Rosemarie Fröber

Internal Fixation of Type-C Distal Femoral Fractures in Osteoporotic Bone

BACKGROUND Fixation of distal femoral fractures remains a challenge, especially in osteoporotic bone. This study was performed to investigate the biomechanical stability of four different fixation devices for the treatment of comminuted distal femoral fractures in osteoporotic bone. METHODS Four fixation devices were investigated biomechanically under torsional and axial loading. Three intramedullary nails, differing in the mechanism of distal locking (with two lateral-to-medial screws in one construct, one screw and one spiral blade in another construct, and four screws [two oblique and two lateral-to-medial with medial nuts] in the third), and one angular stable plate were used. All constructs were tested in an osteoporotic synthetic bone model of an AO/ASIF type 33-C2 fracture. Two nail constructs (the one-screw and spiral blade construct and the four-screw construct) were also compared under axial loading in eight pairs of fresh-frozen human cadaveric femora. RESULTS The angular stable plate constructs had significantly higher torsional stiffness than the other constructs; the intramedullary nail with four-screw distal locking achieved nearly comparable results. Furthermore, the four-screw distal locking construct had the greatest torsional strength. Axial stiffness was also the highest for the four-screw distal locking device; the lowest values were achieved with the angular stable plate. The ranking of the constructs for axial cycles to failure was the four-screw locking construct, with the highest number of cycles, followed by the angular stable plate, the spiral blade construct, and two-screw fixation. The findings in the human cadaveric bone were comparable with those in the synthetic bone model. Failure modes under cyclic axial load were comparable for the synthetic and human bone models. CONCLUSIONS The findings of this study support the concept that, for intramedullary nails, the kind of distal interlocking pattern affects the stabilization of distal femoral fractures. Four-screw distal locking provides the highest axial stability and nearly comparable torsional stability to that of the angular stable plate; the four-screw distal interlocking construct was found to have the best combined (torsional and axial) biomechanical stability.

Distal femur fractures of the elderly--different treatment options in a biomechanical comparison.

BACKGROUND Fractures of the distal femur, especially in the elderly patient, are an unsolved problem in orthopaedic and trauma surgery. Poor bone stock quality caused by osteoporosis often results in bad implant anchorage in the distal part with a high risk of secondary failures such as cutout. This study investigates the biomechanical characteristics of four implants with different distal locking options under quasi-static torsional and cyclic axial loading. Therefore, an osteoporotic bone model simulating severe osteoporotic conditions was used. METHODS Four different implants (T2 intramedullary nail, supracondylar nail (SCN), distal femoral nail (DFN) and the AxSOS angular stable plate) with different distal locking options were instrumented using an osteoporotic bone model. Five specimens per implant and per loading type (torsional and axial) were used. Mechanical testing was performed under physiologic loading conditions. First, a torsional test was performed in internal and external rotation (10 Nm), with a new specimen; a stepwise cyclic axial loading was conducted until failure of the construct. FINDINGS For torsional loading, the lowest range of motion (ROM) and neutral zone (NZ) was found for the AxSOS plate construct. The SCN and T2 constructs showed similar results, and the highest ROM and NZ were found for the constructs treated with the DFN. Axial stiffness was highest for SCN constructs and in the same range for DFN and T2. The lowest stiffness showed in the AxSOS plate constructs with 47% of SCN stiffness. Under cyclic axial loading, the SCN constructs showed the highest number of cycles to failure, followed by AxSOS (70%), DFN (69%) and T2 (48%). INTERPRETATION In conclusion of this biomechanical study, we can clinically suggest that, if, in general, torsional stability is required (e.g., for bedridden patients) the AxSOS plate will be sufficient. By contrast, the findings of this study support the fact that the SCN should be considered for mobile patients where early postoperative mobilisation for rehabilitation is desired.

