The complex posttraumatic knee: surgical techniques and implant selection

How to choose the augments, extension stems, and fixation?

Stems in TKA increase mechanical stability and fixation of the prosthesis, ensure correct alignment, and reduce stress load on the proximal tibia and distal femur. The question is whether to use long or short stems, cemented or cementless (hybrid) stems, and whether to add cones. There is no 'one size fits all' approach and treatment needs to be individualized. Stems are often used when the remaining bone stock is insufficient and when grafting for large volume defects is necessary. However, in patients with angular deformities of the femur or tibia, stem extensions are usually not possible, and a corrective osteotomy might be needed in advance if stem fixation is desired. Today, adding a cone might often be a good alternative to a stem extension in primary TKA for PTOA. Cones also facilitate bone grafting. In poor bone stock, cones might still require a stem extension either as a longer stem with hybrid fixation or as a shorter fully cemented stem. Localized medial or lateral uncontained defects at times may require the use of an augment.

Wound closure and complications

Optimized wound closure is crucial to prevent later wound drainage and potential risk of delayed rehabilitation or return to the operating room. Typically, a layered closure is preferred, and should include the

1. Deep capsular layer
2. Subdermal layer
3. Intradermal layer
4. Application of a specific sterile dressing [12].

In patients with a compromised soft-tissue envelope, Boettner favors staples or interrupted nylon sutures for skin closure. A vacuum-assisted wound dressing or temporary immobilization of the knee can also help with wound healing.

Although rare, wound infections can occur after TKA in the form of superficial skin infection, skin necrosis, or wound dehiscence. Periprosthetic joint infection have been reported in 0.5–1.9% of primary TKAs [13] but the incidence might be higher in posttraumatic TKA. For wound drainage in the early postoperative days, surgeons should immobilize the knee for 48 hours and apply an elastic compression bandage. This helps to control early wound drainage in most cases. More problematic is continued drainage beyond 72–96 hours or wound infections that present 3–6 weeks after surgery. Drainage that increases when bending the knee is concerning for an open capsule and connection to the joint itself. In cases of prolonged wound drainage, a deep implant infection is always a concern. Patients at a higher risk include those with diabetes mellitus, older age, connective tissue diseases, malnutrition, rheumatoid arthritis, vascular insufficiency, and smoking; surgeons should take these comorbidities into consideration when selecting the wound closure technique.

Rehabilitation

In patients with PTOA, the focus is on restoring ROM. Boettner recommends that "less is more, focus on the ROM and avoid strength training or other excessive exercises". For patients with compromised soft tissues, our primary goal for the first 4–6 weeks is wound healing as well as at least 110° of flexion and full extension.

Weight bearing is usually possible but might have to be adjusted based on the type of reconstruction. The overall amount of walking should be reduced in the first weeks until ROM is restored.

While the usual sport restriction applies to patients with TKA for PTOA, younger patients with more complex hinge reconstructions should be advised to avoid all impact sports. Longevity of these, often complex reconstructions, has priority over sport.

Conclusion

Posttraumatic TKA are some of the most complex and challenging cases in primary knee arthroplasty. Careful planning of the incision, bone defect reconstruction, and type of implant is strongly recommended to avoid intra- and postoperative complications. The complex nature and to some extent unpredictability of these reconstructions should be communicated to the patient.

Nonunion of the prior fracture is usually a contraindication, especially if it is in the metaphysis or diaphysis. When sufficient bone stock remains distally, it may be preferable to obtain fracture union with revision open reduction and internal fixation. Alternatively, some surgeons recommend using TKA with a longer stem extension for fixation of the nonunion using the bony resections as autograft. In older patients, a distal femoral replacement is an elegant treatment option for patients with extensive distal femoral bone loss.

Malunion also can render a TKA more difficult. For example, a rotational malunion of the femur is rare but can affect patellar tracking. Routine CT version studies of the femur are part of the workup of every femoral fracture prior to TKA. In such a scenario, Boettner recommends that malrotation exceeding > 35° of total anteversion of the femur should be corrected prior to TKA. Restoring limb alignment is critical to ensure function and survivorship of the TKA. Correction of coronal malalignment of the knee at the time of TKA does usually require significant soft-tissue release to correct a deformity in the metaphysis or diaphysis at the level of the joint. Boettner feels that there is usually a limit of 20° of coronal malalignment that can still be corrected at the time of TKA (Figure 3). Persistent malalignment after TKA decreases the long-term survival of the TKA [11]. Again, Part 2  by Fragomen reviews the option of corrective osteotomy prior to TKA.

Medial hardware can be accessed through the standard parapatellar approach and in most cases can be removed at the time of total knee replacement. Through imaging, eg, MRI, CT, and preoperative clinical evaluation, a surgeon should be able to determine the precise location and issues with existing hardware. Optimizing the approach to remove hardware is key in preventing complications. The surgeon needs to make the decision whether to remove all or partially remove the existing hardware and to do so in a one-stage or two-stage approach. "Personally, I try to retain hardware if it does not impact performing the TKA or if there are no signs of a periprosthetic infection", states Boettner. If a surgeon does suspect a periprosthetic infection, all hardware should be removed and a two-stage TKA is usually preferred [7]. This can either be performed by removing the hardware and doing a thorough irrigation and debridement, or in more advanced cases with or without osteomyelitis, bone resections for the planned TKA and implantation of a temporary antibiotic spacer to eradicate the infection might be preferred. Once the infection is cleared the TKA can be performed in a second stage.

For an individualized care, Boettner recommends the following approaches [2]:

• Medial hardware on the proximal tibia or distal femur, which can be accessed through the standard medial parapatellar approach, can be removed at the time of TKA
• Lateral hardware that is not compromising the insertion of a TKA component can be retained
• Lateral hardware that extends into the metaphysis or diaphysis will compromise the TKA and should be removed in a two-stage approach
• Consider a two-stage hardware removal for patients with a history of an open fracture around the joint, wound infection, prior use of external fixators or extended drainage after a primary osteosynthesis.
  
  

Managing bone loss or defects and fixation of implants in the complex total knee arthroplasty

In posttraumatic knees, the patient may present with bone loss either on the tibia, femur, or patella. Standard x-rays or CT imaging facilitate the evaluation of bone defects. While a cavitary defect can usually be addressed with impaction grafting with or without a cone versus filling with bone cement, a segmental defect might require augments. Bony defects involving the insertion of the collateral ligaments can usually be compensated by a more constraint implant; however, a compromise of the patellar tendon insertion on the tibia has significant implications for a TKA. A functioning extensor mechanism is usually required for TKA and in patients with large soft-tissue defects or bone defects involving the extensor mechanism, a fusion might be preferred.

Originally, the Dorr classification [8] determined that any tibial bone loss that involves < 50% of the tibial plateau and is < 5 mm in depth can be filled with cement. For larger defects, and especially in the case of elderly patients, metal augments are the best option. Autogenous bone grafts might be the best option for young patients, where restoring the bone stock might be beneficial for future revision surgeries. A variety of different classification systems exist but the Anderson Orthopedic Research Institute (AORI) classification (Figure 2) is currently the most widely used classification for revision TKA (a more thorough review of these classifications can be found in Qiu et al [9]).