Zementaugmentierte anteriore Densverschraubung bei Densfraktur Typ Anderson II und massiver Osteoporose. Fallbeschreibung

Stent augmentation of an anterior odontoid screw for type 2 odontoid fracture-dislocation in the elderly population: Report of two cases and literature review

The fixation of type 2 odontoid fractures poses significant challenges in the elderly population due to coexistent osteoporosis and communition resulting in a high failure rate with conventional anterior screw fixation. Two elderly patients with unstable odontoid peg fractures and coexistent osteoporosis were treated with stentoplasty and anterior odontoid screw fixation. Additional anterior transarticular C1–2 screws were placed to address C1–2 instability. Both patients made an uneventful clinical recovery. One of the anterior C1–2 screws loosened due to the poor purchase in the osteoporotic bone in one patient. This did not affect the final outcome, and both the patients demonstrated maintained reduction and good alignment of odontoid peg after 2 years of follow-up. There was no intraoperative cement leak, pseudoarthrosis, or loss of reduction. Stentoplasty coupled with the anterior odontoid screw is a safe technique that can provide a biomechanically sound fixation of type 2 odontoid fractures in the presence of osteoporosis and significant communition.

Treatment of Odontoid Fractures: Recommendations of the Spine Section of the German Society for Orthopaedics and Trauma (DGOU)

STUDY DESIGN

Narrative review.

OBJECTIVE

To establish recommendations for the treatment of odontoid fractures based on current literature and the knowledge of the experts of the Spine Section of the German Society for Orthopaedics and Trauma (DGOU).

METHODS

Narrative review of the literature. Analyzing treatment algorithms of German trauma and spine centers as members of the Spine Section of the German Society for Orthopaedics and Trauma (DGOU).

RESULTS

There are many influencing factors leading to appropriate treatment of odontoid fractures such as age, bone quality, arthrosis, classification, and type of the fracture. Conservative nonoperative treatment is appropriate for stable undislocated displaced odontoid fractures. Anterior osteosynthesis with 1 or 2 screws leads to good results in the classical unstable type II odontoid fracture in patients with good bone quality. However, modifiers have been identified by the working group leading to higher complication and failure rates. For these cases, more stable constructs and/or posterior approaches are indicated.

CONCLUSIONS

Operation seems to be standard treatment for odontoid fractures. However, in the aged population, conservative treatment should be considered as morbidity and mortality rise significantly in the group of >75 years. Conservative treatment may also be started within stable nondislocated fractures, but then regular controls have to be performed. If operation is indicated, many influencing factors have to be considered for appropriate approach and technique. The classification of Anderson and D'Alonzo is still standard. To create an adequate treatment algorithm, dislocation displacement and instability have to be identified. Stable odontoid fractures are treated conservatively non-operatively, but if so regular controls have to be performed. Unstable and/or dislocated displaced odontoid fractures are treated by anterior osteosynthesis with 1 or 2 screws. The technique is demanding and leads to elevated complication and failure rates if modifiers are apparent. In these cases, posterior instrumentation or fusion of C1 and C2 is favorable. In the aged population (>80 years), operative therapy is critical as postoperative morbidity complication and mortality rates rise significantly. As there is still some bias in the treatment algorithms, the working group recommends establishment of a prospective study to result in more objective statements.

Computational anatomy of the dens axis evaluated by quantitative computed tomography: Implications for anterior screw fixation

The surgical fracture fixation of the odontoid process (dens) of the second cervical vertebra (C2/axis) is a challenging procedure, particularly in elderly patients affected by bone loss, and includes screw positioning close to vital structures. The aim of this study was to provide an extended anatomical knowledge of C2, the bone mass distribution and bone loss, and to understand the implications for anterior screw fixation. One hundred and twenty standard clinical quantitative computed tomography (QCT) scans of the intact cervical spine from 60 female and 60 male European patients, aged 18-90 years, were used to compute a three-dimensional statistical model and an averaged bone mass model of C2. Shape and size variability was assessed via principal component analysis (PCA), bone mass distribution by thresholding and via virtual core drilling, and the screw placement via virtual positioning of screw templates. Principal component analysis (PCA) revealed a highly variable anatomy of the dens with size as the predominant variation according to the first principal component (PC) whereas shape changes were primarily described by the remaining PCs. The bone mass distribution demonstrated a characteristic 3D pattern, and remained unchanged in the presence of bone loss. Virtual screw positioning of two 3.5 mm dens screws with a 1 mm safety zone was possible in 81.7% in a standard, parallel position and in additional 15.8% in a twisted position. The approach permitted a more detailed anatomical assessment of the dens axis. Combined with a preoperative QCT it may further improve the diagnostic procedure of odontoid fractures. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2154-2163, 2017.

Cement augmented anterior odontoid screw fixation is biomechanically advantageous in osteoporotic patients with Anderson Type II fractures

STUDY DESIGN

A biomechanical human cadaveric study.

OBJECTIVE

The authors tested a cannulated and perforated lag screw and compared in situ polymethylmethacrylate (PMMA) augmentation against nonaugmentation for fixation of osteoporotic type II odontoid fractures.

SUMMARY OF BACKGROUND DATA

Osteoporosis has been identified as a strong predictor for pseudarthrosis after screw fixation of type II odontoid fractures with cut-out through the anterior wall of C2 as the most frequent mode of implant failure. The concept of PMMA augmentation of the proximal screw shank could serve as a useful supplement in this context.

