Limb lengthening is a specialized orthopedic procedure designed to increase the length of a bone, typically in the legs, to correct significant limb length discrepancies or to increase stature. The technique involves a controlled fracture followed by the gradual, mechanical separation of the bone segments, a process called distraction osteogenesis. Because this method requires intentionally creating and managing a fracture while stretching surrounding soft tissues, the risk profile is significantly higher and more complex than most routine orthopedic surgeries.
Acute Surgical Risks
The initial phase involves the surgical implantation of the lengthening device and presents immediate risks common to any major operation. Anesthesia complications are always a consideration, ranging from minor reactions to severe events, especially during long surgical times. Surgeons must be meticulous during the placement of pins, wires, or an intramedullary nail to avoid critical damage.
Immediate neurovascular injury is a serious, though rare, complication where major nerves or blood vessels are damaged during hardware insertion. Injury to the peroneal nerve, for example, can result in foot drop and permanent gait abnormality. Another acute risk is a fat embolism, where fat globules from the bone marrow enter the bloodstream during the bone cutting process, potentially causing a life-threatening pulmonary embolism or respiratory distress.
Deep surgical site infection, known as osteomyelitis when it reaches the bone, is also a risk following the initial operation. Any deep infection requires aggressive antibiotic treatment and often necessitates additional surgery to remove the infected hardware. The post-operative period carries a risk of deep vein thrombosis (DVT), a blood clot that can migrate to the lungs and cause a pulmonary embolism, a risk heightened by the required period of immobilization.
Complications During the Active Lengthening Phase
The active lengthening phase begins five to ten days after surgery, when the bone segments are slowly pulled apart, typically at one millimeter per day. This period can last several months and is characterized by persistent discomfort and a high incidence of complications. Severe pain requiring intensive management is a constant side effect as the bone, nerves, and muscles are stretched.
The most common complication is a pin or wire tract infection, particularly with external fixators, occurring where the metal pins enter the skin. These superficial infections are often treated with oral antibiotics but can progress to a deep-seated infection if neglected. Patients also face device-related issues, such as mechanical failure where the internal nail or external frame may bend, loosen, or break, often necessitating unplanned surgery to replace the faulty hardware.
The rapid stretching of soft tissues can lead to temporary nerve irritation, causing numbness, tingling, or increased sensitivity (hyperesthesia). If the lengthening rate is too aggressive, it can cause compartment syndrome, where swelling and pressure within the muscle compartments cut off blood flow and damage nerves. The surgeon frequently adjusts the daily lengthening amount based on radiographic evidence of new bone formation.
Structural and Bone Healing Issues
The success of limb lengthening depends on distraction osteogenesis, the body’s ability to generate new bone tissue in the gap created by the stretching. A primary complication is non-union, where the bone fails to produce enough new tissue, leaving a fibrous gap that requires a bone graft and further surgery. Conversely, premature consolidation occurs when the bone heals too quickly, bridging the gap before the desired length is achieved, which requires the surgeon to re-fracture the bone.
Delayed union is a common issue where the new bone forms too slowly, dramatically prolonging the time the patient must wear the fixation device. This delay increases the overall treatment time from months to over a year and elevates the risk of other complications. The healing index is a metric used to track this process, with a high index indicating a delayed union.
Another significant structural problem is malunion, where the new bone heals in an incorrect position, resulting in an angular or rotational deformity of the limb. This misalignment can permanently alter the patient’s gait and put undue stress on adjacent joints. Even after successful consolidation and hardware removal, the patient is at risk for a refracture of the newly formed bone if the hardware is removed prematurely or if high-impact activity begins too soon.
Long-Term Functional Impairments
Even when bone healing is structurally sound, the soft tissues—muscles, tendons, and nerves—do not always adapt to the new length as effectively as the bone. The most common long-term functional impairment is joint stiffness and the development of contractures, particularly in the knee and ankle. A contracture occurs when muscles and tendons fail to stretch adequately, becoming permanently tight and fixing the joint in an awkward position.
Joint stiffness limits the range of motion and can severely impede mobility, often requiring intensive, long-term physical therapy or additional surgical procedures to lengthen tight tendons. Patients may also experience residual gait abnormalities, such as a noticeable limp, because the muscles are weaker or the biomechanics of the limb have been permanently altered. Reduced gross motor function and less vitality can persist long-term.
Chronic regional pain is another potential long-term consequence, persisting long after the hardware has been removed and the bone has healed. This pain can stem from nerve sensitivity issues, scar tissue, or the altered stress placed on the joints. Long-term follow-up studies suggest that a reduction in physical function and persistent pain are common trade-offs, particularly if a significant leg length difference remains.