Evaluation of regeneration of semitendinosus tendon using ultrasound imaging and isokinetic strength testing after graft harvest for arthroscopic anterior cruciate ligament reconstruction

Abstract

Background

A lot of the research has been done worldwide evaluating the capacity of the semitendinosus tendon to regenerate which has not been conducted in the Indian population.

Study design

31 patients who underwent unilateral ACL reconstruction with hamstrings were taken into study. All patients underwent ultrasonography imaging of both knees and bilateral isokinetic flexion strength assessment at a one-year postoperative period. Images were obtained at three levels and their dimensions are compared with normal side. Isokinetic testing of the knee is done to evaluate the flexion deficit and is compared to the uninvolved knee.

Results

Out of a total of 31 patients, 14 patients showed no regeneration, 17 showed regeneration at various levels. On isokinetic testing patients with no regeneration showed the highest mean flexion deficit.

Conclusion

The semitendinosus tendon and its regeneration can be visualized well using ultrasonography. After semitendinosus harvesting, the flexion strength will be decreased as compared to the normal knee. The flexion strength in patients who have a regenerated tendon will be higher as compared to those who have no regeneration.

1. Introduction

The anterior cruciate ligament (ACL) is a very commonly injured ligament in sporting as well as non-sporting activities. An epidemiological study of 465 Indian athletes done in 2015 showed that anterior cruciate ligament injury was the most common knee injury (86.5%) followed by meniscal injury (78.24%). The authors also concluded that the highest number of knee injuries was seen in football followed by kabaddi and athletics¹ Another demographic study done in Indian athletes over 10 years showed that Kabaddi accounted for the highest number of ACL injuries followed by football and athletics² It can thus be concluded that kabaddi, football, and athletics account for the highest number of knee injuries in the country.

The surgery is intended to allow early return to the sport of an athlete. In the 21st century, arthroscopic surgery has replaced open reconstruction as it is minimally invasive and makes rehabilitation that much easier.³

The debate remains as to which autogenous graft to use, the patellar tendon-bone (PTB) graft or the Semitendinosus and Gracilis (STG) tendon graft. Both the grafts have their positive and negative factors and graft choice usually varies from doctor to doctor, with patient characteristics also playing some role.⁴ One of the positive points for choosing the STG graft is the ability of the Semitendinosus tendon and Gracilis tendon to regenerate.⁵ Although a lot of the research has been done worldwide, work evaluating the capacity of the semitendinosus tendon has not been conducted in the Indian population. Additionally, most of the studies have used magnetic resonance imaging. Ultrasonography is still not a widely used modality. This study, focused on a young segment of Indian patients, is aimed at evaluating the role of ultrasound imaging for visualizing the semitendinosus tendon after harvest, in an attempt to evaluate, and if possible quantify regeneration. Since ultrasound imaging is a cheaper modality as compared to magnetic resonance, and is readily available at most centers, this can then be promoted as an easily available tool for visualizing the regenerated tendons.

2. Objectives

Objectives are to evaluate the regeneration of the semitendinosus tendon after graft harvest using ultrasonography in the Indian population and to see the relationship between the regenerated tendon and isokinetic flexion strength of the operated knee.

3. Materials and methods

This is a prospective study. The study was done at a single center. The patients were operated at an earlier date and then recalled at one year post-operatively. 31 patients who matched the eligibility criteria were included. Each patient underwent an ultrasonographic assessment of both the knees along with bilateral isokinetic flexion strength assessment. Data collection took place between June 2017 and December 2017.

4. Inclusion criteria

• •All the patients were clinically and radiologically evaluated and diagnosed with anterior cruciate ligament insufficiency.
• •Only patients with unilateral anterior cruciate ligament insufficiency were included.
• •Patients undergoing arthroscopic anterior cruciate ligament reconstruction using semitendinosus and gracilis graft.
• •The surgeries were conducted at our institute by the same team of surgeons.

