Triceps Brachii Anatomy

Origins

• Long head: the infraglenoid tubercle of the scapula, immediately inferior to the glenoid rim. It is the only head that crosses the shoulder joint, and therefore the only head with a shoulder action (extension and adduction). It forms the medial border of the quadrangular space and the lateral border of the triangular space, and divides the two.
• Lateral head: a linear origin on the posterior surface of the humerus, proximal and lateral to the spiral groove, running obliquely from just below the surgical neck down toward the groove, and from the lateral intermuscular septum.
• Medial (deep) head: a broad origin on the posterior surface of the humerus, distal and medial to the spiral groove, extending from the groove down to within 2 cm of the trochlea, and from the medial and lateral intermuscular septa. It lies deep to the other two heads throughout.

The Spiral Groove Divides the Origins

The single most useful way to remember the origins: draw the spiral groove on the posterior humerus. The lateral head arises above and lateral to it; the medial head arises below and medial to it; the radial nerve and profunda brachii run in the groove between them.

Insertion

• A common tendon onto the posterior and superior surface of the olecranon, with a superficial expansion continuing into the deep antebrachial (forearm) fascia and blending laterally with the anconeus fascia.
• Footprint - and two published figures that differ threefold. Yeh and colleagues measured the average bony footprint at 466 mm squared in 27 elbows. Athwal and colleagues, below, measured 44 mm squared for the medial head and 115 mm squared for the combined long and lateral heads in 15 elbows - about 134 mm squared where all three insert together. Both are quoted verbatim from their papers, and neither defines the boundary it measured to, so they are almost certainly not measuring the same thing: a broad osseous attachment area including the fascial expansion, against discrete tendinous insertions. Do not quote a single number as settled. The point that survives either measurement is the clinically useful one - the attachment is broader than the region a suture-anchor repair reconstitutes.
• Layered structure. Athwal and colleagues, dissecting 15 cadaveric limbs, found:
  • In 8 of 15 (53 per cent) the medial head had a SEPARATE insertion onto the olecranon, lying deep to the combined long and lateral head insertion. Mean area of the medial head insertion 44 mm squared; mean area of the combined long and lateral head insertion 115 mm squared.
  • In 7 of 15 (47 per cent) all three heads inserted together, mean area 134 mm squared — but even then the medial head fibres were oriented deep to the long and lateral heads.
• Clinical consequence: an isolated avulsion of the deep medial head can occur with the superficial tendon intact, presenting as pain and subtle extension weakness with an apparently continuous triceps. It has been treated by arthroscopic repair.

Bony Landmarks to Quote

• Long head origin: infraglenoid tubercle, immediately inferior to the glenoid.
• Lateral head origin: begins approximately 3 to 5 cm distal to the greater tuberosity on the posterolateral humerus.
• Medial head origin: extends from the spiral groove to within about 2 cm of the olecranon fossa.
• Insertion: posterior and superior olecranon; bony footprint measured at 466 mm squared, tendinous insertions at about 134 mm squared - see the reconciliation above.

Radial Nerve (C6, C7, C8) — Three Separate Branches

Why This Matters Clinically

• In a radial nerve palsy from a mid-shaft humeral fracture or spiral groove lesion, the triceps is characteristically SPARED. Preserved elbow extension with wrist drop, finger drop and dorsal first web numbness localises the lesion to the spiral groove or distal to it.
• Triceps weakness with a radial palsy implies a lesion proximal to the spiral groove — in the axilla (crutch palsy, "Saturday night" palsy of the high radial nerve) or a posterior cord lesion.
• Gerwin and colleagues found the radial nerve giving several branches to the lateral head as it crossed the posterior humerus, but no branches to the medial head in the posterior aspect of any specimen — confirming that the medial head branch arises proximally and reaches the muscle from a different direction.

The Trifurcation

At the lateral aspect of the humerus the radial nerve trifurcates into:

1. A branch to the medial head of triceps (continuing on to anconeus).
2. The lower lateral brachial cutaneous nerve.
3. The continuation of the radial nerve into the distal arm and forearm.

Nerve Transfer Relevance

• A redundant branch to a triceps head (commonly the long or medial head branch) is a standard donor for transfer to the axillary nerve in C5-C6 brachial plexus injury or isolated axillary nerve palsy. The triceps has three separately innervated heads, so sacrificing one branch leaves extension intact — the anatomical basis for this being the standard salvage for deltoid reanimation.

Named Vessels

• Profunda brachii (deep brachial) artery — the dominant supply. It arises from the brachial artery near the lower border of teres major and enters the posterior compartment with the radial nerve through the triangular interval, then runs with the nerve in the spiral groove.
• Posterior circumflex humeral artery — supplies the proximal portion, particularly of the lateral and long heads, having passed through the quadrangular space.
• Superior ulnar collateral artery — supplies the medial head; it accompanies the ulnar nerve behind the medial intermuscular septum.
• Middle and radial collateral branches of the profunda supply the distal muscle and anastomose around the elbow.

