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The outcomes of motorized intramedullary lengthening have been described in multiple studies with some utilizing patient-reported outcomes but most assessing the accuracy of the nail and its ability to accomplish the orthopedic goals safely. The first papers published on this topic were small, retrospective case series that reflected on the original versions of the Precice (NuVasive, San Diego, CA) and Fitbone (Wittenstein, Igersheim, Germany). Many of these manuscripts with larger patient cohorts have been included in this review. More recently, surgeons have built up a large volume of cases from which to study to answer more specific questions. These studies look at patient populations with more uniform demographics or compare different techniques or surgical methods in order to better understand how we can improve upon the status quo. The implants have been redesigned and improved making certain complications version specific. Efforts to identify model-specific flaws have been brilliantly classified by Lee et al1 into device-related complications of internal lengthening nails. The Stryde nail (NuVasive, San Diego, CA), a stainless steel advancement of the Precice, allows far greater weight bearing and is recently available. There is no clinical Stryde data at this time for implant comparison.
Data are often best conveyed visually, and this review includes several tables for quick reference and comparison of studies (Tables 1–4). A final table has attempted to cull unique patient groups from each center (without counting any patient twice) in order to pool data and draw conclusions on the incidence of the complications that have been reported (Table 5). There are several pearls that have arisen out of the review of these articles which represent the combined experience of many surgeons:
TABLE 1 - Lengthening Outcomes: Femur and Tibia Study (Implant) N (Limbs) BHI (d/cm) (Range/SD) Deformity Correction (Degree) (Range) Lengthening Accuracy-Precision Years Follow Up (Range) and Outcome Author Conclusion Green et al2 (Precice) 31 F-23 T-8 44.5 (SD22.8) NR Length: 33.5 mm (29.4-37.6) Accuracy: 96% achieved planned length 29/31 limbs studied through consolidation. 17/31 two year follow-up. Enneking Functional score improved 18%, AAOS LLM & SF-36 no change Patient-reported outcome scores were not sensitive to this patient population Calder et al3 (Precice) 107 A-73 R-34 A=29 (15-80) R=36 (16-108) Acute deformity correction in 12 patients. Pre-Valgus 20 Pre-Varus 15 (6-20) Pre-sagittal 27 Pre-torsion 28 (25-30). Flexible reamers Length: 46 mm (5-80); 105/107 limbs achieved planned length. Lengthening induced deformity: MAD 5-10 mm: A-15/73, R-7/34; MAD >10 mm: A-10/73, R-9/34 Time F/U NR. Regained full joint motion: A-90%, R-88% Accelerated weight bearing program may lower BHI. Antegrade nail created less deformity Horn et al4 (Precice/Fitbone) 50 P-34 Fit-16 R-23 A-21 T-6 A=34 (18-61) R=40 (24-76) P=0.03 T=76 (49-122) Age<18 healed faster than age>18: (BHI 27 vs. 43, P=0.005) Pre-Valgus Lat MAD 21 (4-50) mm; Pre-Varus Med MAD 31 (14-58) mm RPM. R-Rigid reamers, A/T-Flexible reamers Length: 40 mm (25-65) Lengthening induced MAD=3 mm (0-11) (P=0.9) 2.3 (1-6) Lateral MAD from anatomic axis lengthening was counter-balanced by varus bending of the lengthened femur. Deformity correction then lengthening slowed BHI compared with lengthening alone Szymczuk et al5 (Precice) 62 EF-32 P-30 (All F) EF=29.3 (SD, 12.7) P=34.8 (SD, 11.2) NR Length: 5.6 (SD, 1.7)-EF 4.8 (SD, 1.4)-P All ITB release. >87% achieved planned length in both groups 4.47 (SD, 2.7)-EF 1.86 (SD, 0.7)-P Congenital Femoral Deficiency is challenging. Precice can correct length but knee subluxation may occur and impact lengthening goals Fragomen et al6 (LON vs. Precice) 59 LON-20 P-39 (mixed A/R) LON=42.7 (24.4) P=30.5 (15.3) Not recorded. Flexible Reamers Length: 40.4 mm (SD, 22.9)-LON, 38 mm (SD, 16.8)-P Accuracy (mm): LON-3.6, P-0.3 Precision: LON-0.8, P-1.0 2.3 (1.1-3.1) Knee