Biomechanical and histological observations of the dog patellar tendon after removal of its central one-third

Alteration of patellofemoral contact during healing of canine patellar tendon after removal of its central third

Alterations of the patellofemoral (PF) contact pressure and area were assessed using pressure-sensitive film after the removal of the central third of patellar tendon (PT) with healing over time in twelve dogs. The contralateral knee served as control. Histological sections were prepared for descriptive evaluation. No alterations in PT strain, PF contact pressure and area were measured immediately after the removal of the central third of PT compared with that before its removal. Compared with contralateral control, the healing of the donor PF induced a significantly increased PF contact area but not PF contact pressure in the specimens harvested at 6, 12, and 18 months after operation. Increased PF contact area indicated a proximal shift of the PF joint contact during flexion, which was associated with an increased strain of the healing PT under loading. The healing PT became hypertrophic compared with control, but the differences in the cross-sectional area were reduced over time. Histologically, a poorly organized extracellular matrix was observed at 6 months, with a progressive improvement in collagen fiber alignment up to 18 months postoperatively. The results of this study suggest that the removal of the central third of PT does not immediately change PF contact pressure and areas. However, remodeling of the healing tendon may cause an elongated PT, resulting in an increase in PF contact area under a given quadriceps force by knee extension.

Regeneration of the semitendinosus tendon harvested for anterior cruciate ligament reconstruction. Evaluation using ultrasonography

In a prospective study, 40 consecutive patients who underwent anterior cruciate ligament reconstruction with doubled semitendinosus and gracilis tendon autografts were examined pre- and postoperatively by ultrasound to investigate the anatomy of the donor site before and after the harvest of the tendons. The patients underwent ultrasonography at 2 weeks and 1, 2, 3, 6, 12, 18, and 24 months postoperatively. A total of 298 postoperative sonographic evaluations were performed. The semitendinosus tendon was imaged in the sagittal and axial planes: structure and margins were evaluated with the sagittal views; thickness and width were measured with the axial views. In all cases the following sequence of healing was documented: 2 weeks after surgery the semitendinosus tendon site was occupied by an area of increased thickness and decreased echogenicity, suggesting the presence of traumatic edema of the soft tissue surrounding the tenotomy. At 1 month, an irregular hypoechoic structure appeared in a near-anatomic position; at 2 months after surgery, thickness, width, and cross-sectional area of this structure were significantly greater than preoperatively. The amount of regenerated tissue increased up to that seen in the tissue of the 6-month examinations, which also showed a more uniform echostructure. The scans performed at 1 year showed distinct edges and reduction in thickness and width. At 18 and 24 months the echogenicity of the structure occupying the donor site was very similar to that of the normal semitendinosus tendon. However, this structure was clearly identified about 4 cm proximal to the pes anserinus, revealing a more proximal insertion of the regenerated semitendinosus tendon.

A radiographic and histologic evaluation of the patellar tendon after harvesting its central third

Nineteen consecutive patients undergoing anterior cruciate ligament reconstruction using the central third of the ipsilateral patellar tendon were included in the study. Serial magnetic resonance images revealed that the donor-site gap in the tendon decreased with time (mean follow-up, 26 months). The thickness was significantly increased compared with the intact contralateral patellar tendon, regardless of when the magnetic resonance imaging was performed. Ultrasonography showed the same findings at a mean follow-up of 26 months. Histologic evaluation of the repair tissue in the central part of the tendon, as well as the tissue in the peripheral part of the patellar tendon at the donor site, revealed a significant increase in cellularity and vascularity as compared with normal control tendons. Thus, 2 years after the harvesting procedure, the patellar tendon displayed significant radiographic and histologic abnormalities. On the basis of these findings, reharvest of the patellar tendon, at least up to 2 years after primary harvest, cannot be recommended.

Current trends in anterior cruciate ligament reconstruction. Part II. Operative procedures and clinical correlations

Surgical management of the anterior cruciate ligament-deficient knee has evolved from primary repair to extracapsular augmentation to anterior cruciate ligament reconstruction using biologic tissue grafts. The technique of anterior cruciate ligament reconstruction has improved over the last few decades with the aid of knowledge gained from basic science and clinical research. The biology and biomechanics of anterior cruciate ligament reconstruction were analyzed in the previously published first part of this article. In this second part, current operative concepts of anterior cruciate ligament reconstruction as well as clinical correlations are discussed. The latest information regarding anterior cruciate ligament reconstruction is presented with a goal of demonstrating the correlation between the application of basic science knowledge and the improvement of clinical outcomes.

Animal models of tendon and ligament injuries for tissue engineering applications

Improved methods are needed for prevention and treatment of injuries to the musculoskeletal soft tissues. Tissue engineering techniques have led to more effective clinical protocols for treating these injuries. Improvement of tissue healing through the addition of biologic factors, and the development of biologically active tissue engineered replacements, are two promising areas of research. An essential component of progress in this field is the use of animal models of tendon and ligament injuries, which allows for rigorous testing of hypotheses related to disease pathogenesis and treatment. Because these animal models must be appropriate for the condition being studied, no single model exists that is appropriate for all investigations. It generally is necessary to differentiate between tendon and ligament tissues. Furthermore, ligaments should be divided into intraarticular and extraarticular models, whereas tendons should be divided into intrasynovial and extrasynovial models. Other important factors in the appropriate use of an animal model include size of the animal, anatomic features, and techniques available for tissue analysis. The tissues used should be large enough to allow for accurate and reproducible manipulations (injury creation, repair, reconstruction). In addition, it is preferable to use tissues that are amenable to quantitative analysis.

