In elderly patients, the diagnosis and treatment of CSOTLF is often delayed. Additionally, increasing age leads to worsening of degree of osteoporosis and thoracolumbar kyphosis; these factors lead to intractable low back pain and eventual bilateral lower extremity paralysis, which severely affects the quality of life of patients. Non-surgical treatment methods are often unsuccessful; however, long-segment internal fixation is effective in maintaining spinal stability, correcting posterior convexity deformity, and preventing injured spine collapse and progression of the posterior convexity Cobb angle. However, long segment internal fixation can cause several segmental complications. Among them, PJK is the most common affecting 6%-40% of patients depending on disease type, surgical approach, and follow-up time.[12-14] PJK evaluation criteria are often different for patients with advanced age and excessive deformities. Studies have emphasized that advanced age, BMI, BMD, UIV/LIV fixed position, PJA, LL, SVA, and fixed segments are the main risk factors for developing PJK.[16-18] Clinical observation shows that most patients with PJK develop mild symptoms, requiring only regular check-ups; on the other hand, a few patients may progress to PJF or even neurological damage, which severely affects patients' postoperative functional recovery. Therefore, when using posterior long-segment internal fixation for CSOLTF, active detection of high-risk factors for PJK is important for improving patient prognosis.
(1) Age: Advanced age is a risk factor for developing PJK. Particularly, previous studies found that individuals aged >55 years have the highest incidence of PJK, and the risk increases with age. Kim et al and Yang et al also confirmed that PJK is more prevalent and has a higher incidence in people aged ≥60 years. Patients with PJK can be aggravated by spinal deformities, which leads to changes in paravertebral muscle tissue; furthermore, uneven stresses on the intervertebral discs and small spinal joints can accelerate degeneration. In addition, advanced age is considered to be an important risk factor for revision surgery for PJK.
(2) BMI: Currently, patients with BMI >25 kg/m2 are believed to have high susceptibility to PJK. This relationship may be attributed to the increased load placed on the spine and internal fixation in overweight and obese patients and the forward shift of the body's center of gravity, resulting in increased stress on adjacent segments. Simultaneously, obese and overweight patients have significantly weakened low back muscles, which increases the risk of osteoporosis.
(3) BMD: O'Leary et al showed that patients with osteoporosis are more prone to PJK. Additionally, reduced bone mass and bone microarchitecture disruption reduce screw holding power, which increases the risk of screw loosening and extraction. In addition, lower bone density is associated with reduced muscle tissue in the thoracolumbar segment, which may lead to spinal instability and accelerate the development of PJK.
The results of this study showed that age >70 years, BMI >28 kg/m2, and BMD with T value <3.5 SD, were risk factors for PJK in patients who underwent posterior long segment internal fixation for CSOTLF. This study suggests that strict postoperative weight control and standardized anti-osteoporosis treatment reduce the occurrence of postoperative PJK in elderly patients aged >70 years.
(1) PLC: Posterior spinal surgery may damage the proximal soft tissues, including the supraspinous and interosseous ligaments; furthermore, small joint capsule injuries can lead to decreased local stability and PJK.
(2) Imaging parameters: Iyer et al found that SVA and LL increases and decreases, respectively, with age. When the sagittal sequence is artificially corrected, the organism continues to return to its natural state. In contrast, overcorrection of the deformity increases stress in the proximal-distal junction area and the incidence of PJK. Therefore, the maximum correction of SVA to 0 may not be ideal for the patient. The retrospective study of ANNIS et al found that postoperative PJA >5° and LL correction >30° were independent risk factors for PJK in 135 patients. PI-LL reflects the compatibility between the lumbar curve and pelvic morphology and suggests a compensatory state of sagittal balance of the spine. Senteler et al found a direct relationship between PI-LL and the risk of degeneration of adjacent segments.
(3) UIV/LIV: Additionally, the choice of UIV/LIV is related to the occurrence of PJK; therefore, the apex of posterior convexity and segments with degenerative instability should be avoided as much as possible. UIV fixation to the thoracolumbar segment increases the risk of PJK, which may be attributed to the fixation of the UIV at the transition from thoracic kyphosis to the anterior lumbar convexity. This area is the junctional zone of stress transmission and is relatively less stable due to the lack of thoracic protection, which increases the susceptibly for PJK. When the UIV is fixed above T10, stable rib support exists, which can protect the stability of the adjacent vertebrae and reduce the occurrence of degenerative diseases in the proximal adjacent segments. However, this can cause increased intraoperative bleeding; furthermore, no significant advantages have been found regarding other complications and revision rates. The literature states that LIV fixation fusion to the sacrum/pelvis/iliac bone is twice as effective as preserving lumbosacral motion for PJK. The author believes that fusion to S1 results in a concentration of proximal stresses due to long segment fixation, a weakened sagittal balance of pelvic regulation, and a higher incidence of both postoperative pseudarthrosis and sagittal imbalance. Adult spinal deformities often have structural changes and deformities at the L4/5 segment; therefore, fixation at L5 avoids iliac screws, preserves lumbosacral motion, and reduces sacroiliac joint stresses. However, extended fixation to the ilium can effectively increase fixation strength and stability in the following patients: patients with coronal/sagittal imbalance of the trunk who require orthopedics; those who require three-column osteotomy in the lumbosacral region; those with repeated nail placement or poor stability of S1 screws found intraoperatively; and those with significant lumbosacral instability or revision surgery. However, it should be noted that the choice of UIV/LIV is not absolute fixation; particularly, the patient’s spinal balance should be considered in the decision.