ROM preserved P more accurate and precise than LON, but yields similar BHI and regenerate quality Richardson et al7 (Cost LON vs. Precice) 58 NA NA NA Cost: P-US$44,449; LON-US$50,255 (P=0.482) P fewer surgeries than LON (2.1 vs. 3.1). No significant cost difference Iobst et al8 (Precice) 27 (All R) 42 Pre-Varus: Med MAD 24 (SD12.5) Post Varus: MAD 6.9 (4.8) Pre-Valgus: Lat MAD 23.7 (SD, 11) Post Valgus: 5.4 (4.4). All FAN. All had blocking screws. Mean correction 7 degrees. Post MAD=81% 8 mm flexible reamers Length: 30 Accuracy: 0.8 mm 1.1 (0.6-2.4) ASAMI: E-26, G-1 FAN with blocking screws yields good results and accurate corrections Furmetz et al9 (ISKD) (Orthofix, Lewisville, TX) 31 B-15, NB-16 NR Average deformity corrected: 2.4 (0.8-8.0) deg. Blocking screws used in larger deformity corrections- not randomized. Planning: end-point-first method, rigid reamers Length: 36.8 mm (19.7-66.0) F/U NR Accuracy of deformity correction within 3.0 degrees in >87% of cases Use of dummy nails allowed for very close blocking screw placement ensuring proper alignment. Blocking screws make deformity correction >2 degrees more accurate Lee et al1 (ISKD, P1, P2) 115 F-88 T-27 ISKD-35 P1-34 P2-46 NR Lengthening induced deformity (deg.): F, P1=1.1 deg. (0.7-4) valgus T, P1=5.1 (3.2-8.8) valgus F, P2=0 (±3.5) T, P2=2.8 valgus (2.1 varus-6.7 valgus) Length: P1-49 (±8) P2-51 (±7) Accuracy P1= 1 mm (SD3) Accuracy P2=Femur 0 mm (±2.5), Tibia 2 mm (±2.5) F/U= P1-1.5 (±0.33)mm P2-1.25 (±0.42)mm Newer versions of the Precice address mechanical issues and were not tested Wagner et al10 (Precice-P1) 32 F-24 T-8 36.4 (12.8-113) F=32.4 (13-113) T=48 (22-101) NR Length: 43 mm (15-65) Accuracy 97% Precision 92% 1.6 (1-2) Enneking score improved 3.8pts Precice is comparable to other lengthening nails but an improvement over the ISKD Hammouda et al11 Post Trauma (Precice) 17 All F A-13 R-4 32 (16-51) NR Length: 38 (23-60) Accuracy: 16/17 achieved planned length 2.2 (1-3.7) Acceptable results Hammouda et al12 Troch entry (ISKD, Precice) 31 ISKD-18 P-13 NR NR Flexible Reamers Length: 54 (30-67) 3.5 (1.4-9.0) Acceptable results and no cases of femoral head necrosis Accadbled et al13 (Fitbone) 26 F-15 T-11 F=73±57 T=83.5±65 Pre-Valgus 8.7 (4-15), Post-Valgus 3 (0-5); Pre-Varus 13 (4-20), Post-Varus 2.1 (0-5) Planning: RPM, rigid reamers Length: 45 mm(20-80); 23/26 achieved planned length 3.4 (2-5.3). VAS during distraction 2.5 (0-4). ASAMI Function: E-21, G-1, Pr-1 Good results Karakoyun et al14 (Precice) 27 F-21 T-6 A-11 R-10 34 (27-52) Angular correction 15.5deg (7-25) Rigid reamers Length: 48.2 (34-120) 1.7 (0.4-3.6) Acceptable results Kirane et al15 (Precice) 25 F-17 T-8 NR Lengthening induced deformity: F-MAD 1 Lat(2med-8 lat) F-procurvatum 3deg (0-12) T-MAD 5 Lat (0-8 Lat) Flexible Reamers Length: 35 (14-65) Accuracy 96% Precision 86% 0.3 (0.06-0.6) Expect coronal plane deformity and flexion to occur with lengthening. The tendency for the femur to bend into varus is counteracted by the lateral MAD from lengthening along the anatomic axis Kreig et al16 (Fitbone) 32 F-21 T-11 F=35 (IQR, 27-44) T=48 (IQR, 34-63) Pre-Varus Med MAD 13 (6-50) Post-Varus MAD 4 (38 med-11 lat); Pre-Valgus Lat MAD 13 (5-40) Post-Valgus 0 (10 med-28 lat) RPM Length: 35.3 (20-80) Accuracy: 30/32 within 5 mm of goal 1.3 (1-2.3) ASAMI: E-26, G-5, F-1 The BHI was significantly lower for femur lengthening compared with tibial lengthening A indicates antegrade femur; ASAMI, ASAMI score;17 B, blocking screws; BHI, Bone Healing Index; E, excellent; EF, external fixation; F, Femur; FAN, fixator assisted nailing; Fit, Fitbone; G, good; IQR, interquartile range; ITB, Iliotibial Band; Lat, Lateral; LON, Lengthening Over Nail; MAD, Mechanical Axis Deviation; Med, Medial; NB, No Blocking Screws; NR, Not reported; P, Precice; Pr, Poor; R, Retrograde femur; RPM, Reverse Planning Method;18 T, Tibia; VAS, Visual Analogue Scale.BHI indicates Bone Healing Index; EF, External Fixation; Fit, Fitbone; LON, lengthening over nail; NR, not reported; P, Precice.
