Motoi Yamaguchi

In Vivo Measurement of the Pivot-Shift Test in the Anterior Cruciate Ligament–Deficient Knee Using an Electromagnetic Device

Background The pivot-shift test is commonly used for assessing dynamic instability in anterior cruciate ligament—insufficient knees, which is related to subjective knee function, unlike static load-displacement measurement. Conventional measurements of 3-dimensional position displacement cannot assess such dynamic instability in vivo and produce comparable parameters. Not only 3-dimensional position displacement but also its 3-dimensional acceleration should be measured for quantitative evaluation of the pivot-shift test. Hypothesis Knees with a positive pivot-shift test result have increased tibial anterior translation and acceleration of its subsequent posterior translation, and they are correlated with clinical grading. Study Design Controlled laboratory study. Materials and Methods Thirty patients with isolated anterior cruciate ligament injury were included. Pivot-shift tests were evaluated under anesthesia manually and experimentally using an electromagnetic knee 6 degrees of freedom measurement system. From 60 Hz of 6 degrees of freedom data, coupled tibial anterior translation was calculated, and acceleration of posterior translation was computed by secondary derivative. Results All anterior cruciate ligament—deficient knees demonstrated a positive pivot-shift test result. The coupled tibial anterior translation was 7.7 and 15.6 mm in anterior cruciate ligament—intact and —deficient knees, respectively. The acceleration of posterior translation was —797 and —2001 mm/s 2, respectively. These differences were significant (P < .01). The coupled tibial anterior translation and acceleration of posterior translation in the anterior cruciate ligament—deficient knee were larger in correlation with clinical grading (P = .03 and P < .01, respectively). Conclusion The increase of tibial anterior translation and acceleration of subsequent posterior translation could be detected in knees with a positive pivot-shift result, and this increase was correlated to clinical grading. Clinical Relevance These measurements can be used for quantified evaluation of dynamic instability demonstrated by the pivot-shift test.

Deformation of the acetabular polyethylene liner and the backside gap

Polyethylene wear of acetabular components may cause osteolysis and aseptic loosening in total hip arthroplasty. Case reports of wear between the polyethylene liner and acetabular metal backing (backside wear) have promoted speculation on the clinical importance of debris generation at this site and the potential importance of insert conformity. We examined 90 retrieved nonconforming acetabular components from a single manufacturer. Twenty-four liners (27%) showed polyethylene deformation corresponding to screw holes on the backside surface. The location of screw-hole deformations corresponded to the direction of polyethylene deformation (wear) on the articular surface in all cases. The polyethylene liners with backside deformations were significantly thinner than the liners without deformation (P = .02). The presence of acetabular osteolysis did not significantly correlate with backside deformation, but there was a significant association between osteolysis and wear of the articular surface (P = .0004). In this implant design, backside deformation (wear) may not be due to micromotion at the interface but to the viscoelastic nature of ultra-high-molecular weight polyethylene.

The Use of an Electromagnetic Measurement System for Anterior Tibial Displacement During the Lachman Test

