Intraoperative Complications During Total Knee Arthroplasty

David W. Fitz, MD

Brett Mulawka, MD

Christopher M. Melnic, MD

INTRODUCTION

Total knee arthroplasty (TKA) is a highly successful and cost-effective operation.¹,² Registry data consistently report excellent 10-year survival rates, with 96% in the Swedish Arthroplasty Registry and 94% in the Australian registrar.³ Patient satisfaction is also high, typically reported as >80% having good or excellent outcomes.⁴,⁵,⁶ Such success, in part, has driven the annual incidence of TKA to increase in developed countries.⁷ In the United States, the demand for TKA is projected to rise by 673% to 3.48 million by 2030 and in revision TKA by 601%.⁸ Additionally, this increase in demand is expected to be driven by patients aged <65 years.⁸ Coupled with an aging population, increasing obesity, and the importance of maintaining an active lifestyle, the rise in failed TKAs is inevitable and the burden of revision TKAs will increase.

Compared with primary TKA, revision procedures are more technically demanding and have a higher risk of complications. Extensive scarring can complicate exposure and extensile approaches may be indicated. Local anatomy may be altered and delineation of important structures can be difficult. Component removal, if indicated, must be done with care as to minimize bone loss and fracture. The removal of cement should be done meticulously, as well, to avoid maligning the new implants, creating bone defects and preventing fractures (both on cement removal and implant insertion). Osteolysis and stress shielding can be encountered in the revision setting which can exacerbate the risk of fracture or avulsion of important structures. Stemmed components may be indicated and can lead to iatrogenic fracture.

To minimize complications, a thorough knowledge of anatomy and appropriate surgical technique is essential. Not only does it allow for effective surgical planning, but enables the surgeon to be proactive and anticipate potential complications before they occur. In this chapter, potential intraoperative complications will be described as well as the management and methods to avoid encountering them in the first place.

INTRAOPERATIVE FRACTURE

While intraoperative fractures during primary TKA are well reported in the literature, thankfully they are rare, with an incidence of less than 1%.⁹,¹⁰,¹¹,¹² During revision surgery, like all other complications, the risk increases, with a reported incidence of 3%.¹³,¹⁴,¹⁵ Knee periprosthetic fractures, postoperative and intraoperative, are associated with high morbidity and mortality, with mortality rates as high as 17% at 6 months and 30% at 1 year.¹⁶,¹⁷ Although rare compared to other complications, they are a challenging problem and can lead to significant morbidity and expense. Periprosthetic fractures and infections are associated with the greatest length of stay and cost for revision TKA.¹⁸

Various classification systems have been devised to describe and guide treatment of periprosthetic TKA fractures. In general, these systems focus on a specific anatomic region: distal femur, proximal tibia, and patella. Depending on the system, further details are included such as fracture pattern, chronology, bone quality, treatment recommendations, and outcomes. Currently, the most widely used and cited systems are those described by Lewis and Rorabeck for distal femur fractures, by Felix for tibial fractures, and by Ortiguera and Berry for patella fractures.¹⁹,²⁰,²¹,²²,²³,²⁴ These will be described in detail in the upcoming sections.

In an attempt to standardize and modernize periprosthetic fracture management, the Arbeitsgemeinschaft für Osteosynthesefragen, AO, Foundation developed a comprehensive classification system for all periprosthetic fractures, the United Classification System (UCS).²⁵ The UCS is based on the established Vancouver classification of proximal femur periprosthetic fractures and utilizes the core principles of fracture location, component fixation, and bone stock.²⁶ The UCS has been validated and has substantial inter-and intraobserver reliability for periprosthetic fractures associated with TKA.²⁷,²⁸ Table 53-1 summarizes this approach.

With either primary or revision TKA, fractures can occur at any point during the procedure, from initial exposure to final implantation, and in either the femur, tibia, patella, or combination of all three. Risk factors for periprosthetic fractures include those both patient- and procedure- related. Patient-related risk factors involve conditions that result in osteopenia, including rheumatoid arthritis, advanced age, female gender, malnutrition, osteoporosis, neuromuscular disorders, dementia, and chronic corticosteroid use.²⁹,³⁰,³¹,³²,³³ Procedure-related risk factors include component removal, intramedullary
instrumentation, central box preparation, and trialing of components.⁹,¹³,¹⁴,¹⁵ Understanding and anticipating these risk factors is critical to success and avoiding intraoperative complications.

