- Discussion:
- unicompartmental arthroplasty serves a specific nitch for knees that are too severe for arthroscopic management of medial DJD (see mosaicplasty)
but are not severe enough for total knee replacement;
- recent articles urge caution with this procedure;
- references:
- Early Failures in Unicondylar Arthroplasty
- Failure Mechanisms After Unicompartmental and Tricompartmental Primary Knee Replacement with Cement
- Reintervention after Mobile-bearing Oxford Unicompartmental Knee Arthroplasty
- Technical Goals:
- balance the flexion and extension gaps;
- balance the forces between the medial and lateral compartments (in both flexion and extension)
- maintain anatomic alignment;
- Alignment Influences Wear in the Knee after Medial Unicompartmental Arthroplasty.
- Lateral tibiofemoral compartment narrowing after medial unicondylar arthroplasty.
- Alignment influences wear in the knee after medial unicompartmental arthroplasty.
- The effect of leg alignment on the outcome of unicompartmental knee replacement
- implant considerations:
- Mobile and fixed-bearing (all-polyethylene tibial component) total knee arthroplasty designs. A prospective randomized trial.
- surgical exposure:
- standard minimal anterior approach biased slightly medial to the midline;
- minimal elevation of MCL so as to place the knee in excessive valgus as the knee is balanced;
- minimal incision into the vastus medialis;
- enough fat pad is removed inorder to see the intercondylar notch;
- note that hyperflexion of the knee will cause tightening of the quad mechanism and will limit flexion;
- osteophytes are removed from the notch and the medial aspect of the medial femoral condyle;
- tibial component:
- many systems base alignment of the femoral component off of the tibial component;
- ensure that the tibia position is stable with the toes pointing straight forward (no external rotation)
- tibial component must be aligned in the true AP plane (no internal rotation, no varus);
- a reciprocating saw is carefully applied in the true saggital plane, just medial to the ACL tibial footprint;
- careful to keep the cut in the exact saggital plane;
- proximal tibial cut is made 2 mm below the point of the deepest erosion;
- beaware that the cut needs to be deep enough to avoid sclerotic osteoarthritic bone (which will not hold cement);
- sizing: tibial component needs to cover the entire tibial peripheral cortex;
- posterior slope:
- more than 7 degrees of posterior slope of the tibial implant is avoided (esp if ACL is absent at the time of implantation).
- be aware than some proximal tibial cutting guides have additional built in posterior slope;
- references:
- Stress fracture of the medial tibial plateau after minimally invasive unicompartmental knee arthroplasty. A Report of 2 Cases
- Rapid Poly Failure of Unicondylar Tibial Components Sterilized w/ Gamma Irradiation in Air and Implanted After a Long Shelf Life.
- Posterior Slope of the Tibial Implant and the Outcome of Unicompartmental Knee Arthroplasty.
- Influence of the tibial slope on tibial translation and mobility of non-constrained total knee prosthesis
- Patient, implant, and alignment factors associated with revision of medial compartment unicondylar arthroplasty.
- Proximal tibial meniscal slope: a comparison with the bone slope
- femoral component:
- alignment rod:
- can be helpful in achieving proper orientation of the femoral component;
- rod is inserted along the anteromedial corner of the notch;
- the alignment rod can act as a patellar retractor when the knee is placed in 90 deg flexion;
- in 90 deg flexion the alignment rod should be parallel with the superior surface of the femoral cutting jig;
- preparation for the posterior femoral cut;
- mark down the center of the condyle;
- ensure that the knee is optimally flexed (to much or too little will distort coverage of the anterior femoral surface coverage);
- ensure that the body of the cutting guide is truly aligned along the center of the medial femoral condyle;
- preparation of the distal femoral cut;
- ensure that the body of the distal femoral cutting jig is rotated lateral (about 5-7 deg) in relation to the IM alignment rod;
- remember the femoral component needs to be aligned with the tibial component and not aligned to the anatomic axis;
- after this cut, the meniscus is fully removed;
- must be positioned on adequate base of bleeding subchondral bone;
- potential conflict in need to mill deep enough to get down to subchondral bone, while maintaining flexion and extension balance;
- must be position anterior enough for adequate coverage in full extension, while avoiding patellar impingement;
- must be centered over native anatomy of the medial femoral condyle;
- must have maximal congruent contact with tibial component in full flexion and extension;
- avoid tendency to internally rotate the femoral component;
- with the knee in flexion, slight internal rotation may not seem important, but with knee extension the femur will further internally rotate,
(tibia externally rotates) which will cause the femoral component to be non congruent over the tibia component;
- anatomy and kinematics of the knee joint
- references:
- Influence of rotatory malposition of femoral implant in failure of unicompartimental medial knee prosthesis
- Patellar Impingement Following Unicompartmental Arthroplasty.
- Relative positions of the contacts on the cartilage surfaces of the knee joint
- The influence of presence and severity of pre-existing patellofemoral degenerative changes on outcome of Oxford medial UKR.
- final trial:
- if there is inadequate extension and the knee is in slightly too much valgus, then an additional cut off the distal femur is indicated;
- if there the knee is too tight in flexion and extension then consider an additional proxial tibial cut;
- remember that the final trial should be at a similar hight to the lateral tibial plataue;
- cement technique:
- the cement technique needs to be as optimal as with total knee;
- consider extending the "trough" for the tibial component anteriorly (this will facilitate insertion of the tibial component keel into the slot;
- cement needs to be pressed throughout the medial compartment, and then the undersurface of the tibial component is covered in cement,
before it is impacted into place;
- references:
- Posteromedial compartment cement extrusion after unicompartmental knee arthroplasty treated by arthroscopy: a case report.
- Cement penetration and stiffness of the cement-bone composite in the proximal tibia in a porcine model
- Lateral meniscus and lateral femoral condyle cartilage injury by retained cement after medial unicondylar knee arthroplasty.
- Post Operative Care:
- contractures:
-
Unicompartmental knee arthroplasty for DJD of the knee. Remaining postoperative flexion contracture affecting overall results.
- radiographs:
-
The incidence of physiological radiolucency following Oxford unicompartmental knee replacement and its relationship to outcome.
-
Cementless Oxford unicompartmental knee replacement shows reduced radiolucency at one year.
-
Loosening of the femoral component after unicompartmental knee replacement
- Complications:
- revision to TKR (see
revision TKR)
-
Revision surgery after failed unicompartmental knee arthroplasty: a study of 35 cases.
-
Unicompartmental knee arthroplasty to total knee arthroplasty conversion: assuring a primary outcome.
Three cases of pseudogout complicated with unicondylar knee arthroplasty.
Minimally invasive unicondylar arthroplasty: eight-year follow-up.
Unicompartmental knee arthroplasty: long-term results.
Minimally invasive unicondylar arthroplasty: eight-year follow-up.
Medial Unicompartmental Knee Arthroplasty with the Miller-Galante Prosthesis.
Unicompartmental knee arthroplasty. 2- to 12-year results in a community hospital.
Results of Unicompartmental Knee Arthroplasty at a Minimum of Ten Years of Follow-up.
- Vanguard Biomet Knee
- Repicci Unicondylar Replacement
Alternatives to Total Knee Replacement: Autologous Hamstring Resurfacing Arthroplasty
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