Cartilage decisively shapes the glenoid concavity and contributes significantly to shoulder stability.

PURPOSE: Glenohumeral joint injuries frequently result in shoulder instability. However, the biomechanical effect of cartilage loss on shoulder stability remains unknown. The aim of the current study was to investigate biomechanically the effect of two severity stages of cartilage loss in different dislocation directions on shoulder stability. METHODS: Joint dislocation was provoked in 11 human cadaveric glenoids for 7 different directions between 3 o'clock (anterior) and 9 o'clock (posterior). Shoulder stability ratio (SSR) and concavity gradient were assessed in three states: intact, 3 mm and 6 mm simulated cartilage loss. The influence of cartilage loss on SSR and concavity gradient was statistically evaluated. RESULTS: Both SSR and concavity gradient decreased significantly between intact state and 6 mm cartilage loss in every dislocation direction (p ≤ 0.038), except concavity gradient in 4 o'clock direction. Thereby, anterior-inferior dislocation directions were associated with the highest decrease in both SSR and concavity gradient of up to 59.0% and 49.4%, respectively, being significantly bigger for SSR compared with all other dislocation directions (p ≤ 0.040). Correlations between concavity gradient and SSR for pooled dislocation directions were significant in each separate specimen's state (p < 0.001). CONCLUSION: From a biomechanical perspective, articular cartilage of the glenoid contributes significantly to the concavity gradient, correlating strongly with the associated loss in glenohumeral joint stability. The biggest effect of cartilage loss is observed in the most frequently occurring anterior-inferior dislocation directions, suggesting that surgical interventions to restore cartilage's surface and concavity should be considered for recurrent shoulder dislocations in presence of cartilage loss.

Standardized artificially created stable pertrochanteric femur fractures present more homogenous results compared to osteotomies for orthopaedic implant testing.

BACKGROUND: With regard to biomechanical testing of orthopaedic implants, there is no consensus on whether artificial creation of standardized bone fractures or their simulation by means of osteotomies result in more realistic outcomes. Therefore, the aim of this study was to artificially create and analyze in an appropriate setting the biomechanical behavior of standardized stable pertrochanteric fractures versus their simulation via osteotomizing. METHODS: Eight pairs of fresh-frozen human cadaveric femora aged 72.7 ± 14.9 years (range 48-89 years) were assigned in paired fashion to two study groups. In Group 1, stable pertrochanteric fractures AO/OTA 31-A1 were artificially created via constant force application on the anterior cortex of the femur through a blunt guillotine blade. The same fracture type was simulated in Group 2 by means of osteotomies. All femora were implanted with a dynamic hip screw and biomechanically tested in 20° adduction under progressively increasing physiologic cyclic axial loading at 2 Hz, starting at 500 N and increasing at a rate of 0.1 N/cycle. Femoral head fragment movements with respect to the shaft were monitored by means of optical motion tracking. RESULTS: Cycles/failure load at 15° varus deformation, 10 mm leg shortening and 15° femoral head rotation around neck axis were 11324 ± 848/1632.4 ± 584.8 N, 11052 ± 1573/1605.2 ± 657.3 N and 11849 ± 1120/1684.9 ± 612.0 N in Group 1, and 10971 ± 2019/1597.1 ± 701.9 N, 10681 ± 1868/1568.1 ± 686.8 N and 10017 ± 4081/1501.7 ± 908.1 N in Group 2, respectively, with no significant differences between the two groups, p ≥ 0.233. CONCLUSION: From a biomechanical perspective, by resulting in more consistent outcomes under dynamic loading, standardized artificial stable pertrochanteric femur fracture creation may be more suitable for orthopaedic implant testing compared to osteotomizing the bone.

Local application of a gentamicin-loaded thermo-responsive hydrogel allows for fracture healing upon clearance of a high Staphylococcus aureus load in a rabbit model.

