Introduction

The main postoperative complications in fixation of ulna shaft fractures are non-union and implant irritation using currently recommended 3.5-mm locking compression plates. An alternative approach using a combination of two smaller plates in orthogonal configuration has been proposed. The aim of this study was to compare the biomechanical properties of a single 3.5-mm locking compression plate versus double plating using one 2.5-mm and one 2.0-mm mandible plate in a human ulna shaft fracture model.

Introduction

Distal triceps tendon rupture is related to high complication rates with up to 25% failures. Elbow stiffness is another severe complication, as the traditional approach considers prolonged immobilization to ensure tendon healing. Recently a dynamic high-strength suture tape was designed, implementing a silicone-infused core for braid shortening and preventing repair elongation during mobilization, thus maintaining constant tissue approximation. The aim of this study was to biomechanically compare the novel dynamic tape versus a conventional high-strength suture tape in a human cadaveric distal triceps tendon rupture repair model.

Introduction

Tendon ruptures are a common injury and often require surgical intervention to heal. A refixation is commonly performed with high-strength suture material. However, slipping of the thread is unavoidable even at 7 knots potentially leading to reduced compression of the sutured tendon at its footprint. This study aimed to evaluate the biomechanical properties and effectiveness of a novel dynamic high-strength suture, featuring self-tightening properties.

Introduction

Transosseous flexion-distraction injuries of the spine typically require surgical intervention by stabilizing the fractured vertebra during healing with a pedicle-screw-rod constructs. As healing is taking place the load shifts from the implant back to the spine. Monitoring the load-induced deflection of the rods over time would allow quantifiable postoperative assessment of healing progress without the need for radiation exposure or frequent hospital visits. This approach, previously demonstrated to be effective in assessing fracture healing in long bones and monitoring posterolateral spinal fusion in sheep, is now being investigated for its potential in evaluating lumbar vertebra transosseous fracture healing.

Aim

In this study we investigated the effects of non-steroidal anti-inflammatory drugs (NSAIDs) with different cyclooxygenase (COX) selectivity on orthopaedic device-related infections (ODRIs) in a rat model. Specifically, we aimed to measure the impact of NSAID therapy on bone changes, bacterial load, and cytokine levels after treatment with antibiotics. In addition, we compared the effects of long vs short-term celecoxib (a COX-2 inhibitor) treatment on the same outcomes.

Aim

Debridement, Antibiotics, Irrigation, and implant Retention (DAIR) is a surgical treatment protocol suitable for some patients with fracture related infection (FRI). Clinically relevant pre-clinical models of DAIR are scarce and none have been developed in large animals. Therefore, this project aimed to develop a large animal model for FRI including a DAIR approach and compare outcomes after 2 or 5 weeks of infection.

We investigated the effects of non-steroidal anti-inflammatory drugs (NSAIDs) with different cyclooxygenase (COX) selectivity on orthopaedic device-related infections (ODRIs) in a rat model. We aimed to measure the impact of NSAID therapy on bone changes, bacterial load, and cytokine levels after treatment with antibiotics. We also compared the effects of long vs short-term celecoxib (a COX-2 inhibitor) treatment on the same outcomes.

Skeletally mature female Wistar rats were implanted with Staphylococcus epidermidis- contaminated polyetheretherketone (PEEK) screws in the proximal right tibia and monitored for 7 days. All animals received subcutaneous antibiotics (rifampicin plus cefazolin) for two weeks from day 7 to 21. In phase I of the study, rats were randomly assigned to receive 28 days of oral treatment with acetylsalicylic acid, ibuprofen, celecoxib, or vehicle control. In phase II, an additional group received seven days of celecoxib treatment from day 0 to 7. Bone changes were monitored using in vivo micro-CT and histology. Quantitative bacteriology was performed at euthanasia. Plasma samples were collected to measure cytokine levels on days 0, 6, 20, and 28.

