Unicameral Bone Cyst

 

UBC femurUBC shoulderUBC distal tibia

 

Definition

 

Simple Bone Cyst

- solitary cavity containing clear fluid

- originating in the metaphysis of growing children

- adjacent to the metaphyseal aspect of the growth plate.

 

Etiology

 

? blockage in venous drainage

 

Epidemiology

 

Peak age 9 (3-14)

Male:female 2:1

 

Location

 

90% humerus and femur

Proximal metaphysis where growth is greatest

 

Can occur in calcaneum

 

Types

 

Active UBCLatent UBC

 

Active - adjacent to growth plate / physis

Latent - separated from physis by normal bone

 

Clinical 

 

Asymptomatic

Pain caused by pathological fracture

 

X-ray

 

UBC HumerusUBC Humerus 2

 

Well-defined lucency 

- thin sclerotic rim

- usually central

- thinned cortex with slight expansion

- thin internal septa

- can be multi-loculated

 

Fallen-Leaf (AKA fallen-fragment)

- with pathological fracture

- indicates that the lesion has no matrix and is fluid filled 

 

UBC shoulder

Fallen leaf sign

 

DDx ABC

 

ABC

- eccentric (v central)

- width > physis

- can be very difficult to tell

- requires biopsy

 

MRI

 

UBC MRI 1UBC MRI 2

 

MRI UBC tib 1UBC tibia MRI 2UBC tibia MRI 3

 

Gruenewald et al Br J Radiol 2023

- 36 patients with UBC or ABC

- fluid fluid levels / septation seen in both

- arterial feeders on MRA helped differentiate some ABC's

 

CT

 

CT humerus UBCCT ankle UBC 1CT ankle UBC 2

 

Pathology

 

https://www.pathologyoutlines.com/topic/bonesolitarybonecyst.html

 

Fluids

- contain high levels of prostaglandins

- contain high levels of alkaline phosphatase

 

Gross

 

Cyst

- large intramedullary cavity

- lined with membrane

- contains clear fluid compared with ABC

- can have septations

 

Histology

 

Thin fibrous layer of connective tissue

- cells resembles synovial cells

- few multinucleated giant cells

 

Natural History

 

Urakawa et al BMC Musculoskeletal Dis 2014

- 60 patients with pathological fractures of UBC

- 30% healing rate following fracture and nonoperative care

 

Kim et al J Orthop Surg 2018

- 56 patients with fracture of humerus UBC

- overall healing rate 66%

- diaphyseal / latent lesions and older patients more likely to heal

 

Management

 

Fracture

 

1.  Humerus

 

Typically treat nonoperatively

Obtain union

Consider further intervention when fracture heals and UBC persists

 

Humerus UBC # 1Humerus UBC # 2Humerus UBC # 3

 

2.  Femur

 

Want to prevent fracture and avoid morbidity / deformity

 

UBC fractured femurUBC femur fracture 2Distal femur UBC fracture 2

 

Options

 

Observe

Percutaneous treatment

- cortisone

- bone marrow aspirate / demineralized bone graft

Curettage and bone graft

ORIF

 

Results

 

Kadhim et al J Child Orthop 2014

- systematic review of 62 articles and 3200 UBC

- healing rates

- nonoperative treatment 64%

- methylprednisone injection 77%

- bone marrow injection 78%

- bone marrow with demineralized bone matrix injection 99%

- surgical curettage with bone graft 90%

- flexible IM nails without curettage 99%

- decompression with cannulated screws 89%

 

Aspiration and injection cortisone

 

Technique

 

Inject methylprednisolone

- steroid blocks PGE

 

Results

 

Pavone et al Eur J Orthop Surg Traumatol 2014

- 23 UBC treated with serial injections of methyprednisolone

- good results in 19/23

- refracture in 4/23

- minor skin discoloration in 3 patients

 

Bone marrow aspirate +/- demineralized bone matrix

 

Technique

 

GA / Aspirate from bone marrow

- inject into cyst under image intensifier

 

Results

 

Wright et al JBJS Am 2008

- RCT of bone marrow aspirate v methylpred in 77 patients followed for 2 years

- 42% in the methylpred group healed

- 23% in the bone marrow group healed

 

D'Amato et al Acta Orthop Traumatol Turc 2020

- 24 patients treated with bone marrow concentrate and demineralized bone graft

- 29 had three injections of methylpred

- 83% healing with BMC / demineralized bone graft

- 59% healing with methylpred

 

Curettage + bone graft

 

Bone graft

- allograft

- bioceramics

 

Care with active lesions as don't want to injure growth plate

 

UBC Humerus DrillingUBC Humerus Curettage

 

Humerus bone graft 3Bone substitute UBC

Bone graft with silicone bone substitute (BonAlive)

 

Humerus bone graft 2Humerus bone graft 1

 

Results

 

Hunt et al Orthopedics 2009

- 21 proximal humeral cysts

- treated with curettage / allograft / bone marrow aspirate

- 75% union rate with one surgical procedure

- 95% with two surgical procedures

 

ORIF and bone graft

 

Indication

- fracture

- weight bearing bone

 

UBC femur frac 1UBC femur ORIF 2

 

UBC fractured femurUBC femur ORIF 2

 

Surgical cyst drainage using implants

 

Concept

- venous hypertension cause of cyst

- if allow cyst to drain, will heal

 

Options

- cannulated screws in calcaneum

- flexible nails humerus

- intramedullary nail femur

 

Unicameral Bone CystUnicameral Bone Cyst IM Nail

 

Results

 

Erol et al J Paediatr Orthop B 2017

- humeral simple bone cysts

- 37 curettage and bone graft

- 16 had addition of flexible nails

- 76% healing curettage and bone graft

- 100% healing with flexible nails

 

ORIF + fibular strut allograft

 

UBC humerus fibular strut 1UBC humerus fibular strut 2

 

Jamshidi et al Int Orthop 2018

- 14 cases humerus UBC

- treated with locking plate + fibular allograft

- complete healing in 10, partial healing in 4