Antibiotic-loaded biomaterials (ALBs) have emerged as a potential useful adjunctive antimicrobial measure for the prevention of infection in open fracture care. A biodegradable thermo-responsive poly(N-isopropylacrylamide) grafted hyaluronic acid (HApN) hydrogel loaded with gentamicin has recently been shown to prevent implant-related infection in a rabbit osteosynthesis model. The primary aim of this study was to determine the influence of this HApN hydrogel on bone healing at an early stage (4 weeks). A rabbit humeral osteotomy model with plating osteosynthesis was used to compare fracture healing in rabbits receiving the hydrogel as compared with control animals. The secondary aim was to observe fracture healing in groups treated with and without antibiotic-loaded hydrogel in the presence of bacterial contamination. In all groups, outcome measures were mechanical stability and histological score, with additional quantitative bacteriology in the inoculated groups. Application of the HApN hydrogel in non-inoculated rabbits did not significantly influence humeral stiffness or histological scores for fracture healing in comparison to controls. In the inoculated groups, animals receiving the bacterial inoculum without hydrogel were culture-positive at euthanasia and found to display lower humeral stiffness values and higher histopathological scores for bacterial presence in comparison with equivalents receiving the gentamicin-loaded HApN hydrogel, which were also infection-free. In summary, our data showed that HApN was an effective antibiotic carrier that did not affect fracture healing. This data supported its suitability for application in fracture care. Addition of osteopromotive compounds could provide further support for accelerating fracture healing in addition to successful infection prophylaxis.

Biomechanical investigation of a minimally invasive posterior spine stabilization system in comparison to the Universal Spinal System (USS).

BACKGROUND: Although minimally invasive posterior spine implant systems have been introduced, clinical studies reported on reduced quality of spinal column realignment due to correction loss. The aim of this study was to compare biomechanically two minimally invasive spine stabilization systems versus the Universal Spine Stabilization system (USS). METHODS: Three groups with 5 specimens each and 2 foam bars per specimen were instrumented with USS (Group 1) or a minimally invasive posterior spine stabilization system with either polyaxial (Group 2) or monoaxial (Group 3) screws. Mechanical testing was performed under quasi-static ramp loading in axial compression and torsion, followed by destructive cyclic loading run under axial compression at constant amplitude and then with progressively increasing amplitude until construct failure. Bending construct stiffness, torsional stiffness and cycles to failure were investigated. RESULTS: Initial bending stiffness was highest in Group 3, followed by Group 2 and Group 1, without any significant differences between the groups. A significant increase in bending stiffness after 20'000 cycles was observed in Group 1 (p = 0.002) and Group 2 (p = 0.001), but not in Group 3, though the secondary bending stiffness showed no significant differences between the groups. Initial and secondary torsional stiffness was highest in Group 1, followed by Group 3 and Group 2, with significant differences between all groups (p ≤ 0.047). A significant increase in initial torsional stiffness after 20'000 cycles was observed in Group 2 (p = 0.017) and 3 (p = 0.013), but not in Group 1. The highest number of cycles to failure was detected in Group 1, followed by Group 3 and Group 2. This parameter was significantly different between Group 1 and Group 2 (p = 0.001), between Group 2 and Group 3 (p = 0.002), but not between Group 1 and Group 3. CONCLUSIONS: These findings quantify the correction loss for minimally invasive spine implant systems and imply that unstable spine fractures might benefit from stabilization with conventional implants like the USS.

A rabbit humerus model of plating and nailing osteosynthesis with and without Staphylococcus aureus osteomyelitis.

The local mechanical environment at a fracture is known to influence biological factors such as callus formation, immune cell recruitment and susceptibility to infection. Infection models incorporating a fracture are therefore required to evaluate prevention and treatment of infection after osteosynthesis. The aim of this study was to create humane, standardised and repeatable preclinical models of implant-related bone infection after osteosynthesis in the rabbit humerus. Custom-designed interlocked intramedullary nails and commercially available locking plates were subjected to biomechanical evaluation in cadaveric rabbit humeri; a 10-week in vivo healing study; a dose response study with Staphylococcus aureus over 4 weeks; and finally, a long-term infection of 10 weeks in the plate model.Outcome measures included biomechanical testing, radiography, histology, haematology and quantitative bacteriology. Both implants offered similar biomechanical stability in cadaveric bones, and when applied in the in vivo study, resulted in complete radiographic and histological healing and osteotomy closure within 10-weeks. As expected in the infection study, higher bacterial doses led to an increasing infection rate. In both infected groups, there was a complete lack of osteotomy closure at 4 weeks. C-reactive protein (CRP), lymphocyte: granulocyte ratio and weight loss were increased in infected animals receiving IM nails in comparison with non-inoculated equivalents, although this was less evident in the plate group. In the 10-week infection group, healing does not occur in the plated rabbits. We have successfully developed a rabbit model that is suitable for further studies, particularly those looking into preventative strategies for post-traumatic implant-related osteomyelitis.

Comminuted intraarticular calcaneal fractures: Multiplanar VA locked plating and interlocked nailing incorporate longitudinal strut and provide superior stability - a biomechanical cadaveric study.

