Limb Salvage Using Non-hinged Endoprosthesis and Staged Correction of Leg-length Discrepancy for Children with Distal Femoral Malignant Tumors

Abstract

Objective: Limb salvage in pediatric patients remains a challenge. We describe a staged strategy. The procedure includes: (i) tumor removal and non-hinged static endoprosthesis reconstruction; (ii) leg length discrepancy (LLD) correction by shoe lift or distraction osteogenesis; and (iii) maturity reconstruction by regular endoprosthesis. The aim of the study was to investigate the results of non-hinged static megaprosthesis reconstruction and staged LLD correction in the treatment of malignant tumors in the distal femur in children.

Methods: Non-hinged megaprostheses were implanted in 12 pediatric patients with osteosarcoma in the distal femur. The prosthesis consists of a femoral component with constrained condylar knee (CCK) design, and a tibial component with a small-diameter press-fit stem and derotation fins. A posterior stabilizing polyethylene component is fixed on the tibial component. The cases were prospectively followed up with focus on the growth rate of adjacent uninvolved bone in the salvaged limb, joint stability, knee stability, function outcome, length discrepancy, and surgery-related complications.

Results: There were five girls and seven boys included in the study, with an average age at the time of primary surgery of 10.0 years (range, 8-12 years). All the tumors were located in the distal femur. The average follow up was 76.3 months (range, 24-139 months). The Ligament Augmentation and Reconstruction System (LARS) ligament was used in two patients to enhance the soft tissue reattachment and reconstruct medial collateral ligament (MCL). Ten patients were alive at the final follow-up and two had died of lung metastases. Expected LLD was 6.7 cm (range, 3.0-13.2 cm) at initial surgery. At the final follow-up, nine patients reached skeletal maturity and the actual LLD at the femur was 5.3 cm (range, 3.0-10.1 cm), excluding 1 cm correction at initial surgery by endoprosthesis. The proximal tibia physis showed an average of 86.7% (range, 56.5%-100%) growth of the contralateral side. The mean reduction in tibial length was 1.2 cm (range, 0.5-4.7 cm). Six patients received distraction osteogenesis at a mean length of 5.4 cm (range, 3.0-9.1 cm). Range of knee movement was between 85° and 125°, with an average of 102.5°. The Musculoskeletal Tumor Society 93 score of patients alive was 80.6 (range, 60-90).

Conclusion: Non-hinged static megaprosthesis followed by LLD correction with shoe lift or staged distraction osteogenesis appears to be an alternative option to treat children with malignant bone tumors around the knee.

Keywords: Distraction osteogenesis; Limb length discrepancy; Limb salvage; Osteosarcoma; Skeletally immature.

Figure 1

(A) A hemiarthroplasty megaprosthesis was used to preserve the growth plate in the proximal tibia before 2010. (B) To improve the stability of the knee joint, a non‐hinged CCK design was used in the static megaprosthesis design.

Figure 2

The flow chart showing the principal of staged limb salvage in skeletally immature patients.

Figure 3

An intraoperative photo showing the non‐hinged joint with a posterior stabilizing polyethylene component fixed on the tibial component.

Figure 4

An illustrative case (case 2). (A) The patient was an 8‐year‐old boy with an osteosarcoma of the left distal femur; (B) radiograph 2.5 years after surgery and (C) X‐ray taken 5 years after surgery showing cortical atrophy at host bone–prostheses junction with femoral shortening of 9 cm; (D) shoe lift was used to correct the limb length discrepancy; limb lengthening of 5 cm by OrthoFix apparatus (E) and final tibia length (F).