Outcomes of Allogenic Cages in ALIF and PLIF: Outcomes

A total of 179 FRA Cages were utilized for anterior reconstruction in 137 patients from March 1998 to July 2000. There were 89 men and 48 women. The age range of the patients was from 19 to 73 years, with the average age being 45 years. Sixty-five patients from this group also exhibited comorbidities including smoking (n=46), obesity (defined as > 20% of the ideal body weight, n=12), and diabetes (n=7) (Table 1).

Table 1. Patient Characteristics

 
FRA Spacer
PLIF Spacer
 
(n=137)
(n=13)
Mean age (years)
45
54
Females (n)
48
8
Males (n)
89
5
Smokers (n)
46
4
Obese patients (n)
12
0
Diabetic patients (n)
7
0

The most common preoperative diagnoses were internal disc disruption with disc resorptive syndrome, instability/spondylolisthesis, recurrent disc herniation with instability, degenerative scoliosis, vertebral osteomyelitis, and previous posterolateral arthrodesis that required additional anterior column support. Anterior "stand-alone" devices were used in about 25% (33 /137) of the patients, while the majority of the patients (104/137) had additional posterior instrumentation. Additional posterior pedicle screw fixation was utilized in 49 patients, and translaminar screws (n=55) were more frequently used (Table 2). The additional posterior instrumentation in general, is widely accepted by orthopedic surgeons to provide rigidity, improve fusion rates, reduce post-operative morbidity, and to correct deformity [27]. Pedicle screws were used in patients who had spondylolisthesis, instability, or previous wide decompressive procedures. Patients with pedicle screws more often reported increased myofascial pain most likely secondary to greater soft tissue dissection and surgical exposure. Translaminar screws can be inserted with less dissection and tend to result in less postoperative morbidity. However, there was no difference in the fusion rate whether pedicle screws or translaminar screws were used in this series.

Table 2. Method of Arthrodesis

 
ALIF
alone
ALIF with
posterior
PLIF with
posterior fusion
 
(n=33)
(n=104)
(n=13)
FRA spacers (n)
35
144
-
PLIF spacers (n)
-
-
30
Pedicle screw fixation (n)
0
49
12
Translaminar screw fixation (n)
0
55
1
One-level fusion (n)
27
71
11
Two-level fusion (n)
4
35
2
Three-level fusion (n)
0
1
0

The majority of the patients (n=98) received one biological FRA Spacer, while 39 required two-level biological cages, and only one patient received three-level implants (Table 2). The most common motion segment fused was L5-S1. Patients had either autograft (n=117) taken from the patient's iliac crest, demineralized bone matrix (n=13) or some other graft material (n=2) packed into and around the FRA Spacer to promote a biological environment for arthrodesis. No differences in fusion rates were observed in patients that received autogenous bone versus patients with demineralized bone matrix. Additional postoperative orthosis was not indicated in any of the anterior column support patients. The radiographic outcomes were favorable for the majority (94%) of the patients and therefore demonstrate that arthrodesis was achieved with the biological bone spacer (Figure 5a-c). These results support the theory that additional posterior column fixation predictably achieves a greater incidence of successful anterior interbody fusion. The longest follow-up in this series of patients was 36 months, with an average follow-up of 18 months. At the time of review, there had been no evidence of bone graft rejection/resorption, migration or infection (human immunodeficiency virus, HIV; or hepatitis). Only one patient in this series had to be revised early, because of a postoperative radiculopathy that was felt to be secondary to over-distention resulting in neuropraxia to the right S1 nerve that resolved in about 6 months. One patient had radiographs that demonstrated a L4-L5 graft collapse and change in screw angulation, resulting in a segmental loss of lordosis and deformity.

postoperative lumbar x-rays
Figure 5

Figure 5. (a) Preoperative x-ray of a 40-year-old man with degenerative disc disease and instability at L5-S1. (b) X-ray (1 month after surgery) of an anterior interbody fusionwith femoral ring allograft (FRA) spacer insertion in addition to posterior fusion with translaminar screw fixation. (c) X-ray 6 months after surgery showing successful fusion with the FRA spacer in L5-S1.

Three patients requiring an anterior interbody fusion had clinical failure of the interdiscal electrothermal therapy (IDET) procedure, and in one patient, pseudoarthrosis was suspected (on plain radiographs) but solid arthrodesis was confirmed on additional imaging techniques (CT scan) (Fig. 6). Five patients treated solely with the anterior approach have required additional posterior fusions with instrumentation (5/33), secondary to either persistent pain, lucency of the implant, or motion with dynamic x-rays. Intra-operative fracture of the implant (the smallest size) occurred early in the series in five patients. These patients required removal of the fractured biological spacer and replacement at the time of the initial surgical procedure. This most commonly occurred when the trial spacer was not inserted completely prior to the implant or there was a geometrical mismatch of the endplates to the biological cage. No remaining patients demonstrated any radiographic evidence of motion or failure of consolidations.

postoperative x-rays
Figure 6

Figure 6. A 35-year-old woman had a femoral ring allograft (FRA) spacer in which pseudoarthrosis was suspected on plain films. However, this computed tomography (CT) scan showed that the patient had a solid fusion at the level of surgery.

Updated on: 09/26/12
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Outcomes in Allogenic Cages in ALIF and PLIF: Interbody Spacer
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