Introduction

Proximal junctional kyphosis (PJK) is a common complication that may occur following the surgical treatment of adult patients with spinal deformity. The proximal junctional sagittal angle is defined as the Cobb angle formed by the caudal endplate of the upper instrumented vertebra (UIV) and the cephalad endplate two vertebrae cranial to the UIV. Proximal junctional kyphosis is defined by a proximal junction sagittal angle ≥ 10° and at least 10° greater than the preop measurement [1]. The reported incidence of PJK in the literature varies and depends on the applied definition [1,2,3,4,5]. Glattes et al. [1] reviewed 81 adult deformity patients with a minimum 2-year follow-up and reported a 26% rate of PJK. Instrumentation at the Upper Instrumented Vertebra (UIV) consisted of all hooks in 89% of the patients. Using the same definition, Kim et al. [3] reported a PJK rate of 39% at a minimum of 5-year follow-up. The rate of PJK in adult patients undergoing multilevel fusion for idiopathic scoliosis has been reported to be 20% with a minimum of 2-year follow-up [6]. Overall, most studies report an incidence of PJK between 17 and 46% with the majority occurring within 2 years after surgery and two-thirds occurring within the first 3 months [7,8,9]. The purpose of this review is to provide up to date information on risk factors associated with the development of PJK and strategies to avoid PJK.

Most cases of PJK do not require revision surgery and patients have been shown to have equivalent functional outcomes to those without PJK [1,2,3,4, 6, 7, 10,11,12,13,14]. However, a subgroup of those patients requires revision surgery due to significant kyphosis, pain, poor self-image, or significant neurological deficits, and is defined as Proximal Junctional Failure (PJF). An analysis of 364 adult patients with spinal deformity revealed worse SRS pain scores in patients with PJK despite no significant difference in other SRS domains, total SRS scores, or Oswestry Disability Index (ODI) [15]. The Hart-International Spine Study Group Proximal Junctional Kyphosis Severity Scale (Hart-ISSG PJKSS) was recently developed and has shown strong association with worsening ODI, pain, SRS scores, and revision surgery. The Hart-ISSG PJKSS is a cumulative score of 6 domains that include (1) Neurological deficit (None: 0, Radicular pain: 2, Myelopathy/motor deficit: 4), (2) Focal pain (None: 0, VAS 4 or less: 1, VAS 5 or more: 3), (3) Instrumentation problem (None: 0, Partial fixation loss: 1, Prominence: 1, Complete fixation loss: 2), (4) Change in kyphosis/PLC integrity (0–10°: 0, 10°–20°: 1, > 20°: 2, PLC failure: 2), (5) UIV/UIV + 1 fracture (None: 0, Compression fracture: 1, Burst/chance fracture: 2, Translation: 3), (6) Level of UIV (Thoracolumbar junction: 0, Upper Thoracic: 1). A score of 9 and higher was associated with > 96% incidence of revision surgery [16]. Proximal junctional kyphosis can be categorized into 5 main morphological types: (1) proximal segment degeneration with/without ligamentous laxity; (2) upper instrumented vertebral (UIV) fracture; (3) adjacent vertebral (UIV + 1) fracture; (4) implant–bone interface failure; and (5) a combination of the preceding types with additional adjacent vertebral subluxation [9].

PJK can develop into PJF with increasing pain, spinal instability, risk of neurological injury, and need for revision surgery [10, 14, 17]. PJF has been defined as PJK along with one or more of the following: fracture of the vertebral body of UIV or UIV + 1, posterior osseo-ligamentous disruption, or failure of instrumentation at the UIV [14, 18]. Watanabe et al. [10] evaluated 5 patients each with UIV collapse as well as adjacent vertebral subluxation or adjacent vertebral fracture. They found that patients with PJK from UIV collapse or adjacent vertebral subluxation presented at a mean of 3 months postop compared to 33 months for those with adjacent vertebral fracture. Patients with UIV collapse and adjacent vertebral subluxation were found to be hypokyphotic in the thoracic spine (T5–T12) prior to surgery. Severe neurological deficit was also more common in the patients with UIV collapse and adjacent vertebral subluxation.

