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ORIGINAL ARTICLE
Technical Note Surface Hip Replacement: Rotating The Acetabular Component 1800 To Improve Fixation Utilising Ischio-Pubic Splines In Patients With Shallow Or Deficient Sockets

*H Sharma, FRCS; C Watson, MBBS; S Sinha, MS(Orth); AC Campbell, FRCS(Orth)

*Department of Trauma and Orthopaedics, Monklands Hospital, Airdrie, Lanarkshire, ML6 OJS, UK

Address for Correspondence

Mr Himanshu Sharma,
44 Abercorn Road, Newton Mearns, Glasgow, G77 6NA, UK
Tel:  + 44 141 639 3697
Fax: + 44 141 201 0275
E-mail: hksharma1@aol.com

Abstract

Background: The Hip Resurfacing System offers an attractive option for the treatment of coxarthrosis with gratifying outcome in the young and active patients. Achieving full seating of the acetabular component in shallow or anatomically deficient sockets can sometimes be technically difficult while performing Metal-on-Metal hip resurfacing.
Methods: In shallow or deficient sockets, we described a simple technique by 1800 rotation of the Cormet 2000 metal-on-metal resurfacing pegged acetabular prosthesis. This works by utilising ischio-pubic splines for superolateral socket engagement. Between June 2000 to November 2001, we have used this technique in four hips (three patients, one bilateral) performed in a district general hospital of the UK.
Results: The mean age at primary operation was 37.3 years (range. 34 to 44 years). There were one male and two female patients. There were 2 right sided and 2 left sided procedures. Two cases had dysplastic disease of the hip (DDH), while bilateral case was diagnosed with multiple epiphyseal dysplasia. The follow up ranged from a minimum of 27 months to a maximum of 48 months with an average follow up of 37.2 months. None of the patients needed revision of the components, dislocation or deep infections.
Conclusions: Rotating the acetabular component 1800 in shallow or deficient sockets works satisfactorily by utilizing the ischio-pubic splines for superolateral socket engagement and should be considered as one of the viable option with or without structural augmentation.

Keywords: Metal-on-Metal hip resurfacing, Cemented, Uncemented, Acetabular component, Femoral component.

J.Orthopaedics 2006;3(1)e4

Introduction:

The Hip Resurfacing System offers an attractive option for the treatment of coxarthritis in the young and active patients with gratifying outcome.2,3,5,6 Currently available Metal-on-Metal Resurfacing Hip Systems include Cormet 2000 (Corin Medical), the Birmingham Hip (Midland Medical Technologies) and Conserve Plus (Wright Cremascoli).7 The Cormet 2000 implant design utilises the hybrid principle with an uncemented acetabular and a cemented femoral component.  

Achieving full seating of the acetabular component in shallow or anatomically deficient sockets can sometimes be technically difficult while performing Metal-on-Metal hip resurfacing. On occasion, structural tricortical autografts or allografts are required to obtain a satisfactory positioning of the acetabular component. We describe a simple technique to aid fixation of the uncemented acetabular component in patients with shallow or deficient sockets.

Material and Methods :

The Cormet 2000 acetabular component is available as pegless and pegged cup. In both Cormet cups, there are two sets of anti-rotation splines. These two sets of fins engage the ischium and pubis snugly. In routine cases, the uncemented cup is firmly impacted in place using the cup introducer ensuring anti-rotation splines engaging the ischium and pubis (Figure 1).

In shallow or deficient sockets, we describe a simple technique by 1800 rotation of the Cormet 2000 metal-on-metal resurfacing pegged acetabular prosthesis. This works by utilising ischio-pubic splines for superolateral socket engagement (Figure 2). We have used this technique in four hips (three patients, one bilateral) in a district general hospital of the UK between June 2000 to November 2001. We obtained a successful outcome in all the patients and managed to avoid the need of structural allograft/autograft augmentation in three hips. In one patient, this technique was supplemented with cadaveric allograft.

 

Results :

The mean age at primary operation was 37.3 years (range-minimum-34, maximum-44 years). There were two females and one male. There were 2 right sided and 2 left sided procedures. Two cases had dysplastic disease of the hip (DDH), while bilateral case was diagnosed with multiple epiphyseal dysplasia. Posterior approach was used by single operating surgeon.  

A cementless acetabular component and cemented femoral component were used using single manufacturer implants (Cormet 2000). The follow up ranged from a minimum of 27 months to a maximum of 48 months with an average follow up of 37.2 months. None of the patients needed revision of the components, experienced dislocation or had deep infections.

