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. 2017;37:1–10.

Dynamic Fixation of Humeral Shaft Fractures Using Active Locking Plates: A Prospective Observational Study

Steven M Madey 1, Stanley Tsai 1, Daniel C Fitzpatrick 2, Kathleen Earley 1, Michael Lutsch 1, Michael Bottlang 1,✉
PMCID: PMC5508288  PMID: 28852327

Abstract

Background

Rigid locked plating constructs can suppress fracture healing by inhibiting interfragmentary motion required to stimulate natural bone healing by callus formation. Dynamic fixation with active locking plates reduces construct stiffness, enables controlled interfragmentary motion, and has been shown to induce faster and stronger bone healing in vivo compared to rigid locking plates. This prospective observational study represents the first clinical use of active locking plates. It documents our early clinical experience with active plates for stabilization of humeral shaft fractures to assess their durability and understand potential complications.

Methods

Eleven consecutive patients with humeral shaft fractures (AO/OTA types 12 A-C) were prospectively enrolled at a level I and a level II trauma center. Fractures were stabilized by using active locking plates without supplemental bone graft or bone morphogenic proteins. The screw holes of active locking plates are elastically suspended in elastomer envelopes inside the plate, enabling up to 1.5 mm of controlled interfragmentary motion. Progression of fracture healing and integrity of implant fixation was assessed radiographically at 3, 6, 12, and 24 weeks post surgery. Patient-reported functional outcome measures were obtained at 6, 12, and 24 weeks post surgery. The primary endpoint of this study was plate durability in absence of plate bending or breakage, or failure of the elastically suspended locking hole mechanism. Secondary endpoints included fracture healing, complications requiring revision surgery, and functional outcome scores.

Results

The eleven patients had six simple AO/ OTA type 12A fractures, three wedge type 12B fractures, and two comminuted type 12C fracture, including one open fracture. All active locking plates endured the 6-month loading period without any signs of fatigue or failure. Ten of eleven fractures healed at 10.9 ± 5.2 weeks, as evident by bridging callus and pain-free function. One fracture required revision surgery 37 weeks post surgery due to late fixation failure at the screwbone interface in the presence of a atrophic delayed union. The average Disability of the Arm, Shoulder and Hand (DASH) score improved from 31 ± 22 at week 6 to 13 ± 15 by week 24, approaching that of the normal, healthy population (DASH = 10.1). By week 12, the difference between Constant shoulder scores, expressed as the difference between the affected and contralateral arm (8 ± 8), was considered excellent. By week 24, the SF-12 physical health score (44 ± 9) and mental health score (48 ± 11) approached the mean value of 50 that represents the norm for the general U.S. population.

Conclusion

Absence of failure of the plate and locking holes suggests that dynamic fixation of humeral shaft fractures with active plates provides safe and effective fixation. Moreover, early callus bridging and excellent functional outcome scores suggest that dynamic fixation with active locking plates may promote increased fracture healing over standard locked plating.

Introduction

Concerns that locking plate fixation of fractures might lead to an overly stiff environment for fracture healing resulted in the development of new fixation techniques and implants that promote controlled fracture motion.1-3 These new approaches to fracture fixation, although different in application, have the common goal of producing a fracture environment that promotes secondary bone healing with callus.

Most commonly, surgeons use standard implants and attempt to alter the mechanical environment at the fracture by increasing the working length of the plate over the fracture.4 This technique promotes fracture site motion by plate bending and primarily introduces shear motion to the fracture,5 which may be detrimental to healing.6,7 The use of long working lengths was correlated with increased shear motion and delayed unions after plate fixation of distal femur fractures.7

The introduction of Far Cortical Locking (FCL) technology allowed the use of an implant that was specifically designed to allow controlled axial motion at the fracture.8 In a prospective trial, the use of FCL implants for distal femur fractures showed significantly increased callus formation and decreased nonunion rates relative historical controls.9 Unfortunately, the use of screws as the motion element limits the use of FCL to larger diameter bones, as the flexibility of the screws decreases for shorter screw lengths.

