|Year : 2022 | Volume
| Issue : 1 | Page : 17-21
Semitendinosus tendon morphometry as a graft – A cadaver study
Balakrishna Shetty, Sweekritha Shetty, Prashanth Kasargod Umesh
Department of Anatomy, A J Institute of Medical Sciences and Research Centre, Mangalore, Karnataka, India
|Date of Submission||22-Jul-2021|
|Date of Decision||27-Sep-2021|
|Date of Acceptance||28-Oct-2021|
|Date of Web Publication||01-Feb-2022|
Department of Anatomy, A J Institute of Medical Sciences and Research Centre, Kuntikana, Mangalore - 575 004, Karnataka
Source of Support: None, Conflict of Interest: None
Background: Sports and games have become professional activities. The standard of fitness level is raised. Advancement in arthroscopic anterior cruciate ligament (ACL) reconstruction using free tendon graft is one of the key developments. Autograft with minimal donor site or functional morbidity is the key. The latest is the use of semitendinosus in ACL reconstruction. Preoperative knowledge of graft in terms of size is crucial. The present cadaveric study is an attempt to understand the morphology of the semitendinosus tendon (ST) as tendon graft in the local population. Methodology: A total of 50 male cadaver limbs embalmed with formalin were used for harvesting 50 STs. The exact age and height of the cadavers were not known. The femoral length was used as a measure of body height. Tendon length and quadruple diameters were measured. Anderson–Darling test was used for distribution analysis of all the data. Results: In our study, mean length of the tendon was 27.12 cm which is shorter than the required 28 cm for quadrupling the tendon. The average diameter was 8.14 mm which is slightly more than the minimum required thickness of 8 mm. These two findings suggest that tendons in the Indian population are not long enough for an ideal quadruple graft with more than 8 mm diameter. Conclusion: The result of our study is in conformation with the previous studies on the Indian population and also in the Western population. The height of the individual can be inferred from length of the femur; hence, height can be taken as a good predictor for the length of ST in the Indian population.
Keywords: Anterior cruciate ligament, autograft, cadaveric study, semitendinosus
|How to cite this article:|
Shetty B, Shetty S, Umesh PK. Semitendinosus tendon morphometry as a graft – A cadaver study. Natl J Clin Anat 2022;11:17-21
|How to cite this URL:|
Shetty B, Shetty S, Umesh PK. Semitendinosus tendon morphometry as a graft – A cadaver study. Natl J Clin Anat [serial online] 2022 [cited 2022 May 20];11:17-21. Available from: http://www.njca.info/text.asp?2022/11/1/17/337047
| Introduction|| |
Competitive sports and games have increased the incidence of sports injuries. Adequate treatment of sports injuries to gain back the fitness level has increased the need for advanced surgical skills and techniques. The knee joint is the most commonly injured joint in sports injuries. Anterior cruciate ligament (ACL) and posterior cruciate ligament are the common ligaments involved in these types of injuries. Recent advances in arthroscopic surgery have led to an increased number of reconstruction procedures of cruciate ligaments.
A free tendon graft is used to reconstruct the cruciate ligament tears during injuries to the knee joint. The selection of tendon for the graft depends on its strength. But now depending on the ligaments to be reconstructed graft tendons are selected based on their strength, easy accessibility, and postharvest donor site morbidity.
Phylogenetically degenerating or functionally insignificant tendons such as palmaris longus or plantaris were used initially as free tendon grafts. Then, autogenous patellar tendon as bone tendon-bone graft was popular. The donor site morbidity with patellar tendon graft has led more people to use hamstring tendon (semitendinosus and gracilis [STG] tendon) graft as the primary option. This hamstring graft also had other advantages such as smaller skin incisions and no damage to the extensor mechanism of the knee.
