Surgical technique guide for anterior transposition of the ulnar nerve in cubital tunnel syndrome where simple in-situ decompression is insufficient — subcutaneous, intramuscular and submuscular (Learmonth) techniques, nerve mobilisation with blood supply preservation, and management of revision and complex cases
High-yield overview
Subcutaneous, intramuscular or submuscular (Learmonth) transposition of the ulnar nerve for cubital tunnel syndrome | advanced
Surgical Imaging
The ulnar nerve coursing behind the medial epicondyle through the cubital tunnel; in transposition this segment is mobilised and moved anterior to the epicondyle.Credit: AI-generated medical illustration · OrthoVellum
Critical Danger Structures and Exam Traps
Arcade of Struthers — Proximal Compression Site
Location: A fascial band approximately 8 cm proximal to the medial epicondyle, connecting the medial intermuscular septum to the triceps fascia. The ulnar nerve passes beneath it before entering the cubital tunnel.
The trap: The arcade of Struthers is the most proximal and most commonly missed compression site. If not identified and released, the nerve remains tethered proximally during transposition, creating tension and limiting anterior placement.
The fix: Expose the ulnar nerve at least 8 cm proximal to the medial epicondyle. Identify and divide the arcade of Struthers under direct vision before any transposition.
Medial Intermuscular Septum — Must Be Excised
The critical step: The medial intermuscular septum is a tough fibrous sheet separating the anterior and posterior compartments of the arm. The ulnar nerve passes through it just proximal to the medial epicondyle.
Why excise, not simply release: In its native position the nerve passes through the septum roughly perpendicular to the septal fibres. After anterior transposition, the nerve angles through the septal opening. Any retained septal edge creates a sharp kink that compresses the nerve during elbow flexion. Excise a 2-3 cm window of septum to create a smooth passage.
The trap: Merely incising the septum or failing to excise a generous window — the retained edge will kink the transposed nerve.
Segmental Blood Supply — Preserve Vasa Nervorum
Anatomy: The ulnar nerve receives multiple segmental feeding vessels along its course: the superior ulnar collateral artery, the inferior ulnar collateral artery (via its posterior branch), the posterior ulnar recurrent artery, and the ulnar artery (via multiple branches distal to the cubital tunnel).
The risk: Aggressive circumferential mobilisation strips the vasa nervorum, devascularising a nerve segment. Post-ischaemic fibrosis produces a scarred, non-conducting nerve with worse outcomes than the original compression.
The fix: Mobilise the nerve only as far as necessary for the chosen transposition. Preserve visible fascial attachments and vascular pedicles entering the nerve. Do not skeletonise the nerve circumferentially.
Location: The MABC pierces the deep fascia approximately 2-3 cm anterior to the medial epicondyle and runs subcutaneously distally over the forearm. It provides sensation to the medial forearm.
The risk: The MABC crosses the surgical field and is vulnerable to the skin incision, retractor placement, and deep dissection. Laceration or entrapment produces a painful neuroma of the medial forearm that patients report as a burning, electric-shock pain worse than their original cubital tunnel symptoms.
The fix: Identify the MABC in the proximal aspect of the incision before deepening dissection. Retract it gently with a vessel loop. If it must be divided (rare), bury the proximal stump in muscle to minimise neuroma formation.
Nerve Kinking at Transposition Margins
The problem: After transposition, the ulnar nerve must change direction at both the proximal and distal ends of its new course. If the nerve is angulated too acutely at these transition points, or if a retained structure (septal edge, fascial band) creates a sharp corner, the nerve kinks during elbow flexion — producing compression worse than the original cubital tunnel pathology.
The fix: After placing the nerve in its new bed, perform the "elbow flexion-extension sweep" test: passively flex and extend the elbow while watching the nerve. It should glide smoothly without catching, snapping, or kinking at the proximal or distal margins. If kinking is seen, release the tethering structure — most commonly a residual septal edge, an unexcised fascial band, or an inadequately released Osborne's ligament.
Articular Branches to the Elbow Joint
Location: One to three small articular branches leave the ulnar nerve proximal to the cubital tunnel and supply the medial elbow joint capsule and the ulnar collateral ligament complex.
The risk: Aggressive mobilisation divides these branches. Patients develop post-operative medial elbow pain and a sense of instability or vague aching on valgus stress testing that can be mistaken for UCL injury or failure of the cubital tunnel release.
The fix: Identify articular branches during proximal nerve mobilisation. Preserve them where possible. If they must be divided for adequate nerve mobilisation, warn the patient about possible medial elbow discomfort that may take weeks to months to settle.
