Total Knee Arthroplasty (TKA) MCQs

DISCUSSION: In the setting of valgus deformities, TKA poses different challenges than those encountered when varus deformities are present. Most valgus alignment is attributable to a deformity of the distal femur rather than of the proximal tibia, as seen in varus knees. One of the major anatomical differences is a hypoplastic lateral femoral condyle which, when not recognized and used as a rotational reference point, can lead to internal rotation of the femoral component. This malrotation in turn leads to patellofemoral maltracking or instability, which is a common complication associated with primary TKA. The anteroposterior (Whiteside's) axis is a reliable reference for femoral rotation.

DISCUSSION: In the setting of valgus deformities, TKA poses different challenges than those encountered when varus deformities are present. Most valgus alignment is attributable to a deformity of the distal femur rather than of the proximal tibia, as seen in varus knees. One of the major anatomical differences is a hypoplastic lateral femoral condyle which, when not recognized and used as a rotational reference point, can lead to internal rotation of the femoral component. This malrotation in turn leads to patellofemoral maltracking or instability, which is a common complication associated with primary TKA.

This patient's history and physical findings are concerning for deep infection. Inflammatory markers, including ESR and CRP, should be obtained first. If the levels are elevated, knee aspiration should be performed for the synovial cell count and culture. A bone scan is not indicated in an initial investigation for deep infection; it is rarely helpful and is not cost-effective. CT to assess implant rotation is an appropriate investigation for knee pain when the clinical scenario is not suspicious for a deep infection and when infection has been excluded.

The MRI scan reveals a partial patellar tendon rupture in conjunction with chronic patellar tendinitis. Mild and moderate patellar tendinitis may be treated nonsurgically with rest, stretching, strengthening, and anti-inflammatory drugs. Severe tendinopathy or extensor mechanism disruption is best treated surgically with tendon debridement and repair.

Dynamic patellofemoral joint contact measurements on cadaveric knees with simulated increased Q angle demonstrated that forces shifted to the lateral facet. The lateral shift in the patella was most pronounced from 40 to 90 degrees of flexion. At lower degrees of flexion, the lateral shift was significantly less. At higher degrees of flexion, the continued shift of the patella was not as pronounced.

DISCUSSION: A patient with medial compartment arthritis and a correctable varus deformity with no clinical or examination findings of knee instability most likely has an intact ACL. The pattern of medial compartment osteoarthritis most commonly associated with an intact ACL is that of anteromedial osteoarthritis. An incompetent ACL is commonly associated with a fixed varus deformity and radiographic signs of posteromedial wear. An incompetent ACL is a relative contraindication to a mobile-bearing UKA. When evaluating patients for a mobile-bearing UKA, a stress radiograph will allow the orthopaedic surgeon to determine the correction of the varus deformity and assess the lateral compartment. Inability to fully correct the deformity or narrowing of the lateral compartment with valgus stress should influence the surgeon against UKA. Joint registries across the world have shown decreased survivorship associated with TKA and UKA in men compared to other age groups, but survivorship is lower for UKA than TKA. No studies to date have shown differences in survivorship between fixed- or mobile-bearing UKAs. The complication that is unique to mobile-bearing UKA is bearing spinout, and this occurs in fewer than 1% of mobile-bearing UKA procedures. In vivo and in vitro polyethylene wear in mobile-bearing UKA is low. Arthritis progression may be faster for mobile-bearing UKAs than fixed-bearing UKAs.

DISCUSSIONThe tibial polyethylene insert shows anterior post wear damage from anterior CAM-post impingement in a posterior stabilized knee. It is associated with excessive femoral component flexion and excessive posterior tibial slope in a TKA construct. It is not associated with coronal plane alignment.

External rotation of the femoral and tibial components has been shown to aid in tracking. Likewise, medialization of the patellar button aids in patellar tracking and prevention of lateral subluxations and dislocations.

A 76-year-old woman has had three hip revisions for instability. She presents to the emergency department with another dislocation that occurred while getting up from a low chair. Current radiographs are shown in Figures 1 and 2. Her prior AP pelvis radiograph is shown in Figure 3. ESR and CRP are normal. What is the best plan for definitive treatment?

DISCUSSION: In the setting of valgus deformities, TKA poses different challenges than those encountered when varus deformities are present. Most valgus alignment is attributable to a deformity of the distal femur rather than of the proximal tibia, as seen in varus knees. One of the major anatomical differences is a hypoplastic lateral femoral condyle which, when not recognized and used as a rotational reference point, can lead to internal rotation of the femoral component. This malrotation in turn leads to patellofemoral maltracking or instability, which is a common complication associated with primary TKA.

DISCUSSIONStiffness following TKA is a disabling complication. One option involves MUA, a valuable technique with which to increase range of motion after TKA for patients with stiff knees. A systematic review of the literature was performed to identify studies that reported the clinical outcomes and measured range of motion for patients undergoing MUA. Fourteen studies (913 patients) reported range of motion results following MUA at up to 10-year followup. The review demonstrated that MUA for a stiff primary TKA is an efficacious procedure to restore range of motion, and it carries a low complication rate. Early gains in motion werereported to be maintained in the long term. A second review systematically evaluated the outcomes of 4 treatments for arthrofibrosis that develops subsequent to TKA (MUA, arthroscopic debridement, open surgical release, and revision TKA). This study showed that there were no significant differences in the Knee Society Score of the 4 treatment modalities. Although open surgical release resulted in the greatest increase in range of motion, there were methodological study limitations because the majority of the papers were case series, which decreased the quality of the evidence. Response 1 is correct because the TKA appears appropriately sized and is well aligned. Responses 2 and 3 are incorrect, considering the early time frame (8 weeks) from initial surgery. Although the patella is unresurfaced in the radiographs, there is no indication for revision TKA (even secondary patellar resurfacing) at this early juncture.

