Personalized total knee arthroplasty in patients with extra-articular deformities

Abstract

• Over the years, with a better understanding of knee anatomy and biomechanics, superior implant designs, advanced surgical techniques, and the availability of precision tools such as robotics and navigation, a more personalized approach to total knee arthroplasty (TKA) has emerged.

• In the presence of extra-articular deformities, performing personalized TKA can be more challenging and specific considerations are required, since one has to deal with an acquired pathological anatomy.

• Performing personalized TKA surgery in patients with extra-articular deformities, the surgeon can: (1) resurface the joint, omitting the extra-articular deformity; (2) partially compensate the extra-articular deformity with intra-articular correction (hybrid technique), or (3) correct the extra-articular deformity combined with a joint resurfacing TKA (single stage or two-stage procedure).

• Omitting the acquired lower limb malalignment by resurfacing the knee has the advantages of respecting the joint surface anatomy and preserving soft tissue laxities. On the other hand, it maintains pathological joint load and lower limb kinematics with potentially detrimental outcomes.

• The hybrid technique can be performed in most cases. It circumvents complications associated with osteotomies and brings lower limb axes closer to native alignment. On the other hand, it creates some intra-articular imbalances, which may require soft tissue releases and/or constrained implants.

• Correcting the extra-articular deformity (through an osteotomy) in conjunction with joint resurfacing TKA represents the only true kinematic alignment technique, as it aims to reproduce native knee laxity and overall lower limb axis.

Introduction

Total knee arthroplasty (TKA) is an efficient treatment for end-stage osteoarthritis, and the number of TKAs performed has been exponentially growing over the last decade (1). It is now understood that the systematic goal of a neutral (0°) mechanical alignment (MA) during TKA fails to reproduce individual patient anatomy and joint kinematics (2, 3, 4, 5, 6). A variety of personalized implant alignment techniques, including kinematic alignment (KA) (7), restricted kinematic alignment (rKA) (8), inverse kinematic alignment (9), functional alignment (10), and adjusted mechanical alignment (4), have been proposed to improve TKA outcomes. The ultimate patient-specific technique is KA, in which surgeons aim to reproduce the pre-arthritic knee anatomy by resurfacing the knee joint (resecting bone and cartilage thickness to match that of the implant) (11). Compared to systematic MA, personalized techniques better restore joint surface orientations, native collateral ligament laxities, knee kinematics, and gait (3, 12, 13, 14, 15).

However, one important question remains: should all pre-operative anatomies be reproduced? Not only is there great variability of hip–knee–ankle angle (HKA) between patients (16), but it is also challenging to define boundaries for normal loading conditions within the knee due to the existing high inter-individual and intra-individual variability, influenced by the type of activity (17). Furthermore, some constitutional anatomies might predispose the patient to arthritis (18) and prosthetic complications if recreated during surgery (19). For these reasons, limb and joint alignment boundaries are still debated (19, 20, 21). More outlying anatomies may be biomechanically inferior (8) and considered pathoanatomies. Reproducing aberrant anatomies might affect TKA biomechanics and increase wear.

The proponents of unrestricted KA (all anatomies without limit) consider all anatomical variants as physiological and safe to reproduce (22). On the other hand, reproducing joint anatomy can be questioned when TKA is performed in patients with acquired lower limb anatomical modifications (in the coronal, sagittal, or axial planes). Anatomical alterations may result from metabolic disease (e.g. osteomalacia, osteopetrosis, hypophosphatemic rickets, hypophosphatasia, renal osteodystrophy), congenital abnormalities, previous osteotomy, or malunion of an extra-articular tibia and/or femur fracture (23). Extra-articular deformities can occur in different locations, with varying degrees and involvement of anatomical planes, resulting in a range of severities. As described by Paley (24), the origin of the acquired deformity is the so-called center of rotation and angulation (CORA) which, in the coronal plane, alters the native lateral distal femoral angle (LDFA) or the native medial proximal tibial angle (MPTA), and, in the sagittal plane, alters the posterior distal femoral angle (PDFA) and the posterior proximal tibial angle (PPTA). Rotational deformities at the CORA are also very important. It is widely accepted that extra-articular deformities have repercussions on the mechanics of the knee joint (25) and on the force distribution on the knee joint (26), leading to lower gait quality (27). Since the acquired deformity modifies the patient’s native anatomy, joint kinematics, and articular load, performing true joint resurfacing in this group of patients may be questioned (11).

