Cementless, Cruciate-Retaining Primary Total Knee Arthroplasty Using Conventional Instrumentation: Technical Pearls and Intraoperative Considerations.

BACKGROUND

Total knee arthroplasty (TKA) is commonly indicated for patients with severe tibiofemoral osteoarthritis in whom nonoperative treatment has failed. TKA is one of the most commonly performed orthopaedic surgical procedures in the United States and is associated with substantial improvements in pain, function, and quality of life. The procedure may be performed with cemented, cementless, or hybrid cemented and cementless components. Cementless TKA utilizing contemporary implant designs has been demonstrated to have excellent long-term survival and outcomes in patients who are appropriately indicated for this procedure. The preference of the senior author is to perform this procedure with use of a cruciate-retaining implant design when feasible, and according to the principles of mechanical alignment to guide osseous resection. It should be noted that nearly all recent studies on outcomes following cementless TKA utilize traditional mechanical alignment. Alternative alignment strategies, such as gap balancing and kinematic alignment, have not been as well studied in cementless TKA; however, preliminary short-term studies suggest comparable survivorship with restricted kinematic alignment and gap balancing compared with mechanical alignment in patients undergoing cementless TKA.

DESCRIPTION

Our preferred surgical technique for cementless TKA begins with the patient in the supine position. A thigh tourniquet is applied, and a valgus post is set at the level of the tourniquet. A flexion pad is also placed at 90°, with a bar at 20°. After sterile skin preparation and draping, a time-out is conducted, and the tourniquet is raised. The surgeon makes a medial parapatellar incision, which begins from 1 cm medial to the medial edge of the patella, extending from the tibial tubercle to 2 fingers above the proximal pole of the patella, using a knife and with the knee at 90° of flexion. Scissors are then used to find the fat above the fascia and dissect distally in the same plane. A knife is used to perform a high vastus-splitting, medial parapatellar arthrotomy. Pickups and scissors are then used to perform a partial medial synovectomy, and electrocautery is used to perform a medial peel. As the procedure progresses further medial, the infrapatellar fat pad is excised, followed by the anterior femoral synovial tissue. The surgeon then cuts through the anterior cruciate ligament footprint and origin with the knee flexed before sawing through the tibial spines to decrease the height of the tibial bone block. To prepare the femur, a step drill is inserted into the femoral canal, and the intramedullary alignment guide is placed with the distal femoral cutting guide set to 5° of valgus. The distal femoral cutting guide is then pressed firmly against the distal femur, making sure that the medial side is touching bone, and threaded pins are inserted in the cutting guide under power. The distal femur is then precisely sectioned with use of an oscillating saw equipped with a 21 mm x 90 mm x 1.27-mm saw blade. The surgeon focuses on initiating the cut at the cortices before proceeding further, to avoid cortical blow-out. The resultant cut is meticulously assessed for uniformity and levelness, employing both the alignment rod and the distal cutting guide for verification. Following this assessment, the pins and guide are removed, and any remaining femoral condylar osteophytes are delicately excised with use of a rongeur. The surgeon uses the femoral sizing guide, measures the size of the femur, and double-checks rotation in preparation for the remaining distal femoral cuts. The holes are then drilled to set the rotation for the 4-in-1 cutting guide. When applying the 4-in-1 cutting guide, care is taken to align the guide with the drilled holes in order to avoid inadvertent malrotation. The secure fixation of the block is ensured through the judicious insertion of 2 threaded pins under power at full speed, followed by a more controlled, slower securing process to avoid stripping the threaded pins. Subsequently, the anterior cut is made with the oscillating saw, again with a focus on initiating the cut at the cortices before proceeding further. The posterior cuts are then made in a controlled manner, employing a gentle bouncing technique to facilitate tactile feedback, and keen attention is given to cutting both the medial and lateral cortices of each of the posterior condyles. The anterior chamfer and posterior chamfer are similarly osteotomized. Subsequently, the 4-in-1 cutting guide is gently removed. To complete this phase of the procedure, a curved osteotome and mallet are employed to delicately extract the resected posterior condyles and remove posterior osteophytes as needed. The concave side of the curved osteotome is used with precision to meticulously trace the contours of the condyles, ensuring a precise result. The surgeon places a bump under the knee and extends it to check the medial collateral ligament, quadriceps tendon, patellar tendon, and posterior cruciate ligament to ensure they are intact. To make the tibial cut, the extramedullary alignment guide is placed, and the height of the slot is set to the level of the subchondral bone, aligning the rotation and