JBJS | Altered Fibular Growth Patterns After Tibiofibular Synostosis in Children

The Journal of Bone & Joint Surgery, Volume 83, Issue 2

Articles | February 01, 2001

Altered Fibular Growth Patterns After Tibiofibular Synostosis in Children

Steven L. Frick, MD; Scott Shoemaker, MD; Scott J. Mubarak, MD

Investigation performed at the Department of Orthopaedic Surgery, Children's Hospital-San Diego and University of California at San Diego, San Diego, California
Steven L. Frick, MD Department of Orthopaedic Surgery, Carolinas Medical Center, P.O. Box 38261, Charlotte, NC 28232. E-mail address: sfrick@carolinas.org
Scott Shoemaker, MD Scott J. Mubarak, MD Department of Orthopaedic Surgery, Children's Hospital-San Diego, 3030 Children's Way, San Diego, CA 92123-4208
No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. No funds were received in support of this study.

The Journal of Bone & Joint Surgery. 2001; 83:247-247

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Abstract

Background: Iatrogenic synostosis of the tibia and fibula following an operation on the leg in a child has been reported rarely in the literature, and the effects of this complication on future growth, alignment, and function are not known. This is a retrospective case series, from one institution, of crossunions of the distal parts of the tibia and fibula complicating operations on the leg in children. The purpose is to alert surgeons to this possible complication.

Methods: The senior author identified eight cases of iatrogenic tibiofibular synostosis seen in children since 1985. The patients had various diagnoses and were from the practices of four pediatric orthopaedic surgeons. Synostosis developed in six patients after osteotomies of the distal parts of the tibia and fibula, in one after internal fixation of distal tibial and fibular metaphyseal fractures through a single incision, and in one after posterior transfer of the anterior tibialis tendon through the interosseous membrane combined with peroneus brevis transfer to the calcaneus. Medical records were reviewed, and preoperative and follow-up radiographs were analyzed for changes in the relative positions of the proximal and distal tibial and fibular physes and in the alignment of the ankle.

Results: Five patients were symptomatic after crossunion; they presented with prominence of the proximal part of the fibula, ankle deformity, or ankle pain. Three patients were asymptomatic, and a synostosis was identified on routine follow-up radiographs. Intraoperative technical errors caused two of the crossunions; the cause of the others was unknown. Following tibiofibular synostosis, growth disturbances were noted radiographically in every patient. The normal growth pattern of distal migration of the fibula relative to the tibia was reversed, resulting in a decreased distance between the proximal physes of the tibia and fibula as well as proximal migration of the distal fibular physis relative to the distal part of the tibia. Shortening of the lateral malleolus led to greater valgus alignment of the ankle.

Conclusions: Tibiofibular synostosis can complicate an operation on the leg in a child. After crossunion, the normal distal movement of the fibula relative to the tibia is disrupted, resulting in shortening of the lateral malleolus and ankle valgus as well as prominence of the fibular head at the knee. The synostosis also interferes with the normal motion that occurs between the tibia and fibula with weight-bearing, potentially leading to ankle pain.

Figures in this Article

Introduction

Introduction | Materials and Methods | Results | Discussion | References

A number of common operative procedures used to treat fracture or deformity of the leg and foot in children involve dissection and tissue damage across the interosseous membrane between the tibia and fibula. With any of these procedures, there is a risk of synostosis developing between the tibia and fibula postoperatively. This is an infrequent complication; we know of only one case report of this complication following leg surgery in a child¹. The effects of a crossunion between the tibia and fibula on the growth, alignment, and function of a child's leg are not known.

We report our clinical and radiographic observations in eight cases of iatrogenic synostosis of the distal parts of the tibia and fibula complicating leg surgery in children. We assessed the effects of the crossunion on the relative positions of the proximal and distal tibial and fibular physes and on the alignment of the ankle. We compared observed changes in the growth pattern of the synostosed fibula relative to the tibia as well as changes in ankle alignment to normal growth patterns and alignment in children described in the literature.

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Fig. 1-A:: Figs. 1-A and 1-B Case 6, a nine-year and ten-month-old patient with a left clubfoot who had external rotation osteotomies of the tibia and fibula for the treatment of excessive internal tibial torsion. Fig. 1-A Anteroposterior radiograph showing a shortened lateral malleolus on the left (L), suggesting crossunion. The normal right leg shows the distal fibular physis lying distal to the level of the tibiotalar joint, while the distal fibular physis in the left leg is at the level of the distal tibial epiphysis.

