Lower Limb Revision and Custom Solutions

From Orthodynamics
Author: Justin Quick, Sales Manager, Orthodynamics Ltd

Introduction

At the inception of the then named Orthodesign company, back in 1986, Dr John Bradley and his team put the design of custom implants at the very core of this innovative British manufacturing business. Following the success of these hip solutions, many of the components have evolved into ‘off the shelf’ revision systems subsequently published in the orthopaedic press such as American JBJS, Hip International and Injury, and of course OPN. That ‘ethos’ still exists today, post name-change to Orthodynamics (2001), reflecting the re- positioning the company had undertaken to be recognised as a provider of a wide range of lower limb solutions and knee salvage (arthrodesis) devices.

This metalwork portfolio has been appropriately supported by a range of Spacer products, taking the business into the area of the management of two stage revision of infected joint replacement. This complication of surgery has devastating consequences for the patient, and a return to home, mobile and weight bearing, has been seen to be of great benefit in their rehabilitation from such a complication.

The Cannulok® Revision Hip System

The Cannulok® Revision Hip System has now been in clinical use since 1991. To date, over 1,500 implantations have been carried out in the UK. The Cannulok philosophy now maintains that all stem options are anatomically sided, cannulated and distally locked with an impressive targeting device.

A variety of stem patterns are available ‘off the shelf’ and are described in our product brochure. The most commonly implanted 240mm and 300mm stems have found a real niche in modern management of peri- prosthetic fractures. The operative technique is well described and supported by pre- operative templates and instrumentation enclosures.

Being a cannulated prosthesis, we have designed cannulated instrumentation, which facilitates standard approaches to the hip through the original incision over a well-positioned guide-wire. Should impaction grafting be considered necessary, then recent published work¹ supports this technique, as does the instrumentation. Optimal distal stem positioning is therefore assured.

Custom solutions for the hip

In the most challenging of cases, the “Custom” solution to difficult hip revision need not involve huge costs and excessively long lead times. Most of theses custom solutions are based on the well-established Cannulok® System principles. Orthodynamics has been providing custom hip prosthetic components from its manufacturing base in Christchurch, Dorset since its inception.

Our Bioengineers working on site have over 26 years of collective experience in the interpretation of plain, scaled x- ray films from which a design proposal is produced and subsequently discussed with the operating surgeon. This stage of the process can take as little as 24 hours from receipt of x- ray films, with the manufacturing taking a further 7-10 working days to sterile implant.

The custom option offers an extended choice of fixation scenarios as summarised: -

• Cemented (with the option of proximal cement ‘restriction’) in the metaphyseal femur
• Cementless fixation
• Standard 90 micron plasma coating of Hydroxyapatite
• Roughened titanium plasma coatings
• Bi- coating- roughened and hydroxyapatite combined finish

Fixation can be augmented with all of the above options, either through the positioning of distal cross locking screws (Fig 2) or ‘fluted’ detail for diaphyseal press fit and torsional stability, perhaps facilitating extended trochanteric osteotomy for the removal of well fixed primary stems.

The case below (Figs 3 and 4) is an example of a custom component designed in response to a 47-year-old male who suffered a fracture neck of femur with ipsilateral distal shaft fracture, originally treated with a reconstruction nail. The femoral head failed to unite, requiring hip replacement with continued stabilisation of the distal fracture. The custom stem shown matched the diameter and anterior bow of the femur, extending beyond the distal fracture, with the option to lock at this, or subsequent procedure.

More challenging scenarios

Case study 1
Complications involving complex fracture geometry often mean that there is little bone stock distally to achieve adequate fixation with conventional long stem revision prostheses. Accurately scaled films are the key to successfully planning appropriate prosthesis design (Fig 5). As part of our services, Orthodynamics offer the Superintendent Radiographer special instructions to all departmental staff to assist in this process and these instructions are always included in our product literature.

