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https://www.pobonline.com/articles/100532-forensics-3d-technology-and-the-law

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One of my orthopedic doctors showed me this website, where if you drop the X-ray image into the spot and put patient age and gender, it’ll gave you their bone age which is helpful for fracture and arrest of growth plates. It’s AMAZING!

https://16bit.ai/bone-age

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https://www.medpagetoday.com/endocrinology/type1diabetes/88385

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https://www.computerworld.com/article/3048823/this-is-the-first-3d-printed-drug-to-win-fda-approval.html

This is really awesome, to think that a drug can be formulated to fit a specific patient and even maybe reduce how many drugs a person is on if they need say 3 epilepsy drugs, but can combine properties of the 3 in 1 made for that patient.

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Can’t tell if this is scary or cool as a tattoo lover.

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Digital Tattoos Make Healthcare More Invisible - The Medical Futurist

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Digital tattoos could render our skin an interactive display and make healthcare more invisible in the future. Here's our summary of the latest innovations.

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Another great article about this technology used at the ortho clinic that i work at.

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In this study, we asked the question of whether non-invasive (NI) extendible bone tumour implants are as reliable and reduce infection when compared with patients who received a minimally invasive (MI) extendible implant.

Forty-two NI extendible bone tumour implants were investigated at a mean follow-up of 22 months (range, 1-87 months) and 63 MI implants at a mean follow-up of 49 months (range, 1-156 months).

Kaplan-Meier analysis showed that the probability of MI implant survival was 58.8% compared with 78.6% in NI patients. No significant difference between these two patient groups was found. Infection was the main reason for failure in the MI implant group where nine (35%) implants were revised. However, only one (11%) NI implant was revised for infection ( p = 0.042). None of the NI implants failed due to aseptic loosening; however, six (23%) MI implants were revised for aseptic loosening of the intramedullary stem. Four (15%) of the failed MI implants were revised due to full extension and five (56%) of failed NI implants were replaced as the implant had been fully extended where the patient still required growth.

Conclusion:

Where possible, an NI massive prosthesis should be used in this patient group. Our results suggest that MI prostheses should be infrequently used due to the high incidence of infection. Lengthening of NI prostheses is painless, can be carried out in the clinic and is more cost-effective. However, further work is required to increase the amount of growth potential available in these implants.

Introduction

Skeletally immature patients diagnosed with bone cancer are candidates for limb salvage surgery using an extendible prosthesis. Resection of the bone tumour often involves removing an epiphyseal growth plate, reducing growth of the affected limb. The concept of extendible endoprosthetic replacements was first introduced in Stanmore, England, in 1976 and has been in use since 1983. Extendible devices offer children near normal development and overcome leg-length discrepancy benefiting functional restoration, rapid rehabilitation and quality of life improvement. Minimally invasive (MI) extendible prostheses were designed and introduced in the early 1990s with intramedullary stem fixation and a screw extension mechanism within the shaft of the implant. Extension of the device was produced by making a small skin incision and inserting an Allen key into the screw mechanism that when turned, extended the implant. The main disadvantage of using MI devices is the open surgical procedure that is required to lengthen the implants and the younger the child, the more lengthening procedures are needed. The risk of deep infection increases with the number of surgical procedures and is one of the most devastating complications in bone tumour endoprosthetic surgery. Additional complications associated with multiple surgical procedures for limb lengthening are increased exposure to anaesthetics, ankylosis, nerve damage, soft tissue damage and amputation. Often with the use of MI prostheses, the limb is over extended to reduce the number of surgical procedures.

As a result, non-invasive (NI) growing implants have been developed and these include the Phenix prosthesis and the Stanmore NI growing prosthesis. These NI extendable prostheses can be lengthened without the need for repeated surgery. The Juvenile Tumour System (Stanmore Implants, Elstree, UK) introduced in 2002 as an NI implant combines a magnetic disc, a gearbox and a drive screw, where lengthening is controlled using electromagnetic induction. Once implanted, the leg is placed within the centre of a circular external rotating magnetic field, which synchronizes with and turns a magnetic disc located in the shaft of the prosthesis. The magnetic disc drives the gearbox that lengthens the prosthesis at a controlled rate of 0.23 mm per minute. The Stanmore NI extendable prosthesis can be lengthened in small increments without the need for surgical intervention. The aim of this study was to investigate the effectiveness of the Stanmore MI and NI extendible prosthesis inserted into patients over a 16-year period between 1994 and 2010.

