Eur J Orthop Surg Traumatol DOI 10.1007/s00590-013-1360-5
ORIGINAL ARTICLE
Position of polyaxial versus monoaxial screws in locked plating for proximal humeral fractures: analysis of a prospective randomized study Ben Ockert • Vera Pedersen • Lucas Geyer • Stefan Wirth • Wolf Mutschler • Stefan Grote
Received: 6 October 2013 / Accepted: 31 October 2013 Ó Springer-Verlag France 2013
Abstract Background Aim of the study was to compare the chosen position of polyaxial locking screws with the position of monoaxial screws in the humeral head of proximal humeral fractures treated by locked plating. Methods In a prospective randomized observational study, 124 consecutive patients (mean age 70.9 ± 14.8 years) sustaining a displaced proximal humeral fracture were treated with either monoaxial or polyaxial screwinserted locking plate fixation. The chosen positions of locking screws were identified from standardized postoperative radiographs in anteroposterior and outlet-view, with regard to a regional mapping of the humeral head. Results In monoaxial locking technique, a mean of 6 screws purchased the humeral head (95 % CI 5.1–6.2), and in polyaxial locking technique, a mean of 4 screws (95 % CI 3.3–4.5), respectively. Screws were placed in the regions superolateral: monoaxial 24.8 %, polyaxial 20.7 % (p = 0.49); superomedial: monoaxial 21.9 %, polyaxial 20.0 % (p = 0.433); inferolateral: monoaxial 32.5 %, polyaxial 35.0 % (p = 0.354); inferomedial: monoaxial 20.8 %, polyaxial 24.2 % (p = 0.07), superoposterior: monoaxial 45.5 %, polyaxial 30.8 % (p = 0.57); superoanterior: monoaxial 4.4 %, polyaxial 8.3 % (p = 0.33); inferoposterior: monoaxial 22.5 %, polyaxial 29.8 %
B. Ockert (&) V. Pedersen W. Mutschler S. Grote Department of Trauma and Orthopaedic Surgery, LudwigMaximilians-University, Nussbaumstr. 20, 80336 Munich, Germany e-mail: [email protected] URL: http://www.chirurgische-klinik.de L. Geyer S. Wirth Department of Radiology, Ludwig-Maximilians-University, Nussbaumstr. 20, 80336 Munich, Germany
(p = 0.49) and inferoanterior: monoaxial 27.5 %, polyaxial: 31.2 % (p = 0.09). Conclusion The chosen screws’ position in monoaxial and polyaxial locking plate fixation of displaced proximal humeral fractures do not differ significantly. However, loss of fixation is observed more frequently if the fixation did not include at least one screw within the superoposterior region of the humeral head, suggesting that a screw purchasing the superoposterior region is beneficial in locked plating of proximal humeral fractures. Level of evidence Treatment Study, Level II. Keywords Proximal humeral fracture Locked plating Polyaxial Screw cutout Loss of fixation
Introduction Locking plates are commonly used for the treatment of displaced two-, three- and four-part fractures of the proximal humerus. Locking plates function to assist mechanical bridging by securing anatomic reduction, allowing early range of motion, even in osteopenic bone [1–3]. However, the postoperative complication rate in angular stable-plated three- and four-part humeral head fractures accounts up to 34 % and the rate of an unplanned second operation within 12 months after the fracture is 15–20 % [4–10]. While some of the complications may be related to incorrect surgical technique, secondary fracture displacement and screw cutout are most evident in cases of medial comminution and in the multifragmentary osteoporotic head with insufficient bone stock for screws to purchase [9, 11–13]. Monoaxial locking plates allow insertion of locking head-screws in divergent directions; however, the screw direction is predetermined by threaded screw holes. In
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order to improve an adaptation to individual fracture morphology and to enable screw purchase into regions of stronger bone quality, polyaxial locking plates have been designed potentially enhancing the fixation’s strength. In several biomechanical studies, the advantage of polyaxial screw anchorage has been reported. However, in recently published clinical studies, polyaxial locked plating resulted in no advantage in terms of loss of fixation rate and functional outcome compared to monoaxial fixed angle plating [14–18]. Aim of the present study was to compare the chosen position of polyaxial and monoaxial inserted screws in locked plating of displaced proximal humeral fractures by a radiographic evaluation of a prospectively conducted randomized trial. The hypothesis was that polyaxial locking screws are placed differently compared to monoaxial locking screws with regard to fracture pattern. Furthermore, the relationship between screw position and occurrence of loss of fixation was analyzed.
