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

*Bibliography: TheSpine Journal1(2001)402-407.

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.