Bastian Welke

Purpose: Instrumented posterior lumbar fixation (PLF) with fusion is the surgical standard for treating various degenerative changes or deformities of the spine. Several studies have shown the risk of adjacent segment pathology following fusion. Therefore, revision procedures are often required which involve extension of instrumentation to adjacent levels. The purpose of this study was to evaluate the stability of multisegmental-instrumentation of the lumbar spine when extended with continuous rods or with connectors to the lower mid thoracic spine. Methods: Eight human specimens from Th5 to S1 were used and loaded with moments of 7.5 Nm about the three anatomical axes. A total of eight different PLF configurations were examined, with three conditions in a short Th10-S1 instrumentation and five conditions with a long Th6-S1 instrumentation. Continuous rods, and axial and lateral connectors were used to extend the PLF. Total range of motion (tROM) and total neutral zone (tNZ), as well as the intersegmental range of motion (iROM), were evaluated. Results: Overall, all configurations of the PLF demonstrated high primary stability. The iROM was less than 2 degrees in all segments studied where lengthening was performed with continuous rods or connectors. We found only a few significant differences, which are unlikely to be clinically relevant due to their very small magnitudes. Conclusion: From a biomechanical point of view, the axial and lateral connectors provide comparable primary stability to a continuous rod system. Thus, the use of connectors is likely to be a suitable approach of extending an existing lumbar fixation to the lower and mid thoracic spine. Level of evidence: Biomechanical study.

Introduction: Lumbopelvic fixation is commonly employed to stabilize unstable sacral fractures, particularly U-shaped (US) fractures, which may result in spinopelvic dissociation—leading to significant pain, deformity, and neurological deficits. Due to its superior biomechanical properties, lumbopelvic stabilization (LPS) has become the preferred method for managing such injuries. We aimed to compare the biomechanical stability of US-LPS with conventional LPS and bilateral iliosacral screw (ISS) fixation. Materials and methods: Six human cadaveric pelvic specimens were subjected to axial (750 N) and torsional (8 Nm) loading using a material testing machine (MTM). Seven configurations of LPS were evaluated. The range of motion (ROM) between three anatomical bony segments—the third lumbar vertebral body (LBV3), the first sacral vertebral body (SVB1), and the Crista Iliaca (CI)—was analyzed using an optical tracking system. Measurements included craniocaudal translation and anterior–posterior tilt under axial loading and internal–external rotation under torsional loading. Stiffness was calculated using force–displacement curves obtained via the MTM’s integrated load cells and displacement transducers. Results: Both LPS and US-LPS configurations demonstrated reduced ROM and increased stiffness compared to ISS fixation under axial and torsional loading. US-LPS exhibited marginally greater stiffness than standard LPS. The use of additional cross-connectors in both LPS groups had minimal to no measurable impact on ROM or overall stability. Conclusions: US-LPS offers slightly enhanced biomechanical stability over conventional LPS in the fixation of unstable US sacral fractures. In contrast, standalone ISS fixation did not improve stability compared to the unfixed condition in this cadaveric model.

Introduction: Although three-dimensional marker-based motion analysis is the gold standard for biomechanical investigations, it is time-consuming and cost-intensive. The conjunction of monocular video recordings with pose estimation algorithms addresses this gap. With the Orthelligent VISION app (OPED GmbH) a commercial and easy-to-use tool is now available for implementation in everyday clinical practice. The study investigates the accuracy of the 2D video-based system in measuring joint kinematics, expressed as range of motion, compared to an optoelectronic 3D motion analysis system as the gold standard. Materials and methods: Its accuracy was determined by synchronously measuring ten healthy subjects with Orthelligent and the optoelectronic 3D motion analysis system Qualisys (Qualisys AB) during level walking and at different treadmill walking speeds (1 m/s; 1.4 m/s; 1.8 m/s). Range of motion (RoM) of lower limb joints and time-distance parameters were compared using Bland-Altman plots, t-tests, and correlations between systems. Kinematic outputs of two subjects with a lower limb amputation were also analyzed. Results: The mean RoM deviation was smaller for the knee (3.8°) and hip joints (3.7°) than for the ankle joint (5.4°), but differed significantly between systems in most conditions. The correlation range was 0.36 ≤ r ≤ 0.83, with best results for 1 m/s treadmill walking (mean r = 0.71 across joints). While the accuracy was affected by high inter-subject variability, individual RoM changes from slow to fast walking did not differ between the systems. The kinematics of the prosthetic and sound leg of individuals with an amputation exhibited characteristic patterns in the video-based system, even though side differences were smaller compared to the optoelectronic measurement. Conclusions: The rather high inter-subject variability would make future comparisons between individuals challenging. Nonetheless, the app shows potential for intra-subject progress monitoring.