TABLE 53-1 Unified Classification System for Periprosthetic Fractures: Knee

		V Knee
		V.3 Distal Femur	V.4 Proximal Tibia	V.34 Patella
A
Apophyseal or extra-articular/periarticular	A1	Lateral epicondyle	Medial or lateral plateau, nondisplaced	Disrupted extensor mechanism, proximal pole
	A2	Medial epicondyle	Tibial tubercle	Disrupted extensor mechanism, distal pole
B
Bed of the implant or around the implant	B1	Proximal to stable component, good bone	Stem and component stable, good bone	Intact extensor mechanism, implant stable, good bone
	B2	Proximal to loose component, good bone	Loose stem/component, good bone	Loose implant, good bone
	B3	Proximal to loose component, poor bone/defect	Loose stem/component, poor bone/defect	Loose implant, poor bone
C Clear or distal to the implant	–	Proximal to the implant and cement mantle	Distal to the implant and cement mantle	–
D
Dividing the bone between two implants or interprosthetic or intercalary	–	Between hip and knee arthroplasties, close to knee	Between ankle and knee arthroplasties, close to knee	–
E
Each of two bones supporting one arthroplasty or polyperiprosthetic	–	Femur and tibia/patella
F
Facing and articulating with a hemiarthroplasty	–	Fracture of the femoral condyle articulating with tibial hemiarthroplasty	–	Fracture of the patella that has no surface replacement and articulates with the femoral component of the total knee arthroplasty (TKA)

INTRAOPERATIVE FRACTURE: FEMUR

In both the primary and revision setting, fractures of the femur are the most common, with the medial femoral condyle being the most common femoral location.⁹,¹³ Fractures, however, have been reported in the cortices of the diaphysis, lateral condyle, medial and lateral epicondyle, as well as the supracondylar area. Like all periprosthetic fractures, osteopenic bone, whether from a systemic condition, medication, osteolysis, or iatrogenic weakening, will increase the risk of an intraoperative fracture.

CLASSIFICATION

Lewis and Rorabeck developed the first widely used classification scheme, accounting for both the integrity of the prosthesis and the location of the fracture.²⁰ Type I fractures are nondisplaced with a stable prosthesis. Type II fractures have a displaced fracture but a stable prosthesis. Type III fractures are those with a radiographically or clinically loose prosthesis regardless of the fracture displacement.

Anatomy

A thorough understanding of the femoral anatomy is essential for a successful revision TKA. Native anatomic differences in the diaphysis and metaphysis must be assessed as well as alterations to these areas from the prior surgeries. Extra-articular deformity from prior fractures may alter the geometry of the femoral canal. Cortical thickness can be attenuated in osteopenic bone, and surgeons should take extra care when instrumenting the canal. Hardware and/or cement from previous surgeries should be noted preoperatively and planned for accordingly. If removal is necessitated, the surgeon should address potential stress risers from explanted hardware.

The femoral diaphysis has an anterior bow, and femoral morphology can vary greatly between different races and genders, with increased bowing seen in Asians and females.³⁴,³⁵ There is a risk for fracture or cortical perforation with canal preparation or insertion of diaphyseal-engaging stems. Iatrogenic changes to the femoral diaphysis can also increase the risk of fracture, in
particular femoral notching. In both biomechanical and clinical studies, anterior notching has been documented to compromise the strength for the distal femur and contribute to periprosthetic fractures.²⁹,³⁶,³⁷,³⁸,³⁹ Anterior notching of as little as 3 mm can decrease the mean torsional strength of the distal femur by 29% to 39% and bending strength decreased 18% with full-thickness notching.³⁷,³⁸ Notching, however, may not always predispose to fracture. Ritter et al reviewed 670 primary TKAs and observed notching ≥3 mm in 138 (20.5%) of cases, but only 2 (0.3%) developed a supracondylar femur fracture.³⁶ Osseous remodeling over time may protect against fracture with the risk following notching to be minimized by 6 months postoperatively.³⁶ Nevertheless, the surgeon should avoid notching, especially the anterior-medial cortex, to prevent excessive stress in the distal femur.⁴⁰ The surgeon should be aware of preoperative notching or intraoperative notching and bypass accordingly with stems if encountered.

Metaphyseal anatomy must also be considered in revision TKA. Individuals of small stature and females can have a narrow distal femur. Revision femoral components often have a wider and deeper box cut than primary posterior-stabilized components. With a smaller medial-lateral dimension of the distal femur, the cut is proportionally larger and deeper. The bridge of bone between the proximal corner of the box and the metaphyseal flare can significantly narrow, especially medially. Additionally, positioning the cutting guide too far medial or lateral can further exacerbate this problem. Even with precise surgical technique, box preparation can potentially result in a femoral condyle fracture.

