Advances in Pediatric Limb LengtheningPart 1

Christopher Iobst, MD

Investigation performed at theNemours Children’s Hospital,Orlando, Florida

COPYRIGHT © 2015 BY THEJOURNAL OF BONE AND JOINTSURGERY, INCORPORATED

» Integrated fixation techniques continue to evolve and help todecrease the external fixator duration for pediatric patients under-going limb lengthening.

» Intramedullary limb lengthening is available for pediatric patients.Although this technique has many advantages, the surgeon still needsto be vigilant about potential lengthening complications (contractures,joint subluxation, fractures).

» Preliminary surgery may be necessary to prepare the limb for safelengthening.

Pediatric limb lengthening is anexciting and rapidly developingfield. The primary goal is toproduce healthy regenerate bone

of the desired length without complications.In addition, the experience should be as easyand comfortable as possible for the patientand his or her family. Innovative surgicaltechniques and devices continue to pushsurgeons closer to being able to consistentlyachieve these goals.This reviewwill provide acomprehensive summary of the latest ad-vancements in pediatric limb lengtheningin two parts. This part, Part 1, will coveradvances in the preoperative assessment andmethods to decrease the time spent in anexternal fixator. Part 2 (http://reviews.jbjs.org/content/3/9/e4), which will be pub-lished in a future issue of JBJS Reviews, willcover advances in techniques designed todecrease the time to union and methods torecognize and to avoid complications1.

Preoperative Patient EvaluationClassificationIn pediatrics, it is unusual for a patient topresentwith only a limb-lengthdiscrepancy.

Most patients present with additionalpathologic conditions such as angular, ro-tational, and/or translational bone defor-mities. The stability of the joint proximaland distal to the lengthening segment mayalsobe compromised.The surgeon thenhasto choose whether these additional defor-mities can or need to be corrected andwhether to perform their correction com-binedwith, before, or after the lengthening.Joint contractures can also complicate thepicture. A comprehensive and accuratepreoperative assessment of the limb defor-mity is essential for successful treatment.Two recent classification schemes havebeendescribed to account for the variabilityin deformity presentation. Manner et al.described grading the deformity on thebasis of the number of dimensions involved.Forexample, a one-dimensionaldeformity isconsidered Type I and a four-dimensionaldeformity is Type IV2. The LLRS AIM in-dex, a mnemonic indicating seven pretreat-ment domains (Location and number ofdeformities, Leg-length inequality at matu-rity, Risk factors, Soft-tissue coverage,Angular deformity, Infection/bone quality,

Disclosure: The author did not receive payments or services, either directly or indirectly (i.e., via his

institution), from a third party in support of any aspect of this work. He, or his institution, has had

a financial relationship, in the thirty-six months prior to submission of this work, with an entity in

the biomedical arena that could be perceived to influence or have the potential to influence what is

written in this work. The author has not had any other relationships, or engaged in any other

activities, that could be perceived to influence or have the potential to influence what is written in

this work. The complete Disclosures of Potential Conflicts of Interest submitted by authors are

always provided with the online version of the article.

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andMotion/stability of the joints aboveand below), is a validated rating scaledesigned to assess the complexity of gen-eral lower-limb deformities3. It accountsfor seven domains: the location of thedeformity, leg-length inequality, medicalrisk factors, soft-tissue assessment, angulardeformity, infection andbonequality, andmotionand stabilityof the joints (Table I).

