Boyko Gueorguiev

Quantification of cancellous bone-compaction due to DHS® Blade insertion and influence upon cut-out resistance

BACKGROUND Compaction of cancellous bone is believed to prevent cut-out. This in vitro study quantified the compaction in the femoral head due to insertion of a dynamic hip screw-blade with and without predrilling and investigated the resulting implant anchorage under cyclic loading. METHODS Eight pairs of human cadaveric femoral heads were instrumented with a dynamic hip screw-blade made of Polyetheretherketon. Pairwise instrumentation was performed either with or without predrilling the specimens. CT scanning was performed before and after implantation, to measure bone-compaction. Subsequently the implant was removed and a third scan was performed to analyze the relaxation of the bone structure. Commercial implants were reinserted and the specimens were cyclically loaded until onset of cut-out occurred. The bone-implant interface was monitored by means of fluoroscopic imaging throughout the experiment. Paired t-tests were performed to identify differences regarding compaction, relaxation and cycles to failure. FINDINGS Bone density in the surrounding of the implant increased about 30% for the non-predrilled and 20% for the predrilled group when inserting the implant. After implant removal the predrilled specimens fully relaxed; the non-predrilled group showed about 10% plastic deformation. No differences were found regarding cycles to failure (P=0.32). INTERPRETATION Significant bone-compaction due to blade insertion was verified. Even though compaction was lower when predrilling the specimens, mainly elastic deformation was present, which is believed to primarily enhance the implant anchorage. Cyclic loading tests confirmed this thesis. The importance of the implantation technique with regard to predrilling is therefore decreased.

Angle stable interlocking screws improve construct stability of intramedullary nailing of distal tibia fractures: A biomechanical study

INTRODUCTION Intramedullary nailing is the treatment of choice for most displaced tibial shaft fractures. The ability to maintain a mechanically stable fixation becomes more difficult the further the fracture extends distally or proximally or when unreamed tibial nails are used. We assumed that a new angular stable locking option would provide improved stability and reduced interfragmentary movements in a distal tibia in vitro fracture model. MATERIALS AND METHODS Left and right bones of 8 pairs of human cadaveric tibiae were randomly assigned to either a group with conventional locked or a group with angular stable locked intramedullary nails. Nails of 10-mm-diameter were used after reaming up to 11 mm. A transverse distal osteotomy was performed and the specimens were tested mechanically under eccentric axial load. A video optical measurement system was used to determine the angular displacement of the osteotomy gap during loading. RESULTS Construct stiffness, maximum load of the bone-nail construct and gap angle at 0.5 kN load were measured. The group with the angular stable locking option showed significantly higher stiffness values and reduced fracture gap motion compared to the group with conventional locked nails. DISCUSSION A new angular stable locking option of intramedullary nails provides higher stability in terms of construct stiffness and reduced interfragmentary movements in a distal tibia in vitro fracture model.

Stability of Medial Locking Plate and Compression Screw Versus Two Crossed Screws for Lapidus Arthrodesis

Background: Lapidus (first metatarsocuneiform joint) arthrodesis is an established procedure for the management of hallux valgus. This study investigated the utility of fixation with a medial locking plate with adjunct compression screw versus fixation with two crossed screws. Materials and Methods: Eight pairs of fresh-frozen human specimens were used in a matched pair test. Bone mineral density (BMD) was measured with peripheral quantitative computed tomography (pQCT). Fixation with two 4-mm-diameter crossed screws was compared versus a medial locking plate (X-Locking Plate 2.4/2.7; Synthes, Solothurn, Switzerland) with adjunct 4-mm-diameter compression screw. The specimens were tested in a four-point bending test. Parameters obtained were initial stiffness; plantar joint-line gapping after one cycle, 100 and 1000 cycles; and number of cycles to failure. Failure was defined as more than or equal to 3 mm plantar gapping. Results: The groups did not differ significantly with regard to BMD (p = 0.866) and initial stiffness (p = 0.889). The plate-and-screw construct showed significantly less movement during testing, and significantly (p = 0.001) more cycles to failure than did the crossed-screw construct. There was a significant correlation (crossed-screw construct: p = 0.014; plate-and-screw construct: p = 0.010) between BMD and the number of cycles to failure. Conclusion: Under cyclic loading conditions, the construct using a medial locking plate with adjunct compression screw was superior to the construct using two crossed screws. Clinical Relevance: The medial locking-plate technique described could help shorten the period of nonweightbearing and reduce the risk of non-union.