Materials and method

Between 1994 and 2010, 105 limb salvage surgeries using MI and NI extendible growing prostheses were performed on skeletally immature patients. Sixty-three patients (31 male and 32 female) received an MI prosthesis and 42 (23 male and 19 female) received an NI implant. MI prostheses were implanted between 1994 and 2009 and NI prostheses between 2002 and 2010. All surgeries were performed for primary bone tumour treatment where osteosarcoma was the most common diagnosis. Twenty-nine patients (69.0%) who received an NI implant and 54/63 (85.7%) MI patients were diagnosed with osteosarcoma. All remaining patients were treated for Ewing's sarcoma (13 NI patients and 9 MI patients). The mean MI patient age was 11.67 years (range, 4-16 years) and NI, 10.09 years (range, 5-18 years). Patients in the MI group were followed up at a mean of 49 months (range, 1-156 months) and patients in the NI group, 22 months (range, 1-87 months). Sixty-one distal femoral, 21 proximal tibial, 15 proximal femoral, 4 proximal humeral, 2 mid-femoral and 2 total femoral implants were investigated. Each patient received a unilateral implant with 57/105 (54.3%) inserted into the right limb and 48/105 (45.7%) into the left. The mean amount (with standard error) of bone resected in NI patients was 202.48 ± 8.13 mm and 162.46 ± 6.94 mm in MI patients. Depending on bone quality and surgical choice, implants were either cemented or uncemented (35.7% NI and 49.2% MI implants were cementless devices) and all surgeries were performed at a single institution. No patients were recalled and all data were obtained from the medical records. This study was approved by the Royal National Orthopaedic Hospital Institutional Review Board (SE10.017), where appropriate patients received neoadjuvant chemotherapy and all met the criteria for limb salvage.

All prostheses were manufactured on a customized, case-by-case basis. The extension shaft and intramedullary stem were made from titanium alloy (Ti 318, Ti ₆Al ₄ V), and, when indicated, the stem was shaped to follow the natural curvature of the bone. All NI and MI implants that involved replacement of the knee joint used a SMILES™ rotating hinge total joint (Stanmore Implants). A hydroxyapatite collar, which has previously been shown to enhance osteointegration and bony bridging at the transection site, was located adjacent to the transection site and shoulder of the implant in all patients. The MI implant design consisted of a hollow extension tube that incorporated an extension module manufactured from CoCrMo alloy. The extension module consisted of a telescopic worm wheel screw gearing mechanism that operated with an Allen key. In the MI group, the lengthening procedure required access to the gearing mechanism, which was accomplished through a small skin incision made under general anaesthesia. The Stanmore NI extendible implant has been previously described and extension was undertaken in the outpatient clinic without anaesthesia, using electromagnetic induction of a magnet-driven gearbox within the implant at a rate of 0.23 mm/min at a power of 50 or 100 V. In the NI implant group, the time taken to lengthen the implant was dependent on the discrepancy in leg-length and the site of implantation.

Statistical analysis

Failure was defined as the need for revision of the component and conversion to a different prosthesis. In the NI group, the inability to lengthen was recorded as having a failed gearbox. In the MI implant group, the inability to lengthen was recorded as having a failed extension mechanism. Prostheses with collapsed lengthening mechanisms were listed as failed and recorded as collapsed prostheses. Implants revised due to full extension were also recorded as endoprosthetic failure; however, during revision surgery, only the implant shaft was replaced leaving the intramedullary stem fixation undisturbed. Implant loosening secondary to infection was classified as a failure; however, amputation due to local recurrence and irreversible ischemia were not included in the implant survivorship analysis as these were unrelated to the durability of the prosthesis. The duration of follow-up was from the time of surgery to the time of the latest evaluation. Implant survival was calculated using Kaplan-Meier analysis using overall prosthetic revision and failure due to infection and full extension as the end points. The number of implants that failed due to aseptic loosening was also recorded. Cases without failure were censored either at the time of death or on the date of the last follow-up. The Mantel-Cox log-rank test was used to compare implant survivorship where a p value of <0.05 was considered significant. All analyses were performed using SPSS software (version 17.0; SPSS, Chicago, Illinois, USA).

