Original title: How toenhance the stability
An overview of current
biomechanical and clinical data
Original Author: Benedikt Schliemann , Dirk
Wahnert,Christina Theisen, Mirco Herbort, Clemens Ko sters, Michael J. Raschke,
Ren Zheng, Department of Traumatology and Orthopedics, Sixth Affiliated Hospital of Xinjiang Medical University, AndreWeimann
Original source: Injury,Int. J. Care Injured
46 (2015) 1207C1214
For proximal humeral fractures, the standard treatment is locking plate fixation, although numerous studies in recent years have shown that the complication rate after treatment of proximal humeral fractures with locking plates can be as high as 49%. The two main reasons for this high complication rate are low proximal humeral bone mineral density (BMD) and lack of effective medial support during fixation, resulting in unstable fixation.
In recent years, a number of clinical and biological studies have been conducted with the aim of avoiding these problems. Among these, three principles have been agreed upon to increase the stability of locking plate fixation in proximal humeral fractures: the addition of bone cement to the low BMD area at the screw tip to enhance screw fixation; the use of medial support screws (talar screws); and the use of autologous or allogeneic bone grafts if the medial column is crushed.
A recent guideline review published in Injuy by Benedikt from Germany reviews recent clinical and biomechanical studies on proximal humeral locking plate fixation with the aim of providing a relatively standardized treatment strategy for the management of these complex fractures.
Methods
Any of the following keywords were selected: “stability,” “medial support,” “augmentation,” “bone cement,” “bone graft”, “autologous bone graft”, and “allograft”, combined with “proximal humeral fracture” Only relevant English-language literature was included in the Medline search. The included literature was filtered into three main groups: (1) medial support screws, (2) cement-reinforced fixation, and (3) bone graft-reinforced fixation. In addition, these three groups can be further subdivided into subgroups related to clinical studies and biomechanical studies.
The content of the literature is presented in three main areas: (1) description of the basic principles of the application of medial support screws, cement-reinforced and bone grafting; (2) clarification of the rationale for the application of the three methods to proximal humeral fractures, followed by a detailed review of the results of the included literature on this aspect of the study and its corresponding clinical implications.
Results
I. Medial support screws
Professor Gardner et al. suggested some quantitative criteria to define whether a proximal humeral fracture has stable medial support, and the fracture was considered to have medial support when the following conditions were met: (1) the medial column was intact, anatomically repositioned and non-comminuted (2) a stable fracture with the stem end of the fracture line inserted into the humeral head (3) an interlocking screw driven directly into the proximal humeral head in the inner lower quadrant of the subchondral bone Because medial comminuted fractures are commonly associated with complex proximal humeral fractures, the role of the medial support screw during locking plate fixation is particularly important (Figure 1). Although the screws are driven only inferiorly into the humeral head, they effectively counteract the forces of internal derangement, thus reducing the risk of secondary reduction failure and subsequent collapse of the internal derangement.
Figure 1.
Medial support screws (black arrows) maintain medial humeral column stability during locking plate fixation of proximal humeral fractures.
(1) Biomechanical study
Biomechanical studies related to reinforced fixation with medial support screws during locking plate fixation are scarce, and up to now, the authors have retrieved only two publications related to the study of locking plate fixation with the addition of medial support screws. Also recently, Prof. Katthagen et al. evaluated the fixation strength of medial support screws on an unstable two-part fracture model by inserting two directional locking moment screws and performing stiffness testing tests under rotational, axial, inward and abduction loads, respectively. Only after allograft cortical or cancellous bone grafting did the fixation stiffness, axial and inward fixation failure loads show a significant increase, but this effect was not observed for torsion and stiffness under abduction loads.
On the contrary, in the study by Prof. Bai et al, the unstable two-part fracture model with additional talar screw fixation showed a significant increase in shear and axial loading forces, and in fractures with intact medial cortex, the additional talar screw did not provide enhanced fixation, and similarly, the additional talar screw did not provide the corresponding anti-deformation forces regardless of the intact medial cortex.
(2) Clinical studies
In contrast to the contradictory results of the two biomechanical papers, all clinical studies eligible for inclusion showed good results with locking plate fixation of proximal humerus fractures with medial support screws.
