Flexor digitorum profundus tendon to bone tunnel repair: a vascularization and histologic study in canines

Adjustable-Loop Devices Promote Graft Revascularization in the Femoral Tunnel After ACL Reconstruction: Comparison With Fixed-Loop Devices Using Magnetic Resonance Angiography

Background:

Hamstring tendon grafts are usually fixed in anterior cruciate ligament (ACL) reconstruction using either an adjustable-loop device (ALD) or a fixed-loop device (FLD). The contact area between the graft and the tunnel wall is different between the 2 devices.

Purpose:

To determine using magnetic resonance angiography (MRA) whether ALD and FLD result in different blood flow of the graft in the femoral tunnel during the early postoperative period.

Study Design:

Cohort study; Level of evidence, 3.

Methods:

Between 2008 and 2018, a total of 42 patients (17 men and 25 women) underwent MRA at 3 months after ACL reconstruction. All surgical procedures were performed using semitendinosus tendon autografts folded into 4 strands. Overall, 23 patients underwent the FLD procedure and 19 patients underwent the ALD procedure. The signal intensity of the superior portion of the graft in the femoral tunnel was evaluated using transverse MRA images perpendicular to the femoral tunnel axis.

Results:

MRA images showed high signal intensity in the superior portion of the graft in the femoral tunnel in 94.7% and 60.9% of the ALD patients and FLD patients, respectively, a statistically significant difference (P = .03).

Conclusion:

MRA images at 3 months after surgery revealed that blood flow reached the superior end of the tendon graft in the femoral tunnel in more patients who underwent ACL reconstruction with an ALD compared with an FLD.

Characterization of a purified exosome product and its effects on canine flexor tenocyte biology

Flexor tendon injuries and tendinopathy are very common but remain challenging in clinical treatment. Exosomes-based cell-free therapy appears to be a promising strategy for tendon healing, while limited studies have evaluated its impacts on tenocyte biology. The objective of this study was to characterize a novel purified exosome product (PEP) derived from plasma, as well as to explore its cellular effects on canine tenocyte biology. The transmission electron microscope revealed that exosomes of PEP present cup-shaped structures with the diameters ranged from 80 to 141 nm, and the NanoSight report presented that their size mainly concentrated around 100 nm. The enzyme-linked immunosorbent assay kits analysis showed that PEP was positive for CD63 and AChE expression, and the cellular uptake of exosomes internalized into tenocyte cytoplasm was observed. The cell growth assays displayed that tenocyte proliferation ability was enhanced by PEP solution in a dose-dependent manner. Tenogenic phenotype was preserved as is evident by that tendon-related genes expression (SCX, COL1A, COL3A1, TNMD, DCN, and MKX) were expressed insistently in a high level, while tenocytes were treated with 5% PEP solution. Furthermore, migration capability was maintained and total collagen deposition was increased. More interesting, dexamethasone-induced cellular apoptosis was attenuated during the incubation of tenocytes with a 5% PEP solution. These findings will provide the basic understandings about the PEP, and support the potential use of this biological strategy for tendon healing.

Tensioning Ligament and Tendon Repairs to Bone Using a Modified Screw-post Technique

PURPOSE

The purpose of this study was to demonstrate how to tension tendon and ligament repairs or reconstructions to bone by using an oblique screw-post. A controlled experiment simulating this repair technique is reported, followed by 5 case examples.

METHODS

A wood frame model was used to test 5 initial exposed screw lengths (4, 8, 12, 16, 20 mm) and 5 screw angles [90 (perpendicular to wood plane), 75, 60, 45, 30 degrees]. A spring-based force gauge was tied to the exposed 3.5 mm cortical screw with a washer using a #2 nonabsorbable braided suture, and the screw was fully advanced. System lengths were measured before and after advancement using digital calipers. Screw angles were measured with a protractor. Analysis of variance with post hoc paired t tests was performed to compare changes in system length with different initial exposed screw length and screw angle.

RESULTS

Greater changes in system length was achieved with decreasing screw angle and increasing initial exposed length (P<0.05). A maximum change in system length of 12.4 mm (SD=0.4 mm) was achieved with a 45-degree screw with 20 mm initial exposed length (P<0.05). Five case examples where a screw-post was used to repair tendons and ligaments in the upper extremity are described.

CONCLUSIONS

An oblique screw-post can advance a tendon or ligament repair to bone. This can result in increased tension of the repaired structure, potentially providing a better repair or greater joint stability.