The average cost of revision surgery due to PJF has been estimated at $77,432 [19]. Possible factors that are associated with the decision to perform revision surgery include severe PJK angulation, neurological change, trauma, higher sagittal vertical axis (SVA), and female sex [19]. The rate of early PJF within 28 weeks was found to be 5.6% in a series of 1218 adult patients after surgery for spinal deformity. Failure at the thoracolumbar junction was more common and more likely due to fracture, whereas, failure at the upper thoracic region was more likely due to soft tissue failure. Yagi reported a 1.4% incidence of PJF requiring surgery in 1668 adult patients at a minimum 2-year follow-up [17].

Risk factors

Spine surgeons across the globe have increasingly become aware of the problem of proximal junctional kyphosis and failure. Several potential factors associated with development of PJK have been identified. We will review the risk factors in detail below.

Patient’s age

Older age has been considered to be a risk factor for the development of PJK in patients undergoing spinal deformity correction surgery. Kim et al. [3] reported on adult spine deformity patients with 5-year follow-up and found that a higher prevalence of PJK was seen in patients older than 55 years versus those younger than 55 (59% vs. 31%). Another study from the same institution found that patients who developed PJK had a mean age of 60 years versus a mean age of 50 years for those who did not develop PJK. A meta-analysis of published research up to 2015 suggested age great than 55 as a risk factor for development of PJK [20]. Park et al. also found age to be a significant factor in the development of PJK [21]. However, some others have not found age to be an independent risk factor for the development of PJK [6, 12, 22, 23]. It is possible that older age acts as a proxy to indicate poor bone quality, frailty or poor soft tissue strength but in itself may not be a risk factor. It is also important to note that some of these studies do include pediatric patients as well in their analysis of PJK which may bias the results as PJK rates are low in the pediatric populations [12].

Bone density

Osteopenia and osteoporosis were thought to be risk factors for PJK in a review of patients with idiopathic scoliosis. However, bone quality has not been determined to be an independent risk factor for PJK development in some studies [12, 22]. Bone mineral density (BMD) was not found to significantly increase the rate of PJK in adult idiopathic scoliosis patients, although there was a trend towards it [6]. Hyun and colleagues did identify low BMD (−2.5 vs. −1.3) to be a risk factor for development of PJK as well as lower muscularity and higher fatty degeneration at the level of T10 to L2 [23].

Upper instrumented level (UIV)

Selecting the appropriate upper instrumented level has long been debated. Kim et al. [2] reviewed 125 patients with 2-year follow-up who underwent fusion and instrumentation from the lower thoracic/upper lumbar level to L5 or S1. They saw no significant difference in the rate of PJK whether the UIV was at T9–T10, T11–T12, or L1–L2. However, the small number of patients in each group (37–49) and the high prevalence of PJK (36–55%) in all 3 groups may have led to lower statistical power. In another study with a minimum follow-up of 5 years, Kim et al. reported that UIV in the upper thoracic spine (T2–T6) demonstrated a higher rate of PJK compared to a UIV in the lower thoracic spine or the upper lumbar spine (T11–L2). Interestingly, they did not find a statistically significant difference when adjusted for age [3]. In a study by Boachie-Adjei, no difference in PJK rate was found in a population of adult idiopathic scoliosis with the UIV at T6 or above or a UIV lower than T6 [6]. Kim et al. did find proximal fusion to T1 through T3 to be an independent risk factor (odds ratio: 2.38) for development of PJK in a review of adult and adolescent patients undergoing surgical correction [12]. On the contrary, others have reported a higher rate of proximal junctional kyphosis when the UIV is in the lower thoracic spine as opposed to the upper thoracic spine [19, 21, 24]. Acute proximal junctional failure has been reported to occur less frequently when the UIV is in the upper thoracic spine (20%) [16] compared to the lower thoracic spine (40.2%) and the lumbar spine (41.9%) [25].

Other factors may be important in deciding the UIV in patients with adult scoliosis. Cho et al. [5] reported that the rate of adjacent segment pathology, including PJK, was lower when the UIV was cranial to the upper end vertebra on the coronal plane in patients with adult degenerative scoliosis (9–14% vs. 56%). The UIV ranged from T9 to L2 in their 51 patients with adult degenerative lumbar scoliosis. They recommended choosing a UIV that was cranial to the upper end vertebra in the coronal plane. In addition, they reported a higher incidence of adjacent segment pathology in patients with the UIV at L1–L2 (47%) versus those with UIV between T9 and T12 (9–20%).

