Osteoarthritis: Etiology, Pathogenesis and Treatment Considerations Lee S. Simon, MD Associate Clinical Professor of Medicine Beth Israel Deaconess Medical Center Harvard Medical School
Dec 26, 2015
Osteoarthritis: Etiology, Pathogenesis and Treatment
Considerations
Lee S. Simon, MD
Associate Clinical Professor of Medicine
Beth Israel Deaconess Medical Center
Harvard Medical School
Osteoarthritis• Typically affects people over the age of 50• A biologic process which effects cartilage with
subsequent inflammatory component• Characteristically the major component of the
clinical presentation is pain and decreased function– >75% of people over the age of 75 have x-ray evidence
of disease– > 75% of people over the age of 85 are symptomatic
• Probably affects 16-20,000,000 Americans
Prevalence of Rheumatic Disorders
1050
200
500
1090
3500
5500
7000
10000
2000*
0 2000 4000 6000 8000 10000 12000
Other Arthritis
Ankylosing Spondylitis
Rheumatoid Arthritis
Gout/Pseudogout
Fibromyalgia
Osteoarthritis
Bursitis/Tendinitis
Osteoporosis
Neck and Back Pain
Prevalence (per 100,000)*8000 if subthreshold included.Adapted from Marder WD. Arthritis Rheum. 1991;34:1209–1217.
The Joint as an OrganThe Joint as an Organ
• Cartilage (hyaline, fibro-cartilage)– Hyaline: predominantly type II collagen– Fibrocartilage: predominantly type I collagen
• aneural • avascular • alymphatic• limited capacity for repair after injury
• Menisci (medial, lateral)• Tendons, ligaments,capsule • Bone,periosteum• Synovial fluid/membrane• Muscles
Structure of CartilageStructure of Cartilage
Risk Factors
• Genetics– Abnormal components of the joint as an organ– Abnormal range of motion– Congenital anomolies
• Trauma• Overuse syndromes• Post-infectious• Obesity
Etiopathogenesis
• Normal cartilage and supporting structures subjected to abnormally increased loads– Obesity– Overuse syndromes
• Abnormal cartilage and supporting structures subjected to either minimal loads or abnormally large loads– Inherited defects of structural components (e.g. type II
collagen, cartilage lysis syndrome, hypermobile syndromes)– Ochronosis
OA Biology• Slowly progressive disease• Primarily initially affects cartilage
– Early cellular response: increased synthesis of proteoglycans and collagen followed by increased hydration
– Then later inability to keep up with repair process and failure to replace proteoglycans and collagen
– Consequent loss of cartilage, fissuring of cartilage, subchondral bone sclerosis and finally eburnation with “bone on bone”
• Subsequent inflammatory response to cartilage effects– Clear synovial hypertrophy with consequent stimulus of
inflammatory cytokines (IL-1 and TNF alpha have been shown to be elevated in the joint fluid)
– But these effects are more local: little increase in CRP, few signs and symptoms of systemic inflammatory disease
Conceptual Model of OAConceptual Model of OABiochemical changes/ cells and tissue
Structural changes
Pain and other signs and symptoms
Functional limitation
Reduced quality of life
Surgical replacement
DIPs
PIPs CMCs
OA: Pattern of Joint Involvement
Base of big toe
Neck
Lower Back
Hips
Knees
Diagnosis of OA
• Symptoms– Pain– Decreased function
• Due to boney change • Due to soft-tissue change or swelling• Due to alteration of the normal structures
– Crepitance or “crunching within the joint”
Diagnosis of OA
• Signs– On physical exam
• Asymmetry of findings usually of large joints• Heberdens/Bouchard’s nodes (may be
symmetrical)– Classic hand involvement: DIP/PIP nodular disease
• Some boney swelling• Some swelling and pain out of proportion to
inflammatory findings
Typical OA Hand: Know It When You See It
• Hard boney enlargements
• Heberden’s nodes at the DIP joints
• Bouchard’s nodes at the PIP joints
• Often have “squared” first CMC joint due to osteophytes at that joint
Diagnosis of OA
• By imaging– X-ray
• Presence of osteophytes (biologic evidence of an attempt to repair?)
• Progressive joint space narrowing which is a surrogate measure of cartilage thinning
– Now known not to be linear and some patients are rapid progressors while others are slow progressors or somewhere in between; how to predict which patient falls into which category
• Increased sclerotic change in subchondral bone– When significantly progressive might reflect eburnation
Radiographic Features of the Knee in OA
• Joint space narrowing
• Marginal osteophytes
• Subchondral cysts• Boney sclerosis• Malalignment
Joint space narrowing
Diagnosis of OA
• Imaging– MRI
• Newer technique• Able to provide a 3 D image of the joint as an
organ– Can approximate the volume of cartilage– May be able to identify early change in cartilage
metabolism– Can approximate early bone change (bone
“edema”?)