Only patients who followed a standardized rehabilitation program after arthroscopic anterior cruciate ligament reconstruction set by our institution were included.

5. Exclusion criteria

• •Patients with multi ligamentous injuries.
• •Patients with bilateral knee involvement.
• •Anterior cruciate ligament injuries associated with fractures.

6. Data collection

All 31 patients underwent ultrasonography imaging of both knees and bilateral isokinetic flexion strength assessment at a one-year postoperative period.

7. Rehabilitation protocol

There is a standardized rehabilitation protocol for arthroscopic anterior cruciate ligament reconstruction used in our institution. This program is goal-oriented and progress dependent. It can be used for athletes as well as non -athletic patients.

Strengthening of the hamstring muscles and quadriceps muscles in encouraged. Patients are asked to perform isometric co-contractionsns of the quadriceps and hamstring muscles.

To increase the quadriceps muscle control, the patients are instructed to perform active straight leg raising exercises in all planes with the knee brace.

8. Isokinetic strength testing

Isokinetic strength testing of both the knees was done using a System 4 Pro^tm Biodex Dynamometer.(Fig. 1). The main principle of an isokinetic dynamometer is that the lever arm can be set at a fixed speed to provide resistance and the effort applied by the person being tested will vary at different speeds. The set lever arm speed will allow the machine to measure the torque output of the person throughout the range of motion. This torque production varies with speed. The lower the speed, the more concentric torque can be produced. If the speed is increased the concentric torque will decrease. More motor units can be recruited at lower speeds, which help in the production of more torque. Eccentrically, the higher the speed of the lever arm, the more motor units will be recruited.⁶

Fig. 1.

Isokinectic testing in Biodex.

Isokinetic testing can be used to provide a valid, reliable, objective measure of the muscles’ performance. The real-time data is collected by the software and interpreted. In our study, we were mostly looking at the percentage deficit of the involved knee as compared to the uninvolved knee. A value of 10–15% is an acceptable postoperatively. The highest effort produced by the tested muscle is called peak torque. This is determined by each repetition. The main concern during data interpretation is the Coefficient of Variance (CV). This is the amount of variation that occurred during the test between repetitions. This will vary in cases of pain, apprehension, lack of effort or even poor instruction given to the patient. The CV will determine if the test is reliable and valid or not. In large muscle groups like around the knee joint, less than 15% CV is acceptable. All our patients fell within this normal range.

In our study, the patients underwent isokinetic strength test of both the knees at 60°/second, 180°/second, and 300°/second. Before the testing was done, the patients were asked to perform a 10 -minute, general warm-up. Once done, they were made to sit in the Biodex machine and the lever arm for the involved side was attached. The involved knee was tested at 300°/second, then 180°/second and lastly at 60°/second with a rest period of 15 s between each set. Once completed, a rest period of 1 min was given and the other leg was tested similarly. Each speed consisted of 10 repetitions. The peak torque value was normalized to the bodyweight of the patient. The flexion deficit was determined as compared to the uninvolved knee. None of the patients complained of pain, stiffness or any other complications.

9. Ultrasonography

Ultrasonography was done by a single radiologist having sufficient experience with musculoskeletal ultrasound. Images were acquired in axial and coronal planes from the muscle belly till the insertion site. The target areas were scanned using a Toshiba APLIO 500 ultrasound machine using a linear high-frequency transceiver [~10–14 Mhz frequency range]. Ultrasound B mode was used to assess the anatomy and location of the tendon. The ultrasound image parameters like depth, brightness, number of focus points and focus levels were modified accordingly for each patient.

9.1. Images were obtained at three levels

• 1.Above knee
• 2.Popliteal fossa level
• 3.Below knee level

The height and width of the normal side tendon were measured and compared with the tendon regeneration on the operated site.

10. Results

The mean age of the patients is 27 years (18–36). We observed that the regeneration of the tendon did not seem to depend on the age of the patient(Table 1).

Table 1.

Regeneration in relation to age.

