The Clinical Significance of Using PASS Thresholds When Administering Patient-Reported Outcome Instruments After Anterior Cruciate Ligament Reconstruction

Background: Patient-reported outcome (PROs) instruments of knee function quality of life are routinely administered to patients after anterior cruciate ligament reconstruction (ACLR). The Patient Acceptable Symptom State (PASS), an evidence-based threshold defining perceived outcomes, may be a useful indicator of strength and functional performance.

Purpose: To compare strength and functional performance between patients recovering from ACLR who did and did not meet PASS thresholds on associated PROs.

Study design: Cross-sectional study; Level of evidence, 3.

Methods: A total of 223 patients who had undergone ACLR (106 women, 117 men; 7.62 ± 1.71 months after ACLR) completed isokinetic knee extensor and flexor strength at 90 deg/s, hop performance (single-limb hop for distance [SLHD], triple hop for distance [THD], 6-m timed hop [6MH]), and PROs (International Knee Documentation Committee Subjective Form [IKDC], Knee injury and Osteoarthritis Outcome Score [KOOS], and Anterior Cruciate Ligament Return to Sport After Injury [ACL-RSI]) assessments in a controlled laboratory setting at an academic institution. Independent-samples t tests compared strength and hop measures between patients who did and did not achieve a PASS on the PROs. Limb symmetry index (LSI) was calculated as (ACLR Limb ÷ Contralateral Limb) × 100%. Strength and hop performance LSI outcomes were converted into indicator variables, categorized as either a "pass" or "fail" based on the operational definition of having an LSI value ≥90%. Chi-square tests compared strength and hop LSI PASS status measures to PRO PASS status.

Results: Patients who achieved IKDC_PASS were significantly stronger and had more symmetric limbs than those who did not achieve IKDC_PASS. Values for IKDC_PASS were as follows: knee extension ACLR limb 1.72 ± 0.47 N·m/kg, contralateral limb 2.40 ± 0.45 N·m/kg, LSI 71.64% ± 15.23%; knee flexion ACLR limb 1.04 ± 0.29 N·m/kg, contralateral limb 1.05 ± 0.26 N·m/kg, LSI 99.12% ± 17.22%. Values for IKDC_FAIL were knee extension ACLR limb 1.47 ± 0.52 N·m/kg, contralateral limb 2.25 ± 0.47 N·m/kg, LSI 64.66% ± 17.07%; knee flexion ACLR limb 0.88 ± 0.28 N·m/kg, contralateral limb 0.97 ± 0.28 N·m/kg, LSI 90.46% ± 17.41%. Effect sizes ranged from small to moderate (P < .001; d = 0.3-0.55). IKDC_PASS status was significantly associated with an LSI ≥90% for knee flexion peak torque (χ² = 9.66; P = .002), SLHD (χ² = 9.61; P = .002), and THD (χ² = 3.97; P = .02), with a moderate effect size (P < .05; d = 0.41-0.73). Significant relationships were found with KOOS_PASS (Pain, Activities of Daily Living [ADL], and Sport) and LSI ≥90% for peak knee flexion torque with a moderate effect size (Pain and ADL, P < .001; Sport, P = .04; d = 0.59-0.72) and SLHD with a strong effect size for the Symptom subscale (Symptom, P < .01, d = 1.21; Pain, P = .003; ADL, P = .04; Sport, P = .001). No differences were found in strength outcomes for patients who achieved ACL-RSI_PASS versus those who did not (P > .05). Patients who achieved ACL-RSI_PASS had more symmetric SLHD and THD LSI scores and jumped farther on their contralateral limb for the THD compared with ACL-RSI_FAIL patients (P < .05; d = 0.50-0.64).

Conclusion: Patients meeting thresholds for the IKDC_PASS and KOOS_PASS (Pain, ADL, and Sport subscales) demonstrated greater knee strength bilaterally, and hopped farther and more symmetrically, compared with patients who scored below the PASS threshold on the same PROs. Using PASS thresholds for PROs can aid clinicians when considering when patients can safely return to activities after ACLR.