To address this limitation, an active locking plate was developed with the screw holes in a sliding element that is elastically suspended in a silicone envelope.1

The sliding element and screw move relative to the plate, allowing controlled motion at the fracture site. Bench-top testing has shown that active locking plates are at least as strong as standard locking plates under all three principal loading conditions of bending, torsion, and axial compression, while providing a 77% stiffness reduction and symmetric axial motion at the fracture.1 Furthermore, in vivo studies using the sheep tibia osteotomy model demonstrated that comminuted fractures heal faster and four times stronger with active locking plates than with standard locking plates.10 In a second in vivo ovine study, simple well-reduced fractures healed over two times stronger with active locking plates than with compression plating.11 Bench-top and in vivo studies, however, can only predict clinical durability within the limitations of the experimental model. This prospective observational study documents our early clinical experience with active locking plates for stabilization of humeral shaft fractures. It serves to demonstrate the durability of active locking plates and their elastically suspended locking elements under routine clinical practice.

Patients and Methods

From April 1, 2016 to August 10, 2016, eleven consecutive patients with 11 humeral shaft fractures (AO/ OTA types 12 A-C) were prospectively enrolled in an observational cohort study at a level I trauma center (Legacy, Portland, Oregon) and a level II trauma center (Slocum, Eugene, OR). The internal review boards of both institutions approved the study protocol. Patients were included if they had an acute humeral shaft fracture amenable for surgical stabilization, were at least 18 years old, consented to the study protocol, and were willing and able to participate in scheduled follow-up visits for a minimum of 6 months. Exclusion criteria were pathologic fractures, revision surgery, pregnancy, and polytrauma with an Injury Severity Score (ISS) greater than 27.

Active Plating Constructs:

All fractures were stabilized with active locking plates (G3 Active Plating System, Incipio, Huntington, IN) made of titanium alloy. The cross-sectional geometry of active locking plates was representative of a standard 4.5 mm large fragment plate. In contrast to a standard locking plate, the locking holes of active locking plates were integrated in individual sliding elements that were elastically suspended in a silicone envelope inside lateral plate pockets (Figure 1A-C). Lateral pockets were arranged in an alternating pattern from both plate sides, resulting in a staggered locking hole configuration (Figure 1D). The pocket geometry combined with the silicone suspension allowed controlled axial translation, which enabled up to 1.5 mm of axial motion across a fracture while providing stable fixation in response to bending and torsional loading (Figure 1E).1 The silicone suspension consisted of long-term implantable medical-grade silicone elastomer.

Figure 1.

Figure 1

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Elastic suspension of locking holes inside an active locking plate (A) provides controlled axial motion (B) by means of elastically suspended sliding elements (C). D) 9-hole active locking plate with staggered screw whole pattern. E) Active locking plates provide controlled axial motion of up to 1.5 mm across the fracture zone.

The effect of locking hole suspension in active plates was characterized with a biomechanical study in direct comparison to standard locking plates (Figure 2). Three active locking plates and three standard 4.5 mm locking plates made of titanium alloy that had a comparable cross-sectional geometry were applied to bridge osteotomies in a humeral diaphysis surrogate (#3403-21, Sawbones, Vashon Island, WA), using three bi-cortical locking screws on each side of the osteotomy. Axial compression was applied through spheres proximally and distally to permit physiological bending under axial loading. Constructs were stepwise loaded in 50-N increments up to 350 N, representing the axial humeral load required to lifting a gallon of milk at 90 degrees elbow flexion.12 The resulting motion at the osteotomy was measured with calipers for calculation of construct stiffness.

Figure 2.

Figure 2

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Stiffness characterization of active and standard locked plating constructs applied to bridge a gap osteotomy in a humeral diaphysis surrogate.

Surgical Technique:

All fractures were stabilized with active locking plates without the use of supplemental bone graft or bone morphogenic proteins to solely rely on natural bone healing stimulated by controlled interfragmentary motion. Accordingly, all surgeries were conducted using biological bridge plating techniques that aimed for preservation of soft tissue and functional reduction. Active locking plates accommodated standard 5.0 mm diameter selftapping locking screws, and were applied with three screws proximal and distal to the fracture in a standard bridge plating technique. Because active plating does not require a long bridge span to permit axial motion, one screw on each side was placed directly adjacent to the fracture. Based on the surgeons’ preference, an anterior or posterior approach was used. To generate a dynamic fixation construct, the active locking plate was not compressed onto the diaphysis, and no screws were applied across the fracture that could inhibit interfragmentary motion.