Perspectives on cell and collagen composites for tendon repair

Cell and matrix composites recently have been used to repair tendons and ligaments. In the current study the authors briefly review prior studies in this area, and the contributions these findings have made toward solving this clinical problem. The authors then provide a perspective on the necessary characteristics that the cells and delivery vehicles of these composites must possess, separately and in combination, to function successfully after surgery. The authors conclude by applying these functional tissue engineering principles to two tendon injury models in which mesenchymal stem cells have been suspended in Type I collagen gel to form composites for patellar and Achilles tendon repair. In the first study, mesenchymal stem cells were suspended in gel (5 million cells/mL) with no attempt to align the cells during incubation. The resulting composites were implanted in window defects in one patellar tendon in the rabbit knee, with gel alone in a matching defect on the contralateral side. Biomechanical evaluation at 4 weeks showed that the material properties of the mesenchy-mal stem cell based repairs were 18% to 33% greater than results for contralateral controls. In the second study, mesenchymal stem cells were suspended in gel (4 million cells/mL), contracted on a tensioned suture during incubation, placed in an Achilles gap defect, and compared with repairs of contralateral gap injuries containing suture alone (controls). By 4 weeks, the repairs treated with mesenchymal stem cells had achieved twice the structural properties of the contralateral controls and 50% to 60% of the stiffness and strength of normal tendons that were not surgically treated. In addition, the material properties of the repairs treated with mesenchymal stem cells had increased with time to 37% of normal by 12 weeks after surgery. Both studies reveal the benefits of using pluripotential cells in a collagen gel matrix, and suggest additional research that might enhance the repair quality of healing tendons.

Biomechanical studies of the rabbit patellar tendon after removal of its one-fourth or a half

Effects of the overstressing induced by the harvest of grafts from the patellar tendon on the mechanical properties and morphometry of remaining tendon were studied using a rabbit model. The width of the patellar tendon was reduced by one-fourth or one-half equally removing the medial and lateral portions; by this surgery, the cross-sectional area was decreased by 25 or 50 percent from the original area. After all the rabbits were allowed unrestricted activities in cages for 3 to 12 weeks, their patellar tendons were harvested for mechanical and histological studies. The one-fourth removal induced no significant changes in the mechanical properties, but significantly increased the cross-sectional area. In the case of one-half removal, tensile strength and tangent modulus did not change in some tendons, although the cross-sectional area increased significantly. In the other central half tendons, mechanical strength decreased markedly, while the cross-sectional area increased; hypercellular areas and breakage of collagen bundles were observed in these tendons. These results indicate that the patellar tendon has an ability of functionally adapting to overstressing by changing the cross-sectional area, while keeping the mechanical properties unchanged, if the extent of overstressing is less than 30 percent.

Autologous mesenchymal stem cell-mediated repair of tendon

Mesenchymal stem cells (MSCs) were isolated from bone marrow of 18 adult New Zealand White rabbits. These cells were culture expanded, suspended in type I collagen gel, and implanted into a surgically induced defect in the donor s right patellar tendon. A cell-free collagen gel was implanted into an identical control defect in the left patellar tendon. Repair tissues were evaluated biomechanically (n = 13) and histomorphometrically (n = 5) at 4 weeks after surgery. Compared to their matched controls, the MSC-mediated repair tissue demonstrated significant increases of 26% (p < 0.001), 18% (p < 0. 01), and 33% (p < 0.02) in maximum stress, modulus, and strain energy density, respectively. Qualitatively, there appeared to be minor improvements in the histological appearance of some of the MSC- mediated repairs, including increased number of tenocytes and larger and more mature-looking collagen fiber bundles. Morphometrically, however, there were no significant left-right differences in nuclear aspect ratio (shape) or nuclear alignment (orientation). Therefore, delivering a large number of mesenchymal stem cells to a wound site can significantly improve its biomechanical properties by only 4 weeks but produce no visible improvement in its microstructure.

Anatomical reconstruction of the patellar tendon: a new technique with hamstring tendons and iliotibial tract

A new technique of patellar tendon reconstruction was performed in a patient who lost tendon and tibial tuberosity during wide excision surgery for a malignancy. In this procedure, the tendon was anatomically replaced by a graft composed of ipsilateral hamstring tendons and iliotibial tract, with the biomechanical conditions considered. Both ends of the graft were secured in the size-matched bone tunnels in the patella and tibia by screw post fixation, which is a technique established in ligament reconstruction surgery in the knee joint. At the twenty-month follow-up, the result was deemed successful.

Rehabilitation program for both knees when the contralateral autogenous patellar tendon graft is used for primary anterior cruciate ligament reconstruction: a case study

STUDY DESIGN

Case study of a basketball player who underwent an alternative surgical procedure for anterior (cruciate ligament (ACL) reconstruction and outline of the rehabilitation process designed for this procedure.

OBJECTIVES

To describe the surgical procedure, detail the rehabilitation program, and report on this patient's clinical outcome.

BACKGROUND

Anterior cruciate ligament injury, its treatment, and rehabilitation continue to be an area of interest to both clinicians and researchers. Surgical procedures have been refined and rehabilitation programs are constantly being evaluated and updated to allow the safest and most predictable return to activity. Currently, the autogenous bone-patellar tendon-bone graft is the graft of choice for ACL reconstruction. Typically the graft is taken from the ipsilateral knee. An alternative procedure is to take the graft from the contralateral, noninvolved knee, allowing 2 separate rehabilitation programs to take place.

METHODS AND MEASURES

The patient was followed from the time of injury to 2 years postoperatively. Data collected included range of motion, isokinetic strength scores, ligament stability scores, subjective evaluation, and functional measures.

RESULTS

At 3 weeks postoperative the patient had nearly full range of motion in both knees, normal gait, and was beginning sport-specific drills. He was shooting the basketball and jumping by 5 weeks and returned to competitive sports 6 weeks after surgery. He was able to play in all 32 games of the season, starting in 23 of them.

CONCLUSIONS

Using the contralateral patellar tendon graft may be appropriate for primary ACL reconstruction of patients, particularly those desiring an early expedient return to athletic competition.

Patellar tendon augmentation after removal of its central third limits joints tissue changes

The central third of the patellar tendon is commonly used to reconstruct the injured anterior cruciate ligament. Some studies have noted changes in joint tissues following this procedure. It has been postulated that these changes may be associated with increased stress on the remaining tendon following harvest of the graft. In our study, the central third of the patellar tendon was excised in three groups of rabbits. The central tendon defects in two of the three groups were fitted with different augmentation devices to augment the host tendon during the healing process. All rabbits followed a daily treadmill exercise regimen for 12 weeks following the operation. Biomechanical testing of the tendon revealed that in nonaugmented tendons the cross-sectional area and the length of the patellar tendon significantly increased 112 and 16%, respectively. There was histological evidence of host-tendon remodeling throughout the cross section and extensive fibrosis in the infrapatellar fat pad. Augmentation of the tendon significantly reduced these changes, with the least change noted in the group with the greatest augmentation. The rabbits with augmentation devices retained tendon dimensions similar to those of the contralateral intact tendon, and tendon remodeling occurred only in the defect area. The rabbits with augmentation devices exhibited little to no fibrosis of the fat pad. Structural properties of augmented and nonaugmented tendons were similar despite the size differences, indicating higher tissue quality in the augmented tendons. This study suggested that complications of the knee joint (i.e., tendon proliferation and fat pad fibrosis) noted after anterior cruciate-ligament reconstruction with the autogenous patellar tendon may be limited by the implantation of an augmentation device.

