Semitendinosus tendon regeneration after anterior cruciate ligament reconstruction: can we use it twice?

The Addition of the Gracilis Tendon to a Semitendinosus Tendon Autograft Is Not Associated With Knee Muscle Strength, Subjective Knee Function, or Revision Surgery After Anterior Cruciate Ligament Reconstruction

PURPOSE

To evaluate and compare isokinetic knee muscle (extension and flexion) strength, single-leg hop (SLH) test performance, anterior knee laxity, subjective knee function, and the 2-year revision surgery risk between patients who underwent anterior cruciate ligament reconstruction (ACLR) with semitendinosus tendon (ST) autografts and patients who underwent ACLR with ST and gracilis tendon (ST-G) autografts.

METHODS

We identified patients aged 16 years or older who underwent primary ACLR with hamstring tendon autografts at our institution from January 2005 to December 2020 and had no associated ligament injuries. Isokinetic knee muscle strength and SLH test performance were assessed 6 months postoperatively. Anterior knee laxity (KT-1000 arthrometer, 134 N) was assessed preoperatively and 6 months postoperatively. The Knee Injury and Osteoarthritis Outcome Score (KOOS) was collected preoperatively and 1 and 2 years postoperatively. Patients who underwent revision ACLR at any institution in Sweden within 2 years of primary surgery were identified through the Swedish National Knee Ligament Registry.

RESULTS

A total of 6,974 patients (5,479 with ST and 1,495 with ST-G) were included. There were no significant differences in extension and flexion strength or SLH test performance between the groups. Preoperatively, there was no significant difference in knee laxity between the ST and ST-G groups. Postoperatively, the ST-G group had significantly increased mean side-to-side (STS) laxity (2.1 ± 2.3 mm vs 1.7 ± 2.2 mm, P < .001) and showed a trend toward increased STS laxity according to the International Knee Documentation Committee form, with significantly fewer patients with STS laxity of 2 mm or less (58.4% vs 65.8%) and significantly more patients with STS laxity between 3 and 5 mm (35.0% vs 29.9%) or greater than 5 mm (6.6% vs 4.3%) (P < .001). The only significant difference in subjective knee function was for the KOOS Quality of Life subscale score in favor of the ST group preoperatively (37.3 ± 21.4 vs 35.1 ± 19.9, P = .001). No other significant differences between the groups were found preoperatively and 1 and 2 years postoperatively for any of the KOOS subscales. The overall revision ACLR rate within 2 years of primary surgery was 2.0% (138 of 6,974 patients). The revision ACLR risk in the ST-G group (1.7%, 25 of 1,495 patients) was not significantly different from that in the ST group (2.1%, 113 of 5,479 patients) (hazard ratio, 0.80; 95% confidence interval, 0.50-1.24; P = .32).

CONCLUSIONS

The addition of the gracilis tendon to an ST autograft was not associated with knee muscle strength, SLH test performance, subjective knee function, or the risk of revision surgery after ACLR.

LEVEL OF EVIDENCE

Level III, retrospective comparative study.

Quantification and comparison of tenocyte distribution and collagen content in the commonly used autografts for anterior cruciate ligament reconstruction

Anterior cruciate ligament is a commonly damaged ligament of the knee. Reconstruction of this ligament usually entails the use of graft harvested from the same subject (i.e., autografts). Several tendons, for example quadriceps, patellar or semitendinosus tendon can be used as an autograft. The composition of the tendons is similar to the anterior cruciate ligament but there is no data that directly compares the compositions of the quadriceps, patellar and semitendinosus tendons. This study quantified and compared the tenocyte distribution and collagen content of these tendons from cadavers of South Africans of European Ancestry. The tenocyte distribution and collagen content were assessed using the ImageJ software. The results showed similarities in the collagen content across the tendons in both sexes (P>0.05). The tenocyte distribution was significantly higher in the quadriceps (P=0.019) or semitendinosus (P=0.016) tendon than in the patellar tendon in the female but no difference was seen in the male (P=0.872). This shows that a large harvestable area may not be directly associated with a more abundant collagen content or tenocyte distribution in the tendon. However, sex-specific tenocyte distribution is an important observation that underpins the possible influence of underlying biological factors on the composition of each tendon and this requires further investigations. In all, this study will contribute to knowledge and assist orthopaedic surgeons in making an informed decision on the choice of graft.

