Subcutaneous Border | FCU–ECU Internervous Plane | Workhorse for Nightstick & Both-Bone Forearm Plating
- The plane is a true internervous interval between flexor carpi ulnaris (ulnar nerve) volarly and extensor carpi ulnaris (posterior interosseous nerve) dorsally, developed directly over the palpable subcutaneous border of the ulna along its whole length.
- Because the ulna is subcutaneous, this is a direct approach to the entire shaft with no muscle to traverse — the simplest and safest long-bone exposure in the forearm, used for isolated nightstick fractures, the ulnar side of both-bone fractures, ulnar shortening osteotomy, non-union and lesion surgery.
- The ulnar nerve and artery run on the volar surface of FCU; keeping FCU intact and retracting it volarward protects them. They are most at risk with very volar dissection or proximally near the cubital tunnel.
- The dorsal ulnar cutaneous nerve branches from the ulnar nerve about 5 cm proximal to the wrist and crosses toward the dorsum — protect it during distal-third exposure to avoid a painful neuroma or numbness.
- Apply the plate on the flat dorsal or volar surface, not the subcutaneous crest itself, to avoid hardware prominence; contour to the bone and restore ulnar length and bow for both-bone fractures.
- Most isolated minimally displaced nightstick fractures heal in a brace; reserve ORIF for displacement over 50 percent of shaft width or angulation over 10 degrees, both-bone fractures, Monteggia injuries and open fractures.
When & Why
What it exposes. The direct subcutaneous-border approach gives access to the entire ulnar shaft from the olecranon to the ulnar styloid. It is the workhorse for plating isolated nightstick ulnar fractures, the ulnar side of both-bone forearm fractures, Monteggia fracture-dislocations, ulnar shortening osteotomy, and non-union, malunion or diaphyseal lesion surgery. Why this approach. Because the ulna is subcutaneous along its whole dorsal border, bone is reached directly with no muscle to traverse, down a true internervous plane between flexor carpi ulnaris (ulnar nerve) and extensor carpi ulnaris (posterior interosseous nerve). It is the simplest, safest and most extensile forearm long-bone exposure. Operate or brace? Most isolated, minimally displaced nightstick fractures heal non-operatively — functional bracing gives 99 percent union and good-to-excellent function in over 96 percent (Sarmiento 1998). Reserve the surgical approach for the patterns below.
- Management
- Functional brace / early motion
- Rationale
- 99% union, over 96% good/excellent function with bracing (Sarmiento 1998)
- Management
- ORIF via the subcutaneous-border approach
- Rationale
- Reduce malunion / non-union risk; restore alignment for forearm rotation
- Management
- ORIF of both bones
- Rationale
- Forearm 'ring' — anatomical reduction needed for rotation and the radioulnar joints
- Management
- ORIF of the ulna
- Rationale
- Anatomical ulnar fixation reduces the radiocapitellar joint
Position & landmarks. Supine, arm on a hand table or across the chest, forearm pronated to bring the subcutaneous border uppermost; tourniquet and image intensifier as required. Palpate and mark the subcutaneous crest from olecranon to styloid — the line of the incision.
The Exposure
Work straight down onto the subcutaneous crest, split the FCU–ECU internervous interval, and apply the plate to the flat surface while keeping the ulnar neurovascular bundle volar and the dorsal ulnar cutaneous nerve safe distally.
Exposure sequence
- Supine, arm across the chest or on a hand table; pronate the forearm to bring the subcutaneous border uppermost.
- Tourniquet as required; image intensifier available.
- Palpate the subcutaneous border of the ulna from the olecranon to the ulnar styloid — the incision lies directly over it for the relevant segment.
- Incise skin and subcutaneous fat down to deep fascia directly over the subcutaneous crest for the fracture or osteotomy segment.
- Because the plane is a true internervous interval, the incision is extensile along the whole shaft in either direction.
- Identify and develop the interval between flexor carpi ulnaris (volar) and extensor carpi ulnaris (dorsal), using the crest of the ulna as the guide.
- In the distal third, identify and protect the dorsal ulnar cutaneous nerve (off the ulnar nerve about 5 cm proximal to the wrist) as it crosses toward the dorsum.
- Incise the periosteum along the crest and elevate it minimally — just enough to apply the plate, preserving soft-tissue attachments and blood supply.
- Keep FCU and the ulnar neurovascular bundle volar; do not dissect onto the volar surface of FCU.
- Expose the flat dorsal or volar surface for the plate (avoid the prominent crest itself).
- Reduce the fracture or osteotomy, restoring length, rotation and the ulnar bow.