Follow-up Visits:

Patients were scheduled for 3, 6, 12, and 24-week follow-up examinations. If fracture healing was not confirmed by week 24, follow-up visits were continued until fracture healing or revision surgery, whichever occurred first. None of the 11 patients were lost to follow-up. Patient demographics and injury data are summarized in Table 1. Progression of fracture healing and integrity of implant fixation was assessed on bi-planar radiographs that were obtained post surgery and at each follow-up visit. Patient-reported functional outcome measures were obtained at 6, 12, and 24 weeks post surgery, including the Disability of the Arm Shoulder and Hand (DASH) score,13 and the Constant shoulder score.14 In addition, the Short Form (SF-12) health survey was administered at week 24.

Table 1.

Demographics and Baseline Data

Parameters n (%) Mean (±SD) Range
Gender female 6 (55%)
male 5 (45%)
Age (years) 40 ± 14 22-57
BMI (kg/m2) 31 ± 7 19-41
Smoker 3 (27%)
Diabetes 0 (0%)
Injury mechanism: Motor vehicle accident 5 (45%)
Ground level fall 2 (18%)
Fall down stairs 2 (18%)
Fall from height 2 (18%)
Fracture type: OTA/AO 12-A2 1 (9%)
OTA/AO 12-A3 5 (45%)
OTA/AO 12-B2 3 (27%)
OTA/AO 12-C1 1 (9%)
OTA/AO 12-C3 1 (9%)
Closed/open fracture Closed 10 (91%)
Open 1 (9%)
Plate size: 7 hole 8 (73%)
9 hole 3 (27%)
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Radiographic Analysis of Fracture Healing:

Progression of fracture healing and formation of bridging callus was assessed by compiling serial radiograph summaries for each patient, containing biplanar radiographs obtained post-surgery and at each follow-up time point.9 Two orthopedic surgeons independently evaluated the serial radiograph summaries to determine the timing and presence of callus bridging at weeks 6, 12, and 24 weeks post-surgery. Results of the independent bridging analyses were combined into a single outcome table. In cases where the surgeons’ assessment of bridging callus differed, the patient was assigned the later time point for bridging or “absence of bridging callus” to generate a conservative summary assessment for radiographic fracture union.

Endpoint Analysis:

The primary endpoint of this observational study was plate durability over a 6 months post-operative loading period. Plate failure was defined by bending or fatigue fracture of the plate, breakage of the elastically suspended sliding elements, or failure of the screw head locking interface. Secondary endpoints of this study documented fracture healing, complications, and functional outcome scores. Fracture healing was defined by resolution of pain at the fracture site during load bearing, and by bridging of at least two of the three cortices visible on bi-planar radiographs.9,15,16 Complications were defined as screw breakage, screw pull-out, infection, non-union, and the need for revision surgery. The patients’ return to function was assessed by the validated DASH, Constant, and SF-12 outcome scores.

Statistical Analysis:

Where applicable, observations are reported as mean ± one standard deviation. In the absence of a concomitant control group, statistical analysis was limited to interfragmentary motion and construct stiffness data of the biomechanical study that compared active to standard locked plating constructs, using 2-tailed unpaired Student t tests at a level of significance of α = 0.05.

Results

Fixation Construct:

The stiffness of active locking plates (463±177 N/ mm) was 76% lower than that of standard locking plates (1,957±235 N/mm, p<0.001) (Figure 3A). At 350 N loading, active plating constructs delivered over three times more axial interfragmentary motion (0.86±0.43 mm) than standard locking plates (0.18±0.02 N/mm, p<0.001). At the 100 N load level, active locking plates exceeded the 0.2 mm fracture motion threshold known to promote callus formation (Figure 3B).17-20 Even at 350 N peak loading, standard locking plates did not reach this 0.2 mm motion threshold.

