Osteotomy prior to total knee arthroplasty: optimizing limb alignment

Mapping extraarticular deformities: origin, location, and direction

Imaging evaluation of patients showing extraarticular malignments is invaluable and should include long leg hip-to-ankle x-rays in the AP and lateral planes. To evaluate the location and extent of deformity, several preoperative measurements must be performed in the coronal, sagittal, and axial planes (Table 1 and Figure 1). In the coronal plane, measuring mechanical axis deviation (MAD) will indicate whether the deformity is a valgus or varus [1]. Analysis of the lateral distal femoral angle (LDFA), medial proximal tibial angle (MPTA), and joint line convergence angle (JLCA) allows the surgeon to trace back the origin of the deformity to the tibia, femur, or inside the joint. Similarly, examination of the posterior distal femoral angle (PDFA) and posterior proximal tibial angle (PPTA) provides the surgeon with information about the degree of the deformity in the sagittal plane [1]. A key measurement is determining the center of rotation of angulation (CORA), which is the location where the anatomical axes of the bone proximal and distal to the deformity meet (Figure 1). CORA determines whether a deformity can be successfully corrected through a knee replacement, as the deformity location directly correlates with its impact on limb alignment. As demonstrated by Wolff et al [2], the closer to the knee the deformity is, the greater its effect in overall mechanical alignment is. CORA measurements are used to determine osteotomy planning.

Surgical techniques for corrective osteotomies: which one to choose?

Different osteotomy principles (open vs closed wedge) are often used for osteotomy correction associated with TKA [4]. It is well accepted that different osteotomy solutions influence the future success of TKA [5], and the main determinant when preoperatively designing a corrective osteotomy should be the nature of the deformity alongside patient expectations. For example, in young patients with high activity demands, a staged osteotomy may not only delay joint replacement but also allow the patient to continue with his/her active life [4, 6]. However, pain relief is not as predictable after osteotomy compared with TKA, and it is often associated with longer recovery times [4]. Generally, osteotomy is performed at the site of prior fracture. For example, a surgeon aiming at correcting a distal varus deformity with medial compartment changes will choose a distal femoral valgus osteotomy [1]. Several advantages and limitations have been associated with open and closed wedge techniques when correcting varus or valgus deformities (Table 2) [7]. Regardless of the surgeon's choice, his/her decision must be guided by a balance between the geometrically ideal position and the most favorable location for the healing. And as Brian P Chalmers emphasizes in Part 1 , surgical planning begins with a precise assessment of the posttraumatic deformity. This will allow the surgeon to choose the level of the osteotomy, the angle of the osteotomy based on hip-knee alignment, and the proper wedge size.

Preoperative planning for corrective osteotomies and total knee arthroplasty

Depending on the extent and location of a deformity, it is necessary to evaluate prior to surgery the possible correction of malalignment by either primary TKA, simultaneous corrective osteotomy and TKA, or staged corrective osteotomy and TKA. Primary TKA can correct knee alignment for mild extraarticular deformities located outside the metaphyseal region. In contrast, severe extraarticular deformities with a profound impact on the mechanical axis should not be corrected through TKA, as this correction would require large, asymmetric resections of bone causing ligament instability in an attempt to correct a diaphyseal deformity far from the apex of that deformity [2]. Rotational deformities are a challenge facing the surgeon, as TKA allows for only minimal correction. As Fragomen et al suggested in a recent publication, "a separated staged osteotomy before TKA is highly recommended to avoid complications during the arthroplasty, as patients whose extraarticular deformities are neglected in the setting of TKA will probably require a revision surgery in the near future" [1].

Extraarticular osteotomies and TKA: one- or two-stage procedure?

Currently, there is little consensus in the literature on the superiority of performing an extraarticular corrective osteotomy and TKA as a one-stage or two-stage procedure. However, a single intervention is on the rise as it renders a second anesthesia application and operation unnecessary, is cost-effective, and reduces hospitalization time [14-17]. On the other hand, a two-stage procedure may postpone the need for TKA, especially in younger patients [18, 19]. As Fragomen et al stated recently, "a staged osteotomy allows for greater surgical flexibility to optimize deformity correction, as there is no interference with immediate TKA" [1]. Regardless of whether the osteotomy is staged or simultaneous, the main objective is to restore the mechanical alignment of the femur and tibia to accommodate the prosthetic implant and minimize bone resection, soft-tissue release, and the need for constrained implants [16]. The surgical option will also be determined by whether the deformity can be corrected acutely or gradually.

