γδT Cells Are Essential for Orthodontic Tooth Movement

Sustained mechanical forces applied to tissue are known to shape local immunity. In the oral mucosa, mechanical stress, either naturally induced by masticatory forces or externally via mechanical loading during orthodontic tooth movement (OTM), is translated, in part, by T cells to alveolar bone resorption. Nevertheless, despite being considered critical for OTM, depletion of CD4⁺ and CD8⁺ T cells is reported to have no impact on tooth movement, thus questioning the function of αβT cells in OTM-associated bone resorption. To further address the role of T cells in OTM, we first characterized the leukocytes residing in the periodontal ligament (PDL), the tissue of interest during OTM, and compared it to the neighboring gingiva. Unlike the gingiva, monocytes and neutrophils represent the major leukocytes of the PDL. These myeloid cells were also the main leukocytes in the PDL of germ-free mice, although at lower levels than SPF mice. T lymphocytes were more enriched in the gingiva than the PDL, yet in both tissues, the relative fraction of the γδT cells was higher than the αβ T cells. We thus sought to examine the role of γδT cells in OTM. γδT cells residing in the PDL were mainly Vγ6⁺ and produced interleukin (IL)-17A but not interferon-γ. Using Tcrd-GDL mice allowing conditional ablation of γδT cells in vivo, we demonstrate that OTM was greatly diminished in the absence of γδT cells. Further analysis revealed that ablation of γδT cells decreased early IL-17A expression, monocyte and neutrophil recruitment, and the expression of the osteoclastogenic molecule receptor activator of nuclear factor-κβ ligand. This, eventually, resulted in reduced numbers of osteoclasts in the pressure site during OTM. Collectively, our data suggest that γδT cells are essential in OTM for translating orthodontic mechanical forces to bone resorption, required for relocating the tooth in the alveolar bone.

Development and Function of γδT Cells in the Oral Mucosa

To successfully withstand a wide variety of microbial and mechanical challenges, the immune system of the oral mucosa is composed of tissue-resident and specially recruited leukocytes. These leukocytes facilitate the establishment and maintenance of local homeostasis but are also capable to cause oral pathologies when are unrestrained. γδT cells represent an important tissue-resident innate T-cell population in various mucosal and nonmucosal barrier tissues, in which they are ideally located to assist in immunosurveillance, tissue repair, and homeostasis. Whereas most works studying γδT cells were focused on tissues such as the skin and intestine, these cells in the oral mucosa were only recently thoroughly studied. The findings obtained by those studies appear to be both complementary and contradicting, likely reflecting differences in the experimental settings and the type of transgenic mouse modalities employed by each study. Nevertheless, oral γδT cells were shown to consist of developmentally distinct tissue-resident Vγ6 cells and circulating Vγ1 and Vγ4 subsets that are independently maintained in the oral mucosa. In the gingiva, a particularly challenging barrier tissue due to its proximity to the dental plaque, γδT cells are strategically positioned close to the plaque and represent the major source of IL-17. While this suggests that γδT cells might be involved in controlling the dental biofilm, conflicting data were reported in this regard. In vivo studies have shown that γδT cells either play a protective role during age-associated bone loss or, alternatively, have no impact in this process. Also, recent reports suggested opposing data concerning the impact of γδT cells in experimental periodontitis based on the ligature model. This review summarizes and discusses the most up-to-date literature on oral γδT cells, providing a balanced perspective regarding our current understanding on the development of oral γδT cells and their role under physiologic conditions and certain oral pathologies.

2D-fluoroscopic based navigation for Gamma 3 nail insertion versus conventional procedure- a feasibility study

Background

Intramedullary nailing is a standard surgical procedure for fixation of proximal femoral fractures, but is associated with considerable radiation exposure for controlling the implant placement, due to the percutaneous insertion technique.

The aim of this study was the evaluation of potential benefits of 2D-fluoroscopic based navigation focused on the reduction of radiation exposure, a decrease of procedure time, as well as an increase of accuracy for Gamma3 nail insertions.

Methods

Twenty randomized Gamma3 nail insertions were performed in non-fractured synthetic femora according to the manufactures operation guidelines (group I) or with use of a 2D-fluoroscopic based navigation system (group II). Time of different steps of the procedure and the radiation exposure were measured, as well as the accuracy evaluated in postoperative CT scans.

Results and discussion

All Gamma3 nails were placed without any technical problems. Independent of the used procedure, the overall operating time (group I: 584 ± 99.2 sec; group II: 662 ± 64.9 sec; p=0.06) and accuracy of the final nail-positions were equivalent, but the radiation exposure was significantly reduced (92% reduction in fluoroscopic images and 91% reduction in fluoroscopic time, p< 0.01), using the 2D fluoroscopic based navigation procedure.

Conclusions

2D-fluoroscopic based navigation for Gamma3 nail insertion facilitates a relevant reduction of radiation exposure with equivalent accuracy of the final implant position and no prolonged operating time. This promising procedure modification is independent of different cephalomedullary implant manufacturers and specific implant designs, but needs to be evaluated in further clinical settings.