Considering the new trend toward personalizing TKA, this article aims to provide an updated insight into the different options when performing a TKA in a patient with extra-articular deformities, corresponding to category 6 according to the PAS classification (28).

TKA with extra-articular deformity

Comprehensive analysis, study, and preparation are essential for every case of knee arthritis combined with extra-articular deformities, due to their great variability and the many factors that must be considered before determining the most suitable treatment strategy. Wolff et al. (23) described two critical factors that come into play: the severity of the deformity and its proximity to the joint line. The closer the deformity is to the joint, the greater its impact on the overall mechanical limb alignment, making it challenging to address through TKA alone (23). However, other aspects are paramount, such as the planes where the deformity occurs. Precise evaluation of the deformity needs to be performed before surgery. Long-leg films may be useful for the sagittal and coronal planes, but CT scan evaluation is more precise and essential for measuring axial problems.

The MA perspective

From an MA perspective, the extent to which extra-articular deformity can be corrected solely through TKA, without necessitating an osteotomy, is still debated. The literature suggests that when located outside of the metaphyseal region, isolated TKA can be performed for sagittal deformities up to 20° (29), and femoral and tibial coronal deformities up to 15–20° (25, 29, 30) and 30° (29, 30), respectively. It was pointed out that the extra-articular deformity correction with the intra-articular bone cut adjustment is limited by the collateral ligament; i.e. the bone cut should not violate the collateral attachment (Fig. 1) (31). It should be noted that any intra-articular modification will impact the collateral ligament balance and may require soft tissue releases and/or increased prosthetic constraint (30).

Figure 1.

Treatment strategies for mechanical alignment total knee arthroplasty based on extra-articular deformity. When performing a MA TKA, it is widely accepted to perform an osteotomy of the malunion when the prolongation of the distal tibial axis lies outside the tibial plateau (A), or when the prolongation of the femoral mechanical axis results in a distal femoral cut plane proximal to one of the epicondyles (D) (32). Otherwise (B and C), the surgeon can proceed with the MA TKA and correct the ligament imbalances by using soft tissue releases and/or constrained implants.

Data on rotational/axial deformities are even more scarce. Some authors define rotational/axial deformities as any angle greater than 0° (29), while others report good results of isolated TKA in patients with 10° malrotation (32). Furthermore, tibial and femoral deformities should be addressed differently, as the former impacts only extension, and the latter impacts both flexion and extension. Adding some complexity, many of the extra-articular deformities are multiplanar, which explains why clear standardized guidelines and algorithms were never proposed. Finally, consideration must be given to the involvement of associated soft tissues and adjacent joints.

The personalized alignment perspective

When performing personalized TKA surgery in patients with extra-articular deformities, the surgeon has three main choices: (1) resurfacing the joint, omitting the extra-articular deformity; (2) hybrid technique, where the extra-articular deformity is partially compensated with intra-articular correction, minimizing the ligament imbalance; and (3) correcting the extra-articular deformity combined with a joint resurfacing TKA as a one or two-stage procedure.

The authors employ the term ‘joint resurfacing’ instead of ‘unrestricted kinematic alignment’ because it aims to reproduce the acquired pathoanatomy, thus deviating from kinematic alignment fundamentals. For the same reasons as mentioned above, we refer to ‘hybrid technique’ rather than ‘rkA’. This method involves intra-articular correction of the extra-articular deformity, achieving an acceptable HKA and knee balance.

Correcting the extra-articular deformity (through an osteotomy) in conjunction with joint resurfacing TKA represents the only true kinematic alignment technique, as it aims to reproduce the native knee laxity and overall lower limb axis.

Resurfacing the joint

This technique (Fig. 2) aims to reproduce native articular anatomy and soft tissue laxity. Following the principles of unrestricted KA, the native joint surfaces’ orientations are reproduced (7, 33).

Figure 2.

