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Metal-on-Metal - For Young, Active Patients
Metal-On-Metal
CUP FEATURES
HEAD FEATURES
Large diameter heads; 36-54mm in diameter
(2mm increments)
Superfinished for extreme wear resistance
High carbon cast cobalt chrome
No skirts
12/14 SLT taper
Biggest heads in the industry
Articles of Interest:
Total Hip Dislocation
It is widely held that dislocation occurs in 2-10% of all
primary total hip replacements and as much as 20% in revision
procedures. This summary highlights several articles written
over the last 10 years about hip dislocation and its effects.
BEAULE, PAUL MD, SCHMALZRIED, THOMAS
MD, AMSTUTZ, HARLAN MD,
Jumbo Femoral Head for the Treatment of Recurrent Dislocation
Following THR, JBJS Vol.84-A, Number 2, pp.256-263,
February 2002.
Joint Replacement Institute investigation of 12 hips in
12 patients
Patients had recurrent instability in their hips and underwent
revisions utilizing jumbo femoral heads with an average
size of 44mm
12 patients had an average of 4 previous operations
10 patients received bipolar or fixed heads and 2 patients
received unipolar or modular heads
Average post-op follow-up was 6.5 years
1 patient died, but was stable up until time of death, 10
of the remaining 11 had no additional episodes of instability
1 hip did dislocate again, the cup was then repositioned
and the patient was still stable 7.6 years later
A larger femoral head must travel a greater distance before
subluxing or dislocating, and a greater range of motion
is allowed before the femoral neck impinges
In a previous study of 850 surface replacements, with head
sizes ranging from 38-51mm, the dislocation rate was 0.3%,
thus supporting the use of jumbo heads in the treatment
of dislocations
VON KNOCH, MARIUS MD, BERRY, DANIEL MD, et al, Late
Dislocation after Total Hip Arthroplasty, JBJS
Vol.84-A, Number 11, pp.1949-1953, November 2002.
Mayo Clinic investigation of 19,680 THRs between 1965-1995
Purpose of this study was to determine the prevalence of
late dislocation in THR (greater than 5 years)
The investigators also characterize demographics and other
factors
513 hips dislocated (2.6%) with 32% dislocating 5 or more
years after surgery
Late dislocation was more frequent in women and younger
patients
Late dislocation occurred often in association with poly
wear of more than 2mm
The authors concluded that late dislocations were much more
common than previously thought
ALBERTON, GREGORY, et al, Dislocation after Revision
Total Hip Arthroplasty, JBJS Volume 84-A, Number
10, pp.1788-1791,October 2002.
Mayo Clinic investigation of 1,548 revisions in 1,405 patients
(minimum 2 year follow-up)
Dislocation is the leading cause of failure in revision
total hip arthroplasty
115 or 7.4% of the patients dislocated
Revisions with 28 and 32mm heads were significantly more
stable than with 22mm heads
Overall 36% of the hips remained unstable
7.5% had anterolateral approach, 7.8% had lateral approach
with trochanteric osteotomy, and 6.1% had posterior approach
(no statistical significance in approach was recorded)
Trochanteric non-union was a dominant risk factor for dislocation
(7 of 9 non-unions dislocated)
LACHIEWICZ, PAUL F, KELLY, SCOTT, The Use of Constrained
Components in Total Hip Arthroplasty, JAAOS Volume
10, No.4, pp.233-238, August 2002.
Constrained components are often used as a surgical treatment
for recurrent dislocation
They usually include a locking mechanism incorporated into
the poly liner to keep the femoral head in place
Depuy and SHO designs were looked at in this study
This study showed component failure rates of 4-29% at a
relatively short term follow-up
Failure occurs in four ways: loosening of cup, disassociation
of the constrained liner from the shell, material failure
(breakage), and disengagement of the constraining ring
Acetabular liner thinning and head and neck separation were
also seen
With a failure rate exceeding 20%, in many cases it appears
that constrained liners should not be used prophylactically
based on these results
JOLLES, B.M. MD, et al, Factors Predisposing to Dislocation
after Primary THR: A Multivariate Analysis, The
Journal of Arthroplasty, Vol.17, No.3, 2002.
Investigation of 2,023 THAs performed between 1991 and
1998 at the Orthopedic Hospital de la Suisse Romande, Lausanne,
Switzerland
Many patient related factors have been implicated in dislocations
including but not limited to: age, gender, alcohol abuse,
diagnosis of OA, lack of compliance, and muscle weakness
in the joint
Technical factors are also prevalent causes of dislocation
including inappropriate cup or stem position, posterior
approach, thick implant necks, small femoral heads, and
limited surgeon experience
21 patients who had at least one dislocation were compared
to 21 patients without dislocations
Implant position, seniority of the surgeon, American Society
of Anesthesiologists (ASA) scores, and diminished motor
coordination were recorded
Dislocations rates were 6.9 times higher if total anteversion
was not between 40 and 60 degrees and 10 times higher in
patients with high ASA scores
Patients >80 years of age had a dislocation rate of 9%,
three times higher than the rest of the group
Surgeons should pay particular attention to anteversion
and use the ASA score as a preoperative assessment of dislocation
risk
JOHNSTON, RICHARD C MD, CALLAGHAN, JOHN J MD, et
al, Dislocation after Total Hip Arthroplasty: A Single Surgeon's
Experience, Orthopedic Clinics of North America,
Vol.32, No.4, October 2001.
Study of 4,967 THR (4,164 primaries, 803 revisions) performed
by Richard Johnston between 1970 and 1996 at the University
of Iowa
Surgeon used the Charnley 22mm components between 1970-79,
Iowa 28mm monolithic between 1982-88, modular 22mm components
between 1992-93 and other combinations between 1980-81 and
1994-96
During the 26 year period 7.2% of primary and 11.2% of revision
procedures dislocated
The most startling fact was that the surgeon returned to
22mm heads in 1992 and had a 13.4% dislocation rate in primaries
and 10% in revisions
Another key fact was that the surgeon found that more than
25% of the patients dislocated 2 or more years after the
procedure (normally, most dislocate in the first 3 months)
The final takeaway was that the authors used constrained
components in many revisions for dislocation with a 3.3%
recurrent dislocation rate as opposed to a 33% recurrent
dislocation rate without these constrained components
BARTZ, REED MD, et al, The Effect of Femoral Component
Head Size on Posterior Dislocation of the Artificial Hip Joint,
JBJS Vol.82-A, No.9, September 2000.
6 cadaveric bones were implanted with uncemented hips and
mechanically tested
Range of motion and impingement were tested for 22, 26,
28 and 32mm heads
The results showed that by increasing the head size from
22 to 28mm, range of flexion increased by 5.6 ° and
by 7.6 ° prior to posterior dislocation
Increasing the head size from 28 to 32mm did not provide
more significant improvement
Increasing the head size increases ROM and decreases impingement
and subsequent dislocation
For more information on the Metal-on-Metal
technology such as brochures, articles, video etc., please
contact Ortotech
directly.
 
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