Materials and methods Between Aug. 2006 and Feb. 2010, we conducted a prospective, randomized study by Institutional Review Board approval (Nr. 358-05). Enclosure criteria were a proximal humeral fracture with displacement [1 cm and angulation of fragments [45° on true anterior-posterior (true a.p.) and outlet-view radiographs. The fracture pattern was assessed according to the modified Neer classification [19]. Patients were excluded if exclusion criteria were met, such as open—or pathologic fractures, polytrauma injury or primary nerve palsy. One hundred and twenty-four consecutive patients [89 women (72 %), 35 men (28 %); mean age 70.9 ± 14.8 years] were prospectively randomized for either monoaxial locking plate fixation (n = 66 patients (70 % women); mean age 71.0 ± 15.1 years, Proximal Humeral Internal Locking SystemÒ (PHILOS) Synthes GmbH, Oberdorf, Switzerland)) or polyaxial locking plate fixation (n = 58 patients (74 % women); mean age 70.8 ± 14.6 years, Non-Contact BridgingÒ—Proximal Humerus (NCB-PH) Zimmer GmbH, Winterthur, Switzerland). Randomization was performed by closed envelope technique. Surgical procedure Through a delto-pectoral approach, open reduction and internal fixation was performed by one of seven senior orthopedic trauma surgeons. After reduction in the fracture and restoration of the humeral head-shaft angle, the greater and lesser tuberosities were reduced and sutured (FibreWireÒ size 5, Arthrex 1370 Creekside Boulevard Naples,
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Fig. 1 In polyaxial locking technique, the screw can be angled to a range of 0°–15° off-center. The desired position is secured by a locking cap
Florida, USA). The randomized plate was then positioned on the lateral aspect of the proximal humeral metaphysis. The polyaxial system allows a range of 0°–15° off-center for each screw. A threaded screw cap locks the axis of the screw (Fig. 1). Drilling was performed only through the lateral cortex and the cancellous bone to prevent screw penetration into the glenohumeral joint. By use of image intensifier, the head-screws were placed so that the tip of the particular screw remained in the subchondral area, approximately 5 mm to the cortical margin, in addition to verifying accurate fracture reduction. When necessary, screws were exchanged to accomplish the intended position of the screw tip relative to the subchondral bone. Radiographic evaluation True a.p. and outlet-view radiographs were conducted the day after surgery, as well as 6 weeks, 3, 6 and 12 months postoperatively. All radiographs were evaluated independently by two observers (B.O., L.G.) twice in separate sessions (8 weeks in-between). The screw position was assigned into the following regions in true a.p. radiographs: SL: superolateral, IL: inferolateral, IM: inferomedial, SM: superomedial and outlet-view radiographs. SP: superoposterior, IP: inferoposterior, IA: inferoanterior, SA: superoanterior, SP: superoposterior (Fig. 2). To determine secondary varus displacement and loss of fixation, the head-shaft angle was measured [18]. Consensus decision was made for screw cutout, osteonecrosis and implant related failure. Healing was determined by radiographic evidence of bridging bone on true a.p. and outlet-view radiographs. Statistical analysis Continuous variables were described with use of means and standard deviation. Analysis of variances (ANOVA) was conducted to compare the percentage of screws placed in
Eur J Orthop Surg Traumatol Fig. 2 Position of screws in relationship to the area of the humeral head. Left true a.p., SL superolateral, IL inferolateral, IM inferomedial, SM superomedial. Right outletview. SP superoposterior, IP inferoposterior, IA inferoanterior, SA superoanterior, SP superoposterior
each region for monoaxial and polyaxial screw purchase with respect to fracture type and maintenance of fixation. Statistical analysis was performed using SPSS (version 20.0; SPSS Inc., Chicago, IL, USA).