The autograft of semitendinosus (ST) and gracilis tendons is popular in recent years. Ideally, a graft diameter of 8 mm (minimum of 7 mm) and graft length of a minimum of 7 cm are required for ACL reconstruction for which graft tendon length should be at least 28 cm. The success of the reconstructive procedure mainly depends on the diameter of the graft. Now, newer fixation techniques enable an even shorter length of the tendon. Hence, the use of a single semitendinosus tendon (ST) in triple or quadruple strands sparing the gracilis is the preferred choice.
In clinical results, not much difference was seen between the ST graft alone and the STG graft for ACL reconstruction. However, reduced internal rotation torque and the external to internal rotation ratio were high in the STG group. Hence, sports activities that require full flexion and maximum rotational strength such as long jumps, high jumps, skiing, and football using the ST alone for ACL reconstruction were suggested. Hence, the use of a single ST in triple or quadruple folds sparing the gracilis became the preferred choice.
In the case of the patellar tendon or quadriceps tendon, the surgeon can fix the size of the graft but it is not so when using hamstring tendons. Intraoperatively during the reconstruction procedure, variations were found in the length and thickness of hamstring tendons. In some cases, because of short tendon length, modified procedure involving the gracilis tendon had to be done.
To overcome this problem, preoperative assessment of graft size is necessary. There are very few studies on the hamstring tendon and anthropometry in cadavers. In this cadaveric study, we sought to find some predictive relations between ST size and femur length. So that inadequate single graft size and augmentation with additional tendon can be known preoperatively.
There are four hamstring muscles. Three on the medial side are semimembranosus and semitendinosus and adductor magnus (with exceptions). One on the lateral side is the biceps femoris (long head and short head). Of the four, the semitendinosus and short head of the biceps femoris are small. Semitendinosus as the name suggests has a long tendon extending up to the mid-thigh. It's a fusiform muscle, takes its origin from the ischial tuberosity, and is inserted into to anteromedial surface of the proximal tibia., Along with sartorius and gracilis, semitendinosus forms a conjoined tendon at the insertion called pes anserinus. Gracilis and semitendinosus lie deep to sartorius fascia. Deep to these tendons is the medial collateral ligament which is closely adhered to the bone. Accessory tendons along with the main tendon of ST are the common anatomical variations. Intertendinous adhesions and tendinous extensions called vincula to gastrocnemius fascia are common with semitendinosus.
Hamstrings are the flexors of the knee and rotators of the tibia and also act as rotator and valgus constraints to the knee. This group of muscles is also referred to as guy rope muscles of the leg. The hamstrings are secondary stabilizers of the knee. The ACL is a static (primary) stabilizer while the hamstrings act as dynamic stabilizers against the anterior translation of the tibia. Structurally sacrifice of ST is not logical but functionally postoperative donor site morbidity is comparatively less with the use of ST, hence has become a popular choice of graft in ACL reconstruction.
Hamstring tendons regenerate after tendon harvesting. However, the regeneration rate varies. Suijkerbuijk et al. in his systematic literature review has found hamstring tendons regeneration after 1-year post-ACL reconstruction was 79% (median interquartile range [IQR], 80 [75.5–90]) for semitendinosus and 72% (median [IQR], 80 [61–88.5]) for gracilis. Janssen et al. in their analysis of hamstring regeneration found that both STG tendons regenerated after harvesting for ACL reconstruction. However, there was no functional correlation with tendon regeneration. Konrath in 2016 in his study on regeneration of hamstrings post-ACL reconstruction observed knee flexor weakness due to alterations of muscle-tendon properties of the STG and was more pronounced in cases where there was no regeneration.
| Materials and Methods|| |
A total of 50 lower limbs from 45 cadavers were considered for the study. All were adult male cadavers used for academic teaching of the 1st MBBS students. The study was conducted in the department of Anatomy, AJ Institute of Medical sciences,Mangalore, after obtaining institutional ethics committee approval (AJEC/REV/75/2018, dated-13/06/2018).
