Dynamic radiostereometry can objectively quantify the kinematic laxity patterns and rotation instability of the knee during a pivot-shift test.

PURPOSE: The pivot-shift test is used to clinically assess knee instability in patients with anterior cruciate ligament (ACL) lesions; however, it has low interobserver reliability. Dynamic radiostereometry (dRSA) is a highly precise and noninvasive method for the objective evaluation of joint kinematics. The purpose of this study was to quantify precise knee kinematics during a pivot-shift test using dRSA imaging. METHOD: Eight human donor legs, including hemipelvises, were evaluated. Arthroscopic intervention was performed inducing ligament lesions in the ACL, and anterolateral ligament (ALL) section was performed as a capsular incision. The pivot-shift test was recorded with dRSA on knees with intact ligaments, ACL-deficient and ACL + ALL-deficient knees. RESULTS: A pivot-shift pattern was identifiable after ligament lesion, as a change in tibial posterior drawer velocity from 7.8 mm/s (95% CI: 3.7; 11.9) in ligament intact knees to 30.4 mm/s (95% CI 23.0; 38.8) after ACL lesion to 35.1 mm/s (95% CI 23.4; 46.7) after combined ACL-ALL lesion. The anterior-posterior drawer excursion increased from 2.8 mm (95% CI 2.1; 3.4) in ligament intact knees to 7.2 mm (95% CI 5.5; 8.9) after ACL lesion to 7.6 mm (95% CI 5.5; 9.8) after combined lesion. A statistically significant increase in tibial external rotation towards the end of the pivot-shift motion was observed when progressing from intact to ACL + ALL-deficient knees (p < 0.023). CONCLUSION: This experimental study demonstrates the feasibility of dRSA to objectively quantify the kinematic laxity patterns of the knee during the pivot-shift test. The dynamic parameters obtained through dRSA revealed the kinematic changes from ACL to combined ACL-ALL ligament lesion. LEVEL OF EVIDENCE: Not applicable.

Comparison of cementless twin-peg, cemented twin-peg and cemented single-peg femoral component migration after medial unicompartmental knee replacement: a 5-year randomized RSA study.

BACKGROUND: The component design and fixation method of joint arthroplasty may affect component migration and survival. The aim of this study was to compare fixation of cementless twin-peg (CLTP), cemented twin-peg (CTP) and cemented single-peg (CSP) femoral components of medial unicompartmental knee replacement (UKR). METHODS: Eighty patients (mean age = 63 years, 48 males) with medial knee osteoarthritis were randomized in three ways to CLTP (n = 25), CTP (n = 26) or CSP (n = 29) femoral UKR components. The patients were followed 5 years postoperatively with RSA, bone mineral density (BMD), PROMs and radiological evaluation of radiolucent lines (RLL), femoral component flexion angle and complications. RESULTS: At the 5-year follow-up, femoral component total translation was comparable between the three groups (p = 0.60). Femoral component internal rotation was 0.50° (95% CI 0.3; 0.69) for the CLTP group, 0.58° (95% CI 0.38; 0.77) for the CTP group and 0.25° (95% CI 0.07; 0.43) for the CSP group (p = 0.01). BMD decreased peri-prosthetically (range - 11.5%; - 14.0%) until 6-month follow-up and increased toward the 5-year follow-up (range - 3.6%; - 5.8%). BMD change did not correlate with component migration. Lower flexion angle was correlated with higher 5-year subsidence, total translation, varus rotation and maximum total point motion (p = 0.01). Two patients (1 CLTP, 1 CTP) had RLL in the posterior zone. There were two revisions. CONCLUSION: At 5-year follow-up, fixation of UKA femoral components with twin-peg was not superior to the single-peg design. Cementless and cemented twin-peg femoral components had similar fixation. A lower flexion angle was correlated with higher component migration.

Evaluation of automated radiostereometric image registration in total knee arthroplasty utilizing a synthetic-based and a CT-based volumetric model.

Radiostereometic analysis (RSA) is an accurate method for rigid body pose (position and orientation) in three-dimensional space. Traditionally, RSA is based on insertion of periprosthetic tantalum markers and manual implant contour selection which limit clinically application. We propose an automated image registration technique utilizing digitally reconstructed radiographs (DRR) of computed tomography (CT) volumetric bone models (autorsa-bone) as a substitute for tantalum markers. Furthermore, an automated synthetic volumetric representation of total knee arthroplasty implant models (autorsa-volume) to improve previous silhouette-projection methods (autorsa-surface). As reference, we investigated the accuracy of implanted tantalum markers (marker) or a conventional manually contour-based method (mbrsa) for the femur and tibia. The data are presented as mean (standard deviation). The autorsa-bone method displayed similar accuracy of -0.013 (0.075) mm compared to the gold standard method (marker) of -0.013 (0.085). The autorsa-volume with 0.034 (0.106) mm did not markedly improve the autorsa-surface with 0.002 (0.129) mm, and none of these reached the mbrsa method of -0.009 (0.094) mm. In conclusion, marker-free RSA is feasible with similar accuracy as gold standard utilizing DRR and CT obtained volumetric bone models. Furthermore, utilizing synthetic generated volumetric implant models could not improve the silhouette-based method. However, with a slight loss of accuracy the autorsa methods provide a feasible automated alternative to the semi-automated method.

Migration pattern of cemented Exeter short stem in Dorr type A femurs. A prospective radiostereometry study with 2-year follow-up.

INTRODUCTION: The Exeter short stem (ESS) is 25 mm shorter than the standard length v40 Exeter stem (Stryker) and intended for a narrow femoral diaphysis. The purpose of the study was to evaluate the migration pattern of the cemented ESS. MATERIAL AND METHOD: In a prospective single-center cohort study, 23 patients (21 female) mean age 78 (range 70-89) with hip osteoarthritis and Dorr Type A femurs were included. Preoperative DXA was used to group patients into normal (> - 1) and low (< - 1) T-score. Components were the collarless polished double-tapered Exeter short stem type N°1 L125. Patients were followed for 2 years with model-based RSA (stem migration), regular hip radiographs (stem position and cementation quality), Oxford Hip Score (OHS) and VAS pain. RESULTS: At 2-year follow-up, the stems subsided 1.48 mm (CI 95% 1.69; 1.26) and retroverted 0.45° (CI 95% 0.01; 0.88). From 12 to 24 months, stem subsidence was 0.18 mm (CI 95% 0.1; 0.25) (p = 0.001) and retroversion was - 0.04° (CI 95% - 0.27; 0.18) (p = 0.70). T-score and stem subsidence correlated (rho = 0.48; p = 0.025) and patients with normal T-score (n = 7) had 0.42 mm (CI 95% - 0.01; 0.85) less subsidence as compared to patients with low T-score (n = 15) (p = 0.054). Stems in varus position (n = 9) subsided 1.7 mm (CI 95% 1.35; 2.05) compared to 1.33 mm (CI 95% 1.05; 1.60) for stems in neutral position (n = 13) (p = 0.07). Postoperative cementation quality did not influence 2-year stem migration. OHS improved to 40.7 (CI 95% 36.8; 44.7) and VAS pain at rest and activity decreased to 5 mm and 10 mm, respectively (p < 0.001). CONCLUSION: The 2-year migration pattern of the cemented ESS was similar to reports for the cemented standard length Exeter stem. Low preoperative T-score and varus stem-position showed a tendency for higher stem migration and should be studied as risk factors for failure in larger studies of cemented polished stems.