Simple bone cysts of the proximal humerus presented with limb length discrepancy: A case report

Abstract

Background: Simple bone cysts (SBC) are benign tumor-like bone lesions typically identified in children. While SBC may lead to growth disturbances or growth arrest, such cases are uncommon. The mechanisms behind these observations remain unclear. Additionally, research on the etiology of SBC remains inconclusive, and there has been no consensus on the appropriate timing and methodology for treatment.

Case summary: Here, we present our experience in the successful surgical management of a 10-year-old girl with SBC, who presented with a pathological fracture complicated by malunion of the displaced fracture, varus deformity, and limb length discrepancy. We hypothesized two possible etiologies for the patient's growth arrest and subsequent humerus varus deformity: (1) Direct disruption of the physis by fluid from the cyst itself; and (2) damage to the epiphysis due to repetitive pathological fractures associated with SBC. In addressing this case, surgical intervention was undertaken to correct the proximal humerus varus deformity. This approach offered the advantages of simultaneously correcting angular abnormalities, achieving mild limb lengthening, providing definitive SBC treatment, and reducing the overall treatment duration.

Conclusion: As per current literature, acute correction of acute angular deformity in proximal humeral SBC is not well comprehended. However, in this specific case, acute correction was considered an optimal solution.

Keywords: Benign; Bone cyst; Case report; Growth arrest; Humerus; Limb length discrepancy; Solitary cysts.

Figure 1

Series anteroposterior plain radiographs of the left humerus. A: Preoperative anteroposterior plain radiographs of the left humerus at initial presentation; B: 1-month postoperative anteroposterior plain radiographs of the left humerus; C: 1-year post-operative anteroposterior plain radiographs of the left humerus; D: Anteroposterior plain radiographs of the left humerus at 1-year post-removal of internal fixator; E: 1-year post-removal of internal fixator surgery.

Figure 2

Preoperative magnetic resonance images and pathological results of the patient. Preoperative T2-weighted magnetic resonance images of the left humerus showed a marked deformity of the humeral head and a potential malunion of the displaced fracture in the left humeral neck.

Figure 3

Surgical procedure for acute correction of the proximal humerus for the varus deformity. The red area indicates the location of the simple bone cyst (SBC). A: Osteotomy was performed in the most angulated area, removing the deformity site of the SBC; B: The gap was filled with allograft (donor femoral head); C: The proximal humerus was fixed with an anatomical locking plate (Depuy-Synthesis®, Raynham, MA, United States) in a valgus position.

Figure 4

Two-week postoperative photos of the patient. A: Full active range of motion of the left shoulder; B: About 2-3 cm length discrepancy on the affected side.

Figure 5

Pathological results of the patient. A: Histological results showed fibrous cyst wall with fibrin-like material and calcification; B: Histological results showed cystic wall with cholesterol clefts and surrounding some new bone formation, all of which may be indicative of a diagnosis of a simple bone cyst.

Figure 6

Two hypotheses for the etiology of our patient with simple bone cyst who presented with a pathological fracture, angular deformity, and limb length discrepancy. The red area represents the location of simple bone cyst (SBC); the blue dotted line represents the epiphysis; and the yellow line indicates the affected epiphysis. A–D: The first hypothesis. A: The proximal humeral simple bone cyst extends through the physis on the medial side; B: The SBC subsequently caused growth arrest and varus deformity of the humerus; C: Due to a proximal humerus fracture, additional varus angulation of the humeral head occurs; D: SBC presenting with a pathological fracture, complicated with malunion of the displaced fracture, varus deformity and limb length discrepancy. E–H: The second hypothesis. E: A proximal humeral simple bone cyst develops; F: Repetitive pathological fractures due to SBC damaged the medial epiphysis of the proximal humerus and varus humeral head angulation was established as a consequence; G: The humerus develops varus deformity and a length discrepancy due to a damaged epiphysis; H: SBC presenting with a pathological fracture, complicated with malunion of the displaced fracture, varus deformity and limb length discrepancy.