Proprioceptive capacity of the knee joint area in patients after rupture of the anterior cruciate ligament]

In 30 healthy volunteers with clinically inconspicuous knee joints the proprioception of the knee joint was evaluated by an angle reproduction test. With the same set-up we documented the effect of an elastic knee bandage. We could not document any differences between the left and the right knee joint or between men and women, but at the mid-range of motion, proprioception was worse compared to the end range of motion. The applied elastic knee bandage significantly improved the position sense. Additionally 25 patients with an isolated rupture of the anterior cruciate ligament were evaluated. Fourteen patients were examined preoperatively 11 after operative ACL reconstruction. Preoperatively proprioception was significantly poorer than in the control group. We were able to show a positive influence of a knee bandage on the proprioception of the injured knee as well. Patients after ACL reconstruction showed no significantly better proprioception than the preoperative group.     

Urinary excretion of ifosfamide, 4-hydroxyifosfamide, 3- and 2-dechloroethylifosfamide, mesna, and dimesna in patients on fractionated intravenous ifosfamide and concomitant mesna therapy

Injuries of the anterior cruciate ligament (ACL) and the medial collateral ligament (MCL) are common, accounting for 90% of all knee ligament injuries in young and active individuals. During the last decade, our research center has focused on MCL healing and ACL reconstruction. We have found that the MCL heals without intervention after an isolated injury, and that primary repair offers no apparent advantage. After a combined injury of the ACL and MCL, the ACL requires reconstruction, whereas primary repair again contributes little or nothing toward MCL healing. Midsubstance ACL injuries have limited healing ability. Hence, the treatment of choice for a torn ACL in a young, active patient is generally reconstruction with an autograft or allograft. However, the appropriate replacement graft and reconstruction technique to use are still debated. Current research efforts have been placed on investigating the magnitude and direction of in situ forces in the human ACL. We use a six-component universal force moment sensor combined with a six-degree-of-freedom (DOF) robotic manipulator to learn as well as to reproduce the six-DOF motion of the knee before and after ACL injury. This way, the in situ force in the ACL under an anterior posterior tibial load of 110 N was obtained. This methodology should make it possible to obtain the needed data to aid in better understanding of ACL reconstruction and possible development of improved clinical management.     

Gait biomechanics are not normal after anterior cruciate ligament reconstruction and accelerated rehabilitation

PURPOSE: Accelerated rehabilitation for anterior cruciate ligament (ACL) injury and reconstruction surgery is designed to return injured people to athletic activities in approximately 6 months. The small amount of empirical data on this population suggests, however, that the torque at the knee joint may not return until 22 months after surgery during walking and even longer during running. Although the rehabilitation has ended and individuals have returned to preinjury activities, gait mechanics appear to be abnormal at the end of accelerated programs. The purpose of this study was to compare lower extremity joint kinematics, kinetics, and energetics between individuals having undergone ACL reconstruction and accelerated rehabilitation and healthy individuals. METHODS: Eight ACL-injured and 22 healthy subjects were tested. Injured subjects were tested 3 wk and 6 months (the end of rehabilitation) after surgery. Ground reaction force and kinematic data were combined with inverse dynamics to predict sagittal plane joint torques and powers from which angular impulse and work were derived. RESULTS: The difference in all kinematic variables between the two tests for the ACL group averaged 38% (all P < 0.05). The kinematics were not different between the ACL group after rehabilitation and healthy subjects. Angular impulses and work averaged 100% difference for all joints (all P < 0.05) between tests for the ACL group. After rehabilitation, the differences between injured and healthy groups in angular impulse and work at both the hip and knee remained large and averaged 52% (all P < 0.05). CONCLUSIONS: Results indicated that after reconstruction surgery and accelerated rehabilitation for ACL injury, humans walk with normal kinematic patterns but continue to use altered joint torque and power patterns.     

