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The purpose of the current study was to evaluate the influence of internal and external knee rotation on tibial tunnel position measurements in anterior cruciate ligament reconstruction using the Amis and Jakob line. Anatomic double bundle ACL reconstruction was performed in seven cadaveric knees. Afterwards, the knees were CT scanned, and 3D CT models were established. Utilizing these models, strict lateral and radiographs with the knees in 5°, 10°, and 20° of internal as well as external rotation were established. Using these radiographs, the positions of the anteromedial (AM) and posterolateral (PL) tibial tunnels were measured using the Amis and Jacob line. The tunnel positions of the strict lateral were compared to the rotated radiographs. To assess the inter- and intraobserver reliability, two independent observers measured the tunnel positions, and one observer measured twice. Significant differences for the AM tunnel position were observed if more than 10° of external or 20° of internal rotation were applied. For the PL tunnel position, no significant differences were found between the strict lateral and the rotated radiographs. Inter- and intraobserver reliability was good. The accuracy of the Amis and Jakob line is dependent on the degree of knee rotation and the position of the measured tunnel. Therefore, when using the Amis and Jakob line to determine the tibial tunnel position during surgery, attention should be paid to rotational alignment of lateral radiographs. However, the maximum rotation tested in the present study (20°) showed only a difference in tunnel position of 3.3 % compared to optimal rotational alignment. Thus, in most cases, the effects of minor malrotation on tunnel position measurement should be of minimal clinical significance. Diagnostic study.

Press-fit fixation of patellar tendon bone anterior cruciate ligament autografts is an interesting technique because no hardware is necessary. To date, no biomechanical data exist describing an implant-free double-bundle press-fit procedure. The purpose of this study was to characterize the biomechanical properties of three double-bundle press-fit fixations.In a controlled laboratory study, the patellar-, quadriceps- and hamstring tendons of 10 human cadavers (age: 49.2 ± 18.5 years) were used. An inside out press-fit fixation with a knot in the semitendinosus and gracilis tendons (SG) combined with an additional bone block, with two quadriceps tendon bone block grafts (QU) was compared with press-fit fixation of two bone patellar tendon bone block (PT) grafts in 30 porcine femora. Constructs were cyclically stretched and then loaded until failure. Maximum load to failure, stiffness and elongation during failure testing and cyclical loading were investigated.The maximum load to failure was 703 ± 136 N for SG fixation, 632 ± 130 N for QU and 656 ± 127 N for PT fixation. Stiffness of the constructs averaged 138 ± 26 N/mm for SG, 159 ± 74 N/mm for QU, and 154 ± 50 N/mm for PT fixation. Elongation during initial cyclical loading was 1.2 ± 1.4 mm for SG, 2.0 ± 1.4 mm for QU, and 1.0 ± 0.6 mm for PT (significantly larger for PT and QU between the first 5 cycles compared with cycles 15-20th, P 0.01).All investigated double-bundle fixation techniques were equal in terms of maximum load to failure, stiffness, and elongation. Unlike with single-bundle press-fit fixation techniques that have been published, no difference was observed between pure tendon combined with an additional bone block and tendon bone grafts. All techniques exhibited larger elongation during initial cyclical loading. All three press-fit fixation techniques that were investigated exhibit comparable biomechanical properties. Preconditioning of the constructs is critical.

Osteochondral lesions are often seen in orthopedics, but the available treatment strategies are limited in success. Regenerative medicine provides novel concepts for curing them. The purpose of this study was to test the effects of perfusion and cyclic compression on cell differentiation and mechanical properties using a custom-made biomechanoreactor in a recently established system of human bone marrow stromal cells (hBMSC) cultured in a 3-D collagen I-bone hybrid matrix out of commercially available and separately in human-certified products. Seeded hBMSC were viable for 88 +/- 8.9% during the entire experimental period in the constructs. GAG and DNA levels did not change. Perfusion induced collagen II and cyclic compression increased collagen X expression. Matrix stiffness was significantly increased after 28 days of cyclic compression. Cyclic compression of cell-loaded hybrid constructs enhanced chondrocyte differentiation and matrix stiffness. This system is a promising tool with a view to a later clinical application.

We have read the recent article by Dr. Romano et al. [6] with great interest. The number of periprosthetic infections associated with hip and knee arthroplasties is increasing worldwide. In addition to the clinical problems they present, the financial burden of each case is high and the socioeconomic costs are increasing each year. The current standard treatment options for eradicating such infections are oneand twostage exchanges. The literature overview seems to be biased. The wellperformed review by Jamsen et al. [4] failed to show a difference between the oneand two-stage approaches. Romano et al. conclude that better eradication rates may be achieved by a two-stage approach. We were wondering why the retrospective analysis by Mortazavi et al. [5] was not mentioned although it was online in the summer of 2011 and presented the previous year in a meeting. Mortazavi et al. concluded that there are currently no proper indicators that can guide orthopaedic surgeons in patient selection between a two-stage exchange and a reimplantation. Next, they observed that the failure rate after two-stage reimplantation for infected TKA is relatively high. There were no variables identified that would guide the surgeon to perform the second stage. It is therefore very surprising that 1 year later, another group is able to make a clear statement using a meta-analysis. Next, we would like to mention a recent published article by Singer et al. [7]. They stated that the rate of infection control for one-stage revision of infected knee arthroplasties is still unclear according to the literature. For their series, they observed an infection control rate of 95 % for one-stage protheses and higher knee scores were reported than for two-stage revisions. This contrasts greatly with Dr. Romano et al.’s study. The worst series in the article by Romano et al. comes from our own institution by von Foerster et al. [8]. These patients were treated around 1980. Algorithms regarding topical antibiotic choice have improved in the last three decades, and although they are still missing in the literature, we currently observe better outcomes. This study is the only outlier in their overview and seems to present misleading results and conclusions. The combination of germ-specific systemic and topical antibiotic therapy is the key to success. Recent publications identified much higher infection control rates for the one-stage approach to septic THA exchanges [1, 2]. Such actual data are missing for septic TKA exchanges. As one of the biggest centres for revision arthoplasties in the world, we prefer a one-stage approach in septic TKA surgery because it is well documented that one-stage surgery is associated with less stress for the patient, fewer complications, better surgical conditions and better functional results [3]. There is currently a strong trend favouring one-stage approaches. However, we have to state that valid literature data are still missing and that this review misleads the reader. This comment refers to the article available at doi:10.1007/s00167-012-1885-x.