Hip Int 2014; 24 ( 6): 582-586
DOI: 10.5301/hipint.5000160
ORIGINAL ARTICLE
A radiographic comparison of femoral offset after cemented and cementless total hip arthroplasty James R. Berstock, Adrian M. Hughes, Amy M. Lindh, Evert J. Smith Avon Orthopaedic Centre, Southmead Hospital, Bristol - UK
Restoring femoral offset during total hip arthroplasty is important. Femoral offset and leg lengths are inextricably linked by the caput-collum-diaphysis (CCD) angle of the implant being used. We investigate the restoration of offset and leg lengths using the radiographs of a consecutive series of patients following implantation with either a high CCD angled cementless, or an anatomical CCD angled cemented femoral component. Although our data suggests that we are able to restore femoral offset and leg lengths using either device, we recommend additional caution when using non-anatomical high CCD angled implants. Keywords: Arthroplasty, Replacement, Hip, Cementation, Leg length inequality, Digital radiography Accepted: May 6, 2014
INTRODUCTION Restoration of an appropriate femoral offset is fundamental to the long-term survival of a total hip replacement and is important for providing patients with the satisfaction expected of their hip joint replacement. An appreciation of the biomechanics of the hip joint, in particular the abductor muscle function, is critical. The surgeon’s choice of femoral stem is a key factor in influencing outcomes. The femoral offset is the perpendicular distance measured from the centre of rotation (COR, i.e. centre of the femoral head) to the longitudinal axis of the centre of the femoral canal. The femoral offset determines the abductor lever arm. Optimising femoral offset restores the soft tissue tension, minimises impingement, dislocation and implant loosening, but also improves the postoperative range of movement and normalises the gait pattern (1, 2). A reduced femoral offset disadvantages the abductors by reducing the lever arm, increasing the joint reaction forces of the hip thus leading to increased wear of the bearing surfaces (3, 4). Different brands of contemporary cemented and cementless femoral implants offer a variety of offsets. The ability to alter femoral offset and stem size varies widely between 582
systems. The caput-collum-diaphysis (CCD), or neck shaft angle of the stem, is the key variable, coupling femoral offset with leg length. Few clinical studies offer insight into the choice of implant design and the relationship to femoral offset. We hypothesise that the cemented, anatomical CCD angled device may restore both leg length and femoral offset more reliably than a high CCD angled device. This radiographic study compares the restoration of femoral offset and leg length with both devices.
METHOD AND MATERIALS Two femoral components used routinely in our unit were selected for comparison. The cemented Exeter V40 (Stryker, Newbury, UK) with a neck-shaft angle of 125° was compared with the cementless Taperloc (Biomet, Bridgend, UK) stem with a CCD angle of 138°. An Exceed ABT (Biomet, Bridgend, UK) cementless acetabular cup was used in all of the patients. The radiographs of consecutive patients with unilateral osteoarthritis requiring a total hip replacement between
© 2014 Wichtig Publishing - ISSN 1120-7000
Berstock et al
Fig. 1 - Measurement of offset and leg length from the immediate postoperative radiograph showing a Taperloc stem and Exceed ABT cup.
2010 and 2012 were retrospectively recruited into each group. Younger patients (
DOI: 10.5301/hipint.5000160
ORIGINAL ARTICLE
A radiographic comparison of femoral offset after cemented and cementless total hip arthroplasty James R. Berstock, Adrian M. Hughes, Amy M. Lindh, Evert J. Smith Avon Orthopaedic Centre, Southmead Hospital, Bristol - UK
Restoring femoral offset during total hip arthroplasty is important. Femoral offset and leg lengths are inextricably linked by the caput-collum-diaphysis (CCD) angle of the implant being used. We investigate the restoration of offset and leg lengths using the radiographs of a consecutive series of patients following implantation with either a high CCD angled cementless, or an anatomical CCD angled cemented femoral component. Although our data suggests that we are able to restore femoral offset and leg lengths using either device, we recommend additional caution when using non-anatomical high CCD angled implants. Keywords: Arthroplasty, Replacement, Hip, Cementation, Leg length inequality, Digital radiography Accepted: May 6, 2014
INTRODUCTION Restoration of an appropriate femoral offset is fundamental to the long-term survival of a total hip replacement and is important for providing patients with the satisfaction expected of their hip joint replacement. An appreciation of the biomechanics of the hip joint, in particular the abductor muscle function, is critical. The surgeon’s choice of femoral stem is a key factor in influencing outcomes. The femoral offset is the perpendicular distance measured from the centre of rotation (COR, i.e. centre of the femoral head) to the longitudinal axis of the centre of the femoral canal. The femoral offset determines the abductor lever arm. Optimising femoral offset restores the soft tissue tension, minimises impingement, dislocation and implant loosening, but also improves the postoperative range of movement and normalises the gait pattern (1, 2). A reduced femoral offset disadvantages the abductors by reducing the lever arm, increasing the joint reaction forces of the hip thus leading to increased wear of the bearing surfaces (3, 4). Different brands of contemporary cemented and cementless femoral implants offer a variety of offsets. The ability to alter femoral offset and stem size varies widely between 582
systems. The caput-collum-diaphysis (CCD), or neck shaft angle of the stem, is the key variable, coupling femoral offset with leg length. Few clinical studies offer insight into the choice of implant design and the relationship to femoral offset. We hypothesise that the cemented, anatomical CCD angled device may restore both leg length and femoral offset more reliably than a high CCD angled device. This radiographic study compares the restoration of femoral offset and leg length with both devices.
METHOD AND MATERIALS Two femoral components used routinely in our unit were selected for comparison. The cemented Exeter V40 (Stryker, Newbury, UK) with a neck-shaft angle of 125° was compared with the cementless Taperloc (Biomet, Bridgend, UK) stem with a CCD angle of 138°. An Exceed ABT (Biomet, Bridgend, UK) cementless acetabular cup was used in all of the patients. The radiographs of consecutive patients with unilateral osteoarthritis requiring a total hip replacement between
© 2014 Wichtig Publishing - ISSN 1120-7000
Berstock et al
Fig. 1 - Measurement of offset and leg length from the immediate postoperative radiograph showing a Taperloc stem and Exceed ABT cup.
2010 and 2012 were retrospectively recruited into each group. Younger patients (
