Providing Quantitative Feedback When Teaching Tendon Repair: A New Tool

Flexor tendon repair remains one of the more difficult technical tasks facing the hand surgeon. A good repair must be both strong and able to glide smoothly through the tendon sheath. The purpose of this study is to present a model that allows surgeons to improve their technique of flexor tendon repair by receiving feedback on these important biomechanical parameters. The set-up requires testing equipment found in most biomechanical laboratories and should be available in many academic medical centres. Preliminary data suggest that receiving feedback about the strength and smoothness of a flexor tendon repair may be a very useful tool in helping surgeons improve the overall quality of their tendon repair technique.

Biomechanical effect of rotator cuff augmentation with an acellular dermal matrix graft: a cadaver study

BACKGROUND

Acellular human dermal matrix grafts (Graftjacket; Wright Medical Technology, Arlington, TN, USA) are used clinically for rotator cuff augmentation without a detailed understanding of their biomechanical effects. The purpose of this study was to evaluate the effect of augmentation with dermal grafts on the biomechanical effects of rotator cuff repairs.

METHODS

Nine matched pairs of human cadaveric shoulders were used. A single-row rotator cuff repair combined with an augmentation graft was performed on one shoulder, and a single-row repair was performed on the contralateral shoulder as a control. An acellular dermal matrix graft was sutured to the tendon medially and fixed to the humerus laterally. The constructs were preloaded at 10 N and then cyclically loaded between 10 and 180 N for 1000 cycles, followed by tensile testing to failure at 1.0 mm/s.

FINDINGS

The maximum load of the augmentation group (560.2 N, SD 95.5) was greater than that of the control group (345.7 N, SD 60.8), while the linear stiffness of the augmentation group (65.2 N/mm, SD 15.6) was less than that of the control group (77.2 N/mm, SD 15.7). Reliable gap distance data were not obtained during cyclic loading in 5 of 9 augmented repairs due to the elasticity of the dermal matrix graft.

INTERPRETATION

The dermal matrix graft augmentation increased the maximum load but did not increase the linear stiffness. The elasticity of the dermal matrix graft affected the biomechanical effects of the augmented rotator cuff repairs.

Biomechanical comparison of lesser tuberosity osteotomy versus subscapularis tenotomy in total shoulder arthroplasty

BACKGROUND

Total shoulder arthroplasty is traditionally performed through an anterior deltopectoral exposure with subscapularis tenotomy. Postoperative subscapularis dysfunction is common and adversely affects clinical outcomes. Consequently, surgeon interest in lesser tuberosity osteotomy has grown in an effort to improve subscapularis repair strength. This study investigated the biomechanical strength of subscapularis tenotomy vs lesser tuberosity osteotomy in the setting of total shoulder arthroplasty.

MATERIALS AND METHODS

Uncemented humeral prostheses were placed in 20 paired upper extremities from 10 cadavers. For each respective cadaver, 1 limb underwent lesser tuberosity osteotomy and the contralateral limb underwent subscapularis tenotomy. The cadaveric specimens then underwent cyclic displacement and maximum load to failure testing.

RESULTS

The subscapularis tenotomy specimens exhibited significantly less cyclic displacement (0.8 mm) than the osteotomy group (1.8 mm), with a 95% confidence interval (CI) for the difference of 0.5 to 1.5 mm (P = 0.002). The maximum load to failure was 439 ± 96 N for tenotomy and 447 ± 89 N for osteotomy (95% CI for the difference of -58 to 75), which was not significant (P = .78).

CONCLUSION

Lesser tuberosity osteotomy was not significantly stronger than subscapularis tenotomy in maximum load to failure testing, with minimal clinical significance set at 100 N. Subscapularis tenotomy repair showed statistically significant less cyclic displacement than lesser tuberosity osteotomy. Further research is needed to clarify how the biomechanical results immediately after subscapularis tenotomy and lesser tuberosity osteotomy correlate with clinical outcomes.

WOUND-HEALING PROPERTIES OF TRANSFORMING GROWTH FACTOR β (TGF-β) INDUCIBLE EARLY GENE 1 (TIEG1) KNOCKOUT MICE

Transforming growth factor beta (TGF-β) has a broad effect on wound healing, but many questions remain about the regulation of TGF-β during the healing process. TGF-β inducible early gene 1 (TIEG1) is a primary response gene for TGF-β that controls the activities of the TGF-β/Smad pathway, the primary TGF-β signaling pathway. The purpose of this study was to investigate the role of TIEG1 in cutaneous wound healing using TIEG1 knockout mice. The wound healing in TIEG1 knockout mice and wild-type controls was evaluated by wound breaking strength, Western blot, and histology at postoperative days 3, 7, and 14. Although re-epithelialization of both groups was similarly complete at day 7, the TIEG1 knockout mice had a significantly lower wound breaking strength than the controls at postoperative day 14. These results suggest that TIEG1 expression may be an important factor involved in the initiation and support of normal cutaneous wound healing.

Triceps tendon properties and its potential as an autograft

BACKGROUND

Although the triceps tendon has been used as a graft for ligament reconstruction about the elbow, and has been postulated to be useful as a graft in the treatment of massive rotator cuff tears, no data exists on the tensile properties of the triceps tendon. The purpose of this study was to define the tensile properties of the medial, lateral, and central thirds of the triceps tendon, in order to examine its potential as an autograft for upper extremity pathology.

MATERIALS AND METHODS

Ten fresh frozen upper extremity specimens were used. The triceps tendon was dissected from its musculotendinous junction and left attached to its insertion at the olecranon. The tendon was split into thirds and its tensile properties were recorded using a materials testing machine.

RESULTS

The lateral portion was significantly thinner and less stiff than the medial and central portions (P < .05). It failed at significantly lower ultimate load than the central portion (P < .05). There were no significant differences between the medial, central, and lateral portions of the triceps tendons with regards to ultimate stress (P = .20) or modulus of elasticity (P = .64).

CONCLUSION

Data from the current study were compared to available literature regarding tensile properties of the rotator cuff and elbow ligaments. Both the medial and central portions of the triceps tendon offer sufficient strength to be used in the reconstruction of the rotator cuff or ligament reconstruction in the elbow.

Surface treatment with 5-fluorouracil after flexor tendon repair in a canine in vivo model

BACKGROUND

Topical 5-fluorouracil has been reported to reduce adhesions in animal models of tenolysis. The purpose of this study was to investigate the effects of topical 5-fluorouracil on adhesion formation after tendon repairs were subjected to immediate postoperative rehabilitation in a canine model in vivo.

METHODS

Sixty dogs were randomly assigned to either a 5-fluorouracil treatment (thirty dogs) or a control group (thirty dogs). Each treatment group was then divided into three survival time points: ten days, twenty-one days, and forty-two days. The second and fifth flexor digitorum profundus tendons from each dog were fully lacerated at the zone-II area and then were repaired. Passive motion therapy started at day 5 postoperatively and continued until the dogs were killed. The repaired tendons were evaluated for normalized work of flexion, gliding resistance, repair strength, gene expression for type-I and type-III collagen and transforming growth factor-beta1, and histological appearance.

RESULTS

The normalized work of flexion of the repaired tendons treated with 5-fluorouracil was significantly lower than that of the repaired tendons without 5-fluorouracil treatment at ten days. However, there was no significant difference between treated and untreated tendons at twenty-one and forty-two days. There was also no significant difference in gliding resistance, repair failure strength, or stiffness between treated and untreated tendons at any time point, or in the gross or histological appearance of adhesions at the time of killing. The expression of types-I and III collagen and transforming growth factor-beta1 of the repaired tendon with 5-fluorouracil treatment was significantly lower than that of the tendons without treatment at ten days postoperatively, but not at twenty-one or forty-two days.

CONCLUSIONS

Although 5-fluorouracil treatment can reduce adhesions in in vivo models of tenolysis, this treatment had only a transient effect in an in vivo model of tendon repair that included passive motion.

