Introduction. In daily clinical practice, progression of spinal fusion is typically monitored during clinical follow-up using conventional radiography and Computed Tomography scans. However, recent research has demonstrated the potential of implant load monitoring to assess posterolateral spinal fusion in an in-vivo sheep model. The question arises to whether such a strain sensing system could be used to monitor bone fusion following lumbar interbody fusion surgery, where the intervertebral space is supported by a cage. Therefore, the aim of this study was to test human cadaveric lumbar spines in two states: after a transforaminal lumbar interbody fusion (TLIF) procedure combined with a pedicle-screw-rod-construct (PSR) and subsequently after simulating bone fusion. The study hypothesized that the load on the posterior instrumentation decreases as the segment stiffens due to simulated fusion. Method. A TLIF procedure with PSR was performed on eight human cadaveric spines at level L4-L5. Strain sensors were attached bilaterally to the rods to derive implant load changes during unconstrained flexion-extension (FE), lateral bending (LB) and axial rotation (AR) loads up to ±7.5Nm. The specimens were retested after simulating bone fusion between vertebrae L4-L5. In addition, the range of motion (ROM) was measured during each loading mode. Result. The ROM decreased in the simulated bone fusion state in all loading directions (p≤0.002). In both states, the measured strain on the posterior instrumentation was highest during LB motion. Furthermore, the sensors detected a significant decrease in the load induced rod strain (p≤0.002) between TLIF+PSR and simulated bone fusion state in LB. Conclusion. Implant load measured via rod strain sensors can be used to monitor the progression of fusion after a TLIF procedure when measured during LB of the lumbar spine. However, further research is needed to investigate the influence of daily loading scenarios expected in-vivo on the overall change in implant load

Subtalar arthrodesis known as talocalcaneal fusion is an end-stage treatment for adult hind foot pathologies. The goal of the arthrodesis is to restrict the relative motion between bones of the subtalar joints, aiming to reduce pain and improve function for the patient. However, the change of the subtalar structures through the fusion is considered a disturbance to the joint biomechanics, which have been suggested to affect the biomechanics of the adjacent joints. However, no quantitative data are available to document this phenomenon. The purpose of the current study was to quantify the effects of subtalar arthrodesis on the laxity and stiffness of the talocrural joint in vitro using a robot-based joint testing system (RJTS) during anterioposterior (A/P) drawer test. Six fresh frozen ankle specimens were used in this study. The lateral tissues of the specimens were removed but the anterior and posterior talofibular ligaments and calcaneofibular ligament were kept intact. A/P drawer tests were performed on each of the specimens at neutral position, 5° and 10° of dorsiflexion, and 5?and 10?of plantarflexion using a robot-based joint testing system (RJTS), before and after subtalar arthrodesis. The RJTS enabled unconstrained A/P drawer testing at the prescribed ankle position while keeping the proximal/distal and lateral/medial forces, and varus/valgus and internal/external moments to be zero. This was achieved via a force-position hybrid control method with force and moment control, which has been shown to be more accurate than other existing force-position hybrid control methods. The target A/P force applied during the A/P drawer test was 100N in both anterior and posterior directions. The stiffness and laxity were calculated from the measured force and displacement data. The anterior and posterior stiffness of the talocrural joint were defined as the slope beyond 30% of the target A/P force, and the peak displacements quantified the laxity of the joint. Comparisons of laxity and stiffness between the intact and fusion ankle specimens were performed using Wilcoxon signed rank test (SPSS 19.0, IBM, USA) and a significance level of 0.05 was set. Subtalar arthrodesis did not lead to significant changes in the stiffness and laxity in both anterior and posterior directions (P>0.05). The mean anterior stiffness before arthrodesis was 9.54±1.17 N/mm and was 10.35±2.40 N/mm after arthrodesis. The mean anterior displacements before and after arthrodesis were 9.68±0.94 mm and 8.97±1.42 mm, respectively. Subtalar arthrodesis did not show significant effects on the A/P laxity and stiffness of the talocrural joint in both anterior and posterior directions. This may imply that the motion of the subtalar joints do not have significant effects on the A/P stability of the talocrural joint, which is the main joint of the ankle complex. This agrees with the anatomical roles of the subtalar joints which provide mainly the varus/valgus motions for the ankle complex. The current study provides a basis for further studies needed to evaluate the effects subtalar arthrodesis on the varus/valgus stability

To study the effect of ligament injuries and surgical repair we investigated the three-dimensional kinematics of the ankle joint complex and the talocrural and the subtalar joints in seven fresh-frozen lower legs before and after sectioning and reconstruction of the ligaments. A foot movement simulator produced controlled torque in one plane of movement while allowing unconstrained movement in the remainder. After testing the intact joint the measurements were repeated after simulation of ligament injuries by cutting the anterior talofibular and calcaneofibular ligaments. The tests were repeated after the Evans, Watson-Jones and Chrisman-Snook tenodeses. The range of movement (ROM) was measured using two goniometer systems which determined the relative movement between the tibia and talus (talocrural ROM) and between the talus and calcaneus (subtalar ROM). Ligament lesions led to increased inversion and internal rotation, predominantly in the talocrural joint. The reconstruction procedures reduced the movement in the ankle joint complex by reducing subtalar movement to a non-physiological level but did not correct the instability of the talocrural joint

