gms | German Medical Science

Objectives: A pre-arthritic alignment strategy for medial unicompartmental knee arthroplasty (UKA) aims to restore a patient’s native alignment, guided by re-tensioning of the medial collateral ligament (MCL), which may translate into improved outcomes. The present study aimed to compare outcomes of pre-arthritically and non-pre-arthritically aligned knees following medial UKA.

Methods: A retrospective study of 537 robotic-assisted fixed-bearing medial UKA was conducted. Coronal alignment was assessed using the mechanical hip-knee-ankle angle (mHKA). Pre-arthritic alignment was estimated through the arithmetic hip-knee-ankle (aHKA) algorithm. Knees were grouped according to the difference between postoperative mHKA and estimated pre-arthritic alignment (i.e., aHKA) as Group 1 (pre-arthritically aligned: mHKA restored within 2.0° of the aHKA), Group 2 (mHKA >2.0° overcorrected relative to the aHKA), or Group 3 (mHKA >2.0° undercorrected relative to the aHKA). Outcomes included the Knee Injury and Osteoarthritic Outcome Score (KOOS) for Joint Replacement, Kujala, proportions of knees meeting the patient acceptable symptom state (PASS) for these scores, and survivorship. PASS thresholds for KOOS and Kujala were determined using a receiver operating characteristic curve method.

Results and conclusion: A total of 537 knees were included with a mean follow-up of 4.4±1.6 years, mean age of 63.2±9.0 years, and mean BMI of 29.5±5.2 kg/m². Postoperatively, 369 knees (69%) were pre-arthritically aligned (Group 1), 107 knees (20%) had a postoperative mHKA of >2.0° less than their pre-arthritic alignment (Group 2), and 61 knees (11%) were to restored >2.0° greater than their pre-arthritic alignment (Group 3). Mean KOOS was comparable among groups (Group 1: 84.7±16.2; Group 2: 84.7±14.7; Group 3: 83.2±16.9; p=.790). Mean Kujala was significantly lower in Group 3 (76.0±17.1), compared to Groups 1 and 2 (84.1±14.8 and 85.1±14.2, respectively; p< .01). Multivariable analysis demonstrated that Group 3 was a predictor for a worse Kujala score, independent of age, BMI, gender and postoperative mHKA (Beta = -7.3, [95% confidence interval -12.0 to –2.6]; p=.003). There were no differences among groups in proportions of knees that achieved the PASS, as determined by the ROC analyis, for KOOS (72.0 points); however, the proportion of knees achieving the PASS for Kujala (76.5 points) was lower in Group 3 (59%) compared to Group 1 (74%; p=0.02). Five-year survivorship was higher in Groups 1 and 2 (99% and 100%, respectively) compared to Group 3 (91%; p=.04).

Pre-arthritically aligned knees and knees with relative overcorrection from their pre-arthritic alignment demonstrated improved mid-term patient-reported outcomes and survivorship following medial UKA, compared to non-pre-arthritically aligned knees with>2.0° residual varus relative to their pre-arthritic alignment. These results support the use of a pre-arthritic alignment strategy for fixed-bearing medial UKA to optimize postoperative outcomes.