Combination antibiotic therapy resulted in treatment success in 85.71% of cases, while the addition of long-term celecoxib treatment reduced it to 45.45%. Long-term celecoxib treatment significantly reduced bone loss (33.85% mean difference [95% CI 14.12–53.58], p=0.0004 on day 6 bone fraction) and periosteal reaction (0.2760 μm mean difference [95% CI 0.2073–0.3448], p<0.0001 on day 14 periosteal thickness) during early infection compared to the control group. Short- term celecoxib treatment showed similar radiological results without a reduction in treatment success (88.9%). No differences in the inflammatory markers were observed.

Our findings highlight the potential benefits of short-term use of celecoxib in improving bone fraction during the early post-infection period without impairing the efficacy of antibiotic therapy

In chronically infected fracture non-unions, treatment requires extensive debridement to remove necrotic and infected bone, often resulting in large defects requiring elaborate and prolonged bone reconstruction. One approach includes the induced membrane technique (IMT), although the differences in outcome between infected and non-infectious aetiologies remain unclear. Here we present a new rabbit humerus model for IMT secondary to infection, and, furthermore, we compare bone healing in rabbits with a chronically infected non-union compared to non-infected equivalents.

A 5 mm defect was created in the humerus and filled with a polymethylmethacrylate (PMMA) spacer or left empty (n=6 per group). After 3 weeks, the PMMA spacer was replaced with a beta-tricalcium phosphate (chronOs, Synthes) scaffold, which was placed within the induced membrane and observed for a further 10 weeks. The same protocol was followed for the infected group, except that four week prior to treatment, the wound was inoculated with Staphylococcus aureus (4×10⁶ CFU/animal) and the PMMA spacer was loaded with gentamicin, and systemic therapy was applied for 4 weeks prior to chronOs application.

All the animals from the infected group were culture positive during the first revision surgery (mean 3×10⁵ CFU/animal, n= 12), while at the second revision, after antibiotic therapy, all the animals were culture negative. The differences in bone healing between the non-infected and infected groups were evaluated by radiography and histology. The initially infected animals showed impaired bone healing at euthanasia, and some remnants of bacteria in histology. The non-infected animals reached bone bridging in both empty and chronOs conditions.

We developed a preclinical in vivo model to investigate how bacterial infection influence bone healing in large defects with the future aim to explore new treatment concepts of infected non-union.

The aim of this study was to investigate the effect of different loading scenarios and foot positions on the configuration of the distal tibiofibular joint (DTFJ).

Fourteen paired human cadaveric lower legs were mounted in a loading frame. Computed tomography scans were obtained in unloaded state (75 N) and single-leg loaded stand (700 N) of each specimen in five foot positions: neutral, 15° external rotation, 15° internal rotation, 20° dorsiflexion, and 20° plantarflexion. An automated three-dimensional measurement protocol was used to assess clear space (diastasis), translational angle (rotation), and vertical offset (fibular shortening) in each foot position and loading condition.

Foot positions had a significant effect on the configuration of DTFJ. Largest effects were related to clear space increase by 0.46 mm (SD 0.21 mm) in loaded dorsal flexion and translation angle of 2.36° (SD 1.03°) in loaded external rotation, both versus loaded neutral position. Loading had no effect on clear space and vertical offset in any position. Translation angle was significantly influenced under loading by −0.81° (SD 0.69°) in internal rotation only.

Foot positioning noticeably influences the measurement when evaluating the configuration of DTFJ. The influence of the weightbearing seems to have no relevant effect on native ankles in neutral position.

Implant removal after clavicle plating is common. Low-profile dual mini-fragment plate constructs are considered safe for fixation of diaphyseal clavicle fractures. The aim of this study was to investigate: (1) the biomechanical competence of different dual plate designs from stiffness and cycles to failure, and (2) to compare them against 3.5mm single superoanterior plating.