Protocolo de reabilitação acelerada precoce versus conservadora retardada após reconstrução do ligamento cruzado anterior: Um ensaio prospectivo randomizado

Objective  To compare the effectiveness of the early accelerated rehabilitation and delayed conservative rehabilitation protocols after arthroscopic anterior cruciate ligament reconstruction, in terms of the International Knee Documentation Committee (IKDC) score, pain (according to the Visual Analog Scale), laxity, and stiffness one year postoperatively to determine the best outcome.

Materials and Methods  A total of 80 subjects were divided into 2e groups (early accelerated group and delayed conservative group), which were analyzed by the Pearson Chi-squared and Wilcoxon rank-sum tests.

Results  One year postoperatively, knee laxity was significantly higher ( p  = 0.039) in the early accelerated group compared with the delayed conservative group. Regarding postoperative pain (according to the Visual Analogue Scale) and IKDC scores, both groups presented similar results. The postoperative range of motion was better in the early accelerated group, but this was not statistically significant ( p  = 0.36).

Conclusion  One year postoperatively, the early accelerated rehabilitation protocol was associated with significant knee laxity compared to the delayed conservative rehabilitation protocol.

Proximal hamstring tendon avulsions: comparable clinical outcomes of operative and non-operative treatment at 1-year follow-up using a shared decision-making model

OBJECTIVE

To prospectively evaluate 1-year clinical and radiological outcomes after operative and non-operative treatment of proximal hamstring tendon avulsions.

METHODS

Patients with an MRI-confirmed proximal hamstring tendon avulsion were included. Operative or non-operative treatment was selected by a shared decision-making process. The primary outcome was the Perth Hamstring Assessment Tool (PHAT) score. Secondary outcome scores were Proximal Hamstring Injury Questionnaire, EQ-5D-3L, Tegner Activity Scale, return to sports, hamstring flexibility, isometric hamstring strength and MRI findings including proximal continuity.

RESULTS

Twenty-six operative and 33 non-operative patients with a median age of 51 (IQR: 37-57) and 49 (IQR: 45-56) years were included. Median time between injury and initial visit was 12 (IQR 6-19) days for operative and 21 (IQR 12-48) days for non-operative patients (p=0.004). Baseline PHAT scores were significantly lower in the operative group (32±16 vs 45±17, p=0.003). There was no difference in mean PHAT score between groups at 1 year follow-up (80±19 vs 80±17, p=0.97). Mean PHAT score improved by 47 (95% CI 39 to 55, p<0.001) after operative and 34 (95% CI 27 to 41, p<0.001) after non-operative treatment. There were no relevant differences in secondary clinical outcome measures. Proximal continuity on MRI was present in 20 (95%, 1 recurrence) operative and 14 (52%, no recurrences) non-operative patients (p=0.008).

CONCLUSION

In a shared decision-making model of care, both operative and non-operative treatment of proximal hamstring tendon avulsions resulted in comparable clinical outcome at 1-year follow-up. Operative patients had lower pretreatment PHAT scores but improved substantially to reach comparable PHAT scores as non-operative patients. We recommend using this shared decision model of care until evidence-based indications in favour of either treatment option are available from high-level clinical trials.

Minimal graft site morbidity using autogenous semitendinosus graft from the uninjured leg: a randomised controlled trial

PURPOSE

To quantify the effect on strength of semitendinosus (ST) graft harvest by comparing isokinetic and isometric muscle strength.

