Laura Bragonzoni

Purpose: The purpose of the present study was to assess the kinematical behavior of a multi‐radius posterior‐stabilized (PS) mobile‐bearing (MB) total knee arthroplasty (TKA) during an activity of daily living (Sit‐To‐Stand—STS) and a high demanding motor task (Deep‐Knee‐Lunge—DKL) using model‐based dynamic RSA. We hypothesized the achievement of medial pivoting movement in both motor tasks due to the congruent geometry of the inlay with the femoral component, which should allow good stability of the medial compartment, and to the high magnitude of rotations guaranteed by the MB on the tibial side.Methods: Twenty‐two randomly selected patients were recruited and prospectively evaluated. The PS MB cemented TKA was implanted with the standard technique (medial parapatellar approach, adjusted mechanical alignment). At minimum 9‐month follow‐up, patients were examined with model based Dynamic RSA developed in our Institute (BI‐STAND DRX 2) during the execution of two motor tasks: STS and DKL. The motion parameters were evaluated using the Grood and Suntay decomposition and the low‐point kinematics methods.Results: In the extension phase of DKL femur performed a greater antero posterior translation of 3.8 mm compared to STS between 0° and 20° of knee flexion (p < 0.05).Low‐point analysis showed a medial pivoting movement in both motor tasks: in 62% of patients during STS and 48% during DKL. Varus‐valgus rotations were lower than 1° during all the range‐of‐motion in both motor tasks without differences.Conclusions: Medial pivot was partially produced by this multi‐radius PS MB TKA with some differences during activity of daily living (STS) and high demanding motor task (DKL).Level of evidence: IV.

Purpose Which total knee arthroplasty (TKA) design represents the better solution to restore a correct knee biomechanics is still debated. The aim of this study was to compare posterior stabilized (PS) and cruciate retaining (CR) version of the same TKA design (femoral component with an anatomic sagittal radius—J-curve design) by the use of dynamic Roentgen stereophotogrammetric analysis (RSA). The hypothesis was that the two models influence differently in vivo knee kinematic. Methods A cohort of 16 randomly selected patients was evaluated 9 months after surgery: Zimmer PERSONA® was implanted, eight with CR design and eight with PS design. The kinematic evaluations were performed using a Dynamic RSA (BI-STAND DRX 2) developed in our Institute, during the execution of the sit-to-stand motor task. The motion parameters were obtained using the Grood and Suntay decomposition and the low-point kinematics methods. Results PS TKA lateral femoral compartment had a wider anterior translation (17 ± 2 mm) than the medial one (11 ± 2 mm), while the two compartments of CR TKA showed a similar anterior translation (medial: 9 ± 2 mm/lateral: 11 ± 2 mm). T test for comparison between CR and PS TKA of antero-posterior translation showed a statistically significant difference (p < 0.05) in the flexion range between 15° and 40°. The CR prosthesis did not anteriorly translate during flexion. The PS design translated anteriorly showing a roll-forward mechanism during extension from 80° to 18° of flexion and a posterior translation from 18° to 0°. The same significant differences (p < 0.05) between the PS and CR groups were found comparing the low-point positions of the femoral condyles in the range of flexion between 25° and 40° for the medial compartment and between 15° and 25° for the lateral compartment. Conclusions Dynamic RSA was able to investigate for the first time in vivo the kinematic behaviour of PS and CR version of the same TKA J-curve design. PS type showed a medial pivot during sit-to-stand motion task, while the CR type showed a cylindrical movement. Further studies are needed to evaluate the impact of different TKA designs on clinical results. Level of evidence IV.

The purpose of this study was to perform a mid-long-term clinical and radiographic evaluation of the results obtained in patients older than 75 years treated with minimally invasive unicompartmental knee arthroplasty (UKA). The hypothesis was that UKA is a viable solution for the definitive treatment of localized disease in this age group, with good results and a low failure rate.

