Hypertrophic nonunion management with distraction osteogenesis: a scoping review of the literature

Abstract

Introduction:

Traditionally, stiff hypertrophic nonunions have been managed with open preparation of the nonunion site, which is then secured with internal fixation. Alternative surgical options are available including distraction osteogenesis with an external fixator. There is currently a limited amount of literature pertaining to the use of distraction osteogenesis in the management of hypertrophic nonunion. The aim of this systematic review was to collate and assess the effectiveness of distraction osteogenesis (DO) in the management of hypertrophic nonunions and to evaluate the complications that are commonly reported in the literature.

Methods:

We searched for articles pertaining to the treatment of hypertrophic nonunion using distraction osteogenesis. Several electronic bibliographic databases and clinical trial registries were searched using the MeSH terms “hypertrophic non-union,” “distraction osteogenesis,” “stiff non-union,” and “External Fixation” in various combinations to return the maximal number of studies for review. We performed a systematic review and identified a total of 11 studies eligible for review.

Results:

The review of the literature demonstrated that this technique is highly effective in achieving bony union with minimal complications. The most common complication is mild superficial pin site infections, usually managed with oral antibiotics and effective wound hygiene. Other complications reported were deep pin tract infections, broken hardware, and deformity recurrence due to collapse of regenerate bone.

Conclusion:

The use of distraction osteogenesis with external fixator devices is an effective and safe method for producing bony union in hypertrophic nonunions. There were minimal associated complications.

1. Introduction

Nonunion of a fracture or osteotomy site is a relatively uncommon complication usually due to an inadequate bone healing response, as in the case of infection or compromised vascularity, leading to an atrophic nonunion.^1–3 Other nonunions can present with sufficient vascularization and adequate callus formation, yet union is not achieved because of inadequate stability of the biomechanical environment (Fig. 1). These “hypertrophic” or “stiff” nonunions, according to Perren strain theory, have the vascular capability but lack the mechanical stability for bone formation. Therefore, hypertrophic nonunions have the biological potential for healing, but their biomechanical environment is not optimized.^4,5 Surgical management options for hypertrophic nonunions include stabilization of the nonunion using plates and/or screws, intramedullary (IM) nailing, or external fixation (with or without bone grafting) (Figs. 2 and 3). The implant modalities differ, but each shares a similar goal—to reduce strain across the nonunion site. Decreasing strain or increasing stability at a nonunion site promotes bone formation and subsequent union.⁶ A significant advantage of external fixator application for the management of hypertrophic nonunions lies in their ability to gradually correct large deformities.⁷ This is particularly useful when there is an associated deformity with the nonunion.

Figure 1.

Hypertrophic nonunion with sufficient vascularization and adequate callus formation but inadequate stability of the biomechanical environment.

Figure 2.

Surgical stabilization of the nonunion and deformity correction using external fixation.

Figure 3.

Union evident after removal of the external fixator.

Nonunions commonly present with complex deformity and tenuous skin, which further complicates management; however, using a circular frame, osteogenesis can be induced alongside concomitant percutaneous correction of any associated deformity while protecting vulnerable soft-tissue structures in the area.⁸ Ilizarov described this “tension-stress effect” phenomenon in 1989 stating that callus at a nonunion site can be distracted using simple ring fixation.^9–11 This is analogous to osteotomy distraction in the distraction osteogenesis (DO) process and may be applied here to achieve bone consolidation at a hypertrophic nonunion site. This uses a minimally invasive technique without the need for compression. The underlying premise of distracting a hypertrophic nonunion is similar to the theory of compression at a fracture site.⁶ Distraction increases soft-tissue tension, which increases mechanical stability, thereby reducing strain at the nonunion site, allowing consolidation to occur.⁶ The benefits of this technique using external ring fixation include the ability to perform concurrent corrections such as limb length discrepancy (LLD) and/or angular deformity in addition to addressing the nonunion. Of interest, there is no obligation to expose the nonunion site. This allows for minimization of interference with vulnerable skin and the ability to percutaneously correct deformity with minimal blood loss.^3,4 Monolateral fixation has also been used by some surgeons using this technique because of its simplicity and greater tolerance by patients in comparison with circular fixators; however monolateral constructs prove inferior in the presence of soft bone, oblique angular deformity correction, and proximity to a joint.¹²