Twelve artificial clavicles were assigned to 2 groups and instrumented with titanium matrix mandible plates as follows: group 1 (G1) (2.5mm anterior+2.0mm superior) and group 2 (G2) (2.0mm anterior+2.0mm superior). An unstable clavicle shaft fracture (AO/OTA15.2C) was simulated. Specimens were cyclically tested to failure under craniocaudal cantilever bending, superimposed with torsion around the shaft axis and compared to previous published data of 6 locked superoanterior plates tested under the same conditions (G3).

Displacement (mm) after 5000 cycles was highest in G3 (10.7±0.8) followed by G2 (8.5±1.0) and G1 (7.5±1.0), respectively. Both outcomes were significantly higher in G3 as compared to both G1 and G2 (p≤0.027). Cycles to failure were highest in G3 (19536±3586) followed by G1 (15834±3492) and G2 (11104±3177), being significantly higher in G3 compared to G2 (p=0.004). Failure was breakage of one or two plates at the level of the osteotomy in all specimens. One G1 specimen demonstrated failure of the anterior plate. Both plates in other G1 specimens. Majority of G2 had fractures in both plates. No screw pullout or additional clavicle fractures were observed among specimens.

Low-profile 2.0/2.0 dual plates demonstrated similar initial stiffness compared to 3.5mm single plates, however, had significantly lower failure endurance. Low-profile 2.5/2.0 dual plates showed significant higher initial stiffness and similar resistance to failure compared to 3.5mm single locked plates and can be considered as a useful alternative for diaphyseal clavicle fracture fixation. These results complement the promising results of several clinical studies.

Fracture related infection remains a major challenge in musculoskeletal trauma surgery. Despite best practice, treatment strategies suffer from high failure rates due to antibiotic resistance and tolerance. Bacteriophages represent a promising alternative as they retain activity against such bacteria. However, optimal phage administration protocols remain unknown, although injectable hydrogels, loaded with phage and conventional antibiotics, may support conventional therapy.

In this study we tested the activity of meropenem, and two newly isolated bacteriophages (ϕ9 and ϕ3) embedded within alginate-chitosan microbeads and a hydrogel. Antibiotic and phage stability and activity were monitored in vitro, over a period of 10 days. In vivo, the same material was tested in treatment of a 5-day old Pseudomonas aeruginosa infection of a tibial plate osteotomy in mice. Treatment involved debridement and 5 days of systemic antibiotic therapy plus: i- saline, ii-phages in saline, iii-phages and antibiotics loaded into a hydrogel (n=7 mice/group). To assess the efficacy of the treatments, the infection load was monitored during revision surgery with debridement of the infected tissue after 5,10 and 13 days (euthanasia) by CFU and PFU quantification.

In vitro testing confirmed that the stability of meropenem and activity of ϕ9 and ϕ3, was not affected within the alginate beads or hydrogel over 10 days. The in vivo study showed that all mice receiving phages and antibiotics loaded into a hydrogel survived the infection with a reduction of the bacterial load in the soft tissue. Active phages could be recovered from the infected site at euthanasia (10⁴ PFU/g).

The hydrogel loaded with bacteriophages and meropenem showed a positive result in locally reducing the infection load indicating a synergistic effect of the selected antimicrobials. Overall, our new strategy shows encouraging results for improving the treatment of antibiotic-resistant biofilm infections that are related to medical implants.

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. Joint dislocation was provoked for 11 human cadaveric glenoids in seven different dislocation directions between 3 o'clock (anterior) to 9 o'clock (posterior) dislocation. Shoulder stability ratio (SSR) and concavity gradient were assessed in intact condition, and after 3 mm and 6 mm simulated cartilage loss. The influence of cartilage loss on SSR and concavity gradient was statistically evaluated. Between intact state and 6 mm cartilage loss, both SSR and concavity gradient decreased significantly in every dislocation direction (p≤0.038), except the concavity gradient in 4 o'clock dislocation direction (p=0.088). Thereby, anterior-inferior dislocation directions were associated with the highest loss of SSR and concavity gradient of up to 59.0% and 49.4%, respectively, being significantly higher for SSR compared to all other dislocation directions (p≤0.04). The correlations between concavity gradient and SSR for pooled dislocation directions were significant for all three conditions of cartilage loss (p<0.001). 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 highest effect of cartilage loss was observed in anterior-inferior dislocation directions, suggesting that surgical intervention should be considered for recurrent shoulder dislocations in the presence of cartilage loss.

