Proximal Hamstring and Adductor Lengthening

DEFINITION

Proximal hamstring lengthenings are primarily performed in the treatment of spastic hip subluxation, mainly in children prior to adolescence.
Based on modeling studies, the hamstrings are a significant contribution to increasing the force in spastic hip disease, which causes hip subluxation. They are also a component that keeps the knees flexed and secondarily encourages flexion combined with spastic hip flexors, which causes the knee to fall into internal rotation and adduction, magnifying the influence of the concomitant spastic adductors.
- This posture of hip flexion and internal rotation and adduction, with the addition of high muscle force, tends to drive the hip posterosuperiorly out of the acetabulum.
The primary period during which spastic hip disease occurs is 2 to 8 years of age, although some children are still at risk through their adolescent growth spurt and need to be monitored.

ANATOMY

Hamstring attachments on the pelvis are very broad muscular attachments and do not have a substantial amount of tendon.
The exception to this is that the semimembranosus tends to have a tendinous insertion and may be confused with the sciatic nerve if care is not taken.
There tends to be some broad fascial insertion with both the biceps and the semitendinosus.

PATHOGENESIS

Spastic hip disease is a pathologic force that has both an abnormal direction of the vector and a force vector that is too high caused by spastic muscles.
The muscles, in order of their importance, are the adductor longus, the gracilis, the proximal insertion of the hamstrings, and the iliopsoas.
An important cause of spastic hip subluxation is positioning of the hip into internal rotation and hip flexion and adduction for a significant component of the child’s daily posturing.

NATURAL HISTORY

Abnormal hip subluxation typically begins around 2 years of age and then has a progression of about 10% of migration every 6 months if the progression is occurring.
Therefore, physical examination, monitoring of the hip in abduction, and an anteroposterior (AP) pelvis radiograph in which the Reimer migration index is measured every 6 months would be sufficient to pick up early spastic hip disease.

PATIENT HISTORY AND PHYSICAL FINDINGS

The concern for spastic hip disease is primarily present in children with spasticity, although some adolescents will be at risk.
The primary physical examination finding is the limitation of hip abduction with hips extended and knees extended.
Also, a child whose predominant posture both in sitting and lying is with hip flexion, adduction and internal rotation is at high risk.

IMAGING AND OTHER DIAGNOSTIC STUDIES

The primary radiographic investigation is a supine AP pelvic radiograph in which the Reimer migration index is measured.
- Normal should be 25% or less at all ages. Abnormal is greater than 30%.
If there is a question whether this is the standard hip subluxation predominantly occurring in the posterosuperior aspect of the acetabulum, a computed tomography (CT) scan may be obtained to fully evaluate the position of the hip joint. However, this is not routinely required.

NONOPERATIVE MANAGEMENT

No conservative treatment options have been documented to be efficacious.
There have been several attempts at treating spastic hip subluxation with botulinum toxin injection; however, preliminary evidence suggests that the failure rate is high and the need for later reconstruction will be higher than with adequate surgical release.

SURGICAL MANAGEMENT

Preoperative Planning

The indications for the procedure are a migration index of 30% to 60% in a child who is younger than 8 to 10 years of age and has limited hip abduction, meaning less than 30 degrees of hip abduction with hips and knees extended.
This examination should be performed under anesthesia.
The goal of the treatment is to have the child lie without any force or pushing with bilateral hip abduction of more than 45 degrees at the end of the operative procedure.
The indication for proximal hamstring lengthening is a popliteal angle of greater than 45 degrees with the child under anesthesia.

Positioning

Proximal hamstring release combined with adductor lengthening is performed with the patient supine and with an adhesive drape placed over the groin.

Approach

There are two approaches to proximal hamstring release.
One is a straight posterior approach. However, this approach has the negative consequences of going through the area of major weight bearing for sitting.
For this reason, it is preferred to do an approach through the medial groin as part of an adductor lengthening going through the fascial compartment of the gracilis.
- Only the approach to the gracilis as part of a full adductor lengthening is described here.