Figure 3.

Figure 3

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Biomechanical test results: A) active constructs had on average a 76% lower construct stiffness; B) fracture motion in response to axial loading.

Patient Cohort:

Patient demographics and fracture characteristics are summarized in Table 1. There were 6 male and 5 female patients with an average age of 40 ± 14 years and weight of 90 ± 22 kg. These eleven patients had six simple AO/OTA type 12A fractures, three wedge type 12B fractures, and two comminuted type 12C fracture, including one Gustillo type 1 open fracture. Two of the eleven fractures occurred because of a ground level fall, four fractures resulted from elevated falls or a fall down stairs, and the remaining five fractures resulted from motor vehicle and motorcycle accidents, and one bicycle accident. Three of the eleven patients were smokers. Four of the eleven fractures had poly-trauma with additional extremity fractures (2 patients) or pelvic fracture (2 patient). All eleven patients were available for each follow-up. One patient was not able to complete the Constant shoulder score at week 6, as he remained bedridden from co-morbidities.

Outcomes:

There was no incidence of plate breakage, plate bending, or failure of the elastically suspended locking hole mechanism. Ten of the eleven fractures healed within 10.9 ± 5.2 weeks, as evident by bridging callus and pain-free function (Table 2). One fracture required revision surgery 37 weeks post surgery due to late fixation failure at the screw-bone interface in presence of an atrophic delayed union. The average DASH score of all 11 patients improved from 31 ± 22 at week 6 to 13 ± 15 by week 24, approaching the DASH score of 10.1 representative of the normal, healthy population.21 By week 12, the average Constant shoulder score was considered excellent. By week 24, there was no significant difference in the Constant shoulder score between the affected extremity (82 ± 12) and the contralateral extremity (85 ± 7, p=0.53). By week 24, the SF-12 physical health score (44 ± 9) and mental health score (48 ± 11) approached the mean value of 50 that represents the norm for the general U.S. population22.

Table 2.

Outcome Data

Parameter Results Comments
Enrolled: 11 patients with 11 fractures
Follow-up: Week 3: 11 patients
Week 6: 11 patients
Week 12: 11 patients
Week 24: 10 patients One patient moved from area
Plate breakage: 0
Fixation failure: 1
Complications: 1 fixation failure requiring revsion Atrophic delayed union in heavy smoker
Bridging (≥2 cortices): Week 3: 0 fractures (0%)
Week 6: 4 fractures (36%)
Week 12:10 fractures (91%)
Week 24: 10 fractures (91%)
DASH score Week 6: 31 ± 22
Week 12: 16 ± 17
Week 24: 13 土 15
Constant shoulder score (difference from contralateral arm) Week 6: 17 ± 11
Week 12: 8 ± 8
Week 24: 3 ± 8		 1 patient omitted due to bed confinement
SF-12 (Physical Health Score: PHS) Week 24: 44 ± 9 Data from 9 of 11 patients
SF-12 (Mental Health Score: MHS) Week 24: 48 ± 11 Data from 9 of 11 patients
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Durability and applicability of active plating for different fracture types is demonstrated by two examples of patients of this cohort that represent the opposite ends of the fracture pattern range: first, a patient with a comminuted fracture (patient 10), which is traditionally amenable to bridge plating or intramedullary nailing; and second, a patient with a simple, transverse fracture (patient 5), which is traditionally amenable to compression plating. Patient 10 was a 56 years old male with a history of tobacco use and coronary artery disease. He fell off a 25 foot scaffold and sustained a comminuted, multi-fragmentary AO/OTA type 12C-3 fracture. His fracture was bridged with a 9-hole active locking plate to restore length and anatomic alignment of the humeral shaft. Similar to intramedullary nailing, this biological plating technique aimed for preservation of soft tissue and did not seek to anatomically reduce fragments in the comminution zone. Week 3 radiographs indicated early callus formation, which was confirmed on week 6 radiographs by abundant callus that bridged the comminution zone (Figure 4). Decreasing callus size by week 24 indicated the onset of the callus remodeling phase. Patient 10 reported no pain from his arm at the 3 weeks follow-up, and full range of motion six weeks after surgery. Patient 5 was a 27 years old male without co-morbidities who sustained a simple transverse AO/ OTA type 12A-3 mid-shaft fracture from a ground-level fall during football. The fracture was stabilized with a 7-hole active locking plate to achieve direct apposition without the need for inter-fragmentary compression (Figure 5). Despite absence of a fracture gap, clearly visible bridging callus was present by week 6. Week 12 and 24 radiographs confirmed circumferential callus formation and callus remodeling. This patient reported no pain and full range of motion by week 3, and full strength by week 6 post surgery.