Osteochondral glenoid loss is associated with recurrent shoulder instability. The critical threshold for surgical stabilization is multidimensional and conclusively unknown. The aim of this work was to provide a well- measurable surrogate parameter of an unstable shoulder joint for the frequent anterior-inferior dislocation direction.

The shoulder stability ratio (SSR) of 10 paired human cadaveric glenoids was determined in anterior-inferior dislocation direction. Osteochondral defects were simulated by gradually removing osteochondral structures in 5%-stages up to 20% of the intact diameter. The glenoid morphological parameters glenoid depth, concavity gradient, and defect radius were measured at each stage by means of optical motion tracking. Based on these parameters, the osteochondral stability ratio (OSSR) was calculated. Correlation analyses between SSR and all morphological parameters, as well as OSSR were performed.

The loss of SSR, concavity gradient, depth and OSSR with increasing defect size was significant (all p<0.001). The loss of SSR strongly correlated with the losses of concavity gradient (PCC = 0.918), of depth (PCC = 0.899), and of OSSR (PCC = 0.949). In contrast, the percentage loss based on intact diameter (defect size) correlated weaker with SSR (PCC=0.687). Small osteochondral defects (≤10%) led to significantly higher SSR decrease in small glenoids (diameter <25mm) compared to large (≥ 25mm) ones (p ≤ 0.009).

From a biomechanical perspective, the losses of concavity gradient, glenoid depth and OSSR correlate strong with the loss of SSR. Therefore, especially the loss of glenoidal depth may be considered as a valid and reliable alternative parameter to describe shoulder instability. Furthermore, smaller glenoids are more vulnerable to become unstable in case of small osteochondral loosening. On the other hand, the standardly used percentage defect size based on intact diameter correlates weaker with the magnitude of instability and may therefore not be a valid parameter for judgement of shoulder instability.

Proximal humeral shaft fractures are commonly treated with long straight plates or intramedullary nails. Helical plates might overcome the downsides of these techniques as they are able to avoid the radial nerve distally. The aim of this study was to investigate in an artificial bone model: (1) the biomechanical competence of different plate designs and (2) to compare them against the alternative treatment option of intramedullary nails.

Twenty-four artificial humeri were assigned in 4 groups and instrumented as follows: group1 (straight 10-hole-PHILOS), group2 (MULTILOCK-nail), group3 (45°-helical-PHILOS) and group4 (90°-helical-PHILOS). An unstable proximal humeral shaft fracture was simulated. Specimens were tested under quasi-static loading in axial compression, internal/external rotation and bending in 4 directions monitored by optical motion tracking.

Axial displacement (mm) was significantly lower in group2 (0.1±0.1) compared to all other groups (1: 3.7±0.6; 3: 3.8±0.8; 4: 3.5±0.4), p<0.001. Varus stiffness in group2 (0.8±0.1) was significantly higher compared to groups1+3, p≤0.013 (1: 0.7±0.1; 3: 0.7±0.1; 4: 0.8±0.1). Varus bending (°) was significantly lower in group2 compared to all other groups (p<0.001) and group4 to group1, p=0.022. Flexion stiffness in group1 was significantly higher compared to groups2+4 (p≤0,03) and group4 to group1, p≤0,029 (1: 0.8±0.1; 2: 0.7±0.1; 3: 0.7±0.1; 4: 0.6±0.1). Flexion bending (°) in group4 was higher compared to all other groups (p≤0.024) and lower in group2 compared to groups1+4, p≤0.024. Torsional stiffness remained non significantly different, p≥0.086. Torsional deformation in group2 was significantly higher compared to all other groups, p≤0.017. Shear displacement remained non significantly different, p≥0.112.