Results 124 randomized patients with a mean age of 70.9 ± 14.8 years, sustaining a displaced proximal humeral fracture, were evaluated. The fracture patterns (modified Neer classification) were identified as 2-part fractures: 24 cases (19.4 %), 3-part fractures: 62 cases (50 %), 4-part fractures: 34 cases (27.4 %). A head-splitting fracture was seen in 4 cases (3.2 %). In monoaxial locking technique, a mean of 6 screws purchased the humeral head (95 % CI 5.1–6.2), and in polyaxial locking technique, a mean of 4 screws (95 % CI 3.3–4.5), respectively. In percentages in anteroposterior plane, the screws were placed SL: 32.2 % (95 % CI 28.6; 35.4), SM: 29.5 % (95 % CI 26.4; 32.7), IL: 48.9 % (95 % CI 44.8; 52.9), IM: 32.3 % (95 % CI 28.3; 36.4), and in outlet-view plane screws were placed SP: 31.8 % (95 % CI 29.9; 33.8), SA: 24.2 % (95 % CI 22.3; 26.1), IP: 20.7 % (95 % CI 18.9; 22.6), IA: 23.3 % (95 % CI 21.4; 25.1). With respect to the fracture type, the screws were placed similarly (p = 0.840, ANOVA, Fig. 3). In comparison, the percentages of screws placed in the different regions of the humeral head are given in Table 1. There was no difference in the chosen screw’s position between monoaxial and polyaxial locking technique with respect to the fracture type (p = 0.473, ANOVA). In monoaxial fixation, revision surgery was necessary in 12 cases (18 %). Reasons for revision surgery were secondary varus displacement with subsequent intra-articular screw protrusion (9 cases), subacromial impingement (2 cases), and infection (1 case). In polyaxial fixation, revision
Fig. 3 Percentage of screws placed in regions of the humeral head (outlet-view plane) with respect to fracture type (p = 0.840, ANOVA)
surgery was necessary in 9 cases (16 %, p = 0.693), indicated due to secondary varus displacement (5 cases) subacromial impingement (4 cases). Secondary displacement, screw cut-out and osteonecrosis were observed more frequently if not at least one screw was purchased in the superoposterior region (p = 0.021, Fig. 4).
Discussion The data of this radiographic evaluation from a randomized observational study of 124 patients demonstrate that polyaxial screws are placed similarly to monoaxial screws in locked plating of displaced proximal humeral fractures. Screws were placed rather equally in the humeral head predominantly in the superoantero and superoposterior region. The least screws purchased the anteroinferior part of the humeral head. In cases where loss of fixation was
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Eur J Orthop Surg Traumatol Table 1 Percentages of screws in the different regions of the humeral head Region
Monoaxial % (95 % CI)
Polyaxial % (95 % CI)
p
Superolateral (SL)
31.7 (28.2, 35.1)
32.4 (25.7, 39.2)
0.49
Superomedial (SM)
28.2 (25.0, 31.5)
31.3 (25.1, 37.6)
0.43
Inferolateral (IL)
44.6 (39.7, 49.4)
54.9 (48.1, 61.6)
0.35
Inferomedial (IM)
28.4 (23.6, 33.3)
37.9 (31.0, 44.7)
0.07
Superoposterior (SP)
34.2 (32.2, 36.3)
26.8 (22.8, 30.8)
0.57
Superoanterior (SA)
27.1 (25.4, 28.8)
18.0 (13.7, 22.2)
0.33
Inferoposterior (IP)
17.4 (15.6, 19.1)
27.7 (23.9, 31.5)
0.49
Inferoanterior (IA)
21.3 (19.4, 23.1)
27.5 (23.4, 31.6)
0.09
Percentages of screws placed in the different regions of the humeral head in comparison for monoaxial and polyaxial locking technique
Fig. 4 Percentage of screws purchased in the different regions of the humeral head in cases with postoperative loss of fixation compared to maintenance of fixation. Note that loss of fixation occurred more often if not at least one screw purchased the superoposterior region of the humeral head (*p = 0.021)
evident, the fixation was performed with less screws anchoring the superoposterior region, suggesting that placement of screws in the superoposterior region of the humeral head may be beneficial in locked plating of proximal humeral fractures with both monoaxial and polyaxial instrumentation. Locked plating is an established option in the treatment of displaced proximal humeral fractures. However, recently published studies report on complications in up to 43 % and
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revision surgery in up to 20 % after internal fixation of unstable proximal humeral fractures with locking plates [4, 5, 8, 10]. One reason for the high rate of secondary loss of fixation and screw cutout may be found in the underestimation of the regional differences in bone density of the proximal humerus. Brianza could show in a cadaver study that screws aiming the posterior and superior region of the humeral head purchase significantly better bone quality compared to the anterior aspect of the humeral head [20]. Other authors could demonstrate that in the superoposterior region, the bone mineral density is higher compared to other regions of the humeral head, suggesting