Aims. Mid-level constraint designs for total knee arthroplasty (TKA) are intended to reduce coronal plane laxity. Our aims were to compare kinematics and ligament forces of the Zimmer Biomet Persona posterior-stabilized (PS) and mid-level designs in the coronal, sagittal, and axial planes under loads simulating clinical exams of the knee in a cadaver model. Methods. We performed TKA on eight cadaveric knees and loaded them using a robotic manipulator. We tested both PS and mid-level designs under loads simulating clinical exams via applied varus and valgus moments, internal-external (IE) rotation moments, and anteroposterior forces at 0°, 30°, and 90° of flexion. We measured the resulting tibiofemoral angulations and translations. We also quantified the forces carried by the medial and lateral collateral ligaments (MCL/LCL) via serial sectioning of these structures and use of the principle of superposition. Results. Mid-level inserts reduced varus angulations compared to PS inserts by a median of 0.4°, 0.9°, and 1.5° at 0°, 30°, and 90° of flexion, respectively, and reduced valgus angulations by a median of 0.3°, 1.0°, and 1.2° (p ≤ 0.027 for all comparisons). Mid-level inserts reduced net IE rotations by a median of 5.6°, 14.7°, and 17.5° at 0°, 30°, and 90°, respectively (p = 0.012). Mid-level inserts reduced anterior tibial translation only at 90° of flexion by a median of 3.0 millimetres (p = 0.036). With an applied varus moment, the mid-level insert decreased LCL force compared to the PS insert at all three flexion angles that were tested (p ≤ 0.036). In contrast, with a valgus moment the mid-level insert did not reduce MCL force. With an applied internal rotation moment, the mid-level insert decreased LCL force at 30° and 90° by a median of 25.7 N and 31.7 N, respectively (p = 0.017 and p = 0.012). With an external rotation moment, the mid-level insert decreased MCL force at 30° and 90° by a median of 45.7 N and 20.0 N, respectively (p ≤ 0.017 for all comparisons). With an applied anterior load, MCL and LCL forces showed no differences between the two inserts at 30° and 90° of flexion. Conclusion. The mid-level insert used in this study decreased coronal and axial plane laxities compared to the PS insert, but its stabilizing benefit in the sagittal plane was limited. Both mid-level and PS inserts depended on the MCL to resist anterior loads during a simulated clinical exam of anterior laxity. Cite this article: Bone Jt Open 2023;4(6):432–441

Injuries to the posterior cruciate ligament (PCL) and the posterolateral corner (PLC) of the knee remain a challenging orthopaedic problem. Studies evaluating PCL and PLC reconstruction have failed to demonstrate a strong correlation between the degree of knee laxity as measured by uniplanar testing and subjective outcome or patient satisfaction. The effect that changing the magnitude of posterior tibial slope has on multiplanar, rotational stability of the PCL-deficient knee has yet to be determined. We aimed to evaluate the effect that changes in posterior tibial slope would have on static and dynamic stability of the PCL-PLC deficient knee. Ten knees were used for this study. Navigated posterior drawer and standardised reverse mechanised pivot shift maneuvers were performed in the intact knee and after sectioning the PCL, the lateral collateral ligament (LCL), the popliteofibular ligament (PFL) and the popliteus muscle tendon (POP). Navigated high tibial osteotomy (HTO) was performed to obtain the desired change in tibial plateau slope (+5® or −5® from native slope). We then repeated the posterior drawer and the reverse mechanised pivot shift test for each of the two altered slope conditions. Mean posterior tibial translation during the posterior drawer in the intact knee was 1.4 mm (SD = 0.48 mm). In the PCL-PLC deficient knee, posterior tibial translation increased to 18 mm (SD = 5.7 mm) (P < 0.001). Increasing the amount of posterior tibial slope by 5® reduced posterior tibial translation to 12 mm (SD = 4.7 mm) (P < 0.01). Decreasing the amount of posterior slope by 5® compared to the native knee, increased posterior tibial translation to 21 mm (SD = 6.8 mm) (P < 0.01). There was a significant negative correlation between the magnitude of tibial plateau slope and the magnitude of the reverse pivot shift (R2 = 0.71; P < 0.0001). Mean posterior tibial translation during the reverse mechanised pivot shift test in the intact knee was 7.8 mm (SD = 2.8 mm). In the PCL-PLC deficient knee, posterior tibial translation increased to 26 mm (SD = 5.6 mm) (P < 0.001). Increasing the amount of posterior tibial slope by 5® reduced posterior tibial translation to 21 mm (SD = 6.7 mm) (P < 0.01). Decreasing the amount of posterior slope by 5® compared to the native knee, increased posterior tibial translation to 34 mm (SD = 8.2 mm) (P < 0.01). There was a significant negative correlation between the magnitude of tibial plateau slope and the magnitude of the reverse pivot shift (R2 = 0.72; P < 0.0001). Decreasing the magnitude of posterior slope of the tibial plateau resulted in an increase in the magnitude of posterior tibial translation during the posterior drawer and the reverse mechanised pivot shift test in the PCL-PLC deficient knee. Conversely, increasing the slope of the tibial plateau reduced the amount of posterior tibial translation during the posterior drawer and the reverse mechanised pivot shift test. However, the effect of the increase in slope was not sufficient to reduce posterior tibial translation to levels similar to those of the intact knee