From a biomechanical perspective, helical plating with 45° and 90° may be considered as a valid alternative fixation technique to standard straight plating of proximal third humeral fractures. Intramedullary nails demonstrated higher axial and bending stiffness as well as lower fracture gap movements during axial loading compared to all plate designs. However, despite similar torsional stiffness they were associated with higher torsional movements during internal/external rotation as compared to all investigated plate designs.

Introduction and Objective

Distal femoral fractures are commonly treated with a straight plate fixed to the lateral aspects of both proximal and distal fragments. However, the lateral approach may not always be desirable due to persisting soft-tissue or additional vascular injury necessitating a medial approach. These problems may be overcome by pre-contouring the plate in helically shaped fashion, allowing its distal part to be fixed to the medial aspect of the femoral condyle. The objective of this study was to investigate the biomechanical competence of medial femoral helical plating versus conventional straight lateral plating in an artificial distal femoral fracture model.

Introduction and Objective

Plating of geriatric distal femoral fractures with Locking Compression Plate Distal Femur (LCP–DF) often requires augmentation with a supplemental medial plate to achieve sufficient stability allowing early mobilization. However, medial vital structures may be impaired by supplemental medial plating using a straight plate. Therefore, a helically shaped medial plate may be used to avoid damage of these structures. Aim of the current study was to investigate the biomechanical competence of augmented LCP–DF plating using a supplemental straight versus helically shaped medial plate.

Artificial bone models (ABMs) are commonly used in traumatology and orthopedics for training, education, research and development purposes. The aim of this study was to develop the first evidence-based generic Asian pelvic bone model and compare it to an existing pelvic model.

A hundred clinical CT scans of intact adult pelvises (54.8±16.4 years, 161.3±8.3 cm) were acquired. They represented evenly distributed female and male patients of Malay (n=33), Chinese (n=34) and Indian (n=33) descent. The CTs were segmented and defined landmarks were placed. By this means, 100 individual three-dimensional models were calculated using thin plate spline transformation. Following, three statistical mean pelvic models (male, female, unisex) were generated. Anatomical variations were analyzed using principal component analysis (PCA). To quantify length variations, the distances between the anterior superior iliac spines (ASIS), the anterior inferior iliac spines (AIIS), the promontory and symphysis (conjugate vera) as well as the ischial spines (diameter transversa) were measured for the three mean models and the existing ABM.

PCA demonstrated large variability regarding pelvic surface and size. Principal component one (PC 1) contributed to 24% of the total anatomical variation and predominantly displayed a size variation pattern. PC 2 (17.7% of variation) mainly exhibited anatomical variations originating from differences in shape. Female and male models were similar in ASIS (225±20 mm; 227±13 mm) and AIIS (185±11 mm; 187±10 mm), whereas differed in conjugate vera (116±10 mm; 105±10 mm) and diameter transversa (105±7 mm; 88±8 mm). Comparing the Asian unisex model to the existing ABM, the external pelvic measurements ASIS (22.6 cm; 27.5 cm) and AIIS (186 mm; 209 mm) differed notably. Conjugate vera (111 mm; 105 mm) and diameter transversa (97 mm; 95 mm) were similar in both models. Low variability of mean distances (3.78±1.7 mm) was found beyond a sample number of 30 CTs.

Our analysis revealed notable anatomical variations regarding size dominating over shape and gender-specific variability. Dimensions of the generated mean models were comparatively smaller compared to the existing ABM. This highlights the necessity for generation of Asian ABMs by evidence-based modeling techniques.

