Background
Proximal junctional kyphosis (PJK) following long instrumented fusion is a well-recognized complication that does not negatively affect the clinical outcomes. However, there were few studies with regard to the long-term consequences of PJK. Objective: To investigate the long-term clinical and radiographic consequences of proximal junctional kyphosis (PJK) following the long instrumented fusion for elderly patients with sagittal imbalance.
Methods
Patients older than 60 years who underwent ≥4 fusion including the sacrum for sagittal imbalance were followed up longer than five years. PJK was defined as proximal junctional angle (PJA) >10° without any bony compromise or myelopathy. The radiographic and clinical outcomes were compared between PJK and non-PJK groups. Clinical outcome measures included visual analog scale (VAS) for back and leg, Oswestry disability index (ODI), and Scoliosis Research Society (SRS)-22 scores.
Results
A mean age was 69.2 years. An average follow-up duration was 92.4 months. There were 30 patients in PJK group and 43 in non-PJK group. At the final follow-up, pelvic incidence-lumbar lordosis mismatch, pelvic tilt, and sacral vertical axis were not different between the two groups. In PJK group, PJA significantly increased from 6.5° postoperatively to 21.2° at the final follow-up. At the final follow-up, clinical outcomes were worse in PJK group than in non-PJK group with regard to VAS for back, ODI, and SRS-22 scores except satisfaction domain. Three (10%) of 30 patients underwent a revision surgery for PJK progression.
Conclusions
PJK progressed with time and negatively affect the clinical outcomes in a long-term follow-up after ASD surgery.

To understand the compensatory mechanisms of knee and hip joint for sagittal imbalance, it is very important to investigate the response of each joint to the abnormal condition of other joint. Most of studies so far were limited to the response of spine and hip joint to the sagittal imbalance and it is very rare to include the response of knee joint. We assume four conditions and investigate the response of each joint to the abnormal condition of other joint 1. The normal response of spine and pelvis to the knee flexion contracture 2. The response of spine and pelvis to the correction of knee flexion contracture 3. The response of knee and hip joint to the loss of lumbar lordosis 4. The response of knee and hip joint to the restoration of knee and hip joint The results show that the flextion contracture of knee joint makes hip jont flexed and loss of lumbar lordosis with shift the sagittal balance forward. When flexion contracure was corrected like TKRA, hip joint also extended and lumbar lordosis increase and sagittal balance moves backward. Loss of lumbar lordosis makes more positive sagittal balance and hip joint becomes extended and knee joint flexed. The restoration of lumbar lordosis, sagittal balance shift backward and knee joint extended. However, if restoration of lumbar lordosis is not complete, hip joint remains extended, while knee joint becomes normal position, the extended position.

In General, sagittal spinal imbalance is divided into dynamic and static type. Static sagittal imbalance is due to iatrogenic, post-traumatic causes and the major contributory factor of dynamic sagittal imbalance is degenerative change such as lumbar degenerative kyphosis. The operative technique and method of correction for static sagittal imbalance is established somewhat and dynamic sagittal imbalance has different pathophysiology from the static one. So the operative method for correction of dynamic sagittal imbalance should be different from the static one. The degenerative change and segmental instability of lumbar spine in dynamic sagittal imbalance and accordingly, loss of lumbar lordosis and sagittal imbalance causes lumbar kyphosis and forward bending of the body. But there are a few studies about dynamic sagittal imbalance and there is controversy about operative method for correction of dynamic sagittal imbalance.

Purpose
There is an increasing recognition of the clinical importance of the sagittal balance after lumbar fusion surgery. The purpose of this study to review the etiology of sagittal imbalance after lumbar fusion surgery and report the radiographic and clinical results of surgical treatment of these patients.
Materials and Methods
Retrospective review of revision spine surgery due to sagittal imbalance in 35 patients. Various surgical methods such as posterior–anterior–posterior (PAP) sequential approach, Smith–Peterson osteotomy (SPO), pedicle subtraction osteotomy (PSO), and vertebral column resection (VCR) were performed to restore lumbar lordosis. The outcome variables included preoperative, postoperative, and follow-up radiographic films, and a clinical assessment using Oswestry Disability Index (ODI), SRS 22, and a review of postoperative complications.
Results
The mean age of the patients was 62 years (age range, 49–74), and mean follow-up duration was 31 months (range, 24–37) for clinical and radiographic outcome variables. The mean preoperative LL/PI (lumbar lordosis/ pelvic incidence) ratio was different from postoperative value (P< 0.0001). Twenty one out of 35 patients showed perioperative complications including proximal junctional kyphosis or infection. All functional outcomes measures improved postoperatively (P < 0.0001).
Conclusion
Most common causes of revision spine surgery due to sagittal imbalance include failure to enhance lumbar lordosis, proximal vertebral collapse, and junctional kyphosis. LL/PI ratio was considered as one of the valuable spinopelvic parameter for evaluation of sagittal imbalance. Following surgical treatment, sagittal balance was generally improved with good to excellent clinical outcomes and high patient satisfaction, although the perioperative complication rates are high.