Review Question - QID 219581

Significant preoperative valgus deformities with concomitant knee flexion contracture significantly increase the risk for post-operative common peroneal nerve palsy after total knee arthroplasty (TKA). In such cases, prophylactic common peroneal neurolysis (CPN) should be considered (Answer 3).

Most (>85%) of patients undergoing TKA demonstrate a neutral or varus preoperative coronal plane alignment. Comparatively, valgus deformities are known to be more complex cases regarding achieving optimal coronal plane balancing. The lateral soft tissues are contracted relative to medial soft tissue, and lateral releases (i.e., posterolateral capsule or partial IT band release) are often employed. Notably, the medial collateral ligament is often attenuated from chronic elongation, which can result in the need for thicker polyethylene inserts (>14mm) and/or increased constraint implant designs. In severe cases (>15 degrees valgus), acute correction of valgus deformities may result in iatrogenic stretching of the CPN with resultant foot drop. While this can resolve over time with observation, some patients require subsequent CPN release just below the level of the knee between the anterior and lateral compartments (Answer 3). Concomitant prophylactic CPN release at the time of performing TKA should be considered.

Makhdom and colleagues retrospectively reviewed 9 patients (10 knees) in which prophylactic peroneal nerve decompression was performed at the time of TKA for the indication of severe valgus deformity (>15 degrees). They reported all patients had completely normal motor and sensory function with no complications related to the neurolysis procedure. The authors concluded that prophylactic peroneal neurolysis minimizes the risk of post-operative palsy in high-risk patients and should be considered in patients with severe preoperative valgus deformity.

Patel and colleagues provided a comprehensive review of the incidence, injury mechanism, and recovery of iatrogenic nerve injuries during hip and knee arthroplasty. The authors discuss the common peroneal nerve being most commonly injured via stretching with the acute correction of combined valgus and flexion deformity. They found that most patients tend to improve after this type of injury, although many report persistent weakness with dorsiflexion. The authors conclude that prophylactic decompression in high-risk patients should be considered.

Figures A and B demonstrate this patient’s significant valgus deformity, as evidenced by the lateral tibial plateau's erosion and increased concavity. Illustration A demonstrates this patient’s post-operative imaging, where a condylar constrained knee (CCK) implant was utilized, as evident from the large post’s metal bar.

Answer 1: Pie-crusting the medial collateral ligament with an 18-gauge needle is used for soft tissue balancing in varus deformity TKA procedures. It allows the surgeon to gently titrate the medial soft tissue release to obtain a balanced coronal plane (without releasing the MCL).
Answer 2: In the setting of significant preoperative flexion contractures, it can be difficult to achieve full extension after bony cuts and trialing. Resecting MORE distal femur than a standard TKA procedure can help increase the extension gap to achieve full extension. However, it is generally recommended to attempt soft tissue releases (i.e., posterior capsule release) first to avoid raising the joint line and mid-flexion instability associated with resecting additional distal femur bone.
Answer 4: In the setting of severe coronal plane deformities (>20 degrees varus/valgus), surgeons should consider a staged procedure where an extra-articular corrective osteotomy is performed in advance of TKA. This allows for coronal plane deformity correction to make the eventual TKA procedure technically easier (i.e., less aggressive bony cuts, easier soft tissue balancing) and thus potentially lower the risk for aseptic loosening. However, a medial-opening high tibial osteotomy would worsen this patient’s preoperative valgus deformity.
Answer 5. Patients with significant long-standing coronal plane deformities, such as in this case, should have increased constraint primary implants to avoid instability. This can include using a posterior stabilized implant with a standard post (i.e., posterior stabilized “PS”), thicker constrained post (i.e., constrained posterior stabilized “CPS”), or taller and thicker post (i.e., constrained condylar knee “CCK”, as was used in this case - Illustration A).