Proximal Junctional Kyphosis (PJK)

Proximal junctional kyphosis (PJK) is defined as greater than 10° kyphosis at the upper instrumented vertebra (UIV) compared to preoperative alignment, occurring in 20-40% of adult spinal deformity surgeries. PJK must be distinguished from PJF (proximal junctional failure)—which includes vertebral fracture, ligament rupture, or implant failure at UIV and often requires revision (PJA greater than 28° or change greater than 22°). Risk factors include age over 60, osteoporosis, thoracic UIV, and critically over-correction of sagittal alignment. Most PJK occurs within 3-18 months postoperatively. Prevention strategies include age-adjusted alignment targets (avoid over-correction in elderly), cement augmentation at UIV and UIV+1 in osteoporotic bone, and soft tissue preservation at the proximal junction.

Proximal junctional kyphosis (PJK) is one of the most common mechanical complications following long-segment spinal fusion surgery, particularly in adult spinal deformity (ASD) correction. It represents excessive kyphosis development at the transition zone between the fused and unfused spine.

Definitions:

• PJK: Proximal junctional angle (PJA) more than 10 degrees compared to immediate postoperative values, measured between the UIV inferior endplate and UIV+2 superior endplate
• PJF (Proximal Junctional Failure): PJA more than 28 degrees OR change more than 22 degrees, often associated with fracture, ligament failure, or implant failure

Epidemiology:

Clinical Significance:

• PJK may be asymptomatic or cause significant morbidity
• PJF often requires revision surgery (40% revision rate)
• Healthcare costs substantially increased with PJK/PJF
• Most cases develop within first 18 months postoperatively

Mechanism of Development

PJK results from a mismatch between the mechanical demands at the proximal junction and the capacity of the adjacent tissues to withstand these loads.

Contributing Factors:

1. Abrupt stiffness transition: Rigid fused construct meets mobile unfused spine
2. Altered load distribution: Stress concentration at junctional level
3. Sagittal imbalance: Forward trunk shift increases moment arm at UIV
4. Tissue failure: Bone, ligament, or disc cannot withstand new loads

Anatomical Structures at Risk

Bone:

• UIV vertebral body compression
• UIV+1 vertebral body fracture
• Superior endplate failure

Soft Tissue:

• Posterior ligamentous complex (PLC)
• Interspinous and supraspinous ligaments
• Paraspinal musculature

Disc:

• UIV/UIV+1 disc degeneration
• Accelerated adjacent segment disease

Biomechanical Principles

Stress Concentration:

The junctional zone experiences increased stress due to:

• Transition from fused to mobile segments
• Lever arm effect of long constructs
• Loss of shock absorption from fused discs

Sagittal Compensation:

When PJK develops, the body attempts to compensate:

• Cervical hyperlordosis
• Pelvic retroversion
• Knee flexion

Bone Quality Impact:

• Osteoporotic bone cannot resist vertebral compression
• Reduced pull-out strength of UIV screws
• Cortical thinning increases fracture risk

History

Key Questions:

• When was the index surgery? (Most PJK occurs 3-18 months)
• New or worsening back pain? (Character, location, severity)
• Change in posture or balance?
• Neurological symptoms? (Weakness, numbness, bowel/bladder)
• Functional limitations? (Walking tolerance, ADLs)

Red Flags for PJF:

• Acute pain after minor trauma or sudden onset
• New neurological deficit
• Visible or palpable step-off at fusion end
• Rapidly progressive kyphosis

Physical Examination

Observation:

• Standing posture - increased thoracic kyphosis
• Forward trunk lean
• Compensatory cervical hyperlordosis
• Visible prominence at UIV level

Palpation:

• Tenderness over UIV area
• Step-off or prominence at junctional level
• Muscle spasm

Neurological:

• Full motor examination (especially if PJF suspected)
• Sensory examination
• Reflexes
• Gait assessment

Flexibility:

• Can the kyphosis correct with prone positioning?
• Hip flexion contracture (Thomas test)

Clinical Indicators for Intervention

Surgical Indications:

