1 Introduction

While the term ‘congenital pseudarthrosis of the tibia (CPT)’ is frequently used in the literature, the clinical presentation of tibial dysplasia varies from bowing to frank pseudarthrosis, thus naming this entity is an elusive task.^1–7

CPT is a special type of nonunion, which develops spontaneously or after minor trauma in a dysplastic tibial diaphyseal segment, often associated with Neurofibromatosis type 1.⁸ In most cases, tibial dysplasia develops into pseudarthrosis within the first two years of life.^3,8,9 However, in a few cases, it presents after the age of two years. In a few occasions, the patients present with only bowing without fracture or pseudarthrosis. A review of the literature revealed a state of confusion regarding cases of congenital anterolateral bowing, where cases of tibial hemimelia were included together with cases of congenital segmental tibial dysplasia.^3,9,10

The term congenital pseudarthrosis is a misnomer.^1,2 Moreover, using the term “dysplasia” has not been consistent, and some authors have used the term dysplastic to describe severe forms.¹¹ Consequently, standardization of terms and concepts is important to avoid confusion. In this study, the term congenital segmental tibial dysplasia (CSTD) was used to describe cases that present after the age of two years, whether the case developed pseudoarthrosis or not. To our knowledge, such condition has not been classified before, probably due to the rarity of such a condition.³

The management of CSTD is controversial, as whether to correct a dysplastic yet intact tibia, or to follow conservative management. Hence, predicting whether a dysplastic tibia would develop pseudarthrosis or not, is crucial to decide when to interfere surgically, and for parental counseling.

The aim of this study was to shed light on the late presentation of CSTD, and to provide a prognostic and treatment-oriented classification for this entity.

2 Materials and methods

46 cases who had CSTD were diagnosed and managed in our institute over a period of 20 years (2000–2020). Patients who presented after the age of two years were included, and thus 17 patients out of 46 were included in this study (Table 1). The diagnosis of CSTD was clinically dependent on the presence of anterolateral bowing of the tibia, and radiologically based on the presence of dysplastic segment of the tibia with sclerosis and anterolateral apex angulation.

All patients were examined clinically for signs of NF-1 and its associated pathologies such as pectus excavatum, scoliosis and neurofibromata. The limb was examined for integrity and neurovascular status.

Radiological evaluation included plain radiographs in the antero-posterior and lateral views. Those presented with fractures, previous x-ray records (present with the patient or at the previous treating center) were reviewed for evaluation of the radiographic features of dysplastic segment. Standing x-ray scanogram was performed in cases planned for surgery to analyze deformity and measure limb length discrepancy. CT scan was performed in cases suspected to have insufficiency fractures.

3 Results

17 cases were included, eight were females (47%) and nine were males (53%). Fifteen patients (88%) had signs of NF-1, whereas two children (11.7%) had pectus excavatum.

R-CSTD included four cases (23.5%). They were two females and two males. The average age during the first presentation was 3 + 11 (ranging from 2 + 4–18 years). The average follow-up period was 9 years. Three cases had NF-1, while in one case there was no NF-1. One case had corrective osteotomy of the deformed tibia and fixation by interlocking nail at the age of 16 years.

The P-CSTD cases were 13 cases (76.5%), six females and seven males. The mean age at the time of presentation was 5 + 6 years (ranging from two to seven years). Average follow-up was 4.4 years. In eight patients, spontaneous fracture occurred at the dysplastic area and progressed into CPT, while in five cases, there was a history of minor trauma. NF-1 was found in 12 patients of this group.

In all cases of the R-CSTD group, the tibia had a canalized medullary cavity with anterolateral bowing and segmental cortical sclerosis (Figs. 1 and 2).

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Fig. 1 Example of a case of resolving CSTD A: A male patient, aged two years and three months, note the canalized medulla; B: Same patient at age of five years and two months, medulla remains canalized with no pseudarthrosis; C: Clinical photo of the Same patient at age five years and two months, the patient has NF-1 with multiple café au lait patches and pectus excavatum.

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Fig. 2 a case of resolving-CSTD A, B, C: X-rays at age 2 years, 4 years, 15 years, showing canalized medulla with non-progressive deformity; D: At age 15, prior to corrective surgery, clinically the patient had only cosmetic problem; E: Deformity correction by tibial osteotomy, Fibular osteotomy + On-lay ICBG + ILN done at age 16; F: Proper healing observed after 6 months of follow-up; G: Locking Screws have been removed, the nail was left in place as a permanent intramedullary splint.