Introduction. Anterior tibial translation (ATT) is assessed in the acutely injured knee to investigate for ligamentous injury and rotational laxity. Specifically, there is a growing recognition of the significance of anterior medial rotary laxity (AMRI) as a crucial element in assessing knee stability. Anterior cruciate ligament (ACL) injuries are often accompanied with medial collateral ligament (MCL) damage. It has been suggested that Deep MCL (dMCL) fibres are a primary restraint in rotational displacement. This research aims to quantify the difference in rotational laxity of patients with ACL and MCL injuries to deem if the Feagin-Thomas test can robustly capture metrics of AMRI. 2. Methods. AMRI was assessed using the Feagin-Thomas test in 7 isolated ACL (iACL) injured participants, 3 combined ACL and superficial fibre MCL (sMCL) injuries, 5 combined ACL and deep fibre MCL injuries, and 21 healthy controls. Displacement values were recorded using an optical motion capture (OMC) system and bespoke processing pipeline which map and model the knee's anterior displacement values relative to the medial compartment. Since absolute values (mm) of rotational laxity vary dependant on the person, values were recorded as a proportion of the rotational laxity obtained from the subject's contralateral leg. Values were compared between each patient group using an ANOVA test and Tukey's honesty significant difference post hoc test. 3. Results. The healthy control group had a median proportion of 0.97 (3SF), whilst the iACL was 1.12 (3SF), a 12% increase in rotational laxity in the injured leg. The sMCL group yielded a result of 1.64 (3SF), a 64% increase in rotational laxity in the injured leg; finally, dMCL resulted in a proportion of rotational laxity of 1.90 (3SF), a 90% increase in rotational laxity [table 1]. Whilst all groups showed differences in the increase of rotational laxity, dMCL was significantly different from the healthy control group (P value 0.0041). 4. Conclusion. ACL injuries with MCL involvement led to an increase in anterior medial rotary laxity and this is more evident in patients where deep MCL fibres are involved. The Feagin-Thomas test appears to be sensitive in detecting differences in AMRI and should be considered when performing comprehensive clinical knee examination. For any figures or tables, please contact authors directly

Purpose: Previous research has reported that increasing the posterior tibial slope through an opening wedge osteotomy results in an anterior shift in the position of the tibia relative to the femur. However, the effect of this on anterior cruciate ligament (ACL) strain remains insufficiently understood. The purpose of this study was to examine the relationship between tibial slope and tibial translation, as well as between tibial slope and ACL strain. It was hypothesized that increasing the posterior tibial slope would result in an increase in anterior tibial translation thereby increasing strain in the ACL. Methods: Five cadaveric knees were subjected to a randomized experimental design study. One knee was excluded due to failure of a strain gauge during experimentation, resulting in data for four knees. The femoral and tibial portions of the knee were potted with PMMA and fixed using fixation pins. An anterior-based osteotomy was performed with no osteotomy plate present. A strain gauge was then placed in the anteromedial bundle of the ACL. Each knee was mounted at a flexion angle of 15° and loaded with various combinations of A-P loads (18N, 108N, 209N) and axial loads (216N, 418N), according to the study design. Osteotomies of 5mm and 10mm were then performed and measurements of strain and tibial translation were taken after each according to the study design. Tibial slopes were determined through lateral fluoroscopic imaging. Results: As posterior tibial slope increased, anterior tibial translation increased as anticipated. However, contrary to expectations, as posterior slope increased, ACL strain decreased. One explanation for this result could be that by performing the osteotomy, the insertions sites of the ACL were being moved closer together resulting in increased ACL laxity. At higher slope angles, translation levels off, suggesting constraint of some tissue besides the ACL. Conclusions: Although increasing the tibial slope through opening wedge osteotomy leads to an anterior tibial translation, there is no increase in strain on the ACL. Further studies are needed to examine the effect of opening wedge osteotomy on other soft tissue restraints of the knee