[Delayed diagnosis of fractures of the capitulum of the humerus. Successful internal fixation 6 weeks after the accident]

Fractures of the capitulum of the humerus are rare and difficult to recognize. At present conservative therapy is only indicated in a few cases with no dislocation of the fracture. Otherwise an anatomical reduction and internal fixation should be done as early as possible. This article reports the case of a 51-year-old female patient with bilateral fractures of the capitulum of the humerus which were diagnosed 6 weeks after trauma. In spite of the extra risk of fragment necrosis, a reduction and internal fixation were performed. After rehabilitation, the patient was free of complaints except for a minimal limited range of motion.

[Sustentaculum tali screw placement for calcaneus fractures--different navigation procedures compared to the conventional technique]

AIM

Precise placement of the sustentaculum tali screw is essential for fixation of calcaneus fractures to achieve the best fixation strength. In the clinical practice, this procedure is demanding due to the complex anatomic configuration of the calcaneus and the limited visualisation in the intraoperative fluoroscopic images. The aim of this study was an evaluation of the accuracy for the sustentaculum tali screw placement by using different navigation procedures compared to the standard procedure. The different navigation specific workflows were evaluated and the feasibility of each procedure proven in clinical applications.

METHOD

Eight sustentaculum screws per group were placed in an artifical Synbone model. Different navigation procedures were evaluated: 2D-fluoroscopy (group I), 3D-fluoroscopy (group II), fluoro-free (group III) and compared to the conventional screw placement without navigation (group IV). For each screw the time of fluoroscopy and the duration of the procedure were measured. The accuracy was evaluated postoperatively by computed tomography using axial slices and coronary as well as sagittal reformations. Furthermore, the workflow of each navigation procedure was analysed and proven in clinical applications.

RESULTS

In the experimental setup, no radiation exposure was mandatory for the conventional and fluoro-free procedures, whereas mean fluoroscopy times of 17 +/- 1.03 und 66.8 +/- 0.9 were measured for 2D- and 3D-navigation procedures. In line with this, the overall mean procedure times for the screw placement were 1.26 +/- 0.05 (group IV), 3.49 +/- 0.26 (group III), 13.32 +/- 0.49 (group I) und 19.04 +/- 1.41 minutes (group II). No significant differences were observed for the accuracy of screw placement. In the clinical practice a better orientation was achieved by use of a navigation system. The fluoro-free procedure can be easily integrated into the common operation workflow, whereas the workflow of both image-based navigation procedures is technically demanding.

CONCLUSION

Navigation procedures seem to be helpful for the precise placement of sustentaculum tali screws in cases of operative calcaneus fracture fixation. The kind of application to be used depends on the infrastructure of the department and the navigation-experience of the operating room team. Whereas the fluoro-free procedure is intuitive in use, the 2D-navigation does not justify the extra efforts. The 3D-procedure is the recommended application for surgeons familiar with navigation, providing the best orientation due to the slice image visualisation in all three dimensions.

[Necrotizing fasciitis after "banal" back pain. An unusual course of a retrocoecal appendicitis and its sequellae]

Necrotizing fasciitis is a life-threatening disease which can only be successfully treated by an interdisciplinary team. An immediate and radical debridement with opening of all compartments and debridement of the affected fascia is the basis for a successful therapy. We report about the treatment of a 21-year-old man who was taken to hospital due to "banal" back pain which was caused by a perforated appendicitis. In only 2 days necrotizing fasciitis developed which spread out over the complete right leg.

Differenzierte Behandlung beidseitiger distaler Tibiapseudarthrosen

Operative treatment of distal tibial fractures remains a challenge for the surgeon even today. The soft tissues demand atraumatic operative techniques, although an anatomical reduction of the articular fracture component is mandatory. The nonunion rate increases with disturbed local blood supply, widened fracture gap, unstable fixation. If a nonunion occurs, an individual treatment concept is required, so that even difficult situations can be successfully managed, as described in our case with bilateral tibial nonunions.

[Effects of harvesting the central third of the patella tendon on the kinetics of the knee joint and the retropatellar pressure]

AIM

This biomechanical study was performed to evaluate the consequences of removing the central part of the patellar tendon on the kinematics and kinetics of the femoro-patellar joint. The tendonectomy was performed in the same manner as is frequently done during anterior cruciate ligament reconstructions. Of particular interest in this study was to identify potential factors of the patellar tendon resection which could result in anterior knee pain.

METHOD

A simulated isokinetic knee extension from 120 degrees of flexion to full extension was performed on nine human knee cadaver specimens. Joint kinematics was evaluated with ultrasound sensors, and retropatellar contact pressure was measured using a thin-film resistive ink pressure measuring system. Data were taken before and after resection of the central third of the patellar tendon.

RESULTS

Harvesting of the central third of the patellar tendon resulted in an elongation of the remaining patellar tendon by less then 0.5 mm. Furthermore, increases in patellar flexion lower than 1 degree were observed. Small changes in retropatellar pressure were also observed.

CONCLUSION

The shortening of the patellar tendon due to tendon removal, as already suggested in several previous studies, is not attributed to the removal of the central portion of the tendon itself, but more likely due to secondary scarring contraction of the tissue. The changes of the patellarkinematics and the retropatellar pressure observed in this study are probably not of any clinical significance.