Internal Rotation Measurement of the Knee with Polymer-Based Capacitive Strain Gauges versus Mechanical Rotation Measurement Taking Gender Differences into Account: A Comparative Analysis.

With the conventional mechanical rotation measurement of joints, only static measurements are possible with the patient at rest. In the future, it would be interesting to carry out dynamic rotation measurements, for example, when walking or participating in sports. Therefore, a measurement method with an elastic polymer-based capacitive measuring system was developed and validated. In our system, the measurement setup was comprised of a capacitive strain gauge made from a polymer, which was connected to a flexible printed circuit board. The electronics integrated into the printed circuit board allowed data acquisition and transmission. As the sensor strip was elongated, it caused a change in the spacing between the strain gauge's electrodes, leading to a modification in capacitance. Consequently, this alteration in capacitance enabled the measurement of strain. The measurement system was affixed to the knee by adhering the sensor to the skin in alignment with the anterolateral ligament (ALL), allowing the lower part of the sensor (made of silicone) and the circuit board to be in direct contact with the knee's surface. It is important to note that the sensor should be attached without any prior stretching. To validate the system, an in vivo test was conducted on 10 healthy volunteers. The dorsiflexion of the ankle was set at 2 Nm using a torque meter to eliminate any rotational laxity in the ankle. A strain gauge sensor was affixed to the Gerdii's tubercle along the course of the anterolateral ligament, just beneath the lateral epicondyle of the thigh. In three successive measurements, the internal rotation of the foot and, consequently, the lower leg was quantified with a 2 Nm torque. The alteration in the stretch mark's length was then compared to the measured internal rotation angle using the static measuring device. A statistically significant difference between genders emerged in the internal rotation range of the knee (p = 0.003), with female participants displaying a greater range of rotation compared to their male counterparts. The polymer-based capacitive strain gauge exhibited consistent linearity across all measurements, remaining within the sensor's initial 20% strain range. The comparison between length change and the knee's internal rotation angle revealed a positive correlation (r = 1, p < 0.01). The current study shows that elastic polymer-based capacitive strain gauges are a reliable instrument for the internal rotation measurement of the knee. This will allow dynamic measurements in the future under many different settings. In addition, significant gender differences in the internal rotation angle were seen.

Digital measurement of anterolateral knee laxity using strain sensors.

PURPOSE: The ambition of the research group was to develop a sensor-based system that allowed the transfer of results with strain sensors applied to the knee joint. This system was to be validated in comparison to the current static mechanical measurement system. For this purpose, the internal rotation laxity of the knee joint was measured, as it is relevant for anterolateral knee laxity and anterior cruciate ligament (ACL) injury. METHODS: This is a noninvasive measurement method using strain sensors which are applied to the skin in the course of the anterolateral ligament. The subjects were placed in supine position. First the left and then the right leg were clinically examined sequentially and documented by means of an examination form. 11 subjects aged 21 to 45 years, 5 women and 6 men were examined. Internal rotation of the lower leg was performed with a torque of 2 Nm at a knee flexion angle of 30°. RESULTS: Comparison of correlation between length change and internal knee rotation angle showed a strong positive correlation (r = 1, p < 0.01). Whereas females showed a significant higher laxity vs. males (p = 0.003). CONCLUSIONS: The present study showed that the capacitive strain sensors can be used for reproducible measurement of anterolateral knee laxity. In contrast to the previous static systems, a dynamic measurement will be possible by this method in the future.

Batch Fabrication of a Polydimethylsiloxane Based Stretchable Capacitive Strain Gauge Sensor for Orthopedics.