that best screw fixation might be achieved in the cranio-central and posterior-medial aspect of the humeral head [21, 22]. While monoaxial implants facilitate for insertion of screws convergent and divergent in a multidirectional manner predetermined by threaded screw holes, polyaxial angular stable plating offers the surgeon the ability to adjust screw direction. This may be used in adaption to individual fracture morphology or regional bone quality, potentially enhancing the fixation’s strength. Despite a superior performance for polyaxial locking plates in biomechnical studies [23–25], to the authors’ knowledge, there is no comparative clinical study proving benefits in common fracture treatment. In two studies, polyaxial locking plates were not advantageous over monoaxial locking plates in terms of postoperative complication and patients’ outcome. We therefore analyzed the chosen screws’ position of polyaxial and monoaxial locking technique from a randomized comparative study and hypothesized that in polyaxial locking technique the screws’ position should differ from those of monoaxial screws in locked plating for displaced proximal humeral fractures. From the results of this study, we suggest that the chosen screws’ position in monoaxial and polyaxial locking plates are similarly with respect to the humeral head’s dimensions. Despite the theoretical advantage of polyaxial screw insertion, it had no effect on the chosen screws’ position. This may be one explanation why comparative clinical studies did not show superior results for polyaxial locking technique. In consequence, if the proximal humeral fragment is well restored and a monoaxial plate is placed in the correct manner, the amount of predetermined screws in divergent holes suits for a rigid fixation. However, in cases, where accurate fracture reduction is not satisfactory due to metaphyseal comminution, complexity of the fracture pattern or insufficient bone quality, the ability of polyaxial screw insertion may not improve the surgeon’s opportunities. In turn, polyaxial screws are not placed differently compared to monoaxial screws, if the fracture is anatomically reduced and the plate is sited properly. Nevertheless, polyaxial locking plates may represent a great advantage for instance in revision osteosynthesis or in the treatment
Eur J Orthop Surg Traumatol
of periprosthetic fractures when screws may necessarily be placed unconventionally. One finding of our study is that loss of fixation was observed more frequently if not one screw purchased the superoposterior region of the humeral head. This was seen for both monoaxial and polyaxial locking technique, resulting in secondary varus displacement of the humeral head with subsequent protrusion of screws into the joint. From the results of our study, we suggest that at least one screw should be placed in the superoposterior region of the humeral head. One explanation for this finding may be seen in the fact that the superoposterior region of the humeral head has the strongest bone quality compared to the other regions of the humeral head [20, 21, 26]. We see a limitation in our study due to the point that some of the postoperative X-rays were undertaken with 5°– 10° error of rotation, thus potentially biasing the evaluation. The maximum accuracy in the three-dimensional regional distribution would have been for CT-scan, but supplement X-ray exposure was prohibited due to ethical objections and standardized radiographs in two planes still remain the golden standard for postoperative radiographic evaluation. However, radiographs were taken in two planes in a standardized fashion and two investigators performed evaluations in separated sessions.
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Conclusion The screw position of polyaxial and monoaxial screws is similar in proximal humeral fractures treated by locked plating. The potential effect of polyaxial locking screws enabling a free angle of up to 30° plating may not be fully utilized and may be an explanation while comparative studies could not find significant differences in clinical and radiographic outcomes. If the fracture is anatomically reduced, the humeral head-shaft angle is restored and the locking plate is placed correctly on the lateral aspect closely posterior to the bicipital groove, the direction of screws in a predefined convergent and divergent manner suites for a rigid fixation. Occurrence of secondary displacement may be further reduced by at least one screw in the superoposterior region of the humeral head. Conflict of interest
None.
Ethical standard We verify that this study has been performed in accordance with the ethical standards laid down in the 1964 Declaration of Helsinki and its later amendments. This study has been approved by our local ethical committee.