Congenital Compared with AcquiredLimb-Length DiscrepancyAn important first distinction in theevaluation process is to determine if thelimb-length discrepancy is due to acongenital or an acquired condition.Congenital limb-length discrepanciesare known to be more challenging totreat successfully and require a differ-ent thought process in their planning.Gordon et al. reported a complicationrate of 44% (eleven of twenty-five) forcongenital limb-length discrepanciescompared with 17% (two of twelve) foracquired limb-length discrepancies4.Launay et al. found an increased riskof fracture in patients with achondro-plasia if lengthening was performed be-fore the patient age of nine years and ifthe latency period was less than sevendays5. They also found femoral fracturesin all patients undergoing lengtheningfor congenital femoral deficiency whenthe lengthening percentage exceeded15%and the latency periodwas less thanseven days. The pathoanatomy of thecongenital long bone deficiencies (e.g.,congenital femoral deficiency, tibialhemimelia, or fibular hemimelia) con-tinues to be elucidated. A better under-standing of the bone and soft-tissuedeformity has allowed new reconstruc-tion techniques to be developed. Forexample, a Paley Type 1b congenitalfemoral deficiency is described as a com-bination of abduction, flexion, varus,and external rotational deformities atthe hip. A stepwise reconstruction thataddresses each one of these abnormalitieshas been described6.

Preoperative ConsiderationsThe concept of preparatory operativetreatment has been introduced6,7. This

refers to preparing the limb for length-ening by first stabilizing the adjacentjoints and removing known soft-tissuerestraints. For example, lengtheningfor congenital femoral deficiency canlead to subluxation or dislocation ofthe knee and/or hip joints. Therefore,any acetabular dysplasia should beaddressed with a pelvic osteotomy priorto lengthening. The knee joint mayneed to be protected by extending thefixator across the joint or may need to bestabilized by performing a simultaneousligament reconstruction at the time ofthe lengthening. Soft-tissue restraints,such as the iliotibial band, also need tobeaddressed at the time of the lengthening.Similar preparation has been outlinedprior to lengthening in patients withfibular hemimelia6. This stepwise andcomprehensive approach is vital to thesuccess of the lengthening.

The surgeon must also be cogni-zant that joint contractures can influ-ence the appearance of limb-lengthdiscrepancy. The hip, knee, and anklejoints need to be tested for range ofmotion. Patients can have a true struc-tural limb-length discrepancy, a func-tional limb-length discrepancy, or both.Adduction contracture of the hip, hipflexion contracture, and knee flexioncontracture are contractures that appearto shorten the limb. Hip abductioncontracture and equinus contracture cancause a limb to look longer. Sagittalplane analysis is often overlooked but isvery important. A standing full-lengthlateral radiograph can be made to eval-uate the osseous and soft-tissue defor-mities. This radiograph is made byhaving the patient stand with his or herfoot facing straight ahead and the cas-sette parallel on the lateral aspect of thedesired limb. Without moving theplanted foot, the pelvis and oppositelimb are then externally rotated 45°away. This maneuver allows the radio-graph beam to capture the full lengthof the limb from the hip to the anklewithout obstruction. Externally rotatingthe knee of the target limb about 10°also helps to get a true lateral view ofthe knee with this technique.

It is critical that the surgeon’s pre-operative assessment anticipates factorsthat may predispose the patient to poorbone formation. Host-related factors(theuseofnonsteroidal anti-inflammatorydrugs or systemic illness), local factors(scarred soft-tissue envelope, overlyinginfection, or prior radiation therapy),and iatrogenic factors (poor osteotomylocation selection, suboptimal osteot-omy technique, a.1-cm gap at theosteotomy site during the latency phase,or application of a mechanically unstableframe configuration) all contribute topotential impairment of healthy boneformation8. Prolonging the latency pe-riodordecreasing thedistraction ratemaybenecessary in suchcases toovercometheobstacles to producing a healthy regen-erate bone.

Patient selection for limb length-ening is also extremely important. Limblengthening can be a long, stressfulprocess for everyone involved. A preop-erative assessment of the patient’s psy-chosocial situation is recommendedbefore starting the lengthening9. Riskfactors for a more challenging treatmentprocess have been identified, such asliving with a single parent, having apreexistingmental health condition, andhaving a history of operative treatment.