Polymer-based capacitive strain gauges are a novel and promising concept for measuring large displacements and strains in various applications. These novel sensors allow for high strain, well above the maximum values achieved with state-of-the-art strain gauges (Typ. 1%). In recent years, a lot of interest in this technology has existed in orthopedics, where the sensors have been used to measure knee laxity caused by a tear of the anterior cruciate ligament (ACL), and for other ligament injuries. The validation of this technology in the field has a very low level of maturity, as no fast, reproducible, and reliable manufacturing process which allows mass production of sensors with low cost exists. For this reason, in this paper, a new approach for the fabrication of polymer-based capacitive strain gauges is proposed, using polydimethylsiloxane (PDMS) as base material. It allows (1) the fast manufacturing of sensor batches with reproducible geometry, (2) includes a fabrication step for embedding rigid electrical contacts on the sensors, and (3) is designed to produce sensor batches in which the size, the number, and the position of the sensors can be adapted to the patient's anatomy. In the paper, the process repeatability and the robustness of the design are successfully proven. After 1000 large-strain elongation cycles, in the form of accelerated testing caused much higher strains than in the above-mentioned clinical scenario, the sensor's electrical contacts remained in place and the functionalities were unaltered. Moreover, the prototype of a patient customizable patch, embedding multiple sensors, was produced.

Clinical Outcomes of Arthroscopic Primary Anterior Cruciate Ligament Repair: A Systematic Review from the Scientific Anterior Cruciate Ligament Network International Study Group.

PURPOSE: To perform a systematic review of contemporary studies reporting clinical outcomes of primary anterior cruciate ligament (ACL) repair to determine whether these studies demonstrate any significant benefit of ACL repair and whether there is evidence of a deterioration of mid-term outcomes as seen in historical data. METHODS: A systematic review was conducted in accordance with Preferred Reporting Items for Systematic Reviews and Meta-analyses guidelines. A PubMed search using the keywords "repair" AND "Anterior Cruciate Ligament" was performed (limits: English language, publication date between January 1, 2014, and January 13, 2019). All identified studies reporting clinical outcomes of arthroscopic ACL repair were included. Critical appraisal was conducted using the Cochrane Risk of Bias Tool for Randomized Clinical Trials and the Methodological Index for Non-Randomized Studies. Basic parameters of each study including population characteristics, repair technique, physical examination findings, and clinical outcome scores were recorded and evaluated. RESULTS: Nineteen eligible studies were identified (including 5 comparative studies). None of the comparative studies showed any significant difference between repair and reconstruction groups with respect to International Knee Documentation Committee (IKDC), Lysholm, Tegner, side-to-side laxity difference, Lachman, pivot shift tests, or graft rupture rates. Four non-comparative studies reported outcomes at medium- to long-term follow up (range of mean follow up 43.3-79 months) with a mean Lysholm score between 85.3 and 100, mean IKDC subjective score between 87.3 and 100, and mean Tegner activity score between 5 and 7. CONCLUSIONS: Comparative studies identified no significant differences between ACL repair and reconstruction with respect to Lysholm, IKDC, side-to-side laxity difference, pivot shift grade, or graft rupture rates. However, these studies had major limitations including small numbers and short durations of follow up. Case series demonstrated that excellent outcomes can be achieved at medium- to long-term follow up with the SAR technique. LEVEL OF EVIDENCE: IV; Systematic review of Level II to IV investigations.

Figure-of-4 Cruciate Remnant Objective Assessment Test Reducibility of Anterior Cruciate Ligament Stump for Feasibility of Arthroscopic Primary Anterior Cruciate Ligament Repair.

Suture of the anterior cruciate ligament (ACL) has reemerged as a treatment option for proximal ACL tears. Preoperative imaging can provide insight into the feasibility of performing arthroscopic primary ACL repair, but the final decision is taken only after confirming with arthroscopy that the ACL remnant is reducible. We describe a test called the Figure-of-4 Cruciate Remnant Objective Assessment test that objectively interprets the reducibility of the ACL remnant for arthroscopic primary ACL repair.

Combined Anterior Cruciate and Anterolateral Ligament Reconstruction in the Professional Athlete: Clinical Outcomes From the Scientific Anterior Cruciate Ligament Network International Study Group in a Series of 70 Patients With a Minimum Follow-Up of 2 Years.

