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Research: W. K. Barsoum, R. W. Patterson, C. Higuera, A. K. Klika, V. E. Krebs, and R. Molloy A computer model of the position of the combined component in the prevention of impingement in total hip replacement J Bone Joint Surg Br 2007; 89-B: 839-845 [Abstract] [Full text] [PDF]

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A computer model of the position of the combined component in the prevention of impingement

B Michael Wroblewski   (11 October 2007)

The concept of combined component position in total hip arthroplasty

Brigitte M Jolles, Pierre-Francois Leyvraz   (13 September 2007)

A computer model of the position of the combined component in the prevention of impingement 11 October 2007
B Michael Wroblewski, Professor The John Charnley Research Institute, Wrightington Hospital Send letter to journal: Re: A computer model of the position of the combined component in the prevention of impingement bmwhipdr{at}hotmail.com B Michael Wroblewski	Sir, I would like to comment on the very detailed study by W.K. Barsoum et al. The authors are attempting to establish “the concept of combined component position…” “…as critical elements for stability…” in total hip arthroplasty. They have been able to show “…that there is a relatively safe zone for impingment-free ROM which can be achieved…” but “… it is unique for every patient”. The authors have modelled positions of a hemispherical acetabular component with a 28 mm diameter head, the head-neck diameter ratio of 2.3. Would it be reasonable to suggest that a different approach may be closer to addressing the problem of post-operative instability in total hip arthroplasty? The normal, natural acetabulum is neither anteverted, neutral nor retroverted; it is asymmetrical both in structure and function. The functional range of movement is, primarily, anterior to the coronal plane, while the labral extension of the acetabular rim, posterior to the coronal plane, enhances stability. This has already been put into clinical practice with the angle-bore cup design1 with encouraging results in revisions of failed total hip arthroplasties.2 If impingement is considered to be a problem then the neck diameter could be reduced.3,4 The authors are correct: the problem is unique for every patient, and attention to every detail is essential.1 Attempts to mix designs and techniques is not necessarily the best way forward.5 B.M. Wroblewski FRCS, The John Charnley Research Institute, Wrightington Hospital, Wigan, UK. 1. Wroblewski B.M. Revision surgery in Total Hip Arthroplasty. London: Springer-Verlag, 1990:43-4. 2. Wroblewski BM, Siney PD, Fleming PA. The angle bore acetabular component and dislocation after revision of a failed total hip replacement. J Bone Joint Surg [Br] 2006;88-B:184-7. 3.Wroblewski BM. Direction and rate of socket wear in the Charnley low friction arthroplasty. J Bone Joint Surg [Br] 1985;67-B:757-61. 4. Wroblewski BM, Siney PD, Fleming PA. Reduced diameter neck and its effect on the incidence of aseptic cup loosening in the Charnley LFA. J Bone Joint Surg [Br] 2005;87-B:(Suppl 1)43. 5. Porter M, Stone MH. Total hip arthroplasty using the Wroblewski golf ball cup inserted through the posterior approach. A high rate of dislocation. J Bone Joint Surg [Br] 2004;86-B:643-7.
The concept of combined component position in total hip arthroplasty 13 September 2007
Brigitte M Jolles, MD MSc University of Lausanne - Centre Hospitalier Universitaire Vaudois - Hôpital Orthopédique, Pierre-Francois Leyvraz Send letter to journal: Re: The concept of combined component position in total hip arthroplasty Brigitte.Jolles-Haeberli{at}chuv.ch Brigitte M Jolles, et al.	Sir, We read this article with interest. In it, Barsoum et al studied the optimum position for placement of the components using a three-dimensional computer model to simulate impingement. One of the main consequences of impingement is instability. The authors describe the concept of combined component position, in which anteversion and abduction of the acetabular component, along with femoral anteversion, are all defined as critical elements for stability. It is regrettable that the authors were unable to reference our paper entitled, "Factors predisposing to dislocation after primary total hip arthroplasty: a multivariate analysis."1 We conducted this study to determine the relative influence of various mechanical and patient-related factors on the incidence of dislocation after primary total hip arthroplasty (THA). Of 2,023 THAs, 21 patients who had at least one dislocation were compared with a control group of 21 patients without dislocation, matched for age, gender, pathology, and year of surgery. Implant positioning, seniority of the surgeon, American Society of Anesthesiologists (ASA) score, and diminished motor coordination were recorded. We observed that the dislocation risk was 6.9 times higher if the sum of the cup and stem anteversion was not between 40° and 60°, and concluded that surgeons should pay attention to the total anteversion (cup and stem) when performing a THA. In addition, as referenced in Table 1 of our article,1 the concept of total anterversion is also presented in a textbook.2 The concept of combined component position as a critical element for stability had already been introduced. However, we are happy to see that the authors were able to add a new scientific element to this field. B.M. Jolles, MD, MSc, P.-F. Leyvraz, University of Lausanne, Centre Hospitalier Universitaire Vaudois, Hôpital Orthopédique, Lausanne, Switzerland. 1. Jolles BM, Zangger P, Leyvraz PF. Factors predisposing to dislocation after primary total hip arthroplasty: a multivariate analysis. J Arthroplasty 2002;17:282-8. 2. Ranawat CS, Maynard MJ, Deshmukh RG. Cemented primary total hip arthroplasty. In: Sledge C, ed. Master techniques in orthopaedic surgery: the hip. Philadelphia: Lippincott-Raven, 1998:217-38.