McCormack and colleagues examined why pedicle screws broke after short‑segment posterior fixation of three‑column spine fractures and built a point system to grade the injury preoperatively.
Consecutive series of 28 patients with three‑column thoracic and thoracolumbar fractures fixed with short‑segment VSP plates and screws, University of Missouri, 1986 to 1988, followed at least 3 years.
Methods
Design
Retrospective review of a consecutive series
March 1986 to March 1988
Patients
28 patients with three‑column thoracic or thoracolumbar fractures or fracture‑dislocations
Aged 19 to 47
17 men and 11 women
VSP plates with first generation screws, one level above and below
Posterior autograft fusion
Mean follow‑up 4 years, minimum 3 years
Basis
Comminution on sagittal CT
Fragment apposition on axial CT
Kyphosis correction on preoperative vs postoperative films
Reference standard
Screw breakage on follow‑up radiographs or at implant removal
Key Findings
All 10 patients with broken screws scored 7 or more, and no screw broke in any patient scoring 6 or less.
Half of the patients with broken screws (5 of 10) had the maximum score of 9.
Only 1 of the 10 patients with screw breakage lost reduction, and the other 9 breakages were minimally displaced.
Most broken screws were not visible on radiographs and were found only when the implants were removed.
The authors reported no screw fractures in any anterior or posterior implant after 1988.
The authors note the score does not grade ligament damage, so it cannot be used to make decisions on surgical indications.
Board pearl
Burst fractures scoring 7 or more points broke short‑segment posterior screws. For these the authors added short‑segment anterior vertebrectomy and strut graft fusion.
Load sharing classificationMcCormack, Spine (Phila Pa 1976) 1994
Factor
1 pt
2 pts
3 pts
Comminution (sagittal CT)
≤30% of body
30% to 60%
>60%
Fragment apposition (axial CT)
0 to 1 mm displacement
≥2 mm in <50% of cross‑section
≥2 mm in >50% of cross‑section
Kyphosis correction (plain films)
≤3°
4° to 9°
≥10°
Comminution (sagittal CT)
1 pt≤30% of body
2 pts30% to 60%
3 pts>60%
Fragment apposition (axial CT)
1 pt0 to 1 mm displacement
2 pts≥2 mm in <50% of cross‑section
3 pts≥2 mm in >50% of cross‑section
Kyphosis correction (plain films)
1 pt≤3°
2 pts4° to 9°
3 pts≥10°
Total score
3 to 6No screw fractures in this series.
7 to 9Every screw fracture in this series occurred in this range.
Authors' conclusion
This point system can be used preoperatively to: 1) predict screw breakage when short segment, posteriorly placed pedicle screw implants are being used, 2) describe any spinal injury for retrospective studies, or 3) select spinal fractures for anterior reconstruction with strut graft, short-segment-type reconstruction.
McCormack and colleagues examined why pedicle screws broke after short‑segment posterior fixation of three‑column spine fractures and built a point system to grade the injury preoperatively.
Consecutive series of 28 patients with three‑column thoracic and thoracolumbar fractures fixed with short‑segment VSP plates and screws, University of Missouri, 1986 to 1988, followed at least 3 years.
Methods
Design
Retrospective review of a consecutive series
March 1986 to March 1988
Patients
28 patients with three‑column thoracic or thoracolumbar fractures or fracture‑dislocations
Aged 19 to 47
17 men and 11 women
VSP plates with first generation screws, one level above and below
Posterior autograft fusion
Mean follow‑up 4 years, minimum 3 years
Basis
Comminution on sagittal CT
Fragment apposition on axial CT
Kyphosis correction on preoperative vs postoperative films
Reference standard
Screw breakage on follow‑up radiographs or at implant removal
Key Findings
All 10 patients with broken screws scored 7 or more, and no screw broke in any patient scoring 6 or less.
Half of the patients with broken screws (5 of 10) had the maximum score of 9.
Only 1 of the 10 patients with screw breakage lost reduction, and the other 9 breakages were minimally displaced.
Most broken screws were not visible on radiographs and were found only when the implants were removed.
The authors reported no screw fractures in any anterior or posterior implant after 1988.
The authors note the score does not grade ligament damage, so it cannot be used to make decisions on surgical indications.
Board pearl
Burst fractures scoring 7 or more points broke short‑segment posterior screws. For these the authors added short‑segment anterior vertebrectomy and strut graft fusion.
Load sharing classificationMcCormack, Spine (Phila Pa 1976) 1994
Factor
1 pt
2 pts
3 pts
Comminution (sagittal CT)
≤30% of body
30% to 60%
>60%
Fragment apposition (axial CT)
0 to 1 mm displacement
≥2 mm in <50% of cross‑section
≥2 mm in >50% of cross‑section
Kyphosis correction (plain films)
≤3°
4° to 9°
≥10°
Comminution (sagittal CT)
1 pt≤30% of body
2 pts30% to 60%
3 pts>60%
Fragment apposition (axial CT)
1 pt0 to 1 mm displacement
2 pts≥2 mm in <50% of cross‑section
3 pts≥2 mm in >50% of cross‑section
Kyphosis correction (plain films)
1 pt≤3°
2 pts4° to 9°
3 pts≥10°
Total score
3 to 6No screw fractures in this series.
7 to 9Every screw fracture in this series occurred in this range.
Authors' conclusion
This point system can be used preoperatively to: 1) predict screw breakage when short segment, posteriorly placed pedicle screw implants are being used, 2) describe any spinal injury for retrospective studies, or 3) select spinal fractures for anterior reconstruction with strut graft, short-segment-type reconstruction.