Background: Various techniques are available for the reconstruction of acromioclavicular joint (ACJ) dislocations, with the main focus being on restoration of the AC capsule or coracoclavicular ligaments. Recent research has underlined the significance of the deltotrapezial fascia (DTF) and related muscles as dynamic stabilizers of the ACJ. The Hypothesis was that a reconstruction of the DTF increases the stability of the ACJ in the horizontal plane more than a complete transection of the fascia, while not restoring the stability of the native state. Hypothesis: Reconstruction of the DTF increases the stability of the ACJ in the horizontal plane more than a complete transection of the fascia, while not restoring the stability of the native state. Methods: Five pairs of human cadaveric shoulders including the torsos were included in the study and underwent cyclic anterior- posterior loading using an electromechanical testing machine. The shoulders were put into 3 groups: group N (n = 10): native ACJ; group T (n = 10): ACJ with transected DTF; group R (n = 10): ACJ with reconstruction of the DTF after transection. The dislocation was recorded with a 3D optical measuring system. Results: Group N showed a mean horizontal displacement of 2.94 mm (+/- 1.26), group T showed a mean anterior displacement of 3.33 mm (+/- 1.37), and group R showed a mean anterior displacement of 2.95 mm (+/- 1. 08). The mean anterior displacement for group T was significantly higher after every measured number of cycles compared with groups N and R. There was no significant difference in mean anterior displacement between groups N and R. Conclusion: The transection of the DTF results in significantly reduced stability in the horizontal plane of the ACJ. A reconstruction the DTF restores the stability of the native ACJ in the horizontal plane. Further clinical and biomechanical investigations should focus on reconstruction techniques of the DTF. Level of evidence: Basic Science Study; Biomechanics (c) 2024 The Author(s). This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

In lumbar spinal stabilization pedicle screws are used as standard. However, especially in osteoporosis, screw anchorage is a problem. Cortical bone trajectory (CBT) is an alternative technique designed to increase stability without the use of cement. In this regard, comparative studies showed biomechanical superiority of the MC (midline cortical bone trajectory) technique with longer cortical progression over the CBT technique. The aim of this biomechanical study was to comparatively investigate the MC technique against the not cemented pedicle screws (TT) in terms of their pullout forces and anchorage properties during sagittal cyclic loading according to the ASTM F1717 test. Five cadavers (L1 to L5), whose mean age was 83.3 ± 9.9 years and mean T Score of -3.92 ± 0.38, were dissected and the vertebral bodies embedded in polyurethane casting resin. Then, one screw was randomly inserted into each vertebra using a template according to the MC technique and a second one was inserted by freehand technique with traditional trajectory (TT). The screws were quasi-static extracted from vertebrae L1 and L3, while for L2, L4 and L5 they were first tested dynamically according to ASTM standard F1717 (10,000 cycles at 1 Hz between 10 and 110 N) and then quasi-static extracted. In order to determine possible screw loosening, there movements were recorded during the dynamic tests using an optical measurement system. The pull-out tests show a higher pull-out strength for the MC technique of 555.4 ± 237.0 N compared to the TT technique 448.8 ± 303.2 N. During the dynamic tests (L2, L4, L5), 8 out of the 15 TT screws became loose before completing 10,000 cycles. In contrast, all 15 MC screws did not exceed the termination criterion and were thus able to complete the full test procedure. For the runners, the optical measurement showed greater relative movement of the TT variant compared to the MC variant. The pull-out tests also revealed that the MC variant had a higher pull-out strength, measuring at766.7 ± 385.4 N, while the TT variant measured 637.4 ± 435.6 N. The highest pullout forces were achieved by the MC technique. The main difference between the techniques was observed in the dynamic measurements, where the MC technique exhibited superior primary stability compared to the conventional technique in terms of primary stability. Overall, the MC technique in combination with template-guided insertion represents the best alternative for anchoring screws in osteoporotic bone without cement.

Deformity due to neuromuscular disease is often progressive and associated with reduced vital capacity. In general, all treatment should be performed in specialized centers, since invasive measures are associated with an increased morbidity compared to adolescent scoliosis. Derived from the etiology and the resulting biomechanical basis (characteristics), important aspects and considerations arise for all healthcare institutions from the examination interval to the duration of conservative therapy and initiation of surgical therapy. Proper monitoring and assessment are key components to identify curve progression and to achieve preservation or improvement of basic functions.

