Modified Percutaneous Vertebroplasty with Bilateral Cannulated Screws and Staged Cement Injection for Stage I and II Kummell’s Disease: A Mid-to-Long Term Follow-Up Study

Technical Summary: Modified Percutaneous Vertebroplasty for Kummell's Disease

Problem Statement
Kummell's disease (KD) is a delayed post-traumatic vertebral osteonecrosis characterized by an intravertebral vacuum cleft (IVC). While conventional percutaneous vertebroplasty (PVP) or kyphoplasty (PKP) offers early relief, long-term follow-up reveals significant limitations in KD cases. Unlike simple osteoporotic fractures where cement interdigitates with trabecular bone, cement in KD tends to accumulate within the IVC cavity, forming a distinct mass with a boundary against the surrounding sclerotic bone. This lack of mechanical interlock leads to micromotion and abrasive wear at the cement-bone interface, resulting in cement loosening, progressive vertebral collapse, kyphotic deformity, and potential neurological deficits. Existing modified techniques often fail to fully address the integration between the cement, the screw, and the host bone, or they carry risks of peripedicular cement extravasation.

Methodology
This study retrospectively evaluated 38 patients with Stage I (n=18) and Stage II (n=20) KD treated with a novel modified PVP technique at Yantaishan Hospital between March 2023 and March 2025. The procedure was performed under local anesthesia by senior surgeons using a specific three-step protocol:

1. Bilateral Cannulated Screw Placement: Under fluoroscopic guidance, headless cannulated screws (5.2 mm × 40 mm) were bilaterally inserted into the pedicles. This established immediate internal vertebral support and mechanical anchor points prior to cement injection.
2. Transmidline Steerable Cement Delivery: A steerable bone cement delivery cannula (Ascend™) was advanced over the contralateral guidewire. Its distal curved tip was manipulated to cross the vertebral midline and rest adjacent to the ipsilateral screw.
3. Staged Cement Injection:
   • Phase 1: High-viscosity polymethylmethacrylate (PMMA) cement was injected to primarily fill the contralateral IVC and the peri-screw space.
   • Phase 2: The cannula was retracted within the cleft while injecting small volumes to maximize cleft obliteration.
   • Phase 3: The cannula tip was straightened, and low-viscosity PMMA was infused into the residual IVC and surrounding bone to enhance osseointegration.
   • Final Step: A second cannulated screw was implanted into the contralateral pedicle before cement polymerization to ensure rigid anchorage between the cement and the screw implant.

Clinical outcomes were assessed using the Visual Analogue Scale (VAS) and Oswestry Disability Index (ODI). Radiological outcomes included Anterior Vertebral Height (AVH) and Cobb angle. Patients were followed preoperatively, at day 1, 6 months, 12 months, and at a mean final follow-up of 17.2 months. All patients received standardized anti-osteoporotic management.

Key Contributions
The study introduces a specific technical modification to PVP that addresses the biomechanical failure of conventional KD treatment:

• Integrated Locking Complex: By implanting screws before cement injection and using a steerable cannula to deliver cement across the midline, the technique creates a unified structure where the cement, pedicle screws, and host vertebral bone are mechanically interlocked.
• Staged Injection Protocol: The use of high-viscosity cement followed by low-viscosity cement aims to first obliterate the cleft and then improve the cement-bone interface integration, preventing the formation of an isolated cement block.
• Prevention of Loosening: The design theoretically resists persistent axial loading and interfacial abrasion, addressing the root cause of cement loosening and re-collapse seen in standard PVP.

Results

• Clinical Outcomes: Significant and sustained improvements were observed. VAS scores decreased from a preoperative mean of 6.89 ± 0.87 to 1.26 ± 0.61 at final follow-up (P < 0.001). ODI scores improved from 69.58% ± 9.24% to 17.89% ± 7.03% (P < 0.001).
• Radiological Outcomes: AVH and Cobb angle were significantly restored by postoperative day 1 and remained stable throughout the follow-up period, with no evidence of progressive kyphosis or vertebral height loss.
• Safety: The overall complication rate was 21.1% (8/38), comprising 15.8% cement extravasation and 5.3% adjacent vertebral fractures. No statistically significant differences in complication rates were found between Stage I and Stage II groups.
• Stage Comparison: Although Stage I patients received a larger cement volume (6.83 mL) compared to Stage II (5.78 mL), there were no significant differences in final clinical or radiological outcomes between the two stages.

Significance and Claims
The authors claim that this modified PVP technique is safe, feasible, and effective for treating Stage I and II Kummell's disease. The study suggests that the combination of bilateral cannulated screws, steerable transmidline cement delivery, and staged injection provides sustained pain relief and functional improvement. Crucially, the technique offers a durable correction of vertebral height and kyphosis, potentially preventing the common long-term complications of cement loosening and vertebral re-collapse associated with conventional PVP or PKP.

The paper maintains a modest tone regarding its conclusions, acknowledging limitations such as the small sample size (n=38), single-center design, lack of a randomized control group, and a follow-up period (mean 17.2 months) that, while mid-to-long term, is insufficient to evaluate stability over periods exceeding five years. The authors conclude that while the preliminary results are promising, further multicenter, large-sample, randomized controlled studies with prolonged follow-up are necessary to fully verify the long-term clinical value of this surgical technique.