Managing Severe Deformities With Calipered Kinematic Alignment

Overview

Currently, there is lack of consensus about the universal definition of severe deformity for the arthritic knee. Some consider a deviation of more than 10 degrees for a varus knee as a significant deformity. Others consider a severe deformity as more than 15 degrees for the varus knee and more than 20 degrees for a valgus knee. ^, These angles are relative to a hip-knee-ankle (HKA) angle of 180 degrees, which has been believed traditionally to be neutral for every patient, but has recently been proven to be different and highly variable in the population. Only recently has a universal classification system been proposed for varus knees that considers the amount of deformity and its origin of location, and whether it is metaphyseal or diaphyseal.

Whatever the numerical definition will be, there is consensus among orthopedic surgeons that total knee arthroplasty (TKA) for severely deformed knees poses a challenge. We believe that this challenge has been aggravated for many years by an incorrect approach to TKA that tries to reproduce a neutral alignment, thereby creating a bucket of iatrogenic difficulties, each of which had to be solved. We will propose a different approach for treating complex knees without the creation of nonanatomic complexity, by applying the kinematic alignment (KA) technique.

The etiology of severe deformities has been considered for many years as the result of either long-standing neglected arthritis that deteriorated to a point of extensive bone loss and secondary ligament insufficiency, or of congenital pathologic states such as Blount’s disease or rickets. Both of the latter are rare in the general arthroplasty practice in developed countries, although they may still be found in less developed parts of the world.

Today, the etiology of those deformities as seen from the perspective of constitutional alignment ^, might best be categorized into two separate groups that will be further discussed in this chapter:

1

Severe constitutional varus or valgus (single-level or multi-level) coupled with cartilage wear and occasionally bone loss to create severe deformity.
2

Posttraumatic extra/intraarticular deformities.

Today, the most common treatment workflows for cases with severe deformity include extensive soft tissue releases to attain balance and neutral mechanical alignment (MA), in addition to the use of stems, augments, and constrained or hinged implants. The addition of constrained or stemmed implants increases the cost burden two- to threefold. Extensive releases, reduction osteotomies, and even epicondylar transfers have been described as means to achieve stability. ^, Failure to manage these cases using the aforementioned techniques and restoring mechanically neutral alignment is widely believed to lead to premature loosening and failure. Several methods have been described to address severe deformities using these techniques, with the main emphasis being on short-term survivorship with minimal attention toward functional outcomes.

During the last decade, a better understanding and definition of the phenotypic presentation of constitutional alignment, coupled with a pronounced paradigm shift toward a more natural and anatomic reconstruction of the knee joint, have been gaining traction. At the same time, a changing population demographic skewing toward younger patients with higher expectations for clinical function of their artificial joints has challenged the surgical community to strive for better clinical results. These trends have encouraged alternative solutions and the exploration and optimization of kinematic knee alignment philosophies, even in the context of considerable deformity.

The concept of KA has been extensively studied and is a hot topic of debate in the field of total knee arthroplasty. In KA, the goals of the reconstruction are to restore the native tibial-femoral articular surfaces to their original alignment relative to the long bone anatomic axes, restore the native prearthritic limb alignment, and restore the native soft tissue laxities of the knee.

Unlike traditional mechanical alignment techniques, which focus on making the tibia orthogonal to the floor, KA techniques focus on placing the femoral component to match the native three-dimensional (3D) position of the distal femur as the primary goal of the reconstruction process. Next, by compensating for tibial wear (cartilage and bone) and placing the tibial component in its prearthritic anatomic position, there is no need for ligament releases or other soft tissue interventions to restore normal motion around the knee’s native rotational axes. The result is a well-balanced and more natural-feeling knee, with multiple studies showing favorable patient-related outcome measurements.

With respect to restoring native soft tissue laxity, we note that MA TKA for severe deformity has traditionally emphasized the need for ligamentous release to balance the knee perpendicular to the mechanical axis of the entire limb. The goal is to create “balanced gaps” where the same tension is created between the medial and lateral ligaments both in full extension to 90 degrees of flexion, even though in a normal knee there is more laxity in flexion on the lateral side. We believe there is a price to be paid for every ligament release or soft tissue manipulation, reflected in the way patients perceive their new knee as not natural.

From our perspective, one of the primary benefits of KA TKA is, therefore, its inherent ability to address severe deformity using the same general principles as are used for common minor deformity, with only a few specific considerations.

The aim of this chapter, therefore, is to briefly summarize the following:

•

The caliper-based KA TKA technique applied to severe deformities.
•

The application of KA TKA in six examples, including severe varus deformity, severe valgus deformity, and intra- and extraarticular posttraumatic deformities.
•

Special considerations relative to applying KA TKA to severe deformity.

