- Esser, S.M., Vlietstra, N.J., Farley, D.P., Medicherla, A., Sokn, S.A., Collins, C., McCarthy, J.J, Ploeg, H.L., Zinn, M.R., “An Extramedullary Three Degree of Freedom Limb Deformity Correction Device for Pediatric Applications”, ASME Journal of Medical Devices, submitted March, 2013.
Unequal limb length is common among the human population. Roughly 10% of the world population experiences some mild case of limb shortening. Leg length discrepancy of over 1 cm is seen in 23% of the entire population. Around 30,000 individuals in the United States currently require a corrective device.
Short limbs are a problem that can severely alter the typical growth of a person, particularly children. There are a number of causes that can lead to this abnormality including congenital birth defects, trauma, growth plate arrest, and most commonly osteomyelitis. While shortening of the upper limbs may not cause any significant mobility problems, the shortening of a lower limb can severely affect one’s quality of life. There are myriad of approaches to solve this problem. Some of them are as follows,
- External Fixation devices (EFD) like Ilizarov External Fixation Device, the Taylor Spatial Frame™, and the Monolateral External Fixation Device
- Implantable Intramedullary Devices (IID)
The EFDs have complications like connection of the device itself to the bone using pins and infection at pin insertion sites. These pin or wire site infections can lead to severe pain, inflammation of the limb, osteomyelitis and pathological fractures. Other issues associated with the distraction rate of the bone include neurovascular complications due to rapid length distraction2; contractures of the soft tissues in the limb, as muscle might not be able to accommodate the rapid changes in bone length; and the possibility of partial and full dislocations of adjacent joints during the distraction process. Additional issues that may arise during the distraction process associated with bone formation may involve osteoporosis of the newly distracted bone, which may be due to delayed‐, premature‐, and or non‐union of the newly distracted bone. Another serious complication tends to occur with the Monolateral Lengthening Device. The pins inserted into the bone may produce a cantilevered effect on the bone that can promote angular deformities as the bone distracts.
The most prominent complication of the IID is that an Osteotomy is necessary to completely implant the device. This alone carries an increased risk of osteomyelitis. In all implantations, the epiphyseal plate will be compromised, a narrow medullary canal can discount the patient, the proximal end of the device will fuse to the bone, and the IID will permanently be fixated inside the medullary canal of the distracted bone. With an IID, lengthening distractions are the only option and any angular corrections must be adjusted at surgery or acutely. Despite the increased axial stability associated with the mechanical alignment of the device and the bone, the distracted leg cannot withstand the stress of full weight bearing.
A suggested solution that combines the technologies of the intramedullary lengthening devices and the external fixator devices is an extra medullary implantable device.
The key principles of the device include the following capabilities:
- Allows for distraction and compression
- Can be controlled remotely
- Implantable via minimally invasive techniques
- Allows for correction of angular deformities
- Allows for infusion of bone growth factors and other medications (e.g. pain medications or antibiotics)
We are grateful for the support of
- Wisconsin Innovation & Economic Development Research Program (IEDR)
- UW-Madison Research Funding Program (Fall Competition)