Coxarthrosis (Hip Osteoarthritis)

Introduction

Coxarthrosis — osteoarthritis of the hip joint — is one of the commonest and most disabling musculoskeletal conditions in adults. The disease produces progressive pain, stiffness, and functional limitation, and ultimately reduces quality of life to the point where total hip arthroplasty becomes the most cost-effective intervention in modern orthopedic surgery. The understanding of hip osteoarthritis has evolved substantially in recent decades, with recognition that the great majority of cases previously classified as “idiopathic” or “primary” osteoarthritis are in fact secondary to subtle developmental abnormalities of the hip — femoroacetabular impingement, mild acetabular dysplasia, healed Perthes or SCFE — that produce abnormal joint mechanics over decades and lead to progressive cartilage breakdown. This chapter, synthesizing content from Apley & Solomon’s, Miller’s Review, Operative Hip Arthroscopy, and Orthopaedic Surgical Approaches, addresses the epidemiology and risk factors, pathophysiology, clinical features, imaging, classification, non-operative management, joint-preserving surgery, and total hip arthroplasty for advanced disease.

Epidemiology and Risk Factors

The prevalence of symptomatic hip osteoarthritis is approximately 5-10% of adults over the age of 60, with the prevalence increasing markedly with age and approaching 20% in those over 80. The lifetime risk of symptomatic hip osteoarthritis is approximately 25%. Risk factors include increasing age, female sex (slight predominance in symptomatic disease), obesity (though the association is less strong for the hip than for the knee, reflecting the deeper joint and the role of other factors), occupational and recreational exposure to heavy loading and repetitive impact, prior hip trauma, prior hip disorders (Perthes, SCFE, DDH, FAI), inflammatory arthritis, avascular necrosis, hip dysplasia in adulthood, and genetic factors (a substantial heritable component is established by twin and family studies). The “primary” versus “secondary” classification of hip osteoarthritis is increasingly recognized as a false dichotomy: with careful radiographic and clinical assessment, most “primary” cases reveal an underlying predisposing condition. Cam-type femoroacetabular impingement is the most commonly recognized predisposing morphology in men with hip osteoarthritis, while acetabular dysplasia is the principal predisposition in women.

Pathophysiology

The pathological process of hip osteoarthritis follows the general principles of osteoarthritis at any joint. The earliest changes occur in the cartilage matrix, with disruption of the proteoglycan-collagen architecture, increased water content, fibrillation of the surface, and progressive loss of cartilage thickness. The chondrocytes initially attempt repair through increased synthetic activity but eventually undergo apoptosis, leaving an acellular fibrous tissue that progressively breaks down. The exposed subchondral bone responds with increased density (sclerosis), formation of subchondral

cysts (from synovial fluid intrusion), and peripheral osteophyte formation at the joint margins. The synovium becomes inflamed with low-grade chronic synovitis, contributing to symptoms. The capsule thickens and contracts, producing limited motion. In late disease, complete loss of cartilage with bone-on-bone contact, marked osteophyte formation, and joint deformity produces the characteristic radiographic and clinical features of end-stage disease.

Clinical Features

The classical presentation is of insidious onset of groin pain, typically in middle age or later, often poorly localized initially. The pain may radiate to the buttock, the lateral thigh, the anterior thigh, or — characteristically — the medial knee through the obturator nerve. The classical pattern of mechanical pain — worse with activity and weight-bearing, better with rest — gives way over months to years to “rest pain” with continued discomfort even at rest, and ultimately to night pain and pain at all times. Stiffness, particularly of internal rotation, develops progressively and is among the most reliable functional indicators of disease progression. Functional limitations follow predictable patterns: difficulty putting on socks and shoes, difficulty climbing stairs and getting in and out of low chairs or cars, limp, and progressive reduction of walking distance. Examination findings progress with disease severity. The classical findings of established hip osteoarthritis include: antalgic gait (with reduced stance phase on the affected side); Trendelenburg gait or lurch (from abductor weakness or inhibition by pain); decreased range of motion, with internal rotation typically affected first and most severely, followed by flexion and abduction; positive Thomas test for fixed flexion deformity (the affected hip remains flexed when the contralateral hip is fully flexed); positive flexion-abduction- external rotation (FABER, Patrick) test producing groin pain; apparent leg-length discrepancy with shortening of the affected side; and tenderness over the anterior hip joint. The end-stage hip is held in fixed flexion, adduction, and external rotation, with severe limitation of all motion.