Pyridinoline in relation to ultimate stress of the patellar tendon during healing: an animal study

The ultimate stress of the central one-third of the patellar tendon was studied in a gap wound-healing model in the rat. The specimens were also analyzed for collagen and nonreducible crosslinks, as measured by hydroxyproline and pyridinoline content, respectively. Thirty days after injury, the ultimate stress of the healing patellar tendon was restored to an average of 71% of the control value and remained constant over time. The pyridinoline content of the healing tendon was twice the control value by 30 days after injury and reached a plateau; however, the hydroxyproline content did not change significantly over time. Stepwise regression analysis demonstrated that pyridinoline was a better biochemical marker for ultimate stress than was hydroxyproline. The current study provides insights into the functional behaviour of the healing patellar tendon by establishing the relationship between the two biochemical components and the ultimate stress of the healing patellar tendon. This study also suggests the possibility of using pyridinoline content as an indirect marker of the ultimate stress because in vivo assessment is impossible.

Patellar tendon and infrapatellar fat pad healing after harvest of an ACL graft

Clinical studies have documented proliferation of the host patellar tendon and fibrosis extending into adjacent tissues after reconstruction of the injured anterior cruciate ligament (ACL) using the central one-third of the patellar tendon (PT) as the graft. Such generalized arthrofibrosis has been implicated in knee locking and as possible source of anterior knee pain. However, it is not clinically feasible to measure changes in tendon morphology and mechanical properties and degeneration of peripheral tissues over time following graft harvest. In a rabbit experimental model proliferative changes in the tendon and the infrapatellar fat pad have been documented following harvest of a central third tendon graft without ACL reconstruction. Studies in larger animals have shown significant reductions in the strength and stiffness of the healing patellar tendon, but without assessment of the peripheral tissue response. In the current study an ACL reconstruction was performed in a goat model using an autogenous patellar tendon graft. Extensive tendon and fat pad proliferation were observed along with significant reductions in the biomechanical properties of the host tendon. Significant fat pad fibrosis was documented using biochemical methods. The current data confirm that harvest of an autogenous PT graft for reconstruction of the ACL results in significant changes in the PT and adjacent tissues. These data may help explain some of the clinical complications documented in the reconstructed joint.

Effects of patellar tendon adhesion to the anterior tibia on knee mechanics

The effects of patellar tendon adhesion on the knee extensor mechanism and on the kinematics and contact areas for both the patellofemoral and tibiofemoral joints were determined for five cadaveric knees in an open kinetic chain testing configuration. Patellar tendon adhesion decreased the distance from the inferior patellar pole to the tibial tuberosity, effectively creating patella infera. When compared with the controls, knees with adhesion had medial and distal translation of the patella, as well as increased patellar flexion. Although the patellar articular contact location shifted distally, the overall contact area did not change significantly. For the tibia, adhesion resulted in significant medial, proximal, and anterior translation, and internal rotation. Adhesion also resulted in a posterior shift of the tibial contact location. For the extensor mechanism, adhesion decreased the knee extension force created by the quadriceps muscle on the tibia, indicating a decrease in the effective moment arm of the extensor mechanism. Furthermore, as a result of patellar tendon adhesion, the angle formed by the quadriceps and patellar tendons decreased, suggesting an increase in patellofemoral joint reaction force with adhesion. The increased patellofemoral joint reaction force and the altered contact location may be related to anterior knee pain after knee trauma and knee surgery. Therefore, patients should be observed for subtle patella infera, which may indicate patellar tendon adhesion.

Quadriceps atrophy after partial resection of the patellar tendon: an experimental study in a rat model

Quadriceps muscle atrophy of rats was examined after resection of the central third (group 1) or the lateral two thirds (group 2) of the patellar tendon, the tensor fascia lata (group 3), or the medial hamstring (group 4). The quadriceps atrophied in groups 1 and 2, and more so in group 2, but there was no atrophy in groups 3 or 4. Thus, after an anterior cruciate ligament reconstruction procedure using the patellar tendon, resection of the patellar tendon itself leads to quadriceps atrophy and the extent of atrophy is related to the resected width.

Histological and biomechanical observations of the rabbit patellar tendon after removal of its central one-third

Using 35 Japanese white rabbits, a study was made of tissue regeneration and the mechanical properties of the patellar tendon after removal of its central one-third. After removal of the central one-third of the patellar tendon on one side, in experiment 1 the strength of the entire patellar tendon including the regenerated tissue was compared with that of the patellar tendon on the opposite side with the central one-third removed at the time of killing, and in experiment 2 the strength of only the regenerated tissue was compared with that of the patellar tendon on the opposite side with two-thirds of the medial and lateral sides removed at the time of death. In experiment 1, the maximum load showed no significant difference between the operated side and the control. In one half of the cases, the strength of the operated side including the regenerated tissue was weak, suggesting weakening of the patellar tendon on the residual bilateral sides. In experiment 2, the maximum load of the regenerated tissue was significantly lower than that of the control, the former being 25% of the latter even at 6 months. Histologically, the characteristics of the cells and collagen fibers gradually approached those of normal tissue, but the crimp pattern of the collagen fibers and fibrils was evidently smaller than that of the control. These results indicate that regenerated tissue was still mechanically weak and immature at 6 months.

The reharvested central third of the patellar tendon. A histologic and biomechanical analysis

We assessed the histologic, mechanical, and structural properties of the reharvested central-third patellar tendon in greyhounds. Twelve dogs had the central third of the patellar tendon (5 mm) removed with corresponding bone blocks from the patella and tibia; the remaining tendon defect was loosely closed. Six dogs were sacrificed at 6 months and six at 12 months, and the central third of the patellar tendon was harvested from both the operative and the contralateral control knees. Analysis of the structural changes in the tendons revealed a significant increase in thickness for reharvested tendons at both 6 and 12 months when compared with controls. The entire residual tendons were narrower at 6 months and were shorter at 12 months compared with controls. Mechanical testing showed that the average failure load, ultimate tensile strength, strain at failure, and average modulus for the reharvested central third of the patellar tendon were significantly less than that of controls at both 6 and 12 months. Analysis of collagen fiber size by electron microscopy revealed a significant increase in collagen fiber diameter at 6 months (135 +/- 41 nm versus 49 +/- 4 nm) but no difference between the operative limbs and controls at 12 months. The reharvested bone-patellar tendon-bone complex does not have the same properties as the primary patellar tendon graft up to 1 year after harvest in a canine model, and its use for revision cruciate ligament reconstruction must be carefully reexamined.