coronal axis with the 2nd metatarsal. The tibial slope is also set at this step, with the goal of the resection matching the patient's native tibial slope. Matching is usually achieved by visual inspection of the trajectory of the cutting jig, although the stylus can also be utilized to confirm the appropriate tibial slope. The tibial cut is then completed with use of an oscillating saw. A single-sided reciprocating saw is then used to cut perpendicular to the plateau in the medial compartment while making sure not to extend the cut into the unresected portion of the intact tibial plateau. After removal of the medial plateau fragment, a lamina spreader is placed in the medial compartment; this process is repeated with a second cut in a similar fashion in the lateral compartment to create a triangular bone block that fully preserves the insertion of the posterior cruciate ligament. The medial and lateral menisci are resected, and the gaps are checked with use of a spacer block and alignment rod. The surgeon then sizes the tibia and uses their index fingers to feel both medially and laterally for overhang. An alternative approach is to fully expose the tibia in flexion and to size the tibia under complete visualization of the tibial margins. The tibial trial is then pinned in place after ensuring appropriate external rotation and optimal tibial coverage without overhang. The femoral and tibial trial components are placed, and the surgeon tests 7 things: (1) overall varus-valgus alignment in full extension; (2) degree of extension (specifically noting any amount of recurvatum or flexion contracture); (3) flexion to gravity; (4) anteroposterior stability in flexion (using manual anterior-posterior translation of the tibia); (5) varus-valgus stability in extension, mid-flexion, and full flexion with use of a manual dynamic varus-valgus stress test; (6) patellar tracking; and (7) component rotation. At this point, if any of the above checkpoints are not within acceptable tolerances, additional ligamentous releases or cuts may be performed. After the surgeon is satisfied with the positioning and stability of the trial components, the tibial preparation is completed by seating the feet of the tibial bushing into the tray and drilling the tibia, then punching out the keel. The pins and the tray are removed, the retractors are taken out, and the knee is extended. The surgeon then performs a pulse lavage of the femur and tibia with normal saline solution. The final components are opened, attached to the inserters, and placed in plastic coverings. The final tibial baseplate is inserted and impacted, followed by the femoral component in a similar fashion. We ensure that no soft tissue is incarcerated under the components after impaction. A trial bearing is placed, and the knee is extended. The joint space is then bathed in approximately 500 mL of sterile 0.35% povidone-iodine solution, followed by pulsatile lavage with 1 L of sterile isotonic sodium chloride solution without antibiotics. Stability is then tested again, testing the (7) checkpoints previously discussed. At this point, the only modification that can be made is an increase or decrease in the polyethylene component. Our belief is that any additional changes that require removal or repositioning of the previously implanted cementless femoral and tibial components warrant modification to the cemented TKA. Once satisfied with the stability of the real implants and the trial tibial articular surface, the final polyethylene component is inserted. Finally, the tourniquet is released. The surgeon then irrigates the wound again and closes the arthrotomy and skin. Our preference is to utilize a knotless barbed suture for the arthrotomy closure, followed by 2-0 Vicryl (Ethicon) for subcutaneous closure and 2-0 monofilament knotless barbed suture for skin closure. Some surgeons may choose to utilize a non-barbed suture; however, the use of a barbed suture has been shown to be faster and equally as effective as a non-barbed suture in a large meta-analysis of patients undergoing TKA. Before final closure, the peri-incisional iodophor-impregnated antimicrobial incise drape is peeled back, and sterile 10% povidone-iodine is applied to the skin surrounding the incision. After subcuticular closure, adhesive skin glue is applied, followed by a waterproof dressing with the knee in flexion.

ALTERNATIVES

There are numerous nonoperative treatments available for tibiofemoral osteoarthritis. According to the 2021 American Academy of Orthopaedic Surgeons Management of Osteoarthritis of the Knee (Non-Arthroplasty) Clinical Practice Guideline, these include bracing, nonsteroidal anti-inflammatory drugs, acetaminophen, supervised exercise, patient education, weight loss, and intra-articular corticosteroid injection, among others. When nonoperative treatment has failed, surgical treatment is then indicated for patients who continue to have symptoms that interfere with quality of life. Surgical treatments for tibiofemoral osteoarthritis primarily include unicompartmental knee arthroplasty or TKA, although proximal tibial osteotomy can be performed in some select cases according to disease severity and patient age. Each of these treatments is supported by the recent 2022 American Academy of Orthopaedic Surgeons Management of Osteoarthritis of the Knee (Non-Arthroplasty) Clinical Practice Guideline.

