Unstable Vertebral Body Fractures in Elderly Patients - How Stable is Percutaneous Internal Fixation?

Marc Chmielnicki, Reiner Stenz, Axel Prokop.

Klinikverbund Südwest (Clinics Network South West)
Germany

Address for Correspondence:
Marc Chmielnicki
Klinikverbund Südwest (Clinics Network South West)
Arthur-Gruber-Str. 70
71065 Sindelfingen, Germany

Abstract:

Introduction:

With unstable thoraco-lumbar vertebral fractures primary stabilization with internal fixator is the operative method of first choice. With osteoporosis with older patients anchoring is unsafe and vertebrae may lose height secondarily. We want to analyze retrospectively the behavior of such unstable osteoporotic fractures.

Material and Methods:

In 2007 and 2008 61 patients older than 60 years with an average age of 73 ± 8 years (60-88 years) with unstable thoraco-lumbar vertebral fractures were treated with a percutaneous internal fixator. Preoperatively, postoperatively and after six weeks of functional treatment without a brace the kyphosis angle was determined in a lateral radiography and compared with Student-t-Test. In 7 cases cement-augmented screws were used.

Results:

Kyphosis angle preoperative was 13,9 ± 9,4° and postoperative 8,1 ± 6,7°. Thus a reduction of height of 5,8 ± 5,9° (p < 0,001) was achieved by the operation. Within the first six weeks postoperative, however, loss of height of 7,7 ± 7,4° (p < 0,001) occurred, caused by cutting out of screws through the vertebra, as the screw-rod connections remained constant in all cases without significant changes. With the operations with cement-augmented screws there was no loss of height.

Unstable vertebral fractures with patients over 60 years cannot be held by the fixator alone. Loss of reduction occurred from the cutting-out of screws in osteoporotic bone. Therefore, either in one or in two operations, stabilization of ventral column must be performed, or in addition cement augmentation of pedicle screws.

J.Orthopaedics 2010;7(4)e1

Keywords:

osteoporotic fractures; thoracolumbar spine; Sextant; minimally-invasive

Introduction:

Vertebral fractures are frequent with older patients. Osteoporosis plays an important part with the outset of these fractures. By the 55^th year a significant increase of fracture-incidence can be observed (1), herewith a slight trauma can be the cause for a painful fracture of vertebra, in some cases spontaneous fractures occur without trauma. According to the classification of Magerl (2) different procedures of stabilization can be applied. Whereas compression fractures Magerl A1 and A2 can safely be treated with kyphoplasty to prevent an increasing kyphosis, to reduce vertebra and to relieve pains (3), fractures involving the back column according to Magerl A3, as well as unstable Magerl B- and C-fractures, are an indication for dorsal instrumentation (2). To stabilize in an emergency situation, open or minimally invasive percutaneous systems may be applied. At the moment, there exist several percutaneous systems for dorsal instrumentation (4,5). Minimal invasive technique allows a correct and safe placement of pedicle screws without disadvantage compared to the open method (6). Great advantages of percutaneous application are short incisions and lesser trauma to surrounding tissues. The result is less blood loss and protection of back muscles (7,8). Patients can be faster mobilized and hospital stay shortened (9,10). By a shortened operation time, a risk reduction especially with old patients succeeds (11). To avoid mechanical complications and a cut-out with old patients, pedicle screws may be augmented with cement (12).

We use the CD Horizon Sextant II^TM with cannulated polyaxial screws and the CD Horizon Longitude^TM with cannulated non-polyaxial screws of Medtronic.

The aim of our study was to find out if percutaneous procedures with patients over 60 years are prone to reach a reduction and if sufficient stability during the healing process is achieved. Further it was to be examined whether polyaxial screw-rod connections have sufficient stability.

Materials and Methods:

In 2007 and 2008 we operated altogether 61 (m:f = 23:38) (Tab. 1) patients over 60 years old with unstable monosegmental fractures of thoraco-lumbar transition and lumbar spine (Fig. 1) on a percutaneous internal fixator. After a fall besides conventional X-ray analysis in all cases a CT or MRI was required. 58 times there were Magerl A3- and in 3 cases C1-fractures. 29 patients received the CD Horizon Sextant II^TM (Fig. 2) and 32 patients the CD Horizon Longitude^TM. Median age was 73 ± 9 years (60-88 years) and did not differ significantly within both groups (p = 0,25).Because of considerable osteoporosis with radiologic rarification of trabecles primarily cement-augmented screws were used in 7 cases. PMMA-cement was introduced in the vertebral body after a kyphoplasty of screw site. Median age of patients with cemented screws was 77 ± 7 years (71-88 years).

We examined the patients in a short follow-up interval of six weeks postoperative and determined kyphosis angle as described by Kuklo et al. (13) and compared with postoperative kyphosis angle with Student-t-test. In addition, the screw-screw angle of internal fixator was measured and compared by  Student-t-test with connected probes. Error probability was determined at 0,05.

