The posttraumatic knee: preoperative workup, imaging, and planning

Managing posttraumatic osteoarthritis through nonoperative therapies

As with any patient presenting with knee pain from OA, the first-line approach in managing patients with PTOA is nonoperative. The mainstays of nonoperative management consist of activity modification, weight loss, nonsteroidal antiinflammatory drugs (NSAIDs), and acetaminophen [4]. Intraarticular injections of corticosteroid or viscosupplementation are also options [5, 6]; however, there is increasing evidence of the low cost-effectiveness of viscosupplementation for the treatment of end-stage knee OA [7]. Injections of stem cells and platelet-rich plasma (PRP) is currently in the experimental phase for the treatment of OA and is not generally recommended outside of well-designed research studies [8-10]. Further details about the benefits and limitations of these treatments are displayed in Table 1. When patients have tried many of these modalities but are still having significant pain and dysfunction that considerably affects their quality of life and daily activities, knee arthroplasty is an option.

Preoperative workup for total knee arthroplasty in a posttraumatic knee: getting to know "a difficult knee"

A thorough preoperative evaluation of patients presenting with PTOA remains paramount. This should be approached systematically and include a clinical history, a physical examination, and a radiographic evaluation [13]. These three basic steps can inform whether additional preoperative testing or consultations are needed, and ultimately, if a primary TKA is viable for each individual patient.

Clinical history

Along with the normal history of patients presenting with knee OA (ie, timing/severity/extent of knee, prior treatment modalities, impact on quality of life, etc.), there should be additional focus on the injury and its treatment [13]. Mechanism and timing of the injury, whether the injury was open or closed and/or treated surgically are important factors that should be noted. Additionally, postoperative treatments such as wound drainage and prescription of any antibiotic therapy should be considered. The patient’s postoperative recovery should also be noted, ie, difficulty in achieving ROM, whether a knee manipulation was performed, whether the knee felt stable or lax initially and over time, and whether metal wear was removed or not, as these are all important pieces of a patient's history. Finally, assessing how symptoms have developed over time can point to the potential underlying cause of pain and dysfunction and predict the efficacy of an arthroplasty in solving/alleviating these symptoms.

Physical examination

The physical examination plays an important role in determining if a patient is an arthroplasty candidate and allows the surgeon to make decisions on incision placement and soft-tissue management, intraoperative balancing, and implant selection. While the focus of the preoperative evaluation of the patient varies based on whether the prior injury involved a fracture or was an injury to ligaments and/or tendon damage, the key elements of the examination of the knee remain the same:

• Knee ROM and muscle strength, particularly of the extensor mechanism
• Skin, soft tissue, and neurovascular assessment
• Knee alignment and stability in the coronal and sagittal plane [13].

First, a gait analysis in the office can help assess knee alignment, stability, and ROM. Severe in-toeing or out-toeing likely indicates the presence of a rotational deformity or a hip pathology that should be further evaluated. Hyperextension or a significant varus or valgus thrust gait is a good indicator of dynamic knee laxity. Further, lack of knee flexion during the gait cycle may be indicative of a stiff knee (Table 2) [13].

Passive and active knee ROM and muscular strength are crucial to understanding the difficulty or even viability of a potential TKA. Patients with > 90° arc of active and passive knee ROM do not present any specific additional challenge. However, surgeons should anticipate increased challenges with surgical exposure in patients with a preoperative arc of motion < 90°, and particularly < 60°, and these patients should also be counseled that their postoperative ROM gains will likely be inferior to patients with primary OA undergoing TKA. It remains debatable whether patients with near ankylosis, or < 30° arc of motion, are candidates for primary TKA given these two factors. Furthermore, patients unable to perform a straight leg raise or having an extensor lag > 10° present additional concerns and challenges as the integrity of the extensor mechanism remains vital to the success of a primary TKA.

Assessment of the skin and soft tissue around the knee is paramount, as a healthy soft-tissue envelope is a vital prerequisite for a successful TKA [14]. Prior incisions should be noted and carefully planned if an arthroplasty, with or without hardware removal, is to be performed (Table 2). In such a scenario, gastrocnemius or free flaps should also be noted and should prompt additional evaluation with a computed tomography (CT) angiogram and a consultation with a plastic surgeon. The most concerning finding is very thin skin that is adherent to the bone without a mobile or healthy soft-tissue envelope. Patients displaying thin skin have a significant increased risk of wound complications if an arthroplasty is performed without planning additional soft-tissue coverage. For more tips about how to approach these patients, see the discussion with Friedrich Boettner in Part 3.