Diagnosis of OA
• Biochemical markers– Sources of such markers
• Joint tissue/fluid– Synthetic products of the components of the joint– Products that reflect metabolism of the components of the
joint
• Blood– Circulating in serum: products of cartilage turnover
• Urine– Products of cartilage metabolism which are cleared by the
liver (or elsewhere) from the serum and then possibly further processed and then excreted in the urine
Diagnosis of OA
• Biochemical markers not yet adequate for diagnosis, identifying patients at risk, or measuring outcomes BUT:
• Biochemical markers may in the future with further refinement– be useful in exploratory studies – help identify “at risk” or “resistant” patients– help compare therapies– help patients and doctors to select and monitor therapies– help assess efficacy (? surrogate endpoint)
Definitions of Biomarkers and Surrogate Markers
Biomarker (biological marker) or imaging marker is a characteristic that is measured and evaluated as an indicator of normal biologic processes, pathogenic processes, or pharmacologic responses to a therapeutic intervention.
Definitions
• Clinical endpoint- A characteristic or variable that measures how a patient feels, functions or survives.– VAS pain, WOMAC, HAQ, patient global
assessment
• Surrogate endpoint- A marker intended to substitute for a clinical endpoint.
A surrogate endpoint of a clinical trial is a laboratory measurement or a physical sign used as a substitute for a clinically meaningful endpoint that measures directly how a patient feels, functions, or survives. Changes induced by a therapy on a surrogate endpoint are expected to reflect changes in a clinically meaningful endpoint.
Temple - 1995
Questions Asked
• What valid modifiable risk factors/surrogate endpoints are there for predicting the risk of developing osteoarthritis in humans?– Obesity
• Clear opportunity to enrich a study outcome with more chance of having progressive disease especially if the patient has evidence of early OA (jsn, osteophytes)
• Low percentage of patients with progressive disease without evidence of incipient disease
Questions Asked
• What valid modifiable risk factors/surrogate endpoints are there for predicting the risk of developing osteoarthritis in humans?– Risk factors
• Obesity • Patients with repetitive use syndromes
– Surrogate endpoints• Joint space narrowing is evidence of progressive OA but may
or may not be associated with the important clinical component of symptoms
• Other observed x-ray changes are useful for diagnosis but are not important by themselves without clinical symptoms of disease
• There are no valid surrogate biochemical markers at this time
Questions Asked
• Are joint degeneration and cartilage deterioration:– Signs or symptoms of OA?
• Yes, in the absence of another explanation such as ongoing systemic inflammatory disease these are evidence in the context of symptoms of OA
– Modifiable risk factors/surrogate endpoints for osteoarthritis? • Not generally, the presence of the above findings are part and
parcel to OA; while JSN may be an important way to demonstrate that a structure modifying drug may be active. However, if there is improvement in structure it would be expected at sometime that there would be a linked improvement in symptoms at some time (perhaps even in the future)
– Patients present with pain or other symptoms: joint change and cartilage degeneration in some patients may be associated with pain and loss of function: but not all patients will have symptoms in the context of these changes
• Once a patient has pain, he will have evidence of change, but not all patients with changes will have symptoms
• A spectrum of disease, mild disease is still disease and associated with changed joint tissue whether or not measurable by presently available techniques
Therapy
• Presently is designed to improve modifiable risk factors– Reach ideal body weight in those that are obese
• Decrease body weight a significant decrease in symptoms– Alter life style behaviors such as those associated with overuse
syndromes• Mostly palliative to decrease symptoms of pain leading hopefully
to an improved health related quality of life– Analgesics/anti-inflammatory therapies– Use of assistive devices to “unload” joints– Use of cognitive behavior therapy– Use of physical therapy and exercise therapy
• There are as yet no proven structure modifying therapies– Recent data regarding metalloproteinase inhibitors suggests some
benefit in patients with progressive disease (maybe)
BIOLOGIC MARKERS
HRQOL / UTILITY
PAINPAINPHYSICAL PHYSICAL FUNCTIONFUNCTION
PATIENT GLOBALPATIENT GLOBALIMAGING (≥1YR)IMAGING (≥1YR)
INFLAM-MATION
8%8%36%36%90%90%
OTHER Eg, Performance based Flares Time to Surgery Analgesic Count
MD GLOBALMD GLOBAL
STIFFNESS
Study Design
Arthritis assessments X X X
OA Knee Flare
Rofecoxib 25 mg qd
Week 6
Celecoxib 200 mg qd
Placebo
Week 3BL
BL = baseline
Weeks
Me
an
VA
S (
mm
) Placebo (n=60)Celecoxib 200 mg QD (n=63)Rofecoxib 25 mg QD (n=59)
30
40
50
60
70
0 3 60
*
*P < 0.02 both active treatments vs placebo
80
*
Patient’s Assessment of Pain
0
5
10
15
20
25
30
Celecoxib 200mg QD
Rofecoxib 25mg QD
Placebo
* *
*P<0.03 vs placeboWOMAC = Western Ontario and McMaster Universities Osteoarthritis Index
Me
an
imp
rove
men
t
fro
m b
ase
line
WOMAC Composite Scores at Week 6
PACES: Patient Preference Cross-over Trials Pincus etal Ann Rheum Dis 2004
PACES: Patient Preference Cross-over Trials Pincus etal Ann Rheum Dis 2004