Summary

Substitution of Medial Congruent Polyethylene did not result in improved final range of motion in our patients.

Abstract

Purpose

Patient satisfaction in total knee arthroplasty is directly associated with range of motion. Our purpose was to evaluate the effect of substitution of a less constrained polyethylene on final range of motion in patients undergoing total knee arthroplasty.

Hypothesis

The utilization of Medial congruent polyethylene would lead to improved range of motion at the time of discharge from physical therapy.

Study design: Cohort study (prognosis); Level of evidence: 2

Methods

The authors reviewed a consecutive series of 69 total knee arthroplasties that were performed by the same surgeon. An Ultracongruent Polyethylene was utilized on 33 knees and a Medial congruent on 36 knees. The utilization of the medial polyethylene component represented a running change in the lead authors practice. An independent physical therapist, blinded to the choice of implants, measured Maximum Flexion at the time of discharge from physical therapy. Maximum Flexion was recorded and analyzed between the groups utilizing a t-test. A power analysis conducted prior to data collection indicated the study was adequately powered. A difference of 10 degrees of flexion was set as our minimum clinically significant difference.

Results

33 patients had a TKA with an Ultracongruent Polyethylene (UCP). 36 patients had a TKA with a Medial Congruent Polyethylene (MCP). Patients undergoing TKA with UCP averaged 114.3 degrees of flexion (Range = 80 - 130) at the time of discharge from physical therapy. Patients undergoing TKA with MCP averaged 114.8 degrees of flexion. (Range = 75 - 130). There was no statistically significant difference between groups (p=0.42). Three patients in each group required manipulation under anesthesia at 3 months from the index procedure. With these 6 patients excluded, patients with UCP averaged 117.1 degrees of flexion and patients with MCP averaged 117.7 degrees of flexion.

Conclusion

Utilization of a less constrained polyethylene did not lead to improvement in range of motion. Our results did not correlate with industry sponsored white papers. The difference in our study is likely multifactorial, but may have been affected by the pandemic altering patients willingness to attend outpatient therapy.

Keywords: Case series with retrospective collection of data; knee; arthroplasty; polyethylene; flexion; range of motion.