Proximal Hamstring and Adductor Lengthening for Spastic Hip Subluxation: An Intraoperative Masterclass

Introduction and Epidemiology

Spastic hip disease represents a profound orthopedic challenge, predominantly manifesting in the pediatric cerebral palsy population. The condition is characterized by progressive lateral migration of the femoral head, leading to subluxation and, ultimately, dislocation if left untreated. Proximal hamstring and adductor lengthenings are critical soft-tissue interventions utilized to halt or delay this progression, primarily indicated in children prior to adolescence.

The epidemiology of spastic hip disease is directly correlated with the severity of neurologic impairment. According to the Gross Motor Function Classification System, the incidence of hip displacement approaches zero in GMFCS Level I but escalates to nearly ninety percent in GMFCS Level V. The primary period of risk occurs between two and eight years of age, though adolescents undergoing rapid growth spurts remain susceptible to delayed subluxation.

The pathogenesis of spastic hip subluxation is driven by an imbalance of muscle forces acting across the hip joint. Spasticity in the adductors, flexors, and hamstrings overwhelms the relatively weaker abductors and extensors. This sustained muscular imbalance creates a pathologic force vector. The proximal hamstrings contribute significantly to the forces driving spastic hip disease. By maintaining the knee in a flexed position, the hamstrings secondarily encourage hip flexion when combined with spastic hip flexors. This pathologic posturing forces the hip into internal rotation and adduction, magnifying the influence of the concomitant spastic adductors.

This sustained posture of hip flexion, internal rotation, and adduction, coupled with high muscle force, drives the femoral head posterosuperiorly out of the acetabulum. The natural history of abnormal hip subluxation typically begins around two years of age. Once initiated, the progression of lateral migration averages approximately ten percent every six months. Therefore, rigorous clinical surveillance, monitoring of hip abduction, and serial anteroposterior pelvic radiographs to measure the Reimers migration index are mandatory for early detection.

Surgical Anatomy and Biomechanics

A thorough understanding of the muscular and neurovascular anatomy of the medial thigh and posterior pelvis is essential for performing safe and effective soft-tissue releases in spastic hip disease. The relevant anatomy is divided into the adductor compartment and the posterior hamstring compartment.

Adductor Compartment Anatomy

The adductor musculature originates from the pubis and ischium, inserting along the linea aspera of the femur. The muscles targeted during spastic hip reconstruction include the adductor longus, gracilis, and occasionally the adductor brevis.
The adductor longus arises from the anterior surface of the pubis, just below the pubic tubercle, and constitutes the most anterior and superficial structure of the adductor group.
The gracilis, a biarticular muscle, originates from the lower half of the pubic symphysis and the upper half of the pubic arch, inserting on the medial surface of the proximal tibia as part of the pes anserinus.
The adductor brevis lies deep to the adductor longus and superficial to the adductor magnus.

The obturator nerve provides the primary innervation to this compartment. It divides into anterior and posterior branches at the level of the obturator externus. The anterior branch descends between the adductor longus and adductor brevis, supplying the adductor longus, gracilis, and adductor brevis. The posterior branch descends between the adductor brevis and adductor magnus, supplying the adductor magnus and occasionally the adductor brevis. Surgical dissection must meticulously protect the anterior branch of the obturator nerve during adductor longus and brevis lengthening.

Proximal Hamstring Anatomy

The hamstrings comprise the biceps femoris, semitendinosus, and semimembranosus. The long head of the biceps femoris and the semitendinosus share a conjoined origin on the inferomedial aspect of the ischial tuberosity. The semimembranosus originates from the superolateral aspect of the ischial tuberosity.

The hamstring attachments on the pelvis are broad and muscular, lacking a substantial tendinous component at their absolute origin, with one critical exception. The semimembranosus possesses a distinct tendinous insertion at the ischium. This tendinous structure can be easily mistaken for the sciatic nerve if careful isolation is not performed. Both the biceps femoris and semitendinosus exhibit broad fascial insertions.

The sciatic nerve exits the pelvis through the greater sciatic foramen, emerging inferior to the piriformis muscle. As it descends into the posterior thigh, it lies immediately lateral and deep to the long head of the biceps femoris and the ischial tuberosity. The proximity of the sciatic nerve to the proximal hamstring origin makes it highly vulnerable during proximal release or lengthening procedures.