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23. Wilkens KJ, Curtiss S, Lee MA (2008) Polyaxial locking plate fixation in distal femur fractures: a biomechanical comparison. J Orthop Trauma 22(9):624–628. doi:10.1097/BOT.0b013e318 18896b3 24. Rausch S, Klos K, Stephan H, Hoffmeier K, Gras F, Windolf M, Gueorguiev B, Hofmann GO, Muckley T (2011) Evaluation of a polyaxial angle-stable volar plate in a distal radius C-fracture model—a biomechanical study. Injury 42(11):1248–1252. doi:10. 1016/j.injury.2010.12.005 25. Otto RJ, Moed BR, Bledsoe JG (2009) Biomechanical comparison of polyaxial-type locking plates and a fixed-angle locking plate for internal fixation of distal femur fractures. J Orthop Trauma 23(9):645–652. doi:10.1097/BOT.0b013e3181a567c8 26. Lill H, Hepp P, Gowin W, Oestmann JW, Korner J, Haas NP, Josten C, Duda GN (2002) Age- and gender-related distribution of bone mineral density and mechanical properties of the proximal humerus. Rofo 174(12):1544–1550
ORIGINAL ARTICLE
Position of polyaxial versus monoaxial screws in locked plating for proximal humeral fractures: analysis of a prospective randomized study Ben Ockert • Vera Pedersen • Lucas Geyer • Stefan Wirth • Wolf Mutschler • Stefan Grote
Received: 6 October 2013 / Accepted: 31 October 2013 Ó Springer-Verlag France 2013
Abstract Background Aim of the study was to compare the chosen position of polyaxial locking screws with the position of monoaxial screws in the humeral head of proximal humeral fractures treated by locked plating. Methods In a prospective randomized observational study, 124 consecutive patients (mean age 70.9 ± 14.8 years) sustaining a displaced proximal humeral fracture were treated with either monoaxial or polyaxial screwinserted locking plate fixation. The chosen positions of locking screws were identified from standardized postoperative radiographs in anteroposterior and outlet-view, with regard to a regional mapping of the humeral head. Results In monoaxial locking technique, a mean of 6 screws purchased the humeral head (95 % CI 5.1–6.2), and in polyaxial locking technique, a mean of 4 screws (95 % CI 3.3–4.5), respectively. Screws were placed in the regions superolateral: monoaxial 24.8 %, polyaxial 20.7 % (p = 0.49); superomedial: monoaxial 21.9 %, polyaxial 20.0 % (p = 0.433); inferolateral: monoaxial 32.5 %, polyaxial 35.0 % (p = 0.354); inferomedial: monoaxial 20.8 %, polyaxial 24.2 % (p = 0.07), superoposterior: monoaxial 45.5 %, polyaxial 30.8 % (p = 0.57); superoanterior: monoaxial 4.4 %, polyaxial 8.3 % (p = 0.33); inferoposterior: monoaxial 22.5 %, polyaxial 29.8 %
B. Ockert (&) V. Pedersen W. Mutschler S. Grote Department of Trauma and Orthopaedic Surgery, LudwigMaximilians-University, Nussbaumstr. 20, 80336 Munich, Germany e-mail: [email protected] URL: http://www.chirurgische-klinik.de L. Geyer S. Wirth Department of Radiology, Ludwig-Maximilians-University, Nussbaumstr. 20, 80336 Munich, Germany
(p = 0.49) and inferoanterior: monoaxial 27.5 %, polyaxial: 31.2 % (p = 0.09). Conclusion The chosen screws’ position in monoaxial and polyaxial locking plate fixation of displaced proximal humeral fractures do not differ significantly. However, loss of fixation is observed more frequently if the fixation did not include at least one screw within the superoposterior region of the humeral head, suggesting that a screw purchasing the superoposterior region is beneficial in locked plating of proximal humeral fractures. Level of evidence Treatment Study, Level II. Keywords Proximal humeral fracture Locked plating Polyaxial Screw cutout Loss of fixation
Introduction Locking plates are commonly used for the treatment of displaced two-, three- and four-part fractures of the proximal humerus. Locking plates function to assist mechanical bridging by securing anatomic reduction, allowing early range of motion, even in osteopenic bone [1–3]. However, the postoperative complication rate in angular stable-plated three- and four-part humeral head fractures accounts up to 34 % and the rate of an unplanned second operation within 12 months after the fracture is 15–20 % [4–10]. While some of the complications may be related to incorrect surgical technique, secondary fracture displacement and screw cutout are most evident in cases of medial comminution and in the multifragmentary osteoporotic head with insufficient bone stock for screws to purchase [9, 11–13]. Monoaxial locking plates allow insertion of locking head-screws in divergent directions; however, the screw direction is predetermined by threaded screw holes. In
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Eur J Orthop Surg Traumatol
order to improve an adaptation to individual fracture morphology and to enable screw purchase into regions of stronger bone quality, polyaxial locking plates have been designed potentially enhancing the fixation’s strength. In several biomechanical studies, the advantage of polyaxial screw anchorage has been reported. However, in recently published clinical studies, polyaxial locked plating resulted in no advantage in terms of loss of fixation rate and functional outcome compared to monoaxial fixed angle plating [14–18]. Aim of the present study was to compare the chosen position of polyaxial and monoaxial inserted screws in locked plating of displaced proximal humeral fractures by a radiographic evaluation of a prospectively conducted randomized trial. The hypothesis was that polyaxial locking screws are placed differently compared to monoaxial locking screws with regard to fracture pattern. Furthermore, the relationship between screw position and occurrence of loss of fixation was analyzed.