The goal of this study is to compare the construct stability of long segmental dorsal stabilization in unstable midthoracic osteoporotic fractures with complete pedicle screw cement augmentation (ComPSCA) versus restricted pedicle screw cement augmentation (ResPSCA) of the most cranial and caudal pedicle screws under cyclic loading. Twelve fresh frozen human cadaveric specimens (Th4–Th10) from individuals aged 65 years and older were tested in a biomechanical cadaver study. All specimens received a DEXA scan and computer tomography (CT) scan prior to testing. All specimens were matched into pairs. These pairs were randomized into the ComPSCA group and ResPSCA group. An unstable Th7 fracture was simulated. Periodic bending in flexion direction with a torque of 2.5 Nm and 25,000 cycles was applied. Markers were applied to the vertebral bodies to measure segmental movement. After testing, a CT scan of all specimens was performed. The mean age of the specimens was 87.8 years (range 74–101). The mean T-score was − 3.6 (range − 1.2 to − 5.3). Implant failure was visible in three specimens, two of the ComPSCA group and one of the ResPSCA group, affecting only one pedicle screw in each case. Slightly higher segmental movement could be evaluated in these three specimens. No further statistically significant differences were observed between the study groups. The construct stability under cyclic loading in flexion direction of long segmental posterior stabilization of an unstable osteoporotic midthoracic fracture using ResPSCA seems to be comparable to ComPSCA.

BACKGROUND: Intervertebral fusions in cases of reduced bone density are a tough challenge. From a biomechanical point of view, most current studies have focused on the range of motion or have shown test setups for single-component tests. Definitive setups for biomechanical testing of the primary stability of a 360 degrees fusion using a screw-rod system and cage on osteoporotic spine are missing. The aim of this study was to develop a test stand to provide information about the bone-implant interface under reproducible conditions. METHODS: After pretesting with artificial bone, functional spine units were tested with 360 degrees fusion in the transforaminal lumbar interbody fusion technique. The movement sequences were conducted in flexion/extension, right and left lateral bending, and right and left axial rotation on a human model with osteopenia or osteoporosis -nder permanent maximum load with 7.5 N-m. RESULTS: During the testing of human cadavers, 4 vertebrae were fully tested and were inconspicuous even after radiological and macroscopic examination. One vertebra showed a subsidence of 2 mm, and 1 vertebra had a cage collapsed into the vertebra. CONCLUSIONS: This setup is suitable for biomechanical testing of cyclical continuous loads on the spine with reduced bone quality or osteoporosis. The embedding method is stable and ensures a purely single-level setup with different trajectories, especially when using the cortical bone trajectory. Optical monitoring provides a veryaccurate indication of cage movement, which correlates with the macroscopic and radiological results.

Durch neuromuskuläre Erkrankungen bedingte Deformitäten der Wirbelsäule sind häufig progredient, führen zu Imbalancen bis hin zum Verlust der Sitzfähigkeit und können mit einer reduzierten Vitalkapazität assoziiert sein. Die gesamte Betreuung hinsichtlich der Wirbelsäulendeformitäten sollte in Zentren erfolgen, da häufig besondere Kenntnisse erforderlich sind und invasive Maßnahmen im Vergleich zur adoleszenten Skoliose mit einer erhöhten Morbidität einhergehen. Abgeleitet von der Ätiologie und den daraus resultierenden biomechanischen Grundlagen (Besonderheiten) ergeben sich für alle behandelnden Institutionen wichtige Aspekte und Überlegungen vom Untersuchungsintervall über die Dauer der konservativen Therapie bis hin zum richtigen Zeitpunkt der Einleitung einer operativen Therapie. Eine sorgfältige Überwachung und Kenntnisse der zugrunde liegenden Erkrankungen sind die Schlüsselkomponenten, um eine Kurvenprogression zu erkennen und mit der adäquaten Therapie zum richtigen Zeitpunkt den Erhalt oder die Verbesserung der Funktionalität zu erreichen.

BackgroundFusions in cases of reduced bone density are a tough challenge. As not only does bone quality have an influence on force transmission, these forces must be bridged for much longer time, as a fusion takes longer than in bone-healthy patients. However, cage subsidence or displacement results to loss of reposition and pain. From a biomechanical point of view, the majority of current studies have focussed on the range of motion or have shown test setups for single component tests. Definite setups for biomechanical testing of the primary stability of a 360° fusion using a screw rod system and cage on the osteoporotic spine are missing. The aim of this study is to develop a test stand to provide information about the bone-implant interface under reproducible conditions.MethodsAfter pre-testing with artificial bone, human functional spine units were tested with 360° fusion in TLIF technique. The movement sequences was conducted in flexion, extension, right-left lateral bending and right-left axial rotation on an osteoporotic human model.ResultsDuring the testings of human cadavers, 4 vertebrae were fully tested and were inconspicuous even after radiological and macroscopic examination. 1 vertebra showed a subsidence of 2mm and 1 vertebra had a cage collapsed into the vertebra.ConclusionsThis setup is suitable for biomechanical testing of cyclical continuous loads on the osteoporotic spine. The embedding method is stable and ensures a purely monosegmental setup. The optical monitoring provides a very accurate indication of cage movement, which correlates with the macroscopic and radiological results.