Stability of Medial Locking Plate and Compression Screw Versus Two Crossed Screws for Lapidus Arthrodesis

Background: Lapidus (first metatarsocuneiform joint) arthrodesis is an established procedure for the management of hallux valgus. This study investigated the utility of fixation with a medial locking plate with adjunct compression screw versus fixation with two crossed screws. Materials and Methods: Eight pairs of fresh-frozen human specimens were used in a matched pair test. Bone mineral density (BMD) was measured with peripheral quantitative computed tomography (pQCT). Fixation with two 4-mm-diameter crossed screws was compared versus a medial locking plate (X-Locking Plate 2.4/2.7; Synthes, Solothurn, Switzerland) with adjunct 4-mm-diameter compression screw. The specimens were tested in a four-point bending test. Parameters obtained were initial stiffness; plantar joint-line gapping after one cycle, 100 and 1000 cycles; and number of cycles to failure. Failure was defined as more than or equal to 3 mm plantar gapping. Results: The groups did not differ significantly with regard to BMD (p = 0.866) and initial stiffness (p = 0.889). The plate-and-screw construct showed significantly less movement during testing, and significantly (p = 0.001) more cycles to failure than did the crossed-screw construct. There was a significant correlation (crossed-screw construct: p = 0.014; plate-and-screw construct: p = 0.010) between BMD and the number of cycles to failure. Conclusion: Under cyclic loading conditions, the construct using a medial locking plate with adjunct compression screw was superior to the construct using two crossed screws. Clinical Relevance: The medial locking-plate technique described could help shorten the period of nonweightbearing and reduce the risk of non-union.

Comparison of Two Intramedullary Nails for Tibiotalocalcaneal Fusion: Anatomic and Radiographic Considerations:

Background: Retrograde intramedullary nailing is an established procedure for tibiotalocalcaneal arthrodesis. This study was conducted to see whether, and if so to what extent, nail design modifications would influence the risk to anatomic structures and the bony coverage of the nail base. Methods: Six pairs of thawed fresh-frozen cadaver legs received two different intramedullary nails (N1: straight nail, lateral-medial tip locking; N2: valgus-curved nail, medial-lateral tip locking) under simulated operative conditions. The specimens were dissected; distances between the at-risk structures and the hardware were measured. The hindfoot axis and the volume of the intracalcaneal nail portion were determined with CT. Results: At the plantar entry site, N2 was significantly farther from the flexor hallucis longus tendon (p = 0.047), the medial plantar artery (p = 0.026), and the lateral plantar nerve (p = 0.026) than N1. The lateral-medial calcaneal locking screw of N1 damaged significantly more often the peroneus brevis tendon (p = 0.03) than N2. The proximal tip-locking screw, N2, was significantly farther from the anterior tibial artery (p = 0.075) and the deep (p = 0.047) and superficial peroneal nerves (p = 0.009) than N1; N1 was significantly farther from the great saphenous vein (p = 0.075) than N2. The distal tip-locking screw, N1. damaged significantly more often the extensor digitorum longus (p = 0.007), the anterior tibial artery(p = 0.04), and the deep and superficial peroneal nerves (p = 0.03) than N2. CT did not show any significant changes in the hindfoot axis with either device; intracalcaneal nail volumes were similar. Conclusions: A curved nail can increase the distance to at-risk plantar structures. Medial-lateral nail-tip locking appears to have less risk to neurovascular structures. Clinical Relevance: Safer retrograde intramedullary nailing for tibiotalocalcaneal fusion requires knowledge of the structures at risk and appropriate operative technique.