Tissue shrinkage with the holmium:yttrium aluminum garnet laser. A postoperative assessment of tissue length, stiffness, and structure

The effect of laser energy on the length, stiffness, and structure of connective tissue was examined in a rabbit patellar tendon model. A holmium:yttrium-aluminum-garnet laser was used to deliver a calculated dose of laser energy (300 J/cm2) to one randomly selected patellar tendon in each of 13 adult New Zealand White rabbits. The contralateral patellar tendon was used as a control. Radiopaque markers were placed in the patella and tibial tuberosity to allow for patellar tendon length measurements (via standard lateral radiographs) before and after laser application and at 4 and 8 weeks. Limbs were not immobilized during the postoperative period. The tendons were harvested at 0 weeks (N = 7) and 8 weeks (N = 6) and evaluated for tensile, stiffness, cross-sectional area, histologic changes, and electron microscopic appearance. The results demonstrated significant tendon shrinkage (6.6% +/- 1.4%) after application of the calculated laser energy dose. However, tendon length had increased significantly beyond the immediate postlaser length at 4 weeks and beyond its original length by 8 weeks. At 8 weeks, the lased tendons were significantly less stiff with significantly greater cross-sectional areas than contralateral controls. There was generalized fibroblastic response throughout the entire lased tendon characterized by a marked increase in cellularity. There was also a change from the normal bimodal pattern of large- and small-diameter collagen fibers to a unimodal pattern with predominantly small-diameter fibers in the lased tendons. The tissue alterations seen in this study suggest that the biologic response of connective tissue to laser energy causes a further compromise in tissue integrity, beyond that attributed to the initial physical effects of the laser. These alterations must be taken into consideration when determining postoperative rehabilitation of laser-modified tissues.

Characterization of the repair tissue after removal of the central one-third of the patellar ligament. An experimental study in a goat model

The purpose of this study was to characterize the repair tissue that develops after removal of a portion of the patellar ligament for use as a graft. A six-millimeter-wide strip was obtained from the central portion of the patellar ligament with tibial and patellar bone plugs from one knee (stifle joint) of eight goats. The repair tissue that formed in the defect was characterized in terms of its structural, material, histological, and ultrastructural properties twenty-one months after the operation. The contralateral patellar ligament served as a control. Representative specimens were taken from the proximal, middle, and distal portions of the repair tissue and the control tissue for histological study and examination with transmission electron microscopy. The six-millimeter-long defect filled with repair tissue that increased the cross-sectional area by a mean of 42 per cent compared with the control values (p < 0.05). The maximum force to failure and the ultimate stress of the repair tissue were significantly decreased (by a mean of 51 and 65 per cent, respectively) compared with those of the controls (p < 0.001 for both). The stiffness also was reduced, by a mean of 27 per cent, but this was not significant (p > 0.05). Magnetic resonance imaging of the donor site showed slightly increased signal intensity compared with the intensity on the control side. Histological sections from the donor site contained collagenous (scar) tissue that was less organized, more cellular, and more vascular than the control tissue. Evaluation of the ultrastructure revealed that the repair tissue was composed primarily of collagen fibrils with a small diameter (range, fifty to 100 nanometers).

CLINICAL RELEVANCE

The results of the present study suggest that the repair tissue that develops after removal of a strip of the patellar ligament for use as a graft is not comparable with normal tissue in terms of its structural, material, histological, and ultrastructural properties by twenty-one months. This should be kept in mind when this repair tissue is considered for use as a graft for revision of a reconstruction of the anterior cruciate ligament.

Patella position and biomechanical properties of the patellar tendon 1 year after removal of its central third

OBJECTIVE: The aim of this study was to investigate how the removal of a patellar tendon graft for cruciate ligament reconstruction influences the mechanical properties of the remaining patellar tendon and the position of the patella at the knee joint. DESIGN: The experimental model of this in vivo study was the anterior cruciate ligament reconstruction in sheep. BACKGROUND: While the efficacy of a patellar tendon third as a ligament replacement has been extensively investigated, the consequences for the function of the remaining tendon and patella position remain unclear. METHODS: The central third of the patellar tendon from the right knees of 10 animals was removed for cruciate ligament replacement. One year postoperatively, the position of the patella within the joint and the stiffness and modulus of elasticity of the remaining tendon were compared with the non-operated contralateral controls. RESULTS: The patella position did not change in the operated knee joints in comparison with the controls. The cross-sectional area of the operated patellar tendon increased significantly by scar tissue formation at the defect site. CONCLUSION: Although the inferior mechanical properties of the scar tissue reduced the modulus of, elasticity of the tendon, the increase in cross-sectional area allowed it to develop a structural stiffness similar to the control tendons. RELEVANCE: The central third of the patellar tendon is often used for ligament replacement. Resulting biomechanical and structural changes in the remaining patellar tendon have not been previously reported using an in vivo animal model. The recovery of the biomechanical properties of the partially resected tendons allows for continued function.

Late patellar tendon ruptures after removal of the central third for anterior cruciate ligament reconstruction. A report of two cases

Patellar tendon rupture after removal of the central third for ACL reconstruction is a rare complication. Only nine cases have been previously reported, and all of these occurred within the first 10 months after surgery. We report two cases of late patellar tendon ruptures occurring at more than 3 and 6 years, respectively, after surgery. A review of the literature has suggested but not conclusively supported that devascularization, an alteration in tendon healing and remodeling, or injury to the remaining tendon at the time of graft harvest may be possible causes of this rare complication. Biopsy tissue from any future patellar tendon ruptures after removal of its central third could contribute to a better understanding of this anomaly.

The tendon defect after anterior cruciate ligament reconstruction using the midthird patellar tendon--a problem for the patellofemoral joint?

