The patient presented himself in our outpatient clinic 14 month after primary TKA which was implanted due to symptomatic knee osteoarthritis (OA) elsewhere. The pre-operative radiographs with anterior-posterior (ap.) and lateral view of the right knee are shown (Figure 1a and b). After an initial symptom-relief, stress-dependent pain reoccurred few months after the surgery. After a phase of stable symptoms, exacerbation occurred approximately 12 months postoperatively, including resting and sleeping pain, which triggered the referral to our outpatient clinic with suspicion of prosthetic loosening.
In the clinical presentation a painful swelling at the proximal tibia was palpable without signs of inflammation, knee ligaments were stable, while flexion was limited to 80° due to pain. The obtained radiographs with anterior-posterior (ap.) and lateral view of the right knee (Figure 1c and d) showed a suspect Lodwick-grade II osteolytic lesion of the proximal tibia extending from the central epi- and metaphysis to the anterior and lateral cortical bone. The interface to the intact bone was wide and blurred, the cortical bone showed discontinuation and complex reactions including spiculae (Figure 1c and d), which was confirmed by a local CT-scan (Figure 1e and f). In suspicion of bone malignancy, an open incision biopsy was performed that exhibited a whitish tumor mass with myxoid parts (Figure 1g). Histopathological evaluation revealed the diagnosis of a G2 myxoid chondrosarcoma, without signs of bacterial infection.
Staging was then completed and the case was discussed in the local interdisciplinary tumor board. In summary a local disease stage, without infiltration of popliteal structures or metastases was present, and a wide resection of the tumor with inclusion of the knee prosthesis was indicated according to the disease stage. Since limb-preserving resection and reconstruction is technically tedious and carries the risk of incomplete resection and local recurrence, amputation was also discussed with the patient and his family. In consideration of all pros and cons of the respective approaches, the patient wished to undergo wide tumor resection and reconstruction with a distal femur and proximal tibia replacing hinged knee prosthesis. This was then planned using the radiographs and CT-scans (Figure 1c-f), with the projected resections being located 8 cm proximal of the joint line at the femur and 15 cm distally of the joint line at the tibia. For the reconstruction the MML tumor knee system for distal femoral and proximal tibial replacement (Modular endoprosthetic system Munich-Lübeck, Orthodynamics GmbH, Lübeck, Germany) was chosen (Salis-Soglio et al. 2010), with an alloplastic reconstruction of the extensor mechanism (Holzapfel et al. 2011).
Resection of the knee joint with proximal tibia: Resection steps included scar excision, resection of the inner part of the patella with complete patellar-tendon (Figure 2a), resection of the joint capsule under preservation of the muscle-insertions of the pes-anserinus (Figure 2a) and the biceps-femoris tendons. Resection was initially performed as previously planned as soft tissue structures were without signs of tumor infiltration. After en-bloc resection the distal marrow showed suspicious tissue, therefore the intraoperative decision to extent the resection 5 cm distally was made (Figure 2b), which resulted in macro- and microscopically tumor free margins. The femoral resection was performed as planned 8 cm proximal of the joint line to match the planned implant, while no suspect bone or soft tissue changes were observed at the resection margins (Figure 2c). All resected tissues were sent in for histopathological examination. For reconstruction medullary canals were prepared followed by implantaion of trial-components for joint-line resonstruction, resulting in full extension and flexion without instability. Thorough irrigation was performed between steps and prior to cement fixation of the original components in the previously tested sizes. After reposition and connection, the previously detached tendons were reattached using FiberWire ® sutures (Arthrex, Naples, FL, USA), with reconstruction of the patellar tendon being performed using a Trevira synthetic ligament (Telos, Marburg, Germany) (Figure 2d-f), before tension free wound closure was performed. After surgery full weight-bearing with an extension brace and continuous passive motion was allowed.
The final histopathological examination revealed a pT2 pN0 L0 V0 tumor stage, with proof of the prior G2 grading. Resection status was proven as R0. While the postoperative radiographs (Figure 3a, b) showed correct implant positioning without signs of loosening or fracture, mobilization needed to be restricted due to delayed wound-healing over the site of patellar ligament-reconstruction, due to absent soft-tissue covering. This made operative wound revision necessary, including debridement (Figure 3c), gastrocnemius-flap-reconstruction (Figure 3d) in combination with a mesh-graft (Figure 3e) from the opposite thigh necessary. Thereafter he patient was mobile on the ward stage and healing of the graft was observed, as the patient could be discharged and transferred to a stationary rehabilitation department. Although all intraoperative cultures were sterile, antibiotic prophylaxis was continued orally during rehabilitation. Unfortunately - after initial progress in terms of mobility - the patient developed a progressive respiratory insufficiency due to an alveolitits, and deceased finally after a 4 week course of ICU care. Written consent was obtained from the patient’s wife to publish data and pictures related to the treatment of her husband.
