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Journal Club

May 2010

Prevalence of Malformations of the Hip Joint and Their Relationship to Sex, Groin Pain, and Risk of Osteoarthritis

• Authors: Kasper Kjaerulf Gosvig, Steffen Jacobsen, Stig Sonne-Holm, Henrik Palm and Anders Troelsen
  
• Institution: Department of Orthopedic Surgery, Copenhagen University Hospital of Hvidovre, Hvidovre, Denmark
  
• Journal: J Bone Joint Surg Am. 2010;92:1162-1169.

Introduction

• To determine the prevalence of:
  
  • Acetabular dysplasia
    
  • Coxa profunda +/- protrusio acetabuli
    
  • Pistol grip deformity
    
• To determine the prevalence of groin pain associated with the above
  
• To estimate the adjusted risk of development of hip OA when these abnormalities are present

Methodology

• Data retrieved from the Copenhagen Osteoarthritis Substudy:
  
  • Copenhagen City Heart Study I-III:
    
  • Survey of a predominantly white adult cohort
    
  • Country of Osterbro: 60,000 residents
    
• Databases approved by Danish Ethics Committee:
  
• No additional approvals are required for data processing
  
• 4151 individuals chosen between 1991-1994
  
• AP wt bearing XR of all participants
  
• 1533 men:
  
• Mean age 62
  
• Range 23 to 93
  
• 2618 women:
  
• Mean age 65
  
• Range 22 to 92
  
• Exclusion Criteria:
  
• THJR (1.7%)
  
• Perthes disease (0.6%)
  
• Childhood hip disease (0.8%)
  
• Rheumatoid arthritis (3.4%)
  
• Unreadable radiographs (4%)
  
• Study group = 1332 men, 2288 women
  

• Hips were categorised into five groups based in radiographic discriminators:
  
  1. No malformations
     
  2. Acetabular dysplasia
     
  3. A deep acetabular socket (coxa profunda, protrusio)
     
  4. Pistol grip deformity
     
  5. Combination of a deep socket + pistol grip deformity
     
• XR and responses to a questionnaire completed at the time of the XR were evaluated to determine:
  
• Prevalence of hip malformations, groin pain and hip OA
  
• Relationship between osteophytes and pistol grip deformity
  
• Risk estimates of development of OA
  
• Distribution of malformations in hips with OA

 

• Radiographic evaluation:
  
  • Pistol grip deformity:
    
    • Triangular index ≥0mm
      
  • Acetabular dysplasia:
    
    • Centre edge angle of Wiberg ≤20°
      
  • Deep acetabular socket:
    
    • Centre edge angle ≥45°
      
  • Osteoarthitis:
    
    • Minimum joint space width ≤2mm
      
    • Osteophytic changes assessed by a radiologist

• Questionnaire-based evaluation:
  
• Completed at the time of radiograph
  
• Inquired about pain in the lower back and extremities
  
• Only 1 question was relevant to the study: pain in one or both hips or groin

Results

• Overall prevalence:
  
  • Acetabular dysplasia:
    
    • 4.3% men, 3.6% women
      
  • Deep acetabular socket:
    
    • 15.2% men, 19.4% women
      
  • Pistol grip deformity:
    
    • 19.6% men, 5.2% women
      
  • Combination deep socket + pistol grip:
    
    • 2.9% men, 0.9% women
      
• No significant difference in prevalence of groin pain between groups with or without hip malformations (p>0.13)
  
• No significant relationship between presence of osteophytes and pistol grip deformity (p>0.086)
  
• No association between presence of osteophytes, pistol grip deformity and joint space width:
  
  • ≤2mm (p>0.768)
    
  • >2mm (p>0.102)
    
• Risk ratio for deep acetabular socket (RR2.4) and pistol grip malformation (RR2.2) were significantly elevated
  • (p<0.001)
    
• No significant correlation between:
  
  • OA and acetabular dysplasia (p=0.053)
    
  • OA and sex (p=0.063)
    
  • OA and BMI (p=0.576)
    
• Age was a significant risk factor (p<0.001)
  
• Overall prevalence of hip OA:
  
  • 9.5% men, 11.2% women
    
• Of pts with radiological evidence of OA overall prevalence of concomitant:
  
  • Acetabular dysplasia:
    
    • 3.1% men, 2.7% women
      
  • Deep acetabular socket:
    
    • 27% men, 28.3% women
      
  • Pistol grip deformity:
    
    • 30.2% men, 5.0% women
      
  • Combination deep socket + pistol grip deformity:
    
    • 10.5% men, 0.6% women

Discussion

• pistol grip deformity is primarily a malformation in men
  • study supports theory that pistol grip malformation is secondary to symptomatic or asymptomatic slipped capital femoral epiphysis
• deep acetabular socket (coxa profunda and/or protrusio acetabuli) is a common malformation in the population along with pistol grip malformation.

Pros of Study

• Large cohort size
  
• Large population-based investigation
  
• Standardisation of radiographs according to a protocol

Cons of Study

• Cross-sectional design: limits assessment of cause and effect relationships
  
• AP XR only: underestimation of prevalence
  
• Study cohort advanced age
  
• Questionnaire to evaluate groin pain not validated