Retrospective clinical and radiographic evaluation was performed on 41 patients seen at the Salzburg General Hospital Department of Traumatology on average 2 years following ACL reconstruction. In 26 patients (61%) clinical examination revealed pain trigger points over the donor site of the midthird patellar tendon and in the patellofemoral joint. Functional pain during kneeling activities was observed in 19 patients (46%). Objective measurement of the length of the patellar tendon in bilateral radiographs demonstrated exactly equal patellar tendon length in both knees in 11 patients (27%). The radiographs showed tendon shortening following harvesting of the midthird patellar tendon by 1-3 mm in 7 patients (17%), by 4-6 mm in 16 (39%), and by 6-9 mm in 7 (17%). Average length change in the patellar tendon on the donor side was -3 mm, representing a patellar tendon shortening of 9.8%. On the basis of the OAK score, however, good and very good results were recorded in 33 patients (80%). On the whole, these good overall results were compromised only be patellar tendon defect morbidity. In addition to the local scarring problems at the donor site, shortening of the patellar tendon was observed with changes to patella position and interference with the mechanics of the patellofemoral joint. Tendon shortening can be explained on the basis of cicatricial contraction in the process of autorepair to the tendon defect. The problems affecting the patellofemoral joint are inherent in the therapy and must be treated as a negative factor. In the case of patients whose work requires mainly a kneeling position and those who make significant functional demands of the extension system of the knee, a critical assessment is required of the use of the midthird patellar tendon for anterior cruciate ligament reconstruction.

Graft site morbidity with autogenous semitendinosus and gracilis tendons

To distinguish between morbidity caused by harvesting semitendinosus and gracilis tendons and morbidity associated with anterior cruciate ligament reconstruction surgery, we performed a prospective randomized study using 65 patients who underwent anterior cruciate ligament reconstruction using these tendons. The patients underwent either contralateral (N = 34) or ipsilateral (N = 31) graft harvest. For the nonoperated knees in the ipsilateral harvest group, isometric and isokinetic strength of the quadriceps and hamstring muscles increased to approximately 120% of the preoperative value at 12 months after surgery. Compared with these knees, the tendon harvest did not affect quadriceps muscle strength at all. However, harvest did decrease hamstring muscles strength for 9 months after surgery. The graft harvest in the knees with anterior cruciate ligament reconstruction also did not significantly affect quadriceps muscle strength, but it did significantly decrease hamstring muscles strength only at 1 month. Activity-related soreness at the donor site was rarely restricting and resolved by 3 months. This study demonstrated that the semitendinosus and gracilis tendon graft is a reasonable choice to minimize the donor site morbidity in ligament reconstruction using autografts.

Assessment of patellar height after autogenous patellar tendon anterior cruciate ligament reconstruction

In this study, we sought to determine if a significant change in patellar height occurs after autogenous patellar tendon anterior cruciate ligament (ACL) reconstruction at our clinic. In a series of 71 patients (52 males and 18 females; average age: 22 years; range: 12 to 41) randomly selected, all had undergone an identical autogenous patellar tendon ACL reconstruction, by the same surgeon, and followed the same postoperative accelerated rehabilitation program. All patients had standardized preoperative and postoperative lateral knee radiographs. The patellar tendon length as well as the patellar height and ratio of Blackburne and Peel were measured by the same person for all subjects. The length of the patellar tendon shortened by an average of 0.4 mm (range: 6% lengthening to 12% shortening) which is less than 1% and not statistically significant (P = .068). The Blackburne and Peel ratio for patellar height decreased by 1%, which was also not statistically significant (P = .060). The evidence obtained from this study indicated no significant change in patellar height after autogenous patellar tendon ACL reconstruction combined with postoperative accelerated rehabilitation and no correlations with postoperative complications, secondary surgeries, timing of surgery, age, or anterior knee symptoms.

A biomechanical comparison between the central one-third patellar tendon and the residual tendon

The purpose of this study was to compare the tensile strength of the central one third patellar tendon--as used for reconstruction of the anterior cruciate ligament--to that of the residual patellar tendon. Ten matched pairs of human cadaveric knees were used for this study, each specimen consisting of an intact patella-patellar tendon-proximal tibial unit. One knee from each pair was randomly selected for removal of both the medial and lateral one third of the patellar tendon, leaving the central one third intact. The contralateral knee of each pair underwent removal of the central one third of the patellar tendon, leaving the residual two thirds intact. Each specimen was then mounted in a materials testing machine and tensile tested to failure at a strain rate of 100%.s-1. The most important result to emerge from these experiments was that there was no significant difference in maximum force to failure for the residual patellar tendon compared to the central one third. Thus any thought that removal of the central one third as a graft still leaves a tendon twice as wide and therefore twice as strong as a graft is dispelled by these experiments.

Biomechanical assessment of the healing response of the rabbit patellar tendon after removal of its central third

The objective of this study was to determine the biomechanical properties of the healing patellar tendon after removal of its central third. This was accomplished by removing the central third of the patellar tendon from the right limb of 30 mature New Zealand White rabbits. The tendon of the contralateral normal limb served as the unoperated control. The rabbits were separated into five test groups according to healing time: time of surgery and 1, 2, 3, and 6 months after surgery. The ultimate failure strength of the patellar tendons with the central third removed was significantly less than the failure strength of the contralateral normal patellar tendons at all time intervals after surgery. At the time of surgery, the ultimate failure strength values of the operated patellar tendons were on average 53% of the normal patellar tendons, increasing to 72% of normal at 6 months. There was a significant correlation between the ultimate failure strength of the operated tendons and healing time. The positive slope for this regression indicated that the ultimate failure strength of the operated tendons converged toward normal as healing progressed. Failure mode of the operated tendon did not depend on healing time.

Anterior cruciate ligament patellar tendon reconstruction: it is probably better to leave the tendon defect open!