There are a limited number of studies pertaining to distraction osteogenesis in the management of hypertrophic nonunions. This study aims to analyze and consolidate the current literature while evaluating the advantages and limitations of this technique, comparing the implants used, complications encountered, and union rates achieved.

2. Methods

We searched for articles pertaining to the treatment of hypertrophic nonunion using distraction osteogenesis. Articles were only included if original data reporting on the outcomes of distraction osteogenesis for the management of hypertrophic nonunion were described (Fig. 4).

Figure 4.

Flow diagram.

On December 8, 2022, several electronic bibliographic databases and clinical trial registries were searched using the MeSH terms “hypertrophic non-union,” “distraction osteogenesis,” “stiff non-union,” and “External Fixation” in various combinations to return the maximal number of studies for review. Locations searched included PubMed, the Cochrane Library, ClinicalTrials.gov, the EU Clinical Trials Register, and the International Clinical Trials Registry Platform (World Health Organization). Search results were assessed on 2 separate occasions to ensure data retrieval accuracy. The flow diagram in Figure 1 illustrates this selection process where selection was determined first based on title, then abstract, and finally a full manuscript review. Review of full articles was performed, and any contention was resolved through consensus. Study selection was unblinded, and only those meeting the abovementioned criteria were included.

3. Results

A summary of the 11 eligible studies in which external fixation was used to correct hypertrophic nonunion, including the reported complications, is presented in Table 1.

TABLE 1.

Summary of Eligible Studies

Authors	Year	Journal	Number of Cases of Hypertrophic Nonunion	Fixation Device Used	Percentage Achieving Bony Union (%)	Mean Time to Union (mo)	Complications
Jia Xu, Ya-Chao Jia, Qing-Lin Kang, Yi-Min Chai1	2015	Injury: International Journal of the Care of the Injured	12	Circular external fixator	100	8	Superficial pin tract infection (3), Achilles tendon contracture (2)
Scott Jacob Schoenleber, James Jackson Hutson Jr2	2014	Foot & Ankle International	8	Circular external fixator (3), hexapod external fixator (5)	100	5.8	Superficial pin tract infection (2), pin site infection requiring intravenous antibiotics plus incision and drainage (1), premature consolidation (1), residual LLD (1), broken olive wire requiring reoperation (1)
S. Robert Rozbruch, David L. Helfet, Arkady Blyakher3	2002	Archives of Orthopaedic and Trauma Surgery	2	Hexapod external fixator	100	3.95	No complications reported
S. Robert Rozbruch, John E. Herzenberg, Kevin Tetsworth, H. Robert Tuten, Dror Paley4	2002	Clinical Orthopaedics and Related Research	5	Circular external fixator (2), monolateral external fixator (3)	100	4.4	Superficial pin tract infection (2), knee effusion (1), change in mechanical axis deviation and anatomical femorotibial angle (1)
Michael Saleh, Simon Royston6	1996	Journal of Bone and Joint Surgery	10	Circular external fixator (7), monolateral external fixator (3)	100	10.2	No complications reported
Dror Paley, Maurizio A. Catagni, Fabio Arganani, Angelo Villa, Gian Batista Benedetti, Roberto Cattaneo8	1989	Clinical Orthopaedics and Related Research	3	Circular external fixator	N/A	N/A	No complications reported
Dror Paley, Miland Chaudray, A. Michael Pirone, Pamela Lentz, Douglas Kautz9	1990	Orthopaedic Clinics of North America	2	Circular external fixator	N/A	N/A	Superficial pin tract infection (2)
Maurizio A. Catagni, Francesco Guerreschi, Jeffrey A. Holman, Robert Cattaneo10	1994	Clinical Orthopaedics and Related Research	21	Circular external fixator	100	6.5	Axial collapse of regenerate due to premature removal of the fixator (1)
N. Ferreira, L. C. Marais, C. Aldous11	2015	The Bone and Joint Journal	44	Hexapod external fixator	97.8	5.3	Superficial pin tract infection (9), fine wire breakage secondary to trauma requiring replacement (1)
Mehmet Kocaoǧlu, Levent Eralp, Cengiz Sen, Mehmet Cakmak, Hakan Dincyürek, S. Bora Göksan12	2003	Journal of Orthopaedic Trauma	16	Circular external fixator	100	7.1	Minor pin tract infection (3), deep infection requiring removal, replacement and debridement (1), Kirschner wire breakage (1), deformity recurrence due to patient refusal to wear protective brace (1)
N. Ferreira, L. C. Marais13	2016	Strategies in Trauma and Limb Reconstruction	2	Hexapod external fixator	100	3.1	Superficial pin tract infection (1), deep pin tract infection requiring removal (1)