Angular Stability Potentially Permits Fewer Locking Screws Compared With Conventional Locking in Intramedullary Nailed Distal Tibia Fractures: A Biomechanical Study

Objectives: To compare mechanical stability of angle-stable locking construct with four screws with conventional five screw locking in intramedullary nailed distal tibia fractures under cyclic loading. Methods: Ten pairs of fresh-frozen human cadaveric tibiae were intramedullary nailed and assigned to either an angle-stable locking construct consisting of four screws or conventional five-screw locking. After simulating an unstable distal two-fragmental 42-A3.1 fracture, the specimens were mechanically tested under quasistatic and cyclic sinusoidal axial and torsional loading. Results: Bending stiffness of the angle-stable and the conventional fixation was 644.3 N/° and 416.5 N/°, respectively (P = 0.075, power 0.434). Torsional stiffness of the angle-stable locking (1.91 Nm/°) was significantly higher compared with the conventional one (1.13 Nm/°; P = 0.001, power 0.981). Torsional play of the angle-stable fixation (0.08°) was significantly smaller compared with the conventional one (0.46°; P = 0.002, power 0.965). The angle-stable locking revealed significantly less torsional deformation in the fracture gap after one cycle (0.74°) than the conventional one (1.75°; P = 0.005, power 0.915) and also after 1000 cycles (angle-stable: 1.56°; conventional: 2.51°; P = 0.042, power 0.562). Modes of failure were fracture of the distal fragment, loosening of distal locking screws, nail breakage, and their combination, equally distributed between the groups (P = 0.325). Conclusions: Both the angle-stable locking technique using four screws and conventional locking consisting of five screws showed high biomechanical properties. Hence, angle-stable locking reflects a potential to maintain fixation stability while reducing the number of locking screws compared with conventional locking in intramedullary nailed unstable distal tibia fractures.

Biomechanical evaluation of a new fixation technique for internal fixation of three-part proximal humerus fractures in a novel cadaveric model.

BACKGROUND The optimal surgical treatment for displaced proximal humeral fractures is still controversial. A new implant for the treatment of three-part fractures has been recently designed. It supplements the existing Expert Humeral Nail with a locking plate. We developed a novel humeral cadaveric model and the existing implant and the prototype were biomechanically compared to determine their ability in maintaining interfragmentary stability. METHODS The bone mineral density of eight pairs of cadaveric humeri was assessed and a three-part proximal humeral fracture was simulated with a Greater Tuberosity osteotomy and a surgical neck wedge ostectomy. The specimens were randomly assigned to either treatment. A bone anchor simulated part of a rotator cuff tendon pulling on the Greater Tuberosity. Specimens were initially tested in axial compression and afterward with a compound cyclic load to failure. An optical 3D motion tracking system continuously monitored the relative interfragmentary movements. FINDINGS The specimen stabilized with the prototype demonstrated higher stiffness (P=0.036) and better interfragmentary stability (P values<0.028) than the contralateral treated with the existing implant. There was no correlation between the bone mineral density and any of the investigated variables. INTERPRETATION The convenience of this new IM-nail and locking plate assembly must be confirmed in vivo but the current study provides a biomechanical rationale for its use in the treatment of three-part proximal humeral fractures. The improved stability could be advantageous in particular when medial buttress is missing, even in osteoporotic bone.

Effect on dynamic mechanical stability and interfragmentary movement of angle-stable locking of intramedullary nails in unstable distal tibia fractures: a biomechanical study.

