Treatment Options for the Unstable Total Knee Arthroplasty - Condylar Constrained

Markku T. Nousiainen, B.A.(Hons.), M.S., M.D., FRCSC
Toronto, ON

One of the most common causes of failure in total knee arthroplasty relates to instability. Instability may develop at any time after the index procedure. Although the causes for instability are varied, they must be identified prior to performing a successful revision procedure. Causes include component loosening and/or wear, bone loss, improper component size or position, prosthesis or bone fracture, collateral ligament failure, or extensor mechanism dysfunction. These problems can lead to malalignment of the biomechanical axis of the limb and/or imbalance between the patellar and femoral components and/or the femoral and tibial components.

In all instances, patients will present with one or more of the symptoms of catching, giving away, pain, and/or unsatisfactory function. The surgeon must carefully assess the patient's history, physical examination, and imaging when working up the cause for instability. Knowledge of the significant medical problems such as neuromuscular disorders and obesity must be identified. Assessment of the patient's lower extremity alignment and function in gait, stance, and when on the examining table must be complete. Active and passive range of motion, stability of the femoral and tibial components in the coronal and sagittal planes, stability of the patello-femoral articulation, surgical incisions, and a neurovascular examination should be documented. Four-foot standing radiographs of the lower extremities and serial views of the knee are mandatory; a CT-scan of the knee should be taken to determine the alignment of the components if this is in question. Prior operative notes should be obtained to determine what implants were used and what releases may have been performed.

Once the cause for instability has been identified, the surgeon should develop an appropriate preoperative plan well before the date of surgery. This will provide the necessary time to order appropriate augments, stems, and other special instrumentation sets that may be needed as well as bone graft (one must remember that the mechanical constraint conferred in implants is intended to substitute for deficient collateral ligaments, not for bone loss). It is generally recommended that the least amount of constraint necessary to provide a well-functioning arthroplasty should be used,1,2 as the increased rotatory and shear forces applied through the implant-bone or implant-cement interface may lead to early loosening2. Nevertheless, making a decision on what level of constraint is necessary in the revision situation may still be difficult in the preoperative situation. For this reason, it is always wise to have implants for the next level of constraint in the operating room as a back-up.

Figure 1a
Figure 1b















Figure 1: Anteroposterior (a) and lateral (b) radiographs of patient 12 months after primary total knee arthroplasty. Patient developed attenuation of medial collateral ligament. Image courtesy of Dr. Jeffrey Gollish

The goals of revision surgery for instability require that: 1) the mechanical axis of the limb be corrected to normal, 2) the flexion and extension gaps be properly balanced, and 3) that collateral ligament integrity be property evaluated1. Respecting these three goals, implantation of constrained condylar prostheses is indicated in the following four revision situations.

The first relates to a revision total knee scenario where there is an absent lateral collateral ligament (LCL). This can usually be managed by a posterior stabilized prosthesis as long as the mechanical alignment of the extremity can be placed into slight valgus3. If there is any question about stability intraoperatively, the use of a constrained condylar prosthesis is indicated. The second situation relates to the presence of an attenuated medial collateral ligament which is reconstructable. Here, as long as the mechanical axis can be brought to neutral or slight varus, a constrained condylar prosthesis may be used3. The third scenario involves a revision total knee arthroplasty that exhibits instability in flexion despite implantation of the largest femoral component possible combined with a thick posterior stabilized polyethylene articular surface1. This situation will require a constrained condylar prosthesis to provide stability in flexion. If the constrained condylar prosthesis construct still dislocates, conversion to a linked constrained implant is necessary. The fourth scenario is when the surgeon faces instability in extension secondary to collateral ligament failure1. Here, a condylar constrained prosthesis can be used to confer adequate stability and limit extension past neutral. Again, if any question about stability occurs, then conversion to a linked implant is necessary.

Figure 2a
Figure 2b














Figure 2: Anteroposterior (a) and lateral (b) radiographs of same patient after revision to condylar constrained prosthesis. Image courtesy of Dr. Jeffrey Gollish

What results can one expect in using a condylar constrained implant after revising a total knee arthroplasty for instability? Not surprisingly, outcomes have improved as newer generations of prostheses have been developed and surgeons have learned to better understand the intricacies of how such systems should be used (i.e. the use of augments to manage bone defects, the importance of proper stem insertion and cement technique). Although earlier studies reported a high incidence of radiolucency about the tibial and femoral components (up to 60% incidence around tibial components and 33% around femoral components) at medium-term follow-up (five years),4,5 this has subsequently not been shown to be progressive or correlate with failure4,6. Short and medium-term failure rates were also initially documented as being high (up to 36% in one study)7 but they now vary between 0 and 2%8,9. Some specialty centres report excellent long-term results, with 80% survivorship at 15.3 years10.

In conclusion, the use of a condylar constrained implant in managing instability in the revision total knee arthroplasty situation is dependable as long as the mechanical axis of the limb is corrected, flexion and extension gaps are properly balanced, and collateral ligament integrity is property evaluated. In instances where this implant cannot confer adequate stability, conversion to a linked constrained implant is necessary.


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  10. Trousdale R.T., Beckenbaugh J.P., Pagnano M.W. 15-year results of the total condylar III implant in revision total knee arthroplasty. Proceedings of the sixty-eighth Annual Meeting of the American Academy of Orthopaedic Surgeons, San Francisco 585, 2001.

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