Orthopaedics

 



Distraction osteogenesis
– an alternative to limb amputation

Dr Michael Weber, a specialist in limb lengthening and reconstruction, has moved his practice from Germany to the UAE because of the high demand for his services in the Arab world. Callan Emery speaks to the orthopaedic surgeon about his specialty.
 
A German doctor who specialises in limb lengthening and reconstruction has relocated his practice from Germany to the United Arab Emirates because of the high demand from this region for his expertise. Beside limb deformities acquired largely through trauma, the prevalence of limb deformities of congenital origin is considered to have a relatively high prevalence in the Arab world – due in large part to the high number of consanguineous marriages – although accurate figures are not readily available.

Dr Michael Weber, MD, PhD, a Professor of Orthopaedics and faculty member of the RWTH University in Aachen, Germany, uses an ingenious technique to lengthen limb bones called ‘distraction osteogenesis’. The procedure was pioneered 50 years ago by a Russian orthopaedic surgeon, Gavril Abramovich Ilizarov and offers a favourable alternative to limb amputation.

“These techniques can be used with patients of all ages from newborn to the elderly,” Dr Weber said. “The oldest patient I have operated on was 71. The surgery is minimally invasive, using highly specialised equipment.”

He explained that the lengthening and reconstruction of limb bones is an expensive procedure and that recent German government regulations restricting what he could charge patients meant that in many instances the devices required for the treatment – such as the Taylor Spatial Frame – cost more than he was allowed to charge for the treatment.

As more than 30% of his patients came from the Arab world he was motivated to relocate his practice from Germany to the UAE where he established the Center for Limb Lengthening and Limb Reconstruction at the American Hospital Dubai.

For a more than a year, Dr Weber has directed this new centre, the first of its kind in the UAE, where he receives patients from across the UAE, the wider region and Europe.

Speaking to Middle East Health, he was quick to point out that it was not only congenital factors that were responsible for limb deformities in the region. “Car accidents, for example, also account for many limb deformities, as well as weak bones resulting from vitamin-D deficiency due to a lack of exposure of the patients’ skin to the sun,” he said.

Although Dr Weber uses the distraction osteogenesis technique pioneered by Dr Ilizarov, he has himself developed a number of new techniques – such as the ‘Weber-Cable-Technique’ – which enable this procedure to be used for a wider range of indications. The Weber-Cable Technique is used as a salvage procedure for bone defects.

For those who can afford it, it is a lifechanging treatment enabling those who had been unable to walk or use one of more of their limbs, to do so again – or in the case of many paediatric patients, to do so for the first time.

Highlighting the extent to which this technique can be use to lengthen a deformed limb, Dr Weber pointed out that he lengthened the leg of one of his paediatric patients by as much as 22 cm to match the length of the other leg and enabling the patient to walk properly for the first time.

“In some parts of the world, like the US, where the treatment is very expensive, those who can’t afford it simply have their affected limb amputated,” he said.

He believes this happens a lot in this region as well, but not because they can’t afford the treatment, but rather because they don’t know it exists.

To this end, he has been involved in a number of educational seminars across the region, teaching other orthopaedic surgeons about this technique and how to use it.

Discussing the most recent weekendlong course, he said that some 35 doctors from Iran, Jordan, Oman, Saudi Arabia, Kuwait, Libya and the UAE attended. He said the course should be sufficient for them to start using some of these techniques provided they had sufficient experience in orthopaedic surgery.
 

Taylor Spatial Frame

Dr Weber points out that the technology supporting distraction osteogenesis continues to evolve. The most advanced external ring fixator to date is known as the Taylor Spatial Frame (TSF).

The TSF consists of two aluminium rings connected by six struts. Each strut can be independently lengthened or shortened. Connected to the bone by wires or half pins, the attached bone can be manipulated in six axes (anterior/ posterior, varus/valgus, lengthen/ shorten.) Angular, translational, rotational, and length deformities can all be corrected simultaneously with the TSF. Using computer analysis in 3D the TSF's unique parallel kinematics enables all six degrees of geometric freedom. This gives the surgeon complete freedom to correctly orient and align the broken bone segments.

The TSF is used in both adults and children. It is used for the treatment of acute fractures, mal-unions, non-unions and congenital deformities. It can be used on both the upper and lower limbs.

Once the fixator is attached to the bone, the deformity is characterised by studying the postoperative x-rays. The angular, translational, rotational, and length deformity values are then entered into specialised software online, along with parameters such as the ring size and initial strut lengths. The software then produces a “prescription” of strut changes that the patient can follow. The struts are adjusted daily by the patient until the correct alignment is achieved. Correction of the bone deformity can typically take 3–4 weeks. Once the deformity has been corrected, the frame is then left on the leg till the bone heals. This often takes 3–6 months, depending on the nature and degree of deformity.


Congenital deformities

Limb bone deformities requiring surgery can be either inherited or acquired. Congenital limb bone malformation has a relatively high prevalence in the Arab world gauging by the large number of these types of deformities that Dr Weber sees.

“Congenital deformities account for about 70% of my patients [in the Arab world],” Dr Weber said. The most common of which he treats are fibular hemimelia (the partial or total absence of the fibula), tibial hemimelia (the partial or total absence of the tibia), and congenital tibial pseudarthrosis.

In the “acquired” limb deformity category, deformities generally arise from non union of the bones after trauma, infection of the bone and vitamin-D deficiency.

“I treat a lot of congenital malformations as well as many acquired deformities from trauma injury when the bone doesn’t heal properly,” he said.