Lubricin surface modification improves tendon gliding after tendon repair in a canine model in vitro

This study investigated the effects of lubricin on the gliding of repaired flexor digitorum profundus (FDP) tendons in vitro. Canine FDP tendons were completely lacerated, repaired with a modified Pennington technique, and treated with one of the following solutions: saline, carbodiimide derivatized gelatin/hyaluronic acid (cd-HA-gelatin), carbodiimide derivatized gelatin to which lubricin was added in a second step (cd-gelatin + lubricin), or carbodiimide derivatized gelatin/HA + lubricin (cd-HA-gelatin + lubricin). After treatment, gliding resistance was measured up to 1,000 cycles of simulated flexion/extension motion. The increase in average and peak gliding resistance in cd-HA-gelatin, cd-gelatin + lubricin, and cd-HA-gelatin + lubricin tendons was less than the control tendons after 1,000 cycles (p < 0.05). The increase in average gliding resistance of cd-HA-gelatin + lubricin treated tendons was also less than that of the cd-HA-gelatin treated tendons (p < 0.05). The surfaces of the repaired tendons and associated pulleys were assessed qualitatively with scanning electron microscopy and appeared smooth after 1,000 cycles of tendon motion for the cd-HA-gelatin, cd-gelatin + lubricin, and cd-HA-gelatin + lubricin treated tendons, while that of the saline control appeared roughened. These results suggest that tendon surface modification can improve tendon gliding ability, with a trend suggesting that lubricin fixed on the repaired tendon may provide additional improvement over that provided by HA and gelatin alone.

Gliding resistance and strength of composite sutures in human flexor digitorum profundus tendon repair: an in vitro biomechanical study

PURPOSE

Although the strength of a tendon repair is clearly important, the friction of the repair is also a relevant consideration. The purpose of this study was to characterize the frictional coefficient, gliding resistance, and breaking strength of suture materials and a suture construct commonly used for flexor tendon repair.

METHODS

We measured the friction coefficients of 3-0 braided nylon enclosed in a smooth nylon outer shell (Supramid, S. Jackson, Alexandria, VA), 3-0 braided polyester coated with polybutilate (Ethibond, Ethicon, Somerville, NJ), and 3-0 braided polyester/monofilament polyethylene composite (FiberWire, Arthrex, Naples, FL) sutures. We also measured the gliding resistance, linear breaking strength, and resistance to gapping of zone 2 modified Pennington tendon repairs with the 2 lowest-friction sutures in 20 human cadaveric flexor digitorum profundus tendons.

RESULTS

The braided polyester/monofilament polyethylene composite had a significantly lower friction coefficient (0.054) than either the coated polyester (0.076) or nylon (0.130) sutures. The gliding resistances of the repaired tendons with braided/monofilament polyethylene composite suture and those of coated, braided polyester were similar. The strength of the 2 repairs (force to produce a 2 mm gap) and resistance to gap formation were also not significantly different.

CONCLUSIONS

Braided polyester composite is a low-friction suture material. However, when this suture was used for tendon repair with a locking suture technique, it did not show a significant effect on the gliding resistance and repair strength compared with the same repair using a coated polyester suture.

Prosthesis design and stress profile after hip resurfacing: a finite element analysis

PURPOSE

To evaluate the effect of prosthesis design on stress profile in the proximal femur after hip resurfacing.

METHODS

The von Mises stress profile of the native femur was simulated and compared with that of resurfaced femurs using various prosthetic materials (titanium, cobalt-chrome, ceramic), stem lengths (normal, half, short, and no stem), and femoral head coverage (shell size) [260 degrees, 220 degrees, 180 degrees, and 140 degrees].

RESULTS

Hip resurfacing altered the stress profile of the cancellous (but not cortical) bone of the femoral neck. Maximal cortical stresses were observed at the posterior half of the medial femoral neck. The stress profile of the native femur was most similar to that of the resurfaced femur made of titanium, with a short or no stem and 260 degrees of femoral head coverage (shell size).

CONCLUSION

Optimising prosthesis design by minimising biomechanical alterations seems a valid approach to achieving favourable long-term outcomes. Cadaveric and in vivo studies are needed to confirm the clinical relevance and feasibility.

Effects of carpal tunnel release on the relative motion of tendon, nerve, and subsynovial connective tissue in a human cadaver model

BACKGROUND

The purpose of this study was to evaluate the effect of flexor retinaculum division (simulated carpal tunnel release) on the relative motion of flexor tendon, subsynovial connective tissue, and median nerve in human cadaver specimens.

METHODS

Using fluoroscopy, we measured the relative motion of middle finger flexor digitorum superficialis tendon, subsynovial connective tissue, and median nerve in twelve human cadavers with simulated fist motion. Measurements were obtained for three wrist positions: neutral; 60 degrees flexion; and 60 degrees extension. The shear index was defined as the difference in motion between two tissues (tendon, subsynovial connective tissue, or nerve) relative to tendon excursion, expressed as a percentage. After testing with an intact carpal tunnel, the flexor retinaculum was cut and the testing procedure was repeated.

FINDINGS

With an intact flexor retinaculum, the wrist flexion position showed significantly less displacement for the subsynovial connective tissue and median nerve relative to tendon displacement, and thus the highest potential shear strain between subsynovial connective tissue-tendon, and tendon-nerve. The wrist extension position also had a significantly higher potential shear strain for tendon-nerve compared to the neutral position. After division of the flexor retinaculum, the differences in shear index among wrist positions were reduced. For the wrist flexion position, the subsynovial connective tissue and median nerve displacements significantly increased, indicating lower shear index values.

INTERPRETATION

These findings suggest that division of flexor retinaculum reduces the potential shear strain and thus possibly the risk of shear injury to tissues with the carpal tunnel.

Mechanical strength of bone allografts subjected to chemical sterilization and other terminal processing methods

Infectious disease transmission through the use of human donor allografts can be a catastrophic complication in an otherwise straightforward surgical procedure. The use of bone allograft in reconstructive orthopedic surgeries is increasing, yet severe complications, including death, can result if the transplanted tissues transmit a communicable disease to the tissue recipient. The BioCleanse tissue sterilization process is a fully automated, low-temperature chemical sterilization process that renders allograft tissue sterile. The purpose of this study was to evaluate the effect of a chemical tissue sterilization process on the mechanical strength of cortical bone allografts prior to implantation. Cylindrical cortical bone specimens were harvested from seven human cadaver donors and treated either by: chemical sterilization alone; chemical sterilization and terminal sterilization by gamma irradiation; chemical sterilization, lyophilization, terminal sterilization by STERRAD and rehydration; or untreated. The specimens were tested to failure in axial compression, diametral compression, shear, or bending. There were no significant differences in ultimate stress, strain, or fracture energy between the chemically sterilized and control groups in any of the testing modes.

The effect of wrist position on the relative motion of tendon, nerve, and subsynovial connective tissue within the carpal tunnel in a human cadaver model

The purpose of this study was to measure the effect of wrist position on the relative motion of the middle finger flexor digitorum superficialis (FDS) tendon, subsynovial connective tissue (SSCT), median nerve, and flexor retinaculum during simulated active finger motion. The relative motion of each tissue was measured by fluoroscopy in 10 human cadavers. Measurements were obtained for wrist positions of neutral (0 degree extension), 30 and 60 degrees of flexion, and 30 and 60 degrees of extension. The shear strain index (SSI) was defined as the difference in motion between two tissues (tendon, SSCT, or nerve) divided by tendon excursion, expressed as a percentage. The motion of the tendon, SSCT, and nerve in the 60 degree flexed position was significantly less than the motion in all other wrist positions (p < 0.001). The SSI at 60 degrees of flexion for tendon-SSCT and tendon-nerve were significantly increased compared with all other positions (p < 0.001). Because the SSCT and tendon are physically connected, a decrease in SSCT motion relative to the tendon would increase the shear strain on the SSCT with tendon motion. Thus, this result suggests that the SSCT may be predisposed to shear injury from activity done in 60 degrees of wrist flexion.

Dextrose-induced subsynovial connective tissue fibrosis in the rabbit carpal tunnel: A potential model to study carpal tunnel syndrome?