Prevention

Risk of intraoperative fracture can be minimized through proper preoperative planning and evaluation. Prior incisions should be documented and the soft-tissue envelope assessed. As the blood supply to the skin on the anterior knee is predominantly from medial vessels, the most lateral incision should be chosen. Radiographs should include weight-bearing AP, lateral, and merchant views. The anterior bow of the femur is best visualized on the lateral view and should be utilized for stemmed components. Whole-femur views from the hip to knee should be available as well to assess cortical thickness, extra-articular deformity, and previous hardware. Bone loss and osteolysis can be visualized on radiographs, yet are typically underestimated and underappreciated. The surgeon should have a low threshold to obtain a computed tomography (CT) scan to further delineate the extent and severity of bone loss.

Various steps carry an increased risk for intraoperative fracture during a TKA, and the surgeon should be vigilant at these times to prevent this complication. Fractures have been reported to occur during exposure, component removal, instrumentation, and trialing.¹³,¹⁴ Extensile exposures, which are described in detail in a separate chapter, may be needed to safely expose the knee. During removal of implants, a small oscillating saw or flexible osteotome should be used to carefully disengage the component from the native bone with a goal of minimizing bone loss. If cement remains, this too should be carefully removed, respecting the remaining bone. Residual cement in the femoral canal can deviate intramedullary instrumentation, such as drill bits or reamers, and lead to canal perforation. Preexisting deformity, reactive bone formation, or prior hardware can have a similar effect. Trialing of components should be done carefully in the revision setting, especially if significant bone loss is encountered. A flexion-extension gap mismatch can potentiate an epicondylar avulsion fracture if the knee is brought into extension with a tight extension gap or vice versa. Impaction of trial or final components can cause a fracture as impaction force is critical. If difficulty is encountered during insertion, impaction force should not be increased. Rather, the surgeon should reassess and ensure the distal femur can accommodate the component. There should be a low threshold for obtaining an intraoperative radiograph to assess fit and position, especially if diaphyseal-engaging stems are used.

Stemmed implants have become a mainstay in revision TKA to augment prosthetic stability if metaphyseal bone is compromised. Biomechanical studies have shown that stems increase the mechanical stability by transferring load over a larger area, reducing strain at the bone-component interface.⁴¹,⁴²,⁴³ Both cemented and cementless stem options are available. Cementless, or press-fit, stems must be compatible with the dimensions of the patient’s diaphysis as mismatch can lead to a fracture. Diaphyseal-engaging stems tend to be longer, generally ≥75 mm in length. Slotted, or “clothes-pin,” stems decrease stress at the end of the stem tip.⁴⁴,⁴⁵ Slotted stems also are more forgiving in a highly bowed femur. The stem should be inserted so that the axis of the slot parallels the bow of the femur. Longer stems (≥150 mm) are available with bows to match the natural bow of the femur.

Management

The goals of managing an intraoperative fracture are similar to those of managing any fracture: achieve anatomic reduction with rigid internal fixation that affords early range of motion activities. Intraoperative fractures should be addressed upon identification and if in question radiographs should be obtained during the procedure to identify the fracture. Exposure often needs to be extended to adequately visualize the fracture and for fixation. Excessive soft-tissue stripping, however, should be avoided to not devascularize the fracture fragments and optimize the possibility of union.

Various fixation strategies exist for managing periprosthetic femur fractures that can be employed for intraoperative fractures. These include condylar blade plates, locking and nonlocking plates, interfragmentary lag screws, or intramedullary fixation. Retrograde intramedullary nails are a viable solution for periprosthetic diaphyseal femur fractures, but do require an open box design. In a revision TKA, this is rarely an option given the use of stemmed components and closed box.

