TIMELINE OF GAINS IN QUADRICEPS STRENGTH SYMMETRY AND PATIENT-REPORTED FUNCTION EARLY AFTER ACL RECONSTRUCTION

Strength of the Uninvolved Limb Following Return to Activity After ACL Injury: Implications for Symmetry as a Marker of Sufficient Strength

Background

Muscular strength deficits are common after ACL injury. While the Limb Symmetry Index (LSI), using the uninvolved limb as a reference, is widely used, negative strength adaptations may affect both limbs post-injury. It is uncertain how the strength of the uninvolved limb in those with an ACL injury compares to uninjured individuals, making it unclear whether it is appropriate as a benchmark for determining sufficient strength.

Purpose

To compare the strength of key lower extremity muscles of the uninvolved limb in those with history of ACL injury (ACL-I) to the dominant limb in individuals with no history of ACL injury (control).

Study Design

Cross-sectional study. Methods: A total of 5,727 military cadets were examined, with 82 females and 126 males in the ACL-I group and 2,146 females and 3,373 males in the control group. Maximum isometric strength was assessed for six muscle groups measured with a hand-held dynamometer. Separate two-way ANOVAs with limb and sex were performed for each muscle group.

Results

Significant main effects for limb were observed with the uninvolved limb in the ACL-I group displaying greater strength compared to the dominant limb in the control group for the quadriceps, hamstrings, and gluteus medius, but effect sizes were small (Cohen's d <0.25). Significant main effects for sex were observed with greater male muscular strength in all six muscle groups with small to large effect sizes (Cohen's d 0.49-1.46). No limb-by-sex interactions were observed.

Conclusions

There was no evidence of reduced strength in the uninvolved limb in those with a history of ACL injury compared to the dominant limb in those with no prior ACL injury. This finding suggests that, after clearance to return to activities, the uninvolved limb can be used as a standard for comparison of sufficient strength, including when using the LSI. Level of Evidence: Level 3.

Does It Matter? Isometric or Isokinetic Assessment of Quadriceps Strength Symmetry 9 Months After ACLR in Collegiate Athletes

BACKGROUND

Greater quadriceps strength symmetry is associated with better outcomes after anterior cruciate ligament reconstruction (ACLR). Isometric and isokinetic assessments of quadriceps strength inform therapeutic exercise prescription and return-to-sport decisions. It is unclear whether isometric and isokinetic measures provide similar information post-ACLR.

HYPOTHESIS

Quadriceps strength symmetry is similar between isometric and isokinetic assessments. Isokinetic and isometric strength symmetries have similar associations to functional knee kinetics and self-reported knee function.

STUDY DESIGN

Cross-sectional study.

LEVEL OF EVIDENCE

Level 3.

METHODS

NCAA Division I athletes (N = 35), 8.9 ± 2.5 months post-ACLR completed isometric and isokinetic quadriceps strength assessments, countermovement jumps (CMJs), and treadmill running. Self-reported knee function was assessed using the International Knee Documentation Committee Subjective Knee Form (IKDC). Agreement between isometric and isokinetic strength symmetry was assessed using Bland-Altman analysis, with associations to functional knee kinetics and IKDC assessed using Pearson correlations and linear regressions.

RESULTS

Mean difference in quadriceps strength symmetry between isokinetic and isometric assessments was 1.0% (95% limits of agreement of -25.1% to 23.0%). Functional knee kinetics during running and CMJ were moderately to strongly associated with isometric strength symmetry (r = 0.64-0.80, P < 0.01) and moderately associated with isokinetic strength symmetry (r = 0.41-0.58, P < 0.01). IKDC scores were weakly to moderately associated with isometric (r = 0.39, P = 0.02) and isokinetic (r = 0.49, P < 0.01) strength symmetry.

CONCLUSION

Isokinetic and isometric assessments of quadriceps strength symmetry in collegiate athletes 9 months post-ACLR demonstrated strong agreement. Quadriceps strength symmetry is associated with functional knee kinetic symmetry post-ACLR.