In this pilot study, hypertonic dextrose solution was used to induce fibrosis of the subsynovial connective tissue (SSCT) and create an animal model of potential use in the study of carpal tunnel syndrome (CTS). The SSCT of the carpal tunnel in 15 New Zealand white rabbits were injected with 0.05 ml of 10% dextrose solution in 1 paw and 0.05 ml of saline in the contralateral paw, to serve as a control. The animals were killed at 1, 2, 4, 8, or 12 weeks. While the saline side showed minimal changes at any time period, the hypertonic dextrose side showed progressive noninflammatory SSCT fibrosis, with vascular proliferation and thickening of collagen bundles. Demyelination of the median nerve developed at 12 weeks after the injection on the dextrose side. These findings are similar to the progression of pathology noted in humans with CTS.

Substrate adhesion affects contraction and mechanical properties of fibroblast populated collagen lattices

Fibroblasts can condense a hydrated collagen lattice to a tissue-like structure. The purpose of this study was to evaluate the effect of substrate adhesion on the contraction and mechanical properties of fibroblast populated collagen lattices. Bacteriological grade polystyrene (BGPS) plates and tissue culture polystyrene (TCPS) plates were used as substrates for incubation of fibroblast populated collagen lattices. Hydrophobicity of the polystyrene surfaces was measured by the static sessile contact angle method. Collagen lattice contraction was recorded for 2 weeks, after which the lattices were mechanically tested. The BGPS culture plate had a significantly larger contact angle and was more hydrophobic than the TCPS culture plate. Both hydrophobicity and peripheral detachment of the collagen gel significantly decreased the time lag before initiation of gel contraction and increased the strength of the fibroblast populated collagen lattices. Substrate adhesion affects the contractility and strength of cell seeded collagen gels. This information may be useful in developing tissue engineered tendons and ligaments.

Mechanical properties of intrasynovial and extrasynovial tendon fascicles

BACKGROUND

Tendon grafting in tendon reconstruction often involves the interchange of intrasynovial and extrasynovial tendons. Although many studies have examined the cellular and biological differences between tendons of various sources, few have studied the mechanical properties of these two different types of tendons. The purpose of this study was to investigate the mechanical properties of intrasynovial and extrasynovial tendons.

METHODS

Canine peroneus longus (extrasynovial) and flexor digitorum profundus (intrasynovial) tendons, further subdivided into intrasynovial tendinous and intrasynovial fibrocartilaginous segments, were used in the study. An indentation test was used to measure the compressive modulus. Tensile testing was performed on 400mum longitudinal sections.

FINDINGS

The compressive modulus of the intrasynovial fibrocartilaginous segment was significantly higher than that of the intrasynovial tendinous segment, which was in turn significantly higher than that of the extrasynovial tendon (P<0.0001). The tensile modulus of extrasynovial tendon was significantly higher than that of intrasynovial fibrocartilaginous and intrasynovial tendinous segments (P<0.005). The tensile modulus of the intrasynovial fibrocartilaginous and tendinous segments was not significantly different (P=0.14).

INTERPRETATION

The results suggest that extrasynovial tendons exhibit superior tensile properties but inferior compressive properties when compared to intrasynovial tendons, which is consistent with their biological role in situ, but which could lead to complications when these tendons are repositioned during tendon graft surgery.

Lubricin surface modification improves extrasynovial tendon gliding in a canine model in vitro

BACKGROUND

Lubricin is the principal lubricant in synovial fluid. Although lubricin has been identified in tendons, especially on the surface of intrasynovial tendons such as the flexor digitorum profundus tendon, its ability to improve tendon gliding is unknown. The purpose of this study was to investigate the effects of exogenously applied lubricin on the gliding of extrasynovial tendons in a canine model in vitro.

METHODS

Forty peroneus longus tendons, along with the proximal pulley in the ipsilateral hind paw, were harvested from adult mongrel dogs. After the gliding resistance of the normal tendons was measured, the tendons were treated with one of the following solutions: saline solution, lubricin, carbodiimide derivatized gelatin (cd-gelatin), carbodiimide derivatized gelatin with hyaluronic acid (cd-HA-gelatin), or carbodiimide derivatized gelatin to which lubricin had been added in a second step (cd-gelatin plus lubricin). Tendon gliding resistance was measured for 1000 cycles of simulated flexion-extension motion of the tendon. Transverse sections of the tendons were examined qualitatively at 100x magnification to estimate surface smoothness after 1000 cycles.

RESULTS

There was no significant difference in the gliding resistance between the tendons treated with saline solution and those treated with lubricin alone, or between the tendons treated with cd-HA-gelatin and those treated with cd-gelatin plus lubricin; however, the gliding resistance of the tendons treated with cd-gelatin plus lubricin was significantly lower than that of the tendons treated with saline solution, lubricin alone, or cd-gelatin alone (p < 0.05). After 1000 cycles of tendon motion, the gliding resistance of the tendons treated with cd-gelatin plus lubricin decreased 18.7% compared with the resistance before treatment, whereas the gliding resistance of the saline-solution-treated controls increased >400%. The tendon surfaces treated with cd-gelatin plus lubricin or with cd-HA-gelatin appeared smooth even after 1000 cycles of tendon motion, whereas the other surfaces appeared roughened.

CONCLUSIONS

While the addition of lubricin alone did not affect friction in this tendon gliding model, the results indicate that lubricin may preferentially adhere to a tendon surface pretreated with cd-gelatin and, when so fixed in place, lubricin does have an important effect on tendon lubrication.

Evaluation of the material properties of the subsynovial connective tissue in carpal tunnel syndrome

BACKGROUND

The purpose of this study was to determine the material properties of the normal carpal tunnel subsynovial connective tissue in response to shear stress.

METHODS

The shear modulus and maximum shear strength were measured with a custom-made micro-tester in 10 specimens of subsynovial connective tissue from 10 wrists in eight patients with idiopathic carpal tunnel syndrome and in 10 specimens from five fresh frozen cadavers without a history of carpal tunnel syndrome.

FINDINGS

The mean shear modulus was 22.8 (SD 15.4)kPa for the patient group and 2.7 (SD 1.8)kPa for the control group. The mean maximum shear strength was 54.6 (SD 20.3)kPa for the patient group and 23.3 (SD 10.7)kPa for the control group. The values for the patient group were significantly higher than the control group (P<0.05).

INTERPRETATION

The material properties of subsynovial connective tissue are altered in patients with idiopathic carpal tunnel syndrome. The impact, if any, of these altered properties on carpal tunnel syndrome remains to be elucidated.

Factors related to contraction and mechanical strength of collagen gels seeded with canine endotenon cells

Fibroblasts can construct a hydrated collagen lattice to a tissue-like structure that is greatly influenced by initial culture conditions. The purpose of this study was to investigate the effects of cell concentration and collagen concentration on the contraction kinetics and mechanical properties of resultant endotenon-derived fibroblast-seeded collagen lattice. The experiment was designed to evaluate the effect of cell concentration (0, 0.25, 0.5, and 1.0 x10(6) cells/mL) and collagen concentration (0.5, 1.0, 1.5, and 2.0 mg/mL). Collagen lattice contraction was recorded for 42 days, after which time the lattices were mechanically tested. The collagen lattices seeded with higher initial cell concentration had a shorter contraction lag phase (p < 0.01), and exhibited a higher ultimate stress (p < 0.01) and instantaneous and equilibrium modulus (p < 0.01) than those seeded with a lower initial cell concentration. The collagen lattices cultured with a lower initial collagen concentration also had a shorter contraction lag phase, and exhibited greater instantaneous and equilibrium modulus (p < 0.01) than those cultured with higher initial collagen concentration. The collagen lattices of initial 0.5 mg/mL collagen concentration had the highest value of ultimate stress (p < 0.03).

The mechanical properties of the rabbit carpal tunnel subsynovial connective tissue

The rabbit model is commonly used to study carpal tunnel syndrome (CTS). It has been proposed that the subsynovial connective tissue (SSCT) in the carpal tunnel may play a role in the etiology of CTS, but the material properties of the rabbit SSCT are unknown. The purpose of this study was to develop a method to measure the shear properties of the rabbit SSCT. In six rabbit cadaver forepaws, the excursion of the third digit flexor digitorum superficialis (FDS) and load to failure of the SSCT were measured in a custom device. The mean excursion to full flexion in this model was 7.08mm (S.D. 0.77). The mean shearing force at full flexion was 317 mN (S.D. 166). At full flexion percentage of maximum shear force in the SSCT was 54.5% (S.D. 19.4). The mean energy absorbed at full flexion was 0.29mJ (S.D. 0.31). The mean excursion needed to reach 5% of the maximum shear force was 3.04mm (S.D. 0.99). The testing model presented in this study demonstrates structural parameters to evaluate the shear properties of the SSCT in a rabbit model. The data presented could be used for estimating sample sizes in a more comprehensive study of the effect of CTS on the SSCT properties.

