Correction of Adolescent Hyperkyphosis with Posterior-Only Threaded Rod Compression Instrumentation

• (b, d - Medtronic Sofamor Danek)

Purpose: Traditional treatment for adolescent hyperkyphosis has included apical anterior spine release/fusion (ASF) prior to posterior instrumented fusion. We wished to re-assess the need for ASF when using posterior shortening technique with a threaded rod compression instrumentation system.

Materials: PSF-only group:14 patients, mean age 15.6 yr (range 12.8-18.5), underwent posterior column shortening by chevron-shaped lamina resection and fusion using hybrid hook/screw, dual 4.8mm threaded compression rod instrumentation (TRI). A/PSF group: 7 patients, mean age 15.4 yr (14-16.8), underwent open or endoscopic ASF followed by posterior TRI. 11/21 patients had strict Sorensen criteria of Scheuermann's. At mean f/u of 30 mo. (range 24-56), patients were assessed for amount and maintenance of correction, sagittal balance, and evidence of pseudarthrosis.

Results: Mean preop measured kyphosis in PSF-only was 78.6º (range 67-90), and was corrected to 39.4º (26-55) postop and 39.7º (29-50, 50%) at final f/u. In the A/PSF group, preop kyphosis was 79.0º (62-93), corrected to 41.6º (34-48) postop, and was 42.6º (25-48, 46%) at final f/u. There was no difference in the amount of correction (p=.49) or its maintenance between the two groups. Similarly there were no differences between groups in assessing preop and final T2-12 kyphosis (p=.23), T10-L2 kyphosis (p=.09), T12-S1 lordosis (p=.63), or C7 sagittal balance (p=.08). There was greater correction of Voutsinas' index (PSF-only=.08, A/PSF=.15, p<.001) for the posterior-only group. No patient lost > 8º (range -12 to 8) correction between immediate postop and final f/u, and no instrumentation complications occurred.

Discussion: Historical justification for apical ASF prior to PSF is derived from perceived loss of correction and pseudarthrosis from posterior surgery alone, although Sturm, Ponte and others have reported successful management using Harrington threaded rod instrumentation. Using a shortening technique where chevron-shaped lamina resection is done at each thoracic segment and larger diameter (4.8mm) threaded rods with hooks cephalad to the apex and screws caudal, we have found no advantage in correction imparted by preliminary anterior apical release, nor is there a difference in maintenance of correction. Since no instrumentation failures have occurred, no pseudos are suspected. TRI provides powerful, gradual and evenly-distributed posterior correction due to the mechanical advantage associated with moving nuts along a threaded rod. There is minimal risk of proximal or distal junctional kyphosis since no cantilever forces at the apex are necessary. We conclude that apical ASF is unnecessary when adolescent hyperkyphosis/Scheuermann's is treated by posterior column shortening and TRI.

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