Biomechanics of Spastic Hip Disease

The biomechanical failure in spastic hip disease is characterized by an abnormal direction of the joint reaction force vector combined with an excessively high force magnitude generated by spastic muscles. In order of their deforming contribution, the primary offending muscles are the adductor longus, the gracilis, the proximal hamstrings, and the iliopsoas.

In a normal hip, the joint reaction force is directed medially and inferiorly, promoting concentric development of the acetabulum and the femoral head. In the spastic hip, the hypertonic adductors and flexors shift the resultant vector laterally and superiorly. The proximal hamstrings exacerbate this by limiting knee extension, which alters the pelvic tilt and increases the functional flexion contracture of the hip. This combined vector forces the femoral head against the posterosuperior rim of the acetabulum, leading to progressive acetabular dysplasia, femoral head deformation, and eventual dislocation.

Indications and Contraindications

The primary goal of proximal hamstring and adductor lengthening is to restore muscle balance, halt the progression of lateral migration, and prevent the need for extensive bony reconstruction. The decision to proceed with soft-tissue release hinges on the patient's age, neurologic status, and radiographic parameters, most notably the Reimers migration index.

The Reimers migration index calculates the percentage of the femoral head that lies lateral to Perkins line. A normal index is twenty-five percent or less across all age groups. An index greater than thirty percent is considered abnormal and diagnostic of spastic hip subluxation.

Soft-tissue lengthening is generally indicated for children between the ages of two and eight years who exhibit a migration index between thirty percent and sixty percent. In this cohort, the acetabular dysplasia is typically reversible once the deforming muscle forces are neutralized. Children older than eight years or those with a migration index exceeding sixty percent generally possess fixed bony deformities (coxa valga, excessive femoral anteversion, and true acetabular dysplasia) that will not remodel with soft-tissue release alone. These patients require concomitant varus derotational osteotomy of the femur and potentially a pelvic osteotomy.

Operative vs Non Operative Indications

Non-operative management for established spastic hip subluxation has limited efficacy. While botulinum toxin type A injections into the adductors and hamstrings are frequently utilized to manage tone and improve tolerance to bracing, literature indicates a high failure rate when used as a definitive treatment for hip subluxation. Preliminary evidence suggests that reliance on botulinum toxin delays necessary surgical intervention, ultimately increasing the requirement for complex bony reconstruction compared to timely surgical release.

Hypotonic hip dislocation, congenital hip dislocation, and hip subluxation secondary to developmental dysplasia of the hip represent distinct clinical entities and must be excluded from the differential diagnosis, as their surgical management algorithms differ significantly from those of spastic hip disease.

Pre Operative Planning and Patient Positioning

Preoperative planning relies on a combination of rigorous physical examination and radiographic analysis. The primary physical examination finding indicative of spastic hip disease is the limitation of hip abduction with the hips and knees extended. A careful examination under anesthesia is critical to differentiate between dynamic spasticity and fixed myostatic contracture.

During the examination under anesthesia, the surgeon must perform the Phelps test to assess gracilis contracture. This involves measuring hip abduction with the knee flexed (relaxing the gracilis) versus hip abduction with the knee extended (tensioning the gracilis). A significant decrease in abduction with knee extension confirms a gracilis contracture. The Thomas test is utilized to evaluate hip flexion contractures, while the popliteal angle assesses distal hamstring tightness.

The primary radiographic investigation is a supine anteroposterior pelvic radiograph. The Reimers migration index must be meticulously measured. If there is ambiguity regarding the direction of subluxation, or if the clinician suspects a non-standard subluxation pattern, a computed tomography scan can be obtained to evaluate the three-dimensional morphology of the hip joint. However, advanced cross-sectional imaging is not routinely required for standard posterosuperior spastic subluxation.

Patient Positioning

The patient is typically positioned supine on a radiolucent operating table to allow for intraoperative fluoroscopy. General anesthesia is required, and the use of long-acting paralytics should be discussed with the anesthesia team, as some surgeons prefer to maintain the ability to assess muscle tension and spasticity during the procedure.