Materials and methods Between Aug. 2006 and Feb. 2010, we conducted a prospective, randomized study by Institutional Review Board approval (Nr. 358-05). Enclosure criteria were a proximal humeral fracture with displacement [1 cm and angulation of fragments [45° on true anterior-posterior (true a.p.) and outlet-view radiographs. The fracture pattern was assessed according to the modified Neer classification [19]. Patients were excluded if exclusion criteria were met, such as open—or pathologic fractures, polytrauma injury or primary nerve palsy. One hundred and twenty-four consecutive patients [89 women (72 %), 35 men (28 %); mean age 70.9 ± 14.8 years] were prospectively randomized for either monoaxial locking plate fixation (n = 66 patients (70 % women); mean age 71.0 ± 15.1 years, Proximal Humeral Internal Locking SystemÒ (PHILOS) Synthes GmbH, Oberdorf, Switzerland)) or polyaxial locking plate fixation (n = 58 patients (74 % women); mean age 70.8 ± 14.6 years, Non-Contact BridgingÒ—Proximal Humerus (NCB-PH) Zimmer GmbH, Winterthur, Switzerland). Randomization was performed by closed envelope technique. Surgical procedure Through a delto-pectoral approach, open reduction and internal fixation was performed by one of seven senior orthopedic trauma surgeons. After reduction in the fracture and restoration of the humeral head-shaft angle, the greater and lesser tuberosities were reduced and sutured (FibreWireÒ size 5, Arthrex 1370 Creekside Boulevard Naples,
123
Fig. 1 In polyaxial locking technique, the screw can be angled to a range of 0°–15° off-center. The desired position is secured by a locking cap
Florida, USA). The randomized plate was then positioned on the lateral aspect of the proximal humeral metaphysis. The polyaxial system allows a range of 0°–15° off-center for each screw. A threaded screw cap locks the axis of the screw (Fig. 1). Drilling was performed only through the lateral cortex and the cancellous bone to prevent screw penetration into the glenohumeral joint. By use of image intensifier, the head-screws were placed so that the tip of the particular screw remained in the subchondral area, approximately 5 mm to the cortical margin, in addition to verifying accurate fracture reduction. When necessary, screws were exchanged to accomplish the intended position of the screw tip relative to the subchondral bone. Radiographic evaluation True a.p. and outlet-view radiographs were conducted the day after surgery, as well as 6 weeks, 3, 6 and 12 months postoperatively. All radiographs were evaluated independently by two observers (B.O., L.G.) twice in separate sessions (8 weeks in-between). The screw position was assigned into the following regions in true a.p. radiographs: SL: superolateral, IL: inferolateral, IM: inferomedial, SM: superomedial and outlet-view radiographs. SP: superoposterior, IP: inferoposterior, IA: inferoanterior, SA: superoanterior, SP: superoposterior (Fig. 2). To determine secondary varus displacement and loss of fixation, the head-shaft angle was measured [18]. Consensus decision was made for screw cutout, osteonecrosis and implant related failure. Healing was determined by radiographic evidence of bridging bone on true a.p. and outlet-view radiographs. Statistical analysis Continuous variables were described with use of means and standard deviation. Analysis of variances (ANOVA) was conducted to compare the percentage of screws placed in
Eur J Orthop Surg Traumatol Fig. 2 Position of screws in relationship to the area of the humeral head. Left true a.p., SL superolateral, IL inferolateral, IM inferomedial, SM superomedial. Right outletview. SP superoposterior, IP inferoposterior, IA inferoanterior, SA superoanterior, SP superoposterior
each region for monoaxial and polyaxial screw purchase with respect to fracture type and maintenance of fixation. Statistical analysis was performed using SPSS (version 20.0; SPSS Inc., Chicago, IL, USA).
