The results of this study suggest a future large-scale RCT evaluating the effectiveness of a physiotherapist-guided lower-limb focussed exercise-therapy and education intervention for young adults who have persistent symptoms 1-year post-ACLR is feasible. Potential effectiveness of this intervention is indicated by clinically meaningful within-group improvements in knee-related QoL, and greater improvements compared with the control (trunk-focussed intervention) for self-reported function (KOOS-Sport, GROC), satisfaction (PASS), and objective functional performance (single-hop and one-leg rise). Given many patients cease rehabilitation within six months(20), our results provide clinicians and patients with impetus to continue physiotherapist-guided interventions for individuals with persistent symptoms one year after ACLR.
Feasibility: recruitment, physiotherapy attendance and retention
Of those screened, almost half (47%) were eligible, and we achieved a modest recruitment rate (3 per month). For a large-scale RCT, the number of participating surgeons (and study advertising) would need to be increased, which is possible due to the large number of ACLRs performed worldwide each year(45). Although all eligible participants were willing to enrol, two participants did not commence the intervention, and two others dropped out during the intervention, resulting in an overall drop-out rate of 16%, which is considered acceptable(1, 37). Physiotherapy attendance was high (86–89%), which is similar to previous physiotherapist-guided exercise-therapy RCTs (> 80%) for lower-limb musculoskeletal conditions in young adults(1, 37). Suggestions during feedback from drop-outs and those who attended less than 80% of study appointments (n = 5) aligns with previous reported strategies to maintain attendance – i.e. increasing appointment availability after hours, exercise variety, and strategies to increase motivation(53). These strategies, in addition to consideration of telehealth appointments, and multiple clinic locations might reduce drop-outs and improve attendance in future trials. Two participants sustained hamstring strains in their ACLR limb, and one sustained an ankle sprain as they returned to sporting activities. Graded return to high-speed running protocols should be emphasised in future trials to reduce soft tissue injury risk, especially given ACL injury is a well-recognised risk factor for hamstring strain(28).
Feasibility: adherence to the unsupervised exercise-therapy program
According to Physitrack© adherence data, only half of the prescribed unsupervised exercise-therapy program sessions were completed. However, these data are likely to under-estimate true exercise adherence in this trial, as participants reported inconsistently entering their adherence data in Physiapp© due to technical difficulties, and rarely using the app once familiar with the exercises. Regardless of true adherence rates, participants did report typical barriers to exercise adherence(53, 65), including other commitments (work, study and family), and reduced motivation. Exercise adherence rates were lower than previous reports for rehabilitation during the first 6-months following ACLR (75–80%)(4, 54). This may reflect the burden of exercise-therapy on participants who have already endured unsuccessful rehabilitation with the physical, mental and time commitment it entails. Strategies to increase adherence (to the unsupervised exercise-therapy program and monitoring system) may include goal setting(71), incentivisation, supervised group classes, or alternate exercise options (e.g. non-gym based)(27). Personalised adherence monitoring data collection methods, including paper diaries, email or text questionnaires, and strategies to maintain engagment with apps (e.g. positive reinforcement, benchmarking) should be considered.
Treatment effect: knee-related QoL
Both the lower-limb and trunk-focussed interventions were associated with clinically meaningful (> MID) improvements in knee-related QoL, and the mean between-group differences for KOOS-QoL (7 points) and ACL-QoL (3 points) did not meet clinically meaningful thresholds(41, 57). Our results are similar to the ACL-SPORTS trial, which compared 10 sessions of strength, agility, and plyometric program with perturbation training, versus 10 sessions of the same program without perturbation training, at 6-months post-ACLR(1). Specifically, they reported a meaningful within-group change on the KOOS-Sport and KOOS-QoL (8 to 9 points) and minimal (< 2 points) between-group differences(1).
The small between-group differences in our study were possibly due to the large knee-related QoL improvements in the control (trunk-focussed) group. Improving trunk strength and endurance may have also resulted in a perceived improved performance in sport and work related activities, resulting in better QoL. Improvements in knee-related QoL may be more strongly influenced by education (provided in both groups), and less influenced by specific exercises in the lower-limb or trunk-focussed groups. In both groups, physiotherapists were able to educate participants and address psychological factors (e.g. kinesiophobia, fear, confidence), which are known determinants of adherence, recovery and self-reported outcomes after sports-related knee injury(27, 65). Fewer prescribed exercises in trunk-focussed group may provide greater time to provide educational and psychological support during the 1-to-1 sessions. The physiotherapists reported discussing patient and ACL-specific topics with the trunk-focussed participants, although directed not to do so in the study protocol. Future RCTs may consider evaluating the effects of a lower-limb focussed exercise-therapy with and without education, or comparing lower-limb focussed exercise-therapy and education (similar to the current study) with a comparator that better reflects usual care (e.g. self-directed education and exercise).