Discussion: The plain radiograph shows a defect in the lateral femoral condyle and narrowing of the lateral joint space. The MRI scan shows a lesion consistent with osteonecrosis of the lateral femoral condyle. The treatment alternatives for this condition are an osteotomy or a total knee replacement, but a total knee replacement is the treatment of choice for a 72-year-old patient. Arthroscopy or an osteochondral bone graft will not address her symptoms. A valgus osteotomy will exacerbate the problem by overloading the lateral joint, which is already diseased.

This patient likely is experiencing failure of his UKA secondary to poor patient selection. This young, heavy man likely loosened his component secondary to the ongoing varus alignment of the knee and his elevated weight. Despite this likely scenario, the next step is to determine if an infection is the cause of his pain. Prior to obtaining an aspiration, the surgeon can order an ESR and CRP to determine if aspiration is warranted. If laboratory studies are unremarkable, the surgeon likely can forgo the aspiration and proceed to a revision TKA with possible augments on standby.

The theoretic total knee components will resist anteroposterior motion by making the femoral component “climb the walls” of the tibial component. As drawn, there is no constraint to medial-lateral translation. The cylinder is not rounded on the edges, so varus-valgus motion will impart load from the cylinder to the trough over a small area, thus having a high contact stress.

Excessive resection of the posterior femoral condyles abnormally increases the flexion gap without affecting the extension gap. This leads to flexion instability, classically presenting with poor stair descent and recurrent effusions.

High tibial osteotomy (HTO) is indicated for active patients with unicompartmental knee osteoarthritis and malalignment. Contraindications include inflammatory arthritis, patellofemoral arthritis, flexion contracture > 15 degrees, knee flexion < 90 degrees, bone loss/osteopenia, and smoking. A flexion contracture of 20 degrees is a relative/absolute contraindication as HTO does not correct sagittal plane contractures well.

Operative exploration and decompression of the peroneal nerve-Five patients were treated by operative exploration and decompression of the peroneal nerve for peroneal nerve palsy complicating total knee arthroplasty (TKA). All patients had failed to demonstrate improvement in the peroneal nerve function despite extended conservative care. The procedure was performed five to 45 months after the index TKA. Patients were evaluated and graded preoperatively and postoperatively using the Modified Nerve Palsy Scale of Weber, Daube, and Coventry. All patients demonstrated improved nerve function. Four of five patients had full peroneal nerve recovery. All patients were able to discontinue their ankle-foot orthoses.This is a rarecomplication of TKA, and when conservative nonoperative measures do not lead to sufficient improvement in nerve function, consideration may be given to operative decompression of theperoneal nerve.

Hemophilia A is an X-linked recessive deficiency of factor VIII that can lead to significant bleeding problems including recurrent spontaneous hemarthroses that can lead to synovitis and joint destruction. von Willebrand disease is a lack of von Willebrand factor that leads to decreased platelet aggregation; more commonly patients have mucosal bleeding and not hemarthroses. Vitamin K deficiency is not hereditary; it is typically attributable to inadequate dietary intake, malabsorption, and loss of storage sites from hepatocellular disease. Protein C and S deficiencies are autosomal-dominant diseases that lead to thrombosis, not bleeding, as protein C and S shut off thrombin formation.

A common postsurgical problem after TKA is a sudden increase of pain that typically occurs about 2 to 3 weeks after surgery. ESR findings are not reliable during the acute postsurgical period. A CRP level exceeding 100 mg/L during the acute postsurgical period is a joint aspiration indication. If the patient does not have sepsis, there is no emergency. This pain is likely attributable to too much activity during physical therapy. Observation is recommended for this patient.

DISCUSSION: A patient with medial compartment arthritis and a correctable varus deformity with no clinical or examination findings of knee instability most likely has an intact anterior cruciate ligament (ACL). The pattern of medial compartment osteoarthritis most commonly associated with an intact ACL is that of anteromedial osteoarthritis. An incompetent ACL is commonly associated with a fixed varus deformity and radiographic signs of posteromedial wear. An incompetent ACL is a relative contraindication to a mobile-bearing UKA. When evaluating patients for a mobile-bearing UKA, a stress radiograph aids the orthopaedic surgeon in determining the correction of the varus deformity and assessing the lateral compartment. An inability to fully correct the deformity or narrowing of the lateral compartment with valgus stress should influence the surgeon against UKA. Joint registries across the world have shown decreased survivorship associated with TKA and UKA in men compared with other age groups, but survivorship is lower for UKA than for TKA. No studies to date have shown any differences in survivorship between fixed-bearing and mobile-bearing UKAs. The complication that is unique to mobile-bearing UKA is bearing spinout, which occurs in less than 1% of mobile-bearing UKA procedures. In vivo and in vitro polyethylene wear in mobile-bearing UKA are low. Arthritis may progress faster in patients with mobile-bearing UKAs than in those with fixed-bearing UKAs.