Assessing GrowthAccuracy in predicting the total limb-length discrepancy at skeletal maturity iscritical when trying to make manage-ment decisions inpediatric patients.TheMultiplier method calculates a coeffi-cient for each age to represent the re-ciprocal of growth remaining10. Thecoefficient is independent of growthpercentile, race, nationality, and gener-ation. The Multiplier method has beenshown to be reliable using chronologicage prior to the adolescent growth spurt.However, skeletal age is more accuratethan chronologic age once the adolescentgrowth spurt has begun11. There areseveral free smartphone applications(Multiplier [Rubin Institute for AdvancedOrthopedics, Baltimore, Maryland] andPaley Growth [Paley Foundation, WestPalmBeach, Florida]) available that allow

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TABLE I LLRS AIM Index for Limb Deformity*

Domain Score (points)

Location (no. of deformities per limb of$10° angulation in separate planesand rotation all count as separate deformities)

No deformity 0

One deformity 1

Two deformities 2

Three deformities 3

More than three deformities 4

Leg-length inequality (estimate at skeletal maturity)

0 to 2 cm 0

.2 to 5 cm 1

.5 to 10 cm 2

.10 to 15 cm 3

.15 cm 4

Risk factors (assess clinically)

None 0

Age of less than five or more than forty years Add 1 point

Smoker Add 1 point

Obesity Add 1 point

Other disease (e.g., diabetes) Add 1 point

Soft-tissue coverage

Normal 0

Bruising or contusion 1

Scarring (open grade I) 2

Poor coverage (open grade II) 3

Inadequate coverage (open grade III) 4

Angular deformity (measure and assign greatest primary deformity)

0° to 10° 0

.10° to 20° 1

.20° to 40° 2

.40° to 60° 3

.60° 4

Infection and bone quality (select the most severe)

Normal 0

Osteoporotic 1

Dysplastic 2

Infection 3

Combination 4

Motion and stability of the joints above and below

Normal 0

Decreased motion (,60% of normal) 1

Subluxation of joint 2

Dislocation of joint 3

More than one joint affected 4

LLRS AIM Index scoring (scores range from a minimum of 0 pointsto a maximum of 28 points)

Normal 0

Minimal complexity 1 to 5

Moderate complexity 6 to 10

Substantial complexity 11 to 15

High complexity 16 to 28

*LLRS AIM is a mnemonic of the seven criteria that are required to determine the index.

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quick, easy calculations to be performedin the office setting.

Studies of growth have also iden-tified several useful concepts when ana-lyzing a patient with a limb-lengthdiscrepancy12. The tibial length remainsat a constant 80% of the femoral lengththroughout growth. These relativelengths remain the same regardless of theposition of the child on the growthcurve. Peak growth velocity in the lowerlimbs occurs six months earlier thanspinal growth peak velocity. Growth inthe lower limbs ceases two years andsix months after the onset of puberty.This correlates with the closure of thedistal phalangeal physes, the closure ofthe elbow apophysis, and Risser stage1. Generally accepted methods for pre-dicting the final limb-length deficit atskeletal maturity for congenital malfor-mations have been proposed: to calcu-late the final limb-length discrepancy,the limb-length discrepancy can bemultiplied by 5 at birth, by 3 at thepatient age of one year, by 2 at the pa-tient age of three years in girls and fouryears in boys, and by 1.5 at the patientage of seven years in girls and boys.

Radiographic EvaluationRadiographic assessment of limb-lengthdiscrepancy continues to evolve and tobecome more precise. Children whohave a clinically important limb-lengthdiscrepancy often require multiple ra-diographs to plan treatment and tomonitor outcomes. Therefore, the idealradiographic method for evaluating alimb-length discrepancy should be easilyavailable, accurate, and reliable andshould permit analysis of the entirelower-extremity alignment with mini-mal radiation exposure and no magnifi-cation error13,14. At present, the bestcombination of these traits is a standingfull-length anteroposterior digitalradiograph of both lower extremities,with blocks under the short leg to levelthe pelvis, utilizing a magnificationmarker. Although scanograms or ortho-roentgenograms are designed to elimi-nate magnification errors and are readilyavailable, they have been found to

overlook vital information such as thefoot or ilium height, the mechanical axisof the limb, any coexisting angular de-formities, and the etiology of the leg-length discrepancy15. In addition,standing full-length radiographs havebeen found to be equally as reliable as ascanogram for measuring limb-lengthdiscrepancy14. Therefore, scanogramsand orthoroentgenograms have fallenout of favor as the primary assessmenttool for limb-length discrepancy.

