Function of the anterior cruciate ligament after unicompartmental knee arthroplasty: an in vitro robotic study

The objective of this study was to investigate the role of the anterior cruciate ligament (ACL) in the anterior-posterior (AP) stability of the knee after unicompartmental knee arthroplasty (UKA). AP tibial loads were applied to human cadaveric knee specimens using a robotic testing system. After UKA, the knee exhibited tibial translations similar to that of the native knee, and the forces in the ACL were also similar to those seen in the native knee. The ACL-deficient knee after UKA exhibited significantly greater anterior tibial translations than the native knee and the knee after UKA with an intact ACL. These data suggest that medial UKA does not alter the anterior stability of the knee, but a functional ACL is necessary to ensure normal stability after UKA.     

In-situ force in the medial and lateral structures of intact and ACL-deficient knees

The anterior cruciate ligament (ACL) is the major contributor to limit excessive anterior tibial translation (ATT) when the knee is subjected to an anterior tibial load. However, the importance of the medial and lateral structures of the knee can also play a significant role in resisting anterior tibial loads, especially in the event of an ACL injury. Therefore, the objective of this study was to determine quantitatively the increase in the in-situ forces in the medial collateral ligament (MCL) and posterolateral structures (PLS) of the knee associated with ACL deficiency. Eight fresh-frozen cadaveric human knees were subjected to a 134-N anterior tibial load at full extension and at 15°, 30°, 60°, and 90° of knee flexion. The resulting 5 degrees of freedom kinematics were measured for the intact and the ACL-deficient knees. A robotic/universal force-moment sensor testing system was used for this purpose, as well as to determine the in-situ force in the MCL and PLS in the intact and ACL-deficient knees. For the intact knee, the in-situ forces in both the MCL and PLS were less than 20 N for all five flexion angles tested. But in the ACL-deficient knee, the in-situ forces in the MCL and PLS, respectively, were approximately two and five times as large as those in the intact knee (P < 0.05). The results of this study demonstrate that, although both the MCL and PLS play only a minor role in resisting anterior tibial loads in the intact knee, they become significant after ACL injury. Received: December 3, 1999 / Accepted: July 19, 2000     

Knee biomechanics after UKA and its relation to the ACL--a robotic investigation.

Unicompartmental knee arthroplasty (UKA) has regained popularity in recent years. However, limited data exist on how UKA affects knee biomechanics. The role of the anterior cruciate ligament (ACL) after fixed bearing UKA remains controversial. In this study, a robotic testing system was used to apply a quadriceps/hamstrings load to cadaveric knee specimens in the intact state, after medial UKA, and after transection of the ACL in UKA. The load was applied to the knee from full extension to 120 degrees of flexion in 30 degrees increments. UKA generally did not affect anterior-posterior (AP) femoral position, but did cause external tibial rotation and variations in varus-valgus rotation compared to the intact knee. ACL transection after UKA shifted the femur posteriorly compared to the intact and UKA knees and increased internal tibial rotation compared to the UKA knee at low flexion. The AP motion of the articular contact position in the implant was increased after ACL transection. These data might help explain the mechanism of tibial component loosening and provide insight into further investigations of polyethylene wear in UKA. Based on the kinematic data, the ACL should be functional to provide patients the greatest opportunity for long-term success after medial UKA.     

Interaction between the ACL graft and MCL in a combined ACL+MCL knee injury using a goat model

The optimal treatment for the MCL in the combined ACL and MCL-injured knee is still controversial. Therefore, we designed this study to examine the mechanical interaction between the ACL graft and the MCL in a goat model using a robotic/universal force-moment sensor testing system. The kinematics of intact, ACL-deficient, ACL-reconstructed, and ACL-reconstructed/MCL-deficient knees, as well as the in situ forces in the ACL, ACL graft, and MCL were determined in response to two external loading conditions: 1) anterior tibial load of 67 N and 2) valgus moment of 5 N-m. With an anterior tibial load, anterior tibial translation in the ACL-deficient knee significantly increased from 2.0 and 2.2 mm to 15.7 and 18.1 mm at 30° and 60° of knee flexion, respectively. The in situ forces in the MCL also increased from 8 to 27 N at 60° of knee flexion. ACL reconstruction reduced the anterior tibial translation to within 2 mm of the intact knee and significantly reduced the in situ force in the MCL to 17 N. However, in response to a valgus moment, the in situ forces in the ACL graft increased significantly by 34 N after transecting the MCL. These findings show that ACL deficiency can increase the in situ forces in the MCL while ACL reconstruction can reduce the in situ forces in the MCL in response to an anterior tibial load. On the other hand, the ACL graft is subjected to significantly higher in situ forces with MCL deficiency during an applied valgus moment. Therefore, the ACL-reconstructed knee with a combined ACL and MCL injury should be protected from high valgus moments during early healing to avoid excessive loading on the graft.     