F indicates femur; F/U, follow up; H, humerus; NR, not reported; T, tibia.
AV indicates arteriovenous; AVN, avascular necrosis; BMAC, bone marrow aspirate concentrate; F, femur; Fx, fracture; ISKD, intramedullary skeletal kinetic distractor; ITB, iliotibial band; LLD, limb length discrepancy; NR, not reported; P1, original Precice nail; P2, second-generation Precice nail; P2.1, third-generation Precice nail; R, retrograde; T, tibia; VTE, venous thromboembolism.
Dead nail indicates failure to distraction after implantation; Nail retraction, unwanted backing up of the nail with loss of length; P1, original Precice nail; P2, second-generation Precice nail; VTE, venous thromboembolism.
Many surgeons would say this was intuitive since there is more muscle (blood supply) around a proximal femoral osteotomy site, the knee is not violated, blocking screws and not usually needed, the procedure is faster, and incisions are more hidden. However, data now support this assumption where the antegrade method was shown to yield a lower bone healing index (BHI)3,4,8 and superior hip and knee motion.3 Lengthening along the anatomic axis produces valgus as the knee glides medially, however the significance of this phenomenon has been contested. During antegrade lengthening, the femur tends to drift into varus often resulting in a net minimal deviation of the mechanical axis. In other words, the proximal varus that tends to occur with antegrade lengthening via nail bending often counteracts the lateral mechanical deviation witnessed with lengthening along the anatomic axis.1,4 The use of a medial blocking screw can help counteract this varus bending. Trochanteric nail entry may produce more varus than piriformis entry. There are some cases of lengthening with 8.5 mm diameter nails where the lengthening site bent into enough varus to call it a malunion.1,4 Suffice it to say that simply relying on preoperative radiographic planning may not result in the desired mechanical axis due to the numerous technical and biomechanical variables. Retrograde nailing is still superior for correcting distal femoral deformity and for obtaining a magnetic connection in obese patients.3,8
Prophylactic Iliotibial Band (ITB) Release Avoids Knee ContracturesIn studies where the ITB was routinely released6 or where lengthening averaged 3 cm,2,8 there were very few reports of joint contractures. Cases of congenital femoral deficiency are excluded from this generalization where ITB release does not ensure knee stability.5 By contrast, surgeons that did not release the ITB prophylactically with average lengthening >4 cm were harassed by knee flexion contractures that required later release.3 Recommendations are to release the ITB for femoral lengthening >3 cm,3 but there is no downside to releasing it for all cases.5
Use Blocking ScrewsBlocking screws have become a vital part of the surgeon’s ability to correct deformity with an intramedullary implant and to prevent new deformity during lengthening.8,9,13,29 While most limb lengthening surgeons use blocking screws routinely, few have studied their effectiveness. Furmetz et al9 looked at a nonrandomized cohort of femoral lengthening patients and saw slightly improved results with blocking screws. For larger deformity corrections and for corrections that were unacceptable with reaming alone, blocking screws were used. For small corrections they were not necessary. Authors concluded that these screws should be used for deformity corrections >2 degrees to improve control. One should also appreciate that the mostly excellent outcomes presented in the literature are the result of proper blocking screw use even though not explicitly studied. The incidence of malunion after lengthening was 3% and many of these cases were due to lengthening induced deformity that could have been prevented with blocking screws.
P1 Nails and P2.0 Crowns can FractureAlthough mostly of historical significance, Precice nails have faced adversity with regard to mechanical failure. The original Precice (P1) nail was modular, assembled on the back table, and had a weak spot at the welding seam. This was witnessed to fracture in some cases.1,3,6,30,31 The engineers quickly replaced it with the P2.0 nail which did not fracture but instead had a weak crown at the junction of the large bore and the telescopic portion of the nail. The crown failed in torsion which led to variable mechanical performance including (1) continuing to function in lengthening, (2) not being able to lengthen but not shortening, and (3) shortening (running back) with loss of length. This was detailed meticulously by Lee et al1 who noted that of 14 implanted nails that sustained crown fractures, only 2 of them required revision surgery. The true frequency of crown fracture was most likely higher than the reported 3% since the signs can be subtle and many times it did not lead to a clinical complication. Some reported complications may have been due to unrecognized crown fracture; for example “nail retraction” (running back) may have been the result of a broken crown. The P2.1 was introduced with a much stronger crown, now internalized, that failed at a vastly reduced incidence.