The purpose of our prospective study was to establish whether or not in anterior cruciate ligament (ACL) patellar tendon reconstruction the tendon defect has to be closed. In 50 consecutive ACL patellar tendon reconstructions, the tendon defect was randomly closed (group I) or left open (group II). The following data were recorded from all patients on the 4th and 14th days post operation: range of motion (ROM), pain at rest, pain and validity at isometric contraction, ability of bent leg raising (at 4th day) and straight leg raising (at 14th day). All the patients underwent ultrasonographic examination after 3 months and X-ray scanning at 6 months post operation. Forty patients underwent a CT-scan examination at 6 months. Thirty patients underwent isokinetic testing between 10 and 12 months post operation. Evaluating the immediate post operation data, no statistically significant differences emerged between the two groups. Ultrasonography showed in 68% of the knees of group I (defect closed) a thickened patellar tendon (PT), while in 60% of group II it was of normal thickness. No patients of either group developed patella infera by X-ray evaluation 6 months post operation. CT scans at 6 months showed that 100% of the knees of group I had a thickened PT in toto (nearly twice as thick as normal). Scar tissue was present not only in its central third but also in more than half of the cases in the medial and lateral third. In group II 75% of the patients had a normal thickness PT and 25% presented with only a minimal thickening. Scar tissue was distinguished only at its central third.(ABSTRACT TRUNCATED AT 250 WORDS)

Healing of the patellar tendon after harvesting of its mid-third for anterior cruciate ligament reconstruction and evolution of the unclosed donor site defect

The purpose of this study was (a) to evaluate by ultrasonography the healing of the patellar tendon after its mid-third was removed for anterior cruciate ligament (ACL) reconstruction in two randomized groups of patients in whom the tendon donor site was either left open or closed; (b) to compare clinical, radiographic, and isokinetic studies of these two groups to evaluate the incidence of patellofemoral disorders. We performed 61 ACL reconstructions (22 males, 39 females) using the arthroscopically assisted in-out technique. All operations were performed by the same surgeon, and the patients were all subjected to the same postoperative protocol. The tendon defect was left open in 25 subjects (group A) and was closed in 36 subjects (group B). Postoperative patellar tendon behavior was evaluated in these two groups by ultrasonography at 3, 6, 9, and 12 months. The vertical position of the patella was measured in the follow-up lateral view at 45 degrees of flexion and compared to that of the untreated knee. A clinical evaluation was performed throughout the follow-up period, and patellofemoral problems (pain, stiffness, patello-femoral crepitus) were evaluated and recorded using a modified Larsen and Lauridsen rating scale. Isokinetic evaluation was carried out at 6 months, and a quadriceps index of the two groups was recorded. Ultrasonography showed that healing of the patellar tendon initially progressed with a compensatory hypertrophy in width and thickness. The width was greater in group B (P < 0.01). In group A we observed in the cross-sections a characteristic image of two cords separated by a low signal bridge which we defined as a "binocular pattern." Areas of high ultrasound signal intensities persisted after 1 year in the open group; such areas were filled with scar tissue. In the closed group the ultrasound tendon signal returned to normal at 1 year. At 6 months the clinical, radiographic and isokinetic findings did not significantly differ between the open and closed groups. We conclude that defect closure after patellar tendon harvesting does not significantly influence the extensor apparatus.

The influence of immobilization versus exercise on scar formation in the rabbit patellar tendon after excision of the central third

There is much discussion about the appropriate timing and intensity of rehabilitation after reconstruction of the anterior cruciate ligament with a patellar tendon autograft. The purpose of this study was to look at two extremes (complete immobilization and vigorous, forced exercise) on the extent of scar formation and mechanical properties of the host tendon. Three groups of six Flemish Giant rabbits had the central third patellar tendon removed in one limb. Group I was sacrificed immediately after surgery. Group II was exercised on a treadmill for 12 weeks. In Group III the limb was immobilized for 12 weeks. After 3 months, average length and cross-sectional area from Group II were greater than those of the controls and Group III tendons. Structural properties of all tests limbs were similar to each other but different from controls. Tensile modulus of Group III tendons did not decrease as much that of Group II tendons. Histology revealed a clear demarcation between the central defect and host tendon in Group III, whereas Group II tendons remodeled throughout their cross-sections. We propose that early joint mobility produces large multiaxial stresses in original tendon leading to microdamages and repair processes within the entire host tissue. Less aggressive exercise or delay in joint mobility may help control tissue remodeling.

Changes in the mechanical properties of patellar tendon preparations of spontaneously diabetic dogs under long-term insulin therapy

Diabetes mellitus is known to involve a wide range of musculoskeletal disorders including tendon contracture, tenosynovitis, joint stiffness, and osteoporosis. Recent studies with experimentally induced models of diabetes show that insulin therapy mitigates such alterations. These data are from relatively short-term experiments. This manuscript reports the results of tensile failure experiments on the canine patella-patellar tendon-tibia complex from a group of juvenile diabetic animals that received insulin therapy. The duration of the disease was 4-9 yr. The stiffness of the diabetic preparations in a physiological range of loading was approximately 13% greater than controls (P < 0.05). On the other hand, the strength of the tendon preparation from the diabetic population was not different from controls, but the mode of structural failure for controls was by substance and avulsion fractures while the diabetics failed by tensile fracture of the patella.

Infrapatellar contracture syndrome. Diagnosis, treatment, and long-term followup

Infrapatellar contracture syndrome is an uncommon but recalcitrant cause of reduced range of motion after knee surgery or injury. The results and conclusions presented here are based on a retrospective clinical study evaluating the long-term outcome in 75 patients who developed infrapatellar contracture syndrome. These 75 patients (76 knees) were evaluated at an average followup of 53 months after the index (inciting) procedure or injury. Comparing subgroups within the study population, factors that correlated with poorer results or more severe infrapatellar contracture syndrome were found to be acute anterior cruciate ligament repair or reconstruction, the use of patellar tendon autograft for anterior cruciate ligament reconstruction, nonisometric graft placement, multiple surgical procedures, use of closed manipulation, and the development of patella infera. We concluded that appropriate procedures can substantially increase the range of motion in patients with infrapatellar contracture syndrome. However, residual functional morbidity persists in many patients, and the outcome, as determined by subjective knee function scores, is only fair. The natural history of an anterior cruciate ligament-deficient knee appears to be more benign than the natural history of a knee that develops infrapatellar contracture syndrome.