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Fig. 1-B:: Internal rotation (mortise) radiograph of the left leg shows a synostosis and a proximal position of the distal fibular physis, with mild lateral wedging of the distal tibial epiphysis.

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Fig. 2-A:: Figs. 2-A and 2-B Case 5, a child with bilateral clubfoot who underwent external rotation osteotomies of the distal parts of the tibia and fibula for the treatment of excessive internal tibial torsion at the age of two years and nine months. Fig. 2-A Intraoperative radiograph showing that the tibial osteotomy extends across to partially cut the fibula. A synostosis developed at this level.

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Fig. 2-B:: Anteroposterior radiograph made at the age of seven years and five months, showing prominence of the proximal part of the fibula (the proximal fibular and tibial physes are at the same level), a shortened lateral malleolus (the distal fibular physis is level with the distal tibial physis), and increased ankle valgus on the side of the tibiofibular synostosis (R).

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Fig. 3-A:: Fig. 3-A Studies of normal growth have documented distal migration of the fibula relative to the tibia^3,9-11,15. This drawing shows the total percentage contribution to longitudinal growth from the proximal fibular physis to be greater than that from the distal fibular physis (61% compared with 39%). The proximal fibular physis is also responsible for a greater percentage of longitudinal growth than is the proximal tibial physis (61% compared with 57%)¹¹.

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Fig. 3-B:: Fig. 3-B Drawing showing how tibiofibular synostosis reverses the normal growth pattern of distal migration of the fibula, with the distance between the proximal tibial and proximal fibular physes decreasing and the distal fibular physis moving proximal relative to the tibia. This results in prominence of the fibular head, shortening of the lateral malleolus, and ankle valgus.

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TABLE I: Data on the Patients

Case	Diagnosis	Operation Resulting in Synostosis	Age at Operation (yr + mo)	Age at Diagnosis of Synostosis (yr + mo)	Presenting Symptoms
1	Tibial and fibular fracture	Open reduction and internal fixation	8 + 0	11 + 10	Prominent fibular head, ankle pain
2	Marfan syndrome, calcaneal deformity	Posterior transfer of peroneus brevis and anterior tibialis	8 + 10	11 + 0	Ankle pain, ankle valgus
3	Internal tibial torsion after talipes equinovarus correction	Rotational osteotomy of tibia and fibula	2 + 0	2 + 9	Asymptomatic
4	Idiopathic internal tibial torsion	Rotational osteotomy of tibia and fibula	7 + 6	8 + 0	Ankle pain
5	Internal tibial torsion after talipes equinovarus correction	Rotational osteotomy of tibia and fibula	2 + 9	7 + 5	Ankle valgus
6	Internal tibial torsion after talipes equinovarus correction	Rotational osteotomy of tibia and fibula	6 + 3	9 + 10	Asymptomatic
7	Internal tibial torsion after talipes equinovarus correction	Rotational osteotomy of tibia and fibula	2 + 1	3 + 6	Ankle valgus
8	Internal tibial torsion after talipes equinovarus correction	Rotational osteotomy of tibia and fibula	12 + 1	12 + 9	Asymptomatic

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TABLE I: Data on the Patients

Case	Diagnosis	Operation Resulting in Synostosis	Age at Operation (yr + mo)	Age at Diagnosis of Synostosis (yr + mo)	Presenting Symptoms
1	Tibial and fibular fracture	Open reduction and internal fixation	8 + 0	11 + 10	Prominent fibular head, ankle pain
2	Marfan syndrome, calcaneal deformity	Posterior transfer of peroneus brevis and anterior tibialis	8 + 10	11 + 0	Ankle pain, ankle valgus
3	Internal tibial torsion after talipes equinovarus correction	Rotational osteotomy of tibia and fibula	2 + 0	2 + 9	Asymptomatic
4	Idiopathic internal tibial torsion	Rotational osteotomy of tibia and fibula	7 + 6	8 + 0	Ankle pain
5	Internal tibial torsion after talipes equinovarus correction	Rotational osteotomy of tibia and fibula	2 + 9	7 + 5	Ankle valgus
6	Internal tibial torsion after talipes equinovarus correction	Rotational osteotomy of tibia and fibula	6 + 3	9 + 10	Asymptomatic
7	Internal tibial torsion after talipes equinovarus correction	Rotational osteotomy of tibia and fibula	2 + 1	3 + 6	Ankle valgus
8	Internal tibial torsion after talipes equinovarus correction	Rotational osteotomy of tibia and fibula	12 + 1	12 + 9	Asymptomatic

