Introduction
Fractures of the tibial plateau are often caused by high-energy mechanisms and involve major injury to bone and soft tissue. Complication rates are high because of the diversity and complexity of fracture patterns and the thin soft-tissue envelope around the knee [
1‐
3]. Therefore, treatment and treatment planning are extraordinarily challenging for these fractures [
4]. Goals of surgical treatment of displaced bicondylar tibial plateau fractures include anatomic reduction of the articular surface, restoration of alignment in the coronal and sagittal planes, and stable fixation to enable early knee motion. To provide the stability needed to safely permit early range of motion (ROM) and basic strengthening exercises, many surgeons use combined medial and lateral plating. Many surgeons also use delayed-weightbearing protocols after fixation of bicondylar tibial plateau fractures with metaphyseal comminution because of concern about fixation failure or articular displacement. In 2007, Higgins et al. [
5] performed a biomechanical study comparing dual plate fixation (medial and lateral) with lateral locked plate fixation alone in bicondylar fractures. Specimens were subjected to cyclic loading, simulating forces encountered during early postoperative range of motion (ROM) exercises or activities of daily living [
5]. Dual plate fixation produced significantly less subsidence compared with locked lateral plate fixation alone. However, lateral locking plate fixation alone was deemed sufficient in cases with a large medial fragment with good cortical contact and no coronal fracture line. Otherwise, dual plating was recommended. In biomechanical studies [
5‐
7], combined medial and lateral plate fixation effectively resisted forces encountered during ROM. However, none of these studies reported on fracture displacement or loss of fixation when implementing an early/immediate (at 2 weeks) full weightbearing protocol.
To our knowledge, no biomechanical study has simulated full weightbearing in bicondylar tibial plateau fractures treated with combined medial and lateral plate fixation. Our purpose was to analyze displacement, stiffness, and fixation failure during simulated full weightbearing of bicondylar tibial plateau fractures treated with combined medial and lateral locking plate fixation. We simulated full weightbearing in AO Foundation and Orthopaedic Trauma Association (AO/OTA) 41-C2 fractures (simple articular, multifragmentary metaphyseal fracture). Our model represents a simple articular pattern without articular depression but with metaphyseal comminution necessitating dual plating. We hypothesized that combined medial and lateral plate fixation, although adequate to resist forces during ROM, would be insufficient for immediate full weightbearing.
Results
The mean initial stiffness of the construct was 562 ± 164 N/mm. All combined medial and lateral locking plate constructs maintained the integrity of the fixation in cyclic loading to 1000 N after 10,000 cycles. Mean total displacement values after 10,000 cycles were as follows: lateral, 0.4 ± 0.8 mm; proximal medial, 0.3 ± 0.7 mm; distal medial, 0.3 ± 0.6 mm; and central 0.4 ± 0.3 mm (Table
2).
Table 2
Displacement under cyclic loading at 1000 N after 10,000 cycles and after test completion in 10 fresh-frozen adult human cadaveric tibias with simulated AO/OTA 41-C2 bicondylar tibial plateau fractures (simple articular, multifragmentary metaphyseal fractures) treated with combined medial and lateral plate fixation
1 | 0.1 | 0 | 0 | 0 | 1.9 | 5.0b | 1.5 | 1.5 |
2 | 0 | 0 | 0 | 0.1 | 4.3 | 0.8 | 5.0b | 0.2 |
3 | 0.1 | 0 | 0.2 | 0.4 | 4.8 | 1.6 | 1.7 | 0.5 |
4 | 0 | 0 | 0.1 | 0.1 | 2.8 | 0.2 | 5.0b | 0.1 |
5 | 0.2 | 0.1 | 0.1 | 0.5 | 1.1 | 2.9 | 4.4 | 0.9 |
6 | 0 | 0 | 0 | 0 | 5.1b | 0.2 | 1.9 | 0 |
7 | 2.7 | 2.3 | 2 | 1.6 | 5.3b | 4.2 | 4.3 | 1.3 |
8 | 0.4 | 0.2 | 0.1 | 0.8 | 5.0b | 1.7 | 1.8 | 0.5 |
9 | 0.1 | 0 | 0 | 0.2 | 0.3 | 0.8 | 2.9 | 0.9 |
10 | 0.1 | 0 | 0 | 0.3 | 0.4 | 0.1 | 0.1 | 0.4 |
Mean (SD) | 0.4 (0.8) | 0.3 (0.7) | 0.3 (0.6) | 0.4 (0.5) | 2.2 (1.7) | 1.4 (1.3) | 2.3 (1.4) | 0.6 (0.5) |
Four specimens withstood loading up to 200,000 cycles. The other 6 specimens reached 5 mm of plastic deformation before completing the test: 4 specimens failed at 2800 N, 1 failed at 2000 N, and 1 failed at 1600 N. The mean cyclic load at failure was 2467 ± 532 N, and the mean number of cycles to failure was 53,155 (Table
3). At the end of testing (either failure or after 200,000 cycles), mean displacement was greatest at the distal medial fracture site (2.3 ± 1.4 mm) and lateral fracture site (2.2 ± 1.7 mm). No significant difference was found in stiffness between the failure and non-failure groups (Table
1).
