Extended Lateral Deltoid-Split Approach to the Shoulder

What it exposes. The lateral deltoid-split approach gives direct, linear access to the greater tuberosity, the supraspinatus insertion (footprint), the subacromial bursa and the lateral cortex of the proximal humeral shaft, without detaching the deltoid origin or traversing the deltopectoral interval. For cuff repair it places the surgeon directly over the tear and its footprint; for proximal-humeral minimally invasive plating it allows a subdeltoid extraperiosteal tunnel for a locking plate while sparing the deltoid origin. Primary indications. - Rotator cuff repair - open or mini-open repair of the supraspinatus and adjacent cuff through its lateral footprint.

• Greater-tuberosity fixation - displaced greater-tuberosity fractures and avulsions.
• Minimally invasive plate osteosynthesis (MIPO) of proximal humeral fractures using a lateral locking plate.
• Calcific tendinitis - excision of a resistant calcific deposit in the supraspinatus.
• Open subacromial decompression when combined with cuff repair.
• Drainage or debridement of a localised lateral subdeltoid sepsis or haematoma. Contraindications. - A pre-existing axillary nerve injury with deltoid paralysis (the approach risks the residual functioning anterior branch).
• A large 3- or 4-part proximal humeral fracture needing anterior joint or bicipital-groove access (use the deltopectoral approach instead).
• Poor lateral skin (abrasion, blistering, prior incision compromise).
• Stiffness or contracture that would require wide release. Alternative approaches. - Deltopectoral approach: the standard internervous-plane approach for shoulder arthroplasty and ORIF of complex proximal humeral fractures.
• Anterosuperior deltoid-split approach: an anterior deltoid split used for anterosuperior cuff and subscapularis access.
• Pure arthroscopic cuff repair: when the cuff tear is amenable to an all-inside or trans-tendon technique.
• Extended deltopectoral or anterolateral acromial approach: when broader proximal-humeral exposure is required. ### Three variants of the lateral deltoid split

Lateral split versus deltopectoral. This distinction is a favourite examiner question. The lateral split is a muscle split with no internervous plane for lateral access to the greater tuberosity and cuff, and its critical danger is the axillary nerve. The deltopectoral approach is a true internervous plane (deltoid versus pectoralis major) for anterior and joint access - the standard route for shoulder arthroplasty - and risks the cephalic vein and musculocutaneous nerve. Both spare the deltoid origin if performed correctly.

Bony landmarks to palpate and mark: - Lateral acromion and acromial angle - the proximal origin of the incision and the reference point for measuring the safe zone.

• Posterior corner of the acromion - orientation for the deltoid raphe.
• Greater tuberosity - palpable just distal to the lateral acromion; the primary target.
• Coracoid process - palpated anteriorly to mark the deltopectoral interval and confirm the lateral split is posterior to it.
• Deltoid tuberosity - the deltoid insertion on the lateral humeral shaft, marking the distal limit of orientation. Incision planning. A lazy-S or longitudinal incision centred over the lateral deltoid, beginning at the lateral acromion and extending 5 to 7 cm distally over the greater tuberosity, in the line of the middle-deltoid fibres. For MIPO the incision may be extended to allow plate insertion through a subdeltoid tunnel, but the deltoid split itself must remain within the safe zone. ### The deltoid and the raphe (the anatomy that makes the split safe) All three parts of the deltoid are supplied by the axillary nerve (C5, C6) and insert on the deltoid tuberosity of the lateral humeral shaft. The split passes through the middle (acromial) part, which contains a tendinous inscription (raphe) - an avascular fibrous band about 3 to 5 cm distal to the acromion - and this raphe is the safe window through which the muscle is split.

Innervation of the approach. Because the split passes through deltoid muscle on both sides, the approach has no internervous plane - it is a true muscle-splitting (intramuscular) exposure within the territory of the axillary nerve. Safety depends on splitting through the avascular raphe, keeping the split within the axillary nerve safe zone (no further distal than about 5 cm from the acromion), and placing a stay suture at the distal extent of the split as a physical stop. ### Pre-operative workup that changes the plan - Document an axillary nerve baseline before surgery - test deltoid abduction against resistance and sensation over the regimental badge area (superior lateral cutaneous nerve of the arm). A new post-operative deficit can only be interpreted against a clear pre-operative baseline, and a pre-existing axillary nerve injury is a relative contraindication to a deltoid-splitting approach.