Five MI patients died of metastatic disease and a sixth MI patient died (6.7%) following cardiac arrest. In the NI group, one patient died of metastatic disease. Twenty-five of the 63 (39.7%) MI implants inserted were revised () and 9 of the 42 (21.4%) NI implants were revised ().

Survival analysis

Kaplan-Meier analysis showed the probability of an MI bone tumour implant surviving with respect to implant revision due to implant failure for any cause and at a mean follow-up of 49 months was 58.8%. The survival of an NI implant at a mean of 22 months was 78.6%. No significant difference in overall survivorship between these two patient groups was found (). Implant survival in the NI patient group at 1-year post operation was 97.1 ± 2.8% compared with 96.7 ± 2.3% in MI patients. At 7-year post-surgery implant, survivorship had decreased to 40.4 ± 14.4% in the NI group and 45.0 ± 7.9% in the MI patient group. If full extension was removed from the data as a form of implant failure, survivorship analysis demonstrated that at 7-year post operatively, NI prostheses had a survival rate of 76.3% and MI prostheses a survival of 49.0%.

Implant survivorship analysis with infection as the endpoint showed a significant difference between groups ( p = 0.042; ). Only one NI implant failed due to infection at 20-month post-surgery giving a survival of 94.4% ± 5.4% over the study period of 7 years. The probability of failure due to infection in the MI patient group decreased from 98.3 ± 1.7% at 1-year post-surgery to 76.2 ± 8.3% at 7-year post-surgery.

Full extension accounted for 56% of NI prosthetic failures and 15% of MI implant failures ( p = 0.005). Kaplan-Meier analysis of implant survivorship with full extension as the endpoint showed that at 1-year post-surgery, implant survival was 96.7 ± 3.3% in the NI patient group and 94.8 ± 2.9% for MI prostheses. At 7-year post operation, MI implants demonstrated a survival rate of 76.3 ± 11.1% and NI implants 49.5 ± 7.9% ().

Discussion

Earlier designs of extendible prostheses were modular, where the midsection of the implant was exchanged for progressively longer sections. These designs required large surgical incisions to exchange the extension parts. Therefore, implants were superseded by MI designs, which required a small incision under anaesthesia to expand the prostheses. Expansion of these implants increased the risk of anaesthetic complications and infection and NI designs were introduced in the 1990s. Our study investigated survival of the Stanmore MI and NI extendible prostheses over a period of 16 years. Patient survival compared favourably with other studies that have investigated the use of extendible endoprostheses and our results found no statistically significant difference in overall implant survival when the two groups were compared. The commonest reason for failure of MI endoprostheses was peri-implant infection, whereas full extension was the main reason for NI implant revision surgery.