Imaging

Plain Radiographs The standard imaging assessment is bilateral AP pelvis and lateral views of the hip. The features of hip osteoarthritis follow the universal radiographic criteria of osteoarthritis with hip-specific manifestations: (1) Joint-space narrowing, typically asymmetric with the superior aspect of the joint (between the superior femoral head and the acetabular roof) most commonly involved early in disease; (2) Subchondral sclerosis of both the femoral head and the acetabular roof; (3) Subchondral cyst formation (geodes) in both the femoral head and acetabulum;

(4) Osteophyte formation at the joint margins — particularly the superior acetabular rim, the inferior femoral head and neck, and the medial acetabular floor; (5) Loss of femoral head sphericity from progressive cartilage and bone destruction;

(6) Migration of the femoral head — typically superior or superolateral in idiopathic OA, medial in protrusio-related disease.

The Kellgren-Lawrence classification is the standard radiographic grading: Grade 0, normal; Grade 1, doubtful joint-space narrowing and possible osteophyte; Grade 2, definite osteophyte with possible joint-space narrowing; Grade 3, multiple osteophytes with definite joint-space narrowing, sclerosis, and possible deformity; Grade 4, large osteophytes, marked joint-space narrowing, severe sclerosis, and definite deformity. Tönnis grading is a similar 0-3 system used in hip-specific evaluation, with Grade 1 indicating mild changes (osteophytes, mild sclerosis), Grade 2 indicating moderate changes (cysts, increased sclerosis), and Grade 3 indicating severe changes (significant joint-space narrowing or obliteration, large cysts, severe deformity). MRI and Other Advanced Imaging MRI is not routinely required for the diagnosis of hip osteoarthritis but is useful in early disease where plain radiographs may be normal but symptoms suggest joint pathology, in assessment of associated FAI and labral pathology, and in evaluation for alternative diagnoses (avascular necrosis, occult fracture, infection, malignancy). MR arthrography may identify labral and chondral lesions in the pre-arthritic stage. Specialized cartilage- sensitive MRI sequences (delayed gadolinium-enhanced MRI of cartilage — dGEMRIC; T2- mapping; T1-rho mapping) provide quantitative assessment of cartilage biochemical composition and are used principally in research settings.

Non-Operative Management

The non-operative management of hip osteoarthritis combines patient education, lifestyle modification, pharmacological treatment, and specific physical therapy interventions. Patient education addresses the chronicity and natural history of the disease, expectations for treatment, and the importance of activity and weight management. Weight loss, in overweight or obese patients, reduces both pain and the rate of progression, with documented benefit per kilogram of weight loss. The targets are modest but consistent reductions sustained over years. Physical therapy combines range-of-motion exercises (preventing further loss of motion), strengthening of the hip abductors and quadriceps, and core stabilization. Aquatic exercise is particularly useful for patients with significant pain or weight-bearing limitations. Activity modification addresses the avoidance of high-impact and pivoting activities, the use of assistive devices (cane held in the opposite hand reduces hip joint reaction force by 20-40%), and progressive return to lower-impact activities.