Bone tunnel enlargement after anterior cruciate ligament reconstruction with semitendinosus tendon using Endobutton fixation on the femoral side

We evaluated 29 knees with a minimum follow-up of 2 years after anterior cruciate ligament (ACL) reconstruction using doubled autogenous semitendinosus tendons. On the femoral side, a 5-mm Mersilene tape (Ethicon, Norderstedt, Germany) with an Endobutton (Acufex Microsurgical, Mansfield, MA) was used. The tendon was fixed on the tibial side with two staples. Regarding the IKDC score, 66% of the patients were graded as normal or nearly normal. The anterior laxity side-to-side difference (KT 1000, man-max-drawer) was under 3 mm in 55% and under 5 mm in 90%. Radiographs taken in the lateral and anteroposterior projections of the knee showed sclerotic bone tunnel margins. The diameter of the bone tunnels were measured, corrected for magnification, then compared with the original reamed diameter to determine any change in size. Enlargement of at least 2 mm was identified in 72% of the femoral tunnels and 38% of the tibial tunnels. No correlation was found concerning the enlargement of the tunnel and the IKDC score or the residual joint laxity. We conclude that using an Endobutton-Mersilene construct in ACL reconstruction leads to femoral and tibial bone tunnel enlargement at follow-up of 2 years.     

What would you do? Acute extension block caused by anterior cruciate ligament tear: a case report

Acute knee locking is usually attributed to a displaced meniscus tear. This case involved late diagnosis of mechanical extension block caused by anterior displacement of a torn anterior cruciate ligament (ACL) with impingement in extension. Definitive reconstruction was delayed after debridement of the ACL stump to improve preoperative range of motion. Despite this, the patient still had difficulty regaining extension after surgery. Early treatment of mechanical extension block may facilitate motion recovery after ACL reconstruction.     

Eruption of the permanent upper canine: a radiologic study

Fibroblast-seeded collagen scaffolds or ligament analogs are potentially useful for reconstruction of the anterior cruciate ligament of the knee. To provide lasting benefits, the seeded cells must survive implantation within the harsh synovial environment of the knee joint. Our objective was to determine the in vivo fate of autogenous fibroblast-seeded ligament analogs as a function of fibroblast source (anterior cruciate ligament or skin), implantation site (knee joint or subcutaneous space), and time after implantation (1, 2, 4, 6, or 8 weeks). Before implantation, fibroblasts were labeled with PKH26-GL, a fluorescent membrane dye. Immediately after retrieval of the implant, the viability of the labeled seeded cells was assessed under a fluorescent microscope. Viable seeded fibroblasts remained attached to the collagen fibers within the ligament analogs for at least 4 weeks (skin fibroblasts) or 6 weeks (anterior cruciate ligament fibroblasts) after implantation. A larger number of viable seeded cells were consistently observed in the subcutaneous space than in the knee joint. Scaffold resorption prevented observation at the 8-week time period. Fibroblast-seeded ligament analogs remained viable for prolonged periods in the knee joint and therefore have the potential to influence the formation and remodeling of neoligament tissue after reconstruction of the anterior cruciate ligament.     

Anterior cruciate ligament reconstruction and joint dynamics during stair climbing

Athletes with anterior cruciate ligament (ACL) deficiencies exert decreased knee extension moments during level walking (quadriceps avoidance gait), and yet within a few months of ACL reconstruction they are often expected to return to competitive sport. To investigate this issue further, 10 normal subjects and seven ACL deficient patients were evaluated both pre- and post-operatively (mean follow-up of 6 months), and each performed multiple trials ascending a staircase which consisted of three steps. Bilateral joint angles, moments, powers, and work were measured and the data were ensemble averaged and statistically analyzed (repeated measures ANOVA with significance level set at 0.05). Anterior-posterior knee laxity decreased significantly (from 7.9 mm to 5.8 mm) while subjective knee function also improved following ACL reconstruction (knee score increased from 70.4 to 88.5). Pre-operatively, there were no statistically significant differences in biomechanical parameters between the patients' ACL-deficient and intact sides and the normal subjects. Post-operatively, however, statistically significant reductions were seen for the peak moment (91.9 vs 22.5 Nm), power (181 vs 84 W), and work performed (28.0 vs -5.6 J) at the injured knee, which was also the knee from which the patellar tendon graft had been harvested. These reductions were accommodated by significant increases in excursion, moment, and power at the contralateral ankle joint. The results indicate that while the ACL reconstruction were successful in restoring anterior-posterior knee stability, the decrease in knee power and work performed post-operatively by the injured (i.e., donor) knee suggests that donor site morbidity may need to be critically evaluated over a long-term period.     