(4) Fixed segments: Internal fixation with long segmental pedicle screws increases the incidence of PJK since it can damage more paravertebral muscles and small intervertebral joints while exposing the nail placement point, which affects spinal stability and stress, especially at the proximal junction, the junction that generates lateral stress and causes displacement of the adjacent vertebrae. Kim et al found that patients were at an increased risk for PJK if the number of fixed vertebral bodies was >5. This may be attributed to the significant concentration of stress in the adjacent vertebral body, making the adjacent vertebral body more susceptible to degeneration and displacement.
This study showed that PLC injury, UIV fixation at T10-T12, LIV fixation at S1, preoperative PJA >5°, preoperative SVA >50 mm, preoperative PT >30°, preoperative SS ≤25°, and fixation stages >7 were risk factors for developing postoperative PJK. Therefore, preoperative interventions for high-risk groups and individualized surgical plans can be formulated by identifying risk factors to reduce the incidence of postoperative PJK.
PJK Complication Management
For non-surgical factors, CSOLTF disease mostly occurs in elderly patients with numerous medical comorbidities. Patients with advanced age (>70 years), increased BMI (>28.0 kg/m2), and severe osteoporosis (BMD <3.5 SD) warrant increased preoperative attention to adjust the patient's general comprehensive condition to reduce the incidence of PJK.
(1) Functional exercise of the lumbar back muscles: As patients age, paravertebral muscle atrophy and severe paravertebral fat infiltration lead to decreased paravertebral muscle strength, which significantly increases the risk of postoperative PJK. Therefore, appropriate preoperative muscle exercises can help reduce the occurrence of PJK. (2) Weight reduction: Reducing a patient’s weight can lower the physical stress of the musculoskeletal system in the proximal junction area, which reduces the incidence of PJK. (3) Anti-osteoporosis treatment: Standardized anti-osteoporosis treatment can improve bone calcium content and bone strength, which can help maintain the stability of the internal fixation system and reduce loosening and extraction. Therefore, it can reduce the development of vertebral fractures and collapse in the junction area, which reduce the incidence of mechanical complications.
For surgical factors: (1) Soft tissue protection: Anatomical exposure of the upper end of the vertebral region minimizes the damage to the supra- and interspinous ligaments. Fine separation of the paravertebral muscles in the junctional area, maximum possible preservation of the midline ligament structure, and muscle attachment. (2) Ligamentous strengthening of the junctional area: ligamentous strengthening through tendon grafting or silk wire reinforcement can reduce the stress in the junctional area and increase the strength of the PLC. (3) Non-strength fixation: the use of a plate hook in the proximal fixed vertebrae can provide a relatively non-strength fixation structure, which can help protect the small joints and discs of the adjacent segments, prevent excessive stress concentration in the junctional zone, and reduce the occurrence of PJK or PJF. (4) UIV/LIV selection: in the apex of the lordosis and the segment of degenerative disability, proximal and distal fixed vertebrae should be avoided; on the other hand, proximal fixed vertebrae should be avoided in the thoracolumbar junction area. Regarding distal fixed vertebrae, advantages and disadvantages of fixation in L5, S1, or skeleton should be considered in an individual basis. (5) Bone cement reinforcement: preventive application of bone cement reinforcement to both fixed and adjacent vertebrae to increase the strength of the vertebral body can, to a certain extent, avoid internal fixation failure and adjacent vertebrae fracture. (6) Sagittal restoration: moderate deformity correction while considering overall balance should be performed according to the adult spinal deformity sagittal evaluation standard SRS-Schwab staging requirements and spinal sagittal sequence score (global alignment and proportion score).
This was a single-center retrospective study with a small number of enrolled patients and selection bias. Most of the relevant clinical evaluation information during the follow-up period was provided by the patient through telephone interview or outpatient follow-up, which may have caused errors. Future multicenter prospective studies with large sample sizes are warranted to understand the relationship of PJK with different imaging parameters, and fixed segments. This is to guide the surgical strategy of long segment fixed fusion, minimize the risk of postoperative PJK, and provide guidance on the strategy of revision surgery.