Paul R. Manske

Flexor Tendon Healing

Significant changes in the concepts of tendon physiology and tendon healing have occurred in the last decade. Nevertheless, they reflect questions and controversies which date back many hundreds of years. Investigators and clinicians of today must recognise that, like their predecessors with an interest in flexor tendon surgery, they will contribute to the understanding of this very important structure, but they also will leave unanswered questions for future generations. The current interest in methods to prevent or modify adhesions is based on the presumption that the tendon can participate in the repair process. In this regard, it would be inappropriate to ignore the potential contribution by peripheral cellular elements as well. Surgeons may have moved on from the concept that pricking the tendon causes pain, twitching, and convulsions, but they have not yet clearly defined the repair process and how to consistently obtain healing of a lacerated tendon with a smooth gliding surface.

Engineered allogeneic mesenchymal stem cells repair femoral segmental defect in rats

Bone marrow derived mesenchymal stem cells (MSC) have been shown to be progenitor cells for mesenchymal tissues. These cells may also provide a potential therapy for bone repair. Our previous studies showed that MSC engineered with the gene for bone morphogenetic protein 2 (BMP‐2), a growth factor for bone cells, were capable of differentiating into osteoblast lineage and inducing autologous bone formation in several animal models. Culturing individual MSC for autologous implantation, however, remains problematic. The number of human MSC with osteogenic potential decreases with age, and, in certain diseases, the patients marrow may be damaged or the healthy cells reduced in number. In this study, we used rats with a femoral segmental defect to investigate whether allogeneic BMP‐2 engineered MSC would facilitate bone healing. We show that BMP‐2 engineered allogeneic MSC can repair critical bone defects to the same degree as rats treated with BMP‐2 engineered autologous MSC, if the allogeneic group receives short‐term treatment with immunosuppressant FK506. We also show that allogeneic gene transferred MSC are directly involved in bone repair, in addition to acting as gene deliverers.

The early stages of flexor tendon healing: A morphologic study of the first fourteen days

Healing canine flexor tendons treated with protected early motion were studied by light and transmission electron microscopy in the early stages after repair. Two micrometer sections were made across the repair sites. The repair site configuration varied with the extent of gaps that formed between the tendon ends. Each tendon had areas where the tendon stumps were well coapted, and other areas had defects of up to 3 mm. Some areas had gaps healed by way of a marked cellular response from the epitenon, whereas more closely coapted areas had a greater initial endotenon response. The repair site was revascularized by day 7 in regions with close tendon stump approximation and by 10 to 14 days in regions with larger gaps between the tendon ends.

Biomechanical and histologic characteristics of canine flexor tendon repair using early postoperative mobilization.

The purpose of this experimental study was to evaluate the mechanical and histologic healing of flexor tendon repairs using an early active motion protocol. Three different flexor tendon repair techniques in zone II were used. Forty-seven lacerated canine flexor profundus tendons from 25 dogs were repaired and evaluated at 5, 10, and 21 days after surgery. Eight of 9 Kessler repairs ruptured at days 5 and 10. None of the 19 Savage repairs or the 19 dorsal tendon splint repairs ruptured; 3 of 19 dorsal tendon splint repairs failed owing to adhesions. Smooth tendon gliding was obtained in all specimens in which repair was successful. The gap strength values for both the Savage and dorsal tendon splint repairs improved significantly for day-21 specimens compared to day-5 or day-10 specimens. The ultimate tensile strength showed no reduction during the 3-week period of tendon healing for both repairs. Histologically, there was evidence of progressive healing without surrounding adhesions. The improved suture techniques have the potential to withstand the stress produced by active digital motion protocols.

Intrinsic flexor-tendon repair. A morphological study in vitro.

UNLABELLED Rabbit flexor tendons with a 90 per cent mid-section transverse laceration demonstrated the intrinsic capacity to participate in the repair process in the absence of extrinsic cell sources and without the benefit of nutrition from a circulating blood supply or the influence of synovial fluid. Two cellular processes were involved in the in vitro repair process: (1) phagocytosis occurred by differentiation of fibroblasts from the epitenon--the cells migrated into the repair site and removed cellular debris and collagen fragments, and (2) collagen synthesis occurred primarily within the endotenon cells. CLINICAL SIGNIFICANCE The results of this experimental study support the concept that flexor tendons have the intrinsic capacity to phagocytize old collagen and synthesize new collagen fibrils. Consequently, clinical attempts to prevent or control the peripheral adhesions appear valid, since these adhesions do not appear to be an essential component of the repair process.