Can suture repair of ACL transection restore normal anteroposterior laxity of the knee? An ex vivo study

Recent work has suggested the transected anterior cruciate ligament (ACL) can heal and support reasonable loads if repaired with sutures and a bioactive scaffold; however, use of a traditional suture configuration results in knees with increased anterior–posterior (AP) laxity. The objective was to determine whether one of five different suture repair constructs when performed at two different joint positions would restore normal AP knee laxity. AP laxity of the porcine knee at 60° of flexion was evaluated for five suture repair techniques. Femoral fixation for all repair techniques utilized a suture anchor. Primary repair was to either the tibial stump, one of three bony locations in the ACL footprint, or a hybrid bony fixation. All five repairs were tied with the knee in first 30° and then 60° of flexion for a total of 10 repair constructs. Suture repair to bony fixation points within the anterior half of the normal ACL footprint resulted in knee laxity values within 0.5 mm of the ACL‐intact joint when the sutures were tied with the knee at 60° flexion. Suture repair to the tibial stump, or with the knee at 30° of flexion, did not restore normal AP laxity of the knee. Three specific suture repair techniques for the transected porcine ACL restored the normal AP laxity of the knee at the time of surgery. Additional studies defining the changes in laxity with cyclic loading and in vivo healing are indicated. © 2008 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 26:1500–1505, 2008     

Medial unicompartmental knee arthroplasty in the ACL-deficient knee

Symptomatic osteoarthritis (OA) of the knee develops often in association with anterior cruciate ligament (ACL) deficiency. Two distinct pathologies should be recognised while considering treatment options in patients with end-stage medial compartment OA and ACL deficiency. Patients with primary ACL deficiency (usually traumatic ACL rupture) can develop secondary OA (typically presenting with symptoms of instability and pain) and these patients are typically young and active. Patients with primary end stage medial compartment OA can develop secondary ACL deficiency (usually degenerate ACL rupture) and these patients tend to be older. Treatment options in either of these patient groups include arthroscopic debridement, reconstruction of the ACL, high tibial osteotomy (HTO) with or without ACL reconstruction, unicompartmental knee arthroplasty (UKA) and total knee arthroplasty (TKA). General opinion is that a functionally intact ACL is a fundamental prerequisite to perform a UKA. This is because previous reports showed higher failure rates when ACL was deficient, probably secondary to wear and tibial loosening. Nevertheless in some cases of ACL deficiency with end-stage medial compartment OA, UKA has been performed in isolation and recent papers confirm good short- to mid-term outcome without increased risk of implant failure. Shorter hospital stay, fewer blood transfusions, faster recovery and significantly lower risk of developing major complications like death, myocardial infarction, stroke, deep vein thrombosis (as compared to TKA) make the UKA an attractive option, especially in the older patients. On the other hand, younger patients with higher functional demands are likely to benefit from a simultaneous or staged ACL reconstruction in addition to UKA to regain knee stability. These procedures tend to be technically demanding. The main aim of this review was to provide a synopsis of the existing literature and outline an evidence-based treatment algorithm.     

Medial collateral ligament insertion site and contact forces in the ACL-deficient knee.