Mnemonic
F.O.C.U.SFOCUS — Five Sites of Ulnar Nerve Compression at the Elbow
Mnemonic
T.R.A.N.S.L.A.T.ETRANSLATE — Steps of Anterior Transposition
Mnemonic
B.L.O.O.DBLOOD — Segmental Blood Supply to the Ulnar Nerve
Surgical Indications
Absolute Indications for Transposition (Over In-Situ Release)
Ulnar nerve subluxation or partial dislocation over the medial epicondyle on elbow flexion — in-situ release destabilises the nerve further and leaves it snapping over the epicondyle in its native groove
Prior medial epicondyle fracture with malunion or valgus deformity — the bony geometry of the cubital tunnel is altered and simple decompression does not address the structural abnormality
Revision cubital tunnel surgery after failed in-situ decompression — transposition addresses scar tissue, adhesions, and residual compression; in-situ repeat release has poor outcomes in revision
Severe cubital tunnel syndrome with marked intrinsic muscle wasting and weakness (McGowan grade III, Dellon stage 3) — where the degree of nerve damage suggests the nerve needs a protected, tension-free bed
Throwing athletes or overhead-sport patients where the nerve must be stabilised in a secure position to tolerate repeated valgus stress and elbow flexion
Relative Indications
Moderate disease (McGowan grade II) where the patient's occupation demands reliable grip strength and the surgeon prefers a more definitive procedure
Elbow contracture requiring simultaneous capsular release — transposition avoids the nerve being tethered during contracture release
Patient preference after informed discussion of the trade-offs between simpler in-situ release and more extensive transposition
Contraindications
Absolute:
Active infection at the medial elbow
Severe medical comorbidity precluding tourniquet use and general or regional anaesthesia (relative — consider in-situ release under local if appropriate)
Relative:
Mild disease (McGowan grade I, Dellon stage 1) — in-situ decompression is usually sufficient and carries lower morbidity
Poor soft tissue envelope from prior surgery or trauma — increases wound complication and scar risk
Previous medial epicondylectomy — altered bony anatomy may make transposition bed creation more difficult
Classification Systems
McGowan Classification (1950)
I (mild)
Description
Lesions not detectable clinically
Clinical Features
Intermittent paraesthesiae in the ulnar nerve distribution, no measurable motor weakness, no sensory loss on testing
II (moderate)
Description
Lesions detectable
Clinical Features
Intermittent paraesthesiae with demonstrable intrinsic muscle weakness (Froment sign positive), possible measurable sensory deficit
III (severe)
Description
Severe lesions
Clinical Features
Constant paraesthesiae, marked intrinsic muscle wasting and weakness, clawing of the ring and little fingers, impaired dexterity
Grade
Description
Clinical Features
I (mild)
Lesions not detectable clinically
Intermittent paraesthesiae in the ulnar nerve distribution, no measurable motor weakness, no sensory loss on testing
II (moderate)
Lesions detectable
Intermittent paraesthesiae with demonstrable intrinsic muscle weakness (Froment sign positive), possible measurable sensory deficit
III (severe)
Severe lesions
Constant paraesthesiae, marked intrinsic muscle wasting and weakness, clawing of the ring and little fingers, impaired dexterity
Dellon Clinical Staging (1989)
1 (mild)
Description
Paraesthesiae only
Clinical Features
Provokable by elbow flexion test; no measurable sensory loss on static two-point discrimination; no motor abnormality
2 (moderate)
Description
Intermittent symptoms with measurable deficit
Clinical Features
Measurable sensory deficit (increased two-point discrimination or diminished light touch), mild or no motor weakness
3 (severe)
Description
Constant symptoms with marked deficit
Clinical Features
Constant paraesthesiae, measurable motor weakness with intrinsic wasting, abnormal nerve conduction studies
Stage
Description
Clinical Features
1 (mild)
Paraesthesiae only
Provokable by elbow flexion test; no measurable sensory loss on static two-point discrimination; no motor abnormality
2 (moderate)
Intermittent symptoms with measurable deficit
Measurable sensory deficit (increased two-point discrimination or diminished light touch), mild or no motor weakness
3 (severe)
Constant symptoms with marked deficit
Constant paraesthesiae, measurable motor weakness with intrinsic wasting, abnormal nerve conduction studies
Evidence for Non-Operative Treatment
Conservative Management
Night-time elbow extension splinting (posterior splint or commercial elbow brace at 30-45 degrees of flexion) reduces symptoms in mild cases by relieving pressure on the nerve within the cubital tunnel
Nerve gliding exercises may improve nerve excursion and reduce adhesion-related symptoms
Activity modification (avoiding prolonged elbow flexion, padded elbow rests, ergonomic workspace adjustments) addresses the mechanical factor of compression
Outcome: Conservative treatment is appropriate for McGowan grade I and early Dellon stage 1 disease. A systematic review of non-operative management shows improvement in approximately 50-70% of mild cases, but recurrence is common without modification of provocative activities
Indications for Surgery
Failure of conservative treatment after 3-6 months of consistent nocturnal splinting and activity modification
Progressive neurological deficit (worsening weakness, increasing sensory loss, developing intrinsic wasting) at any stage
Moderate-to-severe disease at presentation (McGowan grade II-III) — many surgeons proceed directly to surgery rather than trial conservative treatment
Evidence for Surgical Treatment
In-Situ Decompression vs Anterior Transposition
Multiple randomised controlled trials and systematic reviews have compared simple in-situ decompression with anterior transposition. The key finding is that for most patients with mild-to-moderate cubital tunnel syndrome, outcomes are broadly comparable between the two approaches.
In-situ decompression advantages: Simpler and faster technique, smaller incision, less dissection, lower complication rate, faster recovery, can be performed under local anaesthesia in some settings
Anterior transposition advantages: Addresses nerve subluxation, moves the nerve away from the bony tunnel entirely, provides a protected bed in revision cases, preferred for structural abnormality (malunion, valgus), allows more thorough exploration of the nerve
Consensus position: For primary cubital tunnel syndrome without subluxation, in-situ decompression is a reasonable first choice in most cases. Anterior transposition is preferred when specific indications are present (subluxation, revision, valgus deformity, severe disease).
Subcutaneous vs Submuscular (Learmonth) Transposition
Subcutaneous transposition is simpler, faster, and has lower morbidity; the nerve is placed in a subcutaneous pocket anterior to the medial epicondyle with a fascial sling to prevent re-subluxation
Submuscular (Learmonth) transposition provides deeper, more secure coverage of the nerve beneath the flexor-pronator mass; the muscle is detached from the medial epicondyle and reattached with suture anchors; more extensive dissection, longer recovery, but preferred in revision cases and throwing athletes
Intramuscular transposition (nerve buried in a groove within the flexor-pronator mass) is an intermediate option but is less commonly performed; it carries a theoretical risk of muscle scarring around the nerve
Surgical Options for Cubital Tunnel Syndrome — Comparison
Key Evidence
Evidence
Prospective randomized controlled study comparing simple decompression versus anterior subcutaneous transposition for idiopathic neuropathy of the ulnar nerve at the elbow
Level I
Bartels RH, Verhagen WI, van der Wilt GJ, Meulstee J, van Rossum LG, Grotenhuis JA • Neurosurgery
Clinical implication: For primary idiopathic cubital tunnel syndrome without specific indications for transposition, simple decompression provides equivalent outcomes with lower morbidity.