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While in the P-CSTD group, there was anterolateral bowing, segmental cortical sclerosis, and any of the following: 1) medullary obliteration, 2) cystic changes, 3) hour-glass appearance, 4) Impending fracture, and 5) and/or progressive deformity (Figs. 3–5).

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Fig. 3 Radiological features of pre-Pseudarthrosis CSTD A,B: Cystic changes at dysplastic zone; C: Stress fracture and increased deformity; D: hour-glass deformity and medullary obliteration; E: Intraoperative image showing medullary obliteration.

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Fig. 4 A male child aged 4 years +6 months, with P-CSTD A-B: Clinical and radiographic presentation, medullary obliteration and stress fracture can be observed; C: Management with Ilizarov and iliac crest bone graft; D: X-rays after healing and ilizarov removal with intramedullary rod in place, full union and remodeling are observed.

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Fig. 5 Example of a cases of pre-Pseudarthrosis CSTD A: a male patient, aged five years at presentation, note the medullary oblitration, a small stress fracture is also seen posteromedially, bracing was initiated; B: same patient at age six years, in addition to the previous features, narrowing of the bone at site of dysplasia is noted; C: Same patient at age 7 years, progressed to a fracture in spite of bracing; D: Casting was ineffective in managing such fracture.

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All patients in the resolving group were managed by orthotic protection of their legs (removable plastic splint) throughout the follow-up period. Patients in the P-CSTD group were managed according to our CPT management protocol, using Ilizarov frame fixation with an intramedullary rod and an onlay iliac crest bone graft. Consolidation of the pseudarthrosis and osteotomies in all cases was achieved.¹²

In the operated cases, we observed a soft tissue thickening of the periosteum in the posteromedial concavity of the dysplastic segment, surface erosion and cyst formation.

4 Discussion

As reported in the literature, most cases of CSTD develop CPT during the first two years of life.^3,8,9 Only a few cases have been able to reach walking age without sustaining a fracture of the dysplastic tibial segment. This entity of late onset pseudarthrosis in a dysplastic tibia is not well defined in the literature. To our knowledge, the only dedicated publication on this subject was in 1993 by J W Roach et al.³ However, they did not provide an exact age at which CPT is considered late, as they included in their study a case aged one year and six months.

Other authors have considered late onset to be those who present with fracture after the age of four years, however, they provided no explanation for setting four years as the higher age limit.^1,13

I.C.Tuncay et al.¹⁰ have described causes of resolving congenital anterolateral bowing, and identified some features to such condition, as presence of a callus triangle in posteromedial aspect of the tibia, a hypoblastic fibula with proximal tibiofibular subluxation, and ankle varus. Cases had no other congenital anomalies or evidence of neurofibromatosis. These cases have been erroneously described as resolving congenital segmental tibial dysplasia, although the features described and the presented cases conform with tibial hemimelia type 2B in Paley's classification, termed Delta tibia, an entity described by several authors.^2,14,15

The average walking age in normal children ranges between 12 and 18 months,^16,17 and considering that withstanding the normal stresses of walking in a dysplastic tibia is exceptional, we considered patients presenting with CSTD at least six months after the walking age to be late-presenting cases.

Different forms of bone changes exist in the dysplastic segment, including obliteration of the medulla, sclerosis, cyst formation, progressive deformity, and insufficiency fracture. However, this does not influence the management once fractured.^1,3 According to our observation, radiological changes in CTSD, before developing pseudarthrosis, can guide the timing of management. The absence of medullary obliteration in CSTD cases is believed to have a good prognostic value, as such cases were less liable to sustain a fracture in the dysplastic segment.