The objectives of this research were to determine the effects of anterior cruciate ligament (ACL) deficiency on medial collateral ligament (MCL) insertion site and contact forces during anterior tibial loading and valgus loading using a combined experimental-finite element (FE) approach. Our hypothesis was that ACL deficiency would increase MCL insertion site forces at the attachments to the tibia and femur and increase contact forces between the MCL and these bones. Six male knees were subjected to varus-valgus and anterior-posterior loading at flexion angles of 0 degrees and 30 degrees. Three-dimensional joint kinematics and MCL strains were recorded during kinematic testing. Following testing, the MCL of each knee was removed to establish a stress-free reference configuration. An FE model of the femur-MCL-tibia complex was constructed for each knee to simulate valgus rotation and anterior translation at 0 degrees and 30 degrees, using subject-specific bone and ligament geometry and joint kinematics. A transversely isotropic hyperelastic material model with average material coefficients taken from a previous study was used to represent the MCL. Subject-specific MCL in situ strain distributions were used in each model. Insertion site and contact forces were determined from the FE analyses. FE predictions were validated by comparing MCL fiber strains to experimental measurements. The subject-specific FE predictions of MCL fiber stretch correlated well with the experimentally measured values (R2 = 0.95). ACL deficiency caused a significant increase in MCL insertion site and contact forces in response to anterior tibial loading. In contrast, ACL deficiency did not significantly increase MCL insertion site and contact forces in response to valgus loading, demonstrating that the ACL is not a restraint to valgus rotation in knees that have an intact MCL. When evaluating valgus laxity in the ACL-deficient knee, increased valgus laxity indicates a compromised MCL.     

Relevance of the Tibial Slope on Functional Outcomes in ACL-Deficient and ACL Intact Fixed-Bearing Medial Unicompartmental Knee Arthroplasty

BackgroundExcessive posterior tibial slope in medial unicompartmental knee arthroplasty (UKA) has been implicated in early failure. The purpose of this study was to evaluate the relationship between preoperative posterior tibial slope and postoperative slope of the implant (PSI) on outcomes in patients with anterior cruciate ligament (ACL) intact and ACL-deficient knees after fixed-bearing medial UKA.MethodsPatients who underwent a medial UKA between 2002 and 2017 with a minimum 3-year follow-up were included. Preoperative posterior tibial slope and postoperative PSI were measured. Outcomes measures included Knee Injury and Osteoarthritis Outcomes Score (KOOS) subscales, Lysholm, and VR-12. Failure was defined as conversion to total knee arthroplasty.ResultsOf 241 knees undergoing UKA, 131 patients (70 women, 61 men; average age of 65 ± 10 years (average BMI of 27.9 ± 4) were included. For all patients, survivorship was 98% at 5 years and 96% at 10 years with a mean survival time for UKA was 15.2 years [95% CI: 14.6-15.7]. No failure had a PSI >7°. There were no superficial or deep infections. There were no significant differences in outcome scores between the ACL intact and the ACL-deficient group; therefore, the data were combined for analysis. At mean 8-year follow-up, KOOS pain scores were better in patients with PSI ≤7° (87 ± 16) than those with PSI >7° (81 ± 15). 76% of patients with PSI ≤7° reached the Patient Acceptable Symptom State for KOOS pain; whereas, 59% of patients with PSI >7° reached PASS for KOOS pain (P = .015).ConclusionPatients with postoperative posterior slope of the tibial implant >7° had significantly worse postoperative pain, without conversion to TKA, and with maintenance of high function. In ACL deficient and intact knees, nonrobotically-assisted, fixed-bearing medial UKA had a 96% survivorship at 10 years.     

全膝关节置换术后股胫关节运动学轨迹的数字化模型研究

 目的 通过透视技术结合数字化模型注册技术分析全膝关节置换术后股骨假体与胫骨垫片之间的相对运动和接触位置。方法 2007年7月至2008年6月,接受GENESISⅡ假体全膝关节置换术患者16例,均为女性;年龄56～76岁,平均66.4岁。随访48～60个月,平均(56±3)个月。采用膝关节学会评分(Knee Society Score,KSS)评价膝关节功能;采用循环透视方法获取影像学数据,对假体逆向数字建模,进行数字模型和影像学数据的匹配,重建膝关节的三维运动;测量股骨内、外髁接触位置的移动,计算胫骨内旋角度,测量股骨凸轮和胫骨立柱的接触时相和范围。结果 末次随访时KSS膝评分(93±5)分,功能评分(88±13)分,与术前比较差异有统计学意义。股骨内髁的移动范围(8.5±2.5) mm,外髁的移动范围(9.5±4.8) mm,胫骨内旋角度2.5°±8.4°。屈膝约30°～40°时凸轮和立柱发生接触,立柱后方的接触范围(8.0±1.8) mm。胫骨平台后倾角度越大,凸轮和立柱的接触越晚。结论 全膝关节置换术后股胫关节的运动学特征与正常膝关节不同,膝关节屈曲10°~30°时股骨内髁前移,屈曲大于40°后股骨内、外髁后移,胫骨平台后倾与凸轮和立柱的接触时相有相关性。     