CLINICAL RELEVANCE

Considerable individual variation suggests mode of contraction should be consistent throughout postoperative assessment. Isometric strength symmetry may be a better indicator of functional knee kinetic symmetry, while isokinetic strength symmetry may be associated more closely with patient-reported outcomes.

Outcomes of Blood Flow Restriction Training After ACL Reconstruction in NCAA Division I Athletes

Background

Blood flow restriction training (BFRT) is a safe and potentially effective adjunctive therapeutic modality for postoperative rehabilitation related to various knee pathologies. However, there is a paucity of literature surrounding BFRT in high-performance athletes after anterior cruciate ligament reconstruction (ACLR).

Purpose

To (1) compare the overall time to return to sports (RTS) in a cohort of National Collegiate Athletic Association (NCAA) Division I athletes who underwent a standardized rehabilitation program either with or without BFRT after ACLR and (2) identify a postoperative time interval for which BFRT has the maximum therapeutic benefit.

Study Design

Cohort study; Level of evidence, 3.

Methods

A total of 55 student-athletes who underwent ACLR between 2000 and 2023 while participating in NCAA Division I sports at a single institution were included in this study. Athletes were allocated to 1 of 2 groups based on whether they participated in a standardized postoperative rehabilitation program augmented with BFRT (BFRT group; n = 22) or completed the standardized protocol alone (non-BFRT group [control]; n = 33). Our primary outcome measure was time to RTS. The secondary outcome measure was handheld dynamometry quadriceps strength testing at various postoperative time points, converted to a limb symmetry index (LSI). Quadriceps strength was not tested between the BFRT and non-BFRT groups because of the limited amount of data on the control group.

Results

The mean age at the date of surgery was 18.59 ± 1.10 years for the BFRT group and 19.45 ± 1.30 years for the non-BFRT group (P = .011), and the mean RTS time was 409 ± 134 days from surgery for the BFRT group and 332 ± 100 days for the non-BFRT cohort (P = .047). For the BFRT group, the mean quadriceps strength LSI increased by 0.67% (95% CI, 0.53%-0.81%) for every week of rehabilitation, and there was a significantly positive rate of change in quadriceps strength in weeks 13-16 compared with weeks 9-12 (ΔLSI, 8.22%; P < .001).

Conclusion

In elite NCAA Division I athletes, a statistically significant delay was observed in RTS with BFRT compared with standardized physical therapy alone after undergoing ACLR. There also appeared to be an early window during the rehabilitation period where BFRT had a beneficial impact on quadriceps strength.

Comparison of Blood Flow Restriction Interventions to Standard Rehabilitation After an Anterior Cruciate Ligament Injury: A Systematic Review

BACKGROUND

Blood flow restriction training (BFR-t) data are heterogeneous. It is unclear whether rehabilitation with BFR-t after an anterior cruciate ligament (ACL) injury is more effective in improving muscle strength and muscle size than standard rehabilitation.

PURPOSE

To review outcomes after an ACL injury and subsequent reconstruction in studies comparing rehabilitation with and without BFR-t.

STUDY DESIGN

Systematic review. Level of evidence, 3.

METHODS

A search of English-language human clinical studies published in the past 20 years (2002-2022) was carried out in 5 health sciences databases, involving participants aged 18-65 undergoing rehabilitation for an ACL injury. Outcomes associated with muscle strength, muscle size, and knee-specific patient-reported outcome measures (PROMs) were extracted from studies meeting inclusion criteria and compared.

RESULTS

The literature search identified 279 studies, of which 5 met the selection criteria. Two studies suggested that BFR-t rehabilitation after an ACL injury improved knee or thigh muscle strength and muscle size compared with rehabilitation consisting of comparable and higher load resistance training, with two studies suggesting the opposite. The single study measuring PROMs showed improvement compared to traditional rehabilitation, with no difference in muscle strength or size.

