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Address correspondence to: Tim Schepers, MD, PhD, Trauma Unit, Academic Medical Center, Meibergdreef 9, P.O. Box 22660, Amsterdam 1100 DD, The Netherlands.
Calcaneal fractures are notoriously difficult to treat and wound complications occur often. However, owing to the rare nature of these fractures, clinical trials on this subject are lacking. Thus, biomechanical studies form a viable source of information on this subject. With our systematic review of biomechanical studies, we aimed to provide an overview of all the techniques available and guide clinicians in their choice of method of fracture fixation. A literature search was conducted using 3 online databases to find biomechanical studies investigating methods of fixation for calcaneal fractures. A total of 14 studies investigating 237 specimens were identified. Large diversity was found in the tested fixation methods and in the test setups used. None of the studies found a significant difference in favor of any of the fixation methods. All tested methods provided a biomechanically stable fixation. All the investigated methods of fixation for calcaneal fractures seem to be biomechanically sufficient. No clear benefit was found for locking plates in the fixation of calcaneal fractures; however, a subtle mechanical superiority might exist compared with nonlocking plates in the case of fractures in osteoporotic bone. Several of the techniques tested would be suitable for a minimal invasive approach. These should be investigated further in clinical trials.
Calcaneal fractures are uncommon, and surgical treatment provides a challenge for surgeons owing to the high risk of wound complications and secondary posttraumatic osteoarthritis (
). Research has shown that patients with a displaced intraarticular calcaneal fracture (Sanders type ≥2) should preferably undergo surgery, not conservative treatment (
). The optimal calcaneal fracture fixation construct should provide rigid fixation of the main fracture fragments, have only minimal prominence of the implant (because of the thin soft tissue layer over a large area of the calcaneus), and should require as little soft tissue dissection as necessary for reconstruction (
Three widely accepted surgical options are available to achieve these goals: open reduction and internal fixation (ORIF) through an extended lateral approach, ORIF through a less invasive approach (i.e., sinus tarsi approach), and a fully percutaneous approach after closed reduction.
ORIF using the extended lateral approach allows for good fracture reduction; however, wound problems can be a major drawback. The rate of postoperative wound infections after ORIF of displaced fractures of the calcaneus is high, ≤25% (
). These less invasive techniques were developed to respect the soft tissue, minimizing the disturbance of the soft tissue envelope to decrease the risk of postoperative wound complications.
Possible internal fixation constructions include (or are a combination of) plates, screws, intramedullary devices, and Kirschner wires. Another option is to add bone substitute to enhance the strength of the screw fixation (
A biomechanical comparison of fixed angle locking compression plate osteosynthesis and cement augmented screw osteosynthesis in the management of intra articular calcaneal fractures.
For osteosynthesis using ORIF, the procedures in the past few years have shown a tendency toward the application of locking plate and screw constructs, creating an angular stable construction. For noncalcaneal fractures, locking plate fixation was found to be beneficial by adding to the strength of the construction (
Indirect, closed reduction comes with a greater risk of incomplete anatomic reduction of the joint surface, especially, if the fracture pattern is complex. When restoration of the anatomy is not possible, patients can develop posttraumatic osteoarthritis and arthrodesis might become necessary to relieve the pain (
Numerous clinical studies on the fixation of calcaneal fractures have been reported. However, because biomechanics are the basis for successful fixation of all fractures, we aimed to provide an overview of the biomechanically tested types of fixation of calcaneal fractures and identify which type of fixation has the best biomechanical properties. Identifying the fixation method with the best biomechanical properties could provide guidance for clinical trials regarding the different types of fixation for calcaneal fractures.
Materials and Methods
Search Strategy
The present systematic review was performed in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines (
The PRISMA statement for reporting systematic reviews and meta-analyses of studies that evaluate health care interventions: explanation and elaboration.
). The online databases of PubMed, Embase, and Web of Science were searched using the following keywords: calcaneus, postmortem, biomechanical, fracture fixation, and their synonyms, each fitted for the specific databases. Full search threads are available in the Appendix.
