1. Impingement with Total Hip Replacement
by Aamer Malik, Aditya Maheshwari, and Lawrence D. Dorr
J Bone Joint Surg Am
Volume 89(8):
August 1, 2007
©2007 by The Journal of Bone and Joint Surgery, Inc.

2. Biomechanics of impingement.
Biomechanics of impingement. Reduced clearance leads to repetitive abutment between the femur and the acetabular rim in the anatomic hip or between the femoral component and the acetabulum in the prosthetic hip. A: A normal anatomic hip and an ideal total hip replacement with a large femoral head and a high head-neck ratio. B: Cam-type impingement in the native hip caused by a reduced femoral head-neck offset and similar impingement in a prosthetic hip with a small femoral head and a skirted femoral neck. C: Pincer-type impingement can result from excessive overcoverage of the femoral head in the native acetabulum or from inadequate removal of acetabular osteophytes in the prosthetic hip. D: A combination of the cam and pincer types of impingement in the native hip as well as in a prosthetic hip with a small femoral head, a head-neck ratio of <2.0, a large cup, and a polyethylene liner with no chamfers.
Aamer Malik et al. J Bone Joint Surg Am 2007;89:
©2007 by The Journal of Bone and Joint Surgery, Inc.

3. Figs. 2-A and 2-B Head size and neck geometry can influence the head-neck ratio, which is the head diameter divided by the neck diameter.
Figs. 2-A and2-B Head size and neck geometry can influence the head-neck ratio, which is the head diameter divided by the neck diameter. These illustrations show the relationship between the cup and liner with different head and neck designs. Fig. 2-A The effect of increasing the femoral head size on impingement. A larger head increases the impingement-free range of motion.
Aamer Malik et al. J Bone Joint Surg Am 2007;89:
©2007 by The Journal of Bone and Joint Surgery, Inc.

4. A trapezoidal stem geometry favors an increase in the impingement-free range of motion compared with that associated with a circular neck design.
A trapezoidal stem geometry favors an increase in the impingement-free range of motion compared with that associated with a circular neck design. The inset picture illustrates the decrease in neck diameter with the trapezoidal design (darkly shaded area) compared with that of a circular neck design (lightly shaded area).
Aamer Malik et al. J Bone Joint Surg Am 2007;89:
©2007 by The Journal of Bone and Joint Surgery, Inc.

5. Aamer Malik et al. J Bone Joint Surg Am 2007;89:1832-1842
©2007 by The Journal of Bone and Joint Surgery, Inc.

6. Aamer Malik et al. J Bone Joint Surg Am 2007;89:1832-1842
©2007 by The Journal of Bone and Joint Surgery, Inc.

7. An osseous anatomic osteoarthritic acetabulum that averages 55° of inclination and 12° of anteversion is shown.
An osseous anatomic osteoarthritic acetabulum that averages 55° of inclination and 12° of anteversion is shown. Placing a cup in this position provides adequate osseous coverage but is unfavorable for wear and stability.
Aamer Malik et al. J Bone Joint Surg Am 2007;89:
©2007 by The Journal of Bone and Joint Surgery, Inc.

8. Lateralizing the cup also is unfavorable with regard to impingement and consequent wear and instability.
Lateralizing the cup also is unfavorable with regard to impingement and consequent wear and instability. If the cup is uncovered, there will be component-to-component impingement (arrows).
Aamer Malik et al. J Bone Joint Surg Am 2007;89:
©2007 by The Journal of Bone and Joint Surgery, Inc.

9. Medializing the cup maintains the cup in 40° of inclination and 25° of anteversion while obtaining correct cup coverage, but it increases the risk of bone-to-bone impingement (arrows).
Medializing the cup maintains the cup in 40° of inclination and 25° of anteversion while obtaining correct cup coverage, but it increases the risk of bone-to-bone impingement (arrows). This can be avoided by adjusting the level of the neck cut or using a longer femoral head or a high-offset stem.
Aamer Malik et al. J Bone Joint Surg Am 2007;89:
©2007 by The Journal of Bone and Joint Surgery, Inc.

10. Palpation to detect possible impingement by assessing the relationship of the tip of the lesser trochanter to the tip of the ischium.
Palpation to detect possible impingement by assessing the relationship of the tip of the lesser trochanter to the tip of the ischium. At least one fingerbreadth of distance should be present. The same test should be done to test for impingement of the greater trochanter against the ilium with the lower limb in external rotation and abduction and to test for impingement of the greater trochanter against the anterior inferior iliac spine with the lower limb in internal rotation, flexion, and adduction.
Aamer Malik et al. J Bone Joint Surg Am 2007;89:
©2007 by The Journal of Bone and Joint Surgery, Inc.