Keywords
bone neoplasms - calcaneus - prostheses and implants
Introduction
The foot is an uncommon location for osseous tumors, comprising ∼ 3% of all skeletal tumors, which occur particularly around the calcaneum.[1]
[2] Radical surgery for these malignant tumors involves the removal of the calcaneal bone, creating a void in the foot which adversely affects the ability to salvage it. Calcaneal replacement surgeries are not commonly performed due to factors involving instability of the prosthesis, soft-tissue defect, and resultant failure which can occur in the postoperative period.[3]
[4] Thus, we herein report a rare case of synovial sarcoma arising from the sheath of the tibialis posterior tendon, with secondary involvement of the calcaneus bone. Considering the previous experiences of different surgeons, a custom-made prosthesis was designed with relevant modifications.
Case Report
This case report was approved by the institutional Ethics Committee (no.139/IEC/PGM/2021), and the informed consent was obtained for the participation of the patient.
A 25-year-old man presented with a history of progressively worse pain in the right foot and difficulty in walking. Clinically, the patient had swelling on the medial aspect of the heel, which was soft to firm in consistency, with a Musculoskeletal Tumor Society (MSTS) score of 12.[5] The neurological examination was unremarkable, and the X-rays were normal, but the magnetic resonance imaging (MRI) scans showed features suggestive of soft-tissue sarcoma arising from the posterior tibialis tendon and secondarily involving the calcaneum of the right foot ([Fig. 1]).
Fig. 1 Magnetic resonance imaging scan showing sarcoma of the tibialis posterior tendon with secondary involvement of the calcaneum.
A biopsy was performed for the histopathological confirmation, which inferred synovial sarcoma.
Planning concerning the calcaneal involvement was performed, and options for calcaneal replacement were offered to the patient. A prosthesis was made on a measure based on Files of Communication of Digital Images in Medicine (Digital Imaging and Communications in Medicine, DICOM, in English) gives computed tomography of both sides (XL Orthotics, India) ([Fig. 2]). The modified prosthesis was coated with hydroxyapatite, covering the body, the posterior, middle and anterior facets of the calcaneum, as well as the holes of the attachment of the calcaneal tendon and plantar fascia. Two additional locking screws were planned from the calcaneum to the talus to provide stability to the construct ([Fig. 3]).
Fig. 2 Transformation of DICOM files for the tridimensional reconstruction and modifications.
Fig. 3 Prototype of the implant and custom-made final prosthesis coated with hydroxyapatite.
Excision of the sarcomatous lesion was performed by extended medial incision. The lesion was involving the tibial nerve as well, so itwas excised along with the tumor tissue and calcaneal bone. The articular surface of the talus and cuboid was removed, leaving the subchondral bone exposed to be articulated with the matched surfaces of the calcaneum, which were coated with hydroxyapatite. The prosthesis of the calcaneum was then fixed by matching the facets with the corresponding facets of the talus and cuboid with the help of a locking screw. The calcaneal tendon and the plantar fascia were repaired with the help of Ethibond (Ethicon, Inc., Raritan, NJ, United States). The soft-tissue defect created was covered with a local sural flap ([Fig. 4]). The patient was then readmitted after 3 weeks for reconstruction of the nerve gap with an interpositional sural nerve graft by anastomosing the proximal stump of the sural nerve with the distal nerve stump of plantar nerve and the distal sural nerve graft with the proximal stump of the tibial nerve to make the foot sensitive to pain ([Fig. 5]).
Fig. 4 (A) Resected synovial sarcoma with calcaneum; (B) reattachment of calcaneal tendon on the prosthesis; (C) implantation of calcaneum with screws and attachment of calcaneal tendon and plantar fascia; and (D) coverage of defect with sural flap.
Fig. 5 Neurotization of the foot using a transfer of the sural nerve to the distal stump of the tibial nerve.
Six weeks postoperatively, the patient was submitted to serial X-rays ([Fig. 6]). The patient was then made to bear weight as per the tolerance of pain at three months. The effect of the anesthesia decreased by 50% during the follow-up period. The patient comfortably walks with support but without any instability, with an MSTS score of 21.[5]
Fig. 6 (A) Postoperative radiograph. (B) Radiograph of the ankle at 3 months. (C) Radiograph of the ankle at 6 months. (D,E) Clinical picture of the patient walking with support.
Discussion
Limb salvage surgeries are always challenging. The challenge increases considerably when the tumor is of a rare variety and there is not much support from the industry in terms of implants and their design. Few case reports[4]
[6] have been published on the biological reconstruction of the resected calcaneum with the use of vascularized iliac crest and composite allograft with pedicled fibula. There are also few studies[7] in which a prosthesis has been developed for the replacement of the calcaneum. Although these past experiences with allografts have yielded acceptable results, the limitation in the strength of these implanted bones is of concern, for these implants can fail on weight-bearing activities.
Most of the available literature is on primary tumors of the calcaneum, in which the soft tissue around the calcaneum is not involved, and reconstruction is possible with the available tissues.[2] The novelty of the prosthesis is represented by the fact that it was customized with the help of data available from the CT scan of the patient's foot, and consisted of a tailor-made replica of the patient's own calcaneum; secondly, we targeted the ingrowth of the subchondral bone of the talus and cuboid to provide long-term stability, so the surface of facets of the implant was coated with hydroxyapatite (in the study performed by Imanishi and Choong,[3] they made a prosthesis which was polished on the articular surfaces); thirdly, we further modified the prosthesis by placing two screw holes in the calcaneum for its fixation to the talus peri-operatively and to provide instant stability to the construct. No such information regarding any modification was available in the literature. The fourth advantage of using this prosthesis was that the anchor points for the attachment of the calcaneal tendon and plantar fascia were printed in such a way as to hold these tissues with the help of sutures passed through the holes; moreover, the hydroxyapatite coating helps incorporate the sleeve of bone, if there is any, to the implant in due time. Lastly, the prosthesis was made of titanium, so it is light and strong enough to bear the weight of the patient in the long term. In conclusion, this technique required few days, including meticulous planning, design of the implant, review of the design by the surgeon, 3D printing, and prototype manufacture.
Resection surgeries result in morbidity due to loss of soft tissue. The defect is covered with the available local flap. Moreover, reconstruction of the sensory supply to the foot was regained by neurotization surgery, which involved anastomosis of the proximal stump of the sural nerve to the distal stump of the posterior tibial nerve. To date, the recovery observed is satisfactory. This type of modification may provide a benchmark to carry out further studies on reconstruction prosthesis to make them more stable and durable.