Joint resurfacing for end-stage medial osteoarthritis with an associated extra-articular femoral varus deformity. Mid-diaphysis varus extra-articular deformity of 10^o with end-stage medial osteoarthritis. Knee resurfacing, omitting the extra-articular deformity, preserves the native knee anatomy and soft tissue laxity. Pathological, acquired limb varus alignment was not corrected.

Omitting the extra-articular deformity, the surgeon resurfaces the knee joint by resecting bone and cartilage thickness equivalent to that of the implant. In the absence of soft tissue modification, the technique can preserve ligament laxities and articular relations/kinematics. On the other hand, preserving the acquired extra-articular deformity does not follow KA principles by preserving a pathological lower limb alignment and related joint load. In other words, the constitutional knee laxity, surrounding soft tissue, and joint spaces will be preserved, but gait, load, and overall lower limb kinematics will remain altered.

Recent studies alleviate concerns about unrestricted KA tibial component migration (34, 35, 36) and present excellent patient-reported outcomes measures (PROMs) and implant survival rates (20, 34, 37, 38). While some authors reported excellent results when the arthritic native anatomy is restored, it is important to recognize that recreating an acquired pathoanatomy does not align with KA fundamentals (Fig. 3).

Figure 3.

Aseptic loosening, ten years after joint resurfacing in a patient with multiplanar extra-articular deformity. (A1, A2, A3) Pre-operative radiographs of a 76-year-old patient with a history of childhood surgery for genu valga and end-stage osteoarthritis combined with severe multiplanar extra-articular deformity. The patient refused the initially proposed two-stage osteotomy-first procedure. A joint resurfacing TKA with an ultracongruent polyethylene was implanted with a personalized instrumentation system. (B1, B2, B3) Immediate post-operative radiographs. The patient complained of pain and knee effusion ten years after the index surgery. (C1, C2, C3) Radiographs reveal osteolysis and probable implant loosening. Periprosthetic joint infection was ruled out. During the revision surgery, both the tibial and femoral components were found to be loose.

Specific situations where joint resurfacing alone may not be advised:

• Deformity affecting adjacent joints:

  Tibial and femoral extra-articular deformities can affect the biomechanics and load distribution of the knee joint as well as the hips and ankles.

  Regarding the ankle, for example, deformities, especially in the tibia, can lead to changes in contact pressure and shear stresses. If associated with symptoms, the deformities require correction before addressing the ankle surgically (39, 40). In such cases, osteotomy to resolve symptoms on the adjacent joint is advised.

• Unilateral deformities influencing gait or affecting the contralateral leg:

  In some cases, gait disorders stem from skeletal deformities leading to a diminished quality of life and increased risk of falls (41, 42). In cases of severe unilateral deformity, correction is often recommended to reduce possible complications arising from their influence on gait. Furthermore, a unilateral deformity, such as severe valgus, can increase the adduction moment on the contralateral, well-aligned leg, potentially predisposing it to varus deformation, similar to windswept deformities (43).

• Axial deformation causing patellar maltracking:

  Patellar osteoarthritis is linked to patellar maltracking, which, in turn, may be attributed to lower limb misalignment (44). As a consequence, when the deformity is the underlying factor responsible for patellar maltracking and its resulting pathology, reproducing the deformity will not change the pathologically acquired biomechanics responsible for the development of the condition.

• Soft tissue involvement:

  Significant deformities can be associated with soft tissue contracture, condylar dysplasia, and/or bone defects on the concave side, and stretched soft tissues on the convex side (43, 45). A pure resurfacing of the knee could, in those situations, leave the knee unbalanced.

• Residual deformity compromises functional results:

  Reduced range of motion can be observed with sagittal deformities, and addressing them by mere resurfacing may reproduce the limitation. Studies have correlated the femoral implant placement in flexion with an increased risk of post-operative flexion contracture (46). Additionally, a lower range of motion and the inability to achieve full extension after TKA have been associated with diminished PROMs and reduced patient satisfaction (47, 48). Moreover, a post-operative recurvatum >5° following TKA is known to impact both function and quality of life (49). Implant design specificity should also be taken into account. For example, using a posterior stabilized TKA, tibial post impingement may be problematic in cases of recurvatum femoral deformity. In such cases, to obtain full knee extension, the relation between the femur and tibia requires to be in hyperextension. A cruciate retaining single radius design may be more forgiving in the same condition.

