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Hip Morphology Influences the Pattern of Damage to the Acetabular Cartilage: Femoroacetabular Impingement as a Cause of Early Osteoarthritis of the Hip.

·J Bone Joint Surg Br·2005·1,955 citations·Hip & Knee
Free Full Text·DOI·PubMed
SummaryAbstract on PubMed →

Beck et al. used direct intraoperative inspection during surgical hip dislocation to test whether cam and pincer FAI produce distinct articular damage patterns. 302 hips were reviewed; 26 isolated cam and 16 isolated pincer cases were analyzed. The study defined the pathomechanics of each impingement type and reframed labral pathology as a consequence of bony impingement, not its cause.

Study Snapshot

Design
Retrospective cohort
Setting: Single center, Bern, Switzerland
Funding: None
Objective
Whether cam vs. pincer femoroacetabular impingement produce distinct acetabular cartilage damage patterns
Outcome(s)
Location and pattern of acetabular cartilage and labral damage at surgery
Subjects
42 hips (26 cam, 16 pincer) from 302 surgical dislocations
Inclusion
  • Surgical hip dislocation for intra-articular pathology
  • Tönnis OA grade <1
  • Isolated cam or isolated pincer morphology
Exclusion
  • Traumatic/post-traumatic conditions, AVN, or prior surgery (n=58)
  • Insufficient radiographs (n=36)
  • Perthes' disease (n=7)

Key Findings

  • The aspherical femoral head in cam impingement acts like an eccentric cam during flexion, concentrating damage at the 1 o'clock anterosuperior acetabulum to a mean depth of 11 mm — roughly one-third of total cartilage thickness at that site.
    –This is full-thickness shear, not surface wear, and it is irreversible once established.
  • Labral-cartilage separation was present in all 26 cam hips: the labrum stays anchored to bone while cartilage peels away from it.
    –What appears arthroscopically as an undersurface labral tear is cartilage delaminating from the labrum — not a labral avulsion.
  • Pincer impingement produced only a narrow circumferential cartilage strip, max depth 4 mm at 12 o'clock, with labral ossification in 11 of 16 hips (5 circumferential).
    –The labrum bears the primary injury in pincer disease; cartilage damage is secondary.
  • Once the overcovered anterior rim blocks flexion, the femoral head levers posteriorly — generating a contrecoup lesion that caused femoral head cartilage damage in 62% and posteroinferior acetabular damage in 31% of pincer hips.
    –This posteroinferior lesion will not appear on a standard anterosuperior MRI scout cut.
  • Isolated morphology was uncommon: only 26 of 149 eligible hips were pure cam and 16 of 149 were pure pincer — most cases are mixed, so expect a combined damage pattern in practice.
  • Cam impingement was predominantly male (24 of 26, mean age 32); pincer was predominantly female (14 of 16, mean age 40).
    –Young man with groin pain thinks cam; middle-aged woman with deep socket thinks pincer.
Board PearlCam FAI shears anterosuperior acetabular cartilage off the labrum; pincer FAI crushes the labrum and creates a posteroinferior contrecoup lesion — treat the bone, not just the labrum.

Clinical Relevance

Before this paper, the labral tear was treated as the primary pathology. Arthroscopic debridement was standard practice, and outcomes were poor precisely because the underlying bony deformity driving the tear was never addressed.

This paper proved the labrum fails because of what the bone is doing — not the other way around. The authors explicitly state that debridement without correcting FAI morphology "may explain the poor results reported after isolated arthroscopic labral debridement."

When you see a young man with groin pain and an aspherical femoral head on cross-table lateral imaging, expect anterosuperior cartilage shear with labral-cartilage separation at 1 o'clock. When you see a middle-aged woman with a deep socket and labral ossification on plain film, look for circumferential labral degeneration and a posteroinferior contrecoup lesion that the standard MRI sequence may miss.

The clinical rule this paper established: always evaluate and correct bony morphology before or during any labral procedure. This is the evidence behind why isolated arthroscopic debridement was abandoned in favor of cam resection and rim trimming.

