Lower Extremity Limb Symmetry Index in Individuals With Knee Soft Tissue Injuries: A Cross-Sectional Study

INTRODUCTION

The knee is the largest and most intricately designed joint in the body, often injured due to physical activity and sports participation, which may contribute to long-term disability and influence the socioeconomic system.^[1] Knee Injury incidence is 2.3/1000 on average, with the highest rate among those aged 15-24.^[1,2] Knee soft tissue injuries, such as anterior cruciate ligament (ACL), posterior cruciate ligament (PCL), and meniscal injuries, often lead to long-term functional impairments, reduced performance, and increased risk of reinjury.^[3,4] Following a knee injury, functional deficits like strength, balance, and the ability to jump are compromised.^[4] These functional deficits can be assessed by using the limb symmetry index (LSI).^[5] LSI quantifies differences in limb function, which includes strength, balance, and jumping ability, and serves as an essential criterion in the conservative management of knee soft tissue injuries in determining decision-making on return-to-activity.^[6,7]

During conservative management of knee soft tissue injuries, LSI is measured by comparing the standardised functional testing (SFT) performance of the injured limb to that of the uninjured limb, where the uninjured limb is taken as a reference.^[7] This SFT includes several tests that combine intricate kinetic chain motions to replicate the demands of sports more accurately.^[8] SFT includes hop tests to evaluate functional capacities, encompassing neuromuscular control, strength, and limb confidence.^[3,9] By using hop tests as a predictive tool, clinicians may be able to identify patients more susceptible to future problems related to knee injuries.^[10]

Clinicians usually compare functions between both limbs by calculating LSI and categorising bilateral limb differences as either symmetrical or asymmetrical. It has a range of 0% to 100%, where 0% indicates total functional asymmetry and 100% indicates total functional symmetry among the limbs.^[11] Before an individual returns to activity, their injured limb needs to function at 80% of the level of their healthy and uninjured limb.^[11,12] The hop test is frequently used for calculating LSI and determining whether the patient can resume their normal activities following knee injuries.^[13]

Early detection of limb asymmetrical variations may reduce potential complications or the risk of long-term issues. Research indicates a healthy population’s LSI is 90% or more symmetrical between both limbs. However, there is a scarcity of robust studies exploring the use of the hop test to determine LSI in patients with knee injuries who have undergone conservative management.^[11]

Therefore, the current study aims to find out the LSI in patients with conservatively managed knee soft tissue injuries and investigate functional asymmetries between the injured and uninjured limbs using the hop test. The results of this study can be beneficial in evidence-based rehabilitative methods so that the patients can reach their fullest functional capacity before returning to activities and eventually decrease the risk of reinjury.

MATERIAL AND METHODS

The study followed the strengthening the reporting of observational studies in epidemiology (STROBE). It is a cross-sectional study with an observational design. The study was conducted from June 2024 to February 2025 in the Justice K S Hegde Hospital. The study protocol was approved (NIPT/IEC/Min/02/2023 – 2024) by the institutional Ethics Committee of Nitte Institute of Physiotherapy, NITTE (Deemed to be University), Karnataka, India. The study protocol was prospectively registered in the Clinical Trial Registry-India (CTRI/2024/06/068902).

We calculated the required sample size using a power calculation procedure. By using the G*Power Version 3.1 software, the sample size of 44 was determined with a precision of 1.6.^[13]

An orthopaedic surgeon screened the participants for inclusion and exclusion criteria. Inclusion criteria were individual with a history chronic meniscal and ACL injuries (1-5 years), Grade 1 injuries,^[14,15] conservatively managed meniscal and ACL injuries, both male and female, BMI within the normal range, age 18-30 years, unilateral history of meniscal and ACL injury, foot posture index score (-1 to 6), able to hold static quadriceps for 30 s in supine. Exclusion criteria were post-surgical lower extremity fracture or surgery, knee pain, neurological conditions, swelling around the knee joint, and ankle instability. Informed consent was ensured, and a questionnaire was administered to collect general demographic data (age, sex), present medical condition, and medical history of each participant. Instructions on how to proceed with the assessment were clearly explained and showed the procedure before every hop test, and the participants performed as many practice trials as needed to feel comfortable with the task before starting the evaluation. Subjects were assessed for LSI via a hop test, and a crepe bandage was tied on the affected limb during the test.

