gms | German Medical Science

The external transpedicular spine fixation was first described in 1977 by Magerl [16]. Using long Schantz screws and an adjustable external fixation device, the system could be applied in a neutral as well as in a distraction or compression mode. Considering a follow up of 52 patients with acute spinal trauma, osteomyelitis and decompression, there was no deep infection and loosing of the screws occurred only in one case [17]. Jeanneret and Magerl proposed the external spine fixation for treatment of vertebral infections with minimally bone loss, inadequate orthotic stabilization and the presence of infected wounds [12]. Biomechanical examinations revealed higher bending moments for the external fixation than for other stabilization systems [30]. Möckel et al. used the percutaneous external fixator for the reduction of A3 fractures, to enable a stand alone anterior internal fixation [19]. Reyes-Sánchez et al. recommended the external spine fixation for the dynamic correction of severe scoliosis [25]. Other authors suggested the external skeletal spine fixation to improve the predictability of lumbar arthrodesis [2].

Magerl’s external four point fixation was the precursor for the internal spine fixation systems [6].

A 50-year-old man suffered a L1 burst fracture (A3.3) in a car accident. Due to a septic implant loosening one year after surgery, the complete implant removal was required. Because of the existing instability and the critical posterior wound conditions with abscess formation in trunk muscles, an external posterior spine fixation was necessary. The following anterior and posterior surgical debridement was supported by local and systemic antibiotics and led to eradication of the infection. The definitive internal spine fixation was performed after 4 weeks (Figure 1 [Fig. 1], Figure 2 [Fig. 2], Figure 3 [Fig. 3]).

A 72-year-old female patient was moved into our hospital with a progressive incomplete spinal cord injury syndrome. She recognized a weakness of her legs and ataxia as well as urinary and rectal dysfunction since 4 days. Two years ago she underwent a posterior stabilization and lumbar interbody fusion due to L2/3 degeneration. The MRI revealed a pronounced inflammation of the posterior parts of spine as well as a septic pedicle screw loosening. Due to the extended anterior and posterior spread of the infection, screw removal was inevitable. The retroperitoneal and posterior surgical debridement was followed by an anterior antibiotic chain interposition and a posterior vacuum closure application. The necessary stability was achieved by temporary external long segment stabilization. After repetitive surgical debridement und soft tissue conditioning the definitive internal instrumentation was possible after 4 weeks (Figure 4 [Fig. 4], Figure 5 [Fig. 5], Figure 6 [Fig. 6], Figure 7 [Fig. 7]).

An 84-year-old female patient underwent surgery, due to a progressive kyphotic deformity and spinal cord compression after L1 fracture in severe osteoporosis 8 weeks ago. She was moved to hospital with extended wound necrosis and exogenous vertebral infection after long segment posterior stabilization. The critical soft tissue conditions and septic pedicle screw loosening required a complete implant removal. Because of the large decompression zone, an external spine fixation was necessary to ensure stability. Repetitive surgical debridement, local and systemic antibiotics and vacuum closure therapy led to soft tissue recovery and CRP normalization. The definitive internal stabilization and wound closure occurred after 4 weeks (Figure 8 [Fig. 8], Figure 9 [Fig. 9], Figure 10 [Fig. 10], Figure 11 [Fig. 11], Figure 12 [Fig. 12], Figure 13 [Fig. 13], Figure 14 [Fig. 14]).

The incidence of the non-specific vertebral osteomyelitis is around 1:250,000 and represents 3–5% of all bone infections [5], [32]. There is an accumulation between 50–70 years. Men are 1.5 to 2 times more involved than women [20]. Depending on the kind of pathogen are distinguished pyogenic, granulomatous and parasitic vertebral infections. Pathogenesis differentiates endogenous forms from exogenous spondylodiscitis. Endogenous forms occur by haematogenous and lymphogenous spread or a direct infiltration from adjacent infected tissues and organs. Interventional therapy and spine surgery are the main cause for exogenous vertebral osteomyelitis. The incidence amounts between 0.1 and 0.6% after micro surgery and between 1.4 to 3% after macro surgery [32]. Vascular supply of the vertebral bodies and intervertebral discs is crucial for the pathophysiology. There is no vascular perfusion in the mature discs. The segmental arteries are end arteries without any anastomoses. The septic infarction of the end arteries leads to osteonecrosis with wedge formation, vertebral compression fracture, spinal instability and deformity with the risk of spinal cord compression [24], [31]. The infection spreading leads to abscess formation and deterioration of neurological deficits. Predisposing factors for the spondylodiscitis are: age [3], spine surgery and visceral surgery [7], diabetes mellitus [14], cardiovascular diseases, renal failure, rheumatism, immunodeficiency [34], drug abuse and HIV [23]. More than 90% are monomicrobial infections. The predominant pathogen is staphylococcus aureus (range 20–84%), followed by enterobacteriaceae (7–33%) and streptococci (5–20%). Coagulase negative staphylococci represent 16% and anaerobes less than 4% [10]. The lumbar spine is affected in 58%, followed by the thoracic (30%) and cervical (12%) spine [20]. The diagnosis is often delayed due to the uncharacteristic symptoms. Non-specific back or neck pain is common. 15% are pain free [27]. Fever is present in 50% [20]. Neurological deficits such as paralysis or sensory deficits, sphincter and urinary dysfunction are present in a third of cases [20]. Dysphagia and torti collis might be a leading symptom when the cervical spine is affected [1]. Although the mortality is reduced since the era of the antibiotics (today under 5%), the outcome is dependent on an early diagnosis and therapy [28]. Instabilities, deformities and the infection spreading are often associated with neurological deficits. Motoric deficits remain in 30% and sensory deficits in 90% [35]. Recurrent infections are reported in 7% [32].