The first such study, pioneered by Professor Gardner et al, included 35 patients (mean age 62 years) in which 18 patients were treated with medial support screws. The results showed a significantly lower rate of repositioning failure in patients with the addition of medial support screws compared to patients without the combination of medial support screws (p
< 0.001). Also in terms of achieving anatomic reduction stability, the authors concluded that the use of medial support screws was a key factor in obtaining stable reduction of the internal fixation of the fracture.
In another prospective randomized study by Prof. Zhang et al. the conclusions are consistent with those of Prof. Gardner et al. 72 patients (mean age 63.2 years) with proximal humeral fractures managed with medially supported screws or locked head screws in conjunction with locking plate fixation were included in the study and the clinical and affective changes in these patients were evaluated after a mean follow-up of 30.8 months. The results showed that the Constant score was significantly higher in patients with medial support screws than in those without (p=
0.01), and the failure rate of internal fixation was also higher in patients without medial support screws than in patients with medial support screws (23.1% vs. 3.4%, p =
0.036). In addition, the authors also observed a higher rate of reduction failure in patients with three to four partial fracture blocks. Thus, the authors concluded that the use of medial support screws enhances the mechanical stability of the locking plate in proximal humeral fractures, which is particularly important in patients with complex proximal humeral fractures, and that internal fixation maintains repositioning for a longer period of time with the aid of medial support screws.
The authors compared data from 36 patients (mean age 62.5 years) with medial support with 27 patients (mean age 61.7 years) without medial support and found that the Neer score of the shoulder joint in patients with medial support was 85.7
± 7.8, while the Neer score of patients without medial support was 78.0 ± 14.2 (p = 0.008). Complication rates were also significantly higher in proximal humerus fractures without medial support (37% vs.
11.1%, p = 0.014).
II. Cement-reinforced fixation
Cement-reinforced fixation has been successfully used in the management of proximal humerus fractures. Both calcium phosphate and calcium sulfate bone cements can be used to fill the fracture gap in proximal humerus fractures, especially in the management of metaphyseal fracture gaps. Head screws with cement-reinforced fixation can be achieved either by inserting bone cement before nailing or by using hollow nails, both of which have been used with good clinical results (Figure 2).
Figure 2.
Hollow nail with cement-reinforced fixation (A), postoperative image (B).
(1) Biomechanical studies
In 2002, Prof. Kwon et al. pioneered a biomechanical study related to the use of calcium phosphate in proximal humeral fractures. The study was performed by applying a cloverleaf plate, an angular blade plate and a kerfing pin to one side of the humerus and adding calcium phosphate bone cement to the other side of the cadaver, and comparing the fixation effect of both sides. The results showed a significant decrease in interfragmentary activity with the calcium phosphate cement-reinforced fixation, as well as a significant increase in torque limit and torsional stiffness with the cement-reinforced fixation.
Table I shows biomechanical studies of locking plate combined with cement-reinforced fixation of proximal humeral fractures. Although the fracture models, testing methods, and loading directions of these studies were not identical, the results were surprisingly consistent: locking plate combined with cement-reinforced fixation for proximal humeral fractures resulted in good biomechanical results.
Table I.
Biomechanical study of proximal humerus fractures with locking plates combined with cement reinforcement
However, one of the major pitfalls of using bone cement is the increase in temperature during its curing process. Professor Blazejak et al. evaluated the thermogenic efficacy of cement-reinforced fixation of cadaveric proximal humerus fracture specimens in a water bath at 37 degrees Celsius (mimicking human body temperature) by adding 0.5 ml of PMMA to each screw and measuring the subchondral bone and joint surface temperatures at the screw tip. The results showed that the subchondral bone temperature was 43.5
°C and 38.6 °C on the articular surface, which did not reach the temperature threshold reported in the literature for osteoclast necrosis or apoptosis. In addition, an in vitro study by Prof. Goetzen et al. also showed that removal of the hollow nail after cement-reinforced fixation with a 2.8 mm hollow nail was not a problem and that no higher torque or other special instrumentation was required for removal.
(2) Clinical studies
Prof. Robinson and Prof. Page were the first to follow the results of 25 proximal humerus fractures treated with brace plate screw internal fixation combined with calcium phosphate reinforcement fixation, showing good reduction and satisfactory fracture healing in all cases after the use of reinforcement fixation during the follow-up period of one to two years after surgery.
There are only two clinical studies evaluating the effectiveness of cement-reinforced locking plate fixation of proximal humeral fractures.
