Functional testing following isolated meniscus repair may help to identify patients who need additional physical therapy prior to a return to activity

A R T I C L E I N F O


INTRODUCTION
Tearing of the meniscus, especially the medial meniscus, can lead to compromised knee stability [1,2].Anterior cruciate ligament (ACL)-deficient knees rely on the meniscus for stability, demonstrating that rotatory stabilisation is a function of the meniscus [3][4][5].The torn meniscus also plays a role in faulty proprioception, impairing the ability of the body to perceive the relative position of the knee [6].An unstable knee and one with impaired proprioception caused by a meniscus tear can lead to degenerative changes in the knee [2,7].Restoring meniscal function in the setting of meniscal tearing is therefore important to the long-term health of the knee.
Surgery on the meniscus is one of the most frequent surgical procedures performed by orthopedic surgeons [8][9][10].When the meniscal tear pattern allows for a meniscal repair, it is ideal to proceed with a repair in order to restore the meniscal function to the best degree possible.Baseline criteria, in the literature, for returning to activity after a meniscal repair include absence of an effusion, full range of motion (ROM) status, and good quadriceps control and strength [11,12].However, given the meniscal properties described earlier, it is also important to restore neuromuscular function to the knee following meniscal repair.Return to activity and neuromuscular functional assessment following meniscal repair is an area in which there is limited literature available.
This institution uses functional testing (FT) that includes hop testing and proprioception tests to assess neuromuscular function prior to a return to activity for multiple post-surgical situations, including meniscal repair and ACL reconstruction.In ACL reconstructions, FT, including hop testing, has been used to evaluate progress during rehabilitation and to identify limb asymmetry [13][14][15][16][17].
The main purpose of this study was to assess the utility of FT as an assessment tool for rehabilitation following meniscal repair.In addition, this study sought to evaluate the timeline for when FT demonstrates return to limb symmetry and compare this to a population of ACL reconstruction patients.The authors hypothesised that the FT would identify patients who have residual neuromuscular deficits but that meniscal repair patients would perform similar to ACL reconstruction patients at an earlier post-operative time-point.

MATERIALS AND METHODS
This study received institutional review board approval under federal guidelines 45 CFR Part 46.110 category (5), research involving no more than minimal risk.A retrospective review was conducted of all patients who underwent an isolated meniscus repair for a peripheral, vertical meniscal tear, either medial or lateral, at our ambulatory surgery center over a two-year period.All patients who completed FT at this institution during post-operative rehabilitation were identified.Only patients who completed the entire FT protocol specific to this institution were included to ensure the same testing protocol for all patients.Performances of the involved and uninvolved limbs, as well as the limb symmetry index (LSI), were recorded.LSI is calculated as the mean score of the involved limb divided by the mean score of the uninvolved limb, with the result multiplied by 100.An LSI score of 90% is required for a passing score at our institution, which is higher than the 85% in validated studies in the ACL population [13,18,19].This institution's FT protocol involves 11 individual test exercises: core plank, single-leg bridge, single-leg reach in the anterior/lateral and anterior/medial planes, single-leg squat, retro step up, stork stance (proprioception), single-leg hop, triple hop, crossover triple hop, and timed hop.Physical therapists supervise the patients while they are performing the FT.For ACL reconstruction patients, FT is performed when the therapist feels the patient has adequately progressed in their rehabilitation to safely participate in FT; this typically occurs roughly 6 months post-operatively.The patient's performance on the FT is then used to aid in decision-making for a return to activity.This same rehabilitation progression criterion was used for the isolated meniscal repair patients as well.Based on therapists' observation, an appropriate timepoint for FT in most isolated meniscal repair patients was felt to be 4 months post-op.
Single-leg bridge is performed when the patient lies supine with knees flexed; one leg is lifted off the floor, and the patient raises back off the floor for 2 s.This is counted as one repetition.Measurements are recorded out of 20 reps.Stand-and-reach tests are performed with the patient standing on one leg and reaching toward the ground with the opposite hand either anterior/medial reach or anterior/lateral reach.Measurements are recorded as distance in cm for each leg from the foot on the ground.Single-leg squat is performed with the patient standing on one leg; the patient squats down to maximal depth and returns to standing.Angle of knee flexion in degrees at maximal squat depth is recorded.Retro step up is performed when a patient steps backwards with one leg onto a step and then controls stepping back down.Various step heights are used, and the maximal step height achieved per leg is recorded.Proprioception is performed with the patient standing on one leg with eyes open.Time to failure up until 60 s is recorded.In single-leg hop the patient stands on one leg and jumps as far as possible with a controlled landing.The maximal distance from start to finish in one jump is measured.Triple hop and crossover hop are performed with 3 consecutive jumps on one leg, one a regular single-leg jump and one with a crossover jump.The maximal distance from start to finish in 3 jumps is measured.Single-leg timed hop is performed with the patient standing on one leg and hopping 6 m as quickly as possible sticking every landing.The quickest time per leg is recorded.
Since these tests are not typically used in the isolated meniscus-repair population but have been well studied in the ACL reconstruction population, the isolated meniscal repair patients were compared to a cohort of ACL reconstruction patients that was matched to the meniscal cohort for age and body mass index (BMI).Based on physical therapist assessment of patients' ability to safely undergo FT, isolated meniscal repair patients were able to undergo testing at roughly 4 months, with some testing completed earlier.ACL reconstruction patients were typically able to undergo the testing at roughly 6 months.For ACL reconstruction patients, this is also consistent with previous literature suggesting that 6 months post operation is an appropriate time when many ACL reconstruction patients may undergo FT [18,20].Therefore, inclusion criteria for the meniscus group were all isolated meniscal repair patients who underwent FT at our institution between 80 and 150 days post-operation during the study period (to represent an average of 4 months post-op).Inclusion criteria for the ACL group were an isolated ACL reconstruction, followed by FT between 151 and 220 days post-operation at our institution (to represent an average of 6 months post-op).The ACL patients were identified over the course of 2 years during the same study period as for the meniscal repair patients.All FT was performed at the same institution.

