A rare case of pycnodysostosis: Technical difficulties in managing long bone fractures

Abstract

Pycnodysostosis is a rare inherited disorder of autosomal recessive trait causing cathepsin K deficiency, leading to failure of osteoclastic activity. Brittle and sclerotic bones which are prone for frequent fractures is the characteristic feature of this congenital disorder. Despite good healing potential there are few issues in the management of fractures in pycnodysostosis patients. In this article we report the challenges faced in managing a fracture of the femoral shaft in a 12 year old girl with pycnodysostosis. For early rehabilitation and to avoid deformity and shortening, we opted for surgical fixation over conservative treatment. Narrow medullary canal ruled out the option for titanium elastic nail fixation. 4.5mm dynamic compression plate was used to fix the fracture. Sclerotic bone made drilling extremely difficult. Deformed femoral shaft allowed plating over the anterior surface only, instead of the routine lateral surface plating. Postoperative fracture healing was satisfactory. Implant was removed after 18 months.

1. Introduction

Pycnodysostosis is a rare autosomal recessive disorder affecting the bones.¹ The basic pathology is cathepsin K deficiency of the lysosomes in the osteoclasts, which leads to incomplete bone resorption, thereby causing sclerotic and brittle bones.² Apart from skeletal and dental manifestations there is no systemic involvement. Frequent fractures, that too more commonly involving the lower limb decrease the productive days in the life of the affected individual. Conservative management of the fracture will be adequate in most of the cases, as the bones have good healing potential. But surgical fixation facilitates early rehabilitation and quick recovery to a functional living. Quality of the bone by itself presents few surgical challenges. In this case report, we share our experience with one such rare case needing surgical fixation.

2. Case report

A 12 year old female child fell from a bullock cart with foot landing first. She started having a sudden severe pain in her left thigh and was not able to bear weight since then. She presented to our institute's emergency department where she was evaluated and found to have swelling and tenderness in her left thigh. She was not able to actively lift the affected limb and the limb was apparently short compared to the non affected side. The limb was splinted and radiological evaluation was done. She was found to have a transverse fracture of the femoral shaft. The quality of the bone was not normal. It was sclerotic and the medullary canal was very narrow (Fig. 1). Retrospectively we made a detailed evaluation of the child. She was short for her age with a height of 138 cm. Her anterior fontanelle was not closed. Her palate was grooved and she had irregular dentition (Fig. 2). Nails of few fingers (1st and 2nd digit of the right hand, 2nd and 3rd digit of the left hand) were grooved (Fig. 3). Further radiological evaluation showed open anterior fontanelle, obtuse angled mandible and short distal phalanx in few digits (Fig. 4, Fig. 5, Fig. 6) which established the diagnosis of this rare disorder - pycnodystosis.

Fig. 1.

X-ray both hips with thigh showing sclerotic bones, pathological fracture in shaft femur and narrow medullary canal.

Fig. 2.

Yellow arrow showing grooved palate and red arrow showing irregular dentition.

Fig. 3.

Small fingers and grooved nails.

Fig. 4.

Skull AP view-yellow arrow showing opened fontanelle and red arrow indicating irregular dentition.

Fig. 5.

Skull lateral view-Yellow arrow showing wormian bones and red arrow showing obtuse angle of the mandible.

Fig. 6.

Bilateral hand X-ray showing short distal phalanx.

To avoid prolonged immobilization and to avoid deformity and shortening we opted for fixing the fracture over conservative treatment. We planned an open reduction and internal fixation with plate osteosynthesis considering the narrow medullary canal. Under spinal anaesthesia with the patient in lateral position surgical field was cleaned and draped. A lateral incision over the mid thigh was made. Soft tissues were dissected in layer, vastus lateralis muscle was split and bone was exposed. Fracture was reduced and held in alignment. An eight holed 4.5mm narrow dynamic compression plate was positioned across the fracture site. Lateral surface of the femur was slightly deformed and was not suitable for plate seating. So it was positioned over the anterior aspect of the femur. Considering the sclerotic nature of the bone we had adequate number of sharp drill bits. As expected this part was tough and challenging. It took 5–10 minutes for drilling each hole and the drill bits were frequently changed. Continuous cold saline irrigation was simultaneously done to prevent thermal necrosis. Necessary precautions were taken to prevent iatrogenic fractures, which is common due to the brittleness of the bone. After fixing the fracture wound was closed in layers and dressed.