Calipered Kinematically Aligned Total Knee Arthroplasty (Linked) Technique Principles and Application to Treating Severe Deformities

The key step of KA reconstruction is to replicate the distal femur’s 3D position, as it is the primary driver of knee kinematics, not the tibia. In this context, it has been noted that there is seldom much bone loss from the femur, whereas most of the intraarticular deformity originates from the proximal tibia. Therefore, once the femoral component is reconstructed as close as possible to its prearthritic state (within 0.5–1 mm), all that is necessary is to match the tibial tray position to that of the reconstructed femur. This can be done through the principles of a “linked technique” (described herein) or according to the basics of KA as discussed in previous chapters.

Surgical technique

Exposure and soft tissue management

A skin incision is performed in the standard fashion, slightly medialized to midline, followed by medial parapatellar capsulotomy. In our practice, the medial parapatellar approach is used both for varus and valgus deformities, with one exception, known preexisting chronic patellar subluxation with valgus deformity, where a lateral parapatellar approach is used. The joint is exposed and the fat pad is excised. Patellar tracking is examined to verify the proper patellar tracking that should be recreated at the end of surgery. The patella is subluxed to the lateral gutter but not everted. Extensive osteophytectomy is done. No release of deep or superficial medial collateral ligament (MCL) is done. Anterior cruciate ligament (ACL) is excised if present and posterior cruciate ligament (PCL) is retained. Suprapatellar synovectomy is performed, and the anterior femoral cortex is exposed with a periosteal elevator to be able to place the anterior reference extramedullary device for the distal cut—setting up the flexion-extension plane of the distal cut. Because no release of MCL is done, a mobile window retractor approach is used and attention is given not to tension the soft tissue too much. We treat flexion contractures at the end of bony cuts after initial full trial is done with posterior femoral osteophyte removal and posterior capsular release, followed by aplastic deformation if required. For valgus knees we apply the same no-release philosophy and avoid releasing posterior-lateral structures, as well as popliteus and lateral collateral ligament (LCL). The only structure that may be released at the end of trial reduction is the ITB, which is rarely required. We do not resurface the patella routinely. For patellar maltracking, we follow a simple algorithm that we apply to all our KA TKA cases:

1

If tracking was proper after initial arthrotomy, it should be tracking the same at the trial phase; if not, varus-valgus (V-V) balance and tibial rotation should be reassessed, as they may influence the patellar tracking. Specifically, this is important if the valgus knee has been undercorrected in error (most probably originating from insufficient varus on the tibial side or too much valgus from the femoral side).
2

If slight lateral tracking is present, we do lateral patellar facetectomy.
3

If there is still maltracking, a patellar resurfacing might be considered.
4

Lateral retinacular release will be used as a last resort: of our 1000 KA TKA cases so far, it has only been required once (for chronic patellar subluxations).

The femur

Step 1: Distal cut

After exposure of the knee through a standard medial parapatellar arthrotomy for both severe varus and severe valgus knees, we assess cartilage wear on the distal aspect of the femur. From the eroded condyle we remove any partially worn cartilage to reference bare subchondral bone with our distal femoral cutting blocks. The flexion-extension axis of the femoral component is set parallel to the anterior surface of the distal femur and perpendicular to the distal articular surface ( Fig. 14.1 ). The V-V angulation and proximal distal position of the femoral component are set using a distal referencing guide that compensates 2 mm when there is cartilage wear on the distal medial femoral condyle in the varus knee, and 2 mm when there is cartilage wear on the distal lateral femoral condyle in the valgus knee. The anterior-posterior (AP) translation and internal-external rotation of the femoral component are set as described in previous chapters, by placing a posterior referencing guide in contact with the posterior femoral condyles and in 0 degrees of relative rotation ( Fig. 14.2 ).

We assess cartilage thickness with a scalpel blade at the most posterior aspect of the posterior condyles; this requires deep flexion for proper assessment. We aim for the same cartilage thickness at both posterior condyles. If one is eroded, it is compensated for by applying a 1- or 2-mm shim between the posterior lateral condyle and the sizer.

The positioning of the posterior referencing guide rarely requires correction, because complete cartilage loss is uncommon on the posterior medial femoral condyles in varus osteoarthritic knees, although it may be found quite often in valgus knees, as they commonly present a flexion disease with posterior erosion pattern. Correction for bone erosion is rarely needed at 0 and 90 degrees of flexion, even in the most arthritic knees.