Inclusion Criteria
Reports were included if they met the following criteria:
1.
The study concerned displaced intraarticular calcaneal fractures (Sanders type ≥2)
2.
The report concerned postmortem (cadaveric) human specimens
3.
The study was a biomechanical study
4.
Internal fixation had been performed
No date limits were imposed on the search. The reports were screened by 2 independent reviewers (S.A.D., F.W.S.), using an online tool (available at: www.covidence.org). Disagreements on inclusion were solved through discussion with a third person (T.S.).
Exclusion Criteria
Studies were excluded based on the full-text. They were excluded if they met the following criteria:
1.
Used nonhuman calcanei (e.g., saw bone)
2.
Not in English.
3.
Study topic of arthrodesis
4.
Conference abstract
5.
Review
The references of the included reports were checked for additional relevant studies.
Data Extraction
Data extraction included the type of fixation technique used; fracture type; number of specimens; bone mineral density and/or age of the specimens; test setup; outcome measures; and major findings and/or conclusions. We did not perform a meta-analysis (due to the heterogeneity of the data) and as a result of this no statistical tests were applied. When addressing statistical significance we cited the authors of the included studies.
Results
The search was performed on September 1, 2016. The search yielded a total of 413 hits, including: 168 (40.68%) Pubmed hits, 168 (40.68%) Embase via Ovid hits, and 77 (18.65%) Web of Science hits.
After identifying the studies in the different databases, duplicates were removed (n = 188 [45.52%]). This left 225 (54.48%) reports to screen by title and abstract. Of those, 206 (49.88%) did not meet inclusion criteria and were excluded. A total of 19 (4.6%) studies were selected for full text screening, of which 5 (1.21%) studies were excluded. The reasons for exclusion were non-English language (n = 2) (
In total, 237 calcanei were investigated. The fractures were inflicted by osteotomy, impact loading, or the use of stress-risers (i.e., load to failure testing). The investigated calcaneal fracture fixation techniques included conventional plates, locking plates, unicortical screws, bicortical screws, small fragment plates, intramedullary devices, augmented screw osteosynthesis, compression bolts, and longitudinal screws added to lateral plates. The results of the included studies are listed in the Table (
A biomechanical comparison of fixed angle locking compression plate osteosynthesis and cement augmented screw osteosynthesis in the management of intra articular calcaneal fractures.
Primary stability of an intramedullary calcaneal nail and an angular stable calcaneal plate in a biomechanical testing model of intraarticular calcaneal fracture.
). The authors concluded that all tested fixation methods seemed to be biomechanically adequate and did not differ significantly from each other. The use of locking devices did not seem to strengthen the construction compared with the conventional devices (
Low profile locking plate versus conventional calcaneus plate
Sanders type 2 to 4 intraarticular fracture; impact loading
NR; median age, 67
14
Cyclic loading; 1000×, preload 20 N to compressive load of 200 N at 6 cycles/min; load to failure
Load to failure; ultimate displacement; work to failure
Locking plates showed some advantages over nonlocking plates but not all differences were significant; locking plates can be beneficial in osteoporotic bone
Anatomic plate and compression bolts versus conventional anatomic plate and cancellous screws
Sanders type 3; osteotomy
NR; mean age, 49
18
Cyclic loading; 1 Hz, 1000 cycles, increasing axial force 20 to 200 N and 20 to 700 N
Mean irreversible deformation; load to failure; ultimate displacement
Anatomic plate and compression bolts provided biomechanical stability as good as, or better than, conventional anatomic plate and cancellous screws under axial loading
Primary stability of an intramedullary calcaneal nail and an angular stable calcaneal plate in a biomechanical testing model of intraarticular calcaneal fracture.
A biomechanical comparison of fixed angle locking compression plate osteosynthesis and cement augmented screw osteosynthesis in the management of intra articular calcaneal fractures.