Simple decompression versus anterior subcutaneous and submuscular transposition of the ulnar nerve for cubital tunnel syndrome: a meta-analysis
Level I
Macadam SA, Gandhi R, Bezuhly M, Lefaivre KA • J Hand Surg Am
Clinical implication: Meta-analytic evidence supports simple decompression as the first-line surgical option for primary cubital tunnel syndrome, reserving transposition for specific indications.
Caliandro P, La Torre G, Padua R, Giannini F, Padua L • Cochrane Database Syst Rev
Clinical implication: The Cochrane review confirms that technique selection should be guided by patient-specific factors rather than evidence of superiority for any single approach.
Anterior transposition compared with simple decompression for treatment of cubital tunnel syndrome. A meta-analysis of randomized, controlled trials
Zlowodzki M, Chan S, Bhandari M, Kalliainen L, Schubert W • J Bone Joint Surg Am
Clinical implication: Used as the evidence base for the AAOS CPG on cubital tunnel syndrome; supports surgeon preference and patient-specific factors guiding technique selection.
The ulnar nerve originates from the medial cord of the brachial plexus (C8, T1) and travels along the medial aspect of the arm in the posterior compartment, posterior to the medial intermuscular septum and anterior to the medial head of triceps.
At approximately the mid-arm, the nerve pierces the medial intermuscular septum to enter the anterior compartment, then runs distally on the posterior surface of the septum in the groove between the medial epicondyle and the olecranon (the cubital tunnel).
It exits the cubital tunnel between the two heads of flexor carpi ulnaris (FCU), entering the forearm deep to FCU and superficial to flexor digitorum profundus (FDP), running alongside the ulnar artery.
The Cubital Tunnel
The cubital tunnel is a fibro-osseous groove bounded by:
Floor: The posterior aspect of the medial epicondyle and the olecranon, with the medial collateral ligament (UCL) complex deep to the floor
Roof: The cubital tunnel retinaculum (Osborne's band/ligament) — a fascial band stretching from the medial epicondyle to the olecranon, bridging the two bony points
Medial wall: The medial epicondyle
Lateral wall: The olecranon
Elbow flexion effect: When the elbow flexes from full extension, the cubital tunnel narrows significantly. The volume of the cubital tunnel decreases by approximately 55% at full flexion (Vanderpool et al., cadaveric study), and the retinaculum tautens over the nerve. Combined with increased intraneural pressure, this explains why nocturnal symptoms are common (patients sleeping with the elbow flexed) and why prolonged or repetitive elbow flexion provokes symptoms.
Arcade of Struthers
A fascial band connecting the medial intermuscular septum to the deep fascia of the triceps, approximately 8 cm proximal to the medial epicondyle
Present in approximately 70% of specimens (cadaveric studies)
The ulnar nerve passes beneath it before entering the cubital tunnel
Can tether the nerve proximally if not released during transposition
Medial Intermuscular Septum
A fibrous sheet separating the anterior (flexor) and posterior (extensor) compartments of the arm
The ulnar nerve passes through an opening in the septum approximately 2-3 cm proximal to the medial epicondyle
After anterior transposition, the nerve passes through this opening at an acute angle — any retained septal edge kinks the nerve, making excision of a window critical
Sites of Compression — Detailed Anatomy
1. Arcade of Struthers
Location
8 cm proximal to ME
What Compresses
Fascial band over the nerve
Surgical Action
Identify and divide under direct vision
2. Medial intermuscular septum
Location
2-3 cm proximal to ME
What Compresses
Septal edge constricts the nerve
Surgical Action
EXCISE a 2-3 cm window of septum
3. Cubital tunnel retinaculum (Osborne's)
Location
Over the groove between ME and olecranon
What Compresses
Tautens with flexion, narrows tunnel volume
Surgical Action
Release the full length of the retinaculum
4. Cubital tunnel floor
Location
Between ME and olecranon
What Compresses
Osteophytes, loose bodies, bony irregularity
Surgical Action
Inspect and debride if bony pathology present
5. FCU aponeurosis
Location
Between the two FCU heads (humeral and ulnar)
What Compresses
Fascial arch over the nerve as it enters the forearm
Surgical Action
Release the connecting aponeurosis completely
Site
Location
What Compresses
Surgical Action
1. Arcade of Struthers
8 cm proximal to ME
Fascial band over the nerve
Identify and divide under direct vision
2. Medial intermuscular septum
2-3 cm proximal to ME
Septal edge constricts the nerve
EXCISE a 2-3 cm window of septum
3. Cubital tunnel retinaculum (Osborne's)
Over the groove between ME and olecranon
Tautens with flexion, narrows tunnel volume
Release the full length of the retinaculum
4. Cubital tunnel floor
Between ME and olecranon
Osteophytes, loose bodies, bony irregularity
Inspect and debride if bony pathology present
5. FCU aponeurosis
Between the two FCU heads (humeral and ulnar)
Fascial arch over the nerve as it enters the forearm
Release the connecting aponeurosis completely
Blood Supply to the Ulnar Nerve
Extrinsic (Segmental) Supply
The ulnar nerve receives named arterial branches along its course that enter the epineurium and form longitudinal anastomoses:
Superior ulnar collateral artery (SUCA)
Level of Contribution
Proximal arm — accompanies the nerve in the posterior compartment
Inferior ulnar collateral artery (IUCA)
Level of Contribution
Distal arm — via its posterior branch, anastomoses with the SUCA
Posterior ulnar recurrent artery
Level of Contribution
Near the cubital tunnel — sends branches to the nerve at the elbow
Ulnar artery
Level of Contribution
Forearm — provides distal supply via multiple branches
Artery
Level of Contribution
Superior ulnar collateral artery (SUCA)
Proximal arm — accompanies the nerve in the posterior compartment
Inferior ulnar collateral artery (IUCA)
Distal arm — via its posterior branch, anastomoses with the SUCA
Posterior ulnar recurrent artery
Near the cubital tunnel — sends branches to the nerve at the elbow
Ulnar artery
Forearm — provides distal supply via multiple branches
Clinical implication: During mobilisation for transposition, the vasa nervorum entering from these arteries are at risk. The nerve must be handled gently and only mobilised as far as necessary. Preserving visible vascular pedicles and fascial connections is critical. The segment from the SUCA/IUCA contributions to the cubital tunnel region is the most vulnerable to devascularisation because it lies between two arterial territories.