METHODS

A total of 18 fresh-frozen human cadaveric C2 vertebrae were harvested (median 86.5 y; range, 69-98 y). Reduced bone quality was verified by quantitative computed tomography. Type II odontoid fractures were created and repaired with a cannulated lag screw, which has perforations in the proximal screw shank. Additional PMMA augmentation was carried out for 9 specimens. The position of the screw and cement distribution were evaluated by computed tomography. Values for maximum force to failure, energy to failure, and stiffness were statistically compared between cement augmented and nonaugmented screws.

RESULTS

Cement distribution in the C2 vertebral body was circumferential around the screw shank without leakage into the spinal canal or into the fracture gap in all 9 specimens. The cement augmented screws showed a 2.4 times higher maximum force to failure (363±94 N, P<0.001), a 2.7 times higher energy to failure (1300±698 mJ, P<0.001), and a 1.76 times higher stiffness (90±35 N/mm, P=0.031) in comparison with the nonaugmented screws.

CONCLUSIONS

Cement augmentation for fixation of osteoporotic type II odontoid fractures showed biomechanical advantages. It was also shown that cement augmentation of the newly developed screw is technically easy and safe under in vitro conditions. The technique might be useful with regard to the surgical treatment of elderly patients with osteoporotic odontoid fractures.

Odontoid balloon kyphoplasty associated with screw fixation for Type II fracture in 2 elderly patients

Anterior screw fixation is a well-recognized technique that is used to stabilize Type IIB fractures of the odontoid process in the elderly. However, advanced age and osteoporosis are 2 risk factors for pseudarthrosis. Kyphoplasty has been described in the treatment of lytic lesions in C-2. The authors decided to combine these 2 techniques in the treatment of unstable fractures of the odontoid. Two approximately 90-year-old patients were treated for this type of fracture. Instability was demonstrated on dynamic radiography in one patient, and the fracture was seen on static radiography in the other. Clinical parameters, pain, range of motion, 36-Item Short Form Health Survey (SF-36) score (for the first patient), and radiological examinations (CT scans and dynamic radiographs) were studied both before and after surgery. After inflating the balloon both above and below the fracture line, the authors applied a high-viscosity polymethylmethacrylate cement. Some minor leakage of cement was noted in both cases but proved to be harmless. The screws were correctly positioned. The clinical result was excellent, both in terms of pain relief and in the fact that there was no reduction in the SF-36 score. The range of motion remained the same. A follow-up CT scan obtained 1 year later in one of the patients showed no evidence of change in the materials used, and the dynamic radiographs showed no instability. This combination of kyphoplasty and anterior screw fixation of the odontoid seems to be an interesting technique in osteoporotic Type IIB fractures of the odontoid process in the elderly, with good results both clinically and radiologically.

[Dislocation of double-threaded screws after stabilization of the odontoid process with the Knöringer technique]

A type III fracture of the odontoid process according to Anderson-D'Alonzo in a 92-year-old patient was stabilized anteriorly with two double-threaded screws using the technique of Knöringer. Postoperatively, cranial dislocation of the screws was evident and attempts to correct the screw position failed resulting in screw proximity to the brain stem. In a second revision the screws could be removed by an anterior approach and fusion was achieved by a posterior approach. Type III fractures of the odontoid process are usually stable and should be treated conservatively. In case of instability posterior stabilization techniques should be selected. Anterior osteosynthesis of the odontoid process with double-threaded screws in osteoporotic bone carries the risk of screw dislocation.

The three-dimensional morphometry of the odontoid peg and its impact on ventral screw osteosynthesis

Ventral screw osteosynthesis is a common surgical method for treating fractures of the odontoid peg, but there is still no consensus about the number and diameter of the screws to be used. The purpose of this study was to develop a more accurate measurement technique for the morphometry of the odontoid peg (dens axis) and to provide a recommendation for ventral screw osteosynthesis. Images of the cervical spine of 44 Caucasian patients, taken with a 64-line CT scanner, were evaluated using the measuring software MIMICS. All measurements were performed by two independent observers. Intraclass correlation coefficients were used to measure inter-rater variability. The mean length of the odontoid peg was 39.76 mm (SD 2.68). The mean screw entry angle α was 59.45° (SD 3.45). The mean angle between the screw and the ventral border of C2 was 13.18° (SD 2.70), the maximum possible mean converging angle of two screws was 20.35° (SD 3.24). The measurements were obtained at the level of 66% of the total odontoid peg length and showed mean values of 8.36 mm (SD 0.84) for the inner diameter in the sagittal plane and 7.35 mm (SD 0.97) in the coronal plane. The mean outer diameter of the odontoid peg was 12.88 mm (SD 0.91) in the sagittal plane and 11.77 mm (SD 1.09) in the coronal plane. The results measured at the level of 90% of the total odontoid peg length were a mean of 6.12 mm (SD 1.14) for the sagittal inner diameter and 5.50 mm (SD 1.05) for the coronal inner diameter. The mean outer diameter of the odontoid peg was 11.10 mm (SD 1.0) in the sagittal plane and 10.00 mm (SD 1.07) in the coronal plane. In order to calculate the necessary screw length using 3.5 mm cannulated screws, 1.5 mm should be added to the measured odontoid peg length when anatomical reduction seems possible. The cross-section of the odontoid peg is not circular but slightly elliptical, with a 10% greater diameter in the sagittal plane. In the majority of cases (70.5%) the odontoid peg offers enough room for two 3.5 mm cannulated cortical screws.