Effect of external extra-articular ligament plasty on the results of anterior cruciate ligament reconstruction with patellar tendon, a 4 years follow-up

PURPOSE OF THE STUDY: The purpose of this study was to compare the functional results obtained when an external extra-articular plasty was added to an anterior cruciate ligament (ACL) reconstruction using an autologous bone tendon-bone patellar tendon graft. MATERIAL AND METHODS: The authors analyzed two consecutive series of 60 and 50 patients operated by the same surgeon for a chronic rupture of the anterior cruciate ligament, one by reconstruction of the cruciate ligament with a free graft of the patellar tendon supplemented by an external extra-articular plasty made with a quadriceps tendon graft and the second with an isolated free patellar tendon graft. Anterior laxity was measured before and after surgery, by dynamic X-rays and by the Medmetric KT-1000 arthrometer. Functional results were evaluated four years after operation, with the French A.R.P.E.GE score based on sport activity level and intensity. RESULTS: Anterior laxity was not different before operation in both groups and there was no difference between males and females. Medmetric KT-1000 arthrometer showed the same negative differential laxity immediately after surgery in both groups and the same evolution during the first 4 years, without any significant difference on laxity on the middle aspect of the knee. Radiological results were different. After a 4 years follow-up, anterior laxity did not show significant difference on the medial compartment of the knee (5.3 +/- 2.3 mm and 5.5 +/- 1.7 mm), but there was a significant minor laxity in the lateral compartment for the lateral extra-articular plasty group (11.0 +/- 2.3 mm against 14.8 +/- 3.8 mm)(p = 0.002). Functional results and sport activity were similar in both groups. Examination showed 4 positive pivot shift tests (2 "sliding" and 2 positive) in the group with extra-articular plasty, even though 8 positive pivot shift tests in the isolated ACL group (5 "sliding" and 3 positive) were found. DISCUSSION: This study, as well as five others studies found in literature, was not randomized. In all these series, the surgical techniques, the rehabilitation programs and the functional score evaluation were too different to allow any pertinent comparison. Extra-articular plasty helps to control the laxity of the lateral compartment of the knee which is incompletely controlled by ACL reconstruction, particularly in chronic cases. This is proved by radiological measurements and pivot shift tests. Jensen in 1983, about 205 patients with a 4 year follow-up and Noyes, which used an allograft patellar tendon, found an advantage to do extra-articular plasty. But Strum (in 1989), as O'Brien (in 1991) and Roth (in 1987), did not found any advantage with extra-articular plasty. CONCLUSION: It is therefore obvious, after a four-year follow-up, that extra-articular supplementation presents an advantage for reconstruction of the ACL. by a free graft of the patellar tendon in chronic cases. Further randomized study will confirm that isolated ACL reconstruction is possible in some well defined categories of anterior laxity.     