Branches at the Elbow
Articular Branches
One to three small branches arise from the ulnar nerve proximal to the cubital tunnel
Supply the medial elbow joint capsule, the olecranon tip, and the ulnar collateral ligament complex
Division during mobilisation produces post-operative medial elbow pain and a vague sense of joint instability
Motor Branch to Flexor Carpi Ulnaris
Typically arises from the ulnar nerve within or just distal to the cubital tunnel
May also arise 2-4 cm proximal to the tunnel in some individuals
Must be identified and protected — division produces FCU weakness (loss of wrist flexion with ulnar deviation)
Articular Branch to the Elbow Joint
Separate from the FCU motor branch
Must be preserved if possible — warn patient if division is unavoidable
Medial Antebrachial Cutaneous Nerve (MABC)
Branches from the medial cord of the brachial plexus (C8, T1)
Runs in the subcutaneous tissue of the medial arm, crossing the surgical field approximately 2-3 cm anterior to the medial epicondyle
Provides sensation to the medial forearm skin
Vulnerable during the skin incision, retractor placement, and subcutaneous dissection
Laceration produces a neuroma causing burning, electric-shock pain in the medial forearm — can be more bothersome than the original cubital tunnel symptoms
Relevant Surface Anatomy
Medial epicondyle: Palpable bony prominence at the medial elbow, approximately 2 cm distal to the intercondylar axis; serves as the centre point for the surgical incision
Olecranon tip: Palpable posteriorly; the cubital tunnel lies between the ME and olecranon
Intercondylar line: Approximately 2 cm proximal to the ME; useful as a proximal reference for the arcade of Struthers
Ulnar nerve: Palpable in the cubital tunnel groove just posterior to the ME; Tinel sign at this point is the most common provocative test (positive in approximately 70% of symptomatic elbows, but less specific than the elbow flexion test)
FCU muscle mass: Palpable just distal to the ME; the nerve exits between its two heads approximately 2-3 cm distal to the ME
Positioning and Preparation
Patient position: Supine, arm abducted 90 degrees on a hand table, forearm supinated with the elbow facing upward. A sandbag or bump supports the arm. The entire arm is prepped from axilla to fingertips to allow full exposure and tourniquet application.
Tourniquet: Upper arm tourniquet (250 mmHg for adults). Inflation confirmed before draping. Alternatively, a forearm tourniquet can be used to allow simultaneous shoulder and elbow surgery if needed, but most surgeons use an upper arm tourniquet for a bloodless field.
Anaesthesia: General anaesthesia or regional (axillary or supraclavicular block). Regional block provides excellent post-operative analgesia. The procedure can be performed under local anaesthesia with sedation in selected cases, but this limits the ability to explore fully and is generally reserved for in-situ decompression.
Examination under anaesthesia: Confirm the diagnosis by palpating the ulnar nerve in the cubital tunnel, testing for subluxation (passively flex the elbow while palpating the nerve over the medial epicondyle), and assessing the range of motion. Document any instability or loose bodies.
Consent: Specifically counsel regarding risk of incomplete relief or recurrence (5-15%), nerve injury including temporary or permanent worsening of ulnar nerve function (less than 2%), medial forearm numbness or MABC neuroma (2-5%), wound infection (less than 2%), elbow stiffness or flexion contracture, and the possibility of revision surgery.
Approach: Hotchkiss Medial Approach to the Elbow
Step 1: Incision and Skin Flaps
Make a longitudinal incision centred on the medial epicondyle, extending approximately 8 cm proximal and 6 cm distal along the course of the ulnar nerve. The incision should curve slightly posteriorly at the level of the medial epicondyle to follow the nerve's course in the cubital tunnel.
Raise full-thickness skin flaps anteriorly and posteriorly, taking care to identify and protect the medial antebrachial cutaneous nerve (MABC) in the proximal subcutaneous tissue. Retract the MABC with a vessel loop.
Clinical Pearl
Technical Tip: 'I extend my incision at least 8 cm proximal to the medial epicondyle so I can identify the ulnar nerve proximal to the arcade of Struthers. The MABC crosses the field about 2-3 cm anterior to the epicondyle — I find it in the subcutaneous fat and loop it early before it gets caught in a retractor. If I cannot find it I assume it is running very close to my planned dissection plane and I slow down.'
Dangers at this step
MABC laceration during skin flap elevation — identify early, loop and protect
Inadequate proximal exposure — if you cannot see the nerve at least 8 cm proximal to the medial epicondyle, you have not exposed enough to release the arcade of Struthers
Inadequate distal exposure — must extend past the FCU heads to release the distal aponeurosis
Step 2: Identify the Ulnar Nerve Proximally and Release the Arcade of Struthers
Identify the ulnar nerve posterior to the medial intermuscular septum in the proximal arm. The nerve appears as a yellow-white cord running alongside the superior ulnar collateral artery. Develop a plane around the nerve using fine scissors and a vessel loop for gentle retraction.
Dissect distally to identify the arcade of Struthers — a fascial band spanning from the medial intermuscular septum to the triceps fascia, approximately 8 cm proximal to the medial epicondyle. Divide it sharply under direct vision with scissors or a scalpel. Confirm the nerve is freely mobile proximal to the arcade after division.
Clinical Pearl
Technical Tip: 'The arcade of Struthers is the first thing I look for once I have identified the nerve proximally. I pass my scissors beneath the fascial band from medial to lateral, confirm the nerve is safe, and divide it. If I miss it, the nerve remains tethered and I cannot transpose it adequately — the proximal tension pulls the nerve back into its old bed.'
