LON method complications: what nine patient series report

LON (lengthening over nail) puts an intramedullary nail inside the bone and an external fixator around it in the same operation. The frame does the distraction, about 1 mm a day; the nail is only a rail. When the target length is reached, the surgeon locks the nail with screws and removes the frame, and consolidation continues on the nail.

LON limb lengthening risks fall into three groups, one per design fact. There is a frame, so there are pin sites, pin-site infection and joint stiffness for as long as it stays on. That was 52 days at a mean 4 cm in the Cairo randomized trial, 94 days at 6.65 cm in a 143-patient Tehran series, and 129 days at 7.4 cm in a Tianjin tibial series. There is metal in the canal while the pins are in, which creates an infection path no other method has. And there are at least two operations by design, usually three once the nail comes out a year or more later.

A pin-site infection in a frame-only lengthening is a skin problem. In LON, the same infection can track down the pin, into the canal and onto the nail. Once bacteria colonize the metal, the usual treatment is nail removal.

The published rates run from zero to 20 percent, and the spread is mostly technique. In the randomized trial from Ain Shams University in Cairo (El-Husseini and colleagues, 2013), 3 of 15 LON limbs (20%) developed deep intramedullary infection against 0 of 16 Ilizarov limbs. A series focused on infection, 118 tibial segments in 63 patients at Korea University Guro Hospital in Seoul (Kim and colleagues, 2011), recorded 13 superficial infections (11%) and 6 deep (5.1%); the nail came out early in 4 of the 6 and at 11 months in the other 2, once callus had bridged. Two series report none: 51 tibiae at Tianjin Medical University General Hospital (Guo and colleagues, 2012) and 27 procedures in Akola, India (Chaudhary, 2008), where every wire and half-pin was kept 3 to 5 mm clear of the nail.

That clearance is the variable. Pooled across four comparative studies (183 nail-assisted limbs against 171 conventional), the difference in intramedullary infection was not statistically significant. The risk is real, and it is avoidable.

LON method infection has a second, far more common form: the pin site. In the Tianjin comparison, pin-track infection occurred in 8 of 51 LON tibiae (15.6%) against 11 of 23 Ilizarov tibiae (47.8%). The Cairo trial counted 5 pin-tract infections in 15 LON limbs and 9 in 16 Ilizarov limbs. Pooled in the 2017 meta-analysis, a nail cut the pin-tract infection rate by 13 percentage points (risk difference −0.13, 95% CI −0.19 to −0.06).

The everyday scale shows in a 143-patient cosmetic series of bilateral tibial LON in Tehran (Motallebi Zadeh and colleagues, 2014): 0.74 complications per segment, falling to 0.45 once pin-tract infection was excluded. Only 44 patients (30.8%) finished with no problem or obstacle. Novikov's 131 cosmetic Ilizarov patients in Kurgan, the frame-only comparator, had a 37% complication rate, 5 major pin-tract infections (3.8%) and 3 cases of osteomyelitis (2.3%).

In practice: daily pin cleaning for the whole frame period, a low threshold for antibiotics, and a named person who checks the pins after you fly home. Pin-site redness in LON is urgent, because the next stop is the nail.

A magnetic nail is one operation plus a removal. Classic Ilizarov is one operation plus a frame removal. LON is two by design and three in practice: the nail-and-frame operation, the frame removal with nail locking at the end of distraction, and the nail removal a year or more later.

In the original Baltimore series, operative time was not significantly different from Ilizarov (p = 0.124), but the cost of treatment and the estimated blood loss were higher with the nail. At Hospital for Special Surgery, Fragomen's group compared 20 femoral LON cases with 39 magnetic-nail cases: LON patients needed the second procedure, reached union later (4.5 versus 3.3 months) and had complications in 9 of 20 femora (45%) against 7 of 39 (18%).

Complications themselves often mean more surgery. In the Istanbul University series of 42 segments in 35 patients (Kocaoğlu and colleagues, 2004), 18 complications occurred in 16 segments (38%), and 16 of those 18 needed an additional operation. Lengthening more than 6 cm, or more than 21.5% of the original bone length, predicted trouble.