Pharmacological treatment follows the standard OA stepwise approach: paracetamol (acetaminophen) for mild symptoms; non-steroidal anti-inflammatory drugs (oral or topical) for moderate symptoms, with attention to cardiovascular, gastrointestinal, and renal risks; opioids reserved for severe symptoms unresponsive to other measures and with awareness of the long-term consequences of opioid use; intra-articular corticosteroid injection for inflammatory flares (with caution about the cumulative effects of repeated injections, which may damage cartilage; the recent FDA caution about cartilage loss with repeated injection has tempered enthusiasm); hyaluronic acid injection (less commonly used in the hip than in the knee, with mixed evidence for efficacy); and platelet-rich plasma (PRP) and other biological injections (under continued investigation). Glucosamine and chondroitin are widely used by patients but have inconsistent evidence for symptom relief and no clearly established effect on disease progression; current major guidelines do not endorse routine use.

Joint-Preserving Surgery

For appropriate younger patients with pre-arthritic or early arthritic hip disease, joint- preserving surgical procedures aim to correct the underlying mechanical abnormality and delay or prevent the progression to end-stage osteoarthritis. The principal options include: Hip arthroscopy for FAI, labral tears, loose bodies, and selected chondral lesions — discussed in detail in the FAI chapter. The role in established osteoarthritis is more limited, with poor outcomes when significant cartilage loss is present (Tönnis grade 2 or higher). Periacetabular osteotomy (Bernese / Ganz PAO) for symptomatic acetabular dysplasia in the young adult with preserved joint space and congruent joint — discussed in detail in the DDH chapter. The procedure produces durable improvement in pain and function and has 20-year survivorship of 60-80% in many series. Femoral osteotomy (proximal femoral varus, valgus, or rotational osteotomy) is occasionally used for specific morphological abnormalities, particularly residual deformity from Perthes disease or SCFE. Hip resurfacing arthroplasty is a partial joint replacement that preserves the proximal femoral bone stock, replacing only the articular surfaces of the femoral head and acetabulum. The procedure had a resurgence in the 2000s but has been substantially curtailed by recognition of the complications of metal-on-metal bearing surfaces (cobalt- chromium ions, adverse local tissue reactions, pseudotumor formation). The procedure remains an option in selected young active male patients with appropriate anatomy, but the use is now restricted to specialist centers with continuing interest.

Total Hip Arthroplasty (THA)

Indications Total hip arthroplasty is indicated for end-stage hip osteoarthritis (Kellgren-Lawrence 3-4, Tönnis 2-3) producing symptoms unresponsive to non-operative management, with

attention to the patient’s functional demands, comorbidities, life expectancy, and bone quality. THA is also performed for advanced rheumatoid arthritis, post-traumatic arthritis, avascular necrosis, and other causes of end-stage hip destruction. Implant Design Considerations Modern THA implants combine four principal components: a femoral stem (cemented or uncemented, with various designs including conventional length, shorter “anatomic” stems, and “neck-preserving” stems); a femoral head (typically 28 mm to 40 mm in diameter, with larger heads providing greater stability but with bearing-specific tradeoffs); an acetabular cup (cemented or uncemented, the latter being the dominant choice in most modern practice); and an acetabular liner (the bearing surface, with several options). Bearing surfaces: The choice of bearing surface is one of the central decisions in modern THA. Metal-on-conventional-polyethylene was the historic standard but had high rates of late osteolysis from polyethylene wear particles. Metal-on-highly-cross-linked- polyethylene (XLPE) has substantially reduced wear rates and is now the standard for most patients. Ceramic-on-XLPE provides further wear reduction and is preferred in younger patients. Ceramic-on-ceramic provides the lowest wear of all bearings but has small risks of squeaking and ceramic fracture. Metal-on-metal bearings (with cobalt-chromium surfaces) had a brief popularity in the 2000s but have been substantially withdrawn from practice because of the systemic and local effects of metal ion release, with a substantial body of literature documenting adverse local tissue reactions, pseudotumor formation, and the failure of large-head metal-on-metal implants.