While there are conflicting data, PJK seems to occur at higher rate when stopped in the lower thoracic spine. However, extending the construct higher increases the risk of catastrophic PJF and neurologic deficit. The amount of correction needed and the increasing stiffness that may occur, must be taken into consideration when choosing the UIV.

Combined anterior–posterior versus posterior surgery

Combined anterior–posterior spinal fusion was found to be a risk factor for the development of PJK versus posterior-only surgery [3]. Interestingly, Yagi et al. reported a higher risk of PJK development in patients with posterior instrumentation alone when compared to anterior instrumentation and combined anterior–posterior instrumentation [6]. Kim et al. [12] found combined anterior–posterior approach to be the strongest risk factor (Odds ratio: 3.36) for the development of PJK in their analysis of 242 patients with adolescent or adult idiopathic scoliosis. Whereas, Hyun et al. and Liu et al. did not find combined anterior–posterior approach to be associated with the development of PJK [20, 23]. This inconsistency in the literature may be due to the heterogeneity in the posterior-based surgical techniques. Preservation of soft tissue structures including ligaments, facet capsules, and muscles may have an effect of development of PJK in patients undergoing posterior surgery. On the other hand, the number of levels addressed via the anterior approach may play a role in the development of PJK in patients that undergo combined anterior–posterior approaches. In addition, anterior–posterior approaches are usually reserved for the largest deformity and may serve as a proxy for a significant acute correction. Unfortunately, the current available literature does not address these details.

Extension of instrumentation and fusion to the sacrum

Patients with instrumentation extending distally to the sacrum have been reported to have a higher risk of PJK versus those with distal instrumentation at L5 or above. However, once adjusted for age, this demonstrated a strong trend but did not reach statistical significance [3]. Similar results were seen by Yagi et al. in their study of 157 patients with adult idiopathic scoliosis where a higher prevalence of PJK was reported in patients with instrumentation to the sacrum compared to the patients where fusion did not extend to the sacrum. Fusion to the sacrum was found to be a risk factor in patients with idiopathic scoliosis but did not show independent association once controlled for other variables [12]. Additional studies have reported a higher incidence of PJK in patients fused to the sacrum (28–41%) [20, 25]. Yet, there are studies reporting no significant difference with extension of instrumentation and fusion to the sacrum [23]. Overall, most studies support an increase in the rate of or a trend towards an increase in the rate of PJK in patients with extension of instrumentation and fusion to the sacrum, perhaps due to the increased rigidity in the construct.

Proximal implants

The use of “soft landing” with hooks instead of pedicle screws at the proximal end of the construct has been advocated by some surgeons to avoid the development of PJK. Kim did report that patients with an all pedicle screw construct had a higher prevalence of PJK compared to those with proximal hooks or all hooks (53% vs. 34%), however, the difference was not significant when adjusted for age greater than 55 [3]. In their analysis of 47 adult patients with long posterior spinal fusion, Hassanzadeh and colleagues [26] reported no incidence of PJK in the group with transverse process hooks at the UIV. Whereas, they reported a 29.6% rate of PJK in patients with pedicle screws at the UIV. All patients had a minimum of 2-year follow-up. It is worth mentioning that in this study, the hook group did have a shorter mean follow-up compared to the pedicle screws group (2.8 vs. 5.7 years).

Another method of creating a less rigid construct proximally is with the use of transition rods. The use of a transition rod (5.5–3.5 mm for titanium and 5.5–4.5 mm for stainless steel) over the last cranially instrumented level was shown in a finite-element analysis (FEA) to reduce nucleus pressure (23% less) and angular displacement (18–19% less) in the level immediately above the instrumentation [27]. Cammarata et al. also found support for the use of transition rods and proximal transverse process hooks based on computer simulations of adult spine models with scoliosis [28].

Finally, the material of the rod can also have an impact on the overall rigidity of the construct and lead to PJK. The use of titanium alloy two-rod construct was reported to show a lower incidence of PJK compared to cobalt chrome multiple-rod constructs (26.5% vs. 60%). In the study of 54 adult patients who underwent surgery for spinal deformity, Han et al. reported that PJK occurred at a mean of 3.6 months postop in patients with cobalt chrome rods versus 26.3 months in those with titanium rods. However, rod fracture rate was significantly higher in the titanium group versus the cobalt chrome group (32.4% vs. 0%) [29].