New technologies have been eval-uated as possible replacements for theconventional computed or digitalradiographs or teleoroentgenogramsfor assessing limb lengths13. Micro-dose digital radiography produces acomputer-generated image of the lowerlimbs made with the patient standing.The source and detector move togetherin scanning the patient so that the pencilradiograph beam is always perpendicularto the patient. A continuous series ofphoton beams collimated to act as a pointsource is projected through the patient tostrike a computerized detector. Thistechnique exposes the patient to a negligi-ble dose of radiation (0.001 to 0.002 cGy)during the scanning process. It hasbeen found to be more accurate thanorthoroentgenograms but still is notreadily available in most physicians’ of-fices. Despite the advantage of avoidingionizing radiation, magnetic resonanceimage (MRI) scanograms have not beenfound to be as accurate as radiographs orcomputed tomography (CT) scanogramsand are inconvenient. CT scanogramshave a lower radiation dose than con-ventional radiographs and are more ac-curate in the assessment of coronal planelength discrepancies than radiographs.However, because these are not weight-bearing images, it is difficult to accuratelyassess limb alignment. Although thislimitation decreases the utility of thistechnique for standard limb-length eval-uation, lateral CT scanograms may be auseful technique to assess leg lengths inpatients unable to stand upright withknee flexion contractures of.30°.

One promising new technologyis the EOS imaging system (Euronext,

Paris, France). This low-dose, biplanar,digital radiographic imaging system useshighly sensitive gaseous photon detec-tors that can produce full-length,weight-bearing images of the lower ex-tremities. Depending on the setting, animage is produced in three to eight sec-onds with forty-three times less radia-tion than a conventional radiograph andsix times less radiation than a CT scan-ogram16. EOS was found to be moreaccurate than conventional radiographsand CT scanograms for the assessmentof limb length in the coronal plane.In addition, full-length orthogonalweight-bearing lateral plane views can beobtained to allow simultaneous evalua-tion of any sagittal plane deformity.Biplanar EOS images can be obtainedfaster, with decreased turnaround be-tween patients, compared with com-puted or digital radiography. However,because of the relatively long acquisitiontime needed (three to eight seconds),movement artifacts in the images are apotential issue.

Indications for Limb LengtheningThe indications for limb lengtheningcontinue to evolve. Traditional teachingstipulates that 0 to 2 cm of limb-lengthdiscrepancy can be ignored, but a dis-crepancy between 2 and 5 cm should betreated with contralateral epiphysiode-sis, and a.5-cm difference should belengthened17. These guidelines providea framework for decision making, but,in reality, each case has its own uniqueset of circumstances that determine thebest treatment choice for the patient andfamily. The current guidelines do nottake into account the patient’s overallheight (or projected height). A 2-cmdiscrepancy is not the same for a1.82-m-tall (six-foot-tall) patient anda 1.52-m-tall (five-foot-tall) patient.Some patients are absolutely botheredby limb-length discrepancies of 1.5 cmand return to the clinic repeatedly untilsomething is done. There are patientswith projected short stature who valueevery millimeter of height and thereforedo not want epiphysiodesis as a treat-ment option. Some families value the

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choice with the fastest recovery time andwant an epiphysiodesis even for largediscrepancies. As the experience withlimb lengthening has increased and thetechnology has improved, it has becomepossible to produce safe, reliable, andcomfortable limb lengthening for pa-tients with mild to moderate discrep-ancies. It is now reasonable to offer limblengthening as the primary treatmentoption for many patients with discrep-ancies of,5 cm.