Surgical Approaches Several surgical approaches to the hip are used for THA, each with advantages and disadvantages: Posterior approach (Moore, Southern, Kocher-Langenbeck): The most commonly used worldwide. The approach divides the gluteus maximus, identifies and protects the sciatic nerve, divides the short external rotators (which are repaired at the end of the procedure), and exposes the hip through a capsulotomy. Advantages include excellent visualization, extensile capacity for revision surgery, and avoidance of disruption to the hip abductor mechanism. The principal disadvantage has been the relatively higher rate of dislocation (although this has been substantially reduced by careful repair of the short external rotators and capsule). Anterolateral approach (Watson-Jones, Hardinge): Approaches the hip between the tensor fasciae latae and the gluteus medius (Watson-Jones) or by splitting the gluteus medius (Hardinge). Lower dislocation rate than posterior but with potential abductor weakness. Direct anterior approach (Smith-Petersen, Hueter): The approach uses the internervous plane between the sartorius and tensor fasciae latae (laterally) and the rectus femoris (medially). Advantages include lower dislocation rate, faster initial recovery, and the ability to perform the procedure with the patient supine for radiographic confirmation

of leg length and implant position. Disadvantages include the learning curve, the risk of lateral femoral cutaneous nerve injury, and the more limited extensile capacity for revision surgery. The direct anterior approach has grown rapidly in popularity since the early 2000s and is now performed by a substantial fraction of modern hip surgeons. Specific Surgical Techniques The technical principles of THA include: appropriate preoperative templating of implant sizes and positions; meticulous attention to acetabular cup orientation (target 40° abduction, 15° anteversion in most cases, with patient-specific adjustments); attention to femoral stem fit and fill (or cementing technique for cemented stems); careful restoration of leg length and offset (with intraoperative measurement); meticulous component reduction; and intraoperative stability assessment. The Lewinnek “safe zone” for cup position (30-50° abduction, 5-25° anteversion) has been refined to more individualized concepts of “functional anteversion” that account for spinopelvic mobility and the resting position of the pelvis in different functional activities. Outcomes of THA The outcomes of modern THA are excellent, with reported survivorship of approximately 95% at 10 years and 85-90% at 20 years in many large series and national registries. The implants now perform durably for a substantial fraction of patients’ lifetime, particularly in older patients who undergo THA in their 60s or 70s. Younger patients (under 60) have less favorable long-term survivorship, with revision rates exceeding 20% at 20 years in some series, reflecting the higher activity demands and the cumulative effects of bearing wear. Complications of THA The principal complications of total hip arthroplasty include: Infection (periprosthetic joint infection, PJI): Rate of 1-2% for primary THA, with substantial morbidity. Diagnosis and treatment are discussed in the chapter on bone and joint infections. Modern prevention strategies include perioperative antibiotic prophylaxis (commonly cefazolin within 60 minutes of incision), antibiotic-loaded bone cement in selected cases, laminar flow operating rooms, body exhaust suits in some centers, careful skin preparation (chlorhexidine-alcohol), and meticulous surgical technique with attention to operative time. Dislocation: Rate of 1-3% in modern primary THA, higher in revision surgery and in patients with neuromuscular conditions. Causes include implant malposition, soft-tissue imbalance, muscle weakness, and patient factors. Treatment of acute dislocation is closed reduction; recurrent dislocation requires revision surgery, typically with revision of component position, use of larger femoral head, dual-mobility cup, or constrained liner. Thromboembolic disease: Deep venous thrombosis and pulmonary embolism are recognized risks; prophylaxis with chemical (low-molecular-weight heparin, aspirin, direct oral anticoagulants) and mechanical (sequential compression devices, early mobilization) measures has substantially reduced rates.

