Surgical Results of Limb Lengthening at the Femur, Tibia, and Humerus in Patients with Achondroplasia

Selection of the Study Subjects

The protocol of this study was reviewed and approved by the Institutional Review Board of the Samsung Medical Center (IRB No. 2018-07-123). The informed consent was waived. From 2003 to 2017, 14 achondroplastic and one hypochondroplasia patients (nine males and six females) underwent limb lengthening. The mean age at the first operation was 11.7 ± 2.3 years (range, 6.8 to 15.4 years), and the mean follow-up duration was 66.7 ± 40.9 months (range, 42.0 to 209.0 months). The initial height, body weight, and body mass index were assessed according to the admission date for the first operation, which were 119.3 ± 11.6 cm (range, 90.0 to 137.0 cm), 35.9 ± 8.4 kg (range, 17 to 47 kg), and 24.9 ± 3.8 kg/m² (range, 20.3 to 32.3 kg/m²), respectively.

Surgical Techniques

All surgical procedures were performed by the senior author (JSS). Regarding the lower limb lengthening, crossed lengthening was performed in 12 patients. The second surgery was performed on the opposite side 322.0 ± 54.8 days (range, 254 to 434 days) after the first surgery. Among the 12 patients, one patient underwent the lower limb lengthening twice for each side (i.e., four operations in total). Of the remaining three patients, one patient underwent bilateral tibial lengthening followed by bilateral femoral lengthening (308 days later) based on patient's choice; two patients visited our center after bilateral tibial lengthening at other center, so only bilateral femoral lengthening was performed at our institution.

Regarding the humeral lengthening, it was performed in 14 patients; one patient has been followed up in the out-patient clinic after the lower limb lengthening performed at our institution. Among the 14 patients, four underwent simultaneous bilateral humeral lengthening, and 10 underwent staged operation with an interval of 258.1 ± 92.7 days (range, 173 to 420 days). As a result, we operated 32 femoral, 28 tibial, and 28 humeral segments.

The osteotomy was outlined with a series of drill holes, and it was gently completed using an osteotome. A single diaphyseal osteotomy was performed for the femur. In 20 femoral segments, an acute correction was additionally performed to correct varus deformity of the femur. Except for two segments using an Ilizarov ring fixator, all the femoral lengthening procedures were performed using a monolateral external fixator (Fig. 1). For the tibia, a single proximal level osteotomy was performed, and an Ilizarov ring fixator was used. A fibular osteotomy was also performed (Fig. 1). In 15 tibial segments, a gradual correction to correct varus deformity of the tibia as well as lengthening was performed. A single diaphyseal osteotomy was performed, and a monolateral external fixator was used for the humerus (Fig. 1). In 11 humeral segments, an acute correction was performed to correct limited extension of the elbow joint or cubitus valgus.

Fig. 1
Simple radiographs taken after external fixator application and osteotomy in the femur (A), tibia (B), and humerus (C).

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Postoperative Protocol

Distraction began approximately 7 days after the surgery at a rate of 0.25 mm every 6 hours. The rate was modified later, based on the radiographic and clinical features. Lengthening was continued considering the desired length and combined difficulties. The external fixators were removed when radiographic evidence of at least three cortices was shown. The mean duration of external fixator application was 236.9 ± 40.1 days (range, 166 to 343 days) for the femur, 242.9 ± 37.9 days (range, 196 to 343 days) for the tibia, and 194.3 ± 33.4 days (range, 152 to 278 days) for the humerus.

Radiographic Measurement

All indicators were measured using the picture archiving and communication system (PACS) system (GE Healthcare, London, UK). The gained length (cm) was defined as a difference in the length of the long bone measured at two time points, immediately before and after lengthening. The lengths of femur and tibia were measured parallel to the long axis on the anteroposterior view. The length of femur was measured from the most proximal part of the femoral head to the most distal part of the femoral condyle. The length of tibia was measured from the most proximal part of the tibial eminence to the midpoint of the tibial plafond.7) The length of humerus was measured parallel to its long axis from the most proximal part of the humeral head to the most distal part of the trochlea on the lateral view.8) Lengthening percentage (LP) was calculated by dividing the gained length by the initial length.9)

The healing index (HI) was calculated by dividing the entire duration of external fixator application by the gained length.6) The consolidation period index was calculated by dividing the duration of consolidation period (from the time of lengthening cessation to the time of external fixator removal) by the gained length. The callus shape was classified into five types: fusiform, cylindrical, concave, lateral, and central.9, 10) The occurrence of subluxation or dislocation of adjacent joints was also assessed.

