and Mark T. Dahl2
Department of Orthopedic Surgery, University of California – Irvine, Orange, CA, USA
Limb Length and Deformity Correction Clinics, Gillette Children’s Specialty Healthcare and University of Minnesota, St. Paul / Minneapolis, MN, USA
KeywordsRegenerateOssificationRate and rhythmFusiformDefect
The following step-by-step guide to the postoperative management of patients undergoing limb lengthening also applies to patients who are having a deformity corrected or a bone segment transported to overcome an osseous defect .
In Operating Room
Use gauze wraps to apply pressure on the operative sites.
Be sure to obtain final roentgenograms before the patient leaves the operating table. The limited image size of intraoperative intensified fluoroscopy often fails to reveal malalignment of the limb as a whole.
Postoperative Day 1
Physical therapy is started on the first postoperative day. The patient must “work” on preventing contractures before lengthening begins.
The patient’s bed must be flat, not elevated behind the knee. Place a pillow under the ankle to force the knee into extension.
Postoperative Days 2–4
The patient’s physical therapy program continues with progressive weight bearing and range of motion of the joints. As mentioned earlier, passive stretching is an important part of the physiotherapy program.
We often discharge the patient from the hospital on days 2, 3, or 4 postoperatively. At the time of discharge, the patient should be off parenteral pain medication, taking only oral painkillers.
Postoperative Days 5, 6, and 7 or Later
One of the most important days for the patient postoperatively is the day that distraction begins. This may occur while the patient is still in the hospital, or it may take place at the first outpatient visit. Remove sutures when appropriate. The latency interval (delay before beginning distraction) after insertion of the implant has allowed the first stage of fracture healing to commence. During distraction, the osteotomy site fracture begins to heal. The newly formed fracture callus attempts to “catch up” with the distracting bone ends, but, under most circumstances, does not consolidate the regenerate bone within the distraction gap until the neutral fixation period following elongation.
In general, the delay (latency) prior to distraction is 5–7 days, for the femur, but may be longer or shorter under certain circumstances. The latency for the tibia should be 10–14 days, since it does not form regenerate bone as readily as the femur.
In pediatric cases. The rapidity of bone growth means that the latency period should be only 4 or 5 days following osteotomy through healthy bone.
Where the corticotomy is oblique. The latency should be shortened by 1–2 days because oblique osteotomies heal more rapidly than transverse ones.
If there has been considerable comminution at the site of osteotomy (the latency interval should be lengthened by 3 or 4 days)
If there has been substantial displacement of the major fragments during osteotomy
If fragments were counterrotated (during torsional osteoclasis of the posterior cortex) more than 30°
If the bone is of poor quality—either extremely dense or osteopenic—the latency interval should be lengthened up to 14 days (or perhaps even longer), especially if the soft tissues surrounding the bone are also of suboptimal quality.
Following the latency interval, the patient is taught to distract the corticotomy gap 0.25 mm every 6 h. This rate and frequency may be altered, depending upon the clinical circumstances.
With an intramedullary lengthening nail, reaming of the marrow canal has the effect of reducing the rate of regenerate ossification. While the femur, surrounded on all sides by thick muscle, responds well to distraction at a speed of 1.0 mm/day (divided into three or four doses of 0.33 or 0.25 mm each), the tibia, whose anterior surface is subcutaneous, often has deficient maturation of the regenerate anteriorly. For this reason, experienced surgeons are now recommending tibial distraction at a rate of 0.75 mm/day in three doses of 0.25 mm each .
For an adult with dense bone and suboptimal surrounding tissues, a more appropriate initial rate and frequency would be 0.25 mm every 12 h. In pediatric cases, however, such a slow rate of distraction might result in premature osseous consolidation, especially if the corticotomy is oblique and through healthy tissues. The fastest rate of distraction, however, is usually 1.0 mm per day at each widening distraction gap.
Have the patient (or responsible individual) practice distraction at the first postoperative visit, making sure that everything is understood.
