Surgical Release of the Sternocleidomastoid Muscle for Congenital Muscular Torticollis

Introduction and Epidemiology

The term torticollis originates from the Latin words tortus (twisted) and collum (neck). It denotes a clinical deformity characterized by involuntary unilateral lateral flexion of the head with contralateral rotation of the cervical spine. Congenital muscular torticollis represents the most common etiology of torticollis in the infant population, primarily driven by a unilateral contracture or fibrosis of the sternocleidomastoid muscle.

Congenital muscular torticollis is recognized as the third most common congenital musculoskeletal anomaly, following developmental dysplasia of the hip and congenital talipes equinovarus. The reported incidence of congenital muscular torticollis ranges broadly from 0.4% to 1.3% of live births. Early recognition is paramount, as untreated congenital muscular torticollis can lead to progressive craniofacial asymmetry (plagiocephaly), orbital dystopia, and secondary cervical scoliosis.

Classification of Congenital Muscular Torticollis

Cheng et al. established a widely accepted clinical classification system that subdivides congenital muscular torticollis patients into three distinct prognostic groups:
1. Sternomastoid Tumor Group: Characterized by a clinically palpable pseudotumor or fibromatosis mass within the sternocleidomastoid muscle belly. This group typically presents earliest and represents the most severe end of the fibrotic spectrum.
2. Muscular Torticollis Group: Patients present with clinical thickening, tightness, or contracture of the sternocleidomastoid muscle on the affected side, but lack a discrete, palpable pseudotumor.
3. Postural Torticollis Group: Patients exhibit all the clinical postural features of torticollis (head tilt and rotational preference) but demonstrate neither a palpable mass nor true passive tightness of the sternocleidomastoid muscle. This group typically has the most favorable prognosis with conservative management.

Pathogenesis and Histopathology

The exact etiology of congenital muscular torticollis remains a subject of academic debate, though it is universally recognized that the terminal event is contracture and shortening of the sternocleidomastoid muscle. Several prominent theories exist regarding the primary insult. The intrauterine crowding theory suggests that constrained fetal positioning leads to localized ischemia of the sternocleidomastoid muscle. Alternatively, the birth trauma theory posits that difficult deliveries (such as breech presentations or forceps-assisted extractions) cause direct mechanical traction injury to the muscle fibers, leading to a localized hematoma, subsequent compartment syndrome within the investing fascia, and eventual fibrotic replacement.

Histopathological analysis of sternocleidomastoid pseudotumors reveals dense, acellular collagenous tissue replacing normal skeletal muscle fibers. As the infant matures, this fibromatosis mass typically regresses over the first four to eight months of life, leaving behind a restrictive band of fibrous tissue that fails to elongate proportionally with the growing cervical spine, thereby tethering the mastoid process to the clavicle and sternum.

Surgical Anatomy and Biomechanics

A profound understanding of the sternocleidomastoid muscle and the complex neurovascular topography of the anterior and posterior cervical triangles is critical for safe surgical intervention. The sternocleidomastoid muscle passes obliquely across the lateral aspect of the neck, effectively dividing the cervical region into the anterior and posterior triangles.

Muscular Origins and Insertions

The sternocleidomastoid muscle originates distally from two distinct anatomical heads:
* Sternal Head: Arises as a rounded, tendinous fasciculus from the superior and anterior surface of the manubrium sterni.
* Clavicular Head: Arises as a broader, fleshy, and aponeurotic band from the superior surface of the medial third of the clavicle. The width of the clavicular origin is highly variable and, in some anatomic variants, may extend laterally to the midpoint of the clavicle.

The two heads ascend superiorly, laterally, and posteriorly, blending into a single muscle belly that inserts onto the lateral surface of the mastoid process of the temporal bone and the lateral half of the superior nuchal line of the occipital bone.

Biomechanics of the Sternocleidomastoid

The sternocleidomastoid is a complex, multi-planar mobilizer of the cervical spine.
* Unilateral Contraction: Flexes the cervical spine ipsilaterally (bringing the ear toward the shoulder) and rotates the head contralaterally (pointing the chin toward the opposite shoulder). This exact posture is the hallmark presentation of a unilateral contracture.
* Bilateral Contraction: Protracts the head forward, flexes the lower cervical spine, and extends the upper cervical spine (atlanto-occipital joint). It also acts as an accessory muscle of respiration by elevating the sternum and clavicle during deep inspiration.

Neurovascular Topography and Internervous Planes

The innervation of the sternocleidomastoid is dual in nature. Motor innervation is primarily supplied by the spinal accessory nerve (Cranial Nerve XI), with additional proprioceptive and motor contributions from the ventral rami of the second and third cervical nerves (C2, C3).