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.

Permeability of the subsynovial connective tissue in the human carpal tunnel: a cadaver study

BACKGROUND

The purpose of this study was to determine the permeability of the normal carpal tunnel subsynovial connective tissue.

METHODS

Subsynovial connective tissue samples (10mm(2)) were obtained from 10 fresh frozen human cadavers without a history of carpal tunnel syndrome. The thickness of the sample was measured using a charge-coupled device laser displacement system. Each specimen was tested for permeability in a closed pressure chamber at 13.8, 41.3, 68.9 and 96.5 kPa.

FINDINGS

Since permeated flow was very low in all specimens, the permeability could be calculated only for eight specimens at 96.5 kPa pressure and for three specimens at 68.9 kPa. The mean permeability at 96.5 kPa was mean 0.89 (SD 0.93)x10(-14)m(4)/Ns and at 68.9 kPa was mean 1.04 (SD 1.54)x10(-14)m(4)/Ns.

INTERPRETATION

The subsynovial connective tissue is the most characteristic tissue in the carpal tunnel; it is found in no other location in such abundance. It is well known that carpal tunnel syndrome is the result of increased pressure within the carpal tunnel. This lack of permeability in the subsynovial connective tissue may explain the predisposition of this region for pressure buildup and subsequent neuropathy.

Direct tendon attachment and healing to porous tantalum: an experimental animal study

BACKGROUND

The ability to directly attach soft-tissue to metal would have broad clinical application. Previous attempts to obtain normal tendon-to-bone attachment strength have been unsuccessful. In the present study, we hypothesized that when the initial interface mechanical environment is carefully controlled, a highly porous form of tantalum metal would allow the ingrowth of tendon tissue with clinically relevant tendon-to-implant fixation strength approaching that of an intact tendon-to-bone insertion.

METHODS

Supraspinatus tendons from forty skeletally mature dogs were reattached to the greater tuberosity between two custom-designed porous tantalum washers. Clinical function as judged on the basis of gait analysis, reattachment fixation strength and stiffness, and tendon function as seen through muscle volume were evaluated preoperatively, immediately postoperatively, and at three, six, and twelve weeks after surgery. Qualitative and quantitative histomorphologic evaluation was performed at three, six, and twelve weeks after surgery.

RESULTS

Gait analysis with use of force-plate measurements demonstrated return to a normal gait pattern by three weeks after surgery. Tendon-implant strength as a percentage of normal, contralateral controls increased significantly, from 39% at the time of surgery to 67% at three weeks, 99% at six weeks, and 140% at twelve weeks (p < 0.0014). The stiffness of the construct also increased and approached that of normal tendon, measuring 47% at the time of surgery, 62% at three weeks, 94% at six weeks, and 130% at twelve weeks (p < 0.0299). Supraspinatus muscle volume initially decreased by 33% but recovered to 92% of normal by twelve weeks (p < 0.01). Histomorphologic evaluation showed Sharpey-like fibers inserting onto the surface of the porous tantalum. Quantitative histomorphometric analysis revealed a time-dependent increase in the density of the collagen tissue filling the metal voids below the implant surface of first the bottom washer and then the top washer.

CONCLUSIONS

Robust biologic ingrowth of tendon into a porous tantalum implant surface can be achieved under conditions of secure initial mechanical fixation. The strength and stiffness of the tendon-implant construct reached normal levels by six to twelve weeks in this animal model.

Enhancing the strength of the tendon-suture interface using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride and cyanoacrylate

PURPOSE

Preventing gap or rupture is important to achieving a successful outcome after tendon repair. Weak sutures break; strong sutures fail by pull-out at the tendon-suture interface. In this study, we investigated the use of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) and cyanoacrylate to enhance the strength of the tendon-suture interface.

METHODS

Twenty-four canine flexor digitorum profundus tendons were used to test EDC and cyanoacrylate reinforcement methods, with 12 tendons in each group. A single-loop suture technique was used to test the tendon-suture interface strength.

RESULTS

The mean ultimate strengths of the EDC group and the cyanoacrylate group were significantly higher than those of their respective control groups. The stiffness of the group with cyanoacrylate-augmented loops was significantly higher than that of its respective control group. There was no significant difference in stiffness between the 2 reinforcement methods.

CONCLUSIONS

Our results suggest that tendon-suture interface reinforcement may improve the pull-out failure strength of a suture construct and thereby increase the effectiveness of stronger suture materials. Future studies might address the effects of different kinds and methods of reinforcement with various suture materials and constructs and in different tissues.

Mechanical properties of patellar tendon allografts subjected to chemical sterilization

PURPOSE

We tested the hypothesis that the preimplantation mechanical properties of BioCleanse-treated bone-patellar tendon-bone (BPTB) allografts are not significantly different from those of untreated specimens.

METHODS

For this controlled laboratory study, specimens were harvested as central third or hemi-BPTB units from both knees of 17 cadaveric tissue donors (11 men and 6 women) aged 19 to 88 years. Donor-matched specimens (20 per group) were randomly assigned to either BioCleanse-treated or untreated control groups. Specimens were subjected to 25 minutes of pretensioning at 89 N and then cyclically loaded under longitudinal tension between 50 N and 250 N for 1,000 cycles at 1 Hz, followed by ramp to failure at 50 mm/min.

RESULTS

No statistically significant difference was found between untreated and BioCleanse-treated specimens in stiffness (235.3 +/- 37.6 N/mm v 222.3 +/- 53.4 N/mm, P = .37), cyclic creep (0.38 +/- 0.42 mm v 0.40 +/- 0.26 mm, P = .81), maximum force (1,685.7 +/- 471.6 N v 1,807.0 +/- 657.8 N, P = .47), or ultimate stress (29.0 +/- 9.8 MPa v 29.0 +/- 12.8 MPa, P = .98).

CONCLUSIONS

The preimplantation mechanical properties of BPTB allografts treated with BioCleanse are not significantly different from those of untreated controls.

CLINICAL RELEVANCE

This laboratory study compares the biomechanical properties of chemically treated allografts, which are currently being used in anterior cruciate ligament reconstruction, with those of nontreated fresh-frozen allografts.

Detection of differential gliding characteristics of the flexor digitorum superficialis tendon and subsynovial connective tissue using color Doppler sonographic imaging

OBJECTIVE

The subsynovial connective tissue (SSCT) is the most characteristic structure in the carpal tunnel and is substantially affected in cases of carpal tunnel syndrome. We investigated the usefulness of Doppler sonography for measuring velocity differences between the flexor tendon and its associated SSCT in the carpal tunnel of cadaver hands.

METHODS

Six human cadaver wrists were used in this study (mean age of death, 82.2 years). The velocity difference between the middle finger flexor digitorum superficialis tendon and its corresponding SSCT was measured on a sonography machine equipped with a fingertip 13-MHz linear probe.

RESULTS

At tendon velocities of greater than 2.5 cm/s, the tendon velocity was significantly greater than the SSCT velocity (P < .05). At less than 2.5 cm/s, there was no significant difference between tendon and SSCT velocities.

CONCLUSIONS

Color Doppler imaging can identify and track SSCT motion separately from that of its associated tendons. Analysis of SSCT motion characteristics by color Doppler imaging may be useful for studying its function clinically.