Hybrid technique

A hybrid approach (Fig. 4) can be taken according to the patient’s condition and surgeon's preferences. This technique is a compromise between preserving natural knee anatomy and soft tissue envelope and obtaining a stable knee and a lower limb alignment compatible with current implant material and fixation methods. Surgeons should try to preserve the articular joint orientations and soft tissue laxities as much as possible. To achieve these goals, the extra-articular deformities will be addressed with intra-articular cut adjustments to the tibia or femur based on the location of the CORA, bringing the tibial and femoral joint surfaces orientations toward the native alignment. By doing so, soft-tissue imbalances will be created and should be addressed by soft tissue releases or implant constraints (50). Soft tissue releases are usually necessary for intra-articular anatomy correction of more than 3° (Figs. 5, 6, 7) (8).

Figure 4.

Hybrid technique for end-stage medial osteoarthritis with an associated extra-articular femoral varus deformity. Mid-diaphyseal varus extra-articular deformity of 10° with end-stage medial osteoarthritis. Hybrid technique: intra-articular correction of the extra-articular deformity, leading to medial–lateral gap and soft tissue imbalance (tight medial and loose lateral). A medial soft tissue release may be sufficient for a mild deformity to obtain a balanced knee. Short, cemented stems with varus–valgus constrained bearing are used if an imbalance persists.

Figure 5.

Hybrid technique TKA in a valgus tibial deformity after high tibial osteotomy. Radiographs of a patient’s left knee with previous high tibial osteotomy. (A^1–3) Tibia have an extra-articular valgus deformity. (B^1–3) Post-operative radiographs where the extra-articular deformities were addressed with intra-articular tibial cut correction (hybrid technique). The femoral bone was resurfaced to preserve the femoral flexion axis and joint line orientation. To avoid extreme residual valgus (HKA), the tibial cut was adjusted in varus to reach an HKA of 3^° valgus. Medio-lateral collateral balance could not be achieved with soft tissue releases, and a semi-constraint implant was required.

Figure 6.

Hybrid technique TKA for a varus femoral malunion with inextricable femoral rod. (A^1–2) Pre-operative radiographs of a patient with a varus malunion of a diaphyseal femoral fracture. His femoral nail is bent at the apex of deformity and inextricable. (B^1–2) Post-operative radiographs where the surgeon used a hybrid technique. To avoid leaving the lower limb in extreme varus (10^°), the femoral distal cut was performed, reducing the varus by 2° (from 3° varus to 1° varus), and the tibial cut was adjusted from 7° varus to 4° varus to obtain an HKA of 5° varus. With such correction (5°), deep and superficial medial collateral ligaments had to be released. A standard uncemented posterior-stabilized implant was used.

Figure 7.

Hybrid technique TKA for a valgus tibial deformity after high tibial osteotomy. Radiographs of a patient’s left knee with previous high tibial osteotomy and sequelae of a diaphyseal tibial fracture. (A) Tibia has an extra-articular valgus deformity. (B) Post-operative radiographs where the extra-articular deformities were addressed with intra-articular tibial cut correction (hybrid technique). The femoral bone was resurfaced to preserve the femoral flexion axis and joint line orientation. To avoid extreme residual valgus (HKA), the tibial cut was adjusted in varus to reach an HKA of 3^° valgus. A standard implant was used to achieve a medio-lateral collateral balance with soft tissue releases.

This is the authors’ preferred technique for most cases, as it circumvents complications associated with osteotomies and re-establishes a lower limb axis closer to the original alignment. In certain cases, intra-articular correction of the extra-articular deformity while simultaneously maintaining knee joint stability and soft tissue balance, is unattainable. For older and sedentary patients in that situation, a varus–valgus semi-constrained implant with supplemental short, cemented stems will be the simplest solution (51). If the patient is young and active, or a satisfactory result cannot be obtained with the above method, and/or a hinged implant is necessary, the authors’ preferred alternative would be to combine a correction osteotomy with a KA-TKA.