1. Neurological deficit from compression
2. Progressive deformity on serial imaging
3. Intractable pain despite conservative measures
4. Documented instability on dynamic films
5. Skin breakdown risk from hardware prominence

Imaging Protocol

Step 1: Standing Full-Length Radiographs

• Compare to immediate postoperative films
• Measure PJA at UIV to UIV+2
• Assess global sagittal alignment (SVA, PI-LL)
• Evaluate hardware position

Step 2: CT Scan (If Indicated)

• Detect vertebral fracture at UIV/UIV+1
• Assess fusion mass (pseudarthrosis)
• Hardware evaluation (loosening, breakage)
• Bone quality assessment (HU values)

Step 3: MRI (If Neurological Symptoms)

• Cord compression assessment
• Soft tissue changes
• Disc pathology
• Posterior element integrity

Key Radiographic Measurements

Essential Measurements:

Dynamic Films (If Instability Suspected):

• Flexion-extension lateral radiographs
• Assess motion at UIV segment
• Document any subluxation

Bone Density Assessment

DEXA:

• Pre-existing T-score for baseline
• Repeat if osteoporosis treatment initiated

CT HU Values:

• UIV and UIV+1 vertebral body density
• Less than 110 HU suggests osteoporosis
• Guides cement augmentation need in revision

Complications of PJK/PJF

Direct Complications:

Complications of Revision Surgery

Early:

• Neurological injury (1-5%)
• Dural tear (5-10%)
• Wound infection (5-10%)
• Blood loss (significant)

Late:

• Recurrent PJK (20-30%)
• Pseudarthrosis (10-20%)
• Adjacent segment disease
• Chronic pain

Risk Factors for Recurrence

Non-modifiable:

• Advanced age
• Poor bone quality
• Long fusion extent

Modifiable:

• Over-correction of alignment
• Inadequate proximal extension
• Failure to address osteoporosis
• Poor soft tissue preservation

Natural History

PJK Without Intervention:

• Many cases remain stable
• Progression rate approximately 20-30%
• Symptomatic improvement possible in some

PJF Without Intervention:

• Generally progressive
• Neurological risk if cord involvement
• Poor quality of life outcomes

Revision Surgery Outcomes

Radiographic:

• PJA correction: 70-80%
• Global alignment improvement: 60-70%
• Fusion rate: 80-90%

Clinical:

• Pain improvement: 60-70%
• Functional improvement: 50-70%
• Patient satisfaction: 60-75%
• Reoperation rate: 20-30%

Prognosis Factors

Favorable:

• Younger age
• Good bone quality
• First revision
• Successful alignment correction
• No neurological deficit

Unfavorable:

• Multiple prior revisions
• Severe osteoporosis
• Persistent sagittal imbalance
• Neurological complications
• Medical comorbidities

Epidemiology in Australia

The ageing Australian population has seen increasing rates of adult spinal deformity surgery, with correspondingly higher numbers of patients at risk for PJK. Australian data mirrors international literature with PJK rates of 20-40% following long-segment fusion surgery.

Management Considerations

Complex spinal deformity surgery and PJK revision procedures are performed at tertiary spine units across major Australian metropolitan centres. Access to specialized imaging, intraoperative neuromonitoring, and intensive care facilities is essential. Rural and regional patients typically require transfer to metropolitan centres for complex revision surgery.

Bone Health Management

Australian guidelines recommend DEXA screening for patients over 50 undergoing major spinal surgery. Bone health optimization with bisphosphonates or denosumab, along with calcium and vitamin D supplementation, aligns with Osteoporosis Australia recommendations. Pre-operative bone health treatment for 3-6 months may be considered in elective cases with severe osteoporosis.

Surveillance and Follow-up

Australian practice involves regular clinical and radiographic surveillance following long-segment spinal fusion. Standing full-length radiographs at 6 weeks, 3 months, 6 months, 12 months, and annually thereafter allow for early detection of PJK progression. Close collaboration between spinal surgeons and rehabilitation physicians optimizes patient outcomes.