Deep infection after endoprosthetic replacement of a bone tumour is a major complication associated with significant morbidity, increased number of surgical procedures, prolonged rehabilitation, pain, worse functional outcome and revision surgery, where failure of revision can result in amputation. Factors that increase infection include radiation therapy, 'maintenance surgery' (e.g. bushing replacement), patellar procedures and anatomic site (particularly involvement of the tibia). Infection has also been associated with difficulty in obtaining soft tissue coverage of the prostheses following limb reconstruction, which is more problematic in proximal tibial replacements. These factors combined with the size of the implant, the peri-operative time and immunosuppression associated with chemotherapy may explain why six patients (five MI and one NI) developed an infection within 7 months of surgery and before any invasive limb lengthening procedures had taken place. This study identified an infection rate of 9.52% in the NI implant group and 20.97% in the MI patient group, which is similar to previous studies where infection rates were measured ranging from 4% up to 40%. In our study, 8 of the 13 reported MI infections occurred after the lengthening procedures had begun and all 8 of these implants were revised. Jeys et al. reported an increased infection risk of 0-5% with each MI lengthening. Grimer et al. reported 5 lengthening-associated infections in a study of 20 patients with extendable tibial prostheses, while studies by Ayoub et al. and Eckardt et al. noted no lengthening-related infections. In our study, most infections appeared after one lengthening procedure with fewer infections noted after three lengthening procedures. However, a study by Hantes et al. reported an increased incidence and severity of complications (including infection) with increases in lengthening and a retrospective study by Eckardt et al. demonstrated significant complications in 56% of patients with extendible prostheses, although this study also showed that the lengthening procedures themselves did not cause any infections. The NI implants investigated in this study were inserted more recently (2002-2010) when compared with MI implants and it is possible that the difference in infection rates may also in part be due to the benefits from recent advances in hospital infection control and patient management. It may also be due to the relatively recent use of a gastrocnemius flap during surgery, which has been shown to decrease the rate of infection in limb salvage procedures. However, in our study, gastrocnemius flaps were used in every case. Silver-coated implants have demonstrated good antimicrobial activity and have been introduced into oncological musculoskeletal surgery with success; however, in this study, none of the NI or MI implants investigated were silver-coated.

Full extension where growth of the limb was still required was the main long-term complication resulting in revision of NI implants. These findings are similar to those reported by Sewell et al. who also found that full extension was a major reason for revision surgery. This may be due to the NI prostheses having a lower lengthening capacity compared with MI prostheses, which is due to the extra size associated with the magnet and gearbox. As full extension is not necessarily 'implant failure', when these results were excluded, survivorship analysis demonstrated that at 7-year post operatively, NI prostheses had a higher survival rate of 76.3% when compared with MI prostheses (49.0%). Complications that may interrupt long-term success due to early revision of an NI implant following full extension are unknown. Optimal fixation of the implant within bone is essential and, therefore, if both bone quality and quantity are sufficient, then it is possible that implant success would not be further compromised. A recent study investigated the use of NI implants for the revision of previous endoprostheses and reported it to be a successful option in the mid-term with a revision-free implant survival of 75% at 2 years reducing to 55% at 5 years. Nevertheless, further investigation is required to establish factors that affect the long-term survival of these implants following both primary and revision surgery.

Aseptic loosening of extendible massive bone tumour endoprostheses is also a major complication causing implant failure. Increased bone resection levels following distal femoral and proximal tibial implant surgery are associated with increased rates of aseptic loosening and results from our study found a 23% MI loosening rate with no NI failures, despite NI patients having a significantly larger mean bony resection level. Prosthetic aseptic loosening is a mid-term complication and has been reported to occur within 3-9 years after primary surgery. Therefore, in our study, it is possible that aseptic loosening of MI prostheses may be increased when compared with NI prostheses due to the longer follow-up period.

Lengthening procedures confer a significant improvement in the functional score of growing patients. In our study, some implants were not lengthened (48/105), with the main reasons being poor general condition, early death or amputation. Fifty-four percent of implants were lengthened and this is similar to lengthening rates reported in the literature (50-75%). Gearbox failure or a collapsed lengthening mechanism resulted in failure in both groups. Early physiotherapy may prevent extensive tissue scarring which may reduce the force exerted on the gearbox during lengthening. The results reported in this study are relatively short-term but show that NI implants may reduce the incidence of decreased ROM and nerve palsies as shorter lengthening episodes can occur more often.

