MCID in patients treated for recurrent patellar instability

Purpose: This study sought to evaluate which factors exert a predictive value for not reaching the minimal clinically important difference (MCID) in patients who underwent a tailored operative treatment approach for recurrent lateral patellar dislocations (RLPD).

Material and Methods: A total of 237 consecutive patients (male/female 71/166; mean age 22.4±6.8 years) with a history of RLPD underwent a tailored surgical treatment approach considering their pathoanatomic risk factor profile and were retrospectively enrolled in this study. The BPII 2.0 and subjective rating of knee joint function and pain (numeric analog scale (NAS); 0-10) were used to evaluate the disease-specific quality of life (QoL) from pre- to postoperatively. Gender, age at the time of surgery, body mass index (BMI), nicotine abuse, presence of psychiatric diseases, cartilage status (AMADEUS score), and established pathoanatomic risk factors for RLPD were assessed and evaluated as potential predictors for achieving the MCID using univariate logistic regression analysis.

Results: In total, the BPII 2.0 increased by an average of 36.1 points from a mean of 43.1 ± 20.9 points (3.2-56.9) preoperatively to 79.1 ± 18.3 points (12.7-87.8) postoperatively (p<0.001). The NAS for knee function increased by an average of 3.8 points from a mean of 4.6 ± 2.05 (0-8) preoperatively to 8.5 ± 1.3 points (5-10) after surgery (p<0.001), and the NAS for pain decreased by an average of 3.8 points from 5.8 ± 2.4 (2 -8) preoperatively to 2 ± 1.9 points (0-10) postoperatively (p<0.001). The MCID for the BPII 2.0 was calculated at 9.5 points. Out of the total cohort, 209 patients reached the BPII 2.0 MCID at final follow-up, whereas 29 did not. Statistical analysis demonstrated that only the preoperative subjective assessment of knee joint function and BPII 2.0 score were significant predictors of whether the MCID will be reached postoperatively. The optimal threshold was calculated at 7 (NAS function) and 65.2 points (BPII 2.0). Additionally, age at the time of surgery should be considered for patients with a preoperative BPII 2.0 score greater than 62.5.

Conclusion: The results of this study indicate that the probability of reaching BPII 2.0 MCID postoperatively depends only on the preoperative disease-specific QoL and subjective rating of knee joint function, as well as age at the time of surgery for patients undergoing tailored surgical treatment of RLPD.

Level of evidence: Level III, retrospective cohort study

Keywords: patellar instability; medial patellofemoral ligament (MPFL); minimal clinically important difference (MCID); patient-reported outcomes (PROMs); knee function; age