Two specific situations deserving specific attention:

1. Axial deformities

   Tibial axial malrotation resulting from extra-articular deformities (below the anterior tibial tuberosity) primarily affects the thigh-foot angle. This is usually well tolerated, and the patient should be informed of this probable post-operative residual deformity since intra-articular correction is not recommended. In contrast, femoral axial malrotation presents two main implications that require comprehensive evaluation. First, these malrotations should be analyzed in conjunction with the patellofemoral joint. Challenges regarding the patellofemoral joint are often found in cases of excessive internal femoral rotation. Pre-operative maltracking should raise a concern.

   Trying to correct femoral axial deformities with intra-articular bone cut adjustments will unbalance mediolateral flexion gaps, which may be unacceptable or mandate semi-constrained implants.

   Intra-articular axial correction limits rely on a few expert opinions; Xiao-Gang et al. (32) and Sculco et al. (29) suggest a limit of 10° and 0°, respectively. Others only note that femoral internal rotation poses greater challenges compared to external rotation (52). Additional procedures, such as patellar resurfacing with a medialized button, lateralization of the femoral component, and release of the lateral retinaculum, may be considered to optimize patellofemoral function. In specific situations, performing a tibial tuberosity advancement osteotomy or cementing the tibia in external rotation in conjunction with a varus–valgus constrained polyethylene (which induces dynamic internal rotation of the tibia) can optimize patellofemoral tracking.

2. Deformities in the sagittal plane

   This is another subject with scarce literature. On the femoral side, some authors accept up to 15° for both intra-articular correction of procurvatum and recurvatum deformities (52), while others suggest values of 10° and 20° for procurvatum and recurvatum, respectively (53). The greater tolerance with recurvatum can be explained by the ability to achieve a greater amount of correction without notching on the anterior femoral cortex. Furthermore, the component position in the sagittal plane needs to be considered. Increased femoral component flexion and posterior tibial slope can lead to femoral cam-tibial post impingement in posterior-stabilized (PS) implants, resulting in polyethylene wear and deformation (54).

   On the tibial side, tibial slope modification to correct an extra-articular sagittal deformity (frequently seen after high tibial osteotomy) may impact the patellar height (baja/alta) and affect the posterior capsule/posterior cruciate ligament (PCL) laxities. Capsular release and posterior cruciate sacrifice may be required when correcting an increased tibial slope. Conversely, correcting a pathological anterior tibial slope may cause flexion instability and require increasing femoral component posterior condylar offset and/or the use of increased bearing constraint. We suggest adjusting the tibial cut angle using a pivot point centered on the tibial surface to minimize the impacts of the sagittal correction between the patella and posterior structures (Fig. 8).

Figure 8.

Pathological anterior slope after high tibial osteotomy. Radiographs of a patient’s left knee with previous high tibial osteotomy. (A) Pre-operative pathological anterior slope after high tibial osteotomy. (B) Post-operative radiographs where the pathological slope was addressed by adjusting the tibial cut angle using a pivot point centered on the tibial surface. Restoring the tibial slope will violate the PCL attachment and increase the flexion space. (C) After a PS TKA, the patient complained of flexion instability and required a femoral implant revision to a two-size larger implant (increasing the posterior condyle's thickness with metallic augments).

KA-TKA and osteotomy

As described in the previous section, there are cases where simple joint resurfacing might excessively impact the lower limb kinematics and, therefore, may not be the ideal solution. The most obvious cases are those where the native axis of the limb is markedly outlier in the coronal plane, even without considering intra-articular wear (outlier MPTA and LDFA angles). Less intuitive but equally significant are axial deformities, especially marked femoral maltotations. If reproduced, they may fail to resolve or may exacerbate patellofemoral symptoms and/or instability. Sometimes, especially in native valgus knees, the two previous deformities are associated in a multiplanar outlier alteration scenario.

In cases of acquired deformity, the sagittal extra-articular deformity could be so severe and/or multiplanar that the intra-articular correction (hybrid technique) would create important imbalances, requiring a constrained prosthesis. Then, the ideal option might be restoring the lower limb anatomy by addressing the extra-articular deformity through an osteotomy combined with KA-TKA (Figs. 9 and 10) (51, 52).