Where the design must involve the provision of adequate fixation often with minimal distal bone stock available, then fully HA roughened coated components are best indicated in this situation, and special challenges lay ahead for the operating surgeon, often choosing to re- inforce the femur with strut allograft (Fig 6). Distal locking with careful consideration to stem length is achieved. HA coating in apposition to host bone at the isthmus ensures the best possible circumstances for oseointegration to proceed.

Case study 2
Indications for our Cannulok solution often involve cases of massive proximal bone loss (Fig 7). Diaphyseal interference fit with HA coated and a distally locked prostheses, can create a bio-mechanically favourable environment for proximal femoral bone stock recovery (Fig 8). Trikha et al² describe the case of a 59-year-old rheumatoid woman who underwent revision hip surgery to a long stem cemented implant following early aseptic loosening. Seven years later, the patient sustained an atraumatic unstable peri- prosthetic fracture. The stem was revised to a fully coated implant.

Two months post-operatively, a second stable peri-prosthetic fracture was sustained, and fixed with cable plate fixation with use of autogenous iliac bone graft. 2 years later, the patient presented with an infected non-union. All metalwork was removed leaving a grossly deficient proximal femur (Fig 7), ectatic in nature with combined cavitary and segmental bone loss and discontinuity mid-shaft. 16 months postoperative, reconstruction with an HA coated Cannulok stem confirms fracture union and bone ingrowth in all areas of the prosthesis (Fig 8).

Periprosthetic fracture management

Commonly seen are transverse fractures (Fig. 9) around a cemented component, these are inherently unstable, leaving the operating surgeon with a number of treatment options. Where the prosthesis is loose, then removal and re- implantation using a definitive longer stem option is eminently preferable (Fig. 10), giving the patient best possible chance of mobilisation and early weight- bearing (Fig. 11).

Early surgical intervention should therefore be a consideration. Cementation, with the aid of proximal cement restriction allows fracture healing to progress unhindered preventing cement migration into the fracture line. On the other hand, increasingly popular is the selection of an appropriately sized, HA coated stem which facilitates a diaphyseal scratch fit of HA in apposition to viable host bone. Fracture healing and oseo- integration is seen to progress rapidly, largely as a result of prosthetic bio- mechanical stability made possible through the use of cross locking screws.

Knee Arthrodesis

One of the more challenging briefs are instructions to proceed with the custom design of our Mayday Knee Arthrodesis Nail (Fig 12).

The device was the inception of Mr J. Miller FRCS, Mayday University Hospital, London, and further design enhancements courtesy of Mr John Newman FRCS, Bristol and his colleague Mr Andrew Porteous, Consultant Surgeon, who published their findings in the JBJS January 2003³.

The device is a two part-interlocking nail, facilitating the approach to the knee through the original incision following previous knee surgery. The design allows for compression and the prompt course to union as reported in the above series (Figs 13 and 14).

In September 2003, there followed a comprehensive review⁴ of the available devices for consideration of arthrodesis of the knee from Mr Manoj Sood, Clinical Lecturer, Institute of Orthopaedics, Stanmore, who reported encouraging results even with end staged, infected cases arthrodesed as a single stage.

Matching the needs of the surgeon who requires a wide range of lower limb revision solutions and knee salvage devices, remains the driving force behind the product portfolio of Orthodynamics.

References

1. Charnley G, Anderson G. Preliminary experience of the Cannulok revision hip prosthesis in late periprosthetic fracture management. Hip International, Vol. 12, n. 1, 2002 – pp. 1-10
2. Trikha P, Singh S, Raynham O, Lewis J, Edge J. Use of an interlocking hydroxyapatite-coated stem in a patient with an infected non-union of a periprosthetic femoral fracture with massive bone loss. J Bone Joint Surg Am, 2004; 86: 1783 - 86.
3. SP White, AJ Porteous, JH Newman, W Mintowt-Czyz, V Barr. Arthrodesis of the knee using a custom-made intermedullary coupled device. J Bone Joint Surg [Br] 2003; 85-B:57-61.
4. M Sood. Knee arthrodesis using short, two-part, modular intramedullary nails. Orthopaedic Product News. Sept/October 2003