Radiofrequency-activated PMMA-augmentation through cannulated pedicle screws: A cadaver study to determine the biomechanical benefits in the osteoporotic spine.

INTRODUCTION: PMMA-augmentation of pedicle screws strengthens the bone-screw-interface reducing cut-out risk. Injection of fluid cement bears a higher risk of extravasation, with difficulty of application because of inconsistent viscosity and limited injection time. OBJECTIVE: To test a new method of cement augmentation of pedicle screws using radiofrequency-activated PMMA, which is suspected to be easier to apply and have less extravasations. METHODS: Twenty-seven fresh-frozen human cadaver lumbar spines were divided into 18 osteoporotic (BMD ≤ 0.8 g/cm2) and 9 non-osteoporotic (BMD > 0.8 g/cm2) vertebral bodies. Bipedicular cannulated pedicle screws were implanted into the vertebral bodies; right screws were augmented with ultra-high viscosity PMMA, whereas un-cemented left pedicle screws served as negative controls. Cement distribution was controlled with fluoroscopy and CT scans. Axial pullout forces of the screws were measured with a material testing machine, and results were analyzed statistically. RESULTS: Fluoroscopy and CT scans showed that in all cases an adequately big cement depot with homogenous form and no signs of extravasation was injected. Pullout forces showed significant differences (p < 0.001) between the augmented and non-augmented pedicle screws for bone densities below 0.8 g/cm2 (661.9 N ± 439) and over 0.8 g/cm2 (744.9 N ± 415). CONCLUSIONS: Pullout-forces were significantly increased in osteoporotic as well as in non-osteoporotic vertebral bodies without a significant difference between these groups using this standardized, simple procedure with increased control and less complications like extravasation.

[Surgical treatment of sternoclavicular joint instability with tenodesis]. / Die operative Therapie der sternoklavikulären Instabilität mittels Tenodese.

BACKGROUND: Instability of the sternoclavicular joint is a very uncommon disorder of the shoulder girdle. Acute traumatic dislocations are commonly treated nonoperatively. But severe displacement or chronic instability with recurrent symptomatic subluxation may require surgical intervention. We present our results with open reduction and internal fixation through an autologous gracilis tendon transplant or fiber tape in 8 patients treated surgically. The operative stabilisation of the sternoclavicular joint reduces pain level and improves function of the shoulder. This technique provides an effective surgical procedure for treatment of symptomatic sternoclavicular joint instability. OBJECTIVE: Restoration of the function and aspect of the sternoclavicular joint. INDICATIONS: Chronic and painful instabilities. CONTRAINDICATIONS: Local infection, tumor. SURGICAL TECHNIQUE: The gracilis tendon graft is harvested as previously described by Petersen. Direct incision over the sternoclavicular joint. Sharp dissection of the periostal sleeve and partial release of sternocleidomastoideus and pextoralis muscle. Resection of osteophytes. Careful placement of a raspatorium under the proximal clavicle and sternum to protect the mediastinal structures. Application of 2.5 or 3.2 mm drill holes to the sternum and the proximal clavicle. The gracilis tendon or the fiber tape is pulled through the drill holes in a figure of eight and then sutured. Recontruction of the joint capsule, closure of the wound. POSTOPERATIVE MANAGEMENT: Gilchrist brace for 3-5 days, functional physiotherapy with a maximum abduction of 90° for 6 weeks. No carrying or lifting of weights greater than 5 kg for 3 months. RESULTS: During the period from January 2006 to December 2010, 8 patients with sternoclavicular instability were treated. Four patients were treated with fiber tape and four were treated with a gracilis tendon autograft. Postoperative all patients described a reduction of pain and improved shoulder function. The Constant score was 72 points, the DASH 58 points.

PMMA-augmentation of incompletely cannulated pedicle screws: a cadaver study to determine the benefits in the osteoporotic spine.

BACKGROUND: Pedicle screw pullout due to poor bone quality, mainly caused by osteoporosis, is a common problem in spine surgery. Special implants and techniques, especially PMMA augmentation, were developed to improve the fixation of pedicle screws. PMMA injection into a pilot hole or through a screw involves the same risks as vertebroplasty or kyphoplasty, regardless of the technique used. Especially when using fully cannulated screws anterior leakage is possible. OBJECTIVE: To prove PMMA injection is safe and possible without leakage through an incompletely cannulated screw and also increases pullout forces in the osteoporotic vertebra. METHODS: Incompletely cannulated pedicle screws were tested by axial pullout in human cadavers, divided into osteoporotic and non-osteoporotic groups. Non-augmented and PMMA-augmented pedicle screws were compared. Twenty-five human vertebrae were measured by DEXA and divided into osteoporotic and non-osteoporotic groups. In each vertebra both pedicles were instrumented with the new screw (WSI-Expertise 6×45 mm, Peter Brehm Inc. Germany); the right screw was augmented with a 3 mL PMMA injection through the screw. On each screw axial pullout was performed after X-ray and CT scan. RESULTS: Radiographs and CT scans excluded PMMA leakage. Cement was distributed in the middle and posterior third of the vertebrae. Pullout forces were significantly higher after pedicle screw augmentation, especially in the osteoporotic bone. All augmented pedicle screws showed higher pullout forces compared with the unaugmented screws. CONCLUSIONS: We minimized the risk of leakage by using a screw with a closed tip. On the whole, PMMA augmentation through an incompletely cannulated pedicle screw is safe and increases pullout forces in osteoporotic bone to the level of healthy bone. Therefore the new incompletely cannulated screw can be used for pedicle screw augmentation.

[PMMA augmentation of pedicle screws: results of a survey in Germany]. / PMMA-Augmentation von Pedikelschrauben: Ergebnisse einer Umfrage in Deutschland.

BACKGROUND: The anchorage of pedicle screws can be challenging in the osteoporotic spine. A promising technique are cement augumented pedicle screws. The goal of this study was to gain more information regarding application of pedicle screw augmentation in Germany. MATERIALS AND METHODS: Participants of the National German Spine Congress 2009 were invited to participate in an internet-based anonymous survey regarding application of pedicle screw augmentation. The questionnaire was related to different aspects of materials and procedures for pedicle screw augmentation. The frequency of answers was divided according to the specialty state of the surgeons: orthopaedic and trauma surgeons vs. neurosurgeons. The Mantel-Haenszel test was applied to evaluate the differences between the groups. RESULTS AND CONCLUSION: 69 (64 %) orthopaedic and trauma surgeons and 39 (36 %) neurosurgeons participated (n = 108). Nearly 80 % of the participants use cement-augmented pedicle screws in their daily practice. Almost 2/3 of the specialists apply cannulated screws or other special screws. The Expedium (Company) screws are particularly preferred. The insertion of screws is combined with kyphoplasty or vertebroplasty in 20 % of the cases. The balloon kyphoplasty was applied most commonly. There was no statistical difference between the surgeon groups regarding the different techniques. The main indications for pedicle screw augmentation were osteoporosis, intraoperative findings as well as loosening of screws, and revision. The most frequently observed complication is cement extravasation into the spinal canal (28 %). The cost issue is considered as being important but unknown to most of the participants. It can be assumed that the use of pedicle screws in Germany is well established in spine surgery, without as yet a standard technique being established.