Reviews of the Stanmore Implants Customised ALM Pelvic Replacement | Which Medical Device

The reconstruction of complex defects in the skeleton is often challenging, particularly in the pelvis, where the size and shape of the defect is highly variable. One promising solution is the combination of computerised navigation and Additive Layer Manufacturing (ALM) which allows oncologic pelvic resection to be planned preoperatively, performed with more accuracy than in the past and to be reconstructed with a customised implant.(1,2). The manufacturing process involves sintering titanium powder with a laser. After each layer is deposited, the implant is lowered a little further into the powder before the addition of the next. The finished implant is polished by hand and the textured bone contact surfaces coated with hydroxyapatite.

This case illustrates the process in an individual with a difficult clinical problem. The implant in this case was designed in collaboration with Stanmore Implants Worldwide; the ALM being performed by Eurocoating SPA.  The patient has given permission for his case and the images to be posted on the Internet.

A previously fit 62 year old man presented with an 18 month history of pelvic and groin pain. Plain x-rays revealed a lytic abnormality in the right acetabulum (Figure 1). Further investigation, including CT guided biopsy confirmed Grade 2 chondrosarcoma arising from the acetabulum and involving the hip joint. MR and CT scans confirmed extensive signal change throughout the iliac blade and no metastases (Figures 2,3 and 4). Best treatment was therefore surgical excision of the hip joint and almost the entire bony hemipelvis, saving only a small part of the superior pubic ramus. Some of the abductor musculature and the iliopsoas was salvageable.

Options for reconstruction after complete iliac resection including the sacro-iliac joint include:

• No reconstruction (hanging hip)
• Implantation of acetabular component into sacrum
• Massive allograft or irradiated autograft
• Rotation of proximal femur and proximal femoral replacement (3)

After discussion of these options with the patient, he elected to proceed to reconstruction using an ALM manufactured implant, understanding the novel nature of the reconstruction.

Preoperative planning was performed using Stryker’s Navigation system, which allows the tumour to be identified and “painted” before surgery, and the osteotomies planned. The available software did not allow integration of navigation and implant design software, therefore the osteotomies were determined in relation to fixed bony landmarks. However, it is likely that these systems will become integrated in due course, and a single planning session will allow the resection planes and implant manufacturing data to be defined together.

Key design concepts were (Figures 5-10):

• Medialisation of the acetabulum to reduce the external rotation moment at the posterior implant/bone interface
• Large acetabular socket to accommodate large head bearing
• Options for 2 sacral bolts and a distal screw
• Hydroxyapatite coated bone ingrowth surfaces
• Flanges anterior and posterior at the sacral junction to provide a press-fit

The procedure involved an extended ilioinguinal approach to the iliac crest, with a separate buttock incision for the ischial osteotomy. The patient was in a lateral position on a beanbag. Once the hemipelvis had been exposed, a navigation tracker was placed in the iliac crest and the osteotomies performed (Figure 11). Great care was taken with the sacral osteotomy in particular as this was the most challenging in terms of tumour clearance and implant fixation.

After delivery of the tumour, the implant was brought into the field and the site of the first sacral bolt identified. The navigation system was re-referenced with a tracker on the spinous process of S1 to allow the passage of the bolt across S1 to be navigated. Once the bolt had been passed, impacting the implant onto the sacrum lead to an excellent press fit, with the anterior plate lying in the predicted position on the superior pubic ramus. The second bolt and screw were not placed, because of concern about critical anatomy for the bolt, and the fact the distal screw hole was not adjacent to bone. The intended locking nut on the left buttock could not be reached, and in view of the length of the procedure and the stability of the implant was not placed. The hip replacement was a standard Exeter cemented implant, with a 36mm head and an x3 crosslinked polyethylene socket. A joint capsule was constructed using a knitted polyester (Trevira ®) tube, into which the overlying muscles were sewn.

Post operative progress was uncomplicated. 48 hours of prophylactic cefuroxime was given, with low-dose subcutaneous tinzaparin during admission. The resection was deemed histologically complete with adequate negative margins. The leg was initially supported in “slings and springs” for seven days, and thereafter a Charnley pillow and abduction brace were used. A small area of superficial wound necrosis at the anterior end of the wound was treated conservatively and subsequently healed. Partial weight bearing was started once the patient became mobile. At six months, the patient was fully weight bearing with a stick, living alone and the implant stable on X-ray (Figure 12).

Customised implants manufactured with additive layer technologies combined with surgical navigation have great potential in the reconstruction of complex bone defects, particularly in the pelvis. The selection of the patient for this case was of great importance as he was fit, active, well motivated and interested in this new approach. The long term outcomes of this reconstruction remain uncertain, but there is the potential for this to be a durable long-term solution.

Cases like this represent the efforts of a large team. Particular thanks to David Fender (Consultant Orthopaedic Surgeon, Newcastle Upon Tyne), Abtin Eshraghi (Stanmore Implants Worldwide), and Michael Ormond (Stryker Corporation) for their help and expertise.

 

Mr Craig Gerrand, Consultant Orthopaedic Surgeon, North of England Bone & Soft Tissue Tumour Service, Newcastle upon Tyne, UK 

 

References:

1. Comput Aided Surg. 2007 Jul;12(4):225-32. Computer assisted pelvic tumor resection and reconstruction with a custom-made prosthesis using an innovative adaptation and its validation. Wong KC, Kumta SM, Chiu KH, Cheung KW, Leung KS, Unwin P, Wong MC.

2. Unfallchirurg. 2003 Nov;106(11):956-62. [Integration of modern technologies in therapy of sarcomas of the pelvis.Computer-assisted hemipelvectomy and implantation of a "custom-made" Bonit gentamycin coated partial pelvic prosthesis].[Article in German]Bastian L, Hüfner T, Mössinger E, Geerling J  Goesling T, Busche M, Kendoff D, Bading S, Rosenthal H, Krettek C.

3. Eur J Surg Oncol. 2003 Feb;29(1):59-63. The swing procedure for pelvic ring reconstruction following tumour excision. Pollock RC, Skinner JA, Blunn GW, Pringle JA, Briggs TW, Cannon SR.