- Apply a contoured 3.5 mm compression or neutralisation plate on the flat dorsal or volar surface (not the crest).
- For both-bone or Monteggia injuries, confirm radial head reduction (the radiocapitellar line) and distal radioulnar joint congruity on imaging.
- Close periosteum and fascia, then subcutaneous tissue and skin.
- Document ulnar nerve and dorsal ulnar cutaneous nerve function; counsel on possible hardware prominence and later plate removal.
The ulnar nerve and artery lie volar to flexor carpi ulnaris and must never enter the dorsal working field. Stay on the subcutaneous border, keep FCU retracted volarward, and in the distal third actively identify and protect the dorsal ulnar cutaneous nerve to avoid a painful neuroma.
Apply the contoured 3.5 mm plate to the flat dorsal or volar surface of the ulna rather than the prominent subcutaneous crest. This preserves soft-tissue attachments, reduces hardware prominence, and — by restoring the ulnar bow — protects forearm rotation and the proximal and distal radioulnar joints.
Dangers & Extensions
Structures at risk, by layer
- Where it is at risk
- Volar to FCU; proximally near the cubital tunnel
- Protection strategy
- Keep FCU intact and retract it volarward; avoid deep volar dissection
- Where it is at risk
- Distal third, crossing to the dorsoulnar hand (about 5 cm above the wrist)
- Protection strategy
- Identify and protect during distal exposure; careful subcutaneous dissection
- Where it is at risk
- Deep dorsal forearm if dissection strays radially or proximally
- Protection strategy
- Stay subperiosteal on the ulna; do not enter the interosseous space unnecessarily
- Where it is at risk
- The subcutaneous crest
- Protection strategy
- Place the plate on the flat dorsal/volar surface, not the crest; counsel on removal
Extensile options. Because the plane is true and internervous along the whole shaft, the incision extends proximally toward the olecranon and distally toward the ulnar styloid to expose any segment. The distal extension is exactly where the dorsal ulnar cutaneous nerve must be sought and protected. Closure. Reapproximate periosteum and fascia, then subcutaneous tissue and skin. The subcutaneous position makes hardware prominence a real concern — counsel on possible later plate removal. Document ulnar nerve and dorsal ulnar cutaneous nerve function before and after the procedure.
Procedures Through This Approach
- Ulnar shaft fracture fixation — plate fixation of displaced nightstick and both-bone ulnar fractures, the principal use of this exposure.
- Monteggia fracture-dislocation — anatomical ulnar fixation restores the radiocapitellar joint.
- Ulnar shortening osteotomy for ulnocarpal impaction.
- Ulnar non-union and malunion reconstruction, and diaphyseal lesion excision or biopsy.
Viva & Exam Focus
FUNDFUND — ulnar shaft plane & dangers
Clinical Decision Scenarios
Practise clinical reasoning and management decisions out loud
“You are about to plate an isolated displaced ulnar shaft fracture. Describe your approach and its internervous plane.”
“A fit adult has an isolated, minimally displaced nightstick fracture. Would you operate?”
Plane & anatomy
- Over the subcutaneous border, olecranon to styloid
- Internervous: FCU (ulnar n.) versus ECU (PIN)
- Ulnar nerve + artery volar to FCU
- Dorsal ulnar cutaneous nerve about 5 cm above the wrist (distal-third risk)
Indications
- Displaced or angulated nightstick fractures
- Both-bone forearm (ulnar side)
- Monteggia — ulnar fixation reduces the radial head
- Ulnar shortening osteotomy; non-union; lesions
Evidence & pitfalls
- Bracing gives 99% union and over 96% good/excellent for isolated fractures (Sarmiento 1998)
- Plate on the flat surface, not the crest — hardware prominence
- Protect the dorsal ulnar cutaneous nerve distally
References
Functional bracing of fractures of the shaft of the ulna
The benchmark for non-operative management of isolated ulnar shaft fractures. Functional bracing achieved union in 99 percent of cases (Level IV; 287 of 444 patients followed), with mean shortening of 1.1 mm, mean angulation of about 5 degrees, and good-to-excellent function in over 96 percent. It frames the operative indications — reserve ORIF for displaced, angulated, both-bone, Monteggia and open patterns. DOI: 10.1097/00005131-199808000-00009.
Surgical exposures in orthopaedics — the anatomic approach (forearm)
Standard reference describing the subcutaneous-border approach to the ulna, its FCU–ECU internervous plane, the volar position of the ulnar neurovascular bundle and the course of the dorsal ulnar cutaneous nerve.