hypothenar eminence is the most common cause. The other routes are few enough to list:

• Fall onto the outstretched hand with the wrist extended
• Avulsion by FCU contraction (rare)
• Repetitive stress in cyclists and racquet sports, and tool use with vibration exposure; stress fractures are rare

Why it is missed. Pisiform fractures are frequently missed on initial presentation. The pisiform overlaps the triquetrum on the standard PA view, and the patient may put the symptoms down to a "wrist sprain". Presentation may be delayed by weeks, and associated injuries can distract from the pisiform.

The bone. The pea-shaped pisiform is the most ulnar and volar bone of the proximal carpal row. It is the only carpal bone with a single articular surface, the pisotriquetral joint with the triquetrum, and that joint is where osteoarthritis develops and where the grind test is aimed.

Its attachments. FCU inserts onto the pisiform, and the bone passes the force on through two ligaments:

• Pisohamate ligament to the hook of hamate, transmitting force to the distal row
• Pisometacarpal ligament to the base of the 5th metacarpal, forming the base of the hypothenar eminence

Its function. The pisiform acts as a fulcrum (hypomochlion) that increases the mechanical advantage of FCU in wrist flexion. It also stabilises the ulnar column of the wrist, resisting triquetral subluxation (Beckers and Koebke, Clin Anat 1998).

Blood supply. The pisiform is supplied by branches of the ulnar artery, and its sesamoid status provides tendon-derived nutrition. Nonunion is uncommon because of this good vascularity, and unlike the scaphoid, AVN is rare.

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Guyon canal. A fibro-osseous tunnel on the ulnar side of the wrist, whose ulnar border and floor are formed by the pisiform and whose radial border is the hook of hamate. It carries the ulnar nerve and artery, which run immediately radial to the pisiform, so a pisiform fracture can cause compression neuropathy within the canal and every one needs the nerve and artery assessed.

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Pisiform fractures are described by pattern, and each pattern carries a default treatment. Whatever the type, the description must include displacement, comminution, pisotriquetral articular involvement, open injury and ulnar-neurovascular symptoms, because these features change treatment.

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History. A direct blow to the hypothenar eminence from a fall or sport, or repetitive handlebar pressure in a cyclist. The pain is localised to the ulnar palm and wrist and is aggravated by gripping and wrist flexion.

Examination. The pisiform is easily palpated at the base of the hypothenar eminence, at the proximal wrist crease on the ulnar side; flexing the wrist against resistance tenses FCU and makes it prominent. In a fracture, direct pressure over it reproduces the pain.

• Point tenderness over the pisiform at the hypothenar base
• Pain with resisted FCU contraction (wrist flexion plus ulnar deviation)
• Pisiform grind test: compress the pisiform against the triquetrum
• Ulnar nerve motor and sensory assessment

Fracture or pisotriquetral arthritis. A fracture follows clear trauma, begins suddenly and swells acutely, and the radiograph shows a fracture line. Arthritis comes on gradually after repetitive use or a prior injury, with minimal swelling, and the radiograph shows joint space narrowing and osteophytes. The grind test may be positive in a fracture and is typically positive in arthritis.

Pisotriquetral instability. Not every symptomatic pisotriquetral problem is a fracture or arthritis: the pisiform can be dynamically unstable, subluxating on its triquetral facet. It arises from ligamentous laxity, an unbalanced FCU pull, or a healed avulsion or malunion that leaves the bone poorly seated, and presents as ulnar-palmar pain and a painful "clunk" with wrist flexion-extension or gripping, often with no fracture line on plain films.

The pisiform shuck (ballottement) test looks for it: grasp the pisiform between thumb and finger and translate it radial-ulnar and proximal-distal against the triquetrum, reproducing pain and excess glide compared with the other side. The grind test is typically positive too, and stress or dynamic imaging can demonstrate the abnormal translation. Management mirrors the fracture pathway, with activity modification, FCU rebalancing or physiotherapy and a diagnostic pisotriquetral injection first, and pisiform excision the definitive option for persistent symptomatic instability.

Radiographs. Ask for dedicated views rather than accepting a generic "wrist series" when pisiform tenderness is present. A normal AP film does not exclude injury, because the pisiform overlaps the triquetrum:

• PA view: the pisiform overlaps the triquetrum and the fracture is often missed
• Lateral view: the pisiform is visible as a separate structure anteriorly
• Carpal tunnel view: the best visualisation of the pisiform
• 30-degree supinated oblique: an alternative view

The carpal tunnel view is an axial view taken with the wrist in maximum extension and the beam angled 25-30 degrees to the palm. It gives the best view of the pisiform, the hook of hamate and the carpal tunnel, and is essential when pisiform pathology is suspected.

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A small fragment. In acute ulnar-sided pain, a small ossicle beside the pisiform may be a fracture fragment rather than an incidental accessory ossicle. Correlate it with focal tenderness and use CT if uncertainty remains; comparison with the opposite wrist can help when a tiny fragment or a normal variant creates doubt.

CT confirms the fracture pattern and defines its orientation, articular extension, comminution and displacement, the features that decide whether immobilisation is sufficient or excision, or rarely fixation, should be considered. Obtain thin-slice CT when focal pisiform tenderness persists despite equivocal standard views.

Two further findings change the plan. An associated hook of hamate fracture means both injuries are addressed, and pisotriquetral joint narrowing marks established arthritis.

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MRI shows occult fractures, bone marrow oedema and ligament injuries. Ultrasound allows dynamic assessment of FCU and the soft tissues.