Dynamic elongation behavior in the medical collateral and anterior cruciate ligaments during lateral impact loading

The objectives of this experimental study were to determine (a) how quickly the medial collateral ligament (MCL) and the anterior cruciate ligament (ACL) elongate when a lateral impact force is imparted to the knee and if a person can react rapidly enough to provide protective muscle forces in the case of such an impact. (b) if the MCL and the ACL elongate simultaneously during a lateral impact, and (c) if resection of the ACL affects elongation of the MCL during a lateral impact. Eight whole-leg cadaver specimens were used. Each leg was mounted vertically in a testing-frame with the knee in 0 and 30° of flexion. A submaximal impact was delivered from the lateral side by a pendulum instrumented with a force transducer. Elongation of the midsubstance of the MCL and the ACL was measured with Hall-effect displacement transducers. The ACL was resected and the entire test sequence was repeated. Following a lateral impact, elongation of the MCL and ACL reached peak values by 70 ms. This study indicated that contraction of the leg musculature would not protect the MCL and ACL from injury when a lateral impact load is applied to the knee. The MCL and the ACL never elongated simultaneously during a lateral impact. After lateral impact loading, the time required to reach maximum elongation (peak delay) averaged 52 ms in the anterior MCL fibers and 61 ms in the ACL when the knee was in 0° of flexion. At 30° of flexion, the peak delay averaged 38 ms in the anterior MCL fibers and 22 ms in the ACL. The peak delay of the ACL was significantly greater than that of the MCL at 0° of the flexion (p < 0.05). The opposite was true at 30° of flexion. Resection of the ACL had only minimal effect on the elongation behavior of the MCL.     

Pressure distribution in the knee joint

Biomechanical factors influencing the patterns of pressure distribution at the articular surface and the subchondral bone are suggested to be most important in the pathogenesis of osteoarthritis and ostechondritis dissecans at the knee joint. Besides this, chronic joint instability is another important factor under discussion in the etiology of osteoarthritis of the knee. The patterns of pressure distribution on the femoral condyles of weight-bearing knee joints were investigated in a biostatic cadaver model. The pressure on the femoral condyles was evaluated using pressure-sensitive films with the knee in different physiological joint positions (extension, 15° and 30° flexion) with and without division of either the medial collateral ligament (MCL), the lateral collateral ligament (LCL), the MCL and the anterior cruciate ligament (ACL), or the LCL and the ACL. Results showed that the location of the contact area and peak pressure depended on the joint position and stage of ligament division. Without ligament division the maximum peak pressure was always observed on the medial condyle. Only after MCL and combined MCL + ACL division did the lateral condyle show in extension a higher peak pressure than the medial condyle. Division of the LCL and LCL + ACL resulted in an increase in peak pressure on the medial condyle, particularly in flexion. The highest peak pressure of all was measured in the 30° flexion position on the medial condyle after division of the LCL. The lowest at all was found on the lateral condyle in 15° flexion after LCL division. Additional ACL division resulted in only minor further changes. These results are important for the interpretation of clinically observed factors discussed in the etiology of secondary osteoarthritis of the knee and contribute to the theory of mechanical induction of osteoarthritis and osteochondritis dissecans.Presented in part at the 21st Congress of the Austrian Society of Orthopedic Surgery; May 5th–June 1st, 1991 in Linz/Austria     

