Medacta GMK Sphere - Tibio-Femoral Offset Measurement; Contraindications; Surgical Approach

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1.3 CONTRAINDICATIONS
Total knee replacement is contraindicated in the following
cases:
•
Progressive local or systemic infection.
•
Muscular loss, neuromuscular disease or vascular
deficiency of the affected limb, making the operation
unjustifiable
•
Severe instability secondary to advanced destruction
of condylar structures or loss of integrity of the lateral
ligament.
Mental or neuromuscular disorders may create an
unacceptable risk to the patient and can be a source of
postoperative complications. It is the surgeon’s
responsibility to ensure that the patient has no known
allergy to the materials used.
The Kinematic Alignment Surgical Technique is
contraindicated also for patients with greater than 5°
valgus deformity with MCL insufficiency.
1.4 SURGICAL APPROACH
The most common surgical approach is the vertical midline
skin incision and a medial parapatellar approach. Other
approaches may be used depending on the surgeon’s
preferences. After exposing the joint via elevation of the
medial retinaculum, flex the knee. Prior to any bone
resection define the normal bony architecture by removing
the osteophytes (including those at the intercondylar
notch) as collectively these contribute to the maintenance
of any malalignment and conceal the true bone size.
Resect the anterior cruciate ligament. If you are using a
GMK Sphere CS insert, resect also the posterior cruciate
ligament which also aids exposure by permitting easier
subluxation of the tibia for its subsequent osteotomy.
CAUTION
If a cruciate retaining insert (CR Insert) is used, the posterior
cruciate ligament must be preserved.
During all procedures it is the intention to replace the bone
and cartilage, that has been lost secondary to the arthritic
process and resected as part of the arthroplasty, with a
similar thickness of polyethylene and metal provided by the
prosthetic components.
2. TIBIO-FEMORAL OFFSET MEASUREMENT
When using a GMK Sphere CR insert, the measurement of
the tibio-femoral offset can be a reference to check the
slope once the trial implants are in place. Flex the knee to
90°. Expose the knee using a medial approach. Position the
arms of the offset caliper against the distal medial femoral
condyle and anterior tibia. Orientate the longer arm parallel
to the patella tendon. Measure the distance. When cartilage
on the medial femoral condyle is worn to the bone subtract
2 mm from the offset measurement.
2.
3.
CAUTION
This measurement is not reliable in case of deficient ACL
with postero-medial wear of the tibia.
To evaluate the slope in such cases please refer to the table
GMK Sphere decision tree - CR insert in chapter 8.1.