4. Discussion

4.1. Historical Significance

The role of distraction to induce tension in the management of nonunion has been described as early as 1965 by Heiple and Herndon¹³ in their study describing the factors affecting the healing of pathologic nonunions. They described how the use of tension across proliferating tissues can help form organized fibrous tissue between fractured bone ends.

An early case report of this technique was published by Paley et al in 1989 who had been using this method since 1981.¹⁴ This study comprised 25 patients with tibial nonunions (22 atrophic, 3 hypertrophic) and bone loss who were managed using the Ilizarov circular fixator apparatus with a monofocal compression-distraction technique without bone grafting. The authors reported that only the patients with hypertrophic nonunions achieved bony union using this technique.

An additional publication by Paley et al¹⁵ in 1990 included 2 hypertrophic nonunions managed with Ilizarov external circular ring fixator apparatus, achieving a mean 4-cm lengthening over a mean 7.1-month period across their total cohort of 29 malunions and nonunions. This article highlighted the importance of compression during the correction process to encourage neocorticalization and remodeling. Paley then went on to subcategorize nonunions into flail, stiff, and lax variations. Stiff nonunions were determined to be those with minimal mobility around the nonunion site, which tended to be hypertrophic, and have the greatest potential for union. Flail nonunions comprise atrophic nonunions, and lax nonunions comprise normotrophic and, as a result, have limited mobility and some fixed deformity. Paley concluded that the DO technique was not suitable for the flail type, and for these cases, the author used a technique of open reduction and resection of the bone ends. In those nonunions deemed to be lax, the author recommended the use of distraction preceded by a short period of compression.

An additional study was published in 1994 by Catagni et al¹⁶ who further studied the utilization of this technique exclusively for hypertrophic nonunion. This was the first study to specifically assess the use of this technique solely for hypertrophic nonunion. Twenty-four nonunions in 19 patients were managed using the Ilizarov ring fixator apparatus solely in distraction, with 100% of patients experiencing eventual bony union within a mean time frame of 6.5 months. A mean limb length discrepancy (LLD) of 39 mm was corrected in this patient sample. A single major complication was noted in this study where 1 patient experienced axial collapse of the bone regenerate because of premature removal of the fixator. Regarding more minor complications, 0.2% of all Kirschner wires required removal with substitution under local anesthesia because of infection. This article concluded that distraction using the Ilizarov apparatus is the preferred treatment modality for stiff hypertrophic nonunions because of its ability to address deformity in the same setting as nonunion surgery.