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|

Hip Morphology Influences the Pattern of Damage to the Acetabular Cartilage: Femoroacetabular Impingement as a Cause of Early Osteoarthritis of the Hip.

·J Bone Joint Surg Br·2005·1,955 citations·Hip & Knee
Free Full Text·DOI·PubMed
SummaryAbstract on PubMed →

Beck et al. used direct intraoperative inspection during surgical hip dislocation to test whether cam and pincer FAI produce distinct articular damage patterns. 302 hips were reviewed; 26 isolated cam and 16 isolated pincer cases were analyzed. The study defined the pathomechanics of each impingement type and reframed labral pathology as a consequence of bony impingement, not its cause.

Study Snapshot

Design
Retrospective cohort
Setting: Single center, Bern, Switzerland
Funding: None
Objective
Whether cam vs. pincer femoroacetabular impingement produce distinct acetabular cartilage damage patterns
Outcome(s)
Location and pattern of acetabular cartilage and labral damage at surgery
Subjects
42 hips (26 cam, 16 pincer) from 302 surgical dislocations
Inclusion
  • Surgical hip dislocation for intra-articular pathology
  • Tönnis OA grade <1
  • Isolated cam or isolated pincer morphology
Exclusion
  • Traumatic/post-traumatic conditions, AVN, or prior surgery (n=58)
  • Insufficient radiographs (n=36)
  • Perthes' disease (n=7)

Key Findings

  • The aspherical femoral head in cam impingement acts like an eccentric cam during flexion, concentrating damage at the 1 o'clock anterosuperior acetabulum to a mean depth of 11 mm — roughly one-third of total cartilage thickness at that site.
    –This is full-thickness shear, not surface wear, and it is irreversible once established.
  • Labral-cartilage separation was present in all 26 cam hips: the labrum stays anchored to bone while cartilage peels away from it.
    –What appears arthroscopically as an undersurface labral tear is cartilage delaminating from the labrum — not a labral avulsion.
  • Pincer impingement produced only a narrow circumferential cartilage strip, max depth 4 mm at 12 o'clock, with labral ossification in 11 of 16 hips (5 circumferential).
    –The labrum bears the primary injury in pincer disease; cartilage damage is secondary.
  • Once the overcovered anterior rim blocks flexion, the femoral head levers posteriorly — generating a contrecoup lesion that caused femoral head cartilage damage in 62% and posteroinferior acetabular damage in 31% of pincer hips.
    –This posteroinferior lesion will not appear on a standard anterosuperior MRI scout cut.
  • Isolated morphology was uncommon: only 26 of 149 eligible hips were pure cam and 16 of 149 were pure pincer — most cases are mixed, so expect a combined damage pattern in practice.
  • Cam impingement was predominantly male (24 of 26, mean age 32); pincer was predominantly female (14 of 16, mean age 40).
    –Young man with groin pain thinks cam; middle-aged woman with deep socket thinks pincer.
Board PearlCam FAI shears anterosuperior acetabular cartilage off the labrum; pincer FAI crushes the labrum and creates a posteroinferior contrecoup lesion — treat the bone, not just the labrum.

Clinical Relevance

Before this paper, the labral tear was treated as the primary pathology. Arthroscopic debridement was standard practice, and outcomes were poor precisely because the underlying bony deformity driving the tear was never addressed.

This paper proved the labrum fails because of what the bone is doing — not the other way around. The authors explicitly state that debridement without correcting FAI morphology "may explain the poor results reported after isolated arthroscopic labral debridement."

When you see a young man with groin pain and an aspherical femoral head on cross-table lateral imaging, expect anterosuperior cartilage shear with labral-cartilage separation at 1 o'clock. When you see a middle-aged woman with a deep socket and labral ossification on plain film, look for circumferential labral degeneration and a posteroinferior contrecoup lesion that the standard MRI sequence may miss.

The clinical rule this paper established: always evaluate and correct bony morphology before or during any labral procedure. This is the evidence behind why isolated arthroscopic debridement was abandoned in favor of cam resection and rim trimming.

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