Variations in the pivot shift test have been proposed by many authors, though, a test comprised of rotatory and valgus tibial forces with accompanied knee range of motion is frequently utilised. Differences in applied forces between practitioners and patient guarding have been observed as potentially decreasing the reproducibility and reliability of the pivot shift test. We hypothesise that a low-profile pivot shift test (LPPST) consisting of practitioner induced internal rotatory and anterior directed tibial forces with accompanied knee range of motion can elicit significant differences in internal tibial rotation and anterior tibial translation between the anterior cruciate ligament (ACL) deficient and ACL sufficient knee. Fresh, frozen cadaver knees were used for this study. Four practitioners performed the LPPST on each ACL sufficient knee. The ACL of each knee was subsequently resected and each practitioner performed the LPPST on each ACL deficient knee. Our quantitative assessment utilised computer assisted navigation to sample (10Hz) the anterior translation and internal rotation of the tibia as the LPPST force vectors were applied. We subsequently pooled and averaged data from all four practitioners and analysed the entrance pivot (tibial reduction with knee range of motion from extension into flexion) and the exit pivot (tibial subluxation with knee range of motion from flexion into extension). We observed a significant difference in anterior tibial translation and internal tibial rotation in the ACL deficient vs. ACL sufficient knees during both the entrance and exit pivot phases of the LPPST. The entrance pivot (n=140) was found to have an average maximum anterior tibial translation of 7.83 mm in the ACL deficient knee specimens compared to 1.23 mm in the ACL sufficient knee specimens (p<0.01). We found the ACL deficient knees to exhibit an average maximum internal tibial rotation of 12.38 degrees compared to 11.24 degrees in the ACL sufficient specimens during the entrance pivot (p=0.04). The exit pivot (n=120) was found to have an average maximum anterior tibial translation of 7.82 mm in the ACL deficient knee specimens compared to 1.44 mm in the ACL sufficient knee specimens (p<0.01). The ACL deficient knees exhibited an average maximum internal tibial rotation of 12.44 degrees compared to 11.13 degrees in the ACL sufficient knee specimens during the exit pivot (p=0.02). Our results introduce a physical exam maneuver (LPPST) consisting of practitioner induced internal rotatory and anterior directed forces, with notable absence of valgus force, on the tibia while applying knee range of motion. Our results demonstrate that the LPPST can elicit significant anterior translation and internal rotary differences in an effort to differentiate between the ACL deficient and ACL sufficient knee. Our work will next seek to explore the clinical reproducibility of this physical exam maneuver

Introduction. Total knee arthroplasty (TKA) is the definitive treatment for osteoarthritis of the knee. The primary goal of the operation is to minimize or eliminate pain associated with osteoarthritis and secondarily to regain functional mobility and stability around the knee joint in order improve overall quality of life. The vast majority of techniques utilized for this procedure involves removal of the anterior cruciate ligament (ACL). In a native knee the ACL is a primary stabilizing ligament and essential for providing proprioceptive feedback. In the absence of the ACL, the kinematics of the knee are compromised. In an effort to more accurately replicate normal knee stability, new implant designs have emerged which maintain an intact ACL. Described herein is a cadaveric study looking at ACL competency after implantation of a TKA in which the cruciate ligaments are preserved. Methods. Twenty fresh, frozen cadaveric knees were utilized in which the ACL was intact. Specimens were excluded if there was concern for ACL stability as determined by physical examination, direct visualization during the arthrotomy and a KT-1000 measurement of anterior tibial translation in millimeters at 67N and 89N of anterior force. Each KT-1000 measurement was repeated three times using three individual examiners at both force values for a total of six data points. Bicruciate retaining components were implanted into each knee using a medial parapatellar approach. After adequate sagittal and coronal balancing was obtained, the knee was reexamined using the KT-1000 protocol described above to assess for any changes in ACL competency. The ACL was then transected and the knee was examined for a third time with the same KT-1000 protocol. For statistical analysis, a 2-way repeated-measures ANOVA was utilized. Pairwise differences were assessed utilizing Fisher's least significant difference method. Results. The KT-1000 measurement in millimeters of anterior tibial translation in relation to the femur provided the primary data points. The anterior translation of the tibia of the cadaveric knees before insertion of the components averaged 2.2mm at 67N of force and 3.6mm at 89N of force. After insertion of the components, the anterior tibial translation averaged 3.6mm at 67N of force and 5.0mm at 89N of force. After the ACL was transected, the averaged KT-1000 measurements were 6.8mm at 67N and 9.2mm at 89N of force. Discussion and Conclusion. Significant debate remains regarding which knee implant provides the optimum outcome in patients undergoing total knee arthroplasty. As the indications for TKA continue to expand and younger more active patients, with higher post-operative performance expectations pursue surgical intervention for degenerative knee osteoarthritis, bicruciate-retaining designs have re-emerged as potential alternative to traditional implants. While this study does demonstrate an increase in anterior translation after implantation of the components, the amount of increased laxity is unlikely to be of clinical significance. Overall ACL integrity is maintained and joint stability preserved