PURPOSE: To evaluate clinical outcomes in professional athletes after combined anterior cruciate ligament (ACL) and anterolateral ligament (ALL) reconstruction at a minimum follow-up of 2 years. METHODS: A retrospective analysis of prospectively collected data from the Scientific Anterior Cruciate Ligament Network International (SANTI) Study Group database was performed. All professional athletes who underwent primary combined ACL and ALL reconstruction between January 2011 and March 2016 were included. Patient assessment included physical examination, pre- and postoperative subjective and objective International Knee Documentation Committee (IKDC), Tegner activity scale, and Lysholm scores. RESULTS: Seventy-two professional athletes underwent primary ACL and ALL reconstruction; 70 (97%) were available, with a mean follow-up of 3.9 years (range, 2-7). The preoperative side-to-side anteroposterior laxity difference was 7.1 ± 1.4 mm, and this decreased significantly after surgery to 0.4 ± 0.9 mm (P < .0001). Pivot-shift grade evolved from 16 grade I (22.8%) and 54 grade II or III (77.2%) preoperatively, to 66 absent pivot shift (94.3%) and 4 grade I (5.7; P < .001). By 1-year postoperatively, 60 athletes (85.7%) returned to professional sport, with a mean time interval of 7.9 months (range, 5-12). Preoperatively, the mean subjective IKDC was 56.1 ± 12.3, the Lysholm score was 48.4 ± 12.5, and the Tegner score was 9.3 ± 1. At final follow-up, the mean subjective IKDC was 90.5 ± 7.6 (P < .0001), the Lysholm score was 94.4 ± 7.5 (P < .0001), and the Tegner score was 8.8 ± 1.5 (P < .004). The objective IKDC evolved from 39 grade C (55.7%) and 31 grade D (44.3%) preoperatively to 65 grade A (92.9%) and 5 grade B (7.1%) (P < .0001). Eleven Patients (15,7%) underwent a subsequent ipsilateral reoperation including 4 (5.7%) revision ACL reconstructions. The risk of graft rupture was significantly higher in female patients (13.6% vs 2.1% in male patients; P = .048). CONCLUSIONS: Combined ACL and ALL reconstruction is associated with excellent outcomes in professional athletes with respect to graft rupture rates, return to sport, knee stability, and reoperation rates after injury. LEVEL OF EVIDENCE: Level IV, case series.

Epidemiological Evaluation of Meniscal Ramp Lesions in 3214 Anterior Cruciate Ligament-Injured Knees From the SANTI Study Group Database: A Risk Factor Analysis and Study of Secondary Meniscectomy Rates Following 769 Ramp Repairs.

BACKGROUND: Ramp lesions are characterized by disruption of the peripheral meniscocapsular attachments of the posterior horn of the medial meniscus. Ramp repair performed at the time of anterior cruciate ligament reconstruction (ACLR) has been shown to improve knee biomechanics. PURPOSE: The primary objectives of this study were to evaluate the incidence of and risk factors for ramp lesions among a large series of patients undergoing ACLR. Secondary objectives were to determine the reoperation rate for failure of ramp repair, defined by subsequent reoperations for partial medial meniscectomy. STUDY DESIGN: Case-control study; Level of evidence, 3. Case series; Level of evidence, 4. METHODS: All patients underwent transnotch posteromedial compartment evaluation of the knee during ACLR. Ramp repair was performed if a lesion was detected. Potentially important risk factors were analyzed for their association with ramp lesions. A secondary analysis of all patients who underwent ramp repair and had a minimum follow-up of 2 years was undertaken to determine the secondary partial meniscectomy rate for failed ramp repair. RESULTS: The overall incidence of ramp lesions in the study population was 23.9% (769 ramp lesions among 3214 patients). Multivariate analysis demonstrated that the presence of ramp lesions was significantly associated with the following risk factors: male sex, patients aged <30 years, revision ACLR, chronic injuries, preoperative side-to-side laxity >6 mm, and concomitant lateral meniscal tears. The secondary meniscectomy rate was 10.8% at a mean follow-up of 45.6 months (range, 24.2-66.2 months). Patients who underwent ACLR + anterolateral ligament reconstruction had a >2-fold reduction in the risk of reoperation for failure of ramp repair as compared with patients who underwent isolated ACLR (hazard ratio, 0.457; 95% CI, 0.226-0.864; P = .021). CONCLUSION: There is a high incidence of ramp lesions among patients undergoing ACLR. The identification of important risk factors for ramp lesions should help raise an appropriate index of suspicion and prompt posteromedial compartment evaluation. The overall secondary partial meniscectomy rate after ramp repair is 10.8%. Anterolateral ligament reconstruction appears to confer a protective effect on the ramp repair performed at the time of ACLR and results in a significant reduction in secondary meniscectomy rates.

