Patellofemoral complications are one of the main problems after Total Knee Arthroplasty (TKA). Retropatellar pressure distribution after TKA can contribute to these symptoms. Therefore we evaluated retropatellar pressure distribution subdivided on the ridge, medial and lateral surface on non-resurfaced patella before and after TKA. Additionally, we analyzed axial femorotibial rotation and quadriceps load before and after TKA. Seven fresh frozen cadaver knees were tested in a force controlled knee rig before and after TKA (Aesculap, Tuttlingen, Germany, Columbus CR) while isokinetic flexing the knee from 20° to 120° under weight bearing. Ridge, medial and lateral retropatellar surface were defined and pressure distribution was dynamically measured while quadriceps muscles and hamstring forces were applied. Aside axial femorotibial rotation and quadriceps load was recorded. There was a significant change of patella pressure distribution before and after TKA (p = 0.004). In physiological knees pressure distribution on medial and lateral retropatellar surface was similar. After TKA the ridge of the patella was especially in higher flexion grades strongly loaded (6.09 +/−1.31 MPa) compared to the natural knee (2.92 +/−1.15 MPa, p < 0.0001). Axial femorotibial rotation showed typical internal rotation with increasing flexion both before and after TKA, but postoperatively it was significantly lower. The average amount of axial rotation was 3.5° before and after TKA 1.3° (p = 0.001). Mean quadriceps loading after implantation of knee prosthesis did not change significantly (575 N ±60 N in natural knee and after TKA 607 N ±96 N; p = 0.28). The increased retropatellar pressure especially on the ridge may be one important reason for anterior knee pain after TKA. The trochlea of the femoral component might highly influence the pressure distribution of the non-resurfaced retropatellar surface. Additionally, lower axial femorotibial rotation after TKA might lead to patella maltracking. Changing the design of the prosthesis or a special way of patella shaping might increase the conformity of the patella to trochlea to maintain natural contact patterns. Das patellofemorale Schmerzsyndrom stellt eines der zentralen Probleme in der Knieendoprothetik dar. Dabei wird angenommen, dass die retropatellare Druckverteilung nach Implantation einer Knietotalendoprothese (KTEP) zu dieser Symptomatik beiträgt. Wir untersuchten daher die retropatellare Druckverteilung unterteilt in First, mediale und laterale Rückfläche vor und nach KTEP. Zusätzlich analysierten wir die tibiofemorale Rotation und die Quadrizepszugkraft vor und nach KTEP. Die Simulation der Kniebewegung erfolgte an sieben humanen fresh-frozen Kniegelenken mit einem kraftgesteuerten Kniegelenkskinemator von 20° bis 120° Flexion mit programmierter Regelung unter konstanter isokinetischer Gewichtskraft an den Sehnen des M. quadriceps, M. semitendinosus und M. biceps femoris. Nach standardisierter Flächendefinition des Firstes, der medialen und lateralen Retropatellarfläche wurde die retropatellare Druckverteilung mittels Druckmessfolie vor und nach Implantation einer KTEP dynamisch gemessen. Zusätzlich wurden die tibiofemorale Rotation, sowie die Quadrizepszugkraft analysiert. Nach Implantation einer KTEP zeigte sich eine signifikante Änderung der retropatellaren Druckverteilung. Im natürlichen Kniegelenk war der retropatellare Druck medial und lateral gleichmäßig verteilt. Postoperativ zeigte sich bei höheren Flexionsgraden ein maximaler retropatellarer Druck besonders im Bereich des Patellafirstes (6,09 +/−1,31 MPa) im Vergleich zum natürlichen Kniegelenk (2,92 +/−1,15 MPa, p < 0,0001). Die axiale tibiofemorale Rotation zeigte die typische Innenrotation bei Flexion und Außenrotation bei Extension sowohl vor als auch nach Implantation einer KTEP; postoperativ war diese Rotation jedoch deutlich vermindert. Die durchschnittliche axiale Rotation betrug 3,5° vor und 1,3° nach KTEP-Implantation (p = 0,001). Die Quadrizepszugkraft änderte sich nach KTEP-Implantation nicht signifikant (575 N ±60 N beim natürlichen Knie und nach KTEP 607 N (±96 N), p = 0,28). Die Implantation einer KTEP führte in unserer Studie zu einer Steigerung des retropatellaren Drucks insbesondere im Firstbereich. Es ist davon auszugehen, dass durch die Erhöhung des retropatellaren Drucks und die ungünstigere Druckverteilung in vivo postoperative Patella Beschwerden entstehen können. Daneben kann die postoperativ verminderte Innenrotation der Tibia bei Flexion des Kniegelenkes zum Patella Maltracking führen. Wird bei der Implantation einer Knieprothese kein Retropatellarersatz durchgeführt ist ein standardisiertes knöchernes “Trimming” der Patella entsprechend dem Trochlea-Design der Prothese zu diskutieren.

