The manifestations of Ollier’s disease usually appear in early childhood because multiple enchondromas near the epiphyseal plate cause severe progressive growth inhibition and angular deformity. As a result of erosion of the adjacent physis, tethering of the physis by a bridging tumor, or abnormally thick periosteal sleeves formed in reaction to a tumor, the diaphyses of the affected bones seem short and widened [13]. Fractures through the tumors may result in induced deformity and LLD [2].

Traditional treatments for Ollier’s disease are similar to those for other benign bone lesions, including enchondromas, and include excision by curettage, corrective osteotomies, bone grafting, and internal fixation [14]. However, complete curettage of the enchondromas is realistically impossible because the lesions are extensive [7]. These methods also cannot resolve the severe LLD.

Recently, Huser et al. reported successful lower limb lengthening using implantable lengthening nails for patients with Ollier’s disease (six patients, 11 segments lengthened) if the bone size and morphology permits. Gradual correction can only be used for length, not rotation or alignment. Acute rotation and deformity correction can only be performed during surgery [15]. However, external fixators allow gradual correction in all planes and correction of LLD, although the risk of transcutaneous fixation infection remains, and the bulk of the fixator presents a major nuisance for patients.

With the development of external fixation technology, the bowing and shortening of a bone segment can often be corrected by corticotomy and lengthening. Some researchers have expressed concerns that the affected bone may be weakened by Ollier’s disease and consequently treatment may result in pathological fractures [8,9,10]. However, other researchers have suggested that lengthening is no more complex compared to cases of LLD due to other causes aside from Ollier’s disease because the growth disorder only involves bone; the soft tissues are normal [16, 16]. In our study, there was no difference in the incidence of complications in the lengthened segments in patients with and without Ollier’s disease when joint stiffness, infection, pathological fracture, vascular impairment, neurapraxia, and non-union were evaluated. External fixation provided sufficient stability for deformity correction and limb lengthening.

Some doctors have noticed that a shorter healing time and early consolidation of the lengthened segment are more common in some patients with Ollier’s disease [18]. There are two solutions to deal with the early consolidation. One is to increase the lengthening rate; the other is to perform osteotomy repeatedly to continue lengthening. Myers noticed a tendency for hypertrophic bone regeneration in patients with Ollier’s disease [19] and recommended a higher rate of distraction. Madan [9] noticed three cases of early consolidation in ten patients that required manipulation under anesthesia and osteoclasis or cessation of lengthening. The target lengthening length can be achieved by performing repeated corticotomy and repeated lengthening. However, this method increases the number of operations, the pain experienced by the patient, and the economic burden. Our preferred option is to increase the lengthening rate. There may be a higher risk of infection, delayed healing, or nonunion, so an appropriate distraction rate that can achieve the target extension length with normal bone union, preventing delayed bone union and nonunion and reducing the hardness of the lengthened segment, should be chosen to meet these demands.

There are different and even contradictory data regarding BHI, EFI, and other measures in different studies. Reported femoral BHI ranged from 22.5 to 35 days/cm, tibial BHI ranged from 21 to 35.7 days/cm, and polysegmental femorotibial BHI ranged from 19.9 to 31.8 days/cm [17, 20,21,22,23]. Watanabe et al. [10] reported lower limb segment EFI values of between 39.7 days/cm in an intralesional distraction osteogenesis group and 30.8 days/cm in an extralesional distraction osteogenesis group. Some of these differences could be caused by the fact that different authors have different definitions of BHI. It is therefore easy to become confused over which segment lengthening rate is appropriate. Consequently, we have clearly defined every concept of LG, DI, LL, LI, BHI, and EFI in Table 1 and Fig. 1 to allow better understanding in this study.

In our study, the healing rate and lengthening rate were higher in patients with Ollier’s disease than in those without (shown in Table 3: objective outcomes in both groups), and the difference was especially significant in the femur. In these conditions, the lengthened segment will undergo early consolidation and fail to achieve the target length and angular correction. These findings mean that we should speed up the lengthening rate (DI, LI, BHI, and EFI), increase the range of angular correction according to the patient, shorten the duration of lengthening, and remove the external fixator early to achieve a good therapeutic effect. If done well, the patients could recover well earlier, reducing both the nursing burden and the financial burden.

As to why lower limb lengthening and deformity correction are accelerated in children with Ollier’s disease, Couvineau et al. speculated that tumors initially develop near the growth plate cartilage where endochondral bone ossification occurs. Endochondral ossification is a highly regulated process that requires the differentiation of mesenchymal cells into hypertrophic chondrocytes and the subsequent replacement of the cartilaginous matrix by mineralized bone. It has been postulated that enchondromas result from abnormalities in signaling pathways controlling the proliferation and differentiation of chondrocytes, leading to the development of intraosseous cartilaginous foci [24]. In our study, the lengthening process accelerated in every phase in patients with Ollier’s disease compared to those without. According to the law of tension stress, the lengthening process stimulates cell division, especially in the diseased segment [11], which may influence signaling pathways. However, there is currently no consensus, and the mechanism needs further study.

There were some limitations to this study. First, Ollier’s disease is a rare disease; consequently, this is a small case series and an increase in numbers would improve the validity of the findings. Second, this was a retrospective case series—the data were limited to only what is reported in the medical records and available radiographs. No gait analysis was performed, and we did not evaluate these patients using the pediatric outcomes data collection instrument or visual analog scale. In the future, we will consider using these to measure functional outcomes. Finally, a larger-scale prospective study is warranted, which should be designed to assess the appearance and function of the affected limb in patients with Ollier’s disease.