Cement augmented screw osteosynthesis versus uniaxial fixed-angle locking plate osteosynthesis
Sanders type 2B; osteotomy
Mean BMD, 0.481 g/cm2, 0.519 g/cm2; mean age, 81
14
Quasi-static compression ramp loading; 20 to 200 N, increasing at 18 N/s; sinusoidal cyclic compression loading; 2 Hz until failure; valley load 50 N, peak load increased cycle by cycle at 0.06 N/cycle, starting at 200 N
Stiffness; range of motion; cycles to failure; load to failure
Cement-augmented screw osteosynthesis significantly superior to conventional fixed-angle locking plate osteosynthesis
The aim of the present systematic review was to provide an overview of the biomechanically tested fixation methods for fixation of the calcaneus fractures and to determine which fixation method has the best biomechanical properties. We systematically retrieved reports on biomechanically tested fixation methods for calcaneal fractures. A wide variety of fixation methods, test setups, and outcome measures was found. Owing to the heterogeneity of the studies, definitive conclusions could not be drawn; however, all tested techniques appeared to be biomechanically adequate. Furthermore, we found a tendency toward the use of minimally invasive and intramedullary fixation methods in recent last years (
Primary stability of an intramedullary calcaneal nail and an angular stable calcaneal plate in a biomechanical testing model of intraarticular calcaneal fracture.
An anatomic plate with compression bolts provides biomechanical stability as good or better than that provided by the conventional anatomic plate and cancellous screws. The construction with compression bolts significantly improved the lower displacement during cyclic loading and the axial load to failure (
). It is not surprising that compression bolts can enhance the stability; however, the possible disruption of the soft tissue caused by compression bolts might have consequences in clinical practice. Additional disadvantages include that a bilateral approach is needed, requiring more extensive dissection, and the construction is bulky under the skin.
Locking plate fixation was biomechanically superior to conventional plating in noncalcaneal fractures (
). This was typically in the case of osteoporotic bone, a condition that causes weakness of the bone and thus more easily leads to loosening of the fixation and subsequent failure to maintain reduction of the fracture (
) found more rigidity in specimens treated with a locked plate compared with a conventional plate, although no significant difference was found in the load to failure. Furthermore, they found that polyaxially locked plates provided increased stability compared with uniaxially locked plates (
). However, they used saw bone specimens instead of human calcanei. It is well known that artificial bones have different biomechanical characteristics than human bone (
). Three studies failed to show a significant beneficial effect of locking plates compared with nonlocking plates in the fixation of calcaneal fractures, questioning the benefit of using locking plates in these patients (
) was the only one to find locking plates to be beneficial in the case of displaced intraarticular calcaneal fractures in osteoporotic bone. However, the difference between ultimate displacement and work to failure was not significant in their study (
) showed that >200 specimens would be needed to demonstrate a significant difference between the constructs. Therefore, clinical benefit from locking plates seems unlikely, and the high number of specimens required does not seem justified.
) showed that either 2 unicortical 4.0-mm diameter cancellous screws or 2 bicortical 3.5-mm diameter cortex screws are biomechanically adequate screw fixation techniques for calcaneal fractures. Although the unicortical screws were placed in dense cancellous bone, the bone bed turned out to be secure enough. The risk of damaging the tendinous and neurovascular structures when penetrating the medial cortex would be eliminated by using unicortical screws (
Augmented screw osteosynthesis was found to be significantly superior to locking plate osteosynthesis. The augmented screw technique facilitates a better grip of the double-threaded screws and the bone (
A biomechanical comparison of fixed angle locking compression plate osteosynthesis and cement augmented screw osteosynthesis in the management of intra articular calcaneal fractures.
). Because of the biomechanical advantages, further clinical research on minimally invasive augmented screw osteosynthesis is recommended.