METHODS

A cohort of 140 patients underwent anterior cruciate ligament (ACL) reconstruction (ACLR) and were randomized to ipsilateral or contralateral ST graft harvest. Isokinetic and isometric muscle strength testing using a dynamometer were collected for the operated and non-operated leg. Patients were assessed pre-surgery and at 6, 12 and 24 months after reconstruction.

RESULTS

ST graft harvest reduced isokinetic flexion muscle strength for 6 months. At 12 months follow up there was no significant difference between the two groups and they were all stronger than pre-injury. No other significant differences were found in any primary or secondary outcome measurements.

CONCLUSION

Solitary ST graft harvest does not appear to result in a permanent reduced isometric or isokinetic quadriceps muscle strength on the side where the graft is harvested. A reduction in hamstring muscle strength of less than 10% can be seen at short-term follow-up with full recovery by 12 months. Most patients report little or no donor site pain. Given these findings, ST autograft is an alternative graft choice that could be used for various reconstructions in terms of donor site morbidity.

LEVEL OF EVIDENCE

Level II.

The modifying factors that help improve anterior cruciate ligament reconstruction rehabilitation: A narrative review

BACKGROUND

The goal of a rehabilitation programme after anterior cruciate ligament (ACL) reconstruction is to manage a patient's goals and expectations (i.e., returning to physical activities and sports) while minimizing the risk of new injury, particularly a new ACL injury. Although general rehabilitation programmes have been proposed, some factors can lead to adapting each programme to each patient.

OBJECTIVE

To describe how different variables, including surgical techniques, sports participation, psycho-social and contextual factors can modify the rehabilitation programme.

METHODS

We performed a narrative review with input from experts in the field (level of evidence 5).

CONCLUSIONS

Modifying factors of the ACL rehabilitation programme are related to the initial lesion or surgery, to sports, or to psychological or social aspects. Regarding the type of graft, the rehabilitation is mainly different in the early postoperative phase; the other phases are not graft-based but rather goal-based rehabilitation. Depending on the meniscal or cartilage repair, the rehabilitation protocol will initially take priority over the anterior cruciate ligament reconstruction protocol. The ACL reconstruction rehabilitation programme should meet the requirements of the anticipated sports, to optimize the athlete's ability to return to the expected level and minimize the risk of reinjury. Psycho-social and contextual factors must also be considered in rehabilitation care to individualize and optimize each patient's programme.

Tendon grafts with preserved muscle demonstrate similar biomechanical properties to tendon grafts stripped of muscular attachments: a biomechanical evaluation in a porcine model

Purpose

(1) To evaluate the biomechanical properties of a porcine flexor digitorum superficialis tendon graft with preserved muscle fibers and (2) to compare these results with the biomechanical properties of a porcine tendon graft after removal of associated muscle.

Methods

Eighty-two porcine forelegs were dissected and the flexor digitorum superficialis muscle tendons were harvested. The study comprised of two groups: Group 1 (G1), harvested tendon with preserved muscle tissue; and Group 2 (G2), harvested contralateral tendon with removal of all muscle tissue. Tests in both groups were conducted using an electro-mechanical material testing machine (Instron, model 23-5S, Instron Corp., Canton, MA, USA) with a 500 N force transducer. Yield load, stiffness, and maximum load were evaluated and compared between groups.

Results

The behavior of the autografts during the tests followed the same stretching, deformation, and failure patterns as those observed in human autografts subjected to axial strain. There were no significant differences in the comparison between groups for ultimate load to failure (p = 0.105), stiffness (p = 0.097), and energy (p = 0.761).

Conclusion

In this porcine model biomechanical study, using autograft tendon with preserved muscle showed no statistically significant differences for yield load, stiffness, or maximum load compared to autograft tendon without preserved muscle. The preservation of muscle on the autograft tendon did not compromise the mechanical properties of the autograft.