Table 3
BMD, stiffness, cycles to failure, and load at failure in10 fresh-frozen adult human cadaveric tibias with simulated AO/OTA 41-C2 bicondylar tibial plateau fractures (simple articular, multifragmentary metaphyseal fractures) treated with combined medial and lateral plate fixation
1 | 0.9 | 551 | 54,411 | 2800 |
2 | 1.1 | 697 | 75,819 | 2800 |
3a | 1 | 514 | NA | NA |
4 | 1 | 576 | 43,575 | 2800 |
5a | 1.2 | 152 | NA | NA |
6 | 1.1 | 712 | 111,884 | 2800 |
7 | 1.2 | 646 | 14,851 | 1600 |
8 | 1.1 | 514 | 18,387 | 2000 |
9a | 1 | 556 | NA | NA |
10a | 1.1 | 708 | NA | NA |
Mean (SD) | 1.1 (0.1) | 562 (156) | 53,155 (3349) | 2467 (485) |
Discussion
The purpose of our biomechanical study was to assess the ability of combined medial and lateral locked plate fixation of bicondylar tibial plateau fractures to resist fracture displacement during simulated full weightbearing. We subjected 10 specimens with simulated bicondylar tibial plateau fractures (AO/OTA 41C2) to repetitive loading using a previously described method. None of the 10 specimens experienced fixation failure after increasing the load to 1000 N at 10,000 cycles. Only small displacements (0–2.7 mm) were observed at this point. These results are consistent with those of a study on dual plate fixation of tibial plateau fractures [
5]. However, only 4 of our specimens withstood maximum load testing (2800 N and 200,000 cycles). Six specimens failed (> 5 mm of displacement) before test completion. These findings support postoperative protocols delaying full weightbearing during the early postoperative period until some bony healing has occurred. Immediate, full weightbearing of bicondylar tibial plateau fractures, even in those with simple articular splits, may be too aggressive despite combined medial and lateral plate fixation [
16]. Malunion, nonunion, and even fixation failure remain concerns with immediate weightbearing. In a web-based survey of 111 Dutch orthopaedic trauma surgeons, only 12% of surgeons recommended immediate weightbearing, with most (56%) recommending initiating weightbearing 6 weeks postoperatively [
17]. Common protocols recommend nonweightbearing for 6 weeks or more, followed by progressive partial weightbearing for 4–6 weeks after visible callus is evident on follow-up radiographs [
18]. The AO recommendations also support toe-touch weightbearing for 6–12 weeks to avoid loss of reduction [
19].
However, restricting weightbearing requires patient compliance and greater energy expenditure compared with full-weightbearing walking [
20,
21]. This need for greater effort may reduce patients’ compliance with rehabilitation protocols. Immediate, full weightbearing after locking plate osteosynthesis for partial articular proximal tibial fractures has been studied and recommended [
22‐
24]. Thewlis et al. [
16] reported on the functional outcomes after surgery of 17 patients with either complete or incomplete articular fractures (AO types 41-B and C). Their results showed no association between weightbearing and patient functional outcomes at 1 year. Williamson et al. [
24] showed that patients who progressed to immediate, full weightbearing after open reduction internal fixation neither lost reduction nor reported worse functional outcomes at 1 year compared with patients who maintained partial weightbearing for 6 weeks. Because patients self-regulate their weightbearing when allowed early, full, earlier weightbearing may be safe [
16,
24]. Although these results may appear to support an accelerated weightbearing protocol after open reduction and internal fixation of complex tibial plateau fractures, until now no biomechanical study has been published to support these results.
To our knowledge, ours is the first study to simulate full weightbearing after bicondylar tibial plateau fracture (AO/OTA 41-C2) fixation with dual plates. Our specimen testing protocol differed from previous studies in small but important ways. Because tibiofemoral contact forces range from 2 to 3 times body weight [
14], we decided to use greater forces of cyclic loading than were used in previous studies [
5,
8,
15]. When simulating 4 weeks of early full weightbearing, we used a 2800-N load to represent force transmitted across the knee during walking in a person weighing 70 kg. In this testing protocol, we assumed that no sufficient bony callus formed before 4 weeks and that an active adult loads each limb approximately 50,000 times per week [
11]. results provide evidence that may help improve postoperative rehabilitation instructions and better define early weightbearing protocols. The fracture models developed by Horwitz et al. [
15] and Gösling et al. [
8] have been used in several biomechanical studies of bicondylar tibial plateau fractures. However, these models do not address the small size of the medial fragment, which requires thorough evaluation and appropriate fixation. The fracture line of the medial fragment can also vary in the coronal plane and commonly results in a posteromedial fragment [
25]. This topic is important for future study of biomechanical stability of the posteromedial fragment in bicondylar tibial plateau fracture fixation.
Our study has several limitations. First, the force applied to the tibial plateau during weightbearing depends on an individual’s body weight and degree of knee flexion. Therefore, some patients may be able to tolerate early, full weightbearing and others may not. Second, a cadaveric study can mimic in vivo bone behavior under loading, but the absence of soft tissue and healing affects fragment stability. Intact surrounding soft tissue or degree of soft tissue injury might increase the stability of fracture in vivo. Third, we used titanium locking compression plates. Construct strength and stiffness might be increased with the use of stainless-steel implants. A larger biomechanical study assessing the effect of stainless-steel versus titanium, as well as variations in BMD and simulated patient weight, may be helpful to determine in which patients early weightbearing may be indicated.
Acknowledgments
For their editorial assistance, we thank Jenni Weems, MS, Kerry Kennedy, BA, and Rachel Box, MS, in the Editorial Services group of The Johns Hopkins Department of Orthopaedic Surgery.
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