TIS
Chapter 16
High Tibial Osteotomy /
Total Knee Replacement
- Introduction
- historically have seen some form of knee replacement since the late 1950's
- first suggestions were replacement of the tibial plateau with acrylic or metal implants
- first constrained total knee prosthesis was developed in 1952
- nonarticulated, unconstrained, multi-condylar replacement developed in the 1960's
- HTO or TVO - high tibial osteotomy/tibial varus or valgus osteotomy
- earliest reports were in 1875
- often a first step before consideration of a TKR
- goal is to balance loads medially and laterally
- correction for valgus not particularly successful in that it
loads the tibial spine rather than the medial compartment as intended;
also effectively lengthens the MCL resulting in joint instability
- currently used for varus deformities to unload the medial compartment
- Insall reports that varus deformities of 100 are nearly always
stable, while those exceeding 100 are more often unstable
Technique:
- a wedge cut is made in the proximal tibia at least 1.5 cm
distal to the joint line; osteotomy is inclined medially and distally;
the tibia is fixated with hardware
From: Insall: Surgery of the Knee. Churchill Livingstone, 1984, p. 568
- rehab consists of PWB within 2 days of surgery, progressing to
FWB within the next two weeks
- ROM and strengthening can progress as tolerated and are symptom-limited
- Total Knee Replacement
Indications:
- tri-compartment or severe bi-compartment degenerative joint disease
- joint instability or loss of motion
- significant deformity, usually despite osteotomy or following failed osteotomy
* young age is a relative contraindication in any joint replacement procedure
- expected life of prosthesis is 13 years
Classifications/materials:
- Resurfacing (unconstrained) : unicondylar, unicompartmental,
bicondylar or total condylar. Bicondylar and total condylar
replacement can be cruciate-retaining or cruciate-existing.
Materials: femoral component: cobalt-chrome alloy
tibial component: high-density polyethylene
patellar component: polyethylene
- Constrained: fixed-axis metal hinge or somewhat loose
(semiconstrained) with some rotation and varus/valgus. These are
generally used only with severe instability
- six year R/U comparing plastic and metal revealed no statistical
difference between the two groups in knee scores
Fixation:
Cement: problems with loosening at the bone-cement interface
Biologic: utilized the rapid postoperative growth of bone into a porous-coated prosthesis
- hybrid (uncemented femoral component): decreases operative time,
reduces polyethylene wear from cement debris, and avoids possible
adverse biologic response to material
- cementless: questionable in patient with poor bone quality; seems
to couple on femoral side, but poorly on tibial side; no statistical
difference in outcome in a 5 year R/U comparing cement and biologic
fixation
Biomechanical considerations:
- Compressive loads
- like other plastics, the tibial component deforms under
relatively low stresses; therefore, conformity must be maximum to
avoid exceeding the elastic limit of the polyethylene
- goal is to transmit forces to the bone over as large an area as
possible to prevent focal loading
- maintaining as much tibia as possible preserves critical cancellous bone
- a more rigid material spreads loads out over a larger area
- wear can be adhesive, abrasive, and fatigue
- AP stability
- constrained prosthesis implies complete conformity between
femoral and tibial components in the sagittal plane, or a hinged
prosthesis is used; this does not provide for a normal changing center
of rotation, and creates a conflict between the cruciates and the
prosthesis resulting in decreased ROM, posterior tilting of the tibial
component and necessary rotation is prevented
- designs supposing the PCL to be intact tend to have less
conformity, relying on the retained ligament to prevent posterior
subluxation; most designs assume no ACL
- in many cases, the cruciates are absent or are not able to be
preserved; therefore partial conformity of the femoral and tibial
surfaces is utilized by the design of the component creating a
compressive force which "limits" undesirable motion; or by adding a
guiding or stabilizing mechanism in the intercondylar area
- nonconstrained prosthesis implies that the tibial plateaus are
flat and the cruciates carry almost all of the forces; accuracy is
vital; however, total reliance on the cruciates will eventually stress
them excessively
- Varus-valgus stability
- end result depends on gait and alignment of the prosthesis. If
force is excessive, high compressive forces result under the force,
and tensile stress occurs on the opposite side
- prosthetic components which decrease varus/valgus tilting are a
large surface area, a central post or two separate posts, and a rigid
connection between the medial and lateral sides
Complications of TKR:
- loosening: bone ingrowth negatively affected by NSAIDS and
surgical oopherectomy
- infection: 0.7% incidence/1000; superficial clear with removing
prosthesis, deep clear best with prosthesis removal
- peroneal palsy: 0.2%/1000 (CPM?)
- patellar subluxation, dislocation, fracture
- wear and tissue reaction: ~10% develop effusion, pain or
decreased ROM at average 4.5 years; polyethylene wear greatest on
medial tibial plateau; many complications on the medial side: tibial
component may sink into the top of the tibia
- osteolysis
- fractures
- instability
- thrombophlebitis
Physical therapy intervention:
- ROM: CPM through 0-30 degrees with gradual increases (expect no
more than 105-115 degrees flexion)
- Ambulation: WBAT
- Strength: Q sets
- SLR
- various open & closed chain activities
- bicycle/restorator
- kinetron