Comparison of Calcaneal Fixation of a Retrograde Intramedullary Nail with a Fixed-Angle Spiral Blade Versus a Fixed-Angle Screw

Background: Retrograde intramedullary nailing is an established technique for tibiotalocalcaneal arthrodesis (TTCA). In poor bone stock (osteoporosis, neuroarthropathy), device fixation in the hindfoot remains a problem. Fixed-angle spiral-blade fixation of the nail in the calcaneus could be useful. Materials and Methods: In seven matched pairs of human below-knee specimens, bone mineral density (BMD) was determined, and TTCA was performed with an intramedullary nail (Synthes Hindfoot Arthrodesis Nail HAN Expert Nailing System), using a conventional screw plus a fixed-angle spiral blade versus a conventional screw plus a fixed-angle screw, in the calcaneus. The constructs were subjected to quasi-static loading (dorsiflexion/plantarflexion, varus/valgus, rotation) and to cyclic loading to failure. Parameters studied were construct neutral zone (NZ) and range of motion (ROM), and number of cycles to failure. Results: With dorsiflexion/plantarflexion loading, the screw-plus-spiral-blade constructs had a significantly smaller ROM in the quasi-static test (p = 0.028) and early in the cyclic test (p = 0.02); differences in the other parameters were not significant. There was a significant correlation between BMD and cycles to failure for the two-screw constructs (r = 0.94; p = 0.002) and for the screw-plus-spiral-blade constructs (r = 0.86; p = 0.014). Conclusion: In TTCA with a HAN Expert Nailing System, the use of a calcaneal spiral blade can further reduce motion within the construct. This may be especially useful in poor bone stock. Clinical Relevance: Results obtained in this study could be used to guide the operating surgeons TTCA strategy.

The anterior jugular venous system: variability and clinical impact.

The anterior jugular venous system, with its interconnections to the subclavian and deep jugular veins, provides a collateral venous network across the midline of the neck area, which is especially important in unilateral occlusion of an innominate vein. We illustrate the variability of this system and its clinical impact on catheterization by three cases of landmark-guided central venous cannulation. Case 1: Cannulation of the left internal jugular vein with a central venous catheter and of the left innominate vein (LIV) with a pulmonary artery catheter resulted in correctly positioned catheter tips. However, these catheters were actually not placed in the innominate vein but coursed through the jugular venous arch. Case 2: Cannulation of the left subclavian vein was complicated by resistance of guidewire advancement at 13 cm. Occlusion of the LIV and enlargement of the jugular venous arch were present. Case 3: Insertion of a pulmonary artery catheter and a central venous catheter through the LIV. The pulmonary artery catheter was correctly placed. The tip of the central venous catheter was mistakenly positioned in the left anterior jugular vein. We describe the normal anatomy of the anterior jugular venous system and its role as a major collateral. Correct placement of central venous catheters may be possible via the anterior jugular venous system. Conversely, central venous catheters malpositioned in the anterior jugular vein can increase the risk for complications and should be removed.

Surgical anatomy of the ureter

Iatrogenic injury to the urinary tract can be caused by any surgeon operating in or around the pelvis and the retroperitoneal abdominal space, with a general incidence of 0.3–1.5%. This includes gynaecologists, general surgeons, urologists, vascular surgeons, neurosurgeons and orthopaedic surgeons. In addition, the impact of technological advances within the surgical field, such as the use of laparoscopy for general surgical and gynaecological procedures, and the application of endoscopic approaches to urological disease, is elucidated here [1].

Temperature influence on DXA measurements: bone mineral density acquisition in frozen and thawed human femora

BackgroundDetermining bone mineral density (BMD) with dual-energy x-ray absorptiometry (DXA) is an established and widely used method that is also applied prior to biomechanical testing. However, DXA is affected by a number of factors. In order to delay decompositional processes, human specimens for biomechanical studies are usually stored at about -20°C; similarly, bone mineral density measurements are usually performed in the frozen state. The aim of our study was to investigate the influence of bone temperature on the measured bone mineral density.MethodsUsing DXA, bone mineral density measurements were taken in 19 fresh-frozen human femora, in the frozen and the thawed state. Water was used to mimic the missing soft tissue around the specimens. Measurements were taken with the specimens in standardized internal rotation. Total-BMD and single-BMD values of different regions of interest were used for evaluation.ResultsFourteen of the 19 specimens showed a decrease in BMD after thawing. The measured total-BMD of the frozen specimens was significantly (1.4%) higher than the measured BMD of the thawed specimens.ConclusionBased on our findings we recommend that the measurement of bone density, for example prior to biomechanical testing, should be standardized to thawed or frozen specimens. Temperature should not be changed during measurements. When using score systems for data interpretation (e.g. T- or Z-score), BMD measurements should be performed only on thawed specimens.