Balancing the PCL in a PCL-retaining total knee replacement (TKR) is important, but sometimes difficult to execute in an optimal manner. Due to the orientation of the PCL it is conceivable that flexion gap distraction will lead to anterior movement of the tibia relative to the femur. This tibio-femoral repositioning influences the tibio-femoral contact point, which on its turn affects the kinematics of the TKR. So far, the amount of tibiofemoral repositioning during flexion gap distraction is unknown which leads to uncertain kinematic effects after surgery. The goal of this study was to quantitatively describe the parameters of the flexion gap (gap height, anterior tibial translation and femoral rotation) and their relationship while the knee is distracted during implantation of a PCL-retaining TKR with the use of computer navigation. Furthermore, the effect of PCL elevation angle on the flexion gap parameters was determined. In 50 knees, during a ligament-guided TKR procedure, the flexion gap was distracted with a double-spring tensor with 100 and 200 N after the tibia had been cut. The flexion gap height, anterior tibial translation and femoral rotation were measured intra-operatively using a CT-free navigation system. PCL elevation was calculated based on the femoral and tibial insertion sites as indicated by the surgeon with the pointer of the navigation system. To identify a relationship between flexion gap height increase and anterior tibial translation, the ratio between anterior translation and gap height increase was determined for each patient between 100 and 200 N. The mean gap height increased 2.2 mm (SD 0.96) and mean increase in anterior tibial translation was 4.2 mm (SD 1.6). Hence, on average, for each mm increase in gap height, the tibia moved 1.9 mm (SD 0.96) in anterior direction. Knees with a steep PCL showed significantly more AP translation for each mm gap height increase (gap/AP-ratio was 1 : 2.31 (SD 0.63)) compared to knees with a flat PCL (gap/AP-ratio was 1 : 1.73 (SD 0.50)). The increase in femur (exo)rotation was on average 0.60° (SD 1.4). With a tensioned PCL the tibia will move anteriorly on average 1.9 mm for every extra mm that the flexion gap is increased. The flexion gap dynamics can be explained in part by the orientation of the PCL: the greater the elevation angle, the more anterior tibial displacement during distraction of the flexion gap. The surgeon must be aware that distraction of the flexion gap influences the tibiofemoral contact point. The tibio-femoral contact point will move posteriorly and stresses in the PCL will rise and produce limited flexion and pain. In case of a conforming insert AP-movement will be limited but high PE stresses may be introduced that can lead to wear. This information may be helpful in selecting the optimal soft tissue balancing procedure and the optimal PE insert thickness in PCL retaining TKR

Background and purpose of the study: the anterior cruciate ligament (ACL) is a continuum of fibres which are differently recruited through range of motion. Two main functional bundles can be identified: the postero-lateral bundle (PLB) which is taut exclusively towards extension and the anteromedial bundle (AMB) which is taut through full range of motion. The purpose of this investigation was to assess the relative contribution of the bundles to intact knee kinematics. Material and methods: fourteen intact cadaver knees were instrumented in a non-ferromagnetic rig and six degrees of freedom kinematics through flexion-extension was recorded with an electromagnetic device under the application of a 90N anterior force or a 5Nm internal rotation torque. The AMB and PLB were alternatively cut first in each knee and knee kinematics was recorded. The other bundle was then dissected and ACL deficient knee kinematics tested. Results: when the AMB was cut anterior tibial translation increased and no effects on rotations were recorded. When the PLB was first cut no significant effects on anterior laxity were observed. Different rotational responses were observed in different knees. After the section of both bundles a larger increase in anterior laxity was observed. The changes in rotation differed from knee to knee. Discussion: The AMB is a primary restraint against anterior tibial translation and has a small and variable effect on rotations. The PLB is a secondary restraint against anterior tibial translation in extension and maintains normal rotational laxity in AMB deficient knees. Therefore, reconstruction of both bundles is theoretically advantageous to restore both intact knee anteroposte-rior and rotational laxity

We report on a minimum 5-year follow-up (mean 7 years) of 28 patients who underwent arthroscopically assisted ACL reconstruction using a patellar tendon graft. Knee function was assessed using Lysholm and Tegner scores and AP translation of the tibia was measured using a Stryker Laxity Tester, comparing the symptomatic with the normal knee. All measurements were made preoperatively and at the latest follow-up. In addition, all patients had standardised weight-bearing radiographs of the knee to assess joint space narrowing using the IKDC radiographic grading. The mean preoperative Lysholm score of 71 (range 46–95) improved to 88 (range 57–100) at follow-up. The mean Tegner Activity score increased from 4.1 (range 1–6) to 7.2 (range 5–10). Preoperatively 17 patients had increased tibial translation of more than 5mm, 9 had 3–5mm and 2 had less than 3mm. At follow-up, 22 knees had less than 3mm tibial translation and 6 had 3–5mm. No patients had more than 5mm of tibial translation compared to the opposite knee. The IKDC radiographic grading of joint space narrowing revealed 14 patients with no narrowing, 11 with a joint space of more than 4mm and knees with a joint space of 2–4mm. Joint space narrowing was seen in patients who had partial or total meniscectomy before or at the time of ACL reconstruction. These results indicate that the satisfactory outcome of ACL reconstruction using contemporary methods is maintained beyond 5 years. However, the 50% incidence of joint space narrowing associated with previous meniscectomy is a cause for concern

