Bifocal Lengthening with Monorail External Frame for Severe Shortening of the Femur: A Case Report

Abstract

Aim and background

Femoral lengthening using a monorail external frame often involves creating two simultaneous distraction sites. This approach allows for a better distribution of the osteogenesis process and can reduce the overall treatment duration, particularly in cases of severe shortening. However, the literature on bifocal femoral lengthening is limited, with reported cases rarely exceeding 10 cm of lengthening. This case report aims to describe the treatment and outcome of a patient who underwent bifocal lengthening with a monorail external frame for severe femoral shortening.

Case description

A 26-year-old female presented with a 23 cm shortening of the left lower limb resulting from previous surgeries for infection. She underwent bifocal femoral lengthening using a monorail external frame, achieving 20 cm of lengthening. Following the removal of the external fixator, a fracture occurred in the regenerated bone, necessitating intramedullary nailing.

Conclusion

For severe femoral shortening, various lengthening techniques can be considered. Bifocal lengthening with a monorail external frame offers specific advantages and disadvantages that should be evaluated based on factors such as required treatment duration, expected patient compliance, and infection risks.

Clinical significance

This case demonstrates that substantial femoral lengthening may be achievable with a monorail external frame, especially when two simultaneous osteotomies are utilised. For large bone regenerates, even with radiographic evidence of callus maturation, internal stabilisation may be advisable, despite the peculiar technical challenges involved.

Introduction

Limb shortening can result from various aetiologies and significantly impact quality of life, with effects proportional to the severity of the condition. A substantial limb length discrepancy in the lower extremities (greater than 10 cm) can impair walking and cause aesthetic and psychological concerns, even with the use of shoe lifts or orthotic devices.

In cases of severe femoral shortening, treatment options include lengthening using external frames (circular or monorail), magnetic nails, or combined techniques.^1–3 In select cases, amputation and prosthetics may also be considered.⁴

Monorail external frame lengthening can be performed at a single site or at multiple simultaneous distraction sites (bifocal/trifocal).⁵ Multi-site lengthening can better distribute the lengthening and reduce treatment duration, particularly in cases of substantial shortening. The literature regarding bifocal femoral lengthening is scarce, and reported cases do not exceed 10 cm of osteogenesis.⁶

This case report describes the treatment of a 26-year-old female who presented with a 23 cm shortening of the left lower limb, predominantly affecting the femur. This was the result of an unspecified infectious disease followed by multiple surgical procedures during childhood. The patient underwent bifocal femoral lengthening using a monorail external frame, achieving a total lengthening of 20 cm. The treatment process extended over approximately 2 years, culminating in the removal of the external fixation device. Shortly thereafter, the regenerated bone fractured, necessitating intramedullary nailing of the femur.

Prior to the development of the manuscript, the patient was informed that data regarding her case would be submitted for publication, and she provided consent.

This case report is the first to underscore the feasibility of achieving extreme limb lengthening with a monorail external frame, while highlighting the need to consider internal stabilisation in these patients due to the high risk of fracture in the regenerated bone, even after a sufficient maturation period.

Case Description

A 26-year-old female patient presented with severe shortening of the left lower limb. This condition was a sequela of an infectious disease contracted during childhood. The patient had undergone multiple surgical interventions in her country between the ages of 3 and 5, although no documentation was provided.

Clinically, the patient exhibited significant shortening of the left lower limb, post-surgical scarring on the left thigh, joint stiffness in the ipsilateral hip and knee, marked muscular atrophy in both the thigh and calf, and equinus contracture of the left foot. The patient was able to walk only with limited autonomy, using a cane and a custom-made orthotic device, and could cover distances of less than 100 m (Fig. 1).

Fig. 1.

Custom-made orthosis consisted of a socket designed to accommodate the foot, along with an artificial leg and foot. The orthosis appeared to be poorly tolerated, with evidence of skin irritation at the level of the socket and at the straps securing the foot

A standing long-leg radiograph confirmed the limb length discrepancy of the left femur (Fig. 2A). Specifically, the distance from the superior aspect of the femoral head to the distal portion of the medial femoral condyle was 23 cm shorter on the affected side compared to the healthy contralateral limb. This discrepancy was attributed to severe shortening of the diaphyseal shaft along with significant varus deformity of the femoral neck. Additionally, there was a 2 cm shortening of the left tibia.

