This study is a prospective observational non-interventional multi-centre cohort study of patients, 12 years or older, initiating a lower limb lengthening procedure with FITBONE and who have a length discrepancy of 30mm or more between the limbs.

The following parameters will be assessed for up to 24 months.

• Pain using the Visual Analog Scale (VAS), Patient Global Assessment (PGA) and Clinical Observer Global Assessment (COGA)
• Patient satisfaction using the Patient Global Impression of change (PGI-C) scale
• QoL using the 36-Item Short Form Survey/Paediatric Quality of Life Inventory (SF-36/PedsQL)

The study period is 24 months post-surgery. Each patient's demographic data, medical history, any relevant concomitant medication, physical examination, range of motion data will be recorded using a standardized case record form after informed consent is provided and the healthcare provider completes a physical examination regarding the patient's conditions and record determination as to whether FITBONE is recommended. The decision to treat, observe, and to include in this observation study is at the discretion of the healthcare provider. This is an observational study and therefore, the participating healthcare provider will manage patients according to the usual clinical practice.

Surgery will be performed according to the standard surgical procedure described previously. Study of Investigational Product(s). Five to ten days after the lengthening nail placement, the lengthening mechanism is operated by transmitting energy necessary for the lengthening from the outside. This period is referred to as the distraction period. The rhythm of lengthening and strict protocol for an individual patient, indicating the daily lengths of lengthening to be applied, are decided by the healthcare provider taking into account all influencing factors. Therefore, the end of the distraction period, bone healing, implant removal, and 6 months post-implant removal may differ by individual. In the event the distraction period is extended by the healthcare provider, the new distraction period will determine the end of the distraction time point. All patients will be followed until the end of the scheduled study period regardless of any change in their treatment or other conditions.

Six visits are planned:

1. Surgery (baseline)
2. End of the distraction phase
3. End of bone healing
4. Implant removal
5. 6-month post-removal
6. 24-month post-surgery The satisfaction will be assessed at implant removal, 6 months post implant removal, and 24 months post-surgery.

The QoL will be assessed at baseline, at 6 months post implant removal, and 24 months post-surgery.

Pain will be assessed at all timepoints. Measurement of pain at the end of the distraction phase, the patient will be requested to report the pain experienced in the past week, at the moment, and during or immediately after the distraction period. At other time points, pain for only at the moment will be captured.

Range of motion (ROM) will be measured at the end of bone healing, and at the 24 months post-surgery.

Lengthening achieved will be measured at the end of bone healing. Any incidence of adverse events will be recorded at any point during the 24-month follow-up period.

Inclusion Criteria:

• Patients aged ≥12 years old, with congenital or acquired lower limb discrepancy greater than 30mm, undergoing femoral or tibia bone lengthening with FITBONE
• Patients with a regular indication for a surgical intervention with FITBONE according to manufacturer IFU
• The patient (or his/her legally acceptable representative) is capable of understanding the content of the Informed Consent Form (ICF)
• The informed consent form is correctly obtained

Exclusion Criteria:

• Patients with a medical condition that is contraindicated according to the FITBONE instruction for use.
• Patients with any conditions that, in the Investigator's opinion, may interfere with the study execution, including those likely to be lost to follow-up.
• Patients who have any conditions or medical condition that, in the investigator's opinion, may interfere with the study's execution or in which the patient should not participate for safety reasons.
• Patients requiring the application of or have already in-situ concomitant devices that cannot be safely removed (except for permitted concomitant devices).
• Patients participating in other clinical or have taken part in any clinical study in the last 3 months.

The aim of the study is to have a representative population of FITBONE patients in France, who are cimpliant with the inclusion criteria, during the 1 year enrollment period. Any centre in France that uses FITBONE in their routine clinical practice will be invited and have the opportunity to participate in this study. All centres must systematically and without exception offer every patient being implanted with FITBONE the opportunity to participate in the study, limiting selection bias and increasing the representativeness of this study to the French population.