Several critical structures lie in intimate proximity to the sternocleidomastoid, necessitating meticulous dissection during surgical release:
* Spinal Accessory Nerve: Penetrates the deep surface of the sternocleidomastoid muscle approximately 3 to 4 centimeters inferior to the mastoid tip. It traverses obliquely through the muscle, giving off motor branches, and exits the posterior border to cross the posterior triangle toward the trapezius.
* Erb Point: Located approximately at the midpoint of the posterior border of the sternocleidomastoid. Here, the anterior branch of the great auricular nerve, the lesser occipital nerve, the transverse cervical nerve, and the supraclavicular nerves emerge.
* External Jugular Vein: Descends vertically, anterior to the proximal sternocleidomastoid, then crosses the muscle obliquely at its midpoint to terminate in the subclavian vein posteroinferiorly.
* Carotid Sheath: The sternocleidomastoid serves as the primary muscular roof protecting the carotid sheath, which contains the common carotid artery medially, the internal jugular vein laterally, and the vagus nerve posteriorly. The internal jugular vein lies immediately deep to the clavicular head of the sternocleidomastoid, separated only by the deep cervical fascia.

Indications and Contraindications

The management algorithm for congenital muscular torticollis begins with non-operative modalities, reserving surgical release for recalcitrant cases or delayed presentations. Physical therapy, emphasizing sustained passive stretching of the sternocleidomastoid, positioning modifications, and active strengthening of the contralateral musculature, yields successful outcomes in over 90% of patients when initiated prior to one year of age.

Surgical intervention is indicated when conservative measures fail to halt the progression of the deformity or when the patient presents beyond the optimal window for non-operative management.

Contraindications to Surgical Release

Surgical release of the sternocleidomastoid is strictly contraindicated in patients where torticollis is secondary to non-muscular etiologies. A comprehensive differential diagnosis must rule out:
* Osseous Anomalies: Klippel-Feil syndrome, congenital hemivertebrae, or atlantoaxial rotatory subluxation (AARS).
* Neurological Disorders: Posterior fossa tumors, syringomyelia, or Arnold-Chiari malformations.
* Ocular Torticollis: Cranial nerve IV (trochlear) palsy, where the head tilt compensates for superior oblique muscle weakness to prevent diplopia.
* Inflammatory Conditions: Grisel syndrome (atlantoaxial subluxation secondary to retropharyngeal inflammation).
* Spasmodic Torticollis: Cervical dystonia, which requires neurological management rather than anatomical release.

Pre Operative Planning and Patient Positioning

Thorough preoperative planning is essential to confirm the diagnosis, quantify the deformity, and select the appropriate surgical approach (unipolar versus bipolar release).

Clinical and Radiographic Workup

Clinical evaluation must include precise goniometric measurement of cervical range of motion. The surgeon should document the degree of lateral flexion and bilateral rotation. Assessment of facial asymmetry should focus on the malar eminence, orbital alignment, and mandibular deviation.

Radiographic evaluation is mandatory prior to surgical intervention. Anteroposterior, lateral, and open-mouth odontoid radiographs of the cervical spine must be obtained to definitively exclude congenital cervical spine anomalies or atlantoaxial instability. In atypical presentations (e.g., presence of neurological deficits, torticollis presenting after 6 months of age without a history of pseudotumor, or severe pain), magnetic resonance imaging (MRI) of the brain and cervical spine is indicated to rule out central nervous system pathology.

Patient Positioning and Anesthesia

The patient is placed in the supine position on the operating table. General endotracheal anesthesia is administered. While the use of neuromuscular blockade is generally safe, some surgeons prefer to avoid long-acting paralytics to allow for intraoperative monitoring or direct stimulation of the spinal accessory nerve, particularly during proximal releases.

A transverse scapular roll is positioned horizontally beneath the shoulders to allow the cervical spine to fall into extension. The head is stabilized on a gel donut and rotated toward the unaffected side. This positioning maximizes the distance between the mastoid process and the sternoclavicular joint, placing the contracted sternocleidomastoid on maximal tension and bringing the fibrotic bands into subcutaneous relief. The anterior neck, mandible, and upper chest are prepped and draped in a sterile fashion, ensuring the face remains visible for intraoperative assessment of head positioning.

Detailed Surgical Approach and Technique

The surgical management of congenital muscular torticollis involves releasing the tethering fibrotic bands of the sternocleidomastoid. The choice between a unipolar distal release, a bipolar release (proximal and distal), or a fractional lengthening (Z-plasty) depends on the severity of the contracture and the age of the patient. For the majority of primary cases, an open distal unipolar release is sufficient and serves as the gold standard.