Dangers at this step
Missing the arcade of Struthers — the most commonly missed compression site; if not divided the nerve is tethered proximally during transposition
Injuring the superior ulnar collateral artery during proximal dissection — this vessel supplies the nerve; preserve it where possible
Confusing the ulnar nerve with the median nerve in the proximal arm — the ulnar nerve runs posterior to the medial intermuscular septum, the median nerve runs anterior to it
Step 3: Release the Medial Intermuscular Septum
Identify the medial intermuscular septum — the thick fibrous sheet between the anterior and posterior compartments. The ulnar nerve passes through an opening in the septum approximately 2-3 cm proximal to the medial epicondyle.
Critical step: Excise a 2-3 cm window of the medial intermuscular septum using scissors or rongeurs. Do NOT simply incise the septum. The excised window must be wide enough that no septal edge remains to kink the nerve as it changes direction after transposition. The nerve, once anteriorly transposed, passes through the septal opening at an oblique angle — a retained edge creates a sharp corner that compresses the nerve during elbow flexion.
After excision, pass a finger or instrument through the septal window to confirm it is smooth and wide with no sharp edges.
Clinical Pearl
Technical Tip: 'I do not just cut the septum — I excise a full 2-3 cm segment with rongeurs and then run my finger through the defect to feel for any remaining sharp edge. A retained septal lip is the most common cause of persistent compression after transposition. The nerve changes direction by almost 90 degrees as it passes through this window after being moved anteriorly, so even a small residual edge can kink it.'
Dangers at this step
Inadequate septal excision — leaving any edge risks kinking the transposed nerve
Injuring the brachial artery or median nerve on the anterior side of the septum during excision
Over-excising the septum and creating an excessively large defect that destabilises the muscle compartments (rare)
Step 4: Release the Cubital Tunnel and Mobilise the Nerve
Open the cubital tunnel retinaculum (Osborne's ligament) along its full length from the medial epicondyle to the olecranon. This exposes the ulnar nerve within the groove.
Carefully mobilise the nerve from the cubital tunnel floor. Preserve any fascial attachments and visible vascular pedicles entering the nerve surface (vasa nervorum). Use gentle blunt dissection with fine scissors and a peanut dissector. Do not skeletonise the nerve circumferentially — preserve as much of the extrinsic blood supply as possible.
Identify and preserve articular branches arising from the nerve proximal to or within the cubital tunnel. These supply the elbow joint capsule and the UCL.
Identify the motor branch to FCU, which typically arises within or just distal to the cubital tunnel. Protect it.
Clinical Pearl
Technical Tip: 'I mobilise the nerve carefully from the cubital tunnel groove, looking for small pulsating vessels on its surface that I must preserve. I do not try to free the nerve circumferentially at any single point — I work progressively, moving a few millimetres at a time and preserving every visible vascular connection. If I see a yellowish vessel entering the nerve, I protect it with a tiny rubber band or leave it within a thin fascial cuff.'
Dangers at this step
Over-dissection stripping the vasa nervorum — devascularises the nerve segment, producing post-ischaemic fibrosis
Division of articular branches — produces post-operative medial elbow pain
Division of FCU motor branch — produces FCU weakness (wrist flexion with ulnar deviation)
Handling the nerve with forceps — use vessel loop for retraction, never crush the nerve directly
Step 5: Release Distal Compression (FCU Heads)
Continue the dissection distally to where the nerve passes between the humeral and ulnar heads of FCU. Identify and release the aponeurotic arch connecting the two FCU heads. This is the most distal compression site and must be released to allow the nerve to glide freely into its transposed position.
The distal release should extend until the nerve is freely mobile and no residual tethering bands remain. In most cases this requires dissection 4-5 cm distal to the medial epicondyle.
Step 6: Choose and Create the Transposition Bed
At this point the nerve is fully mobilised from the arcade of Struthers proximally to past the FCU heads distally. The choice of transposition bed depends on the indication and surgeon preference:
For subcutaneous transposition: Create a subcutaneous pocket anterior to the medial epicondyle by developing a plane between the flexor-pronator fascia and the subcutaneous tissue. The pocket should be generous enough to accommodate the nerve without tension. A fascial sling is created from the antebrachial fascia or a subcutaneous flap to prevent the nerve from subluxing back into the cubital tunnel.
For submuscular (Learmonth) transposition: Detach the common flexor-pronator origin from the medial epicondyle. This is done as an en-masse detachment, not individual muscle releases. The UCL lies deep to the flexor origin and must be protected. The muscle belly is reflected anteriorly, creating a deep bed for the nerve beneath the muscle. The nerve is placed in this bed, and the flexor-pronator origin is reattached to the medial epicondyle using suture anchors or transosseous drill holes.
Clinical Pearl
Technical Tip: 'For the Learmonth procedure I detach the common flexor origin from the medial epicondyle as a single sleeve, leaving a small cuff of tissue on the bone for reattachment. I use a periosteal elevator and stay on the subperiosteal plane to protect the UCL underneath. I reattach with two suture anchors (typically 5.0 mm metal or PEEK anchors) and reinforce with number 2 braided suture through transosseous tunnels if the bone quality allows.'
Dangers at this step
UCL injury during flexor-pronator detachment (submuscular technique) — stay in the subperiosteal plane
Medial epicondyle fracture during anchor placement — use appropriately sized anchors for bone quality
Inadequate sling creation (subcutaneous technique) — the nerve subluxates back into the cubital tunnel post-operatively
Tension on the nerve in its new bed — ensure there is no tethering proximally or distally
Step 7: Position the Nerve in the Transposition Bed
Gently place the ulnar nerve in its new bed (subcutaneous pocket, intramuscular groove, or deep to the flexor-pronator mass). Ensure the nerve lies smoothly without tension, angulation, or rotation. The nerve should not be under tension with the elbow in any position from full extension to full flexion.
For submuscular transposition, before reattaching the flexor-pronator mass, verify that the nerve lies comfortably in its bed with the elbow in full flexion and full extension.
Step 8: Construct the Fascial Sling (Subcutaneous Transposition)
Create a fascial sling from the superficial antebrachial fascia (just proximal to the flexor-pronator fascia) or from a subcutaneous fat-fascial flap. The sling is sutured to the subcutaneous tissue on the medial side of the medial epicondyle, forming a bridge that prevents the nerve from subluxing posteriorly back into the cubital tunnel.