Determination of the in situ loads on the human anterior cruciate ligament

A noncontact, kinematic method was used to determine the lengths and in situ loads borne by portions of the human anterior cruciate ligament (ACL) by the combination of kinematic data from the intact knee and load-length curves of the isolated ACL. Specimens from knees of cadavers of young people were tested in passive flexion and extension as well as with 100 N of anterior tibial drawer at 0, 30, 45, and 90° of flexion. The results showed that the in situ load on the whole ACL (as much as 129 N) can exceed the magnitude of the applied anterior tibial drawer. The load distribution within the ligament changes with flexion of the knee. The anterior and posterior portions share the anterior drawer force equally toward full extension. However, at flexion >45°, the anterior portion supports 90–95% of the load. This information is important for the determination of the function of the entire ACL and of its subportions in response to external loading of the intact knee. In particular, the preferential loading found for one of the portions of the ACL demonstrates that successful operative reconstruction of this ligament may not be achieved simply by reproduction of its gross anatomy; consideration of the role of the ligament in the overall kinematics of the knee is necessary.     

In vivo kinematics of a robot-assisted uni- and multi-compartmental knee arthroplasty

Background

There is great interest in providing reliable and durable treatments for one- and two-compartment arthritic degeneration of the cruciate-ligament intact knee. One approach is to resurface only the diseased compartments with discrete unicompartmental components, retaining the undamaged compartment(s). However, placing multiple small implants into the knee presents a greater surgical challenge than total knee arthroplasty, so it is not certain that the natural knee mechanics can be maintained or restored. The goal of this study was to determine whether near-normal knee kinematics can be obtained with a robot-assisted multi-compartmental knee arthroplasty.

Methods

Thirteen patients with 15 multi-compartmental knee arthroplasties using haptic robotic-assisted bone preparation were involved in this study. Nine subjects received a medial unicompartmental knee arthroplasty (UKA), three subjects received a medial UKA and patellofemoral (PF) arthroplasty, and three subjects received medial and lateral bi-unicondylar arthroplasty. Knee motions were recorded using video-fluoroscopy an average of 13 months (6–29 months) after surgery during stair and kneeling activities. The three-dimensional position and orientation of the implant components were determined using model-image registration techniques.

Results

Knee kinematics during maximum flexion kneeling showed femoral external rotation and posterior lateral condylar translation. All knees showed femoral external rotation and posterior condylar translation with flexion during the step activity. Knees with medial UKA and PF arthroplasty showed the most femoral external rotation and posterior translation, and knees with bicondylar UKA showed the least.

Conclusions

Knees with accurately placed uni- or bi-compartmental arthroplasty exhibited stable knee kinematics consistent with intact and functioning cruciate ligaments. The patterns of tibiofemoral motion were more similar to natural knees than commonly has been observed in knees with total knee arthroplasty. Larger series are required to confirm these as general observations, but the present results demonstrate the potential to restore or maintain closer-to-normal knee kinematics by retaining intact structures and compartments.     

ACL forces and knee kinematics produced by axial tibial compression during a passive flexion–extension cycle

Application of axial tibial force to the knee at a fixed flexion angle has been shown to generate ACL force. However, direct measurements of ACL force under an applied axial tibial force have not been reported during a passive flexion–extension cycle. We hypothesized that ACL forces and knee kinematics during knee extension would be significantly different than those during knee flexion, and that ACL removal would significantly increase all kinematic measurements. A 500 N axial tibial force was applied to intact knees during knee flexion–extension between 0° and 50°. Contact force on the sloping lateral tibial plateau produced a coupled internal + valgus rotation of the tibia, anterior tibial displacement, and elevated ACL forces. ACL forces during knee extension were significantly greater than those during knee flexion between 5° and 50°. During knee extension, ACL removal significantly increased anterior tibial displacement between 0° and 50°, valgus rotation between 5° and 50°, and internal tibial rotation between 5° and 15°. With the ACL removed, kinematic measurements during knee extension were significantly greater than those during knee flexion between 5° and 45°. The direction of knee flexion–extension movement is an important variable in determining ACL forces and knee kinematics produced by axial tibial force. © 2013 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 32:89–95, 2014.     

