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Knee flexion compensation in postoperative adult spinal deformity patients: implications for sagittal balance and clinical outcomes

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Abstract

Purpose

To determine whether maintaining good sagittal balance with significant knee flexion (KF) constitutes a suboptimal outcome after adult spinal deformity (ASD) correction.

Methods

This single-center, single-surgeon retrospective study, assessed ASD patients who underwent posterior spinal fusion between 2014 and 2020. Inclusion criteria included meeting at least one of the following: PI–LL ≥ 25°, T1PA ≥ 20°, or CrSVA-H ≥ 2 cm. Those with lower-extremity contractures were excluded. Patients were classified into four groups based on their 6-week postoperative cranio-hip balance and KF angle, and followed for at least 2 years: Malaligned with Knee Flexion (MKF+) (CrSVA-H > 20 mm + KFA > 10), Malaligned without Knee Flexion (MKF−) (CrSVA-H > 20 mm + KFA < 10), Aligned without Knee Flexion (AKF−) (CrSVA-H < 20 mm + KFA < 10), and Aligned with Knee Flexion (AKF+) (CrSVA-H < 20 mm + KFA > 10). The primary outcomes of this study included one and two year reoperation rates. Secondy outcomes included clinical and patient reported outcomes.

Results

263 patients (mean age 60.0 ± 0.9 years, 74.5% female, and mean Edmonton Frailty Score 3.3 ± 0.2) were included. 60.8% (160/263 patients) exhibited good sagittal alignment at 6-week postop without KF. Significant differences were observed in 1-year (p = 0.0482) and 2-year reoperation rates (p = 0.0374) across sub-cohorts, with the lowest and highest rates in the AKF− cohort (5%, n = 8) and MKF + cohort (16.7%, n = 4), respectively. Multivariable Cox regression demonstrated the AKF− cohort exhibited significantly better reoperation outcomes compared to other groups: AKF + (HR: 5.24, p = 0.025), MKF + (HR: 31.7, p < 0.0001), and MKF− (HR: 11.8, p < 0.0001).

Conclusion

Our findings demonstrate that patients relying on knee flexion compensation in the early postoperative period have inferior outcomes compared to those achieving sagittal balance without knee flexion. When compared to malaligned patients, those with CrSVA-H < 20 mm and KFA > 10 degrees experience fewer early reoperations but similar delayed reoperation rates. This insight emphasizes the importance of considering knee compensation perioperatively when managing sagittal imbalance in clinical practice.

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Data availability

The data used to conduct the analysis presented in this study is not publically available, but available upon request.

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Funding

The authors did not receive support from any organization for the submitted work.

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Authors and Affiliations

  1. Department of Orthopaedic Surgery, The Och Spine Hospital, Columbia University Irving Medical Center, New York, NY, USA

    Sarthak Mohanty, Christopher Lai, Gabriella Greisberg, Fthimnir M. Hassan, Christopher Mikhail, Stephen Stephan, Joshua Bakhsheshian, Andrew Platt, Joseph M. Lombardi, Zeeshan M. Sardar, Ronald A. Lehman & Lawrence G. Lenke

  2. Vagelos College of Physicians and Surgeons, Columbia University, New York, NY, USA

    Christopher Lai

  3. Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA

    Sarthak Mohanty

  4. The Daniel and Jane Och Spine Hospital, New York Presbyterian, Columbia University Medical Center, 5141 Broadway, New York, NY, 10034, USA

    Fthimnir M. Hassan

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  1. Sarthak Mohanty
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Contributions

SM, CL, GG, FMH, CM, SS, JB, AP: Contributed to the concept/design of the work, acquisition, analysis, and interpretation of the data, drafted the work, approved the version to be published, agrees to be accountable for all aspects of the work. JML, ZMS, RAL, LGL: Contributed to the concept/design of the work, revised the work critically for important intellectual content, approved the final version to be published, agrees to be accountable for all aspects of the work.

Corresponding author

Correspondence to Fthimnir M. Hassan.

Ethics declarations

Ethical approval

AAAR6504 This retrospective chart review study involving human participants was in accordance with the ethical standards of the institutional and national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards. The Human Investigation Committee (IRB) of Columbia University Irving Medical Center approved this study.

Informed consent

Informed consent was obtained from all individual participants included in the study.

Conflict of interest

Sarthak Mohanty, Christopher Lai, Gabriella Greisberg, Fthimnir M. Hassan, Christopher Mikhail, Stephen Stephan, Joshua Bakhsheshian, and Andrew Platt have no relevant financial or non-financial interests to disclose. Lawrence G. Lenke has received grant support from AO Spine, International Spine Summit Group, Scoliosis Research Society, EOS Technology and Setting Scoliosis Straight Foundation as a study investigator. Ronald A. Lehman has received grant support from the Department of Defense as a study investigator. Joseph M. Lombardi, Zeeshan M. Sardar, Ronald A. Lehman, and Lawrence G. Lenke have received consulting fees from Medtronic. Lawrence G. Lenke has received consulting fees from Acuity Surgical and Abryx. Lawrence G. Lenke has received reimbursements from Broadwater, AO Spine, and Scoliosis Research Society for attending meetings/travel. Ronald A. Lehman and Lawrence G. Lenke have received royalties and are patent holders from Medtronic. Ronald A. Lehman has received royalties and is a patent holder from Stryker.

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Mohanty, S., Lai, C., Greisberg, G. et al. Knee flexion compensation in postoperative adult spinal deformity patients: implications for sagittal balance and clinical outcomes. Spine Deform 12, 785–799 (2024). https://doi.org/10.1007/s43390-024-00824-z

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