AGE	Regeneration
Below 28 years	52.3%
Above 28 years	50%

Out of the 31 patients involved in the study, 4 (12.9%) are females and 27 (87.1%) are males.

All 31 patients underwent ultrasound assessments on the posteromedial aspects of both knees. The patients were placed in a prone position and the normal knee was examined first and then operated knee. The examinations were done above the knee, at the level of knee and below the knee. Out of a total of 31 patients, 14 patients showed no regeneration, Five patients showed regeneration above the knee, two patients showed regeneration at the level of knee and 10 patients showed regeneration below the knee.

The regenerated tendon was marked and then compared with the normal knee. These regenerated tendons in the operated knees were thinner as compared to the ones in the normal knee.

11. Isokinetic strength testing

Isokinetic strength testing was done after the patients were made to warm up for about 10 min. The lever arm was set at three different speeds 60°/second, 180°/second and 300°/second. 29 (93.5%) patients out of 31 showed some percentage of flexion strength deficit as compared to the normal knee. Two patients showed higher flexion strength in the operated knee as compared to the normal knee. The flexion deficit value was collected from all three speeds, and an average flexion deficit percentage was calculated. The flexion deficit of 10–15% is considered within a normal range. The flexion deficit was compared to the ultrasound images. The patients with no regeneration showed the highest mean flexion deficit and the patients who showed below knee regeneration showed the lowest mean flexion deficit(Table 2).

Table 2.

Comparision between regeration and flexion deficit.

Regeneration	No of patients	Mean deficit%
No regenration	14	28.51%
Above knee	5	14.28%
At knee	2	7.6%
Below knee	10	3.66%

11.1. Statistical analysis

On using the Kruskal-Wallis test for statistical analysis, it was noted that the average flexion deficit was not the same in the patients with no regeneration and patients with some form of regeneration. (P < 0.004).

55% of the patients showed some form of regeneration.

All patients except for two showed a flexion strength deficit as compared to the normal knee. Age and sex did not play any role in tendon regeneration.

12. Discussion

The anterior cruciate ligament injury is one of the most common knee injuries in sports. In India, Soccer and Kabaddi are the sports that show the maximum incidence of this injury.^1,2; these may be contact or non-contact injuries. In the non-athletic population, these are mostly non-contact injuries.⁷ The changing pattern of surgical reconstruction leads to the 4 -strand semitendinosus and gracilis autograft to be the most commonly used. This is due to the ease of harvesting, no disruption of extensor mechanism as in BTB graft, and the significant potential of regeneration.

The regeneration of the semitendinosus tendon after graft harvest for anterior cruciate ligament has been discussed in many studies. Methods evaluate the regeneration of the tendon have been variably described, ranging from MRI, to open surgical visualization of the regenerated tendon. The most widely used modality remains to be magnetic resonance imaging.^8,9 Indirect methods of assessment include strength deficit evaluations with specific machines like isokinetic dynamometer and EMG. Recent interest has focused on ultrasound evaluation which, although is operator dependent, can be used as a cheap and easily available option for this purpose. Most of the studies have found that over a while the tendon will regenerate along its original course. These studies have been based mostly on the use of MRI (Table 4). Ultrasonography and surgical visualization have also been done but there is limited literature regarding these modalities^10,11(Table 3). The functional muscle strength has been evaluated using isokinetic strength testing and electromyography.^12,13 The regeneration has been visualized in most of the studies, using all the above-mentioned modalities. The earliest period after harvest at which the tendon has been seen regenerating is 1 month.

Table 4.

Comparison with studies done using MRI.