The LSI was assessed using the hop test, and the 6-meter crossover hop has excellent test-retest reliability, with an ICC of 0.96. The triple crossover hop test has a good to excellent test-retest reliability with ICC from 0.86-0.96. The lateral hop test has good to excellent test-retest reliability, with an ICC of 0.87-0.95. The medial hop test also has good to excellent test-retest reliability, with an ICC of 0.87-0.95.^[13,10]

Once the institution’s ethics committee had provided ethical clearance, the session started with the measurement of the participant’s height, weight, and limb length. The participants were provided with a 5-min warm-up and lower limb muscles stretching before undertaking four single-legged hopping trials with both the injured and non-injured leg. Three successful trials for every limb were conducted with a 30-s resting interval between trials, and arm use is allowed. Any mistake entered during the tests resulted in the trial being rejected, and the test was redone. Speed information was measured using a stopwatch and a normal tape measure (in cm), respectively.

For the 6-meter crossover hop, subjects were asked to hop 6 m on one limb as fast as possible, jumping diagonally across a 15-cm-wide line and landing in a 30-cm zone. The triple-crossover hop required participants to stay inside two 30-cm-wide lanes while making three alternating hops across a 15-cm-wide line. On the third hop, they needed to balance before putting the other foot on the mat for measurement [Figure 1a]. For the lateral hop, subjects hopped laterally three times as far as possible, balancing and putting the other foot on the mat after the third hop for measurement [Figure 1b]. Likewise, during the medial hop, participants hopped medially three times as far as they possibly could, balancing and placing the opposite foot on the mat following the third hop for measurement [Figure 1c].

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Figure 1a:

Six-meter cross-over hop, triple crossover hop test.

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Figure 1b:

Lateral hop test.

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Figure 1c:

Medial hop test.

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After conducting tests, statistical analysis was performed on the collected data, and frequencies and percentages were analysed. The findings were summarised through different statistical displays to present the results and implications of the study.

RESULTS

The study consists of 67 participants, of whom 44 met the inclusion criteria. A total of 44 participants were included (25 females, 19 males), aged 20-29 years, with knee soft tissue injury.

Table 1 represented the descriptive statistics for age, BMI, duration of physical activity, and years of injury, which were expressed using mean and SD. In contrast, Table 2 showed the distribution of sex, side affected, type of knee injury, and foot dominance, which were expressed in frequency and percentage. Among 44 participants, the majority were female with the left limb affected.

The paired “t” test was used to compare lower extremity LSI according to the affected limb. The independent sample “t” test was used to compare age, BMI, duration of physical activity, and years of injury according to sex [Table 3], which shows no difference (p > 0.05). Table 4 shows a Comparison of lower extremity LSI according to the affected limb. There was a statistically significant difference (p < 0.05) in the 6-meter crossover hop, triple crossover hop, lateral hop, and medial hop, according to the affected limb. Table 5 represents a Comparison of lower extremity LSI according to sex. There was a significant difference (p < 0.05) in the 6-meter crossover hop (unaffected), triple crossover hop (both affected and unaffected), lateral hop (both affected and unaffected), and medial hop (both affected and unaffected) between males and females. Table 6 showed the assessment of lower extremity LSI in individuals with knee soft tissue injuries, irrespective of the limb affected, revealed that the 6-meter crossover hop had an LSI range of 75-90 with a mean of 82.48 ± 3.97, the triple crossover hop ranged from 74-93 with a mean of 85.34 ± 3.99, the lateral hop ranged from 70-92 with a mean of 84.02 ± 3.87, and the medial hop ranged from 75-92 with a mean of 85.75 ± 3.52, and the confidence interval is 95%.

DISCUSSION

The knee is the most frequently injured joint. Fractures, ligament injury, meniscal tear, patella instability, and disruption of the extensor mechanism are common injuries. Many processes can lead to knee injury. Following a knee injury, the functional impairments of reduced strength, balance, and jumping capacity are well established.^[6] There are several balance-assessment tools. Static balance is measurable by using the single-leg stance test, and dynamic balance is measurable by using the hop test.^[16] Clinicians can potentially identify participants who are at higher risk of future knee injury or pathology-related problems by using hop tests as a predictive tool.^[10] Hop tests are widely used to assess functional limb symmetry following knee injury.^[7] Clinicians employ the LSI to measure recovery following lower limb injury, particularly ACL or meniscus injury. It measures the injured leg in relation to the uninjured leg as a percentage. Clinicians can use these standardised functional tests to assess limb function precisely for rehabilitation planning and treatment plans.^[17]

