TKR IN SEVERELY DEFORMED KNEES

Abstract

Treatment by TKR of severe deformities : fixed varus or valgus knee, or flexion contracture, sometimes combined (valgus and flexed knee as for example in rheumatoid arthritis) is frequently a difficult challenge. Seldom a flessum, recurvatum or malrotation have also to be managed.

These deformations, articular, extra-articular or combined can be observed in knee arthritis associated with malalignement, malunion of diaphysis, malunion of lower part of the femur or upper tibia after fracture or osteotomy, chronic juvenile arthritis or rheumatoid arthritis, Paget’s or post-rachitism disease.

In 60′ and 70′ the most difficult cases have been frequently treated by hinge prosthesis with a high percentage of infection and loosening; many of the other cases treated with customary prosthesis had a poor follow-up because instability, luxation, patellar problems, pain or recurrence of the deformity.

Now to obtain the best prosthesis survival rate , the well trained orthopaedic surgeon has to make a good radiographical and clinical examination and the a good planification with the good choices:

• - necessity or not to perform, as a first stage, an osteotomy of femur or tibia to correct a mal-union or a deformity in frontal, sagittal or horizontal plane

• - type of prosthesis ( constrained or not, PCL sparing or sacrificing, mobile bearing ),

• - medial or lateral approach, and then Keblish procedure or not; tibial tubercle osteotomy or quadricepsplasty in stiff knees;

• - sequence and level of tibial and femoral cuts; always perpendicular, for us, to the mechanical axis ,

• - different steps of release of lateral, or medial and sometimes posterior ligamenteous and capsular elements, with many controversies for lateral compartment (iliotibial band, collateral lateral ligament, popliteus, posterolateral capsule, biceps tendon )

• - necessity of medial ligament advancement or thightening when distension in severe valgus knee,

• - repair of bone loss by cement, or more usually by bone graft or metal wedge.

ARTICULAR OR PARA ARTICULAR DEFORMITIES

1) FIXED VARUS KNEE

Treatment of this deformation is usually not so difficult. In case of postero-stabilized prosthesis implantation, after removal of medial condylar and tibial plateau osteophytes resection of PCL and release of semi-membranosus tendon and postero- medial capsule are performed. Pes anserinus and collateral medial ligament release creating a subperiosteal elevation of the medial envelope is sometimes needed for good soft tissue balance; in such case a constrained plateau can be useful.

It is also possible to try PCL sparing but a good tightening of PCL is difficult and reconstruction by bone graft, metal wedge or cement or medial tibial plateau is in most cases necessary to protect tibial insertions of PCL.

2) FIXED VALGUS KNEE

We prefer the Keblish approach to have a direct look on the tightened formations (iliotibial band, lateral collateral ligament, popliteus.

We agree with the Krackow’s classification of valgus knee in 3 groups.

For group 1, according to Whiteside it is possible to spare the PCL in the majority of cases if we accept to use a bone graft or a metal wedge on the lateral femoral condyle or/and tibial plateau taking the medial compartment as a reference.This choice of arthroplasty with PCL retention maintains the right level of the knee joint and offers often a best stability than postero-stabilized prosthesis does; PCL well tightened is a “third ligament” giving frontal stability as proved in traumatology. In fact many surgeons prefer to use postero-stabilized arthroplasty to avoid difficulties in PCL managing, and they release in different controversed steps the lateral elements. If there is instability they implant a more constrained tibial insert than usually. As communicated by Burdin it is also possible to prevent instability by performing a sagittal osteotomy of the lateral condyle around the insertions of popliteus and collateral ligament, and screw it after obtaining a good balance of the knee with the displacement of the osteotomized bone downward and/or posteriorly.

For group 2, which is caracterized by medial collateral ligament instability, it is safer to treat these knees with a postero-stabilized more or less constrained prosthesis than using a PCL sparing one and advancement of the medial ligament.

For group 3, severe overcorrection in valgus after lateral closed osteotomy for tibia varus realizes an upper tibial malunion. Prosthesis implantation is difficult: difficulties of soft tissue balance, conflict between upper tibial lateral cortex and tibial metalback stem, and bad coverage or overlapping of the tibial metalback, unless using a twisted stem. Different options can be choosen:

postero-stabilized prosthesis needs a release of lateral side; the tibial cut perpendicular to mechanical axis resecting bone to the bottom of the lateral defect takes off a too big amount of bone on the medial tibial plateau to have a safe support for metal back. If bone graft of lateral plateau is done to avoid this fact a constrained insert is potentially necessary.

implantation of a PCL sparing prosthesis with also release of lateral soft tissue, and reconstruction of medial tibial plateau and eventually condylar bone loss. For stability of the knee PCL acts as a collateral ligament. correction of the deformity by a new tibial osteotomy and after its consolidation implantation of the prosthesis some months later.

tibial osteotomy and prosthesis can be performed during the same operation, using a long tibial stem, cemented or not to stabilize the osteotomy site.

3) FLEXION CONTRACTURE

Correction of the deformity can be difficult when flexion is more than 30 or 40 degrees; PCL is not always an obstacle for correction. Sometimes initialy anterior bony deformity of the upper tibia has to be resected , especially in rheumatoid arthritis. After regular cut of the distal femur and removing of posterior osteophytes and loose bodies, elevation of posterior capsule from the distal femur is less dangerous than transverse incision of its middle part. If needed proximal attachements of gastrocnemius can also be stripped from the femur. Then if knee extension is not possible with trial component the tightened PCL has to be sacrified, or released or lengthened for some surgeons wanting to spare it. Finally a choice between lengthening of hamstrings and pes anserinus or a new cut of distal femur is necessary with use in some cases of a more constrained tibial plateau. For good tracking of patella lateral retinacular release is also mandatory.

4) FLESSUM, RECURVATUM, MALROTATION

Small flessum or recurvatum in metaphyseal area can be managed with the femoral anterior and posterior distal femoral cuts or tibial cut with sometimes incidence on prosthesis choice and biomechanical consequences.

Malrotation around 15 degrees can also be corrected by implants positioning, and perhaps a little more than 15° using a mobile bearing prosthesis.

EXTRA ARTICULAR OR COMBINED DEFORMITIES

In this type of deformity it can be necessary to perform in the same or in two separate operations its correction by a diaphyseal osteotomy preferably at the site of the deformity.

It is mandatory to have a good fixation of the bone to allow a quick and strong rehabilitation of the knee after prosthesis implantation. Plating, nailing or stabilization by the stem of prosthesis can be used.

At the present time the trend is to reach good correction of the deformity and implantation of the prosthesis at the same time even if the deformity is extra-articular; this challenge can be difficult.