RATIONALE

Historically, the initial generation of cementless TKA implant designs was associated with relatively high rates of failure and poor clinical outcomes when compared with cemented arthroplasty. However, there has been a renewed interest in cementless TKA with modern implant designs that incorporate newer biomaterials and porous coatings, with several recent studies demonstrating equivalence to cemented components at short-term, mid-term, and in some studies long-term follow-up. In a recent study, Kim et al. demonstrated 98% survival free from revision for aseptic loosening at 22 to 25 years postoperatively. In addition to at least equivalent long-term functional outcomes compared with cemented TKA, across multiple studies, several short-term benefits of cementless fixation have been reported, including decreased costs and the avoidance of complications associated with cement debris. Additionally, because there is no need to mix cement, there is a reduced burden of staff training and the elimination of possible variables that may affect cement integrity, in turn leading to improved operative efficiency and shorter operative time. Bone cement implantation syndrome (BCIS) has been reported in up to 28% of cases of cemented TKA, and has a substantial risk of morbidity and mortality. Cement debris can also remain in the knee if not retrieved after cement curing and prior to closure, which is believed to cause discomfort and polyethylene wear. This complication is also avoided when cementless implants are utilized. Additional factors leading to our preference for cementless TKA, when indicated, have not yet been proven in the literature but are intuitive concepts. For example, the lack of cement leads to easier removal of components during revision surgery, and preservation of bone stock is important for performing a successful revision TKA.

EXPECTED OUTCOMES

Cementless TKA using modern implant designs has excellent long-term outcomes at up to 25 years. Kim et al. evaluated 261 patients who underwent bilateral simultaneous TKA with random assignment of cemented and cementless components in contralateral knees. In that study, the mean age was 63 years and the mean follow-up was 24 years. The authors found 98% survival without revision for aseptic loosening at 25 years. Similar findings have also been shown in older patients. For example, in a 2022 study by Goh et al., 7-year survivorship of modern implant designs was 100%. In that study of patients >75 years old, 120 cementless TKAs were matched in a 1:3 ratio with TKAs using cemented implants of the same modern design. Ultimately, no difference was seen in final postoperative scores or improvement in scores at 2 years. Seven-year survivorship free from aseptic revision was 99.4% for patients with cemented implants and 100% for patients with cementless implants.

IMPORTANT TIPS

When deciding to perform cementless TKA, we consider a variety of preoperative factors, such as a history of osteoporosis, preoperative radiographs showing areas of bone loss, and a history of conditions associated with low bone mineral density.Intraoperative factors can also be considered when deciding between cementless and cemented implants. For example, tactile feedback when sawing can help to determine if bone is hard and sclerotic, which we believe indicates a better candidate for cementless implants.○ Note that during tibial preparation in a varus knee, you will typically have substantial sclerosis of the medial tibial plateau and relative osteopenia in the lateral tibial plateau because of longstanding differences in joint loading. This pattern is reversed in valgus knees.○ In general, we believe that the decision regarding bone integrity should be made primarily on the basis of the non-sclerotic side.With use of the techniques described in the present article, we do not have a preoperative alignment threshold or knee range-of-motion criteria for cementless TKA. More research is needed, however, on the long-term outcomes of cementless TKA when utilizing personalized alignment strategies, which may dictate the placement of components in substantial varus or valgus relative to the anatomic axis.When utilizing keeled tibial implants, we recommend drilling in reverse to pack the walls of the drill hole with bone rather than milling it out, which we believe increases support for bone growth.If there is almost no resistance while drilling in reverse, we believe this to be a poor prognostic sign for cementless TKA, and cementing should be considered.When sizing the tibial baseplate, the goal is to maximize the size of the tibia to fit on top of the rim of cortical bone without overhanging. Undersizing may increase the potential for implant subsidence.Osseous cuts with cementless components need to be perfect. Dome-shaped cuts are at risk for rocking and/or toggling, which could contribute to loosening over time.All 4 quadrants of the tibia should be checked to confirm a flat surface.Soft tissues can get incarcerated under the implant, which is of particular concern for cementless implants as this could impair osseous ingrowth.During trialing, ensure that the trial is completely flush on bone, which is an additional check to guard against toggling and/or loosening.When impacting the femoral component, we recommend applying an extension force so that the weight of the inserter does not pull the component into flexion; however, excessive extension force could also cause a fracture.

ACRONYMS AND ABBREVIATIONS

IV = intravenousAP = anteroposterior.