After 6 weeks with 35 patients, stabilization of ventral column was performed. In the Sextant group, the ventral column was stabilized in 18 cases (14 x Kyphoplasty, 4 x Obelisk), in the Longitude group 17 patients achieved stabilization of ventral column (14 x Kyphoplasty, 1 autologous tricortical iliac crest graft and MACS II, 2 x Obelisk). Pains were defined according to Visual analogous scale pre- and postoperatively and incision-suture time was evaluated. Intraoperative blood loss was estimated. Data analysis was done retrospectively.

Fig. 1 Localization of fracture

Fig.2 Radiographs of a case of a Th 12 fracture Magerl Classification A3 preoperative (A), postoperative (CD Horizonâ Sextant IIÔ B) an 6 weeks postoperative (C) and after ventral stabilization with a Obelisk (D)

                 A                                        B                                 C

               D

Results :

The time between incision and suture was 58 ± 38 minutes in the Sextant group, 47 ± 18 minutes in the Longitude group, and 52 ± 29 minutes in both groups combined. No significant difference was found between the two groups (p = 0.065). The hospitalization duration was 10 ± 5 days and the intraoperative blood loss 10-20 ml in both groups.

The preoperative kyphotic angle (Table 2) was 12.7 ± 6.5° in the Sextant group, 15.0 ± 11.4° in the Longitude group, and 13.9 ± 9.4° in all 61 patients. No significant difference was observed between the two groups (p = 0.17). In the Sextant group a restoration of 5.2 ± 4.5° was achieved, resulting in a kyphotic angle of 7.5 ± 5.0° (p < 0.001). In the Longitude group the kyphotic angle was reduced by 6.3 ± 7.0° to 8.7 ± 8.1° postoperatively (p < 0.001), with no significant difference between the two groups (p = 0.338).

Both groups together yielded a restoration in the kyphotic angle from 5.8 ± 5.9° to 8.1 ± 6.7° postoperatively (p < 0.001).

At 6 weeks the Sextant group showed a loss in reduction of 7.7 ± 6.6°, resulting in a kyphotic angle of 15.2 ± 9.0 ° (p < 0.001). At the same time the Longitude group revealed a loss of 7.6 ± 8.3°, resulting in a kyphotic angle of 16.3 ± 9.2 ° (p < 0.001). No significant difference was observed between the two groups (p = 0.353). The screw-rod-screw constructs remained unchanged in all groups, without significant variances.

The VAS pain scores were reduced significantly from a mean value of 6 preoperatively to 2 postoperatively (p < 0.001). In the group of patients with cement-augmented screws (n = 7, males:females = 2:5), significant reduction was achieved (p < 0.001): the preoperative kyphotic angle of 21.3 ± 8.2° was reduced by 9.5 ±  6.7 to 11.8 ± 7° postoperatively. In this group no significant losses in the restored height (p = 0.130) with secondary increase in the kyphotic angle (p = 0,426) were observed (table 2).

No neurological disorders occurred. In one case we removed a postoperative hematoma, in another case a late infection led to early removal of the internal fixation. 

Three cases of secondary screw cut-out were observed with migration of the screw tip into the intervertebral disc, requiring revision of the internal fixation including anterior stabilization. One apoplexy occurred in a female patient during hospitalization, independent of the surgical intervention. Hospital mortality amounted to 0%.

Table 1 Clinical data of patients treated

Table 2 Kyphotic angle and screw-screw angle

Discussion :

In order to prevent recurring kyphosis and neurological damage unstable vertebral fractures are indication for dorsal stabilization. Dorsal instrumentation with internal fixator here is established first treatment. By this measure a quick and safe mobilization of older patients and reduction of pains can be achieved. We postponed an immediate stabilization of ventral column to minimize preoperative mortality and morbidity and thus diminish operation risk.

Alternatively with older patients a kyphoplasty can be used as a minimally invasive procedure. In our patients base we not initially do kyphoplasty. With all fractures damage of posterior column existed, we therefore wanted to avoid dorsal and herewith spinal cement leakage which could cause neurologic damage.

Mueller et al (14) showed in their study with 36 patients with unstable burst fractures of thoraco-lumbar spine a decompression of the spinal canal of approximately 10% by ligamentotaxis. An additional decompression was not performed when neurologic symptoms were not present. Operative technique was carried through in ventral sag with non-polyaxial screws under distraction.

With our data we could show that with a percutaneous fixator even with limited distraction potential of systems alone by ventral sag an expansion of the vertebra and therewith reconstruction of alignment is possible. This reduction, however, with patients over 60 years cannot be upheld alone by the internal fixator. Within only 6 weeks, a secondary kyphosis can occur. A longer post-examination interval was deliberately not chosen, as a significant loss of reduction already after this short time occurred and one could not rely on a spontaneous reconstruction of the secondarily sintered vertebra.

As the screw-rod connection in our investigations remained without change, secondary kyphosis must be caused by a cutting out of screws through the vertebral body. McLain et al (15) could prove a similar loss of reduction of about 10° comparable to our data during healing phase of unstable thoraco-lumbar fractures in their five year follow up with their short-range instrumentation with 6 of 11 patients. An immediate ventral stabilization also with long-range instrumentation led with all patients in their study to a satisfactory clinical result, a secondary kyphosis was prevented, a loosening of internal fixator was not observed. Post-operative pain after ventral stabilization also was significantly less.