Results 124 randomized patients with a mean age of 70.9 ± 14.8 years, sustaining a displaced proximal humeral fracture, were evaluated. The fracture patterns (modified Neer classification) were identified as 2-part fractures: 24 cases (19.4 %), 3-part fractures: 62 cases (50 %), 4-part fractures: 34 cases (27.4 %). A head-splitting fracture was seen in 4 cases (3.2 %). In monoaxial locking technique, a mean of 6 screws purchased the humeral head (95 % CI 5.1–6.2), and in polyaxial locking technique, a mean of 4 screws (95 % CI 3.3–4.5), respectively. In percentages in anteroposterior plane, the screws were placed SL: 32.2 % (95 % CI 28.6; 35.4), SM: 29.5 % (95 % CI 26.4; 32.7), IL: 48.9 % (95 % CI 44.8; 52.9), IM: 32.3 % (95 % CI 28.3; 36.4), and in outlet-view plane screws were placed SP: 31.8 % (95 % CI 29.9; 33.8), SA: 24.2 % (95 % CI 22.3; 26.1), IP: 20.7 % (95 % CI 18.9; 22.6), IA: 23.3 % (95 % CI 21.4; 25.1). With respect to the fracture type, the screws were placed similarly (p = 0.840, ANOVA, Fig. 3). In comparison, the percentages of screws placed in the different regions of the humeral head are given in Table 1. There was no difference in the chosen screw’s position between monoaxial and polyaxial locking technique with respect to the fracture type (p = 0.473, ANOVA). In monoaxial fixation, revision surgery was necessary in 12 cases (18 %). Reasons for revision surgery were secondary varus displacement with subsequent intra-articular screw protrusion (9 cases), subacromial impingement (2 cases), and infection (1 case). In polyaxial fixation, revision
Fig. 3 Percentage of screws placed in regions of the humeral head (outlet-view plane) with respect to fracture type (p = 0.840, ANOVA)
surgery was necessary in 9 cases (16 %, p = 0.693), indicated due to secondary varus displacement (5 cases) subacromial impingement (4 cases). Secondary displacement, screw cut-out and osteonecrosis were observed more frequently if not at least one screw was purchased in the superoposterior region (p = 0.021, Fig. 4).
Discussion The data of this radiographic evaluation from a randomized observational study of 124 patients demonstrate that polyaxial screws are placed similarly to monoaxial screws in locked plating of displaced proximal humeral fractures. Screws were placed rather equally in the humeral head predominantly in the superoantero and superoposterior region. The least screws purchased the anteroinferior part of the humeral head. In cases where loss of fixation was
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Eur J Orthop Surg Traumatol Table 1 Percentages of screws in the different regions of the humeral head Region
Monoaxial % (95 % CI)
Polyaxial % (95 % CI)
p
Superolateral (SL)
31.7 (28.2, 35.1)
32.4 (25.7, 39.2)
0.49
Superomedial (SM)
28.2 (25.0, 31.5)
31.3 (25.1, 37.6)
0.43
Inferolateral (IL)
44.6 (39.7, 49.4)
54.9 (48.1, 61.6)
0.35
Inferomedial (IM)
28.4 (23.6, 33.3)
37.9 (31.0, 44.7)
0.07
Superoposterior (SP)
34.2 (32.2, 36.3)
26.8 (22.8, 30.8)
0.57
Superoanterior (SA)
27.1 (25.4, 28.8)
18.0 (13.7, 22.2)
0.33
Inferoposterior (IP)
17.4 (15.6, 19.1)
27.7 (23.9, 31.5)
0.49
Inferoanterior (IA)
21.3 (19.4, 23.1)
27.5 (23.4, 31.6)
0.09
Percentages of screws placed in the different regions of the humeral head in comparison for monoaxial and polyaxial locking technique
Fig. 4 Percentage of screws purchased in the different regions of the humeral head in cases with postoperative loss of fixation compared to maintenance of fixation. Note that loss of fixation occurred more often if not at least one screw purchased the superoposterior region of the humeral head (*p = 0.021)
evident, the fixation was performed with less screws anchoring the superoposterior region, suggesting that placement of screws in the superoposterior region of the humeral head may be beneficial in locked plating of proximal humeral fractures with both monoaxial and polyaxial instrumentation. Locked plating is an established option in the treatment of displaced proximal humeral fractures. However, recently published studies report on complications in up to 43 % and
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revision surgery in up to 20 % after internal fixation of unstable proximal humeral fractures with locking plates [4, 5, 8, 10]. One reason for the high rate of secondary loss of fixation and screw cutout may be found in the underestimation of the regional differences in bone density of the proximal humerus. Brianza could show in a cadaver study that screws aiming the posterior and superior region of the humeral head purchase significantly better bone quality compared to the anterior aspect of the humeral head [20]. Other authors could demonstrate that in the superoposterior region, the bone mineral density is higher compared to other regions of the humeral head, suggesting that best screw fixation