A novel “pelvic ring augmentation construct” for lumbo-pelvic reconstruction in tumour surgery

Abstract

Reconstructing or augmenting the lumbo-pelvic junction after resection of L5 and part of the sacrum is challenging. Numerous lumbo-pelvic reconstruction methods based on posterior construct and anterior cages have been proposed for cases involving total sacrectomy and lumbar vertebrectomy. These constructs create long lever arms and generate high cantilever forces across the lumbo-sacral junction, resulting in implant failure or breakage. Biomechanical studies have shown that placing implants anterior to lumbo-sacral pivot point provides a more effective moment arm to resist flexion force and improves the ultimate strength of the construct. We present here a novel method to augment a lumbo-pelvic construction using a pelvic ring construct. A 69-year-old lady presented with implant failure of her two previous posterior lumbo-pelvic reconstructions performed by the authors. She initially presented, two and a half years previously with 6 months history of back pain with normal neurological function. MRI scans of her whole spine showed isolated secondaries in the lumbar spine (L4, L5) and sacrum (S1). An abdominal CT scan revealed a primary tumour in her right kidney. Briefly, the first surgery involved a single-stage removal of posterior elements of L4 and L5 and posterior stabilisation from L2 to pelvis, anterior resection of L4 and L5 and partially S1 with implantation of an expandable Synex II cage. The cage was replaced with an anterior rod construct from L2 and L3 to a trans-sacral screw a week later as it had dislodged. The second revision, 9 months later, involved removal of two posterior broken rods which were replaced and converted into a modified four-rod construct. While monitoring her progress, it was subsequently noted that the trans-sacral rod had broken. Therefore, it was decided to augment her lumbo-pelvic construct to prevent eventual catastrophic posterior construct failure. From a posterior approach, contoured rods were passed bilaterally along the inner table of the pelvis under the iliacus muscle up to the anterior border of the pelvis. Using T-connectors, the rods were connected to the posterior lumbo-pelvic construct. Thereafter, two anterior supra-acetabular pelvic screws were connected to a subcutaneously placed rod matched to the shape of the anterior abdominal wall. The pelvic ring construct was completed on connecting this rod with T-connectors to the free ends of the contoured iliac rods. There were no intra-operative complications. At the end of 12 months, she was mobilising with a frame, with no radiological evidence of failure of the construct. However, she died due to disease progression at the end of 15 months. Experience from one clinical case shows that such a construct is feasible and adds a technical option to the difficult reconstruction of lumbo-pelvic junction after tumour surgery.