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TABLE II: Radiographic Parameters

*PTFD = proximal tibia-fibula physeal distance, DFS = distal fibular shortening, TTA = tibiotalar axis, and NA = radiographs not available.

Case	Radiographic Measurements Before Synostosis*	Time from Operation to Diagnosis of Synostosis (yr + mo)	Radiographic Measurements After Synostosis*
1	PTFD: NA	3 + 10	PTFD: 0 mm
	DFS: NA		DFS: moderate
	TTA: NA		TTA: 15° valgus
2	PTFD: NA	2 + 2	PTFD: NA
	DFS: mild		DFS: moderate
	TTA: neutral		TTA: 2° valgus
3	PTFD: 7 mm	0 + 9	PTFD: 5 mm
	DFS: normal		DFS: mild
	TTA: neutral		TTA: neutral
4	PTFD: 4 mm	0 + 6	PTFD: 4 mm
	DFS: normal		DFS: mild
	TTA: 2° varus		TTA: 2° valgus
5	PTFD: 7 mm	4 + 8	PTFD: 0 mm
	DFS: normal		DFS: moderate
	TTA: 0° valgus		TTA: 5° valgus
6	PTFD: 10 mm	3 + 9	PTFD: 8 mm
	DFS: normal		DFS: moderate
	TTA: 2° varus		TTA: 6° valgus
7	PTFD: 9 mm	1 + 5	PTFD: 7 mm
	DFS: normal		DFS: severe
	TTA: 3° varus		TTA: 5° valgus
8	PTFD: NA	0 + 8	PTFD: NA
	DFS: normal		DFS: moderate
	TTA: 7° valgus		TTA: 8° valgus

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TABLE II: Radiographic Parameters

*PTFD = proximal tibia-fibula physeal distance, DFS = distal fibular shortening, TTA = tibiotalar axis, and NA = radiographs not available.

Case	Radiographic Measurements Before Synostosis*	Time from Operation to Diagnosis of Synostosis (yr + mo)	Radiographic Measurements After Synostosis*
1	PTFD: NA	3 + 10	PTFD: 0 mm
	DFS: NA		DFS: moderate
	TTA: NA		TTA: 15° valgus
2	PTFD: NA	2 + 2	PTFD: NA
	DFS: mild		DFS: moderate
	TTA: neutral		TTA: 2° valgus
3	PTFD: 7 mm	0 + 9	PTFD: 5 mm
	DFS: normal		DFS: mild
	TTA: neutral		TTA: neutral
4	PTFD: 4 mm	0 + 6	PTFD: 4 mm
	DFS: normal		DFS: mild
	TTA: 2° varus		TTA: 2° valgus
5	PTFD: 7 mm	4 + 8	PTFD: 0 mm
	DFS: normal		DFS: moderate
	TTA: 0° valgus		TTA: 5° valgus
6	PTFD: 10 mm	3 + 9	PTFD: 8 mm
	DFS: normal		DFS: moderate
	TTA: 2° varus		TTA: 6° valgus
7	PTFD: 9 mm	1 + 5	PTFD: 7 mm
	DFS: normal		DFS: severe
	TTA: 3° varus		TTA: 5° valgus
8	PTFD: NA	0 + 8	PTFD: NA
	DFS: normal		DFS: moderate
	TTA: 7° valgus		TTA: 8° valgus

Materials and Methods

Introduction | Materials and Methods | Results | Discussion | References

Eight patients seen with iatrogenic tibiofibular synostosis since 1985 were identified, either from the practice of the senior author (S.J.M.) or during a weekly radiographic review conference of the orthopaedic cases in our Children's Hospital. The ages of the patients at the time of the initial operation ranged from two years to twelve years and one month, and the ages at the time of the diagnosis of the synostosis ranged from two years and nine months to twelve years and nine months. The patients had a variety of underlying diagnoses and histories (Table ITable I). In six of the patients, the synostosis developed after osteotomies of the distal parts of the tibia and fibula were performed to address a rotational leg deformity. Surgical techniques varied, as the patients were from the practices of four surgeons. All of these six patients had osteotomies of both the tibia and the fibula performed, with an oscillating power saw, through separate medial and lateral incisions. Five of the patients had fixation with crossed Kirschner wires in the tibia and an above-the-knee cast, and one patient had fixation with a plate-and-screw construct in the tibia and a below-the-knee cast. All of these patients had closed suction drainage for one or two days postoperatively.