This article had several contrasting features to the studies published by Paley.^14,15 First, Catagni et al¹⁶ did not perform osteotomy at the nonunion site because it was not necessary for achieving bone union. Fibular osteotomies were performed for all cases of tibial nonunions. Catagni did not use compression as a part of the treatment regime. This is the key biomechanical principle in distraction osteogenesis, which departs from traditional nonunion surgery techniques. Distraction osteogenesis achieves union in hypertrophic nonunion cases by increasing the stability of the biomechanical environment by increasing tension at the nonunion using the soft-tissue structures, which reduces strain in the system.

A similar study conducted by Saleh and Royston in 1996¹² presented a series of 10 hypertrophic nonunions treated with distraction. Seven patients were treated with circular external fixation, and 3 were treated with monolateral external fixation. They reported a 100% union rate at a mean time of 10.2 months following application of the fixator with a mean LLD correction of 35 mm. Complication rates were not discussed within this study. This study, alongside that published by Catagni et al,¹⁶ demonstrated that contrary to popular belief at that time, compression at the nonunion site was not necessary to induce bony union and that union could be achieved using distraction under the appropriate biological conditions. When comparing the use of circular external fixation and monolateral external fixation, they found no discernible difference in union rates.¹²

4.2. Contemporary Significance

A total of 2 subsequent case reports published by Rozbruch et al in 2002^7,8 used a modified surgical technique. In a report of 2 cases,⁷ Rozbruch et al used the hexapod Taylor spatial frame (TSF) system because of the complex nature of deformity present within their cohort. They reported that use of the hexapod TSF system grants the ability to accurately correct length and all aspects of deformity including angulation, translation, length, and rotation. The authors found that through a distraction technique, they were able to achieve a mean lengthening of 19 mm with a mean time to union of 3.95 months. There were no complications reported in this cohort. This is supported by the earlier publication by Rozbruch et al⁸ that assessed 5 patients, 2 of whom were managed using circular external fixation and 3 using monolateral external fixation. The authors found that they were able to achieve a mean length increase of 18 mm with a mean time to union of 4.4 months. In this cohort, compression was not used for stiff nonunions. The term “stiff” was defined as less than 5 degrees of mobility across the nonunion site with attempted mobility.

In 2015, Ferreira et al¹⁷ published a retrospective review of 46 tibial aseptic hypertrophic nonunions managed with the hexapod external fixator. This study is of particular interest because it reports the largest sample size meeting the criteria for this review. Ferreira et al reported matching the contralateral limb within 10 mm in 97.8% of limbs with a mean time to union of 5.3 months using distraction exclusively. One patient's nonunion failed to heal in this study, which the authors retrospectively identified as an undiagnosed pseudarthrosis because of the long-standing nature of the nonunion. This case seemed to be radiographically hypertrophic but was significantly more mobile on examination. All limbs within this study were also corrected to less than 5 degrees of deformity in all planes, leading the authors to conclude that closed distraction of stiff hypertrophic nonunions can reliably induce union while simultaneously and accurately correcting associated deformity.

4.3. Complications

4.3.1. Pin Site Infection

The complications experienced by patients across the literature are consistent and most commonly include the presence of pin tract infection in up to 100% of patients. Most commonly, these represented superficial infections managed with scrutinous care of the pin sites and oral antibiotics. Less commonly, more severe pin site infections were reported, which required IV antimicrobial management or, at most, wire removal and exchange with or without debridement of the local tissues. Severe infections requiring operative management under local or general anesthesia affected significantly fewer patients, ranging from 6.25%¹⁴ to 50%.¹⁸ Other identified complications included a single knee effusion in a patient with pseudogout managed with arthroscopic lavage and pin replacement,⁴ and wire breakages requiring removal and replacement.^5,17,19

4.3.2. Recurrent Deformity

Reports by Paley,¹⁴ Catagni,¹⁶ and Kocaoglu¹⁹ identified patients with recurrent deformity after treatment completion. In 2 cases, this was due to the premature removal of the external fixator before sufficient bone callus had formed. This highlights the necessity to ensure bony union and sufficient healing before removal of the fixator. Paley¹⁵ identified a significant learning curve for surgeons regarding the application of circular external fixation and theorized that the risk of major complications would be significantly reduced once the surgeon's experience had increased, particularly pertaining to the ability to identify sufficient maturity of the regenerate bone.