Femoral neck fractures account for half of all hip fractures and are recognized as a major public health problem associated with a high socioeconomic burden. Whilst internal fixation is preferred over arthroplasty for physiologically younger patients, no consensus exists about the optimal fixation device yet. The recently introduced implant Femoral Neck System (FNS) (DePuy Synthes, Zuchwil, Switzerland) was developed for dynamic fixation of femoral neck fractures and provides angular stability in combination with a minimally invasive surgical technique. Alternatively, the Hansson Pin System (HPS) (Swemac, Linköping, Sweden) exploits the advantages of internal buttressing. However, the obligate peripheral placement of the pins, adjacent to either the inferior or posterior cortex, renders the instrumentation more challenging. The aim of this study was to evaluate the biomechanical performance of FNS versus HPS in a Pauwels II femoral neck fracture model with simulated posterior comminution. Forty-degree Pauwels II femoral neck fractures AO 31-B2.1 with 15° posterior wedge were simulated in fourteen paired fresh-frozen human cadaveric femora, followed by instrumentation with either FNS or HPS in pair-matched fashion. Implant positioning was quantified by measuring the shortest distances between implant and inferior cortex (DI) as well as posterior cortex (DP) on anteroposterior and axial X-rays, respectively. Biomechanical testing was performed in 20° adduction and 10° flexion of the specimens in a novel setup with simulated iliopsoas muscle tension. Progressively increasing cyclic loading was applied until construct failure. Interfragmentary femoral head-to-shaft movements, namely varus deformation, dorsal tilting and rotation around the neck axis were measured by means of motion tracking and compared between the two implants. In addition, varus deformation and dorsal tilting were correlated with DI and DP. Cycles to 5/10° varus deformation were significantly higher for FNS (22490±5729/23007±5496) versus HPS (16351±4469/17289±4686), P=0.043. Cycles to 5/10° femoral head dorsal tilting (FNS: 10968±3052/12765±3425; HPS: 12244±5895/13357±6104) and cycles to 5/10° rotation around the femoral neck axis (FNS: 15727±7737/24453±5073; HPS: 15682±10414/20185±11065) were comparable between the implants, P≥0.314. For HPS, the outcomes for varus deformation and dorsal tilting correlated significantly with DI and DP, respectively (P=0.025), whereas these correlations were not significant for FNS (P≥0.148).

From a biomechanical perspective, by providing superior resistance against varus deformation and performing in a less sensitive way to variations in implant placement, the angular stable Femoral Neck System can be considered as a valid alternative to the Hansson Pin System for the treatment of Pauwels II femoral neck fractures.

Being commonly missed in the clinical practice, Lisfranc injuries can lead to arthritis and long-term complications. There are controversial opinions about the contribution of the main stabilizers of the joint. Moreover, the role of the ligament that connects the medial cuneiform (MC) and the third metatarsal (MT3) is not well investigated. The aim of this study was to investigate the influence of different Lisfranc ligament injuries on CT findings under two specified loads.

Sixteen fresh-frozen human cadaveric lower limbs were embedded in PMMA at mid-shaft of the tibia and placed in a weight-bearing radiolucent frame for CT scanning. All intact specimens were initially scanned under 7.5 kg and 70 kg loads in neutral foot position. A dorsal approach was then used for sequential ligaments cutting: first – the dorsal and the (Lisfranc) interosseous ligaments; second – the plantar ligament between the MC and MT3; third – the plantar Lisfranc ligament between the MC and the MT2. All feet were rescanned after each cutting step under the two loads.

