We describe the application of a non-invasive extendible endoprosthetic replacement in skeletally-mature patients undergoing revision for failed joint replacement with resultant limb-length inequality after malignant or non-malignant disease. This prosthesis was developed for tumour surgery in skeletally-immature patients but has now been adapted for use in revision procedures to reconstruct the joint or facilitate an arthrodesis, replace bony defects and allow limb length to be restored gradually in the post-operative period.

We record the short-term results in nine patients who have had this procedure after multiple previous reconstructive operations. In six, the initial reconstruction had been performed with either allograft or endoprosthetic replacement for neoplastic disease and in three for non-neoplastic disease. The essential components of the prosthesis are a magnetic disc, a gearbox and a drive screw which allows painless lengthening of the prosthesis using the principle of electromagnetic induction. The mean age of the patients was 37 years (18 to 68) with a mean follow-up of 34 months (12 to 62). They had previously undergone a mean of six (2 to 14) open procedures on the affected limb before revision with the non-invasive extendible endoprosthesis.

The mean length gained was 56 mm (19 to 107) requiring a mean of nine (3 to 20) lengthening episodes performed in the outpatient department. There was one case of recurrent infection after revision of a previously infected implant and one fracture of the prosthesis after a fall. No amputations were performed. Planned exchange of the prosthesis was required in three patients after attainment of the maximum lengthening capacity of the implant. There was no failure of the lengthening mechanism. The Mean Musculoskeletal Tumour Society rating score was 22 of 30 available points (18 to 28).

The use of a non-invasive extendible endoprosthesis in this manner provided patients with good functional results and restoration of leg-length equality, without the need for multiple open lengthening procedures.

In skeletally immature patients, resection of bone tumours and reconstruction of the lower limb often results in leg-length discrepancy. The Stanmore non-invasive extendible endoprosthesis, which uses electromagnetic induction, allows post-operative lengthening without anaesthesia. Between 2002 and 2009, 55 children with a mean age of 11.4 years (5 to 16) underwent reconstruction with this prosthesis; ten patients (18.2%) died of disseminated disease and one child underwent amputation due to infection. We reviewed 44 patients after a mean follow-up of 41.2 months (22 to 104). The mean Musculoskeletal Tumor Society score was 24.7 (8 to 30) and the Toronto Extremity Salvage score was 92.3% (55.2% to 99.0%). There was no local recurrence of tumour. Complications developed in 16 patients (29.1%) and ten (18.2%) underwent revision.

The mean length gained per patient was 38.6 mm (3.5 to 161.5), requiring a mean of 11.3 extensions (1 to 40), and ten component exchanges were performed in nine patients (16.4%) after attaining the maximum lengthening capacity of the implant. There were 11 patients (20%) who were skeletally mature at follow-up, ten of whom had equal leg lengths and nine had a full range of movement of the hip and knee.

This is the largest reported series using non-invasive extendible endoprostheses after excision of primary bone tumours in skeletally immature patients. The technique produces a good functional outcome, with prevention of limb-length discrepancy at skeletal maturity.

Introduction:. Non-invasive extendible endoprostheses (NIEE) were primarily developed for salvage after musculo-skeletal tumour surgery in the immature skeleton. However, they may also have a unique application to manage complex limb reconstruction in revision surgery to address limb-length inequality in the mature skeleton. The aim of this study is to present the minimum 2 –year results of using non-invasive extendible endoprostheses for complex lower limb reconstruction. Methods:. Between 2004 and 2013, 21 patients were treated with 23 NIEE. The indication for surgery was salvage of infected prosthesis following primary tumor resection in 6 cases, aseptic prosthesis failure after primary tumour resection in 5 cases, aseptic non-tumor prosthesis failure in 1 case, infected non-tumor prosthesis in 8 cases and symptomatic non-union of graft reconstruction in 3 cases. There were 14 male and 7 female patients with a mean age of 49.8 years (range 19–81). Results:. The mean length gained was 41.5 mm (range 0 to 90) requiring a mean of 7 (0–25) lengthening episodes performed in the outpatient department. 4 cases required revision surgery for persistent infection. These had multiple previous surgeries and inadequate soft tissue coverage. There were also 2 early dislocations in one patient treated successfully with lengthening and 1 failure to achieve desired length. The Mean Musculoskeletal Tumour Society rating score was 19. Conclusion:. The use of NIEE is associated with good functional outcome and offers yet another way of limb salvage. A modest complication rate is noted in this series, which reflects the complexity of these cases

Introduction. Following bone tumour resection, lower limb reconstruction results in leg-length discrepancy in skeletally immature patients. Previously, minimally invasive endoprostheses have been associated with a high risk of complications including joint stiffness, nerve injury, aseptic loosening and infection. The purpose of this study was to examine the outcome of the Stanmore non-invasive extendible endoprostheses used in our institution between 2002 and 2009 and compare them with implants used in the past. Methods. Fifty-five children with a mean age of 11.4 years (5 to 16) underwent limb reconstruction with thirty-three distal femoral, two total femoral, eight proximal femoral and twelve proximal tibial implants. Forty-six endoprostheses were lengthened in clinic without anaesthesia using the principle of electromagnetic induction. Patients were assessed using the Musculoskeletal Tumour Society Score (MSTS) and the Toronto Extremity Salvage Score (TESS). Results. Ten children (18.2%) died of disseminated disease. One child underwent amputation for infected prosthesis. Forty-four patients were reviewed after a mean follow-up of 41 months (16 to 98). The mean MSTS score was 80.7% (26.7-100) and the TESS score was 92.3% (55.2-99). There was no local tumour recurrence. Complications developed in sixteen patients (29.1%). Seven patients (12.7%) underwent ten revision procedures. The mean length gained per patient was 38.6mm (3.5 to 161.5) requiring a mean of 11.3 (1-40) extensions. Ten component exchanges were performed in nine patients (16.4%) after attaining the maximum lengthening capacity of the implant. Eleven patients (20%) were skeletally mature at follow-up, of which ten had equal leg-lengths and nine had full range of hip and knee movement. Overall our outcomes compared favourably with minimal endoprostheses and other non-invasive designs. Discussion. This is the largest reported series of non-invasive extendible endoprostheses, demonstrating good functional outcome with prevention of limb-length discrepancy at skeletal maturity