Prof. Egol et al. in the management of proximal humeral fractures with metaphyseal defects were left untreated (39%), reinforced with cancellous bone graft (32%), and reinforced fixation with calcium sulfate bone cement (29%). The results showed that the application of calcium phosphate reinforced fixation reduced bone resorption at the fracture end. Compared with the use of cancellous bone grafting and shelving without treatment, calcium phosphate was effective in reducing the damage to the bone caused by screws (p
= 0.009), and there were also significantly fewer complications with calcium phosphate cemented fixation.
Professor Somasundaram et al. used calcium sulfate bone cement to fill the metaphyseal defect and enhance fixation with locking plate screws.2 The results showed good fracture healing in 1 patient (22 proximal humeral fractures) with no complications or calcium sulfate-related adverse effects.
To date, no clinical studies corresponding to locking plate combined with hollow and perforated screws with cement-reinforced fixation have been reported, and in addition, a randomized controlled trial comparing locking plate alone with screw-reinforced fixation has yet to be performed.
III. Bone graft
Professor Walch et al. were the first to use intramedullary bone grafting for the treatment of humeral surgical neck bone discontinuity. For fractures with medial humeral cortical discontinuity, intramedullary bone grafting can provide stable medial support and thus prevent medial collapse of the humeral head.
(1) Biomechanical studies
Professor Mathison et al. first investigated the biomechanical changes of locking plates combined with intramedullary implants versus locking plates alone, using six cadaveric specimens with a mean bone age of 85.8 years for comparison of these two fixation methods. A 10 mm wedge osteotomy of the surgical neck of the humerus was performed to simulate a comminuted fracture of the medial column. The results showed that internal fixation failure load could be increased 1.72-fold by intramedullary vascularized fibula grafting (standard deviation 0.54; p
= 0.02) and a 3.84-fold increase in structural stiffness (standard deviation 1.92).
Similar results were obtained in a study by Prof. Bae et al. who performed a comparative study of the biomechanics of locking plates combined with intramedullary implants versus locking plates alone on seven pairs of cadaveric specimens. The results showed a significant reduction in fracture displacement with enhanced fixation with locking plates combined with intramedullary implants, as well as a much higher maximum internal fixation failure load and fixation stiffness than with locking plates alone. Internal humeral collapse and fracture of the plate were common forms of internal fixation failure after locking plate fixation alone, while bone graft-reinforced fixation failure was mainly due to fracture of the humeral head cut out or grafted fibular block.
Professor Chow et al. performed the same study on eight pairs of cadaveric humerus and their results showed that all eight humerus fixed with locking plates combined with intramedullary bone graft reinforcement did not show humeral inversion collapse deformity, while six of the eight humerus fixed with locking plates alone failed fixation due to inversion collapse (p<
0.05).
In a recent study, Prof. Katthagen et al. made a two-segment fracture model of the unstable humerus and implanted femoral cortical bone and cancellous bone into the medial fracture space to enhance locking plate fixation in combination with medial support screws, and the result of doing so was a significant increase in axial stiffness, inversion stiffness, and internal fixation failure load with locking plate fixation alone (p
<
0.017). However, in femoral bone block grafting to restore a medial humeral bone defect, cortical bone is required to support the distal and proximal ends to ensure stable compression fit, in contrast to intramedullary bone grafting, which can also be safely and effectively inserted into the completed comminuted medial column.
Despite the different testing methods in the above studies, the fixation stiffness and the fixation failure load after the intramedullary vascularized fibula graft or medial compression bone graft were much higher than that of the simple locking plate fixation.
(2) Clinical studies
Professor Gardner et al. were the first to report on seven patients with proximal humerus fractures using locking plates in combination with intramedullary vascularized fibular grafts, and they followed the seven patients until fracture healing or no loss of reduction was observed. Their results showed complete fusion of the graft with the humerus at 3 to 4 months postoperatively. However, three of these seven patients underwent revision in the early postoperative period (one patient due to persistent postoperative wound ooze and two patients underwent arthroscopic release for joint flexion less than 110 degrees). Ultimately the authors concluded that the intramedullary implant not only provided medial humeral support but also served as a repositioning tool intraoperatively. Since Professor Gardner’s study, a series of Level IV studies have been published, and Table II shows the current clinical studies related to locking plate combined with autologous or allograft bone reinforced fixation.