Visualizing the Regenerate New Bone
One can easily misinterpret new bone formation in the widening distraction gap if the central beam of the x-ray tube is not directly over the middle of the distraction zone, especially if the tube is close to the patient. Likewise, if the limb is not perpendicular to the x-ray beam (as can happen if a knee flexion contracture is present) and parallel to the image receiver (either film or sensitive plate), distortion and cortex overlap may give the false impression that the bone is forming during distraction, when, in fact, it is not. Repositioning the tube and plate for orthogonal imaging, or repositioning the patient, may be necessary (Figs. 8.1 and 8.2).
To best judge the regenerate, the x-ray beam must be perpendicular to the bone and film (left). Bone angulation, in relation to beam and film , can cause a false reading of regenerate bone in the gap (right). Copyright 2016 NuVasive
Methods to correct the issue of parallax : either tilt the beam and film (left) or reposition the patient (right). Copyright 2016 NuVasive
After One Week of Distraction
The next important contact with the patient comes after 1 week of distraction. Usually, the patient is at home by this time. The first set of roentgenograms should show a gap between the bone fragments that corresponds in width to the rate and frequency of distraction. Thus, if the patient has been lengthening at a rate of 1.0 mm per day for a week, the measured bone gap should be 7.0 mm.
Plan the roentgenographic views to obtain maximum information with the least amount of x-ray exposure for the patient. As a rule, the central x-ray beam must be perpendicular to the osteotomy gap. To be helpful, such a view must show the bone lengthening in the profile of the anticipated deformity. For example, a tibia will deform with its apex anteromedially; hence, the anterolateral oblique view will demonstrate such a deformation before any other projection.
If the bone fragments are not separating, consider the osteotomy incomplete (it is unlikely that the bone will have healed by this time). At times, a residual bridge of the bone holding the fragment together can be pulled apart by continuing distraction, thereby disrupting the bridge. The patient must be warned that he or she may experience acute severe pain in the limb if the bone suddenly yields to the forces generated by the elongated implant. In any case, do not distract the intramedullary lengthening nail for more than 5.0 mm if the bone is not separating, because the sudden elongation can damage nerves or vessels.
The absence of progressive widening of the distraction gap usually means a repeat trip to the operating room for completion of the corticotomy or osteotomy.
Do not expect to see any new bone formation in the gap as soon as 1 week after distraction starts, although a cloudy regenerate may be observed in young children.
Two Weeks of Distraction
After 2 weeks of distraction, the gap should be 14 mm wide (or less if the limb is being elongated at a rate slower than 1 mm per day). Regenerate new bone may not be visible at this stage of distraction. For this reason, the patient should stay on the course and continue distraction at the same rate.
Three Weeks of Distraction
By the third week of distraction, some regenerate new bone should be visible in the distraction gap, usually, as a cloudy haze in adults or a fully formed regenerate (with striations and an early interzone) in children. At this stage, the absence of any evidence of regenerate new bone means that the rate of distraction should be slowed—perhaps to 0.25 mm every 8 or 12 h.
Four Weeks of Distraction
At the end of the fourth week of distraction, the gap will be 28 mm wide at a rate of 1 mm per day. By this time, regenerate new bone must be clearly evident in the distraction gap. If not, reverse distraction—closing the gap at a rate that is tolerable to the patient—generally about 1 or 2 mm per day in divided doses of 0.25–0.5 mm every 6 h. Usually, regenerate new bone will form and be visible before the gap is completely closed, especially if the patient has been bearing weight on the limb.
If no bone forms by the time the gap is fully closed, wait a longer latency interval than initially employed (Ilizarov recommends doubling the latency interval), and begin distracting again at a slower rate (half speed). Follow the post-distraction strategy as before.
Visits During Distraction
With good regenerate formation, the patient is evaluated on a weekly basis. Assess the quality of the regenerate new bone roentgenographically, slowing down, speeding up, or even stopping distraction depending on the quality of bone forming in the distraction gap. Professor Ilizarov recommends resting the limb (stopping distraction) 1 or even 2 days for every 10 days of distraction, although this is rarely done nowadays.
During the weekly visits, check the range of joint motion of the limb. Any progressive loss of motion must be dealt with immediately. In some cases, intensifying the frequency of physiotherapy will overcome the problem. If not, the patient may have to be admitted to the hospital for treatment. It may be necessary to stop distraction altogether during this period, in an attempt to regain motion.