Every lengthening pulls muscle, tendon and nerve along with the bone, and the ankle and knee pay for it. Ankle equinus was the most common problem or obstacle across the 795 cosmetic patients in the Marwan review (211 segments). LON's advantage is that the frame comes off before the consolidation months in which stiffness becomes permanent: in Paley's 1997 comparison, knee motion returned to normal 2.2 times faster with the nail than in the matched Ilizarov femora.

The series bear that out without making the problem disappear. In Tianjin, 3 knee flexion contractures (5.9%) and 4 ankle flexion contractures (7.8%) developed among 51 LON tibiae, all resolved with physiotherapy; the Ilizarov group had 8.7% and 17.4%. At HSS, knee flexion at the end of distraction was 88.8 degrees with LON against 103 with the magnetic nail; both groups reached about 120 degrees at final follow-up.

In the Yonsei University series in Seoul (Park and colleagues, 2008), 56 tibiae lengthened over a nail in adults with idiopathic short stature had fewer complications per tibia than 32 conventional ones, and patients coped better outdoors while the frame was on, but the time to return to previous activities and the function at final follow-up were the same. The frame comes off sooner; the rehabilitation does not.

Lengthening over nail complications on the bone side run in both directions. The nail protects the new bone. Paley's matched comparison recorded 6 refractures of the regenerate in the Ilizarov femora and listed protection against refracture as an advantage of the nail. The Cairo trial recorded 3 refractures and 5 axial deviations with the frame alone, against none with LON. The nail can also fail: in Tianjin, 3 interlocking screws broke during consolidation (5.9% of 51 tibiae) and 1 nail broke (1.9%) in a road accident.

Bone healing is the less predictable side. The Cairo trial had 3 delayed consolidations in 15 LON limbs and none with the frame alone; Tianjin had 1 delayed and 1 premature consolidation in 51, the delayed case needing an iliac-crest graft and a nail exchange. Consolidation itself is not slower on a nail: Tianjin measured 40.7 days per centimeter with the nail against 40.6 without.

Put together, the LON series report 0.43 to 0.74 complications per segment, most of them problems managed without surgery rather than lasting sequelae.

The fairest comparison of LON method complications is the Marwan systematic review of cosmetic stature lengthening (795 patients, 11 studies), which sorted events by Paley's classification: problems (resolved without surgery), obstacles (an unplanned procedure) and complications (still present at the end). LON had the highest problem count of any method, 1.1 per patient, because of pin sites, but a low complication count, 0.1 per patient. Classic Ilizarov had 0.7 problems, 1.5 obstacles and 0.2 complications; the implantable nail had 0.16, 0.23 and 0.02. None of the differences reached statistical significance. The methods differ in frame time and in which risks you take, not in a clean safety ranking.

Frame time is where LON beats Ilizarov without argument: 17.4 days per centimeter against 42.5. Against a magnetic nail, LON loses on precision, on the number of operations and on complications, and wins on two things: the implant is far cheaper, and weight-bearing during distraction is less restricted.

It depends on the surgeon more than the method. LON suits the patient who wants to pay less than a magnetic nail costs, accepts 7 to 18 weeks in a frame, and can commit to daily pin care and a second operation. The comparative series excluded patients with a history of bone infection and those whose deformity needed gradual correction, because a straight nail cannot bend a bone; the Tianjin protocol also required a tibial canal of at least 8 mm to take an unreamed nail.

Five questions separate a careful LON surgeon from a volume one. How do you keep the wires and pins clear of the nail, and by how much? Akola's answer was 3 to 5 mm. How many deep infections have you had, out of how many LON cases? When does the frame come off: weeks after distraction ends, or months? Who checks my pin sites after I fly home? How many operations are in this quote, and is nail removal one of them?

Ask for the surgeon's own numbers in Paley's terms: problems, obstacles, complications. None of the LON method complications above is an argument against the method. They are the list a good surgeon walks you through before you ask.