Figs 2A to F.

Panoramic standing radiographs obtained preoperatively (A). X-ray 1 week postoperatively (B), at 5 months (C), and at 18 months (D). Panoramic standing radiographs after the removal of the external frame (E) and after intramedullary nailing (F)

Considering the patho-anatomy, the patient's functional demands, and expectations, a knee disarticulation was proposed. However, the patient firmly refused the amputation, leading to a discussion about the possibility of lengthening the left femur. The decision to use an external frame rather than internal devices was primarily driven by the patient's surgical history of infection. The monorail external frame with hydroxyapatite-coated screws was selected due to the anticipated long duration of treatment, with the goal of improving patient compliance and psychological tolerance. The patient consented to the proposed procedure and underwent surgery.

The surgery was preceded by meticulous preoperative planning, which aimed to restore the mechanical axis of the femur while considering the planned lengthening. Hydroxyapatite-coated screws, 6 mm in diameter, were applied (three screws to the proximal and intermediate bone segments and four screws to the distal segment). Clamps were applied within a monorail (unilateral uniplanar) external fixation system (Orthofix Limb Reconstruction System™ – LRS). The external fixator frame was placed laterally and parallel to the mechanical axis of the femur to prevent deviations in the frontal plane. No correction was planned in the sagittal plane. A minimally invasive bifocal corticotomy was performed through multiple drill holes, followed by the release of the proximal and distal clamps, both connected to the central clamp by a telescopic arm for controlled distraction osteogenesis.

A 10-day waiting period was observed before starting lengthening at a rate of approximately 1.5 mm per day, equally distributed across the two distraction sites (0.75 mm each) and over three sessions (0.25 mm per session), with adjustments made based on callus formation and the patient's tolerance. The patient was discharged on the 10th postoperative day with instructions for non-weight-bearing, self-administered lengthening, and intensive physiotherapy to maintain the already limited range of motion in the hip and knee. The patient was re-evaluated regularly (every 2–4 weeks), monitoring clinical status and radiographic regenerate quality. When the desired lengthening was achieved (Figs 2B to D), the proximal and distal clamps were locked, and bioelectric stimulation using pulsed electromagnetic fields (BIOSTIM® IGEA, Carpi (MO) – Italy) was initiated, alternating between the distraction sites for 8 hours daily each. Subsequently, magnetotherapy was extended to the left foot due to the development of a severe complex regional pain syndrome (CRPS).

Approximately 9 months after surgery, progressive weight-bearing with aids was permitted, and after an additional 6 months (15 months post-surgery), the external fixation system was dynamised to allow for increased mechanical stimulation of the regenerate while protecting it from torsional and flexional stresses.

Two years postoperatively, with evidence of corticalisation of the regenerate and no further radiographic improvement, the external fixator was removed (Fig. 2E) with the plan to stabilise the operated femur using an intramedullary nail after a 2-week ‘pin holiday’.

The postoperative course was favourable until an accidental fall 10 days after frame removal, resulting in trauma to the left hip and a fracture of the proximal regenerate. The patient then underwent locked intramedullary nailing (Fig. 2F).

At the 4-year follow-up (FU) from the index surgery, the patient is in good general health, uses a 2 cm heel lift on the left side, walks with a moderate limp, and occasionally uses a cane for long distances. The patient has recovered a knee range of motion of approximately 80°, while the hip exhibits flexion exceeding 90° but limited abduction and rotations. She reports no pain and is satisfied with the outcome (Fig. 3).

Fig. 3.

Patient presented with a severe shortening of the left lower limb, clinically measured 25 cm (A). At the 4-year FU, leg length discrepancy is minimal, with significant clinical improvement (B)

Discussion

This case report describes a bifocal femoral lengthening performed using a monorail external frame. The entire treatment process spanned 2 years, concluding with the removal of the external fixation device, a subsequent fracture of the regenerated bone, and intramedullary nailing of the femur.