It is critically important to check the joints for any evidence of subluxation—a problem that could lead to complete dislocation if left unnoticed. Subluxation will mostly involve the knee. Typically, a flexion deformity has preceded the subluxation. The patient will display a “ski-slope knee,” the outward appearance of posterior tibial subluxation on the femur. Obtain a lateral roentgenographic view of the knee. On a roentgenogram of a normal knee, the center of the tibial plateau will be directly under the center of the femoral condyles.
As mentioned in the section dealing with general principles, it is both safer and wiser to stop lengthening a limb that develops a contracture and plan a second-stage procedure at a later time to complete limb elongation.
During lengthening, the bone may deform. When this occurs, correct the deviation or it will progressively become worse. The tactics for deformity correction vary, with blocking screws used for intramedullary lengthening nails .
Judging the Regenerate
The progress and success of a limb lengthening protocol depends, to a considerable extent, on assessing the quality of regenerate bone in a widening distraction gap. Most commonly, this is done with serial standard AP and lateral x-ray studies taken at frequent intervals while bone fragments are moving with respect to each other, and less often during the neutral fixation phase, when the regenerate matures and hardens.
When external fixators are used for limb lengthening, the matter of corticalization of the regenerate is critical, because removal of the frame before the new bone can support weight leads to either bending or breaking of the regenerate.
Although classic Ilizarov teaching is to leave the frame on a limb until the risk of bending or breaking is nil, Western surgeons, Paley in particular,  pressed by their patients for premature fixator removal, have devised devise schemes to support the regenerate with an intramedullary device inserted at the time of fixator application.
Alternatively, a nail or plate can be inserted at the time the frame is removed .
To some extent, lengthening with an intramedullary nail has reduced, but not eliminated, concern about the risk of regenerate bending or fracture because the nail should prevent either eventuality. However, motorized nails are not nearly as strong as trauma nails, so deficient bone formation during elongation, combined with early weight bearing, risks nail breakage and loss of limb alignment—a potentially worse problem that bending or breaking of a bone through newly formed regenerate with no implant in place .
For this reason, the criteria employed with external fixator limb lengthening cases to determine when to allow frame removal and unprotected weight bearing also apply to limb elongation with intramedullary lengthening nails. As mentioned elsewhere, at a minimum, full corticalization of three of four cortices (seen on AP and lateral x-ray views) is required before full weight bearing is allowed. Moreover, the incompletely ossified cortex should be nearly completely corticalized, with, at most, a small triangular defect (called a rat-bite) seen on imaging studies.
Experienced Ilizarov surgeons frequently receive x-ray studies from colleagues asking if the bone in the distraction gap is solid enough to permit frame removal. The bone is rarely ready. Solid-looking regenerate is easy to identify, and anything questionable isn’t ready.
Classification of Regenerate
Li et al. created a classification system based on the quality of ossification and the shape of bone formed in the regenerate zone . The authors identify five distinct shapes (fusiform , cylindrical, concave, lateral, and central) and three different levels of density (low, intermediate, and normal). Likewise, they categorize four patterns of distribution of bone formation (sparse, homogeneous, heterogeneous, and lucent). Combining the latter two features, Li et al. describe ten types of features: soft, stripe, speckle, adjacent, halftone, uniform, irregular, sawtooth, solid, and cystic defects.
Bone Mineral Density
Because such assessments are subjective, a number of researchers have tried to establish quantitative methods of determining when the bone in a regenerate zone is solid enough for fixator removal and/or full weight bearing. Most of these techniques employ some quantitative comparison between the bone along the edge of the regenerate and the bone in adjacent normal region .
Pixel Value Ratio
With digitalized x-ray images, one can compare the intensity of pixels at the edge of the regenerate to pixels in the same location in the adjacent normal bone and create a ratio of such intensities, the “pixel value ratio” (PVR) . Such ratios correspond quite well to relative bone mineral density (BMD) .