A limitation of this study is the relatively small number of patients in each of the surgical reconstruction groups as only 50 paediatric patients are treated for sarcoma with limb salvaging techniques per year in the United Kingdom. A second limitation is that this study was carried out retrospectively with analysis of patients over a relatively short postoperative follow-up period. A recent study by Gilg et al. investigated a similar number of NI extendible implants but at a longer mean follow-up time of 64 months. This study reported a higher implant infection rate (19.6%) and it is conceivable that this difference in outcome may in part be due to our shorter post-surgical follow-up window. In this study, variation was minimized as all implants were made by a single manufacturer. Surgical techniques and patient care were also consistent as all patients were treated at a single institution. MI prostheses are infrequently used at our hospital and results showed that infection (35%) was significantly higher when compared with NI patients (11%). However, at the follow-up period investigated in this study and when all reasons for failure were taken into account, overall implant survival was relatively low in both groups and it is important to consider that rates of implant infection are expected to further increase in both patient cohorts following revision surgery. Lengthening of NI prostheses is painless, can be carried out in the clinic and in cases where multiple lengthening procedures are required, it may be more cost-effective as unlike MI lengthening, it does not require hospitalization, a general anaesthetic and additional surgery. However, to accommodate an NI implant, the amount of bone resected during primary surgery may be increased and further work is required to improve the amount of growth potential available in these implants.

Declaration of conflicting interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding
The author(s) received no financial support for the research, authorship, and/or publication of this article.

References

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Non-invasive massive growing prostheses reduce infection in paediatric cancer patients - Melanie Jean Coathup, Samee Ahmad, Julian F Maempel, Timothy WR Briggs, William J Aston, John A Skinner, Gordon W Blunn, 2019

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In this study, we asked the question of whether non-invasive (NI) extendible bone tumour implants are as reliable and reduce infection when compared with patients who received a minimally invasive (MI) extendible implant. Forty-two NI extendible bone tumour implants were investigated at a mean follow-up of 22 months (range, 1-87 months) and 63 MI implants at a mean follow-up of 49 months (range, 1-156 months).

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The Orthopedic oncologist surgeon that i work with is 1 of 15 in the nation that places these non invasive extendible implants for children with bone cancer. This technology has saved pediatric patients limbs when other providers have recommended amputation. This technology is AMAZING!

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Abstract

Keywords: Bone tumors, expandable prosthesis, limb length discrepancy, limb salvage, noninvasive lengthening

Introduction

Orthopedic oncology has evolved over the past few decades to favor limb salvage over amputations for patients with sarcomas due to increased knowledge about the disease and advances in imaging modalities, surgical techniques, adjuvant, and chemotherapy. Limb-salvage operations have shown a local recurrence rate of between 5% and 10%, comparable with that achieved by amputation.

Cure rates for bone sarcomas are reaching 70% to 80% with limb salvage surgery being performed as a routine. However, encasement of major neurovascular structures by the tumor, local tissue contamination following pathological fractures and local recurrence after the salvage operations may warrant an amputation.

Endoprosthetic reconstruction for limb salvage operations in skeletally immature patients has been a challenge with the fixed-length endoprostheses leading to limb-length inequalities at skeletal maturity. Extendable endoprosthetic replacements have been developed over the years and now are an established and safe alternative allowing limb lengths to be maintained in skeletally immature patients over their period of growth. The gold standard minimally invasive expandable mega prosthesis requires a surgical procedure with a small incision to turn a screw to achieve a lengthening. These prostheses, are good functionally and psychologically, although each lengthening procedure is an operation and is accompanied by pain as well as need for intensive rehabilitation to achieve good function. The risk of stiffness, neurovascular damage, and peri-prosthetic infection is a matter of concern; and in some cases even leading to an amputation.

The externally applied magnetic field to lengthen the noninvasive expandable prosthesis eliminates the pain, stiffness, as well as the risk of infection. The objective of this paper is to present our experience with this implant over the past 8 years while analyzing its benefit and cost effectiveness.

Materials and Methods

Children undergoing limb salvage surgery for bone sarcoma and expected to have a limb-length discrepancy of >3 cm at skeletal maturity were offered the noninvasive expandable endoprosthesis. Those willing to bear the cost of the implant and consented to be a part of the study were included in the study.

Eighteen implants were used in 16 patients with a nonmetastatic primary bone sarcoma (13 osteosarcoma, 1 Ewing's sarcoma, 2 revisions of the standard prosthesis to expandable) were reconstructed with an implant having the noninvasive expansion mechanism (15 distal femoral prosthesis and 3 joint saving intercalary implants) between May 2006 to June 2015. All implants were manufactured by Stanmore implants worldwide based in London, UK [].