Effects of the tibial tunnel position on knee joint stability and meniscal contact pressure after double-bundle anterior cruciate ligament reconstruction

BackgroundTo investigate the effect of the tibial tunnel position on knee stability and the maximum contact area and peak contact pressure on the menisci after double-bundle anterior cruciate ligament (ACL) reconstruction.MethodsTen human knee specimens (mean age: 74.1 ± 15.8 years) were used in this study. The anterior tibial loading test was conducted using a material testing machine at 30°, 60°, and 90° of knee flexion, with the anterior tibial translation (ATT) and the maximum contact area and peak contact pressure on the menisci measured. Outcome measures were compared between the following groups: 1) intact ACL (intact group); 2) anatomical tibial tunnel position (anatomical group) and 3) posterior tibial tunnel position (posterior group) with double-bundle reconstruction, and 4) ACL-deficient (deficient group).ResultsIn response to a 100 N anterior tibial load, the ATT was greater for the posterior and ACL-deficient groups compared to that in the intact group. The normalized maximum contact area of the medial meniscus significantly decreased for the posterior group compared to that in the intact group. The normalized peak contact pressure on the medial meniscus increased in all groups compared to that in the intact group, but with no between-group differences in pressure applied to the lateral meniscus.ConclusionsATT and contact pressure on the medial meniscus increased, concomitant with a decrease in contact area of the medial meniscus, as the position of the tibial tunnel position moved towards a posterior position.     

Fracture of the medial femoral condyle after unicompartmental knee arthroplasty

Periprosthetic fracture is a relatively rare but well-recognized complication after knee joint arthroplasty. We experienced a case of medial femoral condylar fracture among 700 cases of unicompartmental knee arthroplasty (UKA). The patient was a 56-year-old woman who underwent minimally invasive UKA for medial osteoarthritis of the knee. A displaced medial femoral condylar fracture occurred 3 years after UKA. A closed reduction and percutaneous fixation using 3 cannulated cancellous screws was performed. Union of the fracture was achieved, and a full recovery of knee motion was gained after 3 months. The Knee Society knee and function scores were 87 and 80, respectively, at the 2-year follow-up. They were the same as the scores before the fracture took place, and there was no evidence of component loosening or ligament instability.     

Interaction between intrinsic knee mechanics and the knee extensor mechanism

The ability of the quadriceps muscles to extend the knee was studied relative to the intrinsic mechanical features of the knee joint. The quadriceps mechanical efficiency changed by nearly 50% between 0 and 90 degrees of knee flexion. The peak efficiency occurred at approximately 20 degrees of knee flexion. The mechanical efficiency of the quadriceps was dependent on the movement of the net anteroposterior (AP) tibiofemoral contact center of pressure, the change in patellar ligament angle, and the change in the quadriceps-to-ligament force transfer ratio. The average net AP tibiofemoral contact center of pressure moved posteriorly on the tibial plateau as the knee flexed from 0 to 90 degrees. The excision of both cruciate ligaments reversed the posteriorly directed movement of the net AP tibiofemoral contact center of pressure at flexion angles from 60 to 90 degrees, resulting in a reduction in extension moment.     

Interaction between the ACL graft and MCL in a combined ACL+MCL knee injury using a goat model

The optimal treatment for the MCL in the combined ACL and MCL-injured knee is still controversial. Therefore, we designed this study to examine the mechanical interaction between the ACL graft and the MCL in a goat model using a robotic/universal force-moment sensor testing system. The kinematics of intact, ACL-deficient, ACL-reconstructed, and ACL-reconstructed/ MCL-deficient knees, as well as the in situ forces in the ACL, ACL graft, and MCL were determined in response to two external loading conditions: 1) anterior tibial load of 67 N and 2) valgus moment of 5 N-m. With an anterior tibial load, anterior tibial translation in the ACL-deficient knee significantly increased from 2.0 and 2.2 mm to 15.7 and 18.1 mm at 30 degrees and 60 degrees of knee flexion, respectively. The in situ forces in the MCL also increased from 8 to 27 N at 60 degrees of knee flexion. ACL reconstruction reduced the anterior tibial translation to within 2 mm of the intact knee and significantly reduced the in situ force in the MCL to 17 N. However, in response to a valgus moment, the in situ forces in the ACL graft increased significantly by 34 N after transecting the MCL. These findings show that ACL deficiency can increase the in situ forces in the MCL while ACL reconstruction can reduce the in situ forces in the MCL in response to an anterior tibial load. On the other hand, the ACL graft is subjected to significantly higher in situ forces with MCL deficiency during an applied valgus moment. Therefore, the ACL-reconstructed knee with a combined ACL and MCL injury should be protected from high valgus moments during early healing to avoid excessive loading on the graft.     