Introduction: Modular hip implants enables a more precise adaptation of the prosthesis to the patient’s anatomy. However, they also carry the risk of increased revision rates due to micromotion at the taper junction. In order to minimize this risk, one potential solution is to establish an adhesive bond between the metal taper junctions. Load-stable bonding techniques, already successfully employed in dentistry for connecting materials such as metals and ceramics or different alloys, offer a promising approach. Nevertheless, the bond strength of tapered adhesive bonds in modular hip implants has not been investigated to date. Materials and methods: Twenty-eight tapered junctions, consisting of a taper (female taper) and a trunnion (male taper) were turned using TiAl6V4 ELI (n = 16) and CoCr28Mo6 (n = 12). The process parameters cutting speed (v_c = 50 m/min or 100 m/min) and feed (f = 0.1 mm, 0.05 mm or 0.2 mm) were varied for the trunnions. For each set of process parameters, one trunnion and one taper were additionally subjected to sandblasting. To investigate the effect of geometry, angular mismatch in the samples were measured. The taper pairs were bonded with a biocompatible adhesive, and push-out tests were subsequently performed. Results: The push-out forces generated from the taper connections where both tapers were sandblasted showed a mean push-out force of 5.70 kN. For the samples with only the trunnion sandblasted, the mean force was 0.58 kN, while for the samples with only taper sandblasted the mean push-out force was 1.32 kN. When neither of the tapers was sandblasted the mean push-out force was 0.91 kN. No significant effect of the process parameters on the push-out force was observed. Only the reduced valley depth Svk showed a slight correlation for the CoCr28Mo6 samples (R² = 0.54). The taper pairs with taper mismatch (between trunnion and taper) greater than |0.1°| did not show lower push-out forces than the specimens with lower taper mismatch. Conclusions: Sandblasted and adhesive-bonded tapered connections represent a viable suitable alternative for modular hip implant connections. Slight differences in taper geometry do not result in reduced push-out forces and are compensated by the adhesive. In mechanically joined tapers these differences can lead to higher wear rates. Further investigation under realistic test conditions is necessary to assess long-term suitability.

Femoral fractures and severe bleeding frequently occur in old patients showing a delayed healing. As there are no studies investigating the combined effect of high age and severe blood loss on fracture healing, this was examined radiographically and biomechanically in this study. Therefore, young and old male mice were randomly assigned to three operation groups. In the fracture group (Fx), external fixator and osteotomy were applied to the femur. The combined trauma group (THFx) additionally received a pressure-controlled hemorrhage. Sham animals were only implanted with arterial catheter and external fixator. Sacrifice was performed after three weeks and bone healing was evaluated radiologically via µCT, as well as biomechanically using a three-point bending test. A decreased share of callus/total bone volume was observed in old mice with blood loss compared to old Fx. Hemorrhagic shock also reduced the trabecular number in old mice compared to Fx and young THFx. Moreover, a lower elastic limit in old Sham mice without fracture was revealed. Fracture combined with a high loss of blood further reduced the elastic limit in old mice compared to isolated Fx in old animals. In conclusion, this study showed that severe blood loss has a higher negative effect in old mice compared to young ones.

Musculoskeletal research deals with the effects of the orthopedic treatment of pathologies on the biomechanics of the affected areas and on the musculoskeletal system

Introduction: Multiple camera systems are widely used for 3D-motion analysis. Due to increasing accuracies these camera systems gained interest in biomechanical research areas, where high precision measurements are desirable. In the current study different measurement systems were compared regarding their measurement accuracy. Materials and methods: Translational and rotational accuracy measurements as well as the zero offset measurements of seven different measurement systems were performed using two reference devices and two different evaluation algorithms. All measurements were performed in the same room with constant temperature at the same laboratory. Equal positions were measured with the systems according to a standardized protocol. Measurement errors were determined and compared. Results: The highest measurement errors were seen for a measurement system using active ultrasonic markers, followed by another active marker measurement system (infrared) having measurement errors up to several hundred micrometers. The highest accuracies were achieved by three stereo camera systems, using passive 2D marker points having errors typically below 20 μm. Conclusions: This study can help to better assess the results obtained with different measurement systems. With the focus on the measurement accuracy, only one aspect in the selection of a system was considered. Depending on the requirements of the user, other factors like measurement frequency, the maximum analyzable volume, the marker type or the costs are important factors as well.

Tendon injuries still pose a challenge to reconstructive surgeons. Tendon tissue is a bradytrophic tissue and has a poor tendency to heal. Autologous tendon grafts are, therefore, still the gold standard in restorative operations but are associated with significant donor side morbidity. The experimental approach of the present study focused on the use of the biomaterial spider silk as a biocompatible and very stable carrier matrix in combination with a collagen type I hydrogel and adipose-derived stromal cells. The constructs were differentiated by axial strain to tendon-like tissue using a custom-made bioreactor. Macroscopically, tendon-like tissue could be detected which histologically showed high cell vitality even in long-term cultivation. In addition, cell morphology comparable to tenocytes could be detected in the bioreactor-stimulated tendon-like constructs compared to the controls. Immunohistochemically, tendon tissue-specific markers could be detected. Therefore, the developed tendon-like construct represents a promising approach towards patient specific tendon reconstruction, but further studies are needed.