Table 1

The extent of the tumor of involved leg was undertaken using radiographs [] and Magnetic resonance imaging (MRI) [] while disease staging was performed by whole-body ⁹⁹Tc scanning or positron emission tomography scanning and computed tomography (CT) of the chest to detect metastases. There were 15 osteosarcomas, and one Ewing's sarcoma all of which were diagnosed by percutaneous needle biopsy and all patients received neoadjuvant chemotherapy based on international protocols. Enneking staging of musculoskeletal neoplasms was used and all lesion were classified as Stage-IIB lesions. The lesions were resected en bloc with a wide margin of bone of about 3-5 cm for joint involving resections; whereas 2-3 cm of bony margin was maintained for intercalary to the defined limits of the tumor.

The prosthesis was custom-designed using a preoperative CT and MRI of the affected limb to determine the length and diameter of the intramedullary stem after taking into consideration the level of the intended bony resection. Since it is a custom implant; production time is approximately 3-4 weeks and delivery time of 1-2 weeks adds up to 4-6 weeks for the implant to be delivered from date of placing the order with the company. The choice of length options (Currently, the three length options; 50, 70, and 90 mm growth sections are available []) was determined by the length of resection, predicted future growth and anticipated leg-length discrepancy. Longer resection length offered the option to choose a longer expandable growth section for the joint.

Postoperative physiotherapy was started from the next day and patient mobilized as soon as comfortable and pain-free. All patients resumed chemotherapy following suture removal and wound check at 2 weeks. Followup was every 3 months for the first 3 years, every 6 months for the next 2 years and subsequently annually. Limb lengths were recorded at each followup and lengthening was performed at an out-patient clinic in case of limb length discrepancy. Local radiographs obtained after lengthening [] was compared to the immediate previous radiographs to confirm lengthening. The total lengthening performed while allowing knee range of motion and no compromise to the neurovascular status was meticulously recorded for each patient. Patients were functionally evaluated at their latest followup visit using the Musculoskeletal Tumor Society (MSTS) scoring system. The frequency of lengthening sessions was subjective to the patient's ability to visit the out-patient clinic to keep up with the growth of the contralateral limb []. It was in the cases of delayed intervals between lengthenings where jamming of gears or requirement of booster was noted to overcome the soft tissue tension.

Prosthesis and lengthening

We used prostheses by © Stanmore Implants Ltd. namely the Juvenile Tumour System "JTS" noninvasive extendable prosthesis in 13 of our patients [] while custom intercalary lower limb joint sparing noninvasive extendable implants were used in three patients [] designed specifically to treat midshaft intercalary resections in the femur or tibia, which offers custom designed patient specific prostheses with a variety of fixation methods, hydroxylapatite collars, and surface treatments of either silver or titanium nitride.

The custom designed implants are fabricated from titanium alloy (Ti 6Al 4V) and cobalt chromium molybdenum alloy. Remaining gearbox parts and power screw are made of stainless steel, while the magnetic disc is made from rare earth magnetic (NdFeB) material []. Liquid paraffin is used to lubricate the gearbox mechanism.

The portable external drive unit and 220-volt power source allow lengthening in outpatient clinics. A rotating electromagnetic field at a speed of 3000 RPM passes through the coils and placing the prosthesis at its center [] causes rotation of the magnetic disc within the implant and achieves implant lengthening at a rate of 0.23 mm/min - approximately 1 mm every 4 min [].

Results

Eleven boys and five girls with high-grade primary malignant tumors of the lower limbs were treated with resection of the lesion and replacement with the noninvasive extendable endoprosthesis. Their mean age at implantation was 10.25 years. Twelve out of the 16 patients were successfully lengthened without any reported pain during the lengthening process. In one patient reversing the mechanism and shortening by 2 mm was necessary to regain full extension after final lengthening, all other patients regained their usual level of function immediately after or by the day after lengthening with no neurovascular compromise. The rotating implant gearbox, when energized by the external magnetic field, was heard using a stethoscope placed on a bony prominence: The malleolus, tibial shin, or greater trochanter.

