Hip Joint Stability

Hip joint stability is maintained by the relationship between the static osseous structures (acetabulum and the head of the femur), soft tissues (capsule, ligaments, and labrum) of the hip joint, and surrounding hip musculature.

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  I. Acetabulum:

  
  
  
  
  1. 
     

     It approximately creates a hemisphere that allows approximately 170 degrees of femoral head coverage. ¹

     
     
  2. 
     

     It is oriented with 40 to 45 degrees of lateral inclination and 18 to 21 degrees of anteversion allowing for greater posterior coverage. ²

  
  
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  II. Proximal femur:

  
  
  
  
  1. 
     

     The head is considered as two-thirds of a sphere, while the neck is inclined superiorly 130 degrees relative to shaft and 10 degrees anteverted relative to the femoral transcondylar axis. ³

     
     
  2. 
     

     The coxa valga and coxa anteversion are associated with hip instability.

  
  
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  III. Soft-tissue structures contribute the static and dynamic stabilizers of the hip.

  
  
  
  
  1. 
     

     Static stabilizers: these are the labrum, capsuloligamentous complex (iliofemoral ligament, pubofemoral ligament, ischiofemoral ligament, zona orbicularis), and the ligamentum teres.

     
     
     
     
     1. 
        

        Labrum:

        
        
        
        
        1. 
           

           It is in continuity with the bony acetabular rim.

           
           
        2. 
           

           It provides stability to the hip by increasing the acetabular volume by 20% and the acetabular surface area by 25%. ⁴

           
           
        3. 
           

           It increases the intra-articular negative hydrostatic fluid pressure, causing a “suction cup” effect.

           
           
        4. 
           

           It more evenly distributes stresses placed on the hip.

        
        
     2. 
        

        Capsuloligamentous complex:

        
        
        
        
        1. 
           

           Iliofemoral ligament:

           
           
           
           
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             i. It is the strongest ligament of the body.

             
             
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             ii. It runs from the anteroinferior iliac spine to the femoral neck creating a fan-shaped “Y” at insertion proximally and distally along the intertrochanteric line; it takes a spiral trajectory across anterior side of the capsule.

             
             
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             iii. It is taut in extension and external rotation and resists anterior translation.

           
           
        2. 
           

           Pubofemoral ligament:

           
           
           
           
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             i. It has its origination on the iliopectineal eminence of the superior pubic ramus, courses inferoposteriorly, and wraps under the femoral head; it blends with the ischiofemoral ligament with no bony femoral attachment.

             
             
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             ii. It limits external rotation in hip extension and hyperabduction.

           
           
        3. 
           

           Ischiofemoral ligament:

           
           
           
           
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             i. It has a broad triangular origin on the ischial acetabular margin and spirals superolaterally to insert at the base of the greater trochanter.

             
             
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             ii. It restricts internal rotation (in flexion and extension) and posterior translation.

           
           
        4. 
           

           Zona orbicularis:

           
           
           
           
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             i. This is formed by confluent fibers from the medial arms of the iliofemoral ligament and the pubofemoral ligament that run longitudinally in parallel with the femoral neck; it encircles the femoral neck creating the narrowest part of the capsule.

             
             
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             ii. It resists axial distraction; helical orientation of capsuloligamentous fibers creates “screw-home” effect when the hip is in extension.

           
           
        5. 
           

           Ligamentum teres:

           
           
           
           
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             i. It has a pyramidal shape and originates from the acetabular notch and inserts into the fovea capitis of the femur; it has a great length variability.

             
             
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             ii. It is taut in hip adduction, flexion, and external rotation; it the least stable position of the hip.

             
             
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             iii. Its role in hip stability is controversial.

     
     
  2. 
     

     Dynamic stabilizers: these include the iliopsoas, iliocapsularis, rectus femoris, gluteus minimus, and the gluteus medius. The iliocapsularis is the greatest contributor to hip stability in this group.

Traumatic

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  I. Pathomechanism:

  
  

  High-impact trauma with can cause injury to the soft tissues and/or the osseous structures of the hip.

  
  
  
  
  1. 
     

     Posteriorly directed forces through the knee with hip flexed and in neutral adduction may result in pure hip dislocation, subluxation, or, more commonly, fracture-dislocation.

     
     
  2. 
     