Figure 9.

Combined KA-TKA and femoral osteotomy at the level of the CORA for varus femoral deformity with associated sagittal and/or rotational deformity. Mid-diaphyseal varus extra-articular deformity of 10^o with end-stage medial osteoarthritis. The extra-articular malunion was treated with osteotomy and plate fixation at the CORA. Native lower limb alignment was restored with the osteotomy. KA-TKA is performed before or after osteotomy, preserving native knee anatomy and soft tissue laxity.

Figure 10.

One-stage TKA and femoral osteotomy for severe femoral valgus deformity without sagittal and rotational deformity but with a medial collateral ligament insufficiency. (A^1–3) Pre-operative radiographs of a patient with a 17° HKA due to a severe right valgus deformity of the femur resulting failed medial distal closing wedge osteotomy. (B^1–3) Post-operative radiographs showing a lateral distal open wedge femoral osteotomy of 10°, with the wedge filled with bone obtained from the femoral cuts during the prosthesis, combined with an unrestricted KA-TKA. The authors opted for a single-stage procedure: the KA-TKA was performed first, and after closing the arthrotomy, the previously planned osteotomy was performed. The pathological LDFA of 83° was overcorrected to a non-native 93° (6° more compared to the healthy contralateral LDFA): this overcorrection strategy was used to protect the prosthetic knee from pathological opening of the medial compartment due to medial ligament incompetence. Fixation was achieved with a stable locking plate designed for lateral distal femur osteotomy.

The key advantage of this technique is restoring the native lower limb anatomy by correcting the acquired deformity. On the other hand, extra-articular deformity must be accurately studied pre-operatively, based on comparison with the contralateral limb, with the typical planning used for modern osteotomies. Osteotomy correction can be performed either at the level of the CORA or away from it. Although there is limited literature for firm guidelines, our recommended approach is:

1. For diaphyseal CORA with simple pathological deformities in the sagittal plane (no coronal or axial deformity): biplanar metaphyseal osteotomy technique osteotomy with a fixed-angle plate, according to Lobenhoffer principles (55).

2. For diaphyseal CORA with pathologic multiplanar deformity: osteotomy on CORA with stable angle plate or intramedullary nail (Fig. 11).

3. For diaphyseal CORA with simple pathological deformities in the axial or coronal plane, both osteotomy at the level of the CORA and a biplanar metaphyseal osteotomy can be considered. While the latter remains our preferred surgical option, notably due to its favorable healing potential, it is important to recognize that every extra-articular deformity is unique.

Figure 11.

One-stage TKA and femoral osteotomy for simultaneous femoral procurvatum and varus deformity. (A^1–3) Pre-operative radiographs of a patient with a varus and procurvatum deformity of the femur resulting from a childhood fracture. (B^1–2) Post-operative radiographs showing a femoral osteotomy combined with a TKA, following the rKA protocol. The authors opted for a one-stage procedure: the osteotomy was performed first and fixation was achieved with a retrograde intramedullary nail. Navigation-assisted TKA was performed second, allowing for more precise adjustments in implant orientation and soft tissues laxities.

In cases with compromised soft tissues, multiple previous surgeries, or infection at the level of the CORA, performing the osteotomy away from the CORA may indeed be the optimal option. Therefore, the choice between metaphyseal and CORA-level osteotomies should be carefully considered, taking into account individual patient factors and surgical complexities to ensure the best possible outcome.

There is no consensus on whether the TKA or the osteotomy should be performed first as each option has unique advantages and drawbacks (56). The two-stage procedure with the osteotomy performed first could be beneficial in addressing more complex deformities where external fixation and/or multiple osteotomies are required. Furthermore, it is worth noting that while the single-stage procedure seems to be cost-efficient, studies report higher rates of infection, thromboembolism risk, and blood loss (56, 57). If the osteotomy is planned at the level of the diaphyseal CORA, performing the osteotomy before or after the prosthesis is equally possible. Certainly, performing the osteotomy before the prosthesis could create problems of osteotomy mobilization during the implantation of the prosthesis because of the knee mobilizations and the hammering of the components. Whether performed in 1 or 2 stages, performing the osteotomy first leaves open the possibility of further correction of intra-articular alignment if necessary.

