Less invasive lumbopelvic stabilization of posterior pelvic ring instability: technique and preliminary results

Lumbopelvic distraction stabilization with (triangular osteosynthesis) or without additional iliosacral screw allows anatomic reduction of the posterior pelvic ring after severely displaced sacral fractures, correction or resection osteotomies of malunions, respectively, septic sacroiliitis and permits early weight bearing. However, this technique is complicated by wound necrosis or infection in up to 20% to 30%. We describe our experience with a less invasive technique.

Non-photorealistic rendering of virtual implant models for computer-assisted fluoroscopy-based surgical procedures

Surgical navigation systems visualize the positions and orientations of surgical instruments and implants as graphical overlays onto a medical image of the operated anatomy on a computer monitor. The orthopaedic surgical navigation systems could be categorized according to the image modalities that are used for the visualization of surgical action. In the so-called CT-based systems or 'surgeon-defined anatomy' based systems, where a 3D volume or surface representation of the operated anatomy could be constructed from the preoperatively acquired tomographic data or through intraoperatively digitized anatomy landmarks, a photorealistic rendering of the surgical action has been identified to greatly improve usability of these navigation systems. However, this may not hold true when the virtual representation of surgical instruments and implants is superimposed onto 2D projection images in a fluoroscopy-based navigation system due to the so-called image occlusion problem. Image occlusion occurs when the field of view of the fluoroscopic image is occupied by the virtual representation of surgical implants or instruments. In these situations, the surgeon may miss part of the image details, even if transparency and/or wire-frame rendering is used. In this paper, we propose to use non-photorealistic rendering to overcome this difficulty. Laboratory testing results on foamed plastic bones during various computer-assisted fluoroscopybased surgical procedures including total hip arthroplasty and long bone fracture reduction and osteosynthesis are shown.

Posterolateral approach to the displaced posterior malleolus: functional outcome and local morbidity

BACKGROUND: Stable anatomical reconstruction of the joint surface in ankle fractures is essential to successful recovery. However, the functional outcome of fractures involving the posterior tibial plafond is often poor. We describe the morbidity and functional outcome for plate fixation of the displaced posterior malleolus using a posterolateral approach. MATERIALS AND METHODS: The posterolateral approach was used for osteosynthesis of the posterior malleolus in 45 consecutive patients (median age 54 years) with AO/Muller-classification type 44-A3 (n = 1), 44-B3 (n = 35), 44-C1 (n = 7), and 44-C2 (n = 2) ankle fractures. Thirty-three of the patients suffered complete fracture dislocation. Functional outcome at followup was measured using the modified Weber protocol and the standardized AAOS foot and ankle questionnaire. Radiological evaluation employed standardized anterior-posterior and lateral views. RESULTS: The fragment comprised a median of 24% (range, 10% to 48%) of the articular surface. Postoperative soft tissue problems were encountered in five patients (11%), one of whom required revision surgery. Two patients (4%) developed Stage I complex regional pain syndrome. Clinical and radiological followup at 25 months disclosed no secondary displacement of the fixed fragment. The median foot and ankle score was 93 (range, 58 to 100), shoe comfort score was 77 (range, 0 to 100). A median score of 7 (range, 5 to 16) was documented using the modified Weber protocol. CONCLUSION: The posterolateral approach allowed good exposure and stable fixation of a displaced posterior malleolar fragment with few local complications. The anatomical repositioning and stable fixation led to good functional and subjective outcome.

Comparison of theoretical fixation stability of three devices employed in medial opening wedge high tibial osteotomy: a finite element analysis.

BACKGROUND Medial open wedge high tibial osteotomy is a well-established procedure for the treatment of unicompartmental osteoarthritis and symptomatic varus malalignment. We hypothesized that different fixation devices generate different fixation stability profiles for the various wedge sizes in a finite element (FE) analysis. METHODS Four types of fixation were compared: 1) first and 2) second generation Puddu plates, and 3) TomoFix plate with and 4) without bone graft. Cortical and cancellous bone was modelled and five different opening wedge sizes were studied for each model. Outcome measures included: 1) stresses in bone, 2) relative displacement of the proximal and distal tibial fragments, 3) stresses in the plates, 4) stresses on the upper and lower screw surfaces in the screw channels. RESULTS The highest load for all fixation types occurred in the plate axis. For the vast majority of the wedge sizes and fixation types the shear stress (von Mises stress) was dominating in the bone independent of fixation type. The relative displacements of the tibial fragments were low (in μm range). With an increasing wedge size this displacement tended to increase for both Puddu plates and the TomoFix plate with bone graft. For the TomoFix plate without bone graft a rather opposite trend was observed.For all fixation types the occurring stresses at the screw-bone contact areas pulled at the screws and exceeded the allowable threshold of 1.2 MPa for at least one screw surface. Of the six screw surfaces that were studied, the TomoFix plate with bone graft showed a stress excess of one out of twelve and without bone graft, five out of twelve. With the Puddu plates, an excess stress occurred in the majority of screw surfaces. CONCLUSIONS The different fixation devices generate different fixation stability profiles for different opening wedge sizes. Based on the computational simulations, none of the studied osteosynthesis fixation types warranted an intransigent full weight bearing per se. The highest fixation stability was observed for the TomoFix plates and the lowest for the first generation Puddu plate. These findings were revealed in theoretical models and need to be validated in controlled clinical settings.

Periazetabuläre Frakturen bei Hüftprothesen

Periazetabuläre Frakturen bei Hüftprothesen nehmen aufgrund der Überalterung und der zunehmenden Aktivität alter Menschen zu. Die periprothetischen Azetabulumfrakturen werden anhand der Einteilung von Letournel klassifiziert. Wenn beide Azetabulumpfeiler bei Hüftprothese betroffen sind, wird auch von einer Beckendiskontinuität gesprochen. Durch eine laterale Kompression können auch periazetabuläre Schambeinastfrakturen und/oder transiliakale Frakturen auftreten. Für die Therapieentscheidung (konservativ, alleinige Osteosynthese, Revisionshüfttotalprothese mit oder ohne zusätzliche Osteosynthese des Vorder- und/oder Hinterpfeilers) und die Zugangswahl bei operativer Versorgung werden patientenspezifische (Alter, Morbidität, Osteoporose, Aktivitätslevel des Patienten), frakturspezifische (Frakturtyp, Dislokationsausmaß, Impression des Doms oder der Hinterwand) und auch prothesenspezifische Faktoren (Art der implantierten Prothese [Hemiprothese vs. Totalprothese], Pfannenstabilität, Zeichen eines Prothesenabriebs, Ausmaß und Lokalisation einer azetabulären Lyse, Stabilität und Lysezeichen des Prothesenschafts) berücksichtigt. Bei akuten Beckendiskontinuitäten werden neben einer Osteosynthese des dorsalen Pfeilers zunehmend eine schnell ossär integrierbare Pfanne (Tantalum [„Trabecular Metal“: TM]) mit oder ohne Augment und/oder Allograft und allenfalls in einer sog. „Cup-Cage“-Technik (TM-Pfanne mit einem abstützenden Revisionsring [Burch-Schneider-Ring] analog zur Therapie von chronischen Beckendiskontinuitäten empfohlen. Bei großen Lysezonen und starken Dislokationen des vorderen Pfeilers und der quadrilateralen Fläche können intrapelvine Zugänge (modifizierter Stoppa- oder Pararectus-Zugang nach Keel) zur zusätzlichen Zuggurtungsosteosynthese des vorderen Pfeilers und Abstützung der quadrilateralen Fläche gewählt werden.