Internal fixation: intramedullary nailing and plate fixation

In patients where an acute deformity correction of a diaphyseal malunion is feasible, the implantation of intramedullary (IM) nails is preferred. Intramedullary nailing is the insertion of a metal rod into the medullary cavity of the fractured bone and across the fracture to provide solid support [20]. It has the advantage of minimal interference with soft tissues around the fracture, reduced operation times and infection rates [21, 22]. Unfortunately, this technique has certain limitations, such as delayed union or persistence of knee pain [21, 23]. Another fixation modality is the use of internal plates and screws to keep the resected bone in the correct position. While the implantation of plates is technically less demanding than the insertion of a nail, the superiority of plating to intramedullary nailing is debated in the medical community. As Fragomen points out, "both techniques are very good, but intramedullary nailing is most frequently used for diaphyseal deformities whereas plating is preferable for metaphyseal deformities". Indeed, most malunions that require osteotomy prior to knee replacement are located in the femoral midshaft area. These are usually varus deformities and are often accompanied by a rotational problem, which may cause patients pain and even limb shortening. An osteotomy prior to knee reconstruction using an internal nail can correct these malalignments and lengthen the bone if needed, using magnetic technology. This surgical approach can be illustrated by a case from Fragomen: A 63-years-old patient sustained a high-energy trauma in his youth that led to femoral malunion secondary to fracture and advanced PTOA. Alongside significant pain, this patient presented with a 9.7° varus and 38° retroversion deformity (Figure 2). While a primary knee arthroplasty could not satisfactorily address his deformity, a two-stage procedure correcting the malunion and knee replacement would yield a full femoral alignment. To avoid a lengthy intervention with higher infection risk and blood loss, swelling, and inability to mobilize the knee postoperatively, a simultaneous osteotomy and TKA was discarded as surgical approach. Instead, a staged osteotomy to correct the deformity followed by a knee replacement was favored as the best solution. The osteotomy was performed using an antegrade IM nail with precision blocking screws, without incisions around the knee, and saving space for the knee implant in the next surgery (Figure 2). The malalignment of the bone was successfully corrected and the remaining malignment was intraarticular, which could be corrected by a primary knee arthroplasty in the near future.

External fixation

Despite their complex appearance, external fixation devices consist of basic components and can be broadly categorized in unilateral, circular, and hybrid designs. External fixation entails the percutaneous placement of transosseous pins and/or wires secured to an external scaffolding to provide support to a limb [24]. In this way, a bone deformity is corrected by performing a bone osteotomy followed by a progressive displacement of the limb into the aligned position [25]. Hexapod circular fixators deliver varying combinations of controlled compression, distraction, and neutral forces to the attached bone segments, which results in a gradual and multiplanar correction of extraarticular deformities [26]. The advantage of this treatment lies on the bone's own healing potential through distraction osteogenesis to fill in any defects while realigning the limb. Additionally, the incorporation of a computer-aided frame allows the patient to adjust daily the strut's lengths and overall compression exerted by circular rings. Based on the software predictions, the surgeon can prescribe and monitor the progression of limb alignment [27]. The advantages of these are most evident in patients with severe deformities, since the use of hexapod frames also allows a gradual and dynamic accommodation for soft tissues and neurovascular structures to adjust to the new bone position [1]. Once the bone is healed and the realignment of the limb is achieved, the external frame is removed, and TKA can be performed as soon as the bone has filled the pin sites. Disadvantages associated with this technique include patient discomfort and risk of infection [28]. At the pin sites, where the skin has been disrupted, bacteria can penetrate and eventually infect the bone. Most pin infections are treatable with the course of oral antibiotics but must be closely monitored. However, deep-tissue infections and osteomyelitis may occur in up to 4% of cases [29, 30], causing eventual pin removal and delaying the healing process. Educating patients in recognizing the early symptoms of infection and in postoperative pin care is of paramount importance when choosing this treatment option. Another approach to prevent infections at the pin site focuses on the development of materials and specialized coats of pins, such as titanium pins and hydroxyapatite (HA) coatings. Titanium as opposed to stainless steel has been shown to reduce the inflammatory response of the skin [30]. Hydroxyapatite enhances the integration of the pin into the bone, decreases the motion at the interface, and lowers the loosening rate of the pin, which would otherwise be a major contributor to infection [30].

Limb deformity correction after total knee arthroplasty: making a fresh start

Patients whose extraarticular deformity was not successfully addressed during knee reconstruction are often in need of revision surgery. This is mostly due to patients’ reluctance to undergo two operations. In such cases, surgeons may try to correct extraarticular deformities intraoperatively, which can result in a deformity that is not entirely corrected and a slightly misaligned prothesis. Femoral deformities secondary to malunions can often be corrected with an antegrade IM nail if the knee implant is in place [28]. Correction of the alignment will result in a straight diaphysis but will often create a new joint line deformity followed by pain and patient discomfort. As Fragomen recommends: "Patients should be warned in advance of these potential complications. Revision knee replacement will provide the final desired alignment and pain relief. These patients are usually eager to have the second knee replacement surgery as quickly as possible which can be performed at the same time as IM nail removal". A stemmed femoral implant can be used to bypass the osteotomy site to protect against fracture.

Conclusions

Extraarticular corrective osteotomies prior to TKA help converting a very complex situation that would essentially require substantial bone resection or soft-tissue release if done in a one-stage TKA and corrective osteotomy, into a manageable and effective approach. Although patients are reluctant to undergo two surgeries, corrective osteotomies prior to TKA minimize the risk of premature implant loosening and asymmetric wearing, and improve patient quality of life in the long-term.