Proximal ligaments and muscular tissues

A finite-element analysis revealed that removal of interspinous and supraspinous ligaments (ISL/SSL) immediately above the instrumented levels significantly increased pressure in the nucleus (> 50%) and increased angular displacement (19–26%) in the level immediately above the instrumented levels [27]. Another computer-generated model showed significant increase in the proximal junctional angle with resection of the proximal posterior ligaments [28]. Optimal tether configuration to restore these forces has also been completed using finite-element analysis, and a UIV + 2 loop or weave was found to resist the adjacent segment stress the most, preloaded to 100 N [30].

Bess and colleagues performed a biomechanical study on the effect of posterior polyester tethers on PJK and suggested that the posterior tethers created a more gradual transition in the range of motion at the proximal junction compared with pedicle screws and transverse process hooks at the proximal levels [31]. One retrospective review found that tethers reduced the odds of PJK, as did placing the lumbar lordosis lower in the lumbar spine [32]. These same authors looked at a short-term prospective cohort of 184 patients with 3-month f/u, that either had no tether or a polyethelyene tether with and without a crosslink to aid in tensioning. They found that tethers clinically reduced the incidence of PJK at 3 months from 45% without tether to 26.7% [33].

Minimally invasive surgery does have the potential to avoid injury of ISL/ISSL as well as paraspinal muscles. However, thus far a clear advantage of this approach in avoiding PJK or revision surgery from PJK has not been established as an independent factor [34].

Cement augmentation

The development of vertebral body fractures at the proximal junction after a long spinal fusion has prompted investigators and surgeons to consider cement augmentation of vertebral bodies in hopes of reducing PJK associated with vertebral body fractures. Kebaish et al. [35] conducted a biomechanical cadaveric study to determine the effect of prophylactic vertebroplasty at the UIV versus vertebroplasty at both UIV and UIV + 1. Vertebroplasty at UIV alone did not reduce the risk of junctional fractures when compared to cadavers without vertebroplasty. However, vertebroplasty at both UIV and UIV + 1 did significantly reduce the incidence of junctional fractures after a long posterior instrumentation from T10 to L5. While their study does have many limitations, it does suggest that cement augmentation at just the UIV did not reduce the fracture incidence as the fractures still happened at the adjacent level.

Martin, Kebaish and colleagues also reported on 38 adult patients with a T score of < −1 who underwent posterior spinal fusion to the low thoracic spine and had prophylactic vertebroplasty performed at UIV and UIV + 1 [36]. They noted an 8% incidence of PJK and 5% incidence of PJF in this cohort, which was lower than that reported in the literature. These findings were mirrored by a review of cases from Theologis and Burch where patients with no cement augmentation or cement augmentation at only one level had significantly more revision for PJF compared to patients with cement augmentation at UIV and UIV + 1 (19% vs. 0%) [37]. They reported on 51 patients with minimum of 6-month follow-up and UIV in the thoracolumbar spine. The found that patients treated with cement augmentation at UIV and UIV + 1 were 13.1 times less likely to require revision surgery for PJF compared with those without cement augmentation at the 2 levels. However, at 5-year follow-up, the group led by Kebaish reported a PJK rate of 28.2% suggesting no clear benefit of cement augmentation with long-term follow-up [38].

Appropriate alignment

The amount of correction in the sagittal plane is thought to be a contributing factor to the development of PJK after surgery. Yagi et al. found a significantly increased rate of PJK in patients with SVA improvement of more than 50 mm [6]. Maruo and colleagues reported a 41% incidence of PJK in 91 patients at a mean follow-up of 2.9 years [22]. Predictors associated with development of PJK included preoperative proximal junctional angle more than 10°, change in lumbar lordosis of more than 30°, preoperative thoracic kyphosis more than 30°, and pelvic incidence more than 55°. Change in lumbar lordosis of more than 30° and preoperative thoracic kyphosis (TK) of more than 30° were identified as independent risk factors. Liu reported a preoperative TK > 40° as a risk factor for development of PJK in their meta-analysis [20].