In Vivo Motion of Femoral Condyles During Weight-Bearing Flexion After Anterior Cruciate Ligament Rupture Using Biplane Radiography

The purpose of this study was to investigate in vivo three- dimensional tibiofemoral kinematics and femoral condylar motion in knees with anterior cruciate ligament (ACL) deficiency during a knee bend activity. Ten patients with unilateral ACL rupture were enrolled. Both the injured and contralateral normal knees were imaged using biplane radiography at extension and at 15°, 30°, 60°, 90°, and 120° of flexion. Bilateral knees were next scanned by computed tomography, from which bilateral three-dimensional knee models were created. The in vivo tibiofemoral motion at each flexion position was reproduced through image registration using the knee models and biplane radiographs. A joint coordinate system containing the geometric center axis of the femur was used to measure the tibiofemoral motion. In ACL deficiency, the lateral femoral condyle was located significantly more posteriorly at extension and at 15° (p < 0.05), whereas the medial condylar position was changed only slightly. This constituted greater posterior translation and external rotation of the femur relative to the tibia at extension and at 15° (p < 0.05). Furthermore, ACL deficiency led to a significantly reduced extent of posterior movement of the lateral condyle during flexion from 15° to 60° (p < 0.05). Coupled with an insignificant change in the motion of the medial condyle, the femur moved less posteriorly with reduced extent of external rotation during flexion from 15° to 60° in ACL deficiency (p < 0.05). The medial- lateral and proximal-distal translations of the medial and lateral condyles and the femoral adduction-abduction rotation were insignificantly changed after ACL deficiency. The results demonstrated that ACL deficiency primarily changed the anterior-posterior motion of the lateral condyle, producing not only posterior subluxation at low flexion positions but also reduced extent of posterior movement during flexion from 15° to 60°.

Key Points

• Three-dimensional tibiofemoral kinematics and femoral condylar motion in ACL-deficient knees during upright weight-bearing flexion were measured using biplane radiography with the geometric center axis.
• ACL deficiency caused posterior subluxation of the lateral condyle with excess external femoral rotation at early flexion positions.
• On flexion from 15° to 60°, the lateral condyle moved slightly posteriorly in ACL deficiency leading to reduced extent of external femoral rotation.

Key words: anterior cruciate ligament, injury, kinematics, tibiofemoral, femoral condyle, radiography     

Interaction between the ACL graft and MCL in a combined ACL+MCL knee injury using a goat model

The optimal treatment for the MCL in the combined ACL and MCL-injured knee is still controversial. Therefore, we designed this study to examine the mechanical interaction between the ACL graft and the MCL in a goat model using a robotic/universal force-moment sensor testing system. The kinematics of intact, ACL-deficient, ACL-reconstructed, and ACL-reconstructed/MCL-deficient knees, as well as the in situ forces in the ACL, ACL graft, and MCL were determined in response to two external loading conditions: 1) anterior tibial load of 67 N and 2) valgus moment of 5 N-m. With an anterior tibial load, anterior tibial translation in the ACL-deficient knee significantly increased from 2.0 and 2.2 mm to 15.7 and 18.1 mm at 30° and 60° of knee flexion, respectively. The in situ forces in the MCL also increased from 8 to 27 N at 60° of knee flexion. ACL reconstruction reduced the anterior tibial translation to within 2 mm of the intact knee and significantly reduced the in situ force in the MCL to 17 N. However, in response to a valgus moment, the in situ forces in the ACL graft increased significantly by 34 N after transecting the MCL. These findings show that ACL deficiency can increase the in situ forces in the MCL while ACL reconstruction can reduce the in situ forces in the MCL in response to an anterior tibial load. On the other hand, the ACL graft is subjected to significantly higher in situ forces with MCL deficiency during an applied valgus moment. Therefore, the ACL-reconstructed knee with a combined ACL and MCL injury should be protected from high valgus moments during early healing to avoid excessive loading on the graft.