Anterior cruciate ligament (ACL) injuries are frequent among athletes and a leading cause of time away from competition. Stability of the knee involves the ACL for limiting anterior tibial translation and the ALL (anterolateral ligament) to restrain internal rotation of the tibia. Present indications for treatment with a combined ACL-ALL reconstruction remain unclear and mostly subjective. We mathematically modeled the tibial plateau geometry to try and identify patients at risk of ACL injury, and develop an objective trigger point for the decision to proceed with additional surgery to optimize rotational stability in these higher risk patients. We hypothesized that an increased convexity and steepness of the posterior aspect of the lateral plateau would subject knees to higher rotational torques leading to potentially a higher risk of ACL injury. The study design was a case-control study involving ACL reconstruction cases (n=68) and matched controls (n=68) between 2008–2015 at our institution. We used a two-dimensional approach, evaluating sagittal MRI images of the knee to model the posterior convexity of the lateral tibial plateau. Points were selected along the articular surface, and a least-squares regression was used to curve-fit a power function (y = a xn). In the equation, larger coefficient a and n represented steeper slopes. The cases and controls were compared using a Mann-Whitney-U test, and the statistical significance was set at α < 0.05. A subgroup analysis for females and males was also performed for the curve-fit coefficients. We observed a significant difference in the tibial surface geometry between our ACL reconstruction cases and matched controls (Figure 1). The modeled power equation for our ACL cases had larger coefficients compared to controls for all groups. For all pooled subjects, coefficient a (ACL recon cases = 0.90 vs controls = 0.68, p < 0.0001) and coefficient n (ACL recon cases = 0.34 vs controls = 0.30, p = 0.07) (Table 1). For the statistically significant coefficient a, we found it had a sensitivity of 78.9% and specificity of 77.5% for the statistically significant coefficient a, we found it had a sensitivity of 78.9% and specificity of 77.5% for predicting injury, using a cut off coefficient of a = 0.78. The odds ratio was 12.6 [5.5 – 29]. The posterolateral cartilaginous slope of the tibial plateau was mathematically modeled in patients with ACL injury. Patients with ACL injury demonstrated abnormally steep and fast slopes compared to controls that may play predispose to ACL injury by increasing anterior translation forces and internal rotation torques sustained by their knee joint. A steeper slope may also explain high-grade pivot shifts on physical exam that are thought to be a relative indication for adding an associated ALL reconstruction. Our findings are promising for adding more objectivity to surgical decision-making, especially with identifying high-risk patients that may be candidates for combined ACL-ALL reconstructions. For any figures or tables, please contact the authors directly

Conventional computer navigation systems using bone fixation have been validated in measuring anteroposterior (AP) translation of the tibia. Recent developments in non-invasive skin-mounted systems may allow quantification of AP laxity in the out-patient setting. We tested cadaveric lower limbs (n=12) with a commercial image free navigation system using passive trackers secured by bone screws. We then tested a non-invasive fabric-strap system. The lower limb was secured at 10° intervals from 0° to 60° knee flexion and 100N of force applied perpendicular to the tibial tuberosity using a secured dynamometer. Repeatability coefficient was calculated both to reflect precision within each system, and demonstrate agreement between the two systems at each flexion interval. An acceptable repeatability coefficient of ≤3 mm was set based on diagnostic criteria for ACL insufficiency when using other mechanical devices to measure AP tibial translation. Precision within the individual invasive and non-invasive systems measuring AP translation of the tibia was acceptable throughout the range of flexion tested (repeatability coefficient ≤1.6 mm). Agreement between the two systems was acceptable when measuring AP laxity between full extension and 40° knee flexion (repeatability coefficient ≤2.1 mm). Beyond 40° of flexion, agreement between the systems was unacceptable (repeatability coefficient >3 mm). These results indicate that from full knee extension to 40° flexion, non-invasive navigation-based quantification of AP tibial translation is as accurate as the standard invasive system, particularly in the clinically and functionally important range of 20° to 30° knee flexion. This could be useful in diagnosis and post-operative follow-up of ACL pathology

Conventional computer navigation systems using bone fixation have been validated in measuring anteroposterior (AP) translation of the tibia. Recent developments in non-invasive skin-mounted systems may allow quantification of AP laxity in the out-patient setting. We tested cadaveric lower limbs (n=12) with a commercial image free navigation system using passive trackers secured by bone screws. We then tested a non-invasive fabric-strap system. The lower limb was secured at 10° intervals from 0° to 60° knee flexion and 100N of force applied perpendicular to the tibial tuberosity using a secured dynamometer. Repeatability coefficient was calculated both to reflect precision within each system, and demonstrate agreement between the two systems at each flexion interval. An acceptable repeatability coefficient of ≤3mm was set based on diagnostic criteria for ACL insufficiency when using other mechanical devices to measure AP tibial translation. Precision within the individual invasive and non-invasive systems measuring AP translation of the tibia was acceptable throughout the range of flexion tested (repeatability coefficient ≤1.6mm). Agreement between the two systems was acceptable when measuring AP laxity between full extension and 40° knee flexion (repeatability coefficient ≤2.1mm). Beyond 40° of flexion, agreement between the systems was unacceptable (repeatability coefficient >3mm). These results indicate that from full knee extension to 40° flexion, non-invasive navigation-based quantification of AP tibial translation is as accurate as the standard invasive system, particularly in the clinically and functionally important range of 20° to 30° knee flexion. This could be useful in diagnosis and post-operative follow-up of ACL pathology