Fixator ChoicesOnce a decision to lengthen the limbhasbeen made, the surgeon must choosewhether a uniplanar fixator, circularfixator, or intramedullary lengtheningdevice should be used. Uniplanar fixa-tors have traditionally been used pri-marily to lengthen femora and humeri.It is less comfortable to place circularfixators on these proximal limb seg-ments. New designs of uniplanar fixa-tors allow half pins to be placed inmultiple planes and at multiple loca-tions, which helps to improve the sta-bility and options of the construct. Forexample, the half pins are no longerlimited to just placement through theclamp but can be placed out of plane orwith increased spread between fixationpoints. There are also uniplanar fixatorswith attachments that allow the hip orknee joint to be spanned, to undergorange of motion movement, and to beprotected during the lengthening pro-cess. A breakthrough in circular externalfixators occurred with the advent of thehexapodal frame design. These fixatorsare based on concepts similar to flightsimulators (Stewart platform) and allowsix degrees of freedom of movement.The frames can rotate around a virtualpoint in space rather than requiring aphysical hinge. These frames are pairedwith software programs that help thesurgeon plan the deformity correctionand plan the frame size and mountinglocation. The most powerful feature ofthe software is the ability to make ad-justments to the deformity correctionduring the course of treatment withouthaving to return to the operating room.

Because these devices allow the surgeonto correct multiple planes of deformitysimultaneously or sequentially, they areideal for pediatric conditions.

Decreasing External Fixation IndexIntegrated TechniquesExternal fixation remains the mostcommon method of lengthening pedi-atric long bones worldwide. Externalfixation, despite its remarkable capabil-ities, has its shortcomings. It is cum-bersome for the patient. The visibleimplant with pins and wires trans-gressing the soft tissues can create bothphysical and mental discomfort to thepediatric patient. The longer the treat-ment with the external fixator, the lesswell they are tolerated. The externalfixation index measures the number ofdays that the external fixator is attachedto the bone per centimeter of lengthgained. Integrated techniques thatcombine internal and external fixationhave been proposed as a method to de-crease the external fixator index and toimprove patient comfort. In these tech-niques, the external fixator is removedfollowing the distraction period and theregenerate bone is protected with inter-nal fixation during the consolidationperiod. For example, lengthening overan intramedullary nail allows the fixatorto be removed at the end of the distrac-tion phase. The decreased fixator timediminishes fixator-associated issues suchas pin-track infections and contracturesand it improves patient tolerance andcomfort. The nail provides internal sta-bility to the regenerate bone. Conse-quently, the risk of deformity duringlengthening and the risk of fracture ordeformity after external fixator removalare decreased.

Both rigid and flexible intramed-ullary nails have been used in pediatriclengthenings. Gordon et al. describedtheir experience lengthening the femurover a rigid nail in thirty-seven patientswith an average age of 11.6 years4. Theyaveraged 7 cm of lengthening and hadthe fixator removed after eighty-onedays. All but one patient achieved 120°of knee flexion. Four patients had failure

to distract. Gordon et al. recommendedthat, before leaving the operating room,surgeons ensure that the distal portionof the femur can rotate easily around theimplant and that there is no binding ofthe half pins. It is also important thatthe pins are placed perpendicular to thelong axis of the femur to prevent bind-ing. Forty-nine percent of patients hada 7-mmnail inserted. Fractures occurredin five patients at an area just distal tothe tip of the nail or through the distalinterlocking holes. Consequently, ex-changing the nail for a longer nail ofappropriate length to relieve the stressriser in the mid-femur should be con-sidered at the time of fixator removal.Eleven percent of patients developedosteomyelitis and were effectively treatedby nail removal, reaming of the canal, andintravenous antibiotics.

An alternative technique is to inserta reamed nail at the time of fixator re-moval instead of at the time of the indexprocedure.The reamingof the regeneratebone appears to produce revasculariza-tion that can provide abundant newboneformation18. Osseous union occurredin less than one-half of the time com-pared with a control group lengthenedwith an external fixator alone19. A longerand larger nail can also be insertedusing this technique compared withthe small-diameter nails utilized intraditional techniques of lengtheningover a nail.