Effect of curing time and concentration for a chemical treatment that improves surface gliding for extrasynovial tendon grafts in vitro

The purpose of this study was to evaluate whether treatment time and concentration of these reagents have an effect on the resulting gliding resistance. Forty peroneus longus (PL) tendons were used, from 20 adult mongrel dogs, along with the A2 pulley obtained from the ipsilateral hind paw. After the baseline gliding resistance was measured, the PL tendons were treated with one of three concentrations of hyaluronic acid (HA) and 1-ethyl-3-[3-dimethylaminopropyl] carbodiimide hydrochloride (EDC) or N-hydroxysuccinimide (NHS) mixed with 10% gelatin for various times (5, 30, and 60 min). Tendon friction was measured over 1000 cycles of simulated flexion/extension motion. Gliding resistance of the untreated PL tendons had no significant difference among the groups. After surface treatment with low concentration of HA and EDC/NHS for 5-min cure, the gliding resistance was similar to that of the untreated PL tendon and significantly higher than its 30- and 60-min treatment. For the rest of high concentration of HA and EDC/NHS groups, the gliding resistance was lower than that of untreated PL tendon. However, there was no significant difference among the timing points. It is possible to optimize the effect of surface treatment on friction and durability by regulating cure time and concentration of reagents in a canine extrasynovial tendon in vitro.

Anatomic variation of the 5th extensor tendon compartment and extensor digiti minimi tendon

Anatomic variation within the 5th extensor compartment may contribute to the development of tenosynovitis and limit the usefulness of the extensor digiti minimi (EDM) for tendon transfer. The purpose of this study was to assess the anatomic variation of the EDM tendon and its surrounding retinaculum, with particular attention to anatomical variation between specimens. Forty-one fresh cadaver hands were dissected. The length of the 5th compartment retinaculum was noted. The incidence of an intercompartmental septum was noted in each specimen as well as the type of tendinous attachments present between the EDM and extensor digitorum communis (EDC) tendons. The presence and length of any accessory retinacular bands distal to the edge of proper extensor retinaculum was also noted. Only one specimen contained a single EDM tendon, while 71% (n = 29) of specimens contained two slips and 23% (n = 9) had three slips; 24% (n = 10) of EDC tendons had no slip to the small finger, while 61% (n = 25) of specimens had a single slip to the small finger. The EDC's contribution to the small finger was found to be an independent tendon in 42% of cases (n = 17), while 34% (n = 14) of specimens were found to have a common EDC slip, which branched to both the ring and small finger. Three EDM tendons divided distal to the extensor retinaculum, while the remaining EDM tendons divided beneath or proximal to the extensor retinaculum. Seventy-three percent (n = 30) of the specimens had an accessory retinacular band surrounding the EDM tendon identified at the base of the 5th metacarpal. Eighty-eight percent (n = 36) of hands had a septum between the EDM slips. The surgeon should be aware of variability within the 5th dorsal compartment in cases of trauma and in cases of tendon transfer. In our series 30 of 41 specimens were noted to contain an accessory dorsal retinacular band surrounding the EDM and 36 specimens were noted to contain a septum within the 5th compartment. The presence of an accessory retinacular band surrounding the EDM at the level of the 5th metacarpal base is an anatomic finding that requires further investigation.

The number of screws, bone quality, and friction coefficient affect acetabular cup stability

One of the major causes of loosening of cementless acetabular cup implants is insufficient initial stability. This study used three-dimensional finite element models of the pelvis and acetabular components to investigate the effects of the number of screws, bone quality, and friction coefficient of the acetabular cup on the initial stability under normal walking. A commercially available hemispherical acetabular cup with five screw holes was used as the default model. The stiffness of the pelvis and the friction coefficient of the cup were systematically varied, within a realistic range, to assess the initial stability of the acetabular cup. The simulations showed that the inserted screws provide only a localized reduction in the relative micromotion between the cup and pelvis therefore inserting several screw closed together might not be useful. Changes in the pelvic stiffness have a non-linear effect on the initial stability of acetabular cup and the subchondral bone provides good support for fixation of the cementless cup. The friction coefficient of the acetabular cup plays a limited role, comparing with the factor of bone quality, in resisting relative micromotion in the cup-pelvis interface.

Histological and biomechanical evaluation of implanted graft materials in a rabbit vaginal and abdominal model

OBJECTIVE

The objective of the study was to describe the histologic and biomechanical changes of implanted dermal collagen graft materials.

STUDY DESIGN

Twenty rabbits were randomized into 2 groups (6 and 12 weeks, respectively). Each rabbit had 4 graft segments (human dermis, porcine dermis, porcine collagen-coated polypropylene mesh, and autologous fascia) randomly implanted into the abdomen and the vagina. Biomechanical testing and histologic analysis was performed after recovery of graft segments.

RESULTS

Dermal graft segments showed a marked decrease in ultimate strength (84% to 86%) and elastic modulus (73% to 82%) that was significantly different from the decrease seen in autologous fascia or coated synthetic mesh (P < .0008 and P < .0001, respectively). The decrease in ultimate strength was associated with vaginal implantation (P = .057). Dermal graft materials had moderate inflammation and minimal collagen infiltration.

CONCLUSION

The mechanical properties of dermal graft materials decline after implantation. Vaginal implantation may cause a different tissue response to graft material than abdominal implantation. Dermal graft material caused moderate inflammation and minimal collagen ingrowth remote from implantation.

Contraction of collagen gels seeded with tendon cells

Knowledge of the adaptation of the soft tissue to mechanical factors and biomolecules would be essential to better understand the mechanism of tendon injury and to improve the outcome of tendon repair. The responses to these factors could be different for the distinct types of cells in the tendon: cells from the tendon sheath, fibroblasts from the epitenon surface, or fibroblasts from the internal endotenon. In this study, we examined the mechanical and histological characteristics of the rate of contraction of the collagen gel seeded with epitenon and endotenon fibroblasts. The rate of contraction and the mechanical property of the contracted construct depend on the gel concentration and also the treatment of TGF-beta1.

Gliding Resistance of the Flexor Pollicis Longus Tendon after Repair: Does Partial Excision of the Oblique Pulley Affect Gliding Resistance?

BACKGROUND

After tendon repair, it is critical for the repair site to pass smoothly under the pulley edge to promote gliding and reduce the risk of adhesion or rupture. In this study, the authors assessed the effect of partial excision by "squaring off" the distal edge of the oblique pulley on the gliding resistance of the flexor pollicis longus tendon after repair in vitro.

METHODS

Gliding resistance of 10 human thumbs was measured directly with three different sequential conditions: intact flexor pollicis longus tendon with intact A1 and oblique pulleys (group A), intact pulleys after repair of the tendon (group B), and after repair and excision of the distal triangular part (squaring off) of the oblique pulley (group C).

RESULTS

Gliding resistance increased significantly after repair and squaring off the oblique pulley (group A, 0.22 +/- 0.08 N; group B, 1.29 +/- 0.68 N; and group C, 2.01 +/- 0.84 N).

CONCLUSIONS

Previous studies suggest that the trimming of an annular pulley in the finger would not result in any significant mechanical disadvantage if other parts of the pulley system were intact. However, the authors' results suggest that in the case of the thumb oblique pulley, gliding resistance is increased after trimming and tendon repair, and thus the oblique pulley should be left intact if possible.

Internal fixation of dorsally displaced fractures of the distal part of the radius. A biomechanical analysis of volar plate fracture stability

BACKGROUND

Volar plate fixation with use of either a locking plate or a neutralization plate has become increasingly popular among surgeons for the treatment of dorsally comminuted extra-articular distal radial fractures. The purpose of the present study was to compare the relative stability of five distal radial plates (four volar and one dorsal), all of which are commonly used for the treatment of dorsally comminuted extra-articular distal radial fractures, under loading conditions simulating the physiologic forces that are experienced during early active rehabilitation.

METHODS

With use of a previously validated Sawbones fracture model, a dorsally comminuted extra-articular distal radial fracture was created. The fracture fixation stability of four volar plates (an AO T-plate, an AO 3.5-mm small-fragment plate, an AO 3.5-mm small-fragment locking plate, and the Hand Innovations DVR locking plate) were compared under axial compression loading and dorsal and volar bending simulating the in vivo stresses that are generated at the fracture site during early unopposed active motion of the wrist and digits. A single dorsal plate (an AO pi plate) was used for comparison, with and without simulated volar cortical comminution. The construct stiffness was measured to assess the resistance to fracture gap motion, and comparisons were made among the implants.

