Leg lengthening using self-stretching intramedullary nailing: pros and cons and the applicability
During the 1990s, intramedullary nailS with the ability to stretch have been researched and in clinical use. There were 3 types of self-stretched intramedullary nails: the mechanical nails (Albizzia and ISKD), the self-stretching nails using motors (Fitbone) and the magnetic-guided nails (Phenix, Precice). When undergoing leg lengthening with these nails, patients did not have to carry external fixators. Therefore, complications and difficulties from eternal fixation can be avoided, rehabilitation process was smoother, surgical scars were more aesthetic-looking, etc. However, self-stretching intramedullary nailing still possessed many weaknesses that needed to be researched and fixed.
1. Albizzia nails were used for femoral lengthening, with a 11-15mm diameter, a 24-32cm length and the ability to stretch by 6-10cm. Patients could perform self-stretching by rotating the shin inwards and outwards to the thigh, with the rate of 1mm for every 15 rotations. However, many patients suffered from a lot of pain during stretching. Garcia-Cimbrelo reported that 5 out of 24 patients were in great pain while rotating their legs for stretching and 4 out of 24 patients had to stop stretching because of the pain. For Guichet J.M, 13 out of 41 of his patients required several doses of anesthetic for stretching. Therefore, nowadays these type of nails are no longer used.
The Intramedullary Skeletal Kinetic Distractor (ISKD) nails were a modified version of the Albizzia nails. They have a diameter of 10.5-14.5mm and have the same stretching mechanic as that of the Albizzia nails. However, the patients only have to do a 30-degree rotation of their legs, therefore they suffer from less pain during stretching in comparison to leg lengthening procedure using Albizzia nails. The nail is able stretch by 5-8cm. Cole J.D was able to perform lengthening for 16 femurs and 14 tibias with the average stretch length of 4.9cm. The average stretching rate was 0.82mm per day (0.4-1.7mm per day). There were no signs of infection, malunion, nonunion or restricted joint movement. However, there were 2 patients who suffered from broken nail during stretching and had to replace the nails. Because patients only need to do a 30-degree rotation of their their legs to be able to stretch, the nails possess a weakness which is the inability to control the stretching rate. Kenawey M. reported that 1 out of 37 patients could not extend his osteotomy cavity, 8 out of 37 patients had faster stretching rates than expected, which led to slow bone healing. Schieldel F. M. found that the patient’s stretching progress would depend on his activities and pain tolerance. Some cases had to start the stretching process under anesthesia, 18% did not reach the intended stretch length, 36% had broken nails or their nails could not be stretched, 8 patients had poor bone cavities. Mahboubian S. found that stretch control was more difficult and the rate of complications requiring surgical intervention was higher than leg lengthening with an external fixator combined with an intramedullary nail (6 out of 12 compared to 1 out of 20). In addition, these nails were expensive, an average leg lengthening operation in Germany would cost 65,000 euros.
2. Fitbone nails are bone stretching intramedullary nails that use motors. Patients would control the motors through a signal transmission and reception system placed under the skin. The nails have a diameter of 11-13mm and could extend the femurs by 8.5cm and tibias by 6cm. Several clinical studies showed that the reliability and success rates in leg lengthening were higher when using Fitbone nails. However, there were still complications and difficulties such as nail jam, broken nails and motors, limb length discrepancy, expensive price of the nails, etc. According to the report from Singh S., he had successfully performed lengthening for 13 femurs and 11 tibias with the average stretch length of 4cm. The average healing rate was 35 days for each centimeter. However, 2 patients had to replaced their Fitbones nails for bigger ones as the motors could not stretch the bones, 2 patients did not reach the intended stretch length; 3 tibias were slow to heal which required bone grafting and 1 patient has to change his nail. 1 patient suffered from lower limb length discrepancy of 1 cm after his leg lengthening process. In 2006, Krieg A.H. helped stretch 6 femurs and 2 tibias for 8 patients, with stretch lengths ranging from 2.9 to 4.7 cm. The average healing rate was 26 days for each centimeter. However, 1 nail was jammed and 1 was broken.
Betzbone nails (from Germany) are mechanically self-stretched intramedullary nails. They were invented based on Fitbone nails but possess several innovations that get rid of their weaknesses on the steel’s quality and configuration. The operation is simple. The nails are strong and capable of withstanding the body weight right after surgery. Because of their mechanical feature, Betzbone nails can be produced with their size being as small as 9mm (For this type of nail only, a suitable size will be chosen accordingly based on the size of the medullary cavity without the need for drilling a larger hole). When using Betzbone nails, the femur can be stretched by 10-12cm and the tibia can be stretched by 8-10cm. Nowadays Betzbone nails are most commonly used in Germany and Europe. Thus, this type of nail is quite suitable for the physical appearance of most Vietnamese people.
3. Magnetic-guided nails (Phenix, Precice): From 2011, Precice nails from the U.S. were used for leg lengthening. Precice nails could stretch and compress under the control of an external magnetic controller; stretching rates were better controlled. However, this type of nails still possesses many weaknesses. The smallest diameter of the first generation of Precice nails was 10.7mm and the smallest diameter of the second generation (invented in 2013) is 8.5mm. They had the ability to stretch by 5-8cm. A special point to notice is that the canal must be drilled at least 2mm wider than the diameter of the nail (this is a key point that makes it quite difficult to perform for people of short stature in Vietnam, an average Vietnamese person usually has the diameter of the femurs of 9-10mm, and the diameter of the tibias of 8-9mm). The external controller has a strong magnetic field and is approved by the FDA for uses in a medical facility only, so it is annoying for patients who had go to the hospital every day for stretching and inpatients during the whole stretching process. Similar to other types of self-stretching nails, Precice nails could be in risk of fracture when the whole body is compressed. Even when the stretching has ended, a patient was only allowed to withstand compression of up to 22 kg with 8.5mm and 10.7mm diameter nails, and up to 34 kg with 12.5mm diameter nails; only when there is evidence of bone healing shown on X-ray can the compression rate be increased gradually. In 2013, Harris M., Paley D. reported to have successfully performed leg lengthening for 17 patients, with the stretch lengths ranging from 2.7cm to 6.5cm. The stretching rates were from 0.53mm to 1.11 mm per day. However, there were 3 broken nails and 6 nails that had broken stretching parts, 1 leg suffered jamming in the cavity and 4 legs that required soft tissue interverntion surgery.
