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Indigenously Developed Limb Lengthening Prosthesis – Prospect of Helping Children with Limb Length Differences.

Bone cancer disease in children, needs proper treatment plan and management, right from the time of diagnosis. The treatment & management process itself is complex. The treatment plan doesn't end after the surgery and other managements like chemotherapy, radiotherapy, etc. There are other challenges to tackle as well, afterwards.

One such challenge is the 'Limb Length Discrepancy', in case of children recovering from bone cancers of the limbs. In certain type of cases, the growth plates near the joints of the long bones are rendered incapable of functioning, because of the necessary surgical intervention. This leaves the child's affected bone unable to grow in length, in proportion to the overall growing body (since the child is yet to achieve full anatomical height), causing a height difference of the limbs. This leads to various associated problems related to posture, walking, scoliosis, joint pains of hip, knee, ankle, etc.

Such a challenge needs to be addressed using medical devices which can achieve the required lengthening for the child's limb, utilizing the concept of “Distraction Osteogenesis”. Though the concept is not new; various types of solutions have been proposed, tried, and used till date. These are called as the Limb Lengthening Devices.

The two main types of such limb lengthening devices are External fixators & Internal fixators.

External fixators have proven their versatility in dealing with the challenge, but they have their own set of issues, such as:

- more number of skin incisions for the pins increase the chances of pin tract infections.

- nerve or vascular damage, during & after the insertion of the pins.

- invasion of space by the frame attached to the limb for prolonged time period (between 2 to 6 months), which affects daily life activities such as mobility, resting positions, clothing, and aesthetics.

Internal fixators on the other hand, require a primary invasive surgery, to place a limb lengthening device inside the intramedullary canal of the long bone. Basically, they're called as intramedullary expandable nails. Their advantages being:

- more convenient for the patient, for mobility, resting, clothing, aesthetics, etc.

- relatively lesser morbidity for the patient, during expansion phase.

These nails preform the lengthening process either mechanically or electromagnetically.

Below are the intramedullary nails previously developed around the world, which are operated mechanically:

1. Albizzia nail- In this type of nail, the lengthening is performed by a ratchet-type mechanism, where the patient has to perform a 20-degree leg rotation. This type of nail has been criticized due to non-precise counting click techniques, which are prone to human error. Thus the patient is susceptible to make mistakes and perform more or less lengthening than the daily amount of lengthening determined. Origin: France.

2. Betzbone nail- It is a revised version of Albizzia nail. However, it has been criticized upon the claims that the fixation can leave the bones fragile & at risk of fractures, which often requires a replacement surgery with a static intramedullary nail. This leads to more surgical procedures than required for the patients. Origin: Germany.

3. ISKD or Orthofix nail- In this type of nail, the expansion happens with the rotary movement of the knees or ankle. This nail as well, has been criticized for high risk of rapid bone growth, leading to nerve damage or fractures in the bone. Patients have also reported pain associated with the ratcheting movement during lengthening episodes. Origin: Germany.

4. Guichet nail- This nail also boasts full weight-bearing capabilities, but suffers from the similar inherent problems of all ratcheting-type nails. Origin: France.

All the above mechanically operated intramedullary nails suffer from few common drawbacks:

- Unreliable activation of lengthening mechanism

- Human error

- Inaccurate amount of distraction (lengthening)

- Inability to retrograde (decrease or revert the lengthening)

Apart from mechanically operated intramedullary expandable nails, there are ones which are operated electronically. These electronic distraction type intramedullary nails operate by using an electronic, non-invasive controller, which performs the precise lengthening of the intramedullary nail, instead of any mechanical movement of the limb by the patient.

Below are the Electronic distraction type intramedullary nails around the world:

5. Fitbone nail- German scientists designed this type of electronic nail. The lengthening process involves connection to an electrical supply via antenna, which allows energy to be generated for the motor which lengthens the nail. However, it never got into widespread use due to reliability concerns, very high cost, and inaccessibility outside German borders.