Level of evidence

Level III Controlled laboratory study

Is there significant regeneration of the hamstring tendons after harvest for ACL reconstruction? A systematic review of literature

BACKGROUND

Regeneration potential of Hamstring tendons after harvest assumes significant clinical relevance as its use has become widespread today. Methods which best assess the regeneration, extent and type of regeneration, plus issues related to functional loss are important for the surgeon to know. This review looks at the literature to find answers to the above questions.

PURPOSE

To summarize the evidence in support of hamstring tendon regeneration, and the most appropriate modality for evaluation of regeneration. Additionally, to evaluate the regeneration in terms of complete or partial, extent and its impact on strength deficit and functional outcomes.

METHODS

We did a systematic review of literature through specified search engines and identified 30 of 285 studies to be relevant (19 prospective and 11 retrospective).

RESULTS

Evaluation of above data suggests tissue regeneration at harvest sites does occur (78.9% of semitendinosus and 42.7% of gracilis tendons), but this regeneration is variable. No established definition of regeneration exists; MRI is an adequate tool to identify regeneration, while biopsy is confirmative. USG is a cost-effective screening method and can document distal progress of regenerate. Semitendinosus and gracilis tendons regenerate at different rates and extents, and often fuse together, but there is no evidence to state that one regenerates better than the other. Proximal retraction of the muscle-tendon junction occurs, along with some atrophy, which affects function to a variable extent. Strength deficits may persist, but they may not convert to significant functional deficits.

CONCLUSION

There is variable hamstring regeneration after harvest, with poorly defined definition of "regeneration". Some changes in the muscle itself, abnormal distal insertion and absence of regeneration in some are documented, along with strength deficits. Although overall functional deficits have been reported to be minimal, a definite change in the anatomy of the medial hamstrings is a factor to be kept in consideration. More information is needed about the long-term consequences.

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

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.

Knee flexion strength deficits correlate with distal extent of tendon regeneration after hamstring harvest. Preliminary data from an Ultrasound based classification

BACKGROUND

As more evidence comes to light that hamstring harvesting may not be as benign a procedure as previously thought, considerable interest is being generated towards corelating the knee flexural strength deficits with the degree of tendon regeneration. The current study aimed to corelate knee flexion strength deficits with ultrasonographically quantified degree of hamstring regeneration after tendon harvest.

STUDY DESIGN

31 patients of ACL reconstruction with hamstring grafts were divided into 2 groups (6 months and 1-year post op) according to time of follow up. Ultrasonography of both the knees to assess Semitendinosus tendon dimensions was done. Regeneration was classified as non-significant, mild (Zone 1, till 4 cm above the lateral joint line), moderate (Zone 2 ,at the level of the lateral joint line) and significant (Zone 3, 1.5 cm below the lateral joint line) as the regenerate happens from proximal to distal. Regenerate dimensions were compared with US measurements from the opposite knee. Bilateral isokinetic strength tests of the knees were done to evaluate flexion strength, and strength deficits were compared with degree of tendon regeneration.

RESULTS

14 (45%) of cases had no regeneration at both time periods. 7 patients (41%) in the 6-month post-op group showed some form of regeneration, and 10 patients (71%) in the 1-year post-op group showed regeneration. 29/31 patients had some flexion strength deficit. Strength deficit correlated with the level and degree of tendon regeneration, with non-significant regeneration cases showing higher strength deficit (mean - 28.51%), and cases with significant regeneration showing least amount of strength deficit (mean - 3.66%).

CONCLUSION

Flexion strength deficits after hamstring harvest are significant and corelate with degree of tendon regeneration, which improves over time. US is adequate to quantify degree of tendon regeneration, which in turn can help prognosticate return of flexion strength.

