Impact of intra-articular injection on infection risk and therapeutic effect after unicompartmental knee arthroplasty: a retrospective cohort study

Background

Unicompartmental knee arthroplasty (UKA) is an effective treatment for single-compartment knee osteoarthritis. However, some patients experience lateral compartment pain after UKA. The impact of lateral compartment intra-articular injection on infection risk of the medial prosthesis and therapeutic outcomes in these patients remains controversial.

Objective

This study aims to evaluate the impact of lateral compartment intra-articular injection after UKA on the risk of medial prosthetic joint infection, as well as its therapeutic effect on lateral compartment pain and inflammation. We hypothesized that lateral compartment intra-articular injection in patients with post-UKA lateral pain could provide better pain relief and functional outcomes without increasing the risk of medial prosthetic infection.

Methods

This retrospective cohort study included patients who experienced lateral compartment pain after UKA at Jinshan Branch of Shanghai Sixth People's Hospital between January 2018 and December 2020. Patients were divided into two groups: those who received lateral compartment intra-articular injection for pain management (injection group) and those who received only oral medication (control group). The primary outcome was medial prosthetic infection rate within 6 months post-injection. Secondary outcomes included pain scores, knee function, and quality of life.

Results

A total of 249 patients with post-UKA lateral compartment pain were included (144 in the injection group, 105 in the control group). There was no significant difference in medial prosthetic infection rates between the two groups (2.1% vs. 2.9%, p = 0.812). The injection group showed significantly better pain relief (VAS score) and knee function (KSS score) at 1 week and 1 month post-injection (p < 0.05). Quality of life measures (SF- 36) also showed improvements in the injection group at these early time points.

Conclusion

Intra-articular injection after UKA does not increase the risk of infection and may provide better short-term pain relief and functional outcomes. These findings support the safety and potential efficacy of this approach in managing apparent lateral knee post-operative pain and enhancing early recovery after UKA. However, larger prospective studies are needed to confirm these results and further explore the long-term impact of this intervention.