Aamer Malik

Impingement with total hip replacement.

Impingement is a cause of poor outcomes of prosthetic hip arthroplasty; it can lead to instability, accelerated wear, and unexplained pain. Impingement is influenced by prosthetic design, component position, biomechanical factors, and patient variables. Evidence linking impingement to dislocation and accelerated wear comes from implant retrieval studies. Operative principles that maximize an impingement-free range of motion include correct combined acetabular and femoral anteversion and an optimal head-neck ratio. Operative techniques for preventing impingement include medialization of the cup to avoid component impingement and restoration of hip offset and length to avoid osseous impingement.

Imaging and Navigation Measurement of Acetabular Component Position in THA

There are six different definitions of acetabular position based on observed inclination and anteversion made in either the (1) anterior pelvic plane or (2) coronal planes and based on whether each of the observations made in one of these two planes is (1) anatomic, (2) operative, or (3) radiographic. Anteroposterior pelvic tilt is the angle between the anterior pelvic plane and the coronal plane of the body. The coronal plane is a functional plane and the anterior pelvic plane is an anatomic pelvic plane. A cup may be in the “safe zone” by one definition but may be out of the “safe zone” by another definition. We reviewed published studies, analyzed the difference in varying definitions, evaluated the influence of the anterior pelvic tilt, and provided methods to convert from one definition to another. We recommend all inclination and anteversion measurements be converted to the radiographic inclination and anteversion based on the coronal plane, which is equivalent to the inclination and anteversion on the anteroposterior pelvic radiograph.

A Comparison of Surgeon Estimation and Computed Tomographic Measurement of Femoral Component Anteversion in Cementless Total Hip Arthroplasty

BACKGROUND The intraoperative estimation of the anteversion of the femoral component of a total hip arthroplasty is generally made by the surgeons visual assessment of the stem position relative to the condylar plane of the femur. Although the generally accepted range of intended anteversion is between 10 degrees and 20 degrees, we suspected that achieving this range of anteversion consistently during cementless implantation of the femoral component was more difficult than previously thought. METHODS We prospectively evaluated the accuracy of femoral component anteversion in 109 consecutive total hip arthroplasties (ninety-nine patients), in which we implanted the femoral component without cement. In all hips, we measured femoral stem anteversion postoperatively with three-dimensional computed tomography reconstruction of the femur, using both the distal femoral epicondyles and the posterior femoral condyles to determine the femoral diaphyseal plane. The bias and precision of the measurements were calculated. RESULTS The surgeons estimate of femoral stem anteversion was a mean (and standard deviation) of 9.6 degrees +/- 7.2 degrees (range, -8 degrees to 28 degrees). The anteversion of the stem measured by computed tomography was a mean of 10.2 degrees +/- 7.5 degrees (range, -8.6 degrees to 27.1 degrees) (p = 0.324). The correlation coefficient between the surgeons estimate and the computed tomographic measurement was 0.688; the intraclass coefficient was 0.801. Anteversion measured by computed tomography found that forty-nine stems (45%) were between 10 degrees and 20 degrees of anteversion; forty-three stems (39%) were between 0 degree and 9 degrees of femoral anteversion; eight stems (7%) were in anteversion of >20 degrees; and nine stems (8%) were in retroversion. CONCLUSIONS The surgeons estimation of the anteversion of the cementless femoral stem has poor precision and is often not within the intended range of 10 degrees to 20 degrees of anteversion. The implications of this finding increase the importance of achieving a safe range of motion by evaluating the combined anteversion of the stem and the cup.

