The "Crank Shaft" Phenomenon: Treatment Options and Complexity When Growth is Completed.

Jean–Pierre C. Farcy, MD.,
Frank J. Schwab, MD.

The crankshaft phenomenon has been well defined by Jean Dubousset(1). Avoidance of this condition requires careful evaluation of the real growth potential at time of initial spine surgery. The crankshaft deformity can best be compared to a “spiral staircase” which develops progressively after surgical fusion. Posterior fusion which tethered the posterior column of the spine while growth of the anterior column continued induces this deformity that takes place at both ends of the initial fusion and can result in severe spine imbalance.

I want to stress the issue of growth potential since it is too often related to the apparition of the Risser 1 grade. In fact the growth spurt, during which crankshaft is the most likely to develop and be severe, takes place two years prior the elbow growth cartilage closure and starts to decrease before Risser 1. (2.) Secondary sexual attributes are often appearing late, however pubic hair apparition is a good landmark to pinpoint beginning of growth spurt.

After Risser 1 ossification of the iliac crest, crankshaft is less likely to be severe if it takes place, however there are cases in which a delayed growth is usual like in congenital cardiac malformation and other sources of developmental delay. Of note, it is necessary to anticipate crankshaft mainly at the lumbar level in the male children whose fusion was performed for scoliosis in the early teens while growth was expected to linger to the twenties.

Deformities may affects thoracic spine with minimal crankshaft since the frontal balance was preserved at time of fusion and the growth of the anterior column did not induce a progressive spinal curvature most likely prevented by the rib bracing effect. This can lead by the end of growth to a balloon–like chest with short torso and a stable short lordotic thoracic spine. It is not possible to offer safe treatment to the children affected by this condition which is more a cosmetic than a vital problem. The cases to treat are those with severe imbalance and progressive deformity getting worse which carry serious hazards both cosmetic and vital.

Treatment

For treatment Jean Dubousset recommends a three stage procedure under the same anesthesia. First multiple osteotomies of the fusion mass are performed, then the second stage is an anterior release and interbody fusion, followed by the third stage which is posterior re–instrumentation and re–fusion. Posterior instrumentation is nearly always extended either cranially or caudally if not at both ends. The goal is to achieve proper spine balance in all planes of space.

Along similar lines we have treated patients affected by the crankshaft and presenting with deformity after growth has stopped. It is important to note that it is very important to diagnose the complication prior to the end of growth and to treat it in order to avoid deformity of such a magnitude that it is no longer within our means to be corrected. In dealing with adults we found that at surgery, if a three stage approach is applied, that between the second and third stages a real hazard of spine instability can develop which is impossible to fully control while turning the patient for the last stage.

Material and methods:

Two groups of patients:

• 5 young children before growth completion.(4 to 11 )
• 9 grown up adolescents (16 to 20)
• 17 young adults (20 to 30 average age 23).

Technique

Goals:

End plates at both fusion ends must be parallel to the transverse plane. In the frontal plane the plumb line dropped from the odontoid process of C2 must fall over mid sacrum. In the sagittal :plane the plumb line dropped from the odontoid process of C2 must fall between the sacrum promontory and the femoral heads. Solid fusion. L5–S1 disc must be preserved on patients who are ambulators.

The surgical procedures were always done in one sitting, The anterior procedure was performed first to achieve strategic osteotomies and release, bone graft material was placed in front either in a osteo–periostal flap or left in place fragmented at the site of wedge osteotomies. During the second stage posterior “chevron osteotomies” were performed at the level of the anterior strategic wedge osteotomies to correct the spine deformity in shortening the posterior column. Hardware partially in place to insure spine relative stability during manipulation provide for alignment. In a few cases posterior pedicles subtraction osteotomy (3) was performed at the L3 level, in addition of the other osteotomies, to increase lumbar lordosis.

The above described technique providing control of stability between the stages and during the manipulations of the spine to close the osteotomies is safer than the three stage procedures. Therefore it allows to be more aggressive in performing thoracic and thoraco–lumbar osteotomies as deemed necessary.

With regard to instrumentation I recommend multiple rods techniques enabling the correction to be first applied by a cranial construct to a group of spine segments and then connect the cranial construct to a caudal construct which has been installed to correct and fix another group of spine segments. The ultimate final balance can then be obtained in using the connectors which are used to connect the two construct and apply the necessary compression or distraction to achieve balance. If the fusion is extended to the pelvis it is recommended to use iliac CDH screw/nail as a mean of pelvic fixation.

Results

• In 89 % alignment was obtain in 15 of the 31 patients.
• 3 patients with very high pitched deformities due to cervico–thoracic crank shaft in young children were not always amenable to good balance. (81 to 92%)
• 5 adults with multiple planes deformity were subjected to two operations both using two stages but each one concentrating upon one end of the initial fusion to minimize the neurological risk of multiple levels osteotomies on adults. (92% final alignment was obtained)
• 3 patients with severe deformities were partially realigned (50%) irregardless of the curvatures.
• 5 patients have complications with hardware loosening or rupture and requested reoperation with a final result far from optimal (30% correction of Alignment)
• No neurological complications.

Discussion

Among strategic errors which resulted in scoliotic or kyphotic decompensation cranially or caudally the double spiral induced by combination of posterior column tether and anterior column growth is the most challenging deformity to address.

When it is impossible to obtain good realignment, then one must accept the primary goal to be at least a solid fusion. In some of these very difficult cases "better is the enemy of good".

The lumbar spine which is grows more, and for a longer period of time than thoracic spine is often affected with dramatic spiraled curves out of balance, when this type of deformity affects an adult in addition with a sagittal deformity it is necessary to address both deformites. It is recommended to address first the sagittal deformity by a low lumbar osteotomy and after recovery address the frontal and transverse deformity in performing the necessary wedge osteotomy in the transverse best elected plane.

The multiple rod technique is also a guarantee of temporary fixation between stages or while completing an anterior wedge osteotomy by a posterior chevron osteotomy of the fusion mass.

Bibliographie:

J.Dubousset, MD., T. Hering, MD., H. Shaffelbarger,MD. Journal of pediatric orthopedics 1989 tome 5 page 541,550.

A.Demeglio, MD., F. Bonnel. Le rachis en croissance 1990 Springer Varlag

J.P.C. Farcy,MD. F.J.Schwab, MD. Posterior osteotomies with pedicle substraction for flat back and associated syndromes:technique and results of a prospective study.Bulletin Hospital for Joint Diseases. Vol 59 #1 2000. Page11,16.