Gait adaptations before and after anterior cruciate ligament reconstruction surgery

Gait analyses of rehabilitated individuals with anterior cruciate ligament (ACL) deficiency and reconstruction have identified the final adaptations of increased hip extensor torque and hamstring electromyography (EMG) and decreased knee extensor torque and quadriceps EMG during stance. The initial adaptations to injury and surgery are, however, unknown as are the factors that influence the development of the adaptations. Identification of the initial response to injury would provide a basis for determining whether the final adaptations are learned automatically or if they are the result of a lengthy training period in which various factors may affect their development. The purpose of the study was to evaluate the initial effects of ACL injury and reconstruction surgery on joint kinematics, kinetics, and energetics, during walking. Injured limbs from nine subjects with ACL injury were tested 2 wk after injury, and 3 and 5 wk after surgery. Ten healthy subjects were tested. Kinematic and ground reaction data were collected and combined with inverse dynamics to calculate the joint torques and powers. A knee extensor torque throughout most of stance was observed in the injured limbs at all test sessions. This result was in conflict with previous observations of reduced extensor torque or a flexor torque in rehabilitated patients with ACL reconstruction and patients with ACL deficiency. This result also differed from the typical midstance extensor then flexor torque in healthy control subjects. Trend analysis showed a significant (P < 0.001) change in average position at the hip and knee, extensor angular impulse at the hip, and positive work done at the hip 3 wk after surgery followed by a partial rehabilitation at 5 wk after surgery. Power and work produced at the knee were reduced fivefold (P < 0.001) after 5 wk of rehabilitation and did not recover to pre-surgical levels. The existence of a long-lasting knee extensor torque 2 wk after injury indicated that the adaptation process to ACL deficiency is lengthy, requiring many gait cycles, and that numerous factors could be involved in learning the adaptations.     

Proprioceptive capacities of patients with retropatellar knee pain with special reference to effectiveness of an elastic knee bandage

In the presented study, knee joint proprioception of 43 patients with a patellar pain syndrome of the knee joint was evaluated. In a control group, the proprioception of 30 healthy volunteers with clinical and an-amnestic inconspicous knee joints was examined. We tested the proprioceptive capability of the subjects with a passive angle reproduction test. Additionally, all knee joints were measured with and without an elastic knee bandage. The patient group showed significant deterioration of angle reproduction capability (13.2 degrees +/- 6.1 degrees) compared to the control group (7.8 degrees +/- 2.8 degrees). After applying an elastic knee bandage, the angle reproduction capability significantly improved to 9.2 degrees +/- 4.5 degrees. Proprioception of the contralateral, noninvolved knee joint in the patients (11.6 degrees +/- 6.3 degrees) was worse compared to the control group. Applying an elastic knee bandage did not significantly improve the proprioception of the uninjured knee joint.     

Proprioceptive deficits of the knee joint after rupture of the medial meniscus

We assessed knee joint proprioception in 23 patients with an isolated lesion of the medial meniscus. Thirteen patients were tested prior to their arthroscopic operation, and 10 patients were examined after partial arthroscopic resection of the injured meniscus. As a control group we evaluated 30 healthy volunteers with clinically inconspicious knee joints. For documentation of the proprioceptive capabilities we performed an angle reproduction test. Additionally the subjects were tested with and without an elastic knee bandage, to test the influence of such a bandage on knee joint proprioception. Our results showed that preoperatively proprioception was significantly less good than in the control group. We found no influence of the knee bandage on the proprioception of the injured knee. The postoperative group of patients showed significantly better proprioceptive capability than the preoperative patients. The postoperative results did not differ significantly from those of the control group.     

The effect of immediate weightbearing after anterior cruciate ligament reconstruction