In many ways, such quantitative measures correspond to what experienced surgeons do visually when assessing regenerate ossification. We look at the whiteness of the bone along the edge of regenerate cortices and compare it in our mind’s eye to the whiteness of the cortical bone above and below the distraction zone. This visual whiteness comparison is, in reality, a pixel value ratio. If the pixels that make up the image of the regenerate cortex equal in brightness the pixels that make up the adjacent normal cortex, then the ratio value is 1.0 and the cortex can be considered solid.
Thus, using PVR improves regenerate maturation assessment compared to simple BMD measurements with a DEXA scan device (Markel, 1993 #1629).
Diagnostic ultrasound, used increasingly in physician’s offices for joint aspiration, injections, and diagnoses, has the potential for reducing x-ray exposure to patients undergoing limb lengthening. The modality is most often used therapeutically for stimulating maturation of the regenerate  but only rarely has diagnostic ultrasound been proposed for assessing the regenerate. Luk et al. used ultrasound for quantifying mineralization of the regenerate in rabbits subjected to limb elongation . Acoustic reflection in 2D and 3D ultrasonography and ultrasonometry proved more sensitive to early mineralization of newly forming regenerate than did computerized radiography .
Clinicians have not, as yet, taken up this proposal, perhaps because early mineralization is not as important clinically as end-stage calcification of the periphery of the regenerate mass, which shows up so well on ordinary x-ray images and can be quantified with the technology described above.
All of the above techniques were developed during an era when the only means of predictably elongating a bone was to use an external skeletal fixator and Ilizarov principles. Nowadays, however, lengthening with an intramedullary motorized nail is becoming increasingly popular among surgeons in the field. With such a device, the metallic nature of the implant may interfere with pixel quantification and thus reduce the value of such determinations. The problem, as of this writing, has not been fully explored.
The Regenerate Around a Lengthening Nail
As more surgeons use intramedullary lengthening nails , a pattern of regenerate formation that was infrequently observed with external fixator lengthening is now becoming more common, namely, the eggshell > hollow > fusiform archetype. In the past, this pattern, when observed during fixator lengthenings, was considered a sign of instability at the widening distraction zone. After all, a bulging regenerate resembles normal fracture callus when healing of an intrinsically unstable long bone fracture occurs in a cylindrical cast unaccompanied by internal or external fixation. In essence, nature creates a scaffold of new bone at the periphery of a fracture hematoma where the effect of moving bone fragments is least likely to disrupt osteogenesis. The healing bone matures from the outside inwards.
A bulging regenerate, hardening on the outside first, was initially viewed with some concern by limb lengthening surgeons, but time has shown that most regenerates displaying this pattern consolidate nicely, although it takes a while. Protected weight bearing must continue until the well-established three cortices rule is obeyed .
Patterns of Regenerate
We have modified Li et al.’s  classification scheme for regenerate ossification patterns to include variants seen with intramedullary lengthenings as well as other patterns characteristic of normal and rapid maturation of the regenerate (Figs. 8.3, 8.4, and 8.5).
Regenerate at 30 mm: (a) sparse, (b) patchy, (c) fair, (d) good, (e) excellent
Regenerate at 30 mm: (a) concave, (b) central, (c) lateral, (d) rat bite, (e) cylindrical
Regenerate at 30 mm: (a) cystic, (b) mature cystic, (c) eggshell, (d) hollow, (e) fusiform
Biology of the Regenerate
Regenerate new bone in a widening distraction gap is like any rapidly multiplying living thing: its growth can be either retarded or enhanced by environmental factors. In this sense, a limb lengthening surgeon is more a gardener than a carpenter. Thus, anything that slows or accelerated normal fracture healing will have a similar effect on the regenerate in a distraction gap. After all, an osteotomy that creates a regenerate is a non-displaced fracture that heals in an ordinary and natural manner for the 5–7-day latency interval.
Biological Factors Retarding Regenerate
Environmental influences that slow fracture callus and regenerate maturation can be divided into biological, chemical and mechanical factors. Among the biological factors are those directly and indirectly impacting the site of fracture or osteotomy, including soft tissue damage (either acute or old), local circulation, the degree of comminution, anemia, severe malnutrition, vitamin D deficiency, diabetes, hypothyroidism , and past or present radiation of the local tissues.
