Case Presentation
An 8-year-old otherwise healthy boy presented to James C. Wittig, MD with a limp and pain and swelling around his knee. There was no history of trauma. Mom stated that she took him to the emergency room 6 months prior for a limp.
Plain radiographs of the distal femur showed an aggressive permeative appearing lesion that seemed to be producing bone indicative of an osteosarcoma [Figure 1]. An initial chest CT did not show any evidence of metastatic disease.
The patient subsequently underwent an open biopsy that confirmed a high-grade conventional osteosarcoma.
[Figure 1] Initial X-ray showing the mass. [Figure 2] X-ray after completion of preoperative (neoadjuvant) chemotherapy. Chemotherapy resulted in extensive tumor necrosis, leading to calcification of the mass.
Presurgical Approach to Treatment
The patient was started on preoperative chemotherapy consisting of cisplatin, doxorubicin, and high-dose methotrexate. There appeared to be an excellent response after two cycles. The pain had disappeared, and the tumor became heavily calcified [Figure 2]. An excellent response to chemotherapy facilitates limb sparing surgery, enabling the preservation of more normal tissue and maximizing function.
[Figure 3] Expandable prosthesis parts
[Figure 4] Expandable prosthesis in patient
Surgical Approach to Treatment
The patient underwent definitive limb sparing surgery after finishing the preoperative chemotherapy regimen. A medial approach was performed excising the biopsy tract over the medial femoral condyle. After separating the critical neurovascular structures from the tumor, the distal femur was resected removing 25 cm along with a soft tissue margin. Dr. Wittig chose a resection length of the bone that would allow at least a 2 cm margin from the proximal extent of the tumor.
After the femur was removed, attention was focused on the reconstruction of the distal femur and knee joint with a special customized extendible prosthesis that allows for non-invasive lengthening of the prosthesis as the child grows. The child’s leg can be placed into a magnet [Figure 5] in the office which spins around the prosthesis and causes a cork-screw mechanism in the prosthesis to expand. Every 16 minutes under the magnet lengthens the prosthesis 4 mm.
[Figure 5] Magnet used for lengthening in office. The patient's leg is placed in the magnet with the magnet centered over the gears in the prosthesis. This is an example of a patient who underwent an extensible proximal tibia.
A 1 cm cut was made off the top of the tibia plateau that allowed for the preservation of the tibial growth plate. A smooth punch was made through the center of the tibia to allow for a smooth stemmed component. This was followed by the tibial jigs that made cuts through the tibial bone above the growth plate to accommodate the tibial polyethylene component. The femur was reamed for a cemented steam. The final components were assembled on the back table and morse tapers engaged. The components were trialed and fit well. The patella tracked normally and was not resurfaced. The tibial component was cemented in a manner that the cement would not cross the growth plate. The femoral component was subsequently cemented in place and after the cement cured the tibia and femur were connected via the appropriate hinge joint mechanism. The knee was put through full flexion and extension and the patella tracked normally.
Subsequently, the sartorius muscle was mobilized to the medial border of the patella tendon, quadriceps tendon, and the medial aspect of the patella as well as the vastus medialis to close soft tissues over the entire joint and length of the prosthesis. The prosthesis was completely covered with soft tissue to protect the prosthesis from infection should the wound not heal. A drain was then inserted, and the wound was closed in a layered manner.
Postsurgical care
After the procedure, a Jones-type dressing with thick cotton and a posterior splint was placed on the patient keeping the knee in 20 degrees of flexion to control swelling and prevent tension on the blood vessels and nerves in the event of postoperative swelling.
The patient will resume chemotherapy for 4 remaining cycles, and start physical therapy.
[Figure 6] Xray of the femur after the prosthesis was inserted.