6. Precice 2 nail- This nail has the most accurate rate of lengthening, and the patients have reported minimum pain associated with the lengthening process. The lengthening is controlled by an electromagnetic remote controlled device, which when activated, rotates the gears inside & translates the main drive screw. Also, this nail boasts the capability of to retrograde (decrease or revert the amount of distraction), which helps in the control of bone formation and union. However, it is an extremely expensive intramedullary nail, leaving majority of the children unable to access its use and benefits.

The main drawback of the electronic distraction type intramedullary nails being very high cost & poor accessibility for the children around the world.

Here, in The Yellow Ribbon, we developed an intramedullary expanding nail prosthesis prototype, which can help the children who are facing such challenge.

The objectives of the project being:

1. facilitating the artificially assisted growth of the child's affected limb (bone).

2. performing as minimally invasive implantation of the prosthesis (nail), as possible.

3. performing controlled & gradual expansion of the prosthesis mechanically.

4. facilitating the retrograde action (reverting the distraction of bone).

5. encouraging receptive relaxation of the nearby anatomy (muscles, blood vessels, nerves, soft tissue, etc.) during the phase of expansion.

6. making the prosthesis & the relevant treatment available to the children in need, of every section of the society (in terms of cost, ease of manufacturability, distribution, and access).

With above goals in mind, we developed a simpler mechanism with cost effective design. The key highlights of the nail being:

- simpler yet reliable design.

- mechanically operated.

- easier for the surgeons to operate.

- ability to retrograde.

- collapse-proof.

- indigenous manufacturability

- much lesser cost, as compared to other alternatives.

- much wider accessibility to masses.

In-house developed intramedullary expandable nail

The procedure plan to implant and operate our intramedullary expandable nail would be as follows:

1. A minimally invasive surgery would be performed, which would help the child to recover faster.

2. A cut in the affected long bone would be taken (osteotomy), prior to insertion of the nail.

3. The nail would be inserted into the intramedullary canal.

4. The upper and lower segments of the bone (separated by the osteotomy site) will be attached to the nail using appropriate screws, with the help of supporting instrument (guides)

5. The surgical wounds will be closed, and a lateral/ medial (sideways) skin level puncture would be made to access the expansion port of the nail, through the long bone.

6. On the same day of the surgery, 1 mm of distraction/ lengthening would be performed by the surgeon.

7. Followed by the day of surgery, further lengthening would be performed by the surgeon with 1mm of distraction per day, up to the required length of lengthening, using the same port access puncture. Proper antibiotic and antimicrobial dressing would be done after each lengthening procedure to avoid the risks of infection.

The smallest intramedullary nail would have a minimum length of 200 millimeters (20 centimeters), a minimum diameter of 10 millimeters, and the expansion capacity of 55 millimeters (5.5 centimeters).

We started off with the designing multiple iterations of the mechanism, 3D printing their scaled-up versions, evaluating the mechanical reliability and manufacturability. After few iterations, we finalized the 6th iteration of the design (as shown below).

Before and after expansion

Though the project is under the prototyping phase, we're progressing towards the goal of making a certified, reliable, and low cost limb lengthening device which would be helpful to a larger number of children in need.

Trial of metal prototype with femur bone model

Expansion port of the nail (Lateral/ medial side)

Further prospect:

This device would be available in various combinations of lengths, diameters, and expansion capacity, to address a large number of patients of different age groups, heights, and anatomy. Apart from the applications in pediatric cases, this nail would have the ability to help adult patients too, who have similar limb length discrepancy issue.

We're excited with the numerous possibilities, and can't wait to introduce the final versions of our innovation to the masses for use.

We'll keep you updated!


Indigenously Developed Limb Lengthening Prosthesis – Prospect of Helping Children with Limb Length Differences.

Bone cancer disease in children, needs proper treatment plan and management, right from the time of diagnosis. The treatment & management process itself is complex. The treatment plan doesn't end after the surgery and other managements like chemotherapy, radiotherapy, etc. There are other challenges to tackle as well, afterwards.