Pathological calcification

Definition

· accumulation of calcium salts in the soft tissues

· may be dystrophic or metastatic

aetiology

Dystrophic

· occurs in damaged tissues

· dead or degenerative

· two phases

Initiation

· exact mechanism uncertain

· progressive disintegration of dead cells leads to denatured proteins

· exposes groups capable of binding PO₄

· act as nucleation sites for precipitation of calcium

Propagation

· accentuated by hypercalcaemia

Metastatic

· may occur in normal tissue whenever there is hypercalcaemia

· hypercalcaemia may be due to

· hyperparathyroidism

· malignancy

· vitamin D intoxication

· high bone turnover

· renal failure

· exact mechanism unknown

· possibly related to localized high pH

· favours deposition of basic calcium salts

Pathology

Dystrophic

· deposits usually amorphous and noncrystalline

· may be in the form of

· phosphates

· carbonates

· oxalates

· often mixed with iron salts

· hydroxyapatite crystals may form

· may progress to ossification

· often causes organ dysfunction

Dead tissues

· caseation

· parasites

· fat necrosis

· infarcts

· thrombi

· haematoma

Degenerative tissues

· atheroscerosis

· damaged heart valves

· infected lymph nodes

· degenerating tumours

· chondrocalcinosis

· calcium pyrophosphate deposition in cartilage

Metastatic

· may occur widely

· predominantly involves interstitial tissue of

· blood vessels

· kidneys

· lungs

· gastric mucosa

· calcium salt resembles that seen in dystrophic calcification

· rarely causes organ dysfunction

Heterotopic ossification

definition

· formation of bone in extraskeletal tissues

· hydroxyapatite crystals within collagen matrix

· different to calcification

· may be divided into

· myositis ossificans

· heterotopic ossification (associated with arthroplasty)

· neoplastic ossification

Myositis ossificans

definition

· pathological bone formation at site of injury

· myositis ossificans is formation of bone in muscle

classification

Traumatic

· most common (see below)

Nontraumatic

Aetiology

· often associated with neurological injury or disorder

· usually involves joints in neurologically affected extremities

· occurs in

· hip and knee (most common)

· shoulder and elbow (less common)

Clinical features

· initial redness and swelling

· decreased joint ROM

· may be confused with

· cellulitis

· phlebitis

· haematoma

Myositis ossificans progressiva

· rare

Aetiology

· inherited connective tissue disorder

· autosomal dominant

Clinical features

· progressive soft tissue ossification

· lumps in musculature

· esp. in neck and hands

· resultant skeletal malformations

· esp. in hands and feet

· digits shortened and stiff

Aetiology

· unclear

· combination of local and systemic factors

Site

· generally more common

· proximally

· around joints

· most common around

· thigh

· elbow

Severity of injury

· most common cause is single major traumatic incident

· direct blow to muscle

· joint dislocation, esp. with fracture

· may also occur with repeated minor trauma

· eg. in adductor longus insertion in horseriders

Clinical features

· history of localised trauma

· initial pain and swelling

· significant associated warmth

· development of hard mass

· gradual resolution of pain

radiology

· changes occur 2-4 weeks after injury

· initially consist of cotton candy appearance

· becomes more osseous in appearance

· may be resorbed

· may become massive with further injury

· fluffy soft tissue ossification

· not attached to bone

pathology

· muscle undergoes inflammatory reaction

· extensive cellular infiltration

· initial formation of collagen by chondroblasts

· collagen undergoes dystrophic calcification

· chondroblasts differentiate into osteoblasts

· osteoid produced

· may be confused with osteosarcoma

· following features help differentiate

· distant from joints

· intact cortex

· zonation from central immature fibrous tissue to peripheral mature bone

· surrounding diseased and trapped muscle

· normal osteoblasts

treatment

Prevention

· initial

· minimise haemorrhage and inflammation

· ice and elevation

· subsequent

· rehabilitate area

· active ROM

· strengthening

Resection

· indications

· large mass of bone

· significant pain, stiffness and weakness

· should be delayed at least 12 months

· resection while immature predisposes to recurrence

· maturity can be gauged by

· development of mature trabecular pattern on x-ray

· no further progression on x-ray

· no significant increased uptake on bone scan

Heterotopic ossification following THR

epidemiology

· some degree occurs in majority of THRs

· significant amount in 10%

· clinically significant in 1%

· more common in men

Risk factors

Definite

1. previous HO

· in same or other hip

· incidence is 80%

· severity similar to previous occurrence

Probable

1. hypertrophic OA

· hypertrophic changes and osteophyte formation

2. ankylosing spondylitis

· esp. if disease active

3. hyperostosis

· DISH and Forestier’s disease

4. Paget’s disease

· esp. if disease active and in area of hip

5. associated trauma

· preoperative or intraoperative fracture

aetiology

· unclear

· similar cascade to fracture healing

· trigger not identified

classification

Brooker

Class I

· isolated islands of bone

Class II

· bone spurs with gap > 1 cm

Class III

· bone spurs with gap < 1 cm

Class IV

· apparent ankylosis

clinical features

· usually none

· if severe, causes pain and stiffness

· may cause recurrent dislocation from impingement

radiology

Plain x-ray

· new bone in periprosthetic soft tissues

· becomes visible by 3-6 weeks

· extent determined by 3 months

· maturation continues for 12 months

Bone scan

· increased uptake indicates continuing activity

· may remain increased for 12 months

Treatment

Prevention

Surgical technique

· gentle handling of tissues

· avoid muscle stripping

· lavage tissues

· drain wound

Low-dose radiation

· 600 rad within 3 days postoperatively

· affects

· incorporation of graft

· union of trochanter

· porous ingrowth

· risk of maligancy

Medications

NSAIDs

· indomethacin 25 mg tds for 6 weeks

· suppresses formation of heterotopic bone

· theoretically reduces porous ingrowth

· risk of GIT side-effects

· interaction with anticoagulants

· contraindicated in peptic ulcer disease

Diphosphonates

· delay calcification

· thus delay appearance of bone on x-ray

· do not prevent osteoid formation

· calcification occurs once drug stopped

· no longer used

Excision

Indications

· significant amount (grade III or IV) WITH

· significant symptoms (pain, stiffness) OR

· revision of prosthesis

Timing

· usually 12-18 months postoperatively

· guided by

· mature appearance on x-ray

· fall-off in uptake on bone scan

Prophylaxis

· should use NSAIDs or radiotherapy

Results

· usually increases ROM

· unreliable effect on pain

· bone often reforms

Neoplastic ossification

mechanisms

Primary bone formation

· produced by

· osteosarcoma

· osteoblastoma / osteoid osteoma

· direct deposition of pathological woven bone

· via intramembramous ossification

Enchondral ossification

· produced by

· osteochondroma

· enchondroma

· synovial chondromatosis

· enchondral ossification of pathological cartilage

Reactive bone

· occurs adjacent to neoplasm

· formed by host osteoblasts