The two remaining patients with postoperative tibiofibular synostosis had undergone different procedures. One patient had undergone open reduction and internal fixation of distal metaphyseal tibial and fibular fractures through a single posterolateral incision, with later removal of hardware through the same single incision. The other patient, who had Marfan syndrome, underwent a posterior transfer of the anterior tibialis tendon through the interosseous membrane combined with peroneus brevis transfer to the calcaneus to treat a calcaneal deformity.

The diagnosis of tibiofibular synostosis was made when radiographs demonstrated bone-bridging, across the interosseous membrane, connecting the tibia and fibula. As the distal parts of the tibia and fibula overlap on standard anteroposterior radiographs of the leg, an anteroposterior radiograph of the tibia and fibula made with the leg internally rotated (a mortise view) helped to show the interosseous space, allowing definitive identification of synostosis (Figs. 1-AFigs. 1-A and 1-B1-B). In cases where bone-bridging was uncertain, computed tomography was used to confirm the diagnosis.

Radiographs made before and after the development of the synostosis were analyzed, and three measurements were made. Growth disturbances were measured by analyzing the positions of the proximal and distal fibular physes relative to the tibia, and changes in ankle alignment were measured according to the tibiotalar axis.

Positions of the proximal tibial and fibular physes: The normal position of the proximal fibular physis is distal to the proximal tibial physis², and with normal growth the distance between these two physes increases from 0.4 cm in infancy to 2.0 cm at the age of twelve years². We measured the distance (in millimeters) distally from the proximal tibial physis to the proximal fibular physis.

Position of the distal fibular physis relative to the distal part of the tibia: The normal position of the distal fibular physis relative to the distal part of the tibia also varies with age. In infancy the distal fibular physis is at the level of the distal tibial epiphysis, and it migrates or moves distally with age^3,4. The relative position of the distal fibular physis was assessed with the method of Malhotra et al., who classified the fibular position as normal if the distal fibular physis was at or distal to the level of the ankle joint⁵. They graded fibular shortening as mild if the distal fibular physis was at the level of the distal tibial epiphysis, moderate if it was at the level of the distal tibial physis, and severe if it was at the level of the distal tibial metaphysis⁵.

Tibiotalar axis: Changes in alignment of the ankle were measured according to the tibiotalar axis⁶, defined as the angle formed by a line perpendicular to the longitudinal axis of the tibia and a second line drawn across the dome of the talus. The normal range in children has been reported to be from 0° to 3° of valgus⁷, although Beals and Skyhar reported that valgus of as much as 8° may be normal and that ankle alignment varies with age². Most authors^5,8 have reported that the alignment of the ankle is neutral in the coronal plane-that is, the angle between the tibial diaphysis and the ankle joint is 90°.

Preoperative ankle radiographs were available for all but one patient (Case 1), who had undergone the operation elsewhere. Radiographs that included the distal parts of the tibia and fibula and the ankle were available for all patients after the development of the synostosis. Radiographs that also included the proximal parts of the tibia and fibula were available for five of the eight patients prior to synostosis development and for six of the eight patients after synostosis development. When the synostosis had developed following rotational osteotomies of the distal parts of the tibia and fibula, intraoperative and postoperative radiographs were reviewed to look for potential causes of the synostosis. One of us (S.L.F.) performed the radiographic assessments and measurements.