Routine assessment of pulses and the perfusion to the lower extremity is advisable. Concerns for asymmetric pulses, a history of vascular injury or repair, or signs of peripheral vascular disease should prompt additional studies and vascular surgery consultation.

Evaluation of knee alignment in the coronal and sagittal planes as well as knee stability remain important and are often assessed simultaneously. Assessing the resting coronal limb alignment and the correction to neutral or overcorrection in either the varus or valgus planes provides information on the patient’s overall knee stability and competency of specific knee ligaments, including the medial collateral ligament (MCL) and lateral collateral ligament (LCL). The competency of the ligaments can inform the surgeon on potential releases that need to be performed during primary TKA to achieve an optimal balance, as well as the potential need for more constrained implants. Furthermore, competency of the anterior cruciate ligament (ACL), while less important, can be assessed with the Lachman and anterior drawer tests.

Imaging and further workup

Preoperative imaging is a vital component of the preoperative workup and evaluation of patients presenting with PTOA. Particular attention should be paid to extraarticular and intraarticular deformities, overall limb and individual femoral and tibial alignment, as well as the presence and extent of preexisting hardware in/or adjacent to the knee. We will review the most common and important radiographic images and modalities below and highlight the specifics to look for.

Essential images:

• Full-length hip-to-ankle AP and lateral weight-bearing x-ray image: These images allow assessment of overall limb alignment as well as femoral and tibial alignment in both the coronal and sagittal plane.
• A lateral view of the knee: Lateral imaging of the knee is helpful in assessing for osteophytes posteriorly or around the patella, the patellar height, and the tibial slope. Significant osteophytic changes may be indicative of a stiff knee. Severe high-riding patella (patella alta) or low patella (patella baja) may be indicative of extensor mechanism compromise. Further, severe patella baja should be noted as it is often accompanied with significant stiffness, poses a challenge to surgical exposure, and affects the patient’s ultimate knee flexion after TKA.
• Rosenberg view: This posteroanterior x-ray is more sensitive than standard weight-bearing x-rays for the detection of posterior joint space narrowing.
• Patellar skyline view: This imaging allows to detect osteoarthritic changes of the patellofemoral articulation as well as the presence of any patellar tilt, subluxation, or Frank dislocation. Severe preoperative patellar tilt, subluxation, or dislocation may need to be addressed at the time of primary TKA.

The imaging evaluation can be additionally complemented with:

• CT scan: A scan of the knee can be useful to assess the remaining bone available for reconstruction and the position and extent of hardware around the joint.
• CT angiogram: Indicated if there are concerns of the vascular supply to the knee or lower limb. It is also indicated for patients whose physical examination or clinical history suggests a compromise of the knee vessels.
• CT scanogram: A scan including the entirety of both limbs is indicated to determine the presence and extent of rotational malalignment of the limb.
• Magnetic resonance imaging (MRI): This can be useful to assess the extensor mechanism or anatomical integrity of the collateral ligaments. It may also be indicated in a patient with a history of extensive infection to assess for underlying abscesses or foci of osteomyelitis that may not be seen on plain x-rays or CT scan.

Evaluation for infection

In any patient with a history of surgery and retained hardware, a basic evaluation for infection, including a complete blood count (CBC), C-reactive protein (CRP), and erythrocyte sedimentation rate (ESR), should be obtained. If these are elevated or if there is additional clinical suspicion (ie, history of known infection or wound drainage, etc), an aspiration of the knee should be performed for cell count, differential, and culture. As reported by Della Valle et al [16], perioperative analysis of ESR and CRP are excellent screening tools for ruling out infection showing 90.2% and 95% rates of sensitivity, respectively. If both values are normal (ESR ≤ 30 and CRP ≤ 10 mg/dL), the presence of infection is very unlikely. In contrast, greater values are an indication of a potential infection, and aspiration of the synovial fluid of the knee followed by a white blood cell count is recommended (optimal cutoff value of 3,000 white blood cells/mL) [16]. An MRI can also be considered to assess for abscesses or foci of osteomyelitis.

Decision for the patient

Deformity correction, then primary TKA

In patients with significant coronal or sagittal plane deformities, especially extraarticular deformities > 20°, an osteotomy for correction of the deformity should be considered prior to primary TKA [17]. Deformities > 20° would either require significant alteration of the bony cuts, which ultimately may compromise the collateral ligaments and/or long-term function of the knee [17]. They may also require accepting significant limb deformity, which may compromise TKA durability and overall limb function and alignment. Details of performing corrective osteotomies prior to TKA will be covered in detail in Part 2: Osteotomy prior to TKA: optimizing limb alignment by Austin T Fragomen.

