Management of Bone Defectsin TKA

Dr. Mohammad Hossein DehghaniIsfahan Jesus Hospital

Introduction

• more common in revision TKA,

BUT

• they do occur in primary TKA also.

Causes of bone defects in primary TKA

• erosion secondary to angular arthritic change, • inflammatory arthritis,• osteonecrosis, • and fracture.

Bone defects in primary TKA

• typically :asymmetrical & peripheral,

• although contained deficiencies caused by cyst formation may occur.

Bone defects in primary TKA

• In primary TKA ,base of contained and peripheral defects : condensed sclerotic bone,

• In revision surgery, removal of components often leaves osteopenic surfaces

Major Concern

• Diminish of subchondral bone strength distal to the subchondral plate.

• Solution:the level of lateral tibial resection should not exceed 1 centimeter to avoid compromising implant durability,– others have demonstrated that proximal tibial

bone strength is adequate to 20 mm

Solution

Right

Wrong

Management

1. translation of the component away from a defect,

2. lower tibial resection, 3. cement filling, 4. autologous bone graft,5. allograft, 6. wedges or augments, 7. custom implants..

Management(Use of stems )

• in primary TKA:– necessary when bone grafting is required – or when the bone defect compromises fixation

and renders the resurfacing component unstable without the added support of intramedullary fixation

Management (Lateral Translation)

• Lateralizing a smaller tibial component : effectively eliminates bony defect by removing contact of implant with defect

• However, the largest tibial tray size and polyethylene insert should always be favored to create the largest reasonable contact surface to distribute load.

Management (Lateral Translation)

Management (Lower Tibial Resection)

• is often effective • limit of a lower tibial resection is : insertion of

the ITB and infrapatellar ligament. (Gerdy)• Additionally, a lower tibial resection will

complicate component fit because of the natural taper of the tibia, necessitating the use of a smaller tibial component or tapered tibial augments.

Management (Lower Tibial Resection)

Right

Wrong

Management (Cement Filling)

• Lotke &Ritter demonstrated satisfactory long-term results with cement fill provided: – tibial bone defects are no deeper than 20 mm – and involve less than 50% of either plateau.

But– cement fill with or without screw reinforcement is an

inferior method of defect management & radiolucent lines are commonly observed under defects filled with cement.

– larger volumes of cement introduce the risk of thermal necrosis of the cement-bone interface

Management (Cement Filling)

Step-cut filled with cement (under tibialcomponent)

Management(autologous bone graft)

• readily available in primary TKA.• high rates of incorporation• osteoinductive properties • lack of potential disease transmission• typically used when the size criteria for

cement fill are exceeded.

Management (criteria that promote improved outcome)

1. creating viable/bleeding bed of host bone, 2. proper fit and finish of graft in host bed, 3. complete coverage of graft by the component to

avoid graft resorption secondary to stress shielding, 4. optimal alignment of components for even load

distribution, 5. limited weight bearing when larger grafts are used

to allow for graft union, 6. and grafts protected with stems when required .

Management

• Contained defects : easily filled with bone graft,

• Peripheral defects : more challenging.

Bone graft technique (From Behrens JC, Walker PS, Shoji H )

Management(Custom Prostheses and Metal Wedge Augmentation)

• Metal wedge : intraoperative construction of a custom implant to address a bone defect,

• Defects of less than 25 mm

• Custom prostheses : for dealing with larger defects ( > 25mm)

• limitations of practicality and cost

Metal Wedge Augmentation

• available in triangular and rectangular shapes,

• both cemented and cementless options.

• load transfer across a larger defect: a rectangular block and stem augmentation.

– good results using wedges attached with screw fixation

Distal Femoral Defects• frequently observed in valgus deformities

when the lateral femoral condyle is dysplastic.• As with the tibia, defects can be managed with

cement, bone graft, and metal augments.

Condylar resection

Build-up required

A. Contained Defects: managed in the same manner as

contained tibial defects.B. Peripheral Defects :

1. affecting the chamfer cuts, 2. affecting the distal surface, or 3. causing major bone loss.

Femoral deficiencies

• increasing stages of bone loss:– Stage 1• when the femoral osteotomy includes a portion of the

lateral distal femur, but contouring to accommodate the femoral component results in chamfer “air cuts” anteriorly and posteriorly. • cement fill is acceptable for filling anterior and

posterior spaces between bone and prosthesis. The sclerotic bone surface should be prepared to accept cement interdigitation.

Femoral deficiencies

– Stage 2• occurs when the level of the femoral osteotomy passes

distal to the lateral femoral condyle even without chamfer cuts.• In this situation, cement fill typically is unsatisfactory

unless combined with a femoral stem extension. • Even in this instance, a metal augment to the distal

femur is preferred.

Femoral deficiencies

– Stage 3 • refers to massive bone loss of one femoral condyle. • Substantial bone loss can be managed with allograft or

metal block augmentation, • Allograft requires a period of non–weight bearing

postoperatively and a femoral stem extension. The advantage of allograft is that if a revision is required, bone stock may be partially restored. • Metal augments allow quicker rehabilitation without

restricted weight bearing .

Femoral deficiencies

• In general, optimized collateral ligament stability and restoration of normal anatomy is preferable to the use of constrained prostheses.

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