Chapter 7. Diseases of the musculoskeletal system

7.1. Osteoarthritis

Formulating a diagnosis

Components of the diagnosis: form; localization; presence of synovitis; radiographic stage; functional class

Osteoarthritis (OA) is a heterogeneous group of conditions of various etiologies with similar biological, morphological, and clinical manifestations and outcome, which are based on the damage of all joint components, primarily cartilage, subchondral bone, synovial membrane, ligaments, capsules, periarticular muscles.

Osteoarthritis ranks globally among the 50 most common sequelae of diseases and injuries, affecting over 250 million people or 4% of the world’s population.

Form

OA generally can be subcategorized into primary (idiopathic) and se­con­dary OA.

Common causes of secondary OA include posttraumatic, dysplastic, infectious, inflammatory, or biochemical etiologies.

Causes of secondary OA:

• a history of joint injury;
• joint hypermobility syndrome;
• dysplasia of the musculoskeletal system;
• metabolic disorders (hemochromatosis, Wilson disease, Gaucher disease, crystal-associated diseases);
• endocrine diseases (hyperparathyroidism, diabetes mellitus, hypothyroidism).

Localization

According to the number of affected joints, 2 forms may be distinguished:

• local — 1–2 groups of joints
• generalized — 3 or more groups of joints.

Presence of synovitis

Synovitis is an inflammation of joint synovial membrane with effusion formation in it. In case of OA, synovitis is a secondary process, representing aseptic inflammation. Pathogenesis of synovitis is caused by irritation of joint synovial membrane by metabolites of cartilage degeneration. Inflammation of the synovial membrane in case of OA is observed when large joints are affected, most often in gonarthrosis.

Radiographic stage by Kellgren–Lawrence

• I — ambiguous radiological signs.
• II — minimal changes (slight narrowing of the joint gap, single osteophytes).
• III — moderate signs (moderate narrowing of the joint gap, multiple osteo­phytes).
• IV — overt changes (joint gap is practically not traced, crude osteophytes).

Functional class

Functional class depends on how much the patient is able to perform va­rious types of activities — professional, household, self-service.

• I — self-service, non-professional and professional activities are fully preserved;
• II — self-service, professional activities are preserved, non-professional activities are limited;
• III — self-service is preserved, non-professional and professional ac­tivities are limited;
• IV — self-service, non-professional and professional activities are li-
  mited.

Examples of diagnoses

DS: OA, primary, knee joints, radiographic stage II, FC-1.

DS: OA, primary, generalized, recurrent synovitis of the right knee joint, radiographic stage III, FC-2.

Diagnosis verification

Osteoarthritis is typically diagnosed on the basis of clinical (the nature of pain, presence of stiffness and crepitations), and radiographic evidence.

To verify the diagnosis, it is recommended to use the ACR classification criteria for OA (table 7.1).

Table 7.1. Classification criteria for osteoarthritis (R.D. Altman et al., 1991)

Patient's complaints

The primary symptoms of osteoarthritis are joint pain, stiffness, and locomotor restriction. Pain in OA is worse with joint use (usage-related pain) and relieved by rest. Symptoms usually present in just one or a few joints in a middle-aged or older person. Other manifestations in patients with OA include sequelae such as muscle weakness, and poor balance.