Figure 4.

Figure 4.

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Example of a comminuted fracture, stabilized with an active locking plate in a 56 year old male patient with a history of tobacco use and coronary artery disease.

Figure 5.

Figure 5.

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Example of a simple fracture in a 27 year old male patient without co-morbidities. Direct apposition of the fracture without compression yielded natural bone healing by callus formation.

Complications:

One of eleven patients (patient 4) required revision surgery due to failure of screw fixation in the diaphysis. The 22 year old female patient sustained a simple AO/ OTA type 12A humeral mid-shaft fracture and an acetabular fracture in a motor vehicle accident. The patient was morbidly obese with a BMI of 38, and a heavy smoker with hidradenitis suppurativa of the ipsilateral axilla which was thought to increase the risk of local infection. She exhibited delayed, atropic healing of the humeral fracture, with callus bridging of one cortical aspect by week 24. She was allowed to weightbear on crutches immediately after surgery, which exposed the plate construct to early and high loading. At 37 weeks post surgery, one proximal screw broke and the remaining two proximal screws pulled out of the humerus, likely due to the combination of high loading and delayed healing. The patient was revised with a longer plate and bone graft.

DISCUSSION

Introduction of novel implants should be accompanied by an observational study for timely documentation of clinical performance to establish safety and to detect potential risks.23 This observational study was designed to establish the clinical safety and durability of active locking plates by dissemination of our early clinical experience.

Rigid fixation of fractures was introduced to prevent hardware failure in the setting of conventional plates and screws.20,24 Compression of the fracture fragments without interfragmentary motion is required for primary bone healing.20 Compression plate fixation improved construct stability and allowed early mobilization, but introduced problems with fracture healing. In response, more biological fixation techniques, including bridge plate fixation with standard implants and locked plating were introduced to improve fracture healing.25,26 These newer techniques were thought to provide less rigid fixation and more motion at the fracture site for the formation of callus and secondary bone healing. Biomechanical studies, however, confirm that these techniques provide an initial fracture environment that is as stiff as conventional compression plating.27,28 This initial stiffness inhibits callus formation and, in some cases, leads to fracture nonunion.29,30

In contrast, Goodship and Kenwright showed three times greater callus formation using an external fixator which allowed 1 mm interfragmentary motion relative to a rigid external fixator.19 Additionally, they found early motion provided better healing relative to motion introduced later. More recent advances in dynamic fixation include the use of FCL technology which improved fracture healing with significant increases in callus volume relative to historical locked plate controls for distal femur fractures.9 Biomechanical studies show that FCL constructs result in a 78% reduction in stiffness relative to a similar locked plate construct.8 The active plate employed in the current study showed a similar decrease in stiffness, with a 76% decrease in stiffness relative to a similar titanium all locked screw construct.

Observations of this study suggest that active locking plates provide safe and effective stabilization of simple and comminuted humeral shaft fractures. These results are consistent with two in vivo studies of active locking plates using the established ovine tibia fracture healing model.10,11 The first study investigated the effects of interfragmentary motion provided by bridging a 3-mm osteotomy gap with active locking plates in comparison to rigid bridging with standard locking plates.10 The symmetric axial dynamization provided by active locking plates stimulated circumferential callus and yielded faster and stronger healing than standard locking plates. Nine weeks post-surgery, specimens of the active locking group had recovered 81% of their native strength and were 399% stronger than standard locked group specimens, which had recovered only 17% of their native strength.10 The second study investigated the effects of dynamically loading a simple, well-reduced transverse osteotomy stabilized with active locking plates in comparison to standard compression plating.11 Even in absence of a fracture gap, active locking plates stimulated circumferential callus formation by dynamic interfragmentary compression and yielded faster and stronger healing than standard compression plating. Nine weeks post-surgery, specimens of the active locking group had recovered on average 64% of their native strength and were over twice as strong as CP specimens, which recovered 24% of their native strength.11 Those prior studies as well as the present study suggest that natural bone healing may be stimulated by dynamic interfragmentary motion or loading, indicating that active plating may be applicable for bridging of comminuted fractures as well as for stabilization of simple well-reduced fractures.

