Lumbar transpedicular implant failure: a clinical and surgical challenge and its radiological assessment

Abstract

Study design: It is a multicenter, controlled case study review of a big scale of pedicle-screw procedures from January 2000 to June 2010. The outcomes were compared to those with no implant failure.

Purpose: The purpose of this study was to review retrospectively the outcome of 100 patients with implant failure in comparison to 100 control-patients, and to study the causes of failure and its prevention.

Overview of literature: Transpedicular fixation is associated with risks of hardware failure, such as screw/rod breakage and/or loosening at the screw-rod interface and difficulties in the system assembly, which remain a significant clinical problem. Removal or revision of the spinal hardware is often required.

Methods: Two hundred patients (88 women, 112 men) were divided into 2 major groups, with 100 patients in group I (implant failure group G1) and 100 patients in group II (successful fusion, control group G2). We subdivided the study groups into two subgroups: subgroup a (single-level instrumented group) and subgroup b (multilevel instrumented group). The implant status was assessed based on intraoperative and follow-up radiographs.

Results: Implant failure in general was present in 36% in G1a, and in 64% in G1b, and types of implant failure included screw fracture (34%), rod fracture (24%), rod loosening (22%), screw loosening (16%), and failure of both rod and screw (4%). Most of the failures (90%) occurred within 6 months after surgery, with no reported cases 1 year postoperatively.

Conclusions: We tried to address the problem and study the causes of failure, and proposed solutions for its prevention.

Keywords: Fracture fixations, prosthesis; Fusion; Loosening; Lumbar, fixation; Screw, failure.

Fig. 1

Plain X-ray radiographs of the lumbosacral spine of different cases showing different mechanisms and forms of screw breakage.

Fig. 2

Plain X-ray radiographs of thelumbosacral spine of different cases showing different mechanisms and forms of rod breakage. Notice the points of rod failure are always near the screw-plate/rod junction (point of maximum stress).

Fig. 3

(A-C) Plain X-ray radiographs of the lumbosacral spine spine showing screw loosening: one can notice that screws are non-parallel to the endplates and there is gradual increase in the step denoting progressive instability with time.

Fig. 4

Plain X-ray radiographs of the lumbosacral spine showing screw loosening: There is bilateral loosening of more than one screw. The rods are long and the screws show loss of parallelism to the vertebral endplates.

Fig. 5

(A-D) Plain X-ray radiographs of the lumbosacral spine of different cases showing rod loosening (all are long rods transfixing multiple levels).

Fig. 6

Plain tomogram evaluation of bony fusion in the failure group (A) showing a bony bar bridging the left transverse process of L3 & L4, with incomplete merge with the later, (B) showing evidence of incomplete bony fusion between the left transverse processes of D12 and L1, with a bony bar projecting downwards from the right L1 transverse process with no definite fusion with that of L2.

Fig. 7

Plain radiography and coronal reformatted computed tomography images showing different forms of bony fusion in the control group: (A) intertransverse fusion, (B) anterior interbody bony fusion (ALIF with bone graft), (C) anterior interbody cage fusion (ALIF with cages).

Fig. 8

The load-sharing effect of different forces on deformity progression in spondylolisthesis (A); anterior column compression defects (B).

Fig. 9

Plain radiography of the lumbosacral spine showing the screw failure point (the point of maximum stresses secondary to the bending forces applied to the screw). One can note that the point is near the screw-plate/rod junction.

Fig. 10

Plain radiography of the lumbosacral spine and diagrammatic representation showing the effect of triangulation: adds more stability, increasing the chance of good grip (G2) and decreasing the chance of loosening (G1).

Fig. 11

Plain radiography showing the fundamental improvement after the addition of more fixation points in the form of a rigid cross bar (A, C) and/or extra-screws (A-C).