Summary. The presence or absence of crimp within the anterior cruciate ligament (ACL) sub-bundle anatomy was correlated with knee flexion angle changes and provided a measure of differential loading within its sub-bundle microstructure. Introduction. Previous studies have shown that macroscopically the anteromedial (AM) and posterolateral (PL) bundles of the ACL tighten/slacken differently with knee flexion angle. This research used fibre crimp morphology, revealed following in situ fixation of the intact ligament structures, to investigate patterns of differential fibre recruitment across each ACL sub-bundle. Methods. Twelve mature ovine knees were divided into four test-groups of three: control, hyper-extension (8°), neutral position (50°), and deep flexion (170°). For the control group, ligament-bone (tibia) samples were isolated and chemically fixed, unconstrained, in 10% formalin. For the flexed groups the whole joints were first positioned in the relevant angle of flexion using a custom-built rig and formalin-fixed in-situ before undergoing dissection. All ligament-bone samples were decalcified using 10% formic acid and cryo-sectioned in the sagittal plane to obtain 20μm serial slices. These were then examined in their fully hydrated state using differential inference contrast (DIC) microscopy. The degree of crimping, taken as an approximate indicator of elongation and thus loading, was classified as either substantial, intermediate or minimal. Crimp coarseness or wavelength, crimp angle and number of visible apices per unit fibre length were measured and analysed statistically using both ANOVA and post hoc analysis (significance, p < 0.05). Results. Control group. Substantial crimping was present in all regions of both AM and PL bundles. However two distinct crimp morphologies were discerned, coarse and fine. Coarse crimp dominated both the small anterior region of the AM bundle proximal to the tibial plateau and the entire PL bundle. Fine crimp was present in the remaining part of the AM bundle. The wavelengths and maximum angles of the coarse and fine crimp were significantly different at 44.8 ± 5.9 µm/45° and 16.2 ± 3.1 μm/15° respectively. This difference in crimp morphology was consistent along the serial sections of the ACL. From the serial sections, a three dimensional interpretation of the degree of crimping was obtained for the three different loading positions. A summary of the main findings is presented as follows: Hyper-extension. A small antero-medial portion of the AM bundle was substantially crimped (indicating an unloaded state) and the remaining region exhibiting only intermediate crimping; the bulk of the PL bundle was largely free of crimp (indicating a relatively loaded state) except for a substantially crimped region in its postero-lateral aspect. Neutral position. The anterior portion of the AM bundle exhibited minimal crimp but elsewhere was intermediate. The entire PL bundle was substantially crimped. Deep flexion. The substantially crimped medial portion of the AM bundle transformed progressively into an intermediate crimp morphology as the lateral aspect of the bundle was approached. Both the postero-medial and antero-lateral aspects of the PL bundle were largely free of crimp whereas the intervening region was intermediately crimped. Conclusion. Through serial sectioning, this study has revealed differential patterns of fibre recruitment, following loading, in all four quadrants of the sub-bundles of the ovine ACL at different knee flexion angles

The role of vacuum mixing on the reduction of porosity and on the clinical performance of cemented total hip replacements remains uncertain. We have used paired femoral constructs prepared with either hand-mixed or vacuum-mixed cement in a cadaver model which simulated intra-operative conditions during cementing of the femoral component. After the cement had cured, the distribution of its porosity was determined, as was the strength of the cement-stem and cement-bone interfaces.

The overall fraction of the pore area was similar for both hand-mixed and vacuum-mixed cement (hand 6%; vacuum 5.7%; paired t-test, p = 0.187). The linear pore fractions at the interfaces were also similar for the two techniques. The pore number-density was much higher for the hand-mixed cement (paired t-test, p = 0.0013). The strength of the cement-stem interface was greater with the hand-mixed cement (paired t-test, p = 0.0005), while the strength of the cement-bone interface was not affected by the conditions of mixing (paired t-test, p = 0.275). The reduction in porosity with vacuum mixing did not affect the porosity of the mantle, but the distribution of the porosity can be affected by the technique of mixing used.

When performing the Scandinavian Total Ankle Replacement (STAR), the positioning of the talar component and the selection of mobile-bearing thickness are critical. A biomechanical experiment was undertaken to establish the effects of these variables on the range of movement (ROM) of the ankle.

Six cadaver ankles containing a specially-modified STAR prosthesis were subjected to ROM determination, under weight-bearing conditions, while monitoring the strain in the peri-ankle ligaments. Each specimen was tested with the talar component positions in neutral, as well as 3 and 6 mm of anterior and posterior displacement. The sequence was repeated with an anatomical bearing thickness, as well as at 2 mm reduced and increased thicknesses. The movement limits were defined as 10% strain in any ligament, bearing lift-off from the talar component or limitations of the hardware.

Both anterior talar component displacement and bearing thickness reduction caused a decrease in plantar flexion, which was associated with bearing lift-off. With increased bearing thickness, posterior displacement of the talar component decreased plantar flexion, whereas anterior displacement decreased dorsiflexion.