4.4. Advantages

4.4.1. Weight-Bearing

The use of external ring fixators in the management of these conditions has multiple benefits that are evident throughout the literature, including the reduced risk of neurovascular injury with gradual correction compared with acute intraoperative deformity correction and fixation.^7,19 Reduced risk of osteoporosis development and soft-tissue dystrophy was also identified by Paley¹⁵ through the use of this technique because of its ability to allow the patient to mobilize and weight-bear as tolerated from the onset of treatment, which also promotes consolidation of callus. This contrasts with internal fixation devices that often require a period of rest before weight-bearing can commence, as well as the presence of a plaster cast or brace to immobilize the affected area, which may compromise skin integrity, muscle mass, and joint range of motion. It should be noted that monolateral external fixators provide significantly less stability compared with circular ring (Ilizarov) fixators and so the weight-bearing status that is permitted is less with the monolateral fixator. While patients may prefer internal fixation because of its esthetic benefits, early weight-bearing is of particular importance in this setting because bone loading will induce faster union.¹⁵

4.4.2. Gradual and Concurrent Deformity Correction

From a technical perspective, one of the uses of circular external fixators is that the system allows for the correction of large deformities that are not amenable to acute corrections.^5,15 This system also allows for concurrent correction of deformity of foot and joint contractures with or without the need for soft-tissue release. This apparatus also allows accurate postoperative adjustments of a correction schedule within single degree of angulation and single millimeter of lengthening, evidenced by the ability to provide additional residual programs for 8 of the patients studied by Ferreira et al.¹⁷ This capability is limited to circular ring (Ilizarov) external fixators and is not possible with monolateral external fixators.

Of particular interest regarding the complication profile of this procedure is the almost universal attitude of surgeons toward minor pin tract infections, a complication described by Paley as “an unavoidable nuisance.”¹⁴ These were reported to varying degrees within each report with several authors not citing their incidence in their articles whatsoever. This highlights the frequency with which these minor, easily treatable infections occur, with authors viewing these as simply an expected part of the healing procedure. For example, Catagni et al¹⁶ did not include these infections within their description of complications experienced, citing a single collapse of regenerate bone as their sole complication, yet reported that 10% of all pin sites developed a superficial infection (with 2% of these requiring substitution with a new wire). This was echoed by Rozbruch et al⁸ who described the common nature of superficial pin tract infections, occurring in 40% of the patients within their cohort. They suggested that patients should be provided with sufficient education pertaining to recognizing this complication and a 1-week course of oral antibiotics to be taken if it occurs to prevent delays in managing this.

4.5. Limitations

The literature currently available is limited because of the relatively small sample sizes that are reported on, with much of the literature existing pertaining to small case series. The results seen in these cases are reinforced by a larger study conducted by Ferreira et al,¹⁷ highlighting the consistency with which results are achieved using this method of management. The studies available for analysis also assess retrospective data and, as such, are limited by a potential absence of data and the potential for recall bias. The major difficulty encountered through this systematic review included the sparse data available specifically assessing the use of external fixation devices in hypertrophic nonunions.

5. Conclusions

This systematic review of the literature highlights the usefulness of distraction osteogenesis with circular external fixation devices as a safe and optimal management option for patients presenting with stiff or hypertrophic nonunions. The union rate approached 100% within the literature. Union was achieved within 10.2 months of the application of an external fixator, with many within a much shorter time frame. The benefits of distraction osteogenesis in the management of hypertrophic nonunions especially pertain to its ability to allow concurrent and gradual correction of complex deformity, percutaneous intervention with soft-tissue preservation, and the ability to weight-bear in the initial postoperative setting.