The sling must be loose enough that the nerve glides freely beneath it with elbow flexion and extension, but tight enough to prevent posterior subluxation. The nerve should have at least 1-2 cm of excursion beneath the sling during the elbow flexion-extension sweep.
Alternative: A Z-plasty of the subcutaneous fascia can be used instead of a separate sling, creating a lengthened fascial roof over the transposed nerve.
Step 9: Reattach Flexor-Pronator Mass (Submuscular / Learmonth Transposition)
Using suture anchors or transosseous drill holes through the medial epicondyle, reattach the common flexor-pronator origin. The repair must be secure enough to tolerate early mobilisation. Use heavy non-absorbable sutures (number 2 braided) through the anchors or bone tunnels.
Before final tensioning of the repair, confirm the nerve lies freely beneath the muscle without compression. The repaired muscle should not be so tight that it compresses the nerve against the medial epicondyle.
Step 10: Elbow Flexion-Extension Sweep Test
With the nerve in its final position, perform the critical verification test: passively flex and extend the elbow through a full range while watching the nerve.
The nerve should glide smoothly in its new bed. Check specifically for:
Kinking at the proximal margin (where the nerve enters the new bed — check for residual septal edge or fascial band)
Kinking at the distal margin (where the nerve exits the new bed — check for unexcised FCU aponeurosis)
Subluxation back into the cubital tunnel (subcutaneous transposition — check fascial sling adequacy)
Compression beneath the flexor-pronator mass (submuscular transposition — check that the muscle repair does not strangulate the nerve)
Excessive tension with full flexion or full extension
If any abnormality is detected, address it before proceeding to closure.
Clinical Pearl
Technical Tip: 'After positioning the nerve I perform the flexion-extension sweep test at least three times. I watch the nerve carefully at its proximal and distal transitions. If I see any catching or kinking, I go back and look for the cause — usually a residual septal edge proximally or an unexcised band distally. I do not accept anything less than perfectly smooth gliding.'
Dangers at this step
Accepting kinking or catching — this predicts post-operative compression and poor outcome
Not testing through full range — subtle kinking may only appear at extremes of flexion or extension
Subluxation back into the cubital tunnel — inadequate fascial sling in subcutaneous transposition
Step 11: Haemostasis and Wound Closure
Release the tourniquet and achieve meticulous haemostasis with bipolar diathermy. Pay particular attention to bleeding from the septal edges, the periosteum of the medial epicondyle, and the flexor-pronator fascia.
Irrigate the wound with sterile saline.
Close the deep fascia of the forearm with absorbable sutures (2-0 Vicryl) if opened. Close subcutaneous tissue with 3-0 Vicryl. Close skin with 4-0 nylon interrupted sutures or a subcuticular absorbable closure.
Apply a soft, well-padded posterior splint with the elbow at 90 degrees of flexion and the forearm in neutral rotation. The splint should not compress the transposed nerve.
Posterior splint with elbow at 90 degrees flexion, forearm neutral, for 7-10 days
Finger and wrist mobilisation encouraged from day 1
Elevate hand above heart for first 48 hours
Submuscular (Learmonth) transposition:
Posterior splint with elbow at 90 degrees flexion, forearm neutral, for 10-14 days
Finger mobilisation encouraged from day 1
Flexor-pronator repair requires longer protection than subcutaneous transposition
Phase 2: Early Mobilisation (Week 2-4)
Subcutaneous transposition:
Remove splint at 7-10 days, begin active-assisted elbow range of motion
Progress to active elbow flexion and extension within 2 weeks
No resisted forearm pronation or wrist flexion for 4 weeks (protects the sling)
Night-time extension splint optional if patient is a heavy elbow-flexor during sleep
Submuscular (Learmonth) transposition:
Remove splint at 10-14 days, begin active-assisted elbow range of motion
Protect flexor-pronator repair: no resisted gripping, forearm pronation, or wrist flexion for 4-6 weeks
Gradual increase in elbow extension — target full extension by 4-6 weeks
Supervised hand therapy from 2 weeks post-operatively
Phase 3: Strengthening (Week 4-8)
Progressive grip and pinch strengthening
Forearm pronation-supination exercises
Wrist flexion and extension strengthening
Gradual return to activities of daily living
Formal hand therapy continues
Phase 4: Return to Full Activity (Week 8-16)
Subcutaneous transposition: return to full activity and sport at 8-12 weeks
Submuscular (Learmonth) transposition: return to full activity at 12-16 weeks; throwing athletes at 4-6 months with supervised throwing programme
Heavy manual labour: 12-16 weeks for both techniques
Return to Function Timeline
Splint removal
Subcutaneous Transposition
7-10 days
Submuscular (Learmonth)
10-14 days
Full elbow ROM
Subcutaneous Transposition
4-6 weeks
Submuscular (Learmonth)
6-8 weeks
Light activities
Subcutaneous Transposition
2-3 weeks
Submuscular (Learmonth)
3-4 weeks
Return to driving
Subcutaneous Transposition
2-4 weeks
Submuscular (Learmonth)
3-5 weeks
Return to desk work
Subcutaneous Transposition
2-3 weeks
Submuscular (Learmonth)
3-4 weeks
Return to manual work
Subcutaneous Transposition
8-12 weeks
Submuscular (Learmonth)
12-16 weeks
Return to sport (non-throwing)
Subcutaneous Transposition
8-12 weeks
Submuscular (Learmonth)
12-16 weeks
Return to throwing sport
Subcutaneous Transposition
12-16 weeks
Submuscular (Learmonth)
4-6 months
Milestone
Subcutaneous Transposition
Submuscular (Learmonth)
Splint removal
7-10 days
10-14 days
Full elbow ROM
4-6 weeks
6-8 weeks
Light activities
2-3 weeks
3-4 weeks
Return to driving
2-4 weeks
3-5 weeks
Return to desk work
2-3 weeks
3-4 weeks
Return to manual work
8-12 weeks
12-16 weeks
Return to sport (non-throwing)
8-12 weeks
12-16 weeks
Return to throwing sport
12-16 weeks
4-6 months
Neurological Recovery
Expected timeline: Nerve regeneration proceeds at approximately 1 mm per day (or approximately 1 inch per month). Recovery of motor function (intrinsic muscles) is slower than sensory recovery and may continue for 12-18 months post-operatively.