Study	Post-op Duration	Regeneration	Isokinetic Strength
Our Study	6–12 months	Patients showing regeneration (total 55%) – 16% above knee, 7% at knee level, 32% below knee. Patients showing no regeneration – 45%	Flexion deficit No regeneration – 28.51% Above knee regeneration – 14.28% At knee level regeneration – 7.6% Below knee regeneration – 3.66%
Ahlen et al.15	6 months–11 years	88% showed semitendinosus tendon regeneration and 95% showed gracilis tendon regeneration	Significant strength deficit on involved side as compared to normal knee
Burks et al.16	6 months	Inconsistent tendon regeneration seen in 77.7% patients.	Significant strength deficit as compared to the normal knee at 6 months post-op
Choi et al.8	2 years	80% showed semitendinosus tendon regeneration and 75.6% showed gracilis tendon regeneration	Significant difference between the strength deficit in patients with regeneration and patients without regeneration
Eriksson et al.17	6–12 months	12 patients out of 16 showed regeneration of the semitendinosus	Flexion strength in the operated knee was lower as compared to the normal knee
Janssen et al.18	6–12 months	100% showed gracilis regeneration. 63.6% showed semitendinosus tendon regeneration	No significant difference between preoperative and post-operative flexion strength
Murakami et al.19	12 months	100% patients showed regeneration	Isokinetic strength of operated side was significantly lower than normal knee
Nishino et al.20	12–43 months	91.3% patients showed regeneration	Isometric flexion strength was lower in operated knee as compared to normal knee

Table 3.

Comparison with studies done using ultrasound.

Study	Post-op Duration	Regeneration	Isokinetic strength
Our study	12 months	Regeneration seen in 55% (16% above knee, 7% at knee level, 32% below knee No regeneration- 45%)	Flexion Deficit No Regeneration- 28.51% Above knee regeneration- 14.28% At knee level- 7.6% Below knee- 3.66%
Papandrea et al.10	24 months	100% cases showed regentration of ST about 4 cm from normal insertion site	Not done
Bedi et al.11	60 months	Regeneration seen in most patients but not structurally similar to native ST as compared with opposite side	Not done
Stevanovic et al.14	24 months	72% showed regeneration of ST	No significant difference between operated and non operated side

An irregular hypoechoic structure was noted near the anatomical site of the tendon using ultrasonography. By the 18 ^th month there was near complete regeneration. In our study, we have used ultrasonography to see the regeneration in 1 - year post-operative patients. Tendon regeneration was seen in 71% of the patients who were in the 1- year postoperative group.

The patients that had regeneration also showed good isokinetic flexion strength of the knee. The relationship between knee flexion strength and semitendinosus has been discussed in numerous studies. It is still not clear in the literature if the regeneration of the semitendinosus helps in reducing the post-operative flexion strength deficit. In our study, we found a positive correlation between the knee flexion strength and regenerated semitendinosus tendons.

Most of the available literature shows a deficit of isometric flexion strength as compared to the non-operated knee. Only two other studies have compared the isokinetic strength in patients with and without regeneration. Nakame et. Al.²¹ stated that there was no significant difference in knee flexion strength deficit in patients with and without regeneration. Choi et al.⁸ have shown that the strength deficit in patients with the regeneration of the tendons is less as compared to those who do not have regeneration. Our study has also shown similar results.

12.1. Inferences from our study

Although some flexion deficits are noted after semitendinosus harvesting, the potential for graft regeneration and subsequent decrease in the flexion deficit is significant. We were able to demonstrate that ultrasound is a good modality for evaluating the semitendinosus tendon and can be used as a cheap tool for postoperative measurement of regeneration. Ultrasound done at six monthly periods repeatedly showed an increase in the extent of regeneration, and examinations at longer follow up may show even more tendon regeneration. There is a good correlation with residual flexion deficits with the degree of regeneration seen on ultrasound examination, and this combination of clinical evaluation along with the US may work as a cheap option for evaluating the tendon regeneration compared to the more expensive tests.

13. Conclusion

The semitendinosus tendon and its regeneration can be visualized well using ultrasonography.

After semitendinosus harvesting, the flexion strength will be decreased as compared to the normal knee. The flexion strength in patients who have a regenerated tendon will be higher as compared to those who have no regeneration.

14. Limitations of the study

Small sample size. Other modalities could have been added. A longitudinal study is required to track the regeneration progress.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.