Japanese Orthopaedic Association (JOA) clinical practice guidelines on the management of anterior cruciate ligament injury - Secondary publication

BACKGROUND

This clinical guideline presents recommendations for the management of patients with anterior cruciate ligament (ACL) injury, endorsed by the Japanese Orthopaedic Association (JOA) and Japanese Orthopaedic Society of Knee, Arthroscopy and Sports Medicine (JOSKAS).

METHODS

The JOA ACL guideline committee revised the previous guideline based on "Medical Information Network Distribution Service Handbook for Clinical Practice Guideline Development 2014", which proposed a desirable method for preparing clinical guidelines in Japan. Furthermore, the importance of "the balance of benefit and harm" was also emphasized. This guideline consists of 21 clinical questions (CQ) and 23 background questions (BQ). For each CQ, outcomes from the literature were collected and evaluated systematically according to the adopted study design.

RESULTS

We evaluated the objectives and results of each study in order to make a decision on the level of evidence so as to integrate the results with our recommendations for each CQ. For BQ, the guideline committee proposed recommendations based on the literature.

CONCLUSIONS

This guideline is intended to be used by physicians, orthopedic surgeons, physical therapists, and athletic trainers managing ACL injuries. We hope that this guideline is useful for appropriate decision-making and improved management of ACL injuries.

Revision of failed-posterior cruciate ligament (PCL) reconstruction due to tibial tunnel misplacement: A case report

Introduction

Posterior cruciate ligament (PCL) reconstruction failure is a rare condition found. The failure caused by some factors, including improper graft tunnel placement. Although the proper tibial tunnel placement in PCL reconstruction is still controversial, make the tunnel placement anatomically essential to decrease the risk of failure. The use of PCL jig only to guide the direction of tibial tunnel does not always give good results.

Presentation of case

We report a case of 29 year old male with total rupture of ACL and PCL that underwent reconstruction for both ligaments. We found the failure of the PCL graft 2 years after the surgery was related to the tibial tunnel placement which was placed not in proper anatomical site. We performed revision PCL surgery with transseptal portal technique to ensure the tibial tunnel is placed in appropriate position.

Discussion

The cause of failure was associated with misposition of tibial tunnel. The tibial tunnel performed in previous surgery was too anterior than the anatomical foot print. This condition might be caused by surgical technique which depending only on PCL jig to guide the tibial tunnel direction and location. We performed transseptal portal technique get better visualization on the posterior aspect of the knee to achieve the proper direction of tibial tunnel.

Conclusion

The use of PCL jig as the only tools for guiding tibial tunneling should be avoided. Additional tool such as transseptal portal is required to ensure the proper anatomical tibia tunnel in order to achive good PCL graft placement.

ASSESSMENT OF THE REGENERATION CAPACITY OF SEMITENDINOSUS AND GRACILIS TENDONS

Objectives:

To evaluate the regenerative capacity of gracilis (G) and semitendinosus (ST) tendons, to examine the sensitivity and specificity of signs and symptoms in the assessment of hamstring tendons, and to assess the thickness and insertion site of regenerated tendons.

Methods:

Thirty sequential knees were subjected to anterior cruciate ligament reconstruction with semitendinosus and gracilis tendons. After surgery, the patients were followed up clinically with physical examination and magnetic resonance imaging (MRI).

Results:

Overall, 36.66% of the tendons were visible on MRI, whereas 83.33% were palpable. On MRI, the distal insertion site of the regenerated semitendinosus tendon was visible proximal to the landmark of the medial femoral condyle in 28%, at the same level in 16%, and distally in 56% of the cases. Gracilis tendon insertion was visible proximally in 36.66% of cases, at the same level in 10%, and distally in 53.33%. Eleven knees exhibited complete regeneration.

Conclusion:

Partial or total regeneration of the ST and G tendons was apparent on MRI. Palpation is effective for evaluating regeneration of the ST and G tendons; however, MRI is still the gold standard. ST and G tendons regenerated completely in only a small percentage of patients, limiting reuse as a graft in cases with new ligament injuries of the knee. Level of Evidence II, Prospective comparative study.