Results

Introduction | Materials and Methods | Results | Discussion | References

After the synostosis developed, the presenting symptom was ankle pain in three patients, ankle deformity in three patients, and a prominent lateral knee mass (the fibular head) in one patient. Two patients had more than one presenting symptom (Table ITable I). Three patients were asymptomatic, and the tibiofibular synostosis was identified on routine follow-up radiographs. The time from the operative procedure until the recognition of the synostosis ranged from six months to four years and eight months. After the development of synostosis, the distance between the proximal tibial and proximal fibular physes either decreased (four patients) or remained constant (one patient) in the five patients in whom the preoperative and postoperative distances were known. Normally, it should increase with growth. The position of the distal fibular physis, which is normally at or distal to the level of the ankle joint, moved proximally in each patient after the synostosis developed. In seven of the eight patients, the position of the distal fibular physis had been normal before the synostosis developed, and relative shortening of the lateral malleolus developed in all eight after synostosis. Thus, all of the patients had reversal of the normal growth pattern of the fibula relative to the tibia^2,4,9-11, with a decreasing distance between the proximal tibial and proximal fibular physes and proximal migration of the distal fibular physis relative to the distal part of the tibia (Table IITable II).

Seven of the eight patients also had a change toward more valgus ankle alignment after synostosis. Patients who had a longer interval between the operation and the identification of the tibiofibular synostosis had more severe growth disturbances, with a more proximal position of both the proximal and the distal fibular physis relative to the tibia as well as greater ankle valgus. Four of the five patients for whom the interval was greater than one year between the operation that resulted in the synostosis and the identification of the synostosis had ankle valgus of 5° or greater (range, 5° to 15°), with moderate or severe distal fibular shortening (Table IITable II). However, only one patient (Case 1) had ankle valgus of greater than 10°.

Review of the intraoperative radiographs revealed a technical error as a possible cause of the synostosis in two patients. In both, the intraoperative radiographs showed the tibial osteotomy extending across to partially cut the fibula (Fig. 2-AFig. 2-A). Tibiofibular synostosis developed subsequently at this level in both patients.

Discussion

Introduction | Materials and Methods | Results | Discussion | References

Our series demonstrates that tibiofibular synostosis can occur following an osseous operation on the leg in children, especially after distal tibial and fibular osteotomies. This potential complication has rarely been recorded in series of distal rotational osteotomies^12-14; only one case of crossunion after distal tibial and fibular osteotomies has been reported, to our knowledge¹. This case was in a series of sixty-three distal tibial and fibular osteotomies from our institution and is included in this report.

The presumed etiology of iatrogenic tibiofibular synostosis is soft-tissue damage, hemorrhage, or subperiosteal dissection across the interosseous membrane, leading to new-bone formation. In two of our patients, a technical error was visible on intraoperative radiographs, with the tibial osteotomy extending across to partially cut the fibula. In addition, two patients had a synostosis develop proximal to the level of the tibial osteotomy, at the same level as the fibular osteotomy, but there was no radiographic evidence of the fibular cut extending to the tibia in these patients. The other two patients treated with osteotomies had the tibial and fibular cuts made through separate incisions at the same level, which may be a risk factor for later development of crossunion. This finding raises the question of whether the fibula needs to be cut during rotational osteotomies¹⁴. The preference at our institution has been to cut both the tibia and the fibula, theoretically to minimize abnormal stresses at the distal tibiofibular and tibiotalar joints¹.

The phenomenon of distal movement of the fibula relative to the tibia with growth has been documented in studies of normal children. Love et al. studied distal tibiofibular specimens from cadavera ranging in age from full-term stillborn to fifteen years and found "progressive distal migration of the distal fibular physis and epiphysis" with increasing age⁴. Dias measured the relative position of the distal fibular physis in normal children at different ages and found that it moves distally with increasing age³. Kürrholm et al. found "continuous distal movement of the fibular metaphysis relative to the tibial metaphysis"⁹ and stated that the fibula "normally slides distally along the tibia."¹⁰ Hsu et al. described "downward migration of the lateral malleolus,"¹⁵ whereas Pritchett noted that "the fibula descends on the tibia with growth."¹¹

