A German orthopaedic surgeon has found that small modular hip
stems are amenable for use with computer navigation systems.
Djordje Lazovic, MD, began using his technique about 3 years
ago mostly in young patients with good bone stock and discovered
it helped him attain better overall hip biomechanics.
The shorter stem was also easier to implant compared to
traditional or longer prostheses, Lazovic told
Orthopaedics Today International. “Because of the
curvature of the short stem, it goes right through the femoral
neck,” he said.
In addition, this approach tends to be less invasive because
only the femoral neck and little else of the femur needs to be
exposed, he explained.
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Navigation aided surgeons to optimally place a
modular short-stem Metha prosthesis (B. Braun/Aesculap)
in a 54-year-old man. The implant is indicated for young
patients with good bone stock who seek complete range of
motion postoperatively. |
The prosthesis is implanted after making two
osteotomies, the locations of which are shown here.
Lazovic said using navigation makes checking the
osteotomy position easier intraoperatively.
Images: Lazovic D |
Match proximal femur
In the past, Lazovic used the OrthoPilot system (Aesculap AG
& Co.) for a variety of navigated cementless total hip
arthroplasty (THA) surgeries. Today, he almost always places
acetabular cups via navigation regardless of how he implants the
hip stem.
Lazovic shared his recent experiences using OrthoPilot
navigation technology with the Metha modular hip implant (B.
Braun/Aesculap) during the 8th Annual International Conference
on Expertise in Orthopaedic Navigation. Although he has not
formally collected outcomes data, Lazovic discussed his clinical
observations regarding the technique with Orthopaedics
Today International.
“The cup navigation stays the same in both long-stem and
short-stem prostheses,” Lazovic said. However, the short stem
has to be matched to the proximal femur and must be positioned
in a different way than traditional hip stems.
Restore biomechanics
Concerning the Metha implant, Lazovic
said it is important to first use it with traditional
techniques. He completed about 25 THA cases using those
techniques in 2004, initially implanting only the cup
with navigation and later adding the stem to the
navigated procedure.
Lazovic found key differences between navigating the
placement of long- and short-stem prostheses. For
example, with short-stemmed designs, navigating position
and antetorsion are limited by the shape of the proximal
femur, whereas navigation assists with both antetorsion
and stem depth of long-stem prostheses.
The challenge with short-stem THA designs is restoring
biomechanics under these circumstances, Lazovic said.
Custom offset, antetorsion
In the 150 cases completed with the
Metha modular implant, Lazovic found the best approach
was to “just put in the short stem and then navigate
only the biomechanics of its modular cone. He said this
is the major difference in implanting long and short THA
stems.
Adhering to the implant’s indications is also important
regardless of which way it is implanted.
“It is mainly a prosthesis for the younger patient for
whom we want to have as much bone left as possible. We
are preparing for revision surgery … [which] fortunately
will be in several decades, but still we should have a
lot of bone left. For this, the short stem seems to be
suitable,” he said.
However, he ultimately makes the decision about bone
quality intraoperatively.
No dislocations
The Metha implant’s cone portion is
available with various options for central column
diaphyseal (CCD) angle, offset and antetorsion.
Customizing the implant for each patient via the array
of modular options enabled Lazovic to use it in
dysplastic hips where the femoral neck was extremely
anteverted or in antetorsion. In those cases, it helped
him to better restore the biomechanics through small
corrections (15°) rather than large corrections (40°).
Lazovic said he has not had any dislocations in patients
with the Metha prosthesis, “which indicates the
restoration of the biomechanics really is helpful,” he
said. “The smaller prosthesis seems to be good for the
future, especially for the patients’ future.”
Other short-stem THA implants have recently been
introduced in Europe — some designed to better
approximate the anatomy of the proximal femur — but they
are relatively new, so it is too early to comment on
their mid-term results, Lazovic said.
For more information:
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Djordje Lazovic, MD, is director of the Clinic for
Orthopaedics, Pius Hospital Oldenburg. He can be
reached at Georgstr. 12, Oldenburg, Germany 26121;
+49-441-229-1561; e-mail:
Djordje.lazovic@pius-hospital.de. He is a
consultant to B. Braun/Aesculap.
References:
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Braun A, Lazovic D, Zigan R. Modular short-stem
prosthesis in total hip arthroplasty: Implant
positioning and the influence of navigation.
Orthopedics. 2007; 30(10 suppl):S148-S152.
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Lazovic D. Navigated short stem THA. Presented
at the 8th Annual International Conference on
Expertise in Orthopaedic Navigation. Sept.
20-21, 2007. Berlin.