Sensory recovery: Paraesthesiae typically improve within the first 3 months. Two-point discrimination improves progressively but may never return to normal in severe (McGowan grade III) disease. Light touch and pain sensation recover before two-point discrimination.
Motor recovery: Intrinsic muscle re-innervation (interossei, thenar intrinsics, hypothenar muscles) may take 6-18 months. Patients with pre-operative wasting may not fully recover muscle bulk despite good re-innervation.
Factors favouring good recovery: Young age, shorter duration of symptoms, milder pre-operative disease (McGowan I-II), absence of subluxation, primary (not revision) surgery
Recommended at 3-6 months post-operatively to document improvement in conduction velocity and compound muscle action potential amplitudes
Persistent conduction block or significantly slowed velocities at the transposition site suggest residual compression (kinking, inadequate release, scar tissue)
Comparing pre-operative and post-operative studies guides the decision for revision surgery
Special Case: Revision Cubital Tunnel Surgery
Why Revision Is More Difficult
Scar tissue from previous surgery makes nerve identification and mobilisation more hazardous
The nerve's extrinsic blood supply may already be compromised from the first operation
Adhesions between the nerve and surrounding tissues limit mobilisation
Outcomes of revision surgery are generally worse than primary surgery regardless of technique
Revision Strategy
Anterior transposition is generally preferred over repeat in-situ release for revision cases — the nerve is moved away from the scarred cubital tunnel bed entirely
Submuscular (Learmonth) transposition is the preferred technique in most revision cases because it provides the deepest and most secure coverage, protecting the nerve from superficial scar tissue
Careful pre-operative counselling: recovery is slower, improvement rates are lower (approximately 60-80% compared with 80-95% for primary surgery), and complete resolution of symptoms is less likely
Nerve conduction studies and MRI before revision to confirm the site of persistent compression and identify scar tissue
Special Case: Throwing Athletes
Why Transposition Is Preferred in Overhead Athletes
Repeated valgus stress and elbow flexion during throwing places the ulnar nerve under repetitive compression and stretch
Nerve subluxation is common in throwers due to dynamic muscle forces
Simple decompression does not address the instability of the nerve during the throwing motion
The transposed nerve is placed in a protected position that tolerates repeated valgus loading
Technical Considerations
Submuscular (Learmonth) transposition is generally preferred in high-level throwers for the deepest, most secure nerve coverage
The UCL must be carefully assessed — many throwers with cubital tunnel syndrome also have UCL insufficiency (the "valgus extension overload" spectrum)
If simultaneous UCL reconstruction is needed, coordinate the surgical plan: the flexor-pronator detachment for Learmonth transposition provides access to the UCL for graft passage
Post-operative throwing programme: 4-6 months with progressive throwing from flat ground, progressing to mound throwing, under the supervision of a sports physiotherapist
Special Case: Cubital Tunnel Syndrome with Associated Guyon's Canal Compression
Double Crush Phenomenon
The ulnar nerve can be compressed at both the cubital tunnel and Guyon's canal (at the wrist) simultaneously
Patients may have mixed proximal and distal signs — intrinsic wasting with both elbow and wrist provocative tests positive
In-situ release at the elbow alone may produce incomplete relief if the distal compression is not also addressed
Management
Perform nerve conduction studies localising conduction slowing to both sites
If both sites are confirmed, address the cubital tunnel first (anterior transposition) and decompress Guyon's canal in the same procedure or as a staged second procedure
Anterior transposition does not decompress Guyon's canal — the distal site must be released separately through a separate wrist incision
Clinical Decision Scenarios
Practise clinical reasoning and management decisions out loud
Viva scenarioAdvanced
Clinical prompt
“A 32-year-old professional baseball pitcher presents with a 6-month history of progressive paraesthesiae in the ring and little fingers of his throwing arm, worse during and after pitching. Examination reveals mild intrinsic weakness (Froment sign positive), no significant wasting, and a positive elbow flexion test at 30 seconds. Nerve conduction studies show moderate slowing across the cubital tunnel. He also reports medial elbow pain during late cocking phase of pitching. How do you manage him?”
Practical approach
This patient has moderate cubital tunnel syndrome in the context of a throwing athlete, with concurrent medial elbow pain that raises suspicion for associated UCL insufficiency (valgus extension overload spectrum). The management requires addressing both the nerve compression and the potential ligament pathology.
**Pre-operative assessment**: I would obtain an MRI of the elbow to evaluate the UCL. Many throwing athletes with cubital tunnel symptoms also have partial or complete UCL tears. I would also assess for ulnar nerve subluxation on dynamic examination (palpating the nerve while passively flexing the elbow). A positive Tinel sign and positive elbow flexion test confirm the cubital tunnel involvement. If MRI shows UCL tearing, I would discuss combined surgery.
**Surgical plan**: I would perform submuscular (Learmonth) anterior transposition of the ulnar nerve. In a throwing athlete, submuscular transposition is preferred over subcutaneous because it provides the deepest, most secure nerve coverage that tolerates repeated valgus loading. The flexor-pronator detachment for the Learmonth procedure also provides excellent surgical exposure to the UCL if simultaneous reconstruction is needed.
**Technique specifics**: I would release all five compression sites from the arcade of Struthers to the FCU heads, excise the medial intermuscular septum, and transpose the nerve deep to the flexor-pronator mass. The flexor origin is reattached with suture anchors. If UCL reconstruction is indicated, I use a palmaris longus or gracilis autograft passed through bone tunnels in the medial epicondyle and the sublime tubercle of the ulna, docking the graft with interference screw fixation.