Different explanations of the mechanism of this distal migration of the fibula have been offered. Beals and Skyhar theorized that the increase in distance between the distal tibial and distal fibular physes indicated that the growth rate of the distal fibular physis was higher than that of the distal tibial physis². Ogden and McCarthy also stated that the distal migration of the fibular physis was secondary to "different rates of longitudinal growth of the two distal physes."¹⁶ Kürrholm et al.⁹ and Pritchett¹¹ offered a contrasting view, stating that the growth rate of the distal fibular physis is lower than that of the distal tibial physis. They attributed the distal displacement of the fibula relative to the tibia to differential longitudinal growth rates of the proximal physes of the tibia and fibula and to traction forces on the fibula by distal ligamentous structures. Hsu et al. stated that the "downward migration of the lateral malleolus was provided by growth of bone from the proximal fibular growth plate."¹⁵ Pritchett found that the proximal part of the fibula grew slightly faster than the proximal part of the tibia. This finding is in agreement with prior anatomical studies describing increased growth of the proximal part of the fibula compared with that of the distal part of the fibula^17,18. These prior studies demonstrated a complex and unique growth pattern for the tibia and fibula. Makin cited an anatomical study by Hert, from 1959, and stated: "At birth the tibia is 20 per cent of its total length. Until 50 per cent of its length has been reached the lower epiphysis is the dominant one. The upper tibial epiphysis then assumes the major role. The fibula at birth is 20 per cent of its total length but its lower epiphysis is dominant only for 30 per cent of its growth, after which the upper epiphysis predominates. This reversal of role is peculiar to the tibia and fibula and does not occur in other long bones."¹⁸

The radiographic findings in our patients support the theory of Kürrholm et al.⁹, Hsu et al.¹⁵, and Pritchett¹¹ that the distal slide of the fibula is secondary to differing rates of longitudinal growth of the proximal tibial and fibular physes. Hsu et al. noted the ability of proximal fibular growth to "thrust" the lateral malleolus distally, as evidenced by tilting of a syndesmotic screw following union of a fibular pseudarthrosis. We found that tibiofibular synostosis blocks the physiological "thrust" of the proximal to the distal part of the fibula, preventing the relatively greater proximal fibular growth from being transferred distally and resulting in relative shortening of the distal part of the fibula. In addition, it appeared that, in our patients, the "thrust" was transferred back to the proximal part of the fibula, resulting in a more proximal position of the proximal fibular physis relative to the proximal tibial physis, a previously unreported finding, to our knowledge. This proximal displacement of the fibular head occasionally caused a symptomatic prominence (Figs. 2-BFigs. 2-B, 3-A3-A, and 3-B3-B) and may lead to varus instability or deformity of the knee.

Ankle valgus, typically of mild-to-moderate magnitude, developed in seven of our eight patients after crossunion of the tibia. Neither the normal range of ankle valgus in children nor the magnitude needing treatment have been clearly defined^2,3,6-8,18. Tibiofibular synostosis is not one of the many clinical diagnoses previously reported to cause ankle valgus in children^3,5-9,18-26. The etiology of ankle valgus in children with these varying diagnoses is poorly understood⁶, but the common pathophysiology is thought to be relative shortening of the fibula³. The talus loses its lateral support and valgus ankle instability occurs, with abnormal compressive stresses inhibiting growth of the lateral part of the distal tibial epiphysis^3,8,15. This common pathway was evident in our patients following tibiofibular synostosis, with relative shortening of the lateral malleolus after the synostosis leading to increasing ankle valgus over time.

Interestingly, distal tibiofibular synostosis has been previously reported as a treatment method for ankle valgus associated with congenital fibular pseudarthrosis in children. In 1967 Langenskiöld reported on three patients who had stabilization of ankle valgus with this method²⁷. On the basis of our findings and our understanding of normal fibular growth patterns relative to the tibia, we believe that such a strategy would result in progressive shortening of the lateral malleolus and in increased ankle valgus with growth in normal children. In a recent study, progressive valgus deformity did occur in patients with acquired absence of the fibular shaft and ankle valgus who were treated by the Langenskiöld operation (distal tibiofibular synostosis)²⁸. We can only surmise that in the three patients treated by Langenskiöld the valgus stabilized because of abnormal growth patterns in patients who have congenital fibular pseudarthrosis.