If the osteotomy is planned at the metaphyseal femoral level, it should be performed after implanting the prosthesis. The biplanar technique at the femoral level (Fig. 12) offers several advantages over the monoplanar: (1) it increases the osteotomy surface area which speeds up healing; (2) it allows a closure or opening wedge to be performed with anterior support that guarantees rotational and sagittal stability even in case of hinge rupture; (3) it allows an osteotomy to be performed at the metaphyseal, almost epiphyseal, site, without the risk of injuring the prosthetic trochlea, in an area rich in the spongy bone that guarantees excellent and rapid healing.

Figure 12.

One-stage TKA and femoral osteotomy for severe femoral valgus deformity without sagittal and rotational deformity. (A^1–3) Pre-operative radiographs of a patient with a 23° HKA due to a severe right valgus deformity of the femur resulting from a diaphyseal fracture. (B^1–3) Post-operative radiographs showing a lateral distal open wedge femoral osteotomy of 14°, the wedge filled with bone obtained from the femoral cuts during the prosthesis, combined with an unrestricted KA-TKA. The authors opted for a single-stage procedure: the KA-TKA was performed first; the previously planned osteotomy was performed after closing the arthrotomy. The pathological LDFA of 77° was restored to the native 91° (superimposable to the healthy contralateral LDFA). Fixation was achieved with a locking plate designed for lateral distal femur osteotomy.

Tibial metaphyseal osteotomy is more complex. Cases described in the literature recommend a closure osteotomy, temporary fixation with a plate with short screws at the proximal level, and replacement of the proximal short screws with the longest possible ones after implantation of the tibial component. The biplanar technique at the tibial level offers some advantages over monoplanar: (1) it increases osteotomy surface area which speeds healing; (2) it allows for wedge closure while maintaining adequate proximal tibial bone stock without injuring the anterior tibial tuberosity; and (3) it increases rotational and sagittal stability, both pre- and post-operatively.

Different fixation options are available based on the level and type of osteotomy: locking plate, long-stemmed prosthesis, or retrograde intra-medullary nails (56, 57, 58). In addition to the method of fixation, it is crucial to keep in mind that an osteotomy at the diaphyseal CORA might have problems with bone healing, especially if performed with a plate instead of an intramedullary nail, compared with an osteotomy at the metaphyseal site rich in spongy bone. Knee joint kinematics and anatomy, as well as the overall limb alignment, will be respected. However, combined one-stage TKA and osteotomy are associated with higher complications and lower functional score gain compared to isolated TKA with intra-articular deformation correction (25).

Conclusion

Managing end-stage osteoarthritis in patients with extra-articular deformities indeed presents different challenges. Existing literature is limited, and comparative studies of various surgical techniques are lacking. It is essential to approach acquired extra-articular deformities differently from anatomies that are constitutional outliers. The technique selected (resurfacing, osteotomy plus resurfacing, or hybrid) should be based on a precise evaluation of the patient’s characteristics (e.g. age, bone quality, and activity level), the type of extra-articular deformity (level, orientation, and severity), the pre-operative planning by Paley, and the impact of the acquired deformity on the lower limb kinematics, soft tissues, and adjacent articulations. The hybrid technique offers a middle-ground solution, balancing the preservation of natural knee anatomy with the maintenance of acceptable overall limb alignment. This approach circumvents potential complications associated with osteotomies and reduces the risks of abnormal force distribution within the knee joint. On the other hand, joint resurfacing with a well-planned osteotomy offers a unique strategy that reproduces the native axis of the limb and the native kinematics of the knee.

ICMJE Conflict of Interest Statement

The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the study reported.

Funding Statement

The Maisonneuve-Rosemont Foundation funded this study, supporting the arthroplasty fellowship program.

Author contribution statement

GB: drafting and critically revising the manuscript; M-OK: critically revising the manuscript; VM: critically revising the manuscript; MM: critically revising the manuscript; P-AV: drafting and critically revising the manuscript.

Acknowledgement

All figures were created by the authors with BioRender.com.