In 2016, Wiebking U. reported the results of using Precice nails for lengthening for 9 patients (4 femurs, 3 tibias) in the Hannover Medical School Hospital, with the average age of 32 and the average stretch length of 3.5cm. The results showed 2 cases of nonunion and 1 case of broken nail which required a replacement.
In 2019, Calder P. R. and his partners in the Royal National Orthopaedic Hospital (Stanmore) produced a summary report of 107 femur stretching cavities from 92 patients. They included 73 femurs that received nailing from the top (the average stretch length was 4.65cm) and 34 femurs that received nailing from the bottom (the average stretch length was 4.64cm). There were 100 stretching cavities that were fully healed with the average healing rate of 31.6 days for each centimeter. There was no difference in the results between the 2 groups, but the proportion of female patients with hip and knee limitation during and after completion of stretching was higher than that of male patients. Some complications occurred such as 3 cases of nonunion and 5 cases that required additional surgery to lengthen the thigh muscle tendon to improve knee flexion. There were some other minor complications such as the bending of the horizontal pin and bending of the nail, but they did not affect leg lengthening process.
However, Precice nails possess a huge weakness which is the inability to compress the whole body. This is because the nail is weak and the probability of the nail getting bent or jammed is high. Therefore, in 2018, a new generation of nails that solved the weaknesses of Precice nails was created. Called Stryde, this type of nail would replace Precice nails because of its stronger feature. Stryde nails have 3 sizes which are 10mm, 11.5mm and 13mm. They can withstand the maximum weight of 68kg, 91kg and 114kg respectively. The first surgery to use Stryde nails was performed in May 2018.
From May 2018 to October 2019, Robbin C. and Paley D. (3/2020) reported the results of prolonged use of this type of nail for 106 patients with 187 legs. In which, there were 57 patients who underwent lengthening on both legs to increase height (41 cases of femoral lengthening, 4 cases of tibial lengthening, 12 cases of simultaneous lengthening of both femurs and tibias), and 49 patients who underwent leg lengthening due to leg length discrepancy (37 femurs and 12 tibias). All patients showed signs of complete compression after surgery, except for 12 cases where both tibias and femurs were stretched simultaneously. As a result, there was only 1 case of failure due to unstretched nail jam, which required nail replacement. All bone extension cavities healed well. There were no cases of nonunion that required additional bone grafting. Thus, the results were considered to be very good. However, Biodur 108 which is the material needed to manufacture these nails requires re-evaluation now. Moreover, this type of nail only has 3 sizes with the smallest being 10mm. In order to install it, the diameter of the cavity must be 12mm (the average diameter of the Vietnamese medullary cavity is between 10 and 11mm which makes it unsuitable for the vast majority of Vietnamese).
Thus, the use of Precice and Stryde nails is a trend that is still being researched and applied at the moment. These nails are not ready to be widely applied. For Precice nails, the complication rate is still quite high, the nails are weak and the rehabilitation period required before the patient can walk normally is long. Stryde nails are strong and the patient can walk normally soon after surgery. However, they are not suitable for the physical condition of Vietnamese people. Both Precice and Stryde nails have limited stretching rates with the maximum lengths of 5cm (for 10mm nails), 6.5cm (for 11mm nails), and 8cm (for 13mm nails). Especially the prices are quite expensive. The average cost of a leg lengthening surgery using Precice and Stryde nails in the US and Europe is 95,000 – 105,000 USD; in Korea it is 70,000 USD (not including the cost of living during the outpatient period). Currently, these nails are not distributed in Southeast Asian countries.
In summary, leg lengthening using external fixation and internal intramedullary nailing can be troublesome for patients due to entanglement from the fixators. There is a risk of infection of the nail which requires great care of the nail. It leaves more scars and can only be applied to tibial lengthening. However, the legs can be stretched further, the rate of bone healing is high and compression can be restored earlier due to the use of stronger and denser internal nails. Therefore, we have not seen any cases of broken nails. The price is reasonable for the majority of Vietnamese people, only one tenth of the price for self-stretched nails made abroad.
When using self-stretched nails, the advantage is that it can be applied on both femurs and tibias. During the process of stretching, patients can live more comfortably, have convenient rehabilitation practices, avoid complications caused by fixators and have more appealing surgical scars. However, there still exists a small chance of nail jamming. Moreover, the nails are expensive, and the stretching length is limited (by a maximum length of 8cm). Most of these nails have a large diameter, larger than the medullary cavities of tibias and femurs of Vietnamese people who are of short stature (except for Betzbone nails). Therefore, at the moment, this type of nail is mainly used in some developed countries in Europe and North America. Through research and evaluation, we found that Betzbone nails are suitable and well applied to Vietnamese people.
Figure. Electronic self-stretching intramedullary nails
A: Fitbone nail * Source: Harris, M., Paley, D. (2013).
B: Precise nail * Source: Krieg, A. H. (2008).