Most authors have stated that the fibula bears approximately 15% of an axial load across the ankle joint^7,29,30, while simultaneously resisting external rotation and lateral translation forces during the gait cycle^3,25. Scranton et al. described the dynamic function of the fibula and demonstrated an average 2.4-mm distal glide of the fibula during stance²⁵. Tibiofibular synostosis would alter these normal biomechanical functions of the fibula and potentially lead to pain. The literature on tibiofibular synostosis in adults concentrates on these biomechanical alterations of the ankle, with excision of the synostosis recommended for patients who have persistent ankle pain^25,31-33. Ogden noted the late development of vague ankle pain after proximal tibiofibular fusions to treat proximal tibiofibular instability, and he attributed the pain to altered ankle biomechanics³⁴. Three of our patients had poorly localized ankle pain after the synostosis developed. One patient (Case 4) presented with acute pain in the distal part of the leg and had a fracture through the tibiofibular synostosis noted on a computed tomography scan.

In summary, our study showed tibiofibular synostosis to be a potential complication of an operation on the leg in children, especially after combined distal tibial and fibular osteotomies. The previously noted phenomenon of greater growth of the proximal fibular physis, supplying a physiological "thrust" from proximal to distal, is clinically supported by our findings. The altered growth patterns of the tibia and fibula after tibiofibular synostosis in children result in prominence of the fibular head, relative shortening of the lateral malleolus, and the development of ankle valgus. We believe that this is the result of the fibula being tethered to the tibia, preventing the distal migration of the fibula along the tibia that occurs with normal growth. Interruption of the proximal-to-distal fibular "thrust" by either discontinuity (pseudarthrosis, nonunion, or fibular resection) or osseous block (crossunion) will result in shortening of the lateral malleolus and in potential ankle valgus. In the case of crossunion, the thrust will be reversed and can also result in prominence of the proximal part of the fibula.

We recommend close follow-up of children after leg injuries or operations that place them at risk for the development of synostosis. Scrutiny of tibiofibular radiographs, with particular attention paid to the relative position of the distal fibular physis, can aid in early recognition of this complication (Fig. 1-AFig. 1-A). When a tibiofibular crossunion does develop, it creates growth abnormalities that warrant observation and, potentially, treatment, as it may cause progressive deformity or ankle pain. The recognition and understanding of the normal growth pattern of the fibula is important in managing other leg and ankle problems in children, such as physeal arrests of the distal parts of the tibia and fibula, congenital or acquired fibular pseudarthrosis, ankle valgus, terminal overgrowth after below-the-knee amputation, and harvest of fibular autografts.

References

Introduction | Materials and Methods | Results | Discussion | References

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Fig. 1-B:: Internal rotation (mortise) radiograph of the left leg shows a synostosis and a proximal position of the distal fibular physis, with mild lateral wedging of the distal tibial epiphysis.

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TABLE I: Data on the Patients

Case	Diagnosis	Operation Resulting in Synostosis	Age at Operation (yr + mo)	Age at Diagnosis of Synostosis (yr + mo)	Presenting Symptoms
1	Tibial and fibular fracture	Open reduction and internal fixation	8 + 0	11 + 10	Prominent fibular head, ankle pain
2	Marfan syndrome, calcaneal deformity	Posterior transfer of peroneus brevis and anterior tibialis	8 + 10	11 + 0	Ankle pain, ankle valgus
3	Internal tibial torsion after talipes equinovarus correction	Rotational osteotomy of tibia and fibula	2 + 0	2 + 9	Asymptomatic
4	Idiopathic internal tibial torsion	Rotational osteotomy of tibia and fibula	7 + 6	8 + 0	Ankle pain
5	Internal tibial torsion after talipes equinovarus correction	Rotational osteotomy of tibia and fibula	2 + 9	7 + 5	Ankle valgus
6	Internal tibial torsion after talipes equinovarus correction	Rotational osteotomy of tibia and fibula	6 + 3	9 + 10	Asymptomatic
7	Internal tibial torsion after talipes equinovarus correction	Rotational osteotomy of tibia and fibula	2 + 1	3 + 6	Ankle valgus
8	Internal tibial torsion after talipes equinovarus correction	Rotational osteotomy of tibia and fibula	12 + 1	12 + 9	Asymptomatic

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TABLE I: Data on the Patients