CONCLUSION

BFR-t after an ACL injury seems to benefit muscle strength, muscle size, and PROM scores compared with standard rehabilitation alone. However, only 1 large study included all these outcomes, which has yet to be replicated in other settings. Further studies utilizing similar methods with a common set of outcome measures are required to confirm the effects of BFR-t on ACL rehabilitation.

Beware of the "Moving Target" - Uninvolved Limb Strength Increases to Exceed Preoperative Values During Rehabilitation After ACL Reconstruction in Male Professional and Recreational Athletes

OBJECTIVE: To describe the changes in quadriceps and hamstrings muscle strength in the uninvolved limb of male professional and recreational athletes during rehabilitation after anterior cruciate ligament reconstruction (ACLR) and compare to preoperative strength values. DESIGN: Prospective longitudinal study. METHODS: During rehabilitation, 665 participants who underwent unilateral ACLR performed a strength test preoperatively and every 6 weeks after surgery for up to 9 months. Isokinetic quadriceps and hamstrings strength of the uninvolved limb were measured at an angular velocity of 60°/s and normalized to body weight (N·m/kg). RESULTS: Quadriceps and hamstrings strength of the uninvolved limb gradually increased during rehabilitation until 6 months post-ACLR, and plateaued thereafter. Postoperative quadriceps' strength significantly exceeded preoperative values by 3 months for professional (2.99 N·m/kg; 95% confidence interval [CI]: 2.93, 3.04; P = .007) and by 6 months for recreational athletes (2.77 N·m/kg; 95% CI: 2.71, 2.83; P<.001), and hamstrings exceeded presurgery levels by 4.5 months (1.71 N·m/kg; 95% CI: 1.67, 1.74; P<.001 and 1.43 N·m/kg; 95% CI: 1.40, 1.46; P = .002, professional and recreational athletes respectively). CONCLUSION: In male professional and recreational athletes, uninvolved limb quadriceps and hamstrings strength gradually improved after ACLR, until 6 months after surgery. The uninvolved limb's strength may present as a "moving target" that requires consistent monitoring during rehabilitation. J Orthop Sports Phys Ther 2024;54(4):1-9. Epub 14 December 2023. doi:10.2519/jospt.2023.11961.

Effects of a Perioperative Blood Flow Restriction Therapy Program on Early Quadriceps Strength and Patient-Reported Outcomes After Anterior Cruciate Ligament Reconstruction

Background

Quadriceps muscle atrophy remains a limiting factor in returning to activity after anterior cruciate ligament reconstruction (ACLR). Blood flow restriction (BFR) therapy may accelerate quadriceps strengthening in the perioperative period.

Purpose

To evaluate postoperative isometric quadriceps strength in patients who underwent ACLR with a perioperative BFR program.

Study Design

Randomized controlled trial; Level of evidence, 1.

Methods

Patients indicated for ACLR were randomized into 2 groups, BFR and control, at their initial clinic visit. All patients underwent 2 weeks of prehabilitation preoperatively, with the BFR group performing exercises with a pneumatic cuff set to 80% limb occlusion pressure placed over the proximal thigh. All patients also underwent a standardized postoperative 12-week physical therapy protocol, with the BFR group using pneumatic cuffs during exercise. Quadriceps strength was measured as peak and mean torque during seated leg extension and presented as quadriceps index (percentage vs healthy limb). Patient-reported outcomes (PROs), knee range of motion, and quadriceps circumference were also gathered at 6 weeks, 3 months, and 6 months postoperatively, and adverse effects were recorded.

Results

Included were 46 patients, 22 in the BFR group (mean age, 25.4 ± 10.6 years) and 24 in the control group (mean age, 27.5 ± 12.0 years). At 6 weeks postoperatively, the BFR group demonstrated significantly greater strength compared with the controls (quadriceps index: 57% ± 24% vs 40% ± 18%; P = .029), and the BFR group had significantly better Patient-Reported Outcomes Measurement Information System-Physical Function (42.69 ± 5.64 vs 39.20 ± 5.51; P = .001) and International Knee Documentation Committee (58.22 ± 7.64 vs 47.05 ± 13.50; P = .011) scores. At 6 weeks postoperatively, controls demonstrated a significant drop in the peak torque generation of the operative versus nonoperative leg. There were no significant differences in strength or PROs at 3 or 6 months postoperatively. Three patients elected to drop out of the BFR group secondary to cuff intolerance during exercise; otherwise, no other severe adverse events were reported.

