Saddle prosthesis. Functional outcome and complications in 20 cases

Background: The saddle prosthesis is a specific system used forhip joint reconstruction after complete destruction of the inferiorpart of the iliac bone, including the acetabulum. The major indicationsare oncologic surgery and failure of prosthetic surgery. Theusual femoral head of the classic femoral is replaced by a saddlecomponent. The saddle presents a superior concavity which ispress-fit into the iliac crest.Methods: We used this saddle prosthesis in 20 patients for thetreatment of bone tumors: chondrosarcoma (n=14), Ewing’s sarcoma(n=3), giant-cell tumor (n=2), bone metastasis (n=1).Results: Complications were frequent, occurring in 60% of thepatients: only eight patients were totally free of complications.Sepsis occurred in seven patients, immediately after implantation insix, and after replacement in one. The implant was definitivelyremoved in four patients despite repeated open debridement andantibiotic therapy. Two patients presented sacro-iliac dislocation;the inferior part of the sacro-iliac joint had been sacrificed in both.The implant was also directly responsible for specific complications:- anterior or posterior dislocation of the saddle (n=3).- sciatic nerve palsy (n=4). Two different mechanisms of sciaticnerve palsy were observed: postoperative dislocation of the saddleelement and direct compression of the sacral roots because ofoverly medial implantation of the saddle. Complete recovery wasachieved in two patients.- disassembly of the three components of the saddle (n=4).- upward migration of the saddle into the iliac wing (2=2) (radiatedbone).Discussion: Over time, the design of the saddle was improved toprevent dislocations. Two parts of the saddle were enlarged to obtaina better retention effect. We have found that stability can beimproved using an artificial ligament introduced through the iliacwing into the two parts of the saddle. The surgical implantationtechnique was also improved. For us, the saddle prosthesis must beimplanted in the horizontal part of the greater sciatic notch, instrong bone. When this specific area has been resected, a bone graft may be required to obtain a thicker iliac bone for implantation.Finally, among ten survivors with minimum five years follow-up,only four patients still have their initial implant with good anatomicaland functional outcome. The implant was removed in four patientsbecause of infection and in two patients, the prosthesis destroyedthe iliac wing.Conclusion: The saddle prosthesis is an interesting implant butshould be improved. It provides an easy technique for hip jointreconstruction after tumor resection destroying the inferior part ofthe iliac bone. This alternative enables rapid functional recovery.