might be achieved in the cranio-central and posterior-medial aspect of the humeral head [21, 22]. While monoaxial implants facilitate for insertion of screws convergent and divergent in a multidirectional manner predetermined by threaded screw holes, polyaxial angular stable plating offers the surgeon the ability to adjust screw direction. This may be used in adaption to individual fracture morphology or regional bone quality, potentially enhancing the fixation’s strength. Despite a superior performance for polyaxial locking plates in biomechnical studies [23–25], to the authors’ knowledge, there is no comparative clinical study proving benefits in common fracture treatment. In two studies, polyaxial locking plates were not advantageous over monoaxial locking plates in terms of postoperative complication and patients’ outcome. We therefore analyzed the chosen screws’ position of polyaxial and monoaxial locking technique from a randomized comparative study and hypothesized that in polyaxial locking technique the screws’ position should differ from those of monoaxial screws in locked plating for displaced proximal humeral fractures. From the results of this study, we suggest that the chosen screws’ position in monoaxial and polyaxial locking plates are similarly with respect to the humeral head’s dimensions. Despite the theoretical advantage of polyaxial screw insertion, it had no effect on the chosen screws’ position. This may be one explanation why comparative clinical studies did not show superior results for polyaxial locking technique. In consequence, if the proximal humeral fragment is well restored and a monoaxial plate is placed in the correct manner, the amount of predetermined screws in divergent holes suits for a rigid fixation. However, in cases, where accurate fracture reduction is not satisfactory due to metaphyseal comminution, complexity of the fracture pattern or insufficient bone quality, the ability of polyaxial screw insertion may not improve the surgeon’s opportunities. In turn, polyaxial screws are not placed differently compared to monoaxial screws, if the fracture is anatomically reduced and the plate is sited properly. Nevertheless, polyaxial locking plates may represent a great advantage for instance in revision osteosynthesis or in the treatment
Eur J Orthop Surg Traumatol
of periprosthetic fractures when screws may necessarily be placed unconventionally. One finding of our study is that loss of fixation was observed more frequently if not one screw purchased the superoposterior region of the humeral head. This was seen for both monoaxial and polyaxial locking technique, resulting in secondary varus displacement of the humeral head with subsequent protrusion of screws into the joint. From the results of our study, we suggest that at least one screw should be placed in the superoposterior region of the humeral head. One explanation for this finding may be seen in the fact that the superoposterior region of the humeral head has the strongest bone quality compared to the other regions of the humeral head [20, 21, 26]. We see a limitation in our study due to the point that some of the postoperative X-rays were undertaken with 5°– 10° error of rotation, thus potentially biasing the evaluation. The maximum accuracy in the three-dimensional regional distribution would have been for CT-scan, but supplement X-ray exposure was prohibited due to ethical objections and standardized radiographs in two planes still remain the golden standard for postoperative radiographic evaluation. However, radiographs were taken in two planes in a standardized fashion and two investigators performed evaluations in separated sessions.
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Conclusion The screw position of polyaxial and monoaxial screws is similar in proximal humeral fractures treated by locked plating. The potential effect of polyaxial locking screws enabling a free angle of up to 30° plating may not be fully utilized and may be an explanation while comparative studies could not find significant differences in clinical and radiographic outcomes. If the fracture is anatomically reduced, the humeral head-shaft angle is restored and the locking plate is placed correctly on the lateral aspect closely posterior to the bicipital groove, the direction of screws in a predefined convergent and divergent manner suites for a rigid fixation. Occurrence of secondary displacement may be further reduced by at least one screw in the superoposterior region of the humeral head. Conflict of interest
None.
Ethical standard We verify that this study has been performed in accordance with the ethical standards laid down in the 1964 Declaration of Helsinki and its later amendments. This study has been approved by our local ethical committee.
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