Rare case of bilateral atypical subtrochanteric Femoral Fractures in pycnodysostosis patient- a report

Pycnodysostosis is a rare sclerotic bone disease caused by a mutation in the cathepsin K gene. Atypical subtrochanteric femoral fractures are a common problem associated with pycnodysostosis. Fracture healing in pycnodysostosis cases is typically inferior. Jin Park et al report a case of bilateral atypical subtrochanteric femoral fractures in one patient with pycnodysostosis.

The right subtrochanteric fracture was treated with open reduction and internal fixation (open plating), and united through primary bone healing, while the left one was treated with closed reduction and internal fixation (submuscular plating), and united through secondary bone healing. Although the time to bony union was delayed, fracture union after extramedullary osteosynthesis was obtained in both atypical fractures, demonstrating that both primary and secondary bone healing is possible in patients with pycnodysostosis.

A 40-year-old woman sustained a right subtrochanteric femoral fracture after falling from a bicycle. The patient did not remember the family history well. There was no history of previous fractures. The patient had abdominal organomegaly, which was suspected to account for the ovarian cystadenoma that was found on abdominal computed tomography.

Physical examination of the fracture site revealed tenderness over the proximal thigh. There was no open wound. There was no distal neurovascular deficit distally. The patient was of short stature (150 cm), had abnormal facial features due to micrognathia, which included a large nose and abnormal dentition.

Radiographs showed common features of atypical subtrochanteric femoral fracture, including transverse fracture, medial and lateral cortical thickening, and medial cortical spike. A subsequent skeletal survey revealed an open fontanelle, an obtuse mandibular angle, cortical thickening in all long bones, widening of the distal femur (similar to the Erlenmeyer flask deformity), and tapering of the distal phalanges on both feet and hands. No hematological abnormalities were observed.

The patient had generalized increased bone density, as measured through bone densitometry. T scores of the lumber spines (L1, L2, L3, and L4) were+4.3,+4.3,+5.8, and+6.1, respectively. Z scores of the lumber spines (L1, L2, L3, L4) were+5.1,+5.2,+6.6, and+7.0, respectively. The patient was diagnosed with pycnodysostosis based on clinical and radiological findings and genetic analysis for cathepsin K mutation. There was an incomplete transverse fracture in the left subtrochanteric area for which the patient refused preventive interventions.

The right subtrochanteric femoral fracture was secured with fracture site compression using a dynamic hip screw without bone graft. Patient was followed up monthly for 6 months and then every 3 months thereafter. Radiographic union developed very slowly, compared to a patient without skeletal abnormalities. Thirty-three months after surgery, the fracture was finally united, as evidenced by the disappearance of the fracture line in at least three cortices. The range of motion of both the knee and hip was full.

Six years after the index injury of the right femur, the patient slipped while walking and sustained a left subtrochanteric femoral fracture. It was then fixed with a submuscular plating technique—the minimally invasive plate osteosynthesis (MIPO) technique—with a non-contact-bridging locking plate. A bone graft was not performed. Again, radiographic union was very slow to develop, similar to the timeframe for the contralateral side. Twenty four months after surgery, bony union was finally achieved.

Final follow-up was done at 2 years after surgery (8 years after the first index surgery). The patient could walk without pain. The range of motion of both the knee and hip was full.

The authors concluded - although time to bony union is much longer in pycnodysostosis patients than in normal patients, fracture union after extramedullary osteosynthesis can be obtained through either primary or secondary bone healing, and secondary bone healing might be advantageous in terms of fracture healing time.

Level of Clinical Evidence: 4

Further reading:

Bilateral Atypical Subtrochanteric Femoral Fractures with Primary and Secondary Bone Healing in Pycnodysostosis

Jin Park, Seung Jin Lee, Hyo Beom Lee, Sung Yup Hong.

Indian Journal of Orthopaedics (2022) 56:1478–1481

https://doi.org/10.1007/s43465-022-00675-8