Prevention and Treatment of the Crankshaft Phenomenon

38 Prevention and Treatment of the Crankshaft Phenomenon

John P. Lubicky

Goals of Surgical Intervention

1. To prevent the crankshaft process by eliminating anterior column growth at the time of spinal fusion for scoliosis

2. To eliminate further crankshafting and/or correct the effects of it on a previously performed spinal fusion

Diagnosis

The crankshaft phenomenon (CP) is the consequence of continued anterior column growth in the presence of a posterior spinal fusion (PSF). (This must be differentiated from “adding on” and pseudarthrosis.) Because the PSF prevents longitudinal growth of the spine, intercalary vertebral growth in the residual curve causes these vertebrae to rotate toward its convexity, giving the appearance of progression of the previously corrected curve. This process is seen only in skeletally immature individuals. The CP can be recognized by radiographic features: increase in the Cobb angle, increased rotation of the apical vertebrae, changes in the relationship of the spine to the chest wall, trunk shift, and change in the alignment of the posterior instrumentation. Clinically, it is manifested by increasing deformity, especially the rib hump and trunk shift as well as new prominence of the hardware. Prevention of initial and continuing CP is accomplished by growth arrest of the vertebral body growth plates, most commonly via anterior spinal fusion (ASF) (Fig. 38–1).

Prevention of the Crankshaft Phenomenon

Indications

1. Growing children (< 10 years old, premenarchal, open triradiate cartilages, Risser 0 to 1, PGA < 0) with residual curve expected to be > 30 degrees

2. For definitive spinal correction and fusion

3. For “growing rod” constructs

Contraindications

1. Inability to tolerate an anterior procedure (poor lung function, scarring from prior surgery, etc.)

2. Signs of skeletal maturity (>10 years old, post menarchal, closed triradiate cartilages, Risser > 1, PGA > O) with residual curve expected to be < 30 degrees

Procedure

Vertebral body growth arrest via ASF: This is most commonly done in association with PSF (with or without instrumentation). The ASF can be done by open techniques using standard thoracotomy or lumbotomy or by minimally invasive techniques such as thoracoscopy or laparoscopy. An alternative in appropriately selected patients involves an ASF with instrumentation only. ASF can be used in cases of definitive correction and fusion as well as an adjunct in “growing rod” constructs (Figs. 38–2 and 38–3).