Immediate weightbearing has been advocated after anterior cruciate ligament reconstruction and is thought to enhance the return of quadriceps muscle activity and knee extension range of motion without jeopardizing graft integrity. This study examined the effect of immediate weightbearing after anterior cruciate ligament reconstruction on the return of vastus medialis oblique electromyography activity, knee extension range of motion, knee stability, physical examination, Lysholm score, and anterior knee pain. Forty-nine patients (24 men and 25 women) undergoing endoscopic central third patella tendon autograft reconstruction were randomized prospectively into two groups. Group 1 patients underwent immediate weightbearing as tolerated. Group 2 patients were kept nonweightbearing for 2 weeks. All measurements were taken before surgery, 2 weeks after surgery, and between 6 and 14 months (average, 7.3 months) followup. There was no effect of weightbearing on knee extension range of motion or vastus medialis oblique function at followup. In addition, knee stability was not compromised after surgery. Seven of 20 (35%) nonweightbearing patients and only two of 25 (8%) immediate weightbearing patients reported anterior knee pain at followup. Overall, immediate weightbearing did not compromise knee joint stability and resulted in a better outcome with a decreased incidence of anterior knee pain.     

Septic arthritis of the knee following anterior cruciate ligament reconstruction: results of a survey of sports medicine fellowship directors

To determine the incidence of joint sepsis following anterior cruciate ligament (ACL) reconstruction and the prevailing attitudes toward its treatment, we surveyed the directors of Sports Medicine Fellowship programs about their practices in treating and preventing this complication. Of the 74 surgeons surveyed, 61 (82%) responded. These 61 surgeons performed an average of 98 ACL reconstructions yearly; 31 (51 %) routinely used a drain after ACL surgery, 18 (30%) had treated an ACL infection within the past 2 years, and 26 (43%) had treated an infection within the past 5 years. There was no significant difference in the number of infections and the surgeons' case load, graft choice, or method of reconstruction. Fifty-two surgeons (85%) selected culture-specific intravenous (IV) antibiotics and surgical irrigation of the joint with graft retention as initial treatment for the infected patellar tendon autograft, and 39 (64%) chose this regimen to treat the infected allograft. For the resistant infection unresponsive to initial treatment, IV antibiotics with surgical irrigation and graft retention were also selected as the most common treatment combination for 25 (39%) of the 61 respondents. After graft removal, the earliest a revision procedure would be considered was 6 to 9 months. The results of this survey confirm the widely held belief that septic arthritis of the knee is a relatively rare complication following ACL reconstruction. Once an infection is encountered, culture-specific IV antibiotics and surgical joint irrigation with graft retention are recommended as initial treatment. Graft excision and hardware removal is considered only for those infections resistant to initial treatment and for the infected allograft.     

The conservative treatment of complete tears of the anterior cruciate ligament in skeletally immature patients

We describe the results of conservative treatment for complete midsubstance tears of the anterior cruciate ligament (ACL) in 18 skeletally immature patients, followed for a minimum of 36 months. Six patients had an ACL reconstruction during the follow-up period and were assessed immediately before their operation. The average time from initial injury to evaluation was 51 months. All patients had symptoms when reviewed. The modified Lysholm knee score showed one excellent result, one good, eight fair, and eight poor with a mean score of 64.3. Only one patient had returned to her preinjury level of athletics. Secondary meniscal tears were confirmed in six patients, and three more had the clinical signs of a tear at follow-up. Radiological evidence of degenerative changes was found in 11 of the 18 patients. We conclude that the results of non-operative treatment for ACL injuries in this age group are poor and not acceptable.     

The effects of an artificial meniscus substitute in a knee joint with a resected anterior cruciate ligament. An experimental study in rabbits

A Dacron meniscus prosthesis was substituted for the medial meniscus in an anterior cruciate ligament (ACL) resected rabbit knee. At three months, the joints were evaluated biomechanically, with gross and histologic inspection. In a paired comparison with the contralateral knee, differences between ACL resection with intact, incised, or resected medial menisci were evaluated. Knees with intact menisci and ligaments served as controls. Because of cartilage destruction, soft-tissue hypertrophy, and increased anterior laxity, joint stiffness was less than normal in all ACL-resected knees. Ingrowth and stable fixation, especially of the posterior horns of the prostheses and the incised menisci, were rare. Almost all normal menisci had ruptured in the same area. Anterior cruciate ligament resection led to severe osteoarthrosis in both compartments, regardless of initial meniscal treatment. Knees with prostheses had the same incidence and severity of osteoarthrosis as knees with meniscus resection. Anterior cruciate ligament resection alone induced excessive osteoarthrosis and synovitis and diminished the effects of different meniscal treatments three months earlier.     