The use of flexible intramedullarynails has also been combined with pe-diatric limb lengthening.This techniqueavoids potential physeal injuries and therisk of osteonecrosis associated withrigid intramedullary nailing in children.In the femur and tibia, nails of 1.5 to2.0-mm diameter are bent in an arc of40° to 50° and passed across the osteot-omy site to the opposite metaphysis20.Rotation of the curved tip of the nailduring insertion allows the nail to avoidthe half pins and wires of the externalfixator.Thenails add stability andpreventtranslation. One study demonstratedfractures in six (13.6%) of forty-fourbonesegments in patients following lower-extremity limb lengthening with flexible

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intramedullary nailing and fractures infourteen (20.9%) of sixty-seven segmentsin patients without flexible intramedul-lary nailing5. Popkov et al. had 3% re-generate bone deformities between 15°and 40° angulation and 8% fractures in acontrol group of 194 cases of lengtheningcompared with no fractures and onlyone case of a 10° deformity of the regen-erate bone in ninety-two cases of length-ening over a flexible nail20. The healingindex was also reduced in both series withuse of this technique. Launay et al. alsofound better union of the bone callus,shorter fixation, fewerdeformities, andnoinfections in fourteen cases when length-ening the forearm over a flexible intra-medullary nail21. Popkov et al. reportedno deep infections in the group withlengthening over a flexible nail and rec-ommended removing the nail electivelythree to eight months after the frameremoval20.

Because of concerns regarding therisk of intramedullary infection andthe inability to put rigid nails in smallchildren with open physes, an alterna-tive integrated technique, lengtheningover a plate, was developed. This tech-nique uses a submuscular locking plateto protect the regenerate bone instead ofa nail. The plate can be inserted at theindex procedure or at the time of frameremoval. The plate insertion does notviolate the physis and therefore can beused in small children. No deep infec-tions have been reported and any angu-lar deformity of the regenerate can becorrected with adjustment at the time ofplate locking22-24.

Intramedullary Limb LengtheningAlthough these integrated techniqueshave been successful in decreasing theexternal fixation index, they still requirean external fixator for at least a portion ofthe treatment. Intramedullary length-ening systems have been developed in anattempt to achieve distraction withoutany need for external fixation. Com-pletely internal lengthening nails havemany potential advantages over externalfixation, including elimination of pin-track infections, less risk of neurovascular

injury from wire or half pin insertion,improved cosmesis, better body imageand psychological well-being for the pa-tient during treatment, improved rangeofmotion, increased activity levels duringlengthening, and less pain.

Two basic designs of internallengthening devices have been utilized.Onedesignutilizes intermittent rotationof the limb to create distraction. Twoexamples of this are the Albizzia Nail(DePuy, Villeurbanne, France) and theIntramedullary Skeletal Kinetic Dis-tractor (ISKD) (Orthofix, Lewisville,Texas). The Albizzia nail has a ratchetassembly that requires approximately15° of limb rotation to create distrac-tion25; this device is not available in theUnited States. The ISKD was clearedby the Food and Drug Administration(FDA) for marketing in the UnitedStates in 200126. It was designed tolengthen by small (3° to 9°) physiologicoscillations between two telescopic sec-tions connected to a double-clutchmechanism. However, due to the un-controlled lengthening rate and rhythm,the ISKD had a very high complicationrate27-32. It was recently removed fromthe market and is no longer available.

The second type of intramedullarylengthening nail design uses a mecha-nism to push the nail in pure axial dis-traction without requiring rotationthrough the callus. There are currentlytwo nails available with this type ofdesign. The first, called the Fitbone(Wittenstein, Igersheim, Germany),was developed in 199132,33. This steelnail has an electromagnetic motor anda subcutaneous patient-controlled an-tenna that allows fully implantablelengthening. The antenna powers andcontrols the distraction by transcutane-ous transmission of radio-frequencywaves. Although this device has not beenapproved by the FDA and is not cur-rently available in the United States, theinternationally reported results havebeen positive33-37.

The PRECICE nail (Ellipse Tech-nologies, Irvine, California), originallycleared by the FDA in July 2011, is amagnet-operated telescopic internal

lengthening device32. The nail uses a ge-neric rare earth magnet connected to agear box and screw shaft assembly. Anexternal remote control device contain-ing two motor-driven rotating magnetsinteracts with the internal magnet tocreate distraction (or compression). Therate and rhythm of the lengthening canbe precisely adjusted according to eachpatient’s needs.