Conclusion

Integrating BFR into perioperative physical therapy protocols led to improved strength and increased PROs at 6 weeks after ACLR. No differences in strength or PROs were found at 3 and 6 months between the 2 groups.

Registration

NCT04374968 (ClinicalTrials.gov identifier).

Blood Flow Restriction Therapy for 2 Weeks Prior to Anterior Cruciate Ligament Reconstruction Did Not Impact Quadriceps Strength Compared to Standard Therapy

PURPOSE

To evaluate the efficacy of a 2-week home-based blood flow restriction (BFR) prehabiliation program on quadriceps strength and patient-reported outcomes prior to anterior cruciate ligament (ACL) reconstruction.

METHODS

Patients presenting with an ACL tear were randomized into two groups, BFR and control, at their initial clinic visit. Quadriceps strength was measured using a handheld dynamometer in order to calculate peak force, average force, and time to peak force during seated leg extension at the initial clinic visit and repeated on the day of surgery. All patients were provided education on standardized exercises to be performed 5 days per week for 2 weeks between the initial clinic visit and date of surgery. The BFR group was instructed to perform these exercises with a pneumatic cuff set to 80% of limb occlusion pressure placed over the proximal thigh. Patient-Reported Outcome Measurement System Physical Function (PROMIS-PF), knee range of motion, and quadriceps circumference were gathered at the initial clinic visit and day of surgery, and patients were monitored for adverse effects.

RESULTS

A total 45 patients met inclusion criteria and elected to participate. There were 23 patients randomized to the BFR group and 22 patients randomized into the control group. No significant differences were noted between the BFR and control groups in any demographic characteristics (48% vs 64% male [P = .271] and average age 26.5 ± 12.0 vs 27.0 ± 11.0 [P = .879] in BFR and control, respectively). During the initial clinic visit, there were no significant differences in quadriceps circumference, peak quadriceps force generation, time to peak force, average force, pain, and PROMIS scales (P > .05 for all). Following completion of a 2-week home prehabilitation protocol, all patients indeterminant of cohort demonstrated decreased strength loss in the operative leg compared to the nonoperative leg (P < .05 for both) However, there were no significant differences in any strength or outcome measures between the BFR and control groups (P > .05 for all). There were no complications experienced in either group, and both were compliant with the home-based prehabilitation program.

CONCLUSIONS

A 2-week standardized prehabilitation protocol preceding ACL reconstruction resulted in a significant improvement in personal quadriceps peak force measurements, both with and without the use of BFR. No difference in quadriceps circumference, strength, or patient reported outcomes were found between the BFR and the control group. The home-based BFR prehabiliation protocol was found to be feasible, accessible, and well tolerated by patients.

LEVEL OF EVIDENCE

Level II, randomized controlled trial with small effect size.

Predictors of Quadriceps Strength Asymmetry after Anterior Cruciate Ligament Reconstruction: A Chi-Squared Automatic Interaction Detection Decision Tree Analysis

INTRODUCTION

The influence of graft type on the restoration of quadriceps strength symmetry after ACL reconstruction (ACLR) has been widely studied. However, an important consideration when evaluating quadriceps symmetry is the fact that this measure can be influenced by numerous factors beyond graft type. This study sought to determine if graft type is predictive of quadriceps strength asymmetry during the first 12 months post-ACLR taking into consideration potentially influential factors (i.e., age, sex, body mass index, time post-ACLR).