The biomechanics and histopathology of chemically processed patellar tendon allografts for anterior cruciate ligament replacement

A study was initiated to examine chemically processed patellar tendon allografts in sheep anterior cruciate ligament repairs, both mechanically and histologically. One group of animals received frozen, untreated allografts, one group received frozen grafts that were processed with a chloroform-methanol solvent extraction technique, and one group received frozen tendons treated with a permeation-enhanced extraction technique. All animals were operated on unilaterally, with the contralateral knee acting as a normal, intact control. Histologic analysis after 2 months of implantation revealed similar enhanced cellular repopulation in both chemically treated ligament allografts compared with the more hypocellular, untreated grafts. At 6 months the chloroform-methanol group demonstrated a more aggressive chronic cellular response with numerous thick-walled vessels relative to the untreated and permeation-enhanced grafts. Mechanical testing after 6 months of implantation showed statistically similar anterior drawer resistance in all grafted knees, yet the two chemically extracted grafts had significantly less stiffness than untreated anterior cruciate ligament grafts. Both treatment groups also tended to be weaker than the untreated allografts. All anterior cruciate ligament reconstructions showed excessive anterior drawer laxity and, regardless of treatment, had lower strength and less stiffness than normal anterior cruciate ligament tissue at the 6-month period.

Pain after use of the central third of the patellar tendon for cruciate ligament reconstruction. 33 patients followed 2-3 years

We performed reconstruction of the anterior cruciate ligament in 33 patients using the central third of the patellar tendon. In 20 patients we did an arthroscopically-assisted procedure, while 13 patients had an additional mini-arthrotomy through the gap in the patellar tendon. After 2-3 years the subjective knee function, according to the Lysholm score, was excellent or good in 18 knees and fair or poor in 15 knees, mainly due to anterior knee pain. Although 18 patients complained about anterior knee pain, only 1 patient required further surgery. After the operation the patella had a lower position. A flexion contracture was found in 7 patients, and 13 had heterotopic bone formation at the apex of the patella. Although stability was restored in 31 of the 33 reconstructed knees, anterior knee pain was a frequent complication. There were no correlations between the anterior knee pain and patellar height, flexion contracture or heterotopic bone formation.

Review on tension in the natural and reconstructed anterior cruciate ligament

This article reviews the methodology and results of published studies concerned with tension in the natural and reconstructed anterior cruciate ligament (ACL). This also includes studies of fiber length changes with knee motion and the relationships between graft tunnel placements and isometricity. Little work has been done in vivo: in humans, length changes of the anterior ACL fibers have been measured at operation, while animal longitudinal studies have been few and have given conflicting results. Work in vitro has used many methods to study ACL tension directly or indirectly, via length changes in fibers, but many authors have reported variable results, caused partly by inter-specimen differences and lack of control of forces or kinematics. It seems likely that different grafts require different peroperative tensions to restore normal stability when measured immediately after application at one knee position. But graft placement and the angle at which tensioning is performed also matter. Over-tensioning constrains knees under load cycling. Similarly, it is difficult to measure and therefore also to decide how tension should be distributed between an ACL graft and and augmentation to the graft. It was concluded that the published studies provide many guidelines for the effects of different graft placements or tensioning protocols but, overall, there is little firm evidence on which to recommend any particular ACL reconstruction protocol.

Biomechanical and histological properties of the canine patellar tendon after removal of its medial third

Three groups of dogs were used for this study. All dogs had the medial third of the patellar tendon removed from one knee, while the contralateral knee was used as a control. The time zero group was immediately sacrificed; the other two groups were sacrificed at 3 and 6 months. Once the tissues were harvested, the patellar tendon was isolated and biomechanical and histologic analyses were conducted. Three and 6 months after surgery, there was a large amount of visible scar tissue in the tendon. The cross-sectional area of the tendons was 275% and 288% of controls at 3 and 6 months, respectively. The tensile modulus of the tendon was statistically less than controls at both 3 and 6 months. The energy to failure and stiffness of the operated tendons were not statistically different than controls at 3 or 6 months after surgery. The results of this study directly contrast with those of an earlier study of the removal of the central third of the patellar tendon. While a number of factors could explain differences observed between removal of a central or medical third, this study confirms the short-term damaging effects of surgical removal of a portion of the patellar tendon to reconstruct a torn anterior cruciate ligament.

Review of the afferent neural system of the knee and its contribution to motor learning

Understanding the afferent neural system of the knee is considered to be vital to rehabilitation planning. An intricate relationship exists involving the afferent neural receptors in the inert and contractile tissues of the knee. Traditional rehabilitation strategies may not exploit this extensive afferent neural system. Closed kinetic chain functional training (CKCFT) may provide a method for more effectively rehabilitating an injured or reconstructed knee. The rationale for CKCFT has traditionally focused on mechanical aspects. Sensorimotor integration through motor learning is believed to be an important component of CKCFT. The purposes of this review are to discuss: 1) the afferent neural system of the knee with emphasis on the mechanoreceptors, 2) the influence of the afferent neural system of the knee on motor learning, and 3) how CKCFT uses the afferent neural system of the knee and motor learning during knee rehabilitation. This review reinforces the use of CKCFT in knee rehabilitation plans.

Donor-site morbidity after harvest of a bone-tendon-bone patellar tendon autograft

The effects of closure of the peritendineum and bone grafting of the patellar defect after harvest of the bone-tendon-bone patellar tendon autograft was investigated prospectively in two groups of 25 patients. Anterior cruciate ligament (ACL) reconstruction was performed with minimally invasive techniques either arthroscopically or via mini-arthrotomy. Patellar height, size of bony and tendon defects, and overall result were followed up for 2 years postoperatively. The results showed that closure of the peritendineum enhances healing of the patellar tendon defect and restores a normal appearance of the tendon within 2 years. We have stopped bone grafting the patellar defect with cancellous bone because of the risk of formation of painful spurs at the inferior pole of the patella which occurred in 36% of patients.

Quadriceps strength and functional capacity after anterior cruciate ligament reconstruction. Patellar tendon autograft versus allograft

Harvesting the central third of the patellar tendon for autograft anterior cruciate ligament reconstruction is thought to compromise quadriceps strength and functional capacity. We compared objective measurements of quadriceps strength and functional capacity in athletes after patellar tendon autograft or allograft anterior cruciate ligament reconstruction. We looked at 33 active male patients (mean age, 24.3 years) who had anterior cruciate ligament reconstructions 12 to 24 months earlier using patellar tendon autograft (N = 15) or allograft (N = 18) techniques. All patients underwent an intensive rehabilitation program. Quadriceps strength and power were assessed by measuring peak torque at 60 and 240 deg/sec, torque acceleration energy at 240 deg/sec, and the quadriceps index using a Cybex II isokinetic testing device. Functional capacity was evaluated based on the results of 3 specially designed functional performance tests and the hop test. Results revealed no significant difference between autograft and allograft groups with respect to any of these parameters. These findings indicate that harvesting the central third of the patellar tendon for autograft anterior cruciate ligament reconstruction does not diminish quadriceps strength or functional capacity in highly active patients who have intensive rehabilitation. Thus, the recommendation to avoid patellar tendon autograft anterior cruciate ligament reconstruction to preserve quadriceps strength and functional capacity may be unnecessary.