Pedicle Position and Flap Use

• The profunda brachii pedicle enters with the radial nerve in the spiral groove, in the middle third of the posterior arm. This is a Mathes-Nahai type II pattern for the lateral head.
• The lateral head of triceps is a usable pedicled muscle flap for posterior elbow or olecranon cover, based on the radial collateral branch of the profunda brachii. It is a second-line option after the anconeus, whose pedicle is more distal and whose donor morbidity is nil.
• The medial head is not used as a flap, because it is the deep head and its loss would meaningfully weaken extension.
• The lateral arm flap (a fasciocutaneous flap based on the posterior radial collateral artery, raised over the lateral intermuscular septum between triceps and brachialis) is a workhorse free flap whose pedicle lies in this territory — which is why the septum must be preserved if that flap is planned.

The Spiral (Radial) Groove

• Runs obliquely across the posterior humerus from superomedial to inferolateral, containing the radial nerve and profunda brachii vessels.
• Bounded superficially by the lateral head, deep by the medial head. The nerve is therefore sandwiched between the two heads, and the plane between them is the plane in which the nerve is found.
• Distances (Gerwin and colleagues, 10 cadaveric specimens): the nerve crossed the posterior humerus from a mean of 20.7 plus or minus 1.2 cm proximal to the medial epicondyle to 14.2 plus or minus 0.6 cm proximal to the lateral epicondyle.
• Distances (Bono and colleagues, 50 fresh cadaveric limbs): the nerve crossed the lateral intermuscular septum a mean of 17 plus or minus 2.3 cm (range 13 to 22 cm) distal to the top of the humeral head, 12 plus or minus 2.3 cm (range 7.4 to 16.6 cm) proximal to the olecranon fossa — approximately the midpoint of the bone.

The Triangular Interval and Quadrangular Space

• Triangular interval: bounded by teres major (above), long head of triceps (medial) and the humerus or lateral head of triceps (lateral). Transmits the radial nerve and profunda brachii into the posterior compartment.
• Quadrangular space: bounded by teres minor (above), teres major (below), long head of triceps (medial) and the surgical neck of the humerus (lateral). Transmits the axillary nerve and posterior circumflex humeral vessels.
• Triangular space: bounded by teres minor (above), teres major (below) and the long head of triceps (lateral). Transmits the circumflex scapular vessels.
• The long head of triceps is the structure that separates the quadrangular space from the triangular space — a stock viva question.

Medial

• Ulnar nerve behind the medial intermuscular septum in the distal third, accompanied by the superior ulnar collateral artery and by the nerve branch to the medial head of triceps. Any medial dissection at the distal humerus therefore risks all three.
• Medial intermuscular septum — separates the triceps from brachialis. It must be excised for a distance if the ulnar nerve is transposed anteriorly, or the nerve will kink over its sharp edge.

Lateral

• Lateral intermuscular septum and, deep to it anteriorly, brachialis and brachioradialis.
• The radial nerve pierces the lateral septum to enter the anterior compartment; this is where it is tethered and where a Holstein-Lewis distal-third spiral fracture injures it.

Epidemiology and Mechanism

• The least common of all tendon ruptures. Male predominance, typically in the fourth to fifth decades.
• Mechanism: eccentric loading of a contracting triceps — a fall on the outstretched hand with the elbow forced into flexion, or a failed bench press or push.
• Risk factors: anabolic steroid use, local corticosteroid injection, chronic renal failure and secondary hyperparathyroidism, hyperparathyroidism, olecranon bursitis, and previous olecranon fracture surgery.

Classification by Extent

• Partial superficial — long and lateral heads torn, deep medial head insertion intact. Extension preserved but weak.
• Complete — all heads avulsed; extension against gravity lost.
• Isolated deep medial head avulsion — rare; superficial tendon intact, subtle presentation, arthroscopically repairable.

Repair

• Indication: complete ruptures and partial ruptures with greater than about 50 per cent involvement or functional weakness, in patients with reasonable demand.
• Technique matters - but read what was actually measured. Yeh and colleagues biomechanically compared three repairs in 27 cadaveric elbows: cruciate transosseous repair, suture anchor repair, and anatomic (footprint) repair. Load at yield and peak load were similar for all three, so the entire difference between techniques rests on one endpoint - cyclic loading over 1500 cycles produced significantly less displacement with the anatomic footprint repair. Gap formation under repetitive load is a plausible surrogate for what fails during early rehabilitation, and it is the right thing to optimise in the absence of better evidence; but this is a time-zero cadaveric measurement with no healing, and no clinical series has since shown a difference in re-rupture. Say "less gapping in the laboratory", not "better outcome". (The same paper's 466 mm squared bony footprint should be quoted with the caveat set out in the Insertion section above.)
• Chronic or retracted ruptures may require Achilles tendon allograft, anconeus rotation, or a triceps turn-down.

