Impingement in THA. Georgi I. Wassilew. Orthopaedic Department, Centrum für Muskuloskeletale Chirurgie Univ.-Prof. Dr. med. C.

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1 Georgi I. Wassilew Orthopaedic Department, Centrum für Muskuloskeletale Chirurgie Univ.-Prof. Dr. med. C. Perka Charité - Universitätsmedizin Berlin Orthoload club, Berlin

2 Reasons for revision in THA Reason for Revision Australian Registry (%) Swedish Registry (%) England, Wales and Northern Ireland Registry (%) Loosening/Osteolysis Dislocation Infection Others Loosening, osteolysis and dislocation are still the main reasons for THA revision These failures are strongly correlated to impingement and component malpositioning

3 Well functioning THA Conditions for a well functioning THA include: correct component position correct reconstruction of the offset, the center of rotation and leg length

4 Well functioning THA Deviations from these conditions can lead to an impingement, subluxation, dislocation, micro-separation and increased edge - loading.

5 Biomechanics of impingement Different types of THA impingement Which can occure isolated or in combination Implant-implant bone-bone soft tissue-soft tissue

6 Biomechanics of impingement Principles regarding impingement in the natural hip as described by Ganz are the same as in THA impingement Can be divided in femoral (CAM) and in acetabular (Pincer) induced impingement

7 Biomechanics of CAM impingement Cam impingement in a prosthetic hip is caused by any implant features that reduce the head-neck ratio Small head size Skirt on the femoral head Large circular femoral neck

8 Biomechanics of CAM impingement Head size Bigger head size leads to an increased ROM

9 Biomechanics of CAM impingement Skirt on the same femoral head size reduces the ROM

10 Biomechanics of CAM impingement Geometry of the femoral neck circular femoral neck trapezoidal design

11 Biomechanics of pincer impingement Features that increase acetabular impingement include: Lateralized cup placement Acetabular osteophytes

12 Biomechanics of pincer impingement Features that increase acetabular impingement include: Presence of an elevated rim liner

13 Bone-on-bone impingement Surgeon-dependent factors placing the hip at risk for femoral bony impinging against the pelvis at the extremes of motion include: Short leg length Short offset

14 Implant-positioning Respect of these safe zones should reduce the impingement, subluxation and dislocation rates Lewinnek 1978 JBJS Inclination: 40 ± 10 Anteversion: 15 ± 10 Widmer und Zurfluh 2004 JOR Inclination: Anteversion: Malik et al 2007 JBJS Inclination: ~ 40 Anteversion: 25 ± 10 Antetorsion-stem: Dorr et al CORR Inclination: ~ 40 Anteversion: Antetorsion-stem : combined Anteversion: 25 45

15 Reality regarding cup malposition

16 Risk factors for cup malpositioning Factors correlated to malpositioned cups include: Surgical approach (MIS) Low volume surgeons High BMI

17 Microseparation 1. Medial and/or high acetabular cup position 2. Reduced femoro-acetabular offset head separates from the cup during the swing phase of walking upon heel strike, the head contacts with the superior rim of the cup and produces rim wear

18 Tribological effects of malpositioning and impingement Hard-hard and soft-hard bearings show excellent wear rates under standard conditions

19 Tribological effects of malpositioning and impingement Under advers condition

20 Metal-on-metal Standard conditions Advers conditions Me-Me-THA mm 3 /MZ 3 mm 3 /MZ Resurfacing 0.1 bis 0.4 mm 3 /MZ 71 mm 3 /MZ More than 100 fold increase of wear rates

21 Metal-on-metal Clinical findings Massive osteolysis Pseudotumors High serum metall-ion levels

22 Polyethlyen-on-Ceramic Standard conditions HXLPE 5 bis 10 mm 3 /MZ Microseparation HXLPE 25.6±5.3 mm3/mz reduced to 5.6±4.2 mm 3 /MZ Possible explanation During head separation, the synovial fluid is grabbed by the head and possibly leads to an improved lubrication

23 Polyethlyen-on-Ceramic Clinical findings Polyethylen with impingement signs show wear rates of 0.33 mm/year without impingement signs of 0.19 mm/year

24 Ceramic-on-ceramic Standard conditions Advers conditions abduction angle 65 Biolox forte 0,03 0,09 mm 3 /MZ 0,09 mm 3 /MZ Biolox delta 0,05 mm 3 /MZ 0,05 mm3/mz Microseparation 1,84 mm 3 /MZ

25 Ceramic-on-ceramic clinical findings Retrieval studies Mean wear rate 0,025 mm 3 /year Anteversion less than 15 the wear rate increases to 1,2 mm 3 /year 0 mm 3 /year Anteversion 15 Stripe wear as sign of microseparation and edge loading were found in up to 50%

26 Avoiding impingement Component positioning by the use of combined anteversion Restore biomechanics leg length offset center of rotation

27 Use of navigation system Show Accurate cup and stem orientation Precise reconstruction of offset and leg length compared to conventional implant placement

28 Thank you!