The average distances between MT1 and MT2 in the intact feet under 7.5 kg and 70 kg loads were 0.77 mm and 0.82 mm, whereas between MC and MT2 they were 0.61 mm and 0.80 mm, without any signs of misalignment or dorsal displacement of MT2. A slight increase in the distances MT1-MT2 (0.89 mm; 0.97 mm) and MC-MT2 (0.97 mm; 1.13 mm) was observed after the first disruption of the dorsal and the interosseous ligaments under 7.5 kg and 70 kg loads. A further increase in MT1-MT2 and MC-MT2 distances was registered after the second disruption of the ligament between MC and MT3. The largest distances MT1-MT2 (1.5 mm; 1.95 mm) and MC-MT2 (1.74 mm; 2.35 mm) were measured after the final plantar Lisfranc ligament cut under the two loads. In contrast to the previous two the previous two cuts, misalignment and dorsal displacement of 1.25 mm were seen at this final disrupted stage.

The minimal pathological increase in the distances MT1-MT2 and MC-MT2 is an important indicator for ligamentous Lisfranc injury. Dorsal displacement and misalignment of the second metatarsal in the CT scans identify severe ligamentous Lisfranc injury. The plantar Lisfranc ligament between the medial cuneiform and the second metatarsal seems to be the strongest stabilizer of the Lisfranc joint. Partial lesion of the Lisfranc ligaments requires high clinical suspicion as it can be easily missed.

Displaced intraarticular calcaneal fractures are debilitating injuries with significant socioeconomic and psychological effects primarily affecting patients in active age between 30 and 50 years. Recently, minimally and less invasive screw fixation techniques have become popular as alternative to locked plating. The aim of this study was to analyze biomechanically in direct comparison the primary stability of 3 different cannulated screw configurations for fixation of Sanders type II-B intraarticular calcaneal fractures.

Fifteen fresh-frozen human cadaveric lower limbs were amputated mid-calf and through the Chopart joint. Following, soft tissues at the lateral foot side were removed, whereas the medial side and Achilles tendon were preserved. Reproducible Sanders type II-B intraarticular fracture patterns were created by means of osteotomies. The proximal tibia end and the anterior-inferior aspect of the calcaneus were then embedded in polymethylmethacrylate. Based on bone mineral density measurements, the specimens were randomized to 3 groups for fixation with 3 different screw configurations using two 6.5 mm and two 4.5 mm cannulated screws. In Group 1, two parallel longitudinal screws entered the tuber calcanei above the Achilles tendon insertion and proceeded to the anterior process, and two transverse screws fixed the posterior facet perpendicular to the fracture line. In Group 2, two parallel screws entered the tuber calcanei below the Achilles tendon insertion, aiming at the anterior process, and two transverse screws fixed the posterior facet. In Group 3, two screws were inserted along the bone axis, entering the tuber calcanei above the Achilles tendon insertion and proceeding to the central-inferior part of the anterior process. In addition, one transverse screw was inserted from lateral to medial for fixation of the posterior facet and one oblique screw – inserted from the posterior-plantar part of the tuber calcanei – supported the posterolateral part of the posterior facet. All specimens were tested in simulated midstance position under progressively increasing cyclic loading at 2 Hz. Starting from 200N, the peak load of each cycle increased at a rate of 0.1 N/cycle. Interfragmentary movements were captured by means of optical motion tracking and triggered mediolateral x-rays.

Plantar movement, defined as displacement between the anterior process and the tuber calcanei at the most inferior side was biggest in Group 2 and increased significantly over test cycles in all groups (P = 0.001). Cycles to 2 mm plantar movement were significantly higher in both Group 1 (15847 ± 5250) and Group 3 (13323 ± 4363) compared to Group 2 (4875 ± 3480), P = 0.048. Medial gapping after 2500 cycles was significantly bigger in Group 2 versus Group 3, P = 0.024. No intraarticular displacement was observed in any group during testing.

From biomechanical perspective, screw configuration implementing one oblique screw seems to provide sufficient hindfoot stability in Sanders Type II-B intraarticular calcaneal fractures under dynamic loading. Posterior facet support by means of buttress or superiorly inserted longitudinal screws results in less plantar movement between the tuber calcanei and anterior fragments. On the other hand, inferiorly inserted longitudinal screws seem to be associated with bigger interfragmentary movements.