• Imaging. True AP (in the scapular plane), axial and Y-view radiographs; MRI for cuff integrity, tear size, retraction and fatty infiltration; CT for proximal humeral fractures to define fragment geometry and plan screw placement; ultrasound as a dynamic tool for cuff assessment and deposit localisation.
• For MIPO, measure the head-shaft angle and varus displacement on CT, plan calcar screw support and the lateral locking-plate position, and confirm the fracture is reducible through a deltoid-sparing lateral route. For cuff repair, quantify retraction (Patte) and fatty infiltration (Goutallier) on MRI to decide whether the footprint can be reached through a lateral split alone.

Work from the skin down to the greater tuberosity through the avascular raphe of the middle deltoid, capping the split with a stay suture to protect the axillary nerve, then enter the subacromial space to reach the cuff footprint and lateral cortex.

Structures at risk, by layer

Axillary nerve injury management. A recognised intra-operative injury should be documented and the nerve explored if a transection is suspected. Most post-operative deficits are neurapraxia from traction or retraction during the deltoid split and are managed expectantly: fit a sling to prevent inferior shoulder subluxation, maintain passive range of motion, and arrange electromyography and nerve conduction studies at about three weeks (when Wallerian degeneration allows an axonal injury to be distinguished from neurapraxia). If there is no clinical or electromyographic recovery by three months, refer for nerve exploration or transfer. Extensile options. Extend proximally along the lateral acromion for combined subacromial work, but respect the deltoid origin - never detach the acromial deltoid to gain exposure. The split must not be extended distally beyond the safe zone (about 5 cm from the acromion) because of the axillary nerve; when more distal humeral access is needed, develop the subdeltoid extraperiosteal plane to pass a plate, or use a separate, more distal lateral incision. For complex proximal humeral fractures, plan the approach on imaging rather than converting under stress intra-operatively, and convert to a deltopectoral approach when anterior or joint access becomes necessary - always preferred over forcing or over-splitting a lateral exposure. Closure - the deltoid repair is critical. Repair the deltoid split meticulously side-to-side through the raphe and overlying fascia, using heavy absorbable or non-absorbable suture. A secure deltoid repair is essential to prevent dehiscence and post-operative abduction weakness, and is as important as the index procedure itself. Achieve meticulous haemostasis, close the subcutaneous layer to take tension off the skin, and close the skin with a subcuticular suture or staples. Immobilise in a sling with an abduction pillow after cuff repair, more liberally after stable greater-tuberosity fixation or plating, and begin pendulum exercises per the rehabilitation protocol; document deltoid function and sensation on recovery. ### Complications

Outcomes. The determinant of outcome after this approach is not the split itself but the procedure it delivers and whether the deltoid - the motor of abduction - is preserved and soundly repaired. Good prognostic factors are a correct indication, an intact deltoid with a secure repair, anatomical or near-anatomical reduction, and early supervised rehabilitation; poor factors are axillary nerve injury, deltoid dehiscence, poor bone quality compromising fixation, and stiffness from delayed or over-protected rehabilitation.

• Proximal humerus ORIF with a locking plate - minimally invasive lateral locking-plate fixation of proximal humeral fractures through a subdeltoid tunnel.
• Rotator cuff repair - single- or double-row repair of the supraspinatus to its footprint.
• Greater-tuberosity fracture fixation - screw or suture fixation of a displaced fragment.
• Calcific tendinitis of the shoulder - open excision of a resistant deposit.
• Open subacromial decompression - acromioplasty when combined with cuff repair.
• Arthroscopy-assisted mini-open cuff repair - arthroscopy first to localise the tear, release adhesions and place sutures, then a short lateral split to deliver the repair.

Guidelines, registries and global practice The lateral deltoid-split approach is used worldwide for rotator cuff repair, greater-tuberosity fixation and minimally invasive plating of proximal humeral fractures, and its principles are common to the advanced orthopaedic practice or advanced orthopaedic practice, DNB or MS, MRCS and SICOT examination systems. Two ideas are universal: the approach is a muscle split rather than an internervous-plane exposure, and the axillary nerve is the single critical structure to protect.

Anatomical evidence. Cadaveric studies consistently place the anterior branch of the axillary nerve on the deep surface of the deltoid a mean of roughly 5 to 7 cm distal to the lateral acromion, defining the safe zone within which a deltoid split is performed. Global practice variation. In high-resource settings, arthroscopy-assisted and locking-plate MIPO techniques dominate and fluoroscopy is routine; in resource-limited settings, the same open lateral split is used for cuff and tuberosity work without arthroscopy, and fixation may rely on non-locking small-fragment plates or tension-band constructs - the axillary nerve safe zone remains the unifying safety principle. Consent (globally applicable): discuss axillary nerve injury with potential deltoid paralysis, deltoid dehiscence, stiffness, infection, and failure of the cuff repair or fracture fixation.