C-reactive protein is the most important laboratory parameter. It is increased in most cases and a decisive trend parameter [5], [11]. Blood cell sedimentation rate and leukocytes are not specific. Blood cultures are positive in 70% [21]. Detection of the pathogen is crucial for the success of the antibiotic therapy. Percutaneous biopsy is positive in 43–78% [33]. Open biopsy is recommended in the absence of pathogen-proof [17]. Histology is important to exclude malignant processes [21].

MRI is the modality of choice for the radiological diagnosis. It has a reported sensitivity of 96% and specificity of 93%. Decreased signal intensity from disc and adjacent vertebral bodies on T1-weighted images and increased signal intensity on T2-weighted images are typical for the osteomyelitis. Gadolinium enhancement differentiates the vertebral osteomyelitis from degenerative and malignant processes. Due to the persistence of radiological alterations, the MRI control is recommended after 8 weeks [4]. The PET CT is another diagnostic modality. Its availability is limited. It has a reported sensitivity of 100% and a specificity of 90.5% with an excellent distinction between degeneration and inflammation.

There are no prospective and randomized studies for therapy recommendation, neither for surgical nor antibiotic therapy. Duration of the antibiotic therapy is not uniform – periods between 6 and 14 weeks are reported in literature [18]. Roblot et al. found no correlation between the duration and the re-infection rate [26].

The conservative treatment is justified in vertebral osteomyelitis with mild symptoms, absence of instabilities and abscess formations. Surgery is recommended if there is no improvement of the clinical findings after 6 to 8 weeks, or there is deterioration in the MRI control [29]. An early re-evaluation is necessary to avoid pseudarthrosis (up to 50%), instabilities, deformities, neurological deficits and chronic pain [32]. Otherwise, surgery is inevitable. The aim of the surgical therapy is the eradication of the infection and the reconstruction of the sagittal profile [9]. There is also no standard procedure in surgery: posterior, anterior or combined procedures are recommended. However, surgical debridement and stable internal fixation of the involved segments leads to healing of the most endogenous vertebral infections.

The major challenge is the therapy of the exogenous vertebral infections, especially after macro surgery. These infections are complicated by the impairment of the posterior parts of the vertebral column (necrosis and infection of trunk muscles, subcutaneous layer and skin). In these cases an implant removal is inevitable. This results in another complication: iatrogenic instability. Because of the extent of the posterior decompression, the stand alone anterior instrumentation is not possible in most cases. There is a need for a posterior stabilization. If the local findings prohibit an internal stabilization, the temporary external spine fixation is an alternative, till the wound closure is possible. As mentioned above the biomechanical properties are excellent. The external stabilization enables sufficient stability and thereby supports the soft tissue conditioning, e.g. using VAC therapy.

The patients benefit from the early mobilization. Isometric muscle training, postural and breathing exercises start directly after surgery.

However, the percutaneous Schantz screw implantation is risky. Screw malpositions occur in 25%. Nerve irritation, liquor leakage and superficial infections are described. Pin track infections are described in over 50% [8], [13], [22]. The after care is sophisticated. Especially the supine position is uncomfortable – an individually adapted foam mattress is necessary.

The therapy of the endogenous and exogenous vertebral osteomyelitis is an individual therapy. The challenge is eradication of the infection and reconstruction of the alignment. Therefore, different surgical and non surgical procedures are proposed.

The external spine fixation is a salvage procedure in the management of the exogenous spine infection with critical soft tissue conditions. Its use is always an individually decision.

The incidence of the vertebral osteomyelitis is rare. However, due to the increasing spine surgery, the risk of exogenous vertebral infections will increase. In contrast to the endogenous form, the main problem of the exogenous vertebral infection is the involvement of the posterior parts of the spine. This is a major challenge for the spine surgeon and requires an individually therapy regime. We demonstrated three cases of exogenous spine infections and presented the modality of temporary external spine fixation, till the soft tissue conditions allowed a definitive internal stabilization.

The external spine fixation is a salvage procedure in the treatment of exogenous spine infections. Its use is always an individual decision.

The authors declare that they have no competing interests.