Custom Mega Prosthesis
INTRODUCTION

Orthopaedic Oncology has been well accepted as a subspecialty in Orthopaedic Surgery in this millennium. The hallmark of Orthopaedic Oncology is Limb Salvage Surgery. Limb Salvage by Custom Mega Prosthetic Replacement has been accepted as the primary option in the management of malignant and aggressive benign tumors.
 
The effective chemotherapeutic regimens and refinement in surgical technique have made limb salvage the standard approach and amputation is done only in very rare instances. The limb sparing procedure does not shorten disease free interval or compromise long-term survival. The progress in biomedical engineering along with better surgical and chemotherapy techniques has increased overall five year survival rate after endoprosthetic replacement from 20% to 85% in the past three decades.
 
This improved survival has placed the emphasis on the assessment of the quality of life and the functional outcome of the various forms of limb salvage. The various alternatives to limb salvage like resection arthrodesis, rotationplasty, osteochondral allografts have several drawbacks as reported by various authors. The superior results along with the minimal complications have established endoprosthetic replacement as the primary modality in the management of malignant bone tumours of the lower limb. The focus has now shifted from the controversy of the various forms of limb salvage to the methods to enhance the functional and oncological outcome after endoprosthetic replacement. This study analyses my experience with Custom Mega Prosthesis for bone tumors, from Chennai, India.
AIM OF THE STUDY
The aim of this study was to evaluate the oncological results, functional results and complications in Limb Salvage Surgery by Custom Mega Prosthesis and to analyze the survival of the patient, limb and prosthesis.
MATERIAL AND METHODS
The period of study was between 1988 and 2008 (21 years), 1500 cases of Custom Mega Prosthetic replacement were performed as part of the Madras Bone Tumour Service comprising four Institutions namely, Government General Hospital, Cancer Institute, Apollo Cancer Hospital and M.N.Orthopaedic Hospital.
 
The age of the patients ranged from four years to 74 years averaging 26. The histopathological diagnosis was osteosarcoma in 58% of the patients, Giant cell tumour in 21%, chondrosarcoma in 6%, metastasis in 5%, Ewings sarcoma in 3% and malignant fibrous histiocytoma in 2% of the patients. The various other tumours that were diagnosed in small numbers where Aneurysmal Bone Cyst , Aggressive Fibromatosis, Paget’s Sarcoma, Soft Tissue Sarcoma, Fibrous Dysplasia, Non Hodgkin’s Lymphoma, Brown Tumour, Chondro Myxoid Fibroma, Fibrosarcoma,Lasmacytoma, Synovial Sarcoma.
 
Anatomically the distal femur distal femur was the commonest site involved(43%)followed by proximal tibia (27%), proximal humerus (6%) and proximal femur (8%). The other sites involved were shaft of femur (3%), distal radius (1.8%), shaft of humerus (1.6%), distal tibia (1.6%), pelvis (5%), distal humerus (3%). A small number of patients had involvement of the anatomical sites like shaft of tibia, scapula, proximal ulna, fibula, carpus.
 
Staging of the tumours was done according to the Musculo Skeletal Tumour Society (MSTS) system. The stage distribution was in B2-46,B3-98. In Malignant tumours  IA - 294, IB -100, IIA - 313, IIB - 317, IIIA –21, IIIB – 11. Ours being a referral centre – 62% of patients came to us after open biopsy, and only 13% had a closed needle biopsy as desired. The diagnosis was confirmed by FNAC in 12%. The dimensions of the prosthesis were determined using scanograms.  CT scans and MRI were used when indicated.The custom mega prosthesis that was used was manufactured indigenously, and stainless steel prosthesis was used in 87% and titanium alloy prosthesis in 12%. Various types of prosthesis were used depending on the anatomical region replaced. The margins of excision achieved were wide in 72%, marginal in 26%. Majority of the patients (47%) had between 100 to 150 mm of bone resected. 53% of the patients with high grade malignant tumours, had chemotherapy according to the regimen that was in use at that particular period of time. 4% of the patients underwent radiotherapy for conditions like Ewings sarcoma, lymphoma.
RESULTS
The results were analyzed in 1100 patients, of whom 33 patients were lost to follow up during various periods of the study. Analysis was done based on the modified rating scale of the Musculoskeletal Tumour Society. The functional result achieved was excellent in 60 %, good in 23%, fair in 11% and poor in 6 %. At the time of the most recent follow up, 970 patients (77%) were continuously disease free, 19 % had died due to disease and 3% were alive with the disease.
 
The common complications encountered in our study were grouped into early and late complications. Among the early complications, skin flap necrosis occurred in 26 patients. This was managed with additional plastic surgery procedures. Aseptic loosening of the prosthesis was the commonest late complication and was mostly asymptomatic. Prosthesis related failures such as bending of prosthesis and prosthesis disassembly occurred in 68 patients. These patients were managed with a revision of the prosthesis. Infection was seen in 36 patients, of whom 28 responded to wound lavage and antibiotics, while prosthesis had to be removed in 8 patients. The oncological complications seen were Local recurrence and systemic metastasis.
CONCLUSION
With the improvement in surgical techniques several drawbacks of custom mega prosthetic replacement have been overcome and the indications for the use of this technique in various scenarios have been extended. We have been able to achieve oncological cure rates and functional results, comparable to International standards using the indigenously manufactured custom mega prosthesis.