Postoperative alignment has an important role in protecting against development of PJK. Achieving ideal global sagittal alignment has been reported to have a lower incidence of PJK (19% vs. 45%) [22]. Ideal alignment in this study by Maruo et al. of 90 adult patients was defined as sagittal vertical axis (SVA) < 50 mm, pelvic tilt (PT) < 20°, and pelvic incidence-LL (PI-LL) <  ± 10° [22]. Reames and colleagues reported inadequate correction of the SVA as a risk factor for development of PJK [39]. However, “overcorrection” can also lead to development of PJK, especially in the older age group as reported by Kim [40]. Older patients with postoperative SVA closer to 0 mm and a lumbar lordosis closer to the pelvic incidence had a significantly higher incidence of PJK requiring surgery than those with postoperative SVA close to 4 cm and lumbar lordosis closer to PI-10°. Patients that developed PJK requiring surgery had an SVA correction of more than 5–8 cm [20, 21, 23, 40]. A larger preoperative SVA and a larger postoperative SVA correction have also been found to be associated with the development of spondylolisthesis at the proximal junction in addition to proximal junctional failure [17]. Smith and colleagues confirmed this finding as they reported on 173 adult patients with significant preoperative sagittal imbalance (SVA > 50 mm, global sagittal alignment [PI + LL + TK] > 45°, or PI-LL > 10°) [25]. They found postoperative SVA < 50 mm to be a significant risk factor for development of acute PJF in this patient population. However, the amount of SVA correction was not associated with PJF as an independent risk factor. In this patient population with significant preop sagittal imbalance, the incidence of acute PJF was found to be 35% within 6 months of surgery.

Most recently, the postoperative Global Alignment and Proportion (GAP) Score has been introduced as a predictor of mechanical complications including PJK [41]. The GAP score parameters include relative pelvic version (measured minus the ideal sacral slope), relative lumbar lordosis (measured minus the ideal lumbar lordosis), lordosis distribution index (L4–S1 lordosis divided by the L1–S1 lordosis multiplied by 100), relative spinopelvic alignment (measured minus the ideal global tilt), and an age factor [41]. The study showed a low mechanical complication rate of 6% in patients with proportionate alignment versus 47% in patients with moderate disproportion and 95% in patients with severe disproportionate state. There have been some modifications to the original GAP score that have added variables for BMI, and bone mineral density that have improved its accuracy. [42] In addition, there is evidence that the GAP score does predict ODI, and increased PJK angle at 2 years, and that the largest driver is global tilt [43]. However, external validation of the GAP principle did not reveal a significant association between the GAP score and development of mechanical failure [44]. In addition, the GAP analysis is performed postoperatively and its utility in preventing PJK or other mechanical complications remains questionable.

There has also been mathematic prediction of PJK based on the preop TK, postop LL and the ratio of the pre- and postop PT/SS [45]. Finally, there has been research to use ideal age-based alignment to determine the appropriate correction. Lafage et al. used a simulation to calculate the projected alignment in patients following PJK and compared this to their age-based goal [46]. They found that PJK was associated with patients that had an overcorrected spine, compared to their age goal.

Conclusion

Proximal Junctional Kyphosis is a common phenomenon following the surgical treatment of adult spinal deformity. We have identified several risk factors for the development of this complication and suggested some potential solutions. The solutions focus on preoperative planning, balanced alignment and potential surgical intervention to augment the proximal fixation and ligaments. Unfortunately, there are insufficient data at this time to suggest one solution that can prevent this complication. Clearly more investigation with prospective data is warranted.

The authors tips for decreasing the incidence of Proximal Junctional Kyphosis:

  • Optimize Bone Mineral Density prior to surgery when possible (6 months of treatment)

  • Aim for age-based alignment goals, (SVA closer to 40 mm as opposed to 0 mm, lumbar lordosis closer to PI-10 as opposed to PI + 10 especially in older patients)

  • For patients with preoperative thoracic kyphosis greater than 40 consider UIV in the upper thoracic spine

  • For patients with preoperative SVA > 50 mm consider UIV in the upper thoracic spine

  • Use softer landing at the proximal level: this can be achieved using hooks instead of pedicle screws for fixation at the proximal level(s) or using transition rods with the smaller diameter of the rods at the proximal levels.

  • Contour the rod into a gentle kyphosis at the proximal end of the construct

  • Consider cement augmentation at UIV and UIV + 1 especially when UIV is in the thoracolumbar spine (T9–L2) for patients who have osteopenia/osteoporosis

  • Avoid disruption of posterior ligamentous complex (ISL/ISSL), facet capsules and paraspinal musculature at the proximal level.

  • Polyethelyene tethers may play a role in reducing the incidence of PJK, but longer-term clinical studies are needed.