Step 2: Sizing the Femur, Referencing Its Native Posterior Condylar Axis and Placement of the 4:1 Resection Guide

After the distal cut is completed and quality assurance with the caliper is completed (accounting for 2-mm worn cartilage and 1-mm saw kerf), an AP sizer is positioned to set the component rotation and select the component size. Next, the 4:1 cutting guide is applied to complete the preparation for the femoral cuts. The caliper is used to measure bone resected from the posterior condyles to confirm the appropriate femoral rotation ( Fig. 14.3 ).

Step 3: Preliminary trial and knee balancing with shims

Once the femoral preparation is completed and calipers used to ensure the bone cuts were appropriate, a femoral component trial is positioned in situ. The knee is then taken through a range of motion (ROM), and any cartilage and bone loss on the eroded side is compensated for by using a semiflexible shim available in increments of 1 mm, for balancing the knee ( Fig. 14.4 ).

The knee is then tested for stability through a full ROM, with the patella reduced in the trochlea to avoid tethering. The implant should recreate a negligible V-V opening and lack of rotational movement in full extension, and a physiologic and individualized progressive laxity on the medial and the lateral side with increasing flexion. At 90 degrees, the lateral side should open significantly more than on the medial side ( ).

This initial trial with a reduced patella gives valuable information to the surgeon about the balance, soft tissue behavior, and tracking of the patella, before the tibial cut.

At this step, and before the tibial cut, it is mandatory to check for intimate contact between the femoral trial to the tibial plateau, both medially and laterally at the points of contact. If interference with the eminence or base of the tibial spines is present, or the spines force the femoral component into a nonanatomic position, we recommend resecting them using a saw.

For severe deformities, especially those that present significant tibial bone loss (mainly posterior,-medial) it is not uncommon that a thick shim, or even a few shims, are required to balance the knee to achieve the goals of KA: negligible V-V laxity in extension and lateral opening in flexion to varus stress.

Step 4: Linkage and tibial osteotomy

The proximal tibia cut can be done independently as described in previous chapters or by a linked method to the femoral component at the end of the preliminary trial step. The idea of this technique is that the femur is prepared for compensating for cartilage loss. Once preparation is complete, a femoral component is positioned, the proximal tibial cutting jig is coupled to the femoral component, and the cut is guided by the already positioned femoral component trial, linking the coronal plane cut of the tibial surface to the distal femur when appropriately balanced in extension and flexion.

Linked technique for proximal tibial osteotomy

After completing a satisfactory preliminary trial, the knee is flexed to 90 degrees with the shim in place. Two drills holes are made in the distal holes for the pegs in the femoral component ( Fig. 14.5 ). A device that links the rotational plane of these two holes to the proximal tibial cutting block is applied in 90 degrees of flexion with the shim still in place ( Fig. 14.6 ). Once the linkage is completed, the tibial cutting jig is pinned in place and the link device is removed.

At this stage, the V-V obliquity of the tibial cut is set, leaving only the resection height (usually 10 mm from the highest tibial-plateau articulating point) and posterior slope to adjust ( Fig. 14.7 ).

The gaps are subsequently rechecked ( Fig. 14.8 ), either with trial components or spacer blocks. As the knee has been already balanced and rectangular space has been created in extension, additional balance is rarely required; however, if required, it will be done by tibial recut (either additional height resection of 2 mm or 2-degrees V-V recut guides) and not by soft tissue release.

Case examples that demonstrate how the principles of the technique are applicable to reconstructing severe deformities follow.

Case 1: Kinematically Aligned Total Knee Arthroplasty for Severe Varus Deformity

A 72-year-old female, 22-years status post left proximal tibial plateau fracture treated with screw fixation, presented with varus deformity and severe disabling left knee pain that had failed conservative treatment. Her ROM was 5 to 100 degrees of flexion, with 23 degrees of varus deformity ( Fig. 14.9 ). The patient underwent KA TKA with the addition of a tibial stem to support the proximal medial tibial bone after the removal of the previously placed hardware. Furthermore, an intraoperative evaluation of the wear pattern of the medial femoral condyle revealed bone loss, and the decision was taken to compensate for this with a 1-mm shim to restore the native 3D position of the femur. Caliper measurements of a 5-mm distal medial femoral condylar resection and an 8-mm distal lateral femoral condylar resection confirmed that the correct planned resection was performed but that a 1-mm shim would be required medially. When evaluating the cartilage of the posterior femoral condyle, we noted an uncommon wear pattern requiring compensation with a 2-mm shim to restore anatomic rotation and AP component placement. Following resection, a caliper was used to confirm a 5-mm posterior medial and 7-mm posterior lateral cut.