Chemical Factors Retarding Regenerate
The chemical factors that adversely influence bone and regenerate healing are those that reduce inflammation, the first phase of fracture healing. Thus, any anti-inflammatory medication, steroidal or nonsteroidal, has this adverse effect. Likewise, commonly used over-the-counter pills, while not as powerful as prescription medications, should not be used during distraction osteogenesis.
Mechanical Factors Retarding Regenerate
Mechanical factors that retard regenerate ossification center around weight bearing activities. With external fixation, weight bearing to tolerance is promoted. Unfortunately, when intramedullary lengthening nails are employed, concern about nail breakage makes surgeons exceedingly caution about unprotected weight bearing. Nevertheless, partial weight bearing, as discussed below, remains a hallmark of proper postoperative care during limb elongation.
Throughout the course of regenerate maturation, the patient must be encouraged to bear weight on the limb, lest the regenerate fail to ossify (Fig. 8.6).
Patience is a virtue. (a–d) Gradual distraction. (e) Wispy new bone formation at the periphery of the regenerate, a common pattern seen in intramedullary lengthening. (f–h) With partial weight bearing, the regenerate matures
Visits During Maturation
Evaluate patients monthly during regenerate maturation, checking the quality of the maturing bone with roentgenograms. The patient’s weight-bearing and functional capacity should increase steadily during this period. Investigate any decline in the patient’s ability to use the elongated limb.
Tardy Regenerate Ossification
At times, maturation of the regenerate can be maddeningly slow. This problem is more distressing when an external skeletal fixator has been used for the procedure, when compared to an intramedullary lengthening nail. This is because the patient, perhaps expecting a short fixator application, comes to hate the device surrounding his or her limb. Indeed, strategies such as lengthening over an intramedullary nail (a combination of an intramedullary nail and external skeletal fixator) or lengthening and then nailing (substituting an intramedullary nail for an external fixator before the bone is fully mature) have become popular with many surgeons [15–17].
An intramedullary lengthening nail is far more tolerable than a cumbersome external device secured to the limb with transosseous pins or wires. Thus, patient-doctor negotiations, so common during external fixation treatment, are rarely as intense with intramedullary devices.
Moreover, it appears that the regenerate matures faster with IM lengthening, in a case matched study, when compared to circular external fixator lengthening .
Stimulating Regenerate Ossification
On occasion, regenerate maturation slows progressing or stops altogether, with a radiolucent defect where bone should be forming. Needless to say, any factor—biological, chemical, and mechanical—that inhibits bone formation should be eliminated. Inquiring about over-the-counter anti-inflammatory medication, for instance, may yield a surprising affirmative answer. Poor nutrition, low vitamin D, concomitant diseases, smoking, and other adverse factors will defeat any surgeon waiting for regenerate to mature (Fig. 8.7).
Absent regenerate ossification. At a 30 mm gap size, when faced with absence of early evidence of regenerate new bone in a distraction gap, slow, stop, or even reverse distraction, advancing at a much slower rate thereafter. A bone graft was needed. Courtesy of John E. Herzenberg, M.D. Used with permission from the Rubin Institute for Advanced Orthopedics, Sinai Hospital of Baltimore
A modality that has been proven to enhance fracture healing will likely do the same for a distraction gap regenerate. Needless to say, weight bearing is first on the list of mechanical factors that can enhance bone formation within the regenerate. The amount of weight is not as important as the rhythmic pattern, one step per second, typically supported with crutches or a walker at first and then a cane later. The patient must experience what 30 pounds of weight bearing feels like on a bathroom scale, to get the proper sensory feedback from the lower extremity. As the weight increases, the patient needs to check again on a scale, for the same reason as above.
With external fixation lengthening, pain is often a serious inhibitor of ambulation, almost always relate to transcutaneous implant inflammation. Since no through-skin implant is used with intramedullary lengthening nails, such pain will not occur. Likewise, the pain of limb stretching settles down once length goal is achieved, so weight bearing must be encouraged.
Patchy osteopenia of the bone in adjacent regions of the bone surrounding the regenerate is a sign of inadequate weight bearing. After all how could the regenerate ossify if the rest of the limb is de-ossifying ?