Case 1:

The patient is a 63-year-old female, with a long history of scoliosis. She was braced as a child and presented with increasing back pain and leg symptoms of neurogenic claudication and left sided lumbar radiculopathy. Both back and leg symptoms significantly improved with lying down. On physical exam, she is well balanced but does have significant truncal rotation with Adams forward bend test. She has no objective weakness on exam. Initial scoliosis X-rays in Fig. 1 show a retroverted pelvis, and loss of lumbar lordosis with accompanying significant coronal lumbar and thoracic curves. MRI (Fig. 2) demonstrating significant foraminal stenosis greater on the left. The preop GAP score is 7, with a PI-LL mismatch of 22 degrees. Her bone health was optimized prior to surgery and her DEXA T score was −1.5. Preop ODI was 32.

Fig. 1
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63-year-old female with adult spinal deformity. PI-LL: 22, PI: 48, LL: 26, PT: 22

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Fig. 2
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MRI scan showing the lumbar deformity and severe multilevel stenosis

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Once she had failed non-operative measures, surgery was planned to antevert the pelvis and realign the spine in both the coronal and sagittal plane. She underwent an anterior lumbar interbody fusion (ALIF) at L4–L5 and L5–S1 to release the spine and introduce lordosis 2/3 of the lordosis in the distal lumbar segments. A posterior segmental instrumentation and fusion was then performed from T9 to S1/Pelvis with multilevel decompression. For prevention of PJK, a simple UIV + 1 tether is tied to a crosslink which is tensioned. A transverse process hook was also placed on the right side to help pull the proximal thoracic curve over. Postoperatively she was maintained in an off the shelf TLSO brace for 3 months to protect the upper segment. The final alignment is acceptable, with good sagittal and coronal alignment at 2 years (Fig. 3). Final ODI is 16, with GAP of 3, PI-LL of 0, and no evidence of PJK.

Fig. 3
figure 3

2 years postop with good alignment and no PJK. PI-LL: −0.7, PI: 48, LL: 48, PT: 10

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Case 2:

The patient is a 67-year-old female, with back and bilateral leg pain from neurogenic claudication. Her symptoms improved with lying down. She has a past medical history significant for diabetes and is on insulin for control with an A1C of 7.6. She is also on Fosamax for osteoporosis with DEXA T-score of −2.0. Past surgical history is significant for a prior laminectomy 8 years ago for leg pain, which helped her at that time. She has also had a right femoral neck fracture that was fixed with a hemiarthroplasty. On exam, she has no focal deficits, she has normal strength, but has a sagittal deformity which is more problematic than the coronal deformity. She can only take a few steps with significant back and leg pain and has an ODI of 37. Her preop images are in Figs. 4 and 5, which show a PI-LL mismatch of 33, and a GAP of 11.

Fig. 4
figure 4

67-year-old female with adult spinal deformity. PI-LL: 33, LL: 7, PI: 45, PT: 36

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Fig. 5
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MRI showing multilevel stenosis

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Once she failed non-operative measures, she underwent a similar anterior–posterior spinal realignment and fusion as in case 1. The final construct was a reconstruction from T10–S1/pelvis with the use of transverse process hooks at the top of the construct for a “soft” landing. Postoperatively she was maintained in an off the shelf TLSO for 3 months to protect the upper segment. Her initial postoperative images are in Fig. 6, with improved PI-LL of −6, and GAP of 2. Unfortunately, she developed progressive kyphosis above the construct, and by 3 months had a significant thoracic gibbus and pain. She began to experience some thoracic myelopathy symptoms, and an MRI revealed adjacent level stenosis (Fig. 7). Her Hart-ISSG PJKSS was 11. She was subsequently revised from T4 to T10, and a T9/10 decompression. This likely represents an over correction of the lumbar lordosis for her age and medical comorbidities (diabetes, osteoporosis). Her final alignment still has some upper thoracic kyphosis that she is tolerating well but has moderate pain in this area. She has a high C2 SVA, despite a normal C7 SVA, and the final alignment is concerning for needing additional surgery. Final ODI at 2 years is 25 (Fig. 8).

Fig. 6
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Initial postop X-rays with good alignment. PI-LL: −3, LL: 48. PI: 45

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Fig. 7
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Development and progression of PJK with fracture at UIV + 1

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Fig. 8
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Revision of instrumentation up to T4 for development and progression of PJK. PI-LL: −3, LL: 48. PI: 45, C7 SVA 34 mm, C2 SVA 88 mm

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