Case	Diagnosis	Operation Resulting in Synostosis	Age at Operation (yr + mo)	Age at Diagnosis of Synostosis (yr + mo)	Presenting Symptoms
1	Tibial and fibular fracture	Open reduction and internal fixation	8 + 0	11 + 10	Prominent fibular head, ankle pain
2	Marfan syndrome, calcaneal deformity	Posterior transfer of peroneus brevis and anterior tibialis	8 + 10	11 + 0	Ankle pain, ankle valgus
3	Internal tibial torsion after talipes equinovarus correction	Rotational osteotomy of tibia and fibula	2 + 0	2 + 9	Asymptomatic
4	Idiopathic internal tibial torsion	Rotational osteotomy of tibia and fibula	7 + 6	8 + 0	Ankle pain
5	Internal tibial torsion after talipes equinovarus correction	Rotational osteotomy of tibia and fibula	2 + 9	7 + 5	Ankle valgus
6	Internal tibial torsion after talipes equinovarus correction	Rotational osteotomy of tibia and fibula	6 + 3	9 + 10	Asymptomatic
7	Internal tibial torsion after talipes equinovarus correction	Rotational osteotomy of tibia and fibula	2 + 1	3 + 6	Ankle valgus
8	Internal tibial torsion after talipes equinovarus correction	Rotational osteotomy of tibia and fibula	12 + 1	12 + 9	Asymptomatic

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TABLE II: Radiographic Parameters

*PTFD = proximal tibia-fibula physeal distance, DFS = distal fibular shortening, TTA = tibiotalar axis, and NA = radiographs not available.

Case	Radiographic Measurements Before Synostosis*	Time from Operation to Diagnosis of Synostosis (yr + mo)	Radiographic Measurements After Synostosis*
1	PTFD: NA	3 + 10	PTFD: 0 mm
	DFS: NA		DFS: moderate
	TTA: NA		TTA: 15° valgus
2	PTFD: NA	2 + 2	PTFD: NA
	DFS: mild		DFS: moderate
	TTA: neutral		TTA: 2° valgus
3	PTFD: 7 mm	0 + 9	PTFD: 5 mm
	DFS: normal		DFS: mild
	TTA: neutral		TTA: neutral
4	PTFD: 4 mm	0 + 6	PTFD: 4 mm
	DFS: normal		DFS: mild
	TTA: 2° varus		TTA: 2° valgus
5	PTFD: 7 mm	4 + 8	PTFD: 0 mm
	DFS: normal		DFS: moderate
	TTA: 0° valgus		TTA: 5° valgus
6	PTFD: 10 mm	3 + 9	PTFD: 8 mm
	DFS: normal		DFS: moderate
	TTA: 2° varus		TTA: 6° valgus
7	PTFD: 9 mm	1 + 5	PTFD: 7 mm
	DFS: normal		DFS: severe
	TTA: 3° varus		TTA: 5° valgus
8	PTFD: NA	0 + 8	PTFD: NA
	DFS: normal		DFS: moderate
	TTA: 7° valgus		TTA: 8° valgus

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TABLE II: Radiographic Parameters

*PTFD = proximal tibia-fibula physeal distance, DFS = distal fibular shortening, TTA = tibiotalar axis, and NA = radiographs not available.

Case	Radiographic Measurements Before Synostosis*	Time from Operation to Diagnosis of Synostosis (yr + mo)	Radiographic Measurements After Synostosis*
1	PTFD: NA	3 + 10	PTFD: 0 mm
	DFS: NA		DFS: moderate
	TTA: NA		TTA: 15° valgus
2	PTFD: NA	2 + 2	PTFD: NA
	DFS: mild		DFS: moderate
	TTA: neutral		TTA: 2° valgus
3	PTFD: 7 mm	0 + 9	PTFD: 5 mm
	DFS: normal		DFS: mild
	TTA: neutral		TTA: neutral
4	PTFD: 4 mm	0 + 6	PTFD: 4 mm
	DFS: normal		DFS: mild
	TTA: 2° varus		TTA: 2° valgus
5	PTFD: 7 mm	4 + 8	PTFD: 0 mm
	DFS: normal		DFS: moderate
	TTA: 0° valgus		TTA: 5° valgus
6	PTFD: 10 mm	3 + 9	PTFD: 8 mm
	DFS: normal		DFS: moderate
	TTA: 2° varus		TTA: 6° valgus
7	PTFD: 9 mm	1 + 5	PTFD: 7 mm
	DFS: normal		DFS: severe
	TTA: 3° varus		TTA: 5° valgus
8	PTFD: NA	0 + 8	PTFD: NA
	DFS: normal		DFS: moderate
	TTA: 7° valgus		TTA: 8° valgus