Conventional computer navigation systems using bone fixation have been validated in measuring anteroposterior (AP) translation of the tibia. Recent developments in non-invasive skin-mounted systems may allow quantification of AP laxity in the out-patient setting. We tested cadaveric lower limbs (n=12) with a commercial image free navigation system using passive trackers secured by bone screws. We then tested a non-invasive fabric-strap system. The lower limb was secured at 10° intervals from 0° to 60° knee flexion and 100N of force applied perpendicular to the tibial tuberosity using a secured dynamometer. Repeatability coefficient was calculated both to reflect precision within each system, and demonstrate agreement between the two systems at each flexion interval. An acceptable repeatability coefficient of ≤3mm was set based on diagnostic criteria for ACL insufficiency when using other mechanical devices to measure AP tibial translation. Precision within the individual invasive and non-invasive systems measuring AP translation of the tibia was acceptable throughout the range of flexion tested (repeatability coefficient ≤1.6 mm). Agreement between the two systems was acceptable when measuring AP laxity between full extension and 40° knee flexion (repeatability coefficient ≤2.1 mm). Beyond 40° of flexion, agreement between the systems was unacceptable (repeatability coefficient >3 mm). These results indicate that from full knee extension to 40° flexion, non-invasive navigation-based quantification of AP tibial translation is as accurate as the standard invasive system, particularly in the clinically and functionally important range of 20° to 30° knee flexion. This could be useful in diagnosis and post-operative follow-up of ACL pathology

Given their role in reducing anterior tibial translation, the recruitment patterns and viscoelastic properties of the hamstring muscles have been implicated as neuromuscular factors contributing to the ACL gender bias. Nevertheless, it is uncertain whether patterns of aberration displayed by the female neuromuscular system significantly alters the antagonist moments generated by the hamstrings during maximal effort knee extension. The purpose of the current study was to examine the effect of gender on hamstring antagonist moments in order to explain the higher ACL injury rates in females. Eleven females (age 30.6 ± 10.1 years, mass 62.1± 6.9 kg, height 165.9 ± 4.6) and 11 males (age 29.0 ± 8.2 years, mass 78.6± 14.4 kg, height 178.5± 6.2) were recruited as subjects. Surface electrodes were placed over the semitendinosus (ST) and biceps femoris (BF) muscles of the dominant and non-dominant limbs. Each subject performed two sets of five maximal extension and flexion repetitions at 180-1. EMG, isokinetic torque and knee displacement data were sampled at 1000Hz using an AMLAB data acquisition system. Average hamstring antagonist torque data across the range of knee flexion for female subjects was significantly higher (%Diff=24%) than for the male control subject. Statistical analyses revealed a significant main effect of gender (F = 4.802; p = 0.036). Given that females possess a more compliant ACL and hamstring musculature, compared with their male counterparts, an augmented hamstring antagonist may represent a compensatory neuromuscular strategy to increase knee stiffness to control tibial translation and ACL strain. The results of this project suggest that it is unlikely that gender-related differences in hamstring antagonist torque is one of the predisposing factors contributing to the higher ACL injury rates in females

Background: Studies have shown that normal tibio-femoral rotational kinematics is not regained following single-bundle ACL reconstruction and that 14–30% of patients may have a residual “pivot glide”. It has been suggested that 2-bundle reconstruction could better control this laxity, but this not been demonstrated conclusively in-vivo. This study tested the hypothesis that 2-bundle ACL reconstruction improves the control of the Pivot Shift. Methods: We measured the mean maximum tibial translation and coupled rotation occurring during the pivot shift (using a previously validated surgical navigation based methodology) in 35 consecutive patients undergoing hamstrings ACL reconstruction. 17 patients had a standard single-bundle reconstruction and 18 patients a 4-tunnel, 2-bundle reconstruction. 10 pivot shift tests were performed pre- and post operatively by a single operator and the differences compared. Results: The two groups were equally age and sex matched. There was no difference in pre-operative pivot shift measurements. 2-bundle reconstruction decreased the tibial rotation occurring with the pivot shift test more than single-bundle reconstruction (Table 1). There was no detectable difference in the control of tibial translation. Conclusions: This study quantifies, in-vivo, the differences between single and 2-bundle ACL reconstruction in controlling pivot shift. It suggests that anatomic, 2-bundle ACL reconstructions could reduce pivot instability more effectively than a single-bundle. Whether the 10% additional control of the rotational component of the pivot improves functional stability or is necessary every patient and, in the longer term, limits the development of gonarthrosis secondary to abnormal motions, remains to be seen