Following the diagnosis, treatment involves the use of one a number of ring fixator devices, such as the mini ring fixator, the Ilizarov apparatus, the Taylor Spatial Frame, or motorised nails, such as the Fitbone nail. All of these have specific indications for use.
 

The intramedullary nail

An alternative to the external ring fixator device is the intramedullary rod or nail. It is an internal device that is implanted in the intramedullary canal of a surgically fractured longbone. There is a motor inside the nail with an antennae attached which is implanted under the skin. With a remote device the patient can activate the motor within the nail via the antennae to lengthen the nail gradually and so steadily increase the length of the bone as it continues to grow to heal the fracture.

Dr Weber says his surgery has exclusive right to the Fitbone nail in the UAE. http://www.fitbone.dk/en/? Technique:The_Fitbone_nail

The Fitbone nail has several advantages:
•There is no connection through the skin
•No need for pin site care - and no pin hole problems
•The scarring is minimal
•The patients have less pain

 

Complications

It is essential that this procedure is carried out by an expert orthopaedic surgeon as there is a risk of severe bone infection and other complications like contractures of joints if the pins are not fitted correctly or the postoperative management is not appropriate.

Recommended reading: Complications of Ilizarov leg lengthening: a comparative study between patients with leg length discrepancy and short stature. – B. Vargas Barreto, et al.

Reference: Int Orthop. 2007 October; 31(5): 587–591. doi: 10.1007/s00264-006-0236-2 PMCID: PMC2266651 http://www.ncbi.nlm.nih.gov/pmc/ articles/PMC2266651


Lengthening the bone

There are a range of ring fixator devices; however, the procedure for using these devices is similar. After thorough measurements of the required length and correct positioning of the limb there is an initial surgery, during which the bone is surgically fractured and the external ring apparatus is attached with pins penetrating the soft tissue and into the bone – one part to the distal portion of the bone and the other the proximal segment. After 7 days the bone begins to form a fracture callous and the fractured bone begins to grow together. While the bone is growing, the frame is adjusted at regular intervals by turning a set of screws which gradually increases the space between the two rings and thus the proximal and distal portions of the bone are slowly drawn apart (distraction) while the fracture callous continues to grow between the two – in a sense tricking the bone to continue growing. This is distraction-osteogenesis.

“This is a natural process,” Dr Weber explained. “You always have a weaker and softer area in the middle of the callus so this is why you can do the lengthening. And all the surrounding tissue – nerves, muscle, tendons – grow with the bone as it is being lengthened – the same process as in a growing child.”

He said that the bone grows at a rate of about 3 cm per month.

“We always use some form of fixator device. However, we prefer to use the external ring fixator because it provides the best correctability of the deformities, the best mobility for the patients with full weight bearing and has all the different sizes we need for paediatric to adult patients,” Dr Weber explained. “Once the frame is fitted, the patient can walk around and lead a pretty much normal life. The patient will generally wear it for several months, depending on the length of new bone that’s required.”

As an alternative of the external fixator the implanted motorised intramedullary fitbone nail can be used for lengthening.

When the bone growth has reached the required length and the fracture callus completely maturated, the frame is removed and the treatment is complete.

 

Long-standing question in bone biology answered

A long-standing question in bone biology has been answered: It is the spindly extensions of bone cells that sense mechanical stimulation and signal the release of bone-growth factors, according to research from The University of Texas (UT) Health Science Center at San Antonio.

The study, reported recently in Proceedings of the National Academy of Sciences of the United States of America, offers an important clue for developing therapies to treat the bone-thinning disease osteoporosis and bone loss associated with aging, said Jean Jiang, PhD, senior corresponding author from the Department of Biochemistry, UT Health Science Center Graduate School of Biomedical Sciences.

Sensitive extensions

“Osteocytes are the most abundant cells in bone,” Dr Jiang said. “In the field of bone biology, there was a long-standing debate as to which part of the osteocyte senses mechanical loading. In this study, we demonstrate for the first time that it is the extensions, which are called dendrites.”

Regular physical exercise is highly beneficial in maintaining bone health and in prevention of bone loss and osteoporosis. Mechanical stimulation of the bone through weight bearing is critical for promoting bone remodeling, said Sirisha Burra, PhD, lead author from the Department of Biochemistry.

“Maintenance of bone health depends on the osteocytes’ ability to sense the stimulation,” Dr Burra said. “If osteocytes lose this ability, it could possibly lead to diseases such as osteoporosis. Hence, it is important to understand this mechanism.”

Mechanical impact

The Health Science Center collaborated with Southwest Research Institute in San Antonio to estimate the mechanical impact of force applied to the dendrites. Magnitudes of mechanical stress were determined.

“Understanding how bone cells sense and respond to mechanical signals within the skeleton is an inherently multidisciplinary problem,” said co-author Daniel P Nicolella, PhD, institute engineer in the Mechanics and Materials Section at Southwest Research Institute. “We determined the mechanical stresses applied to the osteocytes in these experiments so that they can be compared to the mechanical signals predicted to occur within the skeleton during routine physical activities.”

Intriguing idea

Apart from its clinical implications, the study is intriguing because it “brings in a novel thought that different parts of a single cell can have different material and sensory properties,” Dr Jiang said. “Different parts of the cell can react differently to the same stimulus. This is a very important fact to consider while studying cellular signaling and regulatory mechanisms.”

● Citation: doi: 10.1073/pnas.1009382107


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ate of upload: 25th Sep 2010

                                  
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