Background: Short-stemmed total hip arthroplasty (THA) is well established and gaining popularity in Germany. The perception that short stems may predispose to primary instability in the femur has resulted in a more thorough follow-up of younger patient cohorts than the typical uncemented THA population. To address this issue, an evidence-based approach is presented for a retrospective mid-term survival analysis of a large registry-based cohort in primary cementless THA comparing short stems with a matched group of conventional stems. Material and methods: Propensity score matching (PSM, see Infobox 1) was used on 131,580 primary cementless THAs fulfilling the inclusion criteria performed between November 2012 and September 2019 and the cumulative probability of revision (CPR) of short and conventional stems for any reason, for reasons excluding prosthetic joint infection (PJI), and due to PJI were compared. Results: After PSM at 1:1 balanced groups of 17,526 short stems and of 17,526 conventional stems were achieved demonstrating no significant difference for CPR for any reason and for reasons excluding PJI. Matched CPR for any reason was 2.9% (95% confidence interval, CI, 2.4–3.5%) 5 years after primary THA in the short stem and 3.1% (95% CI 2.7–3.4%) in the conventional stem group. The CPR excluding PJI was 2.2% (95% CI 1.7–2.7%) vs. 2.1% (95% CI 1.8–2.4%). In contrast, the incidence of PJI was statistically significant lower for short stems. Conclusion: For the considered period, there was no statistically significant survival difference in uncemented THA between comparison groups but a lower incidence for PJI in short-stem THA. Further analyses of registry data are required to rule out range of indications and late mechanical failure of short stems.

Aims: This study compares the re-revision rate and mortality following septic and aseptic revision hip arthroplasty (rTHA) in registry data, and compares the outcomes to previously reported data.Methods: This is an observational cohort study using data from the German Arthroplasty Registry (EPRD). A total of 17,842 rTHAs were included, and the rates and cumulative incidence of hip re-revision and mortality following septic and aseptic rTHA were analyzed with seven-year follow-up. The Kaplan-Meier estimates were used to determine the re-revision rate and cumulative probability of mortality following rTHA.Results: The re-revision rate within one year after septic rTHA was 30%, and after seven years was 34%. The cumulative mortality within the first year after septic rTHA was 14%, and within seven years was 40%. After multiple previous hip revisions, the re-revision rate rose to over 40% in septic rTHA. The first six months were identified as the most critical period for the re-revision for septic rTHA.Conclusion: The risk re-revision and reinfection after septic rTHA was almost four times higher, as recorded in the ERPD, when compared to previous meta-analysis. We conclude that it is currently not possible to assume the data from single studies and meta-analysis reflects the outcomes in the ‘real world’. Data presented in meta-analyses and from specialist single-centre studies do not reflect the generality of outcomes as recorded in the ERPD. The highest re-revision rates and mortality are seen in the first six months postoperatively. The optimization of perioperative care through the development of a network of high-volume specialist hospitals is likely to lead to improved outcomes for patients undergoing rTHA, especially if associated with infection.Cite this article: Bone Joint J 2024;106-B(6):565–572.