Treatment of comminuted intraarticular calcaneal fractures remains controversial and challenging. The aim of this study was to investigate the biomechanical performance of three different methods for fixation of such fractures. Comminuted calcaneal fractures, including Sanders III AB fracture of the posterior facet and Kinner II B fracture of the calcaneocuboid joint (CCJ) articular calcaneal surface, were created in 18 human cadaveric lower legs by osteotomizing. The ankle joint, medial soft tissues and midtarsal bones along with their ligaments were preserved. The specimens were randomized to three groups for fixation with either (1) 2.7 mm variable-angle locking lateral calcaneal plate (Group 1), (2) 2.7 mm variable-angle locking anterolateral calcaneal plate in combination with one 4.5 mm and one 6.5 mm cannulated screws (Group 2), or (3) interlocking calcaneal nail with 3.5 mm screws in combination with three separate 4.0 mm cannulated screws (Group 3). All specimens were biomechanically tested to failure under axial loading in midstance foot position. Each test commenced with a quasi-static compression ramp from 50 to 200 N, followed by progressively increasing cyclic loading at 2 Hz. Starting from 200 N, the peak load of each cycle increased at a rate of 0.2 N/cycle. Interfragmentary movements were captured by motion tracking. In addition, mediolateral X-rays were taken every 250 cycles with a triggered C-arm. Böhler angle after 5000 cycles (1200 N peak load) increased significantly more in Group 1 compared to both other groups (P ≤ 0.020). Varus deformation of 10° between the calcaneal tuberosity and the lateral calcaneal fragments was reached at significantly lower number of cycles in Group 1 compared the other groups (P ≤ 0.017). Both cycles to 10° plantar gapping between the anterior process and the calcaneal tuberosity fragments, and 2 mm displacement at the CCJ articular calcaneal surface revealed no significant differences among the groups (P ≥ 0.773). From a biomechanical perspective, treatment of comminuted intraarticular calcaneal fractures using anterolateral variable-angle locking plate with additional longitudinal screws or interlocked nail in combination with separate transversal screws provides superior stability as opposed to lateral variable-angle locked plating only.

Biomechanical evaluation of a new gliding screw concept for the fixation of proximal humeral fractures.

AIMS: Plating displaced proximal humeral fractures is associated with a high rate of screw perforation. Dynamization of the proximal screws might prevent these complications. The aim of this study was to develop and evaluate a new gliding screw concept for plating proximal humeral fractures biomechanically. METHODS: Eight pairs of three-part humeral fractures were randomly assigned for pairwise instrumentation using either a prototype gliding plate or a standard PHILOS plate, and four pairs were fixed using the gliding plate with bone cement augmentation of its proximal screws. The specimens were cyclically tested under progressively increasing loading until perforation of a screw. Telescoping of a screw, varus tilting and screw migration were recorded using optical motion tracking. RESULTS: Mean initial stiffness (N/mm) was 581.3 (sd 239.7) for the gliding plate, 631.5 (sd 160.0) for the PHILOS and 440.2 (sd 97.6) for the gliding augmented plate without significant differences between the groups (p = 0.11). Mean varus tilting (°) after 7500 cycles was comparable between the gliding plate (2.6; sd 1.9), PHILOS (1.2; sd 0.6) and gliding augmented plate (1.7; sd 0.9) (p = 0.10). Similarly, mean screw migration(mm) after 7500 cycles was similar between the gliding plate (3.02; sd 2.85), PHILOS (1.30; sd 0.44) and gliding augmented plate (2.83; sd 1.18) (p = 0.13). Mean number of cycles until failure with 5° varus tilting were 12702 (sd 3687) for the gliding plate, 13948 (sd 1295) for PHILOS and 13189 (sd 2647) for the gliding augmented plate without significant differences between the groups (p = 0.66). CONCLUSION: Biomechanically, plate fixation using a new gliding screw technology did not show considerable advantages in comparison with fixation using a standard PHILOS plate. Based on the finding of telescoping of screws, however, it may represent a valid approach for further investigations into how to avoid the cut-out of screws.Cite this article: Y. P. Acklin, I. Zderic, J. A. Inzana, S. Grechenig, R. Schwyn, R. G. Richards, B. Gueorguiev. Biomechanical evaluation of a new gliding screw concept for the fixation of proximal humeral fractures. Bone Joint Res 2018;7:422-429. DOI: 10.1302/2046-3758.76.BJR-2017-0356.R1.

The role of a small posterior malleolar fragment in trimalleolar fractures: a biomechanical study.