RESULTS

The volar AO locking and DVR plates had greater resistance to fracture gap motion (greater stiffness) compared with the volar AO nonlocking and AO T-plates under axial and dorsal loading conditions (p < 0.01), with no significant difference between the AO volar locking and DVR plates. The volar AO locking plate had greater resistance to fracture gap motion than did the volar AO nonlocking plate under axial loading and dorsal bending forces (p < 0.01). The dorsal pi plate had the greatest resistance to fracture gap motion under axial loading and volar and dorsal bending forces (p < 0.01). However, the pi plate was significantly less stable to axial load and dorsal bending forces when the volar cortex was comminuted (p < 0.01).

CONCLUSIONS

In this model of dorsally comminuted extra-articular distal radial fractures, dorsal pi-plate fixation demonstrated better resistance to fracture gap motion than did the four types of volar plate fixation. The AO volar locking and DVR plates conferred the greatest resistance to fracture gap motion among the four volar plates tested. Volar locking technology conferred a significant increase in resistance to fracture gap motion as compared with nonlocking plate technology.

The relation between micromotion and screw fixation in acetabular cup

One of the major causes inducing loosening in the cementless acetabular cup implanting is its insufficient initial stability. In this study, three-dimensional finite element models of the pelvis and acetabular components were developed to investigate the relationship between relative micromotion, initial stability, and screw fixation under six daily activity loadings. A commercial available hemispheric cup with five screw holes was used as the target acetabular cup. The simulation results showed that if screws were placed closed together, when the screw number increased from 1 to 5, the peak micromotion decreased less than 14%, from 126.5 to 108.8 microm, while the stable region, micromotion less than 28 microm, enlarged only by 40%, from 46.1% to 64.7%. However, if the screw could be placed near the cup rim, a single rim screw, 202.1 microm micromotion, could provide better stability than that of four dome screws, 209.6 microm micromotion, placed closed together. To conclude, multiple cup screws should be placed near cup rim and as separate as possible to enlarge the stable region and reduce the peak micromotion between cup and acetabulum.

Scleral penetration force requirements for commonly used intravitreal needles

INTRODUCTION

Repeated intraocular injections have become routine practice. It is important to determine how to make them as painless as possible. We wished to examine the force required to penetrate the sclera with different gauge needles.

METHODS

Recently enucleated eyes had 4 mm scleral punch biopsies performed. The scleral disks were mounted on a fixed load cell and either a new needle or a needle that had previously penetrated a rubber vial was attached to a linear stage and the maximum penetration force measured.

RESULTS

The 27-gauge needles required almost twice as much force to penetrate the sclera than either the 30- or the 31-gauge. In addition, the 30- and 31-gauge appeared to require similar force. In all cases, following vial perforation, there was an increase in the amount of force required to penetrate the sclera. The amount of force was variable.

DISCUSSION

Smaller gauge needles require less force to penetrate the sclera and needles that have been used to penetrate rubber vials require more force.

Effects of screw eccentricity on the initial stability of the acetabular cup

One of the major failure modes of cementless acetabular components is the loosening of the acetabular cup, which is mostly attributable to insufficient initial stability. A hemispherical cup with a porous coating which is inserted with press-fit fixation and secured with several screws is one of the most widely used approaches. Many studies have found that bone screws are very helpful aids for cup fixation, but the optimal surgical technique for inserting screws has not been clearly reported. In this study, hemispherical cups were fixed into blocks of foam bone with zero to three screws. The effects of three types of screw eccentricity (a 1-mm offset and angular eccentricities of 15 degrees and 25 degrees ) on the initial stability of the acetabular cup were evaluated. The experimental results indicate that increasing the number of screws enhances the cup stability in the case of ideal screwing (i.e., with no eccentricity). An angular eccentricity of 15 degrees did not affect the cup stability for fixation with one or two screws. However, the presence of 25 degrees of angular eccentricity significantly reduced the stability of the cup, while 1 mm of offset eccentricity produced an even greater impact.

Tensile strength of a new suture for fixation of tendon grafts when using a weave technique

PURPOSE

To evaluate a new corner stitch construct for tendon graft or tendon transfer fixation and compare the tensile strength with a conventional central cross-suture design in human cadaver tendons.

METHODS

Flexor digitorum profundus tendons of the index, middle, and ring fingers (48 total) were used as recipients and palmaris longus, extensor indicis proprius, and extensor digitorum communis tendons of the index finger (48 total) were used as grafts from 16 fresh-frozen human cadaver hands. We compared the cross-stitch technique with a new corner stitch technique in tendon repairs made with 1, 2, or 3 weaves (8 per group). Tendons were sutured at each weave with either 2 full-thickness cross-stitches or 4 partial-thickness corner stitches of 4-0 nylon. Mattress sutures also were placed through the free tendon end for each repair type. The tensile strength of the tendon-graft composite was measured with a materials testing machine.

RESULTS

The tensile strength of the repairs increased significantly with the number of weaves. When 2 or 3 weaves were used with the corner stitch or when 3 weaves were used with the cross-stitch, the repairs were significantly stronger. Although no significant difference in strength to failure was noted when comparing cross and corner stitches with equivalent numbers of weaves, qualitatively there was a difference in mode of failure with the 3-weave corner stitches failing primarily by intrasubstance tendon failure and the 3-weave cross-stitch repairs failing by tendon pullout.

CONCLUSIONS

The corner stitch is as strong as conventional cross-stitch repairs and its superficial placement may be more favorable to tendon blood supply. This repair may be advantageous for clinical applications.

Rotator cuff repair using an acellular dermal matrix graft: an in vivo study in a canine model

PURPOSE

Large rotator cuff tears present a challenge to orthopaedic surgeons. Because tissue may be insufficient or of inadequate quality to undergo repair, a variety of materials have been used as adjuncts. Human dermal tissue may be processed to render it acellular, and thus less immunogenic, but with the extracellular matrix left intact, creating a collagen scaffold with favorable characteristics. Because of these traits, use in rotator cuff repair was proposed.

METHODS

A canine model for a full-thickness infraspinatus tendon tear was used. Tendon was excised from the bony interface to the myotendinous junction, and a human acellular dermal matrix graft (experimental) or the autologous excised tendon (control) was used to bridge the defect. Animals were sacrificed, and shoulders were evaluated histologically and biomechanically.

RESULTS

At time 0, strength of control and experimental repairs was similar. At 6 weeks, the strength of the experimental repair was half that of the control side. Strength of control specimens remained the same at 6 and 12 weeks, but by 12 weeks, the strength of the experimental repair was equal to that of the control. Histologically, cells infiltrated the control and experimental specimens by 6 weeks; chronic inflammation was consistent with surgery and repair. At 6 months, control and experimental specimens mimicked normal tendon structure grossly and histologically.

CONCLUSIONS

Use of human acellular dermal matrix as a patch is a viable option in this model of large rotator cuff defects. Within 6 weeks, histologic evidence of native cell infiltration and neotendon development was observed. Within 12 weeks, the strength of the dermal matrix graft repair was equivalent to that of autologous tendon. At 6 months, control and graft specimens mimicked normal tendon structure grossly and histologically.

CLINICAL RELEVANCE

This study provides in vivo animal data to support the use of this acellular dermal matrix graft for repair of full-thickness rotator cuff defects. Additional studies are indicated to determine the role of this material in the treatment of humans with rotator cuff tears.