Unlike other reported cases where bifocal lengthening with a monorail external frame was applied to smaller defects, our strategy addressed a severe 23 cm shortening while balancing the risks of infection and pushing the biological capacity of the bone regenerate to its limits.

The monorail external frame offers several advantages in the treatment of severe shortening of long bones: Ease of application (though requiring meticulous preoperative planning), the ability to make real-time adjustments, improved patient acceptance, and thus better compliance.⁷ Additionally, this method is biologically less invasive as it preserves both endosteal and periosteal vascularisation, also allowing safer management of infected cases or those at risk of infection.⁸ However, the monorail external frame is less mechanically stable compared to circular frames or intramedullary systems.⁹ It is also important to consider the decreased ability to apply rigid fixation, which inevitably leads to a longer treatment duration, with an increased risk of secondary deformities, soft tissue contractures with joint stiffness, and pin-tract infections.⁶

Circular frames offer greater construct stability and, combined with extreme versatility in all planes, allow for better management of complex deformities in the lower limbs.¹ However, these systems are bulky, poorly tolerated, and often rejected by patients when long-duration treatment is proposed.

Another alternative is all-inside distraction osteogenesis, made possible by extendable intramedullary nails or plates.^10,11 Nails, in particular, have the significant advantage of being minimally invasive and extremely well-tolerated by patients, providing excellent mechanical stability (providing stable in-axis fixation with earlier full weight-bearing).⁸ The disadvantages include limitations in the possible lengthening (although multiple distraction procedures with the same apparatus are possible), fewer possibilities for angular corrections, and the risk of secondary deformities or deep infection. These systems also tend to be more expensive compared to external fixators and are often less favoured by novice surgeons, who may be more comfortable with external devices.

In this particular case, the decision to use the monorail external frame was based on the surgeon's greater familiarity with the technique, the ability to better control the regenerate, and the perceived safety advantages of external fixation given the risk of recurrent infection. A knee disarticulation would have allowed for a predictable clinical outcome, rapid recovery, and excellent expectations for prosthetic fitting, resolving both the problem of limb length discrepancy and knee stiffness. However, the patient refused the amputation.

The Orthofix LRS system was used, providing modularity and ensuring satisfactory stability even in biomechanically unfavourable cases.^6,7 The use of hydroxyapatite-coated screws was necessary due to the long treatment duration, as this coating reduces the risk of loosening and screw tract infections, ensuring stability at the bone interface.^12,13 Also, the use of tapered screws contributes to a very stable fixation to the bone.¹⁴

Bifocal distraction osteogenesis allows for a reduction in treatment time and a more effective distribution of lengthening along the diaphyseal axis, thereby preventing potential deformities that may arise when extensive lengthening is concentrated on a single osteotomy site.^5,15 Yushan et al. describe a series of eight patients who underwent bifocal lengthening with a monorail external frame for post-traumatic shortening of the femur (mean lengthening 67.5 mm), reporting satisfactory postoperative outcomes.⁶ Additionally, a digital 3D method is reported to ensure proper anatomical reconstruction. The same author presents highly convincing results regarding the application of the same technique to the tibia.⁵

Regardless of the surgical strategy, extensive lengthening (>10 cm) poses unique challenges: It requires substantial rehabilitative efforts to prevent muscle contractures, joint stiffness, or instability. Additionally, due to the long treatment duration, proper management of pin-tracts is crucial, and psychological support is essential, especially for younger patients. Potential complications such as CRPS or secondary deformities must also be prevented or promptly addressed.¹⁶ In fact, these are procedures with high complication rates that increase proportionally with the extent of the planned lengthening.