Evaluation of a Customized Artificial Osteoporotic Bone Model of the Distal Femur

In the development of new implants biomechanical testing is essential. Since human bones vary markedly in density and geometry their suitability for biomechanical testing is limited. In contrast artificial bones are of great uniformity and therefore appropriate for biomechanical testing. However, the applied artificial bones have to be proved as comparable to human bone. An anatomical shaped artificial bone representing the distal human femur was created by foaming polyurethane. To get a bone model with properties of osteoporotic bone a foam density of 150 kg/m3 was used. The biomechanical properties of our artificial bones were evaluated against eight mildly osteoporotic fresh frozen human femora by mechanical testing. At the artificial bones all tested parameters showed a very small variation. In contrast significant correlation between bone mass density and tested parameters was found for the human bones. The artificial bones reached 39% of the compression strength and 41% of the screw pullout force of the human bone. In indentation testing the artificial bones reached 27% (cancellous) and 59% (cortical) respectively of the human bones strength. Regarding Shore hardness artificial bone and human bone showed comparable results for the cortical layer and at the cancellous layer the artificial bone reached 57% of human bones hardness. Our described method for customizing of artificial bones regarding their shape and bone stock quality provides suitable results. In relation to the as mildly osteoporotic classified human bones we assume that the biomechanical properties matching to serve osteoporotic bone.

[The altered membrane of the erythrocyte. I. Ultrahistochemical and biocellular investigations for the detection of activated acetylcholinesterase (ACHE) and demasking of IgG receptor sites (author's transl)].

Zusammenfassung Es wurde versucht, verschiedene Zustandsformen der Erythrocytenmembran im Hinblick auf den Grad ihrer Desintegration naher zu charakterisieren. Als Kriterien wurden die Bindungsfahigkeit gegenuber autologem bzw. allogenem IgG, der Aktivierungsgrad der am intakten Erythrocytenplasmalemm inhibierten membransessilen Acetylcholinesterase und die Mernbranvesiculation herangezogen. Die Befunde belegen, das offenbar mit dem Schweregrad der Membrangefugestorung die IgG-Bindung anwachst und die Acetylcholinesterase zunehmend aktiviert wird. Das Enzym kann dann spektrophotometrisch und ultrahistochemisch erfast werden. Die Mikrovesiculation wird als Ausdruck tiefgreifender Membrangefugestorungen auigefast. Am konservierten Erythrocyten wird sie als ein lokaler Membran-Remodellierungsprozes angesehen, Starkere Erythrocytenschadigung, wie nach mechanischem Stress, Warmesohock und Inkubation in Harnstoff, fuhrt zu vergleichsweise hoheren Vesiculationsraten, teilweise zu Zellfragmentation. An stark spektrinverarmten Erythrocytenschatten tritt Mikrovesiculation spontan ein und fuhrt zum volligen mikrovesicularen Zerfall der Schattenmembran. Das membranassoziierte autologe IgG wird mit immunologischen und ultrahistochemischen Methoden nachgewiesen. Seine Bedeutung als homoostatisch wirksames Immunsignal fur die Elimination von in vivo oder in vitro gealterten Erythrocyten, Erythrocytenschatten und -vesiceln durch das Reticulo-Histiocytare-System wird anhand von Modellversuchen aufgezeigt. Molekulare Mechanismen zur IgG-Receptordemaskierung und A.cetylcholinesteraseaktivierung in der alterierten Erythrocytenmembran werden diskutiert.