Optimization of surface modifications of extrasynovial tendon to improve its gliding ability in a canine model in vitro

Previous studies have shown that the carboxyl groups in hyaluronic acid (HA) could be activated by 1-ethy 1-3-[3-dimethylaminopropyl] carbodiimide hydrochloride (EDC)/N-hydroxysuccinimide (NHS) to form intermediate O-acylisoureas, which can chemically bind to exposed amino groups on the tendon surface, leading to improved gliding ability. However, the optimal ratio and concentrations of the components in this chemical mixture were not investigated. The purpose of this study was to optimize the constituents of this tissue engineering approach to tendon surface modification, to reduce friction and improve durability. Peroneus longus (PL) tendons (n=40) were harvested from adult mongrel dogs along with the A2 pulley obtained from the ipsilateral hind paw. After the gliding resistance of the normal PL tendon was measured, the tendons were treated under varying concentrations of HA (0.5, 1, and 2%) and EDC/NHS (0.05, 0.25, and 1%) mixed with a 10% gelatin. Tendon friction was measured for 1000 cycles of simulated flexion/extension motion. Following testing, the residual HA on the tendon surface was evaluated by immunohistochemisty. The gliding resistance of the untreated PL tendons had a mean value of 0.087+/-0.021 N. After surface treatment, there was no significant difference in friction due to HA concentration alone, but the concentration of EDC/NHS and the interaction between HA concentration and EDC/NHS concentration had a significant effect on friction. Regardless of HA concentration, the friction after 1000 cycles was significantly decreased in preparations which included a 1% concentration of EDC/NHS. The tendons with lower gliding resistance presented a smoother surface on light microscopy and maintained more residual HA on the tendon surface. By varying the relative concentrations of HA, EDC, and NHS it is possible to optimize the effect of surface treatment on friction and durability in a canine extrasynovial tendon in vitro.

Effect of wrist and ulna head position on gliding resistance of the extensor digitorum minimi and extensor digitorum communis III tendons: a cadaver study

While attrition from sharp bony surfaces is the most common cause of extensor digiti minimi (EDM) tendon rupture, the etiology of other cases of spontaneous EDM tendon rupture is still unknown. Friction within the compartment may play a role, especially with ulna dislocation. The purpose of this study was to compare gliding resistance of the EDM tendon with that of a tendon which rarely ruptures spontaneously, the extensor digitorum communis of the middle finger (EDC III) tendon, under various wrist and ulna head positions. Eight fresh frozen cadavers were used. Gliding resistance between the tendon and its sheath in each compartment was measured in five different wrist positions and three different ulna head positions. Gliding resistance of the EDM tendon (0.13 +/- 0.03 N) was significantly greater than the EDC III tendon (0.09 +/- 0.03 N) (p < 0.05). For the EDM tendon, the gliding resistance in ulnar deviation or pronation was higher than the gliding resistance in neutral, radial deviation, or supination (p < 0.05), and the gliding resistance with ulnar lengthening (over 6 mm) or dorsal ulnar dislocation (over 9 mm) was higher than in neutral ulnar head positioning. For the EDC III tendon, the gliding resistance in ulnar deviation was significantly higher than the gliding resistance in neutral, radial deviation, or supination, or dorsal dislocation with ulnar lengthening (p < 0.05). Wrist ulnar deviation, ulnar dorsal dislocation (over 9 mm), and ulnar lengthening (over 6 mm) increased the gliding resistance of the EDM tendon. In patients at risk for EDM rupture, such as those with rheumatoid arthritis or distal radioulnar joint osteoarthritis, avoiding such positions may be advantageous.

Morphological changes of collagen fibrils in the subsynovial connective tissue in carpal tunnel syndrome

BACKGROUND

Pathologic changes occur commonly in the subsynovial connective tissue in patients with carpal tunnel syndrome. The purposes of this study were to investigate the ultrastructural changes of the subsynovial connective tissue in these patients and compare them with the findings in cadaver controls.

METHODS

The diameter and density of collagen fibrils were measured by transmission electron microscopy in specimens of subsynovial connective tissue from ten patients with idiopathic carpal tunnel syndrome and from ten fresh-frozen cadavers of individuals without known symptoms of carpal tunnel syndrome.

RESULTS

We noted deformed collagen fibrils with a spiraled appearance in the specimens from the patients. We also observed phagocytosis of elastin fibrils in all of those specimens. These changes were noted only rarely in the cadaver controls. The mean diameter (and standard deviation) of the collagen fibrils was 45.5 +/- 8.0 nm in the control group and 54.8 +/- 15.2 nm in the patient group (p < 0.05). The mean number of collagen fibrils per 0.04 microm2 (density) was 201.38 +/- 48.88 in the control group and 157.08 +/- 54.38 in the patient group (p < 0.05).

CONCLUSIONS

These ultrastructural findings suggest that subsynovial collagen in patients with carpal tunnel syndrome is structurally different from that in individuals without carpal tunnel syndrome, but the processes resulting in that abnormal morphology remain to be elucidated.

Effect of finger ulnar deviation on gliding resistance of the flexor digitorum profundus tendon within the A1 and A2 pulley complex

PURPOSE

To evaluate the effect of ulnar deviation of the finger on gliding resistance of the flexor digitorum profundus tendon within the A1 and A2 pulley complex.

METHODS

Thirty-two human cadaveric fingers (index through small fingers) were used. The gliding resistance was measured at 5 different angles of ulnar deviation (0 degrees, 15 degrees, 30 degrees, 45 degrees, 60 degrees).

RESULTS

There was a significant increase in gliding resistance with increased ulnar deviation. The gliding resistances at 0 degrees, 15 degrees, 30 degrees, 45 degrees, and 60 degrees of ulnar deviation were 0.40+/-0.13 N, 0.44+/-0.13 N, 0.55+/-0.17 N, 0.74+/-0.21 N, and 1.02+/-0.30 N, respectively. The gliding resistance at 60 degrees was significantly greater than at all other angles; 45 degrees ulnar deviation had significantly higher gliding resistance than 0 degrees, 15 degrees, and 30 degrees; and 30 degrees ulnar deviation had significantly higher gliding resistance than 0 degrees.

CONCLUSIONS

A greater angle of ulnar deviation causes higher gliding resistance during motion of the flexor digitorum profundus tendon within the A1 and A2 pulley complex. The gliding resistance increases significantly at angles greater than 30 degrees of ulnar deviation. The increased tendon loading needed to overcome increased gliding resistance caused by ulnar deviation could result in a vicious cycle of progressive ulnar deviation. Although mild degrees of ulnar deviation may be well tolerated mechanically a reasonable therapeutic guideline might be to prevent deviation from exceeding 30 degrees.

Development of a biologic prosthetic composite for cartilage repair

At present there is no satisfactory treatment for deep osteochondral defects. Here we report the development of a biologic prosthetic composite containing periosteum from 2-month-old rabbits and a porous tantalum scaffold. When cultured under chondrogenic conditions, the composites form a robust hyaline-like cartilage outgrowth that is attached to the porous scaffold by fibrous tissue ingrowth. The mechanical properties of these composites are similar to those of normal osteochondral plugs after only 6 weeks in culture. Thus, porous tantalum scaffolds are compatible with the chondrogenic capacity of periosteum. We hypothesize that these periosteum-porous tantalum composites will be useful for the repair of major osteochondral defects. However, in vivo experiments using biological resurfacing of large osteochondral defects with a porous tantalum scaffold and autologous periosteal graft in animal models are necessary to further explore this possibility. The implications of a successful method for cartilage regeneration would be great in terms of the number of patients affected and the quality of life for each of those patients.

Contribution of the interosseous membrane to distal radioulnar joint constraint

PURPOSE

Although forearm injuries are accompanied frequently by rupture to the interosseous membrane (IOM) diagnosis of the extent of IOM injury is difficult. In this study we evaluated distal radioulnar joint (DRUJ) laxity caused by both partial and complete IOM disruption and compared these quantitative measurements with the common clinical manual evaluation of DRUJ laxity and dislocatability.

METHODS

Human cadaveric forearms (n = 8) were used in this study. Skin, muscles, and tendons were removed. The specimens were mounted on an experimental apparatus that allowed the radius to move freely about the fixed ulna. Tests were performed in neutral rotation, 60 degrees pronation, and 60 degrees supination. Under various conditions of IOM sectioning testing was performed by volary and dorsally translating the radius relative to the ulna in the coronal plane of the radius. Testing was performed both qualitatively as would be performed in the clinic and quantitatively with an instrumented probe.

RESULTS

Our results show that dorsal dislocation of the radius relative to the ulna strongly suggests distal IOM rupture. Disengagement of the radius from the DRUJ indicated injury to the distal and middle IOM. The distal IOM constrained volar and dorsal laxity of the radius at the DRUJ in all forearm rotation positions. The midportion of the IOM constrained laxity except in the volar direction of the pronated forearm. The proximal IOM did not constrain the proximal radius except dorsally for the pronated forearm position.