LLD and hip-knee-ankle (HKA) alignment in lower limbs at the last follow-up were measured using a long bone radiograph obtained in standing position. LLD was defined as difference between the vertical heights of the two lower limbs. HKA alignment was defined as alignment between the mechanical axis of the femur and that of the tibia. All indicators were measured twice (at an interval of minimum 2 weeks) by two observers, and the mean values were used for analysis. Intraclass correlation coefficients were calculated to evaluate reliabilities and all were > 0.8.

Clinical Outcomes

Limitation of range of motion (ROM) of adjacent joints was assessed. In addition, the patients were asked to rate their overall satisfaction with results as very satisfied, satisfied, fair, or dissatisfied.

Complication

Difficulties that occurred during the follow-up period were subclassified into problems, obstacles, and true complications based on a classification described by Paley.11)

Statistical Analysis

ANOVA with LSD post-hoc test and Fisher's exact test were used to compare the surgical results according the lengthening sites. Paired t-tests were performed for comparison between preoperative and postoperative values. Mann-Whitney U-tests and Fisher's exact tests were used in subgroup analysis. IBM SPSS ver. 23.0 (IBM Corp., Armonk, NY, USA) was used, and the significance level was set at p < 0.05.

Radiographic Measurements

The mean gained length for the femur, tibia, and humerus was 8.3 ± 1.9 cm (32.1% ± 10.8%), 8.5 ± 1.5 cm (42.0% ± 10.3%), and 7.4 ± 1.6 cm (40.4% ± 10.4%), respectively. The LPs of tibial and humeral lengthening were greater than that of femoral lengthening (p = 0.001 and p = 0.003, respectively). The consolidation period index of humeral lengthening was lower than those of femoral and tibial lengthening (p = 0.043 and p = 0.023, respectively). Other comparisons showed no significance. Subluxation or dislocation of adjacent joints was not observed. Detailed results of radiographic indicators are shown in Table 1. The mean HKA alignment of 30 lower limbs in 15 patients was 9.7° ± 9.4° before surgery, and it significantly improved to −0.5° ± 4.9° at the last follow-up (p < 0.001). Of the 12 patients who underwent crossed lengthening, five patients showed LLD ≥ 1.0 cm. Among their 24 lower limbs, three showed valgus alignment ≥ 5° and one showed varus alignment ≥ 5°. Detailed alignment and length discrepancy of 24 lower limbs are presented in Table 2. Using the criteria of 5° and 1 cm, six showed satisfactory results in both alignment and length discrepancy at the last follow-up (Fig. 2).

Fig. 2
Long bone radiographs taken before the lower limb lengthening (A) and at the last follow-up (B). During the 4 years and 8 months of follow-up, the male patient (#2 in Table 2) gained 28 cm of height including physiological growth after the crossed lower limb lengthening. At the last follow-up, both alignments and length discrepancy of lower limbs were satisfactory. Dotted lines that connect the centers of the hip and ankle in each lower limb pass near the center of the knee at the last follow-up.

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Table 1
Results of Analysis of Radiographic Indicators

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Table 2
Final Alignment and Length Discrepancy of Lower Limbs in Patients Who Underwent Crossed Lengthening

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Clinical Outcomes

Limitation of the ROM or instability of the adjacent joints was not observed. All patients were satisfied with their surgical results: very satisfied, eight; satisfied, seven. In particular, 14 patients who underwent humeral lengthening were able to reach the perineal area and perform perineal hygiene independently.

Complications

The most common problem was the pin site infection. Three fractures after removal of the external fixators occurred but united following immobilization. Three femoral fractures, eight equinus deformities, and four cases with premature consolidation of the fibula were surgically treated. Obstacles related to humeral lengthening were not observed: the frequency (0%) was significantly lower than that for tibial lengthening (42.9%, p < 0.001). The frequency of total difficulties in humeral lengthening (42.9%) was significantly lower than that in femoral lengthening (68.8%, p = 0.039). We did not experience intraoperative injuries associated with late sequelae. Details are described in Table 3.

Table 3
Difficulties That Occurred during Limb Lengthening and Follow-up

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Subgroup Analysis

To analyze the significant factors associated with complications, subgroup analyses were performed: the group with fractures after external fixator removal (n = 6) vs. the group without (n = 82); premature consolidation group (n = 4) vs. remaining tibial segments (n = 24); and equinus deformity group (n = 8) vs. remaining tibial segments (n = 20). Among the various comparisons, eight tibial segments with equinus deformity showed significantly lower LP than the other 20 tibial segments (35.2% vs. 44.7%, p = 0.043). No other comparisons showed significance.