METHODS

We retrospectively reviewed quadriceps strength data from 434 patients (303 female patients and 131 male patients) who had previously undergone ACLR with an autograft (hamstring tendon, quadriceps tendon [QT], patellar tendon [PT]) or allograft. Chi-Squared Automatic Interaction Detection decision tree analysis was used to evaluate if graft type is predictive of quadriceps strength asymmetry during the first 12 months post-ACLR taking into consideration age, sex, body mass index, and time post-ACLR.

RESULTS

The best predictor of quadriceps strength asymmetry was graft type. Specifically, three graft categories were identified: 1) allograft and hamstring tendon autograft, 2) PT autograft, and 3) QT autograft. The average quadriceps strength asymmetry for each of the three identified categories was 0.91, 0.87, and 0.81, respectively, and differed statistically from each other ( P < 0.001). The second-best predictor of quadriceps strength asymmetry was sex, albeit only in the PT and QT groups (with female patients having increased asymmetry). Female patients post-ACLR with a QT autograft were at highest risk for quadriceps strength asymmetry.

CONCLUSIONS

Graft type and sex are important predictors of quadriceps strength asymmetry after ACLR. Clinicians should take these factors into consideration when designing rehabilitation protocols to restore quadriceps strength symmetry during the postoperative period.

Range of Motion, Strength, and Function After ACL Reconstruction Using a Contralateral Patellar Tendon Graft

BACKGROUND

Regaining preinjury levels of activity and progressing rehabilitation factors after anterior cruciate ligament (ACL) reconstruction have shown mixed results.

PURPOSE

To evaluate the timing and rate of return for knee range of motion (ROM), stability, strength, and subjective scores after ACL reconstruction with contralateral patellar tendon graft (PTG).

STUDY DESIGN

Case series; Level of evidence, 4.

METHODS

Included were 2148 patients (1238 male patients, 910 female patients) who underwent primary ACL reconstruction with a contralateral PTG between 1995 and 2017 and had complete objective data through 3 months of follow-up. All patients participated in a rehabilitation program specific to goals for each knee. Patients were evaluated objectively with goniometric measurement of ROM, isokinetic quadriceps strength testing, and laxity with a KT-2000 arthrometer. Subjective data were collected at 2 and 5 years.

RESULTS

Normal extension on the reconstructed knee was attained for 95% of patients at 1 week postoperatively; normal flexion on the reconstructed knee was reached by 77% of patients by 3 months. At 3 months postoperatively, mean limb symmetry index strength was 104%, and the strength on the ACL-reconstructed and graft-donor knees was 87% and 86% of their respective preoperative strength. Mean manual maximum side-to-side difference in laxity was 2.0 mm at 1 month. Most patients (90%) returned to level 8 sports or higher and did so at an average of 5.7 months. Mean International Knee Documentation Committee scores for the ACL-reconstructed and graft-donor knees were 89 and 91 at 2 years (n = 1015 patients) and 84 and 90 at 5 years (n = 1275 patients), respectively. Mean Cincinnati Knee Rating Scale scores for the ACL-reconstructed and graft-donor knees were 92 and 96 at 2 years (n = 1184) and 88 and 94 at 5 years (n = 1236), respectively.

CONCLUSION

For patients who underwent ACL reconstruction with a contralateral PTG, postoperative ROM and strength were restored quickly by splitting the rehabilitation into different goals between the two knees. Using a contralateral PTG, this structured rehabilitation plan can lead to a relatively quick return to sport and good subjective long-term outcomes.

Quadriceps Strength following Anterior Cruciate Ligament Reconstruction: Normative Values based on Sex, Graft Type and Meniscal Status at 3, 6 & 9 Months

Background

Higher postoperative quadriceps function has been positively associated with surgical outcomes after anterior cruciate ligament reconstruction (ACLR). However, the impact of autograft harvest and/or a concomitant meniscal procedure on the recovery of quadriceps strength is not well defined.

Purpose

To describe postoperative recovery of quadriceps strength following ACLR related to autograft selection, meniscal status, and sex.

Study Design

Retrospective Cohort.