For the adductor lengthening, the hips are placed in a frog-leg position (flexed, abducted, and externally rotated) to place the adductor musculature under tension. Following the adductor release, the patient may remain supine with the hips flexed and knees extended to access the proximal hamstrings via a modified lithotomy approach, or the patient may be repositioned prone. The prone position provides superior visualization of the ischial tuberosity and the sciatic nerve, particularly in larger or older children, though it requires a mid-procedure repositioning and re-draping.

Detailed Surgical Approach and Technique

The surgical objective is to achieve adequate lengthening of the offending musculature while preserving sufficient strength to prevent irogenic complications such as excessive abduction or crouch gait.

Adductor Longus and Gracilis Lengthening

1. Incision and Dissection: With the hip in the frog-leg position, a 3 to 5 centimeter longitudinal incision is made over the palpable origin of the adductor longus, approximately 1 centimeter distal to the pubic crease. Subcutaneous tissues are bluntly dissected to expose the deep fascia.
2. Isolation of Adductor Longus: The deep fascia is incised longitudinally. The adductor longus is identified as the most superficial and anterior muscle belly. A right-angle clamp is passed deep to the adductor longus tendon near its origin on the pubis. Care must be taken to stay strictly extra-muscular to avoid bleeding.
3. Tenotomy: A transverse tenotomy of the adductor longus is performed close to its origin. The muscle belly is allowed to retract distally.
4. Isolation of Gracilis: Retraction of the adductor longus exposes the underlying adductor brevis and the medially situated gracilis. The gracilis is identified by its distinct fascial sheath and its position posterior and medial to the adductor longus.
5. Gracilis Lengthening: Depending on the severity of the contracture and the preoperative Phelps test, the gracilis may undergo a complete tenotomy at its origin or an intramuscular lengthening (fractional lengthening) at its musculotendinous junction.
6. Assessment of Adductor Brevis: The anterior branch of the obturator nerve is identified resting on the anterior surface of the adductor brevis. This nerve must be visualized and protected. If hip abduction remains restricted (less than 45 degrees) after the release of the longus and gracilis, a fractional lengthening or partial tenotomy of the adductor brevis is performed, ensuring the nerve is retracted safely out of the surgical field.
7. Closure: The wound is irrigated, and hemostasis is achieved. The deep fascia is left open to prevent compartment syndrome. The subcutaneous tissue and skin are closed in layers.

Proximal Hamstring Lengthening

1. Incision and Dissection: With the patient prone or in modified lithotomy, a transverse incision is made within or slightly inferior to the gluteal fold, centered over the ischial tuberosity. Alternatively, a longitudinal incision can be utilized. Subcutaneous fat is dissected to expose the inferior border of the gluteus maximus.
2. Exposure of the Ischial Tuberosity: The inferior border of the gluteus maximus is retracted superiorly. The ischial tuberosity and the origin of the hamstring musculature are palpated and visually identified.
3. Identification of the Sciatic Nerve: This is the most critical step of the procedure. The sciatic nerve must be identified lateral and deep to the long head of the biceps femoris. It is surrounded by areolar tissue. The nerve should be gently exposed but not aggressively dissected to prevent devascularization or neuropraxia. A vessel loop may be placed loosely around the nerve for continuous identification.
4. Isolation of the Conjoined Tendon: The conjoined tendon of the long head of the biceps femoris and the semitendinosus is identified originating from the inferomedial aspect of the ischial tuberosity.
5. Lengthening of the Conjoined Tendon: A fractional lengthening is typically preferred over a complete tenotomy to preserve some hamstring function and prevent severe anterior pelvic tilt. Transverse incisions are made in the aponeurotic fascia of the biceps femoris and semitendinosus, leaving the underlying muscle fibers intact. The hip is flexed and the knee extended to stretch the muscle and allow the fascial gaps to widen.
6. Isolation and Lengthening of the Semimembranosus: The semimembranosus is identified originating superolaterally on the ischial tuberosity. As noted in the anatomic considerations, this muscle possesses a distinct tendinous insertion. The tendon is carefully isolated, ensuring it is not confused with the adjacent sciatic nerve. A fractional lengthening or Z-lengthening of the semimembranosus tendon is performed.
7. Final Assessment: The hip is taken through a range of motion. The popliteal angle and hip flexion contracture are reassessed to ensure adequate release has been achieved.
8. Closure: Hemostasis is meticulously achieved, as the posterior thigh is prone to hematoma formation. The subcutaneous tissues and skin are closed in a standard fashion.