Proceed with primary TKA

Patients with intraarticular or extraarticular deformities < 20°, especially those further from the knee joint, and an intact soft-tissue envelope, a functional knee ROM, and a functional extensor mechanism, are generally candidates for primary TKA. We recommend templating primary TKA bony cuts on long leg x-rays in the coronal and sagittal planes. If the cuts and resultant implant position resembles a primary TKA and overall limb alignment, component position, and ligaments are not compromised, it is safe to proceed with TKA without a prior osteotomy. This can be exemplified with the case study of a 67-year-old male patient who presented with end-stage OA secondary to a femoral and patellar fracture. This injury occurred 25 years ago and led to the appearance of an extraarticular deformity of 10° valgus (Figure 1). He was diagnosed with severe patella baja and posttraumatic patellar deformity. Physical examination of the patient revealed a preoperative ROM between 5° and 100° and laxed MCL. The patient was considered a candidate for TKA, as preoperative templating on AP hip-to-ankle x-ray images indicated standard femoral and tibial cuts. During the surgical procedure, a primary implant with a thicker and constrained polyethylene was used to balance the laxed MCL.

There are important decisions to consider in preoperative planning, such as surgical incision, exposure techniques (ie, quadriceps snip), staged vs simultaneous removal of hardware, partial vs complete removal of hardware, implant selection (eg, are stems or augments required?), and level of constraint necessary. A thorough clinical history, physical examination, and radiographic evaluation outlined here will give surgeons the necessary information to make these decisions and a comprehensive plan for these challenging cases. Details, tips, and tricks in performing these difficult TKAs will be discussed in further detail in Part 3: The complex posttraumatic knee: surgical techniques and implant selection by Boettner.

Primary total knee arthroplasty generally contraindicated

Patients with PTOA with severe preoperative stiffness/ankylsois, extensor mechanism insufficiency, and/or severely damaged soft-tissue envelope pose a particular challenge to arthroplasty surgeons and severely compromise the success of a primary TKA. While it ultimately depends on the extent of each of these three factors and their correctability, these patients are in general not candidates for primary TKA and should be offered alternative surgical options. This was the case of a 34-year-old male patient who had a motor vehicle accident, which resulted in an open periarticular fracture of the lateral femoral condyle (Figure 2). The fracture was initially managed by plating and the skin was closed. The patient had infection, malunion, and subsequent hardware removal. On presentation, his ROM was 20–30°. Reconstruction of the knee through TKA was not deemed possible, as he presented a severely compromised extensor mechanism, ie, his patella was fused to the femur at the metaphyseal region, near ankylosis, and his skin was adherent to the underlying skin.

In such scenarios, where the functionality of the quadriceps, patella, or any other component of the extensor mechanism is damaged beyond repair, patients will be offered above-the-knee amputation or arthrodesis to regain mobility and quality of life [18, 19]. While there are few studies comparing both procedures, the clinical and functional outcomes of arthrodesis vs amputation are similar [20]. Arthrodesis alleviates joint pain while providing a durable weight-bearing function. However, the functional limitations imposed by this treatment needs to be carefully explained to the patient, whose ability to perform routine activities such as tying his shoes or sitting in a chair will be severely compromised [21]. Conversion of a knee fusion to TKA is also possible, even if several studies have reported high complication rates and very low favorable outcomes [22]. Hence, patients should be counseled about the limitations imposed by arthrodesis in the setting of TKA.

Conclusions

Patients with PTOA present a particular challenge for arthroplasty surgeons. A thorough clinical history, physical examination, and radiographic analysis are critical in determining the viability of primary TKA for each individual patient and in preoperative planning for patients who are candidates for TKA. Prior incisions, prior or existing hardware, intraarticular and/or extraarticular deformities, potentially diminished knee ROM, and potential compromise to the extensor mechanism, ligaments, and/or soft-tissue envelope add complexity and require thorough preoperative assessment and planning (Figure 3). Most patients, especially those with intraarticular deformities or extraarticular deformities ≤ 20°, intact extensor mechanisms, and soft-tissue envelopes, can proceed with complex primary TKA. Patients with significant extraarticular deformities > 20°, especially those near the knee joint, may benefit from a corrective osteotomy prior to TKA. Finally, patients with significant soft-tissue compromise, an insufficient extensor mechanism, or severe stiffness/ankylosis may not be candidates for knee replacement surgery, and other options such as arthrodesis or amputation should be considered.