TOTAL KNEE ARTHROPLASTY IN VALGUS DEFORMED KNEE
By
Dr. Laxmikanth. SP.G in M.S. OrthoGandhi Medical College
GENU VALGUM
Causes :
Idiopathic Post traumatic Rickets and Osteomalacia Neoplastic diseases (chondrosarcoma ) Rheumatoid arthritis Osteoarthritis Neuropathic joints Dysplastic bone diseases
TKA in Fixed-valgus deformity knee is difficult and challenging to surgeon.
The correction varus deformity is easier than valgus one.
Factirs that makes TKA in valgus knee difficult are :
ambiguity regarding sequence of ligament release. More chances of patellofemoral maltracking. Common peroneal palsy. More chances of flexion-extension gap mismatch.
In valgus knee, deficient in lateral bone and cartilage leads to adaptive changes occur in following structures,
Contractures and tightening of postero lateral capsule lateral collateral ligament arcuate ligament popliteus tendon iliotibial band lateral intermuscular septum.
PATHOPHYSIOLOGY
Stretching and attenuation of the medial ligaments can occur
Bony deformities:
Femur—The postero lateral femoral condyle is smaller.
Tibia—The tibia is externally rotated, the tibial tubercleis positioned laterally. The lateral plateau :central bone resorption and peripheralosteophyte formation.
Patella—The patella is often subluxed laterally. The lateralfacet is deformed (flattened or concave),with large traction osteophytes , Patella alta.
Ipsilateral hip, ankle and foot to be examined ---- whether they are contributing to knee pathology Alignment of both lower extremities is observed for extra-articular deformities. Stability in coronal and sagital plane should be looked for. To correct large angular deformities bone grafting and modular implants may be needed. Patellofemoral tracking thoroughly examined for any subluxation, mobility. Posterior structures examined for any popliteal cyst etc..
PRE OPERATIVE EVALUATION
RadiographsAP View : Weight bearing AP view superior than supine.
Lateral View :
Patellar height and patellofemoral joint can be visualised.As patella alta common with valgus knee this view is necessary.
Normal :1.02+/- 0.2.Patella alta : (LT/LP 1.2), Patella baja (LT/LP 0.8).
Insall-Salvati Ratio:
Merchant View :Superior than lateral view
Provides the most optimal assessment of,
Patellofemoral alignment Joint space, Articular surfaces.
Standing 52-Inch Cassette(“Three Joint View”) :
Gives information about,
The overall alignment (mechanical axis) of the lower extremity.
To know the degree of varus or valgus alignment at both knees and their relative leg length.
Presence of important extra-articular deformities (with prior trauma ,Paget’s disease)
Implant selection
In young patients --PCL substituting posterior stabilized implant
In elderly low-demand patients ---constrained condylar knee
Cases with bone deficiency---a modular implant with metal augments, offset stems, and variable tibial polyethelene thicknesses may be useful.
SURGICAL TECHNIQUE
Approaches
Bone preparation
Soft tissue balancing
Patellofemoral tracking
Surgical approaches
Skin incision -- anterior midline incision.
For arthrotomy -- medial parapatellar retinacular approach
Disadvantages :
Patellar maltracking is more common. Increased potential for inaccurate flexion-extension gap balancing . Increases external rotation of the tibia Access to the posterolateral corner is more difficult Vascularity to the quadriceps patella tendon (QPT) mechanism and lateral skin is at risk.
Some surgeons prefer lateral approach for valgus kneeAdvantages :
Improved access to the pathologic postero lateral corner
Preserves vascularity because the medial side is untouched; Centralizes the QPT mechanism, which optimizes patella tracking
Not routinely used because Damage to genicular arteries Not familiar with techniques of exposure and closure
Bone preparation:
FEMUR :
Femoral component rotational alignment is important in the valgus knee to attain,
Equal flexion extension gap Normal patellofemoral tracking Joint line level
The intramedullary alignment rod should be slightly medial to the center of the patellar groove.
The cutting guide is set at a 5° valgus angle.
This will align the joint surface perpendicular to the mechanical axisof the femur and parallel to the epicondylar axis.
In some cases resection from the medial side results in minimal or no resection from the lateral side of the distal femur.
For accurate rotational alignment either the APaxis or the epicondylar axis of the femur is used asanatomical reference for resection.
The posterior femoral condyles are unreliable as posterolateral femoral condylar deficiency
The tibial cut should be made at 90+/- 2 degrees to the long axis of the tibial shaft in both the coronal and sagital planes.
Over-resection of the proximal tibia to address a bony defect, and to create a flat surface for the tibial component may damage ligament attachments and may sacrifice excessive amounts of bone.
The medial tibia is referenced and 10 mm of bone is resected.Bony defects can be addressed with cement, bone, or metal augments. The MCL must be protected during resection.
TIBIAL CUT :
SOFT TISSUE RELEASE
The purpose of our release is to provide ligamentous balance with rectangular flexion and extension gaps ,while maintaining lateral side stability of the knee in flexion.
The release can be a full release, partial release, or Z-lengthening
Release is performed in a step-by-step controlled fashion and reassessed with laminar spreaders after each step
At the end of release, The mechanical axis passes through the centre of the knee. The flexion and extension gaps are equal and symmetrical.
The order of release varies among surgeons.
LCL and popliteus tendons, provides lateral stability in both flexion and extension.
IT Baand and posterolateral capsule, provides lateral stability only in extension.
SO, Release in flexion first and then proceed in extension.
Tight in both in Flex and ext
LCL and popliteus release
ITB &Post capsule release
PCL, IMS, Lat gastro release
Tight only in extension
IT Band release
Post capsule release
CONSTRAINED CONDYLAR KNEE
Pie-Crusting Technique
Based on palpation of taut soft tissues followed by their selective release with multiple stabs with 15 no..blade.
Multiple horizontal incisions given from inside to out.
Begin at the level of the joint line and can extend 10 cm proximally. This works like a tensor and allows the lateral tissues to lengthen and slide with some degree of continuity
It is performed only after final implantation of all total knee components, just before wound closure.
MEDIAL LIGAMENT ADVANCEMENT
It should be done when medial ligaments are too lax, after complete release of lateral ligaments
Described by Krackow
Two types Proximal advancement on femur Distal advancement on tibia
Procedure:
Elevation of the femoral origin of the medial collateral ligament.
Proximal advancement using a locking-loop type of suture within the substance of the ligament.
This suture is secured around a screw and washer with a staple placed at desired site on medial epi-condyle.
Finally ,
Patellar maltracking is often associated with a valgusdeformity.
If necessary a lateral retinacular release shouldbe performed.
VALGUS KNEE WITH BONE DEFECT causes:
Arthritis with angular deformityLateral condylar hypoplasiaOsteonecrosis TraumaPost surgical ( HTO, TKA )
TYPES: Contained or cavitary defects ---intact rim of cortical bone surrounding the deficient area. Noncontained or segmental defects ---more peripheral and lack a bony cortical rim.
Treatment options:
Small defects (<5 mm) typically are filled with cement. Contained defects can be filled with impacted cancellous bone graft. Larger noncontained defects can be treated by Structural bone grafts(auto or allografts ) Modular implants Screws with cement or graft.
CEMENT FIXED SCREWS
ALLOGRAFT
MODULAR IMPLANT
AUTOGRAFT FOR TIBIAL BONE DEFECT
AUTOGRAFT FOR FEMORAL BONE DEFECT
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