| [BACKGROUND]The full recovery of digit function remains a difficult clinical problem following zone2flexor tendon injuries. The most frequent cause of failure after flexor tendon repair is the formation of adhesions. Long period immobilization of the repaired flexor tendon has been demonstrated to have a negative effect on the rehabilitation of repaired tendons and have a positive edffect on the adhesion formation. Both passive flexion-active extension and active rehabilitation have shown advantages and disadvantages in tendon healing. Kleinert et al developed a passive flexion-active extension regimen, and several authors have indicated that protected passive mobilization can inhibit adhesion formation and improve tendon excursion. SilfverskiOld KLsuggested that a passive flexion-active extension program had more joint motion and tendon excursion than did a passive regimen clinically. Even so, it still does not produce a satisfactory result. Other authors indicated that an early active mobilization program with more effective tendon gliding and less adhesion formationproduces more joint motion but results in unacceptably high rupture rates.The anatomy of animal modelGordon M suggested that the long toe of the chicken is an excellent model for experimental tendon repaire studies, because the arrangement of the flexor tendons and sheath is similar to that of the human hand.There are three phalanges, two interphalangeal joints, six annular and two cruciate pulleys in human hand. Comparing to chickens’, there are phalanges, three interphalangeal joints and three annular pulleys which are associated with each interphalangeal joints and are located proximal to the joint.The reason of choosing flexor Tendon in zone twoThe scarring is evident in zone two, located between the distal palmar crease and the distal interphalangeal joint, due to the fact that two tendons are located in an tunnel reinforced by a set of pulleys that stabilize the tendon during the flexion movement.The choice of frequency of controlled passive motion.Shinro Takai designed a study to determine the effects of frequency and duration of controlled passive motion on the healing flexor tendon following primary repair. There are two groups based on frequency of controlled passive motion. In one group, motion was applied at a frequency of12cycles/min for5min/day; the other group was applied at a lower frequency of1cycle/min for60min/day, evaluating by glidingfunction, tensile properties, as represented by linear slope, ultimate load, and energy absorption. He indicated that frequencyof controlledpassive motion rehabilitation is a significant factor in acceleratingthe healingresponse following tendon repair, and higher frequency-controlledpassivemotion has a beneficial effect.Some authors recommended that tendon properties decrease from the fifth day to the fourteenth day after flexor tendon repair. High rupture rates have been observed during this particular period.Different rehabilitation protocolsEarly Controlled passive mobilization (Passive Flexion-Active Extension)Young developed an early passive mobilization program with dynamic flexion traction. During the subsequent decades the "passive flexion-active extension" techniques of mobilization are widely used and modified by several authors.SAVIO L-Yfound positive effects of controlled passive motion on primary tendon repair. In this study, there are seven groups based on duration (3to12weeks post repair) and mode of immobilization and partial mobilization. Tendon properties and the gliding function which was tested biomechanically were significantly better than those subjected to continuous immobilization.Reports by Duran&Houser and Strickland also showed that passive motion can be effective in improving tendon excursion if begun within the first few days post repair.Early active mobilizationAoki demonstrated that early active mobilization have increased ultimate tensile strength compared to previous experimental studies have used primarily intermittent passive or constrained mobilization protocols. Several other authors have suggested that the early active motion of the flexor tendons has some advantages (less adhesion formation and less flexion deformity) over other regimens of passive flexion, high rupture rates of the repaired tendons remain an issue of concern.