In 2009 Palmisani et al (16) compared different percutaneous fixator models with 51 patients with 64 fractures and were able to find significant loss of reduction of 3,9° after 14 months only with patients who had been treated with CD Horizon Longitude^TM with polyaxial screws. Ventral procedures were not applied. In this collective, patient age however was with 45 years distinctly younger than with our patients. Observation time was longer than in our examinations. Logroscino et al (17) used a long dorsal instrumentation with multimorbid old patients by inserting screws in 2 vertebra each above and below the fractured vertebra. In 9 examined cases in a one year follow-up no signs of loosening or fatigue of material were noticed. Therefore they considered this construction as more stable than monosegmental procedure with this patient collective. Because of small case numbers, however, further investigation with a bigger collective is demanded.

Ataka et al (18) were able to prove a loss of reduction of 4,1° in their investigations in a 25 months follow-up on 14 patients with a median age of 73 years. With unstable osteoporotic fractures, they used an internal fixator with open approach. Loss of reduction was less marked than in our study, but patient number in their study was small, thus no valid statement can be pronounced.

Numerous studies as to resistance of pedicle screws in osteoporotic bone have already been published. Thus Soshi et al (19) already in 1991 were able to prove a significant decreased resistance of screws in osteoporotic bone in a cadaver study. Mean age of participants with 71 years was comparable to our collective. In the study, they could prove - depending on the degree of osteoporosis - a 50-70% diminished strength of screws in bone. Additionally, they showed that cement augmentation led to a significant improvement of screw firmness with little and median osteoporosis (Jikei Grade I-II), with a severe osteoporosis (Jikei Grade III) no significant improvement of strength could be verified. Yet in the study, there was always chosen the pull-out strength along long axis of screw. Cutting out of screws with fixator in place however means a pull and shear movement within the vertebra. Hence, these results cannot be completely compared to our results. Biological aspects like bone growth in screw-threads, sclerosis of bone etc. are not taken into consideration in a cadaver study. We could only prove with a very small collective of 7 patients that by cement augmentation of pedicle screws an improved stability in bone of the fixator can be achieved. For valid evidence, though, bigger case numbers are needed.

The different techniques of cement augmentation were examined by Becker et al in 2008 (12) in an experimental cadaver study. Mean patient age was 79,8 years (72-89 years) and was therewith comparable to our collective. In the study the augmentation techniques of vertebroplasty, kyphoplasty and augmentation by cannulated screws were compared. Like us they used a PMMA-bone cement. They could prove a significant nearly double as high firmness in osteoporotic bone by cement augmentation with cannulated screws and with vertebroplasty-augmented screws. But they didn’t find superior firmness of screws with kyphoplasty-augmented screws. In our cases we did not either use kyphoplasty for cement augmentation, therefore we were also able with our small case number to prove a significantly increased strength of screws. After first bad experiences we abandoned cementing via perforated screws, as a percutaneous application was difficult, only possible with expensive additional modules of single-use. Frequently there were problems with cement extrusion in the thread of rod connections.

Halvorson et al (20) could also show in a cadaver study that there is a linear correlation between pull-out strength and bone density with pedicle screws. They didn’t mention patients’ age. In addition they found that predrilling of holes of pedicle screws caused a significant worsening of screw-anchoring in osteoporotic vertebra. In this study, pull-out strength was also chosen along screw long-axis. For this reason, these results are not completely comparable to our results, but they show a possible factor which might have caused instability of construction. In our case screw-holes were predrilled with a tap, lately corticalis is only cut with 2-3 screw threads. Thereby we hope to achieve increased density of spongiosa around the screws.

In our retrospective study, measuring of the bone density was not possible for no valid statement concerning bone density from MRI-pictures can be made. A quantification of bone quality could therefore not be done in our study. Following demographic investigations, we had to suppose a diminished bone quality by osteoporosis in our patient collective.

To sum up, this means that treatment of unstable vertebral fractures with osteoporotic bone quality with percutaneous fixator systems Sextant II^TM and Longitude^TM allows a reconstruction of fractured vertebra, that this reduction cannot be upheld by the fixator alone. This is caused by cutting-out of screws through the vertebral body. Cement augmentation of pedicle screws and an early stabilization of ventral column may be corrective measures.

Reference:

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19. Soshi S, Shiba R, Kondo H, Murota K (1991) An Experimental Study on a Transpedicular Screw Fixation in Relation to Osteoporosis of the Lumbar Spine. Spine 16:1335-1341

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This is a peer reviewed paper 

Please cite as: Marc Chmielnicki: Unstable Vertebral Body Fractures in Elderly Patients - How Stable is Percutaneous Internal Fixation?

J.Orthopaedics 2010;7(4)e1

URL: http://www.jortho.org/2010/7/4/e1

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