Biomechanical evaluation of different suture materials for arthroscopic transtibial pull-out repair of posterior meniscus root tears.

PURPOSE: To evaluate the biomechanical properties of four different suture materials for arthroscopic transtibial pull-out repair of posterior meniscus root tears, with special focus on the meniscus-suture interface. METHODS: Forty fresh-frozen lateral porcine menisci were used. The posterior meniscus root was sutured in a standardized fashion with a simple stitch using four different suture materials: group A, No. 2 PDS™; group B, No. 2 Ethibond™; group C, No. 2 FiberWire™; and group D, 2-mm Fibertape™. Meniscus-suture constructs were subjected to cyclic loading followed by load-to-failure testing using a servo-hydraulic material testing machine. RESULTS: During cyclic loading, group D showed a significantly higher displacement after 100, 500, and 1,000 cycles compared to group A (p < 0.001, p = 0.001, and p = 0.001), and a significantly higher displacement after 100 and 500 cycles compared to group B (p = 0.010 and p = 0.045). Group C showed a significantly higher displacement compared to group A after 100 cycles (p = 0.008). The highest maximum load was observed in group D, with significant differences compared to group A (p = 0.013). Group B showed a significantly higher stiffness compared to group A (p = 0.023), and both group C and group D showed a significantly higher stiffness compared to group A and group B (p < 0.001). CONCLUSION: None of the evaluated suture materials provided clearly superior properties over the others during both cyclic loading and load-to-failure testing. Based on the results of this study, FiberWire™ may be the preferred suture material for transtibial pull-out repair of posterior meniscus root tears because of comparably low displacement during cyclic loading and high values for maximum load and stiffness. In the clinical setting, FiberWire™ may improve healing rates and avoid progressive extrusion of the meniscus after transtibial pull-out repair of posterior meniscus root tears.

Biomechanical comparison between suture anchor and transtibial pull-out repair for posterior medial meniscus root tears.

BACKGROUND: Posterior medial meniscus root (PMMR) tears have a serious effect on knee joint biomechanics. Currently used techniques for refixation of the PMMR include the transtibial pull-out repair (TP) and suture anchor repair (SA). These techniques have not been compared biomechanically. HYPOTHESIS: The SA technique provides superior biomechanical properties compared with the TP technique. STUDY DESIGN: Controlled laboratory study. METHODS: A total of 24 fresh-frozen porcine tibiae with attached intact medial menisci were used. The specimens were randomly assigned to 3 groups (8 specimens each). A standardized PMMR tear was created in 16 specimens. Refixation of the PMMR was performed by either the TP or SA technique. The native PMMR was left intact in 8 specimens. All specimens were subjected to cyclic loading followed by load-to-failure testing. Displacement after 100, 500, and 1000 cycles; maximum load to failure; stiffness; and displacement at failure were recorded. RESULTS: Both repair techniques showed a significantly higher displacement during cyclic loading and a significantly lower maximum load and stiffness during load-to-failure testing compared with the native PMMR (P < .05). The SA technique showed a significantly lower displacement after 100, 500, and 1000 cycles (P < .001) and a significantly higher stiffness (P = .016) compared with the TP technique. Maximum load did not differ significantly between the SA and TP techniques (P = .027, Bonferroni adjustment). No significant difference between the 3 groups was observed for displacement at failure (P > .05). CONCLUSION: The SA technique provided superior biomechanical properties compared with the TP technique. Both repair techniques did not reach the strength of the native PMMR. CLINICAL RELEVANCE: The favorable biomechanical properties of the SA technique might be beneficial for healing of the repaired PMMR and restoration of meniscus function. Because of inferior time zero stability compared with the native PMMR, slow rehabilitation is recommended after meniscus root repair.

Anatomical two-bundle medial patellofemoral ligament reconstruction with hardware-free patellar graft fixation: technical note and preliminary results.