Sports-related wrist and hand injuries: a review

Background

Hand and wrist injuries are common during athletics and can have a significant impact especially if initially disregarded. Due to their high level of physical demand, athletes represent a unique subset of the population.

Main body

The following is an overview of hand and wrist injuries commonly seen in athletics. Information regarding evaluation, diagnosis, conservative measures, and surgical treatment are provided.

Conclusion

Knowledge of these entities and special consideration for the athlete can help the team physician effectively treat these players and help them achieve their goals.

Quantitative evaluation of revascularization at bone tunnels and grafts with contrast-enhanced magnetic resonance angiography after anterior cruciate ligament reconstruction

PURPOSE

Quantitative evaluation of vascular ingrowth to the bone tunnel walls and tendon graft after anterior cruciate ligament reconstruction for up to two years post-surgery using magnetic resonance angiography (MRA).

METHODS

The study population consists of 100 patients that underwent reconstruction with multi-stranded semitendinosus tendons. The patients were retrospectively divided into those that underwent MRA two, three, four to six, and ≥ seven months after surgery (46, 17, 16, and 21 patients, respectively). Digital imaging and communication in medicine (DICOM) MRA images were imported into image processing software (OsiriX®), and the mean signal-to-noise ratio (SNR) of the bone tunnel walls in the femur and tibia and tendon graft parenchyma in the bone tunnels were measured.

RESULTS

On MRA, the signal intensities of the bone tunnel walls in the femur and tibia (12.6 ± 3.41 and 10.7 ± 3.04) were greater than that in the tendon graft (2.65 ± 1.94 and 2.50 ± 2.02, respectively) at two months after surgery. At three months after surgery, the intensities of the tendon grafts (6.25 ± 2.18 and 5.77 ± 1.57, respectively) were greater than those of the bone tunnel wall (2.56 ± 1.29 and 2.50 ± 1.11, respectively). At four to six months, the intensities in the bone tunnel wall were 1.76 ± 0.73 and 1.62 ± 0.72, respectively, and those in the tendon graft were 5.01 ± 2.11 and 4.01 ± 2.35, respectively. At ≥ seven months after surgery, the intensities in the bone tunnel wall were 1.36 ± 0.63 and 1.21 ± 0.87, respectively, and those in the tendon graft were 4.25 ± 1.87 and 3.44 ± 1.99, respectively.

CONCLUSION

Blood flow was seen around the bone tunnel on the femoral and tibial sides two months after ACL reconstruction and in the tendon graft parenchyma three months after surgery. The remodeling process continued after seven months.

Magnetic resonance angiography evaluation of the bone tunnel and graft following ACL reconstruction with a hamstring tendon autograft

PURPOSE

In this study, magnetic resonance angiography (MRA) was performed in the early phase after anterior cruciate ligament (ACL) reconstruction to analyse the changes in nutrient blood vessels and blood flow to the femoral and tibial tunnels and the intraosseous tendon grafts.

METHODS

The subjects were 30 patients who underwent single-bundle ACL reconstruction with an autogenous hamstring tendon. MRA was performed at 2, 3, and 6 months postoperatively (n = 10 at each time point). The mean overall signal-to-noise ratios (SNRs) in the tunnel regions and in the region of the tendon graft were compared in each femur and tibia.

RESULTS

Blood vessels from arteries reached the femoral and tibial tunnels 2 months postoperatively. The tunnel walls showed high signal intensity, while the intraosseous tendon grafts had lower intensity. SNRs showed significant differences between the femoral and tibial tunnels overall and the intraosseous tendon grafts. At 3 and 6 months postoperatively, the signal intensity of the tunnel walls was decreased significantly, while that of the intraosseous tendon grafts was also decreased, but not significantly. At these times, the SNRs of the femoral and tibial tunnels did not differ significantly, both overall and in the region of the intraosseous tendon grafts.

CONCLUSION

Revascularization around the femoral and tibial tunnels occurred at 2 months postoperatively, with blood flow subsequently decreasing over time until 6 months. This revascularization may be involved in bone tendon healing and maturation of the tendon graft within the bone tunnels. Evaluations of revascularization by MRA may show the maturation stage of the graft and guide medical rehabilitation.

LEVEL OF EVIDENCE

IV.