All the studies that evaluated the biomechanical properties of the intramedullary nail concluded that the construction was as strong as, or stronger than, conventional plates and locking plates (
Primary stability of an intramedullary calcaneal nail and an angular stable calcaneal plate in a biomechanical testing model of intraarticular calcaneal fracture.
). Combined with the posterior minimally invasive approach, the use of the intramedullary nail might improve outcomes in clinical practice owing to the lowered risk of secondary loss of reduction and the lowered risk of wound complications (
Primary stability of an intramedullary calcaneal nail and an angular stable calcaneal plate in a biomechanical testing model of intraarticular calcaneal fracture.
). However, this technique is only applicable for fractures with a small number of (large) fragments and, therefore, is of use only for a subset of patients.
Conventional techniques might not be replaced completely by minimally invasive techniques owing to the inability to completely reduce severely comminuted fractures. However, minimally invasive techniques are continuously undergoing refinement to improve the quality of the reduction. The sinus tarsi approach (when necessary), combined with percutaneous invasive internal fixation, seems to be an adequate approach for treating intraarticular calcaneal fractures and has recently gained the attention of surgeons (
Most of the included studies created the calcaneal fractures using an osteotomy. Fractures created by osteotomy lack the interdigitation found in fractures clinically (
). The extent to which this influences the results is not clear. It is easy to conceptualize the idea that when performing an osteotomy the “smooth” surface of the created fracture will have less grip than that resulting from the natural interdigitation, which causes more friction and, therefore, creates a stronger construction.
One limitation of the included studies was that by dissecting the surrounding structures of the calcaneus, their stabilizing forces were also removed. However, because it is even more difficult to re-create a specific fracture in an intact foot (
), it might be too complicated to leave those structures in place. Our review is also limited because the homogeneity of the included results was uncertain. At face, the cadaver specimen are probably similar in regard to biomechanical properties, although we cannot be certain about this.
Research on cadavers also differs from clinical practice because bone repair will not occur. In living bone, micromotion is known to stimulate the healing of the bone, enhancing the fracture fixation construct (
). Therefore, constructions that are too rigid might hamper micromotion and thus hamper fracture healing.
Furthermore, the fracture types and test setup varied among the included studies, and different outcome measures were used (e.g., load to failure, range of motion, construct stiffness, number of cycles to failure, fragment displacement, work to failure, mean irreversible deformation). All these differences complicate the comparability of the included studies.
Not only the biomechanical properties, but also the biologic issues and clinical relevance should be considered. Other factors relevant to clinical use include the implant costs, technical ease of use, and effects on local soft tissues and fracture healing biology (
). These factors must be considered when interpreting the results of the present study.
To the best of our knowledge, the present study was the first complete overview of fixation methods for calcaneal fractures and their biomechanical properties in cadaveric specimens. For future research, a more uniform method of inflicting injuries and performing testing and more uniform use of outcome measures would ease the interpretation of results and help in comparing the different techniques with each other.
In conclusion, owing to the heterogeneity of the studies, definitive conclusions could not be drawn. However, all the investigated methods of fixation of calcaneal fractures seemed to be biomechanically sufficient. No clear benefit seems to exist for the use of locking plates in the fixation of calcaneal fractures; however, they might provide a subtle mechanical superiority compared with nonlocking plates in the case of fractures in osteoporotic bone. Several of the techniques tested are suitable for a minimal invasive approach and should be investigated further in clinical trials. We recommend future research be performed using methods comparable to the currently available data to simplify the interpretation of the results.
Acknowledgments
We would like to thank Ms. Faridi-van Etten (clinical librarian) for her assistance with compiling the search strategy.
A biomechanical comparison of fixed angle locking compression plate osteosynthesis and cement augmented screw osteosynthesis in the management of intra articular calcaneal fractures.
The PRISMA statement for reporting systematic reviews and meta-analyses of studies that evaluate health care interventions: explanation and elaboration.
Primary stability of an intramedullary calcaneal nail and an angular stable calcaneal plate in a biomechanical testing model of intraarticular calcaneal fracture.
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