Complications and Management

While proximal hamstring and adductor lengthenings are highly effective, they carry a distinct complication profile. Iatrogenic nerve injury, over-lengthening, and recurrent subluxation represent the most significant risks.

The sciatic nerve is at high risk during proximal hamstring lengthening due to its immediate proximity to the biceps femoris origin and the semimembranosus tendon. Sciatic nerve palsy can result from direct transection, excessive traction, or postoperative hematoma compression. The obturator nerve, specifically the anterior branch, is similarly at risk during adductor brevis release.

Over-lengthening of the adductors can lead to an excessive abduction posture, which interferes with sitting and perineal care, and can occasionally cause secondary hip subluxation in the inferior or anterior direction. Over-lengthening of the hamstrings can precipitate a severe anterior pelvic tilt, exacerbating lumbar lordosis, and may lead to a stiff-knee gait or genu recurvatum if the knee extensors are spastic.

Recurrence of spastic hip subluxation is a known complication, particularly in children who undergo soft-tissue release at a very young age (under four years) or those with a high GMFCS level. These patients require continued radiographic surveillance and may eventually require bony reconstruction.

Common Complications and Salvage Strategies

Post Operative Rehabilitation Protocols

The immediate postoperative phase focuses on maintaining the achieved length of the musculature and preventing recurrent contracture during the healing phase.

Following wound closure, patients are typically placed in bilateral long-leg casts with an abduction bar (Petrie casts) or a rigid custom-molded hip abduction orthosis. The hips are immobilized in approximately thirty to forty-five degrees of abduction and neutral rotation. The knees are maintained in full extension. This immobilization is generally maintained for three to six weeks, depending on the surgeon's preference and the severity of the preoperative contractures.

Upon removal of the casts or orthosis, a rigorous physical therapy protocol is initiated. The primary goals of rehabilitation are:
1. Maintenance of Range of Motion: Passive and active-assisted stretching of the adductors and hamstrings to prevent scar contracture and loss of the surgically achieved length.
2. Strengthening of Antagonists: Intensive strengthening of the hip abductors (gluteus medius) and hip extensors (gluteus maximus) is critical. Restoring power to these muscle groups helps counteract the underlying spasticity of the flexors and adductors, thereby stabilizing the femoral head within the acetabulum.
3. Gait Training: For ambulatory patients (GMFCS Levels I-III), gait training focuses on utilizing the newly acquired range of motion, improving step length, and correcting compensatory mechanisms such as crouch gait or scissoring.

Weight-bearing status is generally guided by patient comfort and tolerance, as soft-tissue releases do not require a period of strict non-weight-bearing. However, the use of assistive devices (walkers, crutches) is often necessary during the initial transition out of immobilization due to temporary weakness and altered proprioception.

Summary of Key Literature and Guidelines

The management of spastic hip disease is heavily guided by established surveillance protocols and seminal biomechanical studies.

The American Academy for Cerebral Palsy and Developmental Medicine has published extensive guidelines regarding hip surveillance in children with cerebral palsy. These guidelines emphasize that the frequency of radiographic screening must be dictated by the child's GMFCS level. Children at GMFCS Levels III, IV, and V require AP pelvic radiographs every six to twelve months during the high-risk period of two to eight years of age.

Reimers' original description of the migration percentage remains the gold standard for quantifying hip displacement. His work demonstrated that a migration percentage exceeding thirty-three percent is rarely self-correcting and strongly correlates with progressive dysplasia and eventual dislocation.

Gage's extensive research on clinical gait analysis and muscle force vectors provided the biomechanical foundation for understanding how spastic hamstrings and adductors drive the femoral head posterosuperiorly. His work underscored the importance of addressing the proximal hamstrings to correct the functional flexion contracture of the hip and knee.

Furthermore, studies by Flynn et al. and others have evaluated the long-term efficacy of soft-tissue releases. The consensus in the academic literature is that adductor and proximal hamstring lengthenings are highly effective at halting the progression of hip displacement in appropriately selected patients (RMP 30-60%, age 2-8 years). However, the literature also clearly documents the limitations of soft-tissue surgery, noting a high failure rate when applied to hips with an RMP greater than sixty percent or in older children with established bony deformity, reinforcing the necessity of timely intervention and appropriate surgical selection.

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