The objective of this study was to evaluate the symmetry of both limbs using the hop test and to find out the difference in strength and stability in both limbs using the LSI. The measurement of lower extremity LSI through hop tests has been established as a valid and objective tool for the assessment of functional recovery in patients with knee soft tissue injury.^[17] This study included 44 participants aged 20 to 29 years, with a BMI ranging from 18.5 to 24.8 kg/m², a duration of physical activity ranging from 120 to 300 min/week, and years of injury ranging from 1-5 years [Tables 1 and 2]. A study conducted by Madsen et al. found that complete demographic details are important to get a limb’s maximum effort and can predict the LSI of participants.^[11]

A key finding of this study was the comparison of lower extremity LSI between the affected limb and the unaffected limb, as well as between males and females, which showed significant differences in hop test performance (p <0.05) [Tables 4 and 5]. We hypothesise that males had a statistically significant difference in LSI when compared with females, due to differences in muscle strength and biomechanical variations.^[18] These findings indicate that participants with knee soft tissue injury may have functional impairments in the affected side.^[19] Hoher et al. also found a significantly lower LSI in the case of an injured limb compared to a non-insured limb.^[20] Reid et al. highlighted the importance of LSI in evaluating lower limb function following an injury and showed that hop tests are accurate measures of rehabilitation, and the lower LSI seen in this study supports their findings.^[9]

This study also found the lower extremity LSI in individuals with knee soft tissue injuries; irrespective of limb affected reveals: the six meters crossover hop ranged from 75-90, triple crossover hop ranged from 74-93, lateral hop ranged from 70- 92 and the medial hop ranged from 75-92 [Table 6] As per Logerstedt et al., LSI >90% implies safe return to sport, depicting near-equivalence between limbs. An LSI of 80-89% indicates moderate asymmetry and tolerable, limited, or low-impact activity. Scores of <80% reflect high risk, rendering return to high-demand activity unsafe. LSI is a useful tool to inform safe and functional return-to-activity decisions. This study further supports the use of LSI as a rehabilitation metric, particularly in sports physiotherapy settings. This information can be used as a starting point for rehabilitation programmes to track improvement and reduce the risk of reinjury.^[17]

This study utilised the hop test to determine LSI, a valid method for assessing subjective physical performance after a knee injury. When 44 individuals with knee soft tissue injuries were examined, the results revealed an asymmetry between the affected and unaffected limbs. The findings provide important information on LSI, allowing therapists to use it as a benchmark for rehabilitation. By contrasting the injured limb with the unaffected one, the study offers valuable insights into functional limitations and the efficacy of conservative management techniques. To achieve a more thorough assessment, further research, functional performance testing, and specialised biomechanical evaluations (such as motion analysis and electromyography) could be integrated. Future studies should also contemplate using longitudinal designs to follow recovery patterns over long periods. Instruments like repeated measures assessments, e.g., hop tests, strength measurements, and patient-reported outcome measures (e.g., KOOS, ACL-RSI), can offer important insights into functional recovery as well as long-term results. Nevertheless, our findings highlight the contributions to rehabilitation strategies by identifying discrepancies in limb symmetry among individuals with knee soft tissue injuries. The study noted a few limitations. Firstly, as a cross-sectional study, it does not permit long-term follow-up to evaluate changes over time. Secondly, functional evaluations may be necessary, since the hop test might not fully capture all aspects of lower limb function. Thirdly, the lack of blinding of assessors and the potential influence of physical activity history or dominant leg on the subject.

CONCLUSION

The research highlights the importance of the LSI in evaluating functional recovery following knee soft tissue injuries, providing insightful information for patients, practitioners, and researchers. For patients, LSI testing using hop tests offers a quantitative measure of recovery, guaranteeing safe return to activity while reducing the potential for reinjury. Clinicians use these standardised functional tests to assess limb function precisely for rehabilitation planning and treatment plans.

Nonetheless, this research is not without its limitations. Due to its cross-sectional design, long-term follow-up is not feasible, which restricts the understanding of how LSI evolves during the recovery period. Furthermore, while hop tests are standardised and widely used, they may not capture all aspects of lower limb function, such as neuromuscular control or proprioceptive feedback. Since the present study is time-bound, the sample size is relatively small; thus, the results of the study should be generalised with caution.

For research purposes, the results demonstrate the necessity of further research using larger sample populations and long-term follow-up to cross-validate the outcomes and optimise rehabilitation protocols. Integrating advanced biomechanical testing techniques, including motion analysis and electromyography, would make the LSI a more useful clinical tool. In general, this research helps enhance rehabilitation interventions, maximise patient outcomes, and promote evidence-based practice in musculoskeletal and sports physiotherapy.