An important entity to distinguish from CSTD is the anterolateral tibial blowing due to other conditions, especially tibial hemimelia. The main differentiating features are (1) Large magnitude deformity at birth (2) Resolving deformity course (3) No NF-1, (4) Short tibia (5) Intact but short fibula (6) Tibiofibular subluxation (7) Skin dimple (8) Duplication of big toe (9) Mild Ipsilateral femoral shortening.^2,14,15

Several classifications for CPT were proposed in the literature, starting in 1973, when Anderson⁶ proposed a classification according to the radiological appearance. However, this classification had no impact on management, and neurofibromatosis was considered not to be associated with the cystic form, which is inconsistent the subsequent findings.^9,11

Boyd⁴ in 1982, proposed a classification which had a prognostic value, but had no guide to the management. Crawford's⁷ classification was introduced in 1986, it was only descriptive and has no prognostic or therapeutic value; however, it was the most commonly used classification due to its simplicity, and the combination of clinical with radiological findings.

In 2000, EI-Rosasy-Paley¹⁸ classification has linked the clinical mobility of CPT with the radiological features at the time of presentation and relation to previous operations, and correlated all to the management.⁹ However, they classified cases of pseudarthrosis only, with no account for the dysplastic cases that have not developed pseudarthrosis.

In 2006, Weber M.² proposed a classification for “Congenital Crural segmental dysplasia”, a new term created to include non-CPT cases of dysplasia.¹⁹ Although this classification considered P-CSTD types and provided a guide for the management, it was of a complex nature and difficult to memorize, which limited its application. Moreover, the term CSTD is more accurate in describing tibial pseudarthrosis, as the Latin origin of “crus” means the whole leg, including both tibia and fibula. However, fibula is not necessary for a management guided classification of tibial Pseudarthrosis, as in our experince, coexistance of fibular pasudoarthrosis had no influence on the healing of the tibia. Furthermore, fibular pseudarthrosis was independently classified by Trigui M. et al.²⁰ with management based on ankle stability.^20–22

Since there is both a biological problem in bone healing and mechanical disadvantage of a bowed weight-bearing bone, the dysplastic tibia is best treated in a manner to address both problems. McFarland B,⁵ has proposed his bypass technique to prevent the development of pseudarthrosis in CSTD using different grafting materials. Recently, Laine JC et al.²³ described the outcome of anterolateral epiphysiodesis to gradually correct the deformity, and reported reconstitution and remodeling of the dysplastic segment of the tibia. Although 5 of the 10 presented cases were over the age of two years and had no previous tibial fracture, the disease course was modified by distal tibial guided growth, making case comparison with our series a difficult task. It is indeed an interesting approach and further studies would be needed to confirm these findings.

The main question is “to operate or not to operate” on the dysplastic yet intact tibia. This is a matter of debate, knowing that such osteotomy may induce a recalcitrant nonunion. According to our approach, it is of utmost importance to differentiate between a resolving CSTD (R-CSTD) and the pseudarthrosis type (P-CSTD). In the first type, surgery can be postponed, since the development of pseudarthrosis is less likely. If reached skeletal maturity, the remaining deformity can be managed by corrective osteotomy and properly fixed in a more favorable condition. While in the cases where pseudarthrosis is considered inevitable (P-CSTD), full attack by intramedullary rod, bone graft and Ilizarov frame provides proper construct that allows for proper healing and excellent union rates.¹²

A simple classification with prognostic value has been proposed for CSTD cases that did not fracture until after the age of two years. This differentiation will aid in decision making and preoperative counseling, offering the possibility to wait for five years, allowing the bone to grow, and making surgical intervention much easier if fracture occurred.

One of the limitations of the study is the small number cases included, especially the resolving CSTD category, which only comprised of 4 cases. However, this was justified by the fact that the condition is relatively rare. We also did not compare outcome of surgical management in early and late presenting CPT. Moreover, a comparison of surgical outcomes between early and late development of CPT was not performed in this study.

Funding/sponsorship

This research did not receive any specific grant from funding agencies in the public, commercial or not-for-profit sectors.

Authors contribution

Mahmoud Abdel-Monem El-Rosasy (Contribution: Conceptualization, Methodology, Validation Investigation, Resources, Data curation, writing original draft, review and editing, supervision, project administration)

Mostafa Elsebai Hammad (Contribution: Conceptualization, Methodology, Validation, Investigation, Data curation, writing original draft, review and editing, Visualization)

Abdullah Ahmed Nada (Contribution: Conceptualization, Methodology, Validation, Investigation, Data curation, writing original draft, review and editing)

Informed consent

It was obtained from all cases involved in the study regarding the use of data and clinical images.

This study was approved by the institutional Ethical committee.