Post operative period was uneventful and rehabilitation began on day one. Patient was made to walk non weight bearing and knee range of motion exercise was started. Patient was discharged on the fifth post operative day. Sutures were removed after 10 days. During subsequent follow-ups weight bearing and physical activities were increased based on radiological signs of union and consolidation. Radiological evaluation at six months follow up revealed complete union and by the eighteenth month, when there was very good consolidation implant removal was done (Fig. 7, Fig. 8). Precautions were taken to prevent iatrogenic fracture and implant breakage. After implant removal patient continued her routine daily activities.

Fig. 7.

X-ray of femur before implant removal showing union and consolidation.

Fig. 8.

X-ray of femur after implant removal.

3. Discussion

The estimated prevalence of pycnodysostosis is one per 1.7 million.^3,4 It is an autosomal recessive disorder due to the defect in the gene encoding cathepsin K (CTSK), which is a lysosomal enzyme in the osteoclast.² This defect in the osteoclasts leads to inadequate bone turnover producing weak and brittle bones. Short stature, osteosclerosis, micrognathia, open fontanelles, irregular teeth with hypodontia, grooved palate, obtuse angle of the mandible, acroosteolysis of the terminal phalanges causing short finger tips and grooved nails are the characteristic features of this disorder.⁵ Patient may also present with deformities like coxa vara, coxa valga, genu varum, genu valgum, kyphosis and scoliosis. For an orthopedician, frequent fractures, sclerotic and deformed bones with narrow medullary canal are the important things to be taken into consideration. Adolescent and adult patients most often require surgical management of the fracture to avoid deformity, shortening and to accelerate the rehabilitation.⁶ Unlike other unaffected individuals, surgical fixation of the fracture is not an easy job. As seen from our case, the narrow medullary canal rules out the option of any intramedullary fixation device. Reaming such a narrow medullary canal in a sclerotic bone can cause iatrogenic fracture. Naturally plate osteosynthesis is the only available surgical option. But this is also not a straight forward procedure. Drilling the sclerotic bone is extremely difficult. It needs adequate number of sharp and strong drill bits. In addition it is a time consuming job and the complication of thermal necrosis from excessive drilling causes further trouble. Bone can be deformed complicating the seating of the plate over it. Just like our case, we may end up in placing the plate over an unintended surface. Identifying these issues preoperatively will prepare us for these intra-operative challenges. Choosing the correct implant, maintaining sharp drill bits in adequate numbers, preferably newer ones and copious saline irrigation during drilling are few things we should always consider before operating on this rare case. Most important thing is to equip ourselves with adequate number of surgical hands to counter the fatigue due to excessive drilling. In a study by Kumar et al. emphasis has been made upon the individualization of treatment of osteopetrosis in an adult case with similar preoperative planning and choice of implant helped in successful management.⁷ So in other osteopetrotic conditions such as Progressive diaphyseal dysplasia (Camurati-Engelmann disease), Idiopathic non-familial acro-osteolysis may require similar careful management of fractures depending upon individual patient. Other osteopetrotic conditions such as osteopetrosis, skeletal fluorosis, osteopoikilosis, myelofibrosis and pagets disease will pose similar challenges. A similar case report of osteopetrosis done by Kumar et al, laid emphasis on individualization of treatment with good preoperative planning for better outcome.⁷ We also need to keep in mind the nature of the bone and its high refracture rate, so in this study patient was provided with protective bracing and mobilized with support for a period of 6 weeks until next followup.

Conflicts of interest

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