Superior fixation and less periprosthetic stress-shielding of tibial components with a finned stem versus an I-beam block stem: a randomized RSA and DXA study with minimum 5 years' follow-up.

Background and purpose - The stem on the tibial component of total knee arthroplasty provides mechanical resistance to lift-off, shear forces, and torque. We compared tibial components with finned stems (FS) and I-beam block stems (IS) to assess differences in implant migration. Patients and methods - In a patient-blinded RCT, 54 patients/knees (15 men) with knee osteoarthritis at a mean age of 77 years (70-90) were randomly allocated to receive tibial components with either a FS (n = 27) or an IS (n = 27). Through 5 to 7 years' follow-up, implant migration was measured with RSA, periprosthetic bone mineral density (BMD) was measured with DXA, and surgeons reported American Knee Society Score (AKSS). Results - At minimum 5 years' follow-up, maximum total point motion (MTPM) was higher (p = 0.04) for IS (1.48 mm, 95% CI 0.81-2.16) than for FS (0.85 mm, CI 0.38-1.32) tibial components. Likewise, total rotation (TR) was higher (p = 0.03) for IS (1.51˚, CI 0.78-2.24) than for FS (0.81˚, CI 0.36-1.27). Tibial components with IS externally rotated 0.50° (CI -0.06 to 1.06) while FS internally rotated 0.09° (CI -0.20 to 0.38) (p = 0.03). Periprosthetic bone stress-shielding was higher (p < 0.01) up to 2 years' follow-up for IS compared with FS in the regions medial to the stem (-13% vs. -2%) and posterior to the stem (-13% vs. -2%). Below the stem bone loss was also higher (p = 0.01) for IS compared with FS (-6% vs. +1%) up to 1-year follow-up. Knee score improved similarly in both groups up to 5 years' follow-up. Interpretation - Periprosthetic bone stress-shielding medial and posterior to the stem until 2 years, and tibial component migration at 5 years, was less for a finned compared with an I-shaped block stem design.

Preoperative lateral subluxation of the patella is a predictor of poor early outcome of Oxford phase-III medial unicompartmental knee arthroplasty.

BACKGROUND AND PURPOSE: There is disagreement in the literature about the importance of patellofemoral joint degeneration and knee pain for the outcome of unicompartmental knee arthroplasty (UKA). We therefore investigated the importance of selected predictors including patellofemoral joint degeneration and the location of preoperative knee pain for the early outcome of UKA. PATIENTS AND METHODS: The study group comprised 260 consecutive patients from 5 hospitals who underwent Oxford UKA for anteromedial osteoarthritis. Data were collected at baseline and included pain location, radiologically observed degeneration of the patellofemoral joint including subluxation of the patella, intraoperative cartilage status of the patellofemoral joint, disease-specific knee status, and Oxford knee score (OKS). Outcomes were evaluated after 1 year using the OKS, global patient satisfaction, and global patient result. RESULTS: The average OKS score at baseline was 24 (SD 7), and it was 40 (SD 8) at the 1-year follow-up. 94% of the patients claimed improvement after the operation and 90% were satisfied with the UKA. Lateral subluxation of the patella was a predictor of poor outcome, and the preoperative OKS score was also a predictor of outcome. Full-thickness cartilage loss at any location gave a similar outcome to that with a normal or near-normal joint surface, and likewise, preoperative anterior knee pain was not a predictor of outcome. INTERPRETATION: We conclude that the good early outcome after UKA in this study is in line with the best reported results. Patellofemoral degeneration should not be considered a contraindication to Oxford UKA. Patients with lateral subluxation of the patella have an increased risk of a poor result after UKA and should preferably be offered a total knee replacement.

Implant fracture of the Regenerex® modular metal tibial component: A report of three cases.

BACKGROUND: Implant fractures are a very rare complication in primary total knee replacement (TKR) surgery and with modern implant designs and improved metals these events have nearly been eliminated. In this case series we report three cases of tibial metal baseplate fractures in uncemented Regenerex® TKR. METHODS: Cases originated from a prospective case series of 80 patients operated between 2013 and 2016. Five patients were pilot cases and 75 were participants in a prospective randomized double-blinded clinical trial that evaluated different adjuvant bone anti-resorptive medical therapies. All patients were treated with an uncemented press-fit Regenerex® Porous Titanium Construct tibial tray and matching cemented (Refobacin Bone Cement R) patella and femoral components (hybrid implant). RESULTS: We report three cases of medial side metal baseplate fractures of a modular finned tibial stem. All three baseplate fractures were in male patients. Confirmed failure of the implant occurred after 10, 12 and 23 months, in situ, with a mean follow-up of 15 months (range 10-23). CONCLUSIONS: Based on the current case series we cannot make any causal inferences. Failures may represent a multifactorial process with a cascade of events with implant failure as the result. However, like in most other case reports of metal failures in the literature, the implant fractures in this report were located on the medial side of the tibial component in male patients.

Does the position of the femoral tunnel affect the laxity or clinical outcome of the anterior cruciate ligament-reconstructed knee? A clinical, prospective, randomized, double-blind study.

PURPOSE: The aim of this study was to evaluate whether a change in the femoral graft insertion site between the 1-o'clock (high) and 2-o'clock (low) positions could change the laxity, the score on the 2000 International Knee Documentation Committee (IKDC) Knee Examination Form, or the score on the 2000 subjective IKDC Knee Evaluation Form in the anterior cruciate ligament (ACL)-reconstructed knee. METHODS: The study was designed as a prospective, randomized, double-blind investigation. We randomized 30 patients to the low tunnel position group and 30 to the high tunnel position group. Four-stranded semitendinosus and gracilis single-bundle grafts were used. At follow-up, the patients were examined according to the IKDC evaluation form and the IKDC examination form. The exact measurements of laxity at 25 degrees and 70 degrees were performed by use of the Rolimeter (Aircast, Boca Raton, FL). Standardized radiographs were evaluated. RESULTS: In total, 26 patients in the low tunnel position group and 25 in the high tunnel position group completed the study. At follow-up, we found no significant difference in the laxity at 25 degrees and 70 degrees or scores on the IKDC examination form. We found a significant difference in the scores on the IKDC evaluation form, favoring the low position, with a subjective score of 82.8 versus 70.4. CONCLUSIONS: A change in the femoral tunnel placement from 1 o'clock to 2 o'clock did not result in a detectable change in the sagittal laxity at 25 degrees and 70 degrees , on the pivot-shift test, or on the IKDC examination form scores. However, we found a significant difference between the two groups in the scores on the IKDC evaluation form, most evident in the subgroups dealing with the patient's subjective knee stability. We conclude that it is possible to improve the clinical result in 1-bundle ACL reconstruction by lowering the tibial tunnel angle and thereby lowering the femoral tunnel toward the 2-o'clock position. LEVEL OF EVIDENCE: Level I, therapeutic prospective randomized trial.