The small between-group differences also indicate that our lower-limb focussed intervention could be improved to deliver greater improvements in knee-related QoL. The KOOS-QoL scores remained lower than uninjured normative values(47), satisfaction with knee function was less than 70% in the lower-limb focussed group at follow-up, and side-hop improvements were small (< MID)(38, 55). Our low functioning participants may not have had sufficient time to progress to multidirectional plyometric exercises and improve function to an advanced level acceptable for return to jumping and pivoting sports. A longer intervention, with more frequent supervised sessions (either 1-to-1 or group exercise classes) may provide further opportunity for education, exercise technique feedback and progression. Given the potential benefits, dedicated time for education in 1-to-1 sessions, or during group exercise classes, similar to other effective exercise and education interventions (e.g. GLA:D® program for older individuals with knee OA(58)) should be considered. More time to discuss patient-specific goals, exercise preferences, and assess progress may enable exercise prescription to be individualised, and increase motivation and adherence.
Treatment effect: secondary subjective outcomes
A number of secondary PROs displayed more improvement in the lower-limb focussed group, including the KOOS-Sport subscale, GROC and PASS. The lower-limb focussed group had a 27% increase in people participating in Level 3 activities who were previously sedentary, as many participants commenced strength-training and running. Ongoing strength-training and running participation may be important for future knee-joint and overall health(16, 18), given a less active lifestyle and weight gain (i.e., increased BMI) is common after ACL injury(64), which may increase the risk of early OA progression(51, 70). Combined, the improvements in satisfaction, self-reported function and physical activity may reduce future healthcare use (e.g. pain medication, surgery).
Treatment effect: secondary objective outcomes performance
Clinically meaningful between-group differences favouring the lower-limb focussed group were observed for the single-hop and one-leg rise ACLR limb performance (24 cm and 10 repetitions, respectively) and LSI (16% and 16%, respectively). While the one-leg rise has no MID, a difference of 10 repetitions, and 16% on the LSI is considered clinically meaningful for other tests(38, 55). In the lower-limb focussed group, the LSI improvements for the single-hop (29%) were larger than those in the ACL-SPORTS trial (10%) with a similar intervention(1). This larger improvement we observed may be due the lower baseline function of our participants compared to the ACL-SPORTS trial where all participants had already achieved ≥ 80% LSI, begun running, and had no pain(1).
Our previous observational study(49) indicates that LSI improvement can reflect worsening contralateral limb function, rather than improved ACLR limb function. Therefore, it is important to note that in the current interventional study, LSI improvements occurred alongside clinically meaningful improvements in both limbs, indicating the increase in LSI was due to greater improvement in the ACLR limb. Given poor function on hop-tests at 1-year post-ACLR may be associated with an increased risk of future OA(48, 52) and reinjury(30), addressing persisent functional deficits may be an important step forward in secondary prevention of posttraumatic knee OA. Considering the influence of the lower-limb focussed intervention in this study on OA risk factors, future larger-scale trials should consider longer-term follow-up and include imaging assessment to determine structural joint trajectory and relationship with symptoms(15), physical activity monitoring, healthcare utilisation, and cost-effectiveness evaluation.
Given the small sample size, the estimated treatment effects in this study should not be intepreted as supporting one intervention over the other. A limitation of the current study is that the lower-limb focussed group started with worse QoL compared to the trunk-focussed group (Table 4). However, improvements in both groups were clinically meaningful, and no participants achieved the maximum KOOS-QoL and ACL-QoL score. Consistent with other ACLR cohorts(56) and RCTs(1), there was large individual variation in both groups for baseline scores (i.e., SDs) and changes between baseline and follow-up for all primary outcomes (Fig. 2), affecting our ability to identify between-group treatment effects. Future large-scale RCTs, including stratification for factors that may affect baseline status or treatment response (e.g. sex)(19) are now needed. We did not assess lower-limb or trunk strength so we cannot indicate if the improvements in functional performance or PROs were mediated by strength increases. Future trials should include muscle capacity (strength, power) testing, to also ensure that adequate loading and progression has occurred to stimulate muscle capacity improvements(9). Many participants (> 50%) had a surgical review during the trial, and were given “clearance for return-to-sport”, which may have improved PROs or physical activity in both groups. Future trials should regularly (weekly or monthly) monitor all types of physical activity completed during the intervention period. Despite these limitations, this was a pilot feasibility study, with the purpose of recognizing improvements that could be made to the study design and protocols for future trials.