Methods

One hundred and twenty-five participants who underwent ACLR with either a hamstring tendon (HT), bone-patellar tendon-bone (BPTB) or quadriceps tendon (QT) autograft were included. At postoperative months 3, 6 and 9, each participant completed an isometric quadriceps strength testing protocol at 90-degrees of knee flexion. Participants' quadriceps average peak torque (Q-AvgPKT), average peak torque relative to body weight (Q-RPKT), and calculated limb symmetry index (Q-LSI) were collected and used for data analysis. Patients were placed in groups based on sex, graft type, and whether they had a concomitant meniscal procedure at the time of ACLR. At each time point, One-way ANOVAs, independent samples t-test and chi-square analyses were used to test for any between-group differences in strength outcomes.

Results

At three months after ACLR, Q-RPKT was significantly higher in those with the HT compared to the QT. At all time points, males had significantly greater Q-RPKT than females and HT Q-LSI was significantly higher than BPTB and QT. A concomitant meniscal procedure at the time of ACLR did not significantly affect Q-LSI or Q-RPKT at any testing point.

Conclusion

This study provides outcomes that are procedure specific as well as highlights the objective progression of quadriceps strength after ACLR. This information may help better-define the normal recovery of function, as well as guide rehabilitation strategies after ACLR.

Level of Evidence

3.

Arthrogenic Muscle Inhibition Following Anterior Cruciate Ligament Injury

Arthrogenic muscle inhibition (AMI) is a common impairment in individuals who sustain an anterior cruciate ligament (ACL) injury. The AMI causes decreased muscle activation, which impairs muscle strength, leading to aberrant movement biomechanics. The AMI is often resistant to traditional rehabilitation techniques, which leads to persistent neuromuscular deficits following ACL reconstruction. To better treat AMI following ACL injury and ACL reconstruction, it is important to understand the specific neural pathways involved in AMI pathogenesis, as well as the changes in muscle function that may impact movement biomechanics and long-term structural alterations to joint tissue. Overall, AMI is a critical factor that limits optimal rehabilitation outcomes following ACL injury and ACL reconstruction. This review discusses the current understanding of the: (1) neural pathways involved in the AMI pathogenesis following ACL injury; (2) consequence of AMI on muscle function, joint biomechanics, and patient function; and (3) development of posttraumatic osteoarthritis. Finally, the authors review the evidence for interventions specifically used to target AMI following ACL injury.

Limb preference impacts single-leg forward hop limb symmetry index values following ACL reconstruction

Following anterior cruciate ligament (ACL) reconstruction limb dominance for performing tasks is not considered when making rehabilitation progression decisions. The purpose of this study was to determine if strength and functional outcomes differ between individuals who injured their preferred or nonpreferred jumping limb and to determine if these same outcomes differ between individuals who injured their preferred or nonpreferred limb used to kick a ball. A secondary purpose was to determine the association of quadriceps strength and single-leg forward hop performance with patient self-reported function. Forty individuals with ACL reconstruction (age = 20.0 ± 4.6 years, height = 174.2 ± 12.7 cm, mass = 71.2 ± 12.7 kg, time since surgery = 5.3 ± 0.8 months) were included in the study. Primary outcome measures included, International Knee Documentation Committee Subjective Knee Form (IKDC) scores, quadriceps limb symmetry index (LSI) values, and single-leg forward hop LSI values. Limb preference was defined two ways, kicking a ball and performing a unilateral jump. There were no significant differences between groups based on injury to the preferred limb to kick a ball for any of the outcome variables. Individuals who injured their nonpreferred jumping limb demonstrated significantly (p = 0.05, d = 0.77) lower single-leg forward hop LSI values (81.1% ± 19.5%) compared to individuals who injured their preferred jumping limb (94.1% ± 12.6%), but demonstrated no differences in IKDC scores or quadriceps LSI values. Quadriceps LSI and single-leg forward hop LSI explained 73% of the variance in IKDC scores, but quadriceps LSI had the strongest association (r = 0.790). These findings suggests that limb preference influences single forward hop LSI values and should be considered following ACL reconstruction.