Periprosthetic fracture: Both intraoperative (femoral fracture during stem insertion, acetabular fracture during cup insertion) and postoperative (atraumatic in osteoporotic bone or traumatic from fall) fractures occur. The Vancouver classification of postoperative periprosthetic femoral fractures (Type A — trochanteric; Type B1 — at stem with well- fixed stem; Type B2 — at stem with loose stem; Type B3 — at stem with loose stem and poor bone stock; Type C — distal to stem) guides treatment. Aseptic loosening: Once a major cause of long-term failure, now substantially reduced by improved implant designs, bearing surfaces, and cementing techniques. Modern uncemented implants show very low rates of aseptic loosening in long-term follow-up. Osteolysis and wear: The historical complication of polyethylene wear with secondary osteolysis has been substantially reduced by highly cross-linked polyethylene. Long-term follow-up of modern bearings shows wear rates below the threshold for osteolytic complications. Leg-length discrepancy: Apparent or true leg-length differences are common and a major cause of patient dissatisfaction. Careful preoperative templating, intraoperative measurement, and patient counseling regarding expectations are essential. Heterotopic ossification: Bone formation in the soft tissues around the hip can produce stiffness and discomfort. Risk factors include male sex, hypertrophic osteoarthritis, prior heterotopic ossification, and certain underlying conditions. Prophylaxis options include perioperative indomethacin (typically 75 mg twice daily for 2-6 weeks) or single-dose perioperative radiotherapy (700-800 cGy within 24-48 hours of surgery). Other complications: Sciatic, femoral, or lateral femoral cutaneous nerve injury; vascular injury; trochanteric bursitis; persistent pain of various etiologies.

Special Considerations

Young Patients and Hip Preservation The young patient with hip pain demands particularly careful assessment for hip- preserving options before consideration of THA. The decision is informed by the morphological features (FAI, dysplasia, prior childhood disease), the radiographic stage of arthritis (early-stage disease may benefit from hip preservation; established arthritis typically does not), the patient’s functional demands, and the realistic expectations for joint-preserving surgery in delaying rather than preventing the eventual need for arthroplasty. THA in Specific Conditions Hip dysplasia: THA in the dysplastic hip is technically challenging because of the small, anteverted acetabulum, the high-riding femoral head, and the soft-tissue contractures. Specific techniques include placement of the acetabular cup at the level of the true acetabulum (with or without bone graft for superior coverage), use of small-diameter cups, femoral shortening osteotomy in severe shortening, and careful soft-tissue release.

Avascular necrosis: THA is the standard for advanced AVN with collapse. The technical issues are similar to those for primary OA, with attention to the often-younger age of the patient and the choice of durable bearings. Inflammatory arthritis: THA in rheumatoid arthritis and other inflammatory arthropathies follows similar principles but with attention to systemic medical management of the underlying disease, perioperative coordination with the rheumatologist, and elevated rates of infection in patients on biological therapies (the timing of biological agent suspension perioperatively follows specific guidelines). Revision THA: Revision of a failed THA is technically demanding, with management of bone defects (using bone grafts, augments, or revision components), the choice of bearings appropriate to the revision setting, and the management of infection if present. The Paprosky classification of acetabular and femoral bone defects guides reconstruction planning.

Summary and Take-Home Points

Coxarthrosis is a common and disabling condition with substantial impact on quality of life. The disease is increasingly understood as the late consequence of subtle developmental hip abnormalities — FAI, dysplasia, prior childhood disease — that produce abnormal joint mechanics over decades. Clinical assessment by careful history and physical examination (with attention to mechanical pain pattern, internal rotation loss, Trendelenburg gait, Thomas test, FABER test), combined with standardized plain radiographs (Kellgren- Lawrence and Tönnis grading), establishes the diagnosis and stages the disease. Non- operative management combining education, weight loss, physical therapy, activity modification, and pharmacological treatment provides the foundation of care for all patients. Joint-preserving surgery — hip arthroscopy for FAI, periacetabular osteotomy for dysplasia, femoral osteotomy for specific deformities — is indicated for the appropriate younger patient with pre-arthritic disease. Total hip arthroplasty, the most cost-effective intervention in modern orthopedic surgery, is indicated for end-stage disease with appropriate consideration of bearing surface, surgical approach, and patient factors. Modern THA produces excellent long-term outcomes with 10-year survivorship of approximately 95% and substantial improvement in pain, function, and quality of life. The principal complications of infection, dislocation, periprosthetic fracture, and aseptic loosening are managed by careful surgical technique, appropriate implant selection, and prompt recognition of complications when they occur.