Risk factors and load distribution
Advanced age, obesity, genetic predisposition, trauma, and hip dysplasia contribute to the development of hip osteoarthritis.
To minimize pain and slow down joint destruction, understanding the biomechanics of load distribution is essential. Rules for the patient (using the affected right joint as an example):
- The cane must be held in the left hand (contralateral to the affected side).
- A heavy load (e.g., a bag) should be carried in the right hand (ipsilateral).
Rationale: if the load is carried in the opposite (left) hand, an additional tilting force arises. To keep the pelvis in balance, the abductor muscles of the right hip will have to contract sharply, which will significantly increase the compressive load on the diseased joint.
Femoroacetabular impingement (FAI)
A frequent cause of joint degeneration is FAI — a pathological abutment between the proximal femur and the acetabulum during flexion and rotation. It is important to distinguish between an asymptomatic anatomical anomaly (which many people have) and a clinical syndrome accompanied by pain.
Two main types of deformity are distinguished:
- Cam impingement. Smoothing of the junction between the femoral head and neck due to bone overgrowth. The non-spherical head exerts a shearing effect on the acetabular cartilage and the anterosuperior part of the labrum.
- Pincer impingement. Excessive overgrowth of the acetabular rim. It leads to tears within the labrum itself, most commonly in the anterosuperior quadrant, as well as «contrecoup» cartilage damage in the posteroinferior region.
Injury to the acetabular labrum (the cartilaginous rim that deepens the socket and reduces contact pressure) causes groin pain, clicking, and joint locking.
Clinical and imaging diagnostics
Patients with an acetabular labrum tear often demonstrate the «C» sign: they cannot point to the pain with a single finger and instead grasp the hip joint with their hand (thumb on the back, fingers in the front).
Provocative tests are used to verify the diagnosis (from a supine position with the hip and knee flexed at 90°):
- Anterosuperior tear test: pain is provoked by flexion, slight adduction, and internal rotation.
- Posterior tear test: pain occurs with abduction and external rotation.
Instrumental methods:
- MR arthrography (with intra-articular contrast) is the gold standard for detecting labral tears.
- X-ray — reveals bony deformities (present in ≥85% of patients with labral tears). To assess the Cam type, the Dunn lateral view (45°) is used and the alpha angle is measured. The Pincer type is characterized by the cross-over sign (the anterior acetabular rim crosses the posterior one).
- CT — optimally visualizes bone anatomy for preoperative planning.
Surgical treatment
When conservative methods fail to relieve the disabling symptoms of terminal coxarthrosis, total hip arthroplasty is indicated.
During surgery, the destroyed femoral head (caput femoris) and acetabulum are replaced with implants. The design includes a femoral stem, neck, head, metal cup, and plastic liner. The procedure is highly effective, and complications occur in only ~1% of cases, although mechanical wear of the components is inevitable over time.
Older disabling techniques, such as arthrodesis (joint fusion), are now rarely used even in young patients. Several other approaches (hyaluronic acid injections, surface arthroplasty, arthroscopic debridement, and FAI surgery) are considered controversial methods whose efficacy is questioned.
Briefly: answers to topical questions
Which specific hip abductor muscles contract to keep the pelvis in balance when carrying a load?
To keep the pelvis in balance when supporting body weight on one leg, the gluteus medius and gluteus minimus muscles contract.
- The gluteus medius muscle (m. gluteus medius) generates a powerful force to counterbalance body weight.
- The gluteus minimus muscle (m. gluteus minimus) functions together with the gluteus medius to abduct the greater trochanter.
In coxarthrosis, the patient subconsciously avoids tensing these muscles to reduce the compressive load on the joint, which leads to an antalgic gait.
What are the radiographic stages of coxarthrosis according to the Kellgren-Lawrence classification?
According to the Kellgren-Lawrence classification, there are four stages of osteoarthritis, although available sources describe only the initial phases:
- Stage 0 — radiographic changes are completely absent.
- Stage I — joint space narrowing is absent or barely noticeable, small marginal osteophytes appear (doubtful changes).
- Stage II — slight joint space narrowing is observed (minimal changes).
This classification is based exclusively on radiographic criteria.
Which drug groups are used for the conservative treatment of coxarthrosis in the early stages?
Sources indicate that conservative treatment of coxarthrosis is used at all stages of the disease. The following drug groups and methods are mentioned:
- Chondroprotectants — chondroitin sulfate and glucosamine.
- Proinflammatory cytokine inhibitors — diacerein and unsaponifiables.
- Intra-articular glucocorticosteroids — only for relieving acute inflammation and reactive synovitis; use is limited.
- Intra-articular viscosupplementation drugs — hyaluronic acid preparations, whose efficacy is questioned.
Sources also classify pharmacological and non-pharmacological methods as conservative treatment, but the specific use of NSAIDs is not described in the presented material.
The load rule in coxarthrosis: «Cane in the healthy hand, bag in the diseased hand». This blocks the dangerous tilting force and saves the joint from overload by the abductor muscles.
Class and exam questions
What is the difference between FAI anatomy and clinical FAI syndrome?
FAI anatomy is an isolated bone deformity detected on X-rays in 24–50% of absolutely healthy people. FAI syndrome is diagnosed only when this anomaly is combined with clinical symptoms (pain, clicking).
Which diagnostic imaging method is best for detecting an acetabular labral tear?
The method of choice is MR arthrography with contrast injection into the joint. Standard MRI without contrast may miss clinically significant tears.
What does an increased alpha angle on a radiograph indicate?
The alpha angle is used for quantitative assessment of Cam deformity. Its increase indicates pronounced pathological bone overgrowth in the head-neck junction zone of the femur.
Why is arthrodesis not performed for coxarthrosis?
Arthrodesis (joint fusion) leads to complete loss of mobility in the joint. Due to the extremely high success rate and predictability of modern arthroplasty, this surgery is hopelessly outdated today.
What else to study on this topic
- Hip joint biomechanics: force vectors and abductor muscle function
- Histological structure and biomechanical function of the acetabular labrum
- Contrecoup cartilage injuries in pincer impingement
- Method of measuring the alpha angle and center-edge angle on spinal radiographs
- Materials and components of a total hip arthroplasty prosthesis
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