Discussion :

The Hip Resurfacing System offers a rapidly growing option for the treatment of coxarthritis in the young and active patients.2,3,5,6 Out of currently available Metal-on-Metal Resurfacing Hip Systems (Cormet 2000, Birmingham Hip and Conserve Plus,  the Cormet 2000 implant design utilises the hybrid principle with an uncemented acetabular and a cemented femoral component.  

Corin Medical started using an uncemented acetabular component with a cemented femoral component in 1994. Enhancements were made to the prosthesis such as the introduction of metal porous coating overlaid with hydroxyapatite on the external surface of the cup, and an improved face mounted introduction method subsequently.4 The original Cormet cup design incorporated two sets of three anti-rotation splines; two long splines with one small spline above. It was found that the cups were occasionally difficult to fully impact, especially in hard bone, and that in these cases they sometimes did not fully seat in the prepared acetabulum. The spline arrangement has been modified lately by removing the superior spline and thinned down the two remaining splines in profile (but with the overall length maintained) so that they cut into the ischium and pubis more easily.1  

The Cormet acetabular cup is equatorially expanded - a 54 mm diameter cup has a diameter of 54 mm at the pole and a diameter of 56 mm at the rim. Therefore, it allows a perfect hemi-sphere to be reamed (54 mm diameter) for the implant, which gives a 2mm press-fit at the mouth of the device and a line-to-line fit at the pole. This results in improved stress distribution to the acetabulum. Most current cementless acetabular cup systems in Metal-on-Metal hip resurfacing now utilise this hemispherical expansion principle, as the advantages of a well-fixed press fit primary fixation are well recognized.1,4  

The management of younger patients with abnormal hip anatomy leading to secondary osteoarthrosis is an orthopaedic challenge. Long term outcome, safety, clinical effectiveness and cost effectiveness of the Metal-on-Metal hip resurfacing procedure in such patients is poorly understood. A simple technique is described here to aid fixation of the uncemented acetabular component in patients with shallow or deficient sockets by rotating the acetabular component 1800 with or without structural augmentation. This works satisfactorily by utilising the ischio-pubic splines for superolateral socket engagement. 

Conservative hip arthroplasty with resurfacing of the acetabulum and femoral head is an attractive concept in young and active patients.2,4 Preservation of bone stock is important for young patients who are likely to need more than one operation in their lifetime. The closer is the anatomy to normal, the better the function of resurfacing. Achieving full seating of the acetabular component in anatomically deficient sockets in patients with abnormal coxanatomy can sometimes be technically difficult while performing Metal-on-Metal hip resurfacing.This study supports the resurfacing hip arthroplasty proponents as a practical and potentially useful treatment method in young and active arthritic hips with abnormal hip anatomy as well.

Conclusion:

In summary, Metal-on-metal resurfaced hips with appropriate case selection can yield satisfactory results in the young and active patients with abnormal coxanatomy. This technique used in three patients with successful outcome and averted the need of structural graft augmentation.                                                                                              

Reference :

  1. The Cormet 2000TM Resurfacing Hip System. Operative technique. Cormet.com.

  2. De Smet KA, Pattyn C, Verdonk R. Early results of primary Birmingham hip resurfacing using a hybrid metal-on-metal couple. Hip international. 2002;12(2):158-162.

  3. Ebied A, Journeaux S. Metal on metal hip resurfacing. Current orthopaedics. 2002;16:420-425. 

  4. McMinn D, Pynsent P. ‘Metal/Metal Hip Resurfacing With Hybrid Fixation: Results Of 1,000 Cases - A Personal Series.’ Trans American Academy of Orthopaedic Surgeons, San Francisco, 2001.

  5. McMinn D, Treacy R, Lin K, Pynsent P. Metal on metal surface replacement of the hip. Experience of the McMinn prosthesis. Clin Orthop. 1996;329 Suppl:S89-98.

  6. Mont MA, Rajadhyaksha AD, Hungerford DS. Outcomes of limited femoral resurfacing arthroplasty compared with total hip arthroplasty for osteonecrosis of the femoral head. J Arthroplasty. 2001;16(8 Suppl 1):134-9.

  7. National institute for clinical excellence. Guidance on the use of metal on metal hip resurfacing arthroplasty. 2002.

 

This is a peer reviewed paper 

Please cite as : H Sharma: Technical Note Surface Hip Replacement: Rotating The Acetabular Component 1800 To Improve Fixation Utilising Ischio-Pubic Splines In Patients With Shallow Or Deficient Sockets

J.Orthopaedics 2006;3(1)e4

URL: http://www.jortho.org/2006/3/1/e4

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