CONCLUSIONS

The IOM, in particular the distal IOM, plays an important role in constraining dorsal dislocation of the radius at the DRUJ.

Canine carpal joint fusion: a model for four-corner arthrodesis using a porous tantalum implant

PURPOSE

Interest has focused on porous materials that promote bony ingrowth. In this study a porous tantalum implant was used as an adjunct to intercarpal stabilization in a canine model of wrist arthrodesis.

METHODS

A defect was created at the junction of the radiocarpal, ulnocarpal, and fourth carpal bones, analogous to a four-corner fusion site in humans. A tantalum cylinder was press-fit and stabilized with K-wires. Controls were represented by creating the defect without implant placement. Animals were killed at 4, 8, and 12 weeks.

RESULTS

Histology showed bony ingrowth as early as 4 weeks and mechanical testing showed a statistically significant increase in strength of the construct over time. Controls failed to achieve union at any time point.

CONCLUSIONS

The implant served as an adjunct to stabilization of the carpus in this model of four-corner fusion, suggesting a novel application of this material in conditions in which bone graft has been required previously. This study represents a preliminary investigation of the use of a tantalum device for intercarpal stabilization; it does not compare this technique with conventional methods.

Immunolocalization of collagen types in the subsynovial connective tissue within the carpal tunnel in humans

The tenosynovium within the carpal tunnel consists of a single layer of synovial cells, which lines the bursae within the carpal tunnel, and the subsynovial connective tissue (SSCT), which contains the tendon vasculature and other structural elements. In this study, we used immunogold labeling to localize collagen types within the SSCT in three cadaver specimens and three patients with carpal tunnel syndrome. Positive labeling for collagen types I, III and VI was found with immunoelectron microscopy. Collagen types I and III were codistributed within the SSCT. Type VI was primarily located in microfibrillar structures between collagen bundles, between elastin and collagen bundles and between collagen bundles and cells. There was no difference in the distribution of collagen types when comparing cadaver specimens and carpal tunnel patients.

Gliding resistance of the extensor pollicis brevis tendon and abductor pollicis longus tendon within the first dorsal compartment in fixed wrist positions

PURPOSE

While the etiology of de Quervain's disease is unknown, repetitive motion coupled with awkward wrist position and septation within the first dorsal compartment are considered causative factors. We hypothesize that these conditions might produce high gliding resistance, which could then induce micro-damage of the tendons and retinaculum. The purpose of this study was to measure the gliding resistance of the extensor pollicis brevis and abductor pollicis longus tendons within the first dorsal compartment in a human cadaver model.

METHODS

Fifteen human cadaver wrists, which included eight septation and seven non-septation wrists in the first dorsal compartment, were used. Gliding resistance of the extensor pollicis brevis and abductor pollicis longus tendons was measured in seven wrist positions: 60 degrees extension, 30 degrees extension, 0 degrees, 30 degrees flexion, 60 degrees flexion in neutral deviation and 30 degrees ulnar deviation, 15 degrees radial deviation in neutral extension/flexion.

RESULTS

The overall gliding resistance was not different between septation and non-septation wrists (0.21 versus 0.19 N for abductor pollicis longus and 0.21 versus 0.15 N for extensor pollicis brevis, respectively), but there was a significant effect on gliding resistance due to wrist position (p<0.05) in both tendons. Interaction between wrist position and septation status was observed in the extensor pollicis brevis tendon (p<0.05). With septation, the gliding resistance of the extensor pollicis brevis was significantly higher in 60 degrees wrist flexion (0.51 N) compared to all other wrist positions tested (all less than 0.26 N) (p<0.05). In the non-septation group, gliding resistance was significantly higher in 60 degrees flexion (0.20 N) and 60 degrees extension (0.22 N) compared to the other five wrist positions (all less than 0.15 N) (p<0.05). Although no significant difference was observed, the extensor pollicis brevis tendon with septation tended to have higher gliding resistance than that without septation in wrist flexion. In 60 degrees of wrist flexion the abductor pollicis longus tendon had significantly higher gliding resistance (0.33 N) than the other wrist positions (all less than 0.26 N) (p<0.05).

CONCLUSIONS

A combination of septation and wrist position significantly affected extensor pollicis brevis tendon gliding resistance in this cadaver model. These factors may contribute to the development of de Quervain's disease.

Effect of elbow position on canine flexor digitorum profundus tendon tension

Tendon injury in the finger remains a clinical challenge to hand surgeons. A canine model is commonly used to study biological effects of tendon injuries and their treatment. There is an important anatomical difference between human and canine anatomy that may be overlooked, however, namely that most of the flexor digitorum profundus (FDP) muscle in dogs takes its origin from the medial epicondyle of the humerus, whereas in humans this muscle arises purely from the forearm. Therefore, elbow position can affect the tension of this muscle in dogs, while having no effect in humans. The purpose of this study was to measure the effect of elbow position on tendon tension in the canine digit in vitro. Elbow position had a significant effect on tendon tension. Digit motion with the elbow fully flexed resulted in significantly higher tendon tension compared to digit motion with the elbow flexed 90 degrees or fully extended, regardless of digit or wrist position (p<0.05). The tension with the elbow flexed 90 degrees was also significantly higher than with the elbow fully extended (p<0.05). The maximum tendon tension with the elbow fully flexed was more than eight times larger than that of the fully extended elbow (p<0.05). We conclude that, in the canine model, elbow position is an important parameter that affects the passive tension applied to the flexor digitorum profundus, and, by implication, to any repair of that tendon. Dog flexor tendon rehabilitation protocols should therefore specify elbow position, in addition to wrist and digit position.

Flexor digitorum profundus tendon tension during finger manipulation

Abstract The purpose of this study was to measure the tension in the flexor digitorum profundus (FDP) tendon in zone II and the digit angle during joint manipulations that replicate rehabilitation protocols. Eight FDP tendons from eight human cadavers were used in this study. The dynamic tension in zone II of the tendon and metacarpophalangeal (MCP) joint angle were measured in various wrist and digit positions. Tension in the FDP tendon increased with MCP joint extension. There was no tension with the finger fully flexed and wrist extended (synergistic motion), but the tendon force reached 1.77 +/- 0.43 N with the MCP joint hyperextended 45 degrees with the distal interphalangeal and proximal interphalangeal joints flexed. The combination of wrist extension and MCP joint hyperextension with the distal interphalangeal and proximal interphalangeal joints fully flexed, what the authors term "modified synergistic motion," produced a modest tendon tension and may be a useful alternative configuration to normal synergistic motion in tendon rehabilitation.

Finkelstein's test: a biomechanical analysis

PURPOSE

Finkelstein's test is the classic diagnostic test for de Quervain's disease. Finkelstein hypothesized that the entry of the muscle bellies of the extensor pollicis brevis (EPB) and abductor pollicis longus (APL) tendons into the first extensor compartment was responsible for the findings observed in his now eponymous test. We agree with Finkelstein's hypothesis and further hypothesize that this position would induce measurable bulk (muscle mass within the retinaculum) and tethering (stretching of synovial tissue) effects within the compartment. To test this latter hypothesis we measured the excursion and gliding resistance of the EPB and APL tendons within the first compartment.

METHODS

Fifteen fresh-frozen cadavers were used. Gliding resistance and excursion were measured in 4 different wrist positions, including the wrist position of Finkelstein's test (30 degrees ulnar deviation). The bulk and tethering effect was calculated based on the mean gliding resistance over the tendon proximal/distal excursion cycle and the gliding resistance at the terminal distal excursion.

RESULTS

The EPB tendon excursion was significantly more distal in 30 degrees ulnar deviation than in 60 degrees extension. Additionally the bulk and tethering resistance was significantly greater in 30 degrees ulnar deviation compared with 60 degrees extension. For the APL tendon there was no significant difference in either the tendon excursion or the bulk and tethering resistance between 30 degrees ulnar deviation and 60 degrees extension.

CONCLUSIONS

We showed that in the position of Finkelstein's test the EPB tendon is significantly more distal and has significantly greater bulk and tethering effect compared with the other EPB positions. This is not the case for the APL tendon in the position of Finkelstein's test. These results suggest that an abnormal Finkelstein's test reflects differences of the EPB more than it does the APL.