Increasing lordosis of the occipitocervical junction after arthrodesis in young children: the occipitocervical crankshaft phenomenon.

Five children were treated before age 6 years with occipitocervical fusion for occipitocervical instability. Long-term (average, 11.8 years; range, 8.4-14.5 years) follow-up revealed increasing lordosis across the fused segment in four of the patients, a finding we here refer to as the occipitocervical crankshaft phenomenon. On average, occipitocervical lordosis increased 1.06 degrees per level fused per year until skeletal maturity. Although such a progression might be expected, to our knowledge this is the first report of its occurrence. Compensatory subaxial motion was able to overcome this increase in all of the patients. We recommend occipitocervical fusion in a neutral or slightly flexed position in the very young child to account for this predictable increase in lordosis.