Functional Effects of Single Semitendinosus Tendon Harvesting in Anatomic Anterior Cruciate Ligament Reconstruction: Comparison of Single versus Dual Hamstring Harvesting

Background

This study aimed to determine the effects of single semitendinosus tendon (ST) harvesting for anterior cruciate ligament (ACL) reconstruction by comparing outcomes of single ST and semitendinosus-gracilis tendon (ST-G) harvesting.

Methods

ACL reconstruction with ST-G harvesting (D group, n = 60) or single ST harvesting (S group, n = 60) were included according to inclusion criteria. Subjective assessments included subjective International Knee Documentation Committee score, Lysholm score, and Tegner activity scale score. Objective assessments included isokinetic strength and functional tests. These tests were completed at 36 months of follow-up. Magnetic resonance imaging (MRI) and second-look arthroscopy findings were evaluated. In the S group, regeneration properties were assessed by serial ultrasonography (US).

Results

The S group showed significantly less deep flexor strength deficit than the D group (p < 0.001). Deep flexor power deficits showed significant correlation with the shift of musculotendinous junction of the ST. There was significant difference in the cocontraction test between the groups (p = 0.012), and the S group tended to show better results in other functional tests at the last follow-up. There were no significant differences in graft tension and synovial coverage on second-look arthroscopy between the groups. In the S group, the regeneration rates assessed by US at the joint line and distal insertion were 81.7% and 80%, respectively at 6 months of follow-up.

Conclusions

The S group showed significantly less deficit in deep flexor strength and tended to show better clinical results at the last follow-up than the D group. In the S group, more than 80% showed good regeneration at the 6-month follow-up. Hence, single ST harvesting is effective in minimizing flexor weakness and functional deficits and shows great potential for regeneration.

Capacity of muscle derived stem cells and pericytes to promote tendon graft integration and ligamentization following anterior cruciate ligament reconstruction

PURPOSE

The aim of this study is to examine the capacity of muscle tissue preserved on hamstring tendons forming candy-stripe grafts in order to improve tendon to bone ingrowth and ligamentization. We hypothesized that muscle tissue does possess a stem cell population that could enhance the healing process of the ACL graft when preserved on the tendons.

METHODS

Human samples from gracilis and semitendinosus muscles were collected during ACL surgery from ten patients and from these tissue samples human muscle-derived stem cells and tendon-derived stem cells were isolated and propagated. Both stem cell populations were in-vitro differentiated into osteogenic lineage. Alkaline phosphatase activity was determined at days zero and 14 of the osteogenic induction and von Kossa staining to assess mineralization of the cultures. Total RNA was collected from osteoblast cultures and real time quantitative PCR was performed. Western-blot for osteocalcin and collagen type I followed protein isolation. Immunofluorescence double labeling of pericytes in muscle and tendon tissue was performed.

RESULTS

Mesenchymal stem cells from muscle and tendon tissue were isolated and expanded in cell culture. More time was needed to grow the tendon derived culture compared to muscle derived culture. Muscle derived stem cells exhibited more alkaline phosphatase actvity compared to tendon derived stem cells, whereas tendon derived stem cells formed more mineralized nodules after 14 days of osteoinduction. Muscle derived stem cells exhibited higher expression levels of bone sialoprotein, and tendon derived stem cells showed higher expression of dental-matrix-protein 1 and osteocalcin. Immunofluorescent staining against pericytes indicated that they are more abundant in muscle tissue.

CONCLUSIONS

These results indicate that muscle tissue is a better source of stem cells than tendon tissue. Achievement of this study is proof that there is vast innate capacity of muscle tissue for enhancement of bone-tendon integration and ligamentization of ACL hamstring grafts and consequently muscle tissue should not be treated as waste after harvesting.