Tendon grafts: their natural history, biology and future development

The use of tendon grafts has diminished as regimes of primary repairs and rehabilitation have improved, but they remain important in secondary reconstruction. Relatively little is known about the cellular biology of grafts, and the general perception is that they have little biological activity. The reality is that there is a wealth of cellular and molecular changes occurring with the process of engraftment that affect the quality of the repair. This review highlights the historical perspectives and modern concepts of graft take, reviews the different attachment techniques and revisits the biology of pseudosheath formation. In addition, we discuss some of the future directions in tendon reconstruction by grafting, which include surface modification, vascularized tendon transfer, allografts, biomaterials and cell-based therapies.

The fate and role of bone graft-derived cells after autologous tendon and bone transplantation into the bone tunnel

BACKGROUND

Grafting bone between the tendon graft and the bone tunnel in anterior cruciate ligament reconstruction increases the mechanical strength of the tendon graft. However, the biological role of the bone graft is unclear. The purpose of this research was to elucidate the role of bone graft cells after autologous tendon graft into the bone tunnel with an autologous bone graft in green fluorescent protein (GFP) transgenic rats.

METHODS

The Achilles tendons of Sprague-Dawley (SD) wild-type rats and bone of GFP rats were harvested and transplanted into bone tunnels drilled in the femurs at the knees of SD rats. The femurs were harvested at 1, 2, and 4 weeks after transplantation and histologically investigated using hematoxylin and eosin staining and immunostaining of heat shock protein 47 (HSP47), macrophages, and type I and type III collagens. Biomechanical tests were performed on the tendon graft 2 and 4 weeks after transplantation to evaluate the ultimate force to failure.

RESULTS

A small number of GFP-positive cells was seen in the tendon graft 2 weeks after transplantation. The cell count in the tendon graft was increased at 4 weeks after transplantation. HSP47-positive cells and macrophage-stained cells present in the tendon graft corresponded with the GFP-positive cells. By 2 weeks after transplantation, the relative areas of immunostained type I and III collagens in the tendon graft had declined significantly in the bone graft group compared to the control. The ultimate failure load in the bone graft group was higher than that in the control group at both 2 and 4 weeks after transplantation.

CONCLUSIONS

This research showed that, within 4 weeks of transplantation, bone graft cells migrate to the tendon graft, where they differentiate into cells involved in collagen production and macrophages. Bone graft cells may contribute to the early stage remodeling of tendon grafts.

Distal attachment of flexor tendon allograft: a biomechanical study of different reconstruction techniques in human cadaver hands

We compared the mechanical force of tendon-to-bone repair techniques for flexor tendon reconstruction. Thirty-six flexor digitorum profundus (FDP) tendons were divided into three groups based upon the repair technique: (1) suture/button repair using FDP tendon (Pullout button group), (2) suture bony anchor using FDP tendon (Suture anchor group), and (3) suture/button repair using FDP tendon with its bony attachment preserved (Bony attachment group). The repair failure force and stiffness were measured. The mean load to failure and stiffness in the bony attachment group were significantly higher than that in the pullout button and suture anchor groups. No significant difference was found in failure force and stiffness between the pullout button and suture anchor groups. An intrasynovial flexor tendon graft with its bony attachment has significantly improved tensile properties at the distal repair site when compared with a typical tendon-to-bone attachment with a button or suture anchor. The improvement in the tensile properties at the repair site may facilitate postoperative rehabilitation and reduce the risk of graft rupture.

The effect of tendon surface treatment on cell attachment for potential enhancement of tendon graft healing: an ex vivo model

For both tendon allografts and autografts, the surface, initially optimized for gliding, may not be ideal to facilitate tissue integration for graft healing to host tendon or bone. As a prelude to studying tendon-bone integration, we investigated the effect of surface treatments with trypsin or mechanical abrasion on cell attachment to the tendon surface in a canine ex vivo intrasynovial tendon tissue culture model. Intrasynovial tendon allograft surfaces were seeded with cells after the following treatments: (1) no treatment, (2) mechanical abrasion, (3) trypsin, and (4) abrasion and trypsin. The area covered by cells was determined using confocal laser microscopy at one and two weeks. Results were compared to untreated extrasynovial tendon. Additional tendons were characterized with scanning electron microscopy. Tendons with trypsin treatment had significantly more surface coverage with cells than the other groups, after both one and two weeks of culture. In terms of the cellular shape and size, cells on tendons with trypsin treatment spread more and were more polygonal in shape, whereas tendons with mechanical abrasion with/without trypsin treatment contained smaller, more spindle-like cells. Surface roughening can affect cell behavior with topographical stimulation. Trypsin surface digestion exposes a mesh-like structure on the tendon surface, which could enhance cell adherence and, possibly, tendon/bone healing.

