Reviews of the Stanmore Implants METS Femoral Reconstruction System | Which Medical Device

Device features and design

The Stanmore METS system is a modular titanium endoprosthetic system for the reconstruction of large bone defects, usually after tumour resection. The system was introduced in 2001 and now includes kits for the reconstruction of the proximal, distal and total femur, the proximal tibia, proximal humerus and the pelvis. The ability of Stanmore Implants Worldwide to manufacture custom implants with short turn-around times mean that a solution can usually be found for almost any reconstructive challenge.

The proximal femur has a 12/14 eurotaper, and the system comes with 28mm and 32mm heads for use with a socket of corresponding size. There are two options for trochanteric reattachment. One has hydroxy-apatite coated teeth, onto which the trochanter can be fixed using a clamp and screws, the other is a smooth component which allows the passage of wires or heavy sutures through the device for trochanteric reattachment.

The knee is based on the SMILES rotating hinge knee, which has a long track record, although a fixed hinge option is available. The tibial component has either a polyethylene sleeve which is cemented into the tibia (see photos) or a metal-clad version which allows the use of tibial plates to increase the height of the joint line or replace resected bone. The hinge allows a few degrees of hyperextension to compensate for quadriceps weakness. Some patients find this takes a little getting used to.

The stems come with an optional HA coated collar, which has been effective in reducing loosening of massive endoprostheses. Components engage with each other with tapers which include an anti-rotation lug. Tapers can be disengaged using a specific tool introduced into a hole in the side of the implant.

The system allows resection of almost any length of bone, in 15mm increments. The shortest proximal resection is 82 mm which takes you below the level of the lesser trochanter. A total femoral reconstruction can be performed using a linkage piece connecting the proximal and distal systems. A full set of trials comes with the trays.

The Device in Use

In use, this is a straightforward system, which is elegant in its simplicity, compared with other more complex systems. Components come packed in distinctive high-quality purple boxes, which are popular amongst theatre staff and are seldom discarded.

Trial and assembly is generally straightforward. I seldom use the trochanteric clamp in the proximal femur, as I have not found it particularly effective – the trochanter can fragment and migrate (Cribb et al, 2005). The HA coated teeth are sharp and this may be contributory. My impression is that most surgeons rely instead on soft tissue repair. This typically involves a trochanteric slide approach to the proximal femur where possible, using the holes in the implant to bring the trochanter onto the surface of the implant with non-absorbable sutures or wires and then performing a careful repair of the soft tissues. I routinely suture the abductors into the fascia lata, with the aim of constructing a soft tissue envelope that will act as an abductor of the hip. I have used the Dall-Miles system, but these are stainless steel wires against a titanium implant, and this may be a corrosion risk, and in any case these also tend to fragment.

Despite a careful soft tissue repair, there is a functional price to pay with resecting the proximal femur, and this is occasionally a consideration in those cases of metastatic bone disease where the choice of a femoral replacement over a hip replacement stem can be finely balanced.

The HA collar encourages ingrowth of bone and soft tissues around the collar of the implant, but this is not always seen on postoperative radiographs. Elevating a periosteal sleeve on the resection side of the osteotomy and laying it down over the base of the HA collar after implantation may be helpful, as may bone-grafting around the collar. As a general point, and not related specifically to this device, there is also a mild concern about the rotational stability of the reconstruction, particularly if significant reaming of the femoral canal has been required to get the stem inserted, or in a revision situation. The reconstruction then involves cementing a relatively smooth (although fluted) stem into what can be a smooth cylinder of bone. Concerns about this can be addressed by requesting a custom collar with a plate attached, lending more rotational stability.

When cutting the tibia for the knee system, a zero degree cut is required, either using the enclosed jigs or the tibial jig of a knee replacement system if you prefer. In some patients, tibial bone can be very hard and may resist the use of the supplied tibial reamer. It can help to drill it using a standard tibial drill in this situation. When inserting the tibial polyethylene component, I prefer just to cement the surface directly in contact with the tibial plateau rather than filling the canal with cement.

Published results

In a series of 100 patients undergoing proximal femoral reconstruction using this system, the implant performed similarly to custom systems, with 5 revisions for acetabular pain, one for tumour progression but none for implant failure. A paper by Cribb et al, presented at the British Orthopaedic Oncology Society suggested a trochanteric hook clamp provided better trochanteric fixation than the HA coated implant.

Conclusions

This is an excellent system, which represents a highly cost-effective (in the UK at least) straightforward and flexible solution for the reconstruction of large bone defects of the femur (there are systems for the proximal tibia and the proximal humerus). The trochanteric fixation solution is not ideal, but this does not detract from the overall effectiveness of the system. Stanmore Implants Worldwide has an excellent reputation as a responsive and experienced provider of custom solutions to complement this system.

Mr Craig Gerrand,
Consultant Orthopaedic Surgeon, Freeman Hospital, Newcastle upon Tyne, UK
The author has no financial or other pecuniary interest in the device or device manufacturer reviewed.

 

References

Chandrasekar CR, Grimer RJ, Carter SR, Tillman RM, Abudu A, Buckley L. Modular endoprosthetic replacement for tumours of the proximal femur. Journal of Bone and Joint Surgery (Br). 91B, 1, 108-112

Cribb GL, Deogaonkar K, Cool WP. Abductor reattachment in modular megaprostheses for proximal femoral metastases – Abstract of presentation at British Orthopaedic Oncology Society. Proceedings of the Journal of Bone and Joint Surgery (Br), 2005. 87B. Suppl 2.

Related MHRA Alerts:

There has been two MHRA alerts in November 2008 and April 2009 related to this device, following mislabelling of two components, but this should not adversely impact on device performance. Care should be taken to ensure the implants match the packaging.