The data for the study was collected by dissecting 50 intact semitendinosus muscle tendons of which, 22 were right sided and 28 were left sided. Only in five cases, bilateral tendons could be used. The semitendinosus muscle was separated from its attachments. The intact tendons in full length from muscle bulk to insertion were detached. Later, all the muscle tissues were removed from the musculotendinous junction. The synovial covering was removed from the tendons. The tendon length was measured from insertion to musculotendinous junction using a measuring (commercially available tailor) tape. The tendon was then tagged and numbered.
The length of the femur in all the limbs was measured as the distance between the anterior superior iliac spine and the medial joint line, with the hip and knee in a neutral position, and the side right or left noted.
Arthrex-Graft Sizing Block (AR-1886) which has 4.5–12 mm holes in 0.5 mm increments was used for tendon diameter measurements [Figure 1]. First, the tendon was folded over to double and again folded (double folded), held with thread and artery forceps. The quadruple diameter of tendons was measured by passing through the different holes in the graft sizing block and recorded.
|Figure 1: Quadruple tendon diameter measurement and Arthrex Graft Sizing Block (AR-1886). Demonstration of quadruple tendon diameter measurement using Graft Sizing block. Arthrex-Graft Sizing Block (AR-1886) which has 4.5–12 mm holes in 0.5 mm increments|
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The femur length was correlated with ST length and quadrupled diameter.
All data were checked for distribution analysis using Anderson–Darling test between tendon length, quadrupled tendon diameter, and femur length (height). A correlation statistic was attempted to evaluate the strength and direction of association between two continuous variables that are linearly related. Pearson's product-moment correlation coefficient, “r” was used (range from −1 for perfect –ve and +1 for perfect +ve linear relations). A value of zero indicates that there is no relationship between variables.
A scatter plot was used to demonstrate the relationship for two variables, ST length and femur length against each other, to visually inspect the linearity. If nonlinearity was found, then we planned for transforming the data to run a Spearman's correlation instead.
The correlation statistics were evaluated using Minitab 18.0 (© 2021 Minitab, LLC). P = 0.05 was considered to define the statistical significance for all values.
| Results|| |
The present study was done on 50 embalmed lower limbs. The mean length of the ST is 27.12 ± 1.81 cm and the mean quadruple diameter is 8.14 ± 0.67 mm. The mean femur length is 45.72 ± 2.8 cm [Table 1].
|Table 1: Morphometric data on semitendinosus – length, diameter, and femur length|
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The range of ST length varied from 22 cm to 30 cm and femur length varied from 39 cm to 50 cm.
Out of the 50 samples collected, 24 tendons had a required length of 28 cm or more which estimates to be 48%. Only three had <24 cm in length of the tendon. In 38 specimens, quadruple diameter of the tendon of 8 mm or more is seen amounting to 76% of the total samples.
Anderson–Darling test was used to check the normality of data, using empirical cumulative distribution function and if the deserved difference is adequately large, we reject the null hypothesis of population normality. The data distribution analysis was found parametric (test P > 0.05).
The Pearson correlation coefficient between tendon length and femur length was positive (correlation: ST length vs. femur length, Pearson correlation = 0.425, P = 0.002). However, the tendon diameter versus the femur length was not statistically significant (correlation: ST-Q diameter, femur length, Pearson correlation = 0.059, P = 0.682). The results indicate conclusive evidence for an association between tendon length and femur length. The correlation graphs are depicted in [Figure 2] and [Figure 3].