The number of lengthening procedures for each patient varied from one to twelve. The mean time from the implantation to the latest followup was 49.56 months (2-84). The mean lengthening achieved during each procedure was 4.18 mm. Patients were lengthened by a mean of 31.64 mm (2-65 mm), the mean knee flexion angle being 110° (70° to 120°).

The mean MSTS score was 28.83 of 30 (ranging 24-30).

The implant related issues during the study were seen in five patients of which only two required interventions for the failure of lengthening mechanism while 1 fully extended prosthesis at 50 mm was re-implanted with an implant with lengthening potential of 90 mm in to maintain equal limb lengths []. There was jamming of gears in two patients that resolved without intervention and did not affect lengthening. One patient lengthened at 50% boost while another patient required 100% boost to facilitate lengthening. In one patient, open surgery and release of peri-prosthetic membrane were undertaken for inability to extend in spite of 100% boost and manipulation.

One case developed a flexion deformity with periarticular contracture which was initially manipulated under GA to achieve only a 25° flexion and hence had to undergo open surgery with quadricepsplasty and release of quadriceps and iliotibial band. The same patient later developed periprosthetic infection. In the total of two cases that developed delayed infection, implant was removed and length maintained by an antibiotic cement spacer over a K-Nail until infection was controlled and the implant could be re-implanted []. Before re-implantation prostheses were treated with ethylene oxide sterilization instead of autoclaving to prevent damage to the magnet gear system. Three patients died of disseminated metastatic disease, and one patient died of leukemia from complications to chemotherapy.

In our series, there has been no prosthetic failure or stem fracture and no evidence of loosening in all but one case where femoral intramedullary stem loosening was noted 6 years postimplantation following the full expansion of the implant which was revised successfully to another JTS implant and successfully lengthened thereafter.

Discussion

Limb-salvage procedures for patients with bone tumors is an established treatment, but in children: Skeletal immaturity leading to limb-length inequality at the end of the growth phase has long been a challenge to the orthopedic oncologists. In the past, modified adult endoprostheses have been developed with modular midsections that were exchangeable for progressively longer sections. The advent of the minimally invasive designs excelled over the modified adult prostheses, but lengthening was under anesthesia and required a small surgical incision to expand the prosthesis. This implant continues to remain the gold standard for limb salvage in skeletally immature patients but with the risk of anesthetic complications and infection.

In the mid-80s, Professor John T. Scales of the Centre for Biomedical Engineering (Institute of Orthopaedics), the pioneer of much of the limb salvage implant technology and Mr. Rodney Sneath, a leading orthopedic oncology surgeon, originated the concept of a noninvasive extendible implant. During the late 80s, the project was begun and the technology platform selected.

The first designs capable of noninvasive expansion were introduced in the 1990s. The Phenix prosthesis (Phenix Medical, Paris, France) in 1990, lengthened on the controlled melting of a polyethylene tube with a spring, using an external electromagnetic field.

Unlike with the Repiphysis (a competing implant manufactured by Wright medical technologies), in our series there were no breakages; specifically due to the gear based lengthening mechanism of the implant.

The use of expandable endoprostheses to maintain leg length in the skeletally immature has become the most acceptable method of treatment, we attempted to over-lengthen the prosthetic replacement at insertion by 1-2 cm, avoiding damage to neurovascular structures and to reduce the number of further lengthening procedures by reducing the length discrepancy.

It is recognized that there is an increased risk associated with the lengthening and the mechanical reliability of extendible implants as compared to the adult endoprosthesis.

The key advantages of the noninvasive lengthening prosthesis used in our patients lies in the fact that first; the prosthesis stays in situ indefinitely and does not need to be changed at the end of the growth period as there is no reversal of lengthening by the failure of gear mechanism reported till now. Revision is only likely to be necessary if the patient grows in excess of the maximum possible lengthening of the implant. Second, the lengthening is measured and controlled (rate of 0.23 mm/min) allowing accurate record of limb lengthening each session and expansion of implant remaining for future growth.