[Methods]Animal modelThirty-two adult white Leghorn chickens weighing1.3～1.5kg were involved. Under aseptic conditions, zigzag incisions were made on the plantar surface of the left third digits over zone2. The flexor sheath was opened longitudinally between the proximal and distal pulleys. The flexor digitorum profundus tendon was isolated, and a transverse complete laceration was made to both the superficial and deep tendons with a scalpel blade. Flexor digitorum profundus tendon was repaired with the modified Kessler technique. The sheath was completely repaired and then the skin was closed. The third digit was then placed in a dorsal low temperature thermoplastic splint with the ankle plantar flexed at60degrees, the metatarsophalangeal joints flexed to30degrees and the interphalangeal joints extended fully. The unoperated control foot was left free to allow for ambulation.Rehabilitation protocol32chickens were randomly assigned into4equally sized groups with different rehabilitation regimens. All of the operated digits were immediately immobilized in the splint for3days.The PAA groups were treated with a passive flexor-active extension regimen at a frequency of12cycles/min for5min/day, and the splints were removed at5days,9.5 days, or14days after surgery. The unrestricted active motion group (UA) had the splint removed after3days and was treated with an unrestricted active mobilization program.Biomechanical evaluationRang of motionThe active range of motion of the3interphalangeal joints generated by pulling the tendon with the mechanical testing machine was measured with a goniometer.The proximal end of the flexor digitorum profundus tendon of the third digit was held by a clamp from the material testing machine. Fifty grams of weight were attached to the tip of the third digit for full extension. The unoperated specimen was loaded at a constantspeed of0.4mm/s until the tip of the operated toe nearly touched the plantar surface of the foot; the value (X) of the load was then recorded immediately, as was the range of motion of the3interphalangeal joints. The operated specimen was then loaded at a constantspeed of0.4mm/s until the load increased to X, at which point the range of motion was recorded.Tensile propertiesTensile testing was conducted with a material testing apparatus. The bone-tendon complex was placed in the tendon clamps, and the proximal tendon was covered with dry gauze to reduce slippage. The specimen was loaded until failure at a constantspeed of0.4mm/s, and the load-elongation curve was recorded. To reduce the error produced by different initial tendon lengths, the elongation was normalized by Do, and the result was expressed as the percent elongation. To minimize specimen variability, the operative specimens were normalized using the controls. Tensile properties such as the peak force, stiffness, and energy absorption were recorded using the load-percent elongation curve.[Results]Rupture ratesRupture of the repaired tendon was observed in6chickens during the3weeks healing process—2in both PPA-5and UA, and one each in both PAA-9.5and PAA-14.All ruptures occurred at the repair site. Range of motionThe values were normalized by calculating operated value divided by control value. All4groups had significant between-group differences.The first interphalangeal joint:The rang of motion were (23±2)%,(45±4)%,(60±3)%,(72±3)%for experimental groups PAA-14, PAA-9.5, PAA-5, UA respectively.The second interphalangeal joint:The rang of motion were (22±3)%in PAA-14,(44±4)%in PAA-9.5,(61±3)%in PAA-5, and (72±3)%in UA.The third interphalangeal joint:The rang of motion were (27±2)%,(45±4)%,(58±3)%,(69±5)%.Tensile propertiesThe peak forces were (37±9)N,(14±6)N,(3±1)N,(14±7)N for experimental groups PAA-14, PAA-9.5, PAA-5, UA respectively.The stiffness values were (342±116) N/mm/mm in PAA-14,(187±99) N/mm/mm in PAA-9.5,(60±22) N/mm/mm in PAA-5, and (113±84) N/mm/mm in UA.The energy absorptions were (3±1) N/mm/mm,(0.5±0.4) N/mm/mm,(0.1±0.3) N/mm/mm,(0.8±0.4) N/mm/mm for the four groups.There were significant effects on the peak forces or the energy absorptions between PAA-9.5and UA, and therefore, no statistically significant differences were demonstrated between PAA-9.5and UA for these measures or between PAA-5and UA in terms of stiffness.The values were normalized by the ratio calculated in the following formula. VALUE operatedVALUE controlThe peak forces were (35±8)%,(14±6)%,(2±1)%,(14±6)%for experimental groups PAA-14, PAA-9.5, PAA-5, UA respectively.The stiffness values were (49±5)%in group PAA-14,(28±12)%in PAA-9.5,(11±4)%in PAA-5,and (22±15)%in UA. The energy absorptions were (22±4)%,(6±3)%,(0.8±0.4)%and (7±3)%for the four groups.There were no significant effects on the peak forces or the energy absorptions between PAA-9.5and UA, and therefore, no statistically significant differences were demonstrated between PAA-9.5and UA for these measures or between PAA-5and UA in terms of stiffness.Compared against the active flexion program, PAA-14had higher tensile properties (P≤0.005), while PAA-5showed the greatest decrease (P≤0.005).[Discussion]The above results may indicate that the PAA-9.5and UA groups provide the ideal balance of the combined protocols. These protocols leave surgeons with2choices:1) adopting an active flexed motion regimen, where doctors must endure a high risk of rupture with the benefit of good joint motion with moderate tensile properties, or2) adopting a less aggressive motion regimen such as PAA-9.5, where there is a low rupture rate and moderate tensile properties but less improvement in joint motion than with UA. |
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