|Figure 2: Scatter plot showing the correlation between semitendinosus tendon length (cm) and femur length (cm). Correlation: ST-length, Femur length. Positive Pearson correlation of ST-length and Femur length, r = 0.425, P = 0.002|
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|Figure 3: Scatter plot showing the correlation between ST length (cm) and ST quadruple diameter (mm). Correlation: ST- Q diameter, ST length. Pearson correlation of ST-Q diameter and ST length, r = 0.059, P = 0.682, not statistically significant|
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| Discussion|| |
The study of the ST length and diameter is of surgical importance in the repair of ACL tears. The harvesting of ST graft alone for ACL reconstruction depends on its length and quadrupled diameter. In our morphological study of ST in cadavers, the mean length of the tendon was 27.12 cm which is shorter than the required 28 cm for quadrupling the tendon. The average quadrupled diameter is 8.14 mm which is slightly more than the ideally required thickness of 8 mm. In our study, 48% of the tendons are of the required length of 28 cm or more, only three are <24 cm in length. Quadruple diameter of the tendon of 8 mm or more found in 76%. These two findings suggest that tendons in the Indian population are not long enough for an ideal quadruple graft with more than 8 mm diameter. However, 7 mm diameter graft with triple folding is possible which is functionally adequate though not ideal. Triple strand graft with a 7 mm diameter is 240% stronger than native ACL.,,,
The average size of the ST graft is smaller in length in the Asian population, in contrast to the Western population.
Tan et al. in 1998 found in his cadaver study on the Chinese population smaller in length and thickness, more vertically placed ACL in contrast Western population. There are no studies on the size of ACL in the Indian population. Probably Indians ACL and tendon length are proportionately smaller compared to the Western population.
Height is the best predictor among anthropometric data in ST graft size in most Western studies.,,,
In our study, length of the tendon correlates with the length of the femur. Diameter does not correlate with the length of the tendon or the length of the femur. No other anthropometric data were available for correlations.
A cadaveric study by Pichler et al. in 2008 found correlations between the length of the femur and the length of the ST in the whole study population. However, the findings were significant in female cadavers and height was considered as a predictive factor for the length of tendons in women only.
Asif et al. found that thigh circumference and height are significant predictors of tendon graft diameter and gave the equation: graft diameter (mm) = 0. 079 height (cm) +0.068 thigh circumference (cm) −9.031. Mulenga found that the height of a person is directly proportional to the femur length and is four times the femur length, therefore, the longer the femur the taller the person, and vice versa in the Zambian population.
In a study on the Indian population, Prasad and Challa could not find anthropometric measurements such as weight, gender, and activity level as definitive predictors for the hamstring graft diameter during harvest but found a correlation between the height of the patients and length and diameter of the tendon.
Predictability of tendon size for graft using anthropometric data is of immense help for surgeons and patients undergoing reconstruction with a tendon graft.
The ACL is 31–35 mm in length and 31.3 sqmm in cross-section. Semitendinosus has 75% and gracilis has 49% strength of the ACL. The strength of the tendon reduces by 50% after graft fixation. Therefore, the ideal graft should be double the strength of ACL. In the case of the semitendinosus, tendon quadrupling increases the strength of the graft.
For secure fixation of graft, minimum length of the graft in the tunnel should be 2 cm. The intra-articular length of the graft is 3 cm. Therefore, minimum required length of graft will be 7 cm as 2 cm in femoral tunnel, 2 cm in the tibial tunnel, and intra-articular length 3 cm. Graft tendon length should be a minimum of 28 cm (adequate length) to be used as a four-stranded graft.
Limitations of this study are small sample size, absence of female cadavers, age, weight, height not known, formalin embalming, and not being able to harvest bilateral tendons.
| Conclusion|| |
The result of our study is in conformation with the previous studies on the Indian population and also in the Western population. As the length of the femur correlates with the height of the individual, height can be taken as a good predictor for the length of ST length in the Indian population. Our findings suggest that tendons in the Indian population are not long enough for an ideal quadruple graft for ACL reconstruction. However, functionally adequate graft with triple folding is possible.
We would like to thank and pay respect to all those kind hearts who have donated their body for research and education purposes without whom this work would not have been accomplished.
We sincerely acknowledge Dr. TV Tantri, HOD Department of Anaesthesia, AJ Institute of Medical Sciences and Research Centre, Mangalore, for his contribution in statistical analysis.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3]