Despite an adequate waiting period, extensive lengthening pushes the biological capacity of the bone regenerate to its limits, with a potential risk of regenerate maturation defects. In this specific case, a fracture occurred in the proximal regenerate bone. At this site, a reduction in the diameter of the bone segment was evident, attributable to suboptimal production and maturation of the regenerate bone. This defect, combined with the fact that the subtrochanteric region represents the area most subjected to compressive and tensile loads, led to a fracture following a low-energy fall. It is important to note that preventive internal fixation was considered after an adequate period following frame removal, namely, pin holiday.¹⁷ The staged conversion was scheduled to allow for the healing of the pin-tracts and to reduce the risk of deep infection in the setting of intramedullary nailing. The accidental fall, unfortunately, accelerated the clinical timeline, converting a prophylactic procedure into an emergent one. During preoperative planning, a CT scan revealed a severely narrowed and almost obliterated intramedullary canal in the distal regenerate portion. Despite this, intramedullary nailing was preferred over plating and was performed using the smallest available diameter nail (8 mm). Despite significant technical challenges, the intramedullary nailing was successfully completed, with excellent results at a 2-year FU. In the literature, there are reports of internal stabilisation following lengthening with external fixators, such as through plating or intramedullary nailing.^18,19 However, this practice is increasingly less utilised, being often reserved for cases involving bone transport for infections or tumours, due to the growing use of all-inside systems.^10,20

The primary limitation of this study is that it describes a single case report, which may not be generalisable to all patients with severe limb length discrepancies. The treatment required an exceptionally long duration of 2 years, necessitating high patient compliance and psychological resilience that may not be feasible for all candidates. Additionally, while the monorail external frame is effective, it possesses inherent mechanical instability compared to circular frames or internal devices, which contributed to the risk of secondary complications. Finally, the suboptimal maturation of the regenerate bone in this extreme lengthening case underscores the biological limits of distraction osteogenesis.

Conclusion

This case report underscores the feasibility of achieving substantial long bone lengthening with a monorail external frame through bifocal distraction osteogenesis.

This procedure may be associated with substantial risk of complications and should be considered only in carefully selected cases where alternative treatment strategies have been thoroughly explored and discussed with the patient. This reconstructive strategy requires meticulous preoperative planning, an experienced surgeon, and close clinical FU.

This case report also highlights the need to consider internal fixation of the regenerated bone due to the high risk of fracture, even after a sufficient maturation period.

Clinical Significance

Monorail external frames enable up to 20 cm femoral lengthening, especially when two distraction osteotomies are performed simultaneously.

Bifocal lengthening using a monorail external frame demands careful preoperative planning, an experienced surgical team, and diligent clinical monitoring.

In cases involving extensive distraction osteogenesis, internal stabilisation may be recommended, even when radiographic evidence indicates callus maturation.

Intramedullary nailing through regenerated bone is associated with specific technical challenges and should be performed by experienced surgeons.

Key Learning Points

• Monorail external frames can achieve extreme femoral lengthening through bifocal distraction osteogenesis.

• Meticulous preoperative planning and frame alignment parallel to the mechanical axis are mandatory to prevent secondary deformities.

• Massive lengthening challenges bone regenerate maturation; radiographic appearance of callus may not always correlate with mechanical stability.

• Internal fixation should be strongly considered after frame removal in extreme lengthening to prevent fractures, despite the peculiar technical challenges involved.

Ethical Approval

The patient was informed that data regarding her case, including clinical images, would be submitted for publication, and she provided written informed consent. All procedures performed were in accordance with the ethical standards of the institutional research committee and the 1964 Helsinki Declaration and its later amendments.

Data Availability Declaration

The data supporting the findings of this case report are included within the article. Further clinical details are available from the corresponding author upon reasonable request.

AI Disclosure

The authors declare that no generative AI or AI-assisted technologies were used in the drafting, clinical analysis, or data interpretation of this manuscript.

Acknowledgement

The authors would like to thank the patient for her cooperation and consent to share her clinical journey for medical education and research purposes. Acknowledgements are due to IGEA (Carpi, Italy) for the complimentary provision of the bioelectric stimulation device.

Authors' Contributions

Giuseppe Geraci, Cesare Faldini, Vitantonio Digennaro: Conception and design of the technique, final approval of the version to be submitted.

Cesare Faldini, Alberto Di Martino: Final approval of the version to be submitted.

Giuseppe Geraci, Riccardo Ferri, Federico Ruta: Drafting the article.

Giuseppe Geraci, Cesare Faldini: Performed the surgical procedure.

Orcid

Giuseppe Geraci https://orcid.org/0000-0002-9640-5031

Alberto Di Martino https://orcid.org/0000-0002-0716-4951