Statistical analysis
Comparison between meniscal and ACL groups, for each aspect of the functional test, was calculated using a 2-tailed unpaired t-test, with significance being p < 0.05.

RESULTS
A total of 26 patients who underwent an isolated meniscal repair fulfilled our inclusion criteria (Table 1).In this group, there were 19 males and 7 females.The average age at the time of surgery was 21.9, and the average BMI at surgery was 25.7.Eight of the patients had a lateral meniscus repair, 17 had a medial meniscus repair, and one had simultaneous medial and lateral meniscus repairs.A total of 39 patients met inclusion criteria for the ACL cohort.There were 19 males and 20 females in this group.The average age at surgery was 22.8, and BMI was 25.1.There were no statistically significant differences in age (p ¼ 0.88) or BMI (p ¼ 0.18) between the two cohorts; there were more females in the ACL cohort.The average time from surgery to FT for the meniscus cohort was 111 days with a standard deviation (SD) of 22.2 days and was 181 days with an SD of 23.0 days for the ACL cohort.
For the meniscus cohort on the four hop tests, there were multiple patients who did not meet the 90% LSI-score mark: this included 30% of patients for single-leg hop, 29% for single-leg crossover triple hop, 36% for single-leg triple hop for distance, and 20% for single-leg timed hop (Table 2).The parameter with the greatest number of patients not achieving 90% LSI-score mark was the retro step up, with 45% of patients not achieving that cut-off.
There were no statistically significant differences in average LSI scores between the meniscus and ACL cohorts for all non-hop tests: single-leg bridge, single-leg squat, single-leg reach anterior/lateral, single-leg reach anterior/medial, eyes-open proprioception, and retro step up (Table 3).For the meniscus cohort, the average LSI score was > 90 for most tests; however, it was <90 in single-leg squat (88.4) and retro step up (89.4).Similar results were found in the ACL cohort, where the average LSI score was <90 only in retro step (84.5) up.
There were no statistically significant differences between the cohorts for any of the four hop tests.Single-leg hop showed the largest deficits of the four hop tests in both cohorts (Table 3).