Impingement of the Native Hip Joint

![Graphic][1] Impingement at the hip is a common cause of osteoarthritis. ![Graphic][2] Impingement is mostly due to morphologic changes as a consequence of in utero malformation or childhood hip disease such as Legg-Calve-Perthes disease or slipped capital femoral epiphysis. ![Graphic][3] On the basis of patterns and stages of labral and chondral injuries, impingement has been classified as cam type, pincer type, or mixed cam-pincer type. ![Graphic][4] The diagnosis is based on the medical history and the findings on physical examination and imaging studies. ![Graphic][5] Hip impingement is a mechanical problem, and nonoperative treatment will not correct the pathomechanics. Surgical correction should be considered prior to the onset of arthritis and must be designed to protect the vascularity of the femoral head. Impingement of the hip joint has been a hidden disease until the current decade. Femoroacetabular impingement was identified as a dynamic cause of osteoarthritis by Ganz et al.1-22, although Murray23 and Stulberg et al.24 had identified the so-called tilt deformity and pistol-grip deformity, respectively, as probable causes. Impingement within the hip joint is an abutment conflict between the bone of the femur and that of the pelvis. Impingement in young patients is a mechanical problem caused by biological structural patterns or by overuse, particularly in athletes or in very flexible hips. Leunig et al.14 observed evidence of impingement with aging in the acetabula of patients (sixty-nine to ninety-seven years of age) with a femoral neck fracture and not uncommonly in cadavers of donors who were sixty to ninety years old at the time of death. The cause of impingement in the osseous hip can be developmental, as a result of childhood conditions such as Legg-Calve-Perthes disease and slipped capital femoral epiphysis; it may also result from posttraumatic or post-osteotomy morphologic changes in inclination and anteversion angles1 … [1]: /embed/inline-graphic-1.gif [2]: /embed/inline-graphic-2.gif [3]: /embed/inline-graphic-3.gif [4]: /embed/inline-graphic-4.gif [5]: /embed/inline-graphic-5.gif

A validation model for measurement of acetabular component position.

There is no agreement on a standard approach to evaluating acetabular cup orientation, ideal target orientation, or a standardized measurement method for cup orientation in total hip arthroplasty. The purpose of this study was to investigate a simple method for validating measurements of acetabular orientation obtained using computer navigation and computed tomography scans. This study validated the imageless navigation system to be accurate with a precision of 1 degrees and a bias of 0.02 degrees for inclination and a precision of 1.3 degrees and a bias of 0 degrees for anteversion measurements. From this study, we propose that acetabular cup alignment is accurately assessed using computer navigation. We suggest acetabular orientation be reported in the radiographic plane (coronal plane), which incorporates pelvic tilt and therefore is more functional definition of cup position.

Impingement as a Mechanism of Dissociation of a Metasul Metal-on-Metal Liner

This case report is of a patient with disassociation of the acetabular cup liner caused by impingement. The cup inclination (39 degrees) and anteversion (24 degrees) were good as measured by computer navigation. Impingement occurred because the head-neck ratio was 2.0, and the hip length and offset were short by one head length. Successful revision without intraoperative impingement was accomplished with one size head larger (32 mm; head-neck ratio, 2.3) and one size longer to correct hip length and offset.

Computer Navigation with Posterior MIS Total Hip Arthroplasty

The majority of literature on computer-assisted surgery of the hip shows how navigation assists the surgeon in more accurate component placement as compared with techniques that use mechanical guides or are freehand.1–5 Our work has been with imageless navigation technology, which allows real-time intraoperative knowledge of the quantitative direction and depth of reaming; adjustment during reaming for variations in the bony anatomy to allow for correct cup coverage with optimal inclination; and adjustment of the anteversion of a cup to a desired combined anteversion through knowledge of the fixed femoral anteversion.6

The Role of Implant Design and Soft Tissue Structures on CCK Knee Joint Stability

+*Wang, X; *Malik, A; *Padgett, DE; *Wright, TM *Hospital for Special Surgery, New York, NY +Weill Graduate School of Medical Science of Cornell University, New York, NY xiw2003@med.cornell.edu INTRODUCTION Constrained condylar knee (CCK) implants are widely used in revision total knee arthroplasty (TKA) and, in recent years, increasingly in primary TKA, especially in the presence of functional loss of the collateral ligaments or severe joint deformity . In 2007, of 3058 TKAs performed at Hospital for Special Surgery, 450 were CCK implants. Shortand mid-term results show low failure rates, but complications include increased polyethylene wear and aseptic loosening. Both these complications could be caused by the increased constraint provided between the large, rectangular tibial post and the intercondylar femoral box. Little is known, however, about the relative constraint provided by post-box contact, by collateral ligaments, and by contact between the bearing surfaces of the tibial and femoral components. Such information would provide objective measures from which to determine the need for a CCK implant, would establish the role of soft tissue balancing, and would suggest design improvements to minimize mechanical complications while maximizing constraint. Thus, we sought to determine how load is shared between post-box contact, the tibiofemoral bearing surfaces, and the surrounding soft tissues.