Two days later, because of increasing pain and swelling of the left knee, his family doctor arranged further radiographic examinations with MRI and CT scans, revealing the Hoffa fracture. The patient was then referred to a medical center for traumatic surgery. Surgical treatment consisted of diagnostic arthroscopy, open reduction of the fracture, and internal fixation with three 40-mm headless compression screws (Figure 3). The screws were placed in posterior to anterior and caudal to cranial directions. The anterior horn of the lateral meniscus was fixed to the joint capsule using FiberWire 2-0, and the ruptured retinaculum was fixed to the medial patellar margin with two Mitek anchors. A 3 × 3 cm tumor close to the articular capsule turned out to be a lipoma and not, as initially suspected, a neurofibroma.
After surgery, the knee was stabilized with a knee orthosis, and partial weight-bearing was prescribed for 10 weeks. Fracture healing was regular. In <4 months after the accident, the patient returned to work without any orthopaedic therapeutic appliances. In this case, the occurrence of a femoral fracture after a low-velocity trauma was probably influenced by reduced bone quality because of an underlying NF1, but NF1 did not influence fracture healing. Two years after the operation, the range of motion of both knees was unlimited, and no osteoarthrotic changes were noticed.
Manfredini et al7 studied 19 subjects with unicondylar fractures of the femur; associated lesions were found to be frequent, such as other femoral fractures, patellar fracture, and anterior cruciate ligament rupture. Although in most cases, Hoffa fractures occur as a result of high-velocity trauma,6–8 Vaishya et al9 presented the case of a Hoffa fracture with ipsilateral patellar dislocation resulting from a household trauma. Comparable to our patient, the patient reported by Vaisha et al9 was first seen in a local hospital, where the patellar dislocation was treated while the Hoffa fracture was initially missed by the radiologist.
Pathologic tissue resulting from neurofibromatosis rarely affects a joint directly. In our patient, a tumor adjacent to the joint capsule turned out to be a lipoma after histopathologic examination, containing no tissue of a neurofibroma. Bone deformities of the lower limb in patients with NF1 have been described in several reports, in particular, congenital anterior bowing of the tibia and congenital pseudoarthrosis of the tibia. Skeletal dysplasia has also been reported in patients such as ours. Because of a pronounced thoracolumbar kyphoscoliosis and a reduced bone density, he had to undergo extensive surgery 10 years before the reported accident.
Bone tissue is a composite of a collagenous framework, integrated small proteins, and a mineral phase with carbonated hydroxyapatite. Defects in any of those components can cause low bone mass or diminished bone quality, or both. Poor bone quality is a known risk factor for fractures. NF1 was found to be associated with reduced bone mineral density. Contemporary studies reveal that about 48% of subjects with NF1 show osteopenia and 25% to 28% show osteoporosis.2,10 In our patient, diminished bone quality had been verified even before the accident. This might explain the occurrence of a Hoffa fracture after a low-velocity accident.
Fracture risk is also evidently age dependent. In a study by Heervä et al,2 there was no increase in fracture risk of NF1 patients aged 17 to 40 years compared with control subjects without NF1. The authors speculate that bone strength would be the highest in this age group of patients with NF1, and subsequently bone mineral density would worsen with aging. Fracture risk was evaluated in children aged 3 to 16 years with NF1, showing a relative risk ratio for fractures of 3.4,2 whereas fracture risk of adults with NF1 older than age 40 years was about fivefold higher than in the control group. This is in contrast to the young adult patient mentioned here. Impaired fracture healing is frequently observed in patients with NF1. However, in the above-mentioned study by Heervä et al2 with 460 patients with NF1, all but one of the 60 fractures had healed. These results are in accordance with the actual case, where no delayed fracture healing was observed.
In a study by Bel et al5 with 163 distal femoral fractures, of which 18% were Hoffa fractures, 50% of patients reported moderate pain. Osteoarthritis was found in 12% of patients and was associated with malunion. Valgus-varus deformity was found in 10% cases, flexion-recurvation deformity in 5%, and an AP or lateral articular surface step-off in 12%. In our patient, currently no osteoarthritis and no joint deformation has occurred.
Hoffa fractures are unusual fractures and might initially remain undiagnosed. They normally result from high-velocity trauma but may also occur after minor trauma in subjects with diminished bone quality. This case report shows that knowledge about rare injuries and genetic disorders, such as neurofibromatosis-1, is important in helping to find a complete diagnosis and to provide an adequate therapy.
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Keywords:Copyright © 2017 The Authors. Published by Wolters Kluwer Health, Inc. on behalf of the American Academy of Orthopaedic Surgeons
Hoffa fracture; Femoral fracture; Neurofibromatosis-1; High-velocity trauma; Osteopenia; Skeletal deformities