Introduction: Existing literatures regarding the impact of alignment parameters relative to the thoracolumbar inflection point(IP) remains to be sparse. Our objective was to determine the impact of IP, lumbar lordosis apex(LLA), and other parameters on complications, reoperations, and outcomes.
Methods: Surgical ASD patients with available 2-year(2Y) data that were fused in the lower thoracic(T7-T12) to pelvis were included. Parameters relative to the IP, IP from UIV, LLA, and theoretical IP based on pelvic incidence in the normative populations from Roussouly morphology were assessed. Cases were evaluated based on IP changes by at least 1 level from baseline(BL) into Caudal(L), Same(S), or Cranial(H). The analysis controlled for invasiveness, baseline deformity, frailty, and PJK prophylaxis.
Results: 435 patients met inclusion. The mean baseline IP was at L1-L2 interbody space, which was corrected more cranial postoperatively to the L1 body. Development of PJF/PJK with reoperation was associated with a more caudal BL IP(L2 inferior end plate[EP] vs L1 body, p<.001). In adjusted analysis, a more caudal BL IP had 25% higher odds of developing PJF by 2Y(OR:1.26[CI:1.08-1.46],p=0.003). Postoperative normalization to theoretical Roussouly IP had decreased rates of rod breakage(4.5% vs 9.3%,p=.049), but higher rates of PJF(13.1% vs 7.7%,p=.044). Stratifying groups based on IP change from BL, rates of PJK and PJF by 2Y were higher in H(both p<.003), with no difference in meeting Roussouly target IP. There were 4.4x lower odds of developing PJF in L and 2.0x in S compared to H(p <.05). Increased distance of UIV to IP was associated with mechanical complications(MC)(p <.05). Decreased distance between LLA-IP at BL was associated with MC(p=.04).
Conclusion : Although correction of the IP to normative values decreased rates of MC, PJK rates remain high depicting other factors being at play. These correlations between the IP with the UIV and LLA underscore the pivotal role of IP in achieving adequate realignment.
.jpg)