Effects of ketorolac on bone repair: A radiographic study in modeled demineralized bone matrix grafted rabbits

The treatment of instability of the multiply reoperated knee is a complex problem. The causes for failure are numerous and include repeated trauma, insufficient fixation and non-anatomic placement of the graft, inadequate replacement material, isolated anterior cruciate ligament (ACL) reconstruction in complex knee instability or the use of a ligament prosthesis. With every surgical procedure, however, the anatomical and technical conditions become worse. Problems like degenerative changes, joint stiffness and gait abnormalities occur and often become a more focal point than the instability itself. The purpose of this paper is to present the problems and the dilemma of instability of the multiply reoperated knee and the possible solutions. Between 1976 and 1996, a total of 1752 ACL reconstructions were carried out in Munich and Hannover. Of these, 228 (13%) were revision, mostly of failed ACL reconstructions performed elsewhere. Since 1989, we have chosen the severest cases from this group (more than three operations on the same knee) for this study. Seventeen patients were investigated who had undergone up to 25 operations. The mean number of operations was 7. All primary operations were performed in other hospitals. In 10 cases only the ACL reconstruction was performed as a final procedure, mostly in combination with other procedures like medial meniscus replacement, extra-articular stabilization or arthrolysis. In the other cases operations such as osteotomies, arthrodesis or amputation were necessary. The results present the main dilemma in instability of the multiply reoperated knee since they were not successful in all patients. Finally, 15 patients report still having instability, pain or swelling in isolation or in combination. Nine patients were satisfied with their subjective results. Even after the socalled definitive procedures, certain complications arose. The main goal in the treatment of instability of the multiply reoperated knee is to avoid a series of operations, hospitalization and history of illness. General revision surgery for the entire complaint is not the aim of the treatment. The specific problem of the patient should be extracted from the complex situation, and this should be solved with the most limited procedure possible only.     

Mechanisms of anterior cruciate ligament neovascularization and ligamentization

Columbia-Rambouillet cross-bred sheep were used to study the revascularization and ligamentization process of anterior cruciate ligament (ACL) reconstruction over a 6-month period using basic histology, immunohistochemistry, and electron microscopy. The reconstruction technique studied was a quadruple-hamstring, interference screw fixation technique. Further, these specimens, after retrieval at 6, 12, and 26 weeks, were compared with human arthroscopic 'second looks' and with 10 en bloc specimens obtained when a cruciate-sacrificing total knee replacement was performed. The study showed that, with this reconstruction technique, Sharpey's fibers were seen at 6 weeks in both sheep and human specimens. The intratunnel specimens showed proliferative chondrification, then ossification of the matrix. Intra-articular neovascularization, ligamentization, and junction ossification occurred. Myoblasts or smooth muscle cells appear to mediate the ligamentization as evidenced in electron microscopy by proliferate collagen manufacture. These myoblasts were seen in both the healing sheep and human second looks, but not seen in mature ACL grafts or in normal ACLs. At 6 months postoperatively, the sheep ACL reconstruction appeared clinically, histologically, and immunohistochemically indistinguishable from the normal sheep ACL. A correlation of this work with published animal studies in which biomechanical testing was performed and with human 'second looks' would imply that an ACL reconstruction may be vulnerable during this period of neovascularization and ligamentization.     

