Amyloidosis of Femoral Neck: An Unusual Cause of Pathologic Fracture

The deposition of amyloid within human tissue can be detrimental to the proper functioning of multiple organ systems. While the infiltration of the amyloid protein within the musculoskeletal soft tissues can lead to compressive neuropathies, tendon irritation or rupture, and joint stiffness, pathologic fracture as a result of amyloid deposition in bone is a rare manifestation of amyloidosis.

Christopher A. Worgul et al presents a case of pathologic fracture of the femoral neck from amyloid deposition in a 59-year-old male on chronic hemodialysis who was found to have lytic lesions in his proximal femur. At the time of hemiarthroplasty, histopathologic analysis of a femoral head sample revealed apple-green birefringence of the deposits under polarized light, consistent with amyloid deposition. The case report has been published in "Arthroplasty Today" journal.

The authors recommended - 'Clinicians should have a high index of suspicion for the atypical presentation of amyloidosis in a patient on chronic hemodialysis with lytic bone lesions.

The patient is a 59-year-old male who presented with 4 weeks of worsening left hip pain and inability to ambulate. He has a past medical history of end-stage renal disease secondary to diabetes mellitus and hypertension and was on hemodialysis 3 times per week for the past 6 years. He had also been followed by a rheumatology team for a history of monoclonal gammopathy of unknown significance and synovial hypertrophy in his bilateral shoulder, wrist, and knee joints. A prior knee synovial biopsy, with Congo red stain, was negative for amyloid in the past. The overall impression at that time was that his polyarticular arthritis was likely due to rheumatoid arthritis, and he was started on prednisone and etanercept.

Physical examination of the left hip revealed tenderness over the anterior groin and posterior buttock. Left hip range of motion was limited due to pain from approximately 300-800 of flexion. Gentle internal and external rotation resulted in pain for the patient. The left foot was neurovascularly intact distally.

Serology revealed a white blood cell count of 6.5 K/mL (4.0-11.0 K/mL), erythrocyte sedimentation rate of 108 mm/h (0-20 mm/h), and C-reactive protein of 93.4 mg/L (0-5.0 mg/L). Radiographs of the left hip revealed significant osteolytic lesions in the femoral head and neck area, concerning for an impending femoral neck fracture. Computed tomography of the left hip again demonstrated osteolytic lesions in the femoral head and neck concerning for diffuse disease.

The patient underwent a fluoroscopy-guided aspiration of the left hip synovial fluid and an ultrasound-guided biopsy, which revealed minimal effusion but greatly thickened synovium of the left hip. Microbiologic analysis of the synovial fluid revealed a total nucleated cell count of 12/mL, no organisms, and no crystals. Cultures revealed no growth after 30 days. Pathologic analysis of the left hip synovium demonstrated dense fibroconnective tissue without inflammation. When a Congo red stain was performed on the specimen, Congo red-positive amyloid deposits were present, consistent with light-chain (AL)-type interstitial amyloid deposition. Given the diffuse disease present within the proximal femur and the absence of any lesions distally, the patient was indicated for a left hip hemiarthroplasty with a cemented femoral stem for prophylactic stabilization of the impending femoral neck fracture.

The patient underwent an uncomplicated left hip hemiarthroplasty via a direct anterior approach with a cemented femoral stem (DePuy Synthes/Johnson & Johnson, Warsaw, IN) and a metal bipolar head construct. No obvious femoral neck fracture was noted intraoperatively.

The femoral head was sent for histopathologic review, which revealed acellular pink amorphous material indicative of amyloid deposition. When the sample was stained with Congo red, the deposits displayed apple green birefringence under polarized light. Immunohistochemical staining of the bone marrow was positive for CD138þ plasma cells.

The patient had an uneventful postoperative course and was able to bear full weight and ambulate without assistive devices by his 2-week postoperative appointment. Final radiographs at 16 months postoperatively revealed the components to be in stable position with an intact cement mantle and no evidence of osteolysis."

Pathologic fractures of the femoral neck as a result of amyloid deposition can be a source of considerable morbidity, and prophylactic fixation of large lesions may be crucial for fracture prevention. Although amyloidosis can affect several biologic systems, amyloid protein deposition within the musculoskeletal system can be the first manifestation, and orthopedic surgeons may find themselves at the forefront to prevent a pathologic fracture and coordinate further care in a patient with this complex disease" the authors commented.

Further reading:

Amyloidosis of the Femoral Neck: An Unusual Cause of Pathologic Fracture

Christopher A. Worgul, David M. Freccero.Arthroplasty Today 16 (2022) 73- 77

https://doi.org/10.1016/j.artd.2022.03.014