Clinical benefits

X-pander has 4 main functions, each of which leads to a number of clinical and economical benefits for the involved patients, surgeons and hospitals/clinics. The 4 functions are listed below and the direct effects with beneficial results are explained. X-panders main functions are to:

 

1. Perform a per-operative measurement of the diameter of the reamed acetabulum.

2. Indicate whether the reamed acetabulum has achieved a satisfactory geometry for press-fitting the cup.

3. Give an indication of the bone-quality (elasticity) of the acetabular bone.

4. Give an indication of the optimum position of the acetabular cup to be inserted.

 

These are 4 very important factors in providing a good, functional and stable hip implant.

 

 

1. Diameter

X-pander can measure the diameter of the reamed acetabulum with an accuracy of ± 0,5mm. Knowing the actual diameter of the reamed acetabulum will help the surgeon to choose the right cup size. Choosing the right cup size will mean:

 

Fewer aseptic cup-loosenings. Common knowledge and basic biomechanics agree that better cup-fixation leads to decreased risk of aseptic cup-loosenings. 41,1% of all revision surgeries are performed due to aseptic loosening of the cup [DSECA] and hence aseptic loosening of the cup is the most frequent cause of complications in hip-implant surgery [K. H. Widmer, 2002].

 

In general the cup achieves a better press-fit as it makes a good fit in the cavity, and therefore the amount of operations where stabilizing screws are needed will decrease. For an explanation of the benefits of eliminating the use of screws see NOTE 1.

 

 

 

2. Geometry

When expanding the Measuring Head of X-pander in the reamed acetabulum, the surgeon can obtain tactile information indicating whether the Measuring Head, simulating the implant cup, has a good grip in the acetabulum. Should the reamed acetabulum for example have a more elliptical rather than round shape, which is often known to be the case [J. R. Macenzie, 1994 and K. S. Kim, 1995], X-pander allows the surgeon to detect this, as the measuring head can rotate between only two contact points with the bone. When this is detected the surgeon gets a second chance to ream a satisfactory round shape in the acetabulum. Achieving a good round shaped cavity will mean:

 

• Fewer aseptic cup-loosenings. When the gaps between the implant and the bone become fewer and smaller, the cup will have better fixation and fewer patients will return for a second operation. This is true both for patients returning within the first couple of weeks after the primary operation and for patients returning several years after [J. R. Macenzie, 1994 and K. S. Kim, 1995 and I. R. Spears, 1999].


• The amount of operations where stabilizing screws are needed to compensate for the poor fit will decrease. For an explanation of the benefits of using no screws see NOTE 1.

 

 

3. Bone-quality

When the X-pander Measuring Head is expanded in the acetabulum until it aligns with the bone, the surgeon will achieve tactile information of the quality/elasticity of the bone by feeling the resistant force when expanding the Measuring Head further (the surgeon will gain more experience with this the more times he/she uses X-pander). When the surgeon knows whether the acetabulum is very elastic, very stiff or somewhere in between, he/she can use this information when deciding how much the cup should be oversized compared to the acetabular cavity (“oversized” meaning how much lager the diameter of the cup should be compared to the cavity). When the right oversize is found it means:

 

• Due to fewer instances where a too large cup is inserted, the numbers of patients in whom one or more fractures occur in the acetabular bone are expected to decrease [Y. S. Kim, 1995]. This again leads to shorter hospitalization, shorter rehabilitation time and less pain for the involved patients.


• Another benefit of decreasing the number of too large cups inserted is that fewer cups will be subject to increased deformation [M. Squire, 2006]. This corresponds to fewer cups with increased liner-wear and following decreased implant lifetime. This ultimately leads to fewer long-term re-operations [K. F. Orishimo, 2003].


• The amount of operations where stabilizing screws are needed to compensate for the poor fit will decrease. For an explanation of the benefits of using no screws see NOTE 1.

 

 

4. Position

When measuring the reamed acetabulum, the surgeon will gain useful information concerning positioning of the cup. Malpositioning of the cup is proven to be the result of 50% of all total hip implant procedures [H. Malchau, 2010]. When a cup is positioned correctly, it means:

 

• Fewer cups will dislocate, meaning that fewer patients will need second surgery [P. André 2002]. Dislocation of the joint is the cause of 17.4% of all revision surgeries [DSECA].


• The amount of wear-debris particles coming from the artificial joint will be kept at a minimum, thus minimizing the risk of particle induced bone loss [J. T. Moskal, 2013].


• Fewer instances of cup impingement with the psoas ligament – this means less patient pain and thus decreased risk for second surgery being necessary [J. T. Moskal, 2013].

 

 

NOTE 1: When the cup is stabilized with screws, the screw holes allow wear-debris particles from the polyethylene wear component (or chrom-cobolt in case of metal on metal articulations) to migrate along the screw-paths into the patient’s bone where it causes the bone to degenerate, [S. M. Röhrl, 2004]. This, typically within 10-15 years, causes the bone to become week around the implant cup and in some cases it loosens. This means that the patient has to undergo revision surgery and this second procedure is often difficult and results in poor outcome because of the damaged bone. Based on clinical experience it is expected that the use of X-pander will result in a decrease of the number of operations where stabilizing screws are used by 50%.

 

 

 

 

Reference list

 

[DSECA] – The average value of the most recent (2014) national hip registries for Denmark, Sweden, England/Wales/Northern Ireland, Canada and Australia.

 

[K. H. Widmer, 2002] – K. –H. Widmer et al., Load Transfer and Fixation Mode of press-fit Acetabular Sockets, The Journal of Arthroplasty, 2002.

 

[S. M. Röhrl, 2004] - Stephan Maximilian Röhrl, Wear and fixation of the acetabular component, Umeå University Medical Dissertations, 2004.

 

[J. R. Macenzie, 1994] - James R. Macenzie et al., Areas of Contact and Extent of Gaps With Implantation of Oversized Acetabular Components in Total Hip Arthroplasty, Clinical Orthopaedics and Related Research, 1994.

 

[K. S. Kim, 1995] - K.S. Kim et al., Reamed Surface Topography and Component Seating in press-fit Cementless Acetabular Fixation, The Journal of Arthroplasty, 1995.

 

[I. R. Spears, 1999] - Ian R. Spears et al., The influence of friction and interference on the seating of a hemispherical press-fit cup: a finite element investigation, Journal of Biomechanics, 1999.

 

[Y. S. Kim, 1995] - Young Sik Kim et al., Fracture of the acetabulum during insertion of an oversized hemispherical component, The Journal of Bone and Joint Surgery, 1995.

 

[M. Squire, 2006] – Matthew Squire et al., Acetabular Component Deformation with Press-Fit Fixation, The Journal of Arthroplasty, 2006.

 

[K. F. Orishimo, 2003] – Karl F. Orishimo et al., Relationship Between Polyethylene Wear and Osteolysis in Hips with a Second-Generation Porous Coated Cementless Cup After Seven Years of Follow-up, The Journal of Bone and Joint Surgery, 2003.

 

[H. Malchau, 2010] – Henrik Malchau et al., Risk factors for Cup Malpositioning, Clinical Orthopaedics and Related Research, 2010.

 

[P. André 2002] - Pascal-André et al., Vertical Acetabular Positioning With an Inclinometer in Total Hip Arthroplasty, The Journal of Arthroplasty, 2002.

 

[J. T. Moskal, 2013] – Joseph T. Moskal et al., Improving the Accuracy of Acetabular Component Orientation: Avoiding Malpositioning, The Journal of Bone and Joint Surgery, 2013.