**Post-operative rehabilitation**: The throwing programme is a staged process spanning 4-6 months. Phase 1 (0-2 weeks): posterior splint at 90 degrees. Phase 2 (2-6 weeks): active-assisted elbow ROM, protect flexor-pronator repair. Phase 3 (6-12 weeks): progressive strengthening. Phase 4 (3-4 months): interval throwing programme on flat ground. Phase 5 (4-6 months): mound throwing and return to competition.
**Key counselling points**: Recovery of intrinsic muscle function may take 12-18 months. Return to competitive pitching at the pre-injury level is expected in approximately 80-85% of professional pitchers after combined nerve transposition and UCL reconstruction (data from elbow reconstruction registries). However, some loss of velocity and control is possible in the first full season back.
Viva scenarioAdvanced
Clinical prompt
“A 55-year-old woman presents 18 months after an in-situ cubital tunnel decompression on her dominant hand. She had initial improvement for 6 months but now has recurrent paraesthesiae and progressive intrinsic weakness. Nerve conduction studies show persistent moderate slowing across the cubital tunnel. She works as a typist and is frustrated with the recurrence. What are your surgical options and how would you proceed?”
Practical approach
This is a revision scenario after failed in-situ decompression. The recurrence of symptoms after an initial improvement suggests the nerve may be compressed by scar tissue at the decompression site, that the release was incomplete (a compression site was missed), or that a structural issue such as subluxation was not addressed at the index procedure.
**Pre-operative workup**: I would obtain an MRI of the elbow to evaluate for scar tissue around the nerve, persistent bony compression, nerve subluxation, or other pathology. I would repeat nerve conduction studies with inching across the elbow to localise the precise site of compression. I would also assess for double crush at Guyon's canal with wrist-level nerve studies.
**Surgical decision**: The definitive procedure for revision cubital tunnel syndrome is anterior transposition — typically submuscular (Learmonth) transposition. This moves the nerve entirely away from the scarred cubital tunnel bed into a fresh, protected position deep to the flexor-pronator mass. Simple repeat in-situ decompression in a revision setting has significantly worse outcomes than transposition.
**Why submuscular over subcutaneous in revision**: The submuscular position provides deeper coverage and is less susceptible to superficial scar tissue. The nerve is protected beneath the flexor-pronator mass, which acts as a biological cushion. In revision surgery, the soft tissue planes are disrupted and a subcutaneous transposition may leave the nerve directly under scar-prone skin.
**Counselling before revision**: I would explain that revision surgery has lower success rates than primary surgery — approximately 60-80% improvement versus 80-95% for primary transposition. Recovery is slower, and complete resolution of symptoms is less likely. There is a risk of further worsening of ulnar nerve function. The patient's occupation as a typist depends on fine motor control of the fingers, so she needs realistic expectations about the timeline for intrinsic muscle recovery (12-18 months).
**Technique in revision**: The previous incision is used (extended if necessary). Dissection is more difficult due to scar tissue from the first surgery. The nerve is identified proximal to the previous decompression site where tissue planes are more normal. All compression sites are re-released, the septum is excised, and the nerve is transposed submuscularly. Meticulous haemostasis is critical to minimise further scar formation.
Viva scenarioAdvanced
Clinical prompt
“You are performing an anterior subcutaneous transposition for cubital tunnel syndrome. During the procedure, after transposing the nerve anterior to the medial epicondyle and constructing a fascial sling, you notice that the nerve kinks at the proximal margin when you flex the elbow past 90 degrees. What has gone wrong and how do you fix it?”
Practical approach
Nerve kinking at the proximal margin of the transposition during the elbow flexion-extension sweep test indicates that a structure is tethering the nerve or creating an acute angle as it enters the new bed. This is an intraoperative finding that MUST be resolved before closure — leaving it untreated will produce persistent post-operative compression.
**Most common cause**: Incomplete excision of the medial intermuscular septum. The nerve, once transposed anteriorly, passes through the septal opening at an oblique angle (approximately 60-90 degrees from its previous trajectory). Any retained septal edge acts as a fulcrum, kinking the nerve when the elbow flexes and the nerve is drawn taut.
**My approach to fixing this**:
1. Extend the septal excision — use rongeurs or scissors to remove an additional 1-2 cm of septum, widening the window. Run my finger through the defect to confirm no sharp edges remain.
2. If septal excision is adequate and kinking persists, look for an unexcised fascial band (sometimes a separate fascial slip proximal to the septum or the proximal edge of Osborne's ligament that was not fully released).
3. If kinking persists despite adequate septal excision, check for a retained arcade of Struthers that was incompletely divided.
4. After addressing the cause, repeat the flexion-extension sweep test. The nerve must glide smoothly at all positions.
**Other considerations**: The kinking could also be caused by an inadequate sling that is too tight, creating a constriction point. If the sling is the cause, loosen or reconstruct it. Alternatively, the nerve may have been transposed under too much tension — if the proximal mobilisation was insufficient, the nerve is being pulled as the elbow flexes. In this case, extend the proximal mobilisation further (additional release of the arcade of Struthers or more proximal nerve freeing).
**The principle**: Do not accept ANY kinking or catching on the sweep test. Re-explore and release the cause before proceeding to closure. This is a critical error-prevention step that directly impacts the outcome of the surgery.
Exam day cheat sheet
Ulnar Nerve Anterior Transposition — Exam Day Summary
References
Evidence
Prospective randomized controlled study comparing simple decompression versus anterior subcutaneous transposition for idiopathic neuropathy of the ulnar nerve at the elbow
Level I
Bartels RH, Verhagen WI, van der Wilt GJ, Meulstee J, van Rossum LG, Grotenhuis JA • Neurosurgery
Clinical implication: For primary idiopathic cubital tunnel syndrome without specific indications for transposition, simple decompression provides equivalent outcomes with lower early morbidity.
Simple decompression versus anterior subcutaneous and submuscular transposition of the ulnar nerve for cubital tunnel syndrome: a meta-analysis
Level I
Macadam SA, Gandhi R, Bezuhly M, Lefaivre KA • J Hand Surg Am
Clinical implication: Meta-analytic evidence supports simple decompression as the first-line surgical option for primary cubital tunnel syndrome, reserving transposition for specific indications.
