Patient-perceived knee enlargement after total knee arthroplasty: prevalence, risk factors, and association with functional outcomes and radiological analysis

Purpose

In clinical practice, many patients complained that their knees became larger after total knee arthroplasty (TKA), yet no studies have described this phenomenon. We named this as “patient-perceived enlargement of knee” (PPEK). This study aimed to investigate the prevalence of PPEK after TKA; assess the association between PPEK and demographics, surgical options, or component size; assess the influence of PPEK on patient satisfaction and functional outcomes; and determine whether there was radiological difference between patients with or without PPEK.

Methods

We reviewed patients that underwent unilateral primary TKA between May 2018 and April 2019. We investigated the prevalence of PPEK and acquired functional scores and satisfaction. Patients were divided into two groups according to whether they complained of PPEK. In radiological evaluation, we measured anterior and posterior condyle offset (ACO and PCO) of the femur, tibial coverage lines, tibial overhanging lines, and femoral overhanging lines.

Results

A total of 389 patients were enrolled and 101 patients felt their knee became “larger” after TKA. Patients with PPEK had significantly shorter height and lower weight, yet component size distribution showed no statistical difference. Patients with PPEK had significantly lower functional scores and satisfaction. Patients with PPEK had significantly larger ACO, shorter postoperative PCO, more ACO increase, and less anterior underhang of the tibia.

Conclusion

PPEK is common in TKA patients, especially in individuals with smaller height and weight. PPEK is associated with poor satisfaction and lower functional scores. In radiology, post-operative ACO, PCO, and anterior underhang of the tibial component were correlated with PPEK.