Definition
Chronic, non metabolic bone disorder
Characterised by increased bone resorption, bone formation and remodelling
Epidemiology
Rare < 40
1 – 3 % population over 60
M > F
Aetiology
Unknown
Paramyxovirus implicated
- measles
- RSV
- canine distemper virus
Electron Microscope
- viral like inclusion bodies in osteoclasts
No presence of specific viral antibodies
Pathophysiology
Intense focal resorption of normal bone by abnormal osteoclasts
- primary abnormality
- osteoclasts large, very active, numerous with excess nuclei
- make large resorptive cavities in bone matrix
In response, osteoblasts recruited
- activity very rapid
- because of this, newly formed bone is not organised and remains irregular and woven in nature
- less resistant and more elastic
- prone to deformity and fracture, especially in weight bearing extremities
3 phases
1. Initial short lived burst of multinucleate osteoclastic activity, causing resorption
- this phase has marked elevation of serum alkaline phosphatase level
2. Mixed phase of both osteoclastic and osteoblastic activity, with increased bone turnover
- leads to structurally abnormal bone
3. Final sclerotic phase
- bone formation exceeds bone resorption
Types
Monostotic 25%
Polyostotic 75%
Sites
Pelvis
Lumbosacral spine
Femur
Tibia
Presentation
Usually incidental x-ray or elevated alk phosphatase
Bone pain
Bone deformity
Fracture
Arthropathy
- incidence may be no higher than normal population
- patterns are different
- i.e. coxa vara and protrusio in hip
Neurological complication
- deafness / involvement of petrous temporal bone
- cranial nerve palsy
- spinal cord compression
Pain / sarcomatous transformation
- beware patient with increasing pain / fracture
- may develop OS in tibia / pelvis
X-ray
All three stages may be present in same patient and same bone at same time
First stage
- lytic areas
- osteoporosis circumscripta cranii
- less commonly in long bones (advancing V shaped lytic lesion)
Third stage
- dense sclerosis
Deformity
- sabre tibia
- coxa vara / protrusio hip
- skull (leonine)
Bone scan
Shows increased uptake
Biochemistry
Diagnosis
- urinary hydroxyproline levels
Calcium
- may be elevated after bed rest
ESR
- may be elevated in malignant transformation
Serum alkaline phosphatase
- enzyme on osteoblasts
- good indicator of activity
Histology
Rarely needed
Predisposes to fracture
Mosaic pattern of poorly organised lamellar bone
Mulitnucleated osteoclasts
Management
Non operative Management
Bisphosphonate
Indications
Bone pain
Neurological symptoms
Long bones with risk of fracture
Risk of spinal neural compression
Preoperative
Bed rest induced hypercalcaemia
Aim
Reduce alk phos to normal
Results
Reid et al N Engl J Med 2005
- RCT of single infusion of risedronate v 30mg per day for 30 days
- reduction of Alk Phos at least 75% as end point
- faster, more complete and longer lasting effect with IV infusion
- good therapeutic response in both groups
Miller Am J Med 1999
- RCT comparing risedronate to etidronate
- risedronate had better and longer lasting remission
- also had more significant reduction in pain relief
Operative Management
Hip pain
DDx
- fracture (tension side)
- bone pain (treat with bisphosphonates)
- hip OA (confirm with intra-articular HCLA)
- tumour
THA
Surgical issues
Bleeding
- known to have excess bleeding
- reduce vascularity with medical treatment
- use cell saver
Hard bone
- difficult reaming and broaching
- may need burrs to enter femur
Cement v Uncemented
Protrusio
- medial bone graft, lateral offset liners +/- antiprotrusio cages
Fracture
- intra-operative and post-operative
HO
- may need prophylaxis
Results
Lusty et al J Arthroplasty 2007
- 23 THR in Paget's followed on average for 6.5 years
- 1 aseptic loosening
- 2 periprosthetic fractures
TKA
Surgical issues
Bone very hard and deformed
- difficulties with IM and EM jigs
- navigation may be advantageous
Corrective osteotomy
- may be required
- in tibia especially
- metaphyseal best site for healing
- healing times are probably delayed
Results
Lee et al J Arthroplasty 2005
- 17 TKR followed up for 9 years
- 1 revision for aseptic loosening at 10 years
- no deep infection or substantial HO