Rehabilitation

• Typically splinted in about 30 degrees of flexion for 2 weeks, then progressive passive and active-assisted flexion with extension assisted, avoiding resisted extension for around 6 weeks and heavy loading for 4 to 6 months.

Triceps Insufficiency After Total Elbow Arthroplasty

The characteristic late soft-tissue failure of total elbow arthroplasty, and the reason approach selection matters so much.

The Mayo experience (Celli, Arash, Adams and Morrey): of 887 total elbow arthroplasties performed between 1982 and 2001, 16 elbows in 14 patients required a subsequent procedure for triceps insufficiency (excluding those following debridement for infection). Mean age 54 years; mean follow-up after reconstruction 67 months.

Three reconstruction techniques were used, selected on tissue quality, tendon retraction and the state of the olecranon:

• Direct suture repair — 7 elbows. Used when the tendon is of good quality and minimally retracted.
• Anconeus rotation — 4 elbows. The anconeus is rotated proximally on its recurrent posterior interosseous pedicle to fill a defect and reinforce the repair.
• Achilles tendon allograft — 4 elbows. Used for substantial tissue loss or marked retraction, the calcaneal bone block being fixed to the olecranon.

Outcomes: extension against gravity was restored in 15 of 16 elbows. By the Mayo Elbow Performance Score, 11 excellent, 3 good, 2 clinical failures.

Prevention

• Approach selection. A triceps-on (para-tricipital, Alonso-Llames) approach, working on either side of an intact triceps, avoids the problem entirely and is increasingly favoured for arthroplasty. Where exposure demands it, the Bryan-Morrey triceps-reflecting approach preserves continuity between the triceps, the forearm fascia and the ulnar periosteum, so nothing is truly detached.
• Repair technique. If the extensor mechanism is reflected, it must be reattached through cruciate transosseous drill holes in the olecranon with heavy non-absorbable suture, not simply sutured to periosteum.
• Rehabilitation. Protect active extension for 6 weeks; avoid resisted extension and pushing up out of a chair with the operated arm.
• Risk factors: rheumatoid tissue, previous surgery through the same approach, corticosteroid use, infection, and revision surgery.

Radial Nerve Palsy and the Triceps

• Humeral shaft fracture is the commonest cause of a traumatic radial nerve palsy — reported in roughly 8 to 12 per cent of humeral shaft fractures overall, and higher for distal-third spiral (Holstein-Lewis) patterns, where the nerve is tethered as it pierces the lateral intermuscular septum.
• The triceps is characteristically spared, because the branches to the long and lateral heads are given off in the axilla and at the groove, and the medial head branch arises proximally.
• Localisation rule:
  • Triceps preserved, wrist drop, finger drop, dorsal first web numbness: lesion at or distal to the spiral groove.
  • Triceps weak as well: lesion proximal to the groove — axilla (crutch palsy) or posterior cord.
• Prognosis: the large majority of palsies after closed humeral shaft fracture recover spontaneously. Observation with a wrist and finger extension splint and serial examination is standard, with electrodiagnostic study at around 3 months and exploration considered if no recovery by 3 to 6 months.
• Iatrogenic palsy after open reduction is a different matter and warrants a lower threshold for early exploration, especially if the nerve was seen and intact at the index operation.

Snapping Triceps

• The medial head of triceps can snap over the medial epicondyle in elbow flexion, often together with a subluxating ulnar nerve, producing a double snap. It is important to recognise, because transposing the ulnar nerve alone will not cure the symptom if the medial head is the snapping structure; the hypertrophic medial head must be resected or reduced.

Triceps Tendinopathy

• Insertional tendinopathy at the olecranon, common in throwers, weightlifters and gymnasts. Tender at the insertion, painful on resisted extension. Managed with load modification and eccentric loading; corticosteroid injection is avoided because of the rupture risk at this insertion.

Olecranon Bursitis

• The olecranon bursa lies superficial to the triceps insertion. Septic bursitis (usually Staphylococcus aureus) must be distinguished from a septic elbow joint: in bursitis, passive elbow motion is relatively preserved and pain-free in mid-range, whereas septic arthritis produces severe pain on any passive movement.

Valgus Extension Overload

• In throwing athletes, repetitive valgus force plus terminal extension drives the posteromedial olecranon against the trochlea, producing posteromedial osteophytes and chondral wear. The triceps drives the terminal extension component. Osteophyte resection must be conservative, because over-resection of the olecranon increases strain on the ulnar collateral ligament.