Accurate distraction control in in-tramedullary lengthening devices iscritical because too rapid a process canlead to nonunion, nerve damage, andjoint contractures, and too slow a pro-cess runs a risk of premature consolida-tion. Unlike the rotatory lengtheningnails, the PRECICE nail has demon-strated excellent accuracy and rate con-trol in two series of patients38,39.

Devices that require rotationthrough the callus to lengthen, such asthe ISKD and the Albizzia nails, havebeen reported to be quite painful forthe patient. It is theorized that the ro-tation leads to friction andmuscle spasmpain. In one series of lengthening withthe Albizzia nail, 39% (twelve of thirty-one) of patients required readmissionto perform ratcheting under generalanesthesia25. This type of pain has beennotably absent in the pure axial length-eningdevices such as theFitbone and thePRECICE nail32,34. In a series of thir-teen patients, Herzenberg et al. com-pared pain scores for lengthening withthe PRECICE nail and for lengtheningwith external fixation. They found de-creased pain with internal lengthening(a visual analog scale [VAS] pain scoreof 7 points for external fixation and3 points for the PRECICE nail) anddecreased duration of need for painmedication (12.5 weeks for externalfixation to 5.2 weeks for the PRECICEnail). There was also more comfortduring physical therapy and a quickerreturn to full weight-bearing with thePRECICE nail40.

The largest published case seriesusing the PRECICE nail, 155 cases,revealed seven mechanisms that failedto lengthen, two due to operator errorby the surgeon’s team in applying the

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external remote control device thewrong way and five after meeting excessresistance from the callus32. The totalnumber of nail breakages for the first155 PRECICE lengthenings was three.By comparison, in forty-four cases usingthe Fitbone, there were five cases thathad failure of the lengthening mecha-nism and one case that had nailbreakage33-35.

Two potential failure modes werenoted with the first version of thePRECICE nail: the junction of thegears to the lead screw, and the weldsof the nail on either side of the drivemechanism32. The PRECICE 2 (P2)addresses these weaknesses and wascleared for use by the FDA in October2013. The P2 is at least two timesstronger in bending fatigue strengthand has a three times stronger couplingbetween the gears and lead screw. TheP2 is available in 50 and 80-mm strokelengths and is also available in a smallerouter diameter (8.5 mm).

As experience with the use ofintramedullary lengthening nailsincreases, the following recommenda-tions have been proposed to help achieveoptimal outcomes when utilizing thesedevices. Preoperatively, the bone sizemust be assessed. It must be largeenough to accommodate the reamingrequired for insertion of the nail (1.5 to2 mm larger than the diameter of thenail). Because the nail is straight, the os-teotomy should be planned at the apex ofthe femoral bow to limit the amount ofbinding in the canal. Although short naillengths are preferred to limit the amountof binding, the overall length shouldbe chosen so that at least 5 cmof the thickpart of the nail remains in the distal seg-ment at the end of distraction. The nailshould be inserted with minimal resis-tance to avoid damaging the distractionmechanism. It is not recommended tohitthe nail with any forceful blows duringthe insertion process. If the width of themedullary canal is larger than that ofthe nail at the osteotomy level, blockingscrews should be used. For example,while lengthening a tibia,muscular forcesare known to induce valgus and apex

anterior deformity into the regeneratebone. Blocking screws placed posteriorand lateral to the nail in the proximalsegment will resist this tendency. Toconfirm completion of the osteotomy,the bone should be rotated around thenail. Steinmann pins or half pins can beused to ensure rotational control of thesegments during nail insertion41.