Prevent Delayed Union and NonunionWhile uncommon, delayed union and nonunion are concerns (2% and 1% incidence, respectively) that can usually be prevented by surgical technique and careful observation. The percutaneous osteotomy with drill holes (vent holes), followed by reaming, followed by an osteotome has earned an outstanding track record for high-quality regenerate formation. The bone “swarf”12 (reamings) deposited at the corticotomy site through the vent holes may have much to do with the rapid healing and low BHI seen in most series (antegrade femur average 33 d/cm) (Table 1). The vast majority of surgeon-authors used this method with great results. In contrast, osteotomy over an existing nail (which does not require reaming) with subsequent lengthening has produced slower healing with a higher BHI (average, 52 d/cm).32 The optimal rate for lengthening is patient specific. Frequent follow-up radiographs are needed to modulate rate and rhythm to avoid poor regenerate. Once established, the management of these complications is similar among studies and includes: stopping lengthening, accordion oscillation of the regenerate, injection of bone marrow aspirate, open autologous bone grafting, and exchange nailing with a trauma nail. The phenomenon of partial bone union was raised by Wagner et al10 whereby the regenerate unites strongly on one side but not on another. Although technically healed, the construct relies on an intramedullary implant to prevent fracture. Authors recommend grafting of the partial defect to reconstruct the bony cylinder allowing for eventual nail removal.
The Tibia is Not the FemurOutcomes for tibia lengthening using motorized intramedullary nails are commonly wrapped into mixed series of tibia and femur analyses (Table 1). Many studies have isolated the results of these 2 different long bones, but the quantity of tibial cases reported is low. Several issues unique to the tibia have borne out from these series. The tibia heals more slowly than the femur even using identical methods (average, BHI 57 vs. 33 d/cm, respectively). This means that the latency needs to increase and the distraction rate for the tibia needs to decrease. In the tibia, it is more difficult to prevent procurvatum deformity at the time of nail insertion and during lengthening.4 A posterior blocking screw is recommended to mitigate this complication.9,29,33 Valgus deformity during lengthening, the need for syndesmotic (fibular length stabilization) screws, and accurate start point are all challenges specific to the tibia. Compartment syndrome was not reported but remains a possible and potentially devastating complication. Peroneal nerve entrapment is rarely reported10 but demands vigilance.
OtherLocking bolt migration has been reported in many papers and was handled with reinsertion (or removal) of the bolt.3,4,16 NuVasive now has fully threaded screws that can be used in lieu of the smooth bolts which may reduce this phenomenon. Dead nails are nails that fail to distract which typically refers to a freshly implanted Precice that fails the intraop distraction test and needs to be replaced. While the company tests every nail before shipping and the incidence of malfunction is low (1%), it is not zero. Therefore, every nail should be tested in vivo on the operating room table after insertion and before leaving the room. Some cases of the Fitbone nail had a malfunctioning transmitter that required replacement. The original version of the Fitbone had reports of running back which were prevented in the second iteration of the implant. In the upper extremity, retrograde humeral lengthening created elbow contractures and antegrade lengthening created shoulder stiffness. In antegrade nailing, it is recommended to avoid the bony insertion point of the rotator cuff but rather to split the cuff and enter the joint to create a start point for the nail.24 The Precice nail was often too long for the humerus, an obstacle that was solved by creating a small gap at the osteotomy site21 or cutting down either (or both) end of the nail.19
REFERENCES 1. Lee DH, Kim S, Lee JW, et al. A comparison of the device related complications of intramedullary lengthening nails using a new classification system. Bio Med Res Int. 2017:803251010. 2. Green SA, Fragomen AT, Herzenberg JE, et al. A magnetically controlled lengthening nail: a prospective study of 31 individuals (The Precice intramedullary nail study). J Limb Length Recon. 2018;4:67–75. 3. Calder PR, McKay JE, Timms AJ, et al. Femoral lengthening using the Precice intramedullary limb-lengthening system. Bone Joint J. 2019;101-B:1168–1176. 4. Horn J, Hvid I, Huhnstock S, et al. Limb lengthening and deformity correction with externally controlled motorized intramedullary nails: evaluation of 50 consecutive lengthenings. Acta Orthop. 2019;90:81–87. 5. Szymczuk VL, Hammouda AI, Gesheff MG, et al. Lengthening with monolateral external fixation versus magnetically motorized intramedullary nail in congenital femoral deficiency. J Pediatr Orthop. 2019;39:458–465. 6. Fragomen AT, Kurtz A, Barclay JR, et al. A comparison of femoral lengthening methods favors the magnetic internal lengthening nail when compared with lengthening over a nail. HSS J. 2018;14:166–176. 7. Richardson SS, Schairer WW, Fragomen AT, et al. Cost comparison of femoral distraction osteogenesis with external lengthening over a nail versus internal magnetic lengthening nail. J Am Acad Orthop Surg. 2019;27:e430–e436.
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