Maintenance of Coronal Alignment and Joint Line Obliquity Has No Effect on Unicompartmental Knee Arthroplasty: Clinical Results at Five Years Follow-Up.

BACKGROUND

The applicability of the coronal plane alignment of the knee (CPAK) classification for unicompartmental knee arthroplasty (UKA) is not yet clear. The current study aimed to address the following questions: 1) what is the distribution of the CPAK classification among patients who underwent medial UKA? and 2) what would be the clinical outcomes for patients whose coronal alignment and joint line obliquity have either changed or been maintained postoperatively?

METHODS

This retrospective study involved 325 patients treated with fixed-bearing medial UKA between 2017 and 2019 following a kinematic alignment strategy and using cemented resurfacing implants. Long-leg standing radiographs were utilized for all preoperative and postoperative measurements. There were two independent observers who measured the alignment parameters. The patient's CPAK classification diagram was subsequently created. At the last follow-up, patients' outcomes were assessed using the clinical scores.

RESULTS

The CPAK type 1 was the most prevalent type among 150 (46.1%) patients. Postoperatively, the most common CPAK type was type 2. In comparison to the preoperative distribution, there was a decrease in the prevalence of Types 1 and 4 in the postoperative distribution, whereas an increase in the distribution of all other types was noted. A total of 203 patients (62.4%) experienced CPAK classification change postoperatively, of which 122 patients (37.5%) maintained their original preoperative CPAK classification (P = 0.003). At a mean follow-up of 66.1 months (range, 54 to 75), implant survival (P = 0.9) and all clinical scores were similar between the CPAK Maintained and Changed groups (P > 0.05 for all).

CONCLUSIONS

The use of UKA may alter the preoperative CPAK distribution in more than half of the patients. Following UKA, a maintained coronal alignment and joint line obliquity do not have an impact on either patient-reported outcomes or implant survival.

LEVEL OF EVIDENCE

IV, retrospective cohort series.