A magnetic resonance imaging with and without contrast showed a low-intensity signal mass in T1 and high-intensity signal mass in T2 with aggressive, extra-compartmental bone involvement (stage IB, possible IIB) in the patella of probable primary origin (Figs. 3 through 5).
An ultrasound-guided core needle biopsy was performed. Histological analysis showed predominately fibroblastic malignant cells with abundant osteoid production. Therefore, fibroblastic osteosarcoma was diagnosed.
Regarding the tumor staging study, the chest, abdomen, and pelvic CT scan was normal and a Tc-99m bone scan showed tracer uptake only in the right patella.
Following neoadjuvant chemotherapy, a total patellectomy, including the quadriceps and patellar tendon, Hoffa's fat pad, and medial and lateral patellar retinacula, was performed. Then, the extensor mechanism was reconstructed with a large bone-tendon allograft, using an entire frozen extensor mechanism which had a total length of 20 cm, including a patella that measured 5 cm in width and 4 cm in length. It was carefully selected from the bone bank because it had measurements similar to our patient (Figs. 6 through 8).
A medial parapatellar approach was performed, including the skin contaminated by the prior biopsy and a wide resection of the extensor mechanism, including 5 cm of the quadriceps tendon above the patella and 3 cm of the internal and external retinacula, the entire Hoffa's fat pad, patella tendon, and its insertion into the tibial tubercle. The margins obtained were negative at the time of resection. The tibial area chosen as the site for reattaching the distal part of the allograft was that which faced the femoral trochlea when the knee was at 25° to 30° of flexion, thus preventing patella baja. There, in a fairly medial area in order to favor appropriate patellar tracking, a rectangular bed was constructed using a saw, osteotome, and high-velocity drill. A rectangular relief, which had been previously chiseled into the allograft, was embedded into the tibia and fixed with 2 compression bone screws and washers.
In the proximal part of the allograft, end-to-end suturing was performed on the quadriceps tendon with 3.0 nonabsorbable suture with the knee in full extension. The medial and lateral retinacula were also sutured. Once the allograft was secured, extensor mechanism tracking and strength was checked and found to be satisfactory. The Caton-Deschamps index was 0.8 (normal 0.8 to 1.2). A drain was placed, which was removed at 48 hours when the wound was checked. The patient was then allowed to walk with touch-down weight-bearing crutches and with the knee immobilized in extension. Isometric static quadriceps contractions were encouraged. After 4 weeks, passive and active movement with a knee brace was also encouraged, with flexion limited to 90° for 4 more weeks. Between week 8 and week 12, passive flexion was not permitted so as to minimize possibility of graft failure and early attenuation.
In the postoperative period, following wound healing at 20 days, the patient started coadjuvant chemotherapy. Six months after completing chemotherapy, a Positron Emission Tomography (PET)-CT scan showed metastatic lung and pleural tumor infiltration. This finding forced to perform an en bloc resection of all lung nodules by thoracic surgeons and to start chemotherapy.
At present, after more than 5 years of follow-up, the patient is tumor disease-free with no pain or instability and a range of 120/0 in the operated knee, which allows her to do recreational sports activity.
For treatment of osteosarcoma of the patella, techniques as varied as knee arthrodesis6 or amputation of the limb7 have been described.
When there is evidence of tumor contamination of the joint, a megaprosthesis is considered the procedure of choice. However, despite its advantages over arthrodesis, this technique is not without risk, including local recurrence and periprosthetic infection8,9.
Some authors, such as Okada et al.10, have reported optimal functional results after performing a patellectomy without reconstruction in cases of postradiation osteosarcoma of the patella. Despite this, various works have indicated that this technique reduces knee function11.
Nowadays, progress on techniques for reconstruction of the extensor apparatus allows for the limb to be conserved and knee function to be recuperated when the tumor is localized in the patella and does not affect the joint.
Multiple procedures for this reconstruction have been described. Aoki et al.12 present the case of an osteosarcoma of the patella treated with a wide resection and reconstruction with a free anterolateral thigh flap. On the other hand, Ansari et al.13 describe reconstruction using a medial gastrocnemius flap in a patient with patellar sarcoma secondary to Paget disease of bone.
Some articles defend the use of an autologous graft. A work by Valsalan and Zacharia14 describes a case of Ewing sarcoma of the patella treated with a wide resection and reconstruction with an autologous graft of the ipsilateral Achilles tendon. Other authors have reported good results using autologous hamstring tendons15 or latissimus dorsi muscle flaps16. Despite the advantages that reconstruction with an autologous graft offers, it also includes morbidity in the donor site, an increase in surgical times, and allows for reconstruction of the anatomy that is less precise than with a large bone-tendon allograft.
As first published by Cho et al.17, in our patient, who had osteoblastic intraosseous osteosarcoma of the patella, we opted for a wide resection and bone-tendon allograft. Following resection of the patellar tendon, retinacula, Hoffa's fat pad, patella, and quadriceps tendon, the extensor mechanism was reconstructed with a bone attachment using a large bone-tendon allograft that included the quadriceps tendon, patella with medial and lateral retinacula, and patellar tendon1. In contrast to the reconstruction options described above, this procedure allows for reconstruction of the function of the patella.
A key aspect of the procedure is allograft selection. In our case, the excellent coordination with the tissue extraction teams and Regional Tissue Bank allowed us to have available an allograft with dimensions that were very similar to our patient. It is also important to construct the distal bone portion of the allograft in a shape that fits into the bed so that when it is fit into the tibia of the recipient, it is stable on its own. Finally, fixing the graft when the knee is in full extension is essential in order to prevent severe extensor lag, as the graft stretches out over time.
Possible postoperative complications of the described procedure include infection or risk of fracture, especially in patients who receive radiation therapy18. In addition, patella baja19 could arise from an error in selecting the place to anchor the distal end of the allograft, although postimmobilization retraction of the patella tendon and surrounding tissues may also be involved. In our case, in addition to the aforementioned intraoperative measures, we allowed for gentle, progressive mobilization of the knee as soon as the proximal suture of the allograft allowed for it (4 weeks). With these measures, there was no functional limitation or anterior knee pain, allowing for the patient to perform regular sports activities.
We conclude that the wide resection with reconstruction using an extensor mechanism allograft is an appropriate alternative in patients with aggressive tumors of the patella with no evidence of joint contamination. It allows for flexion-extension function of the knee to be preserved with appropriate tumor resection margins.
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