Management of a Massive Solitary Femoral Condyle Bone Cyst at the Site of Knee Osteoarthritis with a Synthetic Bone Graft and Primary Robotic-assisted Cementless Total Knee Arthroplasty: A Case Report

Abstract

Introduction: Subarticular cystic lesions, also known as geodes, present a challenge in the management of patients undergoing primary total knee arthroplasty (TKA). Although multiple treatment options are available for addressing these lesions, uncertainty persists regarding the optimal approach.

Case report: A 58-year-old man with a history of rheumatoid arthritis presented with several years of left knee pain. Evaluation showed severe left knee degenerative osteoarthritis complicated by the presence of a large lateral femoral condyle cyst. After failing conservative management, a robotic-assisted cementless cruciate-retaining TKA was indicated. The large bone cyst was managed with augmentation using synthetic bone grafting. 1 year postoperatively, he showed excellent clinical outcomes and radiographic evidence of osteointegration.

Conclusion: This case highlights the value of robotic-assisted technology to plan and execute bone grafting of a large femoral cystic lesion while performing TKA with primary components. A computed tomography-imaged robotic TKA offers the potential benefit of screening bone cysts and thus planning a surgical approach in which bone preservation can be maximized.

Keywords: Robotic arthroplasty; bone cyst; bone void filler; geode; injectable regenerative graft.

Figure 1

Pre-operative anteroposterior (a) and lateral (b) radiographs of the left knee demonstrating severe osteoarthritis with a large cystic lesion on the lateral femoral condyle.

Figure 2

Pre-operative computerized tomography scan of the left knee showing a large cystic lesion of the lateral condyle.

Figure 3

Computed tomography-based 3D surgical planning of tibial and femoral implant positioning.

Figure 4

Intraoperative pictures showing cyst exposure (a) and filling (b). The red dotted lines illustrate approximate bone resection required to perform a box cut for a posterior substituting or varus-valgus constrained femoral component, which would have resulted in a drastic reduction of the native bone stock.

Figure 5

Immediately post-operative lateral (a) and anteroposterior (b) radiographs showing a well-fixed prosthesis and proper filling of the large cyst with bone graft (yellow arrows).

Figure 6

12-month post-operative lateral (a) and anteroposterior (b) radiographs showing excellent osteointegration of the large bone cyst.