     Anteriorly directed forces on externally rotated and extended hip can cause anterior hip instability.

     
     
  3. 
     

     Repetitive microtrauma is seen in sports requiring continuous hip joint rotation and axial loading.

Atraumatic

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  I. Pathomechanism:

  
  
  
  
  1. 
     

     Repetitive hip joint rotation and axial loading in the setting of anatomic abnormalities of the hip result in damage to the soft-tissue stabilizers of the hip.

     
     
  2. 
     

     Connective tissue disorders such as Ehler–Danlos syndrome, Marfan’s syndrome, and osteogenesis imperfecta confer the risk of developing microinstability.

     
     
  3. 
     

     Iatrogenic instability may present as a postoperative complication in patients without prior history of instability.

  
  
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  II. Causes of atraumatic hip instability:

  
  
  
  
  1. 
     

     Bony abnormalities: conflicts due to abnormal osseous morphology may lead to subluxation or dislocation of the hip, often with repetitive injury to the adjacent soft-tissue stabilizers.

     
     
     
     
     1. 
        

        Developmental dysplasia of the hip (DDH).

        
        
     2. 
        

        Femoroacetabular impingement (FAI): CAM or pincer impingement.

        
        
     3. 
        

        Legg–Calvés–Perthes disease.

        
        
     4. 
        

        Acetabular retroversion.

     
     
  2. 
     

     Connective tissue disorders: abnormalities in the formation of collagen can result in capsuloligamentous insufficiency and laxity.

     
     
     
     
     1. 
        

        Down’s syndrome.

        
        
     2. 
        

        Ehlers–Danlos syndrome.

        
        
     3. 
        

        Marfan’s syndrome.

        
        
     4. 
        

        Benign hypermobility syndrome.

     
     
  3. 
     

     Iatrogenic: unrepaired capsulotomy, overzealous acetabular rim resection, or component malposition during prior hip surgery may predispose to secondary hip instability.

     
     
     
     
     1. 
        

        Total hip arthroplasty.

        
        
     2. 
        

        Open hip procedures (hip dislocations required trochanteric osteotomy and capsulotomy).

        
        
     3. 
        

        Hip arthroscopy without capsular repair.

     
     
  4. 
     

     Idiopathic:

     
     
     
     
     1. 
        

        Generalized laxity.

        
        
     2. 
        

        Subclinical connective tissue disorder.

        
        
     3. 
        

        Borderline and hip dysplasia.

     
     
  5. 
     

     Extra-articular causes of hip instability:

     
     
     
     
     1. 
        

        Pelvic malalignment (e.g., ankylosing spondylitis; instability is due to increased pelvic tilt classically with increased risk of anterior instability).

        
        
     2. 
        

        Iliopsoas tendinitis.

        
        
     3. 
        

        Abductor/gluteal insufficiency.

        
        
     4. 
        

        Sacroiliitis.

        
        
     5. 
        

        AIIS (anteroinferior iliac spine) impingement with prior rectus avulsion or proximal injury.

History

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  I. Patients often present with complaints of hip pain and apprehension or subjective feeling of the hip giving way during certain at-risk activities (rising from seated position, rolling over in bed).

  
  
  
  
  1. 
     

     Insidious onset and gradually worsening symptoms without a specific precipitating event is more characteristic of atraumatic causes of instability.

     
     
  2. 
     

     Pain most often reported in the inguinal fold or anterolateral hip.

     
     
  3. 
     

     Posterior instability can present as posterior hip/buttock pain. This typically occurs with rise from seated position or position of sleep (adduction, IR [internal rotation]), or with anterior impingement that permits levering out of the head.

     
     
  4. 
     

     History of clicking, locking, and giving way should be investigated.

     
     
  5. 
     

     Attention should be given to symptoms elicited by activities with repetitive hip rotation, axial loading, or the extremes of motion.

     
     
  6. 
     

     Any previous ipsilateral hip injuries or surgeries should be noted.

     
     
  7. 
     

     Patients with hip dislocation should be immediately identified based on substantial symptoms and difficulty with weight bearing.

  
  
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  II. Medical and family history should be explored for connective tissue disorders and hypermobility.

  
  
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  III. Referred pain from the sacroiliac joint and/or lumbar spine with radicular symptoms can be confused with primary hip pathology and should be ruled out.