The purpose was to assess the effect of the posterior slope on the long-term outcome of unicompartmental arthroplasty in knees with intact and deficient anterior cruciate ligaments. We retrospectively reviewed ninety-nine unicompartmental arthroplasties after a mean duration of follow-up of sixteen years (12 to 20 years). At the time of the arthroplasty, the anterior cruciate ligament was considered to be normal in fifty knees, damaged in thirty-one, and absent in eighteen. At the most recent follow-up, we measured the posterior tibial slope and the anterior tibial translation on standing lateral radiographs. In the group of seventy-seven knees that had not been revised by the time of the most recent follow-up, there was a significant linear relationship between anterior tibial translation (mean, 3.7 mm) and posterior tibial slope (mean, 4.3) (p = 0.01). The mean posterior slope of the tibial implant was significantly less in the group of seventy-seven knees without loosening of the implant than it was in the group of seventeen knees with loosening of the implant (p = 0.03). Five ruptures of the anterior cruciate ligament occurred in knees in which the ligament had been considered to be normal at the time of implantation; the posterior tibial slope in these five knees was greater than 13 degrees. Clinical evaluation revealed normal or nearly normal anteroposterior stability at the time of the most recent follow-up in all sixty-six unrevised knees in which the anterior cruciate ligament had been present at the time of implantation. Of the eighteen knees in which the anterior cruciate ligament had been absent at the time of the arthroplasty, eleven still had the implant in situ at the time of the most recent follow-up; the mean posterior tibial slope in these 11 knees was less than 5 degrees. Seven knees in which the anterior cruciate ligament had been absent at the time of the arthroplasty were revised. In these 7 knees, the tibial prosthesis was implanted with a posterior slope greater than 8 degrees. These findings suggest that more than 7 degrees of posterior slope of the tibial implant should be avoided, particularly if the anterior cruciate ligament is absent at the time of implantation. An intact anterior cruciate ligament, even when partly degenerated, was associated with the maintenance of normal anteroposterior stability of the knee for an average of sixteen years following unicompartmental knee arthroplasty

Many patients who undergo a total knee arthroplasty (TKA) wish to return to a more active lifestyle. The implant must be able to restore adequate muscle strength and function. However, this may not be a reality for some patients as quadriceps and hamstrings muscle activity may remain impaired following surgery. The purpose of this study was to compare muscle activity between patients implanted with a medial pivot (MP) or posterior stabilized (PS) implant and controls (CTRL) during ramp walking tasks. Fifteen patients were assigned to either a MP (n=9) or PS (n=6) TKA operated by the same surgeon. Nine months following surgery, the 15 patients along with nine CTRL patients completed motion and EMG analysis during level, ramp ascent & descent walking tasks. Wireless EMG electrodes were placed on six muscles: vastus medialis (VM), vastus lateralis (VL), biceps femoris (BF), semimembranosus (SM) muscles, gastrocnemius medial head (GM), and gastrocnemius lateral head (GL). Participants completed three trials of each condition. EMG data were processed for an entire gait cycle of the operated limb in the TKA groups, and for the dominant limb in the CTRL group. The maximum muscle activity achieved with each muscle during the level trial was used to normalize the ramp trials. The onset and offset of each muscle was determined using the approximated generalized likelihood ratio. Peak muscle activity (PeakLE), total muscle activity (iEMG), and muscle onsets/offsets were determined for each muscle for the ramp ascent and descent trials. Non-parametric Kruskal Wallace tests were used to test for statistical significance between groups with α=0.05. During the ramp up task, both MP and PS groups had significantly greater PeakLE and iEMG for the hamstring muscles compared to the CTRL, whereas the PS group had significantly greater PeakLE compared with the MP group for the SM muscle. During the ramp down task, both MP and PS groups had significantly greater PeakLE and iEMG for the SM and GL muscles compared to the CTRL. The PS group also had significantly greater iEMG for the BF and VM muscles compared to the CTRL. The MP group had a significantly earlier offset for the SM muscle compared to the CTRL. Stability in a cruciate removing TKA is partially controlled by the prosthetic design. During the ramp up task, the TKA groups compensated the tibial anterior translation by activating their hamstrings more and for a longer duration. The MP group required less hamstrings activation than the PS group. During the ramp down task, TKA patients stiffened their knee in order to stabilize the joint. The quadriceps, hamstrings and GL muscle were activated more and for a longer duration than the CTRL group to protect the tibial posterior translation. The PS group required greater BF and VM iEMG than the MP group. Even if surgery reduced pain, differences in muscle activity exist between TKA patients and healthy controls. The prosthetic design provides some stability to the knee, and the MP implant required less muscle activation than the PS implant to stabilize the knee joint