The capsule's contribution to total hip construct stability--a finite element analysis

Instability is a significant concern in total hip arthroplasty (THA), particularly when there is structural compromise of the capsule due to pre-existing pathology or due to necessities of surgical approach. An experimentally grounded fiber-direction-based finite element model of the hip capsule was developed, and was integrated with an established three-dimensional model of impingement/dislocation. Model validity was established by close similarity to results from a cadaveric experiment in a servohydraulic hip simulator. Parametric computational runs explored effects of graded levels of capsule thickness, of regional detachment from the capsule's femoral or acetabular insertions, of surgical incisions of capsule substance, and of capsule defect repairs. Depending strongly upon the specific site, localized capsule defects caused varying degrees of construct stability compromise, with several specific situations involving over 60% decrement in dislocation resistance. Construct stability was returned substantially toward intact-capsule levels following well-conceived repairs, although the suture sites involved were often at substantial risk of failure. These parametric model results underscore the importance of retaining or robustly repairing capsular structures in THA, in order to maximize overall construct stability. 

Avulsion injuries of the flexor digitorum profundus tendon

Avulsions of the flexor digitorum profundus tendon may involve tendon retraction into the palm and fractures of the distal phalanx. Although various repair techniques have been described, none has emerged as superior to others. Review of the literature does provide evidence-based premises for treatment: multi-strand repairs perform better, gapping may be seen with pullout suture-dorsal button repairs, and failure because of bone pullout remains a concern with suture anchor methods. Clinical prognostic factors include the extent of proximal tendon retraction, chronicity of the avulsion, and the presence and size of associated osseous fragments. Patients must be counseled appropriately regarding anticipated outcomes, the importance of postoperative rehabilitation, and potential complications. Treatment alternatives for the chronic avulsion injury remain patient-specific and include nonsurgical management, distal interphalangeal joint arthrodesis, and staged reconstruction.

The effect of tissue culture on suture holding strength and degradation in canine tendon

The purpose of this study was to assess tendon metabolism and suture pull-out strength after simple tendon suture in a tissue culture model. One hundred and twelve flexor digitorum profundus tendons from 28 dogs were cultured for 7, 14, or 21 days with or without a static tensile load. In both groups increased levels of matrix metalloproteinase (MMP) mRNA was noted. Suture pull-out strength did not decrease during tissue culture. While the presence of a static load had no effect on the pull-out strength, it did affect MMP mRNA expression. This tissue culture model could be useful in studying the effect of factors on the tendon-suture interface.

Evaluation of the vascular status of autogenous hamstring tendon grafts after anterior cruciate ligament reconstruction in humans using magnetic resonance angiography

The purpose of this study is to evaluate the vascular status of autogenous semitendinosus grafts after anterior cruciate ligament reconstruction in humans using magnetic resonance angiography. Twelve patients (mean age, 24.3 years) who underwent anterior cruciate ligament reconstruction with the 4-strand semitendinosus tendon were studied. All patients underwent contrast-enhanced magnetic resonance angiography and second-look arthroscopy in their reconstructed knees on an average of 15.8 months (range 9-22 months) after surgery. Blood vessels to the graft were visualised and contrast medium enhancement for visualising the femoral tunnel, graft, and tibial tunnel was evaluated. Magnetic resonance angiography showed that a branch of the middle genicular artery extended to the upper side of the graft through the posterior capsule and that branches of the inferior genicular artery ended at the lower side of the graft in all patients. These were consistent with the actual findings of the second-look arthroscopy. We found contrast medium enhancement in the femoral and tibial tunnels in all patients. The effect of enhancement at 9 months after ACL reconstruction was higher than that at 22 months. The graft showed enhancement patterns in the posterior portion of the femoral side and the anterior portion of the tibial side. This study demonstrated that the branches of the middle and inferior genicular arteries provide blood supply to the graft, which may influence the maturation of the graft. The revascularisation of the bone tunnels could play an important role in the healing of the ligament-bone tunnel junction.