PURPOSE The purpose of this study was to assess quantitative anterior/posterior values during the Lachman test by an electromagnetic measurement system and to compare data with KT-1000 arthrometric measurements (MEDmetric, San Diego, CA), as well as the measurement of radiologic laxity by dynamic radiographs. METHODS We used an electromagnetic device to quantitatively evaluate anterior knee displacements. We tested 82 knees in 41 patients (30 isolated anterior cruciate ligament [ACL]-deficient, 11 ACL-reconstructed, and 41 contralateral ACL-intact knees). Anterior displacements during the Lachman test were calculated by the electromagnetic measurement system and fluoroscopic measurement, and anterior displacements were also measured by the KT-1000 arthrometer. Anterior/posterior displacements measured by these methods were compared, and correlations were assessed. RESULTS In ACL-deficient knees, mean anterior/posterior displacement (±SE) was 22.4 ± 0.8 mm in electromagnetic measurements, 22.0 ± 0.7 mm in fluoroscopic measurements, and 15.0 ± 0.6 mm in KT-1000 measurements. In contralateral ACL-intact knees, it was 15.7 ± 0.6 mm, 15.6 ± 0.5 mm, and 9.9 ± 0.4 mm, respectively. In ACL-reconstructed knees, it was 15.7 ± 0.7 mm, 16.2 ± 0.8 mm, and 11.2 ± 0.6 mm, respectively. In all knee conditions, significant differences between fluoroscopic measurements and KT-1000 measurements were detected (P < .01). Significant differences were also detected between electromagnetic measurements and KT-1000 measurements (P < .01). No significant differences were detected between fluoroscopic measurements and electromagnetic measurements. A strong correlation was obtained between KT-1000 measurements and fluoroscopic measurements (r = 0.62, P < .01) and between electromagnetic measurements and KT-1000 measurements (r = 0.64, P < .01). However, the strongest correlation was observed between electromagnetic measurements and fluoroscopic measurements (r = 0.96, P < .01). CONCLUSIONS An electromagnetic measurement system to test anterior/posterior tibial translation determined that quantification of the Lachman test could be performed as accurately as fluoroscopic measurements. LEVEL OF EVIDENCE Level II, development of diagnostic criteria on basis of consecutive patients with universally applied reference gold standard.

Comparison of transportal and outside-in techniques for posterolateral femoral tunnel drilling in double-bundle ACL reconstruction -three-dimensional CT analysis of bone tunnel geometry

PURPOSE To comparatively analyze the geometry of the posterolateral femoral (PL) tunnel in double-bundle ACL reconstruction between far anteromedial transportal (TP) and outside-in (OI) drilling techniques based on three-dimensional computed tomography (3DCT) image analysis. METHODS Forty patients who underwent anatomic double-bundle hamstring ACL reconstruction using the TP (n: 20) or OI (n: 20) method with postoperative CT data available were included in the study. The analyzed parameters were as follows: location of the intraarticular tunnel aperture, tunnel length, bending angle (angulation of the graft at the intraarticular tunnel aperture), and long axis of the tunnel aperture/drill diameter ratio as a parameter of ellipsoidal geometry. RESULTS Anatomical tunnel placement was achieved in both groups. Coalition of the AM and PL tunnel apertures was found in 3 knees in the TP group and 1 knee in the OI group, though no significant difference in the rate of this problem was demonstrated between the groups (P: 0.30). The tunnel length was not significantly different between the groups, while the graft bending angle at the tunnel aperture was significantly larger in the OI group than the TP group (99.4° vs. 63.6°). The long axis/drill diameter ratio averaged 1.23 in the TP group and 1.13 in the OI group with significant intergroup difference. CONCLUSION When drilling the PL femoral tunnel in double-bundle ACL reconstruction, anatomic placement of the intraarticular tunnel aperture was feasible in both the TP and OI techniques. The tunnel aperture was rounder and the graft bending angle in knee extended position at the intraarticular aperture was more acute in the OI technique than the TP technique. LEVEL OF EVIDENCE Level IV (retrospective comparison of the two patient groups treated at different hospitals).

3-D/4-D Registration of Artificial Knee Implants with Predicting Dynamic Knee Kinematics

X-ray fluoroscopic images are widely used for evaluating the knee kinematics after the total knee Arthroplasty, TKA in short. There are some conventional methods for estimating the motion of the knee implant in vivo using single-plane fluoroscopic images and 3-D geometric models of the knee implant. However, these methods have a problem that estimation results are dependent on the initial pose and position given at the start frame of sequence for analysis because these methods analyze the motion of a series of the knee implant for every frame based on the pose and position estimated at the previous frame. This paper proposes a 3-D/4-D registration method that estimates the initial pose and position by predicting dynamic knee kinematics. To quantitatively evaluate our method, it was applied to computer-simulated images and phantom images that took the knee implant in vitro fixed with arbitrary pose and position by a jig. The experimental results showed that the proposed method could estimate the pose of within the error of 0.04 deg in the computer-simulated images and 0.82 deg in the phantom images, and the accuracy was improved in comparison with the conventional methods.