DISCUSSION
The most important finding of this study is that all but two of the mean LSI scores for the meniscus patients were above 90%, indicating that, on average, meniscal repair patients have good improvement in neuromuscular function by 4 months post operation.Additionally, the meniscus-repair patients who are 4 months post-operative scored similarly to the ACL reconstruction patients who are 6 months post-operative.This suggests that isolated meniscal repair patients may be able to return to activity earlier than ACL reconstruction patients.An important caution on timing, however, is that despite the finding that many of the meniscal repair patients performed well on FT at 4 months post operation, there were some who did not perform well.This can indicate that having isolated meniscal repair patients perform FT may be helpful in the evaluation of return to activity and that those patients may need to undergo further physical therapy prior to a return to sports.This study has begun to address how patients perform functionally before they return to their activity following isolated meniscus repair.
LSI scores and raw involved-leg average scores demonstrate that at 4 months post operation from an isolated meniscus repair, patients generally perform well on a functional test.The lowest LSI average score was in retro step up and single-leg hop, which were below 90% but above 85%.Based on this data, for isolated meniscal repair patients who have been diligent with rehabilitation, 4 months may be a reasonable timepoint to consider a return to activity.
ACL reconstruction patients undergoing FT at 6 months post operation generally performed well on FT but still had some asymmetry demonstrated by an LSI score of <90% in retro step up (84.5%) and single-leg hop (89.9%).These findings are consistent with previous literature [16,17,[21][22][23].Since there were minimal differences between the 6-month ACL patients and the meniscal repair patients, it is reasonable to conclude that meniscal repair patients generally rehabilitate to a similar functional level at an earlier time-point than ACL reconstruction patients.
The FT has most commonly been used to determine return to activity following an ACL reconstruction [11].While the ACL plays a clear role in neuromuscular function, it is likely that the meniscus also plays a role in neuromuscular function around the knee since the menisci function in transmitting load, shock absorption, proprioception, and joint stability [6,7,[24][25][26].Further evidence for this is that in ACL-deficient knees, the menisci play a larger role in the overall stability of the joint [1,4,5,27].Therefore, being able to detect deficiencies in neuromuscular function about the knee following an isolated meniscus repair is important to determine a patient's readiness for return to activity and risk of re-injury.Our data suggest that FTs can provide insight into these deficiencies.Despite the fact that many patients who underwent a meniscus repair performed well on the FT at 4 months post operation, there were some who did not, and these patients would likely benefit from further rehabilitation prior to a return to activity.In addition, some of the meniscal repair patients at the authors' facility were excluded from the study because they were not felt to be ready for FT by the physical therapist at a time-point that fit into the 4-month window for this cohort.This unfortunately is a flaw in the study we could not control, given the decision to proceed with FT is at the discretion of the physical therapist.This suggests, however, that there are additional meniscal repair patients not included in this study who would benefit from post-operative evaluation usingFT.Future research, in the form of a prospective study, would be valuable to determine if the evaluation of FT in isolated meniscal repair patients prior to a return to activity reduces re-injury rates or allows them to return to activity at a higher level of performance.
Limitations of this study include its retrospective nature.Because of this, there was some variability in post-operative timing of each FT between patients due to differing progression in their rehabilitative therapy.Attempts to ameliorate this, by limiting the included patients to a specified range of post-operative time-points, were made.In addition, because of the retrospective nature of the study, we are not able to report how many patients were not included in the study because they completed FT outside of the specified post-operative window or were not felt to be ready for FT within the specified post-operative window.When comparing the meniscal and ACL cohorts, there was a difference based on sex.We attempted to fully match the cohorts; however, it was not possible to match age, BMI, and sex in retrospective data, so emphasis was placed on age and BMI.Both medial and lateral meniscal repair patients were included, and it is possible that the neuromuscular function of each meniscus is different.In terms of the meniscal repair and ACL reconstruction comparison, it is possible that it is underpowered.The primary goal of that analysis was to put meniscal repair patients' return of function on the timeline of the much better researched timeline of ACL reconstruction patients.A final important factor to take into consideration is the comparison between ACL reconstruction rehabilitation and meniscus rehabilitation.Both structures serve different primary functions, and the rehabilitation is therefore different; however, there are similarities as well since both protocols inherently focus on strength, ROM, proprioception, and stability [18,[28][29][30][31][32][33][34][35].

CONCLUSION
A majority of isolated meniscal repair patients perform well on FT by 4 months post-operatively and similar to patients undergoing isolated ACL reconstruction at 6 months post-operatively.Not all patients performed well on FT at 4 months post-operatively however, so there may be a role for FT in isolated meniscal repair patients, and those patients may need further PT prior to a return to sports.

Table 1
Patient demographic information and number in meniscus and anterior cruciate ligament cohorts.

Table 2
Average involved leg, uninvolved leg, and Limb Symmetry Index scores for the meniscus cohort only.

Table 3
Average Limb Symmetry Index scores for each of the two cohorts.p-values under anterior cruciate ligament cohorts are values compared to the meniscus cohorts (with 95% confidence intervals).