The operative word in this debate is always. In my opinion, there are some cases better served by extra-articular correction. The question then becomes which ones, and how does the surgeon determine? There are 4 considerations: the magnitude of the deformity, the relationship of the deformity to the knee, the side of the deformity (varus or valgus), and whether the femur or the tibia is affected by the deformity. A larger deformity is more important, but just as important is its relationship to the knee. Large deformities distant to the knee have little impact on the knee. Varus deformities require lateral intra-articular overresection, which produces lateral instability. Valgus deformities require medial overresection, which produces medial instability. Lateral instability is stabilized by the dynamic lateral stabilizers (popliteus, lateral head of the gastrocnemius, biceps femoris, and iliotibial tract) and is better tolerated than medial instability. The best way to determine the consequence of the malalignment in question is to template the knee by drawing the mechanical axis from the femoral head or ankle to the center of the knee, and then the resection level that will be required. This will demonstrate the amount of overresection required to correct the extra-articular deformity, and in some cases will indicate the advantage of an extra-articular correction.
Although it may be argued that intra-articular correction of extra-articular deformity is optimal for patients older than 60 years with deformities of <20°, and perhaps thats an acceptable criterion, not all patients are older than 60 years and not all deformities are <20°. If some patients need to be corrected other than intra-articularly, and I submit that there are, we must know how to distinguish them. This article presents the criteria by which patients who need extra-articular correction can be distinguished from those for whom intra-articular is effective.1
Most deformities come from intra-articular bone loss. The degree of the deformity is irrelevant. If the bone loss is intra-articular, the deformity is always corrected intra-articularly. An extra-articular deformity can come from various sources: congenital deformity, metabolic deformity (rickets), trauma, and surgery. A surgical deformity from a badly done high tibial osteotomy may be the most difficult to correct intra-articularly (Figure 1).
Several issues must be considered when choosing between intra- and extra-articular corrections: the magnitude of the deformity, the distance from the knee, whether the deformity is in the femur or the tibia, and the direction of the deformity (flexion, extension, varus, valgus, or rotation).
A 50-year-old woman presented with severe deformities of both femurs and both tibias from childhood rickets, with superimposed intra-articular bone loss from long-standing osteoarthritis secondary to the malalignments (Figure 2). She was restricted to household ambulation with a walker. Templating showed that the level of resection required for intra-articular correction would result in resection of the lateral femoral epicondyle, but the tibial deformity could be corrected intra-articularly. Total knee replacement (TKR) included a supracondylar femoral osteotomy done at the same time as the TKR and through the same incision (Figure 3). Correction was less than perfect on the right side, but the patient became an independent community ambulator.
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Figure 3: Postoperative radiographs showing alignment achieved by supracondylar osteotomies done at the same time as the TKRs. Figure 4: The resection line, drawn perpendicular to the mechanical axis of the tibia, shows that correcting both the intra-articular valgus deformity and the extra-articular deformity from the malunion would sacrifice the entire medial metaphysis.
Magnitude of the Deformity
It stands to reason that a small deformity will require only a small compensatory correction within the bony cuts for the TKR, and therefore is easily accomplished. There comes a point when the severity of the deformity will not allow correction within the ligamentous envelop that will leave that envelop functional. It would still be possible to correct the deformity intra-articularly, but a completely constrained prosthesis (hinge) would be required. However, magnitude alone is insufficient information.
Distance From the Knee
A 20° valgus deformity in the subtrochanteric region will have a negligible impact on the knee. The same deformity in the supracondylar region produces nearly the same amount of valgus deformity of the knee. The farther a deformity is from the knee, the lesser the impact on the knee. Although there are complex mathematical formulas for calculating this, simple templating will demonstrate the impact of the deformity on the resections necessary to correct the deformity, whatever the magnitude and distance from the knee. By drawing a straight line from the center of the femoral head to the center of the knee (or the center of the ankle to the center of the knee), the mechanical axis for the reconstructed joint is created. A line perpendicular to this mechanical axis and intercepting one of the surfaces of the joint line will show the kind of intra-articular deformity that will need to be created to correct the extra-articular deformity (Figure 4).
Deformity in the Femur Vs in the Tibia
Femoral and tibial deformities are not equal. Any compensatory bone cuts made on the distal femur affect stability only in extension. Compensatory cuts on the tibia affect stability throughout the whole range of motion. Therefore, it is easier to stabilize the knee, destabilized by a compensatory tibial cut, through a ligamentous reconstruction or a ligamentous release if the deformity is in the tibia vs in the femur.
Direction of the Deformity
The deformities addressed in this article are varus and valgus deformities. Severe flexion, extension, and rotational deformities require a corrective osteotomy, either before or at the same time as a TKR. Smaller deformities are unlikely to play as important a role as even moderate varus and valgus deformities. A varus deformity requires a compensatory lateral resection. A valgus deformity requires a medial overresection The compensatory overresection produces instability that must be addressed, either by soft tissue balancing or the use of a constrained prosthesis. Therefore, a valgus deformity corrected intra-articularly produces medial instability and a varus deformity similarly corrected produces lateral instability. Medial and lateral instability are not equally important. Lateral instability is less important because the lateral side of the joint is dynamically stabilized by the muscles on the lateral side, including the biceps femoris, the iliotibial tract, the lateral head of the gastrocnemius, the popliteus, and even the quadriceps. The muscular stabilizers on the medial side are not nearly as effective. Therefore, valgus deformity will be harder to correct and stabilize than varus deformity (Figure 3).
Analyzing patients who present with extra-articular deformity in this way will help to sort out which cases may benefit from an extra-articular correction either before or in conjunction with a TKR.
- Wolff AM, Hungerford DS, Pepe CL. The effect of extraarticular varus and valgus deformity on total knee arthroplasty. Clin Orthop Relat Res. 1991; (271):35-51.
Dr Hungerford is from the Department of Orthopedic Surgery, The Johns Hopkins University, Baltimore, Maryland.
Dr Hungerford has no relevant financial relationships to disclose.
Presented at Current Concepts in Joint Replacement 2008 Winter Meeting; December 10-13, 2008; Orlando, Florida.
Orthopaedic Crossfire is a registered trademark of A. Seth Greenwald, DPhil(Oxon).
Correspondence should be addressed to: David S. Hungerford, MD, Department of Orthopedic Surgery, The Johns Hopkins University, 5601 Loch Raven Blvd, Baltimore, MD 21239.