Snapping and Impingement After Fixation

• Prominent olecranon hardware (tension band wires) irritates the triceps insertion and the subcutaneous tissue and is the commonest reason for implant removal after olecranon fracture fixation.

The Four Options at the Distal Humerus

Bryan-Morrey Triceps-Reflecting Approach in Detail

• Described in 1982 by Bryan and Morrey, prompted by the problem of triceps avulsion and loss of continuity after total elbow arthroplasty.
• The defining feature is continuity. The triceps mechanism is reflected from medial to lateral in continuity with the forearm fascia, the olecranon periosteum and the ulnar periosteum. The tendon is never divided or detached from the fascial sleeve; a subperiosteal sleeve of tissue is peeled off the olecranon carrying the extensor mechanism with it.
• The ulnar nerve must be identified and mobilised first, since the dissection begins medially.
• The ulnar collateral ligament may be released from the humerus for more exposure, but must then be securely reattached.
• A lateral-to-medial variant exists (the extensor mechanism reflected the other way).
• In their series of 49 consecutive total elbow arthroplasties, Bryan and Morrey reported no loss of triceps function and no significant weakness.
• Reattachment is through cruciate transosseous drill holes in the olecranon with heavy non-absorbable suture.

Olecranon Osteotomy Technique

• Chevron (apex distal) osteotomy, made intra-articularly at the bare area of the sigmoid notch — the transverse non-articular strip roughly 2 to 2.5 cm from the tip of the olecranon, where there is no cartilage to damage.
• Pre-drill and pre-tap the fixation (an intramedullary screw or tension band) before making the cut, so the reduction is anatomic on closure.
• Protect the ulnar nerve medially throughout.
• Never perform an olecranon osteotomy if arthroplasty is a possibility — the osteotomy destroys the bone the implant needs and adds a non-union risk to an already compromised elbow.

Posterior Approach to the Humeral Shaft

• Interval: none in the classical description; the triceps is split between the long head (medial) and lateral head, then the medial head is split in the midline down to bone. Not a true internervous plane.
• The radial nerve is the limiting structure, and the numbers are:
  • It crosses the posterior humerus from 20.7 cm proximal to the medial epicondyle to 14.2 cm proximal to the lateral epicondyle.
  • A standard triceps-splitting approach exposes 15.4 cm of humerus measured from the lateral epicondyle before reaching the nerve.
  • Mobilising the nerve proximally adds 6 cm.
  • The modified posterior approach — identifying the nerve distally where it crosses the lateral humerus, then reflecting both the lateral and medial heads medially — exposes 26.2 cm of diaphysis, essentially the whole bone.
• Practical sequence: find the nerve distally in the lateral intermuscular septum region first, where it is predictable, then work proximally along it. Do not start proximally and hope.

Distal Humeral Plating

• Parallel (medial and lateral column) plating versus orthogonal (posterolateral and medial) plating — both are accepted. Parallel plating provides greater construct stiffness in most biomechanical studies; orthogonal plating is technically easier and may suit certain fracture geometries.
• The principle that matters more than the configuration: as many screws as possible through the plate into the distal fragment, each engaging a fragment on the opposite side, and the plates compressing the supracondylar level and being long enough that the fixation is stable at the arch of the elbow.

Triceps Tendon and Muscle as Reconstructive Material

Why Elbow Extension Is Reconstructed in Tetraplegia

Active elbow extension is transformative for a tetraplegic patient: it enables overhead reach, transfers and pressure relief, wheelchair propulsion up a slope and stabilisation of the arm for any distal function including a subsequent grip reconstruction. It is often prioritised over hand reconstruction because a hand that cannot be positioned is of limited use.

Reconstructing a Deficient Extensor Mechanism

Selected on tissue quality, degree of retraction and the state of the olecranon (the Mayo algorithm):

1. Direct repair. Good tissue, minimal retraction. Cruciate transosseous drill holes through the olecranon with heavy non-absorbable suture. Used in 7 of 16 Mayo cases.
2. Anconeus rotation. Moderate defect with a viable anconeus. The muscle is rotated proximally on its recurrent posterior interosseous pedicle and sutured into the defect. Used in 4 of 16 cases. It also provides vascularised soft tissue cover.
3. Achilles tendon allograft. Substantial tissue loss or marked retraction. The calcaneal bone block is fixed to the olecranon and the tendon fanned out and sutured to the remaining triceps. Used in 4 of 16 cases.
4. Triceps turn-down as an alternative autologous option where sufficient proximal tendon remains.

Result to quote: extension against gravity restored in 15 of 16; 11 excellent, 3 good, 2 failures by the Mayo Elbow Performance Score at a mean of 67 months.