PURPOSE: Various techniques for reconstruction of the medial patellofemoral ligament (MPFL) have been developed. In this article, a modified technique for anatomical two-bundle MPFL reconstruction with hardware-free patellar graft fixation is described and the preliminary results of this technique are presented. METHODS: A modified surgical technique for MPFL reconstruction with a gracilis tendon autograft and hardware-free patellar graft fixation using two short oblique bone tunnels is described in detail. Complications and preliminary results of this procedure were assessed in 19 patients at a mean follow-up of 16 ± 3 months using the Kujala score, Tegner scale, and Insall score. RESULTS: No postoperative patellar dislocation or subluxation was reported. Eighty-nine per cent of the patients were either satisfied or very satisfied with the overall outcome. The mean Kujala score was 92 ± 7 (range 69-100), and the median Tegner scale was 5 (range 3-7). According to the Insall score, the results of 18 patients (95%) were rated as good or excellent. Postoperative complications occurred in 3 patients (16%), with two of them persisting only temporary. CONCLUSIONS: The described technique for anatomical two-bundle MPFL reconstruction is a safe and effective surgical procedure for the treatment of lateral patellar instability, with several methodical advantages compared to similar techniques. Further evaluation in a larger patient cohort with a longer follow-up is necessary to confirm these short-term results. LEVEL OF EVIDENCE: IV.

A comparison of techniques for fixation of the quadriceps muscle-tendon complex for in vitro biomechanical testing of the knee joint in sheep.

Whilst in vitro testing can contribute to a better understanding of the biomechanical interactions at the knee joint, the application of physiological-like muscle forces in vitro remains challenging. One main difficulty seems to be the adequate fixation of the muscle-tendon complex to the mechanical apparatus that provides the forces in vitro. The goal of this study was to compare the ability of different muscle-tendon fixation mechanisms, including a new technique developed to optimise the interface grip of the soft tissues, to reliably transmit physiological in vivo loads through the muscle-tendon complex to the attached bone. The fixations of three quadriceps components in 16 right knees of skeletally mature female merino sheep were loaded to failure using four different fixation techniques (aluminium clamp, freeze clamp, suture technique and a new extension hull technique). Each technique was tested 12 times: 4 times on each individual quadriceps component. A factorial analysis for repeated measurements was undertaken to examine differences between the different fixation techniques. The extension hull technique and the aluminium clamp performed similarly, exceeding the computationally determined physiological forces in all but one trial and achieved higher failure loads than the suture technique. Although the freeze clamp reached the highest mean load to failure, it also failed more often than the extension hull technique. This comparison of the fixation techniques suggests that the new extension hull technique is a suitable fixation method for applying physiological-like muscle loading in an in vitro set-up. It cannot only be handled in a very simple manner, but also possesses a compact, lightweight construction, providing the possibility for the application of more complex loading conditions that include, e.g. the action of multiple muscles of the knee flexor and extensor group concurrently.

Radiographic landmarks for femoral tunnel placement in medial patellofemoral ligament reconstruction.

BACKGROUND: Reconstruction of the medial patellofemoral ligament has recently become popular for restoring patellofemoral stability. Femoral insertion site anatomy of the medial patellofemoral ligament has been described. This anatomical insertion has been inferred to be the isometric point in medial patellofemoral ligament reconstruction, but data about radiographic landmarks for a postoperative or intraoperative control are missing. PURPOSE: To determine the radiographic landmarks for control of postoperative and intraoperative femoral medial patellofemoral ligament insertion. STUDY DESIGN: Descriptive laboratory study. METHODS: Eight fresh-frozen human knees were dissected, and the medial patellofemoral ligament was exposed. After identification of the femoral medial patellofemoral ligament insertion site, the insertion center was marked with a lead ball of 2-mm diameter. Straight lateral radiographs were taken, and posterior-anterior as well as proximal-distal position were evaluated. RESULTS: Six of 8 insertion points were anterior to a line representing an extension of the posterior cortex, 1 point was touching this line, and 1 point was posterior to it. All points were situated distal to the posterior origin of the medial femoral condyle and proximal to the most posterior point of the Blumensaat line. CONCLUSION: A reproducible anatomical and radiographic point, 1 mm anterior to the posterior cortex extension line, 2.5 mm distal to the posterior origin of the medial femoral condyle, and proximal to the level of the posterior point of the Blumensaat line on a lateral radiograph with both posterior condyles projected in the same plane, shows the mean femoral medial patellofemoral ligament center. CLINICAL RELEVANCE: This radiographic point may be useful both intraoperatively and postoperatively.