AIMS: The aim of this study was to investigate the effect of a posterior malleolar fragment (PMF), with < 25% ankle joint surface, on pressure distribution and joint-stability. There is still little scientific evidence available to advise on the size of PMF, which is essential to provide treatment. To date, studies show inconsistent results and recommendations for surgical treatment date from 1940. MATERIALS AND METHODS: A total of 12 cadaveric ankles were assigned to two study groups. A trimalleolar fracture was created, followed by open reduction and internal fixation. PMF was fixed in Group I, but not in Group II. Intra-articular pressure was measured and cyclic loading was performed. RESULTS: Contact area decreased following each fracture, while anatomical fixation restored it nearly to its intact level. Contact pressure decreased significantly with fixation of the PMF. In plantarflexion, the centre of force shifted significantly posteriorly in Group II and anteriorly in Group I. Load to failure testing showed no difference between the groups. CONCLUSION: Surgical reduction of a small PMF with less than 25% ankle joint surface improves pressure distribution but does not affect ankle joint stability. Cite this article: Bone Joint J 2018;100-B:95-100.

Ankle joint pressure changes in high tibial and distal femoral osteotomies: a cadaver study.

AIMS: To assess the effect of high tibial and distal femoral osteotomies (HTO and DFO) on the pressure characteristics of the ankle joint. MATERIALS AND METHODS: Varus and valgus malalignment of the knee was simulated in human cadaver full-length legs. Testing included four measurements: baseline malalignment, 5° and 10° re-aligning osteotomy, and control baseline malalignment. For HTO, testing was rerun with the subtalar joint fixed. In order to represent half body weight, a 300 N force was applied onto the femoral head. Intra-articular sensors captured ankle pressure. RESULTS: In the absence of restriction of subtalar movement, insignificant migration of the centre of force and changes of maximal pressure were seen at the ankle joint. With restricted subtalar motion, more significant lateralisation of the centre of force were seen with the subtalar joint in varus than in valgus position. Changes in maximum pressure were again not significant. CONCLUSION: The re-alignment of coronal plane knee deformities by HTO and DFO altered ankle pressure characteristics. When the subtalar joint was fixed in the varus position, migration of centre of force after HTO was more significant than when the subtalar joint was fixed in valgus. Cite this article: Bone Joint J 2017;99-B:59-65.

Are two retrograde 3.5 mm screws superior to one 7.3 mm screw for anterior pelvic ring fixation in bones with low bone mineral density?

OBJECTIVES: Osteosynthesis of anterior pubic ramus fractures using one large-diameter screw can be challenging in terms of both surgical procedure and fixation stability. Small-fragment screws have the advantage of following the pelvic cortex and being more flexible.The aim of the present study was to biomechanically compare retrograde intramedullary fixation of the superior pubic ramus using either one large- or two small-diameter screws. MATERIALS AND METHODS: A total of 12 human cadaveric hemipelvises were analysed in a matched pair study design. Bone mineral density of the specimens was 68 mgHA/cm3 (standard deviation (sd) 52). The anterior pelvic ring fracture was fixed with either one 7.3 mm cannulated screw (Group 1) or two 3.5 mm pelvic cortex screws (Group 2). Progressively increasing cyclic axial loading was applied through the acetabulum. Relative movements in terms of interfragmentary displacement and gap angle at the fracture site were evaluated by means of optical movement tracking. The Wilcoxon signed-rank test was applied to identify significant differences between the groups RESULTS: Initial axial construct stiffness was not significantly different between the groups (p = 0.463). Interfragmentary displacement and gap angle at the fracture site were also not statistically significantly different between the groups throughout the evaluated cycles (p ⩾ 0.249). Similarly, cycles to failure were not statistically different between Group 1 (8438, sd 6968) and Group 2 (10 213, sd 10 334), p = 0.379. Failure mode in both groups was characterised by screw cutting through the cancellous bone. CONCLUSION: From a biomechanical point of view, pubic ramus stabilisation with either one large or two small fragment screw osteosynthesis is comparable in osteoporotic bone. However, the two-screw fixation technique is less demanding as the smaller screws deflect at the cortical margins.Cite this article: Y. P. Acklin, I. Zderic, S. Grechenig, R. G. Richards, P. Schmitz, B. Gueorguiev. Are two retrograde 3.5 mm screws superior to one 7.3 mm screw for anterior pelvic ring fixation in bones with low bone mineral density? Bone Joint Res 2017;6:8-13. DOI: 10.1302/2046-3758.61.BJR-2016-0261.