Hamstring Tendon Regeneration After Harvesting: A Systematic Review

BACKGROUND

Hamstring tendons are often used as autografts for anterior cruciate ligament (ACL) reconstruction. However, no systematic review has been performed describing consequences such as hamstring tendon regeneration rate and determinants of hamstring tendon regeneration.

PURPOSE

To summarize the current literature regarding hamstring tendon rate regeneration, the time course of regeneration, and determinants of hamstring regeneration.

STUDY DESIGN

Systematic review.

METHODS

A search was performed in the Embase, Medline (OvidSP), Web of Science, Cochrane, PubMed, and Google Scholar databases up to June 2014 to identify relevant articles. A study was eligible if it met the following inclusion criteria: tendons were harvested, regeneration at harvest site was assessed, population size was at least 10 human subjects, full-text article was available, and the study design was either a randomized controlled trial, prospective cohort study, retrospective cohort study, or case control study. A risk of bias assessment of the eligible articles was determined. Data describing hamstring tendon regeneration rates were pooled per time period.

RESULTS

A total of 18 publications met the inclusion criteria. The mean regeneration rate for the semitendinosus and gracilis tendons was, in all cases, 70% or higher. More than 1 year after harvesting, 79% (median [IQR], 80 [75.5-90]) of the semitendinosus tendons and 72% (median [IQR], 80 [61-88.5]) of the gracilis tendons were regenerated. No significant differences in regeneration rate could be found considering patient sex, age, height, weight, or duration of immobilization. Results did not clearly show whether absence of regeneration disadvantages the subsequent hamstring function. Five studies measured the regeneration rate at different moments in time.

CONCLUSION

Hamstring tendons regenerated in the majority of patients after ACL reconstruction. The majority of the hamstring tendon regeneration was found to occur between 1 month and 1 year after harvest. No significant determinants for hamstring tendon regeneration could be identified because of a lack of research. The function and strength of the regenerated hamstring remained unclear.

Mesenchymal stem cells reside in anterior cruciate ligament remnants in situ

PURPOSE

It has been reported that the anterior cruciate ligament (ACL) has certain self-healing ability after acute injury or with primary suture repair. Many studies have confirmed that a remnant preservation technique with ACL reconstruction contributes to biological augmentation for ACL healing. However, it remains unclear whether mesenchymal stem cells (MSC) reside in ACL remnants in situ. The aim of this study was to investigate the methods of culture and identification of MSC derived from the remnants of ACL rupture patients and to analyse these MSC's properties.

METHODS

The cells of ACL remnants from the ACL rupture patients were isolated by the methods of enzymatic digestion and cultured in vitro to the third passage under the microscope to observe their morphology and growth status. The third passage of isolated cells was analysed for the identification of immunophenotype, osteogenic, adipogenic and chondrogenic differentiation.

RESULTS

On the third to fifth days of in vitro culture, a few cells of long fusiform shape appeared and were adherent to the plastic walls. On the sixth to ninth days, cells clustered and colonies were observed. The third passage cells showed uniform cell morphology and good proliferation, with appearance of the typical surface markers of MSC, CD29, CD44, CD90 and CD105. The surface markers of CD34 and CD45 of haematopoietic stem cells were not expressed. Under appropriate conditions of in vitro culture, isolated cells could be differentiated into osteoblasts that deposit mineralised matrix and express early osteogenic markers, adipocytes that accumulate lipid droplets in cytoplasm and chondrocytes that secrete chondrogenic-specific matrix aggrecan and collagen II. Real-time polymerase chain reaction (PCR) analysis demonstrated that the specific mRNA expression of osteogenesis, adipogenesis and chondrogenesis increased significantly compared with the control groups at day zero.

CONCLUSIONS

Stem cells derived in situ from the human ACL stump were successfully isolated and characterised. Those isolated cells were identified as MSC according to their adherent ability, morphology, surface markers and multilineage differentiation potential. MSC derived from ACL remnants could be a potential source of seeding cells for ligament regeneration.