Cyclic stress analysis of flexor tendon repair

A method of evaluating flexor tendon repair techniques with the use of cyclic testing is presented. This type of evaluation complements the presently used load-to-failure tests by providing more detailed information about gap formation at the repair site. During load-to-failure testing in this study, core sutures alone demonstrated initial gap formation at 0.85 kg tensile force or more; yet on cyclic testing all techniques demonstrated gap formation of 1.9 mm or greater at 0.5 kg tensile force. Thus cyclic testing demonstrated gap formation not readily apparent on load-to-failure testing. An epitenon stitch placed circumferentially around the laceration site added strength in both load-to-failure and cyclic tests, and significantly reduced gap formation regardless of the core suture technique.

Effect of motion and tension on injured flexor tendons in chickens

This study was undertaken to evaluate the individual effects of motion and tension on the healing response of injured flexor profundus tendons in chickens. Partial midsection transverse lacerations of the profundus tendons were produced in 53 chickens. Postoperatively, they were assigned randomly to four management groups: both motion and tension; only motion, no tension; no motion, only tension; no motion and no tension. Biomechanical results at 4 weeks showed that breaking strength significantly increased with both motion and tension, significantly decreased with neither, and was intermediate with only motion or only tension. Histologic evaluation generally showed the greatest cellular activity with both motion and tension, the least with neither, and an intermediate response with one or the other alone. Collagen fiber staining was increased primarily in the tension groups. The finding that both motion and tension enhance the tendons response to injury encourages the development of active mobilization protocols following tendon repair.

Differences between locking loops and grasping loops: Effects on 2-strand core suture***

The differences between locking and grasping configurations used to suture lacerated flexor tendons were evaluated using a 2-strand core model in human cadaver tendon. Locking suture configurations tighten around bundles of tendon fibers with tension, while grasping loops do not tighten around but pull through tendon fibers and distract with tension. The greatest tensile strength was found in 1-locking, 2-locking, and 2-grasping suture loop configurations per suture strand. The 2-grasping loops per suture strand, however, had the greatest distraction (gapping) as the suture material pulled through the tendon. A single locking configuration per strand yielded the maximum tensile strength with reduced distraction (gapping) at the repair site.

Flexor tendon healing in the rat: a histologic and gene expression study☆

PURPOSE To establish a rat flexor tendon laceration and repair model to investigate the molecular mechanisms of flexor tendon healing. METHODS Surgery was performed on rat flexor digitorum longus tendons from both hind feet. Repaired tendons were harvested at 0, 3, 7, 14, 21, 28, 42, 56, and 84 days after surgery. Histologic study (first 84 days) and gene expression study (first 28 days) of several collagens and matrix metalloproteinases (MMPs) were performed. RESULTS In the histologic study pre-existing collagen bundles were degraded between days 7 to 21. Newly formed collagen fibers crossed the repair site by day 28. Remodeling of the collagen fibers continued until day 84. Gene expression of type I collagen decreased initially and then returned gradually to the initial level by day 28, whereas expression levels of types III, V, and XII collagen were increased after surgery. The expression levels of MMP-9 and MMP-13 peaked between days 7 to 14, whereas MMP-2, MMP-3, and MMP-14 levels increased after surgery and maintained high levels until day 28. CONCLUSIONS The rat tendon laceration model represented the entire tendon healing process. The results of this study suggest that MMP-9 and MMP-13 participate only in collagen degradation, whereas MMP-2, MMP-3, and MMP-14 participate not only in collagen degradation but also in collagen remodeling.

Mechanical properties of various circumferential tendon suture techniques

We evaluated the mechanical properties of six different circumferential tendon sutures with a variable number of suture strands. Seventy-two human cadaver flexor profundus tendons were cut and repaired using only a 6/0 polypropylene circumferential suture. The six running suture techniques were: Simple; Simple-locking; Lembert; Halsted; Cross-stitch; Lin-locking; using 10, 14 and 18 suture passes. The increased suture passes increased both tensile and gap strengths. The tensile strength of the Lin-locking technique (29 to 63 N) was significantly stronger than the others, followed by Cross-stitch (27 to 38 N), Halsted (21 to 27 N), Lembert (20 to 27 N), Simple (11 to 22 N) and Simple-locking (10 to 17 N). The gap strength values were between 3 to 14 N, with no significant differences between the techniques. The resistance to gliding, as measured by work of flexion, was not affected by the number of strands. However, the Lin-locking significantly increased the resistance to gliding (33-36%) compared to the other techniques (6-21%); there were no significant differences between these five techniques.