Unipolar Distal Release Technique

1. Incision and Superficial Dissection: A 3 to 4 centimeter transverse incision is made within a natural skin crease (Langer's lines) approximately 1 to 2 centimeters superior to the medial clavicle and sternal notch. The subcutaneous tissue is sharply divided to expose the platysma muscle.
2. Platysmal Division: The platysma is incised transversely in line with the skin incision. Subplatysmal flaps are elevated superiorly and inferiorly using blunt and sharp dissection to expose the underlying investing layer of the deep cervical fascia and the distal sternocleidomastoid.
3. Identification of Neurovascular Structures: The external jugular vein is identified, typically running along the lateral border of the sternocleidomastoid. It must be carefully mobilized and retracted laterally. The anterior jugular vein may be encountered medially and should be retracted or ligated if it impedes access.
4. Isolation of the Sternal and Clavicular Heads: The investing fascia over the sternocleidomastoid is incised longitudinally. The sternal head is identified as a distinct, often heavily fibrotic, tendinous structure. A right-angle clamp (Mixter) is carefully passed immediately deep to the sternal head, from medial to lateral.
5. Division of the Sternal Head: Using electrocautery or a scalpel, the sternal head is divided over the right-angle clamp. The surgeon must remain acutely aware that the internal jugular vein and carotid artery lie deep to this plane, separated only by the deep cervical fascia.
6. Division of the Clavicular Head: Attention is then turned to the clavicular head. The right-angle clamp is passed deep to the clavicular fibers. Given the broad nature of the clavicular insertion and its intimate proximity to the subclavian and internal jugular veins, this step requires meticulous blunt dissection. The clavicular head is completely transected.
7. Fascial Release: Following transection of both muscular heads, the deep cervical fascia and any residual fibrotic bands within the anterior or posterior triangles must be systematically palpated and released. The surgeon then turns the patient's head to the ipsilateral side and flexes the neck contralaterally to confirm complete restoration of normal cervical range of motion. Any remaining tethering structures are selectively divided.

Bipolar Release Technique

In severe cases, older children, or revision surgeries where a distal release alone fails to restore full range of motion, a concomitant proximal release is indicated.

1. Proximal Incision: A transverse incision is made approximately 1 centimeter inferior to the tip of the mastoid process, hidden within the hairline or a high cervical crease.
2. Identification of the Proximal SCM: Dissection is carried down through the subcutaneous tissue to expose the proximal insertion of the sternocleidomastoid.
3. Protection of the Spinal Accessory Nerve: The critical step in a proximal release is avoiding injury to the spinal accessory nerve. The nerve enters the anterior border of the muscle approximately 3 to 4 centimeters distal to the mastoid tip. Therefore, the release must be performed as close to the mastoid insertion as possible.
4. Proximal Transection: The tendinous insertion of the sternocleidomastoid is isolated and transversely divided off the mastoid process.

Alternative Approaches: Z Plasty and Endoscopic Release

For older children or adolescents where the loss of the sternocleidomastoid contour may result in an unacceptable cosmetic deficit, a fractional lengthening or Z-plasty of the distal sternal tendon may be performed. This technique maintains the V-shaped contour of the anterior neck while providing the necessary elongation.

Endoscopic sternocleidomastoid release has been described as a minimally invasive alternative aimed at reducing scar burden. However, it requires a steep learning curve, specialized equipment, and carries a theoretically higher risk of incomplete release or inadvertent vascular injury due to the limited field of view. It is generally reserved for highly specialized centers.

Complications and Management

Surgical release of the sternocleidomastoid is generally safe, but the complex regional anatomy presents significant risks if tissue planes are not respected. Complications can be broadly categorized into neurovascular injuries, mechanical failures, and cosmetic issues.

Meticulous hemostasis is achieved prior to closure. The wound is irrigated copiously. The platysma is repaired with interrupted absorbable sutures to prevent scar widening, and the skin is closed with a running subcuticular suture. No deep drains are typically required unless a significant dead space remains.

Post Operative Rehabilitation Protocols

The success of surgical intervention for congenital muscular torticollis is heavily dependent on a rigorous and compliant postoperative rehabilitation program. Surgery merely eliminates the mechanical tether; physical therapy is required to retrain the cervical musculature, correct learned postural habits, and remodel the healing scar tissue.

Immediate Postoperative Phase

Historically, patients were immobilized in a Minerva cast or halo-thoracic orthosis to maintain an overcorrected position. Contemporary protocols have largely abandoned rigid immobilization in favor of early mobilization. Postoperatively, a soft cervical collar or a custom Tubular Orthosis for Torticollis (TOT collar) may be utilized

Clinical & Radiographic Imaging