First steps. Confirm the diagnosis with a carpal tunnel and a lateral view, assess the ulnar nerve, and splint the wrist in a neutral position with ice and elevation for the swelling. Ulnar nerve symptoms call for urgent decompression. The imaging is reviewed for the fracture pattern at 1-2 weeks, which sets the path.

Algorithm

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Conservative treatment suits a non-displaced simple fracture, a chip or avulsion fracture with minimal symptoms, and the patient who prefers a non-operative trial, and has a high success rate for stable patterns. The wrist goes in a short arm cast for 4-6 weeks, in slight flexion and ulnar deviation, with follow-up radiographs at 2-3 weeks to confirm position and transition to a splint if comfortable.

Primary excision is indicated for:

• Comminuted fracture pattern, where the fragments are unreconstructable
• Displaced fracture with articular involvement
• Open fracture with soft tissue injury
• Patient preference for definitive treatment

Delayed excision follows failed conservative care:

• Nonunion after conservative treatment
• Post-traumatic pisotriquetral arthritis
• Chronic pain unresponsive to conservative measures
• Malunion with symptomatic articular incongruity
• Pisotriquetral instability (subluxation)

Set-up. Supine with the arm on a hand table, under regional or general anaesthesia and an upper-arm tourniquet. The approach is volar and longitudinal, along the FCU tendon.

Excision. The key steps:

• Identify and protect the ulnar nerve in Guyon canal
• Incise the FCU tendon sheath longitudinally
• Shell out the pisiform from within the tendon
• Preserve distal FCU continuity to the 5th metacarpal

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ORIF. Rarely performed; excision is usually preferred. It is considered for:

• A large displaced fragment amenable to fixation
• A young, active patient wishing to preserve the anatomy
• An acute fracture with good bone quality

The approach is volar, similar to excision, with mini-fragment screws (1.5-2.0mm) and protected mobilisation after fixation. If fixation fails, excision may be needed.

Closure. Close the FCU tendon sheath if possible, then subcutaneous absorbable sutures and skin with nylon or absorbable sutures, under a bulky soft dressing with a wrist splint.

FCU weakness, if chronic, also reduces grip.

Guyon canal syndrome. Compression from a pisiform fracture weakens the intrinsic muscles (interossei, lumbricals 3-4 and the hypothenar muscles) and numbs the hypothenar eminence and the ulnar 1.5 digits. Pisiform fractures typically affect Zone 1 or 2 of the canal:

• Zone 1: motor and sensory, proximal to the bifurcation
• Zone 2: motor only (deep branch), with intrinsic weakness and no sensory loss
• Zone 3: sensory only (superficial branch), with numbness and no weakness

Guyon canal or cubital tunnel. Both weaken the interossei and lumbricals 3-4; the discriminator is the dorsal ulnar cutaneous branch. It leaves the nerve proximal to Guyon canal, so compression at the pisiform spares dorsal hand sensation, whereas cubital tunnel syndrome at the elbow does not.

Progression. Motion and loading advance according to tenderness and radiographic union, and return to sport or work is judged on strength recovery and symptoms. Persistent focal pain should prompt CT for delayed union or pisotriquetral incongruity.

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Goals. Rehabilitation aims for:

• Full wrist ROM by 6-8 weeks
• Functional grip strength by 8-12 weeks
• Pain-free activity by 12 weeks
• Return to sport by 3-4 months

Red flags. Watch for:

• Increasing pain after initial improvement
• Numbness or tingling in the ulnar distribution
• Weakness of the intrinsic muscles
• Signs of infection: redness, swelling, discharge

After conservative treatment. Non-displaced patterns have a high union rate and a low complication rate, and most patients make a full recovery (Athanasiou 2018).

After excision. Pain relief is reliable, with visual analogue scores falling from 6.8 to 1.1 in De Almeida's 2019 series. Grip typically recovers to about 86% of the contralateral side, a reduction of about 14%, leaving a minimal functional deficit and high patient satisfaction. Persistent symptoms after excision should be interpreted with examination, tenderness in the pisotriquetral bed and the ulnar-nerve findings, not the AP view alone.

Return to activity. Most patients return at 3-4 months, and full recovery is expected. Sport-specific rehabilitation guides the return, and occupational demands influence it.

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The long view. Pisiform fractures generally have favourable long-term outcomes: non-displaced fractures heal reliably with conservative treatment, and even when excision is required, function is excellent with minimal grip strength loss. The key to good outcomes is early diagnosis, appropriate treatment selection and attention to ulnar nerve status.

Global epidemiology. The pisiform is fractured uncommonly, accounting for roughly 1-2% of carpal fractures, with carpal injuries themselves being dominated by the scaphoid. Most pisiform and pisotriquetral injuries follow a direct blow or a fall onto the extended, ulnar-deviated wrist (commonly cyclists landing on a handlebar) and predominate in active adults (Athanasiou 2018). Pisotriquetral osteoarthrosis is described as the second most common degenerative wrist arthritis after scaphotrapezial disease (Beckers and Koebke 1998). There is no dedicated national registry for carpal sesamoid fractures; the evidence base is small retrospective series and case reports rather than randomised trials.

Practice variation. Because evidence is limited to small series, thresholds for excision versus a prolonged conservative trial differ between centres. The consistent international theme is reliable relief from excision for refractory or comminuted disease, and immobilisation for non-displaced patterns. There are no implant or device registry data because excision (the dominant operation) uses no implant; mini-fragment screws for the rare ORIF are universally available.