Condylar blade plates historically were the mainstay treatment for periprosthetic femur fractures,³¹,⁴⁶,⁴⁷ but their use has diminished with the advent of modern plating systems (locked and nonlocked). Rigid distal fixation was unpredictable with blades, especially in osteoporotic bone and distal fracture patterns. Significant failure rates, upwards of 80%, were reported in osteoporotic bone and comminuted fractures.⁴⁸ Attempts to enhance fixation were attempted and included various allograft solutions and polymethylmethacrylate.⁴⁶,⁴⁷,⁴⁹ Currently, its use should be reserved for minimally comminuted, displaced fractures in patients with good bone stock.³⁰

Modern plating systems employ locking screw technology to create rigid fixed-angle constructs and have become the mainstay of treatment for periprosthetic femur fractures (Fig. 53-1). In most plating systems, strategically placed screws have the option to be rigidly secured to the plate at a fixed angle, similar to the condylar blade. The use of multiple fixed-angle screws in the distal segment increases fixation and stability.⁵⁰ Toggle of the screw at its interface with the plate is prevented, providing a rigid internal scaffold for the fragments. Locking plates also afford the benefit of including unicortical locking screws. A large intercondylar box or femoral diaphyseal stem can preclude the ability to use bicortical fixation, but a unicortical locking screw can still provide support. Some plating systems have also incorporated polyaxial screw options, incorporating screw angulation with locking technology. Screws can be inserted in a 15-degree cone around a central axis and still lock into the plate, allowing the surgeon more options to gain fixation into optimal bone and around the prosthesis.⁵¹ Other plate designs accommodate cables, which can be useful in the diaphyseal segment if stemmed components are in place or an ipsilateral total hip arthroplasty is present. Favorable results have been reported with locking plates with a recent systematic review reporting 87% union rates.⁵² There are potential disadvantages to locking plates including nonunion/malunion, hardware failure, and infection, but the reported complication rate is lower than other fixation methods.⁵²

FIGURE 53-1 AP (A) and lateral (B) radiographs 1 year following a revision arthroplasty. A lateral locking plate was employed for fracture fixation.

Bypassing a distal femur fracture with a longer diaphyseal-engaging stem, is a possible treatment option and is supported in the literature.¹⁹,³²,⁵³,⁵⁴ The stem should bypass the fracture by at least two cortical diameters. Cables can be used for additional fixation if significant deformity is present.

Condyle fractures are the most common intraoperative femur fracture encountered during revision surgery.¹³,¹⁴ For these as well as epicondylar fractures, interfragmentary lag screw fixation may be acceptable in non-and minimally displaced fractures.⁵⁴ A diaphyseal-engaging stem is indicated in comminuted and displaced fractures to off-load forces at the fracture.⁵⁴ Washers can be used in cases of poor bone quality. In condylar fractures, a buttress plate can be added to resist shear forces.

Bone grafting may be considered to augment healing. Healy et al reported improved union rates with addition of bone graft (autogenous iliac crest or femoral head allograft).⁴⁶ Cement should be used judiciously around the fracture, limited to being placed at or proximal to the fracture line, so as to avoid interference with bone healing.

Postoperatively, weight-bearing and range of motion should be dictated by fixation. If rigid fixation is achieved, range of motion should be started immediately to prevent stiffness. Protected weight-bearing should be considered for 4 to 6 weeks when an intraoperative distal femur fracture is encountered. In a review of intraoperative fractures during aseptic revision TKA, Sassoon et al reported weight-bearing limitations in 22% of patients.¹³

INTRAOPERATIVE FRACTURE: TIBIA

Compared to periprosthetic femur fractures, periprosthetic tibia fractures are rare in both the primary and revision setting.⁹,¹³,¹⁴ With diaphyseal-engaging press-fit stems, however, tibial fractures are more common than femur fractures.¹⁵ Like femoral fractures, the risk is increased in the revision setting. Felix et al reported over a five times greater risk during revision surgery.²¹ Intraoperative tibia fractures can occur throughout the bone with fractures reported in the medial and lateral tibial plateaus as well as the anterior, posterior, medial, and lateral cortices of the diaphysis.⁹,¹³,¹⁴,¹⁵ Patient-related risk factors for tibia fractures are similar to those of femoral fractures and include anything that weakens the bone. In the revision setting, this includes osteolysis and stress shielding.

Classification

Felix, Stuart, and Hanssen’s Mayo classification for periprosthetic tibial fractures is the most commonly used system.²¹ It characterizes fractures based upon three characteristics: anatomic location, implant stability, and timing. Type I fractures are at the level of the tibial plateau and involve the implant baseplate-bone interface. Type II fractures are more distal at the diaphyseal-metaphyseal junction and involve the implant stem-bone interface. Type III fractures occur distal to the tibial stem or keel. Type IV fractures involve the tibial tubercle. These fractures are further subclassified whether the implant is radiographically stable (subclass A) or loose (subclass B) and whether the fracture occurred intraoperatively (subclass C).

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