The effect of carbodiimide-derivatized hyaluronic acid and gelatin surface modification on peroneus longus tendon graft in a short-term canine model in vivo

PURPOSE

We have recently reported that application of carbodiimide-derivatized hyaluronic acid and gelatin (cd-HA gelatin) to a peroneus longus tendon graft increased tendon graft gliding ability and decreased work of flexion compared with untreated grafts in a canine model in vivo. In this study, we investigated the effect of this modification on adhesions, stiffness, strength of the distal attachment, and fibroblast count.

METHODS

A total of 24 dogs were used for this study. The peroneus longus tendons of each hind leg were grafted into the 2nd and 5th digits of one forepaw in each dog. One peroneus longus tendon was treated with cd-HA gelatin prior to grafting, and the other one was immersed in 0.9% saline solution as a control. Animals were killed 1, 3, or 6 weeks postoperatively.

RESULTS

The adhesion score of cd-HA gelatin-treated tendons was significantly less than that in the saline-treated tendons at all time points. There was no significant difference in the indentation stiffness between HA- and saline-treated grafts at any time point. For the ultimate force at the distal attachment, there was a significant difference among the time points, with a steady increase over time, but no significant difference between treated and control tendons at any time point. There was no significant difference in fibroblast count between treated and control tendons at any time point.

CONCLUSIONS

Although gross adhesion formation was less, there was no significant difference in strength at the distal tendon-bone interface, cellularity, or tendon graft stiffness when comparing saline-treated and cd-HA gelatin-treated tendon grafts in vivo.

Early healing of flexor tendon insertion site injuries: Tunnel repair is mechanically and histologically inferior to surface repair in a canine model

Orthopedic injuries often require surgical reattachment of tendon to bone. Tendon ends can be sutured to bone by direct apposition to the bone surface or by placement within a bone tunnel. Our objective was to compare early healing of a traditional surface versus a novel tunnel method for repair of the flexor digitorum profundus (FDP) tendon insertion site in a canine model. A total of 70 tendon-bone specimens were analyzed 0, 5, 10 or 21 days after injury and repair, using tensile and range of motion mechanical testing, histology and densitometry. Ultimate force (a measure of repair strength) did not differ between surface and tunnel repairs at day 0. Both repair types had reduced strength at 10 and 21 days compared to 0 days, indicative of deterioration of suture grasping strength (tendon softening). At 21 days, tendons repaired in a bone tunnel had 38% lower ultimate force compared to surface repairs (p = 0.017). Histological findings were comparable between repair groups at 5 and 10 days but differed at 21 days, when we saw evidence of maturation of the tendon-bone interface in the surface repairs compared to an immature fibrous interface with no evidence of tendon-bone integration in the tunnel repairs. After accounting for bone removed by the tunnel, no difference in bone mineral density or trabecular bone volume existed between surface and tunnel repairs. If the results of our animal study extend to healing of the human FDP insertion, they indicate that FDP tendons should be reattached to the distal phalanx by suture to the cortical surface rather than suture in a bone tunnel.

Where tendons and ligaments meet bone: attachment sites ('entheses') in relation to exercise and/or mechanical load

Entheses (insertion sites, osteotendinous junctions, osteoligamentous junctions) are sites of stress concentration at the region where tendons and ligaments attach to bone. Consequently, they are commonly subject to overuse injuries (enthesopathies) that are well documented in a number of sports. In this review, we focus on the structure-function correlations of entheses on both the hard and the soft tissue sides of the junction. Particular attention is paid to mechanical factors that influence form and function and thus to exploring the relationship between entheses and exercise. The molecular parameters indicative of adaptation to mechanical stress are evaluated, and the basis on which entheses are classified is explained. The application of the 'enthesis organ' concept (a collection of tissues adjacent to the enthesis itself, which jointly serve the common function of stress dissipation) to understanding enthesopathies is considered and novel roles of adipose tissue at entheses are reviewed. A distinction is made between different locations of fat at entheses, and possible functions include space-filling and proprioception. The basic anchorage role of entheses is considered in detail and comparisons are explored between entheses and other biological 'anchorage' sites. The ability of entheses for self-repair is emphasized and a range of enthesopathies common in sport are reviewed (e.g. tennis elbow, golfer's elbow, jumper's knee, plantar fasciitis and Achilles insertional tendinopathies). Attention is drawn to the degenerative, rather than inflammatory, nature of most enthesopathies in sport. The biomechanical factors contributing to the development of enthesopathies are reviewed and the importance of considering the muscle-tendon-bone unit as a whole is recognized. Bony spur formation is assessed in relation to other changes at entheses which parallel those in osteoarthritic synovial joints.