Despite all of the described ad-vantages over external fixation, intra-medullary lengthening devices are notwithout their own potential complica-tions. Joint contractures or subluxationscan still occur, and there is no easyway tocorrect one when it appears. With ex-ternal fixators, the joint can be spannedprophylactically or fixation across thejoint can be added at the time earlysubluxation is noted. Internal length-ening nails do not have a similar rescuemaneuver. Therefore, it is importantthat the follow-up radiographs at eachvisit are critically evaluated, not just forthe length achieved and the quality ofthe regenerate bone, but also for evi-dence of early joint subluxation. Fortibial lengthening, physical therapyshould focus on ankle dorsiflexion andknee extension. The patient shouldwearan ankle dorsiflexion splint during theday and a knee extension brace at night.If necessary, an extra-articular tibio-calcaneal screw can be inserted to lockthe ankle in neutral position during thelengthening process42. For femorallengthening, therapy should focus onknee flexion or extension and hip ex-tension. During the lengthening pro-cess, hip abduction of,20° or kneeflexion of,45° is an indication to stopthe lengtheninguntil adequatemotion isrecovered32,41. If joint subluxation isnoted, lengtheningmust be stopped andefforts to restore joint congruency andstability must be undertaken.

Another concern is the effect oflengthening the lower extremity alongthe anatomic axis rather than the me-chanical axis. Intramedullary lengtheninginduces a lateral shift of the mechanicalaxis of about 1 mm for every 1 cm oflengthening. This shift should be an-ticipated preoperatively, especially in

patients with any preexisting valgusdeformity43.

Finally, because the nails are in-tentionally short to avoid the bow ofthe femur, a stress riser is created in themid-femur (or tibia) at the endof thenail.It is recommended to avoid the distalanteroposterior locking screw drill-hole,as it potentially increases the stress at thislevel in the femur and leaves a subcuta-neous screw head in the tibia32.

In contrast to external fixation,intramedullary lengthening does notallow for secondary deformity correc-tions during the lengthening process.Deformity correction is possible withthe nail but must be done acutely. Thisrequires meticulous preoperative plan-ning and careful intraoperative tech-nique. The reverse planning techniqueallows the deformity to be analyzed andan acute correction planned with use ofa retrograde femoral nail44. Fixator-assisted nailing techniques allow theosteotomy to maintain the new cor-rected position while the reaming andnail insertion take place45. Blockingscrews should be inserted inmetaphysealbone to guide the reaming and nailpath, if necessary. It is also possible toperform deformity correction with useof a second osteotomy proximal or distalto the end of the nail and a locking plate.Alternatively, the lengthening proce-dure can be staged, with fixator-assistednailing or plating initially performedto correct the deformity. After the oste-otomy has healed, exchange nailing canbe performed with use of a telescopicnail, with an osteotomy to lengthenthe bone.

Alternative LengtheningTechniqueOne recently described technique pro-duces lengthening without the use ofany implants46. Limpaphayom andPrasongchin described stimulating growthin the short limb of patients with openphyses by stripping and dividing theperiosteum of the lower-extremity longbones. This technique is theorized toincrease the blood flow to the physis andto reduce the tethering effect of the

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periosteum on the growth plate. In eightof eleven patients, with an average pre-operative discrepancy of 6 cm, the limb-length discrepancy corrected to within2 cm within twenty-five months. How-ever, the authors did not recommendthis technique for patients with discrep-ancies of.6 cm.

ConclusionPediatric limb lengthening is a rewardingbut challenging endeavor. A thoughtfuland comprehensive preoperative planwill help to minimize the obstacles tosuccess. Limb-lengthening techniquesanddevices continue toevolve inaneffortto improve outcomes as well as patientcomfort and satisfaction. New intra-medullary limb-lengthening nails areextremely promising in this regard.However, the surgeon still needs to becautious when using these nails. Theprocess of limb lengthening, regardlessof the device used to achieve it, stillcarries the inherent risks of fracture,infection, joint contracture, and jointsubluxation or dislocation. The sur-geon must be cognizant of these po-tential complications at all times andbe prepared to manage them whenthey occur.

Source of FundingThere was no source of external fundingfor this study.

Christopher Iobst, MD1

1Nemours Children’s Hospital,13535 Nemours Parkway,Orlando, FL 32827

E-mail address:christopher.iobst@nemours.org

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