Tibial rotation and translation provide important stability parameters after ACL reconstruction. An accurate tool for a combined pre- intra- and postoperative stability measurement is not in clinical use so far. Navigation of the drill canals for the ACL placement and evaluation of possible impingement problems has been introduced for some years already, while measurement of the tibial translation and rotation is only available for a short time and only available for a few navigation modules. Navigation provides an accuracy of 1mm/1°, therefore navigated measurement of tibial rotation and translation were evaluated in this study with a new developed mechanical device and directly compared to conventional measurement techniques. Accuracy of navigation was compared with the KT1000 for the anterior-posterior (AP) translation and to a new developed goniometer tool concerning the rotational range of motion. Comparative tests included plastic whole leg models and specimens. Tests were repeated with intact and dissected ACL′s. A conventional navigation system (Vector Vision, Brainlab, Germany) was used in all cases. This included software developed for fluoroscopy based navigated ACL reconstruction. The following knee kinematics were detectable with the navigation system: Flexion/Extension degrees of the knee joint (°); AP translation of the tibia in relation to the femur (mm); Axial tibial rotation relative to the femur (°). Validation of Navigation: first neutral tibial rotation was defined and marked in the knee joint in neutral position. All rotational measurements were done with a new developed goniometer tool and compared to the navigated technique. Then the knee was rotated externally until 45° (maximum) and internally 45° (maximum), by single 2.5° steps. These measurements were repeated in 0°, 30°, 60° and 80° knee flexion. All tests were repeated three times and performed by 3 different observers. A total of 1296 measurements were done. Measurements of the tibial translation were compared with the KT 1000 for the specimen testing. Results revealed: accurate navigated measurement of tibial rotation in plastic and specimen models; variation of absolute AP translation values between KT1000 and navigation; variation of the AP translation corresponding to the ACL condition; increased range of total tibial rotation after dissecting the ACL compared to the intact ligament. Restoration of the rotational stability and limiting of the AP translation is necessary to provide normal knee kinematics after ACL reconstructions. Intraoperative measurements of these stability parameters are demanding and so far not established with navigation systems or conventionally. As our results show, navigation offers an accurate technique for measurement of the AP translation and rotation of the knee with intact and dissected ACL’s under laboratory conditions. General use in the evaluation of a successful ACL reconstruction becomes possible intraoperative and might be reproducible for further measurements. Clinical studies are needed to improve our results

The purpose of this study was initially to examine the effect of tibial slope on anterior tibial translation in the ACL deficient knee measured objectively using the KT 1000 arthrometer. Patients were then evaluated one year post ACL reconstruction to determine the effect of tibial slope on the outcome of ACL reconstruction. One-hundred patients (male = 70, female 30) aged between 14 and 49 years (Mean = 28.70, SD 8.80) with a diagnosis of isolated anterior cruciate ligament rupture were prospectively recruited. All participants had intact ACLs of the contralateral limb. The following information was recorded for all patients preoperatively and one year post surgery; time from injury to surgery, IKDC objective and subjective assessment and KT 1000 arthrometer readings. Tibial slope was assessed from long tibial lateral x-rays as described by Dejour and Bonnin. Finally, assessment of the menisci occurred intra-operatively. Tibial slope was correlated with KT 1000, meniscal integrity and IKDC assessments. Patients underwent an arthroscopic hamstring ACL reconstruction using Endobutton and Intrafix fixation. All procedures were performed by one surgeon. Pre Reconstruction – Bivariate correlations showed a significant correlation between tibial slope and KT 1000 (r= .29, p < .001). This relation was strengthened when the integrity of the menisci were controlled for (r = .32, p < . 001). When time to surgery was controlled for, correlations between tibial slope and KT 1000 were unaffected. There was also a negative correlation between medial meniscal integrity and time to surgery (r = −.41, p < . 001). No relationships between time to surgery and KT 1000 were evident. Post Reconstruction – Eighty patients were evaluated at a one year post surgery. One patient had a rerupture. The mean KT 1000 difference was 1mm. KT 1000 was > 2mm in 9% and > 5mm in the re rupture only. The mean subjective IKDC score was 89. Using objective IKDC 89% were classified as normal, 10% as nearly normal and 1% as severely abnormal (the rerupture). Bivariate correlations showed no significant correlation between tibial slope and post operative KT 1000 (r= .178, p = .0.115). This study demonstrates a significant relationship between increasing tibial slope and anterior tibial translation of the ACL deficient knee. The relationship did not exist in the post ACL reconstructed knee. However this needs to be investigated further with greater numbers and in the ACL revision group

Aims

A functional anterior cruciate ligament (ACL) or posterior cruciate ligament (PCL) has been assumed to be required for patients undergoing unicompartmental knee arthroplasty (UKA). However, this assumption has not been thoroughly tested. Therefore, this study aimed to assess the biomechanical effects exerted by cruciate ligament-deficient knees with medial UKAs regarding different posterior tibial slopes.