Early and regular physiotherapy is important to maintain a good range of movement, prevent peri-prosthetic adherent tissue/scar formation and allow extension of the prosthesis to be achieved with less force on the gearing mechanism. Immediately after lengthening, some decrease in terminal knee range of motion was noted, which recovered completely with exercise.

The patient resumes all activities of daily living.

Restrictions to contact sports and loading activities, running and jumping are avoided to increase the life of the implant and delay need for revision due to implant failure.

Better stem fixation and reduced loosening rates were an incidental finding and could be attributed to the use of a hydroxyapatite-coated collar on the proximal stem of the femoral component, permitting bone bridging over the implant ingrowth and reducing the chance of aseptic loosening by forming a biological purse string/bonding at the stem prosthesis junction.

Saving the natural knee joint gives the patient greater joint longevity than would be otherwise available with an implant. Patients gain further benefit from natural motion and a far greater range of movement, proprioception and natural sensation as was seen in the 3 cases implanted with the custom intercalary diaphyseal reconstruction expandable prosthesis.

The functional and oncological outcomes, complications such as infection and stiffness are a comparable match to those with the standard nonexpandable implants.

We expect the jamming of expansion mechanism to reduce with evolution and improvement in technology.

Financial cost efficiency

Noninvasive expandable implants are more expensive than minimally invasive lengthening implants. However, in the longer term, they are a cost-effective solution for those patients that will require multiple lengthening procedures. If the patient is nearing skeletal maturity and the expected extension required is <25 mm, a noninvasive mechanism would not be the most cost-effective solution financially, unless there was an increased risk of infection.

The noninvasive expandable implant also has significant health economic benefits. A recent US study identified that it costs US$ 267 to undertake a noninvasive lengthening procedure compared to approximately US$ 8,000 if surgery is required. In the Indian scenario, the cost of each invasive lengthening procedure would range anywhere from 20,000 to 50,000 INR and assuming each patient with a minimum bony resection; a 50 mm extension of the implant requires a minimum of five sittings to be able to lengthen regularly and comfortably. There are other "hidden" cost-savings too with the noninvasive lengthening: These include in-patient care, surgical and physical rehabilitation which are not necessary for noninvasive lengthening. The risk of infection is ever-present, and there are documented cases of infection that can be directly related to the invasive extension procedure. The cost to revise an infected prosthesis to both the patient and health service provider is significant. Minimizing surgical intervention minimizes the risk of infection, a solution which is provided by the noninvasive extendable implant; where there is no cost of lengthening as it is an outpatient procedure but the high cost of the implant is a barrier to widespread use (varies from 17 to 20 lakh INR).

Nonfinancial cost efficiency: Quality of life

Limb-salvage in the skeletally immature is predominantly about minimizing the decline in quality of life for the patient. The simplest solution for many patients would be an amputation but, in today's society, this would be unacceptable. Now, after many years of research and development, there is the technology available to maintain equal limb lengths at skeletal maturity. The noninvasive extendable implant eliminates the inconvenience to both, the patient and family if they require multiple hospitalizations for invasive lengthening. This implant allows limb lengths to be maintained without any pain, functional compromise or risk of infection.

Conclusion

The noninvasive expandable prosthesis is an ideal implant for skeletally immature patients undergoing limb salvage surgery for bone sarcoma who are expected to have more than 3 cm of limb length discrepancy at maturity. The initial high cost compared to a minimally invasive expandable implant can be recovered as there is no additional cost of lengthening. Lengthening is painless with no loss of function. The small amounts of lengthening at more frequent intervals are more physiological than with the minimally invasive type where more lengthening is done to minimize the number of procedures. As we present the largest case series in India, this unique prosthesis has shown promising early results, but additional data are required about its long term structural integrity.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

References

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Growing Without Pain: The Noninvasive Expandable Prosthesis is Boon for Children with Bone Cancer, as well as Their Surgeons!

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Keywords: Bone tumors, expandable prosthesis, limb length discrepancy, limb salvage, noninvasive lengthening Orthopedic oncology has evolved over the past few decades to favor limb salvage over amputations for patients with sarcomas due to increased knowledge about the disease and advances in imaging modalities, surgical techniques, adjuvant, and chemotherapy.