We have compared the cost:benefit ratio of the new type of non invasive extendable prostheses with the old type which required lengthening under general anaesthetic with an invasive procedure. Over the past four years we have inserted 27 non invasive endoprostheses (cost £14,000). Two have failed to lengthen due to problems with the inbuilt motor. So far there have been no infections, no loosenings and no patient has required revision. The lengthenings are painless and take half an hour. In the past 25 years we inserted 175 extendable endoprostheses (cost £7,000). All lengthenings were performed under a general anaesthetic. The risk of infection was initially 20% at ten years but had decreased to 8%. Pain and stiffness arose in about 10% requiring physiotherapy or occasionally manipulation under anaesthetic. Assuming the following costs (current NHS cost) are accurate and appropriate, then the non invasive extendable prosthesis becomes cost effective when Cost EPR < Cost old EPR + (Additional risk physio(P) x cost) + (additional cost x number of lengthenings (L)) + (additional cost of revision for infection x risk of infection (R)). 14000 < 7000 + (300 x P) + (1500 x L) + (20000 x R). Assuming a 10% need for physiotherapy, four lengthenings and a 10% risk of infection gives: 14000 < 7000 + (30) +(6000) + (2000) = 15030. Given the high complication rate of the old type of extendable procedure and assuming there are few if any with the non invasive type, then the non-invasive endoprostheses becomes cost effective if more than three lengthenings are required. They are certainly more popular with parents and children alike!

Introduction: Since 1975, 6 types of extendable endo-prostheses have been developed at Biomedical Engineering, UCL, and Stanmore Implants Worldwide in conjunction with the surgeons at this centre. Aims: To establish whether developments in design have had the desired effect of improving both implant survivorship and functional outcome. Methods: This was a retrospective study using case notes, hospital databases and a radiological review, combined with contemporary functional outcome assessments (MSTS, TESS, SF36). Results: 161 consecutive prostheses in 138 paediatric patients, between the years of 1983 – 2005, were implanted for primary bone tumours. Mean age was 10.3 (3 – 18), 81 were males and 57 females. There were 136 primary procedures and 25 revisions. 6 prostheses that used ball bearings to achieve length (designed in 1981) were implanted, 3 (50 %) were revised due to mechanical failure. 19 prostheses that utilised external C-washes (1998) to achieve length were implanted, 6 (32 %) were revised, half of these for mechanical failure. Of the 98 minimally invasive prostheses (1992) that utilized an Allan key and screw-jack mechanism to lengthen, 14 (14 %) were revised, half of these for infection. 17 non-invasive extendable endoprostheses (2001) that are lengthened by electromagnetic coupling have been implanted so far. There has only been 1 (6 %) revision. This was due to full extension being reached. Conclusions: Design improvements in growing endoprostheses since 1983 have led to improved survivorship. Initially this led to a reduction in mechanical failure and latterly to a reduction in infection, as indications for revision. Key Words: Bone tumour, children, endoprosthesis, survivorship

Aims

Extendible endoprostheses have been available for more than 30 years and have become more sophisticated with time. The latest generation is ‘non-invasive’ and can be lengthened with an external magnetic force. Early results have shown a worryingly high rate of complications such as infection. This study investigates the incidence of complications and the need for further surgery in a cohort of patients with a non-invasive growing endoprosthesis.

Conventional growing rods are the most commonly used distraction-based devices in the treatment of progressive early-onset scoliosis. This technique requires repeated lengthenings with the patient anaesthetised in the operating theatre. We describe the outcomes and complications of using a non-invasive magnetically controlled growing rod (MCGR) in children with early-onset scoliosis. Lengthening is performed on an outpatient basis using an external remote control with the patient awake.

Between November 2009 and March 2011, 34 children with a mean age of eight years (5 to 12) underwent treatment. The mean length of follow-up was 15 months (12 to 18). In total, 22 children were treated with dual rod constructs and 12 with a single rod. The mean number of distractions per patient was 4.8 (3 to 6). The mean pre-operative Cobb angle was 69° (46° to 108°); this was corrected to a mean 47° (28° to 91°) post-operatively. The mean Cobb angle at final review was 41° (27° to 86°). The mean pre-operative distance from T1 to S1 was 304 mm (243 to 380) and increased to 335 mm (253 to 400) in the immediate post-operative period. At final review the mean distance from T1 to S1 had increased to 348 mm (260 to 420).

Two patients developed a superficial wound infection and a further two patients in the single rod group developed a loss of distraction. In the dual rod group, one patient had pull-out of a hook and one developed prominent metalwork. Two patients had a rod breakage; one patient in the single rod group and one patient in the dual rod group. Our early results show that the MCGR is safe and effective in the treatment of progressive early-onset scoliosis with the avoidance of repeated surgical lengthenings.

Cite this article: Bone Joint J 2013;95-B:75–80.