Purposes: To determine the long‐term survival rate of an all‐polyethylene tibial unicompartmental knee arthroplasty (UKA) in a large series of consecutive patients and to investigate the possible factors that could influence the outcome.Methods: A retrospective evaluation of 273 patients at 6–13 years of follow‐up was performed. Clinical evaluation was based on KSS and WOMAC scores. Subjective evaluation was based on a visual analogue scale for pain self‐assessment. Radiographic evaluation was performed to assess femoral‐tibial angle (FTA), posterior tibial slope (PTS) and tibial plateau angle (TPA). A Kaplan–Meier survival analysis was performed assuming revision for any reason as primary endpoint.Results: The 10‐year implant survivorship was 87.6 %. Twenty‐five revisions (9.2 %) were performed, and aseptic loosening of the tibial component was the most common failure mode (11 cases, 4 %). The comparison of survival rate according to age at surgery did not show significant difference. Age at surgery, FTA, TPA and PTS were not related to higher risk of revision. No correlations were found between BMI, age at surgery and clinical scores. Finally, no statistical differences of radiographic measurements were found between revisions and non‐revisions.Conclusions: The present study has demonstrated on a large series of patients that UKA with an all‐polyethylene tibial component, with an accurate technique and a proper patient selection, can provide a satisfactory clinical and functional outcome and a good overall survivorship of the implant at long‐term follow‐up. These advantages could be achieved at a lower cost.Level of evidence: Retrospective Therapeutic Study, Level IV.

The main purpose of the present study was to determine long-term implant fixation of 15 unicompartmental knee arthroplasty (UKAs) with an all-poly tibial component using Roentgen stereophotogrammetric analysis (RSA) at a mean 10-year follow-up. The secondary purpose was to investigate whether the progressive loss of implant’s fixation correlates with a reduction in Knee society score (KSS). Fifteen non-consecutive patients with primary knee osteoarthritis received a UKA with an all-poly tibial component were assessed using KSS scores pre-operatively and post-operatively and RSA on day 2 after surgery, then at 3, 6, and 12 months and yearly thereafter. The mean last follow-up was 10 years. An increase in maximum total point motion (MTPM) values from 6 months to 1 year post-operatively was found respect to post-operative reference. Implants’ displacement values were always p < 0.001). Also in a long-term follow-up evaluation, RSA is an effective tool to predict functional results after an all-poly UKA providing also a relevant predictive value at 1 year follow-up, and this can be very useful for both patients and surgeons. Diagnostic studies, Level III.

We performed a retrospective clinical and radiographic evaluation of 83 nonconsecutive patients operated in our institute between February 1996 and March 2003 with a mean follow‐up of 60 months to assess the efficiency of unicompartmental knee replacement (UKR) performed with a minimally invasive technique. The aim of this study was to correlate the clinical outcome with the pre‐ and post‐operative alignment and with implant positioning on coronal and sagittal plane. Eighty‐three nonconsecutive patients (60 males, 23 females) underwent cemented UKR (De Puy Preservation Uni with all‐poly tibial component), for both medial OA (80 patients) and AVN of the medial femoral condyle (3 patients). All patients were available at final follow‐up evaluation, and they all presented an evident varus alignment at pre‐operative clinical and radiographic evaluation. At radiographic measurement, we considered a knee with femoro‐tibial angle (FTA) > 175° as varus knee, 170° < FTA < 175° as normal knee and a knee with a FTA < 170° as a valgus knee. Moreover, we considered a tibial plateau angle (TPA) > 90° for valgus knee and a TPA < 90° for varus knee. According to Hospital for Special Surgery (HSS) scoring system, at a mean follow‐up of 60 months, 61 (74%) cases were excellent (100‐85 points), 15 (18%) cases were good (84‐70 points) and 7 cases (8%) had fair results (<70 points). In our series, patients with an excellent clinical result presented a mean varus deformity of 7.2° (3.6°–10.8°) pre‐operatively. According to literature, we demonstrated that a small amount of undercorrection with a small amount of residual varus deformity of 3°–5° is the goal to be reached in order to avoid both rapid degeneration of the nonreplaced compartment and the premature loosening of the replaced compartment. We performed a mean axial correction of 5° (SD 3.9°), leaving a mean axial varus deformity of 2.2° in the excellent group. In our series, the group with excellent results also showed a post‐operative PTS of 7° (2.4°–11.6°), while mean pre‐operative PTS was 6.5° (2.7°–10.3°). In this study, results have shown that minimally invasive UKR producing a small amount of varus undercorrection in selected patients with medial tibio‐femoral osteoarthritis or moderate avascular necrosis of the medial femoral condyle provides excellent clinical and functional results. Overcorrection of varus malalignment with a UKR may produce both rapid degeneration of the lateral tibio‐femoral compartment and the early failure of the replaced compartment.