Not all humeral fractures require surgical treatment. Studies suggest that the nonunion rate after nonoperative treatment is below 10%.31,32 Authors often cite the large range of motion at the shoulder and elbow as justification for accepting malunions of up to 30 degrees in the humeral shaft.33 A recent investigation argued that malunions may be more functionally detrimental than once thought,34 and suggested operative treatment for displaced or angulated fractures. Relative to nonoperative treatment, operative treatment of humeral shaft fractures using intramedullary nails or plates results in a slightly higher nonunion rate of 10-15%.35 Nonunions of long bone fractures, including the humerus, are devastating to patient outcomes.36 Additionally, treatment of a humeral nonunion as a complication of attempted fixation is much more difficult than treatment of a nonunion after non-operative treatment,37 meaning that when surgical intervention is chosen, it is imperative to obtain a union after the index surgery. Compared to intramedullary nailing of comminuted fractures, active plating precludes insertion site morbidity and may provide improved control of rotational alignment. Compared to compression plating of simple fractures, active plating may not only provide faster and stronger healing, but may also be more forgiving, since it does not require perfect anatomic reduction and compression necessary to achieve absolute stabilization.

This study was limited to the use of a large fragment plate, as a small fragment plate was not yet commercially available. No patients reported discomfort related to the plate. Clinically, the use of large fragment plates is recommended to allow early mobilization using crutches in the multiply injured patient. The strategy of using thin plates has been proposed as a technique to achieve a flexible fixation construct. This approach provides dynamization at cost of strength, which necessarily will increased the risk of plate fatigue and fixation failure. For this reason, allowing immediate weight bearing on a humeral fracture fixed with a small fragment plate is only recommended in patients below 70 kg.38 Large fragment plates should sustain crutch weight-bearing of comminuted humeral shaft fractures in patients weighing 90 kg or less.39 Active plating can provide dynamization without reducing construct strength, allowing the use of large fragment plates. The early return to function, with reported post-operative week 3 activities including push-ups, baseball, and resuming a full work schedule as a hair dresser, demonstrates the benefits of combining dynamization with a strong fixation construct. However, the foremost challenge for any osteosynthesis construct is the concurrence of prolonged excessive loading and delayed healing. Even in the presence of these coinciding adverse events in patient 4, weighing 109 kg, the active locking plate supported the prolonged and elevated loading without failure.

Several additional limitations should be considered when interpreting the study results. For timely dissemination of our early clinical experience with active plating constructs, this observational study has a relatively short follow duration of six months. This limited follow-up was considered acceptable based on precedence9,40 and given the fact that 10 out of 11 fractures had healed without complications. After fracture healing, active locking plates are effectively unloaded and prevent stress shielding of the diaphysis due to the elastic suspension of the locking screws. Most importantly, this observational study was only designed to evaluate the safety and efficacy of fracture stabilization with active locking plates. In addition to providing our early clinical experience in a timely manner, results of this study provide pilot data for the design and sample size estimation of a future randomized controlled trial required to evaluate differences in clinical outcomes between active plating and rigid locked or compression plating.

In conclusion, absence of plate failure suggests that dynamic fixation of humeral shaft fractures with active plates provides safe and effective fixation. Moreover, early callus bridging and functional outcome scores suggest that dynamic fixation with active locking plates may promote increased fracture healing over standard locked plating, enabling earlier return to function. However, this hypothesis on the stimulatory effect of dynamic fixation on fracture healing requires investigation in a future randomized controlled trial.

Source of Funding

Financial support for this study has been provided by Zimmer Biomet.

References

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