Distal fibular impending fracture secondary to distal tibial interosseous osteochondroma after physeal fusion

PV Raja Rao, Himanshu Sharma and P Moses

Abstract

Osteochondromas arising from the interosseous border of the distal tibia and involving distal fibula are not common. We present a 16 year old young man with an erosion and weakness of the distal fibula, secondary to an osteochondroma arising from the distal tibia. Early excision of this deforming distal tibial osteochondroma avoided the future risk of pathological fracture of the distal fibula, ankle deformities and syndesmotic complications.

Keywords: osteochondroma, erosion, distal, tibia, fibula

Introduction

Osteochondromas arising from the interosseous border, deforming distal tibia and fibula and occurring prior to physeal fusion are well reported in the literature. Plastic deformation of tibia and fibula, mechanical blocking of joint motion, syndesmotic problems (synostosis or diastasis), varus or valgus deformities of the ankle and subsequent degenerative changes in the ankle joint are some of the documented complications in the neglected cases [1,8]. Prior to skeletal maturity, a pathological fracture usually occurs if the osteochondroma is pedunculated [3]. However, the progressive growth of a sessile lesion in the distal metaphyseal region of the leg can lead to pressure erosion and scalloping of the neighbouring bone and a fracture may possibly ensue [2,7].

We describe a 16 year old young man who presented to the emergency department with an inversion injury to the ankle. A solitary osteochondroma arising from the left distal tibia, eroding the distal fibula was detected in the presence of completed physeal growth.

Case report

A 16-year-old young man sustained an inversion injury to the left ankle while playing football. He attended the emergency department with a painful, swollen ankle and difficulty in weight bearing. Clinical diagnosis was a sprained ankle. Ankle x-rays showed no bony injury. The exostosis was discovered incidentally on radiographs, which were ordered to exclude a fracture, after observing positive Ottawa ankle rules. The patient was referred to the fracture clinic with this incidental finding. On further questioning in the clinic, the patient confirmed the appearance of a swelling on the left lower leg few months previously with minimal discomfort on weight bearing. Examination of left leg and ankle revealed a swelling and fullness on the antero-lateral aspect of the left distal leg with minimal local tenderness. There was no erythema or locally raised temperature. Ankle movements were normal. There was no distal neurovascular deficit.

Anteroposterior and lateral radiographs of the left ankle revealed a well-defined bony exostosis, arising from the interosseous border of distal tibial metaphysis, eroding the distal fibula (Figure 1 and 2).

Figure 1 Anteroposterior radiograph of ankle revealing distal tibial osteochondroma with erosion of the the distal fibula.

Figure 2 Lateral radiograph of ankle revealing distal tibial osteochondroma with marked thinning of the distal fibula.

The patient was initially put in an ankle foot orthosis. An MRI scan was ordered once the decision was made to undertake operative intervention. It was consistent with a large, broad based benign osteochondroma arising from the lateral aspect of distal tibia with an uncalcified cartilagenous cap. This led to a marked pressure erosion of the distal fibula, which was only 5 mm thick at the narrowest point (Figure 3).

Figure 3 T1W MRI Scan of distal leg showing a large broad-based osteochondroma arising from the lateral aspect of distal tibia with uncalcified cartilagenous cap. The lesion had caused a marked pressure erosion of distal fibula, which is only 5mm thick at the narrowest point.

The patient underwent excision of the osteochondroma through an anterior approach without fibular osteotomy. Intra-operatively, the fibula was found to be quite thin and weak. However, its outer cortical shell was intact. The inferior tibio-fibular joint was stable. Histology confirmed the clinical diagnosis of osteochondroma with no malignant transformation. Post-operatively, the patient was mobilised, non-weight bearing in a below knee plaster, for four weeks. Further mobilisation was undertaken with a gradual transition from partial to full weight bearing. At one year follow-up, he had made a complete recovery with full return of ankle functions. The fibula had recovered the full thickness. The patient has been discharged with advice to return to the clinic if recurrence is suspected.

Discussion

Osteochondromas are the most common benign bone tumours (40% of all benign, 10% of all primary skeletal tumours). They present most often in the second decade of life. The metaphyses of proximal tibia, distal femur, distal tibia, distal fibula, proximal femur and proximal humerus are the most commonly affected sites [1,8]. Osteochondromas arising from the tibial interosseous border and causing fibular erosion with imminent fractures after skeletal maturity are rare.

Osteochondromas usually follow a predictable course. The lesion slowly increases in size until physeal fusion. After skeletal maturity, the growth of this tumour slows down and eventually ceases in virtually all the cases. The main symptom is a mass or bony lump. Progressive enlargement of osteochondromata may cause nerve compression or skeletal deformity resulting in pressure symptoms. Malignant transformation to chondrosarcoma is rare (less than 1%) and should be suspected in the presence of increasing pain and sudden increase in the size of lesion in patients presenting after skeletal maturity [5].

The decision to treat distal tibial osteochondromas non-operatively carries the risk of persistence of symptoms and ankle deformity. Mirra (1989) reiterated the importance of complete resection of the cartilaginous cap to prevent recurrence [6]. In the previously published literature, anterior [3], posterior [7] and trans-fibular approach with fibular reconstruction [4] are described, although anterior approach without fibular osteotomy is associated with the least postoperative morbidity and was successfully used in this case.

This case highlights the need to have a high index of clinical suspicion of the osteochondromas in adolescent patients presenting as ankle sprain and found to have a palpable mass with unrestricted motions. Early excision of the osteochondromas deforming the distal aspect of tibia and fibula obviates the need for complex reconstructive surgery.

References

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