BACKGROUND Unstable distal tibia fractures are challenging injuries that require surgery. Increasingly, intramedullary nails are being used. However, fracture site anatomy may cause distal-fragment stabilization and fixation problems and lead to malunion/nonunion. We studied the influence of angle-stable nail locking on fracture gap movement and other biomechanical parameters. METHODS Eight pairs of fresh human cadaver tibiae were used. The bone mineral density (BMD) was determined. All tibiae were nailed with a Synthes Expert tibial nail. Within each pair, one tibia was randomized to receive conventional locking screws; the other, angle-stable screws with sleeves. A 7-mm osteotomy was created 10 mm above the upper distal locking screw, to simulate an AO 42-A3 fracture. Biomechanical testing involved nondestructive mediolateral and anteroposterior pure bending, followed by cyclic combined axial and torsional loading to catastrophic failure. The neutral zone was determined. Fracture gap movement was monitored with 3-D motion tracking. RESULTS The angle-stable locked constructs had a significantly smaller mediolateral neutral zone (mean: 0.04 degree; p=0.039) and significantly smaller fracture gap angulation (p=0.043). The number of cycles to failure did not differ significantly between the locking configurations. BMD was a significant covariate affecting the number of cycles to failure (p=0.008). However, over the first 20,000 cycles, there was no significant correlation in the angle-stable construct. CONCLUSIONS Angle-stable locking of the Expert tibial nail was associated with a significant reduction in the mediolateral neutral zone and in fracture gap movement. Angle-stable fixation also reduced the influence of BMD over the first 20,000 cycles.

A biomechanical study on proximal plate fixation techniques in periprosthetic femur fractures

INTRODUCTION Proximal plate fixation is a crucial factor in osteosynthesis of periprosthetic femur fractures. Stability and strength of different fixation concepts for proximal plate fixation were compared. MATERIALS AND METHODS Twelve fresh frozen, bone mineral density matched human femora, instrumented with cemented hip endoprosthesis were osteotomized simulating a Vancouver B1 fracture. Specimens were instrumented with locking compression plates, fixed proximally with either locking attachment plate (LAP), monocortical screws, cerclage plus monocortical screws (1cerclage) or cerclages only (4cerclages). Cyclic testing was performed with monotonically increasing load until failure. Relative movements at the proximal plate-femur interface were registered by motion tracking. RESULTS The LAP construct exhibited a significantly longer cumulative survival (failure criterion 1mm separation at the proximal plate fixation) compared to the monocortical (p=0.048) and 4cerclages constructs (p=0.012) but not to 1cerclage constructs. CONCLUSION Bicortical screw anchorage improves proximal plate fixation in periprosthetic fractures. The cerclage-screw combination is a valuable alternative especially in osteoporotic bone.

Comparison of Calcaneal Fixation of a Retrograde Intramedullary Nail with a Fixed-Angle Spiral Blade Versus a Fixed-Angle Screw

Background: Retrograde intramedullary nailing is an established technique for tibiotalocalcaneal arthrodesis (TTCA). In poor bone stock (osteoporosis, neuroarthropathy), device fixation in the hindfoot remains a problem. Fixed-angle spiral-blade fixation of the nail in the calcaneus could be useful. Materials and Methods: In seven matched pairs of human below-knee specimens, bone mineral density (BMD) was determined, and TTCA was performed with an intramedullary nail (Synthes Hindfoot Arthrodesis Nail HAN Expert Nailing System), using a conventional screw plus a fixed-angle spiral blade versus a conventional screw plus a fixed-angle screw, in the calcaneus. The constructs were subjected to quasi-static loading (dorsiflexion/plantarflexion, varus/valgus, rotation) and to cyclic loading to failure. Parameters studied were construct neutral zone (NZ) and range of motion (ROM), and number of cycles to failure. Results: With dorsiflexion/plantarflexion loading, the screw-plus-spiral-blade constructs had a significantly smaller ROM in the quasi-static test (p = 0.028) and early in the cyclic test (p = 0.02); differences in the other parameters were not significant. There was a significant correlation between BMD and cycles to failure for the two-screw constructs (r = 0.94; p = 0.002) and for the screw-plus-spiral-blade constructs (r = 0.86; p = 0.014). Conclusion: In TTCA with a HAN Expert Nailing System, the use of a calcaneal spiral blade can further reduce motion within the construct. This may be especially useful in poor bone stock. Clinical Relevance: Results obtained in this study could be used to guide the operating surgeons TTCA strategy.