Table 2.
Clinical studies related to locking plates in combination with autologous or allograft bone reinforcement
The study by Prof. Zhu et al. was the only case-control study in which 18 patients with four-part fractures of the proximal humerus were treated with locking plates combined with enhanced fixation with autologous iliac crest bone graft, and 22 patients with the same type of fracture were treated with locking plates alone in the control group. After a mean follow-up of 25.4 months, the range of motion in all directions was significantly higher in the experimental group than in the control group (p
<
0.001), and the VAS pain score was lower in the experimental group than in the control group, and the SF-36 Quality of Life Scale questionnaire score was also significantly higher in the experimental group than in the control group. In addition, Professor Hinds et al. pointed out that the difference between locking plates combined with endosteal fibula-supported implant-reinforced fixation was not statistically significant between elderly patients and non-elderly patients.
Discussion
The results of the literature search indicate that medial support screws, cement-reinforced fixation and the application of bone graft are the three most commonly used modalities to enhance the stability of locking plate fixation. Some of the current limitations are the low level of evidence associated with some studies and the small number of prospective randomized clinical trials of these three modalities, but the conclusions drawn from the current literature suggest that these three modalities may help achieve good quality of reduction and reliable clinical outcomes in the management of complex proximal humeral fractures.
The most commonly used treatment for proximal humeral fractures is the locking plate, but its high complication rate, especially in older adults with osteoporosis, is particularly striking. Although not every complication requires revision, the fact that up to one-third of patients require postoperative revision is unacceptable, making it imperative to investigate new ways to prevent internal fixation failure. The current studies have focused on controlling and modifying these factors.
Almost all of the literature agrees that the medial support screw has a significant role in maintaining the retention of repositioning. First, medial support screws reduce the incidence of repositioning failure; second, the combined application of medial support screws results in good functional recovery after surgery. From a biomechanical point of view, the structural stiffness and internal fixation failure load of medial support screws in two-part humeral fractures remains controversial, although the stability of two-part humeral fractures is inherently higher compared to complex humeral fractures, and thus the effectiveness of medial support plates in such fractures is reduced. However, it is also not encouraging that the number of biomechanical studies on the use of medial support screws in more complex proximal humeral fractures is also not very high.
Although these biomechanical studies are not currently tested in the same way, the application of cement-reinforced fixation improves fixation stiffness, internal fixation failure load, and reduces micromovement between fracture fragments, regardless of the type of fracture. Case reports of cement-reinforced fixation indicate that the application of bone cement is safe and does not increase the risk of damage to cartilage or bone, and that the incidence of complications following cement-reinforced fixation is low.
However, it should be noted that there is not enough clinical evidence that bone substitutes can be used as a routine treatment, and there is no clear specification of the type of screws that require cement-reinforced fixation, with some scholars recommending a combination of cement-reinforced fixation when the screws are driven to the anterolateral part of the humerus where the bone density is low, and otherwise only to the middle of the humeral head. Therefore, the next research task should focus on finding specific areas in the middle of the femoral head where the stability of internal fixation can be increased.
A large surgical incision is required to facilitate insertion of the bone graft into the proximal humerus, but bone grafting is increasingly becoming a safe and effective way to enhance the stability of locking plate fixation. The incidence of common complications (e.g., hematoma and infection) associated with the use of bone graft for enhanced fixation has not increased. Although the follow-up period of some of the current studies is short, no reset failure has been observed in the literature. The results of biomechanical studies are also consistent with clinical findings, so that the use of bone graft-reinforced fixation on top of a locking plate may improve the stiffness of the fixation and the internal fixation failure load, while avoiding displacement of the fracture fragment.
Conclusion
In conclusion, medial support screws, cement-reinforced fixation, and bone graft-reinforced fixation may improve the stability of proximal humeral fractures when fixed with locking plates. Although not supported by strong evidence, the use of all three modalities has moved toward achieving and maintaining a secure reduction, even in complex humeral fractures. Medial support plates do not require an enlarged approach and have not been associated with adverse events, so they are routinely used in all patients with proximal humeral fractures to enhance the support of the medial humeral column. The potential of bone cement and bone graft to enhance fixation is very promising, but complete clinical implementation is unrealistic at this time, and more large and high-quality clinical studies are needed to confirm their specific effects.