Allogeneic transplantation of selected CD34+ cells from peripheral blood: experience of 62 cases using immunoadsorption or immunomagnetic technique. Spanish Group of Allo-PBT

Disruption of the anterior cruciate ligament (ACL), a primary stabilizer of the knee, can produce disability. The purpose of our work has been to study the normal ACL in humans, in the presence of normal muscle function and body weight, and develop clinical criteria for reconstruction, establish a basis for rehabilitation programs, and evaluate how knee braces protect this important ligament. The strain behavior of the ACL has been measured by arthroscopic implantation of the Differential Variable Reluctance Transducer while subjects are under local anesthesia. Movement of the knee from a flexed to an extended position, either passively or through contraction of the leg muscles, produces an increase in ACL strain values. Isolated contraction of the dominant quadriceps with the knee between 50 degrees and extension creates substantial increases in strain. In contrast, isolated contraction of the hamstrings at any knee position does not increase strain. With the knee un-weighted, the protective strain shielding effect of a functional knee brace decreases as the magnitude of anterior shear load applied to the tibia increases. A different behavior occurs during weight bearing, the strain shielding effect of the brace remains constant as the magnitude of anterior load increases. Our approach is novel in that it can be used to measure on important portion of the ACLs strain distribution while clinically relevant loads are applied to the knee, subjects perform rehabilitation exercises, or in the presence of different orthoses such as functional knee braces.     

Haptoglobin polymorphism, iron metabolism and mortality in HIV infection

Simultaneous ACL and PCL ruptures are rare but serious injuries resulting in distinct instability of the knee joint followed by an early degenerative arthritis. This combined trauma, which is often accompanied by additional ligament lesions, originates from a knee dislocation. While the conservative treatment of this complex instability is abandoned, the operative procedures are not yet standardised. The timing of the cruciate ligament reconstruction depends on the additional injuries, but generally the postprimary treatment is performed. Autografts and allografts, which can be also combined, are available for the reconstruction of the cruciate ligaments. The arthroscopic assisted operation starts with the drilling of all tibial and femoral tunnels using standard ACL and PCL arthroscopic instruments. The PCL is positioned after the graft has been transported into the joint through an anterolateral port, the ACL graft is positioned through the tibial drill hole and both are anchored first on the femoral and then on the tibial site i.e. with interference screws. In the postoperative rehabilitation neither immobilisation nor brace are used and progressive range of motion is allowed. The arthroscopic assisted reconstructions of the ACL and increasingly of the PCL are becoming standard procedures, but the technically difficult combined ACL/PCL reconstruction is restricted to a small number of arthroscopists. The first clinical results demonstrate, that the arthroscopic operation is comparable to the open reconstruction.     

Material and functional properties of articular cartilage and patellofemoral contact mechanics in an experimental model of osteoarthritis

The purposes of this study were to determine the in situ functional and material properties of articular cartilage in an experimental model of joint injury, and to quantify the corresponding in situ joint contact mechanics. Experiments were performed in the anterior cruciate ligament (ACL) transected knee of the cat and the corresponding, intact contralateral knee, 16 weeks following intervention. Cartilage thickness, stiffness, effective Young's modulus, and permeability were measured and derived from six locations of the knee. The total contact area and peak pressures in the patellofemoral joint were obtained in situ using Fuji Pressensor film, and comparisons between experimental and contralateral joint were made for corresponding loading conditions. Total joint contact area and peak pressure were increased and decreased significantly (alpha=0.01), respectively, in the experimental compared to the contralateral joint. Articular cartilage thickness and stiffness were increased and decreased significantly (alpha=0.01), respectively, in the experimental compared to the contralateral joint in the four femoral and patellar test locations. Articular cartilage material properties (effective Young's modulus and permeability) were the same in the ACL-transected and intact joints. These results demonstrate for the first time the effect of changes in articular cartilage properties on the load transmission across a joint. They further demonstrate a substantial change in the joint contact mechanics within 16 weeks of ACL transection. The results were corroborated by theoretical analysis of the contact mechanics in the intact and ACL-transected knee using biphasic contact analysis and direct input of cartilage properties and joint surface geometry from the experimental animals. We conclude that the joint contact mechanics in the ACL-transected cat change within 16 weeks of experimental intervention.