Development of a technique for cement augmentation of nailed tibiotalocalcaneal arthrodesis constructs

BACKGROUND Tibiotalocalcaneal arthrodesis with a retrograde nail is an established procedure. Many patients considered for this arthrodesis have poor bone stock, which may make it difficult to obtain construct stability. This study was undertaken to determine whether stability could be enhanced by the cement augmentation of the calcaneal locking screws. METHODS A cannulated and perforated screw, and a technique for cement augmentation via this screw, were developed. Eight pairs of human cadaver bones were instrumented with a retrograde intramedullary device (Expert Hindfoot Arthrodesis Nail, Synthes AG, Solothurn, Switzerland). Within each pair, one specimen was randomized to have the nail interlocked in the calcaneus with two conventional screws; while the other specimen was similarly instrumented with the use of two cement-augmented screws. The bone mineral density was determined. In quasi-static tests, the neutral zone and the range of motion of the constructs were determined. Subsequently the specimens were tested in dorsiflexion/plantar flexion until failure occurred. The neutral zone and the range of motion of the constructs were determined every 200 cycles. FINDINGS Augmentation resulted in significantly greater stiffness and a significantly smaller range of motion in the quasi-static dorsiflexion/plantar flexion test, and in a significantly smaller neutral zone in all quasi-static tests. With cyclic loading, the number of cycles to failure was significantly larger in the augmented group. In both groups, bone mineral density was significantly correlated with the number of cycles to failure. Two augmented screws broke. INTERPRETATION Cement augmentation confers significant mechanical benefit in hindfoot arthrodesis and therefore can be used as a salvage procedure. Further development should be performed to validate the concept.

Sports Activity After Surgical Treatment of Intra-articular Tibial Plateau Fractures in Skiers

Background: Tibial plateau fractures occur frequently while participating in winter sports, but there is no information on whether skiers can resume sports and recreational activities after internal fixation of these fractures. Hypothesis: Skiers can resume low-impact sports activity after internal fixation of tibial plateau fractures. Study Design: Case series; Level of evidence, 4. Methods: A total of 103 patients were surveyed by postal questionnaires to determine their sports activities at a mean of 7.8 ± 1.8 years after internal fixation of intra-articular tibial plateau fractures. The survey also included the Lysholm score, the Tegner activity scale, and a visual analog scale (VAS) for pain. Results: At the time of the survey, 88% of the patients were engaged in sports activities (rate of return to sports, 88%), and 53% continued to participate in downhill skiing. The median number of different activities declined from 5 (range, 1-17) preoperatively to 4 (range, 0-11) postoperatively (P < .01). Sports frequency and duration per week did not change: 3 (range, 1-7) preoperatively versus 3 (range, 0-7) postoperatively (P = .275) and 4 hours (range, 1-16 hours) preoperatively versus 3.5 hours (range, 0-15 hours) postoperatively (P = .217), respectively. Median values of all outcome scores declined: Lysholm score, 100 (range, 85-100) preoperatively versus 94.5 (range, 37-100) postoperatively (P < .01); VAS, 0 (range, 0-7) preoperatively versus 1 (range, 0-8) postoperatively (P < .01). Median Tegner activity scale scores declined in all age groups except for patients aged 51 to 60 years. The ability to participate in sports at the time of follow-up compared with the ability before the accident was rated as “similar” by 57 patients (62.0%) and as “worse” by 35 patients (38.0%). The more severe fracture types, B3 and C3 according to the AO classification system, were associated with poorer outcomes related to return to sports and functional scores. Conclusion: A large percentage of skiers with surgically treated intra-articular tibial plateau fractures cannot continue to participate in downhill skiing; however, the majority could resume an active lifestyle for several years after the trauma. Fracture type seems to be an important factor influencing physical activity and general functional outcome.