Patellar tendon length change after anterior cruciate ligament reconstruction using the midthird patellar tendon

The purpose of this study was to determine if use of the midthird patellar tendon autograft contributes to or causes patellar tendon shortening or patella baja in anterior cruciate ligament reconstruction. Thirty-six patients undergoing arthroscopically assisted midthird patellar tendon autograft anterior cruciate ligament reconstruction were studied prospectively. Intraoperative patellar tendon length changes were measured. Half of the patients had the tendon defect closed and half had it left open (closing peritenon only). Radiographic tendon length changes and patella baja were assessed using Insall-Salvati and Blackburne-Peel ratios measured on 45 degrees lateral knee radiographs using an adjustable polypropylene jig. Bilateral films were obtained preoperatively and at 2 weeks, 3 months, and 6 months postoperatively. No patients demonstrated evidence of patellar tendon shortening greater than the 5.5% measurement error. Tendon defect closure resulted in negligible tendon shortening intraoperatively, averaging 2.28% (1.11 mm). Of the 18 patients whose defects were closed, 5 showed no shortening. The remaining 13 patients had measurable tendon shortening less than 4% (2 mm). No patients developed patella baja.

An in vitro analysis of patellofemoral contact areas and pressures following procurement of the central one-third patellar tendon

Patients have complained of pain after the use of the central one-third patellar tendon for reconstruction of the anterior cruciate ligament-deficient knee. This study investigated the effect on patellofemoral contact areas and pressures of harvesting the central 10 mm of the patellar tendon in five cadaveric knees. Isometric quadriceps forces were applied to produce approximately 30% of reported maximum voluntary extension moments at the knee. Using Fuji pressure-sensitive film, measurements were recorded for three states: the normal knee, after the graft removal, and after the tendon was closed. Contact areas and pressures were measured at 20 degrees, 30 degrees, 60 degrees, and 80 degrees of knee flexion in each specimen. Tests of the reproducibility of our methods were performed. Average patellofemoral contact areas for three states ranged from 1.6 cm2 at 20 degrees of knee flexion to 3.0 cm2 at 60 degrees. The average patellofemoral contact pressures ranged from 1.9 MPa at 20 degrees of knee flexion to 3.0 MPa at 30 degrees. At each flexion angle there were no significant differences in average patellar contact area or pressure for the three states (P < 0.05). These results suggest that neither harvesting the central 10 mm of the patellar tendon, nor closing the gap, significantly alters patellofemoral contact area or pressure.

Arthroscopically assisted anterior cruciate ligament reconstruction with the pes anserine tendons. Comparison of results in acute and chronic ligament deficiency

Fifty anterior cruciate ligament-deficient knees treated consecutively with arthroscopically assisted reconstruction using a pes anserine tendon autograft were retrospectively studied. The mean followup was 36.7 months (range, 26 to 58). All patients had reconstruction with a double-stranded graft. The mean injury to surgery interval was 9.6 days in 22 patients (acute group) and 22.5 months in 28 patients (chronic group). Objective outcome, which was noted to be more optimal in the acute group, was better than subjective outcome in either group. Examination revealed 95% of patients treated acutely and 82% of those treated later to have 1+ or less Lachman test result (P < 0.036) and 96% of the acute group and 82% of the chronic group to have an absent pivot shift (P < 0.036). Eighty-eight percent of acutely treated patients had a KT-1000 result of < or = 3 mm, as compared to 61% of chronically treated patients (P < 0.001). Loss of range of motion was significantly greater in the acute group (P < 0.018). Using a strict overall rating system, patients reconstructed earlier were noted to have a better outcome compared to those after delayed reconstruction (P < 0.021). Cumulative meniscal injury appears to be the most significant contributing factor.

Extensor mechanism function after patellar tendon graft harvest for anterior cruciate ligament reconstruction

We evaluated extensor mechanism function in 10 patients after they had arthroscopically assisted ACL reconstruction using the central third of the patellar tendon. The patients were randomly selected 12 to 24 months after reconstruction. All had rehabilitation where range of motion was initiated within the 1st postoperative week. All patients stated that they were satisfied and considered their knee to be stable. The KT-1000 maximum measurements (30 to 40 pounds) averaged an increase of 1.7 mm when compared with the opposite knee. Subjective complaints, such as anterior knee pain, grating, and weakness, were common and only 3 of 10 patients returned to all of their preinjury sports. Persistent radiographic abnormalities were common. Physical examination and functional testing also revealed persistent dysfunction of the extensor mechanism in patients with radiographic abnormalities. Isokinetic testing at 60 deg/sec showed an average quadriceps deficit of 18% compared to the normal extremity. Axial computed tomography scans revealed significant decrease in quadriceps cross-sectional area. Magnetic resonance imaging and computed tomography confirmed persistent defects at the harvest site; there was significant anterior knee scar formation in these patients. Despite achieving ligamentous stability, patients still experienced permanent weakness, functional deficits, patellar chondrosis, and pain after ACL reconstruction using the central one-third of the patellar tendon.

Magnetic resonance imaging evaluation of the patellar tendon after use of its central one-third for anterior cruciate ligament reconstruction

Magnetic resonance imaging was used to evaluate the remaining patellar tendon after its central one-third had been harvested for anterior cruciate ligament reconstruction. Twenty patients were studied at either 6 weeks, 4, 6, 9, or 18 months postoperatively. The average thickness, width, cross-sectional area, and signal intensity of the operated and contralateral non-operated tendons were calculated and compared for each magnetic resonance imaging scan. A significant increase in the thickness was noted at all periods of followup, but no change in width occurred despite the defect being closed at the time of surgery. High signal intensity was present in the early periods, which signified edema and scar tissue. Signal intensity decreased at subsequent follow-up periods until at 18 months the operated tendon appeared normal. These findings indicate that the patellar tendon has the potential to regenerate and remodel in the postoperative period.