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2013년 10월 8일 화요일

Influence of bone mineral density on pedicle screw fixation: a study of pedicle screw fixation augmenting posterior lumbar interbody fusion in elderly patients

Brief review


*Title: Influence of bone mineral density on pedicle screw fixation: a study of pedicle screw fixation augmenting posterior lumbar interbody fusion in elderly patients
척추경나사못고정술에서 골밀도의 영향: 고령환자의 후방 요추체간 유합술에서 척추경 나사못 고정의 연구

*Author: Koichiro Okuyama, Eiji Abe, Tetsuya Suzuki, Yasuki Tamura, Mitzuho Chiba, Kozo Sato




Background context: 
-Some biomechanical studies have demonstrated that bone mineral density of the lumbar spine (BMD) affects the stability of pedicle screws in vitro.

-Common problem: screw bending, breakage, loosening(radiolucency in the bone screw interface).


Purpose: 
-To investigate influence of BMD on loosening and related failure of pedicle screws in vivo.


Study design/setting: 
-A clinical study of 52 patients who underwent pedicle screw fixation augmenting posterior lumbar interbody fusion (PLIF).


Patient sample:
Subject number: 52 patients (13 men + 39 women)

Mean age: 63 years (range, 45–76 yr)

Mean follow-up period: 2.8 years (range, 2–6 yr).


Outcome measures: 
-statistically analyzed(Relationship between BMD, screw loosening, and its related failures)


Methods:
-BMD was measured by the dual energy X-ray absorptiometry (DEXA) method.

-Two authors did radiographic assessments.

52 patients were divided into 3 groups as below.
1. Union: n=40
(no movement on the lateral view in the flx-ext in the fixed segment and continuity of trabecular bony bridging at the fixed interbody space.)

2. Non union: n=4
(any movement or discontinuity)

3. Undetermined union: n=8
(continuity of the trabecular bony bridging was vague in spite of no movement of the fixed segment in the flx-ext.)


Results:
The mean BMD values are as follow. (Unit: g/cm2 / mean±S.D.)

All patients: 0.879±0.215

Patients with or without screw loosening
-with screw loosening: 0.720±0.078 (n=11)
-without screw loosening: 0.922±0.221 (n=41).

>>Significant difference between with and without screw loosening 
(the mean BMD of patients ,P<.01).


▶Union patients
-Union patients: 0.934±0.210 (n=40)
-Non union: 0.674±0.104 (n=4)
-Undetermined union: 0.710±0.116 (n=8)

>>Union was significantly greater than those with Nonunion and Undetermined union (P<.05).




Conclusion:
-BMD has a close relation with the stability of pedicle screws


-BMD value below 0.674±0.104 g/cm2 suggests a potential increased risk of “nonunion” when pedicle screw fixation is performed in conjunction with PLIF.